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	claims	1. A multi-beam x-ray beam system comprising:a point focus x-ray source; anda housing with a first part and a second part, the second part being moveable relative to the first part, the second part including a plurality of 2-dimensional multilayer x-ray optics that condition the beam in two directions that are perpendicular to the axis of the x-ray beam, each optic, through the movement of the second part relative to the first part, being positioned to a working position so that the optic receives the x-rays from the x-ray source and directs the x-rays of different performance characteristics to a desired location. 2. The x-ray beam system of claim 1, wherein the second part includes a coarse alignment mechanism so that each optic is coarsely aligned when the optic is positioned to its working position, the optic being coarsely aligned to a desired source focal spot and with an intended beam direction and beam position. 3. The x-ray beam system of claim 1, wherein each optic is factory pre-aligned so that the optic is coarsely aligned to a desired source focal spot and with an intended beam direction and beam position. 4. The x-ray beam system of claim 1, wherein the first part includes an alignment mechanism to precisely align each optic when the optic is positioned to its working position, the optic being precisely aligned to a desired source focal spot and with an intended beam direction and beam position. 5. The x-ray beam system of claim 1, wherein the second part includes an alignment mechanism to precisely align each optic when the optic is positioned to its working position, the optic being precisely aligned to a desired source focal spot and with an intended beam direction and beam position. 6. The x-ray beam system of claim 1, wherein the optic housing is a rotary housing with an outer shell and an inner shell, the inner shell being the second part and the outer shell being the first part, the plurality of optics in the inner shell being in a circular geometry and being rotatable relative to the outer shell, each optic being positioned to its desired working position by rotating the inner shell relative to the outer shell. 7. The x-ray beam system of claim 1, wherein the optic housing is a housing with an outer shell being the first part, the second part with the plurality of optics having a linear array or a matrix structure and being movable relative to the outer shell, each optic being positioned to its working position by translating the second part relative to the outer shell. 8. The x-ray beam system of claim 1, wherein the x-ray source includes an anode with different target materials and a cathode that delivers an electron beam to the different materials to form different source focal spots that emit different spectrums. 9. The x-ray beam system of claim 8, wherein the cathode is an electron gun with an electro-magnetic deflection mechanism to steer the electron beam to the different target materials. 10. The x-ray beam system of claim 1, wherein the x-ray source includes an anode with different target materials and is repositionable so that the different materials are positioned under an electron beam to generate x-rays with different spectrums. 11. The x-ray beam system of claim 1, wherein the 2-dimensional multilayer x-ray optics are graded d-spacing multilayer optics. 12. The x-ray beam system of claim 11, wherein the graded multilayer optics are any combination of collimating optics and focusing optics with a different combination of performance attributes including divergence, focal length, working energy, and energy bandwidth. 13. The x-ray beam system of claim 11, wherein each of the 2-dimensional multilayer optics is made of two 1-dimensional optics either in a side-by-side geometry or in a sequential Kirkpatrick-Baez geometry. 14. The x-ray beam system of claim 11, wherein the 2-dimensional optics have a parabloidal geometry for collimating the x-ray beams or an ellipsoidal geometry for focusing the x-ray beams.
050842340	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, the essential protecting components preventing escape of radioactive radiation and substances are schematically shown as provided in a boiling water reactor. The fuel elements 10, being each composed of a plurality of fuel rods, are arranged in a reactor pressure vessel 12 being filled with water to about two thirds of capacity. The reactor vessel 12 consists of a special steel and has a wall thickness of about 20 cm. For the controlling of the reactor core, i.e. for the controlling of the nuclear fission, the reactor vessel 12 has arranged therein a plurality of so-called control rods 14 which are provided between the fuel elements 10 and, by drive means 16 outside of reactor vessel 12, are displaceable in lengthwise direction. The fuel elements 10 have a cladding 18. Further, circulation pumps 20 for circulating the water are provided in the reactor vessel 12. A feedwater line 22 and a steam discharge conduit 24 are connected to the reactor vessel 12. The water coming from the condenser flows, via conduit 22, into the reactor vessel 12, is heated therein due to the energy released during nuclear fission and, at the same time, is evaporated. Through conduit 24, the water issues from the reactor vessel 12 and reaches the turbines. The reactor vessel 12 is surrounded by a concrete shell 26, having a thickness of about two meters, which is also called a biological shield. The reactor vessel and the concrete shell thereof are accommodated in a steelmade safety container having a wall thickness of about 3 cm. The safety container 28 has its outside provided with a sealing skin having a wall thickness of about 4 mm. The safety container 28 is arranged within the reactor building 30. The reactor building consists of steel-reinforced concrete and primarily serves for protection against external influences. The absorption casing of the invention is arranged on the respective inner side of the safety container 28 and of the reactor building 30. The absorption casing consists of a plurality of layers. Hereunder, the construction and the series of the layers are described with respect to an absorption casing which is arranged on the inner side of the reactor building 30 (FIG. 2). The inner surface of the wall of the reactor building 30 has a layer 32 of titanium applied thereto. This titanium layer 32 is provided for absorbing the radioactive radiation of plutonium and, therefore, is necessary only with fast breeding reactors wherein plutonium is obtained upon nuclear fission. Nonetheless, the titanium layer 32 has been included in FIG. 2 for reasons of completeness. On the titanium layer, there is provided a layer 34 of an elastic material having a thick layer 36 of lead arranged thereon. The lead layer 36 serves for absorbing the gamma radiation. As seen from the reactor core, a layer 38 of cadmium, boron, hafnium or beryllium for the absorption of neutron radiation is arranged before the lead layer 36. The interspace between the layer 38 and the lead layer 36 is filled by a layer 40 of elastic material. At a distance to the layer 38, there is arranged a layer 42 of aluminium for absorbing the alpha and beta radiation. Finally, on the inner side of the aluminium layer 42 being averted from layer 38, a layer 44 of a zirconium alloy is provided. The zirconium-alloy layer 44 prevents escape of gaseous fission products and, forming the innermost layer on the inside of the absorption casing, has the smallest distance to the nuclear reactor. The interspace between the zirconium-alloy layer 44 and the aluminium layer 42 as well as the interspace between the aluminium layer 42 and the layer 38 are filled with elastic material 46 and 48, respectively. The individual layers 42-44 are assembled from individual plate members. All of the plates of the same layer are bolted to each other; the plates of different layer are also bolted to each other. The elastic material of the layers 34, 40, 46 and 48 compensates the mechanical stresses in the absorption casing which are caused by the differences in expansion and shrinking of the layers upon heating and cooling, respectively. The absorption casing of the invention can also consist of self-supporting layers. In this case, the zirconium-alloy layer 44, the aluminium layer 42, the layer 38 of cadmium, boron, hafnium or beryllium, the lead layer 36 and, if provided, the titanium layer 32 will be arranged at mutual distances; the interspaces in this case can remain substantially free of material so that the layers of elastic material can be omitted. Instead of these layers 34, 40, 46 and 48 of elastic material, deformable spacers can be used which are fastened to the layers between which they are arranged. As already mentioned, the innermost layer 44 is made from a zirconium alloy. As a material for the layer 44, Zircaloy is particularly suited (Zircaloy is a registered trademark). However, also every other zirconium alloy offering reliable protection against gaseous fission products can be used as a material for the layer 44. The thickness of the individual layers for absorbing alpha, beta, gamma and neutron radiation and for sealing the absorption casing against gaseous fission products is chosen in dependence of the intensity of radiation. As to the thickness of the individual layers relative to each other, it is to be noted that the zirconium-alloy layer 44, the aluminium layer 42, the layer 38 of cadmium, boron, hafnium or beryllium, and the titanium layer 32 have substantially the same thickness while the lead layer 36 is substantially of triple thickness in comparison to each of the before-mentioned layers. The relation of the individual layers with respect to their thickness is graphically rendered in FIG. 2; in this graphic representation, the steel-reinforced concrete wall of the reactor building 30, having a thickness of about 1.50 m, can be shown in part only.
063303019	abstract	An x-ray analysis system including a focusing optic for focusing an x-ray beam to a focal point, a first slit optically coupled to the focusing optic, a second slit optically coupled to the first slit, and an x-ray detector, where the focal point is located in front of the detector.
	claims	1. A beam control assembly to shape a ribbon beam of ions for ion implantation, the beam control assembly comprising:a first bar;a first coil disposed on the first bar, wherein the first coil is the only coil disposed on the first bar, and wherein the first coil includes windings of electrical wire;a second bar disposed opposite the first bar with a gap defined between the first bar and second bar, wherein the ribbon beam travels between the gap;a second coil disposed on the second bar, wherein the second coil is the only coil disposed on the second bar, wherein the second coil includes windings of electrical wire, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first dimension corresponds to the longitudinal axis of the first and second bars, wherein the first coil is fixed to a first position in the first dimension on the first bar, and wherein the second coil is fixed to a second position in the first dimension on the second bar, and wherein the first and second positions are different;a third bar adjacent to the first bar;a third coil disposed on the third bar, wherein the third coil is the only coil disposed on the third bar, wherein the third coil includes windings of electrical wire;a fourth bar adjacent to the second bar;a fourth coil disposed on the fourth bar, wherein the fourth coil is the only coil disposed on the fourth bar, wherein the fourth coil includes windings of electrical wire;a first electrical power supply connected to the first coil without being electrically connected to any other coil;a second electrical power supply connected to the second coil without being electrically connected to any other coil;a third electrical power supply connected to the third coil without being electrically connected to any other coil; anda fourth electrical power supply connected to the fourth coil without being electrically connected to any other coil. 2. The beam control assembly of claim 1, wherein the first bar is located at a first position in the second dimension and extends into the first dimension, wherein the second bar is located at the first position in the second dimension and extends into the first dimension. 3. The beam control assembly of claim 1, wherein the first bar is located at a first position in the second dimension and extends into the first dimension, wherein the second bar is located at a second position in the second dimension and extends into the first dimension, and wherein the first and second positions are different. 4. The beam control assembly of claim 1, wherein the third bar is located at a third position in the second dimension and extends into the first dimension, wherein the fourth bar is located at the third position in the second dimension and extends into the first dimension. 5. The beam control assembly of claim 1, wherein the third bar is located at a third position in the second dimension and extends into the first dimension, wherein the fourth bar is located at a fourth position in the second dimension and extends into the first dimension, and wherein the third and fourth positions are different. 6. A beam control assembly to shape a ribbon beam of ions for ion implantation, the beam control assembly comprising:a first bar;a first coil disposed on the first bar, wherein the first coil is the only coil disposed on the first bar, and wherein the first coil includes windings of electrical wire;a second bar disposed opposite the first bar with a gap defined between the first bar and second bar, wherein the ribbon beam travels between the gap;a second coil disposed on the second bar, wherein the second coil is the only coil disposed on the second bar, and wherein the second coil includes windings of electrical wire;a third bar adjacent to the first bar;a third coil disposed on the third bar, wherein the third coil is the only coil disposed on the third bar, wherein the third coil includes windings of electrical wire;a fourth bar adjacent to the second bar;a fourth coil disposed on the fourth bar, wherein the fourth coil is the only coil disposed on the fourth bar, wherein the fourth coil includes windings of electrical wire, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first dimension corresponds to the longitudinal axis of the first and second bars, wherein the third coil is fixed to a third position in the first dimension on the third bar, and wherein the fourth coil is fixed to a fourth position in the first dimension on the fourth bar, and wherein the third and fourth positions are different;a first electrical power supply connected to the first coil without being electrically connected to any other coil;a second electrical power supply connected to the second coil without being electrically connected to any other coil. 7. The beam control assembly of claim 1, wherein the first, second, third, and fourth bars extend in the first dimension across the entire beam width. 8. The beam control assembly of claim 7, wherein the first, second, third and fourth bars extend from one side of the beam control assembly. 9. The beam control assembly of claim 1, wherein the first, second, third, and fourth bars extend in the first dimension across a portion of the beam width. 10. The beam control assembly of claim 9, wherein the first and second bars extend from one side of the beam control assembly, and wherein the third and fourth bars extend from an opposite side of the beam control assembly as the first and second bars. 11. The beam control assembly of claim 1, wherein a portion of the ribbon beam adjacent to the first coil overlaps with a portion of the ribbon beam adjacent to the third coil. 12. An ion implanter to implant ions using a ribbon beam of ions, comprising:an ion source;an accelerator configured to accelerate the ion disposed adjacent to the ion source;a beam control assembly disposed adjacent to the accelerator, the beam control assembly comprising:a first bar;a first coil disposed on the first bar, wherein the first coil is the only coil disposed on the first bar, and wherein the first coil includes windings of electrical wire;a second bar disposed opposite the first bar with a gap defined between the first bar and second bar, wherein the ribbon beam travels between the gap;a second coil disposed on the second bar, wherein the second coil is the only coil disposed on the second bar, wherein the second coil includes windings of electrical wire, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first dimension corresponds to the longitudinal axis of the first and second bars, wherein the first coil is fixed to a first position in the first dimension on the first bar, and wherein the second coil is fixed to a second position in the first dimension on the second bar, and wherein the first and second positions are different;a third bar adjacent to the first bar;a third coil disposed on the third bar, wherein the third coil is the only coil disposed on the third bar, wherein the third coil includes windings of electrical wire;a fourth bar adjacent to the second bar;a fourth coil disposed on the fourth bar, wherein the fourth coil is the only coil disposed on the fourth bar, wherein the fourth coil includes windings of electrical wire;a first electrical power supply connected to the first coil without being electrically connected to any other coil;a second electrical power supply connected to the second coil without being electrically connected to any other coil;a third electrical power supply connected to the third coil without being electrically connected to any other coil; anda fourth electrical power supply connected to the fourth coil without being electrically connected to any other coil; anda target area disposed adjacent to the beam control assembly, the target area configured to position a work piece. 13. A method of controlling a ribbon beam of ions, the method comprising:applying an electrical charge to a first coil using a first electrical power supply, wherein the first electrical power supply is connected to the first coil without being electrically connected to any other coil, wherein the first coil is disposed on a first bar, wherein the first coil is the only coil disposed on the first bar, and wherein the first coil includes windings of electrical wire;applying an electrical charge to a second coil using a second electrical power supply, wherein the second electrical power supply is connected to the second coil without being electrically connected to another other coil, wherein the second coil is disposed on a second bar, wherein the second coil is the only coil disposed on the second bar, wherein the second coil includes windings of electrical wire, wherein the second bar is disposed opposite the first bar with a first gap defined between the first bar and second bar, wherein the ribbon beam travels between the first gap, wherein the ribbon beam has a beam width and travels in a beam direction, wherein a first dimension corresponds to the beam width and a second dimension corresponds to the beam direction of the ribbon beam, wherein the first dimension corresponds to the longitudinal axis of the first and second bars, wherein the first coil is fixed to a first position in the first dimension on the first bar, and wherein the second coil is fixed to a second position in the first dimension on the second bar, and wherein the first and second positions are different;applying an electrical charge to a third coil using a third electrical power supply, wherein the third electrical power supply is connected to the third coil without being electrically connected to another other coil, wherein the third coil is disposed on a third bar, wherein the third coil is the only coil disposed on the third bar, wherein the third coil includes windings of electrical wire, wherein the third bar is adjacent to the first bar, and wherein the ribbon beam travels between the gap; andapplying an electrical charge to a fourth coil using a fourth electrical power supply, wherein the fourth electrical power supply is connected to the fourth coil without being electrically connected to another other coil, wherein the fourth coil is disposed on a fourth bar, wherein the fourth coil is the only coil disposed on the fourth bar, wherein the fourth coil includes windings of electrical wire, wherein the fourth bar is adjacent the second bar, wherein the fourth bar is disposed opposite the third bar with a second gap defined between the third bar and fourth bar, and wherein the ribbon beam travels between the second gap.
	description	This application is based upon and claims the benefits of priority from the prior Japanese Patent Applications No. 2008-077296, filed in the Japanese Patent Office on Mar. 25, 2008, the entire content of which is incorporated herein by reference. The present invention relates to a nuclear reactor vibration surveillance system for structural integrity monitoring of a nuclear reactor internal component and its method. As a technique for checking the structural health of a nuclear reactor internal component, there is known a method that measures the vibration amplitude or vibration frequency of the reactor internal component and evaluates the measurement values or trend thereof. In order to measure the vibration of the reactor internal component, a method is generally adopted in which a vibration sensor is installed in the reactor, and a signal from the vibration sensor is sent outside the reactor by means of a signal cable. However, in this method, it is necessary to lay the signal cable inside and outside the nuclear reactor, so that it takes quite a lot of work to prepare for the measurement. In order to cope with this problem, an ultrasonic vibration measurement system has been proposed as disclosed in Japanese Patent No. 3,782,559 (the entire content of which is incorporated herein by reference). In this ultrasonic vibration measurement system, an ultrasonic sensor is placed on the outer surface of a reactor pressure vessel, and an ultrasonic pulse is allowed to propagate in the reactor through the reactor pressure vessel. The ultrasonic pulse propagating in the reactor collides with and reflected by a reactor internal component such as a shroud or jet pump under water. The reflected ultrasonic pulse is retuned once again to the ultrasonic sensor through the reactor pressure vessel. If the reactor internal component such as a shroud vibrates, the propagation time of the returned reflected ultrasonic pulse is slightly changed due to the vibration. Assuming that the change in the propagation time of the ultrasonic pulse is Δt (sec), the vibration amplitude L (m) of the reactor internal component such as a shroud is calculated by using the following equation (1). Δ ⁢ ⁢ L = C ⁢ ⁢ Δ ⁢ ⁢ t 2 ( 1 ) “C” is the acoustic velocity (m/sec) of reactor water. By plotting the ΔL in time series, the vibration waveform of the reactor internal component such as a shroud can be synthesized. In the conventional nuclear reactor vibration surveillance system and its method, an ultrasonic sensor employed is configured both as a transmitter and receiver of the ultrasonic. Thus, for example, in the case where the reactor internal component such as a jet pump is arranged inclined relative to the reactor pressure vessel, the ultrasonic pulse is obliquely reflected by the jet pump, so that the reflected ultrasonic pulse is not returned to the ultrasonic source position. As a result, the ultrasonic sensor cannot receive the reflected ultrasonic pulse, making it impossible to measure the vibration of the reactor internal component. The present invention has been made to solve the above problem, and an object thereof is to provide a nuclear reactor vibration surveillance system for structural integrity monitoring of a nuclear reactor internal component and its method capable of measuring the vibration of an in-reactor stricture arranged inclined relative to a reactor pressure vessel. According to a first aspect of the present invention, there is provided a nuclear reactor vibration surveillance system comprising: a first ultrasonic transducer for transmission which is arranged on the outer surface of a reactor pressure vessel and is configured to convert a transmission signal into an ultrasonic pulse signal and allow the ultrasonic pulse to be transmitted to a reactor internal component; an ultrasonic transmitter which is electrically connected to the first ultrasonic transducer and is configured to transmit the transmission signal; a second ultrasonic transducer for reception which is arranged on the outer surface of the reactor pressure vessel and is configured to receive a reflected ultrasonic pulse reflected by the reactor internal component and convert the received reflected ultrasonic pulse into a reception signal; an ultrasonic receiver which is electrically connected to the second ultrasonic transducer and is configured to receive the reception signal; a signal processor which is electrically connected to the ultrasonic transmitter and ultrasonic receiver and is configured to input a signal to the ultrasonic transmitter and receive a signal from the ultrasonic receiver so as to apply signal processing to the signal; and a display unit which is configured to display vibration information of the reactor internal component obtained as a result of the signal processing by the signal processor. According to a second aspect of the present invention, there is provided a nuclear reactor vibration surveillance method comprising: allowing an ultrasonic pulse to be transmitted to a reactor internal component using a first ultrasonic transducer for transmission which is arranged on the outer surface of a reactor pressure vessel; receiving a reflected ultrasonic pulse reflected by the reactor internal component using a second ultrasonic transducer for reception which is arranged on the outer surface of the reactor pressure vessel; and applying signal processing to the received reflected ultrasonic pulse signal to measure the vibration of the reactor internal component. Embodiments of a nuclear reactor vibration surveillance system and its method will be described below with reference to the accompanying drawings, in which the same numerals are given to the same components and thus the overlapped descriptions will be omitted. FIG. 1 is a view schematically showing a configuration of a nuclear reactor vibration surveillance system according to a first embodiment of the present invention. A basic configuration of the nuclear reactor vibration surveillance system will be described with reference to FIG. 1. As shown in FIG. 1, an ultrasonic transducer 1 for transmission and an ultrasonic transducer 2 for reception are arranged on the outer surface of a reactor pressure vessel 3. The ultrasonic transducer 1 for transmission is electrically connected to an ultrasonic transmitter 6 arranged outside or inside a containment vessel 5 through a cable 4a by way of a containment vessel signal outlet port 5a of the containment vessel 5. Similarly, the ultrasonic transducer 2 for reception is electrically connected to an ultrasonic receiver 7 arranged outside or inside a containment vessel 5 through a cable 4b by way of a containment vessel signal outlet port 5a of the containment vessel 5. The ultrasonic transmitter 6 and the ultrasonic receiver 7 are electrically connected to a signal processor 8. The signal processor 8 is electrically connected to a display unit 9. The display unit 9 is configured to display a vibration waveform, vibration spectrum or the like analyzed by the signal processor 8. FIG. 2 is an explanatory view showing a propagation state of an ultrasonic signal of FIG. 1. As shown in FIG. 2, a trigger pulse is input from the signal processor 8 to the ultrasonic transmitter 6 disposed at the outer surface of the reactor pressure vessel 3. When an electrical pulse signal 10 is added to the ultrasonic transducer 1 for transmission by the ultrasonic transmitter 6, the electrical pulse signal 10 is converted into an ultrasonic signal in the ultrasonic transducer 1 for transmission and, accordingly, an ultrasonic pulse 11 is generated. The generated ultrasonic pulse 11 propagates into the reactor water 12 through the wall of the reactor pressure vessel 3. An incident ultrasonic pulse 13 that has propagated in the reactor water 12 is reflected by a reactor internal component 14 such as a jet pump. When the surface of the reactor internal component 14 is inclined relative to the reactor pressure vessel 3, a reflected ultrasonic pulse 15 propagates in an inclined direction corresponding to the inclination angle of the reactor internal component 14 according to the law of reflection. The reflected ultrasonic pulse 15 propagates at an inclination angle until it reaches the boundary between the reactor water 12 and the reactor pressure vessel 3. At this time, the reflected ultrasonic pulse 15 becomes a reflected ultrasonic pulse 16 which propagates in the reactor pressure vessel 3 at a larger inclination angle due to refraction. The ultrasonic transducer 2 for reception, which is arranged at a reaching point of the reflected ultrasonic pulse 16 that has previously calculated, detects the reflected ultrasonic pulse 16. The reflected ultrasonic pulse 16 detected in this manner is converted into an electrical pulse signal in the ultrasonic transducer 2 for reception. The electrical pulse signal is then subjected to signal processing such as amplification, filtering and the like in the ultrasonic receiver 7. The signal processed in the ultrasonic receiver 7 is converted into a digital signal by the signal processor 8 which is constituted by a microcomputer or a frequency demodulator (FM demodulator, FM: Frequency Modulation), whereby vibration information is obtained. Then, the vibration information of the reactor internal component 14 obtained through the processing in the signal processor 8 is displayed on the display unit 9. More specifically, the display unit 9 displays the input information including a vibration amplitude waveform, vibration frequency response, change trend of a vibration amplitude or vibration phase. In the present embodiment described above, a method of measuring the vibration using an ultrasonic pulse signal will be described with reference to FIG. 3. FIG. 3 is an explanatory view showing a method of measuring the vibration using the reflected ultrasonic signal of FIG. 1. As shown in FIG. 3, a DC (Direct Current) pulse signal is used as the electric pulse signal 10 to be converted into an ultrasonic pulse. The ultrasonic pulse 11 from the ultrasonic transducer 1 for transmission is transmitted through the reactor pressure vessel 3 at a right angle relative to a wall of the reactor pressure vessel 3. In the reactor water 12, the incident ultrasonic pulse 13 propagates at a right angle relative to a wall of the reactor pressure vessel 3. The incident ultrasonic pulse 13 is reflected by the reactor internal component 14. When the reactor internal component 14 is inclined at an angle of θ (degrees) relative to the reactor pressure vessel 3, the reflected ultrasonic pulse 15 propagates in the direction of 2θ (degrees). At the time when the reflected ultrasonic pulse 15 reaches the boundary between the reactor water 12 and the reactor pressure vessel 3, the ultrasonic pulse 16 is further refracted due to oblique propagation of the ultrasonic pulse because of a difference in the acoustic velocity between the reactor water 12 and the reactor pressure vessel 3. That is, the refraction angle α (degrees) at which the reflected ultrasonic pulse 15 propagates in the reactor pressure vessel 3 is calculated by using the following equation (2) according to Snell's law. α = sin - 1 ⁡ ( C vessel C water ⁢ sin ⁢ ⁢ 2 ⁢ ⁢ θ ) ( 2 ) In the above equation, “Cwater” is the acoustic velocity (m/sec) of an ultrasonic wave in the reactor water 12, and “Cvessel” is the acoustic velocity (m/sec) of an ultrasonic wave in the reactor pressure vessel 3. As is understood from the equation (2), the refraction angle α (degrees) is determined by the acoustic velocity of the reactor water. The acoustic velocity of the reactor water depends on the temperature of the reactor water. As described above, the ultrasonic pulse that has propagated in the reactor pressure vessel 3 at the refraction angle α (degrees) is received by the ultrasonic transducer 2 for reception. In order to receive an ultrasonic echo with high sensitivity, the position of the ultrasonic transducer 2 for reception may need to be adjusted depending on the temperature of the reactor water. As described in Handbook of Ultrasonic Technology (Nikkan Kogyo Shinbun Ltd., revised fourth edition, pages 1,202 to 1,203), the acoustic velocity (Cwater) at a temperature of 25 degrees Celsius is 1,497 (m/sec), while the acoustic velocity (Cwater) at 287.8 degrees Celsius is reduced to 980 (m/sec). Assuming that the acoustic velocity (Cvessel) in the pressure vessel is 6,000 (m/sec) and θ is 1 degree, 8 degrees is obtained as the propagation angle α (25) at a temperature of 25 degrees Celsius, and 12.3 degrees is obtained as the propagation angle α (287.8) at 287.8 degrees Celsius. Here, it is assumed that the plate thickness of the nuclear reactor pressure vessel 3 is 160 mm. In this case, when the temperature of the reactor water is increased from 25 degrees Celsius to 287.8 degrees Celsius, the optimum reception position of the ultrasonic transducer 2 for reception is changed by about 12 mm (160 mm×tan(8 degrees)−160 mm×tan(12.3 degrees)=−12.4 mm). As described in Handbook of Non-destructive Inspection [new edition] (edited by The Japanese Society for Non-Destructive Inspection, April, 1978, pages 458 to 459) and Handbook of New Non-destructive Inspection (edited by The Japanese Society for Non-Destructive Inspection, October, 1992, pages 313-314), an ultrasonic inspection method that uses two ultrasonic transducers to measure the plate thickness or detect defects has widely been used. In the above documents, the positions of the two ultrasonic transducers are determined in consideration of only the plate thickness D of the reactor pressure vessel 3. However, in order to receive the ultrasonic echo from the reactor internal component 14 at an optimum position, the position of the ultrasonic transducer 2 for reception is adjusted in consideration of the temperature of the reactor water in the present embodiment. The ultrasonic transducer 2 for reception detects ultrasonic pulses 17a and 17b with respect to the electrical pulse signal 10 which is the ultrasonic pulse transmitted from the ultrasonic transducer 1 for transmission. FIGS. 4A to 4C are explanatory views showing the ultrasonic pulse to be transmitted of FIG. 1 and ultrasonic pulses to be received of FIG. 1. FIG. 4A is a timing chart of the electrical pulse signal 10 which is the ultrasonic pulse transmitted from the ultrasonic transducer 1 for transmission, FIG. 4B is a timing chart of the ultrasonic pulse 17a received by the ultrasonic transducer 2 for reception, and FIG. 4C is a timing chart of the ultrasonic pulse 17b received by the ultrasonic transducer 2 for reception. When the reactor internal component 14 is vibrated, the arrival times at which the received ultrasonic pulse signals 17a and 17b are detected vary in proportion to the vibration amplitude of the reactor internal component. Assuming that the propagation time when the reactor internal component 14 is not vibrated is T (sec) as shown by a solid line in FIG. 3, the propagation time T is calculated using the following equation (3). T = D C vessel ⁢ ( 1 + 1 cos ⁢ ⁢ α ) + L C water ⁢ ( 1 + 1 cos ⁢ ⁢ 2 ⁢ ⁢ θ ) ( 3 ) Further, when the reactor internal component 14 is vibrated with a vibration amplitude of ΔL as shown by a broken line in FIG. 3, L becomes L+ΔL. Assuming that a change of the propagation time T of the ultrasonic pulse is Δt, the propagation time Δt is calculated by using the following equation (4). Δ ⁢ ⁢ t = D C vessel ⁢ ( 1 + 1 cos ⁢ ⁢ α ) + L C water ⁢ ( 1 + 1 cos ⁢ ⁢ 2 ⁢ ⁢ θ ) - D C vessel ⁢ ( 1 + 1 cos ⁢ ⁢ α ) - L + Δ ⁢ ⁢ L C water - L + Δ ⁢ ⁢ L C water ⁢ ( 1 + 1 cos ⁢ ⁢ 2 ⁢ θ ) ⁢ ⁢ Δ ⁢ ⁢ t = Δ ⁢ ⁢ L C water ⁢ ( 1 + 1 cos ⁢ ⁢ 2 ⁢ ⁢ θ ) ( 4 ) Accordingly, the vibration amplitude ΔL is calculated by using the following equation (5). Δ ⁢ ⁢ L = C water ⁢ cos ⁢ ⁢ 2 ⁢ ⁢ θ 1 + cos ⁢ ⁢ 2 ⁢ ⁢ θ ⁢ Δ ⁢ ⁢ t ( 5 ) Thus, by measuring the change Δt of the propagation time in the signal processor 8 shown in FIG. 1, the vibration amplitude ΔL can be measured. Assuming that the time interval at which the ultrasonic pulse signal 10 is generated is Ts (sec), the vibration amplitude can discretely be measured for each time interval Ts (sec). FIG. 5 is an explanatory view showing a method of reconstructing actual vibration waveform from the discrete measurement values of the vibration amplitude of FIG. 1. As shown in FIG. 5, actual vibration waveform can be obtained. The sampling theorem is used to reproduce a vibration signal having a frequency of f (Hz). The time interval Ts (sec) at which the ultrasonic pulse signal is generated, satisfy the following equation (6). f ≤ 1 2 ⁢ Ts ( 6 ) For example, in order to reproduce a vibration amplitude of 100 Hz, at least, the ultrasonic pulse signal should be generated at an interval of 200 Hz (Ts=50 msec). According to the present embodiment, even when the reactor internal component 14 is arranged inclined relative to the reactor pressure vessel 3, the reflected ultrasonic pulses 17a and 17b from the reactor internal component 14 can be received by using the ultrasonic transducer 1 for transmission and ultrasonic transducer 2 for reception, whereby the vibration of the reactor internal component 14 can be measured. FIG. 6 is a view schematically showing a configuration of a nuclear reactor vibration surveillance system according to a second embodiment of the present invention. FIGS. 7A and 7B are explanatory views showing a time relationship and frequency relationship between a transmission RF pulse and a reception RF pulse of FIG. 6. FIG. 7A is a timing chart of the transmission RF pulse transmitted from the ultrasonic transducer for transmission, and FIG. 7B is a timing chart of the reception RF pulse received by the ultrasonic transducer for reception. In FIG. 6, the same reference numerals as those in FIG. 1 denote the similar parts as those in FIG. 1, and thus the overlapped descriptions will be omitted. As shown in FIG. 6 and FIG. 7A, an RF (Radio Frequency) pulse signal 18 is used as an ultrasonic pulse signal to be generated from the ultrasonic transmitter 6. That is, when the RF pulse signal 18 shown in FIG. 7A is input to the ultrasonic transducer 1 for transmission, an incident ultrasonic RF pulse 19 generated at that time also becomes an RF pulse signal. The frequency of the carrier of the RF pulse signal thus generated is assumed to be f (Hz). This RF pulse signal propagates in the reactor water 12, reflected by the reactor internal component 14, refracted at the boundary between the reactor water 12 and the reactor pressure vessel 3, and received by the ultrasonic transducer 2 for reception. The received reception RF pulse signal 20 is observed at a time interval of the propagation time T or (T+Δt), as in the case of the ultrasonic pulse signal to be transmitted and ultrasonic pulse signal to be received of FIG. 4. The reflected RF pulse signal is Doppler-shifted by the vibration of the reactor internal component 14 and, accordingly, the frequency of the reflected RF pulse signal is changed. Assuming that the vibration speed of the reactor internal component 14 is V (m/sec), the frequency change Δf (Hz) in this case can be calculated by using the following equation (7). Δ ⁢ ⁢ f = 2 ⁢ f ⁢ ⁢ V C water ⁢ cos ⁢ ⁢ 2 ⁢ ⁢ θ ( 7 ) In the above equation, “Cwater” is the acoustic velocity (m/sec) of an ultrasonic wave in the reactor water 12, and θ is the inclination angle (degrees) between the reactor pressure vessel 3 and the reactor internal component 14 shown in FIG. 6. The frequency change Δf is measured in the signal processor 8 shown in FIG. 6 using a frequency demodulation circuit. The vibration speed V (m/sec) can be calculated back from the frequency change Δf obtained using the equation (7). Also in this case, the vibration speed is discretely measured and, therefore, as in the case of the method shown in FIG. 5, the measurement value is input to the signal processor 8 and then the sampling theorem is used to synthesize a vibration speed waveform. The obtained data is then converted into a vibration amplitude waveform or vibration acceleration waveform, which is then displayed on the display unit 9. According to the present embodiment, by using the RF pulse signal 18 in place of the DC pulse signal used in the first embodiment, it is possible to detect the Doppler shift of the ultrasonic pulse signal generated with the vibration of the reactor internal component 14 to allow the vibration amplitude and vibration speed to be measured simultaneously, thereby improving measurement accuracy. FIGS. 8A and 8B are explanatory views showing a configuration of a nuclear reactor vibration surveillance system according to a third embodiment of the present invention. FIG. 8A is a view showing a positional relationship between the reactor pressure vessel and reactor internal component, and FIG. 8B is a cross-sectional view taken along VIIIb-VIIIb of FIG. 8A as viewed from above. In FIGS. 8A and 8B, the same reference numerals as those in FIG. 1 denote the similar parts as those in FIG. 1, and thus the overlapped descriptions will be omitted. As shown in FIG. 8B, the reactor internal component 14 is represented by a circle. The ultrasonic transducer 1 for transmission is moved on the outer surface of the reactor pressure vessel 3 in the circumferential direction so that the position at which the ultrasonic pulse reflects onto the reactor internal component 14 is changed. Correspondingly, the position of the ultrasonic transducer 2 for reception is moved. According to the present embodiment, the vibration of the reactor internal component 14 can be measured even when the reactor internal component 14 has a curved surface. Further, by using the vibration waveforms before and after change of the vibration measurement position, the vibration of the reactor internal component 14 can be measured more in detail. FIGS. 9A and 9B are explanatory views showing a configuration of a nuclear reactor vibration surveillance system according to a fourth embodiment of the present invention. FIG. 9A is a view showing a positional relationship between the reactor pressure vessel and reactor internal component, and FIG. 9B is a cross-sectional view taken along IXb-IXb of FIG. 9A as viewed from above. As shown in FIG. 9B, the reactor internal component 14 is represented by a circle. The incident angle of the ultrasonic pulse to be transmitted from the ultrasonic transducer 1 for transmission is changed from β to γ so that position at which the ultrasonic pulse reflects onto the reactor internal component 14 is changed. Correspondingly, the reception angle of the ultrasonic pulse received by the ultrasonic transducer 2 for reception is changed from β to γ. According to the present embodiment, by changing the ultrasonic pulse incident angle from β to γ, it is possible to change the measurement point of the vibration without moving the positions of the ultrasonic transducer 1 for transmission. Further, by using the vibration waveforms of the reactor internal component 14 before and after the change of the incident angle and reception angle, the vibration of the reactor internal component 14 can be measured more in detail. FIGS. 10A and 10B are explanatory views showing a configuration of a nuclear reactor vibration surveillance system according to a fifth embodiment of the present invention. FIG. 10A is a view showing a positional relationship between the reactor pressure vessel and reactor internal component, and FIG. 10B is a cross-sectional view taken along Xb-Xb of FIG. 10A as viewed from above. In FIGS. 10A and 10B, the same reference numerals as those in FIG. 1 denote the similar parts as those in FIG. 1, and thus the overlapped descriptions will be omitted. As shown in FIG. 10B, the reactor internal component 14 is represented by a circle. The position of the ultrasonic transducer 1 for transmission is changed so that the position at which the ultrasonic pulse reflects onto the reactor internal component 14 is changed. Correspondingly, the reception angle of the ultrasonic pulse is changed from β to γ without moving the ultrasonic transducer 2 for reception. According to the present embodiment, it is possible to change the measurement position of the vibration without moving the ultrasonic transducer 2 for reception. Further, by using the vibration waveforms of the reactor internal component 14 before and after the change of the position of the ultrasonic transducer 1 for transmission, the vibration of the reactor internal component 14 can be measured more in detail. FIGS. 11A and 11B are explanatory views showing a configuration of a nuclear reactor vibration surveillance system according to a sixth embodiment of the present invention. FIG. 11A is a view showing a positional relationship between the reactor pressure vessel and reactor internal component, and FIG. 11B is a cross-sectional view taken along XIb-XIb of FIG. 11A as viewed from above. In FIGS. 11A and 11B, the same reference numerals as those in FIG. 1 denote the similar parts as those in FIG. 1, and thus the overlapped descriptions will be omitted. As shown in FIG. 11B, the reactor internal component 14 is represented by a circle. The incident angle of the ultrasonic pulse to be transmitted from the ultrasonic transducer 1 for transmission is changed from β to γ without moving the ultrasonic pulse of the ultrasonic transducer 1 for transmission so that position at which the ultrasonic pulse reflects onto the reactor internal component 14 is changed. Correspondingly, the position of the ultrasonic transducer 2 for reception is moved to change the reception position of the ultrasonic pulse. According to the present embodiment, it is possible to change the measurement position of the vibration without moving the ultrasonic transducer 1 for transmission. Further, by using the vibration waveforms of the reactor internal component 14 before and after the change of the position of the ultrasonic transducer 2 for reception, the vibration of the reactor internal component 14 can be measured more in detail. FIGS. 12A and 12B are explanatory views showing a configuration of a nuclear reactor vibration surveillance system according to a seventh embodiment of the present invention. FIG. 12A is a characteristic view showing a display method of the original frequency of the reactor internal component which have no extraordinary frequency, and FIG. 12B is a characteristic view showing a setting method of a threshold value. As shown in FIG. 12A, the frequency analysis of the vibration information of the reactor internal component 14 which has been obtained through the processing of the signal processor 8 is performed to calculate the difference in frequency ΔF. Then, as shown in FIG. 12B, the temporal change of the difference in frequency ΔF of the reactor internal component 14 is displayed on the display unit 9. According to the present embodiment, the temporal change of the difference in frequency ΔF is displayed based on the measured vibration signal. This makes it easier to grasp occurrence of abnormal vibration, thereby increasing reliability of the vibration surveillance. Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above embodiments but may be modified in various ways by combining the configurations of the above embodiments without departing from the scope of the present invention.
044328940	summary	This invention relates to a process for the treatment of radioactive liquid wastes containing detergents, and particularly of laundry drainage containing detergents used for cleaning contaminated working clothes. At atomic power stations, etc. the radioactive laundry drainage containing detergents resulting from washing of contaminated working clothes usually amounts to several thousand cubic meters a year. These radioactive liquid wastes contain surface active agents such as sodium dodecylbenzenesulphonate and alkylphenol polyoxyethylene ether, which are ingredients of detergents. In general, radioactive liquid wastes are subjected to a final treatment after concentration to about 1/500 their original volume by evaporation or reverse osmosis. It is well-known, however, that radioactive liquid waste containing a surface active agent, if concentrated in its original condition, generates foams to prevent its concentration. Addition to the liquid waste of anti-foams such as powdered activated carbon (see Japanese Laid-open Patent Application No. 124,800/1976) and used ion exchange resin (see Japanese Laid-open Patent Application No. 101,100/1979), which adsorb the surface active agent, have hitherto been proposed as a means to prevent the foaming. On the other hand, some of the present inventors recently developed a process of converting the radioactive liquid waste which has been concentrated and made smaller in volume into powder by the use of a thin film evaporator and thereafter pelletizing the powdered waste for the convenience of storing it. The thin film evaporator is an apparatus having wiping blades within; the radioactive liquid waste is brought into contact with the heated inner wall of the apparatus in the form of a thin film, part of the waste is evaporated while it goes down along the wall and the remains are recovered in the form of powder. The following defects have been found for the first time as a result of the studies made by the present inventors. The process has a defect that the radioactive liquid waste fed to and concentrated in the evaporator tends to adhere to the blades, the recovered powdery material shows a high moisture content and at times the waste comes out of the apparatus without having been converted to powder, as was discovered later by the inventors. We then experimented on the effect of various kinds of adsorbent, which were added in accordance with the concentration of the detergent in the waste to counteract the surface active agent contained in the detergent, upon the powder-forming capacity of said evaporator, and found that although the capacity was clearly improved by the addition of adsorbent, the amount of the recovered powdery material was increased embarrassingly. This is a very serious problem, for in the treatment of radioative liquid waste it is most highly desirable to minimize the volume of the finished product in powder or pellet form. The object of the present invention is to produce a powdery material of low moisture content out of radioactive liquid waste containing detergents by adding a minimum of adsorbent to the waste. The invention is characterized in that an adsorbent is added in a quantity which corresponds to the chemical oxygen demand (COD) concentration of the waste when radioactive liquid waste containing detergents is to be converted to powder. It is based on our discovery that the COD concentration of the waste is the good measure of the total amount of the substances which hinder powder formation and are therefore to be removed by adsorbents. In other words, it has been found that not only detergents or surface active agents but also various auxiliaries included in the detergents for the purposes of pH adjustment and uniform distribution of surface active agent and impurities in the waste due to stains, etc. on clothing affect powder formation adversely. Accordingly, an optimum amount for additives can never be attained by merely determining the concentration or quantity of detergents or surface active agents in the waste and then estimating, on the basis thereof, the amount of adsorbents to be added for the purpose of restraining the foaming due to the presence of surface active agents, and consequently the additive amount is found to have been either so small as to increase the moisture content of the resultant powder or so large as to increase the amount thereof embarrassingly. On the other hand, the necessary and sufficient amount of adsorbents to be added for which the presence of auxiliaries, stains, etc. has been taken into account can be estimated on the basis of COD concentration of the waste, for the COD concentration sensitively corresponds to the types of surface active agents and auxiliaries, degree of deterioration of said agents due to stains, etc. on clothing, and other factors. Examples of suitable adsorbents are powdered active carbon, molecular sieve, silica gel, alumina, and other powdered adsorbents having a large surface area. The impurities in the radioactive waste are adsorbed by addition of a necessary quantity of the adsorbent. More particularly, the surface active agents that cause foaming are adsorbed all but entirely and the foaming ceases to occur in the course of powder formation, and consequently the moisture content of the resultant powder decreases remarkably. The invention is also characterized in that the radioactive waste converted to powder by the above process is further pelletized. The powder to be pelletized contains the adsorbent incorporated in powder form, the adsorbent particles having adsorbed a moderate amount of moisture coming from the waste on their porous surfaces. These porous surfaces help combine all the powder particles into tight pellets. For this reason the resultant pellets exhibit a breaking strength about 1.5 to 2 times as high as that of pellets containing no adsorbent. The pellets should be made as strong as possible lest they should cause breakage and scatter radioactive substances during their transportation. It is therefore an advantage of the present invention that the resultant pellets exhibit a higher breaking strength as well as a lower moisture content. It is a third characteristic of the invention that a thin film evaporator provided with wiping blades is employed for the formation of powder. Abrasion of the wiping blades poses a serious problem for the thin film evaporator, for the blades tend to come in contact with the inner wall of the evaporator during their rotation at high speed. In the present invention the powdered adsorbent added to the liquid waste serves as a buffer between the inner wall and the wiping blades to retard the rate of abrasion of the blades remarkably. It is a fourth characteristic of the invention that the liquid waste of a fixed COD concentration can be used for powder formation by adjusting the concentration of the radioactive waste to be converted to powder instead of varying the amount of the adsorbent to be added according to the COD concentration of the radioactive waste. In the invention the amount of adsorbent to be added is unchanged, since the COD concentration is fixed beforehand.
	summary
049903039	claims	1. In a fuel element for use in a nuclear reactor which includes a fissionable material contained within a zirconium-alloy cladding tube, the improvement which comprises: a coating on the inside of the zirconium-alloy cladding tube, said coating including a boron-containing glass compound. 2. The fuel element of claim 1 in which the coating's boron-containing compound includes boron enriched to at least a 80% level of to give a desired nuclear poison level for use in the nuclear reactor. 3. The fuel element of claim 1 in which the coating's boron-containing compound includes 15Na.sub.2 O.sup..multidot. 85B.sub.2 O.sub.3 or 20Li.sub.2 O.sup..multidot. B.sub. 2O.sub.3. 4. The fuel element of claim 1 in which the zirconium-alloy includes tin in the approximate range of from 1.20 to 1.70. 5. The fuel element of claim 1 in which the coating is a residue of a sol-gel. 6. The fuel element of claim 1 in which the coating is a residue of a sol-gel that has been heated to approximately 400 .degree. C.
063013193	description	DESCRIPTION OF THE PREFERRED PRACTICE The drawing schematically shows a temporary RPV head 10 resting on the flange 12 of a RPV 14 inside of circumferentially spaced studs, represented by stud 16 used to fasten the upper head (not shown) to the flange 12 during on-line power operations. As shown, the temporary RPV head 10 is in the process of being installed on the RPV 14 during, for example, a refueling outage when the reactor vessel 14 would be submerged under 20 to 30 feet of water or more (not shown) above the circumferential flange 12. The temporary RPV head 10 has an elliptical dome 20 and a circumferential flange 22. As shown, the dome 20 may be welded to the top surface of the flange 22 along its inner and outer diameters. The elliptical design advantageously provides high strength so that the thickness of the dome may be about 1 inch or less and support the weight of a heavy flange 22 during installation and later support the weight of the water above it. The dome 20 may have a vent 26 with a vent connection 28 for connecting with a tube (not shown) extending out of the water pool in order to remove water from the RPV 14 after the temporary RPV head 10 has been installed and then to refill the RPV 14 after completing the activity. The dome 20 may also have a passageway 31 for connection with a supply line (not shown) for introducing air or other gas into the RPV to displace the water. Three or more circumferentially spaced connector sockets, represented by connector socket 30, are attached to the dome 20 by support plates 32. As shown, connector socket 30 engages a mating connector 36 carried by a RPV internals lifting rig, such as the lifting rig of U.S. Pat. No. 4,272,321 and like assemblies. RPV internals lifting rigs used in the nuclear power industry structurally vary and are frequently employed with either roto-lock type or screw type connectors. The accompanying drawing shows the connector socket 30 and mating connector 36 as female and male elements of roto-lock type connections. The connector sockets 30 should be located on the elliptical dome 20 and otherwise adapted to carry the weight of the dome 20 and flange 22 without significant elastic deformation of the dome 20 when transported and to not interfere with support bars, legs and other structural members of the lifting rig. The flange 22 has a pair of circumferentially extending, radially spaced, seal rings, such as O-rings 40 and 42 for sealingly resting upon the RPV flange 12. The O-rings 40 and 42 may be fabricated of an elastomer such as an ethylene propylene diene co-polymer. The O-rings may be retained by the flange 22 in a dovetailed groove as shown in the accompanying drawing or by retaining means shown by U.S. Pat. No. 4,980,117. Advantageously, such seal rings 40 and 42 will form liquid-tight seals with the RPV flange 12 under the weight of the temporary RPV head 10 and a static head of twenty (20) feet of water or more without marking or damaging the RPV flange. In addition, mechanical fasteners are not needed to provide water-tight seals and pumps are not needed to pump out large volumes of in-leaking water. A vent 44 extends from between the O-rings 40 and 42 to a vent port 46 for connecting with a vent tube, such as vent tube 48 having a Swageloc connector or other suitable connector. Advantageously, the vent 44 may be employed in a leak test to verify that a liquid-tight seal has been established. Thus, for example, after the temporary RPV head 10 has been installed, the vent tube 48 connected and the water in the RPV 14 drawn down to a level below the flange 12, an air pressure in the vent 44 of about 20 psi or more may be established. If the pressure is maintained for about 5 minutes or longer, then the operator knows that a leak-tight temporary seal 20 has been installed. If the pressure can not be maintained, the temporary RPV head 10 may be raised upwardly of the RPV flange 12 and then reseated and the seal retested. If the pressure can not be maintained, temporary RPV head 10 may be removed from the RPV 14 and the O-rings 40 and/or 42 replaced. While a present preferred embodiment of the present invention has been shown and described, it is to be understood that the invention may be otherwise variously embodied within the scope of the following claims of invention.
	description	The present application claims the benefit of U.S. Provisional Patent Application No. 61/980,559, filed on Apr. 16, 2014, the contents of which are herein incorporated by reference in its entirety. The disclosed invention relates generally to radiation therapy systems, such as linear accelerator (linac) systems, and to radiation shields for use with such systems. A typical example of a radiation therapy photon producing linac system comprises a linac device placed within a large, thick, concrete-lined room or bunker. The linac usually rotates on a horizontal axis around a patient lying on a horizontal platform. Primary radiation is generated from the head of the linac. Primary radiation can emanate in multiple directions and potentially has considerable penetrating power depending on the energy range of the linac. Secondary radiation arises when primary radiation interacts with components of the linac, the patient, equipment in the bunker, and/or the walls of the bunker. Secondary radiation typically has less penetrating power, but remains an exposure health risk. The primary radiation beam is collimated to be mostly unidirectional. As the patient is treated, much of the primary radiation beam exits the patient and hits the thick walls of the bunker. The bunker is intended to shield the staff and the public from both primary radiation and secondary radiation. The bunker's shielding walls are stationary and completely decoupled from the linac device itself. Some such systems have a shield, or beam stopper, opposing the radiation source and that stays aligned with (and in opposition to) the radiation source as the two rotate. Configurations of linac systems may be limited in their directional geometry by their inherent size, orientation of beams relative to the patient, and integrated devices used in the control and guidance of the linac beam. Examples of radiation therapy systems are disclosed in U.S. Pat. Nos. 6,512,813 and 7,758,241; and in Pub. Nos. US 2012/0150016; US 2012/0150018; US 2012/0294424; and US 2013/0144104. This disclosure includes embodiments of radiation therapy systems in combinations with shielding for both primary and secondary radiation. This disclosure also includes embodiments of components of such systems, such as rail devices (or rail structures) to which one or more radiation sources and, optionally, one or more imaging sources may be coupled; such components may also include a housing for covering at least a portion of such rail devices. This disclosure also includes embodiments of shields, including shields having a dome shape and including a pivotable door that can cover an opening through which a patient may enter the shield. Some embodiments of the disclosed systems comprise a radiation therapy apparatus that includes an inner layer having a radiation delivery device and a primary radiation shielding device; and an outer layer having a secondary radiation shielding device. In some embodiments, the outer layer comprises a dome shape. In some embodiments, the inner layer further comprises one or more rails mounted on an inner surface of the inner layer, the rails being disposed in a circular shape. In some embodiments, the radiation delivery device and the primary radiation shielding device are disposed on the one or more rails, the primary radiation shielding device disposed opposite the radiation delivery device and configured to block primary radiation emitted from the radiation delivery device. In some embodiments, the apparatus further comprises a treatment table disposed inside the one or more rails. In some embodiments, the treatment table comprises a platform supported by one or more legs connected to the inner surface of the inner layer. In some embodiments, the treatment table is configured to isocentrically rotate 360 degrees around a vertical axis. In some embodiments, the treatment table is configured to move in a lengthwise direction, a widthwise direction, and an orthogonal direction relative to a horizontal axis, thereby allowing up to 4-pi (4π) steradians of beam entry toward the patient. In some embodiments, the inner layer further comprises one or more imaging sources. In some embodiments, the one or more imaging sources are disposed on the one or more rails. In some embodiments, the inner layer further comprises one or more imaging panels. In some embodiments, the one or more imaging sources are disposed on the one or more rails, the one or more imaging panels disposed opposite the one or more imaging sources and configured to receive radiation emitted from the one or more imaging sources. In some embodiments, the one or more imaging sources are X-ray emitting devices. In some embodiments, the one or more imaging sources provide one or more of 2D images, 3D images, 2D plus time images, and 3D plus time images. In some embodiments, the radiation delivery device comprises one or more of a linac device or a Co-60 emitting device. In some embodiments, the primary radiation shielding device comprises a beam block. In some embodiments, the radiation delivery device and the primary radiation shielding device rotate around a horizontal axis in synchrony with each other. In some embodiments, the radiation delivery device and the primary radiation shielding device rotate around a vertical axis in synchrony with each other. Some embodiments of the disclosed systems comprise a radiation therapy apparatus that includes an inner layer having a radiation delivery device and a primary radiation shielding device; and an outer layer having a secondary radiation shielding device, where the inner layer is movable in relation to the outer layer and the outer layer is disposed in a cylindrical tube shape. In some embodiments, the inner layer further comprises one or more rails mounted on an inner surface of the inner layer, the rails being disposed in a circular shape around a horizontal axis. In some embodiments, the radiation delivery device and the primary radiation shielding device are disposed on the one or more rails, the primary radiation shielding device disposed opposite the radiation delivery device and configured to receive primary radiation emitted from the radiation delivery device. In some embodiments, the radiation delivery device and the primary radiation shielding device rotate around a horizontal axis in synchrony with each other. In some embodiments, the radiation delivery device further comprises a treatment table disposed inside the one or more rails. In some embodiments, the treatment table is movable and configured to slide in a longitudinal direction along the horizontal axis. In some embodiments, the one or more rails are disposed to slide in a longitudinal direction along the horizontal axis. In some embodiments, the outer layer covering the ends of the tube comprises doors, the doors configured to enable the treatment table to enter the tube through a first door and exit the tube through a second door. Some embodiments of the disclosed systems comprise a radiation therapy apparatus, comprising a radiation delivery device disposed to rotate around a horizontal axis; a primary radiation shielding device; and an outer layer comprising a secondary radiation shielding device, configured to cover the radiation delivery device. In some embodiments, the outer layer comprises a dome shape. In some embodiments, the radiation delivery device further comprises one or more rails mounted on an inner surface of the outer layer, the rails being disposed in a circular shape. In some embodiments, the primary radiation shielding device is disposed on the one or more rails, the primary radiation shielding device disposed opposite the radiation delivery device and configured to block primary radiation emitted from the radiation delivery device. In some embodiments, the radiation delivery device comprises one or more of a linac device or a Co-60 emitting device. In some embodiments, the primary radiation shielding device comprises a beam block. In some embodiments, the radiation delivery device and the primary radiation shielding device rotate around a horizontal axis in synchrony with each other. In some embodiments, the radiation therapy apparatus comprises a secondary shielding device comprising a cylinder-shaped portion and a ring-shaped portion. In some embodiments, the ring-shaped portion is disposed to cover a radiation delivery device, and a primary radiation shielding device. In some embodiments, a housing is configured to cover the secondary shielding device. In some embodiments, the radiation therapy apparatus comprises one or more rails disposed in a circular shape and configured to rotate around a horizontal axis. In some embodiments, the radiation delivery device and the primary radiation shielding device are coupled to the one or more rails, the primary radiation shielding device being disposed opposite the radiation delivery device and configured to receive primary radiation emitted from the radiation delivery device. In some embodiments, the apparatus is configured so that the radiation delivery device and the primary radiation shielding device can rotate around a horizontal axis in synchrony with each other. In some embodiments, the apparatus further comprises a treatment table disposed inside the one or more rails. In some embodiments, the treatment table is movable and configured to slide in a longitudinal direction inside the inner layer. In some embodiments, the housing comprises one or more doors coupled to the third cylinder-shaped section. In some embodiments, a radiation therapy apparatus further comprises a gear device. In some embodiments, a rotating member is coupled to the gear device, the rotating member configured to rotate around a vertical axis. In some embodiments, the inner layer comprises a ring structure coupled to the rotating member. In some embodiments, the ring structure rotates around the vertical axis. In some embodiments, the apparatus further comprises a treatment table disposed inside the ring structure. In some embodiments, the treatment table is supported by one or more legs coupled to the outer layer. In some embodiments, the apparatus further comprises a floor, the floor being coupled to the ring structure and configured to rotate around a vertical axis. In some embodiments, the floor further comprises one or more openings disposed around the one or more legs, the openings configured to enable the floor to avoid contact with the one or more legs when the floor rotates about the vertical axis. In some embodiments, the apparatus is configured so that the radiation delivery device and the primary radiation shielding device can rotate around a horizontal axis in synchrony with each other. In some embodiments, the apparatus is configured to provide 4π steradians of radiation coverage to the isocentrically rotating treatment table. In some embodiments, a method of manufacturing a radiation therapy device comprises disposing a radiation delivery device on an inner layer; disposing a primary radiation shielding device on an inner layer, where the primary radiation shielding device is configured to block a primary radiation beam emitted from the radiation delivery device; and disposing an outer layer covering the inner layer, the outer layer comprising a secondary radiation shielding layer configured to block secondary radiation. In some embodiments, a radiation therapy apparatus comprises a circular rail structure comprising a radiation delivery device and a primary radiation shielding device. In some embodiments, the rail structure is disposed to rotate around a horizontal axis. In some embodiments, a bed is configured to isocentrically rotate 360 degrees around a vertical axis and is disposed at a center of the circular rail structure. In some embodiments, a secondary radiation shielding device is configured to cover the radiation delivery device and the primary radiation shielding device. In some embodiments, the bed is further configured to move in a vertical direction and configured to receive 4π steradians of radiation coverage. In some embodiments, a radiation therapy apparatus comprises a circular rail structure comprising a radiation delivery device and a primary radiation shielding device. In some embodiments, the rail structure is disposed to rotate around a horizontal axis. In some embodiments, a bed is configured to move in three spatial directions and is disposed at a center of the circular rail structure. In some embodiments, a secondary radiation shielding device is configured to cover the radiation delivery device and the primary radiation shielding device. In some embodiments, the bed is further configured to move in directions that comprise length, width, and depth and receive 4π steradians of radiation coverage. The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. Two items are “couplable” if they can be coupled to each other. Unless the context explicitly requires otherwise, items that are couplable are also decouplable, and vice-versa. One non-limiting way in which a first structure is couplable to a second structure is for the first structure to be configured to be coupled (or configured to be couplable) to the second structure. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially,” “approximately,” and “about” may be substituted with “within [a percentage] of” what is specified, where the percentage includes 0.1, 1, 5, and 10 percent. The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a systems, or a component of a systems, that “comprises,” “has,” “includes” or “contains” one or more elements or features possesses those one or more elements or features, but is not limited to possessing only those elements or features. Likewise, a method that “comprises,” “has,” “includes” or “contains” one or more steps possesses those one or more steps, but is not limited to possessing only those one or more steps. Additionally, terms such as “first” and “second” are used only to differentiate structures or features, and not to limit the different structures or features to a particular order. Any embodiment of any of the disclosed systems or system components (such as shields) can consist of or consist essentially of—rather than comprise/include/contain/have—any of the described elements and/or features. Thus, in any of the claims, the term “consisting of” or “consisting essentially of” can be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb. The feature or features of one embodiment may be applied to other embodiments, even though not described or illustrated, unless expressly prohibited by this disclosure or the nature of the embodiments. Details associated with the embodiments described above and others are presented below. Referring now to the drawings, and more particularly to FIG. 1, system 10, which is one embodiment of the disclosed systems, is shown. In the embodiment shown, a modular dome 12, door 14, and base 16 comprise an outer shielding layer for a radiation therapy device. Floor 22 may be disposed inside base 16. In the embodiment shown, dome 12 is comprised of two sections 68 coupled together with fasteners 70. In other alternative embodiments, dome 12 may comprise a single section or more than two sections coupled together, and may be characterized as a stationary element. Sections 68 may be coupled together such as by riveting, bolting, welding, bonding, brazing, dimpling, or the like. In the embodiment shown, ring 54 is disposed within dome 12. Inner face 60 may be configured to rotate about a horizontal axis. This rotation enables collimator 38, a primary shielding device (not shown), imaging sources 46a-b, and imaging panels 50a-b to be positioned in various configurations about treatment table 64. In the embodiment shown, treatment table 64 is disposed around an isocenter of ring 54 and comprises bed 72 disposed centrally on treatment table 64. The isocenter of ring 54 represents the point in space where radiation beams emitted from collimator 38 intersect as inner face 60 rotates. Treatment table 64 may rotate about a vertical axis via tracks, rollers, ball bearings, or the like. In the embodiment shown, treatment table 64 further comprises one or more legs 66 coupling treatment table to the center of floor 22. One or more legs 66 may be disposed on a side of channel 24. In some embodiments, legs 66 may be configured to move or telescope in a vertical direction. In the embodiment shown, treatment table 64 is disposed over channel 24 and is configured with adequate height to allow collimator 38, imaging sources 46a-b, and imaging panels 50a-b, protruding from (or otherwise having portions positioned more inwardly than) inner face 60 to clear the underside of treatment table 64. In some embodiments, treatment table 64 may move up and down in a vertical direction via legs 66. In the embodiment shown, ring 54 is disposed to provide a source-to-isocenter distance of greater than 1 meter (m) between a radiation source (not shown) and the isocenter. FIGS. 2A and 2B show an embodiment of the disclosed shields, which can be retrofitted to an existing radiation therapy system or used with one of the disclosed radiation therapy systems. Dome 12 can be coupled to base 16 such as by riveting, bolting, welding, bonding, or the like. Door 14 can be coupled to the top of dome 12 in such a way as to allow door 14 to rotate around dome 12 on a vertical axis. Door 14, as the depicted embodiment shows, may have a curved surface or profile that matches or cooperates with an adjacent surface or profile of dome 12. Accordingly, dome 12 and door 14 may, together, have a substantially dome configuration. In the embodiment shown, door 14 is disposed on the outside of dome 12 and enabled to partially rotate around dome 12. In other embodiments, door 14 may be disposed on the inside of dome 12 and/or may be enabled to completely rotate around dome 12. The bottom of door 14 can be disposed in guide 18. Guide 18 may be set into base 16 and outside a side face of dome 12 in an arc shape. Alternatively, guide 18 may be disposed on top of base 16. Door 14 may slide along guide 18 using tracks, rollers, ball bearings, or the like. Dome 12 may be configured with an opening. In the embodiment shown, opening 20 is disposed in a face of dome 12. Opening 20 is sufficiently large to admit one or more humans to the interior of dome 12. In the embodiment shown, door 14 is disposed to cover and uncover opening 20 by rotating around dome 12 along the path of guide 18. In the embodiment shown, floor 22 is disposed over the bottom of dome 12. The top of floor 22 may be on the same horizontal plane as the top of base 16. Alternatively, floor 22 may be on a different horizontal plane than the top of base 16. In the embodiment shown, the outer layer of the depicted system—including dome 12, door 14, and base 16—is constructed of a single type or multiple types of radiation shielding material such as lead, steel, tungsten, concrete, or the like. In the embodiment shown, the thicknesses of dome 12, door 14, and base 16 are sufficient to block secondary radiation. For purposes of description, primary radiation comprises radiation emitting directly from a radiation delivery device passing through the opening of collimator 38. Secondary radiation comprises all other radiation present, such as radiation emitted from the radiation delivery device in other than the intended therapeutic direction, radiation scattered within a patient, or radiation scattered within a treatment room. As shown in FIG. 3, floor 22 may be disposed to cover the bottom of dome 12. Floor 22 may comprise a covering over open space between the top surface of the bottom of dome 12 and the bottom surface of floor 22. Alternatively, floor 22 may comprise a solid material coupled to the bottom of dome 12 and filling in the bottom of dome 12. FIG. 3 also shows an embodiment of another component of the disclosed systems—a channel that supports a rotating rail structure to which the radiation delivery device and, optionally, one or more imaging sources may be coupled. In the embodiment shown, channel 24 is inset into floor 22 and positioned such that a plane located at and parallel to the top of surface of channel 24 is coincident with a plane positioned on the surface of floor 22. Alternatively, the top of channel 24 may be positioned above or below the surface of floor 22. In the embodiment shown, the bottom surface of channel 24 is an arc shape, which in some embodiments can mirror or match the arc shape of dome 12. Channel 24 also includes a structural framework 26 that spans the sides and bottom surface of channel 24. Channel 24 may be supported in the system by being coupled to base 16, such as by legs 28, which may be coupled to floor 22. Channel 24 may comprise rolling mechanisms 30 disposed intermittently along the inside surface (such as along both the sides and bottom) of framework 26, which mechanisms will facilitate the movement of the rail structure described below. Rolling mechanisms 30 can be tracks, rollers, ball bearings, or the like. In an alternative embodiment, channel 24 may be solid, and may not include framework 26. FIG. 4 shows an embodiment of another component of the disclosed systems—a rotating rail structure to which the radiation delivery device and, optionally, one or more imaging sources may be coupled. In the embodiment shown in FIG. 4, rail structure 32 comprises one or more rails 34 disposed in a circular shape. In the embodiment shown, rails 34 are 0.050 m thick and have 0.45 m of distance between an outer rail 34a and inner rail 34b. In the embodiment shown, a diameter of rail structure 32 is 3.4 m and an inner diameter is 2.95 m. In other embodiments involving the depicted structures, other dimensions may be used. In the embodiment shown, radiation delivery device 36 and collimator 38 are provided. Radiation delivery device 36 may comprise a linac, proton or ion beam accelerator, Co-60 isotopic source, ortho- or supervoltage X-ray generator, or other particle accelerator. Radiation delivery device 36 may be coupled to one or more rails 34 in a stationary position. Alternatively, radiation delivery device 36 may be coupled to one or more rails 34 so as to allow radiation delivery device to move along rail structure 32. In the embodiment shown, radiation delivery device 36 is affixed to receptacle 37, which is coupled to rail structure 32. In the embodiment shown, radiation delivery device 36 further comprises collimator 38. Alternatively, radiation delivery device 36 may be provided without collimator 38. In the embodiment shown, collimator 38 is positioned to have emission face 40 directed toward the inner area and center of rail structure 32. In the embodiment shown, collimator 38 is 0.500 m long. In other embodiments involving the depicted structures, other dimensions may be used. In the embodiment shown, primary shielding device 42 is provided. Primary shielding device 42 may be a beam block and may be comprised of lead, steel, tungsten, concrete, or other suitable shielding material. In the embodiment shown, the thickness of primary shielding device 42 is sufficient to block a primary radiation beam of radiation delivery device 36 without additional assistance. Primary shielding device 42 may be configured to block radiation so that it reduces at least 99.9% of the radiation resulting from the operation of radiation delivery device 36. Primary shielding device 42 may be coupled to one or more rails 34 in a stationary position. Alternatively, primary shielding device 42 may be coupled to one or more rails 34 so as to allow primary shielding device 42 to move along rail structure 32. In the embodiment shown, primary shielding device 42 is affixed to receptacle 43, which is coupled to rail structure 32. In the embodiment shown, primary shielding device 42 is positioned to have receiving face 44 directed toward the inner area and center of rail structure. In the embodiment shown, primary shielding device 42 is positioned opposite radiation delivery device 36 on rail structure 32. In some embodiments, an opposite position comprises being positioned at a 180° angle from another position. By positioning primary shielding device 42 opposite radiation delivery device 36, primary shielding device 42 directly receives and blocks primary radiation emitted by radiation shielding device 36. In the embodiment shown, primary shielding device 42 is 0.850 m wide and 0.170 m thick. In other embodiments involving the depicted structures, other dimensions may be used. In the embodiment shown, one or more imaging sources 46a, 46b are provided. Imaging sources 46a-b may comprise X-ray, cone beam computed tomography (CT), ultrasound imaging, positron emission tomography (PET), single photon emission computed tomography (SPECT), or magnetic resonance imaging (MRI) technologies. Imaging sources 46a-b may be coupled to one or more rails 34 in a stationary position. Alternatively, imaging sources may be coupled to one or more rails 34 so as to allow imaging sources 46 to move along rail structure 32. In the embodiment shown, imaging sources 46a-b are affixed to receptacles 47a-b, respectively, which are coupled to rail structure 32. In the embodiment shown, imaging sources 46a-b are positioned to have emission faces 48a-b directed toward the inner area and center of rail structure 32. Imaging sources 46a-b may be provided intermittently on rail structure 32 between radiation delivery device 36 and primary shielding device 42. In the embodiment shown, one or more imaging panels 50a-b are provided. Imaging panels 50a-b may receive the emission of X-rays or the like from imaging sources 46a-b. Imaging panels 50a-b may be coupled to one or more rails 34 in a stationary position. Alternatively, imaging panels 50a-b may be coupled to one or more rails 34 so as to allow imaging panels 50a-b to move along rail structure 32. In the embodiment shown, imaging panels 50a-b are affixed to receptacles 51a-b, respectively, which are coupled to rail structure 32. In the embodiment shown, imaging panels 50a-b are positioned to have receiving faces 52a-b directed toward the inner area and center of rail structure 32. Imaging panels 50a-b may be provided intermittently on rail structure 32 between radiation delivery device 36 and primary shielding device 42. In the embodiment shown, imaging panels 50a-b are positioned opposite imaging sources 46a-b on rail structure 32. By positioning imaging panels 50a-b opposite imaging sources 46a-b, imaging panels 50a-b directly receive imaging radiation emitted by imaging sources 46a-b. FIG. 5 shows rail structure 32 in operative relation with framework 26, and further shows an embodiment of another component of some of the disclosed systems—treatment table 64. In the embodiment shown in FIG. 5, rail structure 32 is combined with framework 26 and treatment table 64. Rail structure 32 is configured to be set into framework 26 and slide along rolling mechanisms 30. In the embodiment shown, outer rails 34a of rail structure 32 are disposed on a top surface of rolling mechanisms 30 disposed on the bottom of framework 26. In the embodiment shown, inner rails 34b are disposed on a bottom surface of rolling mechanisms 30 disposed on the sides of framework 26 in an arc shape. Rolling mechanisms 30 may be coupled to one or more electric power sources such as an electric motor, which may be configured to power the rotation of rolling mechanism 30. In the embodiment shown, as rolling mechanisms 30 rotate, outer rails 34a and inner rails 34b are moved along rolling mechanisms 30. This action rotates rail structure 32 around treatment table 64. Although not shown, braking mechanisms may also be coupled to framework 26 for applying to one or both of the outer and inner rails in order to stop the motion of the rails as desired. In the embodiment shown, collimator 38, imaging sources 46a-b, and imaging panels 50a-b, are disposed to rotate around treatment table 64 as rail structure 32 rotates. Collimator 38, imaging sources 46a-b, and imaging panels 50a-b may be configured to pass underneath training table 64 as rail structure 32 rotates. FIGS. 6A and 6B show an embodiment of another component of the disclosed systems—a housing for the rotating rail structure to which the radiation delivery device and, optionally, one or more imaging sources may be coupled. In the embodiment shown in FIGS. 6A and 6B, the outer housing, which is depicted as ring 54, comprises outer face 56, side faces 58, and inner face 60. Inner face 60 comprises openings or holes 62 disposed at intermittent intervals along the surface of inner face 60, which openings are configured to allow through-placement of portions of the relevant radiation source(s), imaging source(s), and their respective shields/panels. The portions of ring 54 other than inner face 60 may comprise two halves or other multiple modular pieces coupled together, with each half or piece including a portion of outer face 56 and a side face 58. In the embodiment shown, the outer and side faces of ring 54 are stationary and are coupled to floor 22 in any suitable manner. Inner face 60 may be coupled to rail structure 32 so as to rotate with rail structure 32 around a horizontal axis; thus, inner face 60 may be movable relative to the outer and side faces of ring 54 and may also be movable through channel 24 and underneath floor 22. In certain embodiments, ring 54 may comprise an inner layer disposed inside an outer layer such as dome 12. FIG. 7 shows a cross section of an exemplary embodiment of system 10. In the embodiment shown, dome 12 is coupled to base 16, with the bottom of dome 12 resting within base 16. Door 14 is disposed outside the outer surface of dome 12 and configured to rotate around (or at least partially around) dome 12. Ring 54 is contained inside dome 12 and a portion of the inner face of ring 54 is disposed in channel 24 underneath floor 22. In the embodiment shown, outer face 56 of ring 54 is stationary and is affixed to floor 22 at the edge of channel 24 via framework 26. In the embodiment shown, framework 26 comprises rolling mechanisms 30 disposed on the inner surface of framework 26 of channel 24. In the embodiment shown, rail structure 32 is disposed inside of ring 54 and configured to rotate around a horizontal axis within the outer portion of ring 54. In the embodiment shown, rail structure 32 passes underneath floor 22 and is configured to rotate by rolling on rolling mechanisms 30. Rail structure 32 may be coupled to a power source providing the power necessary for the rotation of rail structure 32. In the embodiment shown, radiation delivery device 36, imaging sources 46, primary shielding device 42, and imaging panels 50 are intermittently coupled in a stationary manner to rail structure 32. In the embodiment shown, imaging sources 46a-b are intermittently disposed on one side of radiation delivery device 36 while imaging panels 50a-b are intermittently disposed on the other side of radiation delivery device 36. In alternative embodiments, imaging sources 46 and imaging panels 50a-b may be alternately coupled along rail structure 32. In the embodiment shown, imaging panels 50a-b are disposed opposite imaging sources 46a-b. In the embodiment shown, primary shielding device 42 is disposed opposite radiation delivery device 36. Collimator 38, imaging sources 46a-b, and imaging panels 50a-b are configured to protrude through openings 62 (shown in FIGS. 6A-B) disposed in inner face 60 of ring 54. In an alternative embodiment, collimator 38, imaging sources 46a-b, and imaging panels 50a-b may be disposed inside ring 54. In the embodiment shown, rail structure 32 and inner face 60 of ring 54 are configured to rotate on a horizontal axis around treatment table 64. In the embodiment shown, treatment table 64 is configured in a horizontal position and coupled to floor 22 via one or more legs 66. Treatment table 64 may be centrally located within ring 54 and configured to rotate about a vertical axis. In alternative embodiments, treatment table 64 may be configured to move spatially in three dimensional directions or be coupled to a surface other than floor 22, such as an inner wall of dome 12 or an outer face 56 or side face 58 of ring 54. In the embodiment shown, radiation delivery device 36 and imaging sources 46a-b emit radiation onto treatment table 64. In the embodiment shown, as treatment table 64 rotates about a vertical axis and rail structure 32 rotates about a horizontal axis, a patient lying on treatment table 64 may receive radiation treatment from multiple directions and angles. These multiple directions and angles may be represented in steradians, or solid angle units. In the embodiment shown, a combination of the rotation of treatment table 64 and the rotation of rail structure 32 enables 4π steradians of radiation coverage to be applied to a patient situated at the isocenter. FIG. 8 depicts a side, schematic view of a second embodiment of the disclosed systems. In the embodiment shown, radiation delivery device 36 is disposed inside dome 12. In the embodiment shown, dome 12 is configured as a secondary radiation shielding device. Radiation delivery device 36 may be coupled to arm 74. Radiation delivery device 36 may be disposed to rotate about a horizontal axis around treatment table 64. Treatment table 64 may be disposed to rotate about a vertical axis. In the embodiment shown, emission face 40 of radiation delivery device 36 is disposed to emit a radiation beam to the intersection of the rotational axes of treatment table 64 and radiation delivery device 36. Therefore, in the embodiment shown, as treatment table 64 rotates on a vertical axis and radiation delivery device 36 rotates on a horizontal axis, a patient lying on treatment table 64 may receive radiation treatment from multiple directions and angles. In the embodiment shown, inner layer 76 is coupled to the inner surface of dome 12. Inner layer may comprise rail structure 32 (which may comprise, as explained above, one or more rails 34). In the embodiment shown, primary shielding device 42 is coupled to inner layer 76 and disposed to rotate around a horizontal axis. In the embodiment shown, primary shielding device 42 rotates to a position opposite emission face 40 of radiation delivery device 36. In doing so, primary shielding device 42 may rotate to a position underneath floor 22. This enables the primary shielding device 42 to absorb the primary radiation emitted from radiation delivery device 36. Primary shielding device 42 may rotate in synchrony with (or synchronously with) or independently of radiation delivery device 36. FIGS. 9A-B depict a side view and a top down view of a third embodiment of the disclosed systems. In the embodiment shown in FIGS. 9A-B, dome 12 is configured as a secondary radiation shielding device. In the embodiment shown, inner layer 76 is coupled to the inner surface of dome 12. Inner layer 76 may comprise rail structure 32 (which may comprise, as explained above, one or more rails 34). In the embodiment shown, radiation delivery device 36 and primary shielding device 42 are coupled to inner layer 76 and disposed to rotate around a vertical axis in a horizontal plane. The horizontal plane may coincide with the diameter of the dome 12. In the embodiment shown, primary shielding device 42 is disposed in a position opposite emission face 40 of radiation delivery device 36. This enables the primary shielding device 42 to absorb the primary radiation emitted from radiation delivery device 36. Primary shielding device 42 may rotate in synchrony with (or synchronously with) or independently of radiation delivery device 36. In the embodiment shown, treatment table 64 may be disposed at the center of dome 12. In the embodiment shown, treatment table 64 is configured to slide in each of a lengthwise (L), widthwise (W), and depthwise (D) direction, as shown by arrows in FIGS. 9A-B. Therefore, in the embodiment shown, as treatment table 64 moves in three spatial directions, a patient lying on treatment table 64 may receive radiation treatment from multiple directions and angles. FIG. 10 shows a fourth embodiment of the disclosed systems. In the embodiment shown in FIG. 10, the system's outer layer comprises a secondary radiation shield in the form of housing 78, which may be configured as a partial or complete cylinder (both of which may be characterized as cylinder-shaped) with at least one closable opening though which a patient and/or others may pass in preparation for radiation therapy. As shown in the depicted embodiment, the closable opening may be positioned at one end of the housing (though in other embodiments it may be located elsewhere), and housing 78 may comprise one or more doors 80 coupled to a central portion of the cylinder-shaped structure for opening/closing to thereby cover the closable opening; such doors may be disposed at one or both ends of housing 78. Housing 78, including doors 80, may comprise the same material(s) as dome 12 and door 14. In the embodiment shown, rail structure 32 is disposed inside housing 78 and coupled to framework 26. In the embodiment shown, framework 26 is disposed to move longitudinally along base 16, which is coupled to housing 78. In the embodiment shown, framework 26 moves via threaded bars 79 coupled to base 16 and along guides 18 disposed on the bottom surface of base 16. As rail structure 32 moves longitudinally, telescoping panels 81 disposed between threaded bars 79 may be configured to retract in a longitudinal direction toward doors 80. In the embodiment shown, radiation delivery device 36, imaging sources 46a-b, imaging panels 50a-b, and primary shielding device 42 are coupled to rail structure 32 and disposed to rotate around a horizontal axis passing through the center of rail structure 32. Rail structure 32 may be configured as shown in FIG. 4. In the embodiment shown, rail structure 32 is disposed within channel 24 and configured to rotate within channel 24 via rolling mechanisms 30. In the embodiment shown, primary shielding device 42 is disposed in a position opposite emission face 40 of radiation delivery device 36. This enables primary shielding device 42 to absorb the primary radiation emitted from radiation delivery device 36. Primary shielding device 42 may rotate in synchrony with (or synchronously with) radiation delivery device 36. In the embodiment shown, treatment table 64 may be disposed on a horizontal axis at the longitudinal center of housing 78. In the embodiment shown, treatment table 64 is coupled to telescoping legs 66, which attach treatment table 64 to floor 22. In the embodiment shown, treatment table 64 is configured to move up and down in a vertical direction via legs 66. In the embodiment shown, treatment table 64 is further configured to move in a horizontal directions. In the embodiment shown, radiation delivery device 36 and primary shielding device 42 may rotate azimuthally on rail structure 32 as rail structure 32 moves longitudinally along the horizontal axis via threaded bars 79. FIG. 11 shows a fifth embodiment of the disclosed systems. In the embodiment shown in FIG. 11, the system's outer layer comprises a secondary radiation shield in the form of housing 78, which may be configured as a partial or complete cylinder (both of which may be characterized as cylinder-shaped) with at least one closable opening though which a patient and/or others may pass in preparation for radiation therapy. As shown in the depicted embodiment, the closable opening may be positioned at one end of the housing (though in other embodiments it may be located elsewhere), and housing 78 may comprise one or more doors 80 coupled to a central portion of the cylinder-shaped structure for opening/closing to thereby cover the closable opening; such doors may be disposed at one or both ends of housing 78. Housing 78, including doors 80, may comprise the same material(s) as dome 12 and door 14. In the embodiment shown, rail structure 32 is disposed inside housing 78 and coupled to framework 26. In the embodiment shown, framework 26 is disposed in a fixed position within base 16. In some embodiments, framework 26 may be disposed centrally within housing 78. In the embodiment shown, radiation delivery device 36, imaging sources 46a-b, imaging panels 50a-b, and primary shielding device 42 are coupled to rail structure 32 and disposed to rotate around a horizontal axis passing through the center of housing 78. Rail structure 32 may be configured as shown in FIGS. 4-5. In the embodiment shown, primary shielding device 42 is disposed in a position opposite emission face 40 of radiation delivery device 36. This enables primary shielding device 42 to absorb the primary radiation emitted from radiation delivery device 36. Primary shielding device 42 may rotate in synchrony with (or synchronously with) radiation delivery device 36. In the embodiment shown, the system includes a table system 61 that includes treatment table 63 that may be disposed on a horizontal axis at the longitudinal center of housing 78. As shown in FIG. 12, which illustrates the table system shown in FIG. 11, table system 61 also includes a treatment table guide 65 along which treatment table 63 may slide. Treatment table guide 65 may be configured to remain stationary. In the embodiment shown, table system 61 also includes pedestal 67 to which treatment table guide 65 is coupled (e.g., affixed), and pedestal 67 may be configured to remain stationary. In some embodiments, pedestal 67 may be affixed to floor 22. In some embodiments, pedestal 67 may be affixed beneath floor 22 and may protrude above floor 22. In some embodiments, pedestal 67 may be affixed to rear wall 85 of housing 78. In some embodiments, treatment table 63 of table system 61 is moveably affixed to treatment table guide 65 and configured to move longitudinally along a horizontal axis as well as vertically and laterally. In the embodiment shown, radiation delivery device 36 and primary shielding device 42 may rotate azimuthally on rail structure 32 as treatment table 63 moves longitudinally along the horizontal axis over treatment table guide 65. FIGS. 13A-D show a sixth embodiment of the disclosed systems. In the embodiments shown in FIGS. 13A-D, the system's outer layer comprises a housing 78, which may be configured as a partial or complete cylinder (both of which may be characterized as cylinder-shaped) with at least one closable opening though which a patient may pass in preparation for radiation therapy. As shown in the depicted embodiment, the closable opening may be positioned at one end of the housing (though in other embodiments it may be located elsewhere), and housing 78 may comprise one or more doors 80 coupled to a central portion of the cylinder-shaped structure for opening/closing to thereby cover the closable opening; such doors may be disposed at one or both ends of housing 78. In the embodiment shown, rail structure 32 is disposed inside housing 78 and coupled to framework 26. In the embodiment shown, framework 26 is disposed in a fixed position within base 16. In some embodiments, framework 26 may be disposed centrally within housing 78. In the embodiment shown, radiation delivery device 36, imaging sources 46a-b, imaging panels 50a-b, and primary shielding device 42 are coupled to rail structure 32 and disposed to rotate around a horizontal axis passing through the center of housing 78. Rail structure 32 may be configured as shown in FIGS. 4-5. In the embodiment shown, primary shielding device 42 is disposed in a position opposite emission face 40 of radiation delivery device 36. This enables primary shielding device 42 to absorb the primary radiation emitted from radiation delivery device 36. Primary shielding device 42 may rotate in synchrony with (or synchronously with) radiation delivery device 36. In the embodiment shown, the system includes a table system that includes treatment table 63 that may be disposed on a horizontal axis at the longitudinal center of rail structure 32. In some embodiments, the table system, which may be like table system 61 but may lack pedestal 67, may include treatment table guide 65 along which treatment table 63 may slide. In some embodiments, treatment table guide 65 may be coupled (e.g., affixed) to modular shield 86 and configured to be stationary. In such embodiments, treatment table 63 may be moveably coupled to treatment table guide 65 and configured to move longitudinally along a horizontal axis as well as vertically and laterally. In some embodiments, treatment table 63 may be affixed in a stationary manner to treatment table guide 65. In such embodiments, treatment table guide 65 is configured to be movably coupled to modular shield 86 and can slide on a horizontal axis. In the embodiments shown in FIGS. 13A-D, modular shield 86 comprises a cylinder portion 88 and a ring portion 89 and acts as a secondary shielding device. In the embodiment shown, cylinder portion 88 and ring portion 89 are situated around treatment table 63 and rail structure 32, respectively. Therefore, the secondary shielding of the system of this embodiment is reduced azimuthally as compared to other embodiments described herein. In the embodiment shown, cylinder portion 88 is disposed in a cylinder shape and extends along the longitudinal center of housing 78. In the embodiment shown, cylinder portion 88 comprises a gap having a width of rail structure 32. In the embodiment shown, the gap in cylinder portion 88 is configured to avoid obstructing the movement of collimator 38, imaging sources 46a-b, imaging panels 50a-b, and primary shielding device 42 as rail structure 32 rotates. In some embodiments, treatment table 63 may be positioned over the gap. In such a configuration, the gap in cylinder portion 88 enables radiation emitted from collimator 38 to reach a patient lying on treatment table 63. In the embodiment shown in FIGS. 13A-D, ring portion 89 of modular shield 86 has a partial ring shape and is disposed within housing 78 to cover the outside surfaces of rail structure 32. In the embodiment shown, rail structure 32 is disposed to rotate freely within ring portion 89. In the embodiment shown, ring portion 89 is coupled to cylinder portion 88 at both sides of the gap in cylinder portion 88 to form modular shield 86. In the embodiment shown, ring portion 89 is further coupled to the top of base 16. In the embodiment shown in FIG. 13A, collimator 38, imaging sources 46a-b, imaging panels 50a-b, and primary shielding device 42 are disposed inside ring portion 89. In the embodiments shown, radiation delivery device 36 and primary shielding device 42 may rotate azimuthally on rail structure 32 as treatment table 63 moves longitudinally along a horizontal axis over treatment table guide 65. FIGS. 14A-C shows a seventh embodiment of the disclosed systems. In the embodiment shown, modular dome 12, door 14, and base 16 comprise the secondary shielding layer of the system. In the embodiment shown, bed 72 of the system is disposed at an isocenter of dome 12 and is coupled to one or more legs 66. In the embodiment shown, one or more legs 66 couple bed 72 to the surface of base 16 in a stationary position. In some embodiments, bed 72 may be configured to move in three spatial directions. In some embodiments, the three spatial directions may be lengthwise, widthwise, and depthwise. In the embodiment shown, openings 90 are situated in floor 22 and disposed on both sides of channel 24. In the embodiment shown, legs 66 extend below floor 22 through openings 90 to the surface of base 16. In the embodiment shown, floor 22 is configured to be partially movable about a vertical axis. In the embodiment shown, openings 90 are large enough to accommodate a movement of floor 22 associated with a rotation of ring 54 about the vertical axis. In the embodiment shown, the system includes primary gear 92, which is disposed horizontally within base 16 (and outside dome 12) and firmly coupled (e.g., attached, by welding for example) to framework 26 or ring 54. In the embodiment shown, gear 92 is configured to partially rotate about a vertical axis. In the embodiment shown in FIG. 14B, as gear 92 rotates, channel 24 rotates, resulting in ring 54 rotating about the same vertical axis as gear 92. In the embodiment shown, floor 22 abuts framework 26 and rotates as ring 54 rotates. In the embodiment shown, the system includes one or more motors 94 that are coupled to one or more secondary gears 96. In the embodiment shown in FIG. 14C, secondary gears 96 are powered by motors 94 to partially rotate about respective vertical axes (that are parallel to the axis about which gear 92 can rotate). In the embodiment shown, secondary gears 96 are coupled to primary gear 92. In the embodiment shown, as secondary gears 96 rotate, they drive primary gear 92 to rotate. In the embodiment shown, rail structure 32 is disposed within ring 54 and may be configured as shown in FIGS. 4-5. In the embodiment shown, primary shielding device 42 is disposed in a position opposite emission face 40 of collimator 38. This enables primary shielding device 42 to absorb the primary radiation emitted from collimator 38. Primary shielding device 42 may rotate in synchrony with (or synchronously with) collimator 38. In the embodiment shown, the rotation of ring 54 about the vertical axis combined with the rotation of rail structure 32 about the horizontal axis enables radiation to be applied to a patient on bed 72 from many different angles. In some embodiments, the disclosed secondary radiation shields are configured as mobile units that will be unconnected to the structural framework of the buildings in which they can be used. They can substantially cover the disclosed treatment tables, rings, and radiation delivery devices. As a result, leakage radiation produced by the radiation delivery devices and not intended for therapeutic usage should not be able to breach the secondary radiation shield. Therefore, anyone outside the secondary radiation shield should not be materially affected by primary or secondary radiation. The above specification and examples provide a complete description of the structure and use of exemplary embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the disclosed devices are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, components may be combined as a unitary structure and/or connections may be substituted. Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.
	claims	1. A method of fabricating a flat product of zirconium alloy, comprising:one of preparing and casting a zirconium alloy ingot containing at least 95% by weight of zirconium, and including impurities and alloying elements;shaping the ingot in order to obtain a flat arrangement;subjecting the flat arrangement to a β quenching operation under conditions that are determined to obtain within the flat arrangement an acicular structure at an end of the β quenching;subjecting the flat arrangement, after the β quenching, to a rolling operation performed in a single rolling sequence without intermediate annealing, the rolling performed at a temperature lying in a range ambient to 200° C., with a reduction ratio lying in a range 2% to 20%; andsubjecting the rolled flat arrangement to an annealing treatment in the α range or in the α+β range, performed in a temperature range 500° C. to 800° C. for 2 mm to 10 h. 2. A method according to claim 1, wherein the alloy element contents by weight are Sn=1.2% to 1.7%, Fe=0.07% to 0.20%, Cr=0.05% to 0.15%, Ni=0.03% to 0.08%, O=900 ppm to 1600 ppm. 3. A method according to claim 1, wherein the alloy element contents by weight are Sn=1.2% to 1.7%, Fe=0.18% to 0.24%, Cr=0.05% to 0.15%, O=900 ppm to 1600 ppm. 4. A method according to claim 1, wherein the alloy element contents by weight are: Sn=0.5% to 2%, Nb=0.5% to 2%, Fe=0.1% to 0.5%. 5. A method according to claim 1, wherein an alloy element contents by weight are: Sn=0.5% to 2%; Fe=0.1% to 1%; Cr=0.1% to 1.2%. 6. The method according to claim 1, wherein the alloy element contents by weight are: Nb=1.5% to 3.5%; Sn=0.5% to 2%. 7. The method according to claim 1, wherein the rolling following the β quenching is performed with a reduction ratio of 5% to 16%. 8. The method according to claim 7, wherein the rolling following the β quenching is performed with a reduction ratio of 5% to 10%. 9. The method according to claim 1, wherein the cooling of the β quenching is performed at a speed of at least 1° C./s. 10. A zirconium alloy flat product, obtained by the method:one of preparing and casting a zirconium alloy ingot containing at least 95% by weight of zirconium, and including impurities and alloying elements;shaping the ingot in order to obtain a flat arrangement;subjecting the flat arrangement to a β quenching operation under conditions that are determined to obtain within the flat arrangement an acicular structure at an end of the β quenching;subjecting the flat arrangement, after the β quenching, to a rolling operation performed in a single rolling sequence without intermediate annealing, the rolling performed at a temperature lying in a range ambient to 200° C., with a reduction ratio lying in a range 2% to 20%; andsubjecting the rolled flat arrangement to an annealing treatment in the a range or in the α+β range, performed in a temperature range 500° C. to 800° C. for 2 mm to 10 h. 11. The zirconium alloy flat product according to claim 10, wherein the element is formed into a fuel assembly element for a light water reactor. 12. The zirconium alloy flat product according to claim 10, wherein the zirconium alloy flat product is a box for a boiling water nuclear reactor. 13. The zirconium alloy flat product according to claim 10, wherein the zirconium alloy flat product is a grid for one of a boiling water reactor and a pressurized water reactor. 14. The zirconium alloy flat product according to claim 10, wherein the zirconium alloy flat product is a central tube defining, a circulation path.
042279682	summary	FIELD OF THE INVENTION The present invention relates to a nuclear-reactor assembly and, more particularly, to an assembly which consists of a pressure vessel containing the nuclear reactor and additional vessels arrayed around the reactor vessel for components of the system, for example heat exchangers, which communicate with the central or reactor vessel by horizontal passages which can lie in a common horizontal plane. BACKGROUND OF THE INVENTION It is known to provide prestressed pressure vessels of cast material, e.g. cast iron or steel, as pressure vessels for nuclear-reactor installations and particularly for housing the high-temperature reactor core. In such systems it is also a common practice to provide a number of heat-exchange components and horizontal gas passages which communicate between the heat exchangers and the reactor vessel for connecting the high-temperature reactor with the primary coolant flow. In such systems, the pressure vessel for the high-temperature reactor can be centrally located and the centrally disposed reactor vessel can be surround by a plurality of pressure vessels each containing heat-exchanger or other components. These auxiliary vessels may also be provided as separate prestressed pressure vessels of cast material. The component vessels can be disposed in a partial circle around the central or reactor vessel, i.e. can be annularly spaced therearound. Prior to the development of such systems, efforts in this field concentrated upon the provision of a completely integrated reactor assembly in which the high-temperature reactor and the primary coolant components, such as tube furnaces or steam generators (more generally referred to as heat exchangers) were provided in a common prestressed concrete pressure vessel. When, however, attempts are made to construct similar vessels from cast materials such as cast iron or cast steel (more generally cast metals) problems were encountered not only because of the large quantities of materials which were required and their expense, but also because the fabrication time was realtively great and it was difficult, even with existing casting technology, to fabricate such vessels. This is especially the case because nuclear-reactor installations with their primary coolant components are extremely large and the tendency toward the fabrication of still larger units is increasing. The fabrication of a single pressure vessel for such systems has thus become not only difficult but also uneconomical. As a result, it has been proposed to substitute for this single housing for the integrated system, an arrangement in which the high-temperature reactor and the primary coolant components are contained in separate pressure vessels in a satellite construction wherein the component vessels are disposed around a central reactor vessel. In this case, the pressure vessels for the primary coolant components are disposed in a partial circle around the reactor pressure vessel. Two horizontal gas conduits generally connect each of the component vessels with the high-temeprature reactor vessel for the delivery of the gas to the component vessel and return of the primary coolant to the reactor, respectively. These gas conduits required a correspondingly large number of passages in the cylinder walls of the prestressed pressure vessels which detrimentally effected the strength of both the reactor vessel and the component vessel. Naturally, attempts were made to overcome this weakening of the reactor vessel by reinforcement, although this increases the cost and amount of material which must be used. In the German patent publication (open application or Offenlegungsschrift) No. 23 26 917, there is described a nuclear-reactor installation in which the nuclear reactor is contained in a high-pressure vessel which is, in turn, surrounded by a cylindrical concrete containment or structure. Two heat exchangers are, in this system, connected with the reactor pressure vessel by coaxial ducts and are received, in turn, with respective burst-resisting containments reinforced by steel reinforcing cables or the like and composed of concrete. The containments are each applied to a concrete cylinder and the two concrete cylinders form part of the cylindrical concrete housing and are adapted to receive the drive motors for the primary coolant circulating pumps. It is also known in this art to provide a reinforced concrete pressure vessel for nuclear reactors in which the desired or required volume is subdivided between two or more vessels each of which can be prestressed and all of which can be collectively surrounded by further prestressing cables into a unit. In this construction, represented by the German Patent document (open application or Offenlegungsschrift) 16 84 594, the central vessel is larger than the peripheral vessels and serves to receive the nuclear reactor while four smaller vessels grouped around the central vessel receive the primary coolant components such as heat exchangers and coolant circulation components. The central vessel and the outer vessels are provided with horizontal passages so that the central vessel is connected with each of the outer vessels by two gas conduits. In still another prior-art proposal, the pressure vessel for the high-temperature reactor is connected with the pressure vessels for the steam-generating components by burst-resisting connecting passages disposed beneath these pressure vessels. In this fashion the weakening of the cylindrical wall portions of the pressure vessels is avoided but the cost is increased since the passages must be sufficiently prestressed and strengthened in a redundant manner. OBJECTS OF THE INVENTION It is an object of the present invention to provide a nuclear reactor installation or assembly whereby the disadvantages of the aforedescribed systems are avoided. Another object of the invention is to provide a pressure-vessel assembly, especially for a high-temperature nuclear reactor, in which weakening of the vessel walls is avoided but more direct gas passages can be provided that have been used at least in the last-mentioned prior-art solution. It is also an object of the invention to provide a pressure-vessel assembly which affords a compact construction at relatively low cost and which does not require special prestressing or reinforcing of the gas passages. SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention in which the pressure vessel assembly for the nuclear reactor installation comprises a cylindrical central vessel of cast metal and intrinsically prestressed, in addition to a plurality of peripheral, satellite or outer auxiliary pressure vessels which also may be axially and peripherally prestressed individually and likewise composed of cast material being generally of cylindrical configuration and annularly spaced about the central vessel over at least a partial circle. According to the invention, each of the peripheral vessels is connected to the central vessel by a horizontal passage, the horizontal passages of all of the vessels lying in a common horizontal plane. In accordance with an essential feature of the invention, the central vessel is provided with generally tangential and vertical planar surfaces in this horizontal plane while the pripheral of auxiliary vessels likewise have generally tangential and vertical surfaces. More particularly, at least one of the vertical surfaces of the central vessel lies perpendicular to the axis of each of the horizontal passages while at least one of the surfaces of each of the auxiliary vessels lies perpendicular to its horizontal passage and is flat against or flush with the corresponding horizontal surface of the passage of the central vessel communicating with its passage. More particularly, the substantially cylindrical pressure vessels have in the region of the horizontal gas passages, which lie in a horizontal plane and run generally radially, an array of vertical planar surfaces. At least a portion of the planar surfaces of the reactor vessel are thus at right angles to the horizontal (radial) gas passages and each component vessel has a planar surface which lies directly against a corresponding planar surface of the central or reactor vessel. The component vessels are angularly spaced and the spaces between the individual component vessels, at least in the region of these vertical planar surfaces and the horizontal plane of the passages, is filled with support blocks until the assembly of component vessels and support blocks form a circle which completely surrounds the reactor vessel. The support blocks, in turn, have planar surfaces which directly abut, on the one hand, the planar surfaces of the reactor vessel between those planar surfaces against which the component vessels lie, and the lateral planar surfaces of the component vessels themselves. The support blocks and the component vessels thus form a composite disk which, in accordance with another essential feature of the invention, is prestressed inwardly by at least one peripheral prestressing strand surrounding this composite or compound disk. The inward prestress, therefore, applies the component vessels against the reactor vessel and, in addition, wedges the support blocks against the component vessels. The prestress is thus in the horizontal direction. Each of the pressure vessels can, in accordance with a feature of the present invention, be prestressed in vertical and horizontal directions as well, i.e. by vertical prestressing cables extending along generatrices of the pressure vessel and received in the walls thereof. These vertical prestressing cables or bars can be used also to hold cover and base plates onto the cylindrical wall structures of the pressure vessels. The peripheral prestressing can be afforded by external cables or bands which are stressed inwardly while extending around the individual pressure vessels. The vertical and horizontal prestressing systems can be dimensioned to maintain the pressure forces on the walls of the vessel in equilibrium when the reactor system is in operation. In addition, when the pressure vessels are composed of cast iron or cast steel blocks, they can hold the joints between the blocks closed against any inward pressure which can normally develop in the reactor or auxiliary vessels. In the region of the disk-shaped composite body, moreover, the horizontal prestressing arrangements of the individual vessels can be omitted since the horizontal prestress is provided by the common prestressing member or members which encircle the compound disk. In this case, the inner prestress afforded by this peripheral prestressing member or such prestressing members is such that the prestress balances the internal forces and sheer-resisting keys or the like need not be employed to prevent separation at the junctions of the various members. The resulting structure has been found to be extremely compact and of exceptionally low cost since only in the region of the horizontal gas passages is it necessary to provide an inward prestressing member that surrounds all of the pressure vessels, i.e. the entire assembly. The use of the vertical prestressing members for the individual pressure vessels is uninhibited by this outer prestressing member or such outer prestressing members. The system of the present invention has, by comparison with the integrated structures mentioned previously, a much shorter reaction time, thereby reducing the cost of setting up the assembly. The individual vessels are more readily accessible so that maintenance and repair of the components is possible with less difficulty. Naturally, individual satellite vessels can be replaced if necessary when relining or reinsulation is necessary, e.g. upon the failure of a liner or layer of insulation. The heat-exchanger components which can be introduced into the component vessels can be steam generators which can be connected to electric-current generating systems and it has been found to be advantageous to provide the blowers, pumps and motors for circulating the cooling gases above the heat exchangers in the component vessels. One or more of the component vessels can be used for other purposes as may be required. For example, the waste-heat recovery system of the nuclear reactor can be installed in one or more component vessels. Such a system can include, in the conventional manner, a plurality of blowers with or without recuperative heat exchangers and a number of coolers. The component vessel or vessels for the waste-heat removal system can be interposed between other heat exchanger vessels, i.e. those for steam generation and either the steam-generating vessels or the waste-heat recovery vessels can be provided with blowers with or without recuperators and coolers. It has been found to be advantageous to provide at least one disk-shaped composite body. However, the construction can also be made in such a manner that two disk-shaped composite bodies are provided on above the other with the upper body lying just above the horizontal gas passages with the lower body lying just below them. Advantageously the pressure vessels are composed of grey cast iron or cast steel while the support blocks are composed of grey cast iron and are made of hollow construction. This utilizes substantially less material. In the plane of the passages, moreover, the reactor vessel can have the configuration of a polygon, i.e. all of the vertical surfaces may angularly adjoin other vertical surfaces all around the periphery of the vessel. The component pressure vessels, however, may be prismatic only in part, in the region in which they contact the support blocks or the central vessel, and may have a cylindrical curvature elsewhere, e.g. in the region in which they are contacted by the stressing element which passes around the composite disk. The support blocks may be composed of hollow members with converging flanks which are wedged between converging flanks of successive component vessels. Two such blocks may be provided in each gap between a pair of component vessels.
	summary
046876200	abstract	A method of operating a pressurized water nuclear reactor comprising determining the present core power and reactivity levels and predicting the change in such levels due to displacer rod movements. Groups or single clusters of displacer rods can be inserted or withdrawn based on the predicted core power and reactivity levels to change the core power level and power distribution thereby providing load follow capability, without changing control rod positions or coolant boron concentrations.
	description	Embodiments of the present invention relate to EUV radiation generation, and more particularly, to an apparatus and a method for generating a EUV radiation source. Semiconductor integrated circuits are typically manufactured using a lithographic process. Lithography may involve, e.g., coating a semiconductor wafer with a photosensitive resist, projecting light through a patterned mask onto the resist, and developing the exposed resist. The wavelength of light used in the lithography process is a key factor in the drive for higher levels of microcircuit integration. Since the minimum processing dimension of lithography depends on the wavelength of light used, it is necessary to shorten the wavelength of the irradiated light in order to improve the integration degree of the integrated circuit. In recent years, extreme ultraviolet (EUV) radiation which radiates extreme ultraviolet radiation with wavelengths from 13 nm to 14 nm, has been developed as semiconductor lithography light source to meet the demands for micro-miniaturization of semiconductor device. There are a number of methods of generating EUV radiation. In one example, EUV radiation may be generated through plasma in which high temperature plasma is first created by heating and excitation of an extreme ultraviolet radiating species and then the EUV radiation radiated from the plasma is extracted. However, both higher-harmonic generation as well as thermally produced plasma processes require very high peak power. In addition, the laser produced plasma EUV light source has a relatively low repetition rate. Another method of generating EUV radiation is free electron laser (FEL). A FEL involves interaction between a high brightness electron beam and an intense light beam while traveling through a periodic magnetic field to generate coherent electromagnetic radiation. Specifically, an electron beam is first accelerated to almost the speed of light with very high kinetic energies from about 100 MeV to 1 GeV. The accelerated beam in turn passes through a FEL oscillator, a periodic transverse magnetic field produced by an array of magnets with alternating poles within an optical cavity along the beam path. The acceleration of the electrons along this path results in the release of photons, which, with appropriate optical system, may emit a coherent light beam of extremely high power. The optical system typically includes a ring resonator having multiple mirrors. While these have proven effective for wavelengths ranging from the far IR to the UV, it becomes difficult to implement FEL for EUV generation because the reflectivity of metals and other mirror coatings drops significantly at shorter wavelengths and thus lack of good reflecting surfaces to form the mirrors. Another FEL method involves a process of self-amplified spontaneous emission (SASE). These FELs do not use resonator mirrors and may operate at short wavelengths on a single pass of a high brightness electron through a long undulator. In particular, all electrons are initially distributed randomly and emit their incoherent spontaneous radiation. Through the interaction of their radiation and oscillations of electrons, they drift into microbunches separated by a distance equal to one radiation wavelength. Through this interaction, all electrons begin emitting coherent radiation in phase. However, SASE requires a very bright electron beam (i.e., high peak current, low emittance and small energy spread) and a comparatively long undulator to build up beam intensity from spontaneous noise to a saturated intensity. It is within this context that aspects of the present disclosure arise. According to aspects of the present disclosure, a system comprises an accelerator unit including an array of spatially separated charged particle emitters, an optical-frequency modulator and an undulator. Each emitter in the array has an electrostatic potential difference with respect to an immediately adjacent emitter in the array produces a charged particle beamlet. The beamlets are converged as one spatially overlapped energy-modulated charged particle beam at the output of the accelerator unit. The optical-frequency modulator modulates the beamlets from the accelerator unit with an infrared radiator. Charged particles in the modulated beamlets are, in turn, bunched together to form a bunched energy-modulated charged particle beam. If the charged particle emitters may be electron emitters, each charged particle beamlet is an electron beamlet, and the charged particle beam is an electron beam. In some implementations the electron emitters may be DC electron guns. In some implementations the optical frequency modulator may include a laser. In certain of these implementations (but not all), the laser may be a Nd:YAG laser. An undulator or other free-electron radiation device may be located at a point of optimum bunching of the modulated electron beam to generate a coherent radiation output from modulation of the bunched energy-modulated electron beam. Because the beam entering the undulator is already bunched, the bulk of the electrons suffer an energy loss from radiating. In some implementations, the array of emitters may be placed at a mid-plane of a half-chicane to spatially overlap the array of beamlets at an exit of the chicane. In some implementations, the electric potential difference between the emitters in the array may be adjustable. In some implementations, one or more of the emitters in the array are configured to be selectively switched on or off. In some implementations bunch compressor may be located along a beam propagation pathway between the optical frequency modulator and the undulator to compensate for lateral charged particle dispersion. In some implementations each of the beamlets may be accelerated to about 100 KeV from the respective emitter in the array. In some implementations an output beam from the undulator may be collected at a potential slightly below that of the potential used to accelerate the beamlets. In some implementations the accelerator unit may include a half chicane having two bending magnets configured to bend the beamlets from the emitters in the array so as to laterally converge the beamlets to form the charged particle beam output from the accelerator unit. In some implementations, the optical-frequency modulator may be an inverse free electron laser. Should the transverse emittance of the beam be sufficiently small, some implementations may allow for the use of an inverse-transition radiation accelerator, inverse-Cerenkov accelerator or a laser-driven photonic accelerator structure as a means to modulate the energy of the beamlets. In some implementations the emitter array, half-chicane and the modulator may serve as an injector of a bunched particle beam for laser-driven particle accelerators. According to certain aspects of the disclosure a method of generating EUV radiation may involve emitting an array of spatially separated beamlets. Each beamlet is produced by a corresponding array of electron emitters. Each electron emitter is at an electrostatic potential difference with respect to an immediately adjacent emitter in the array, whereby the array of electron emitters produces a corresponding array of electron beamlets having different energies. The electron beamlets are converged laterally to form an electron beam. The beamlets in the electron beam are modulated longitudinally with infrared radiation to form a modulated beam. The electrons in the modulated beam are bunched longitudinally to form a bunched beam. The bunched beam interacts with an undulator to generate a coherent radiation output. In some implementations of the method the bunched beam may be compressed laterally to correct electron dispersion or to focus the beam. In some implementations the wavelength of the coherent output radiation may be adjusted by adjusting the electrostatic potential difference between adjacent emitters in the array. In some implementations, a pulse period of the coherent output radiation may be adjusted by selectively switching one or more of the electron emitters on or off so as to adjust a number of beamlets emitted. According to certain aspects of the disclosure a method of generating a bunched particle beam may involve emitting an array of spatially separated beamlets. Each beamlet is produced by a corresponding array of charged particle emitters. Each emitter is at an electrostatic potential difference with respect to an immediately adjacent emitter in the array. As a result, the array of emitters produces a corresponding array of charged particle beamlets having different energies. The beamlets are converged laterally to form an energy modulated direct current charged particle beam. The beamlets in the charged particle beam are modulated longitudinally with infrared radiation to form a modulated beam. The charged particles in the modulated beam are bunched longitudinally to form a bunched energy-modulated charged particle beam. In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. The drawings show illustrations in accordance with examples of embodiments, which are also referred to herein as “examples”. The drawings are described in enough detail to enable those skilled in the art to practice the present subject matter. The embodiments can be combined, other embodiments can be utilized, or structural, logical, and electrical changes can be made without departing from the scope of what is claimed. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. In this document, the terms “a” and “an” are used, as is common in patent documents, to include one or more than one. In this document, the term “or” is used to refer to a nonexclusive “or,” such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. As used herein, the term “light” generally refers to electromagnetic radiation characterized by a frequency somewhere in a range of frequencies running from the infrared through the ultraviolet, roughly corresponding to a range of vacuum wavelengths from about 1 nanometer (10−9 meters) to about 100 microns. As used herein, the term extreme ultraviolet (EUV) generally refers high-energy electromagnetic radiation, in the part of the electromagnetic spectrum spanning vacuum wavelengths from about 124 nm down to about 10 nm, and therefore (by the Planck-Einstein equation) having photons with energies from about 10 electron volts (eV) up to 124 eV (corresponding to 124 nanometers (nm) to 10 nm respectively). Aspects of the present disclosure include electrostatic particle accelerator units for EUV free-electron sources instead of RF or plasma wakefield accelerators. This application may eliminate the need for an RF pulsed time structure as well as the need for high-power klystrons and corresponding pulsed power supplies. Additionally, with respect to plasma wakefield accelerators, the present invention may eliminate the need of tera-watt or petta-watt pulsed lasers that also have to run at low repetition rates. FIG. 1 is a diagram of a system for generation of EUV radiation according to an aspect of the present disclosure. The EUV radiation generation system 100 includes an accelerator unit 110, an optical frequency modulator 120, a bunch compressor 130, and an undulator 140. The accelerator unit 110 may include an array of electron emitters 112 and a half magnetic chicane 114. Specifically, a linear array of electrostatic electron emitters 112 may be located at the dispersive plane (i.e., the mid-plane) of the half-chicane 114. By placing the array of emitters 112 at the mid-plane of the half-chicane the array of electron beamlets 116 of different energy from the emitters overlap at an exit 115 of the half-chicane 114. By way of example and not by way of limitation the half-chicane 114 may include first and second bending magnets 114A, 114B configured to bend the electron beamlets 116 in opposite senses by approximately equal amounts. The electron emitters 112 are arranged proximate an energy dispersive plane of the half-chicane 114 such that higher energy beamlets from emitters at higher potential are bent less than lower energy beamlets from emitters at lower potential. The different amounts of bending of the beamlets of different energies by the magnets 114A, 114B results in the beamlets 116 converging laterally as they exit the half-chicane 114. In one example, the electron emitters may be direct current (DC) electron guns. Also, the electron emitters may be laser-driven photocathodes. The emitters in the array are placed with the same spatial distance in the dispersive plane from each other. Also each emitter has an electrostatic potential difference to the immediately adjacent emitter in the array. For example, the first emitter in the array is in few volts different from the second emitter and the second emitter is in same few volts different from the third. Such arrangement of the electron emitters forms a chirped electron source. A control circuit may be provided and configured to adjust or change the voltage difference between the emitters. Each emitter in the array produces a beamlet 116. The kinetic energy of the beamlets has to be high enough, and as an example, the beamlets emitted by the DC gun array are accelerated to about 100 KeV. In addition, each of the electron emitters may be selectively switched on or off. Particularly, a control system may be optionally provided to control the on/off function of each emitter such that the number of the electron emitted turned on is adjustable. The chicane 114 may include two dipole magnets to bend the path of the accelerated electrons as they travel in a magnetic field change direction. In the chicane 114, the electrons with lower energy take longer flight paths and are delayed in comparison to electrons with higher energy. By appropriate adjustment on the displacement and energy difference between the emitters in the array, all the electron beamlets may be converged as one energy-modulated direct current (DC) electron beam 118 at the exit of the chicane 114. FIG. 2A show relative beam energy of the illustrative continuous electron beamlets, each beamlet separated by few volts. FIG. 2B show currents of the illustrative electron beam 118 at the exit of the accelerator unit 110. The energy-modulated DC electron beam 118 from the accelerator unit 110 enters an optical-frequency modulator 120 for energy modulation. In one example, the modulator 120 is an inverse free electron laser (IFEL). The optical-frequency modulator 120 may include an infrared radiation generator 122 producing infrared radiation. In one example, the infrared radiation generator 122 is a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser. Nd:YAG lasers typically emit light with a wavelength of 1064 nm in the infrared. In the IFEL, the electron beam 118 moves through an undulator magnet. The infrared radiation sent through the electron beamlets also propagates inside the magnet. The alternating magnet provides a magnetic field such that the electron beam 118 is forced to wiggle in a direction transverse to the direction of propagation. The transverse motion of the electrons can be coupled with the transverse motion of the electric field of the infrared radiator. This coupling causes energy exchange between the infrared radiation and the electrons. As such, a modulated beam 128 is generated and output from the optical frequency modulator 120. The frequency modulator 120, buncher 130 and undulator 140 can all be floated to an arbitrary electrostatic potential with 150 so as to control the kinetic energy of the beam in that section. FIG. 2C shows the relative beam energy of an illustrative modulated beam 128 after modulation by an IFEL. FIG. 2D shows the currents of the illustrative modulated beam 128. After the energy modulation, the modulated electrons are left to propagate in a drift space where fast electrons catch up with the slower ones. This causes electrons to bunch at the frequency of the infrared radiator and results in the density modulation of the beamlets with the electron bunches representing RF current. Specifically, the fast electrons in a first beamlet in the array overtake the slower ones in the same beamlet to form a first electron bunch. The fast electrons in a second beamlet which is at few volts different from the first beamlet catch up with the slower electrons in the same beamlet, thereby forming a second electron bunch. Because of the voltage difference between the beamlet, the second bunch is spatially apart from the first bunch. As such, the voltage difference between beamlets may be adjusted so that each beamlet bunches with a timing increment which is the EUV wave oscillation period. Thus, the wavelength of the output radiation from the system 100 can be adjusted by adjusting the voltage difference between emitters 112. Also, a bunch compressor 130 may be provided along the electron propagation pathway between the optical frequency modulator 120 and the undulator 140. The bunch compressor 130 reduces the path length for optimal bunching to occur, and thereby allows the bunched electron beam have high peak current density. The bunch compressor 130 may be described generally as an element that has high dispersion in the longitudinal phase-space. The bunch compressor is similar to a simple drift, but allows optimum bunching to occur in a much shorter distance of travel. Hence the beam comes to a longitudinal focus (bunching) sooner than if one just allows for drift. Therefore the lateral growth tends to be less and hence higher peak current density is usually attainable. In one example, the bunch compressor 130 may be a magnetic chicane built from a set of bending magnets. In particular, a magnetic chicane may include four dipoles to produce magnetic fields effective to spatially disperse electrons in the bunched electron beam as a function of electron energy and focus the bunched electron beam. The electrons in the head of the modulated electron beam have a lower energy than those in the back. When the electrons travel through the curved trajectories of the chicane, the high energy electrons take a shorter path and catch up to the electrons in the head, and thereby compressing the bunched electron beam. FIGS. 2E and 2F show the relative beam energy and currents of the illustrated compressed electron beam 138 after electrons bunching in drift spaces have been compressed by the bunch compressor 130. As seen in FIG. 2E, the electrons bunch at a spatial frequency corresponding to the wavelength of the infrared radiation. The bunching of electrons in the beam 138 constitutes an RF current as shown in FIG. 2F. The compressed electron beam 138 enters an undulator 140 at the longitudinal focus of the beam array. In one example, the undulator 140 consists of an array of dipole magnets which produce a transverse, spatially periodic magnetic field. When the compressed electron beam 138 passes through, the magnetic field of the undulator 140 bends the beamlets back and forth in the traverse direction. Each time an electron in the beam 138 is deflected, it emits a broadband burst of synchrotron radiation. Due to the bunching of the electrons, the synchrotron radiation emitted by emitted by electrons can be made coherent. The wavelength of the resulting coherent radiation 141 depends partly on the energy of the electrons traversing the undulator 140 and partly on the spatial period of the undulator. By way of example, and not by way of limitation, the undulator 140 may be a soft-magnet undulator that uses an actively powered coil producing magnetomotive force to generate magnetic flux. A magnetic yoke may be used to direct the flux across the undulator gap. In addition, engineered magnetic pole tips may be used to concentrate the magnetic flux density. Alternatively, besides an undulator there are other methods that a free electron beam can produce coherent radiation. Such methods include use of a transition radiation surface, refractive index medium for Cerenkov radiation, or even a photonic to convert the electron pulse structure to the equivalent photon pulse structure. In all these methods the surrounding medium or construct allows for an electromagnetic wave mode that co-propagates with a phase velocity equal to the velocity of the electrons. This allows for transfer of the electron kinetic energy to the co-propagating electromagnetic mode. Additionally, the system 100 may include a high voltage generator 150 such as Van de Graaf generator to accelerate beams to a few MeV. In the case where the beamlets 116 are produced by DC power, the beam energy from the undulator 140 may be recovered, e.g., by capturing the electron beam 138 with a Faraday cup floated at a voltage slightly lower than the voltage of the initial DC sources in the accelerator unit 110. As used herein, a voltage is slightly lower if it is close to the accelerating voltage, e.g., as applied by the Van de Graaf generator 150, but lower by an amount that accounts for energy losses in the electron beam 138, including losses resulting from generation of the coherent radiation 141. As such, instead of disposing the spent beam at full energy which may create radiation and heat, the energy of the beam may be reused. With a system according to the present disclosure, adjustments on the voltage difference between the beamlets 116, the system may generate coherent radiation at various wavelengths. In addition, the system may generate broadband radiation at a pulse period that can be adjusted by turning selectively turning the electron emitters 112 on or off. In other words, the pulse duty cycle can be controlled by the number of the emitters turned on. As shown in FIG. 3, the pulse train has a repetition rate equal to the wavelength of the infrared radiator. FIG. 3 also shows, with 20 beamlets, an EUV light pulse of about 800 attoseconds may be obtained. Each beamlet may have a current of 10 milliamperes (10 mA) for a total beam current of 200 mA. To lengthen the pulse, more emitters in the array may be turned on to produce more beamlets. Aspects of the present disclosure provide for generation of coherent output radiation that is broadly tunable over a wide range of wavelengths. Using spatially separated electron beam emitters to produce beamlets at different energies, a free electron laser may use simple electrostatic acceleration. This allows for a simpler, less expensive and less complex source of EUV radiation. Aspects of the present disclosure have a wide range of applications and are not limited to implementations involving radiation sources, such as free electron lasers. For example, the emitter array 112, half-chicane 114 and the modulator 120 may serve as an injector of a bunched particle beam for laser-driven particle accelerators. It is noted that in such implementations, the emitter array may include an array of charged particle emitters other than electron emitters. By way of example, and not by way of limitation, the emitter array 112 may be an array of ion beam emitters. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.” Any element in a claim that does not explicitly state “means for” performing a specified function, is not to be interpreted as a “means” or “step” clause as specified in 35 USC §112, ¶ 6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 USC §112, ¶ 6.
	description	Many other advantages of the present invention will become clear by reading the following examples, provided evidently as illustrative but non-limiting. Comparative Example of Degreasing This example is a comparative example of the degreasing efficiency of a composition and a process in conformity with the invention relating to solutions and a process of prior art. In this example, the surface to be degreased is an austenitic steel blade covered with about 1 g/cm2 of one of the following mixtures A and B which represent the greasy substance to be dissolved. Mixture A: 0.9% by weight of TBP+0.1% by weight of a mixture comprising 60% of HDBP and 40% of H2MBP. Mixture B: 0.7% by weight of TPH+0.27% by weight of TBP+0.03% by weight of a mixture comprising 60% by weight of HDBP and 40% by weight of H2MBP. The process according to prior art comprises the following sequences, in this order, and with agitation of the solutions used, by means of a magnetic stirring bar, at 500 rev/min: soaking of each blade in a solution of nitric acid at 5 mol.lxe2x88x921 at a temperature of 50xc2x0 C. for 60 minutes, rinsing of each blade with water at a temperature of 50xc2x0 C. for 5 minutes, soaking of each blade in a caustic soda solution at 5 mol.lxe2x88x921 at a temperature of 50xc2x0 C. for 120 minutes, rinsing of each blade with water at a temperature of 50xc2x0 C. for 5 minutes, soaking of each blade in a solution of nitric acid at 5 mol.lxe2x88x921 at a temperature of 50xc2x0 C. for 60 minutes, and rinsing of each blade with water at a temperature of 50xc2x0 C. for 5 minutes. The process according to the invention comprises soaking each blade in a composition according to the invention, without agitation, at a temperature of 20xc2x0 C. In this example, two different compositions according to the invention are used. Each of these two compositions comprises 0.12% by weight of ether of oleic alcohol and polyoxyethylene glycol with 20 units of ethylene oxide, Trademark SIMULSOL 98 manufactured by the company SEPPIC (formula (I) above) and 0.57% by weight of block copolymer with 45 ethylene oxides and 9 propylene oxides Trademark SYNTHIONIC P8020 manufactured by the company WITCO (formula (II) above). The first of these two compositions, hereinafter called composition 1, comprises 0.5 mol.lxe2x88x921 of NaOH, and the second of these compositions, hereinafter called composition 2 comprises 1 mol.lxe2x88x921 of NaOH. The cloud point of these two compositions is 38xc2x0 C. The degreasing efficiency of these two processes was compared by measuring the contact angle between an aqueous solution and each degreased metallic blade, using the SCHULTZ method, and by measuring the minimum contact time for total degreasing of these blades. A wetting angle equal to 0 represented total degreasing of the surface, that is to say recuperation of the grease from the metallic surface. In order to displace this grease, the aqueous solution must allow its micellisation. Table 1 below groups the results of these measurements: The results of this example show that the degreasing of each blade, by the prior art process, covered with mixture A or mixture B, is only partial for a total time of 255 minutes for this process, at a temperature of 50xc2x0 C. and for very concentrated solutions of nitric acid and caustic soda. Whilst the process and the composition according to the invention provide total degreasing of the blades, whatever the mixture A or B covering these blades, for a total treatment time of 200 and 30 minutes, for solutions up to ten times less concentrated than the solutions of prior art, and at ambient temperature. In addition, supplementary trials have shown that a blade degreased with composition 1 or 2 is perfectly wettable by 5N nitric acid, which is not the case for a blade degreased by the solutions and process of prior art. Kinetics of Degreasing of a Surface with a Composition According to the Invention In this example, a metallic blade covered with 0.75 g/cm2 of a mixture C of solvent TPH+TBP+HDBP+H2MBP comprising respectively 70; 27; 1.8 and 1.2% by weight of these solvents and a metallic blade covered by 1.2 mg/cm2 of a mixture D of solvent TBP+HDBP+H2MBP comprising respectively 90; 6 and 4% by weight of these solvents, were degreased by soaking without agitation in an aqueous solution of the composition according to the invention comprising 0.5 mol.lxe2x88x921 of caustic soda, 0.12% by weight of SIMULSOL 98 (Trademark) and 0.57% by weight of SYTHIONIC P8020 (Trademark). Degreasing was carried out at ambient temperature. The degreasing kinetics were followed by measuring over time, and at regular intervals, the surface tension xcex3cosxcex8 of each blade using the WILHELMY submerged blade method and thus determining the corresponding cosxcex8. Table 2 below groups the results of this example. According to the results in this example, it appears that about 120 minutes are required for complete degreasing (cosxcex8=1) of the blade covered with mixture C and 180 minutes for complete degreasing of the blade covered with mixture D under the same conditions as for the composition according to the invention. Identical kinetic trials corresponding to those of this example were carried out with a concentration of caustic soda, in the composition according to the invention, of 1 mol.lxe2x88x921. The degreasing kinetics were much faster, since 30 minutes were sufficient for complete degreasing of the blade covered with mixture D. These trials showed that the solubility of mixture D is 305 times higher with caustic soda at 1 mol.lxe2x88x921 than with caustic soda at 0.5 mol.l1xe2x88x92. In comparison, treatment of the same blades by caustic soda at a concentration of 0.5 mol.lxe2x88x921, without surfactant with agitation of 500 rev/min, for 120 minutes, did not obtain complete degreasing of the blades. In fact, the cosxcex8 obtained by this treatment was only 0.81. Complementary tests showed that a dilution of a composition according to the invention by a factor of 2 raised the degreasing time by the same factor. Efficiency of Degreasing of a Surface with a Slightly Foaming Composition According to the Invention This example illustrates the efficiency of degreasing a surface by the slightly foaming solutions according to the invention. In this example, the compositions used comprised a constant caustic soda concentration equal to 0.5 mol. lxe2x88x921, and a constant concentration of ether of oleic alcohol and polyoxyethylene glycol equal to 0.2% by weight. The fatty alcohol used was SIMULSOL 98 (Trademark) manufactured by the SEPPIC company. These compositions comprise a variable concentration of block copolymer of the Trademark SYNTHIONIC P8020 manufactured by the WITCO company, and also comprise a foam inhibitor again in a concentration which is also variable. This foam inhibitor agent is an alkyl phosphate of the Trademark MONTALINE ANP manufactured by the SEPPIC company. The surface to be degreased is a steel blade covered with 1 mg/cm2 of TBP. The degreasing was carried out at ambient temperature and without agitation of the degreasing solutions. The degreasing efficiency of these solutions was evaluated by measuring the cloud point (in xc2x0 C.) of each of these solutions, by measurement of the time, in minutes, needed for each of these solutions to degrease the metallic blade completely to obtain a surface tension such that cosxcex8≅1, and by measurement of the quantity (in g/l) of TBP which each solution can dissolve. The following table 3 groups the results of this example. These results show that for a concentration of caustic soda of 0.5 mol.lxe2x88x921 and for a concentration of SIMULSOL 98 of 0.2% by weight, the composition according to the invention comprising 0.35% by weight of SYNTHIONIC P8020 and 0.4% by weight of MONTALINE ANP seems to be the most efficient for dissolving TBP. Trials for putting these compositions into circulation, by airlift, showed that the production of foam is sufficiently low not to choke the airlift separator trap. Example of a Foam Comprising the Composition According to the Invention The solutions used to form the foam of this example comprise. a concentration of SIMULSOL 98 (Trademark) greater than or equal to 0.4% by weight, a concentration of SYNTHIONIC (Trademark) greater than 0.26% by weight, and also comprise a foam destabilising agent. This destabilising agent is MONTALINE ANP (Trademark) described above as a foam inhibitor. In this example, all the compositions comprise a constant concentration of caustic soda equal to 0.75 mol.lxe2x88x921. Foams were produced from these compositions by a static generator composed of a cylinder 120 mm long and 8 mm in diameter filled with 3.24 g of porous packing of the FORAFLON type (Trademark). The generator was fed with each foaming solution by using a gear pump with flow rate of liquid of 23 to 28 l/hr and of air of 88 l/hr in normal conditions of temperature and pressure. The foams were obtained at a flow rate of 120 to 130 l/hr, with expansion ranging from 6 to 7 and a lifetime of 15xc2x12 minutes. In this example, measurements were taken of the quantity of TBP and its derivatives HDBP and H2MPB (in g/kg) which can be dissolved in different compositions according to the invention. Tests were carried out at ambient temperature. Table 4 below groups the results obtained in this example. These results show that when the levels of SIMULSOL 98 and SYNTHIONIC P8020 are raised, the dissolving of TBP is raised. Supplementary tests with a composition comprising 0.75 mol.lxe2x88x921 NaOH, 0.8% by weight of SIMULSOL 98 (Trademark), 0.6% by weight of SYNTHIONIC P8020 (Trademark) and 0.4% of MONTALINE ANP (Trademark) made it possible to produce, with a flow rate of 1200 l/hr of air and 200 l/hr of liquid, a foam with a flow rate of 1400 l/hr, with a lifetime of 20 minutes. These foam compositions showed a degreasing efficiency identical to that of the preceding examples 1 to 3, concerning the liquid composition according to the invention. Example of a Gel Comprising the Composition According to the Invention The gel produced in this example comprises 1 mol.lxe2x88x921 NaOH, 0.2% by weight of SIMULSOL 98 (Trademark), 0.45% by weight of SYNTHIONIC P8020 (Trademark) and also comprises a viscosity agent. This viscosity agent is xanthan gum KELZAN 140X (Trademark) and is added to the composition according to the invention at 1.2% by weight. The gel obtained has a viscosity of 0.8 Pa.s (800 cps) which varies little with temperature. This gel makes it possible to degrease a metallic blade covered with TBP and its derivatives with the same efficiency as the compositions of examples 1 to 3 above. Comparative Example of Radiochemical Decontamination of a Surface Between a Process According to the Invention and a Process of Prior Art This example is a comparative example of the efficiency of radiochemical decontamination of a surface by a process of the present invention compared with radiochemical contamination according to prior art. In this example, the surfaces to be degreased and to be radioactively decontaminated are approximately cylindrical sections in stainless steel coming from organic phase probes from a nuclear fuel extraction plant. They are numbered from 1 to 9. These surfaces were put in contact with TBP, TPH, HDBP and H2DBH, and their radioactivity is due to more than 98% of ruthenium 106 (106Ru). Before taking samples, they underwent a rinsing with concentrated nitric acid and then measurement of their radioactivity in 106Ru. Hereinafter this radioactivity will be named Ao and will correspond to the activity of each surface before radiochemical decontamination. The radiochemical decontamination processes in this example comprise a degreasing of each surface, either according to a prior art process described in example 1, or according to the process of the invention, and radioactive decontamination by erosive treatment. The process according to the invention used in this example comprises the following three stages, in this order: soaking of the surface in a nitric acid solution at 5 mol.lxe2x88x921 for one hour at 50xc2x0 C. with agitation, soaking of the surface in a solution according to the invention comprising 0.5 mol.lxe2x88x921 of NaOH, 0.12% by weight of SIMULSOL 98 (Trademark) and 0.57% by weight of SYNTHIONIC P8020 (Trademark) at 21xc2x0 C. without agitation, and soaking in a solution at 0.5 mol.lxe2x88x921 for one hour at 50xc2x0 C. with agitation. Measurement of the residual radioactive activity 106Ru (AR1) was carried out for each surface after degreasing, and before radioactive decontamination, to measure the decontamination of the surface due to degreasing. Working from these measurements, a radioactive decontamination factor FD1=Ao/AR1 was calculated for each degreased surface. Table 5 groups the results of these measurements and makes it possible to compare the degreasing effect of the invention on radioactive decontamination of a surface, compared with prior art. with A0: 106Ru activity of the surface before degreasing AR1 : 106Ru residual activity of the surface after degreasing FD1 : decontamination factor of the surface after degreasing=Ao/AR1 These results show that the residual activity of the surfaces after degreasing treatment according to the invention is homogeneous and its average value is 0.32xc3x97106 Bq, that is an average decontamination factor FD1 of the order of 25. The surfaces degreased by the prior art process show much higher residual activities than those of the invention, such as 6xc3x97106 Bq and 1.37xc3x97106 Bq, that is to say a decontamination factor of 10 and 3.5 respectively. The process according to the invention therefore seems significantly more efficient than the prior art process for degreasing a surface, and even for radioactive decontamination of this surface. After these degreasing treatments, some of the surfaces underwent radioactive decontamination by an erosive treatment. This erosive treatment was either a cerium IV erosive treatment (T.E. Ce IV) for 2.5 hours, or an HF erosive treatment (T.E. HF) for 5.5 hours, or a ruthenium erosive treatment (T.E. Ru) for 2 hours, this latter treatment being followed by soaking in HNO3 for 1 hour. These treatments have been described above. After this radioactive decontamination treatment, the loss in weight xcex94m due to the erosive treatment and the residual activity 106Ru (AR2) of each surface degreased and decontaminated were measured. From this latter measurement, a total decontamination factor FDT=A0/AR2 was determined for each surface. The FDT decontamination factor is that obtained for degreasing and decontamination of each surface. Table 6 below groups the results of these measurements and calculations. These results demonstrate greater efficiency of radiochemical decontamination by the process according to the invention than by the prior art process. In fact, the residual activity AR2 106Ru is about 10 to 20 times lower for a surface treated by the process according to the invention than by the prior art process, whatever the complementary treatment used: whether it be erosive, for example for Ce IV or HF, or specific for ruthenium. This improvement can be explained in particular by better preparation of the surfaces to be decontaminated by the degreasing process according to the invention compared with the prior art process. These results also show that the degreasing process according to the invention is compatible with erosive treatments. These results also show that the weight losses xcex94m measured are comparable for all surfaces, whatever the degreasing process and erosive treatment used. Thus there is no modification of erosion kinetics to be attributed to the degreasing treatment. Complementary tests showed that a degreasing according to the invention applied for 3 hours, with the composition described above, without agitation, is just as efficient as with agitation. These tests were prolonged up to 3.5 hours, and showed that maximum efficiency, in these concentration conditions, and at a temperature of 25xc2x0 C., was obtained in 3 hours, in particular concerning the residual activity of 106Ru. Decontamination of an Active Cell by a Gel According to the Invention In reprocessing plants, the cleaning of extraction units by solvent requires, before any decontamination, efficient degreasing so as to extract the TBP and its radiolysis products from the metallic surfaces. The decontaminated cell had the function of partition U/Pu (2nd extraction cycle). Contamination of the floor of this cell was caused by leaks of solvent containing U and Pu which were more or less spread by the interveners. Part of this solvent was more or less radiolysed, which produced the black tarry deposits. The average level of alpha surface contamination was estimated at a little below 2 Mbq/cm2, that is, taking into account a floor surface of about 30 m2, a total activity of alpha emitters of 0.57 Tbq. The average isotopic composition, (% by weight) determined on the recuperated wastes was as follows: Pu238: 0.64 Pu239: 81.3 Pu240: 14.61 Pu241: 2.48 Pu242: 0.89 Am241: 0.38 The dose rates measured in the cell fluctuated before each decontamination operation, between 0.3 and 10 mGy/hr according to the zones. The formula according to the invention used had the following characteristics: Simulsol 98: 2.0 g/l; 0.2% by weight Synthionic P8020: 4.8 g/l; 0.48% by weight Montaline ANP: 3.0 g/l; 0.3% by weight NaOH: 1.0 mol/l water qsp: 1 l The gel was applied on the floor (30 m2) using a roller per portion of 5 to 6 m2, insisting in particular on the zones identified as being the most irradiating. After a contact time of 2 hours with the flooring, the contaminated gel was recuperated using a scraper and then submitted to natural drying in its original pot. The most contaminated part of the cell (process side) was cleaned in 4 sequences without about 2 kg gel/m2. The rest of the cell was treated with 2 sequences (20 to 25 m2 per 25 kg gel, that is about 1 kg gel per m2). An acid rinsing (10 l nitric acid) was necessary to eliminate the final traces of gel present on the flooring. The cell flooring was perfectly wettable by nitric acid after the degreasing. The nitric acid used was recuperated with the aid of polypropylene cloths. The results obtained are summarised in table 7 below: It is to be noted that after degreasing, the absorbed dose rates measured in the cell had fallen in the interval [2.10xe2x88x922, 3.10xe2x88x922]mGy/hr, that is a reduction factor of the dose rate of between 10 and 500. Evaluation of the Wastes Produced In order to be studied under good conditions, the solids were divided into batches weighing about one hundred grams each. These batches were then measured individually by neutron counting (measurement of neutrons from spontaneous fission) and by gamma spectrometry. The relative error of this type of measurement determined after a series of tests involving over a hundred different measurements is 25%. The evaluation of the wastes generated is as follows for 53 kg of wastes and 73 g of plutonium: for 13 kg of cloths (acid rinsing) and vinyl clothing: 7.2 g Pu. for 40 kg of solid wastes composed of dried gels mixed with bentonite: 65.8 g of Pu. The application of a surfactant formulation conditioned in gel form made it possible to degrease and decontaminate the floor of a cell which had been used for 6 years for U and Pu partitions (2nd extraction cycle). The strong points of this surfactant formulation are as follows: good degreasing of the surface practically without any mechanical effect even in the zones covered with tarry deposits (radiolysis of the solvent), putting into suspension the metal dibutyl phosphates which are the carriers of the main part of the radiochemical activity. These results are encouraging for the applications of this surfactant formulation under liquid form.
	summary
	claims	1. Reflective optical element having an optically effective surface and comprising:an element substrate;a reflection layer system;at least one deformation reduction layer which, upon the optically effective surface being irradiated with electromagnetic radiation, reduces a maximum deformation level of the reflection layer system in comparison with an analogous construction of a reflective optical element without the deformation reduction layer; andan intermediate layer arranged between the reflection layer system and the deformation reduction layer and configured to block transfer of surface roughnesses to the reflection layer system,wherein the reflection layer system comprises at least one layer composed of a first material having a first coefficient of thermal expansion, and the at least one deformation reduction layer comprises a second material having a second coefficient of thermal expansion, and wherein the first and the second coefficients of thermal expansions have mutually opposite signs. 2. Reflective optical element according to claim 1, wherein the first material comprises at least one of zirconium (Zr), yttrium (Y), molybdenum (Mo), niobium (Nb), silicon (Si), germanium (Ge), rhodium (Rh), ruthenium (Ru), ruthenium dioxide (RuO2) and ruthenium-silicon (RuSi). 3. Reflective optical element according to claim 1, wherein the second material is selected from the group consisting essentially of ZrMo2O8, ZrW2O8, HfMo2O8, HfW2O8, Zr2(MoO4)3, Zr2(WO4)3, Hf2(MoO4)3, Hf2(WO4)3, ScF3, ZnC2N2, ZnF2, Y2W3O12 and BiNiO3. 4. Reflective optical element according to claim 1, wherein the intermediate layer comprises at least one of quartz and silicon (Si). 5. Reflective optical element according to claim 1, wherein the intermediate layer is unprocessed. 6. Reflective optical element according to claim 1, wherein the intermediate layer is mechanically processed or ion beam figured. 7. Reflective optical element according to claim 1 and configured for an operating wavelength of less than 30 nm. 8. Reflective optical element according to claim 1, configured as a mirror for a microlithographic projection exposure apparatus or a mask inspection apparatus. 9. Reflective optical element according to claim 1, configured as a reticle for a microlithographic projection exposure apparatus. 10. Optical system of a microlithographic projection exposure apparatus, comprising at least one reflective optical element according to claim 1 and configured into an illumination device or a projection lens of the projection exposure apparatus. 11. Optical system of a mask inspection apparatus, comprising at least one reflective optical element according to claim 1 and configured into an illumination device or an inspection lens of the mask inspection apparatus. 12. Microlithographic projection exposure apparatus comprising an illumination device and a projection lens, wherein the projection exposure apparatus comprises a reflective optical element according to claim 1 configured into the illumination device or the projection lens. 13. Mask inspection apparatus comprising an illumination device and an inspection lens, wherein the mask inspection apparatus comprises a reflective optical element according to claim 1 configured into the illumination device or the inspection lens. 14. Reflective optical element having an optically effective surface and comprising:an element substrate;a reflection layer system;at least one deformation reduction layer which, upon the optically effective surface being irradiated with electromagnetic radiation, reduces a maximum deformation level of the reflection layer system in comparison with an analogous construction of a reflective optical element without the deformation reduction layer; andan intermediate layer arranged between the reflection layer system and the deformation reduction layer and configured to block transfer of surface roughnesses to the reflection layer system,wherein an effective volume change ΔVeff of an arrangement comprising the reflection layer system and the deformation reduction layer that results from a heating of the optically effective surface by a predetermined temperature difference is a maximum of 90% of a volume change V1 of the reflection layer system alone that results from the heating. 15. Reflective optical element according to claim 14, wherein the effective volume change ΔVeff of the arrangement is a maximum of 90% of the volume change V1 for a heating of the optically effective surface (by a temperature difference of at least 1K. 16. Reflective optical element having an optically effective surface and comprising:an element substrate;a reflection layer system; andat least one deformation reduction layer which, upon the optically effective surface being irradiated with electromagnetic radiation, reduces a maximum deformation level of the reflection layer system in comparison with an analogous construction of a reflective optical element without the deformation reduction layer;wherein the at least one deformation reduction layer comprises a heat distribution layer at a location facing the element substrate, and wherein the heat distribution layer has a thermal conductivity that is greater than a thermal conductivity of the element substrate alone. 17. Reflective optical element according to claim 16, wherein the heat distribution layer has a thermal conductivity of at least 100 W/mK. 18. Reflective optical element according to claim 16, wherein the heat distribution layer comprises at least one material selected from the group consisting essentially of graphite, aluminium (Al), silver (Ag), gold (Au), copper (Cu) and ZrW2O8. 19. Reflective optical element according to claim 16, wherein a heat insulation layer configured to delay entry of heat into the element substrate is arranged between the element substrate and one of the reflection layer system and the deformation reduction layer. 20. Reflective optical element according to claim 19, wherein the heat insulation layer comprises quartz. 21. Reflective optical element according to claim 16, further comprising:an intermediate layer arranged between the reflection layer system and the deformation reduction layer and configured to block transfer of surface roughnesses to the reflection layer system.
	abstract	It is described a portable X-ray system (200), which has sensing means for detecting whether an anti scatter grid (230) is attached to a portable detector (240) or not. The system is able to automatically change the default exposure settings (265 a, 265b, 265 c, 265 d), when a grid (230) is removed or attached to the portable detector (240). Thus, the risk of an under- or an over-exposure of the image will be reduced.
	abstract	High aspect ratio micromachined structures in semiconductors are used to improve power density in Betavoltaic cells by providing large surface areas in a small volume. A radioactive beta-emitting material may be placed within gaps between the structures to provide fuel for a cell. The pillars may be formed of SiC. In one embodiment, SiC pillars are formed of n-type SiC. P type dopant, such as boron is obtained by annealing a borosilicate glass boron source formed on the SiC. The glass is then removed. In further embodiments, a dopant may be implanted, coated by glass, and then annealed. The doping results in shallow planar junctions in SiC.
	description	The present invention concerns a nuclear fuel assembly bottom nozzle, of the type comprising a perforated plate to allow water to pass through it, the nozzle having lateral faces, and at least one anti-debris element positioned on a lateral face to block out debris likely to infiltrate between the bottom nozzle and another adjacent bottom nozzle. A nuclear fuel assembly for a pressurized water reactor (PWR) traditionally comprises a bundle of nuclear fuel rods and an armature, the armature comprising a bottom nozzle, an upper nozzle, guide tubes connecting the bottom nozzle to the upper nozzle, and retention grids attached on the guide tubes. The rods extend between the bottom nozzle and the upper nozzle, and through the grids that retain them on the armature. In operation, the assembly is positioned in a nuclear reactor such that the rods extend vertically, and water flows at a high speed along the rods of the nuclear fuel assemblies, passing through the bottom nozzle and the upper nozzle. The water serves as coolant for the heat exchanges, and moderator for the nuclear reaction. There is a risk of the debris transported by the water damaging the rods of the fuel assembly and requiring that the reactor be stopped to change a rod or an entire assembly. Yet the assemblies are costly, and stopping the reactor is expensive for the operator. To limit this risk, the bottom nozzle has, inter alia, the function of filtering the debris to prevent it from passing through the bottom nozzle. Nevertheless, a risk remains that debris may infiltrate between two bottom nozzles of two assemblies positioned side by side in the reactor. JP 6003470 describes a bottom nozzle of the aforementioned type, comprising an anti-debris element positioned on a lateral face of the nozzle, the anti-debris element being made of a shape memory alloy such that the anti-debris element protrudes from the lateral face from a temperature close to the operating temperature of the reactor (indicated as being 300° C.) to filter the debris, and does not protrude from the lateral face below that operating temperature to facilitate the insertion or removal of the assembly into or out of the core of the reactor, respectively. However, this bottom nozzle does not make it possible to filter the debris infiltrating between the assemblies during the start and stop phases of the reactor, during which the temperature of the reactor is much lower than the operating temperature, even when these phases are critical. The start phases are in particular critical due to the fact that the debris can be due to manipulations done during the stop of the reactor, before it is restarted. An object of the invention is to provide a nuclear fuel assembly bottom nozzle allowing effective blocking of the debris while facilitating the installation of the assembly inside the reactor. To that end, the invention provides a bottom nozzle of the aforementioned type, characterized in that, in the free state, the or each anti-debris element permanently projects from the lateral face on which it is positioned, the or each anti-debris element being elastically deformable so as to retract towards the lateral face in the event of a force being exerted on the anti-debris element towards the lateral face. According to other embodiments, the bottom nozzle comprises one or several of the following features, considered alone or according to all technically possible combinations: it comprises a groove formed in the lateral face such that the anti-debris element retracts into the groove in the event of a force being exerted on the anti-debris element towards the lateral face; the anti-debris element is elongated and has two lateral portions bearing on the lateral face and a central portion protruding from the lateral face, the lateral portions moving away from each other in the event of a force being exerted on the anti-debris element towards the lateral face; the lateral portions are bearing on the bottom of the groove with a width larger than the distance between the free edges of the lateral portions of the anti-debris element in the free state, the central portion protruding through an opening of the groove emerging on the lateral face. the opening has a width smaller than said distance between the free edges of the lateral portions of the anti-debris element in the free state; the groove is defined by a slot formed in the lateral face and forming the bottom of the groove and at least one retention element extending overhanging from one edge of the slot, the free end of the retention element defining the opening; it comprises two retention elements extending overhanging one another from opposite edges of the slot and defining the opening between their free edges; it comprises a series of retention elements spaced apart and distributed along a lateral portion in the direction of the length of the anti-debris element, each retention element keeping the lateral portion bearing on the lateral face and allowing sliding of the lateral portion on the lateral face; a lateral portion comprises, on its free edge, notches in which the retention elements ensuring the retention of the lateral portion on the lateral face are received; the anti-debris element comprises at least one flat lug extending a lateral portion in the direction of the length of the anti-debris element and engaged under a retention element provided to keep the lateral portion bearing against the lateral face while allowing sliding of the lateral portion on the lateral face; and the or each anti-debris element comprises orifices for the circulation of water through the anti-debris element. The invention also provides a nuclear fuel assembly including a bundle of nuclear fuel rods and a maintenance frame of the rods, the frame comprising an upper nozzle and a bottom nozzle between which the rods extend, the bottom nozzle being a bottom nozzle as defined above. FIG. 1 shows two identical nuclear fuel assemblies 2 placed side by side on the lower plate 4 of the core of a pressurized water nuclear reactor (PWR). Each assembly 2 is elongated along a longitudinal axis L that extends substantially vertically when the assembly 2 is positioned in the core of the reactor. Hereinafter, the terms “top” and “bottom” are used in reference to the position of the assembly 2 in the reactor. Each assembly 2 comprises a bundle of nuclear fuel rods 6 and a retention frame 8 for the rods 6. Each rod 6 traditionally comprises a tubular sheath filled with nuclear fuel pellets. The frame 8 comprises a bottom nozzle 10, an upper end 12, guide tubes 14 and retention grids 16. The bottom nozzle 10 and the upper nozzle 12 are spaced along the axis L. The guide tubes 14 extend between the nozzles 10, 12 and connect the nozzles 10, 12 to each other. The gates 16 are attached on the guide tubes 14 and distributed between the nozzles 10, 12. The rods 6 extend parallel to the axis L through the grids 16 that ensure the longitudinal and transverse retention of the rods 6. As shown in FIG. 2, each bottom nozzle 10 comprises a filtering plate 18, support feet 20, and anti-debris elements 22 attached and positioned on lateral faces 24 of the bottom nozzle 10. The plate 18 extends transversely to the axis L. It for example has a polygonal profile, here a square profile. Alternatively, it has a hexagonal profile. The feet 20 extend downward from the corners of the plate 18. The bottom nozzle 10 bears on the lower plate 4 via the feet 20. Each anti-debris element 22 protrudes from the lateral face 24 on which it is mounted. The lower plate 4 is provided with water inlet orifices 26. At least one orifice 26 emerges under the bottom nozzle 10 of each assembly 2. As shown in FIG. 3, the plate 18 is perforated to allow water to circulate through it. To that end, the plate 18 for example comprises a plurality of channels 28 going all the way through the plate 18. Each anti-debris element 22 assumes the form of an elongated elastic blade and extends parallel to the ridge 30 defining the upper edge of the lateral face 24. FIGS. 4 and 5 are cross-sectional views along IV-IV of FIG. 3, in which the anti-debris element 22 is shown in the free state and in a compressed state, respectively. As shown in FIG. 4, the anti-debris element 22 is received in a groove 32 defined in the lateral face 24, and protrudes from the lateral face 24 through an opening 34 of the groove 32 emerging on the lateral face 24. The groove 32 is defined by an elongated slot 36 formed in the lateral face 24 and retention elements 38 extending from opposite edges of the slot 36 towards each other, and giving the groove 32 a T-shaped section. The opening 34 is defined between the free edges of the retention elements 38. It has a width W1 smaller than that W2 of the bottom 40 of the groove 32. The bottom 40 is flat and parallel to the lateral face 24. The anti-debris element 22 has a hat-shaped transverse section, and comprises two flat lateral portions 42 and a curved central portion 44 protruding from the lateral face 24. The lateral portions 42 are received in the groove 32, in the lateral spaces defining the bars of the T-shaped section defined between the bottom 40 and the retention elements 38. The width W3 of the anti-debris element 22 considered between the free edges of the lateral portions 42 is smaller than that W2 of the bottom 40 and larger than that W1 of the opening 34. As a result, the anti-debris element 22 is retained transversely to its length in the groove 32. The central portion 44 has a width W4 smaller than that W1 of the opening 34. The central portion 44 is curved so as to protrude from the lateral face 24 through the opening 34 in the free state of the anti-debris element 22. The central portion 44 permanently protrudes from the lateral face 24 in the free state of the anti-debris element 22, regardless of the temperature, more particularly in the range of the temperatures encountered in nuclear reactors during the normal and energy production operating phases, the stop phases, and the transitional start and stop phases. This temperature range is generally between ambient temperature, or about 20° C., and about 350° C. The retention elements 38 are received in clearances 46 formed in the lateral face 24 along the slot 36, such that the retention elements 38 are on the same level as the lateral face 24. The retention elements 38 are for example fastened using mechanical fastening members 47 such as screws, rivets . . . , diagrammed by broken lines. Alternatively or optionally, the retention elements 38 are fastened on the lateral face 24 by welding. In the illustrated example, each retention element 38 assumes the form of a continuous elongated bar extending over the majority of the length of the lateral portion 42 it covers. Alternatively, one retention element 38 is replaced by a plurality of retention elements spaced out and distributed along the anti-debris element 22. As shown in FIG. 5, the anti-debris element 22 is adapted to elastically deform and retract into the groove 32 in the event a force is applied on the central portion 44 and oriented towards the lateral face 24, as illustrated by the arrow F1 in FIG. 5. In this case, the anti-debris element 22 elastically deforms by crushing the central portion 44 and spacing the lateral portions 42 apart from each other and sliding the latter on the bottom 40, as illustrated by the arrows F2 in FIG. 5. During operation, in reference to FIG. 2, water is injected through the orifices 26, and circulates in the core of the reactor from the bottom towards the top, through and between the assemblies 2. The water is injected under the bottom nozzles 10. It circulates through the plates 18 and between the rods 6 of each assembly 2. It also circulates between the assemblies 2, passing through passages defined between the adjacent lateral faces 24 of the bottom nozzles 10 of each pair of adjacent assemblies 2. The water serves as a moderator fluid to moderate the nuclear reaction, and as coolant to remove the heat created in the rods 6 due to the nuclear reaction. The plate 18 of each bottom nozzle 10 allows the water to pass that circulates in the reactor and blocks any debris that may be present in the water. The anti-debris elements 22 arranged on the lateral faces 24 block the debris that may be present in the flow of water passing between the assemblies 2. More precisely, the anti-debris elements 22 of the two lateral faces 24 opposite the bottom nozzles 10 reduce the width of the passage defined between these two lateral faces 24, so as to block any debris. The anti-debris elements 22 permanently protruding in the free state from the lateral faces 24 make it possible to block the debris transported by the flow of water flowing between the assemblies in all of the operating phases of the reactor, and in particular during the transitional start and stop phases. To remove an assembly 2 from the reactor or introduce it into the reactor, a hook is used that grasps the assembly 2 by its upper nozzle 12. The risk related to this type of operation is of the bottom nozzle 10 touching a rod 6 or a grid 16 of another adjacent assembly 2 in the core of the reactor, and causing damage to the manipulated assembly or one of the adjacent assemblies by possibly creating debris. The anti-debris elements 22 able to retract when they are pushed on limit this risk during handling, and also make it possible to ensure better guiding of the assembly during its insertion or removal from the core of the reactor. Due to their elasticity, they then resume their initial configuration blocking debris. The anti-debris elements 22 are preferably made of materials with a high limit of elasticity, such as, for example, nickel- or iron-based superalloys, titanium alloys or certain stainless steels with structural hardening, for example those defined by standards AMS (Aerospace Material Specification) 5629 and AMS 5643. In the illustrated example, the retention elements 38 are attached and fastened on the lateral faces of the bottom nozzle 10. In one alternative not shown, the retention elements are integral with the lateral face 24, a groove 32 for example being machined in the lateral face 24 using a T-shaped burr. The embodiments of FIGS. 6 and 7 differ from the preceding embodiment in the shape of the retention elements. In the embodiment of FIG. 6, the bottom nozzle 10 comprises several retention elements 38 spaced apart and distributed along each lateral portion 42 of each anti-debris element 22. Each retention element 38 comprises a base 50 for fastening the retention element 38 on the bottom 40 of the groove 32, and a disc-shaped head 52 larger than the base 50. Each lateral portion 42 comprises a plurality of notches 54 for receiving a base 50 of a retention element 38 that are distributed along the free edge of the lateral portion 42. Each notch 54 emerges on the free edge of the lateral portion 42. Each notch 54 is large enough to receive the base 50 of a retention element 38, but too narrow to allow the passage of the head 52 of said retention element 38. Each notch 54 extends towards the inside of the anti-debris element 22 so as to make it possible to space the lateral portions 42 away from each other during crushing of the central portion 44 towards the bottom 40 of the groove 32. In the embodiment of FIG. 7, each anti-debris element 22 is retained only at its ends. To do this, each lateral portion 42 of an anti-debris element 22 is provided with a flat extension 56 extending the lateral portion 42 in the direction of the length of the anti-debris element 22, and retention elements 38 are provided in the form of corner plates 58 fastened in clearances 60 provided on the lateral faces 24 of the bottom nozzle 10, so as to cover the extensions 56. Each corner plate 58 covers one corner of the bottom nozzle 10 and is used to fasten two anti-debris elements 22 arranged on two adjacent lateral faces 24 of the bottom nozzle 10. In one alternative, two corner plates 58 positioned on a same corner are replaced by a single corner plate. Alternatively or optionally, one corner plate 58 is replaced by two plates each serving to fasten an anti-debris element 22. In the alternative illustrated in FIGS. 8 and 9, the anti-debris element 22 differs from that of the alternative of FIGS. 3 to 5 in that it comprises orifices 60 for circulating water through the anti-debris element 22, in order to offer less resistance to the flow of the water and allow cooling of the fuel rods 6 situated on the periphery of the fuel assemblies 2. The orifices 60 are formed in the central portion 44 distributed along the latter part. In the illustrated example, the anti-debris element 22 comprises a series of lower orifices 60 formed in the lateral portion of the central part 44 adjacent to the lower lateral part 42, and a series of upper orifices 60 formed in the lateral portion of the central part 44 adjacent to the upper lateral part 42. The lower orifices 60 are situated between the apex 62 of the central portion 44 and the lower lateral portion 42. The upper orifices 60 are situated between the apex 62 and the upper lateral portion 42. As illustrated in FIG. 9, during operation, water circulates through the anti-debris element 22 while entering under the anti-debris element 22 via the lower orifices 60, and exiting via the upper orifices 60. To ensure good circulation of the water, each lower orifice 60 is positioned opposite an upper orifice 60 along the anti-debris element 22. As illustrated in FIG. 8, the orifices 60 have an elongated oblong shape transversely to the anti-debris element 22. Alternatively or optionally, the orifices are oblong and elongated in the direction of the length of the anti-debris element 22 or diagonally in relation to the flow. The orifices 60 can have other geometric shapes and/or be positioned in staggered rows or positioned in a single series. The anti-debris element 22 can also have different combinations of orifices 60 with different shapes and positions. The invention is not limited to the illustrated embodiments. It is for example possible to combine the embodiments of FIGS. 3, 6 and 7 to provide different types of retention elements or anti-debris elements 22 made in several parts. It is also possible to have anti-debris elements 22 only on two lateral faces 24 of the bottom nozzle 10, for example, the two lateral faces opposite the bottom nozzles 10 of the two adjacent assemblies and the other two lateral faces of the bottom nozzle 10 being free of anti-debris elements 22. The invention applies to nuclear fuel assembly bottom nozzles for pressurized water reactors (PWR). The invention generally applies to bottom nozzles of any type of nuclear fuel assembly.
052689433	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, there are two sources of coolant to make up for losses of coolant in the nuclear reactor 22. An inlet 32 of high pressure makeup tank 33 is coupled by valves 35 to the reactor coolant inlet or "cold leg" 36. The high pressure makeup tank 32 is also coupled by motorized valves 38 and check valves 42 to a reactor vessel injection inlet 44. The high pressure makeup tank 33 is operable to supply additional coolant to the reactor coolant circuit 46, at the operational pressure of the reactor, to make up for losses. However, the high pressure makeup tank 33 contains only a limited supply of coolant. A much larger quantity of coolant water is available from the in-containment refueling water storage tank 50, at atmospheric pressure due to vent 52, which opens from tank 50 into the interior of the containment building 54. When the reactor 22 is operating, the coolant circuit operational pressure is on the order of 2,250 psi (150 bar). Therefore, in order to add coolant to the reactor vessel 60 and the coolant circuit 46 coupled thereto, the system must be depressurized, i.e., brought down to atmospheric or nearly atmospheric pressure in the containment. According to the invention, the coolant circuit 46 is depressurized in stages, to limit the thermal and hydraulic loading on the conduits 36, 56 and the reactor vessel 60 due to depressurization by venting into the containment 54. The nuclear reactor 22 in the example shown is depressurized by venting the coolant circuit 46 into the containment 54 in four stages of decreasing pressure, the last stage characterized by direct coupling of the coolant circuit 46 to the interior of the containment 54. In the last stage, coolant from the refueling water storage tank 50 can be fed by gravity through motorized valve 62 and check valves 64 into the reactor vessel injection inlet 44. Additionally, in the last stage the containment building 54 can be flooded with water from the refueling water storage tank 50. Water in the containment 54 thus drains by gravity into the coolant circuit 46 and is boiled by the nuclear fuel. Steam thereby generated is vented into the containment 54, where water condenses on the relatively cooler containment walls. The condensed water drains back into the bottom of the containment 54 and is recycled, the system providing a passive cooling means independent of pumps and other actively powered circulation elements. During staged depressurization as shown in FIG. 1, three initial stages are achieved successively by opening the initial stage depressurization valves 72 coupled via spargers 74 between the coolant circuit 46 and the containment shell 54. The respective valves 72 in each depressurization leg 76 are opened at successively lower pressures and preferably are coupled between the coolant system pressurization tank 80 and the spargers 74 submerged in the refueling water supply tank 50 in parallel legs along conduits 76. The successively opened conduits 76 are progressively larger for the successive stages, thus venting the coolant circuit 46 more and more completely to the containment 54. The final stage of depressurization, achieved by opening valve means 82, can use the largest conduit 84 and directly couples the coolant circuit 46 to the containment shell 54 (rather than through the spargers 74 in the refueling water supply tank 50), for example opening in a loop compartment in the containment 54 containing the reactor outlet conduit 56 which leads to an electrical steam generator (not shown). The coolant circuit 46 of a reactor having such passive cooling safeguards, including a staged depressurization system, is coupled according to the invention to a residual heat removal system 90, whereby makeup water can be supplied to the coolant circuit 46 before depressurization reaches the final stage. The residual heat removal system 90 normally is activated only during shutdown, for removing normal decay heat from the reactor core. Whereas the residual heat removal system is manually activated, it is not intended as a safety-grade apparatus for cooling in the event of an accident. However, by arranging a coupling between the residual heat removal system 90 and the reactor coolant circuit 46, it is possible to use the residual heat removal pumps for moving coolant from the refueling water supply 50 into the coolant circuit 46 or for cooling the water in the refueling water supply 50. Referring to FIG. 1, a nuclear reactor having a reactor vessel 60 disposed in a containment shell 54, has a normally pressurized coolant circuit 46 including the reactor vessel. A refueling water storage tank 50 at atmospheric pressure is coupled to a coolant addition system 92 operable to depressurize the coolant circuit 46 for adding coolant from the refueling water storage tank 50 to the coolant circuit at reduced pressure. A residual heat removal loop 94 having at least one pump 96 and at least one heat exchanger 98, the residual heat removal loop 94 having an inlet 102 and an outlet 104, is coupleable to the coolant circuit 46 by manually operable valves 106, 108. Suitable check valves 109 are provided in series at the outlet of the residual heat removal loop 94. The preferred system as shown in FIG. 2 includes two residual heat removal legs 94 having respective pumps 96 and heat exchangers 98. When the residual heat removal pumps 96 are coupled by the valves 106, 108 between the refueling water supply 50 and the coolant circuit 46, i.e., during depressurization of the coolant circuit prior to reaching the final stage of depressurization, the pumps 96 inject water from the refueling water supply 50 into the direct vessel injection line 112. Injection can occur when the reactor coolant circuit pressure drops to below the shutoff head of the pumps 96. Inlet isolation valves 110 and outlet stop-check isolation valves 111 separate the two parallel coupled residual heat removal legs 94. The pumps 96 can be protected from overpressure problems by including bypass paths 113, having restricted orifices 114 for bleeding off pressure in the event the pumps are activated when the outlet valve 108 is closed or when the pumps 96 cannot exceed the pressure head of the line leading to the reactor injection inlet 44. Referring again to FIG. 1, the stages of depressurization can be triggered based on the level of coolant in the coolant makeup tank 33. For example, the level of coolant can be determined using sensors 122 disposed at different levels on tank 33, coupled to the reactor control system (not shown) for opening the staged depressurization valves 72 upon reaching a corresponding coolant level. The pumps 96 discharge into the coolant circuit 46 at a point downstream of the coolant makeup tank 33. Therefore, operation of the pumps 96 can effectively shut off flow from the coolant makeup tank 33. The fluid pressure head loss H.sub.F due to friction between the direct vessel injection port 132 and the connection 134 of the residual heat removal system discharge line 104 is set, by appropriate adjustment of the dimensions of orifice 133, to be equal to the elevation head difference (H.sub.ELEV) from connection 134 to the water level 136 in the coolant makeup tank 33. Therefore, if the head loss H.sub.F from point 132 to point 134 corresponds to the fluid pressure head due to an elevation in the coolant makeup tank 33 above the coolant elevation at which the final stage depressurization valves 82 are opened, then the final stage depressurization valves 82 will not be opened during injection of coolant from the residual water supply 50 by residual heat removal pumps 96. Activation of the residual heat removal system 90 during depressurization thus prevents the automatic depressurization system from advancing to the stage at which the containment is flooded. Inasmuch as the coolant circuit 46 is pressurized during operation of the reactor, the stages of depressurization involve a loss of coolant from the reactor coolant circuit 46 at varying rates. The venting of steam and water removes coolant from the circuit 46 and moves the coolant into the refueling water supply tank 50 through the spargers 74, or into the containment structure 54 directly via final stage conduit 84. Accordingly, the level of coolant in makeup tank 33 falls during operation of the depressurization system. The falling level of the makeup supply triggers the next stage of depressurization, proceeding through each of the stages following initiation of automatic depressurization The residual heat removal system 90 precludes unnecessary flooding of the containment 54, for example when the automatic depressurization system 90 is activated inadvertently, or when the loss of coolant triggering the initial stage depressurization is not of a critical nature. If a critical loss of coolant accident occurs, the residual heat removal system 90 still can be activated manually, without adverse effects. Whether or not the operators activate the residual heat removal pumps 96, if the level in the coolant makeup tank 33 drops to the level at which final stage depressurization is triggered (e.g., at 25% of the volume of the coolant makeup tank), the coolant circuit 46 is vented to the containment 54, and coolant flows by gravity from the refueling water supply 50 to the coolant circuit 46 and/or to the bottom of the containment 54, effecting passive cooling. Thus the invention does not hinder the passive cooling system, and in fact provides an additional core cooling margin while protecting against unnecessary flooding of the containment building 54. The preferred valving arrangement as shown in FIG. 2 includes at least one inlet valve 142 coupled to an inlet 102 of the residual heat removal system 90, selectively coupling the residual heat removal system to one of the coolant circuit 46 and the refueling water storage tank 50, and at least one outlet valve 144 coupled to an outlet 104 of the residual heat removal system 90, selectively coupling the residual heat removal system 90 to either the coolant circuit 46 or the refueling water storage tank 50. This provides the further capability of using the residual heat removal system 90 to cool the refueling water storage tank 50. For this purpose the inlet 102 and outlet 104 of the residual heat removal system 90 both are coupled to the refueling water supply tank 50, in a coolant loop apart from the reactor coolant circuit 46. Cooling of the refueling water supply 50 is useful in the event a supplemental heat exchanger 152 is arranged in the refueling water supply tank 50, or if the refueling water supply 50 has become heated by operation of the depressurization system to vent steam and hot water into the refueling water supply. The foregoing discussion includes only a single core makeup tank and a single direct reactor vessel injection line. In the event the passive cooling system employs more than one high pressure makeup tank and/or direct reactor vessel injection port, then it is necessary to couple one or more legs of the residual heat removal system to each of the high pressure tanks and/ direct injection ports, substantially as shown in FIG. 1. For example, in FIG. 2, two direct reactor vessel injection ports are shown coupled to the residual heat removal system. The invention having been disclosed, a number of alternatives will now become apparent to those skilled in the art. The foregoing embodiments are illustrative, and are not intended to limit the particulars of the invention in which exclusive rights are claimed. Reference should be made to the appended claims rather than the discussion of preferred embodiments, in order to assess the scope of the invention in which exclusive rights are claimed.
047909609	summary	BACKGROUND OF THE INVENTION The present invention relates to a process for the stripping of cesium ions from aqueous solutions in which a precipitation agent is added to the aqueous solution and the resulting precipitate, containing the Cs.sup.+ ions, is stripped from the solution. Cs-137 in its property as hard gamma ray emittor, is a particularly undesirable fission product in medium radioactive aqueous waste products (MAW), and renders more difficult the processing and solidification of MAW. A prior selective stripping of the Cs-137 would considerably simplify the further processing of medium radioactive waste products. After stripping the Cs-137 from the MAW, the shielding of the concentrate and/or the solidified ultimate waste package could be totally or at least partially omitted. In addition, such a process could also be profitably used for obtaining or stripping of Cs isotopes from highly active waste solutions as they occur, for example, in the reprocessing of nuclear fuels in the first extraction cycle. Here, the extraction of pure isotopes or isotope mixtures of cesium would be of practical importance for radio-chemical use and as radiation or heat source. In the past, attempts have been made to precipitate Cs.sup.+ ions with sodium tetraphenylborate (commercial name Kalignost), but it has been determined that such a precipitation cannot be done either selectively or in an acid milieu. The stripping of cesium is done, according to a known process, mainly by coprecipitation reactions. However, the coprecipitation does not supply satisfactory decontamination factors for Cs (DF values). Thus, other processes were locked for which would permit a selective stripping of the cesium radionuclides. The extraction procedures which have so far been developed for Cs.sup.+ ions are not suitable for stripping Cs.sup.+ from a typical MAW with its high content of NaNO.sub.3 and free nitric acid. J. Rais and P. Selucky proposed an extraction system for stripping Cs.sup.+ from aqueous solutions, which uses 2,3,11,12-dibenzo-1,4,7,10,13,16-hexa-oxo-cyclo-octadeca-2,11-dien (dibenzo-18-crown-6DB-18-C-6 for short) in an organic phase and sodium tetraphenylborate was added to the aqueous phase which forms a Cs.sup.+ containing adduct to be extracted. (Czechoslovakian Patent CS-PS No. 149,404). However, the process is limited to alkaline Cs.sup.+ solutions (pH 11 to 13) because sodium tetraphenylborate is hydrolyzed in the acid range. In addition, the process only works well in the absence of substantial amounts of Na.sup.+ and K.sup.+. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a process of the type stated above in which cesium can be stripped selectively, with high effectiveness from aqueous solution, as compared to other alkaline metal cations, such as Li.sup.+, Na.sup.+ and K.sup.+. Additional objects and advantages of the present invention will be set forth in part in the description which follows and in part will be obvious from the description or can be learned by practice of the invention. The objects and advantages are achieved by means of the processes, instrumentalities and combinations particularly pointed out in the appended claims. To achieve the foregoing objects and in accordance with its purpose, the present invention provides a process for the stripping of cesium ions from aqueous solution in which a precipitation agent is added to the aqueous solution and the resulting precipitate, containing the Cs.sup.+ ions, is separated from the solution, comprising adding a sodium or lithium tetraphenylborate having electron-attracting substituents on the phenyl rings as a precipitation agent. Preferably, the compounds which are used as precipitation agents are compounds in which the phenyl rings are substituted one to five times. Particularly good results are obtained with a compound which is disubstituted, in each of its phenyl rings in the 2,4 positions of the phenyl rings. However, compounds which are fourfold substituted in each of its phenyl rings in the 2,3,5,6 positions of the phenyl rings, or fivefold substituted in each of its phenyl rings in the 2,3,4,5,6 positions of the phenyl rings can also be successfully used. A particularly advantageous version of the process according to the present invention occurs when the substituents on the phenyl rings are fluorine atoms. An effective embodiment of the process occurs when the addition of the precipitation agent and/or the precipitation reaction, as such, takes place or is done at a temperature of between 239.degree. K. and 303.degree. K. Preferably, the precipitation agent is added to the solution at a slight excess with regard to the cesium content, e.g. between 1.2 times to 5 times the stoichiometrically-needed amounts. The stripping of the precipitates, can be done, for example, either through filtration, liquid extraction, centrifugation or flotation. A particularly good stripping is attained with the process according to the invention when the solution containing the cesium ions (a) is adjusted to a Cs.sup.+ concentration in the range of between 10.sup.-1 and 10.sup.-3 mol/l and (b) the precipitation agent is added to the solution from step (a) and the resulting precipitate is stripped off. Steps (a) and (b) can be repeated at least once to achieve a desired decontamination of existing Cs-137 with the repetition of step (a) being conducted with inactive cesium (as carrier). Thus, in the repetition of step (a) inactive cesium is added to adjust the solution to the concentration in the range of between 10.sup.-1 and 10.sup.-3 mol/l. The precipitation reaction preferably takes place in the presence of an acid concentration in the range of between 0 and 6 mol/l. In one preferred embodiment of the present invention, the separation of the precipitate from the solution occurs by means of extraction with an organic solvent. For example, chloroform; diethyl ether ligroine (b.p. 40.degree.-60.degree. C.) 2:1 [vol./vol.]; 4-methyl-2-pentanone (5% by volume in chloroform); or 4-methyl-2-pentanone (5% by volume in toluol) can be employed as organic solvent. It is understood that both the foregoing general description and the following detailed description are exemplary and explanatory, but are not restrictive of the invention.
048511811	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light water moderation type nuclear reactor, more particularly to a pressurized water type nuclear reactor with a once-through method or a boiling water type nuclear reactor with a once-through method. 2. Description of the Prior Art The method of utilizing the fuel materials in a light water moderation type nuclear reactor (hereinafter referred to as a light water reactor) is largely classified into the once-through method and the reprocessing and recycling method. With the once-through method the light water reactor uses the enriched uranium and in this method none of the fuel materials contained in the used fuel rods which are taken out of the light water reactor is reused (recycled) in the light water reactor. This once-through method or system cycling cost when cost of the reprocessing fuel is higher than that of the enriching uranium. Additionally, the purpose of the reprocessing and recycling method or system is to make new fuel rods by reprocessing fuel materials in the used fuel rods and to charge those new fuel rods into the light water reactor to reuse the fuel materials. One method to effectively use the fuel materials by the once-through method is to greatly increase the take-out burnup from the fuel assembly, that is, to realize a high degree of the burnup. The fuel assembly includes many fuel rods. It is required to raise the enrichment of the enriched uranium so as to achieve the high degree of the burnup. However, to realize such a raised enrichment of the enriched uranium, the following problems occur. In the center of the reactor core of the light water reactor there are the fuel assemblies with large difference in the neutron infinite multiplication factor because of a high enrichment of new fuel assemblies and the large take-out burnup. A difference in the output power share proportions of the individual fuel assemblies, therefore, the output power mismatch grains larger and also the output power peaking becomes larger. Further, as the enrichment increases, the surplus reactivity which has to be controlled in the initial stage of the burning increases. Therefore, the conventional fuel assembly using the fuel rods containing gadolinia has to increase the number of the fuel rods which contain the gadolinia. The fuel rods of reactor core of the conventional pressurized water type nuclear reactor have uniformly the ratio (r.sub.H/U) of the number of hydrogen atoms to the number of fuel material atoms of about 2.0. The characteristics of the reactor core of the conventional pressurized water type nuclear reactor is represented by the curve P.sub.5 (a dashed line) as shown in FIG. 11. The initial enrichment of the fuel rods of the conventional light water reactor is raised until the take-out burnup E.sub.b represented by the curve P.sub.5 as shown in FIG. 11 is realized. With this reactor core the initial neutron multiplication factor is large, and in order to suppress this, a large amount of the burnable poison material such as gadolinium has to be put in the fuel assemblies at the expense of the neutron economy. Furthermore, the mingling of the fuel assemblies, which are much different in the neutron multiplication factor, into the reactor core makes it difficult to flatten the output power distribution. The maximum burnup is restricted by the fuel rods having the peak power with the result of the lowered average take-out burnup. The mismatch in the neutron multiplication factor of the conventional light water reactor is large, therefore the average take-out burnup from the fuel assembly can not be made high. The realization of the high degree of the burnup can not realize is impossible. The conventional light water reactor has a uniform ratio (r.sub.H/U) (about 2.0) of the number of hydrogen atoms to the number of fuel material atoms in the reactor core. The variation of the neutron multiplication factor in the conventional light water reactor is shown the curve P.sub.4 (a dashed line) shown in FIG. 10. In the conventional light water reactor the fuel assemblies are exchanged for the new fuel assemblies at the burnup E.sub.c. Namely the average take-out burnup of the fuel rods charged in the reactor core of the conventional light water reactor is the burnup E.sub.c. The amount of the charged fuel in the conventional light water reactor is the same throughout the reactor core. The average take-out burnup E.sub.c of the fuel rods in the reactor core is not made larger, therefore the uranium saving can not be achieved in the conventional light water reactor. From the standpoint of the effective use of the uranium resources, a light water reactor has been proposed in which the conversion from uranium-238 to a fissile product (plutonium-239) is improved. In the "General Features of Advanced Pressurized Water Reactors with Improved Fuel Utilization" by Werner Oldekop et al in the Nuclear Technology, vol. 59, November 1982 P. 212-227, a high conversion reactor (HCR) was proposed to lower the ratio (V.sub.H /V.sub.F) of the volume of light water and the volume of fuel material in the reactor core of the light water reactor from conventional 2.0 to 0.5 and raise the average energy of neutrons to make the plutonium conversion rate higher than 0.9. As a construction to bring about this ratio (V.sub.H /V.sub.F) of the volume of light water and the volume of fuel material of 0.5 a dense lattice construction is employed. Because of the dense lattice construction, the high conversion reactor (HCR) has following serious problems therein raised from the aspects of the heat transfer or the floating. Such problems are as follows, for example, the pressure drop in the reactor core becomes about four (4.0) times as much as that of the conventional light water reactor, or by the unexpected accident with coolant loss the emergency coolant hardly enters into the reactor core. The high conversion reactor (HCR) including this example aims at an effective utilization of the fuel material by reprocessing and recycling the fuel assemblies taken out of the reactor core. In the high conversion reactor (HCR) the fuel cycle including the steps of the fuel reprocessing, the fuel reworking, etc. must be completed. Furthermore, even if the above described problems in the high conversion reactor (HCR) were solved therein, the utilization quantity of uranium in the high coversion reactor (HCR) may be not reach more than about two-and-a-half (2.5) times as much as that of the conventional light water reactor. SUMMARY OF THE INVENTION One object of the present invention is to provide a light water moderation type nuclear reactor wherein an amount of the natural uranium required to develop unit energy in the light water reactor can be reduced without reusing the fuel materials. Another object of the present invention is to provide a light water moderation type nuclear reactor wherein uranium consumption in the reactor core can be reduced efficiently. Further, an object of the present invention is to provide a light water moderation type nuclear reactor wherein a take-out burnup can be increased efficiently. Still another object of the present invention is to provide a light water moderation type nuclear reactor wherein a production of the plutonium in the fuel rods can be increased during the first half of the life time of the fuel rods. Furthermore, an object of the present invention is to provide a light water moderation type nuclear reactor wherein fissile materials in the fuel rods can be burned effectively during the second half of the life time of the fuel rods. A further object of the present invention is to provide a light water moderation type nuclear reactor wherein a mismatch in the neutron multiplication factors among the fuel rods can be made relatively small. Still another object of the present invention is to provide a light water moderation type nuclear reactor wherein a ratio of the number of hydrogen atoms to that of fuel material atoms can be adjusted minutely. Still a further object of the present invention is to provide a light water moderation type nuclear reactor wherein thermal neutrons can be utilized effectively. The present invention has a feature that in a radial direction of the reactor core, areas having different average densities of the fuel rods per unit cross-sectional area are provided, and the fuel rods which are arranged in a first area with larger average density of the fuel rods per unit cross-sectional area are subsequently moved to a second area where the fuel rods are arranged in the area with smaller average density of the fuel rods per unit cross-sectional area, the fuel rods being arranged in the second area with smaller average density of the fuel rods per unit cross-sectional area having bean burned in the first area with larger average density of the fuel rods per unit cross-sectional area. For increasing the plutonium production in the reactor core it is only required to shift the neutron energy spectrum to the high energy side in order to raise the rate of capturing and absorbing neutrons by uranium-238. For this it is necessary to lower the ratio of the number of hydrogen atoms to that of uranium atoms which has the largest moderation power for neutron. With a once-through light water reactor it is necessary to burn up most effectively plutonium-239, plutonium-241 and the enriched uranium-235 that are produced as the fissile materials. This requires that methods for improving the moderation of neutrons and raising its rate of absorption of the fissile materials by increasing the proportion of the thermal neutrons. It can be achieved by increasing the ratio of the number of hydrogen atoms to that of uranium atoms. This means that, as far as the neutron moderation is concerned, namely the ratio of the number of hydrogen atoms to that of uranium atoms, the measure for increasing the production of plutonium and the measure for the high efficiency burnup of the fissile materials (plutonium-239, plutonium-241 and uranium-235) are measures. The present invention aims to realize in the same reactor core the above contradicting measure at the same time to produce more of the fissile materials and, furthermore, to utilize the fissile materials more efficiently for the saving of uranium consumption and the increasing burnup which will be described below in reference to FIG. 12 and FIG. 13. A reactor core 45 is divided radially by partition members 49 into a first area 46, a second area 47, . . . , and a Nth area 48 as shown in FIG. 12. The ratio of the number of hydrogen atoms to that of uranium atoms, i.e., r.sub.H/U in the first area is a.sub.1, r.sub.H/U in the second area is a.sub.2, and r.sub.H/U in the Nth area is a.sub.N ; and the following relations hold therein: EQU a.sub.1 <a.sub.2 < . . . <a.sub.N The value of a.sub.1 is made to be between 1.0 and 2.0 which is smaller than the ratio of the number of hydrogen atoms to that of uranium atoms of the conventional light water reactor, and the value of a.sub.N is made to be over 5.0 which is larger than the value of the conventional light water reactor. New fuel rods with the burnup of 0 are charged at first to the first area 46 and it is burned to the shift point E.sub.1 as shown in FIG. 13. Next, the fuel rods which have been burned to the shift point E.sub.1 are moved to the second area 47. When those fuel rods are burned to the shift point E.sub.2 in the second area 47, those fuel rods are moved to the third area. New fuel rods which were first charged to the first area 46 move successively from the first area 46, to the second area 47, . . . , to the Nth area 48 during their life time by carrying out the above mentioned moving at each fuel exchange, and at the time of the (N-1)th fuel exchange the fuel rods which have been burned to the point E.sub.N in the Nth area are taken out. Accordingly during the first half of the life time of the fuel rods the fuel rods stay in the areas where the ratio of the number of hydrogen atoms to that of uranium atoms is small and the increased production of plutonium in the fuel rods is attempted. Since during the second half of the life time of the fuel rods the fuel rods stay in the area where the ratio of the number of hydrogen atoms to that of uranium atoms is large, it is possible to effectively burn the fissile materials in the fuel rods. FIG. 14 shows the variation in the conversion ratio (the ratio of the atom number concentration of the initial uranium-235 to that of the fissile materials after burning for the fuel rod) of about 4% uranium enrichment with the ratio of the number of hydrogen atoms to that of uranium atoms as the parameter. When the ratio of the number of hydrogen atoms to that of uranium atoms in the first area 46 is about 1.1, about 95% of the fissile materials in the initial uranium-235 atoms number concentration remain after the burning 30 GWd/t. The partition members 49 shown in FIG. 12 are the boundary layers that divide areas 46, 47 and 48, and the partition members 49 are provided as separators so that between the areas there is no flow of the coolant (light water) through them. The material for those partition members 49 is selected from a low neutron absorption, for example, zircalloy, etc. FIG. 13 shows a variation in the neutron multiplication factor for the burnup during the life time of the fuel rods according to the present invention. Even if the average neutron multiplication factor does not meet the critical condition in the first area 46, it may be designed so as to make the average neutron multiplication factor for whole area meet the critical condition. After second area 47, if necessary, the gadolinium is added to each of the areas 47 and 48 to control the reactivity. FIG. 15A, FIG. 15B and FIG. 15C show the power densities for the areas 46, 47 and 48 in the reactor core according to the present invention and also the radial distribution of the flow rate of the coolant (light water). The power density is higher in the area nearer to the center because that area is charged with denser fuel rods. The flow rate of the coolant is adjusted by an orifice provided at the coolant inlet of the reactor core so that the temperature of fuel rods and the temperature of the fuel cladding tube in each area will not exceed the standard value in the design. Furthermore, at the reactor core where the coolant is boiled, it is also possible to adjust the ratio of the number of hydrogen atoms to that of uranium atoms by adjusting the coolant flow rate to change the void factor in each of the areas. According to the present invention during the time from charging the fuel rods to the reactor core to subjecting the fuel rods to discharging treatment, the fuel rods are taken out and the burnup of the fuel rods can be improved trememdously, allowing the effective utilization of the fuel materials.
	claims	1. A radiation source including iridium wherein the density of the active insert containing the iridium is in a range of 30 to 85 percent of the density of 100% dense pure iridium. 2. The radiation source of claim 1 wherein the iridium is in a range of 40 to 70 percent of the density of 100% dense pure iridium. 3. The radiation source of claim 1 wherein the iridium is in a range of 50 to 65 percent of the density of 100% dense pure iridium. 4. The radiation source of claim 1 wherein the iridium is in the form of microbeads containing Iridium-192. 5. The radiation source of claim 4 wherein the microbeads of Iridium-192 are in a random or partly random packed configuration. 6. The radiation source of claim 1 wherein the iridium is Iridium-192 contained within and metal, alloy, compound, or composite and formed into a sphere or quasi-sphere. 7. The radiation source of claim 6 wherein the Iridium-192 is contained within a metal, alloy, compound, or composite material and formed or shaped by a capsule cavity into a sphere or quasi-sphere by a method of physical compression or compaction. 8. The radiation source of claim 1 wherein the iridium is in the form of approximately 0.4 mm. diameter microbeads or approximately 0.3 mm diameter microcylinders containing Iridium-191, prior to neutron irradiation. 9. The radiation source of claim 8 wherein the microbeads or microcylinders of Iridium-191 are in a random-packed or partly random configuration. 10. The radiation source of claim 1 wherein the iridium is in the form of microbeads with a diameter of 0.25-0.60 mm. or microcylinders with a diameter of 0.20-0.50 mm, containing Iridium-191, prior to neutron irradiation. 11. The radiation source of claim 1 wherein the iridium is in the form of approximately 0.3 mm diameter wire containing Iridium-191, prior to neutron irradiation, which is then cut after activation to form microcylinders. 12. The radiation source of claim 1 wherein the iridium contains Iridium-191 in the form of a metal, alloy, compound or composite, prior to neutron irradiation. 13. The radiation source of claim 1 wherein the iridium contains Iridium-191 in the form of a metal, alloy, compound or composite, which is formed into a disk, hemi-ellipsoid or other thin flat shape less than 0.75 mm. thick, prior to neutron irradiation so that it can be activated in conventional activation target canisters and formed into a sphere or quasi-sphere after activation. 14. The radiation source of claim 1 further including a spherical or quasi-spherical source cavity in which the iridium is contained. 15. The radiation source of claim 1 wherein the radiation source is comprised of a plurality of disks of iridium in the form of a metal, alloy, compound or composite. 16. An activation target insert formed in a disk-shape and including a plurality of microbeads or microcylinders of iridium. 17. The activation target insert of claim 16 wherein the microbeads are spherical or quasi-spherical in shape or formed as microcylinders. 18. The activation target insert of claim 17 wherein the radiation target insert includes a plurality of at least partially concentric rings which hold the microbeads. 19. The activation target insert of claim 18 wherein the plurality of rings are concentric with respect to a rotational axis of the radiation target insert and are diagonally offset with respect to a direction perpendicular from the rotational axis. 20. The activation target insert of claim 19 further including cone-shaped walls. 21. The activation target insert of claim 20 wherein the cone-shaped walls of successive radiation target inserts nest with each other. 22. The activation target insert of claim 16 wherein the microbeads have a diameter of approximately 0.4 mm or the microcylinders have a diameter of approximately 0.3 mm. 23. The activation target insert of claim 16 wherein the iridium is in the form of microbeads with a diameter of 0.25-0.60 mm. or microcylinders with a diameter of 0.20-0.50 mm. 24. The activation target insert of claim 16 wherein the iridium includes Iridium-192. 25. The activation target insert of claim 16 wherein the iridium includes Iridium-191 and is activated by neutron irradiation.
042343844	claims	1. Support structure for the core of a gas cooled high temperature, high capacity reactor said core comprising a bed of spherical fuel elements and being surrounded by an annular side reflector, said support structure comprising: a plurality of layers of prismatic graphite blocks, arranged upon each other, said layers being constructed as a closed unit without expansion gaps with the blocks of one layer being interkeyed with the blocks of adjacent layers, and with the upper layers being composed of a plurality of preferably hexagonal graphite blocks; a plurality of spherical fuel element removal passageways through the support structure; a plurality of passages through said blocks for the cooling gas of the reactor; a plurality of support units disposed as the lower layer of the support structure and consisting of several support segments fitted together to preferably form a hexagonal cross section; a plurality of round columns supporting said support unit and having a column head and carrying a limited number of the hexagonal graphite blocks of said layers; and a plurality of cooling gas channels disposed in locations of the bottom layer, representing the juncture of three support units. 2. The support structure of claim 1 wherein the upper layers of the graphite blocks are designed with respect to their height so that a conical inlet is formed for the spherical fuel elements supported in the core and that the support units are designed conformingly in the area of the fuel element removal tubes with respect to their cross section. 3. Support structure of claim 2 wherein the support structure is constructed of three layers with the uppermost and the intermediate layer each comprising a central graphite block surrounded by six graphite blocks and aligned with one of the round columns and with each of the peripheral graphite blocks associated with three different central graphite blocks. 4. The support structure of claim 3, further comprising a plurality of cooling gas collector spaces disposed in the intermediate layer wherein each of the hexagonal graphite blocks of the uppermost layer possess a plurality of small vertical borings for transport of the cooling gas, said borings being connected with said collector spaces; wherein the collector spaces of the peripheral graphite blocks are designed in the form of continuous borings aligned with said cooling gas channels, located in the bottom layer; and wherein the collector spaces are connected in the central graphite blocks by way of connecting borings with the continuous borings in the peripheral graphite blocks associated with said central blocks. 5. The support structure of claim 1, further comprising a continuous vertical separating gap between the support structure and the side reflector.
	description	The United States Government has rights to this invention pursuant to Contract No. DE-AC02-06CH11357 between the United States Government and UChicago Argonne, LLC representing Argonne National Laboratory. 1. Field of the Invention The present invention relates to atomic layer deposition coatings onto porous materials to provide nuclear fuel pellets and claddings of superior mechanical and thermal properties, which will help increase such components' operational life and improve the efficiency and safety of current light water nuclear reactors. 2. Background of the Invention The inside of a nuclear reactor is an extremely harsh environment. Not only are materials subject to temperatures as high as 1800° C. at the center of the fuel pellet and to highly corrosive steam, but they are also subject to damage from neutron bombardment. Neutrons cause fission reactions in typical Light Water Reactors (LWRs). LWRs utilize the energy produced from fission reactions occurring in the fuel elements to heat water or steam in the reactor core. This water or steam travels through a heat exchanger to heat clean water into clean steam, and this clean steam turns downstream turbines to produce mechanical energy or motion. The mechanical energy turns a generator which results in the production of electricity. The water or steam in the reactor core is part of a closed loop that does not mix with, or contaminate, the clean water used to turn the turbines. A representation of a typical LWR arrangement is depicted in FIG. 1A. A nuclear reactor core 20 contains a series of co-planarly arranged fuel rods 24 between which are positioned control rods 22. The control rods 22 are made of highly neutron absorbent materials such as silver, indium, hafnium, boron, and cadmium. Depending on power requirements called for by the grid, the control rods 22 are either partially or fully inserted or removed from between the fuel rods to moderate the flux of neutrons, and therefore the amount of fission. This moderation is proportional to the amount of energy produced. As depicted in FIG. 1B, the fuel rods 24 house the fissile material, typically in the form of fuel pellets 26. In a typical LWR, the fuel pellets 26 contain the fissile material, usually in the form of a sintered oxide, such as uranium dioxide. Encapsulating the fuel pellets 26 is a cladding layer 28, which is typically made of zirconium or a zirconium alloy. As can be seen in FIG. 1C, the cladding material 28 surrounds the fuel pellet 26, but a gap 30 must be provided to allow for the expansion of the fuel pellet 26 and the cladding layer 28. Expansion occurs primarily because of the nuclear irradiation. Because the fuel pellet 26 and cladding 28 are constantly being bombarded by neutrons, individual atoms on the lattice structure of the fuel pellet 26 and cladding 28 are displaced. During the operational life of the fuel pellet 26 and cladding 28, each atom is displaced from its lattice site thousands of times on average. These displacements lead to the agglomeration of defects, which can create large voids in the lattice structure. The structural changes to the atomic lattice happen randomly in prior art sintered fuel pellets and in zirconium-based claddings, which means that the fuel pellets 26 and cladding 28 do not expand uniformly or quickly. Structural changes to the atomic lattice do not reach dynamic equilibrium before the fuel pellets 26 have materially degraded and need to be replaced. Further, the cladding 28 can no longer be trusted to contain the nuclear fuel. The mechanical degradation of the fuel pellet 26 and cladding 28 raises concerns of contamination. Maintaining the separation of reactor core coolant water and clean water for powering the turbines is critical to the operation of a nuclear power plant. Contamination of the clean water can happen through a variety of circumstances. Meltdown, in particular, can lead to a severe breach of containment. Meltdown occurs when a component or components of the reactor core melt, releasing radioactive materials, including the fuel and fission products. When the fuel pellets 26 and cladding 28 are mechanically vulnerable, the possibility of leaching nuclear material into the coolant water is greatly increased. Typical fuel pellets are made of sintered uranium dioxide (UO2). The uranium present in the pellets is mostly uranium-238, which has been enriched to contain approximately three percent uranium-235. The uranium-235 is the major fuel of the LWR, but the uranium-238 is fissionable and produces plutonium-239, which also fuels the LWR. In some reactors, the pellets are made of both uranium and plutonium oxides and are referred to as mixed oxide fuels. Claddings 28 are commonly made of a zirconium-based alloy. Zirconium has exceptional properties for use in nuclear reactors including low-neutron absorption, high hardness, ductility, and corrosion resistance. Zirconium alloys typically contain greater than 95% zirconium and other metals, such as tin, niobium, iron, chromium, and nickel. However, zirconium is prone to hydrogen embrittlement at high-temperatures, especially after a loss-of-coolant-accident (LOCA). The zirconium will react with the water or steam and form an oxide, which produces hydrogen gas. Not only does the presence of hydrogen gas increase the risk of an explosion, but it causes hydrogen embrittlement. The hydrogen embrittlement leads to blistering and cracking of the cladding 28 through which radioactive materials can escape. Further, despite zirconium's low neutron absorption, the cladding 28 experiences significant radiation expansion during its operational life. In a nuclear reactor, the fuel capacity of the uranium dioxide is generally not completely consumed. Over the 3-5 year operational life of a prior art uranium dioxide pellet, only approximately 5% of the available fuel has been fissioned. Replacement of the fuel pellets 26 and cladding 28 is necessitated by the mechanical degradation of those components. Therefore, not only is much of the fuel wasted, but it also must be carefully stored. Storage can be accomplished on-site, but often times the radioactive waste materials must be moved to other locations to accommodate the large amount of storage necessary. Another problem facing prior art fuel pellets 26 and claddings 28 is the heat conduction from the center of the pellet 26 to the exterior of the cladding 28. Thermal transport of heat from the fuel elements is critical for optimized reactor operations. The performance of nuclear fuels strongly depends on the operating temperature. Optimized thermal transport also extends the operation limit of nuclear fuels. Fuel porosity and fuel stoichiometry are critical factors in thermal transport. The heat conduction of uranium dioxide is poor relative to that of the cladding material. This can cause high heat build-up within a fuel rod, leading to failure. Over time, temperatures at the center of the fuel pellet 26 become much higher than at the exterior of the cladding 28. At an operational temperature of 1800° C., the heat conduction of uranium dioxide is approximately 2 W/mK (where mK is meters-Kelvin), while the heat conduction of zirconium is 35 W/mK. The poor heat conduction is exacerbated by the expansion gap 30 between the pellet 26 and the cladding 28. A need exists in the art to increase the efficiency and operational life of nuclear fuel pellets. Such a pellet would allow for a more complete fission of the fuel material. More fissions would increase the operational life of the fuel pellet, which would cut down on the amount of pellets that would have to be used. This, in turn, would reduce the waste produced and lessen the need for storage facilities and transportation to storage facilities. Another need exists in the art for a cladding that is able to withstand extreme temperatures, oxidation, and hydrogen embrittlement. The cladding should resist bubbling and cracking and prevent the escape of radioactive materials. Further, such a cladding should have a long operational life. Still another need exists in the art for a fuel pellet and cladding that is designed to aid in the prevention of meltdown. Such a pellet would allow for the efficient conduction of heat out of the nuclear reactor core, preventing the build-up of heat and an increase in temperature. This improved conductivity would also allow for a more efficient transfer of energy to the water in the heat exchanger, which would mean that more useful energy is produced by each fission. An object of the present invention is to provide a nuclear fuel substrate that overcomes many of the drawbacks of the prior art. Another object of the present invention is to improve the heat conduction through a nuclear fuel rod. A feature of the present invention is nuclear fuel deposited onto porous support material. An advantage of the invention is that such a deposition minimizes expansion that otherwise occurs with nuclear fuel upon heating. This minimization in expansion allows for minimization of any gap between fuel and cladding during fuel assembly, and even physical contact of the fuel with the cladding during fuel assembly. Another object of the present invention is to increase the efficiency of nuclear reactors. A feature of the present invention is the use of porous support materials for nuclear fuel. An advantage of the invention is that the pores provide a means for efficient gas venting from the fuel and perhaps out of the cladding. This controlled release of gas which develops during nuclear fuel use, prevents expansions of the fuel and/or the cladding due to increased gas pressure. Still another object of the present invention is to provide an alternative to sintered uranium dioxide fuel pellets. A feature of the present invention is that atomic layer deposition of fuel allows for other uranium compounds to be utilized. An advantage is that these other uranium compounds provide better heat conduction, thereby increasing the safety and efficiency of the reactor core. Yet another object of the present invention is to increase the usable life of nuclear fuel pellets. A feature of the present invention is that nuclear fuel pellet begins their operational lives near a dynamically stable equilibrium as a result of the designed porosity. An advantage of the present invention is that typical deterioration of material properties of the pellets and cladding is minimized, thereby leading to extended life cycles of the fuel. Yet another object of the present invention is to reduce the waste of nuclear fuel materials. A feature of the present invention is a more complete use of fissile materials. An advantage of the present invention is that less fuel materials are needed and less spent nuclear fuel materials have to be stored. Yet another object of the present invention is to provide a more efficient fuel pellet with a longer operational life that can be used in currently operating nuclear reactors. A feature of the present invention is that the fuel pellets are the same size and offer the same amount of heat as currently available sintered fuel pellets. An advantage of the present invention is that currently operating reactors do not need to be retrofitted in order to accommodate the presently invented fuel pellets. Yet another object of the present invention is to provide a silicon carbide (SiC) cladding material for use with nuclear fuel scenarios. A feature of the present invention is the resistance to extreme environments, including temperature resistance, corrosion resistance, oxidation resistance, and a resistance to hydrogen embrittlement. An advantage of the present invention is that SiC cladding can withstand rapid water cooling, which takes place when the reactor core overheats. Yet another object of the present invention is to provide an SiC cladding for nuclear fuel configurations. A feature of the invention is atomic layer deposition (ALD) of a uniform and nearly defect-free coating of SiC on aerogel substrates. An advantage of the present invention is that the defect free coatings confer improved corrosion and wear resistance to the claddings. The present invention relates to a nuclear fuel pellet, comprising a porous substrate, at least one layer of a fuel containing material deposited upon said porous substrate via atomic layer deposition, wherein the layer deposition is controlled to prevent agglomeration of defects. The present invention is also directed to a method of fabricating a nuclear fuel pellet, said method comprising the steps of selecting a porous substrate, depositing at least one layer of a fuel containing material onto the substrate and terminating deposition when a predetermined porosity is achieved. The present invention provides a nuclear reactor fuel cladding, said cladding comprising a porous substrate and at least one layer of silicon carbide deposited on the substrate. The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. As used herein, an element step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. Furthermore, the references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property. The invented method imparts size selected porosity to substrates which are subsequently overlayed by adherent film comprising nuclear fuel. This engineered porosity of the resulting pellet enables the fuel to begin its operational life at near equilibrium state. The degradation of fuel cladding from nuclear bombardment can be reduced, thereby increasing the operational life of the pellet and allowing for more fission reactions. Porosity can vary from about 3 to about 30 percent, and preferably from 15 to 30 percent of volume of the fuel. A model of suitable porous material includes pores approximately 0.02 mm and approximately 0.2 mm apart in both azimuthal and axial directions. The resulting distance between pores in the radial direction is also approximately between 0.02 mm and approximately 0.2 mm. The distance between the uppermost plane of pores and the top surface of the fuel element is approximately about 0.01 mm to 0.1 mm as is the distance between the lowermost plane of pores and the bottom surface of the fuel element. These values enable a uniform distribution of pores in the volume, for example when dealing with pores between 10 and 200 microns in diameter. However, spatial distribution of pores may be non-uniform (i.e., heterogeneous) to enhance the heat transport in the material. Various pore configurations are also suitable, including but not limited to spherical-, ellipsoid- and cylindrical- (i.e. disc-shaped pores) shapes. In an embodiment of the invention, at fixed total porosity, certain heterogenous spatial distributions of pores lead to improved thermal transport (i.e., lower centerline temperature of the fuel pellet) compared with homogeneous distributions. Situating larger pores at higher temperature regions (inner area regions) and smaller pores at lower temperature regions (outer edge areas) improves heat transport in the fuel pellet. ALD is a sequential, self-limiting synthesis technique that allows conformal coating of large areas and complex shapes. ALD is sequential because alternating precursors are introduced to the substrate, forming a layer over the substrate one atom thick. The second precursor is introduced, which reacts with the first precursor, again forming another layer that is a single atom thick. ALD is self-limiting because the precursors wet the entire substrate surface. When the second precursor is introduced, the reaction with the first precursor proceeds until there is no available reaction area. The remainder of the precursor is pumped away. As can be seen in FIG. 2A, the fuel pellet 26 is formed from a porous substrate 32. An exemplary substrate is an aerogel. Aerogels have enough structural integrity to hold their shape, while also having an extremely low density. As applied by the inventors, ALD allows for creating open (i.e., pores extending completely through the substrate) or closed pores. Closed pores provide a means for retaining the gas and avoid gas release into the plenum (i.e., the head space between the pellets and the top of the rod. Open pores allow the gas to collect in the plenum for extraction via a vent in the rod. Suitable materials from which the aerogel can be constructed are carbon, beryllium oxide, aluminum, or tungsten. These materials are capable of high thermal conduction and can readily be made into aerogels. Aerogels have been created with a density of which would allow room for a large volume of fissile material to be deposited. In an embodiment of the invention, the fuel is deposited throughout the support substrate and not just on its surface. The higher the volumetric density of the fuel, the better. Aerogels can be created via sol-gel processes. First, a colloidal suspension of solid particles is created. This requires mixing precursor solutes with a solvent. The precursor and solvent will undergo a reaction, which produces the suspended particles. These particles begin to interlink, at which point a catalyst may be used to increase reaction rate. Interlinking stops when a gel has been formed. Residual reagents are removed in a way to prevent gel damage. Specifically, supercritical drying is used, whereby the liquid is heated and pressurized until a supercritical fluid state is reached. The pressure is then dropped, causing the fluid to gasify, and the gas is removed. In the case of the fuel pellets 26, the aerogel would be created near net shape. The porous substrate 32 is serially contacted with a plurality of precursors. By alternating precursors, the thickness of the deposition can be controlled as can be seen in FIG. 2A. Because of the low density of the porous substrate 32 compared to the fuel it supports, the overall size of the pores 34 in the fuel pellet 26 can be controlled by limiting the number of deposited layers 36. The surface reaction is depicted in FIG. 3A and FIG. 3B. Specific moieties covalently or noncovalently linked to surfaces of the gel terminate in hydroxyl groups. These hydroxyl groups react with a first fuel precursor, such as uranium hexafluoride (UF6). This results in the generation of an ether group comprising four fluorines and two oxygens bound to a central uranium atom. Upon creation of the tetrafluorouranium moiety, the reaction chamber is flushed, replaced or otherwise neutralized. A suitable replacement means is a relatively inert gas, such as nitrogen, helium or argon. After reaction atmosphere neutralization, water is then introduced into the atmosphere in an amount and for a time sufficient to react with the remaining four fluorine atoms. This water reaction generates four leaving groups (hydrofluoric acid) which are substituted by hydroxyl moieties. The reaction environment is then replaced with an inert gas again. The first precursor is reintroduced in an amount and for a time sufficient to react with the hydroxyls. The above reaction sequence results in the production of a layer of uranium dioxide upon the porous substrate 32. However, it should be noted that other precursors will generate different layers, which can be used in place of the uranium dioxide, or in combination with the uranium dioxide. The invention is particularly suitable for use with metallic fuels such as uranium-zirconium, uranium-molydenum and uranium nitride. As noted supra, state of the art sintered uranium dioxide fuel pellets have a density of approximately 93% prior to service. After 40 GWd/t (gigawatt-days/metric ton [a measure of nuclear fuel burnup]), the density is decreased another 5% to 88%. Then the pellet is replaced. By contrast, the invented fuel pellet 26 enters service at approximately 90% density. However, the porosity would be structured such that atom displacements would not create randomly distributed voids and bubbles in the lattice. Consequently, the fuel pellet 26 does not experience a substantial decrease in density. The pellets 26 enter service at near net shape, which means that the pellets 26 do not experience significant radiation expansion. The invented method and resulting product allow for substantial physical contact between exterior peripheries of the pellets and cladding encircling those pellets. (As noted supra, state of the art sintered pellets require a gap 30 to allow for expansion.) The gap 30 is substantially diminished or removed entirely, which will allow for better heat conduction from the pellet 26 to the cladding 28. The invented porous substrate improves heat conduction. A feature of the invention is that materials chosen for the porous substrate 32 have thermal conductivities much higher than that of uranium dioxide, which would provide additional heat dissipation from the center of the fuel pellet 26. An aerogel with high thermal conductivity, such as beryllium oxide (330 W/mK), tungsten (173 W/mK), carbon (up to 165 W/mK), or aluminum nitride (285 W/mK), would provide a network of heat dissipation to limit heat build-up at the center of the fuel pellet 26. The invented method and composite provides cladding more resistant to the harsh conditions of nuclear reactors. This results in higher efficiencies and enhanced safety. Moreover, the operational life of cladding is extended, thereby minimizing reactor shutdown time and exposure to radioactive materials. The invention also provides cladding 28 formed from a porous substrate 38, as depicted in FIG. 4A. In an embodiment of the invention, the porous substrate is an aerogel comprising a material that can withstand the temperatures produced in fission reactions. Also, combinations of such constituents are suitable such that a support comprises a heterogeneous mixture of components. A preferred component is SiC aerogel. Another preferable substrate is SiC cloth, available from Nippon Carbon Co., Ltd. in Japan and Ube Industries, Ltd. in Japan. SiC cloth has high strength and temperature resistance. The present invention seeks to use ALD to fill the porosity of SiC aerogels or SiC cloth. The porous substrate 38 is then exposed to alternating precursors A′ and B′. The process would proceed much like the process of creating the fuel pellets with the exception that no pores would be left in the cladding. Layers 40 would be deposited via ALD until a uniform and largely defect-free coating has been applied. A first precursor of silane (SiH4) would be followed by a second precursor of acetylene (C2H2). The silane would be introduced in a reaction chamber set at 900° C. for at least 10 seconds. The chamber would then be flushed with an inert gas, such as nitrogen. The second precursor, acetylene, would be introduced and reside in the chamber for approximately 10 seconds. The chamber would be flushed with inert gas again. Water vapor would be introduced for an appropriate residence time. Finally, the chamber would be flushed with inert gas a final time before the first precursor is reintroduced, starting the process of building the next layer of SiC. An additional benefit of an SiC cladding is an increased thermal conductivity compared to that of zirconium-based claddings. The thermal conductivity of zirconium decreases with increasing temperature, but at operational temperatures of 500-600° C., the conductivity of SiC is approximately 140 W/mK. As mentioned supra, zirconium-based alloys have a heat conductivity of approximately 35 W/mK at operational temperatures. Accordingly, an SiC cladding would provide better heat dissipation, thereby preventing temperature buildup in the fuel pellets and increasing operating efficiency of the reactor. The fuel pellets 26 and cladding 28 of the present invention also have the advantage that they can be used with currently operating LWRs. The fuel pellets 26 of the present invention can simply replace the currently used sintered fuel pellets. There would not have to be any retrofitting of equipment to accommodate the switchover to the presently invented fuel pellets 26. The SiC cladding 28 could also simply replace the cladding currently used in LWRs. It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting, but are instead exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112(f) unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. The present methods can involve any or all of the steps or conditions discussed above in various combinations, as desired. Accordingly, it will be readily apparent to the skilled artisan that in some of the disclosed methods certain steps can be deleted or additional steps performed without affecting the viability of the methods. As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” “more than” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. In the same manner, all ratios disclosed herein also include all subratios falling within the broader ratio. One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the present invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Accordingly, for all purposes, the present invention encompasses not only the main group, but also the main group absent one or more of the group members. The present invention also envisages the explicit exclusion of one or more of any of the group members in the claimed invention.
	description	The present disclosure relates to a boiling water reactor blade guide and exchange tool. This section provides background information related to the present disclosure which is not necessarily prior art. The control rods in a boiling water reactor contain an absorbent material that when positioned in the reactor core can be used to slow the fission rate of the nuclear fuel. However, the absorbent material is subject to degradation after extended use. Therefore, it is periodically necessary to replace the control rods. In order to remove a control rod from its core location, or cell, it is necessary to provide access to the control rod by removing the fuel and the fuel support associated with the control rod to be removed. It is also necessary to disconnect the control rod from its drive. Tools commonly used to remove the fuel include the fuel grapple and a blade guide which supports the control rod while two of the four fuel bundles are being removed. A control rod unlatching tool is used to disconnect the control rod from its drive. Tools used to remove and/or replace the control rods include a grapple for lifting the fuel support and a grapple for lifting the control rod. These can be separate tools or their functions combined into one tool. The fuel support and control rod are lifted out of their cell and a new control rod and the same fuel support are placed back in the cell. The new control rod is reconnected to the drive without need of tools. A blade guide is placed in the cell and the control rod is then inserted to allow for fuel installation. Two fuel bundles are then placed in the cells next to the blade guide. The blade guide is then removed and two additional fuel bundles are installed in the locations of the vacated blade guide, to complete the control rod and fuel replacement for that cell. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. The present disclosure provides a blade guide and exchange tool which is comprised of two separate tools: the blade guide tool and the blade exchange tool which, when combined, form the blade guide and exchange tool. The blade guide tool seats on the fuel support and extends up through the top guide. The blade guide tool is used to support a control rod while moving fuel in and out of the cell. In addition to the guiding features, the blade guide tool contains the fuel support grapple that is actuated via a rod that extends from the grapple to the top of the blade guide tool. The rod is actuated by the blade exchange tool after it is mated to the blade guide tool. The blade guide tool also contains a spring-loaded extension rod, extending the full length of the tool, that is in line with the core support alignment pin commonly called the 315 pin. When the blade guide seats on the fuel support, this extension rod contacts the 315 pin causing the rod to lift. The lifted rod engages a mechanism on the blade exchange tool which opens two air switches. The open air switches allow airflow to the fuel support grapple cylinders therefore allowing for operation of the fuel support grapple. When the fuel support is lifted off the core plate, the spring-loaded extension rod loses contact with the 315 pin which causes it to move down. When the rod is down, it disengages from the mechanism on the blade exchange tool which causes the valves to close and disables actuation of the fuel support grapple. Initially, two of the four fuel bundles in the cell of the control rod to be replaced are removed using the fuel grapple. The blade guide is then installed in the removed fuel locations to support the inserted control rod as the remaining two fuel bundles are removed from the cell. The control rod can now be fully retracted to its back-seated position, as there is no fuel remaining in the cell. The blade exchange tool is connected to an air supply hose and to a hoist via a 12-foot cable attached to the control rod grapple. The blade exchange tool is then lowered onto the blade guide tool and connected to it. The blade exchange tool contains a handle latch, fuel support grapple actuators, a control rod grapple, and air switches to control airflow to the fuel support grapple actuators. When the blade guide and blade exchange tools are connected and grappled together, the tool is referred to as the blade guide and exchange tool. When the connection of the two tools is made, the control rod grapple engages the center tubes of the blade guide tool, which act as a guide for the grapple to keep it centered in the cell as it is lowered approximately 10 feet to engage the control rod handle. With the blade guide seated on the fuel support and on the 315 pin, the control rod grapple is lowered onto the control rod handle. Air is then supplied to the tool to grapple the control rod and fuel support. The hoist is raised to lift the control rod into the tool until the control rod grapple contacts the underside of the blade guide handle. At this point, raising the hoist further will also lift the blade guide, the exchange tool, and the fuel support. The tool and components are lifted out of the cell, via the hoist, and transported to the exchange area. The control rod is then lowered and seated in the exchange container. Air is supplied to the disengage (or open) side of the exchange tool to disengage the control rod grapple. The control rod grapple air supply (engage and disengage) bypass the air switches and therefore will always operate regardless of being on or off the 315 pin. The disengage action will not actuate the fuel support grapple since the blade guide tool is not engaged on the 315 pin. When off the 315 pin, the air switch is closed preventing airflow to the fuel support grapple. At this point, the control rod is seated in the container, the control rod grapple is disengaged from the control rod handle, and the fuel support is still grappled by the tool. The fuel support can now be lifted off the spent control rod, by raising the hoist, and placed onto a new control rod located in another storage container. The new control rod is grappled by the hook, lifted into the tool, and then out of the storage container. The control rod and fuel support are transported back to the core and reinstalled in the cell. After the fuel support and control rod are seated in the guide tube and the fuel support has engaged the 315 pin, both the fuel support and control rod can be released. The blade exchange tool can be lifted off the blade guide tool. The blade guide tool remains to allow for blade insertion and loading of two fuel bundles into the cell. After this step, the blade guide is removed via the fuel grapple, and two additional fuel bundles can be loaded in its place. According to an aspect of the present disclosure, a combined blade guide and exchange tool includes a blade guide tool having a lower end and an upper end and a plurality of frame rails supporting a pair of collet housings at a lower end of the blade guide tool. A pair of fuel support grapple actuating rods are supported between the plurality of frame rails and have a first end engaging a pair of collets within the pair of collet housings and a second end disposed at the upper end of the blade guide tool. A blade exchange tool is releasably mounted to the upper end of the blade guide tool and includes a pair of upper collets for engaging the pair of fuel support grapple actuating rods. The blade exchange tool further includes a trolley and hook assembly attached to a cable guided by the blade exchange tool and adapted for engaging and lifting a control rod. Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer, or section from another region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the example embodiments. Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. With reference to FIGS. 1-4, a blade guide and exchange tool 10 is shown including a blade guide tool 12 and a blade exchange tool 14 removably assembled to the blade guide tool 12. In FIGS. 1, 2, 3A and 4B, a base 12a of the blade guide 12 is shown engaged with a fuel support 16 which is disposed next to a core support 18. As best shown in FIGS. 3A, 3B, a control rod 20 includes a plurality of blades 22A-22D formed in a cruciform shape and extending through a cruciform passage 24 in the fuel support 16. As is known in the art, the control rod 20 contains an absorbent material that when positioned in the reactor core can be used to slow the fission rate of the nuclear fuel. The fuel support 16 includes four pockets 26 each for receiving the base of a fuel bundle (not shown). The base 12a of the blade guide tool 12 includes a pair of collet housings 30 which each house a collet assembly 32, best shown in FIGS. 17-19. The pair of collet housings 30 are connected to a pair of outer frame rails 34a, 34b and a pair of inner frame rails 36a, 36b. A top plate 38 is attached to the tops of the outer frame rails 34a, 34b and the inner frame rails 36a, 36b. A plurality of brace plates 40 are disposed between corresponding ones of the outer frame rails 34a, 34b and the inner frame rails 36a, 36b. The brace plates 40 each include a guide hole 42 extending there through. A pair of fuel support grapple actuating rods 44 extend through each of the guide holes 42 of the brace plates 40 and have a bottom end that engages a collet assembly 32 within the pair of collet housings 30 and have a top end that is disposed in a corresponding guide housing 46 extending below the top plate 38. A spring 47 is disposed in the guide housing 46 for biasing the fuel support grapple actuating rods 44 in an upward direction. A core support pin actuating rod 48 is disposed within, and extends along a length of one of the outer frame rails 34a. The core support pin actuating rod 48 has a lower end that is guided within a guide housing 50 and engaged by a core support pin 52 (best shown in FIGS. 17-19) when the blade guide tool 12 is properly seated in the fuel support 16. The core support pin 52 extends upward from the core support 18 and when engaged by the core support pin actuating rod 48, causes the core support pin actuating rod 48 to move upward in order to cause activation of an air switch actuator assembly 54 of the blade exchange tool 14, as will be described in further detail herein. As best shown in FIG. 8, the blade exchange tool 14 includes a base plate 56 to which the air switch actuator assembly 54 is mounted along with a pair of upper collet housings 58. A pair of air cylinders 60 are mounted on each of the collet housings 58. The baseplate 56 includes an opening 62 (best shown in FIG. 8) therein for receiving a U-shaped handle 64 extending from the top plate 38 of the blade guide tool 12. The upper collet housings 58 are each mounted in additional holes in the baseplate 56 and extend below the baseplate 56 and are adapted to be received in corresponding holes 66 (as shown in FIGS. 11-13) in the top plate 38 of the blade guide tool 12. As shown in FIGS. 8 and 9, a mounting structure 68 is mounted to the baseplate 56 adjacent to the opening 62 and includes a handle engagement bracket 70 mounted thereto. The handle engagement bracket 70 includes a slot 72 for receiving the handle 64 of the blade guide tool 12 and also defines a cable guide 74 for receiving and guiding a cable 76 there through. The cable 76 is attached to a slider 80 which supports an engagement hook 82 and pneumatic hook actuator assembly 84. The slider 80 is engageable with the inner rails 36a, 36b to traverse along the length of the inner rails 36a, 36b. The slider 80 can be lowered by the cable 76 along the inner rails 36a, 36b and can bring the hook 82 into engagement with an upper handle 20A of the control rod 20. The hook 82 can be pneumatically engaged by the cylinder of the hook actuator assembly 84 and the cable 76 can be utilized to raise the control rod 20. As best shown in FIG. 9, a pair of downwardly protruding guide plates 88 extend below the baseplate 56 of the blade exchange tool 14 to guide the slider 80 into its transition between the inner rails 36a, 36b. As best shown in the partially cutaway view of FIG. 10, each of the upper collet housings 58 include an upper collet 90 disposed within the housing and engaged with the air cylinder 60 for activation. The upper collets 90 are engageable with the upper end of the fuel support grapple actuator rods 44 to latch onto the actuating rods 44 and to press the actuating rods 44 downward into the lower collet housings 30 as shown sequentially in FIGS. 17-19, for engaging the lower collets 32 to spread laterally outward to engage an inwardly extending lip 92 surrounding the fuel bundle pockets 26 of the fuel support 16 by a hook portion 94 on the ends of each collet section 32. Accordingly, the lower collets 32 are engageable with the fuel support 16 in order to lift the fuel support 16 out of the core along with the control rod 20. As mentioned above, the core support 18 includes a core support pin 52 which causes the core support pin actuating rod 48 to move upward in order to cause activation of an air switch actuator assembly 54 of the blade exchange tool 14. The air switch actuator assembly 54 includes a housing 100 which supports a core support pin flag 102. The core support pin flag 102 is engaged with an upper end of the core support pin actuating rod 48 which presses the core support pin flag 102 upward when the core support pin actuating rod 48 is pushed upward by engagement with the core support pin 52 when the blade guide tool is properly engaged with the fuel support 16. As shown in FIG. 16, an air switch 104 is mounted to the air switch actuator assembly 54 and includes a cam follower 106 and switch arm 107 engaged with a cam surface 108 on the core support pin flag 102. As the core support pin flag 102 is pushed upward, the switch arm 107 of the air switch 104 is actuated to allow delivery of pneumatic air pressure to a latch that latches the blade exchange tool 14 to the blade guide tool 12 and, when not actuated, to prevent delivery of pneumatic air pressure to a release side of the collet air cylinders 60. As best shown in FIG. 10, a blade guide hook 110 is mounted on the mounting structure 68 for securing the handle engagement bracket 70 to the handle 64 of the blade guide tool 12 to prevent separation there from. The blade guide hook 110 can be actuated manually or by a pneumatic actuator. When the cable 76 is lowered to allow the slider 80 and hook 82 to be positioned relative to the handle 20a of the core 20, the cylinder of the hook actuator assembly 84 can be activated to engage the hook 82 to the handle 20a. During operation, the blade guide and exchange tool 10 is comprised of two separate tools, the blade guide tool 12 and the blade exchange tool 14 which when combined, form the blade guide and exchange tool 10. With two of the fuel bundles removed, the blade guide tool 12 seats on the fuel support 16 and extends up through a top guide of a cell. The blade guide tool 12 is used to support a control rod 20 while moving fuel in and out of the cell. In addition to the guiding features, the blade guide tool 12 contains the fuel support grapple lower collets 32 that are actuated via the actuating rods 44 that extends from the collets 32 to the top of the blade guide tool 12. The actuating rods 44 are actuated by the blade exchange tool 14 after it is mated to the blade guide tool 12. The blade guide tool 12 also contains a spring-loaded pin actuating rod 48 that is in line with the core support alignment pin 52 and extends the full length of the blade guide tool 12. The pin actuating rod 48 is used to operate the air switch 104 of the blade exchange tool 14 to control airflow to the fuel support grapple collets 32 when the pin actuating rod 48 is either engaged, or not engaged, on the alignment pin 52. The blade guide tool 12 is installed first into the cell of the control rod 20 to be removed. The blade guide tool 12 supports the inserted control rod 20 as the remaining two fuel bundles are removed from the cell and supports the control rod 20 as it is fully retracted to its back-seated position. The blade exchange tool 14 is connected to an air supply hose and to a hoist via a 12-foot cable attached to the control rod grapple 20a. The blade exchange tool 14 is then lowered onto the blade guide tool 12. The blade exchange tool 14 contains a connecting hook 110 to join the blade guide tool 12 and the blade exchange tools 14 together, and a pair of air actuators 60 for the fuel support grapple collets 32. When the blade guide tool 12 and the blade exchange tool 14 are connected and grappled together, the tool 10 is referred to as the blade guide and exchange tool 10. After connection of the two tools 12, 14, the upper collets 58 lock onto the fuel support grapple actuating rods 44 of the blade guide tool 12 to guide the blade exchange tool 14 as it is lowered onto the control rod handle 20a. Air is supplied to the tool 14 to grapple the control rod 20 via hook 82 and fuel support 16 via the lower collets 32. The control rod 20 is then lifted into the tool 10 until the control rod slider 80 contacts the top and of the blade guide and exchange tool 10 at which point the blade guide and exchange tool 10, along with the control rod 20 and fuel support 16 are also lifted. The tool 10, control rod 20, and fuel support 16 are removed from the cell and transported to the exchange area. The control rod 20 is lowered and seated in an exchange container. The fuel support grapple collets 32 will not release since the tool 10 is not engaged with the core support alignment pin 52 and therefore the air switch 104 is closed preventing airflow to the retract side of the fuel support grapple collets 32. The fuel support 16 can now be lifted off the spent control rod 20 and placed onto a new control rod 20 located in another storage container. The new control rod 20 is grappled by the hook 82, lifted into the tool 10, and then reinstalled in the cell. After the fuel support 16 and control rod 20 are seated in the guide tube, both are released and the blade exchange tool 14 can be lifted off the blade guide tool 12. The blade guide tool 12 remains to allow for blade insertion and loading of two fuel bundles. The core support pin actuating rod 48 is engaged with the core support pin 52 to allow the air release to the air cylinders 60 of the upper collets 90 via the air switch actuator assembly 54. Accordingly, the blade guide tool 12 is then removed via release of the collets 32 and so additional fuel bundles can be loaded. With the present disclosure, the blade guide function and the control rod exchange function are combined into one tool therefore two in-core alteration steps, the need to remove and reinstall a blade guide. The present disclosure also provides verification checks (315 pin engagement and fuel support grappling) that are located at the top of the tool (as opposed to other tools which have verifications at the bottom of the tool) and can easily be viewed and verified by an underwater camera. The ease of verification checks saves considerable time in the overall exchange process. The grid guide is a separate tool used with other control rod exchange tools but is not needed with the blade guide and exchange tool of the present disclosure, as the blade guide portion of the tool serves the grid guide function. This eliminates setup and installation of this tool and therefore saves time and radiation exposure to the worker. The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
	abstract	A method for manufacturing a porous fuel comprising uranium, optionally plutonium and at least one minor actinide is provided. The method may comprise the following successive steps: a) a step for compacting as pellets a mixture of powders comprising uranium oxide, optionally plutonium oxide and at least one oxide of a minor actinide, at least one portion of the uranium oxide being in the form of triuranium octaoxide U3O8, the other portion being in the form of uranium dioxide UO2; b) a step for reducing at least one portion of the triuranium octaoxide U3O8 into uranium dioxide UO2.
	abstract	A system and method for identifying an optimal landing energy of a probe current in a scanning electron microscope system. A probe current having a known landing energy is directed at a sample for producing a signal electron beam. The current of the signal electron beam is measured by directing the beam to a current detector for calculating a current yield, which is the ratio of the signal current to the probe current. The landing energy can then be changed for subsequent measurements of the signal current to identify the landing energy which produces a desired current yield. Once identified, the landing energy value can be used to produce a signal electron beam directed towards an imaging detector to generate topographic images of samples.
052672743	abstract	A method of analysis of rock samples taken from the bore of a well being drilled or from the Earth's surface and performed upon the apatite grains contained within the samples. The apatite grains are separated from the surrounding rock, polished to expose internal surfaces, and etched with acid to reveal the presence and characteristics of fission tracks within the apatite to determine the geological characteristics of the apatite. The grains containing the apatite are viewed under an optical microscope or other imaging apparatus and apatite crystals or crystal fragments which contain etched fission tracks are selected for analysis. If selected for analysis, measurements may be taken to determine the size and shape of the etched pits intersecting the apatite grain surface. The measurements are taken using a digitizing apparatus interconnected to a computer and containing a point light source superimposed upon the apatite grains viewed through the microscope. The measurements are used to determine the chemical composition of the apatite and in conjunction with data gathered by already existing methods, the fission track age and distribution of perceived track lengths for the fluorine-rich apatite grains are calculated. Determining chemical composition of apatite by this method eliminates procedures which are labor intensive, lengthy, costly, and potentially hazardous. The data derived from the analysis of the etched fission tracks are used as input criteria for existing kinetic modelling programs currently in use to constrain the temperature history of the apatite grains.
053435087	summary	FIELD OF THE INVENTION This invention relates to a nuclear reactor fuel assembly and, more particularly, to a nuclear reactor fuel assembly skeleton structure and, still more particularly, to a device which retains a nuclear fuel rod spacer grid on a fuel assembly. BACKGROUND OF THE INVENTION Commercial nuclear reactors used for generating electric power include a core composed of a multitude of fuel assemblies which generate heat used for electric power generation purposes. Each fuel assembly includes an array of fuel rods and control rod guide tubes held in spaced relationship with each other by grids of "egg-crate" configuration spaced along the fuel assembly length. The grids are generally of a first and second plurality of half-slotted Inconel or Zircaloy straps in egg-crate configuration and are spaced along the fuel assembly to provide support for the fuel rods, maintain fuel rod spacing, promote mixing of coolant, provide lateral support and positioning for control assembly guide tubes and provide lateral support and positioning for an instrumentation tube. The grids along with the control assembly guide tubes and the top and the bottom nozzles form what is known as the skeleton of the fuel assembly. Typically, the guide tubes are screwed into the top and bottom nozzles, the multiple Zircaloy spacer grids are welded to the guide tubes, and the Inconel grid is mechanically attached to the bottom nozzle or guide tube. There is the problem, however, that the skeleton twists from the torquing of the screws as the guide tubes are fastened to the bottom nozzle reducing the straightness of the skeleton. Previously, attaching the Inconel spacer grid to the guide tubes has required complicated machined or welded components which are costly. Thus, it is a problem in the prior art to reliably and economically increase the integrity of the skeleton assembly. SUMMARY OF THE INVENTION It is an object of the present invention to economically provide a device for reliably retaining a spacer grid on a fuel assembly. It is a further object of the present invention to increase the integrity of a nuclear reactor fuel assembly skeleton structure. It is a further object of the present invention to provide a device which reduces the twisting of the fuel assembly skeleton resulting from torquing of the screws which connect the bottom nozzle to the guide tubes. It is a further object of the present invention to provide a simple, low cost device to replace more complicated machined and/or welded components to retain a spacer grid on a fuel assembly. Additional objects, advantages and novel features of the invention will be set forth in the description which follows, and will become apparent to those skilled in the art upon reading this description or practicing the invention. The objects and advantages of the invention may be realized and attained by the invention of appended claims. To achieve the foregoing and other objects, in accordance with the present invention, as embodied and broadly described herein in a nuclear reactor fuel assembly having top and bottom nozzles and nuclear fuel rod spacer grids therebetween for supporting at least one nuclear fuel rod and at least one guide tube fastened to the top and bottom nozzles, a device is for retaining a nuclear fuel rod spacer grid on the guide tube and on the top and bottom nozzles. The tubular retainer means has a first end and a second end and a lumen extending longitudinally therethrough. The retainer means has an upper portion located at the first end for retaining the spacer grid and a lower portion located at the second end for retaining at least one of the guide tubes. The lower portion has an aperture communicating with the lumen whereby the guide tube is inserted through the lumen of the retainer means and a shoulder portion on the guide tube extends through the aperture to retain the lower portion of the retainer means between the shoulder of the guide tube and a surface of the bottom nozzle when the guide tube is attached to the nozzle thereby retaining the spacer grid on the guide tube and bottom nozzle.
	summary
	summary
050531891	abstract	A new system is provided for control rod guidance support with wear mitigating features in a nuclear reactor pressure vessel.. The upper guide tube and the lower guide tube structures house the control rod when it is withdrawn from the fuel core.. The upper guide tube has a top enclosure plate with a drive rod opening therethrough sized to provide a predetermined clearance space between the drive rod and the top enclosure plate and to direct coolant flow between the upper and outlet plenums and through the guide tube assembly to allow transmittal of upper plenum bypass cooling flow to the outlet plenum.. Structure is provided for restricting coolant flow through the top plate clearance space to reduce control rod wear. A coupler secures the drive and control rods in end-to-end relation within the guide tube assembly. The coupler is located just below the top guide tube enclosure plate with the control rod fully withdrawn. The coolant restricting structure includes a flow restricting sleeve secured to the coupler and extending upwardly over the drive rod through the top guide tube enclosure plate. A flow restrictor is located above and secured to the top guide tube enclosure plate, and it has an upper portion disposed about and spaced from the flow restricting sleeve to provide a flow gap having a flow area substantially equal to the clearance space. The flow restrictor is otherwise structured to provide at least one contraction-expansion loss above the top guide tube plate for guide tube coolant flow through the flow gap.
047818832	summary	BACKGROUND OF THE INVENTION The present invention is related to the longterm storage of spent fuel that has been removed from a nuclear reactor, and more particularly, to a spent fuel storage cask having a continuous grid basket assembly which supports the spent fuel and which dissipates heat generated by the spent fuel. FIG. 1 illustrates a typical fuel assembly 20 for supplying nuclear fuel to a reactor. Assembly 20 includes a bottom nozzle 22 and a top nozzle 24, between which are disposed elongated fuel rods 26. Each fuel rod 26 includes a cylindrical housing made of a zirconium alloy such as commerically available "Zircalloy-4", and is filled with pellets of fissionable fuel enriched with U-235. Within the assembly of fuel rods 26, tubular guides (not shown) are disposed between nozzles 22 and 24 to accommodate movably mounted control rods (not illustrated) and measuring instruments (not illustrated). The ends of these tubular guides are attached to nozzles 22 and 24 to form a skeletal support for fuel rods 26, which are not permanently attached to nozzles 22 and 24. Grid members 28 have apertures through which fuel rods 26 and the tubular guides extend to bundle these elements together. Commerically available fuel assemblies for pressurized water reactors include between 179 and 264 fuel rods, depending upon the particular design. A typical fuel assembly is about 4.1 meters long, about 19.7 cm wide, and has a mass of about 585 kg., but it will be understood that the precise dimensions vary from one fuel assembly design to another. After a service life of about 3 years in a pressurized water reactor, the U-235 enrichment of a fuel assembly 20 is depleted. Furthermore, a variety of fission products, having various half-lives, are present in rods 26. These fission products generate intense radioactivity and heat when assemblies 20 are removed from the reactor, and accordingly the assemblies 20 are moved to a pool containing boron salts dissolved in water (hereinafter "borated water") for short-term storage. Such a pool is designated by reference number 30 in FIG. 2. Pool 30 is typically 12.2 meters deep. A number of spent fuel racks 32 positioned at the bottom of pool 30 are provided with storage slots 34 to vertically accommodate fuel assemblies 20. A cask pad 36 is located at the bottom of pool 30. During the period when fuel assemblies 20 are stored in pool 30, the composition of the spent fuel in rods 26 changes. Isotopes with short half-lives decay, and consequently the proportion of fission products having relatively long half-lives increases. Accordingly, the level of radioactivity and heat generated by a fuel assembly 20 decreases relatively rapidly for a period and eventually reaches a state wherein the heat and radioactivity decrease very slowly. Even at this reduced level, however, rods 26 must be reliably isolated from the environment for the indefinite future. Dry storage casks provide one form of long-term storage for the spent fuel. After the heat generated by each fuel assembly 20 falls to a predetermined amount--such as 0.5 to 1.0 kilowatt per assembly, after perhaps 10 years of storage in pool 30--an opened cask is lowered to pad 36. By remote control the spent fuel is tranferred to the cask, which is then sealed and drained of borated water. The cask can then be removed from pool 30 and transported to an above-ground storage area for long-term storage. The requirements which must be imposed on such a cask are rather severe. The cask must be immune from chemical attack during long-term storage. Furthermore, it must be sufficiently rugged mechanically to avoid even tiny ruptures or fractures during long-term storage and during transportation, when the cask might be subjected to rough treatment or accidents such as drops. Moreover, the cask must be able to transmit heat generated by the spent fuel to the environment while nevertheless shielding the environment from radiation generated by the spent fuel. The temperature of the rods 26 must be kept below a maximum temperature, such as 375.degree. C., to prevent deterioration of the zirconium alloy housing. Provisions must also be made to ensure that a chain reaction cannot be sustained within the cask; that is, that the effective criticality factor K.sub.eff remains less than one so that a self-sustaining reaction does not occur. These requirements impose stringent demands upon the cask, which must fulfill its storage function in an utterly reliable manner. SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a mechanically rugged storage cask which prevents fission products and radiation from escaping into the environment while dissipating heat generated by spent fuel. Another object of the present invention is to provide a storage cask which is sufficiently versatile to accomodate spent fuel in various different forms, including fuel assemblies having different dimensions and fuel in consolidated form, and to store different forms of spent fuel simultaneously. Another object of the present invention is to provide a storage cask having a grid basket assembly for supporting spent fuel and for conducting heat generated thereby to the walls of the cask. Another object of the present invention is to provide cell assemblies for use in cooperation with the grid basket assembly when spent fuel assemblies are stored. Another object of the present invention is to provide a storage cask wherein heat is transmitted from the grid basket assembly to channel sections affixed to the inner walls of the cask via thin gaps between the channel sections and the edges of the elements forming the grid basket assembly, the channel sections additionally permitting movement of the grid basket assembly with respect to the walls of the cask during temperature variations. These and other objects can be attained by providing a container having a grid basket assembly which includes a plurality of metal plates joined together to provide a matrix of storage slots for the spent fuel, and elongated channel sections which are affixed to the inside walls of the container and which accommodate the edges of the plates in order to transmit heat from the grid basket assembly to the walls of the container without preventing relative movement between the grid basket assembly and the walls. In accordance with one aspect of the invention, the metal plates of the grid basket assembly provide elongated storage slots having generally rectangular cross sections, and consolidation canisters or cells having walls which include neutron moderating material are mounted in the storage slots. Such cells accommodate spent fuel assemblies and can be individually configured in accordance with the dimensions of the fuel assemblies which they are to receive. Each cell can include four panel portions which are affixed to the walls of the storage slots by tabs. Alternatively, the cells may include shell elements which have wall portions that are spaced apart from the walls of the storage slots and corner poritons that project outward to contact the walls of the storage slots. In other embodiments, the cells may include shell elements having walls which provide substantially rectangular cross sections, with spacer elements being provided in the form of dimples in the shells or spacer members affixed to the shells. Regardless of the cell embodiment, at least some of the walls of the cells include sheets of boron carbide or other "neutron poison" supported by wrapper elements, which may include apertures to permit visual confirmation that neutron poison is present and to facilitate drainage of borated water when spent fuel is being loaded into the cask. A consolidation canister containing fuel rods, instead of a cell for receiving a fuel assembly, is deposited in a storage slot if the slot is to be used for storage of fuel in consolidated form. In accordance with another aspect of the invention, the grid basket assembly is supported above the floor of the container in order to facilitate drainage of borated water. This may be accomplished by providing cut-outs at the lower ends of the plates forming the grid basket assembly, by terminating the channels of the channel sections above the floor of the container in order to support the plates above the floor, or by providing support elements disposed between the floor of the container and the lower ends of the plates of the grid basket assembly. These support elements can have flanges which are positioned to permit consolidation canisters to rest on the cask floor but to support the lower ends of the cells. Alternatively, the cells can be mechanically attached to the grid assembly at one region so that the cells can move with respect to the grid basket assembly at other places as temperature changes, or hooks can be provided at the upper ends of the cells in order to hang the cells from the plates of the grid basket assembly. The grid basket assembly is preferably fabricated by making slots from the bottom to the middle of a first set of plates, making corresponding slots from the top to the middle of a second set of plates, and interdigitating the plates to provide a matrix of elongated storage slots having rectangular cross sections.
	abstract	A system and method are provided for enabling a systematic detection of issues arising during the course of mask generation for a semiconductor device. IC mask layer descriptions are analyzed and information is generated that identifies devices formed by active layers in the masks, along with a description of all layers in proximity to the found devices. The IC mask information is compared to a netlist file generated from the initial as-designed schematic. Determinations can then made, for example, as to whether all intended devices are present, any conflicting layers are in proximity to or interacting with the intended devices, and any unintended devices are present in the mask layers. Steps can then be taken to resolve the issues presented by the problematic devices.
	description	This application is the U.S. National Phase under 35. U.S.C. § 371 of International Application PCT/EP2012/076894, filed Dec. 26, 2012, which claims priority to French Patent Application No. 1162529, filed Dec. 29, 2011. The disclosures of the above-described applications are hereby incorporated by reference in their entirety. This invention relates to a control method for a pressurised water nuclear reactor to minimise effluent volumes and loads applied to control clusters of a pressurised water nuclear reactor. The method according to the invention is particularly suitable for control of a nuclear reactor in frequency regulation or load following. It may be useful, particularly in countries like France in which 80% of electricity is generated by nuclear reactors, for the global power output by reactors to vary so as to adapt to the needs of the electrical network that they supply: this is then called network following or load following. The purpose of frequency regulation is to regulate production in real time to match consumption of electrical energy, for which variations with small amplitudes occur. With load following, the power produced by the reactor is regulated so as to correspond to a program predetermined by the electricity network operating service. This prediction is usually daily but it can be weekly with daily adjustments. Load following can equally well cover one or several daily variations and prolonged operation at low power between full power and zero power. Thus, it is particularly desirable to be able to operate reactors at low power for a long period during which the network demand is low, before returning to nominal power PN if necessary. Frequency regulation is applied in parallel to this load following program, to adapt production of the reactor to match real network needs. Power supplied by the reactor is regulated by control means positioning control clusters composed of neutron absorbing elements at different insertion positions in the core, to more or less absorb neutrons and possibly adjusting the concentration of a neutron absorbing compound such as boron, in the primary coolant, as a function of the required power and/or measurements output from the reactor core instrumentation. For example, the control means are composed of a set of electronic and electrical equipment which, starting from measurements derived from instrumentation lines and comparing them with thresholds, create displacement orders for control clusters and/or modification of the boron concentration in the primary coolant by injection of water (dilution) or boron (boration). Different methods for controlling a pressurised water nuclear reactor are known. In general, control consists of controlling and regulating at least the average temperature of the primary coolant Tmoy and the distribution of thermal (and neutron) power and particularly the axial power distribution in order to prevent the formation of a power unbalance between the high and low zones of the core. The methods of regulating these parameters vary depending on the different control modes used, namely control modes commonly called mode mode A, mode G, mode X and mode T. In general, the average temperature Tmoy is regulated by displacement of the control clusters as a function of the different parameters such as the power demand from the turbine, the current value of the coolant temperature and a set temperature, and/or possibly modification of the boron concentration in the primary coolant to prevent control clusters from being inserted too far which could disturb the axial power distribution. The choice of the method of controlling a nuclear reactor is determined considering the fact that action of control clusters has immediate effects while action by injection of boron in solution is comparatively slower. Control mode A aims to keeping the average temperature of the coolant equal to the value of the reference temperature by displacement of the control clusters, the reference temperature being programmed as a function of the load (FIG. 1). When the operator reduces (or increases) the turbine load, the regulation system causes insertion (or extraction) of clusters to control the average temperature of the coolant such that it is equal to the reference temperature Tref, with an uncertainty defined by a dead band with a constant amplitude of about 0.5 to 1° C. around the value of the reference temperature (shown in dashed lines in FIG. 1). In moving, the control clusters disturb the power distribution, and particularly the axial distribution. When the axial unbalance limit is reached, the reduction (or increase) in load is accompanied by boration (or dilution) of the coolant in the primary circuit, so that the control clusters will not be inserted (extracted) beyond the limiting insertion position corresponding to the required limit of the axial unbalance. If a request for a fast power return occurs during a load following low level, there is a risk that the control clusters move quickly to the high stop without dilution action taking place quickly enough to prevent it. In this case, the load increase has to be slowed to make it compatible with the inertia of dilution/boration effects, otherwise significant cooling could occur which would be damaging to the strength of the mechanical equipment. Therefore, mode A is not particularly suitable for load following or frequency regulation. In order to overcome this disadvantage, a method has been developed to control the temperature of the coolant of a conventional pressurised water reactor (i.e. a reactor controlled in mode A) to improve the load following capacity of the reactor. Such a method is disclosed in document FR2583207. To achieve this, the method defines a reference temperature TPROG (FIG. 2) during load variations that is different from the reference temperature TREF during operation under stable conditions. The reference temperature during a load variation called the programmed reference temperature (TPROG), attempts to follow a set value that also minimises variations in the boron concentration of the coolant. This programmed reference temperature is limited to an upper limit and a lower limit, these limits delimiting a region in which the variation profile of the programmed reference temperature during load following can be programmed. FIG. 2 shows a programmed profile for variation of the reference temperature during load following to change from 100% nominal power to 50% nominal power followed by a return to 100% nominal power. Programming such a reference temperature variation profile has a secondary advantage that it reduces the number of steps of the cluster control mechanisms in some operating cases such as frequency regulation. However, this reduction in the number of steps is not particularly significant and it cannot significantly increase the life of these control mechanisms. Despite the use of this control method to improve the load following capacity of a reactor controlled in mode A, fast or large amplitude power variations are always difficult particularly due to the limited action speed of boration or dilution operations. There are also other known control modes that are more suitable for load following, namely modes G, X and T. Mode G allows for the possibility of a fast return to 100% nominal power by removing the control clusters, when determining the insertion position of control clusters. To achieve this, control mode G controls two types of groups of control clusters with different neutron absorptivity values. The insertion position of one of the groups depends on the power level and guarantees the possibility of a fast return to nominal power PN. The word “fast” refers to a sufficiently fast load increase so that the variation of the xenon concentration is low, in other words a load increase with a load buildup rate typically between 3% and 5% PN/min. The other group of control rods is heavier, and is specifically used for control of the average temperature Tmoy of the reactor, and indirectly by dilution and boration operations, to control of the axial power distribution. Control modes X and T are advanced control modes that take account of the capacity to increase to power Pmax previously chosen by an operator between the current power and 100% nominal power, in positioning the control clusters. The capacity to increase to power Pmax, means the possibility of quickly increasing power, in other words at a rate of increase typically between 2% and 5% PN/min, from a low power to a high power (set value Pmax) previously defined by the operator during programming of load following. Unlike mode A, control modes G, X and T are modes that are adapted to operation of pressurised water reactors in load following or in frequency regulation. However, temperature regulation nevertheless makes significant use of the control rods and treatment of effluents is expensive for the operator and makes it necessary to create waste, although the allowable volume of waste is becoming more and more strictly controlled (environmental impact). The number of steps that can be performed by control cluster control mechanisms is limited. This limit might be reached before the 60 years life of the reactor if manoeuvres are made frequently. The control mechanisms would then have to be replaced, which would require an expensive and complex maintenance operation. This is the context in which the invention aims to solve the problems mentioned above by proposing a method of controlling a nuclear reactor and to optimise displacements of control rods during variations of the reactor power in load following or in frequency regulation and volumes of effluents created by dilution/boration operations of the primary coolant during variations of the reactor power during load following, regardless of the control mode used for the nuclear reactor. To achieve this, the invention discloses a method of controlling a pressurised water nuclear reactor, said reactor comprising: a core generating thermal power; means of acquiring magnitudes representative of core operating conditions (thermal power, temperature of the primary coolant); said method comprising a step to regulate the temperature of the primary coolant if the temperature of the primary coolant, for a given thermal power, is outside a predefined set temperature interval depending on the reactor power, said set temperature interval being characterised by: a variable amplitude on a thermal power range between N % and 100% nominal power, where N is between 0 and 100; a zero amplitude at 100% nominal power; a zero amplitude at N % nominal power; said regulation not taking place while the temperature of the primary coolant is inside said temperature interval for a given thermal power. “Variable amplitude” means an amplitude that varies as a function of the thermal power, in other words with a variation (increase or reduction) of the amplitude as a function of the thermal power, as opposed to a constant amplitude over a thermal power range. Zero amplitude corresponds to a unique value of the set temperature (point value). Thus according to the invention, the set temperature is not defined exclusively by a temperature value associated with a thermal power, but rather by a “set temperature range” delimited by a high limit and a low limit, in which the temperature of the primary coolant can fluctuate freely during load following or during frequency regulation without triggering any regulation of the primary coolant temperature causing a displacement of the control rods and/or a modification of the boron concentration. The definition of a set temperature interval for a given thermal power thus advantageously uses the effects of the reactivity related to temperature variations of the primary coolant within the set temperature interval to minimise actions to control the reactor reactivity. Thus, a free variation of the primary coolant temperature within the temperature interval can reduce actions of actuators (reduction or even elimination of some steps of cluster control mechanisms) and effluent volumes. Advantageously, the set temperature interval has a maximum temperature amplitude for a thermal power or range of thermal powers on which frequency regulation is required for a nuclear reactor functioning in load following. Thus, at a given power level, the set temperature interval is defined by a high allowable temperature (upper limit) and a low allowable temperature (lower limit), the difference between the high limit and the low limit defining the amplitude of the temperature interval. Thus, the method according to the invention does not impose that a particular linear profile of the set reference temperature should be followed during load following. Such a set temperature profile makes it necessary to regulate the average temperature of the coolant by displacements of control clusters and/or modification of the boron concentration, as soon as the average temperature of the coolant varies from the set temperature defined by the set temperature profile, taking account of a “dead band” around the temperature profile so that the different uncertainties in temperature measurements can be taken into account. Thus, the set temperature range thus defined by the plurality of variable amplitude temperature intervals, should be differentiated from a “dead band” around the reference temperature (FIG. 1). Conventionally, a dead band has a small and constant amplitude of the order of a maximum of 0.5 and 1° C., and is used to limit unwanted actions on control clusters within a range consistent with the accepted temperature uncertainty. The control method for a pressurised water nuclear reactor according to the invention may also have one or several of the following characteristics, considered individually or in any technically possible combination: the set temperature interval has a maximum temperature amplitude for a thermal power or a range of thermal powers on which a frequency regulation of the nuclear reactor is made; the amplitude of said interval is maximum between 40% and 80% nominal power; the amplitude of said interval is maximum between 80% and 100% exclusive of the nominal power; said set temperature interval lies within a zone in which the lower limit corresponds to the set temperature at 0% nominal power and the upper limit corresponds to the set temperature at 100% nominal power; the method comprises a step to regulate at least one other core parameter among the axial power distribution and the capacity for instantaneous return to power when the primary coolant temperature is within the set temperature interval; said temperature interval has a variable amplitude at least over a thermal power range of between 50% and 100% nominal power; said set temperature interval is surrounded by a dead band. FIG. 3 shows a first example embodiment of a set temperature range made on the temperature program of a nuclear reactor operating in load following. It is considered that load variations are most frequently made between 50% or 60% nominal power (PN) and 100% PN, therefore this is the variation range in which the maximum gain should be made on control cluster displacements. At 0% PN and 100% PN, the set temperature is defined by a single value of the set temperature (i.e. by a zero temperature amplitude) rather than a set temperature range. Set temperature values TREFMIN at 0% PN and TREFMAX at 100% PN are conventionally defined so as to minimise any impacts on accident studies and taking account of the capability of producing a sufficient steam pressure for the turbine. In general, the set temperature values TREFMIN at 0% PN and TREFMAX at 100% PN according to the invention are identical to the set temperature values according to the state of the art for these same thermal power values. From 0% to 35% PN, the set temperature is conventionally made by a set temperature varying linearly as a function of the reactor power, a single value of the set temperature being associated with a given thermal power of the reactor. Between 35% and 100% nominal power (PN), the set temperature is defined by a temperature range 10 composed of a plurality of set temperature intervals ΔTREF with variable amplitudes as a function of the thermal power, the temperature range 10 being delimited by a high threshold value TCMAX and a low threshold value TCMIN. Between 60% and 100% PN, the maximum limiting value of set temperature intervals ΔTREF is constant and corresponds to the set temperature at 100% PN, namely TCMAX. Between 35% and 60% PN, the minimum limiting value of set temperature intervals ΔTREF is constant and corresponds to the set temperature at 25%, namely TCMIN. The set temperature range 10 thus shown as an example allows a maximum temperature variation of the primary coolant at a thermal power of 60% PN. Thus, no temperature regulation actions are initiated as long as the temperature of the primary coolant is within the range (within a dead band ΔBM around the set temperature interval ΔTREF). Thus, the temperature range 10 shown in FIG. 3 minimises actions, for example such as displacements of control clusters, during operation of a nuclear reactor operating in load following and for which load variations due to frequency regulation (for example ±5%) are usually made around 60% nominal power. FIG. 4 shows a second example embodiment of a set temperature range 20 made on the temperature program of a nuclear reactor operating in load following. This second set temperature range is defined to allow a maximum variation of the primary coolant temperature at 50% PN, a value at which frequency regulation is preferred. In the same way as for the first example described above, the set temperatures at 0% PN and at 100% PN is defined by a single set value TREFMIB (at 0% PN) and TREFMAX (at 100% PN) so as to minimise any impacts on accident studies and to take account of the steam pressure demanded by the turbine. Values of set temperatures TREFMIN at 0% PN and TREFMAX at 100% PN are identical to the set temperature values according to the state of the art for these same values of the thermal power, the variation of the set temperature TREF as a function of the thermal power according to the state of the art being shown as a dashed straight line reference TREF in FIG. 4 for comparison purposes. According to another embodiment (not shown), the temperature range may also include: a first part, for example between 0% and 35% nominal power, in which temperature intervals have a variable amplitude that increases as a function of the power, a second part, for example between 35% and 70% nominal power, in which temperature intervals have a constant non-zero maximum amplitude, and; a third part, for example between 70% and 100% nominal power, in which temperature intervals have a variable amplitude that decreases as a function of the power. This temperature range thus described is particularly suitable for nuclear reactors operating in load following with low load levels (between 35% and 70% PN) different from the level at which the frequency regulation is done. In parallel with this regulation to maintain the primary coolant temperature within a set temperature interval, the other core parameters, namely the axial power distribution (axial offset) and the capacity for instantaneous power buildup (Pmax) are always controlled in parallel, by varying the positions of the control clusters and the boron concentration of the primary coolant. FIGS. 5a, 5b and 5c show temperature variations of the reactor and the position of a group of control clusters resulting from use of the control method according to the invention during operation in frequency regulation shown particularly by the graph in FIG. 5a. FIG. 5b more particularly shows free temperature variations (curve T2) in the set temperature interval ΔTREF delimited by threshold values TCMAX and TCMIN. For comparison, the graph also shows temperature variations (curve T1) resulting from a temperature regulation relative to a reference temperature TREF for the same operation in frequency regulation. Therefore free variation of the primary coolant temperature will compensate for power variations. Thus, the method according to the invention can eliminate the compensation of power variations by a very large number of movements of control clusters so as to keep the primary coolant temperature as close as possible to the reference set temperature TREF. FIG. 5c shows the gain in cluster movements obtained by use of the method according to the invention, for the example of operation in frequency regulation shown in FIG. 5a. Curve P1 shows cluster movements necessary to maintain the temperature of the primary coolant as close as possible to the reference set temperature TREF (application of a control according to the state of the art), and curve P2 shows cluster movements necessary to maintain the temperature of the primary coolant within the set temperature interval. Thus, the use of the set temperature range to regulate the temperature of the nuclear reactor during operation in frequency regulation can significantly reduce or even eliminate control cluster movements. The use of a temperature range according to the invention also has the advantage that it reduces effluent volumes during operation of the nuclear reactor in load following. Thus, during operation in load following as shown as an example by the graph in FIG. 6a, free variation of temperature within the set interval makes it possible to correct the effects of reactivity by taking account of the Xenon effect (shown by the graph in FIG. 6b) to reduce the number of steps of control cluster control mechanisms (not shown) and reduce the volumes of effluents (shown in FIG. 6d). To achieve this, FIG. 6c shows temperature variations during load following shown in FIG. 6a and FIG. 6d shows variations in the boron concentration during this same load following. The graph shown in FIG. 6c more particularly shows free temperature variations (curve T2) within the set temperature interval ΔTREF delimited by threshold values TCMAX and TCMIN resulting from use of the control method according to the invention. For comparison, the graph also shows temperature variations (curve T1) resulting from a temperature regulation relative to a reference temperature TREF resulting from use of a control method according to the state of the art. The graph shown in FIG. 6d more particularly shows the variations in the boron concentration (curve C2) during load following resulting from use of the control method according to the invention. For comparison, the graph also shows variations in the boron concentration (curve C1) during the same load following resulting from the use of a control method according to the state of the art. As shown in FIG. 6d, the free temperature variation within the set temperature interval can retard the beginning of dilution (curve C2). When the temperature reaches a threshold value of the set temperature interval (TCMIN at time t3), regulation is necessary to keep the temperature within the set temperature interval ΔTREF (from time t3 to time t4). Therefore this regulation is made by dilution starting from t3. At time t4, the reactor temperature returns within the set temperature interval ΔTREF and dilution is stopped. Starting from time t5, boration is applied to compensate for the temperature that reaches the threshold value TCMAX and it is continued starting from t6 so as to compensate for the reduction in Xenon that can be seen on the curve in FIG. 6b. Thus, FIG. 6d shows the reduction in effluent volumes generated during a load following as an example (curve C2) compared with volumes of effluents generated by use of a control method according to the state of the art (curve C1). The invention has been described particularly for application with control mode T; however, the invention is also applicable to all control modes known to those skilled in the art and not only to the control modes mentioned in this application.
056174659	abstract	A scan-type X-ray imaging system and method are disclosed. Image detection is effected by use of a fixed phosphor converter screen covering the entire field of view so that X-rays passed through an object, or a body portion, positioned at a scan area, are received at the converter screen and light signals, proportional to the received X-rays, are coupled through a movable coupler, having an input portion movably engaging the converter screen, to a movable sensor that converts received light signals to electrical output signals indicative of the object, or body portion, then at the scan area. The input face of the coupler, preferably a fiber optic coupler, is held in positive engagement with the converter screen throughout movement of the coupler relative to the converter screen by a force, such as by an air cushion between the object, or body portion, positioner and the converter screen, by establishing a vacuum between the input face of the coupler and the converter screen, and/or by springs biasing the coupler face plate toward engagement with the converter screen.
	claims	1. A method for operating a particle therapy system, the method comprising:generating and accelerating irradiation particles;generating a particle beam from at least a portion of the generated irradiation particles;automatically measuring a particle beam intensity of the particle beam;automatically sequentially irradiating a plurality of scanning points with the particle beam in accordance with a predefined irradiation plan, wherein the irradiation plan assigns an irradiation dose to each scanning point of the plurality of scanning points, and wherein a set-point value for the particle beam intensity is assigned to each scanning point of the plurality of scanning points based on the irradiation dose assigned to the scanning point by the predefined irradiation plan; andautomatically influencing the particle beam intensity as a function of the measured particle beam intensity and the setpoint value of the scanning point that is to be irradiated. 2. The method as claimed in claim 1, further comprising directing the particle beam to a particle beam output of a treatment station,wherein the particle beam intensity is measured at the particle beam output. 3. The method as claimed in claim 1, wherein generating the particle beam comprises decoupling a fraction of the generated irradiation particles with the aid of a knock-out exciter, influencing the particle beam intensity with a radio frequency power of the knock-out exciter being set automatically. 4. The method as claimed in claim 1, wherein the setpoint value of the particle beam intensity has a non-constant variation over time. 5. The method as claimed in claim 1, wherein a proportional regulating function, an integrating regulating function, or a differentiating regulating function is used to influence the particle beam intensity. 6. The method as claimed in claim 1, wherein generating and accelerating the irradiation particles comprises using a linear accelerator and a synchrotron or a cyclotron. 7. The method as claimed in claim 1, further comprising directing the particle beam to one treatment station of a plurality of treatment stations, the particle beam intensity being measured at each treatment station of the plurality of treatment stations,wherein the measured particle beam intensity of the one treatment station is automatically used for influencing the particle beam intensity. 8. The method as claimed in claim 1, further comprising determining information relating to quality of a particle generation device that generates and accelerates the irradiation particles,wherein the information is determined automatically as a function of the measured particle beam intensity and the setting of the fraction of the decoupled irradiation particles. 9. A particle therapy system comprising:a particle generation device operable to generate and accelerate irradiation particles;a beam generating device operable to generate a particle beam from at least a portion of the generated irradiation particles;a measuring device operable to automatically measure a particle beam intensity of the particle beam;a raster scan controller configured to sequentially irradiate scanning points with the particle beam in accordance with a predefined irradiation plan, wherein the irradiation plan assigns an irradiation dose to each of the scanning points, and wherein a set-point value for the particle beam intensity is assigned to each of the scanning points based on the irradiation dose assigned to the scanning point by the predefined irradiation plan; anda particle beam influencing device that is coupled to the raster scan controller and is configured to alter the particle beam intensity as a function of the measured particle beam intensity and the assigned setpoint value for the particle beam intensity of the scanning point that is to be irradiated. 10. The particle therapy system as claimed in claim 9, further comprising a particle beam feeder unit operable to direct the particle beam to a particle beam output of a treatment station,wherein the measuring device is disposed at the particle beam output. 11. The particle therapy system as claimed in claim 9, wherein the beam generating device comprises a knock-out exciter having a control input operable to adjust a radio frequency power, the knock-out exciter being operable to vary a decoupled fraction of the irradiation particles, andwherein the particle beam influencing device sets the control input of the knock-out exciter as a function of the measured particle beam intensity and the predefined setpoint value for the particle beam intensity in order to alter the particle beam intensity. 12. The particle therapy system as claimed in claim 9, wherein the setpoint value for the particle beam intensity has a non-constant variation over time. 13. The particle therapy system as claimed in claim 9, wherein the particle beam influencing device comprises a proportional controller, an integrating controller, or a differentiating controller. 14. The particle therapy system as claimed in claim 9, wherein the particle generation device comprises a linear accelerator and a synchrotron or a cyclotron. 15. The particle therapy system as claimed in claim 9, further comprising:a particle beam feeder unit operable to direct the particle beam to one treatment station of a plurality of treatment stations, wherein a measuring device operable to automatically measure the particle beam intensity of the output particle beam is provided at each treatment station of the plurality of treatment stations; anda switchover unit configured to direct the measured particle beam intensity of the one treatment room to the particle beam influencing device. 16. The particle therapy system as claimed in claim 9, further comprising a quality determining device operable to determine information relating to quality of the particle generation device as a function of the measured particle beam intensity and the influencing of the particle beam intensity. 17. The particle therapy system as claimed in claim 9, wherein the particle therapy system is configured for:generating and accelerating the irradiation particles;generating the particle beam from at least the portion of the generated irradiation particles; automatically measuring the particle beam intensity of the particle beam;automatically sequentially irradiating the scanning points with the particle beam in accordance with the predefined irradiation plan; andautomatically influencing the particle beam intensity as a function of the measured particle beam intensity and the setpoint value of the scanning point that is to be irradiated. 18. A non-transitory computer readable medium comprising a computer program product that, when executed by a particle beam influencing device of a particle therapy system, causes the particle beam influencing device to perform a method for operating the particle therapy system, the method comprising:generating and accelerating irradiation particles;generating a particle beam from at least a portion of the generated irradiation particles;automatically measuring a particle beam intensity of the particle beam;automatically sequentially irradiating a plurality of scanning points with the particle beam in accordance with a predefined irradiation plan, wherein the irradiation plan assigns an irradiation dose to each scanning point of the plurality of scanning points, and wherein a set-point value for the particle beam intensity is assigned to each scanning point of the plurality of scanning points based on the irradiation dose assigned to the scanning point by the predefined irradiation plan; andautomatically influencing the particle beam intensity as a function of the measured particle beam intensity and the setpoint value of the scanning point that is to be irradiated. 19. A non-transitory electronically readable data medium on which is stored electronically readable control information that is configured such that the electronically readable control information performs a method for operating a particle therapy system when the electronically readable data medium is used in a particle beam influencing device, the method comprising:generating and accelerating irradiation particles;generating a particle beam from at least a portion of the generated irradiation particles; automatically measuring a particle beam intensity of the particle beam;automatically sequentially irradiating a plurality of scanning points with the particle beam in accordance with a predefined irradiation plan, wherein the irradiation plan assigns an irradiation dose to each scanning point of the plurality of scanning points, and wherein a set-point value for the particle beam intensity is assigned to each scanning point of the plurality of scanning points based on the irradiation dose assigned to the scanning point by the predefined irradiation plan; andautomatically influencing the particle beam intensity as a function of the measured particle beam intensity and the setpoint value of the scanning point that is to be irradiated. 20. The method as claimed in claim 3, wherein the setpoint value of the particle beam intensity has a non-constant variation over time.
047642815	claims	1. A method of treating a heavy metal radioisotope-bearing liquid to remove a substantial portion of the metal radioisotope metals therefrom without substantial sludge formation comprising: contacting said liquid with a water-insoluble carboxylated cellulose in an amount sufficient to cause precipitation of a substantial portion of the heavy metal radioisotope in the liquid. contacting said liquid with a water-insoluble carboxylated cellulose in an amount sufficient to cause precipitation of a substantial portion of the heavy metal radioisotope in the liquid. contacting said liquid with a water-insoluble carboxylated cellulose in an amount sufficient to cause precipitation of a substantial portion of the heavy metal radioisotope in the liquid; and adding sodium diethyldithiocarbamate to said liquid in an amount sufficient to reduce precipitation time. 2. The method of claim 1 wherein the water-insoluble carboxylated cellulose is a salt of carboxymethylcellulose. 3. The method of claim 2 wherein the water-insoluble salt of carboxymethylcellulose is aluminum carboxymethylcellulose or chromium carboxymethylcellulose. 4. The method of claim 3 wherein the water-insoluble salt of carboxymethylcellulose is aluminum carboxymethylcellulose. 5. The method of claim 1 wherein the metal precipitated from said liquid is a radioactive metal selected from the group consisting of radium, radon, rhenium, molybdenum, praseodymium, polonium, lead, astatine, bismuth, thallium, mercury, zirconium, barium, promethium, uranium, cesium, strontium, ruthenium, neptunium, technetium, iodine, thorium, niobium, cerium, rubidium, palladium, curium, plutonium, tellurium, samarium, americium, protactinium, lanthanum, indium, neodymium, lutetium, rhodium or mixtures thereof. 6. The method of claim 5 wherein the metal precipitated from said liquid comprises radium, uranium, cesium, stontium, ruthenium, rhenium, neptunium, technetium or rhodium. 7. The method of claim 1 wherein the said liquid includes an aqueous liquid. 8. The method of claim 7 wherein the said aqueous liquid comprises natural waters, wastewaters, manufacturing effluents, or water-containing mixtures. 9. The method of claim 7 including adjusting the pH of said liquid above 6.0 and below 9.0 before contacting said liquid with the insoluble carboxylated cellulose. 10. The method of claim 9 wherein the insoluble carboxylated cellulose is a salt of carboxymethylcellulose. 11. The method of claim 1 further comprising initially treating said liquid with an oxidizing agent to destroy one or more interfering ions. 12. The method of claim 11 wherein said oxidizing agent is selected from the group consisting of ozone (O.sub.3), chlorine gas (Cl.sub.2) and hypochlorite ion (OCl.sup.-). 13. The method of claim 11 wherein said interfering ion is cyanide (CN.sup.-). 14. A method of treating a heavy metal radioisotope-bearing liquid containing a non-aqueous liquid, to remove a substantial portion of the metal radioisotope metals therefrom without substantial sludge formation comprising: 15. The method of claim 14 wherein the said non-aqueous liquid comprises oil, petroleum distillates or lubricants. 16. A method of treating a heavy metal radioisotope-bearing liquid to remove a substantial portion of the metal radioisotope metals therefrom without substantial sludge formation comprising:
062367013	summary	TECHNICAL FIELD The present invention relates to a fuel assembly for a boiling water reactor which is adapted, during operation of the reactor, to allow cooling water to flow upwards through the fuel assembly while absorbing heat from a plurality of fuel rods which are surrounded by a fuel channel, whereby part of the cooling water is transformed into steam, and where the fuel assembly comprises a steam conducting channel through which the steam is allowed to flow through the fuel assembly towards the outlet end thereof. BACKGROUND ART In a boiling water nuclear reactor, moderated by light water, the fuel exists in the form of fuel rods arranged in a certain, normally symmetrical pattern, a so-called lattice, and is retained at the top by a top tie plate and at the bottom by a bottom tie plate. A fuel assembly comprises one or more bundles of fuel rods which are surrounded by a fuel channel with a substantially square cross section. In the core of the reactor, the fuel assemblies are arranged vertically and spaced from each other. During operation, the water is admitted through the bottom of the fuel assembly and then flows upwards through the fuel assembly past the fuel rods. The heat emitted by the fuel rods is taken up by the water which starts boiling, whereby part of the water is transformed into steam. The water and the steam are passed out through the upper end of the fuel assembly. The produced steam is delivered to turbines which drive generators where electrical energy is generated. A disadvantage with a boiling reactor is the high proportion of steam by volume in the upper part of the fuel assembly. When the proportion of steam by volume rises in the coolant, its ability to carry off heat from the fuel rods is reduced, thus increasing the risk of dryout, which in turn leads to an increase of the risk of fuel damage. Still another problem with a high steam volume in the fuel is that steam is inferior to water as moderator, which results in the moderation being insufficient whereby the fuel is utilized inefficiently. In the lower part of the fuel assembly, the moderator consists of water whereas the moderator in the upper part of the fuel assembly consists of both steam and water. This means that the fuel in the upper part of the fuel assembly cannot be utilized efficiently. It is, therefore, desirable to keep down the steam volume in the coolant while at the same time maintaining the steam generation at a high level. The faster the steam disappears out from the fuel assembly, the lower the steam volume. A separation of the steam flow and the water flow in the upper part of the fuel assembly thus gives the steam flow a higher velocity than the water flow, whereby the proportion of steam by volume in the fuel assembly is reduced. In this way, the margin with respect to dryout is improved and the fuel in the upper part of the fuel assembly is utilized in a better way. U.S. Pat. No. 5,091,146 discloses a fuel assembly which attempts to achieve a separation of the steam flow and the water flow in the upper part of the fuel assembly by arranging a steam pipe above one or more part-length fuel rods, that is, fuel rods extending from the bottom tie plate but terminating below and at a distance from the top tie plate. In this way, the steam which is generated in the coolant is to be diverted. The pipe has openings both in its upper and its lower end. The disadvantages of such a pipe are several. For one thing, it may be expensive to manufacture, and, for another, it gives an increased pressure drop in the upper part of the fuel assembly. Another disadvantage is that it may be difficult to cause the continuously produced steam to enter the pipe. Admittedly, the pipe is provided with openings and other devices to cause the steam to flow into the pipe and to prevent water from entering the pipe, but it is still doubtful whether this is an effective way of causing the steam to enter the tube. SUMMARY OF THE INVENTION The object of the invention is to provide a fuel assembly which in a simple and efficient way separates the steam flow and the water flow at least partially, thus obtaining a lower proportion of steam by volume in the fuel assembly. What characterizes a fuel assembly according to the invention will become clear from the appended claims. A fuel assembly according to the invention comprises a vertical channel which conducts steam upwards through the fuel assembly during operation of the reactor. This channel has no walls but only comprises an empty volume between the fuel rods and will hereinafter be referred to as a steam conducting channel. The fuel assembly is designed such that the coolant, that is, water and steam, is caused to rotate around the steam conducting channel so as to form an upward eddy. The eddy rotates so fast that the steam separates from the water with the aid of the centrifugal force. The water, which is heavier than the steam, is thrown outwards and away from the steam conducting channel, whereas the lighter steam is pressed against the centre of the eddy and hence against the steam conducting channel. This gives the steam a considerably higher speed than the natural speed and the steam is able to leave the fuel assembly, at a high speed, via the steam conducting channel. In this way, the proportion of steam by volume in the fuel assembly is reduced. To achieve a rotation of water and steam around the steam conducting channel, this channel is surrounded by fuel rods arranged in concentric rings with a substantially circular shape. The steam conducting channel is arranged in the centre of these rings. The fuel rods in the rings are arranged such that their upper ends are displaced in a tangential direction in relation to their lower ends, so as to form a helix. In this way, the coolant is forced to rotate around the steam conducting channel while at the same time moving upwards through the fuel assembly.
	description	1. Field of the Invention The present invention relates to a glass substrate for manufacturing a thermal-assisted magnetic recording disk and a thermal-assisted magnetic recording disk. 2. Description of the Related Art With an increase of amount of information to be handled in the recent information processing, the recording capacity of a magnetic recording disk such as the hard disk is increased with each passing year, with which the recording density of the magnetic recording disk is also increased year after year. For example, in recent years, even a magnetic recording disk having an ultra-high recording density of 100 gigabytes per inch has been developed. As a method of realizing the high recording density, it is often employed to lower the flying height of the magnetic head from the main surface of the magnetic recording disk. However, if there is an undulation with a period such that the magnetic head cannot approach the main surface of the magnetic recording disk, the flying height cannot be set beyond the surface roughness. To cope with the problem, for example, a technology for lowering the flying height is disclosed in Japanese Patent Application Laid-open No. 2000-200414, by suppressing the surface roughness of a glass substrate that becomes a base material for the magnetic recording disk with the average roughness of equal to or smaller than 1 nanometer and the maximum roughness of equal to or smaller than 15 nanometers. Another method of realizing the high recording density includes a method of using a thermal-assisted magnetic recording system. In this method, when performing a magnetic recording, a laser device installed at near field illuminates an area where information is to be recorded with a laser light to lower the coercivity by increasing the temperature of the area, so that the magnetization of the area by the magnetic head becomes easy. By employing this method, because the recording magnetic portion can be formed using magnetic material having a high stead-state coercivity, it is possible to increase the recording density by narrowing the width of each recording track of a magnetic recording disk while preventing a loss of magnetization due to thermal fluctuation. Hereinafter, the magnetic recording disk employing the thermal-assisted magnetic recording method is referred to as a thermal-assisted magnetic recording disk. However, in the thermal-assisted magnetic recording method, the temperature-elevated area is spread beyond the area where the recording is performed due to the thermal diffusion. As a result, a partial magnetization occurs also in a track adjacent to the recording track, resulting in a possibility of leading a degradation or a loss of data in the adjacent track, which is called the cross write. To cope with this problem, for example, in Japanese Patent Application Laid-open No. 2007-134004, a technology is disclosed in which the cross write is prevented by keeping an area where the temperature is elevated by the laser illumination from being spread to an adjacent recording track by separating each recording track with a non-magnetization portion having a thermal conductivity equal to or lower than one hundredth of that of the recording track. Nevertheless, the conventional thermal-assisted magnetic recording disk still has a problem of the cross write even when the non-magnetization portion is provided between the recording tracks. It is an object of the present invention to at least partially solve the problems in the conventional technology. According to one aspect of the present invention, there is provided a glass substrate for fabricating a thermal-assisted magnetic recording disk by forming a plurality of recording magnetization portions arranged in a concentric manner around a center of the glass substrate and a plurality of non-magnetization portions having a thermal conductivity lower than that of the recording magnetization portions each between adjacent recording magnetization portions along a circumferential direction on a main surface of the glass substrate. A mean squared roughness of a surface of an area where each of the non-magnetization portions is formed is equal to or smaller than 1 nanometer. Furthermore, according to another aspect of the present invention, there is provided a thermal-assisted magnetic recording disk including a glass substrate; a plurality of recording magnetization portions arranged in a concentric manner around a center of the glass substrate; and a plurality of non-magnetization portions having a thermal conductivity lower than that of the recording magnetization portions each between adjacent recording magnetization portions along a circumferential direction on a main surface of the glass substrate. A mean squared roughness of a surface of an area where each of the non-magnetization portions is formed is equal to or smaller than 1 nanometer. The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. Exemplary embodiments of a glass substrate and a thermal-assisted magnetic recording disk according to the present invention will be explained in detail below with reference to the accompanying drawings. It should be mentioned that the present invention is not to be considered limited to the embodiments. FIG. 1 is a schematic cross sectional diagram of a thermal-assisted magnetic recording disk 10 according to an embodiment of the present invention. As shown in FIG. 1, the thermal-assisted magnetic recording disk 10 (hereinafter, “magnetic recording disk 10”) includes a glass substrate 1 having a hole 1a at its center, a recording layer 2, and a protecting layer 3. The recording layer 2 and the protecting layer 3 are formed on the main surface of the glass substrate 1. The glass substrate 1 can be fabricated using, for example, glass ceramics such as amorphous glass and crystallized glass. However, based on a perspective of moldability and workability, it is preferable to use the amorphous glass. For example, it is desirable to use alumino-silicate glass, soda-lime glass, soda-lime alumino silicate glass, alumino-boro-silicate glass, boro-silicate glass, air-cooling-treated or liquid-cooling treated physical tempered glass, or chemical tempered glass. The protecting layer 3 is for protecting the recording layer 2 from the outside environment and is formed with dielectric material that is optically transparent with respect to a light having a wavelength of 400 nanometers, which is the wavelength of a laser light used in the thermal-assisted magnetic recording method, such as silicon nitride (SiN) and silicon dioxide (SiO2). FIG. 2 is a partial enlarged view of a boundary between the glass substrate 1 and the recording layer 2 in the magnetic recording disk 10 shown in FIG. 1. As shown in FIG. 2, the recording layer 2 includes a plurality of recording magnetization portions 21 and a plurality of non-magnetization portions 22. Each of the recording magnetization portions 21 is formed in a concentric manner around the hole 1a on a surface 11a of an area 11 of the glass substrate 1 to form a recording track of the magnetic recording disk 10. Each of the recording magnetization portions 21 is formed with magnetic material such as Co alloy, Fe alloy, or Tb—Co based rare earth transition metal amorphous alloy. Each of the recording magnetization portions 21 has a width of, for example, 140 nanometers and a thickness of, for example, 30 nanometers. Each of the non-magnetization portions 22 is formed in a concentric manner around the hole 1a on a surface 12a of an area 12 of the glass substrate 1, in a similar manner to each of the recording magnetization portions 21, and intervenes between the recording magnetization portions 21 along the circumferential direction. Each of the non-magnetization portions 22 is formed with dielectric material that is optically transparent with respect to a light having a wavelength of 400 nanometers, which is the wavelength of a laser light used in the thermal-assisted magnetic recording method, such as SiN and SiO2. Each of the non-magnetization portions 22 has a width, for example, 30 nanometers to 140 nanometers and a thickness of, for example, 30 nanometers. The thermal conductivity of each of the non-magnetization portions 22 is lower than the thermal conductivity of each of the recording magnetization portions 21, preferably be equal to or lower than one hundredth of the thermal conductivity of each of the recording magnetization portions 21, for example, 1×10−3 W/(m·K) to 1 W/(m·K). When recording information on the magnetic recording disk 10, an area of the recording magnetization portion 21 where the information is to be recorded is illuminated with a laser light to increase the temperature, and a magnetization is performed by a magnetic head in a state in which the coercivity of the area is lowered. At this time, because the thermal conductivity of the non-magnetization portion 22 of the magnetic recording disk 10 is low, a spread of the temperature-elevated area of the recording magnetization portion 21 due to the thermal diffusion to the adjacent recording magnetization portion 21 is suppressed, and as a result, the cross write is suppressed. In addition, because the mean squared roughness of the surface 12a of the area 12 of the magnetic recording disk 10 where the non-magnetization portion 22 is formed is equal to or smaller than 1 nanometer, the temperature rise of the non-magnetization portion 22 is prevented at the time of a laser illumination, and as a result, the cross write is more definitely suppressed. FIG. 3 is a schematic diagram for explaining a mechanism of operation of the present invention. A laser light L1 illuminated on the area of the recording magnetization portion 21 where the information is to be recorded causes the temperature of the area to be elevated. The thermal conduction in the recording magnetization portion 21 is expressed by Equation (1), where Q1 is incident energy on the recording magnetization portion 21 from the illumination of the laser light L1, T1 is temperature of the recording magnetization portion 21, k1 is thermal conductivity of the recording magnetization portion 21, T3 is temperature of the area 11 of the glass substrate 1, A1 is contact area between the recording magnetization portion 21 and the area 11, and x is thickness of the recording magnetization portion 21. Q 1 = k 1 ⁢ A 1 ⁢ T 1 - T 3 x ( 1 ) Between the temperature-elevated recording magnetization portion 21 and the non-magnetization portion 22, the thermal conduction is low because there is a difference in the thermal conductivity. On the other hand, a thermal radiation L2 is generated from the recording magnetization portion 21. The intensity I of the thermal radiation L2 is expressed by Equation (2), where a is a constant that is dependent on the material of the recording magnetization portion 21.I=aT14 (2) When the thermal radiation L2 reaches the surface 12a of the area 12 where the non-magnetization portion 22 is formed, a part of the thermal radiation L2 is converted into a heat due to the surface roughness of the surface 12a. The amount of heat generated at this time is expressed by Equation (3), where A2 is the contact area between the non-magnetization portion 22 and the area 12, α is a coefficient that is dependent on the material of the glass substrate 1, and t is the mean squared roughness of the surface 12a. Q2=A2I(1−e−αt) (3) The thermal conduction in the non-magnetization portion 22 is expressed by Equation (4), where k2 is the thermal conductivity of the non-magnetization portion 22, A2 is the contact area between the non-magnetization portion 22 and the area 12, T2 is the temperature of the non-magnetization portion 22, and T4 is the temperature of the area 12 of the glass substrate 1. Q 2 = k 2 ⁢ A 2 ⁢ T 2 - T 4 x ( 4 ) The temperature T4 can be estimated by Equation (5). T 4 = T 1 + T 3 2 ( 5 ) Therefore, by using the above equations, the temperature T2 cab be expressed by Equation (6). T 2 = xa k 2 ⁢ ( 1 - ⅇ - α ⁢ ⁢ t ) ⁢ T 1 4 + T 1 - Q 1 ⁢ x 2 ⁢ k 1 ⁢ A 1 ( 6 ) As shown in Equation (6), the temperature T2 of the non-magnetization portion 22 is dependent on the mean squared roughness t of the surface 12a of the area 12 where the non-magnetization portion 22 is formed. Therefore, if the mean squared roughness t is decreased, the temperature T2 is decreased. If the mean squared roughness t is equal to or smaller than 1 nanometer, the temperature T2 becomes sufficiently low, and as a result, the cross write can be more definitely suppressed. It means that the above result can be obtained if the mean squared roughness t is equal to or smaller than 1 nanometer, and the means squared roughness of the surface 11a of the area 11 where the recording magnetization portion 21 is formed is not particularly limited. In addition, if the surfaces 11a and 12a of the areas 11 and 12 where the recording magnetization portion 21 and the non-magnetization portion 22 are formed, respectively, have an average roughness equal to or smaller than 1 nanometer and the maximum roughness equal to or smaller than 15 nanometers, the flying height of the magnetic head can be kept low, which is desirable because the recording density can be increased. The glass substrate 1 having the mean squared roughness equal to or smaller than 1 nanometer can be fabricated as follows. A coring is performed on a glass plate that is a raw material to mold an annular-shaped glass substrate. The molded glass substrate is lapped using a known lapping machine that can lap both surfaces of the glass substrate at the same time. Then, the lapped glass substrate is polished to finally fabricate the glass substrate 1 having a desired thickness. When fabricating the glass plate as the raw material, a redraw method, in which a preform glass plate fabricated using a float method or the like is softened by heating the preform glass plate and drawn in a desired thickness, is employed, as disclosed in Japanese Patent Application Laid-open No. H11-199255, it is more preferable because a glass plate having an extremely small mean squared roughness can be easily fabricated. Embodiment examples and comparison examples of the present invention are explained below. However, the present invention is not to be considered limited to the embodiment examples. A 643-micrometer-thick glass plate made of alumino-silicate glass is fabricated using the redraw method, and an annular-shaped glass substrate is molded with the outer diameter of 65 millimeters and the inner diameter of 20 millimeters by coring the glass plate. A lapping and a polishing are performed on the glass substrate using a commercially available lapping and polishing machine with a plurality of different lapping and polishing conditions, and finally a 636-micrometer-thick glass substrate is fabricated. The surface roughness of the fabricated glass substrate is measured using an atomic force microscope, and four glass substrates having the maximum roughness of 15 nanometers, the average roughness of 1 nanometer, and different mean squared roughness with one another are selected. A recording magnetization portion made of Co alloy having a thickness of 30 nanometers and a width of 140 nanometers is formed on the main surface of the glass substrate in a plurality of tracks. A non-magnetization portion made of SiN having a thickness of 30 nanometers and a width of 140 nanometers is formed between the tracks, and a protecting layer is formed, to fabricate magnetic recording disks according to embodiment examples 1 to 3 and a comparison example 1. The mean squared roughness of the magnetic recording disks are 1 nanometer, 0.1 nanometer, and 0.5 nanometer for the embodiment examples 1 to 3, respectively, and 5 nanometers for the comparison example 1. An experiment of confirming an occurrence of the cross write is performed by applying the fabricated magnetic recording disks in a magnetic recording disk device. In this experiment, the wavelength and the power of a laser light is 400 nanometers and 0.5 milliwatt, respectively. And then, the temperatures of a recording magnetization portion and a non-magnetization portion are obtained when the recording magnetization portion is illuminated with the laser light. FIG. 4 is a table showing the maximum roughness Rmax, the average roughness Ra, the mean squared roughness Rq, the temperature difference T1−T2 between a recording magnetization portion and a non-magnetization portion, and the result of judging occurrence of the cross write of magnetic recording disks according to the embodiment examples 1 to 3 and the comparison example 1. As shown in FIG. 4, in the cases of the embodiment examples 1 to 3, the temperature difference T1−T2 is as large as equal to or higher than 150° C., and the cross write does not occur, resulting in a judgment of “GOOD” in all cases. However, in the case of the comparison example 1, the temperature difference T1−T2 is as small as 150° C., and the cross write occurs, resulting in a judgment of “BAD”. As described above, according to one aspect of the present invention, because the mean squared roughness of the surface area where the non-magnetization portion is to be formed is equal to or smaller than 1 nanometer, the temperature rise of the non-magnetization portion when the recording magnetization portion is illuminated with a laser is prevented. Therefore, it is possible to realize a glass substrate for manufacturing a thermal-assisted magnetic recording disk with a capability of definitely preventing the occurrence of the cross write and a thermal-assisted magnetic recording disk. Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
052271277	description	DESCRIPTION OF THE PREFERRED EMBODIMENT One preferred embodiment of the filtered venting system located in association with a reactor containment vessel according to the present invention will be described hereunder with reference to FIG. 1. Referring to FIG. 1, a filtered venting system 20 to countermeasure severe accidents is installed in a reactor building 21 of a light water reactor. In the reactor building 21, there is also installed a reactor containment vessel (RCV) 22, in which a reactor pressure vessel 23 is incorporated. A suppression pool 24 is arranged at a lower portion of the RCV 22 and the suppression pool 24 includes an gas chamber 24a to which a venting line 25 of the filtered venting system 20 is connected. To the venting line 25 are incorporated in order isolation valves 26, 26, a rupture disk 27 and a check 30 constructed as a filtering device. In the filter vessel 30 there are disposed a water filter 31 and a stainless fiber filter 32. The filter vessel 30 has a top portion from which a venting line 33 of downstream side extends, and to the venting line 33 are incorporated in order a check valve 34, a pressure control throttle 35 and a rapture disk 36 as an assembly to be connected to a stack, not shown, through which the venting line 33 opens to the external atmosphere. As described before, the venting line 25 disposed upstream side of the filter vessel 30 has one end communicated with the gas chamber 24a in the suppression pool 24 and the other end connected to the filter vessel 30. A line 39 of a stand-by gas treatment system (SGTS) 38, called hereinlater SGTS line 39, is connected at its one end to a portion of the venting line 25 disposed at the upstream side of the filter vessel 30. The SGTS line 39 has another end opened to an inner ambient atmosphere in the reactor building 21 and is equipped with at its intermediate portions in order, inlet or intake valves 40, outlet fans 41, isolation valves 42 and a check valve 43 all of the SGTS 38. Outlet valves 45 for the SGTS bypassing the rapture disk 36 are incorporated to the downstream side venting line 33. As described above, the stand-by gas treatment system (SGTS) 38 is integrated with the filtered venting system 20, thereby constituting an integrated filtered venting system as a single system. A bypass circuit 46 bypassing the isolation valves 26 and the rupture disk 27 is incorporated to the venting line 25 disposed upstream side of the filter vessel 30, and isolation valves 47 are assembled with this bypass circuit 46 for the venting operation of an operator. Concretely, the isolation valves 47 are disposed for the purpose such that the operator carries out the venting operation before the inner pressure of the RCV 22 reaches an actuating pressure of the rupture disk 27 or the operator carries out a back-up operation in case of failure of the rupture disk operation. Redundancy or multiplicativeness is applied to the dynamic equipments, except for the check valves 28, 34 and 43 and the rupture disks 27 and 36, which have to be operated after the accident. The filter vessel 30 includes a gas chamber 30a above the water filter 31, and an inert gas, preferably N.sub.2 gas, supply line 48 is communicated with the gas chamber 30a to supply the inert gas thereinto. The interior of the filter vessel 30 is filled up with the inert gas such as N.sub.2 during a reactor steady operation period by the supply of the N.sub.2 gas from the feed line 48 for preventing burnable gas such as H.sub.2 or CO gas contained in the atmosphere in the RCV 22 from burning in the filter vessel 30 after the accident. Further, a filter means of a kind other than that mentioned above, such as a sand filter, may be disposed in the filter vessel 30 in substitution for the stainless fiber filter 32, but it is not necessarily required to always fill the interior of the filter vessel 30 with N.sub.2 gas. In this case, it will be unnecessary to dispose the rapture disk 36 and the outlet valves 45 for the SGTS to the downstream side venting line 25. Furthermore, it may be possible to make redundant the check valve and the rapture disk for the improvement of the reliability of the system. A water feed line 50 is connected to the filter vessel 30, and in FIG. 1, reference numerals 51 and 52 denote a drain line and a deaerator line, respectively. The filtered venting system for the reactor containment vessel of the structure described above operates in the following manner. If the DBA occurs in the light water reactor of a nuclear power plant, at least one series of DGs are provided to be operative, and accordingly, the outlet fans 41, the inlet valves 40, the isolation valves 42 and the outlet valves 45 of the SGTS 38 can be made operative by the operation of the DG. Accordingly, the equipments such as outlet fans 41 start to operate automatically in response to a signal informing the detection of the occurrence of the DBA and the outlet fans 41 start to suck the ambient atmosphere in the reactor building 21. In this operation, since the outlet or exhaust line including the outlet fan or pump of the SGTS 38 according to this filtered venting system is connected to the venting line 25 disposed at the upstream side of the filter vessel 30 of the system 20, the sucked ambient atmosphere in the reactor building 21 is introduced into the filter vessel 30, in which the radioactive substance contained in the sucked atmosphere is then removed. The atmosphere cleaned by the filtering function of the filter vessel 30 is discharged externally into atmosphere through the stack, not shown. During this operation, the ambient atmosphere in the reactor building 21 is sucked from the SGTS 38 by the outlet fans 41 and then treated, so that the radioactive substance leaking at the DBA from the RCV 22 into the reactor building 21 can be prevented from further releasing into the external atmosphere, whereby the safeness to the public environment and people can be ensured. On the contrary, when the severe accident occurs, it is considered that the all DGs become unusable. In such a case, all the dynamic equipments including the outlet fans 41 and the inlet valves 40 of the SGTS 38 will become inoperative. Further, since the dynamic systems including such as a core cooling system become also inoperative, the core is damaged and the radioactive substance is released from the damaged nuclear fuel, and hence, there causes a fear of releasing the radioactive substance into the RCV 22 and the inner pressure in the RCV 22 becomes high pressure due to the decay heat released by the nuclear fuel. However, when the inner pressure reaches to a constant value, the rupture disk 27 operates to thereby deliver the atmosphere in the RCV 22 into the filter vessel 30 through the venting line 25. On the way of this flow of the atmosphere, the radioactive substance contained in the atmosphere of the RCV 22 can be fully removed in and by the filter vessel 30 and the cleaned atmosphere is then discharged into the environmental atmosphere through the stack. As described above, at the occurrence of the severe accident, the atmosphere in the RCV 22 can be automatically released into the environmental atmosphere in accordance with the increasing of the inner pressure in the RCV 22, so that any driving source such as a.c. power source for this purpose, whereby the pressure in the RCV 22 can be maintained to a value approximately of an atmospheric pressure and the soundness of the RCV 22 can thus be maintained. In the assumption of an occurrence of the severe accident, such a condition as that the radioactive substance is infinitively released into the environment can be preferably prevented, thus ensuring the safeness to the public. Moreover, as described hereinbefore, according to the integrated filtered venting system 20, the radioactive substance can be removed by utilizing the same filter vessel 30 in an occurrence of the DBA as well as the severe accident for ensuring and maintaining the safeness to the public. Furthermore, since the filtered venting system according to the present embodiment is provided with the safety function as the stand-by gas treating system essential to the occurrence of the DBA, the filtered venting system and, hence, the total power plant can be designed and installed as an engineered safety features in dependency on the safeness standard prescribed by a national standard with the high reliability and performance being maintained, whereby the reliability, such as redundant design or anti-earthquake design, of the venting function can be ensured at the occurrence of the severe accident. In the described preferred embodiment, the venting line 25 of the filtered venting system 20 is connected to the gas chamber 24a in the suppression pool 24, the venting line 25 may be communicated with a drywell 54 defined in the RCV 22. Furthermore, many other changes or modifications for the arrangements of the outlet fans 41, the inlet valves 40, the isolation valves 42 and the line 39 for the SGTS 38 may be made according to the present invention, and for one example, the outlet fans 41 may be substituted with outlet pump means.
	abstract	A compact high-gradient, very high energy electron (VHEE) accelerator and delivery system (and related processes) capable of treating patients from multiple beam directions with great speed, using all-electromagnetic or radiofrequency deflection steering is provided, that can deliver an entire dose or fraction of high-dose radiation therapy sufficiently fast to freeze physiologic motion, yet with a better degree of dose conformity or sculpting than conventional photon therapy. In addition to the unique physical advantages of extremely rapid radiation delivery, there may also be radiobiological advantages in terms of greater tumor or other target control efficacy for the same physical radiation dose.
	summary
048760560	abstract	A method and an apparatus are provided for measuring the flow rate of a fluid in a duct, for example in an under-sea crude oil pipeline, in which samples of a radioactive tracer are injected, at intervals, into the duct and the passage of the samples of tracer detected by a scintillator. The tracer is generated by irradiating a large volume of a liquid obtained from the environment of the duct with a neutron source, so that the sample has been irradiated for a prolonged period prior to injection.
	description	The present application is related to and claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Related Applications”) (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s)). For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of United States Patent Application entitled METHOD AND SYSTEM FOR THE THERMOELECTRIC CONVERSION OF NUCLEAR REACTOR GENERATED HEAT, naming RODERICK A. HYDE; MURIEL Y. ISHIKAWA; NATHAN P. MYHRVOLD; JOSHUA C. WALTER; THOMAS WEAVER; VICTORIA Y. H. WOOD AND LOWELL L. WOOD, JR. as inventors, filed Apr. 13, 2009, application Ser. No. 12/386,052, now U.S. Pat. No. 9,691,507 which is currently, or is an application of which a currently application is entitled to the benefit of the filing date. For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of United States Patent Application entitled METHOD, SYSTEM, AND APPARATUS FOR THE THERMOELECTRIC CONVERSION OF GAS COOLED NUCLEAR REACTOR GENERATED HEAT, naming RODERICK A. HYDE; MURIEL Y. ISHIKAWA; NATHAN P. MYHRVOLD; JOSHUA C. WALTER; THOMAS WEAVER; LOWELL L. WOOD, JR. AND VICTORIA Y. H. WOOD as inventors, filed Jul. 27, 2009, application Ser. No. 12/460,979, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of United States Patent Application entitled METHOD, SYSTEM, AND APPARATUS FOR THE THERMOELECTRIC CONVERSION OF GAS COOLED NUCLEAR REACTOR GENERATED HEAT, naming RODERICK A. HYDE; MURIEL Y. ISHIKAWA; NATHAN P. MYHRVOLD; JOSHUA C. WALTER; THOMAS WEAVER; LOWELL L. WOOD, JR. AND VICTORIA Y. H. WOOD as inventors, filed Jul. 28, 2009, application Ser. No. 12/462,054, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. Thermoelectric devices and materials can be utilized to convert heat energy to electric power. Thermoelectric devices are further known to be implemented within a nuclear fission reactor system, so as to convert nuclear fission reactor generated heat to electric power during reactor operation. In one aspect, a method includes but is not limited to, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy and supplying the electrical energy to at least one mechanical pump of the nuclear reactor system. In addition to the foregoing, other method aspects are described in the claims, drawings, and text forming a part of the present disclosure. In one or more various aspects, related systems include but are not limited to circuitry and/or programming for effecting the herein-referenced method aspects; the circuitry and/or programming can be virtually any combination of hardware, software, and/or firmware configured to effect the herein-referenced method aspects depending upon the design choices of the system designer. In one aspect, a system includes but is not limited to a means for, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy and a means for supplying the electrical energy to at least one mechanical pump of the nuclear reactor system. In addition to the foregoing, other system aspects are described in the claims, drawings, and text forming a part of the present disclosure. In one aspect, a system includes but is not limited to at least one thermoelectric device for converting nuclear reactor generated heat to electrical energy upon a nuclear reactor system shutdown event and at least one electrical output of the at least one thermoelectric device electrically coupled to at least one mechanical pump of the nuclear reactor system for supplying the electrical energy to the at least one mechanical pump of the nuclear reactor system. In addition to the foregoing, other system aspects are described in the claims, drawings, and text forming a part of the present disclosure. In addition to the foregoing, various other method and/or system and/or program product aspects are set forth and described in the teachings such as text (e.g., claims and/or detailed description) and/or drawings of the present disclosure. The foregoing is a summary and thus may contain simplifications, generalizations, inclusions, and/or omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is NOT intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes and/or other subject matter described herein will become apparent in the teachings set forth herein. In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. Referring generally to FIGS. 1A through 1G, a system 100 for the thermoelectric conversion of nuclear reactor generated heat upon a nuclear reactor shutdown event 110 is described in accordance with the present disclosure. Upon a shutdown event 110 (e.g., routine shutdown or emergency shutdown) of a nuclear reactor system 100, a thermoelectric device 104 (e.g., a junction of two materials with different Seebeck coefficients) may convert heat (e.g., operational heat, decay heat, or residual heat) produced by the nuclear reactor 102 of the nuclear reactor system 100 to electrical energy. Then, the electrical output 108 of the thermoelectric device 104 may supply electrical energy to a mechanical pump 106 of the nuclear reactor system 100. In embodiments, the nuclear reactor 102 of the nuclear reactor system 100 may include, but is not limited to, a thermal spectrum nuclear reactor, a fast spectrum nuclear reactor, a multi-spectrum nuclear reactor, a breeder reactor, or a traveling wave reactor. For example, the heat produced from a thermal spectrum nuclear reactor may be thermoelectrically converted to electrical energy via one or more than one thermoelectric device 104. Then, the electrical output 108 of the thermoelectric device may be used to supply electrical energy to a mechanical pump 106 of the nuclear reactor system 100. By way of further example, the heat produced from a traveling wave nuclear reactor may be thermoelectrically converted to electrical energy via one or more than one thermoelectric device 104. Then, the electrical output 108 of the thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of the nuclear reactor system 100. In another embodiment, the nuclear reactor shutdown event 110 may be established by a signal from an operator. For example, the nuclear reactor shutdown event may be established by a remote signal, such as a wireline signal (e.g., copper wire signal or fiber optic cable signal) or a wireless signal (e.g., radio frequency signal) from an operator (e.g., human user). Then, upon establishing the nuclear reactor shutdown event 110 via a signal from an operator, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. In another embodiment, the nuclear reactor shutdown event 110 may be established by a reactor control system (e.g., a system of microprocessors or computers programmed to monitor and respond to specified reactor conditions, such as temperature). For instance, the nuclear reactor shutdown event may be established by a wireline signal (e.g., digital signal from microprocessor) sent from a reactor control system. In a further embodiment, the reactor control system may be responsive to one or more signals from a safety system (e.g., thermal monitoring system, radiation monitoring system, pressure monitoring system, or security system). For instance, at a critical temperature a safety system may send a digital signal to the reactor control system. In turn, the nuclear reactor shutdown event may be established via a signal from the reactor control system. In a further embodiment, the safety system of the nuclear reactor system may be responsive to a sensed condition of the nuclear reactor system 100. For example, the safety system of the nuclear reactor system 100 may be responsive to one or more external conditions (e.g., loss of heat sink, security breach, or loss of external power supply to support systems) or one or more internal conditions (e.g., reactor temperature or core radiation levels). By way of further example, the safety system, upon sensing a loss of heat sink, may send a signal to the reactor control system. In turn, the reactor control system may establish the nuclear reactor shutdown event 110. Then, upon establishing the nuclear reactor shutdown event 110 via a signal from a reactor control system, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. In an embodiment, upon a nuclear reactor shutdown event 110, nuclear reactor generated heat may be converted to electrical energy via a thermoelectric device 104 placed in thermal communication (e.g., placed in thermal communication ex-situ or in-situ) with a portion of the nuclear reactor system 100. For example, the thermoelectric device 104 may be placed in thermal communication with a portion of the nuclear reactor system 100 during the construction of the nuclear reactor system 100. By way of further example, the nuclear reactor system 100 may be retrofitted such that a thermoelectric device 104 may be placed in thermal communication with a portion of the nuclear reactor system 100. Further, the thermoelectric device 104 may be placed in thermal communication with a portion of the nuclear reactor system 100 during operation of the nuclear reactor system 100 via a means of actuation (e.g., thermal expansion, electromechanical actuation, piezoelectric actuation, mechanical actuation). Then, a thermoelectric device 104 in thermal communication with a portion of the nuclear reactor system 100 may convert nuclear reactor generated heat to electrical energy. In another embodiment, upon a nuclear reactor shutdown event 110, nuclear reactor generated heat may be converted to electrical energy via a thermoelectric device 104 having a first portion 124 in thermal communication with a first portion 125 of the nuclear reactor system 100 and a second portion 126 in thermal communication with a second portion 127 of the nuclear reactor system 100. For example, the first portion 124 of the thermoelectric device 104 may be in thermal communication with a heat source 128 of the nuclear reactor system. By way of further example, the heat source 128 may include, but is not limited to, a nuclear reactor core, a pressure vessel, a containment vessel, a coolant loop, a coolant pipe, a heat exchanger, or a coolant of the coolant system 154 of the nuclear reactor system 100. In another embodiment, the second portion 127 of the nuclear reactor system may be at a temperature lower than the first portion 125 of the nuclear reactor system 100. For example, the first portion 125 of the nuclear reactor system 100 may comprise a portion of the primary coolant system (e.g., at a temperature above 300° C.) of the nuclear reactor system 100 and the second portion 127 of the nuclear reactor system 100 may comprise a portion of a condensing loop (e.g., at a temperature below 75° C.) of the nuclear reactor system 100. By way of further example, the second portion 127 of the nuclear reactor system 100 may include, but is not limited to, a coolant loop, a coolant pipe, a heat exchanger, a coolant of a coolant system 154, or an environmental reservoir (e.g., a lake, a river, or a subterranean structure). For instance, a first portion 124 of a thermoelectric device 104 may be in thermal communication with a heat exchanger of the nuclear reactor system 100 and the second portion 126 of the thermoelectric device 104 may be in thermal communication with an environmental reservoir, such as a lake. In another embodiment, the thermoelectric device 104 and a portion of the nuclear reactor system 100 may both be in thermal communication with a means for optimizing thermal conduction 162 (e.g., thermal paste, thermal glue, thermal cement, or other highly thermally conductive materials) between the thermoelectric device 104 and the portion of the nuclear reactor system 100. For example, the first portion 124 of the thermoelectric device 104 may be contacted to the first portion 125 of the nuclear reactor system 100 using thermal cement. In an embodiment, the thermoelectric device 104 used to convert nuclear reactor generated heat to electrical energy may comprise at least one thermoelectric junction 117 (e.g., a thermocouple or other device formed from a junction of more than one material each with different Seebeck coefficients). For example, the thermoelectric junction 117 may include, but is not limited to, a semiconductor-semiconductor junction (e.g., p-type/p-type junction or n-type/n-type junction) or a metal-metal junction (e.g., copper-constantan). By further example, the semiconductor-semiconductor junction may include a p-type/n-type semiconductor junction (e.g., p-doped bismuth telluride/n-doped bismuth telluride junction, p-doped lead telluride/n-doped lead telluride junction, or p-doped silicon germanium/n-doped silicon germanium junction). In another embodiment, the thermoelectric device 104 used to convert nuclear reactor generated heat to electrical energy may comprise at least one nanofabricated thermoelectric device 121 (i.e., a device wherein the thermoelectric effect is enhanced due to nanoscale manipulation of its constituent materials). For example, the nanofabricated device may include, but is not limited to, a device constructed in part from a quantum dot material (e.g., PbSeTe), a nanowire material (e.g., Si), or a superlattice material (e.g., Bi2Te3/Sb2Te3). In another embodiment, the thermoelectric device 104 used to convert nuclear reactor generated heat to electrical energy may comprise a thermoelectric device optimized for a specified range of operating characteristics 122. For example, the thermoelectric device optimized for a specified range of operating characteristics 122 may include, but is not limited to, a thermoelectric device having an output efficiency optimized for a specified range of temperature. For instance, the thermoelectric device 104 may include a thermoelectric device with a maximum efficiency between approximately 200° C. and 500° C., such as a thermoelectric device comprised of thallium doped lead telluride. It will be appreciated in light of the description provided herein, that a nuclear reactor system 100 incorporating a thermoelectric device 104 may incorporate a thermoelectric device having a maximum output efficiency within the operating temperature range of the nuclear reactor system 100. In another embodiment, the heat generated by the nuclear reactor 102 may be converted to electrical energy using a first thermoelectric device optimized for a first range of operating characteristics and a second thermoelectric device optimized for a second range of operating characteristics 123. For example, the output efficiency of a first thermoelectric device may be optimized for a first range in temperature and the output efficiency of a second thermoelectric device may be optimized for a second range in temperature. For instance, the nuclear reactor generated heat may be converted to electrical energy using a first thermoelectric device having a maximum efficiency between approximately 500° and 600° C. and a second thermoelectric device having a maximum efficiency between approximately 400° and 500° C. In a further embodiment, the heat generated by the nuclear reactor 102 may be converted to electrical energy using a first thermoelectric device optimized for a first range of operating characteristics, a second thermoelectric device optimized for a second range of operating characteristics, and up to and including a Nth device optimized for a Nth range of operating characteristics. For instance, the nuclear reactor generated heat may be converted to electrical energy using a first thermoelectric device with a maximum efficiency between approximately 200° and 300° C., a second thermoelectric device with a maximum efficiency between approximately 400° and 500° C., and a third thermoelectric device with a maximum efficiency between approximately 500° and 600° C. In another embodiment, the heat generated by the nuclear reactor 102 may be converted to electrical energy using two or more series coupled thermoelectric devices 104. For example, the heat generated by the nuclear reactor 102 may be converted to electrical energy using a first thermoelectric device S1 and a second thermoelectric device S2, where the first thermoelectric device S1 and the second thermoelectric device S2 are electrically coupled in series. By way of further example, the heat generated by the nuclear reactor 102 may be converted to electrical energy using a first thermoelectric device S1, a second thermoelectric device S2, a third thermoelectric device S3, and up to and including an Nth thermoelectric device SN, where the first thermoelectric device S1, the second thermoelectric device S2, the third thermoelectric device S3, and the Nth thermoelectric device SN are electrically coupled in series. In another embodiment, the heat generated by the nuclear reactor 102 may be converted to electrical energy using two or more parallel coupled thermoelectric devices 104. For example, the heat generated by the nuclear reactor 102 may be converted to electrical energy using a first thermoelectric device P1 and a second thermoelectric device P2, where the first thermoelectric device P1 and the second thermoelectric device P2 are electrically coupled in parallel. By way of further example, the heat generated by the nuclear reactor 102 may be converted to electrical energy using a first thermoelectric device P1, a second thermoelectric device P2, a third thermoelectric device P3, and up to and including an Nth thermoelectric device PN, where the first thermoelectric device P1, the second thermoelectric device P2, the third thermoelectric device P3, and the Nth thermoelectric device PN are electrically coupled in parallel. In another embodiment, the heat generated by the nuclear reactor 102 may be converted to electrical energy using one or more than one thermoelectric module 148. For example, a thermoelectric module in thermal communication with the nuclear reactor system 100 (e.g., first portion of a thermoelectric module in thermal communication with a heat source 128 and the second portion of a thermoelectric module in thermal communication with an environmental reservoir 140) may convert nuclear reactor generated heat to electrical energy. For example, the thermoelectric module 148 may comprise a prefabricated network of parallel coupled thermoelectric devices, series coupled thermoelectric devices, and combinations of parallel coupled and series coupled thermoelectric devices. By way of further example, a thermoelectric module 148 may include a first set of parallel coupled thermoelectric devices, a second set of parallel coupled thermoelectric devices, and up to and including a Mth set of parallel coupled thermoelectric devices, where the first set of devices, the second set of devices, and the Mth set of devices are electrically coupled in series. By way of further example, a thermoelectric module 148 may include a first set of series coupled thermoelectric devices, a second set of series coupled thermoelectric devices, and up to and including a Mth set of series coupled thermoelectric devices, where the first set of devices, the second set of devices, and the Mth set of devices are electrically coupled in parallel. In an embodiment, the heat generated by the nuclear reactor 102 may be converted to electrical energy using one or more than one thermoelectric device sized to meet a selected operational requirement 150 of the nuclear reactor system 100. For example, the thermoelectric device may be sized to partially match the heat rejection of the thermoelectric device with a portion of the heat produced by the nuclear reactor system 100. For instance, the thermoelectric device may be sized by adding or subtracting the number of thermoelectric junctions 117 used in the thermoelectric device 104. By way of further example, the thermoelectric device may be sized to match the power requirements of a selected operating system (e.g., control system, safety system, or coolant system). For instance, the thermoelectric device may be sized to match the mechanical pump power requirements of a coolant system 154 of the nuclear reactor system 100. In certain embodiments, the thermoelectric device 104 used to convert heat produced by the nuclear reactor system 100 to electrical energy may be protected via regulation circuitry 170, such as voltage regulation circuitry (e.g., voltage regulator), current limiting circuitry (e.g., blocking diode or fuse), or bypass circuitry (e.g., bypass diode or active bypass circuitry). For example, the regulation circuitry used to protect the thermoelectric device 104 may include a fuse, wherein the fuse is used to limit current from passing through a short-circuited portion of a set of two or more thermoelectric devices 104. In a further embodiment, bypass circuitry configured to actively electrically bypass one or more than one thermoelectric device 104 may be used to protect one or more than one thermoelectric device 104. For example, the bypass circuitry configured to actively electrically bypass a thermoelectric device 104 may include, but is not limited to, an electromagnetic relay system, a solid state relay system, a transistor, or a microprocessor controlled relay system. By way of further example, the microprocessor controlled relay system used to electrically bypass a thermoelectric device 104 may be responsive to an external parameter (e.g., signal from an operator) or an internal parameter (e.g., current flowing through a specified thermoelectric device). In another embodiment, one or more than one thermoelectric device 104 used to convert heat produced by the nuclear reactor system 100 to electrical energy may be augmented by one or more than one reserve thermoelectric device 188 (e.g., a thermoelectric junction or a thermoelectric module) and reserve actuation circuitry 189. For example, the electrical output 108 of one or more than one thermoelectric device 104 may be augmented using the output of a reserve thermoelectric device 188, where the one or more than one reserve thermoelectric device may be selectively coupled to one or more than one thermoelectric device 104 using reserve actuation circuitry 189. For example, in the event a first thermoelectric device 104 of a set of thermoelectric devices fails, a reserve thermoelectric device may be coupled to the set of thermoelectric devices in order to augment the output of the set of thermoelectric devices. By way of further example, the reserve actuation circuitry 189 used to selectively couple the one or more reserve thermoelectric devices 188 with the one or more thermoelectric devices 104 may include, but is not limited to, a relay system, an electromagnetic relay system, a solid state relay system, a transistor, a microprocessor controlled relay system, a microprocessor controlled relay system programmed to respond to an external parameter (e.g., required electrical power output of nuclear reactor system 100 or availability of external electric grid power), or a microprocessor controlled relay system programmed to respond to an internal parameter (e.g., output of one or more than one thermoelectric device 104). In another embodiment, the electrical output 108 of one or more than one thermoelectric device 104 used to convert heat produced by the nuclear reactor system 100 to electrical energy may be modified using power management circuitry. For example, the power management circuitry 197 used to modify the electrical output 108 of a thermoelectric device 104 may include, but is not limited to, a power converter, voltage converter (e.g., a DC-DC converter or a DC-AC inverter), or voltage regulation circuitry. By way of further example, the voltage regulation circuitry used to modify the electrical output 108 of a thermoelectric device 104 may include, but is not limited to, a Zener diode, a series voltage regulator, a shunt regulator, a fixed voltage regulator or an adjustable voltage regulator. In an embodiment, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy during initiation of a nuclear reactor shutdown. For example, during initiation of a routine nuclear reactor shutdown (e.g., scheduled shutdown) or an emergency nuclear reactor shutdown (e.g., SCRAM), the thermoelectric device 104 may convert heat produced by the nuclear reactor system to electrical energy. In another embodiment, preceding initiation of a nuclear reactor shutdown, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. For example, preceding initiation of a routine nuclear reactor shutdown or emergency nuclear reactor shutdown, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. In an additional embodiment, following initiation of a nuclear reactor shutdown, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. For example, following initiation of a routine nuclear reactor shutdown or emergency nuclear reactor shutdown, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. In another embodiment, upon a nuclear reactor shutdown event 110, nuclear reactor generated decay heat may be thermoelectrically converted to electrical energy. For example, after the shutdown of a nuclear reactor system 100, a thermoelectric device 104 may convert the persisting radioactive decay heat to electrical energy. Then, the electrical output 108 of the thermoelectric device may be used to power the mechanical pump 106. In an additional embodiment, upon a nuclear reactor shutdown event 110, nuclear reactor generated residual heat may be thermoelectrically converted to electrical energy. For example, after the shutdown of a nuclear reactor system 100, a thermoelectric device 104 may convert the residual heat of the nuclear reactor to electrical energy. Then, the electrical output 108 of the thermoelectric device may be used to power the mechanical pump 106. In an embodiment, the electrical output 108 of a thermoelectric device 104 may supply electrical energy to a mechanical pump 106 circulating coolant through a portion of the reactor core or a heat exchanger 162 of the nuclear reactor system 100. For example, the electrical output 108 of a thermoelectric device 104 may supply electrical energy to a mechanical pump 106 circulating coolant through the heat exchanger between the primary coolant loop and an intermediate coolant system of a nuclear reactor system 100. In another embodiment, the electrical output 108 of a thermoelectric device 104 may supply electrical energy to a mechanical pump 106 circulating a pressurized gas coolant (e.g., helium, nitrogen, supercritical CO2, or steam) of a coolant system 154 of a nuclear reactor system 100. For example, the electrical output 108 of a thermoelectric device 104 may supply electrical energy to a mechanical pump 106 circulating pressurized helium through the primary coolant system of a nuclear reactor system 100. In another embodiment, the electrical output 108 of a thermoelectric device 104 may supply electrical energy to a mechanical pump 106 circulating a liquid coolant of a coolant system 154 of the nuclear reactor system 100. For example, the liquid coolant circulated by the mechanical pump 106 may include, but is not limited to, a liquid metal coolant (e.g., liquid sodium, liquid lead, or liquid lead bismuth), a liquid salt coolant (e.g., lithium fluoride or other fluoride salts), or a liquid water coolant. Further, the mechanical pump 106 may circulate a liquid coolant through a coolant pool of a pool-type nuclear reactor system 100. For instance, the mechanical pump 106 may circulate liquid sodium in a pool-type breeder nuclear reactor system 100. In another embodiment, the electrical output 108 of a thermoelectric device 104 may supply electrical energy to a mechanical pump 106 circulating a mixed phase coolant of a coolant system 154 of the nuclear reactor system 100. For example, the mechanical pump 106 may circulate a gas-liquid (e.g., steam-liquid water) mixed phase coolant of a coolant system 154 of a nuclear reactor system 100. In another embodiment, the electrical output 108 of a thermoelectric device 104 may be used to partially drive a mechanical pump 106 of the nuclear reactor system 100. For example, the electrical output 108 of a thermoelectric device 104 may partially drive a mechanical pump 106 coupled to a coolant system 154 (e.g., primary coolant system or secondary coolant system) of the nuclear reactor system 100. In an embodiment, the electrical output 108 of a thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of a nuclear reactor system 100 and coupled in series with an additional mechanical pump. For example, a first mechanical pump 106 may be driven by the electrical output 108 of a thermoelectric device and may, in combination with a series connected additional mechanical pump, circulate a coolant through a coolant system 154 of the nuclear reactor system 100. In another embodiment, the electrical output 108 of a thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of a nuclear reactor system 100 and coupled in parallel with an additional mechanical pump. For example, a first mechanical pump 106 may be driven by the electrical output 108 of a thermoelectric device and may, in combination with a parallel connected additional mechanical pump, circulate a coolant through a coolant system of the nuclear reactor system 100. In another embodiment, the electrical output 108 of a thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 in order to provide supplemental pumping power 157 to the coolant system 154. For example, the mechanical pump 106 driven by the electrical output 108 of the thermoelectric device 104 may be used to supplement the pumping power of another mechanical pump. For instance, during partial loss of external electric power, in which external grid power to a first mechanical pump partially fails, the electrical output 108 of one or more than one thermoelectric device 104 may be used to drive a second mechanical pump 106 in order to supplement the pumping power 157 of the first mechanical pump. By way of further example, the supplemental pumping power 157 provided by a mechanical pump 106 driven by the electrical output 108 of a thermoelectric device 104 may be used to enhance the mass flow rate of coolant in a coolant system 154. In another embodiment, the electrical output 108 of a thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 in order to provide auxiliary pumping power 159 to the coolant system 154. For example, during malfunction of a first mechanical pump, in which the first mechanical pump totally fails, the electrical output 108 of one or more than one thermoelectric device 104 may be used to drive a second mechanical pump 106 in order to provide auxiliary pumping power 159 to the coolant system 154 of the nuclear reactor system 100. By way of further example, the auxiliary pumping power 159 provided by a mechanical pump 106 driven by the electrical output 108 of a thermoelectric device 104 may be used to establish a mass flow rate of coolant in a coolant system 154. By way of further example, a mass flow rate may be established by a mechanical pump 106 driven by the electrical output 108 of the thermoelectric device 104, where the mass flow rate is established in order to maintain coolant circulation in a coolant system 154 of the nuclear reactor system 100. For instance, the established coolant mass flow rate may maintain coolant circulation in a portion of the nuclear reactor system 100, including, but not limited to, a reactor coolant pool, a reactor coolant pressure vessel, a reactor heat exchange loop, or an ambient coolant reservoir. By way of further example, a mechanical pump 106 driven by the electrical output 108 of a thermoelectric device 104 may be used to establish a mass flow rate 160 in a liquid sodium coolant of a primary coolant loop of a nuclear reactor system 100 in order to maintain circulation of the liquid sodium coolant. Following are a series of flowcharts depicting implementations. For ease of understanding, the flowcharts are organized such that the initial flowcharts present implementations via an example implementation and thereafter the following flowcharts present alternate implementations and/or expansions of the initial flowchart(s) as either sub-component operations or additional component operations building on one or more earlier-presented flowcharts. Those having skill in the art will appreciate that the style of presentation utilized herein (e.g., beginning with a presentation of a flowchart(s) presenting an example implementation and thereafter providing additions to and/or further details in subsequent flowcharts) generally allows for a rapid and easy understanding of the various process implementations. In addition, those skilled in the art will further appreciate that the style of presentation used herein also lends itself well to modular and/or object-oriented program design paradigms. FIG. 2 illustrates an operational flow 200 representing example operations related to the thermoelectric conversion of nuclear reactor generated heat to electrical energy upon a nuclear reactor system shutdown event. In FIG. 2 and in following figures that include various examples of operational flows, discussion and explanation may be provided with respect to the above-described examples of FIG. 1, and/or with respect to other examples and contexts. However, it should be understood that the operational flows may be executed in a number of other environments and contexts, and/or in modified versions of FIG. 1. Also, although the various operational flows are presented in the sequence(s) illustrated, it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. After a start operation, the operational flow 200 moves to a converting operation 210. Operation 210 depicts, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy. For example, as shown in FIG. 1, upon a shutdown event 110 of a nuclear reactor system 100, a thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. Then, supplying operation 220 depicts supplying the electrical energy to at least one mechanical pump of the nuclear reactor system. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of the nuclear reactor system 100. FIG. 3 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 3 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 302, an operation 304, and/or an operation 306. At operation 302, nuclear reactor generated heat may be thermoelectrically converted to electrical energy during initiation of a nuclear reactor shutdown. For example, as shown in FIG. 1, during initiation of a nuclear reactor shutdown 102, a thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. At operation 304, nuclear reactor generated heat may be thermoelectrically converted to electrical energy preceding initiation of a nuclear reactor shutdown. For example, as shown in FIG. 1, preceding initiation of a nuclear reactor shutdown 102, a thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. At operation 306, nuclear reactor generated heat may be thermoelectrically converted to electrical energy following initiation of a nuclear reactor shutdown. For example, as shown in FIG. 1, following initiation of a nuclear reactor shutdown 102, a thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 4 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 4 illustrates example embodiments where the converting operation 210 may include at least one additional operation. Additional operations may include an operation 402, an operation 404, and/or an operation 406. At operation 402, upon a nuclear reactor system shutdown event, nuclear reactor generated decay heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 may convert radioactive decay heat produced by the nuclear reactor system 100 to electrical energy. At operation 404, upon a nuclear reactor system shutdown event, residual nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 may convert residual heat produced by the nuclear reactor system 100 to electrical energy. At operation 406, upon a nuclear reactor system shutdown event established by at least one signal from an operator, nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, a nuclear reactor system shutdown event 110 may be established by at least one signal from an operator 111 (e.g., a human user). Upon establishing the nuclear shutdown event, a thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 5 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 5 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 502, an operation 504, an operation 506, and/or an operation 508. At operation 502, upon a nuclear reactor system shutdown event established by at least one reactor control system, nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, a nuclear reactor system shutdown event 110 may be established by a reactor control system 112. Upon establishing the nuclear shutdown event, a thermoelectric device 104 may then convert heat produced by the nuclear reactor system 100 to electrical energy. Further, at operation 504, upon a nuclear reactor system shutdown event established by a reactor control system responsive to a signal from a safety system, nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, a nuclear reactor system shutdown event 110 may be established by a reactor control system responsive to a signal (e.g., wireline signal or wireless signal) from a safety system 113 (e.g., security system or temperature monitoring system). Upon establishing the nuclear reactor shutdown event, a thermoelectric device 104 may then convert heat produced by the nuclear reactor system 100 to electrical energy. Further, at operation 506, upon a nuclear reactor system shutdown event established by a reactor control system responsive to a signal from a safety system, where the safety system is responsive to a sensed nuclear reactor system condition, nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, a nuclear reactor system shutdown event 110 may be established by a reactor control system responsive to a signal from a safety system 113, where the safety system is responsive to a sensed condition 114 of the nuclear reactor system 100. Upon establishing the nuclear reactor system shutdown event, a thermoelectric device 104 may then convert heat produced by the nuclear reactor system 100 to electric energy. Further, at operation 508, upon a nuclear reactor system shutdown event established by a reactor control system responsive to a signal from a safety system, where the safety system is responsive to a sensed external condition of the nuclear reactor system, nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, a nuclear reactor system shutdown event 110 may be established by a reactor control system responsive to a signal from a safety system 113, where the safety system is responsive to a sensed external condition 115 (e.g., security breach or access to external power supply) of the nuclear reactor system 100. Upon establishing the nuclear reactor system shutdown event, a thermoelectric device 104 may then convert heat produced by the nuclear reactor system 100 to electric energy. FIG. 6 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 6 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 602. Further, at operation 602, upon a nuclear reactor system shutdown event established by a reactor control system responsive to a signal from a safety system, where the safety system is responsive to a sensed internal condition of the nuclear reactor system, nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, a nuclear reactor system shutdown event 110 may be established by a reactor control system responsive to a signal from a safety system 113, where the safety system is responsive to a sensed internal condition 116 (e.g., temperature or radiation levels of reactor) of the nuclear reactor system 100. Upon establishing the nuclear reactor system shutdown event, a thermoelectric device 104 may then convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 7 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 7 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 702, an operation 704, an operation 706, and/or an operation 708. At operation 702, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least one thermoelectric device. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 placed in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. At operation 704, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least one thermoelectric junction. For instance, upon a nuclear reactor system shutdown event 110, a thermoelectric junction 117 (e.g., thermocouple) placed in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, at operation 706, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least one semiconductor-semiconductor junction. For example, as shown in FIG. 1, the thermoelectric device 104 may comprise a semiconductor-semiconductor thermoelectric junction 118 (e.g., p-type/p-type junction of different semiconductor materials). For instance, upon a nuclear reactor system shutdown event 110, a semiconductor-semiconductor junction 118 placed in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, at operation 708, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least one p-type/n-type semiconductor junction (e.g., p-doped lead telluride/n-doped lead telluride junction). For example, as shown in FIG. 1, the thermoelectric device may comprise a p-type/n-type semiconductor junction 119. For instance, upon a nuclear reactor system shutdown event 110, a p-type/n-type semiconductor junction placed in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 8 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 8 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 802. Further, at operation 802, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least one metal-metal thermoelectric junction. For example, as shown in FIG. 1, the thermoelectric device 104 may comprise a metal-metal thermoelectric junction 120 (e.g., copper-constantan junction). For instance, upon a nuclear reactor system shutdown event 110, a metal-metal thermoelectric junction 120 placed in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 9 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 9 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 902, an operation 904, and/or an operation 906. The operation 902 illustrates upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device, the thermoelectric device having at least a first portion in thermal communication with a first portion of the nuclear reactor system and at least a second portion in thermal communication with a second portion of the nuclear reactor system. For example, as shown in FIG. 1, a first portion 124 of a thermoelectric device 104 may be in thermal communication with a first portion 125 of a nuclear reactor system 100, while a second portion 126 of the thermoelectric device 104 may be in thermal communication with a second portion 127 of the nuclear reactor system. Then, upon a nuclear reactor system shutdown event 110, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, the operation 904 illustrates upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device, the thermoelectric device having at least a first portion in thermal communication with at least one heat source of the nuclear reactor system. For example, as shown in FIG. 1, the first portion 125 of the nuclear reactor system may comprise a heat source 128 of the nuclear reactor system 100. Therefore, a first portion of a thermoelectric device 124 may be in thermal communication with a heat source 128 of the nuclear reactor system 100. Then, upon a nuclear reactor system shutdown event 110, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, the operation 906 illustrates upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device, the thermoelectric device having at least a first portion in thermal communication with at least a portion of a nuclear reactor core, at least a portion of at least one pressure vessel, at least a portion of at least one containment vessel, at least a portion of at least one coolant loop, at least a portion of at least one coolant pipe, at least a portion of at least one heat exchanger, or at least a portion of the coolant of the nuclear reactor system. For example, as shown in FIG. 1, the first portion 125 of the nuclear reactor system 100 may include, but is not limited to, a nuclear reactor core 129, a pressure vessel 130 of the nuclear reactor system 100, a containment vessel 131 of the nuclear reactor system 100, a coolant loop 132 of the nuclear reactor system 100, a coolant pipe 133 of the nuclear reactor system, a heat exchanger 134 of the nuclear reactor system 100 or the coolant 135 of the nuclear reactor system 100. By way of further example, a first portion of a thermoelectric device 124 may be in thermal communication with a coolant loop 132 of the nuclear reactor system 100. Then, upon a nuclear reactor system shutdown event 110, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 10 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 10 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 1002, and/or an operation 1004. Further, the operation 1002 illustrates upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device, the thermoelectric device having at least a second portion in thermal communication with a second portion of the nuclear reactor system, the second portion of the nuclear reactor system at a lower temperature than the first portion of the nuclear reactor system. For example, as shown in FIG. 1, a second portion 126 of a thermoelectric device 104 may be in thermal communication with a second portion 127 of a nuclear reactor system 100, where the second portion 127 of the nuclear reactor system 100 is at a lower temperature than the first portion 124 of the nuclear reactor system 100. Then, upon a nuclear reactor system shutdown event 110, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, the operation 1004 illustrates upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device, the thermoelectric device having at least a second portion in thermal communication with at least a portion of at least one coolant loop, at least a portion of at least one coolant pipe, at least a portion of at least one heat exchanger, at least a portion of the coolant of the nuclear reactor system, or at least a portion of at least one environmental reservoir. For example, as shown in FIG. 1, the second portion 127 of the nuclear reactor system 100, which is at a temperature lower than the first portion 124 of the nuclear reactor system, may include, but is not limited to, a coolant loop 136 of the nuclear reactor system 100, a coolant loop 137 of the nuclear reactor system 100, a heat exchanger 138 of the nuclear reactor system 100, coolant 139 of the nuclear reactor system 100, or an environmental reservoir 140, such as a body of water. By way of further example, the second portion 126 of a thermoelectric device 104 may be in thermal communication with a coolant pipe 137 of the nuclear reactor system 100, where the coolant pipe 137 is at a temperature lower than the first portion of the nuclear reactor system 124. Then, upon a nuclear reactor system shutdown event 110, the thermoelectric device 104 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 11 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 11 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 1102, an operation 1104, an operation 1106, and/or an operation 1108. At operation 1102, upon a nuclear reactor system shutdown event, thermal spectrum nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 may convert heat generated by a thermal spectrum nuclear reactor 141 of a nuclear reactor system 100 to electrical energy. At operation 1104, upon a nuclear reactor system shutdown event, fast spectrum nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 may convert heat generated by a fast spectrum nuclear reactor 142 of a nuclear reactor system 100 to electrical energy. At operation 1106, upon a nuclear reactor system shutdown event, multi-spectrum nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 may convert heat generated by a multi-spectrum nuclear reactor 143 of a nuclear reactor system 100 to electrical energy. At operation 1108, upon a nuclear reactor system shutdown event, breeder nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 may convert heat generated by a breeder nuclear reactor 144 of a nuclear reactor system 100 to electrical energy. FIG. 12 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 12 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 1202, an operation 1204, an operation 1206, and/or an operation 1208. At operation 1202, upon a nuclear reactor system shutdown event, traveling wave nuclear reactor generated heat may be thermoelectrically converted to electrical energy. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 may convert heat generated by a traveling wave nuclear reactor 145 of a nuclear reactor system 100 to electrical energy. At operation 1204, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least two series coupled thermoelectric devices. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a first thermoelectric device S1 electrically coupled in series to a second thermoelectric device S2 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, a first thermoelectric device S1, a second thermoelectric device S2, a third thermoelectric device S3, and up to and including a Nth thermoelectric device SN may be used to convert nuclear reactor generated heat to electric energy, where the first thermoelectric device S1, the second thermoelectric device S2, the third thermoelectric device S3, and up to and including the Nth thermoelectric device SN are series coupled. At operation 1206, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least two parallel coupled thermoelectric devices. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a first thermoelectric device P1 electrically coupled in parallel to a second thermoelectric device P2 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, a first thermoelectric device P1, a second thermoelectric device P2, a third thermoelectric device P3, and up to and including a Nth thermoelectric device PN may be used to convert nuclear reactor generated heat to electric energy, where the first thermoelectric device P1, the second thermoelectric device P2, the third thermoelectric device P3, and up to and including the Nth thermoelectric device PN are parallel coupled. At operation 1208, upon a nuclear reactor system shutdown event, nuclear reactor generated heat may be converted to electrical energy using at least one thermoelectric module. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric module 148 placed in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. For example, a thermoelectric module may comprise a prefabricated network of a number of series coupled thermoelectric devices, a number of parallel coupled thermoelectric devices, or combinations of parallel coupled thermoelectric devices and series coupled thermoelectric devices. FIG. 13 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 13 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 1302, and/or an operation 1304. The operation 1302 illustrates, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device sized to meet at least one selected operational requirement of the nuclear reactor system. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 sized to meet an operational requirement 150 (e.g., electric power demand) of the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. The operation 1304 illustrates, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device sized to at least partially match the heat rejection of the at least one thermoelectric device with at least a portion of the heat produced by the nuclear reactor. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 sized to match the heat rejection 151 of the thermoelectric device with the heat produced by the nuclear reactor 102 of the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 14 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 14 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 1402, and/or an operation 1404. Further, the operation 1402 illustrates, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device sized to at least partially match the power requirements of at least one selected operation system. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 sized to match the power requirements of a selected operation system 152 (e.g., coolant system, control system, or security system) of the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. Further, the operation 1404 illustrates, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device sized to match the power requirements of at least one mechanical pump. For example, as shown in FIG. 1, upon a nuclear reactor system shutdown event 110, a thermoelectric device 104 sized to match the power requirements of a mechanical pump 153 (e.g., mechanical pump used to circulate coolant in the primary coolant system) of the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 15 illustrates an operational flow 1500 representing example operations related to the thermoelectric conversion of nuclear reactor generated heat to electrical energy upon a nuclear reactor system shutdown event. FIG. 15 illustrates an example embodiment where the example operational flow 200 of FIG. 2 may include at least one additional operation. Additional operations may include an operation 1510, an operation 1512, and/or an operation 1514. After a start operation, a converting operation 210, and a supplying operation 220, the operational flow 1500 moves to a driving operation 1510. Operation 1510 illustrates at least partially driving at least one mechanical pump. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a mechanical pump 106 of the nuclear reactor system 100. The operation 1512 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100. Further, the operation 1514 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system, the at least one mechanical pump in series with at least one additional mechanical pump. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a first mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100, where the first mechanical pump 106 is coupled in series 155 with a second mechanical pump. FIG. 16 illustrates alternative embodiments of the example operational flow 1500 of FIG. 15. FIG. 16 illustrates example embodiments where the operation 1510 may include at least one additional operation. Additional operations may include an operation 1602. Further, the operation 1602 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system, the at least one mechanical pump in parallel with at least one additional mechanical pump. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a first mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100, where the first mechanical pump 106 is coupled in parallel 156 with a second mechanical pump. FIG. 17 illustrates alternative embodiments of the example operational flow 1500 of FIG. 15. FIG. 17 illustrates example embodiments where the operation 1510 may include at least one additional operation. Additional operations may include an operation 1702, and/or an operation 1704. Further, the operation 1702 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system, the at least one mechanical pump supplying supplemental pumping power to the at least one coolant system. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100, where the mechanical pump 106 provides supplemental pumping power 157 to the coolant system 154. Further, the operation 1704 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system, the at least one mechanical pump supplying supplemental pumping power to the at least one coolant system, the supplemental pumping power enhancing a pumping mass flow rate. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100, where the mechanical pump 106 provides supplemental pumping power 157 to the coolant system 154 in order to enhance the pumping mass flow rate 158 of the coolant. FIG. 18 illustrates alternative embodiments of the example operational flow 1500 of FIG. 15. FIG. 18 illustrates example embodiments where the operation 1510 may include at least one additional operation. Additional operations may include an operation 1802, an operation 1804, and/or an operation 1806. Further, the operation 1802 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system, the at least one mechanical pump supplying auxiliary pumping power to the at least one coolant system. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100, where the mechanical pump 106 provides auxiliary pumping power 159 to the coolant system 154. Further, the operation 1804 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system, the at least one mechanical pump supplying auxiliary pumping power to the at least one coolant system, the auxiliary pumping power establishing a coolant mass flow rate. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100, where the mechanical pump 106 provides auxiliary pumping power 159 to the coolant system 154 in order to establish a mass flow rate of the coolant. Further, the operation 1806 illustrates at least partially driving at least one mechanical pump coupled to at least one coolant system of the nuclear reactor system, the at least one mechanical pump supplying auxiliary pumping power to the at least one coolant system, the auxiliary pumping power establishing a coolant mass flow rate, the coolant mass flow rate maintaining circulation in at least one reactor coolant pool, at least one reactor coolant pressure vessel, at least one reactor heat exchanger, or at least one ambient coolant. For example, as shown in FIG. 1, the electrical output 108 of the thermoelectric device 104 may be used to partially drive a mechanical pump 106 coupled to a coolant system 154 of the nuclear reactor system 100, where the mechanical pump 106 provides auxiliary pumping power 159 to the coolant system 154 in order to establish a coolant mass flow rate for maintaining circulation in a reactor coolant pool, a reactor coolant pressure vessel, a reactor heat exchange loop, or an ambient coolant. FIG. 19 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 19 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 1902. Further, the operation 1902 illustrates, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one nanofabricated thermoelectric device. For example, as shown in FIG. 1, the thermoelectric device 104 may comprise a nanofabricated thermoelectric device 121 (e.g., device constructed using a quantum well material, a nanowire material, or superlattice material). For instance, upon a nuclear reactor system shutdown event 110, a nanofabricated thermoelectric device 121 in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 20 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 20 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 2002. Further, the operation 2002 illustrates, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device optimized for a specified range of operating characteristics. For example, as shown in FIG. 1, the thermoelectric device 104 may comprise a thermoelectric device optimized for a specified range of operating characteristics 122 (e.g., temperature or pressure). For instance, upon a nuclear reactor system shutdown event 110, a thermoelectric device optimized for a specified range of operating characteristics 122 in thermal communication with the nuclear reactor system 100 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 21 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 21 illustrates example embodiments where the operation 210 may include at least one additional operation. Additional operations may include an operation 2102. Further, the operation 2102 illustrates, upon a nuclear reactor system shutdown event, thermoelectrically converting nuclear reactor generated heat to electrical energy using at least one thermoelectric device optimized for a first range of operating characteristics and at least one additional thermoelectric device optimized for a second range of operating characteristics, the second range of operating characteristics different from the first range of operating characteristics. For example, as shown in FIG. 1, a first thermoelectric device optimized for a first range of operating characteristics and a second thermoelectric device optimized for a second range of operating characteristics 123, wherein the first range of operating characteristics is different from the second range of operating characteristics, may be placed in thermal communication with the nuclear reactor system 100. For instance, upon a nuclear reactor system shutdown event 110, the first thermoelectric device and the second thermoelectric device 123 may convert heat produced by the nuclear reactor system 100 to electrical energy. FIG. 22 illustrates an operational flow 2200 representing example operations related to the thermoelectric conversion of nuclear reactor generated heat to electrical energy upon a nuclear reactor system shutdown event. FIG. 22 illustrates an example embodiment where the example operational flow 200 of FIG. 2 may include at least one additional operation. Additional operations may include an operation 2210. After a start operation, a converting operation 210, and a supplying operation 220, the operational flow 2200 moves to an optimizing operation 2210. Operation 2210 illustrates substantially optimizing the thermal conduction between a portion of at least one nuclear reactor system and a portion of at least one thermoelectric device. For example, as shown in FIG. 1, at the position of thermal communication between the thermoelectric device 104 and the nuclear reactor system 100, the thermal conduction between the thermoelectric device 104 and the nuclear reactor system 100 may be optimized. For example, the thermal conduction optimization 162 may include, but is not limited to, placing thermal paste, thermal glue, or a highly thermal conductive material between the thermoelectric device 104 and the nuclear reactor system 100. FIG. 23 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 23 illustrates example embodiments where the operation 220 may include at least one additional operation. Additional operations may include an operation 2302, an operation 2304, and/or an operation 2306. The operation 2302 illustrates supplying the electrical energy to at least one mechanical pump of the nuclear reactor system, the at least one mechanical pump circulating coolant through a portion of at least one nuclear reactor core or a portion of at least one heat exchanger. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a nuclear reactor system 100, wherein the mechanical pump 106 circulates coolant through a nuclear reactor core or a heat exchanger 162. The operation 2304 illustrates supplying the electrical energy to at least one mechanical pump of the nuclear reactor system, the at least one mechanical pump circulating at least one pressurized gas coolant. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a nuclear reactor system 100, wherein the mechanical pump 106 circulates a pressurized gas coolant 163 (e.g., helium) through a portion of the nuclear reactor system 100. The operation 2306 illustrates supplying the electrical energy to at least one mechanical pump of the nuclear reactor system, the at least one mechanical pump circulating a mixed phase coolant. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a nuclear reactor system 100, wherein the mechanical pump 106 circulates a mixed phase coolant 164 (e.g., mixture of gas and liquid coolant) through a portion of the nuclear reactor system 100. FIG. 24 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 24 illustrates example embodiments where the operation 220 may include at least one additional operation. Additional operations may include an operation 2402, and/or an operation 2404. The operation 2402 illustrates supplying the electrical energy to at least one mechanical pump of the nuclear reactor system, the at least one mechanical pump circulating at least one liquid coolant. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a nuclear reactor system 100, wherein the mechanical pump 106 circulates a liquid coolant 165 (e.g., liquid water) through a portion of the nuclear reactor system 100. Further, the operation 2404 illustrates supplying the electrical energy to at least one mechanical pump of the nuclear reactor system, the at least one mechanical pump circulating at least one liquid metal coolant. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a nuclear reactor system 100, wherein the mechanical pump 106 circulates a liquid metal coolant 166 (e.g., liquid sodium) through a portion of the nuclear reactor system 100. FIG. 25 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 25 illustrates example embodiments where the operation 220 may include at least one additional operation. Additional operations may include an operation 2502. Further, the operation 2502 illustrates supplying the electrical energy to at least one mechanical pump of the nuclear reactor system, the at least one mechanical pump circulating at least one liquid salt coolant. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a nuclear reactor system 100, wherein the mechanical pump 106 circulates a liquid salt coolant 167 (e.g., fluoride salts) through a portion of the nuclear reactor system 100. FIG. 26 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 26 illustrates example embodiments where the operation 220 may include at least one additional operation. Additional operations may include an operation 2602. Further, the operation 2602 illustrates supplying the electrical energy to at least one mechanical pump of the nuclear reactor system, the at least one mechanical pump circulating liquid water. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a nuclear reactor system 100, wherein the mechanical pump 106 circulates a liquid water coolant 168 through a portion of the nuclear reactor system 100. FIG. 27 illustrates alternative embodiments of the example operational flow 200 of FIG. 2. FIG. 27 illustrates example embodiments where the operation 220 may include at least one additional operation. Additional operations may include an operation 2702. Further, the operation 2702 illustrates supplying the electrical energy to at least one mechanical pump of a pool type nuclear reactor system. For example, as shown in FIG. 1, the electrical output 108 of a thermoelectric device 104 may be used to supply electrical energy to a mechanical pump 106 of a pool cooled 169 nuclear reactor system 100. FIG. 28 illustrates an operational flow 2800 representing example operations related to the thermoelectric conversion of nuclear reactor generated heat to electrical energy upon a nuclear reactor system shutdown event. FIG. 28 illustrates an example embodiment where the example operational flow 200 of FIG. 2 may include at least one additional operation. Additional operations may include an operation 2810, an operation 2812, an operation 2814, and/or an operation 2816. After a start operation, a converting operation 210, and a supplying operation 220, the operational flow 2800 moves to a protecting operation 2810. Operation 2810 illustrates protecting at least one thermoelectric device with regulation circuitry. For example, as shown in FIG. 1, one or more than one thermoelectric device 104 may be protected using regulation circuitry 170, such as voltage regulation circuitry (e.g., voltage regulator) or current limiting circuitry (e.g., blocking diode or fuse). The protecting operation 2812 illustrates protecting at least one thermoelectric device with bypass circuitry. For example, as shown in FIG. 1, one or more than one thermoelectric device 104 may be protected using bypass circuitry 172, such as a bypass diode. Further, the operation 2814 illustrates protecting at least one thermoelectric device with bypass circuitry configured to electrically bypass the at least one thermoelectric device. For example, as shown in FIG. 1, one or more than one thermoelectric device 104 may be protected using bypass circuitry configured to electrically bypass 174 one or more than one thermoelectric device 104. Further, the operation 2816 illustrates electrically bypassing the at least one thermoelectric device using at least one electromagnetic relay system, at least one solid state relay system, at least one transistor, at least one microprocessor controlled relay system, at least one microprocessor controlled relay system programmed to respond to at least one external parameter, or at least one microprocessor controlled relay system programmed to respond to at least one internal parameter. For example, as shown in FIG. 1, one or more than one thermoelectric device 104 may be electrically bypassed using an electromagnetic relay system 176, a solid state relay system 178, a transistor 180, a microprocessor controlled relay system 182, a microprocessor controlled relay system programmed to respond to one or more than one external parameters 184, or a microprocessor controlled relay system programmed to respond to one or more than one internal parameters 186. FIG. 29 illustrates an operational flow 2900 representing example operations related to the thermoelectric conversion of nuclear reactor generated heat to electrical energy upon a nuclear reactor system shutdown event. FIG. 29 illustrates an example embodiment where the example operational flow 200 of FIG. 2 may include at least one additional operation. Additional operations may include an operation 2910, and/or an operation 2912. After a start operation, a converting operation 210, and a supplying operation 220, the operational flow 2900 moves to an augmenting operation 2910. Operation 2910 illustrates selectively augmenting at least one thermoelectric device using at least one reserve thermoelectric device and reserve actuation circuitry configured to selectively couple the at least one reserve thermoelectric device to the at least one thermoelectric device. For example, as shown in FIG. 1, the electrical output from one or more than one thermoelectric device 104 may be augmented using one or more than one reserve thermoelectric device 188, where the one or more than one reserve thermoelectric device 188 may be selectively coupled to the thermoelectric device 104 using reserve actuation circuitry 189. The augmenting operation 2912 illustrates selectively coupling at least one reserve thermoelectric device to the at least one thermoelectric device using at least one relay system, at least one electromagnetic relay system, at least one solid state relay system, at least one transistor, at least one microprocessor controlled relay system, at least one microprocessor controlled relay system programmed to respond to at least one external parameter, or at least one microprocessor controlled relay system to respond to at least one internal parameter to the at least one thermoelectric device. For example, as shown in FIG. 1, the electrical output from one or more than one thermoelectric device 104 may be augmented using one or more than one reserve thermoelectric device 188, where the one or more than one reserve thermoelectric device 188 may be selectively coupled to the thermoelectric device 104 using a relay system 190, an electromagnetic relay system 191, a solid state relay system 192, a transistor 193, a microprocessor controlled relay system 194, a microprocessor controlled relay system programmed to respond to at least one external parameter 195, or a microprocessor controlled relay system programmed to respond to at least one internal parameter 196. FIG. 30 illustrates an operational flow 3000 representing example operations related to the thermoelectric conversion of nuclear reactor generated heat to electrical energy upon a nuclear reactor system shutdown event. FIG. 30 illustrates an example embodiment where the example operational flow 200 of FIG. 2 may include at least one additional operation. Additional operations may include an operation 3010, and/or an operation 3012. After a start operation, a converting operation 210, and a supplying operation 220, the operational flow 3000 moves to an output modifying operation 3010. Operation 3010 illustrates modifying the at least one thermoelectric device output using power management circuitry. For example, as shown in FIG. 1, the electrical output of a thermoelectric device 104 may be modified using power management circuitry, such as a voltage converter (e.g., DC-DC converter or DC-AC inverter). The operation 3012 illustrates modifying the at least one thermoelectric device output using voltage regulation circuitry. For example, as shown in FIG. 1, the electrical output of a thermoelectric device 104 may be modified using voltage regulation circuitry, such as a voltage regulator (e.g., Zener diode, an adjustable voltage regulator or a fixed voltage regulator). Those having skill in the art will recognize that the state of the art has progressed to the point where there is little distinction left between hardware, software, and/or firmware implementations of aspects of systems; the use of hardware, software, and/or firmware is generally (but not always, in that in certain contexts the choice between hardware and software can become significant) a design choice representing cost vs. efficiency tradeoffs. Those having skill in the art will appreciate that there are various vehicles by which processes and/or systems and/or other technologies described herein can be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle; alternatively, if flexibility is paramount, the implementer may opt for a mainly software implementation; or, yet again alternatively, the implementer may opt for some combination of hardware, software, and/or firmware. Hence, there are several possible vehicles by which the processes and/or devices and/or other technologies described herein may be effected, none of which is inherently superior to the other in that any vehicle to be utilized is a choice dependent upon the context in which the vehicle will be deployed and the specific concerns (e.g., speed, flexibility, or predictability) of the implementer, any of which may vary. Those skilled in the art will recognize that optical aspects of implementations will typically employ optically-oriented hardware, software, and or firmware. In some implementations described herein, logic and similar implementations may include software or other control structures. Electronic circuitry, for example, may have one or more paths of electrical current constructed and arranged to implement various functions as described herein. In some implementations, one or more media may be configured to bear a device-detectable implementation when such media hold or transmit device-detectable instructions operable to perform as described herein. In some variants, for example, implementations may include an update or modification of existing software or firmware, or of gate arrays or programmable hardware, such as by performing a reception of or a transmission of one or more instructions in relation to one or more operations described herein. Alternatively or additionally, in some variants, an implementation may include special-purpose hardware, software, firmware components, and/or general-purpose components executing or otherwise invoking special-purpose components. Specifications or other implementations may be transmitted by one or more instances of tangible transmission media as described herein, optionally by packet transmission or otherwise by passing through distributed media at various times. Alternatively or additionally, implementations may include executing a special-purpose instruction sequence or invoking circuitry for enabling, triggering, coordinating, requesting, or otherwise causing one or more occurrences of virtually any functional operations described herein. In some variants, operational or other logical descriptions herein may be expressed as source code and compiled or otherwise invoked as an executable instruction sequence. In some contexts, for example, implementations may be provided, in whole or in part, by source code, such as C++, or other code sequences. In other implementations, source or other code implementation, using commercially available and/or techniques in the art, may be compiled//implemented/translated/converted into a high-level descriptor language (e.g., initially implementing described technologies in C or C++ programming language and thereafter converting the programming language implementation into a logic-synthesizable language implementation, a hardware description language implementation, a hardware design simulation implementation, and/or other such similar mode(s) of expression). For example, some or all of a logical expression (e.g., computer programming language implementation) may be manifested as a Verilog-type hardware description (e.g., via Hardware Description Language (HDL) and/or Very High Speed Integrated Circuit Hardware Descriptor Language (VHDL)) or other circuitry model which may then be used to create a physical implementation having hardware (e.g., an Application Specific Integrated Circuit). Those skilled in the art will recognize how to obtain, configure, and optimize suitable transmission or computational elements, material supplies, actuators, or other structures in light of these teachings. The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transmission logic, reception logic, etc.), etc.). In a general sense, those skilled in the art will recognize that the various embodiments described herein can be implemented, individually and/or collectively, by various types of electro-mechanical systems having a wide range of electrical components such as hardware, software, firmware, and/or virtually any combination thereof; and a wide range of components that may impart mechanical force or motion such as rigid bodies, spring or torsional bodies, hydraulics, electro-magnetically actuated devices, and/or virtually any combination thereof. Consequently, as used herein “electro-mechanical system” includes, but is not limited to, electrical circuitry operably coupled with a transducer (e.g., an actuator, a motor, a piezoelectric crystal, a Micro Electro Mechanical System (MEMS), etc.), electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of memory (e.g., random access, flash, read only, etc.)), electrical circuitry forming a communications device (e.g., a modem, communications switch, optical-electrical equipment, etc.), and/or any non-electrical analog thereto, such as optical or other analogs. Those skilled in the art will also appreciate that examples of electro-mechanical systems include but are not limited to a variety of consumer electronics systems, medical devices, as well as other systems such as motorized transport systems, factory automation systems, security systems, and/or communication/computing systems. Those skilled in the art will recognize that electro-mechanical as used herein is not necessarily limited to a system that has both electrical and mechanical actuation except as context may dictate otherwise. In a general sense, those skilled in the art will recognize that the various aspects described herein which can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, and/or any combination thereof can be viewed as being composed of various types of “electrical circuitry.” Consequently, as used herein “electrical circuitry” includes, but is not limited to, electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of memory (e.g., random access, flash, read only, etc.)), and/or electrical circuitry forming a communications device (e.g., a modem, communications switch, optical-electrical equipment, etc.). Those having skill in the art will recognize that the subject matter described herein may be implemented in an analog or digital fashion or some combination thereof. Those skilled in the art will recognize that at least a portion of the devices and/or processes described herein can be integrated into a data processing system. Those having skill in the art will recognize that a data processing system generally includes one or more of a system unit housing, a video display device, memory such as volatile or non-volatile memory, processors such as microprocessors or digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices (e.g., a touch pad, a touch screen, an antenna, etc.), and/or control systems including feedback loops and control motors (e.g., feedback for sensing position and/or velocity; control motors for moving and/or adjusting components and/or quantities). A data processing system may be implemented utilizing suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems. One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken limiting. Although a user is shown/described herein as a single illustrated figure, those skilled in the art will appreciate that the user may be representative of a human user, a robotic user (e.g., computational entity), and/or substantially any combination thereof (e.g., a user may be assisted by one or more robotic agents) unless context dictates otherwise. Those skilled in the art will appreciate that, in general, the same may be said of “sender” and/or other entity-oriented terms as such terms are used herein unless context dictates otherwise. With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity. The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting, and/or logically interactable components. In some instances, one or more components may be referred to herein as “configured to,” “configurable to,” “operable/operative to,” “adapted/adaptable,” “able to,” “conformable/conformed to,” etc. Those skilled in the art will recognize that such terms (e.g., “configured to”) can generally encompass active-state components and/or inactive-state components and/or standby-state components, unless context requires otherwise. While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B. With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.
	claims	1. A system for detecting the presence of fissionable material, the system comprising:a source of radiation that is switchable between a screening mode and a verification mode, the source configured to:produce, in the screening mode, a first type of radiation having a first energy and a second type of radiation having a second energy, the second energy being higher than the first energy,direct, in the screening mode, the first type of radiation and the second type radiation toward a physical region, such that the first type of radiation propagates towards the physical region in a first direction and the second type of radiation propagates towards the physical region in a second direction that is substantially parallel to the first direction;produce, in the verification mode, a third type of radiation, anddirect, in the verification mode, the third type of radiation toward the physical region, the third type of radiation being sufficient to induce fission in a fissionable material;a sensor system comprising:a sensor configured to sense radiation comprising the first energy and the second energy from the physical region, anda sensor configured to sense a fission product; anda processor operable to:access data sensed by the sensor configured to sense radiation comprising the first energy and the second energy,determine, for the physical region represented by the accessed data, an absorption of the first type of radiation and the second type of radiation,determine whether the physical region is a region of interest based on the absorption, andcause the source of radiation to switch from the screening mode to the verification mode when the physical region is a region of interest. 2. The system of claim 1, wherein the first type of radiation is x-ray radiation, and the second type of radiation is x-ray radiation. 3. The system of claim 2, wherein to determine whether the physical region is a region of interest based on the absorption, the processor is operable to determine an effective atomic number of the physical region. 4. The system of claim 1, wherein the third type of radiation is x-ray radiation having an energy that is higher than the energy of the first energy. 5. The system of claim 4, wherein the first type of x-ray radiation has an energy spectrum with a maximum energy of 6 MeV, the second type of x-ray radiation has an energy spectrum with a maximum energy of 9 MeV, and the third type of x-ray radiation has an energy spectrum with a maximum energy of 10 MeV. 6. The system of claim 1, wherein the first type of radiation, the second type of radiation, and the third type of radiation are the same type of radiation. 7. The system of claim 1, wherein the first type of radiation, the second type of radiation, and the third type of radiation are different types of radiation. 8. The system of claim 1, further comprising a track configured to:support the source, andenable the source to move along the track with respect to the physical region. 9. The system of claim 8, wherein the source and the sensor system move concurrently with respect to the physical region. 10. The system of claim 9, wherein the physical region is a region within a larger region, the source moves with respect to the larger region during the screening mode, and the physical region is determined to be a region of interest, and further comprising moving the source to the physical region during the verification mode. 11. The system of claim 1, further comprising a photo-neutron conversion target configured to produce, in response to interaction with the third type of radiation, a neutron of sufficient energy to cause fission in a fissionable material. 12. The system of claim 11, wherein the photo-neutron conversion target is made of beryllium, deuterium, or lithium. 13. The system of claim 11, wherein the conversion target is between the source and the physical region. 14. The system of claim 13, wherein the conversion target is coupled to the source. 15. The system of claim 1, wherein the source of radiation comprises a first source of radiation and a second source of radiation that is separate from the first source of radiation, the first source of radiation producing the first type of radiation and the second type of radiation in the screening mode, and the second source of radiation producing the third type of radiation in the verification mode. 16. The system of claim 1, wherein the first type of radiation, the second type of radiation, and the third type of radiation are produced by a single source of radiation that is configured to operate in multiple modes, including the screening mode and the verification mode. 17. A method of detecting the presence of fissionable material, the method comprising:directing, from an imaging system in a screening mode, a first type of radiation towards a physical region, the first type of radiation having a first energy;directing, from the imaging system in the screening mode, a second type of radiation towards the physical region, the second type of radiation having a second energy that is higher than the first energy, and the second type of radiation propagating in a direction that is substantially parallel to a direction of propagation of the first type of radiation;determining an absorption characteristic of the physical region based on an absorption of the first type of radiation and the second type of radiation by the physical region;determining, from the absorption characteristic, whether the physical region is a region of interest;switching the imaging system from the screening mode to a verification mode in response to determining that the physical region is a region of interest;directing, from the imaging system in the verification mode, a third type of radiation toward the physical region, the third type of radiation being sufficient to induce fission in a fissionable material; anddetermining whether a fissionable material is present in the physical region based on an interaction between the third radiation and the physical region. 18. The method of claim 17, wherein the first type of radiation is x-ray radiation, the second type of radiation is x-ray radiation, and the third type of radiation is a photon or a neutron. 19. The method of claim 17, further comprising detecting radiation from a fission product emitted from the physical region after the source of the third type of radiation is turned off. 20. The method of claim 17, wherein the absorption characteristic comprises an effective atomic number. 21. The method of claim 17, wherein the physical region is a region of interest, and further comprising:moving the imaging system during the screening mode, andmoving the imaging system to the physical region at the beginning of the verification mode. 22. The method of claim 17, further comprising identifying fissionable material. 23. An imaging system for discriminating fissionable materials from among other high-effective atomic number materials, the imaging system comprising:a source configured to:produce dual-energy x-ray radiation sufficient to cause fission in fissionable materials, the dual-energy x-ray radiation comprising a first beam of energy at a first energy and a second beam of energy at a second energy, anddirect the dual-energy x-ray radiation sufficient to cause fission in fissionable materials towards a physical region, the first beam of energy propagating in a direction that is substantially parallel to a direction of propagation of the second beam of energy;a sensor configured to sense x-ray radiation and a product of fission from the physical region;a processor configured to:determine an absorption of the dual-energy x-ray radiation by the physical region based on the sensed x-ray radiation, anddetermine whether the physical region includes fissionable material based on the presence of a product of fission. 24. The system of claim 1, wherein the processor is further operable to cause the sensor system to switch between the screening mode and the verification mode when the physical region is a region of interest. 25. The system of claim 1, wherein the third type of radiation comprises a neutral particle. 26. The system of claim 1, wherein both the sensor configured to sense radiation comprising the first energy and the second energy and the sensor configured to sense a fission product are mounted on a single gantry. 27. The system of claim 1, wherein the third type of radiation propagates along a direction that is substantially parallel to the first direction. 28. The method of claim 17, further comprising:determining a characteristic of the region of interest,modifying the third type of radiation based on the characteristic, andscanning the region of interest with the modified third type of radiation. 29. The method of claim 28, wherein the characteristic of the region of interest comprises an effective atomic number, and modifying the third type of radiation comprises selecting the third type of radiation based on the effective atomic number. 30. The method of claim 29, wherein selecting the third type of radiation based on the effective atomic number comprises selecting one of a neutron probe or a photon probe. 31. The method of claim 17, further comprising presenting a perceivable indication when a fissionable material is present.
	abstract	A pair of linear arrays of gamma thermometer (GT) sensors arranged in a nuclear reactor core including: a first linear array of GT sensors, wherein the GT sensors are arranged asymmetrically along a length of the first linear array; a second linear array of GT sensors, wherein the GT sensors are arranged asymmetrically along the second linear array and wherein the second linear array of GT sensors is asymmetrical with respect to the first linear array of GT sensors, and the first linear array positioned in the reactor core at a first core location and the second instrument housing positioned at a second core location, wherein a line of symmetry of the core extends through a center of the core and the first core location is the same horizontal distance from the line of symmetry as the second core location.
048779628	abstract	An ion implantation method for a substrate of (100) silicon is disclosed in which the implantation is performed on a substrate which is tilted with respect to an incident ion beam and is rotated in its own plane by 15.degree. to 75.degree. from a position in which the (110) crystal planes of the silicon would be aligned with the incident ion beam. The substrate is then rotated in its own plane by 90.degree., 180.degree., and 270.degree. from its initial position and ion implantation is performed at each position using the same dose of ions. The initial angle of rotation is preferably about 45.degree..
053393422	abstract	A fuel assembly for a boiling water reactor includes approximately mutually parallel fuel rods in a bundle having upper and lower ends. A skeleton holding the bundle has a handle, an upper tie plate retained on the handle at the upper end of the bundle, a lower tie plate at the lower end of the bundle, and at least one support element joining together the lower tie plate and the upper tie plate. The skeleton and the bundle are inserted in a fuel assembly case. A redundant support device holds the lower tie plate, the fuel assembly case and the upper tie plate together, when the handle is lifted.
047537736	summary	FIELD OF THE INVENTION This invention relates to a steam generator heated by liquid metal, such as may be used in nuclear energy power plants. More particularly, the invention relates to a steam generator for using the heat from a nuclear reactor coolant system to generate high pressure steam and provide improved fail-safe conditions for a reactor coolant system. BACKGROUND OF THE INVENTION Nuclear reactors cooled by a liquid metal such as sodium are well known, and the circulating hot liquid metal coolant has been utilized for generating power by heat transfer from the liquid metal to water, which in turn is converted to high pressure steam. The steam is then cycled to a turbine-generator power conversion system for generating electricity. A major drawback and a safety problem in such steam generators is the need to protect the system against the violent metal-water reactions that may result from a leak in the liquid metal and/or water circulation systems. Should the liquid metal reactor coolant come into direct contact with steam or water leaking out from the steam generator tube, a violent chemical reaction occurs with a corrosive byproduct (e.g., NaOH) and free hydrogen. Conventional reactor-power plant systems employ an intermediate liquid metal heat exchange circuit to protect the reactor core in the event of a leak. Typically, such an intermediate system includes an expansion vessel, complex piping circuits, a heat exchanger, a pump, liquid metal purification equipment, fill and drain systems, electrical preheat systems, and the attendant instruments, controls and structures for housing and support of these components. From the standpoint of efficiency, design simplicity and conservation of physical space and other resources it would be highly advantageous to eliminate such intermediate systems, however a steam generator design of exceptional reliability or with special protective features such as a double tube wall design would be required. A drawback of known double tube steam generator systems is their inefficiency in transferring heat from the liquid metal coolant to water. Prior art steam generators of double wall construction have relied on inert gas as a heat transfer medium, however an inert gas barrier is extremely inefficient for this purpose. U.S. Pat. Nos. 3,545,412, 3,613,780 and 3,907,026, for example, show apparatuses wherein closely placed tubes containing liquid metal or water are surrounded by inert gas, or wherein water tubes are run through a sleeve containing inert gas separating the water and liquid metal coolant. Other prior art duplex tube steam generators have used bonded tubes or duplex tubes with mercury as the intermediate heat transfer agent. Bonded tubes can experience difficulties associated with loss of contact stress due to thermal aging. Duplex tubes with mercury pose a safety problem for the reactor core, because typical liquid metal coolants, i.e., sodium, react with the mercury to form an amalgam. Furthermore, conventional steam generators are large and bulky due to use, typically, of straight tube design. As a result, integration of a steam generating system with the reactor is often complex and costly. Furthermore, such steam generator designs present difficulties in locating a failed tube and in accomodating tube-to-tube and tube-to-shell temperature gradients. Conventional steam generator systems are also characterized by fabrication and repair drawbacks. Many of the structures are large and custom-manufactured for the particular plant they are used in; and in the event of a structural failure, such as a ruptured water pipe, the entire plant must be shut down in order to isolate the source of the trouble, which can lead to the development of significant temperature transients. Special structures (e.g , gantries or large cranes) may also have to be assembled to repair or replace the damaged components. Finally, conventional steam generator systems often require additional auxiliary systems for decay heat removal. SUMMARY OF THE INVENTION Accordingly, it is a primary object of this invention to provide a novel and highly reliable liquid metal steam generator particularly well suited for application in a nuclear power plant. It is a further object to provide a liquid metal steam generator having improved reliability and safety over prior art designs. It is a further object of this invention to provide a modular steam generator which has an integral barrier between the hot liquid metal and water systems which does not require a pump, separate piping or an intermediate heat exchanger. It is a further object of this invention to provide a steam generator with an efficient heat transfer path between the liquid metal coolant and water. All of the aforementioned disadvantages of the prior art are addressed, and the aforementioned objects attained, by the present invention. The steam generator disclosed herein utilizes stagnant (non-circulating) liquid metal as a heat transfer medium, which is confined to the annulus area of a compact co-axial double tube assembly. Water is conducted through the inner tube, and the double tube assembly is immersed in hot liquid metal coolant. The liquid metal in the annulus area acts as an efficient heat transfer agent between the reactor coolant and the water. A multiplicity of double tube assemblies are grouped together to form tube bundles, and the tube bundles are fabricated to assume a configuration permitting optimal heat exchange from the hot liquid metal coolant (in which the tube bundles are immersed) and the water carried in the inner tube of each double tube assembly. The particular configuration of the tube bundles is such that a compact unit is formed, which additionally provides great surface area for heat transfer between the liquid metal coolant and the water, across the stagnant liquid metal barrier in the annular gap. Many such configurations, affording compactness and efficient heat exchange, are possible. For example, single or multiple U-shaped tube bundles, a helical coil or concentric or interlocking multiple helical coils, or, most preferably, a serpentine (sinusoidal) coil. The large number of double tube assemblies also provides increased safety in operation, because in the event of an inner tube failure, the metal-water reaction is confined to the annulus area of the duplex tube. The liquid metal in the annular gap is the same as or compatible with the liquid metal coolant, therefore an outer tube failure has no hazardous effects. The steam generator of the present invention may be viewed as the juxtaposition of three closed systems: a circulating water system, a stagnant liquid metal barrier system, and a circulating liquid metal coolant system. The circulating water system begins at a water inlet that may be connected to an outside feedwater source. From the inlet, the water proceeds via a multiplicity of water-carrying tubes into the body of the steam generator, each of the tubes joins a separate outer tube to form a concentric double tube assembly, and bundles of such double tubes are wound in a particular configuration as mentioned above to form a heat exchanger unit or module. By heat transferred from the outside of the double tube across the annular gap, the water is converted to superheated steam which exits the system at a steam outlet, which may in turn be connected to a turbine generator for the production of electricity. The stagnant liquid metal barrier system begins at a disengaging chamber, which is completely closed within the steam generator during normal operation of the system. Water-carrying tubes enter the disengaging chamber, where the tubes join with the enclosing outer tubes of the concentric double tube assemblies. The annular gap formed by the joining of inner (water-carrying) and outer tubes is in open communication with the disengaging chamber. The multiplicity of double tubes, as mentioned above, forms a heat exchange unit or module, having a configuration such as a single or multiple U-turns, a helical coil pattern, or a serpentine (sinusoidal) coil pattern. The double tube continues from the heat exchange unit to a closed disengaging chamber where the outer tubes of the double tube assemblies end, and the inner tubes continue on to a steam outlet. The initial disengaging chamber for the outer tube may be the same as or different from the terminal disengaging chamber for the outer tube. Part of the volume of the annular gap between the inner tube and the outer tube of each double tube assembly is filled with a liquid metal which effectively transfers heat from the outside of the double tube assembly to the inner (water-carrying) tube. The volume of the disengaging chamber(s) and any unfilled volume of the annular gap are preferably filled with an inert gas, such as argon. The circulating liquid metal coolant system begins at a hot liquid metal coolant inlet which may be connected to the cooling system of a nuclear reactor. Hot liquid metal enters through the hot liquid metal coolant inlet and is directed into contact with the double tube bundles. Heat from the liquid metal coolant is transferred across the barrier liquid metal in the annular gaps of the double tube assembles to the water carried in the inner tubes, creating superheated steam. After transferring heat to the double tube heat exchange unit, cold liquid metal coolant flows away from the unit and is directed out of the steam generator via a cold liquid metal coolant outlet, which may be connected to the core inlet area of a nuclear reactor. Preferably the steam generator assembly described herein is interconnected with a nuclear reactor vessel as detailed in commonly assigned, co-pending U.S. application Ser. No. 582,096, filed Feb. 21, 1984, which is incorporated herein by reference. The double tube design of the steam generator allows the closest possible contact between the three closed systems while still providing a barrier between the liquid metal coolant and the water. Using liquid metal as a heat transfer agent is much more efficient than inert gas. Using a multiplicity of double tube assemblies increases the heat transfer surface area in direct contact with the hot liquid metal coolant, while dramatically reducing the volume of liquid metal coming into contact with water, in the event of a leak in an inner tube. In addition, using a coil configuration (e.g., helical coil, serpentine coil, etc.) conserves space and inherently accommodates thermal gradients while permitting unobstructed flow of the liquid metal coolant. Generally, the steam generator comprises a vessel that is subdivided into upper (hot) and lower (cold) liquid metal plenums. In operation, hot liquid metal flows into the steam generator upper plenum, flows through a distributor inlet above the one or more heat exchange units (modules), flows downward over the heat exchange units, transferring heat through the barrier liquid metal (in the double tube annular gaps) to the water flowing within the inner tube of the double tube assemblies. The cooled liquid metal exits into the steam generator lower plenum and is discharged from the steam generator vessel. Optionally, an electromagnetic or centrifugal pump may be connected to the lower plenum, e.g., in the core of the steam generator (see FIG. 1), and a portion of the liquid metal coolant reaching the lower plenum passes into the pump and is discharged at high velocity through a pump eductor back to the reactor. The remaining liquid metal coolant in the lower plenum enters the eductor and passes, mixed with the flow from the electromagnetic pump discharge, through a diffuser to convert the velocity head to a pressure head, and thence to the reactor inlet. As disclosed in more detail below, the double tube assemblies may be used directly for decay heat removal, eliminating the need for a separate decay heat removal system. In addition, the embodiments of the steam generator described herein premit the use of an external air cooling system as an alternative means of decay heat removal.
	description	1. Field of the Invention The present invention relates to an imaging system, and in particular to a charged particle multi beamlet lithography system or inspection system. 2. Description of the Related Art Currently, most commercial lithography systems use a mask as a means to store and reproduce the pattern data for exposing a target, such as a wafer with a coating of resist. In a maskless lithography system, beamlets of charged particles are used to write the pattern data onto the target. The beamlets are individually controlled, for example by individually switching them on and off, to generate the required pattern. For high resolution lithography systems designed to operate at a commercially acceptable throughput, the size, complexity, and cost of such systems becomes an obstacle. One type of design used for charged particle multi-beamlet systems is shown for example in U.S. Pat. No. 5,905,267, in which an electron beam is expanded, collimated and split by an aperture array into a plurality of beamlets. The obtained image is then reduced by a reduction electron optical system and projected onto a wafer. The reduction electron optical system focuses and demagnifies all the beamlets together, so that the entire set of beamlets is imaged and reduced in size. In this design, all the beamlets cross at a common cross-over, which introduces distortions and reduction of the resolution due to interactions between the charged particles in the beamlets. Designs without such a common cross-over have also been proposed, in which the beamlets are focused and demagnified individually. However, when such a system is constructed having a large number of beamlets, providing multiple lenses for controlling each beamlet individually becomes impractical. The construction of a large number of individually controlled lenses adds complexity to the system, and the pitch between the lenses must be sufficient to permit room for the necessary components for each lens and to permit access for individual control signals to each lens. The greater height of the optical column of such a system results in several drawbacks, such as the increased volume of vacuum to be maintained and the long path for the beamlets which increases e.g. the effect of alignment errors caused by drift of the beamlets. Furthermore, existing charged particle beam technology is suitable for lithography systems for relatively course patterning of images, for example to achieve critical dimensions of 90 nm and higher. However, a growing need exists for improved performance. It is desired to achieve considerably smaller critical dimensions, for example 22 nm, while maintaining sufficient wafer throughput, e.g. between 10 and 60 wafers per hour. The present invention aims to provide a multiple beamlet charged particle lithography system able to achieve smaller critical dimensions, for example 22 nm, while maintaining sufficient wafer throughput, for example between 10 and 60 wafers per hour. The insight underlying the present invention is that this higher resolution can be obtained in a multi-beamlet charged particle system by considerably reducing the spot size while at the same time considerably increasing the current generated in the system. Not only is a reduced spot size required to achieve the desired performance, but also a reduced point spread function of beamlets is required to maintain sufficient exposure latitude. Sufficient exposure latitude requires a relatively high ratio of peak exposure level on the target from a beamlet compared to base or background level of exposure as normally caused by the peripheral Gaussian parts of neighbouring beamlets. Designing a system to generate beamlets having a smaller point spread function, however, considerably reduces the charged particle current that may be applied to the target by each beamlet. The requirements of reduced spot size, increased current, and reduced point spread function implies a considerable increase in the number of beamlets in the system. This creates a problem due to the limited physical dimensions of the projection optics in a multi-beamlet system, which are typically limited to a size corresponding to the size of the die to be exposed. The number of projection lenses that can be constructed within such dimensions using known techniques is considerably smaller than the number of beamlets required to achieve the desired wafer throughput given the above requirements. The present invention addresses this problem by providing an imaging system having multiple beamlets per projection lens. In one aspect the invention provides for a system having a reduced number of elements in the imaging system, resulting in a less complex and less costly system. In another aspect the invention provides for a system having a shorter projection column, reducing the effect of drift of the charged particles and reducing the size of the system housing. In one aspect the present invention provides a charged particle multi-beamlet system for exposing a target using a plurality of beamlets. The system includes a charged particle source for generating a charged particle beam, a beamlet aperture array for defining groups of beamlets from the generated beam, a beamlet blanker array comprising an array of blankers for controllably blanking the beamlets, a beam stop array for blocking beamlets deflected by the blankers, the beam stop array comprising an array of apertures, each beam stop aperture corresponding to one or more of the blankers, and an array of projection lens systems for projecting beamlets on to the surface of the target, wherein the system images the source onto a plane at the beam stop array, at the effective lens plane of the projection lens systems, or between the beam stop array and the effective lens plane of the projection lens systems, and the system images the beamlet aperture array onto the target. The source may be imaged onto a plane at or between the beam stop array and the effective lens plane of the projection lens systems using a condenser lens array, and the condenser lens array is preferably positioned upstream of the beamlet aperture array, thus reducing column length. In a further aspect, the beamlet blanker array plane is imaged on the target rather than onto the plane of the beam stop array as in prior systems. The system may also include a sub-beam aperture array for defining sub-beams from the generated beam, wherein the beamlet aperture array defines the groups of beamlets from the sub-beams. The sub-beams are preferably focused onto a plane at or between the beam stop array and the effective lens plane of the projection lens systems by a condenser lens array, and the condenser lens array is preferably positioned between the sub-beam aperture array and the beamlet aperture array. In another aspect the system also provides a charged particle multi-beamlet system for exposing a target using a plurality of beamlets. The system includes a charged particle source for generating a charged particle beam, a first aperture array for defining groups of beamlets from the generated beam, a second aperture array, a beamlet blanker array comprising an array of blankers for controllably blanking the beamlets, a beam stop array for blanking beamlets deflected by the blankers, the beam stop array comprising an array of apertures, each beam stop aperture corresponding to a plurality one or more of the blankers, and an array of projection lens systems for projecting beamlets on to the surface of the target, wherein the system images the source onto a plane at the beamlet blanker array, and the system images the beamlet blanker array onto the target. The source may be imaged onto the target via a plane at the beamlet blanker array by a first condenser lens array. A further aspect of this design is that the first aperture array is imaged onto the plane of the beam stop array. The system may also include a second condenser lens array for converging the groups of beamlets onto a plane at or between the beam stop array and the effective lens plane of the projection lens systems. Each lens of the condenser lens array preferably focuses a group of beamlets to a corresponding aperture in the beam stop array. Alternatively the system may include a beamlet manipulator for converging the groups of beamlets towards a common point of convergence for each group, instead of the second condenser lens array. The common point of convergence for each group of beamlets is preferably at a corresponding aperture in the beam stop array, and the beamlet manipulator may comprise a beamlet group deflector. In a further aspect, the invention provides a system comprising at least one charged particle source for generating a charged particle beam, a first aperture array for creating sub-beams from the generated beam, a condenser lens array for focusing the sub-beams, a second aperture array for creating a group of beamlets from each focused sub-beam, a beamlet blanker for controllably blanking beamlets in the groups of beamlets, and an array of projection lens systems for projecting beamlets on to the surface of the target, where the condenser lens array is adapted for focusing each sub-beam at a point corresponding to one of the projection lens systems. The following is a description of various embodiments of the invention, given by way of example only and with reference to the drawings. FIG. 1 shows a simplified schematic drawing of an embodiment of a charged particle multi-beamlet lithography system based upon an electron beam optical system without a common cross-over of all the electron beamlets. Such lithography systems are described for example in U.S. Pat. Nos. 6,897,458 and 6,958,804 and 7,019,908 and 7,084,414 and 7,129,502, U.S. patent application publication no. 2007/0064213, and copending U.S. patent application Ser. Nos. 61/031,573 and 61/045,243, which are all assigned to the owner of the present invention and are all hereby incorporated by reference in their entirety. In the embodiment shown in FIG. 1, the lithography system comprises an electron source 1 for producing a homogeneous, expanding electron beam 20. Note that the electrons will appear to originate from a point above the source, i.e. a virtual source above the source 1, where there will be a virtual cross-over of the electrons, as describe in U.S. Pat. No. 6,897,458. Beam energy is preferably maintained relatively low in the range of about 1 to 10 keV. To achieve this, the acceleration voltage is preferably low, the electron source preferably kept at between about −1 to −10 kV with respect to the target at ground potential, although other settings may also be used. The electron beam 20 from the electron source 1 passes a collimator lens 3 to produce a collimated electron beam 21, which impinges on an aperture array 4, which blocks part of the beam and allows a plurality of beamlets 22 to pass through the aperture array. The aperture array 4 preferably comprises a plate having through holes. Thus, a plurality of parallel electron beamlets 22 is produced. The system generates a large number of beamlets 22, preferably about 10,000 to 1,000,000 beamlets, although it is of course possible to use more or less beamlets. Note that other known methods may also be used to generate the collimated beam 21, and other known methods may also be used to generate the beamlets 22. The plurality of electron beamlets 22 pass through a condenser lens array 5 which focuses the electron beamlets 22 in the plane of a beamlet blanker array 6. In this way the source 1 is imaged onto the beamlet blanker array 6. Condenser lens array 5 is preferably constructed similarly to the array of projection lens systems described below, and preferably comprises plates or substrates with apertures formed in them. Three substrates are shown in FIG. 1 although fewer or more substrates may be used, it being preferred to use as few substrates as possible to reduce the complexity and cost of the system. The apertures are preferably formed as round holes though the substrate, although other shapes can also be used. In one embodiment, the substrates are formed of silicon or other semiconductor processed using process steps well-known in the semiconductor chip industry. The apertures can be conveniently formed in the substrates using lithography and etching techniques known in the semiconductor manufacturing industry, for example. The lithography and etching techniques used are preferably controlled sufficiently precisely to ensure uniformity in the position, size, and shape of the apertures. The substrates are preferably coated in an electrically conductive coating to form electrodes. The conductive coating preferably forms a single electrode on each substrate covering both surfaces of the plate around the apertures and inside the holes. A metal with a conductive native oxide is preferably used for the electrode, such as molybdenum, deposited onto the substrate using techniques well known in the semiconductor manufacturing industry, for example. An electrical voltage is applied to each electrode to generate electrostatic lenses at the location of each aperture, the strength of the lenses being dependent on the voltage used. Each electrode is controlled by a single control voltage for the complete array. Thus, in the embodiment shown with three electrodes there will be only three voltages for all the thousands of lenses of the condenser array. It should be noted that the condenser lens array (in any of the embodiments) may comprise a single condenser lens array or a set of condenser lens arrays, as would be known to a person of skill in the field of electron-optics. This beamlet blanker array 6 preferably comprises a plurality of blankers which are each capable of deflecting one or more of the beamlets 22. The beamlet blanker array 6 is described in more detail below, and details of the beamlet blanker array and data path for controlling the beamlet blanker array are also provided in U.S. Pat. Nos. 6,958,804 and 7,019,908, U.S. patent application publication no. 2007/0064213, and copending U.S. patent application Ser. No. 61/045,243. Subsequently, the beamlets 22 enter end module 7. The end module 7 is preferably constructed as an insertable, replaceable unit which comprises various components. In this embodiment, the end module comprises a beam stop array 8, a beam deflector array 9, and a projection lens arrangement 10, although not all of these need be included in the end module and they may be arranged differently. The end module 7 will, amongst other functions, provide a demagnification of about 25 to 500 times, preferably in the range 50 to 200 times. A slightly lesser demagnification is required in systems generating patterned beamlets, in the range 25 to 100 times, as described below for the systems of FIGS. 4 and 5. The end module 7 preferably deflects the beamlets as described below. After leaving the end module 7, the beamlets 22 impinge on a surface of a target 11 positioned at a target plane. For lithography applications, the target usually comprises a wafer provided with a charged-particle sensitive layer or resist layer. In the end module 7, the undeflected electron beamlets 22 first pass beam stop array 8. This beam stop array 8 largely determines the opening angle of the beamlets. In this embodiment, the beam stop array comprises an array of apertures for allowing beamlets to pass through. The beam stop array, in its basic form, comprises a substrate provided with through holes, typically round holes although other shapes may also be used. In one embodiment, the substrate of the beam stop array 8 is formed from a silicon wafer with a regularly spaced array of through holes, and may be coated with a surface layer of a metal to prevent surface charging. In one embodiment, the metal is of a type which does not form a native-oxide skin layer, such as CrMo. Each opening or aperture in the beam stop array 8 corresponds with one or more elements of the beamlet blanker array 6. In one embodiment, the openings in the beam stop array 8 are aligned with the elements of the beamlet blanker array 6. The beamlet blanker array 6 and beam stop array 8 operate together to block or let pass the beamlets 22. If beamlet blanker array 6 deflects a beamlet, it will not pass through the corresponding aperture in beam stop array 8, but instead will be blocked by the substrate of beam stop array 8. But if beamlet blanker array 6 does not deflect a beamlet, then it will pass through the corresponding aperture in beam stop array 8 and will then be projected as a spot on the surface of target 11. In this way the individual beamlets may be effectively switched on and off. Next, the beamlets pass through a beam deflector array 9 which provides for deflection of each beamlet 21 in the X and/or Y direction, substantially perpendicular to the direction of the undeflected beamlets 22. Where the wafer is supported on a stage providing mechanical movement in the X-direction, the deflection in the X-direction may be small and used to correct for errors in the stage positioning, and deflection in the Y-direction larger, preferably in the range of 2 μm. Separate deflectors may be provided for deflection in each direction, and more than one deflector array may be used for deflection in the Y-direction. Next, the beamlets 22 pass through projection lens arrangement 10 and are projected onto a target 11, typically a wafer, in a target plane. For consistency and homogeneity of current and charge both within a projected spot and among the projected spots on the target, and as beam stop plate 8 largely determines the opening angle of a beamlet, the diameter of the apertures in beam stop array 8 are preferably smaller than the diameter of the beamlets when they reach the beam stop array. In one embodiment, the apertures in beam stop array 8 have a diameter are in a range of 5 to 20 μm, while the diameter of the beamlets 22 impinging on beam stop array 8 in the described embodiment are typically in the range of about 15 to 75 μm. The diameter of the apertures in beam stop plate 8 in the present example limit the cross section of a beamlet, which would otherwise be of a diameter value within the range of 30 to 75 μm, to the above stated value within the range of 5 to 20 μm, and more preferably within the range of 5 to 10 μm. In this way, only a central part of a beamlet is allowed to pass through beam stop plate 8 for projection onto target 11. This central part of a beamlet has a relatively uniform charge density. Such cut-off of a circumferential section of a beamlet by the beam stop array 8 also largely determines the opening angle of a beamlet in the end module 7 of the system, as well as the amount of current at the target 11. In one embodiment, the apertures in beam stop array 8 are round, resulting in beamlets with a generally uniform opening angle. FIG. 2 shows an embodiment of end module 7 in more detail, showing the beam stop array 8, the deflection array 9, and the projection lens arrangement 10, projecting an electron beamlet onto a target 11. The beamlets 22 are projected onto target 11, preferably resulting in a geometric spot size of about 10 to 30 nanometers in diameter, and more preferably about 20 nanometers. The projection lens arrangement 10 in such a design preferably provides a demagnification of about 100 to 500 times. In this embodiment, as shown in FIG. 2, a central part of a beamlet 21 first passes through beam stop array 8 (assuming it has not been deflected by beamlet blanker array 6). Then, the beamlet passes through a deflector or set of deflectors arranged in a sequence forming a deflection system, shown as beam deflector array 9. The beamlet 21 subsequently passes through an electro-optical system of projection lens arrangement 10 and finally impinges on a target 11 in the target plane. The projection lens arrangement 10, in the embodiment shown in FIG. 2, has three plates 12, 13 and 14 arranged in sequence, used to form an array of electrostatic lenses. The plates 12, 13, and 14 preferably comprise plates or substrates with apertures formed in them. The apertures are preferably formed as round holes though the substrate, although other shapes can also be used. In one embodiment, the substrates are formed of silicon or other semiconductor processed using process steps well-known in the semiconductor chip industry. The apertures can be conveniently formed in the substrates using lithography and etching techniques known in the semiconductor manufacturing industry, for example. The lithography and etching techniques used are preferably controlled sufficiently precisely to ensure uniformity in the position, size, and shape of the apertures. This uniformity permits the elimination of the requirement to individually control the focus and path of each beamlet. The substrates are preferably coated in an electrically conductive coating to form electrodes. The conductive coating preferably forms a single electrode on each substrate covering both surfaces of the plate around the apertures and inside the holes. A metal with a conductive native oxide is preferably used for the electrode, such as molybdenum, deposited onto the plate using techniques well known in the semiconductor manufacturing industry, for example. An electrical voltage is applied to each electrode to generate electrostatic lenses at the location of each aperture, the strength of the lenses being dependent on the voltage used. Each electrode is controlled by a single control voltage for the complete array. Thus, in the embodiment shown with three electrodes lens there will be only three voltages for all the thousands of lenses. FIG. 2 shows the plates 12, 13, and 14 having electric voltages V1, V2 and V3 respectively applied to their electrodes. The voltage differences between the electrodes of plates 12 and 13, and between plates 13 and 14, create electrostatic lenses at the location of each aperture in the plates. This generates a “vertical” set of electrostatic lenses at each position in the array of apertures, mutually aligned, creating an array of projection lens systems. Each projection lens system comprises the set of electrostatic lenses formed at corresponding points of the arrays of apertures of each plate. Each set of electrostatic lenses forming a projection lens system can be considered as a single effective projection lens, which focuses and demagnifies one or more beamlets, and has an effective focal length and an effective demagnification. In systems where only a single plate is used, a single voltage may be used in conjunction with a ground plane, such that electrostatic lenses are formed at the location of each aperture in the plate. The projection lens arrangement preferably forms all of the focusing means for focusing the beamlets onto the target surface. This is made possible by the uniformity of the projection lenses, which provide sufficiently uniform focusing and demagnification of the beamlets so that no correction of the focus and/or path of individual electron beamlets is required. This considerably reduces the cost and complexity of the overall system, by simplifying construction of the system, simplifying control and adjustment of the system, and greatly reducing the size of the system. In one embodiment, the placement and dimensions of the apertures where the projection lenses are formed are controlled within a tolerance sufficient to enable focusing of the electron beamlets using one or more common control signals to achieve a focal length uniformity better than 0.05%. The projection lens systems are spaced apart at a nominal pitch, and each electron beamlet is focused to form a spot on the surface of the target. The placement and dimensions of the apertures in the plates are preferably controlled within a tolerance sufficient to achieve a variation in spatial distribution of the spots on the surface of the target of less than 0.2% of the nominal pitch. The projection lens arrangement 10 is compact with the plates 12, 13, 14 being located close to each other, so that despite the relatively low voltages used on the electrodes (in comparison to voltages typically used in electron beam optics), it can produce very high electrical fields. These high electrical fields generate electrostatic projection lenses which have a small focal distance, since for electrostatic lenses the focal length can be estimated as proportional to beam energy divided by electrostatic field strength between the electrodes. In this respect, where previously 10 kV/mm could be realized, the present embodiment preferably applies potential differences within the range of 25 to 50 kV/mm between the second plate 13 and third plate 14. These voltages V1, V2, and V3 are preferably set so that the difference in voltage between the second and third plates (13 and 14) is greater than the difference in voltage between first and second plates (12 and 13). This results in stronger lenses being formed between plates 13 and 14 so that the effective lens plane of each projection lens system is located between plates 13 and 14, as indicated in FIG. 2 by the curved dashed lines between plates 13 and 14 in the lens opening. This places the effective lens plane closer to the target and enables the projection lens systems to have a shorter focal length. The high electrical fields used to generate the electrostatic projection lenses can cause bowing or buckling of the plates 12, 13, 14. Because of the tight tolerances required for the positioning of the projection lenses, even a small amount of bowing of the plates can be detrimental. Struts running across and affixed to the surface of the plates may be used to stiffen the plates to reduce this problem. The struts are preferably constructed of an insulating material to further electrically isolate the plates to further prevent flash-over or shorting of electrical charge. FIG. 2 also illustrates deflection of a beamlet 21 by deflection array 9 in the Y-direction, illustrated in FIG. 2 as a deflection of the beamlet from left to right. In the embodiment of FIG. 2, an aperture in deflection array 9 is shown for one or more beamlets to pass through, and electrodes are provided on opposite sides of the aperture, the electrodes provided with a voltage +V and −V. Providing a potential difference over the electrodes causes a deflection of the beamlet or beamlets passing though the aperture. Dynamically changing the voltages (or the sign of the voltages) will allow the beamlet(s) to be swept in a scanning fashion, here in the Y-direction. In the same way as described for deflection in the Y-direction, deflection in the X-direction may also be performed back and/or forth (in FIG. 2 the X-direction is in a direction into and out of the paper). In the embodiment described, one deflection direction may be used for scanning the beamlets over the surface of a substrate while the substrate is translated in another direction using a scanning module or scanning stage. The direction of translation is preferably transverse to the Y-direction and coinciding with the X-direction. In the application of the projection system for lithography, a beamlet should be focused and positioned at ultra high precision, with spot sizes of tens of nanometers, with an accuracy in size of nanometers, and a position accuracy in the order of nanometers. The inventors realized that deflecting a focused beamlet, for example several hundreds of nanometers away from the optical axis of a beamlet, would easily result in an out-of-focus beamlet. In order to meet the accuracy requirements, this would severely limit the amount of deflection or the beamlet would rapidly become out of focus at the surface of target 11. The inventors recognized that the focal length should be of such limited magnitude that any deflector or deflector system should be located before the projection lens despite the evident occurrence of off-axis aberrations with such an arrangement. The arrangement shown in FIGS. 1 and 2 of the deflection array 9 upstream and projection lens arrangement 10 downstream furthermore allows a strong focusing of beamlet 21, in particular to permit a reduction in size (demagnification) of the beamlets of at least about 100 times, and preferably about 350 times, in systems where each projection lens system focuses only one beamlet (or a small number of beamlets). In systems where each projection lens system focuses a group of beamlets, preferably from 10 to 100 beamlets, as in the systems of FIGS. 4 and 5, each projection lens system provides demagnification of at least about 25 times, and preferably about 50 times. This high demagnification has another advantage in that requirements as to the precision of the apertures and lenses before (upstream of) the projection lens arrangement 10 are much reduced, thereby enabling construction of the lithography apparatus, at a reduced cost. Another advantage of this arrangement is that the column length (height) of the overall system can be greatly reduced. In this respect, it is also preferred to have the focal length of the projection lens small and the demagnification factor large, so as to arrive to a projection column of limited height, preferably less than one meter from target to electron source, and more preferably between about 150 and 700 mm in height. This design with a short column makes the lithography system easier to mount and house, reduces the size of the vacuum chamber required to house the system, and also reduces the effect of drift of the separate beamlets due to the limited column height and shorter beamlet path. The smaller drift reduces beamlet alignment problems and enables a simpler and less costly design to be used. This arrangement, however, puts additional demands on the various components of the end module. Additional details of the end module and projection lens arrangement are provided in copending U.S. patent application Ser. Nos. 61/031,573 and 61/045,243. FIG. 3 is a perspective view of one of the plates 12, 13 or 14, which preferably comprise a substrate, preferably of a material such as silicon, provided with holes 18. The holes may be arranged in triangular (as shown) or square or other suitable relationship with mutual distance P (pitch) between the centre of neighboring holes of about one and a half times the diameter d7 of a hole 18. The substrates of the plates according to one embodiment may be about 20-30 mm square, are preferably located at a constant mutual distance over their entire area. In one embodiment, the substrate is about 26 mm square. The total current of the beamlets required to achieve a particular throughput (i.e. a particular number of wafers exposed per hour) depends on the required dose, the area of the wafer, and the overhead time (e.g. the time to move a new wafer into position for exposure). The required dose in these shot noise limited systems depends on the required feature size and uniformity, and beam energy, among other factors. To obtain a certain feature size (critical dimension or CD) in resist using electron beam lithography, a certain resolution is required. This resolution comprises contributions due to the beam size, the scattering of electrons in the resist, and secondary electrons mean free path combined with acid diffusion. These three contributions add up in a quadratic relation to determine the total spot size. Of these three contributions the beam size and the scattering depend on the acceleration voltage. To resolve a feature in the resist the total spot size should be of the same order of magnitude as the desired feature size (CD). Not only the CD but also the CD uniformity is important for practical applications, and this latter requirement will determine the actual required spot size. For electron beam systems, the maximum single beam current is determined by the spot size. For small spot size the current is also very small. To obtain a good CD uniformity, the required spot size will limit the single beam current to much less than the current required to obtain a high throughput. Thus a large number of beamlets is required (typically more than 10,000 for a throughput of 10 wafers per hour). For an electron beam system, the total current through one lens is limited by Coulomb interactions between electrons, so that a limited number of beamlets can be sent through one lens and/or one cross-over point. This consequently means that the number of lenses in a high throughput system also needs to be large. In a preferred embodiment, a very dense arrangement of a large number of low energy beamlets is achieved, such that the multiple beamlets can be packed into an area comparable in size to the size of a typical wafer exposure field. The pitch of the apertures in the plates 12, 13 and 14 of the projection lens is preferably as small as possible to create as many electrostatic lenses as possible in a small area. This enables a high density of beamlets. The large number of beamlets spaced closely together in a high density arrangement also reduces the distance the beamlets must be scanned across the target surface. However, reduction in the pitch for a given bore size of the apertures is limited by manufacturing and structural problems caused when the plate becomes too fragile due to the small distances between the apertures, and by possible aberrations in a lens caused by fringe fields of neighboring lenses. The multi-beamlet charged particle system is designed to considerably reduce the spot size while at the same time considerably increasing the current generated in the system. In doing so, it was also realized that by increasing the current in the system, the total current on the target is also increased to limit development of shot noise. At the same time, however, the number of electrons impinging on the target surface per square critical dimension (i.e. per unit of area of CD squared) should be maintained constant. These requirements necessitate modification to the design of the charged particle system, as discussed in detail below, and for optimum performance a target with relatively high sensitivity resist is required, by way of example typically from 30 μm/cm2 as currently practiced to double that value. The spot size is preferably in the same order of magnitude as the desired critical dimension (CD) size. Not only is a reduced spot size required to achieve the desired performance, but also a reduced point spread function of beamlets is required to maintain sufficient exposure latitude. Sufficient exposure latitude requires a relatively high ratio of peak exposure level on the target from a beamlet compared to a base or background level of exposure as normally caused by the peripheral Gaussian parts of neighbouring beamlets. Designing a system to generate beamlets having a smaller point spread function, however, considerably reduces the charged particle current that may be applied to the target by each beamlet. Irrespective of the brightness of the charged particle source used, the preceding requirements of reduced spot size, increased current, and reduced point spread function implies a considerably more than linear increase in the number of beamlets in the system compared to the reduction in critical dimension at the same wafer throughput. The requirement for a considerable increase in the number of beamlets in the system creates a practical problem due to the limited physical dimensions of the projection optics of a multi-beamlet lithography system. The projection optics in such systems are typically limited in size to accommodate, for example the fields of the target to be exposed by the system. There is a limit to the number of lenses that may be physically realized within a relatively small area that the projection optics, i.e. the end projection module may occupy in practical designs. At the reduced critical dimensions to be achieved, the number of lenses that can be constructed within these dimensions using known techniques is considerably smaller than the number of beamlets required to achieve the desired wafer throughput. One solution is to reduce the image of the aperture array 4 using a condenser lens or series of condenser lenses, thereby also reducing the pitch of the beamlets. However, this solution typically results in a common cross-over of all the beamlets, which causes a significant amount aberration. This is not desirable, particularly in view of the present requirements, and would further complicate the system to counteract this aberration. The solution adopted is to add a group deflector array or a condenser lens array for directing a group of beamlets towards each single projection lens system for projecting onto the target. This minimizes aberration in the system while allowing a disproportionate increase in the number of beamlets in the system. Because part or all of the plurality of beamlets directed through to each projection lens system may be blanked at any point in time during operation, the system according to the present invention is also referred to as a patterned beamlet system. This patterned beamlet system may also be regarded as a multiplicity of miniaturized imaging systems arranged side by side. FIG. 4 illustrates one embodiment of a design according to the invention, for enabling an increased number of beamlets in the system, permitting increased current at the wafer or reduced spot size or both. The embodiment shown in FIG. 4 is constructed generally as described for the system of FIG. 1, except that the beamlets are arranged in groups so that multiple beamlets may be focused by a single projection lens system. In this embodiment, an aperture array 4A produces beamlets 22 from the collimated beam 21. The beamlets 22 are focused by condenser lens array 5A in the plane of a second aperture array 4B, with the result that the source 1 is imaged onto beamlet blanker array 6 (and also the aperture array 4B when this is integrated with the beamlet blanker array). The source 1 is in the focal plane of the collimating lens 3, which produces parallel beams in the collimated beam 21, and the beamlets 22 produced from collimated beam 21 are then focused in the plane of aperture array 4B. The beamlets 22 are arranged as groups, and a second condenser lens array 5B focuses each group of beamlets approximately in the plane of beam stop array 8 and towards a corresponding aperture in beam stop array 8. The beamlets are thus focused in front of the target 11. In principle each group of beamlets can be concentrated (i.e. directed to a single point where they intersect and cross-over) either at the relevant aperture of beam stop array 8, or at the effective lens plane of the relevant projection lens system. In practice it is preferred to concentrate the beamlets somewhere between these two points. Concentrating the beamlets at the beam stop array may create a lens error, while concentrating the beamlets at the effective lens plane of the projection lens may cause a dose error. Alternatively, a group deflector array 5B can be provided instead of a second condenser lens array, providing a deflector for each beamlet. The group deflector array deflects the beamlets so that each group of beamlets converges to a cross-over point approximately at the plane of beam stop array 8, or the effective lens plane of the relevant projection lens system, or between these two points. A beamlet blanker array 6 is positioned after the aperture array 4B. Note that beamlet blanker array 6 may alternatively be positioned before aperture array 4B, or the beamlet blanker array 6 may be integrated with the second aperture array 4B in a single component which functions as both the second aperture array and beamlet blanker array. The beamlet blanker array 6 operates, as in the system of FIG. 1, to deflect beamlets so that the deflected beamlets are blocked by beam stop array 8. Beamlets which are not blanked (i.e. not deflected by beamlet blanker array 6) will fall on a corresponding aperture in beam stop array 8 and a central part of the unblanked beamlet will pass through the aperture and will be deflected by deflection array 9 and focused onto the target 11 by projection lens arrangement 10. This results in the beamlet blanker array 6 (and the aperture array 4B when integrated with the beamlet blanker array) being imaged onto the target 11. This has the benefit of greater stability in the system because errors in the size and positioning of lenses, apertures and other elements of the system upstream of the aperture array 4B will have reduced or no impact on the system downstream of aperture array 4B. FIG. 4 shows three groups of three beamlets deflected by condenser array 5B, so that three beamlets are directed through each projection lens system in the end module 7. In this embodiment there are thus three times as many apertures in aperture array 4A, condenser lens array 5A, aperture array 4B, and beamlet blanker array 6, than there are projection lens systems formed in the end module 7. Although three beamlets per projection lens system is shown in FIG. 4, other numbers of beamlets per projection lens system may also be used, and groups of up to 100 beamlets or more can be directed through each projection lens system. In a preferred embodiment, groups of 49 beamlets in an array of 7 by 7 are deflected through each projection lens system. Although FIG. 4 shows the arrays 4A, 5A, 5B, 4B, and 6 being approximately the same size as the beam stop array 8 and other components of end module 7, they may be may larger, particularly for designs having a large number of beamlets per projection lens system which necessitates a larger number of apertures in the arrays 4A and 5A compared with the end module 7. Preferably the apertures in the beam stop array 8, which define the beamlet opening angle, are relatively small as if they were limiting only a single beamlet. Larger apertures would require a larger deflection path, would be more susceptible to “tail” effects caused by only partial blanking of a blanked beamlet, and would further reduce the limited space available on beam stop array 8 for blanking beamlets. In this design, with multiple beamlets passing through each projection lens system, the charged particle optics slit does not consist of a regular array of beamlets but of a regular array of groups of beamlets. At any instant some of the beamlets in a group may be directed through a corresponding opening in beam stop array 8 and projected onto the target, while other beamlets are deflected an additional amount by beamlet blanker array 6. This additional deflection causes these beamlets to miss the corresponding opening in beam stop array 8 so they are blocked from reaching the target, and are thereby blanked or “switched off” as described previously. In this way the beamlets are modulated, and each group of beamlets exposes a pattern determined by the beam blanker array 6, and each group can be considered as a single patterned beamlet. While the system of FIG. 4 provides for multiple beamlets per projection lens system, it also results in a more complex system requiring two sets of condenser lens arrays 5A and 5B, and a total of six components in the embodiment shown where each condenser lens array comprises three substrates. This also results in a greater projection column length (greater distance from source to target) which is undesirable. The system typically operates in a vacuum chamber, and a longer column requires a larger and more expensive chamber. A longer column also increases the path length of the beamlets, increasing the effect of beamlet drift. FIG. 5 illustrates an alternative arrangement of the system which reduces the complexity and column length of the system. The system of FIG. 5 includes an aperture array 4C to produce larger sub-beams 25. The sub-beams pass through a condenser lens array 5C focusing the sub-beams approximately in the plane of beam stop array 8 and at a corresponding opening in beam stop array 8. In principle each sub-beam can be focused either in the plane of beam stop array 8 or at the effective lens plane of the corresponding projection lens system, or somewhere between these two planes. This results in the source 1 being imaged onto this plane (i.e. the beam stop array 8 or the effective lens plane of the projection lens systems or a plane between them). The sub-beams 25 impinge upon aperture array 4D which includes a number of apertures in the path of each sub-beam, thus producing a group of beamlets 23 from each sub-beam 25. The groups of beamlets, being formed from the sub-beams, are also focused in a plane at the beam stop array 8 or the effective lens plane of the projection lens systems or between them, and each group of beamlets is directed towards a corresponding opening in beam stop array 8. Alternatively, a group deflector array can be provided after the aperture array 4D instead of condenser lens array 5C, providing a deflector for each beamlet 23. The group deflector array deflects the beamlets so that each group of beamlets converges to a cross-over point approximately at the plane of beam stop array 8, or the effective lens plane of the relevant projection lens system, or between these two points. These beamlets 23 then pass through beamlet blanker array 6, which operates as previously described. Beamlets which are not blanked (i.e. not deflected by beamlet blanker array 6) will fall on a corresponding aperture in beam stop array 8 and a central part of the unblanked beamlet will pass through the aperture and will be deflected by deflection array 9 and focused onto the target 11 by projection lens arrangement 10. This results in the aperture array 4D being imaged onto the target 11. This has the benefit of greater stability in the system because errors in the size and positioning of lenses, apertures and other elements of the system upstream of the aperture array 4D will have reduced or no impact on the system downstream of aperture array 4D. In the example shown in FIG. 5, the aperture array 4D produces a group of three beamlets 23 from each sub-beam 25. The group of beamlets, if undeflected by beam blanker array 6, strike the beam stop array 8 at a corresponding opening so that the three beamlets are projected onto the target by the projection lens system 10. In practice, a much larger number of beamlets may be produced for each projection lens system 10. In a practical embodiment, as many as 50 beamlets may be directed through a single projection lens system, and this may be increased to 200 or more. As shown in FIG. 5, the beamlet blanker array 6 may deflect individual beamlets 23 in a group of beamlets at certain times in order to blank them. This is illustrated in FIG. 5 by the left-hand sub-beam 25, in which the middle beamlet 23 has been deflected to a location on the beam stop array 8 near to but not at an opening so that the beamlet is blanked. In the middle sub-beam 25 the right-hand beamlet 23 has been deflected and is blanked, and in the right-hand sub-beam 25 no beamlets are deflected and blanked. The advantage realized in the embodiment of FIG. 5 is a system having multiple beamlets per projection lens while also reducing the number of components required to generate and focus the beamlets. Compared with the system of FIG. 4, the system of FIG. 5 requires only one condenser lens array (or alternatively a group deflector array) and reducing the number of condenser lens components from six to three in the embodiment shown. Fewer components permits a reduction in the length of the projection column, reducing the size and cost of system and the vacuum chamber housing the system, and reducing the effect of beamlet drift. A disadvantage when compared to the system of FIG. 4 is the lower total current at the target. FIG. 4 generates beamlets directly from the collimated beam 21 and includes the additional condenser lens array 5A which focuses the beamlets onto aperture array 4B. The system of FIG. 5 generates the beamlets from the sub-beams using aperture array 4B, and omits condenser lens array 5A, resulting in lower transmission of the collimated beam 21 to the target. However, this disadvantage is reduced in systems having a large number of beamlets. In a preferred embodiment, the system of FIG. 5 generates approximately 13,000 sub-beams and approximately one million beamlets. The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention, which is defined in the accompanying claims.
	claims	1. An apparatus for detecting and locating a radioactive source emitting gamma rays, comprising: gamma-ray sensor; a plurality of measuring means capable of receiving a light signal emitted by the sensor; analyzing means for comparing signals output by the measuring means in order to determine a direction in which the source is offset with respect to a detection axis; means for defining a central axis of the apparatus; and means for imparting a movement to the apparatus in response to movement instructions as long as the analyzing means indicate that the central axis of the apparatus is not in correspondence with the source. 2. The apparatus as claimed in claim 1 , characterized in that the means for sensing the gamma rays consist of a collimator and a scintillating crystal capable of emitting a light signal under the effect of a gamma ray. claim 1 3. The apparatus as claimed in claim 2 , characterized in that the collimator has a central area comprising a plurality of mutually parallel channels which are perpendicular to the surface of said collimator. claim 2 4. The apparatus as claimed in claim 3 , characterized in that the central area has four channels. claim 3 5. The apparatus as claimed in claim 4 wherein the collimator furthermore has a peripheral area comprising a plurality of divergent channels making, with the channels of the central area, an angle which increases with their distance from the central area. claim 4 6. The apparatus as claimed in claim 3 wherein the collimator furthermore has a peripheral area comprising a plurality of divergent channels making, with the channels of the central area, an angle which increases with their distance from the central area. claim 3 7. The apparatus as claimed in claim 1 , characterized in that the plurality of means for measuring the gamma-ray flux consists of a plurality of single-anode photomultipliers capable of receiving the light signal emitted by the sensor means. claim 1 8. The apparatus as claimed in claim 7 , characterized in that the number of photomultipliers is four. claim 7 9. The apparatus as claimed in claim 1 , characterized in that the plurality of means for measuring the gamma-ray flux consists of a multi-anode photomultiplier. claim 1 10. The apparatus as claimed in claim 1 , characterized in that the means for analyzing the gamma-ray flux are electronic means. claim 1 11. The apparatus as claimed in claim 1 , characterized in that the means capable of defining the central axis of the apparatus are in the form of at least two coherent light sources generating narrow light beams, the Intersection of which corresponds to the perpendicular at the center of the sensitive area of the apparatus. claim 1 12. The apparatus of claim 1 wherein said means for defining the central axis comprises a light rays. claim 1
062663895	abstract	An exposure apparatus comprises an X-ray source (2-3, 100, 101), an illumination system (4-7) for guiding said X-ray from an X-ray source to a mask (8), a projection system (9) for projecting a pattern on said mask by guiding said X-ray to an exposed plane (10) through a mask, wherein a projection system comprises a plurality of mirrors (91-94), and at least one reflection mirror (91) is interchangeable with a reflection mirror (97) having a different surface shape.
	description	This application is a continuation of prior co-pending application Ser. No. 11/425,222, filed on Jun. 20, 2006, which itself is a continuation-in-part of prior application Ser. No. 11/247,953, filed on Oct. 11, 2005 and now issued as U.S. Pat. No. 7,362,229 on Apr. 22, 2008, which itself is a continuation-in-part of prior co-pending application Ser. No. 10/915,957, filed on Aug. 11, 2004, the benefit of the filing dates of which is hereby claimed under 35 U.S.C. §120. Prior co-pending application Ser. No. 11/425,222 is also a continuation-in-part of prior application Ser. No. 10/862,122, filed on Jun. 3, 2004 and now issued as U.S. Pat. No. 7,117,121 on Oct. 3, 2006, the benefit of the filing date of which is hereby claimed under 35 U.S.C. §120. Prior co-pending application Ser. No. 10/915,957 and prior application Ser. No. 10/862,122 are also both continuation-in-parts of prior application Ser. No. 10/219,892, filed on Aug. 15, 2002 and now issued as U.S. Pat. No. 6,804,626 on Oct. 12, 2004, which itself is a continuation-in-part of prior application Ser. No. 09/951,104, filed on Sep. 11, 2001 and now issued as U.S. Pat. No. 6,671,646 on Dec. 30, 2003, the benefit of the filing dates of which is hereby claimed under 35 U.S.C. §120. Every day, millions of people rely on mass transportation to safely transport them to and from their destinations. For example, many children rely on school buses to transport them to and from school. However, all too often, a school bus driver makes the last stop for the day and returns the bus to the school bus yard only to discover that a child has failed to unload at the appropriate bus stop and is still on the bus. Although this situation is undesirable because of the unnecessary delay and the concern caused to parents, it can be remedied by a return trip to the child's bus stop (or home) to properly deliver the child. Far worse is the result when the school bus driver does not discover that a child has fallen asleep on the bus, and the school bus is parked in a yard overnight with the child still onboard. As a result, a child can be left alone on the bus in the yard for hours, with the parents experiencing much greater concern, believing that their child might have been abducted after getting off the bus. Clearly, it would be desirable to ensure that every school bus driver does a post-trip inspection of the school bus immediately after completing the driver's route, e.g., after the bus is returned to the yard where it is kept during the day or overnight, to determine if any child remains on the bus. There is another reason why vehicle inspections are important. Many adults rely on mass transit systems, such as trains and buses, to transport them to and from work. Tragically, a terrorist attack that consisted of a series of ten explosions occurring onboard four commuter trains left approximately 200 people dead and more than 1,800 people wounded in Madrid, Spain, when bombs packed in sports bags left on the trains detonated. It would be desirable to check for packages left on vehicles after each trip is completed, to ensure that any suspicious package is identified and appropriate measures taken. Such an inspection would also be useful in detecting packages inadvertently left on the vehicle, thereby facilitating their return to the rightful owner. U.S. Pat. No. 5,874,891 (Lowe) discloses one prior art device that seeks to remind the driver to check for remaining passengers or articles left behind on a bus and to perform an inspection of the rear door on a bus to ensure that it is working properly. The system uses the existing wiring of the school bus and is coupled to the ignition, lighting, and rear door switches of the bus. When the driver turns on the ignition of the bus at the start of a run, the system enters a stand-by state until a light activating switch has been turned on and off. At this point, the system is in an armed state while the driver completes the run. When the run is complete and the driver turns off the ignition switch, the system enters an alarm state, and a buzzer sounds immediately. The buzzer is silenced only when the driver walks to the back of the bus and opens and closes the rear door. It is expected that while moving to the rear of the bus, the driver will inspect for people still on the bus, or articles that have been left behind. However, this system only alerts those who are within hearing distance of the alarm sounding inside the bus and does so immediately upon the vehicle being powered off at any time, even before a run is completed. Furthermore, if the vehicle is parked alongside other buses, it is not apparent which bus has an alarm activated, since there is no unique identification of the bus in which the alarm is active. And the alarm can only be silenced by manually engaging or disengaging a switch to open and close the rear door, which may not require the driver to walk all the way to the rear of the bus, since the rear door is a few rows in front of the last row of seating in the bus. The disclosed system is only usable on a bus with a rear door, which most school buses do not include. Thus, it is apparent that the prior art does not teach or suggest a complete solution to the problems discussed above. It would therefore be desirable to provide a method and apparatus for performing an inspection usable for any type of vehicle that provides an alarm not only to the driver but also to those outside the vehicle, and only at a location where the inspection should occur. This alarm should be provided if it is determined that the inspection has not been performed before a predefined event has occurred. In addition, the method and apparatus should provide a unique identification to monitoring personnel of any vehicle where the required inspection apparently has not been completed. This application specifically incorporates by reference the disclosures and drawings of each patent application and issued patent identified above as a related application. The present invention verifies whether an inspection has likely been performed during a specified period. The present invention is particularly well suited to determining whether a post-trip inspection of a vehicle has been performed. The vehicle can be any form of conveyance that carries one or more passengers or cargo, including over the road vehicles, air vehicles, marine vehicles, fresh water vehicles, submersibles, and space vehicles. It is important that a post-trip inspection be carried out for the reasons noted above. This invention thus can provide evidence that a person making the inspection was at least actually physically present at a checkpoint or location that is reached by moving through the vehicle, so that the person should have completed the inspection. The inspection may be done because of safety, maintenance, or security concerns, or for other reasons, such as checking for a person who might still remain on the vehicle. Accordingly, one aspect of the present invention is directed to a method for verifying that a post-trip inspection of a vehicle has been performed. The first step is to detect that the vehicle has completed a trip. Next, a signal is produced indicating that a person has moved through the vehicle to a predefined location within the vehicle. While this approach cannot guarantee that the person actually did the inspection, it can provide evidence that the person moved through the vehicle along a path that would be followed if conducting the post-trip inspection. Since time may be important, the method determines if the signal has been received before a predefined event occurs. The predefined event can be a lapse of a predefined interval of time since detecting that the vehicle completed the trip, a lapse of a predetermined time after powering off the vehicle, or activation of a switch that is external to the vehicle, where activation of the switch is intended to indicate that at least the post-trip inspection has been completed. If the signal has not been received before a predefined event occurs, then the method determines that the person cannot yet have completed the post-trip inspection of the vehicle, which produces an alarm condition. The alarm condition is preferably either an audible alarm that is audible outside the vehicle, or a visible alarm that is visible outside the vehicle. When detecting that the vehicle has completed a trip, the method may include the step of uniquely identifying the vehicle and sensing the vehicle arriving at a location that corresponds to an end of the trip. For example, to uniquely identify the vehicle, a token on the vehicle can be remotely read. Since the token is uniquely associated with the vehicle, the arrival of that specific vehicle at the end of its trip is thus detected. Furthermore, the step of transmitting the signal can occur several different ways. In one embodiment, a token that is disposed in the predefined location is read. The person moving through the vehicle can carry a portable device used to read the unique identification code that is disposed at the predefined location. The portable device also preferably displays at least one prompt to the person regarding the post-trip inspection. For example, the display may prompt the person to check for a child remaining on a school bus, or to check for a package that may have been left on the vehicle. In a second embodiment, the steps include actuation of a switch that is disposed in the predefined location. The switch is actuated by the person upon reaching the predefined location. Alternatively, a unique identification code that is disposed proximate the predefined location is read with a sensor. Another aspect of the present invention is directed to a system for verifying whether a post-trip inspection of a vehicle has been performed. The system includes a detector, sensor, and monitor disposed in a location separate from the vehicle. The detector detects when the vehicle has completed a trip by producing a first signal indicative thereof. A suitable detector may be a pressure sensor disposed at a location corresponding to an end of the trip and which responds to a weight of the vehicle by producing the first signal, or a light sensor that detects passage of the vehicle as the vehicle interrupts light received from a source, or a video camera disposed at a location corresponding to an end of the trip and which produces an image of at least a portion of the vehicle that is indicative of the vehicle. Another type of detector that may be used responds to a signal from a radio frequency (RF) source. In this case, either the RF source or the RF detector can be disposed on the vehicle, and the other of the RF source and the RF detector disposed at the location corresponding to the end of the trip. The detector can also be a token reading device that responds to a token disposed on the vehicle, which is read by the token reading device when the vehicle completes the trip, or a responder that responds by producing the first signal when the responder is proximate a token. Again, either the token or the responder can be disposed on the vehicle, and the other of the two devices disposed so as to detect the vehicle as it completes a trip. A sensor produces a second signal indicating that a person has reached a predefined location within the vehicle, where the predefined location is accessible only by moving through an interior of the vehicle while nominally completing a post-trip inspection. The sensor includes a responder that responds by producing the second signal when the responder is proximate a token. Either the token or the responder is disposed at the predefined location within the vehicle and the other of the token and the responder is portable and carried by a person moving to the predefined location within the vehicle. The responder includes a display on which at least one prompt regarding the post-trip inspection is displayed to a person. A monitor that receives the first signal from the detector and the second signal from the sensor is also included in the system. The monitor produces an indication that the person cannot yet have performed the post-trip inspection of the vehicle if, after the first signal was received by the monitor, the second signal has not been received by the monitor before a predefined event occurs. The indication is an alarm condition and includes at least one of a status message displayed on the monitor, an audible sound, and a visible light. The predefined event comprises at least one of a lapse of a predefined interval of time since detecting that the vehicle completed the trip, a lapse of a predetermined time after powering off the vehicle, and activation of a switch that is external to the vehicle, wherein activation of the switch is intended to indicate that at least the post-trip inspection has been completed. The first signal is conveyed to the monitor over at least one of a wireless communication link or a wired communication link. The second signal is conveyed to the monitor over at least one of a wireless communication link; and a wired communication link. One of the first signal and the second signal uniquely identifies the vehicle. In one preferred embodiment of the system, also included are a transmitter for transmitting the second signal produced by the sensor and a receiver that receives the second signal. The receiver produces an output in response to the second signal, and the output signal is conveyed to the monitor. In another preferred embodiment, the sensor also includes a switch that is actuated by a person arriving at the predefined location, causing the first signal to be produced. A transmitter activated by the switch transmits the first signal. The system can include an optically encoded identifier, and the sensor then comprises an optical reader for reading the optically encoded identifier. Either the optical reader or the optically encoded identifier is disposed at the predefined location within the vehicle, and the other of the optical reader and optically encoded identifier is carried by a person to the predefined location within the vehicle. In accord with the present invention, the inspection is not limited to the interior of the vehicle, and includes external locations as well. In a generally similar embodiment of the invention, the invention determines whether a person was in a position to make a pre-trip inspection of a vehicle, with respect to both internal and external portions of the vehicle, and embodies similar steps and components. A first signal is generated after a triggering condition indicates the vehicle has completed a trip, or is ready to start a trip. A second signal is generated once the inspection has been completed. After a predetermined event has occurred, such as the expiration of a predefined time period, a monitor that has received the first signal determines if the second signal has also been received, and if not, an indication is provided that the inspection has not yet been completed. Yet another embodiment of the present invention determines whether a person was in a position to perform at least one of a pre-trip inspection and a post-trip inspection. This embodiment differs from those described above in that the first signal is not transmitted to a monitor; instead, the first signal (generated after a triggering condition indicates the vehicle has completed a trip, or is ready to start a trip, as described above) is sent to a sensor. The sensor is configured to determine if a person has been proximate at least one predefined location associated with the vehicle. The sensor is configured to transmit a wireless communication to a remote receiver indicating the inspection has not been not completed, if: (1) the sensor has received the first signal; (2) a predetermined event has occurred; and (3) the sensor has not detected that a person has been proximate the at least one predefined location. In this embodiment, a signal is sent when it is determined that the required inspection has not been performed, and in the earlier described embodiments, it is the lack of a second signal that indicates the required inspection has not been performed. This invention can also determine whether a person was in a position to carry out other types of inspections that are not limited to inspections of a vehicle. This Summary has been provided to introduce a few concepts in a simplified form that are further described in detail below in the Description. However, this Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Figures and Disclosed Embodiments are not Limiting Exemplary embodiments are illustrated in referenced Figures of the drawings. It is intended that the embodiments and Figures disclosed herein are to be considered illustrative rather than restrictive. No limitation on the scope of the technology and of the claims that follow is to be imputed to the examples shown in the drawings and discussed herein. Applicability of the Present Invention The present invention is applicable to verifying whether a person was in a position to perform an inspection within a period of time designated for the inspection to occur. The present invention is particularly well suited to pre-trip inspections, or post-trip inspections, of any conveyance device that carries one or more passengers (or cargo). This invention can provide evidence that a person who is intended to make the inspection was actually physically present at a predefined location associated with the vehicle, where such a location corresponds to a part of the vehicle that requires inspection. For example, the predefined location might be the rear of a school bus, so that the person must move through the vehicle along a path that would enable an inspection to be done. The invention does not actually confirm that the person looked for all conditions that are to be checked during the inspection, but at least, can confirm that the person was likely to have performed the inspection. For time critical inspections, the invention can also ensure that the person reached the predefined location within a predetermined time interval after a triggering condition (such as the arrival of the vehicles at a designated location, or the powering up or powering down of the vehicle) has been detected. Moreover, the invention is applicable to ensuring that inspections are likely to have been performed on trains, buses, vans, cars, aircraft, water vessels, ferries, cargo containers, cargo vessels, and any other device in which freight or people are conveyed between two points. The purpose of the inspections may be for safety, maintenance, security, or other reasons. A particularly important motivating factor for developing this invention was to provide a system useful to ensure that a school bus was checked for students who might have failed to disembark at a usual stop, and who remain on the school bus at the end of the route. Thus, while a specific preferred embodiment described herein is a system and method configured to verify that a post trip inspection of a school bus has been performed, it should be understood that the present invention is not limited to post trip inspections, or inspections only in school buses. The present invention can be implemented in regard to any type of transportation or shipping vessel, as well as to inspections unrelated to vehicles. Furthermore, the present invention can be applied to pre-trip inspections and to verify that a person was in a position to perform a required inspection during a trip. While many trips are of short duration and no in-trip inspection is required or reasonable, many trips associated with marine vessels (such as cruises, or the delivery of cargo) are of long duration. During such a trip, the present invention can be employed to verify whether required inspections of the vehicle were likely performed. Further, the present invention can be employed in connection with inspections that are not associated with a vehicle, as will be discussed in greater detail below. The present invention can store data providing evidence that a person reached the predefined location associated with the vehicle. While the data accumulated with the present invention are not conclusively presumptive evidence that the person carefully carried out the inspection, in most cases, if the person is required to visit a predefined location, e.g., at the rear of the vehicle interior, it is very likely that the person will actually do the inspection. By encouraging the person making an inspection to be physically disposed to carry out an inspection, and by providing evidence of that fact in the data recorded, there should be at least a justifiable presumption that the person actually did the inspection. FIG. 1 illustrates the overall, logical steps implemented in connection with the present invention and is applicable to embodiments of the invention in which a post-trip inspection of the interior of a vehicle is required (for example, inspecting a school bus to ensure no child has been left in the bus). From a start block 10, a step 12 provides that a detector detects a vehicle completing a trip and optionally, determines the identification of the vehicle. Details of how this step can be carried out are described below. The detector transmits a first signal (to a monitor), either by wire or wirelessly, in a step 14, to indicate that the vehicle being detected has completed a trip. At some time after the transmission of the first signal, a person should begin to move towards a predefined location in the interior of the vehicle that is to be inspected, reaching the predefined location, as noted in a step 16. This predefined location can be anywhere on the interior of the vehicle, but preferably is selected so that in order to reach the predefined location, a person has to move through the interior of the vehicle to a position where the person should visually perceive a condition of the vehicle, or any other person or any package or parcel remaining in the vehicle. Alternatively, the predefined location can be disposed within a portion of the vehicle that requires a post-trip inspection, such as a cargo hold. For example, as described below, a school bus that has just finished its run for the day should be inspected for safety and maintenance issues, but more importantly, to ensure that no children remain on board. If the predefined location is located at the rear of the school bus, it is very likely that the school bus driver will notice if there are children remaining on board if the driver proceeds to the back of the bus along the central aisle. In contrast, if the conveyance is an airplane having multiple overhead storage bins that need to be inspected, the person should be required to move down the aisle to the rear of the aircraft while inspecting each of the bins. In this scenario, the person needs to individually inspect each cargo bin and each seating row to make sure that all articles have been removed so that there are no unauthorized articles (or passengers) remaining onboard. A person might be required to enter a cargo hold to inspect it for unauthorized packages or to detect damaged cargo that might have shifted during a flight. Those of ordinary skill will understand that the post-trip inspection can be for many reasons other than the exemplary ones noted above. It is also important that the term “post-trip inspection” not be interpreted in a limiting fashion. As used herein and in the claims that follow, this term is intended to encompass the arrival of a vehicle at any designated location where an inspection is intended to be carried out by a person. The person can be an operator of the vehicle or any other person who has been assigned the responsibility for making such an inspection. Once the person reaches the predefined location, as noted in step 16, the person should access a sensor in a step 18, causing a second signal to be output, as shown in a step 20. The sensor can take different forms, as discussed below. Both the first signal and the second signal will be provided to a monitor as shown in a step 22. The second signal can be provided by storing data indicating that the sensor was accessed, and subsequently downloading the data to the monitor, by transmitting the second signal as an RF signal. The second signal is thus conveyed to the monitor over either a wireless communication link or a wired communication link. Next, a decision step 24 determines whether the person completed the post-trip inspection of the vehicle before a predefined event occurs. The predefined event may be a lapse of a certain interval of time after detecting that the vehicle completed the trip. For example, a person may be given 15 minutes to reach the predefined location from the time that the detector detected that the vehicle completed the trip. The predefined event can also be a lapse of a predetermined time after powering off the vehicle. For instance, a person may only have five minutes to reach the predefined location after the vehicle is powered off. Or the predefined event can be the activation of a switch that is external to the vehicle. For example, in order to be paid for working that day, a driver who has completed a trip and is checking out may be required to insert a time card into a time clock (to be stamped with the current time), which activates a switch signaling the occurrence of the predefined event. In a step 26, if the monitor receives the second signal before the predefined event occurs, then the monitor will do nothing, or more preferably, will produce an indication that the post-trip inspection was performed. Conversely, in a step 28, if the monitor does not receive the second signal before the predefined event occurs, then the monitor will produce an alarm indication that the post-trip inspection was not performed. The alarm can be visual, audible, or both and may also include display of a message on the monitor indicating which vehicle has not been inspected as required. Once this indication is produced, appropriate steps can be taken to address the failure of the person to complete the post-trip inspection properly, in a step 30. For example, a school bus that was not inspected properly will be inspected by management or administrative personnel, to ensure that any child or package remaining on the bus is found. The process is then complete. FIG. 2A illustrates how the present invention is employed in connection with a bus arriving at an end of its route. As shown in this Figure, a school bus 42 is pulling into a school bus yard 40 where the school bus is due for a post-trip safety and security inspection. For example, this post-trip inspection will be repeated at the end of the day in the school bus yard after all of the school children have been dropped off at their respective bus stops. The term “school bus yard” is used herein to encompass an area where one or more school buses are temporarily stored when not in use, e.g., over night or on weekends, etc. The school bus yard is just one example of a location where some type of scheduled event such as a maintenance inspection, a safety inspection, vehicle refueling, vehicle cleaning, and/or vehicle loading and unloading of either passengers or cargo is carried out in regard to a vehicle. School bus 42 enters the school bus yard through a sliding gate 46. Adjacent to sliding gate 46 is disposed an RF detector 48 that detects school bus 42, as the school bus drives past the open sliding gate at the end of its trip. RF detector 48 can produce an RF signal to query an RFID 50 that is located on school bus 42 to determine its unique identity, based upon changes in the resulting RF signal that is then received by RF detector 48. These bi-directional RF transmissions are shown by a dash line 52. RF detector 48 conveys this information as signal, to a monitor 54 that is disposed in an administrative office 56. The signal that detector 48 sends to the monitor is conveyed over a wired or wireless link, as indicated by shown as a dotted line 58, and is the first signal that monitor 54 receives in connection with school bus 42 reaching the end of its trip at the school bus yard. Alternatively, it will be appreciated that RF detector 48 can simply comprise an RF receiver that responds to an RF signal transmitted from a transmitter on the school bus. Also shown are school buses 44 that have already had their post-trip inspection performed. In addition, this invention is not limited to verifying that the post-trip inspection has occurred for a newly arrived school bus before another school bus arrives at the gate. For instance, immediately after the detector has detected school bus 42, another school bus may be pulling though the gate and will similarly be detected and preferably identified. Those skilled in the art will recognize that the positions of RF detector 48 and RFID 50 (or the RF transmitter) are interchangeable. For example, when school bus 42 pulls into the school bus yard through gate 46, RF detector 48 detects that a specific school bus has completed a trip. Instead, the RF detector can be located on the school bus (rather than fixedly mounted near the sliding gate in the school bus yard) and can then query the RFID that is now located in the yard (rather than on the school bus), but this approach will not determine the unique identity of the school bus. It is also contemplated that many other types of detectors could be used in place of the RF detector and RFID (or transmitter) described above, so long as the detector conveys a first signal over either a wireless communication link or a wired communication link to the monitor to at least detect the arrival of the school bus in the school yard. For example, the detector may be a pressure plate 63 that is embedded in the sliding gate entrance or under an assigned stall 65 where the school bus is parked after completing its trip, such that the weight of the school bus triggers this pressure sensitive plate, producing the first signal conveyed to monitor 54, as indicated by dot line 58′. The sensitivity of this pressure plate would be selected to only detect a school bus and not other lighter weight vehicles, particularly, if the pressure plate is disposed at the sliding gate. By using pressure plate 63 in an assigned stall, the likely identity of the school bus being parked in that stall will be indicated to monitor 54. The detector may be also comprise one or more light sensors, such as a photocell that detects reflected from the school bus or detects the interruption of light from a suitable source and is placed strategically to detect a school bus as it completes its trip, but not smaller vehicles. While conventional light detectors can identify that a school bus has completed a trip, they cannot identify a specific school bus that has completed the trip. However, a light detector that detects an encoded pattern such as a bar code that is applied to a side of the school bus, using reflected light from the encoded pattern, could be used to identify a specific school bus completing its trip. A further possible type of detector comprises a video camera disposed proximate the area where the school bus completes its trip. The video camera would be used to produce an image of a license plate or a visual identification number applied on the side or the top of the exterior of the school bus, which with appropriate optical character recognition software used to process the image, would enable the arrival of a specific school bus in the school bus yard to be detected. FIG. 2A also illustrates a second signal that is sent to receiver 62 located in the school bus yard office, as illustrated by a dash-dot line 60. It originates, for example, from a portable device (not shown) that is being used proximate the rear of the interior of a school bus 45 that has just been parked. The details of the portable device will be described in conjunction with FIG. 4 and FIG. 5. Returning to FIG. 2A, this second signal is emitted by the portable device if the person making the post-trip inspection has moved through the interior of school bus 45 carrying the portable device to the predefined location within the school bus where a token (not shown) is disposed. The token (e.g., an RFID) is read by the portable device, which thus serves as a sensor of the token. The portable device includes a transmitter that sends the signal to a receiver 62. Receiver 62 then produces an output that is coupled to monitor 54. This output in response to receipt of the second signal will preferably include the unique identification of the vehicle and a confirmation that the token was read, actuating the portable device to transmit the second signal. Although it cannot be guaranteed that a person actually carried out the post-trip inspection, if the person has had to move through the interior of the school bus to a predefined location near the rear of the school bus interior and be physically disposed adjacent to the token, it is likely that the person will have done the inspection, either at the predefined location or along the route the person moved to reach the predefined location. The monitor now utilizes reception of the first signal and the receiver output to determine the status of the post-trip inspection. If the person has reached the predefined location and (as described above) has employed the portable device to transmit the second signal to the receiver before a predefined event occurs, the monitor will preferably display a status message (not shown) and record data to indicate that the post-trip inspection was likely completed as desired. For example, the monitor may display a message that “School bus 45 has been likely been inspected” or “School bus 45 appears to be in compliance with post-trip inspection requirement.” Conversely, if the person has not reached the predefined location and employed the portable device to transmit the second signal to receiver 62 before the predefined event occurs, the monitor will display a status message (not shown) to indicate that the post-trip inspection was not completed as desired and will store data to that effect. More likely, the monitor may be coupled to an alarm system 67, as shown in FIG. 2A, to produce either an audible or visual alarm, e.g., using a claxon horn (not shown) mounted in the school yard, or the bus may have an audible alarm that is triggered by the monitor. The monitor may also itself emit a visual alarm in the form of blinking or flashing lights or there may be blinking or flashing lights on alarm system 67, which is mounted in the schoolyard. In addition, the monitor may cause the school bus lights to blink or flash to provide an alarm indication. Regardless of the method selected to sound the alarm, the alarm should be heard and/or be visible outside the school bus such that the alarm indication will alert persons in the vicinity where a post-trip inspection should have been done that the post-trip inspection was not properly performed. For example, it is critical that if there is a child left on the school bus, the child be promptly found and steps taken to transport the child to an appropriate guardian. Similarly, there might be unauthorized articles left behind on the school bus that should be returned to a rightful owner, or which could pose a danger, and these unauthorized articles should be found and disposed of properly. FIG. 2B illustrates an application of the present invention in an airport 66. As described above, the invention is not limited to vehicles that convey passengers on wheels over pavement, it may be applicable to airplane post-trip inspections. An airplane 64 is illustrated in FIG. 2B after just landed at airport 66 and prior to taxiing to an airport terminal 68. An airplane 64a is parked and has just had its post-trip inspection performed. An RF detector 48a queries an RFID 50a that is located on airplane 64 to determine its unique identity. These transmissions between the RF detector and RFID are shown by a dash line 52a. RF detector 48a subsequently conveys this information to a monitor 54a that is located in the airport terminal. This signal that detector 48a sends to the monitor corresponds to a first signal indicating the arrival of airplane 64 at the airport, as it completes its trip. FIG. 2B also illustrates a second signal indicated by a dash-dot line 60a that is sent to a receiver 62a located in the airport terminal. This second signal is transmitted by the portable device (not shown) that is carried on the airplane after reading a token 45a that is on the aircraft in a predefined location. In a manner similar to the exemplary school bus application of the present invention illustrated in FIG. 2A and discussed above, this second signal is emitted if the person has moved through the interior of the airplane to the predefined location within the airplane where token 45a is disposed and reads the token with the portable device. The portable device has a transmitter and responds to reading the token sending the second signal to receiver 62a. Receiver 62a then produces an output in response to receipt of the second signal, and the output is coupled to monitor 54a. This output will include the unique identification of the airplane and a confirmation that the token was read. The monitor then uses the reception of the first signal and the receiver output to indicate the status of the post-trip inspection. If a person has reached the predefined location and used the portable device to read the token so that the portable device transmits the second signal to the receiver before a predefined event has occurred, the monitor will preferably either produce a written status message (not shown) to indicate that the post-trip inspection was completed and store that information as data, or simply do nothing. For example, the monitor message or printout may read “Airplane 64a has been inspected,” or “Airplane 64a is in compliance.” Conversely, if a person has not reached the predefined location and enabled (as described above) the portable device to transmit the second signal to the receiver before the predefined event has occurred, the monitor may produce a written status message (not shown) to indicate that the post-trip inspection was not completed, and may also cause an alarm indication that alerts appropriate other personnel to take steps appropriate to address the failure of the post-trip inspection to be properly completed. FIG. 3A is an illustration showing a post-trip inspection in the interior of the school bus in accord with one preferred embodiment of this invention. As explained above, post-trip inspections may be made for security reasons, e.g., to either ensure that only authorized passengers remain in the vehicle, or to ensure that no unauthorized packages remain in the vehicle, or to check on the safety of vehicle components and/or maintenance. In the illustration of FIG. 3A, school bus 42 has completed its run for the day, and a person 80 is making a post-trip inspection to check for any child 88 who remains on the school bus. The child may still be on the school bus because of being asleep, mentally disabled, or may have failed to unload at an appropriate bus stop because of uncertainty, or for some other reason. A predefined location 82 in this preferred embodiment is at the back of the bus where a token 85 is disposed. Person 80 is instructed via at least one prompt on a portable device 86, which is being carried by the person, to look for children who may still be on the bus. Thus, as person 80 walks from the front of the bus to the rear along the central aisle, the person can visually perceive whether a child 88 is present in any of the seats on the bus. When the person reaches the rear of the bus, the person moves portable device 86 within a predefined range of token 85. A sensor 84 (which is shown in FIG. 5) on portable device 86 responds to token 85 when the portable device is held less than the predetermined distance from the token, recording data indicating that the person had moved to a position that would enable the person to readily inspect the interior of the bus for any child 88, who remained on the bus after the route had been completed. Portable device 86 also includes a transmitter 120 (also shown in FIG. 5), and when it reads token 85, will send a signal to receiver 62, as shown in FIG. 2A. In this preferred form of the present invention, the token that is preferably employed is a radio frequency identification (RFID) tag that is attached with a fastener or an appropriate adhesive to a point near the predefined location within the interior of the bus or other vehicle. One type of RFID tag that is suitable for this purpose is the WORLDTAG™ token that is sold by Sokymat Corporation. This tag is excited by an RF transmission from portable device 86 via an antenna (not shown). In response to the excitation energy received, the RFID tag modifies the RF energy that is received from the antenna in a manner that specifically identifies the vehicle associated with the RFID tag, and the modified signal is detected by sensor 84, as shown in FIG. 5. An alternative type of token that can also be used in this invention is an IBUTTON™ computer chip, which is armored in a stainless steel housing and is readily affixed to a frame or other portion of the vehicle, adjacent to the predefined location that the person is supposed to reach when performing the post-trip inspection. The IBUTTON chip is programmed with JAVA™ instructions to provide a recognition signal when interrogated by a signal received from a nearby transmitter, such as from an antenna on portable device 86. The signal produced by the IBUTTON chip is received by sensor 84, which determines the identification of the vehicle associated with the token. This type of token is less desirable, since it is more expensive, although the program instructions that it executes can provide greater functionality. Yet another type of token that might be used is an optical bar code in which a sequence of lines of varying width encode light reflected from the bar code tag. Other types of light reflective or light absorbing optical patterns can alternatively be employed. The encoded reflected light is received by sensor 84, which in this embodiment, comprises an optical detector. Optically encoded pattern recognition technology is well understood in the art and readily adapted for identifying a particular vehicle. One drawback to the use of an optically encoded tag as a token is that the optically encoded pattern can eventually become covered with dirt or grime that must be cleaned before the encoded pattern can be properly read. If the optically encoded pattern is applied to a plasticized adhesive strip, it can readily be mounted to any surface and then easily cleaned with a rag or other appropriate material. Yet another type of token usable in the present invention is a magnetic strip in which a varying magnetic flux encodes data identifies the particular vehicle associated with the token. Such magnetic strips are often used in access cards that are read by readers mounted adjacent to doors or in an elevator that provides access to a building. However, in the present invention, sensor 84 on portable device 86 comprises the magnetic flux reader. The data encoded on such a token are readily read as the portable device is brought into proximity of the varying magnetic flux encoded strip comprising the token. As yet another alternative, an active token can be employed that conforms to the BLUETOOTH™ specification for short distance data transfer between computing devices using an RF signal. However, it is likely that the range of the signal transmitted by the token would need to be modified so that it is substantially less than that normally provided by a device conforming to the BLUETOOTH specification. It is important that the portable device be able to detect that it is proximate the component only within a predetermined maximum range selected to ensure that the operator is positioned to actually carry out an inspection of the component. As a further alternative, it will be appreciated that the token can be carried to the predefined location by person 80, where a fixed reading device is installed, so that the hand carried token is then read by the reading device. Any of the various types of tokens discussed above can be hand carried by the person. This approach is less desirable, since it would be preferable to use a portable device to read other tokens on in the vehicle, for example, when carrying out a safety inspection of various components of the vehicle. Each token is associated with a different component that should be inspected, and the portable device stores data confirming that each component was visited and preferably an indication of any problem observed in connection with a component thus inspected. FIG. 3B illustrates a post-trip inspection of the school bus for another purpose in the first preferred embodiment. Person 80 is instructed via at least one prompt on portable device 86 to look for any unauthorized items left on the bus such as knives or other weapons, chemicals (e.g., mace or pepper spray), explosives, matches, or any other undesirable article. Also detected in such an inspection would be any packages or articles inadvertently left behind by a passenger who rode the school bus. As person 80 walks to the back of the school bus to reach predefined location 82, the person can see any unauthorized packages 90 and 90a still remaining on the bus. When the person reaches the back of the bus, the person moves portable device 86 within a predefined range of token 85. Portable device 86 detects and responds to token 85, recording data indicating that the person had moved to a position along a route that should have readily permitted the person to inspect the bus for unauthorized packages left behind. Portable device 86 also has a transmitter, and when token 85 has been read, will send a signal to receiver 62, as shown in FIG. 2A. FIG. 4 is an illustration of portable device 86 and shows two exemplary prompt messages that may be displayed to direct the person performing the post-trip inspection to look for specific items. For example, before beginning the post-trip inspection indicated in FIG. 3A, person 80 receives a prompt message 102 as shown in FIG. 4, which reads, “Are there any children remaining on the bus?” In response to this prompt, person 80 can depress a control 104 to indicate “Yes” on the portable device, since child 88 remains on the bus, as shown in FIG. 3A. Or during a different post-trip inspection, if all children have unloaded at their appropriate bus stop, the person can depress a control 106 to indicate “No”—there are no children remaining on the bus. In regard to the post-trip inspection shown in FIG. 3B, before beginning the post-trip inspection, person 80 might receive a prompt message 102a on screen 108 of portable device 86 as shown FIG. 4, “Are there any unauthorized packages present on the bus?” In response to this prompt, person 80 can depress control 104 to indicate “Yes” on the portable device, since unauthorized packages 90 and 90a, as shown in FIG. 3B, remain on the bus. Or during a different post-trip inspection, if no articles have been left behind on the bus, the person can depress control 106 to indicate, “No,” there are no articles left on the bus. Those skilled in the art will recognize that many other different prompts may be displayed on the portable device's screen and thus, the prompts are not limited to those exemplary messages shown in FIG. 4. In addition to the “Yes” or “No” response that the person can give, as illustrated in FIG. 4, sub-menus of dependent prompts (not shown) based on the initial prompts 102 and 102a may direct the person to answer additional questions concerning the post-trip inspection. FIG. 5 illustrates the functional components that are included in portable device 86, either on or inside housing 112, which is shown in FIG. 4. A central processing unit (CPU) 114 comprises the controller for portable device 86 and is coupled bi-directionally to a memory 116 that includes both random access memory (RAM) and read only memory (ROM). Memory 116 is used for storing data in RAM and machine instructions in ROM, which control the functionality of CPU 114 when executed by it. CPU 114 is also coupled to receive operator input from controls 118, such as control 104 and control 106, which are shown in FIG. 4. In addition, CPU 114 provides text and graphics to display 108 for displaying the prompts and other messages. Transmitter 120 allows data that have been collected during the post-trip inspection to be transferred either through a wireless RF link, or through a docking station in which the portable device is placed to download stored data. FIG. 6A illustrates the functional components 122 that communicate in the first preferred embodiment to enable the monitor to determine whether the post-trip inspection has been performed before a predefined event occurs. Portable device 86 detects and responds to token 85, recording data indicating that the person was in the predefined location and was thus able to readily have performed the post-trip inspection, such as shown in FIGS. 3A and 3B. Transmitter 120 (shown in FIG. 5) can respond to reading token 85 by sending the second signal to receiver 62. Receiver 62 then produces the output that is conveyed to monitor 54. Monitor 54 can then determine whether person completed the post-trip inspection of the vehicle before the predefined event occurred, since it also receives the first signal from detector 48. If, after the monitor received the first signal, the second signal was received as an RF signal by receiver 62 before the predefined event occurred, then the monitor will produce an indication that the post-trip inspection was performed in the desired manner. But, after the monitor receives the first signal, if the second signal is not received before the predefined event occurs, the monitor indicates that the post-trip inspection was not performed and produces an alarm indication 124. FIG. 6B illustrates an alternative preferred embodiment to enable the monitor to determine whether the post-trip inspection has been performed as desired. Portable device 86 detects and responds to token 85, recording data indicating that the person was in the predefined location and thus, should have readily been able to perform the post-trip inspection, as shown, for example, in FIGS. 3A and 3B. Although portable device 86 has transmitter 120 (shown in FIG. 5) such that when it receives a signal from token 85, it could send the second signal to receiver 62, the second signal can instead be conveyed to monitor 54 by inserting portable device 86 into a docking station 128 that is coupled to the monitor, as shown in FIG. 7. Docking station 128 receives portable device 86 to facilitate downloading the data stored within the portable device. An interface link 130 couples portable device 86 to monitor 54. The interface link conveying the data from portable device 86 can be a universal serial bus (USB) link, a serial RS-232 link, or an Institute of Electrical and Electronics Engineers (IEEE) 1392 link. The docking station may be located inside or close to administrative office 56, as shown in FIG. 2A, or there may be a plurality of docking stations disposed at different locations within the school bus yard. The docking station thus transfers data corresponding to the second signal to monitor 54. The monitor can then determine whether the person completed the post-trip inspection of the vehicle, as described above. FIG. 8 illustrates an example of another preferred embodiment for ensuring a post-trip inspection is likely to be performed, again in regard to school bus 42. Instead of token 85, this embodiment includes a sensor comprising a switch 85a that is disposed proximate predefined location 82 in the school bus. In this embodiment, person 80 does not use the portable reader. Instead, the person walks down the aisle of the bus in order to manually actuate switch 85a before the predefined event occurs. Person 80 is still able to visually perceive that child 88 has remained behind on the bus. But, since there is no portable device present that will act as a transmitter, when person 80 manually actuates switch 85a, a transmitter 134 on the bus is activated to send the second signal to receiver 62. Switch 85a and transmitter 134 may either be coupled to the school bus's battery or may run using a separate power supply (not shown). Also, those skilled in the art will recognize that still other ways can be employed to sense the user at the predefined location and in response, to transmit the second signal. For example, a sensor can be disposed at the predefined location to read a unique identification code on a device carried by person 80. The sensor can be a bar code scanner or other optical or magnetic scanning device. Also, the person can carry the scanning device to the predefined location to read an encoded pattern affixed there, or can carry a key chain on which the encoded optical or magnetic pattern uniquely identifying the bus or other type of vehicles is attached, so that when scanned, the scanning device will transmit the second signal to the monitor. Transmitter 134 could also be utilized to transmit the second signal in response to a correct identifying code being read at the predefined location. FIG. 9 illustrates how the functional components communicate in the preferred embodiment discussed above. An optical or magnetic reader is used to read an appropriately encoded tag, or even a simple switch is activated to indicate that the person was in the predefined location and was thus able to have readily performed the post-trip inspection. The reader and switch are indicated by a reference number 84a. Transmitter 134 responds to the reader or the switch detecting that the person had reached the predefined location and sends the second signal as an RF transmission to monitor 54. Monitor 54 can thus determine whether the person is likely to have completed the post-trip inspection of the vehicle before a predefined event occurred, since it also has received the first signal from detector 48. If after monitor 54 receives the first signal, the second signal was received from transmitter 134 before the predefined event occurs, then the monitor will produce an indication that the post-trip inspection was performed. Otherwise, monitor produces an alarm indication 124 to indicate that the post-trip inspection has not properly been completed. FIG. 10 illustrates functional components of monitor 54. A central processing unit (CPU) 132 is coupled bi-directionally to a memory 140 that includes both random access memory (RAM) and read only memory (ROM). Memory 140 is used for storing data in RAM and machine instructions in ROM that control the functionality of CPU 132 when executed by it, to achieve the functions of the monitor that were disclosed above. CPU 132 is also connected through appropriate data ports to display 138. Optionally, receiver 62 is included within monitor 54, but can instead be external to the monitor. Input/output interface 136 is configured to transfer data from the portable device via a transmitter in the portable device (FIG. 6A), a docking station (FIG. 6B), or a hardwire data link. Receiver 62 receives the RF signal transmitted from portable device 86 or transmitter 134, which is on the vehicle, indicating that the person has reached the predefined location within the vehicle, as explained above. Additional embodiments of the present invention can be implemented wherein more than one predefined location must be visited to complete the inspection, which as described above, may be a pre-trip inspection, a post-trip inspection, or an in-trip inspection (for example, for long trips, such as a voyage on a cruise ship, a cargo vessel, or a military vessel). Each separate predefined location can include a token that must be read using a hand-held reader, as described above. The reader can be programmed to send the second signal only if each token identified for a specific inspection has been read, or the second signal can be sent such that each token that has been read is identified. The monitor can then provide a report as to whether any predefined location was missed in the inspection. If desired, a complete additional inspection can then be performed, or an inspection only of the location that was missed can be performed. Instead of placing a token to be read by a hand held reader at each predefined location, a switch can be installed at each location. When the person is at the location, the person can activate the switch to verify that the person was proximate the specific location. In one embodiment, each switch is coupled to a transmitter that transmits the second signal, indicating that the person was present at that location to the monitor. The monitor can then determine which, if any, of the switches were not actuated to transmit a second signal (as long as the second signals uniquely identify the switch). The switches might be coupled to different transmitters, or all of the switches can be coupled to a common transmitter (for example, each switch is electrically coupled to a transmitter located within or upon the vehicle). The common transmitter can be configured to transmit the second signal after each switch is activated, and the second signal for each switch will uniquely identify the switch. Again, the monitor can determine any switch that was not activated during the inspection. In a different embodiment, the common transmitter is configured such that a second signal is not transmitted until all of the switches are activated. In such an embodiment, the monitor cannot determine a specific switch that was not activated, but can determine that the inspection was not completed properly. The common transmitter embodiment offers the advantage of a lower cost system, since only a single transmitter is required. For vehicles with many switches at different predefined locations, this approach can result in significant cost savings. Many different types of switches can be employed. Mechanically activated switches, such as toggle switches, or switches activated by depressing a button are preferred. Individual switches can be lighted to enable the switch to be more easily located under low light conditions. In some applications, it may be desirable to prevent switches from being activated by unauthorized persons. Switches can be secured by requiring a lock to be unlocked to gain access to the switch. A switch that is activated by reading a magnetic strip, or an optical pattern, such as a bar code, can also be employed. Switches can be configured to respond to a reader, so that each switch includes an RFID tag and is activated only when interrogated by an appropriate reader or RF transmitter (such as the hand held reader described above in connection with FIG. 4). Some RF ID tags respond to an inductively coupled signal as well as RF interrogation. It should be understood that the present invention is not limited to a specific type of switch, and that any switch that can be activated by a person, either by physically manipulating the switch, or by interacting with the switch via some other mechanism (e.g., short distance RF communication or inductive coupling) can be employed. It is important that the switch be activatable only when the person is physically proximate the switch; otherwise, activation of the switch will not serve as an indication that the person was proximate a location requiring inspection. Thus, a switch responsive to activation using RF communication over relatively long distances (i.e., more than a few feet) will not be preferred. On a very complex vessel, such as a large ocean going vessel, it may be desirable to designate many locations, and inspect only a subset of those locations during each inspection. The reader described above in conjunction with FIG. 4 will be particularly useful in such an implementation. Before the inspection is started, the reader (portable device 86) can be programmed with a list of locations that are to be inspected. If the person performing the inspection is sufficiently knowledgeable about the vessel, the reader may provide a brief prompt to guide the person to the first inspection point (e.g., Inspect equipment locker XYZ). More detailed instructions, such as a map of the vessel and the locations of the inspection locations, can be displayed if required. As noted above, the second signal (confirming that the inspection has been completed) may be generated regardless of how many inspection locations were actually visited, if the second signal uniquely identifies each location that was actually visited (i.e., each location where the handheld reader was positioned sufficiently close to a token that is proximate the location, to enable the reader to sense the token). A less useful embodiment would be configured to generate the second signal only if all locations were visited (this would be less efficient, because the monitor would only be able to determine that the inspection was improperly conducted, if at all, rather than being able to determine each location, or locations, that were missed). Enabling an inspection of fewer than all designated inspection locations to be verified may have significant security ramifications. In a large vessel (or a large land-based facility), there will likely be many thousands of separate locations that arguably should be inspected on a regular basis, for example, to ensure the vessel/facility is in good repair, and also to enable suspicious activity to be noticed. It would require an excessive amount of time to inspect 10,000 locations daily, but a subset of those locations could be easily inspected each day. The present invention enables the verification that a person was at a subset of many designated locations before a predetermined event has occurred (such as the end of a work shift, or the end of an allotted amount of time). Switches activated by the user at each location could be used in place of the hand held reader (portable device 86), however, electrically coupling all such switches to a common transmitter would be a significant task. Similarly, providing each switch with its own transmitter would be more expensive to implement than using a hand held reader and tokens (such as RFID tags or bar codes) disposed at each different predefined location. The specific locations inspected at any one time can be based on a predetermined pattern, or can be randomly generated for each new inspection. In addition to randomizing the locations inspected, the monitor and the portable device could be used to randomize when specific locations are inspected. Consider a security sweep of a military facility. If the sweep follows a repeating pattern, an observer might be able to determine that a specific location is regularly inspected at a certain time. Someone wishing to access that location surreptitiously would merely avoid the location at the time indicated by the repeating pattern. The hand held device of FIG. 4 could be provided with a randomizing function, such that a plurality of inspection points is checked in a randomized order, to prevent a pattern from being recognized. This approach might increase the time required for inspections, because the person may have to back track several times, to visit all of the inspection points in the subset. The randomizing function could be implemented by the processor of the portable device, or a randomized list could be provided to the hand held device (for example, when the hand held device is placed in a docking station, as shown in FIG. 7). The list may include all the locations associated with the facility (or vessel), or a subset of the locations to be inspected. The present invention thus enables the verification that a randomized inspection of a plurality predefined locations was likely completed, before a predetermined event has occurred (such as the end of a work shift, or the end of an allotted amount of time). Again, while such a functionality could be enabled by providing a user-activatable switch at each location, a hand held device reading a token disposed at each predefined location is likely to be more cost effective to implement. FIG. 11 illustrates an example including a plurality of predefined inspection locations in a school bus 42a. Again, it should be understood that the present invention is not limited to school buses, or even to vehicles, but can be applied to other inspections, for example, an inspection of a land-based facility, such as a factory or military base. Bus 42a includes a plurality of predefined inspection points. Either a token or a switch with a transmitter is disposed proximate each inspection point, such that activation of the switch or reading of the token provides verification that a person was in a position to perform the required inspection. Thus, person 80 may use a portable reader, if tokens are disposed at each inspection point. As indicated above, some switches can be configured to be activated by a reader, as opposed to being manipulated by the person directly. The person walks to each inspection point, which likely includes locations within the bus and outside the bus. The person then either activates the switch or reads a token disposed at the predefined inspection location. If the person is using a hand held device such as portable device 86 (see FIG. 4), the device can prompt the person to move from one inspection point to the next. In embodiments where a portable device reads each token associated with a predefined inspection location, the second signal is transmitted to the monitor by the portable device, either via a hard wire connection (i.e., by a docking station) or wirelessly. Where each location to be inspected has a switch disposed proximate the location, then the second signal is transmitted either by a common transmitter (such as transmitter 134a, which is electrically coupled to each switch), or by a separate transmitter that is associated with each switch. For a bus, it will likely to be important to inspect an inspection point 150 corresponding to a floor of the bus, an inspection point 152 corresponding to the areas under the seats of the bus, an inspection point 154 corresponding to a driver station, an inspection point 156 corresponding to steps in the bus, an inspection point 158 corresponding to any wheelchair lift in the bus, an inspection point 160 corresponding to any lights for the bus, an inspection point 162 corresponding to the wheel wells of the bus (reading a token or activating a switch for inspection point 162 preferably requires the person to examine the interior of the wheel well), an inspection point 164 corresponding to an engine of the bus, an inspection point 166 corresponding to an exhaust system for the bus, an inspection point 168 corresponding to fuel tanks and or air brake tanks for the bus, and an inspection point 170 corresponding to any emergency exits for the bus. More than one token/switch may be required for each type of inspection point. For example, inspection point 162, corresponding to the wheel wells, will preferably be implemented using four different switches/tokens (one at each wheel well). FIG. 12 illustrates a vehicle 172 that includes a plurality of switches 176a-176h. Each of the eight switches is disposed proximate a predefined inspection point, and each switch is coupled to a common transmitter 174. In this embodiment, the number of transmitters required to transmit the second signal is reduced. As noted above, the common transmitter can be configured to transmit a second signal after each separate switch is activated, which will enable the monitor to identify any switch that was not activated. The common transmitter can also be configured not to transmit the second signal until all of the switches have been activated. This latter embodiment will enable the monitor to determine that the second signal was not received before the predefined event has occurred, thus indicating that the inspection was not properly performed. However, the latter embodiment will not enable the monitor to identify a specific switch that was not activated. FIG. 13 is based on FIG. 1, and has been modified to illustrate that the present invention is not limited to only post trip inspections, or to predefined inspection locations within a vehicle. Thus, block 12a has been changed to provide for detecting a triggering condition, rather than detecting that the vehicle has completed a trip. The triggering condition preferably indicates that the vehicles has either recently completed a trip, or will soon begin a trip. Detecting the completion of a trip has been discussed above. Similar methods can be used to detect that a trip will soon begin. One technique for detecting that a trip will begin is detecting that an engine on the vehicle has been started. Using the example of a school bus, when a driver starts the engine of the bus, a triggering condition (the bus starting) is detected. A circuit coupled to the ignition system of the bus can readily accomplish this task. Some vehicles are moved to a staging area before a trip is begun. For example, airplanes taxi to a certain area on a runway before takeoff. Fleet vehicles (such as police cars, service vehicles, rental cars, and buses) stored in a yard when not in use generally pass through a designated exit before leaving the yard, and a portion of the yard near the exit can be designated as an inspection area. The techniques discussed above for detecting the end of a trip can also be used to detect a vehicle entering such an inspection area. The triggering event can also be the lapse of a predefined interval of time. For example, some vehicle operators may require vehicles to be inspected every 24 hours. Ocean going vessels may have long intervals of time between the “start” of a trip and the “end” of a trip. Such vehicles will may require inspection during the trip. For long trips, the trip can be defined as a plurality of segments, the segments being based on a specific time interval (such as 24 hours) or a specific distance traveled. Thus, a measured time or distance can be used as a triggering condition. Referring once again to the specific differences between FIG. 1 and FIG. 13, block 16a has been changed to indicate that a person has reached a predefined location associated with the vehicle, rather than a predefined location in the interior of the vehicle. Blocks 26a and 28a have been changed to emphasize that the inspection is not limited to just a post-trip inspection, but can be required at any point in a trip, or at any time. FIGS. 14A-14C are flow charts illustrating the steps employed in the present invention to verify whether an inspection has likely been performed. While such inspections are often performed in connection with a vehicle, such as a bus, train, plane, ferry, cruise ship, cargo ship, military vessel and the like, either before, after or during a trip, it should be understood that the present invention can be employed in connection with inspections of a land-based installation, such as a school, factory, museum, office building, public building, power plant, dam, military installation, or any facility where there is a need to determine if a required inspection has likely been performed before a predetermined event occurs. The logical process starts in a block 180. In a block 182, a triggering condition is detected. The purposes of detecting a triggering condition is to define a starting point after which the inspection should be conducted. In the embodiments described above, the starting point is typically associated with the beginning or end of a trip. Particularly for land-based installations, other starting points, such as the beginning of a work shift, will be more appropriate. A predetermined event will be used as an endpoint. The method verifies whether a person was in a location that would have enabled them to conduct the required inspection after the starting point (as indicated by the detection of a triggering condition) and before the endpoint (as indicated by the predetermined event). In some implementations of this invention, the triggering condition will be time dependent. For example, an administrator tasked with overseeing such inspections may mandate that a certain inspection will be conducted between the hours of 6:00 AM and 7:00 AM. In this case, detecting the triggering condition involves detecting that it is 6:00 AM in the corresponding time zone, and the predetermined event is the detection that it is 7:00 AM. Clearly other events can be used as a triggering condition. Unlocking a door into a factory could be a triggering condition, where an inspection of the factory is to be made before a certain assembly line is started (the predetermined event). Certain individuals may be specifically tasked with inspections, and the triggering condition can be based on actions of that employee. Where an employee keeps track of hours worked using a time clock, “clocking in” at the beginning of a shift can be used as a triggering condition, and “clocking out” at the end of a shift can be used as the predetermined event. Some employee badges include tokens (such as RFID tags or magnetic strips encoding employee data) that are read by appropriate sensors as the employee moves through a facility. The detection of an employee identification badge (or a biometric parameter, such as a handprint, a finger print, or a retinal scan) in a specific area can be a triggering condition. It should therefore be understood that the triggering condition is not limited to the conditions described above, but instead, can include almost any conditions, items, and phenomena that can be detected using available sensor technology. In a block 184, the detector that identifies the triggering condition transmits a signal to a monitor. As described above, the function of the monitor is to determine if the predetermined event has occurred, and thereafter, to determine if a signal (indicating that a person was in a position to perform the inspection before the predetermined event occurred) has been received. If this signal has not been received before the predetermined event occurs, the monitor provides an indication of the failure to perform the inspection, so that appropriate action can be taken. The appropriate action may include contacting the person responsible for the inspection to determine why the inspection was not performed, or sending other personnel to complete the inspection. In certain cases, failure to be able to verify an inspection was performed may require preventing a planned action from be taken. For example, in a factory setting, the monitor can be configured to prevent an assembly line from being energized if the monitor determines that a required inspection has not been performed (i.e., that a person was not detected in a location proximate an area to be inspected, after a triggering condition was detected, and before a predetermined event occurs). Generally, the monitor will be disposed in a location remote from the detector. A single monitor can be configured to monitor signals from multiple detectors, and to monitor multiple required inspections. Where a plurality of detectors are employed, each detector preferably uniquely identifies itself, and the triggering condition detected. Each detector can communicate with the monitor via a wired connection or a wireless connection, or a combination thereof. For example, in a large facility, a network of detectors in a single building may be coupled to a common transmitter located in that building, and the common transmitter can wirelessly communicate with the receiver. In a block 186, the monitor waits for the predetermined event to occur. As discussed above in detail, the predetermined event can be the lapse of a specific period of time, or can be the occurrence of a specific event (such as a vehicle or piece of equipment being powered on or off, or an employee logging in or out, or almost any other type of event). Where the specific predetermined event is time based, the monitor is configured to track elapsed time, or is configured to receive notification when the time has elapsed. Where the specific predetermined event is an activity, such as powering up a piece of equipment, the monitor will be configured to detect the activity, or to receive an indication that the activity has occurred. In a decision block 188, after the monitor has detected or received an indication that the predetermined event has occurred, and the monitor determines whether a second signal has been received, indicating that a person has been detected proximate a location requiring inspection, thereby indicating that the inspection could have been performed. If the second signal has been received, the logic terminates in a block 196 (as described above, the monitor can be configured to provide an indication that the inspection was performed). If the second signal was not received before the predetermined event occurred, then in a block 192, an indication is provided that the inspection has likely not been performed. This indication can be a visual readout, a visual or audible alarm, or any combination thereof. In a block 194, appropriate steps are taken to address this condition. Such steps can include, but are not limited to, notifying specific personnel, contacting the person who was to have performed the inspection, sending other personnel to complete the inspection, and preventing certain equipment from being operated until the inspection has been completed. Those of ordinary skill in the art will readily recognize that the appropriate steps to be taken will largely depend on the specific type of inspection being done, and thus, the above corrective actions ought not be considered to limit the invention. FIGS. 14B and 14C illustrate different steps that can be employed to produce the second signal, in accord with the present invention. Referring now to FIG. 14B, as indicated in a block 198, a person is now proximate a location to be inspected (after the triggering condition has been detected). In a block 200, the person activates a switch proximate the location to be inspected. As discussed above, many different types of switches can be employed, including those physically manipulated by the person, and those responsive to a portable device carried by the person. In a block 202, the second signal, indicating the person was proximate the location to be inspected (and thus, that it is likely the inspection has been performed) is sent to the monitor. The switch can include a transmitter that sends the second signal, or the switch can be connected to a separate transmitter (such as the common transmitter of FIG. 12). Where an inspection relates to a plurality of locations and a plurality of switches, the second signal can indicate the switches that have been activated, or the second signal may be transmitted only after all switches are activated. While a portable device (such as that shown in FIG. 4) can be employed in connection with the steps of FIG. 14B (to activate a switch), a portable device will only be required if the switch employed requires the portable device for activation of the switch. In some embodiments, no portable device is required, and the person simply physically manipulates the switch. Referring now to FIG. 14C, in a block 198a, a person with a portable reader (such as the reader of FIG. 4) is proximate a location to be inspected (after the triggering condition has been detected). In a block 200a, the person reads a token proximate the location to be inspected with the reader. As discussed above, many different types of token/readers can be employed, including RFID tags and readers configured to read RFID tags, and optical tokens (such as bar codes) and readers configured to read optical tokens. In a block 202, the second signal, indicating that the person was proximate the location to be inspected (and thus, is likely to have performed the inspection) is sent to the monitor. The portable reader itself can include a transmitter that sends the second signal, or the portable reader may be placed into a docking station (see FIG. 7) to enable the second signal to be transmitted to the monitor. Where an inspection relates to a plurality of locations and a plurality of tokens, the second signal can indicate the tokens that have been read, or the second signal may be transmitted only after all tokens are read. Finally, yet another embodiment of the invention employs the logical steps shown in FIG. 15. In this embodiment, the second signal is sent only if a sensor (disposed at the predefined location to be inspected, or in a reader used to facilitate the inspection) determines that a triggering condition has been detected, and that the person was not proximate the location to be inspected before a predetermined event occurs. The second signal can be sent to a monitor, which then produces an indication the inspection was not performed as described above. Alternatively, the second signal can be transmitted to an individual tasked with performing appropriate steps to correct the failure to inspect. The logical process of this embodiment of the invention starts in a block 204. In a block 182a, a triggering condition is detected. Different types of triggering conditions and detectors have been discussed in detail above, and need not be repeated here. In a block 184a, the detector that identifies the triggering condition transmits a signal to a sensor, rather than to the monitor, as described above. Where the sensor is part of a portable reader (such as the one shown in FIG. 4), the portable reader must be in range of the signal sent by the detector that detects the triggering condition. In this embodiment, the detector will likely transmit the signal as a wireless communication, although if the portable reader is stored in a docking station (see FIG. 7), the detector can send the first signal to the reader via a wired connection. If the sensor is part of a switch disposed at the predefined location to be inspected, the detector may be logically coupled to the sensor/switch, and the sensor/switch can be configured to receive a wireless communication from the detector. In a block 186a, the sensor waits for a predetermine event to occur. In a decision block 206 (i.e., after the predefined event has occurred), the sensor determines if a person has been proximate the predefined location. As discussed in detail above, such a determination can be based on the person activating a switch at the predefined location, or the person can use a portable reader to read an RFID tag or an optical token (or some other token as discussed above). If in a decision block 206, if it is determined that the person has been detected at the predefined location, then the logic is finished, as indicated in a block 196a. If the sensor (which is capable of logical processing) determines that the person has not been detected at the predefined location, then in a block 208, the sensor transmits a second signal (which in this aspect of the invention indicates that the inspection has not been properly executed). Preferably, the sensor includes a transmitter configured to transmit the second signal to a receiver (such as a monitor as described above, or a person tasked with managing the inspection). Where the sensor is disposed at the predefined location (i.e., as the sensor in a sensor/switch activated by the person or by a portable device as described above), the sensor can be physically connected to a monitor or communication system, so that a transmitter is not required. Further, individual sensor/switches can be coupled to a common transmitter, as discussed above (see FIG. 12). If the sensor is part of a portable device reading tokens disposed at the predefined locations, the portable device (which includes the sensor) preferably also includes a transmitter. While portable devices without a transmitter can still send a second signal via wired connection (e.g., using the docking station of FIG. 7), if the portable device does not include a transmitter and is not returned to the docking station, then no second signal could be sent to indicate the inspection had not been completed. Thus, it is preferred for the portable device to include a transmitter. In a block 192a, an indication (such as an alarm) is generated indicating that the inspection was NOT performed. In a block 194a, an appropriate action, such as discussed above, can be taken to correct the failure to properly conduct the inspection. Although the concepts disclosed herein have been described in connection with the preferred form of practicing them and modifications thereto, those of ordinary skill in the art will understand that many other modifications can be made thereto within the scope of the claims that follow. Accordingly, it is not intended that the scope of these concepts in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow.
063273225	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is illustrated a spent fuel pit 10 which contains a plurality of spent nuclear fuel racks 12. The pit 10 is a sealed enclosure comprised of concrete 14 and a sealed metallic liner 16. The spent fuel pit 10 is filled with a shielding medium, such as water containing boric acid 18. Each fuel rack 12 includes a plurality of vertically oriented spaced apart fuel cells 20. Each cell 20 is sized to receive a fuel assembly 50 (described below). Each cell 20 has a metallic can 22 affixed to the top of the cell 20. The can 22 may include a square funnel to guide a fuel assembly 50 into its storage position. As shown in FIG. 2, the can 22 includes two bores 24, 26 in raised plates 25, 27 at diagonally opposite corners. The remaining corners of the can 22 define standoff plates 28, 30. Referring to FIG. 2, a poison rod assembly 40 is shown partially extracted from a fuel cell 20. Each fuel assembly 50 is formed in part from fuel rods 52 which are intermixed with poison rods 42. The fuel rods 52 are generally positioned on the periphery of the fuel assembly 50 and the poison rods 42 are generally positioned in an inner portion of the fuel assembly 50. The poison rods 42 are joined at their top portions by a support web 44. A T-shaped bar 46 is attached to the support web 44 extending upwardly, forming an easily accessible handle for lifting the poison rod assembly 40. When the poison rod assembly 40 is positioned within the fuel assembly 50, each poison rod 42 is disposed within a thimble 48 mounted in the fuel assembly 50. Referring to FIG. 1, a poison rod assembly transfer device 70 of the present invention is illustrated within a spent fuel pit 10. The transfer device 70 is suspended within the spent fuel pit 10 by an overhead crane 60. The overhead crane 60 is coupled to a moveable walkway 62 and gantry 63. The moveable walkway 62 and gantry 63 are mounted on walkway rails 64 located above the water line 18 of the spent fuel pit 10. The crane 60, moveable walkway 62 and gantry 63 are used to lift the transfer device 70 and a poison rod assembly 40 and move them between fuel cells 20. The transfer device 70 is seated on a fuel cell 20 and attached to a poison rod assembly 40 as detailed below. The transfer device 70 includes an elongated outer member 200, and an inner member 230 slidably disposed within the elongated outer member 200. In the preferred embodiment, the elongated outer member 200 will have two distinct portions, an upper portion 90 and a frame assembly 80. The frame assembly 80 supports and protects the poison rod assembly 40 as it is extracted from fuel cell 20. In the preferred embodiment, the upper portion 90 is tubular. The frame assembly 80 is fixed below the upper portion 90. The frame assembly 80 and the upper portion 90 are of an appropriate length so that the top of the upper portion 90 is adjacent to the walkway 62 when the transfer device 70 is seated on a fuel cell 20. As shown diagrammatically in FIG. 3, the upper portion includes outer member 250. Inner member 230 is slidably disposed within the outer member 250 and frame 80, and is coupled with a gripper assembly 210. Gripper assembly 210 is disposed within the elongated outer member 200 and partially disposed within the inner member 230. The gripper assembly 210 includes a gripper 212 disposed within the frame 80. The inner member 230 and outer member 250 can be selectively coupled by an interlock device 280. The interlock device 280 locks the inner member 230 in either an upper position 228 as shown in FIG. 3c or a lower position 229 as shown in FIG. 3a. The inner member 230 is attached to the crane 60 so that, when the inner member 230 is not coupled to outer member 250 and the crane 60 is raised, frame 80 and outer member 250 remain stationary and inner member 230 and gripper assembly 210 move vertically. When the interlock device 280 is engaged, however inner member 230 is coupled to outer member 250 and raising the crane 60 raises the entire transfer device 70. Thus, lifting of a poison rod assembly 40 is accomplished by an operator using crane 60 to position the transfer device 70 over a fuel cell 20 containing a poison rod assembly 40. Once the transfer device 70 is seated on the fuel cell 20, the operator uses crane 60 to lower inner member 230 and gripper assembly 210 until the gripper assembly 210 engages the T-bar 46 of the poison rod assembly 40. When the gripper assembly 210 has engaged the T-bar 46, the operator uses crane 60 to lift the inner member 230, gripper assembly 210 and the poison rod assembly 70. Once the poison rod assembly 40 is withdrawn from fuel cell 20, the operator may use the moveable gantry 63 to reposition the crane 60 and transfer device 70 above another fuel cell 20. The transfer device 70 is seated on the second fuel cell 20 and the poison rod assembly 40 can be inserted into the second fuel cell 20. When the poison rod assembly 40 is seated within the second fuel cell 20, the gripper assembly 210 is disengaged from the poison rod assembly 40 and the transfer device 70 removed. As shown in FIG. 4a, 4b, and 5, the frame assembly 80 includes two C-members 82, 84 held in spaced relation by a plurality of braces 86. The C-members 82, 84 define a, preferably square, frame cavity 88. Each C-member 82, 84 has an upper end 92, located at frame assembly upper end 91, and a lower end 94, 96 located at frame assembly lower end 95. At the lower end 94, 96 of the C-members 82, 84 is a mounting plate 100. Mounting plate 100 has an upper surface 102, an opening 104 and a lower surface 106. The C-members 82, 84 are attached to the mounting plate upper surface 102. The mounting plate opening 104 communicates with the frame cavity 88. The frame assembly 80 further includes a square pedestal 110 attached to the mounting plate lower surface 106. The pedestal 110 is a four-sided structure having an upper surface 111, a lower surface 112 with openings 113, 114 therethrough. The upper surface pedestal opening 113 and lower surface pedestal opening 114 are sized to allow the poison rod assembly 40 to pass therethrough. The upper surface pedestal opening 113 communicates with the mounting plate opening 104. In operation, the poison rod assembly 40 will be lifted through the pedestal 110 and mounting plate 100 by gripper assembly 210 into a position within the frame cavity 88. The pedestal lower surface 112 has at least one projection 116. In the preferred embodiment there are two pedestal projections 116 extending downwardly from diagonally opposite corners. The projection 116 are sized to engage the bore holes 24, 26 on the fuel rod assembly can 22. Thus, seating the transfer device 70 as a fuel cell 20 is accomplished by the operator lowering the device 70 until projection 116 are seated within bore holes 24, 26. Once the projection 116 are so seated, the transfer device 70 is resting on the fuel cell 20. Outer member 250 is fixed at its lower end 252 to frame 80. Thus, when the transfer device 70 is seated on a fuel cell 20, frame 80 and, therefore outer member 250, are fixed in place. As noted above, inner member 230 is slidable disposed within outer member 250. Thus, as shown in FIG. 3, when frame 80 and outer member 250 are fixed in place, inner member 230 can slide between an upper position 228 and a lower position 229 within outer member 250 and frame 80. As shown in FIG. 6, a platform 240 is mounted at the upper end 232 of inner member 230. The lifting platform 240 includes a plate 242 having an upper surface 243, a medial hole 244 therethrough and a lifting bail 246 disposed above the plate 242. The inner member 230 passes through medial hole 244 and has a flange 238 that contacts plate upper surface 243. The crane 60 is attached by conventional means to the bail 246. Thus, raising or lowering inner member 230 or transfer device 70 is accomplished through the crane 60 acting on platform 240. As shown in FIGS. 3, 7a, 7b and 8, the interlock device 280 allows the inner member 230 to be locked in either the upper position 228 or the lower position 229. In the upper position 228, the inner member 230 is raised so that the gripper assembly 210 is adjacent to the top of frame 80. In the lower position 229, the gripper assembly 210 is adjacent to the lower end of frame 80, but spaced above pedestal 110. When the inner member 230 is in either locked position 228, 229, raising or lowering the crane 60 will lift or lower the transfer device 70. When the interlock device 280 is in an unlocked position, raising or lowering the crane 60 will slide the inner member 230 between the upper position 228 and the lower position 229 as shown in FIG. 3b or allow the gripper assembly 210 to be lowered to engage a poison rod assembly 40. The interlock device 280 is located adjacent to the upper end 254 of outer member 250. When the transfer device 70 is seated on a fuel cell 20, the interlock device 280 is positioned adjacent to the walkway 62 where it may be reached by the operator. The interlock device 280 includes a pair of latch members 290, 291, and a release mechanism 300 which includes support collar assembly 301, linking members 282, 283, a double clevis 284, push rod 286, spring 288, and interlock support plate 289. Additionally, outer member 250 has two openings 258, 259, spaced one hundred and eighty degrees apart, located adjacent to the interlock device 280. Finally, inner member 230 has an upper pair of openings 260, 261 and a lower pair of openings 262, 263 each spaced one hundred and eighty degrees apart. The upper openings 260, 261 are located proximal to the upper end of member 230 and the lower openings 262, 263 are spaced approximately 13-15 feet (just over the length of the poison rod assembly) below the upper openings 260, 261. As will be detailed below, spring 288, cooperating with linking members 282, 283 and push rod 286, urge latch members 290, 291 to pass through the outer member openings 258, 259 and either the upper or lower inner member openings 260, 261, 262, 263 whereupon the inner member 230 will be locked in place relative to the outer member 250. Support collar assembly 301 includes a collar 302, pin supports 304, 305, 306, 307, and pins 308, 309. As shown in FIG. 9, collar 302 is rectangular with an offset medial opening 310 therethrough, a push rod opening 312, and a plurality of fastener holes therethrough 314. As shown in FIGS. 7a and 7b, pin supports 304, 305, 306, 307 are disposed below the collar 302 held by fasteners 315 which are disposed within fastener holes 314. It is understood that, although not shown in the elevational views, pin support 306 is located adjacent to pin support 304. As shown in FIG. 10, each pin support 304, 305, 306, 307 has a flat body 320 with an pin opening 322 and a perpendicular mounting flange 324. The mounting flange 324 incorporates threaded fastener holes 326, 328 which cooperate with fasteners 315 to attach the pin supports 304, 305, 306, 307 below and to collar 302. When disposed below collar 302, the pin supports 304, 305, 306, 307 form pairs with aligned pin openings 322. Rotatable pins 308, 309 are disposed within each pair of pin supports 304, 305, 306, 307 passing through pin openings 322. Each pin 308, 309 has an axis of rotation 331, 333. Each pin 308, 309, is fixed to a linking member 282, 283 and to a latch member 290, 291. In the preferred embodiment, as shown on FIG. 11, latch members 290, 291 are butterfly wing shaped plates 350, 351 having a tabs 352, 353, wheel cavities 354, 355, wheels 356, 357, axles 358, 359 and mounting holes 360, 361. Tabs 352, 353 are shaped with a convex outer edge 362, 363, with notches 364, 365, 366, 367 between outer edges 362, 363 and plates 350, 351. Wheel cavities 354, 355 are within either tab 352, 353. Wheels 356, 357 are disposed within either wheel cavity 354, 355 and held in place by either axle 358, 359. Wheels 356, 357 extend beyond outer edges 362, 363. Latch members 290, 291 are fixed to either pin 308, 309 and rotate about either axis 331 or 333. Latch members 290, 291 are attached to pins 308, 309 so that tabs 352, 353 are proximal to outer member 250 and so that latch members 290, 291 are disposed below collar assembly 301. Referring again to FIGS. 7 and 8, interlock support plate 289 is rectangular having push rod opening 342. Interlock support plate 289 is disposed adjacent to the top of outer member 250 above collar assembly 301. Collar assembly 301 is disposed about outer member 250 above openings 258, 259. Collar assembly tab opening 312 and support plate tab opening 342 are aligned vertically. Push rod 286 is slidably disposed through collar assembly tab opening 312 and support plate tab opening 342. Push rod 286 has an upper end 950 and a lower end 351. A ball knob 952 is disposed at push rod upper end 950. Horizontal double clevis 284 is disposed at push rod lower end 351. Linking members 282, 283 are flat rectangular members having a pivot holes 360, 361 at one end and a pin mounting holes 362, 363 at the opposite end. Linking members 282, 283 are rotatably coupled about pivot holes 360, 361 to double clevis 284, one linking member 282, 283 on either side of the double clevis 284. As noted above, linking members 282, 283 are each fixedly attached to a pin 308, 309; this attachment is through pin mounting holes 362, 363. Push rod 286 has a flange 370 disposed at a location spaced above collar assembly 301. Spring 288 is a helical coil spring wrapped about push rod 286 and positioned between collar assembly 301 and flange 370, thus biasing push rod 286 upward. Unless the shield device 420 is engaged (described below), the interlock device 280 engages the inner member 230 and outer member 250 in a similar fashion regardless of whether the inner member 230 is in its upper position 228 or its lower position 229. Accordingly, the following description shall address the operation of the interlock device 280 as if the inner member 230 is in its upper position 228 and tabs 352, 353 of latch members 290, 291 pass through inner member lower openings 262, 263. It is understood however that the following description is equally applicable to the operation of the interlock device 280 with the inner member upper openings 260, 261. As shown in FIG. 8, if crane 60 is lifting inner member 230 while tabs 352, 353 of latch members 290, 291 pass through inner member 230 lower openings 262, 263, inner member 230 will slide within outer member 250 until the lower edge 262a, 263a of lower openings 262, 263 contact notches 365, 367. When the lower edge 262a, 263a of lower openings 262, 263 contacts notches 365, 367, inner member 230 is prevented from sliding within outer member 250. At this point, raising the crane 60 will lift the entire transfer device 70 as the lifting force is transferred from inner member 230 through the interlock device 280 to outer member 250. As shown in FIG. 12A, in operation, as push rod 286 is biased upward by spring 288 into an upper position 390, push rod 286 lifts double clevis 284. Double clevis 284 in turn lifts linking members 282, 283. Linking members 282, 283 act upon either pin 308 or 309 which in turn act upon latch members 290, 291, biasing latch members 290, 291 toward outer member 250. Tabs 352, 353 of latch members 290, 291 pass through outer member openings 258, 259. Unless the shield device 420 is in place, as described below, when the inner member is in either its upper position 228 or its lower position 299, tabs 352, 353 of latch members 290, 291 also pass through either inner member 230 upper openings 260, 261, or lower openings 262, 263. Thus, when the push rod 286 is in its upper position 390 and the outer member openings 258, 259 are aligned with the inner member openings 260, 261 the latch members 290, 291 are in the locked position. To release the interlock device 280 and allow the inner member 230 to slide within outer member 250, an operator must operate the release mechanism 300 by pressing ball knob 952 which will counter act the force of spring 288 acting on push rod 286 and lower push rod 286 into it lower position 400. When push rod 286 is in its lower position 400, push rod 286 lowers double clevis 284. Double clevis 284 in turn lowers linking members 282, 283. Linking members 282, 283 act upon either pin 308 or 309 which in turn act upon latch members 290, 291, rotating latch members 290, 291 away from outer member 250. Tabs 352, 353 of latch members 290, 291 are then removed from outer member 250 openings 258, 259 and either inner member 230 upper openings 260, 261, or lower openings 262, 263. Thus, when the push rod 286 is in its upper position 390 and the outer member openings 258, 259 are aligned with the inner member openings 260, 261 the latch members 290, 291 are in the locked position. With the latch members 290, 291 in the unlocked position, inner member 230 can slide freely within outer member 250. As shown in FIG. 3b, as inner member 230 slides up or down within outer member 250, the inner member openings, either upper or lower, 260, 261, 262, 263, will no longer be aligned with outer member openings 258, 259. Instead, as inner member 230 is being raised or lowered, the outer surface 236 of inner member 230 is exposed through outer member openings 258, 259. Once the outer surface 236 of inner member 230 is exposed through outer member openings 258, 259 the operator may release ball knob 352 and allow latch members 290, 291 to be biased by spring 288 toward outer member 250. Wheels 356, 357 will now contact the outer surface 236 of inner member 230 allowing inner member 230 to slide between latch members 290, 291. When inner member 230 reaches either its upper position 228 or its lower position 229, the inner member openings, either upper or lower, 260, 261, 262, 263 will align with outer member openings 258, 259 and latch members 290, 291 will close, once again locking the inner member 230 within the outer member 250. The interlock device 280 may be disabled by a shield device 420. Disabling the interlock device 280 is desirable when lifting a poison rod assembly 40 from a fuel cell 20. As will be described below, lifting of the poison rod assembly 40 is accomplished by coupling the poison rod assembly 40 to gripper assembly 210 located at the bottom of inner shaft 230. To engage gripper assembly 210 with the poison rod assembly 40, the inner member 230 must be lowered below its lower position 229. To lower inner member 230 below its lower position 229, the interlock device 280 must be disengaged. To prevent the interlock device 280 from re-engaging once inner member 230 returns to its lower position 229 as the poison rod assembly 40 is being lifted, a shield device 420 is used. As shown in FIG. 13, the shield device 420 includes two arcuate shields 422, 424 and mounting arms 426, 428. Mounting arms 426, 428 are attached to inner shaft 218. Inner shaft 218 is rotatably disposed within inner member 230. As part of the lifting operation described below, inner shaft 218 is rotated to latch T-bar 46 in gripper assembly 210. Shields 422, 424 are attached to mounting arms 426, 428 and disposed within inner member 230 adjacent to inner member 230 upper openings 260, 261. Shields 422, 424 are sized to match inner member 230 upper openings 260, 261. As shown in FIGS. 14a and 14b, mounting arms 426, 428 position shields 422, 424 so that when gripper 210 is not latched on a poison rod assembly 40, the shields are rotated away from openings 260, 261 so that the shield device 420 is in an open position. When inner shaft 218 is rotated to latch gripper 210, shields 422, 424 are rotated across openings 260, 261. Thus, when a poison rod assembly 40 is latched in gripper 210 and inner member 230 raised, the shield device 420 is in a closed position, blocking openings 260, 261, preventing interlock device 280 from latching inner member 230 in the lower position 229. As shown in FIG. 15, coupling the poison rod assembly 40 to the transfer device 70 is accomplished by a gripper assembly 210 located at the bottom 234 of inner member 230 which can be rotated between an latched and an unlatched position. The gripper assembly 210 includes a gripper 212, a connecting pin 214, a base 216 and inner shaft 218. The gripper base 216 is a cylindrical member attached to inner member bottom 234, having a greater diameter than the inner member 230 and having two support fingers 217 extending downwardly from the base 216. The gripper base 216 provides support for the gripper 212 which is rotatably disposed about the gripper base 216. The gripper 212 incorporates two J-shaped notches 219 which are spaced approximately one hundred and eighty degrees apart. The J-shaped notches 219 are used to latch onto the T-bar 46 of the poison rod assembly 40. The gripper 212 is disposed on the gripper base 216 so that the J-shaped notches 219 are between support fingers 217. Inner shaft 218 is rotatably disposed within inner member 230 and extends from the bottom 234 of inner member 230 through the flange 238 located at the top of inner member 230. A connecting pin 214 connects the inner shaft 218 to the gripper 212. As shown in FIG. 6, a handle 248 is attached to the upper end of inner shaft 218 at lifting platform 240. When the gripper is positioned over a poison rod assembly 40 with T-bar 46 disposed within notch 219, the operator rotates handle 248 causing shaft 218 and, therefore, gripper 212 to rotate thereby latching T-bar 46 into J-shaped notches 219. In operation, the transfer device 70 is seated on a fuel cell 20 as described above. At this time, inner member 230 in its lower locked position 229. The operator releases interlock device 280 and uses crane 60 to lower gripper assembly 210 onto the poison rod assembly 40. T-bar 46 will fit into the J-shaped notches 219. The operator then turns handle 248 rotating gripper 212 and latching T-bar 46 in the J-shaped notches 219. At the same time, shield device 420 rotates blocking inner member upper openings 260, 261. The operator then uses crane 60 to lift inner member 230, thereby raising gripper 212 and poison rod assembly 40 into frame cavity 88. Once inner member reaches its upper position 229, the interlock device 280 will engage. After the interlock device 280 has been engaged, raising crane 60 lifts the transfer device 70 off fuel cell 20. The operator then uses gantry 64 to reposition the transfer device over a different fuel cell 20. The transfer device 70 is then seated on the second fuel cell 20 as described above. Once the transfer device 70 is seated on the second fuel cell, the operator releases interlock device 280 and lowers crane 60 thereby lowering the poison rod assembly 40 into the new fuel cell 20. After the poison rod assembly 40 is inserted into a second fuel cell 20, the operator turns handle 248 to unlatch the poison rod assembly 40 from gripper assembly 210. Simultaneously, shield device 420 will be withdrawn from inner member upper openings 260, 261. The operator then raises crane 60 to lift inner member 230 until the interlock device 280 engages upper openings 260, 261. Once the interlock device 280 is engaged, crane 60 may lift transfer device 70 off fuel cell 20. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangement disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breath of the appended claims and any and all equivalence thereof.
	summary
	claims	1. A spacer grid (10) for placing and supporting a plurality of longitudinal fuel rods (125) in a nuclear reactor fuel assembly, comprising:a plurality of inner strips (30) intersecting each other to form a plurality of guide tube cells (15) to receive guide tubes (13) therein and a plurality of fuel rod cells (26) to receive the fuel rods (125) therein, with a plurality of mixing blades (27) projecting upward from the inner strips (30) at intersections of the inner strips (30); anda plurality of perimeter strips (40) each of which comprises a plurality of unit strips including intermediate unit strips (40′) and corner unit strips (40″), the perimeter strips (40) encircling the intersecting inner strips (30), and the corner unit strips (40″) forming outermost corner cells of the spacer grid (10), with a grid spring (50) provided on each of the unit strips (40′, 40″), the grid spring (50) comprising:a vertical opening (53) formed at a central area of each of the unit strips;a vertical support part (51) extending vertically in the vertical opening (53) from central portions of top and bottom edges of the vertical opening (53); anda fuel rod support part (52) provided at a central portion of the vertical support part (51), the fuel rod support part (52) being bent to have equiangular surface contact with a fuel rod supported by the grid spring for reducing fretting corrosion of the fuel rod,further comprising inner grid springs on the inner strips, wherein the inner grid springs comprise an opening formed in the inner strips and defined by top, bottom and side edges, two spaced inner support parts extending vertically in the opening between the top and bottom edges of the opening, and an inner fuel rod support part extending transversely between the two spaced inner support parts, the inner fuel rod support part being bent at least two steps along vertical bending lines and defining an equiangular support surface which is equiangular with a fuel rod supported by the inner grid spring, wherein the vertical support part and the two spaced inner support parts are different in structure,wherein each of the intermediate unit strips (40′) has a coolant flow guide vane (57) and a guide tap (58) on an upper edge thereof such that a plurality of coolant flow guide vanes (57) and a plurality of guide taps (58) are alternately arranged along an upper edge of each of the intermediate unit strips (40′), and each of the unit corner strips (40″) having either a coolant flow guide vane (57) or a guide tap (58) on an upper edge thereof to complete an alternate arrangement of the coolant flow guide vanes (57) and the guide taps (58), in cooperation with the intermediate unit strips (40′), wherein each of the plurality of intermediate unit strips (40′) has two guide taps (58) projecting downward at both corners on a lower edge of each of the intermediate unit strips (40′), and each of the plurality of unit corner strips (40″) has a guide tap (58) projecting downward on a lower edge of each of the unit corner strips (40″) for reducing interference between the fuel rods (125) and the spacer grid (10) when the fuel rods (125) are inserted and removed. 2. The spacer grid (10) according to claim 1, wherein the vertical support part (51) is bent at two steps along substantially horizontal bending lines, and the fuel rod support part (52) is equiangular with the fuel rods (125), whereby a uniform contact pressure distribution is provided between the fuel rod support part (52) in contact with the fuel rods (125). 3. The spacer grid (10) according to claim 1, wherein each of the coolant flow guide vanes (57) is bent toward a center of the spacer grid (10), with a width of each of the guide vanes (57) reducing from a position at which each of the guide vanes (57) is initially bent, each of the guide vanes (57) has a tapered shape, with a peak of each of the guide vanes (57) being rounded. 4. The spacer grid (10) according to claim 1, wherein each of the guide taps (58) is bent toward the center of the spacer grid (10), and is rounded at a bent tip thereof to form an arc-shaped edge. 5. The spacer grid according to claim 1, wherein the vertical support part and the two spaced inner support parts have a different geometry. 6. The spacer grid according to claim 1, wherein the vertical support part and the two spaced inner support parts have a different shape. 7. The spacer grid according to claim 1, wherein the two spaced inner support parts are spaced from each other and from the side edges.
052778460	description	The installation comprises a cryogenic grinding unit made up of a crusher-shredder 1 and a granulator 2 which operate at -120.degree. C. The ground waste is passed through a duct 3 to a first metering device 4. A second metering device 5 is fed by a duct 6 coming from a source of additive. The two metering devices 4, 5 open into a duct 7 which is supplied at one end from an air source and which leads to a mixing cyclone 8. From here runs a rod 9 which passes through the side wall of a furnace and opens out close to the bottom 10 of said furnace. The furnace, made of refractory material, comprises two distinct parts. A crucible 11, made of refractory steel at the bottom, containing a molten siliceous bath and equipped with heating means 12, and an upper part 13 made of refractory material. A pouring rod 14 passes through the base 10 and opens into the crucible at a height of 400 mm. The top part 13 has a refractory vault 15 provided with zig-zag passages 16 which sub-divide this top part into a combustion chamber 17 formed above the siliceous bath and below the vault 15 and an evacuation chamber 18 above the vault 15. The top part 13 is equipped with heating means 19. An air ramp 20 opens into the chamber 17. From the chamber 18, a duct 21 leads to an air cooler 22 supplied with air through a duct 23 and communicating via a duct 24 with a chemical neutraliser 25 which converts chlorine into soluble chloride and operates as a closed circuit, with a pump 26 circulating a solution of alkali metal carbonate or sodium carbonate into the neutralizer 25 through a duct 27. A duct 28 leads from there to a very high efficiency filter 29. The efficiency of the filter is 99.98%. This filter is intended to eliminate radioactive aerosols. From the filter 29, a duct 30 leads to a fan 31 and a chimney 32. The following examples illustrate the invention. EXAMPLE 1 The installation shown in the drawing is used to treat waste from the maintenance and repair of hospitals, laboratories and nuclear plants, consisting of plastics, rubber, paper, cotton and cloth. This waste is contaminated by radionuclides with a short half-life and low radioactivity. This waste, ground in the crusher 1 and granulator 2, which operate at -120.degree. C., has a particle size of less than 1 mm in the duct 3. The metering device 4 delivers 667 g of waste per minute to the duct 7. The metering device 5 delivers 19 g of sodium carbonate per minute to the duct 7. The flow rate of air in the duct 7 is 3 normal cubic meters per hour under pressure. The refractory steel crucible 11 has a diameter of 500 mm and a height of 1000 mm, corresponding to a capacity of 196 liters. It contains a molten siliceous bath consisting of 61% by weight of SiO.sub.2 and 39% by weight of a mixture of B.sub.2 O.sub.3 and Na.sub.2 O. The melting point is 900.degree..+-.20.degree. C. The operating temperature is 1000.degree..+-.50.degree. C. The height of the bath at the start of treatment is 400 mm (78 liters corresponding substantially to 195 kg). This mass constitutes the permanent liquid residue in the crucible which is at a temperature of 1000.degree. C. The opening of the injection rod 9 for the waste is 100 mm above the bottom 10. 350 normal cubic meters per hour of air are passed into the combustion chamber 17 via the ramp 20. 2300 normal cubic meters of air per hour are passed through the duct 22 at 20.degree. C., thus enabling the temperature of the gases leaving the duct 21 to be brought down to a temperature of below 100.degree. C. The temperature at the exit from the cooler is about 80.degree. C. The binders and mineral additives to the waste are held in the siliceous bath. The variation in the volume of the bath, for an intake flow rate of 40 kg of waste per hour is 0.7 liters per hour and this bath is poured through the rod 14 every 96 hours for a unit treating 40 kgh.sup.-1. The glass solidifies in the receiving vessel. Its chemical composition hardly varies as a function of time. Analyses of the poured glass after 8 hours treatment shows SiO.sub.2 equals 61%+.epsilon., whereas Na.sub.2 O+B.sub.2 O.sub.3 equals 39%-.epsilon.. The effluent leaving the chimney 32 comprises 49,000 normal cubic meters of CO.sub.2 per hour, 52 cubic meters of H.sub.2 O per hour and 2600 cubic meters of air per hour. The environmental pollution is negligible because the process only emits 97% air at 20.degree. C. Any contaminants are imprisoned in the poured glass or trapped on the specific filter and the HCl content remains less than 100 mg per normal cubic meter. When it is known that this type of waste is currently collected, then compacted and coated with concrete in specific containers and that a 200 liter capacity vessel contains only 30 kg of waste, it will be realised that the process according to the invention makes it possible to reduce the volumes definitively by a co-efficient of about 350, whilst achieving a compact packaging which has good mechanical resistance and is not subject to leaching. EXAMPLE 2 Polyethylene and glass flasks are treated which contain scintillators and nuclear medicine tracers. The installation is the one described in example 1. The metering device 4 supplies 670 g of waste per minute to the duct 7. A metering device 5 supplies 25 g of sodium carbonate per minute to the duct 7. Through the ramp 20, 5 normal cubic meters per hour of air are passed into the chamber 17. 910 cubic meters per hour pass through the duct 23 at a temperature of 20.degree. C. The temperature at the exit from the cooler is about 80.degree. C. In this case, the neutralizer 25 is omitted from the installation. The chemical composition of the bath is 60% by weight of SiO.sub.2 and 40% by weight of a mixture of B.sub.2 O.sub.3 and Na.sub.2 O. The melting point thereof is 900.+-.20.degree. C. Its operating temperature is 1000.+-.50.degree. C. The variation in the volume of the bath essentially caused by the glass flasks for an intake flow rate of 40 kg of waste per hour is 12.5 liters per hour and pouring through the rod 14 is carried out every 8 hours (100 liters. A composition of the glass obtained hardly changes as a function of time, the composition remaining substantially identical to the initial composition. The waste gases leaving through the chimney consist of 16 normal cubic meters of CO.sub.2 per hour, 16 cubic meters of H.sub.2 O per hour and 1000 normal cubic meters of air per hour. The process produces only an effluent which consists of 97% air at 20.degree. C. Any contaminants are imprisoned in the poured glass or trapped on the filter. Currently, these flasks are coarsely ground in order to recover the scintillation residues, then compacted and coated in concrete in specific containers. A 200 liter container of this mixed waste contains only 30 kg of glass. The process makes it possible to reduce volumes by a coefficient of 16 and provides a compact, non-leachable packaging with good mechanical strength. EXAMPLE 3 Waste from the chemical industry consisting essentially of phenyl mercury is treated. The installation used is essentially the same as that used in FIG. 1. The metering device 4 delivers 167 g of waste per minute to the duct 7. The metering device 5 delivers 22 g of a mixture of alkali metal carbonate and silica per minute to the duct 7. 3 cubic meters of air per hour are fed under pressure into the duct 7. 60 normal cubic meters per hour of air are passed to the chamber 17 via the ramp 20. Through the duct 23, 700 normal cubic meters of air are passed each hour at 20.degree. C. The temperature at the exit from the cooler 22 is about 80.degree. C. The chemical neutralizer converts HgO into soluble salts. The bath contains 60% by weight of SiO.sub.2 and 40% by weight of Na.sub.2 O. Its melting point is 900.+-.20.degree. C. Its operating temperature is 1000.+-.50.degree. C. Analysis of the poured bath, after 8 hours treatment, shows SiO.sub.2 equals 60%.+-..epsilon. and Na.sub.2 O equals 40% .+-..epsilon.. The variation in the volume of the bath, for an intake flow rate of 10 kg of waste per hour, is 3.2 liters per hour. The waste gases comprise 11 normal cubic meters of CO.sub.2 per hour, 4 normal cubic meters of H.sub.2 O per hour and 700 cubic meters of air per hour. The process produces a waste product of 98.5% by weight of air at 20.degree. C. (the Hg content is less than 0.3 mg. per normal cubic meter) .
044366949	claims	1. Apparatus for decontaminating the inside walls of a nuclear reactor cavity in a refueling floor, having a raised curb around its periphery which comprises: a chassis having wheels in rolling contact with said floor; first and second curb wheels mounted on said chassis in horizontal rolling contact with said curb; a support member extending upwardly and laterally from said chassis; an elongated mast depending from said support member and into the reactor cavity; at least one reaction wheel carried by said mast for horizontal rolling engagement with the cavity wall; a carriage vertically positionable along said elongated mast; and means carried by said carriage for spraying decontaminating fluid on said cavity wall. 2. The apparatus of claim 1 wherein said chassis includes a motor connected to drive at least one of said floor contacting wheels. 3. The apparatus of claim 1 wherein said curb wheels include adjustable mounting means for varying the distance between each of said curb wheels and said chassis. 4. The apparatus of claim 3 wherein said mounting means comprises a scissors jack. 5. The apparatus of claim 1 wherein said mast includes means for raising and lowering said carriage. 6. The apparatus of claim 5 wherein said raising and lowering means comprises a cable. 7. The apparatus of claim 5 wherein said spraying means comprises water nozzles. 8. The apparatus of claim 7 wherein said carriage includes a protective shroud surrounding said nozzles. 9. The apparatus of claim 8 wherein said curb wheels include adjustable mounting means for varying the distance between each of said curb wheels and said chassis. 10. The apparatus of claim 9 wherein said chassis includes a motor connected to drive at least one of said floor contacting wheels.
	claims	1. A radiation protection arrangement for screening radiation emitted by a radiation source, in particular an X-ray source, havinga screening element which comprises or includes a radiation protection material, anda cover which is matched in shape to the screening element and completely surrounds the latter, it being possible to pull the cover over the screening element and completely separate it therefrom, and wherein, for the purpose of altering the length, there is provided a fixing device such that the cover, with the screening element arranged therein, is turnable up in at least one direction and fixed in the turned-up arrangement. 2. A radiation protection arrangement according to claim 1, whereinthe cover comprises a material which can be sterilized using a suitable device or a suitable process. 3. A radiation protection arrangement according to claim 1, whereinthe fixing device is formed by press studs. 4. A radiation protection arrangement according to claim 1, whereinthe fixing device is formed by a hook-and-burr closure. 5. A radiation protection arrangement according to claim 1, whereinthe fixing device is formed by a tie closure. 6. A radiation protection arrangement according to claim 1, whereinthe cover has means for securing it to a carrier element which holds the screening element. 7. A radiation protection arrangement according to claim 6 whereinthe means for securing are tapes. 8. A radiation protection arrangement according to claim 6, whereinthe means for securing are press studs. 9. A radiation protection arrangement according to claim 6, whereinthe means for securing are hook-and-burr closures. 10. A radiation protection arrangement according to claim 1, whereinthe screening element is formed by a single blanket which includes an X-ray screening material, and the cover is formed by a sheath which is matched in its dimensions to the blanket and is open to one side. 11. A radiation protection arrangement according to claim 1, whereinthe screening element comprises a plurality of slats arranged next to one another and including an X-ray screening material and are secured at one end to a common carrier element, the cover having a plurality of elongate sheaths for receiving a respective slat and connected to one another at one end by way of a common cuff. 12. A radiation protection arrangement according to claim 11, whereinthe slats are arranged such that they overlap. 13. A radiation protection arrangement according to claim 11, whereineach sheath has its own fixing device for the purpose of altering the length. 14. A radiation protection arrangement according to claim 1, whereinthe screening element includes a lead sheet or lead rubber blanket surrounded by a PVC cover. 15. A radiation protection arrangement according to claim 14, whereinthe screening element has a lead equivalence value of approximately 0.5 mm. 16. A radiation protection arrangement according to claim 1, whereinit is arranged on the underside of a radiation protection panel. 17. A radiation protection arrangement according to claim 1, whereinit forms a lower body protection arranged to the side of a medical operating or treatment table. 18. A cover for a screening element which comprises or includes a radiation protection material and is provided for use in a radiation protection arrangement for screening radiation emitted by a radiation source, in particular an X-ray source, the cover being constructed such that it can be pulled over the screening element and completely separated therefrom again. 19. A cover according to claim 18, whereinthe cover comprises a material which can be sterilized using a suitable device or a suitable process. 20. A cover according to claim 18, whereinfor the purpose of altering the length, the cover can be turned up in at least one direction and fixed in the turned-up arrangement using a fixing device. 21. A cover according to claim 18, whereinthe cover is a sheath which is matched in its dimensions to the screening element and is open to one side. 22. A cover according to, claim 18, whereinthe cover has a plurality of elongate sheaths which are connected to one another at one end by way of a common cuff. 23. A cover according to, claim 22, whereineach sheath has its own fixing device for the purpose of altering the length.
	summary
052176827	description	DESCRIPTION OF THE PREFERRED EMBODIMENT The nuclear reactor system shown in FIG. 1 and described in U.S. Pat. No. 4,689,194 contains a principle cooling path with a cooling gas (helium) which flows up through a reactor core in the bottom portion of steel pressure vessel 2 and through a central hot gas conduit to the top portion of vessel 2. The heated gas then flows downward through the principal heat exchangers 9, downward through decay heat exchangers 13 to circulating blowers driven by motors 16 which return the gas flow to the lower part of the reactor core. Decay heat, produced after the reactor is shutdown, can be removed by natural convection if the circulating blowers are no longer available to circulate the gas flow. The principle heat exchanger 9 (only one being shown in FIG. 1) are steam generators with the hot gas from the central conduit flowing through the steam generators 9 from top to bottom whereby the gas temperature is reduced from approximately 700.degree. C. to 250.degree. C. at the outlets of the steam generators. The decay heat exchangers 13 are also traversed by the gas flowing from the top to bottom of the decay heat exchangers after the cooled gas has exited from the outlets of the steam generators 9. The decay heat exchangers 13 are, as a result, exposed to a gas flow at a temperature of about 250.degree. C. during normal operation of the reactor. The decay heat exchangers 13 are connected to an external recooling heat exchanger 22 at a geodetically higher location by two legs 19 and 20 which form a decay heat removal loop 21. A water-steam separator vessel 23 is located in leg 20 between decay heat exchanger 13 and the external recooling heat exchanger 22. The water-steam separator 23 provides for volume equalization in the decay heat removal loop in case of evaporation of the water. The decay heat exchangers 13 are operated, on the secondary side, with cooling water at a pressure chosen such that the cooling water at the outlets of decay heat exchangers 13 does not evaporate during normal operation i.e. when the decay heat exchangers 13 are subjected to a gas temperature of 250.degree. C. from the outlets of steam generators 9. The decay heat removal loop has a low volume of water and is operated, during normal operation of the reactor, by a natural convection flow with shut-off valves 24 being in the open position. If the steam generators 9 are no longer available as a heat sink, they are traversed by hot gas at a temperature of about 700.degree. C. which then enters into the decay heat exchangers 13. This raises the temperature of the decay heat exchangers 13 and leads to evaporation of cooling water in the decay heat removal loops 21 which increases the natural convection flow in loops 21 so that the decay heat is safely removed from the gas flow in the reactor. The increase in natural convection flow in loops 21 when steam generators 9 are not available as heat sinks allows decay heat to be safely removed without incurring a heat loss of the same size during normal operation of the reactor. That increase also happens automatically without the need to actuate any valves, shut-off valve 24 being open during normal operation of the reactor. The decay heat is removed as a result of the rising temperature alone with no additional actuating measures being required. However, with a low water volume in the decay heat removal loops 21, steam will be present in the upper part of hot leg 20 during normal operation of the reactor with water throughout the cold leg 19, the head of water in the cold leg forcing a substantial flow in the loop 21 by natural circulation. This natural circulation flow will result in substantial heat being lost through the decay heat removal loops during normal operation of the reactor. Furthermore, that natural circulation flow can not be restricted during normal operation of the reactor, for instance by an orifice, because it would then be restricted under emergency conditions when it is necessary to safely remove decay heat from the gas flow in the reactor. FIG. 2 shows one proposed system for the removal of decay heat from a CANDU nuclear reactor. The core 41 of a CANDU nuclear reactor has a number of fuel channels 42 extending through the core with cooling water flowing from inlet header 43 via pipes 63 through the channels 42 and via pipes 60 to an outlet header 44. The normal flow of cooling water during normal operation of the reactor is from high temperature outlet header 44 via pipe 61 through a steam generator 46 to a main circulation pump 45 which pumps the cooling water via pipe 62 to low temperature inlet header 43 and back to the reactor core via pipes 63. In this type of system, the main pump 45 will be shutdown when the steam generator 46 is unavailable as a heat sink which may be caused by an accident or when the steam generator is out of service for repairs. The decay heat removal path consists of pipe 14 extending from high temperature outlet header 44 to an inlet of a heat exchanger 11 in a large reservoir 10 of water which forms a heat sink. The tank 10 of water is sufficient large and holds a sufficient volume of water to provide a heat sink for several days. The outlet of heat exchanger 11 is connected to pipe 15 and through a check valve 12 to a low temperature inlet header 43. The check valve 12 opposes the main pump head when the main pump 45 is operating to prevent backflow through pipe 15, heat exchanger 11 and pipe 14 during normal operation. The heat exchanger 11 is located at a higher elevation than the reactor headers 44 and 43 so that a natural convection flow can occur from high temperature header 44 to low temperature header 43 when pump 45 is stopped. In this type of system, when the main pumps are tripped, coolant from high temperature header 44 can start a natural convection circulation flow up pipe 14 down through heat exchange 11 and via pipe 15 through check valve 12 to low temperature header 43. This natural convection flow through the decay heat removal path is of a sufficient size to remove heat generated in the reactor core when the reactor is shutdown. However, in a CANDU reactor, the header to header pressure drop is close to zero and can even be in the wrong direction which creates problems in getting that natural convection circulating flow started. This type of system also requires a large volume of heavy water to be present in the decay heat removal path which adds to the cost of the reactor system. FIG. 3 shows an alternative system, according to the present invention, for removal of decay heat generated in the reactor core after a steam generator is lost as a heat sink. This system substantially avoids problems associated with the previously described systems. The normal flow of cooling water in FIG. 3 is the same as in FIG. 2, i.e. from the outlet header 44 via pipe 61 through steam generator 46 to a main circulation pump 45 and via pipe 62 (62') to inlet header 43. However, a heat exchanger 47 is now located between circulating pump 45 and low temperature header 43. The outlet of the secondary side of heat exchanger 47 is connected via pipe 57 to an inlet of a vapor separator 50 whose outlet is connected via pipe 52 to another heat exchanger 54 in a large reservoir 53 of water which forms a heat sink. The reservoir 53 of water is large enough to provide a heat sink for several days. The outlet of heat exchanger 54 is connected via pipe 56 to an inlet of heat exchanger 47 forming a decay heat removal loop which contains a fluid such as normal water rather than heavy water. This provides a substantial reduction in costs compared to the type of system shown in FIG. 2. A fairly large mass of fluid is located in the decay heat removal loop. Heat exchanger 54 is located at a higher elevation than heat exchanger 47 so that a natural circulation flow can occur from the outlet of heat exchanger 47 through the vapor separator 50 and heat exchanger 54 to the inlet of heat exchanger 47. However, during normal operation of the reactor, the natural convection flow is essentially zero because the decay heat removal loop is pressurized to prevent boiling of the liquid on the secondary side of heat exchanger 47. Also the loop is partially filled to keep the vapor/liquid interface 51 above the level 55 of coolant in the heat sink 53. During normal operation, substantial temperature differences exist around the decay heat removal loop i.e. from hot to cold at the vapor/liquid interface near the inlet to the heat sink 53 and from cold to hot at the inlet to the heat exchanger 47. Heat transfer would occur because of these temperature differences but would be insignificant because of the small heat transfer area. The normal heat losses would be small because the temperature differences within the heat exchanger 47 and within the heat exchanger 54 at heat sink 53 would be small. If the steam generator 46 is lost as a heat sink, the coolant temperature at the outlet on the primary side of steam generator 46 increases which raises the temperature of the heavy water coolant entering the heat exchanger 47. This raises the temperature of the secondary liquid in heat exchanger 47 towards boiling. Boiling results in a large reduction in back pressure due to voiding of the hot leg which causes a recirculating flow to develop by natural convection with cold water entering heat exchanger 47 and a hot vapor/liquid mixture entering the heat exchanger 54 in heat sink 53. In this system, decay heat removal would automatically switch from the steam generator 46 to the alternate heat sink 53 when the steam generator is lost as a heat sink without the need for valves being opened or any other type of intervention. The pressure and inventory of water in the decay heat removal loop would be controlled to maintain the required pressure and level in the steam separator 50. The system can then be periodically tested during normal operation by lowering the pressure in the decay heat removal loop and measuring the temperature rise at the entrance to heat exchanger 54. An eventual reactor cooldown to a temperature near 100.degree. C. can be effected by also reducing the pressure in the decay heat removal loop. If it is required to lower the reactor temperature below 100.degree. C., a liquid with a lower boiling point than water can be used in the decay heat removal loop. Various modifications may be made to the preferred embodiments without departing from the spirit and scope of the invention as defined in the appended claims. For instance, although the preferred embodiments have been described with respect to a CANDU reactor, similar systems may be used in various other types of nuclear reactor.
	description	This application is a continuation of non-provisional U.S. patent application Ser. No. 13/915,643 filed on Jun. 12, 2013, which is a divisional of U.S. patent application Ser. No. 13/076,651 (now U.S. Pat. No. 8,575,564) filed on Mar. 31, 2011, each herein incorporated by reference in their entirety. Field of the Invention The present invention relates to a medical system (referred to as a “particle beam therapy system”, hereinafter) that performs therapy by irradiating a charged particle beam (referred to as a “particle beam”, hereinafter), exemplified by a heavy particle beam such as a carbon beam or a proton beam, onto the diseased site of a cancer or the like. Description of the Related Art Among medical systems that have been developed earlier than particle beam therapy systems and perform therapy by utilizing a radiation such as an X-ray, there has been proposed a medical system that performs therapy of a diseased site evenly with a high dose by irradiating radiations, whose intensity are adjusted, from many directions so that exposure of peripheral tissues is reduced. Here, irradiation onto a diseased site from many directions is referred to as multi-port irradiation. A number of methods have been proposed for multi-port irradiation; they are exemplified, for example, by IMRT (Intensity-Modulated Radiotherapy: referred Documents 1 and 2 in non-patent document 1), which is proposed mainly by Siemens and in which “step and shoot” is performed, and IMAT (Intensity-Modulated Ark Therapy: referred Document 3 in non-patent document 1), which is proposed mainly by ELEKTA. In Patent Document 1, there is proposed a radiation irradiation apparatus that is provided with a plurality of compensators for changing the spatial pattern of the X-ray intensity distribution for each irradiation direction so as to apply a high absorption dose only to a diseased site and that performs multi-port irradiation while automatically changing compensators in accordance with irradiation directions. [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-37214 (FIGS. 17 through 21) [Non-Patent Document 1] Sake Taira. IMRT with Combined Rotating and Fixed Multi-port Irradiation (Cutting Field IMRT). MEDICAL REVIEW NO. 87 (2002); PP. 44-48. [Non-Patent Document 2] Emergency statement for Intensity-Modulated Radiotherapy. JASTRO NEWSLETTER 2002; 63(3): PP. 4-7. With regard to a radiation therapy system utilizing an X-ray or the like, IMRT has been widely applied to clinical practices for a head and neck area, a prostate, and the like and has achieved a superior performance; on the other hand, the problem of excess irradiation has been pointed out. According to Non-Patent Document 2, it is warned that, depending on the contents of a treatment plan, IMRT eventually brings about a phenomenon that is caused by excess irradiation and is harmful to normal tissues, regardless of consciously increasing one-time dose or total dose, or on the contrary, there is caused a risk that underdose irradiation due to being conservative provides an insufficient treatment effect. It is conceivable that one of the causes of the excess irradiation is insufficient irradiation flexibility. The final irradiation field of IMRT in the radiation therapy system utilizing an X-ray or the like described in any one of referred Documents 1 through 3 in non-patent document 1 and non-patent document 2 is realized by superimposing two or more irradiations on one another, utilizing as parameters (1) irradiation energy, (2) an irradiation angle, (3) a transverse-direction irradiation-field limitation through a multileaf collimator referred to as a “MLC”, hereinafter) or the like, and (4) an irradiation dose (weight). In this case, no depth-direction irradiation-field limiter is utilized. The depth-direction irradiation-field limiter is exemplified by a bolus utilized in a particle beam therapy system. The changing form of a diseased site in the depth direction is referred to as a distal form. A bolus is an energy modulator obtained by machining in accordance with this distal form; the energy modulator is formed by machining polyethylene or wax for each patient. An irradiation apparatus provided with a bolus is disclosed, for example, in FIG. 21 of Patent Document 1; this irradiation apparatus can make the shape of an irradiation field coincide with the distal form of a diseased site. However, in a particle beam therapy system, a single bolus cannot be applied as it is to multi-port irradiation. At first, in the case of IMRT, it is required to prepare respective boluses for two or more irradiation directions. In the radiation irradiation apparatus disclosed in Patent Document 1, the compensator, which corresponds to a bolus, can automatically be moved; however, there has been a problem that machining of the bolus requires many labor hours and costs. In the case of IMAT, there has been another further difficult problem; it is required to automatically change the bolus shape in accordance with the irradiation angle that changes on a moment-to-moment basis. At present, this kind of dynamic shape change cannot be realized by a bolus. Accordingly, when the IMRT technology for a radiation therapy system utilizing an X-ray or the like is applied as it is to a particle beam therapy system having a conventional wobbler system, there still exists the problem that it is required to utilize two or more boluses. It is not possible to limit the irradiation field in the depth direction without utilizing a bolus, i.e., it is not possible to raise the irradiation flexibility; therefore, it is impossible to solve the problem of excess irradiation without utilizing a bolus. The objective of the present invention is to solve the foregoing problems. In other words, the objective of the present invention is to solve the problem of excess irradiation in IMRT by a particle beam therapy system. More specifically, the problem of excess irradiation in IMRT by a particle beam therapy system is solved by raising the irradiation flexibility in the depth direction, without utilizing a bolus. There is provided a particle beam irradiation apparatus having a scanning irradiation system that performs scanning with a charged particle beam accelerated by an accelerator and being mounted in a rotating gantry for rotating the irradiation direction of the charged particle beam. The particle beam irradiation apparatus includes a columnar-irradiation-field generation apparatus that generates a columnar irradiation field by enlarging the Bragg peak of the charged particle beam. The particle beam irradiation apparatus according to the present invention performs irradiation in such a way as to generate a columnar irradiation field, which is obtained by enlarging the Bragg peak of a charged particle beam, at the depth corresponding to the distal form of an irradiation subject; therefore, the problem of excess irradiation in IMRT by a particle beam therapy system can be solved by raising the irradiation flexibility in the depth direction, without utilizing a bolus. The foregoing and other object, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. There will be considered IMRT through columnar scanning irradiation, which is the feature of the present invention. In normal spot scanning, a beam spot is irradiated onto a diseased site in a three-dimensional manner, as if painting is performed in a pointillist manner. As described above, the spot scanning is a high-flexibility irradiation method; on the other hand, it takes a long time to perform irradiation onto the whole diseased site. IMRT takes a further long time because it is multi-port irradiation. Accordingly, by enlarging the BP (Bragg peak) in the depth direction comparison with the spot scanning, a columnar irradiation field is generated. FIG. 1 is a configuration diagram illustrating a particle beam irradiation apparatus according to Embodiment 1 of the present invention. The particle beam irradiation apparatus 58 is provided with a columnar-irradiation-field generation apparatus 4 that generates a columnar irradiation field by enlarging the BP in the depth direction; X-direction and Y-direction scanning electromagnets 10 and 11 that scan a charged particle beam 1 in the X direction and the Y direction, respectively, which are directions perpendicular to the charged particle beam 1; position monitors 12a and 12b; a dose monitor 13; a scanning electromagnet power source 32; and an irradiation control apparatus 33 that controls the irradiation system of the particle beam irradiation apparatus 58. The X-direction scanning electromagnet 10, the Y-direction scanning electromagnet 11, and the scanning electromagnet power source 32 configure a scanning irradiation system 34 that performs scanning with the charged particle beam 1. The traveling direction of the charged particle beam 1 is the Z direction. The columnar-irradiation-field generation apparatus 4 is provided with an energy changing apparatus 2 that reduces the energy of a charged particle beam at a position before a diseased site 40, which is the irradiation subject, in the traveling direction of the charged particle beam so as to adjust the depth-direction (Z-direction) position (range) of the Bragg peak BP at the diseased site 40; and a depth-direction irradiation field enlargement apparatus 3 that changes the width of the charged particle beam 1 so as to enlarge the Bragg peak BP in the depth direction. The Bragg peak BP whose width in the depth direction of the diseased site 40, i.e., whose irradiation-direction width has been enlarged is referred to as a Spread-Out Bragg Peak SOBP. In this specification, the irradiation-direction width of the Spread-Out Bragg Peak SOBP is referred to as the depth of SOBP. The X-direction scanning electromagnet 10 is a scanning electromagnet that performs X-direction scanning with the charged particle beam 1; the Y-direction scanning electromagnet 11 is a scanning electromagnet that performs Y-direction scanning with the charged particle beam 1. The position monitors 12a and 12b detect the passing position through which the charged particle beam 1 that has been deflected by the X-direction scanning electromagnet 10 and the Y-direction scanning electromagnet 11 passes. The dose monitor 13 detects the dose of the charged particle beam 1. The irradiation control apparatus 33 controls the columnar irradiation field and the irradiation position on the irradiation subject 40, based on treatment plan data generated by an unillustrated treatment planning apparatus; when the dose measured by the dose monitor 13 reaches the target dose, the charged particle beam is stopped. The scanning electromagnet power source 32 changes setting currents for the X-direction scanning electromagnet 10 and the Y-direction scanning electromagnet 11, based on control inputs (commands), which are outputted from the irradiation control apparatus 33, to the X-direction scanning electromagnet 10 and the Y-direction scanning electromagnet 11. FIG. 2 is a configuration diagram illustrating an energy changing apparatus. FIG. 3 is a configuration diagram illustrating a depth-direction irradiation field enlargement apparatus. The energy changing apparatus 2 is provided with a range shifter 9 whose thickness changes in a stepped form in the width direction (X direction); deflection electromagnets 5 and 6 included in a pair of upstream deflection electromagnets that moves the position, of the charged particle beam 1, in the range shifter 9 through which the charged particle beam 1 passes; a first deflection-electromagnet power source 20 that energizes the pair of upstream deflection electromagnets; deflection electromagnets 7 and 8 included in a pair of downstream deflection electromagnets that returns the charged particle beam 1 that has passed through the range shifter 9 onto the original orbit; a second deflection-electromagnet power source 21 that energizes the pair of downstream deflection electromagnets; and a change control apparatus 22 that calculates the amount of movement, of the orbit of the charged particle beam, that is caused by the pair of upstream deflection electromagnets, based on an energy command value inputted from the irradiation control apparatus 33, and transmits an energization current value to the first deflection-electromagnet power source 20. The change control apparatus 22 also controls the second deflection-electromagnet power source 21. On a beam axis (Z axis) 14, the charged particle beam 1 enters the pair of upstream deflection electromagnets 5 and 6. The orbit of the charged particle beam 1 is moved in the horizontal direction (X direction) on the paper plane of FIG. 2. The deflection electromagnet 5 is to deflect the orbit; the deflection electromagnet 6 is to parallelize the orbit. The deflection electromagnet 5 for changing the orbit deflects the orbit of the incident charged particle beam 1 in such a way that the orbit thereof slants by a predetermined angle θ from the Z axis. The deflection electromagnet 6 for parallelizing the orbit deflects the orbit, which has been slanted from the Z axis by the deflection electromagnet 5 for changing the orbit, to an orbit that is parallel to the Z axis. At the downstream side of the range shifter 9, the deflection electromagnet 7 for deflecting the orbit and the deflection electromagnet 8 for parallelizing the orbit return the charged particle beam 1 onto the beam axis (Z axis) 14. The deflection electromagnet 7 for changing the orbit deflects the orbit of the charged particle beam 1 in such a way that the orbit thereof slants by (360°—the predetermined angle θ) from the Z axis. The deflection electromagnet 8 for parallelizing the orbit deflects the orbit, which has been slanted from the Z axis by the deflection electromagnet 7 for changing the orbit, to an orbit along the Z axis. The operation of the energy changing apparatus 2 will be explained. Because of the pair of upstream deflection electromagnets 5 and 6, the charged particle beam 1 introduced to the energy changing apparatus 2 travels on an orbit that is parallel to the Z axis and is apart from the Z axis by a predetermined distance toward the X direction. Then, as the charged particle beam 1 passes through a portion, of the range shifter 9, having a predetermined thickness, the energy thereof is reduced by an amount that is proportional to the thickness, and hence becomes desired energy. In such a manner as described above, the charged particle beam 1 whose energy has been changed to a desired level is returned onto the extended line of the original orbit, which was the orbit at a time when the charged particle beam 1 has been launched into the energy changing apparatus 2 by the pair of downstream deflection electromagnets 7 and 8. The energy changing apparatus 2 has an advantage in that, when the energy of a charged particle beam is changed so that the range is changed, no driving sound is produced when the range shifter is driven. In addition, the orbit of the charged particle beam 1 deflected by the pair of downstream deflection electromagnets 7 and 8 is not limited to the one that returns onto the beam axis 14; the orbit may be the one that is parallel to the beam axis 14 and returns toward the beam axis 14, or the orbit may be the one that is not parallel to the beam axis 14 and returns toward the beam axis 14. FIG. 3 is a configuration diagram illustrating a depth-direction irradiation field enlargement apparatus. The depth-direction irradiation field enlargement apparatus 3 is provided with a ridge filter 19 formed of approximately triangular prisms that are arranged in the width direction (X direction) and whose heights are different from one another, i.e., configured in such a way as to have a plurality of mountains that have different thickness distributions; deflection electromagnets 15 and 16 included in a pair of upstream deflection electromagnets that moves the position, of the charged particle beam 1, in the ridge filter 19 through which the charged particle beam 1 passes; a first deflection-electromagnet power source 23 that energizes the pair of upstream deflection electromagnets; deflection electromagnets 17 and 18 included in a pair of downstream deflection electromagnets that returns the charged particle beam 1 that has passed through the ridge filter 19 onto the original orbit; a second deflection-electromagnet power source 24 that energizes the pair of downstream deflection electromagnets; and a change control apparatus 25 that calculates the amount of movement, of the orbit of the charged particle beam, that is caused by the pair of upstream deflection electromagnets, based on an SOBP command value inputted from the irradiation control apparatus 33, and transmits an energization current value to the first deflection-electromagnet power source 23. The change control apparatus 25 also controls the second deflection-electromagnet power source 24. On a beam axis (Z axis) 14, the charged particle beam 1 enters the pair of upstream deflection electromagnets 15 and 16. The orbit of the charged particle beam 1 is moved in the horizontal direction (X direction) on the paper plane of FIG. 2. The deflection electromagnet 15 is to deflect the orbit; the deflection electromagnet 16 is to parallelize the orbit. The deflection electromagnet 15 for changing the orbit deflects the orbit of the incident charged particle beam 1 in such a way that the orbit thereof slants by a predetermined angle θ from the Z axis. The deflection electromagnet 16 for parallelizing the orbit deflects the orbit, which has been slanted from the Z axis by the deflection electromagnet 15 for changing the orbit, to an orbit that is parallel to the Z axis. At the downstream side of the ridge filter 19, the deflection electromagnet 17 for deflecting the orbit and the deflection electromagnet 18 for parallelizing the orbit return the charged particle beam 1 onto the beam axis (Z axis) 14. The deflection electromagnet 17 for changing the orbit deflects the orbit of the charged particle beam 1 in such a way that the orbit thereof slants by (360°—the predetermined angle θ) from the Z axis. The deflection electromagnet 18 for parallelizing the orbit deflects the orbit, which has been slanted from the Z axis by the deflection electromagnet 17 for changing the orbit, to an orbit along the Z axis. The operation of the depth-direction irradiation field enlargement apparatus 3 will be explained. Because of the pair of upstream deflection electromagnets 15 and 16, the charged particle beam 1 introduced to the depth-direction irradiation field enlargement apparatus 3 travels on an orbit that is parallel to the Z axis and is apart from the Z axis by a predetermined distance toward the X direction. Then, as the charged particle beam 1 passes through a portion, of the ridge filter 19, having a predetermined thickness distribution, the energy thereof is reduced by an amount that is proportional to the thickness; as a result, there is produced a particle beam in which many kinds of energies whose intensities are different from one another are mixed. The depth of SOBP can be changed in accordance with the height of the ridge filter 19 through which the charged particle beam 1 passes. In such a manner as described above, the charged particle beam 1 whose width has been changed to a desired SOBP depth is returned onto the extended line of the original orbit, which was the orbit at a time when the charged particle beam 1 has been launched into the depth-direction irradiation field enlargement apparatus 3 by the pair of downstream deflection electromagnets 17 and 18. The depth-direction irradiation field enlargement apparatus 3 has an advantage in that, when the depth of SOBP is changed, no driving sound is produced when the ridge filter is driven. In addition, the orbit of the charged particle beam 1 deflected by the pair of downstream deflection electromagnets 17 and 18 is not limited to the one that returns onto the beam axis 14; the orbit may be the one that is parallel to the beam axis 14 and returns toward the beam axis 14, or the orbit may be the one that is not parallel to the beam axis 14 and returns toward the beam axis 14. By mounting the particle beam irradiation apparatus 58 on a rotating gantry, the irradiation system of the particle beam irradiation apparatus 58 can freely be rotated around a patient platform, whereby there can be performed irradiation onto the diseased site 40 from many directions. The rotating gantry rotates the irradiation system of the particle beam irradiation apparatus 58 so as to rotate the irradiation direction. That is to say, multi-port irradiation can be performed in this manner. By use of the ridge filter 19 in the particle beam irradiation apparatus 58, the irradiation field is more enlarged in the Z direction than in the X direction and the Y direction; thus, a beam with a columnar dose distribution (refer to FIGS. 5A through 5D) can be irradiated onto the diseased site 40. Next, a method of performing IMRT through columnar scanning irradiation will be explained. FIG. 4 is a flowchart representing a method of generating a treatment plan utilized in a particle beam irradiation apparatus according to the present invention; each of FIGS. 5A through 5D is a view for explaining the step ST1 in FIG. 4; each of FIGS. 6A through 6C is a schematic diagram for obtaining the initial state in an optimum calculation for a treatment plan. FIGS. 5A through 5D and FIGS. 6A through 6C are examples in which irradiation is performed with a four-port (every 90°) irradiation apparatus. The treatment planning apparatus for generating a treatment plan is provided with an irradiation field arranging unit that arranges columnar irradiation fields in accordance with the distal form of the diseased site (irradiation subject) 40 onto which the charged particle beam 1 is irradiated, and arranges columnar irradiation fields in such a way that the columnar irradiation fields cover the inside of the diseased site (irradiation subject) 40; and an optimization calculation unit that adjusts the arrangement of the columnar irradiation fields in such a way that the irradiation dose onto the diseased site (irradiation subject) 40 falls within a predetermined range, regarding, as the initial state, the state in which the columnar irradiation fields are arranged by the irradiation field arranging unit. A treatment plan includes the operation conditions for the particle beam irradiation apparatus and the rotating gantry; the particle beam irradiation apparatus 58 and the rotating gantry integrally operate based on the treatment plan. At first, as illustrated in FIGS. 5A through 5D, columnar irradiation fields 44a, 44b, 44c, and 44d are arranged in accordance with the distal form of the diseased site 40 (the step ST1). This action is implemented for each port (for each radiation direction). In this situation, the columnar irradiation fields may overlap with one another. Portions where the columnar irradiation fields overlap with one another will be explained later. FIG. 5A is an example of the case where the columnar irradiation fields 44a are arranged in accordance with the distal form of the diseased site 40 at a time when irradiation is performed from an irradiation direction 43a; FIG. 5B illustrates the columnar irradiation fields 44b at a time when irradiation is performed from an irradiation direction 43b; FIG. 5C illustrates the columnar irradiation fields 44c at a time when irradiation is performed from an irradiation direction 43c; FIG. 5D illustrates the columnar irradiation fields 44d at a time when irradiation is performed from an irradiation direction 43d. FIG. 6A illustrates an example of irradiation field arrangement at a time when all irradiations with the respective ports (radiation directions) have been completed. When all irradiations with respective ports (radiation directions) have been completed, it is determined whether or not there exists any remaining irradiation-subject region (the step ST2). In the case where there exists no remaining irradiation-subject region, the step ST2 is followed by the step ST5. In the case where there exists a remaining irradiation-subject region, the second-round arrangement work is performed in the remaining irradiation-subject region in such a way that the arrangement matches the distal form of the remaining irradiation subject (the step ST3). As illustrated in FIG. 6B, in the case where irradiation is performed from the irradiation direction 43c, the columnar irradiation fields 45c are arranged. In this situation, the depth of SOBP in the second-round columnar irradiation field may be different from that in the first-round columnar irradiation field. FIG. 6C illustrates an example of irradiation field arrangement at a time when all irradiations with the respective ports (radiation directions) have been completed. In FIG. 6C, in the case where irradiation is performed from the irradiation direction 43a, the columnar irradiation fields 45a are arranged; in the case where irradiation is performed from the irradiation direction 43b, the columnar irradiation fields 45b are arranged; in the case where irradiation is performed from the irradiation direction 43d, the columnar irradiation fields 45d are arranged. When all irradiations with respective ports (radiation directions) have been completed in the second round, it is determined whether or not there exists any remaining irradiation-subject region (the step ST4). In the case where there exists a remaining irradiation-subject region, the step ST4 is followed by the step ST3; this flow is repeated so that the columnar irradiation fields cover the whole diseased site. In the case where there exists no remaining irradiation-subject region, the step ST4 is followed by the step ST5. In the step ST5, optimization calculation is performed, regarding, as the initial value, the irradiation plan where the columnar irradiation fields have been arranged. After the optimization calculation has been completed, evaluation is performed by use of an evaluation function (the step ST6). It is determined whether or not the value of the evaluation function is allowable in terms of the clinical practice; in the case where it is determined that the value of the evaluation function is not allowable, the step ST6 is followed by the step ST5, and then the optimization calculation is implemented. In the case where the value of the evaluation function is within an allowable range in terms of the clinical practice, the flow is ended. In the treatment-plan optimization work represented in the steps ST5 and ST6, in order to prevent overdosing (excess dose), the arrangement of the columnar irradiation fields is adjusted so that the irradiation dose onto the diseased site 40 falls within a predetermined range. In the foregoing portion where the columnar irradiation fields overlap with one another, overdosing (excess dose) is caused; therefore, in the optimization work, the arrangement of the columnar irradiation fields is changed in such a way that the portions where the columnar irradiation fields overlap with one another are eliminated or reduced. The work in the steps ST1 through ST4 is performed first by the irradiation field arranging unit of the treatment planning apparatus. Next, the treatment planning apparatus will be explained. The detail of a treatment planning apparatus is described in “the Radiation Therapy System Operating Manual for Medical Safety” (by Kozo Kumagai, Publishing Company of JART). A treatment planning apparatus has a comprehensive role; in brief, it can be referred to as a treatment simulator. One of the roles of a treatment planning apparatus is optimization calculation. The optimization work for a treatment plan represented in the steps ST5 and ST6 is performed in the optimization calculation unit of the treatment planning apparatus. The optimization calculation is utilized in searching the optimum beam intensity in an IMRT inverse treatment plan (inverse planning). According to the foregoing operation manual, as the optimization calculation method, there have been tried following methods to date. The methods are the filtered back projection method which was utilized in earlier years in performing IMRT optimization calculation; pseudo annealing, genetic algorithm, and random searching technology that are classified into a probabilistic method; and the gradient method which is classified into the deterministic method that has recently been installed in many treatment planning apparatuses. Although the calculation in the gradient method is high-speed, it has a nature that, once the calculation is trapped in a local minimum (the smallest possible quantity), it cannot get out of the trap. However, at present, the gradient method has been adopted in many treatment planning apparatuses that implement clinic practice IMRT treatment plans. In the gradient method, in order to prevent the situation where the calculation is trapped in another minimum value which is different from the optimum value to be obtained, it is effective to use the gradient method combined with the genetic algorithm or the random searching technology. In addition, it is empirically known that it is desirable that the initial value (a value initially given as a candidate of the solution) in the optimization calculation is close to the optimum solution to be obtained. Thus, in the present invention, an irradiation plan generated in the steps ST1 through ST4 is utilized as the initial value in the optimization calculation. Because, compared with conventional IMRT, its irradiation flexibility in the depth direction is made high for the purpose of matching the distal form of a diseased site, the irradiation plan generated in the steps ST1 through ST4 is sufficiently close to the optimum irradiation. In the optimization calculation, there is calculated a solution that certainly minimizes a given evaluation function. In the case of a treatment planning apparatus, as represented in the foregoing operation manual, the evaluation function, which is the reference for physical optimization, is given as follows. F T ( b -> ) = ∑ i = 1 N ⁢ ( u [ D min - d i ( b -> ) ] + 2 + w [ d i ( b -> ) - D max ] + 2 ) ( 1 ) where Dmin and Dmax are specified dose limits. The character “u” is a weight coefficient for Dmin; “w” is a weight coefficient for Dmax. The character “b” (although indicated with an arrow in the equation (1), indicated without the arrow in the description. Hereinafter, the same applies in the explanation for the equation (1).) is a function of the intensity of a beamlet; di (b) is the dose in a voxel “i” represented by the function “b” of the intensity of a beamlet. [x]+ is x, in the case where x>0, and [x]+ is “0” in other cases. N is the maximum number of voxels. As described above, optimization calculation is implemented in the treatment planning apparatus; therefore, for example, even though, with an initial value, columnar irradiation fields overlap with one another and hence overdosing (excess dose) is caused, the dose is adjusted in an obtained treatment plan. Because being configured as described above, the treatment planning apparatus according to Embodiment 1 can raise the irradiation flexibility in the depth direction, without utilizing a bolus; therefore, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. The advantage of irradiating a beam having a columnar dose distribution will be explained. Originally, in a conventional particle beam therapy system in which it is assumed that irradiation is performed from one direction, the dose distribution in the irradiation system is formed in the following manner. As an example, the Wobbler method will be explained; a Wobbler electromagnet and a scatterer evenly enlarge the irradiation field in the X and Y directions, and based on the XY-plane sectional shape (or the shape projected onto the XY plane, for example,) of a diseased site, the irradiation field is limited by an MLC. The irradiation field is enlarged by a ridge filter in the Z direction and is limited by a bolus in such a way as to coincide with the distal form (the deepest-layer form) of the diseased site. As described above, in the multi-port irradiation by a particle beam therapy system, it is required to utilize a plurality of boluses; therefore, machining of the bolus requires many labor hours and costs. Moreover, the bolus cannot be dynamically deformed; thus, the multi-port irradiation cannot be applied to IMAT. If, in the multi-port irradiation by a particle beam therapy system, the irradiation field can be controlled, as by a bolus, in such a way as to coincide with the distal form (the deepest-layer form) of a diseased site without utilizing a bolus, there can be solved the problem that machining of the bolus requires many labor hours and costs; therefore, the multi-port irradiation can be applied to IMAT, whereby the problem of excess irradiation in IMRT can be solved, i.e., the unnecessary irradiation onto normal tissues can considerably be reduced. That led to the present invention in which a beam having a columnar dose distribution is irradiated. In the present invention, one of the greatest effects of irradiating a beam having a columnar dose distribution is that the irradiation field can be limited in such a way as to coincide with the distal form (the deepest-layer form) of the diseased site 40 without utilizing a bolus and hence the unnecessary irradiation onto normal tissues can considerably be reduced. Another one of the greatest effect, in the present invention, of irradiating a beam having a columnar dose distribution is that an irradiation field can be formed without implementing the intensity modulation which is adopted in a radiation therapy system utilizing an X-ray or the like. Here, for the simplicity, the principle of the intensity modulation may be explained as follows. Irradiation fields having a weak dose distribution are irradiated from many directions so that the irradiation fields overlap with one another; the portion where the doses eventually overlap most with one another obtains the dose distribution, as the irradiation field that provides an treatment effect. In the present invention, as illustrated in FIGS. 6A through 6C, an irradiation field can be formed by combining columnar doses. Additionally, there may be performed irradiation with irradiation fields overlapping with one another in the present invention, as well. It is not allowed that the irradiation dose becomes an underdose (insufficient dose) or an overdose (excess dose) in any portion of a diseased site; however, the dose that is allowable in terms of a clinical practice has a width. An irradiation plan is made by use of a treatment planning apparatus in such a way that the final dose distribution is allowable in each portion of the diseased site. Unlike a conventional radiation therapy system utilizing an X-ray or the like, it is not required to perform intensity modulation of the irradiation field in such a way that it coincides with the distal form of the diseased site; therefore, the treatment planning apparatus is not required to perform calculation for optimizing the intensity modulation. That is to say, there can be solved the conventional problem that it takes a long time to make a treatment plan. Moreover, compared with irradiation of a beam having a spot-like distribution, irradiation of a beam having a columnar dose distribution has an advantage in that the irradiation time is shortened. In the case where multi-port irradiation can be performed in a particle beam therapy system utilizing the treatment planning apparatus according to Embodiment 1, there exist a number of advantages; the following two are the major advantages. The first one is that, in the case where irradiation is performed onto the same diseased site, multi-port irradiation makes wider the body surface area through which a particle beam passes; thus, the damage to the body surface area, which includes normal tissues, can be reduced. The second one is that irradiation can be prevented from being preformed onto a risk site (such as a spinal cord, an eyeball or the like), onto which a particle beam should not be irradiated. As described above, the particle beam irradiation apparatus 58 according to Embodiment 1 is provided with the scanning irradiation system 34 that performs scanning with the charged particle beam 1, and is mounted in a rotating gantry that rotates the irradiation direction of the charged particle beam 1; because the particle beam irradiation apparatus 58 includes the columnar-irradiation-field generation apparatus 4 that enlarges the Bragg peak of the charged particle beam 1 so as to generate a columnar irradiation field, there can be irradiated a columnar irradiation field obtained by enlarging the Bragg peak of a charged particle beam, at the depth in accordance with the distal form of an irradiation subject, in such a way that the columnar field is generated; therefore, there can be raised the irradiation flexibility in the depth direction, without utilizing a bolus. As a result, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. FIG. 7 is a configuration diagram illustrating an energy changing apparatus according to Embodiment 2 of the present invention. An energy changing apparatus according to Embodiment 2 is different from the energy changing apparatus 2a according to Embodiment 1 in that the energy of a charged particle beam 1 is reduced to a desired energy by use of a plurality of absorbers 26a, 26b, 26c, and 26d so that there is adjusted the depth-direction (Z-direction) position (range) of the Bragg peak BP at a diseased site 40, which is an irradiation subject. An energy changing apparatus 2b includes a plurality of absorbers 26a, 26b, 26c, and 26d that are driven by driving devices 27a, 27b, 27c, and 27d. The absorbers 26a, 26b, 26c, and 26d are different in thickness from one another. The thickness of the overall absorber can be changed by combining the respective thicknesses of the absorbers 26a, 26b, 26c, and 26d. A change control apparatus 22 controls the driving devices 27a, 27b, 27c, and 27d so that the charged particle beam 1 passes or does not pass through the absorbers 26a, 26b, 26c, and 26d that correspond to the driving devices 27a, 27b, 27c, and 27d, respectively. The energy of the charged particle beam 1 is reduced by an amount that is proportional to the thickness of the absorber through which the charged particle beam 1 passes, and hence becomes desired energy. As is the case with Embodiment 1, the particle beam irradiation apparatus (refer to FIG. 1) having the energy changing apparatus 2b according to Embodiment 2 can enlarge the Bragg peak BP in the depth direction so as to generate a columnar irradiation field. In the energy changing apparatus 2b according to Embodiment 2, it is not required to deflect the charged particle beam 1; therefore, compared with the energy changing apparatus 2a according to Embodiment 1, the deflection electromagnets 5 through 8 can be removed, whereby the length L1 of the apparatus in the irradiation direction (Z direction) of the charged particle beam 1 can be shortened. Because the length L1 of the apparatus can be shortened, the energy changing apparatus can be made compact. The length L1 of the apparatus in FIG. 2 is the length from the upstream end of the deflection electromagnet 5 to the downstream end of the deflection electromagnet 8. In the particle beam irradiation apparatus (refer to FIG. 1) having the energy changing apparatus 2b according to Embodiment 2, multi-port irradiation can be implemented based on a treatment plan corresponding to the treatment plan generated by the treatment planning apparatus described in Embodiment 1; therefore, as is the case with Embodiment 1, the irradiation flexibility in the depth direction can be raised, without utilizing a bolus. As a result, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. FIG. 8 is a configuration diagram illustrating a depth-direction irradiation field enlargement apparatus according to Embodiment 3 of the present invention. A depth-direction irradiation field enlargement apparatus 3b according to Embodiment 3 is different from the depth-direction irradiation field enlargement apparatus 3a according to Embodiment 1 in that the energy of a charged particle beam is formed of many kinds of energy levels that are mixed by use of a plurality of ridge filters 28a, 28b, 28c, and 28d, i.e., the energy width of the charged particle beam 1 is changed so that the Bragg peak BP is enlarged in the depth direction. The depth-direction irradiation field enlargement apparatus 3b includes a plurality of ridge filters 28a, 28b, 28c, and 28d that are driven by driving devices 29a, 29b, 29c, and 29d. The ridge filters 28a, 28b, 28c, and 28d are different in thickness from one another. The thickness of the overall ridge filter can be changed by combining the respective thicknesses of the ridge filters 28a, 28b, 28c, and 28d. A change control apparatus 25 controls the driving devices 29a, 29b, 29c, and 29d so that the charged particle beam 1 passes or does not pass through the ridge filters 28a, 28b, 28c, and 28d that correspond to the driving devices 29a, 29b, 29c, and 29d, respectively. The energy range of the charged particle beam 1 is widened by an amount that is proportional to the thickness of the ridge filter through which the charged particle beam 1 passes, and hence becomes a desired depth of SOBP. As is the case with Embodiment 1, the particle beam irradiation apparatus (refer to FIG. 1) having the depth-direction irradiation field enlargement apparatus 3b according to Embodiment 3 can enlarge the Bragg peak BP in the depth direction so as to generate a columnar irradiation field. In the depth-direction irradiation field enlargement apparatus 3b according to Embodiment 3, it is not required to deflect the charged particle beam 1; therefore, compared with the energy changing apparatus 2a according to Embodiment 1, the deflection electromagnets 15 through 18 can be removed, whereby the length L2 of the apparatus in the irradiation direction (Z direction) of the charged particle beam 1 can be shortened. Because the length L2 of the apparatus can be shortened, the energy changing apparatus can be made compact. The length L2 of the apparatus in FIG. 3 is the length from the upstream end of the deflection electromagnet 15 to the downstream end of the deflection electromagnet 18. In the particle beam irradiation apparatus (refer to FIG. 1) having the depth-direction irradiation field enlargement apparatus 3b according to Embodiment 3, multi-port irradiation can be implemented based on a treatment plan corresponding to the treatment plan generated by the treatment planning apparatus described in Embodiment 1; therefore, as is the case with Embodiment 1, the irradiation flexibility in the depth direction can be raised, without utilizing a bolus. As a result, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. FIG. 9 is a configuration diagram illustrating a columnar-irradiation-field generation apparatus according to Embodiment 4 of the present invention. A columnar-irradiation-field generation apparatus according to Embodiment 4 is different from the columnar-irradiation-field generation apparatus 4a according to Embodiment 1 in that the energy changing apparatus 2a and the depth-direction irradiation field enlargement apparatus 3a are integrated. The columnar-irradiation-field generation apparatus 4b is provided with range shifters 9a and 9b; ridge filters 19a and 19b; deflection electromagnets 5 and 6 included in a pair of upstream deflection electromagnets that moves the position, of the charged particle beam 1, in the range shifters 9a and 9b and the ridge filters 19a and 19b through which the charged particle beam 1 passes; a first deflection-electromagnet power source 20 that energizes the pair of upstream deflection electromagnets; deflection electromagnets 7 and 8 included in a pair of downstream deflection electromagnets that returns the charged particle beam 1 that has passed through the range shifters 9a and 9b and the ridge filters 19a and 19b onto the original orbit; a second deflection-electromagnet power source 21 that energizes the pair of downstream deflection electromagnets; and a change control apparatus 22 that calculates the amount of movement, of the orbit of the charged particle beam, that is caused by the pair of upstream deflection electromagnets, based on an energy command value inputted from the irradiation control apparatus 33, and transmits an energization current value to the first deflection-electromagnet power source 20. The change control apparatus 22 also controls the second deflection-electromagnet power source 21. The operations of the apparatuses are the same as those in Embodiment 1; thus, explanations therefor will not be repeated. The range shifters 9a and 9b are formed in the same shape and formed of the same material; the ridge filter 19a is formed of the first group of approximately triangular prisms and the ridge filter 19b is formed of the second group of approximately triangular prisms; the height of the first group of approximately triangular prisms is different from the height of the second group of approximately triangular prisms. The height of the second group of approximately triangular prisms of the ridge filter 19b is higher than the height of the first group of approximately triangular prisms of the ridge filter 19a; therefore, the depth of SOBP of the charged particle beam 1 in the case where the charged particle beam 1 passes through the ridge filter 19b can be wider than the depth of SOBP of the charged particle beam 1 in the case where the charged particle beam 1 passes through the ridge filter 19a. The columnar-irradiation-field generation apparatus 4b according to Embodiment 4 changes the energy of the charged particle beam 1 to desired energy, through two kinds of SOBP depths; thus, two kinds of columnar irradiation fields can have desired ranges. There are not provided the pair of upstream electromagnets and the pair of downstream deflection electromagnets for each of the set of the range filter 9a and the ridge filter 19a and the set of the range filter 9b and the ridge filter 19b, but there is provided only one set of the pair of upstream electromagnets and the pair of downstream deflection electromagnets; therefore, compared with the columnar-irradiation-field generation apparatus 4a according to Embodiment 1, the length of the apparatus in the irradiation direction (Z direction) of the charged particle beam 1 can be shortened. By use of the pair of upstream deflection electromagnets and the pair of downstream deflection electromagnets, the energy of the charged particle beam 1 is changed to desired energy through two kinds of SOBP depths; thus, there exists an advantage that, when the width and the range of SOBP are changed, there is produced no driving sound caused due to driving of the range filter or the ridge filter. In order to line up many kinds (more than two) of SOBP depths, it is only necessary to arrange the range filters 9 and the ridge filters 19, the number of each of which corresponds to the number of the kinds of SOBPs. In the particle beam irradiation apparatus (refer to FIG. 1) having the columnar-irradiation-field generation apparatus 4b according to Embodiment 4, multi-port irradiation can be implemented based on a treatment plan corresponding to the treatment plan generated by the treatment planning apparatus described in Embodiment 1; therefore, as is the case with Embodiment 1, the irradiation flexibility in the depth direction can be raised, without utilizing a bolus. As a result, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. In each of Embodiments 1 through 4, it has been explained that the Z-direction enlargement of an irradiation field, i.e., an SOBP is realized by means of the ridge filter 19 (28). As Embodiment 5, there will be explained an embodiment in which in order to enlarge an irradiation field more to the Z direction than either to the X direction or the Y direction, a range modulation wheel RMW (Range Modulation Wheel) is utilized. An RWM, which is an apparatus utilized in an apparatus included in an irradiation system, i.e., utilized in a particle beam irradiation apparatus, is to create an SOBP by enlarging an irradiation field in the traveling direction of a beam. In some cases, an RMW is utilized in a broad beam irradiation method, such as the double scatterer method or the Wobbler method, in which the irradiation field of a beam is temporarily enlarged and then is limited through a collimator or a bolus. Japanese Patent Application Laid-Open No. 2007-222433 discloses an example where an RMW is utilized in the double scatterer method. An RMW according to Embodiment 5 of the present invention will be explained with reference to FIGS. 10 and 11. FIG. 10 is an external view illustrating an RMW according to Embodiment 5 of the present invention; FIG. 11 is a configuration diagram illustrating a depth-direction irradiation field enlargement apparatus according to Embodiment 5 of the present invention. An RMW 35 is configured in such a way that there are arranged a plurality of wedge-shaped energy absorbers (blades) which are each configured with a plurality of pedestals, the respective axis-direction thicknesses of which stepwise increase or decrease. In the example illustrated in FIG. 10, the RMW 35 has three blades 37a, 37b, and 37c. The blades 37a, 37b, and 37c each have six pedestals 36a, 36b, 36c, 36d, 36e, and 36f and a shape in which the respective axis-direction thicknesses of the pedestals stepwise decrease in the clockwise circumferential direction, i.e., in the direction from the pedestal 36a to the pedestal 36f. By utilizing the pedestal 36, RMW 35 is represented in the following manner. The RMW 35 has energy absorbers 37 in each of which a plurality of pedestals 36a through 36f, the respective axis-direction thicknesses of which are stepwise different from one another, are arranged in the circumferential direction; when a charged particle beam 1 passes through the plurality of pedestals 36a through 36f, the energy thereof varies. The blades 37a, 37b, and 37c are arranged in angle ranges 0° to 120°, 120° to 240°, and 240° to 360°(0°), respectively. The six pedestals 36a, 36b, 36c, 36d, 36e, and 36f are arranged in such a way as to be spaced 20° apart from one another. The RMW 35 is disposed in the beam path in a particle beam irradiation apparatus and rotates on a plane perpendicular to the beam path. For example, the RMW 35 is disposed at the upstream side of the scanning irradiation system 34 illustrated in FIG. 1. There will be explained a principle in which an SOBP is formed by the RMW 35. For example, in the case where while the RMW 35 rotates, the charged particle beam 1 passes through a thin portion of the blade (e.g., the pedestal 36f), the attenuation of the beam energy is small and hence a Bragg peak BP is produced in a deep part of a body. In the case where the charged particle beam 1 passes through a thick portion of the blade (e.g., the pedestal 36a), the attenuation of the beam energy is large and hence a Bragg peak BP is produced in a shallow part of a body. Because due to the rotation (circulation) of the RMW 35, the position of the Bragg peak BP fluctuates periodically, there can be obtained, in view of time integration, a flat dose distribution (SOBP) that spreads from a shallow part, which is near to the body surface, to a deep part of a body. By selecting two or more neighboring pedestals and making the charged particle beam 1 pass through only the selected pedestals, two or more depths of SOBP can be formed. For example, the depth of SOBP at a time when the pedestals 36e and 36f are selected is referred to as “SOBP depth 1”. As is the case with SOBP depth 1, the depths of SOBP at times when the pedestals 36d through 36f, 36c through 36f, 36b through 36f, and 36a through 36f are selected are referred to as “SOBP depth 2”, “SOBP depth 3”, “SOBP depth 4”, and “SOBP depth 5”, respectively. In the example utilizing the RMW 35 illustrated in FIG. 10, when the selection is performed in such a way that the pedestal 36f is always included, five depths of SOBP can be formed and based on these depths of SOBP, the depth of SOBP can freely be selected and changed. The RMW 35 according to the present invention is utilized to enlarge a Bragg peak BP more in the depth direction than a conventional spot so that the columnar irradiation fields 44 and (refer to FIG. 6) are created. A particle beam irradiation apparatus according to Embodiment 5 has a configuration illustrated in FIG. 1. In other words, naming from the upstream side of the charged particle beam 1, the particle beam irradiation apparatus according to Embodiment 5 is provided with a columnar-irradiation-field generation apparatus 4, a pair of scanning electromagnets 10 and 11, position monitors 12a and 12b, and a dose monitor 13; the particle beam irradiation apparatus is controlled by an irradiation control apparatus 33. In this regard, however, the columnar-irradiation-field generation apparatus 4 is a depth-direction irradiation field enlargement apparatus 3 (3c) provided with the RMW 35. The columnar-irradiation-field generation apparatus 4 according to Embodiment 5 has an energy changing apparatus 2 and the depth-direction irradiation field enlargement apparatus 3 (3c). The depth-direction irradiation field enlargement apparatus 3c will be explained with reference to FIG. 11. The depth-direction irradiation field enlargement apparatus 3c has the RMW 35, a rotation axle 64 for rotating the RMW 35, a motor (rotation drive device) 62 that drives the rotation axle 64 for rotating the RMW 35, an angle sensor 61 for detecting the rotation angle of the rotation axle 64, and an irradiation-field enlargement control apparatus 65 that transmits to the irradiation control apparatus 33 a control signal Sig1 for controlling the emission start and the emission stop of the charged particle beam 1. The motor 62 and the rotation axle 64 that are arranged at positions that do not interfere with the charged particle beam 1 are coupled with each other, for example, by means of bevel gears (coupling devices) 63a and 63b. The irradiation-field enlargement control apparatus 65 controls the rotation of the motor 62. In this embodiment, the irradiation-field enlargement control apparatus 65 controls the rotation of the motor 62 in such a way that the RMW 35 keeps rotating at a predetermined constant speed. The RMW 35, the rotation axle 64, the motor 62, the bevel gears (coupling devices) 63a and 63b, and the angle sensor 61 configure an RMW apparatus 66. The RMW apparatus 66 changes the position of the RMW 35, through which the charged particle beam 1 passes, so as to vary the energy of the charged particle beam 1. The irradiation-field enlargement control apparatus 65 performs control in such a way that the charged particle beam 1 passes through two or more pedestals 36a through 36f. The operation of the depth-direction irradiation field enlargement apparatus 3c will be explained. There will be explained a case where the depth of SOBP, in a certain columnar irradiation field 44, that is specified in a treatment plan is SOBP depth 4, for example. SOBP depth 4 is formed when the charged particle beam 1 passes through the angles corresponding to the pedestals 36b through 36f. The charged particle beam 1 is irradiated in the columnar irradiation field 44 until the dose specified in a treatment plan is satisfied (the dose reaches a target dose). The charged particle beam 1 passes at least once through the blade 37 in which the pedestals 36a through 36f are provided, by the time the dose of the columnar irradiation field 44 is satisfied. The RMW 35 is controlled by the motor 62 in such a way as to rotate in a direction indicated as a rotation direction 68. The emission of the charged particle beam 1 for the columnar irradiation field 44 is started at a time when the angle sensor 61 detects an angle-area starting angle 20° (140°, 260°), in the angle 20° to 40° corresponding to the pedestal 36b, which is an emission starting angle. When the angle sensor 61 detects the emission starting angle, the irradiation-field enlargement control apparatus 65 outputs the control signal Sig1 (e.g., a first voltage level). In response to the control signal Sig1, the irradiation control apparatus 33 issues an emission start instruction that the emission apparatus of the accelerator emits the charged particle beam 1 to the particle beam irradiation apparatus 58. In response to the emission start instruction, the emission apparatus of the accelerator emits the charged particle beam 1 to the particle beam irradiation apparatus 58 (beam emission procedure). Next, when the angle sensor 61 detects an emission stop angle (120°, 240°, 360°(0°)), the irradiation-field enlargement control apparatus 65 stops the control signal Sig1 (e.g., the level of the control signal Sig1 is changed to a second voltage level). In response to the stop of the control signal Sig1, the irradiation control apparatus 33 issues an emission stop instruction that the emission apparatus of the accelerator stops the emission of the charged particle beam 1 to the particle beam irradiation apparatus 58. In response to the emission stop instruction, the emission apparatus of the accelerator stops the emission of the charged particle beam 1 to the particle beam irradiation apparatus 58 (beam stop procedure). Next, the beam emission procedure and the beam stop procedure are repeated also in the following blade 37 until the dose monitor detects the fact that the dose has been satisfied. When the dose monitor detects the fact that the dose has been satisfied, in response to the satisfaction of the dose, the irradiation control apparatus 33 issues an emission stop instruction that the emission apparatus of the accelerator stops the emission of the charged particle beam 1 to the particle beam irradiation apparatus 58. In response to the emission stop instruction, the emission apparatus of the accelerator stops the emission of the charged particle beam 1 to the particle beam irradiation apparatus 58 (columnar irradiation field stop procedure). After that, the process moves to a procedure in which the next columnar irradiation field is formed. The procedure for forming a columnar irradiation field includes the beam emission procedure, the beam stop procedure, and the columnar irradiation field stop procedure. The particle beam irradiation apparatus 58 having the depth-direction irradiation field enlargement apparatus 3c according to Embodiment 5 can perform irradiation in such a way as to generate a columnar irradiation field, which is obtained by enlarging the Bragg peak of a charged particle beam, at the depth corresponding to the distal form of an irradiation subject, and there can be raised the irradiation flexibility in the depth direction, without utilizing a bolus; therefore, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. The RMW 35 demonstrates an advantageous effect that is not found in a ridge filter. AS illustrated in FIG. 6, in some cases, it is required that in the second-round columnar irradiation field 45, the depth of SOBP is different from the depth of SOBP in the first-round columnar irradiation field 44, depending on the shape of the diseased site 40. In the case where the depth of SOBP is changed by means of a ridge filter, it is required to prepare a plurality of ridge filters, as illustrated in FIGS. 8 and 9. In contrast, in the case of an RMW, the emission start and the emission stop of the charged particle beam 1 are controlled based on the rotation angle of the RMW 35, so that the depth of SOBP can freely be changed. That is to say, as described above, by synchronizing the rotation of the RMW 35 with the timing of beam emission, the depth of SOBP can freely be controlled by means of a single RMW 35. As a result, in the case where a plurality of depths of SOBP is formed, the configuration of the columnar-irradiation-field generation apparatus 4 can be simplified. FIG. 12 is a configuration diagram illustrating a depth-direction irradiation field enlargement apparatus according to Embodiment 6 of the present invention. A depth-direction irradiation field enlargement apparatus according to Embodiment 6 is different from the depth-direction irradiation field enlargement apparatus 3c in that the former has a plurality of RMW apparatuses whose respective numbers of selectable depths of SOPB are different from one another. A depth-direction irradiation field enlargement apparatus 3d illustrated in FIG. 12 is an example of depth-direction irradiation field enlargement apparatus having two RMW apparatuses 66a and 66b. In the foregoing example, an RMW 35a of the RMW apparatus 66a has more selectable depths of SOPB than an RMW 35b of the RMW apparatus 66b has. An irradiation-field enlargement control apparatus 65 selects the RMW apparatus 66a or the RMW apparatus 66b, which is to be utilized, and also controls a driving device 67a that drives the RMW apparatus 66a and a driving device 67b that drives the RMW apparatus 66b. In response to a signal from an angle sensor 61 of the RMW apparatus 66a or a signal from an angle sensor 61 of the RMW apparatus 66b, the irradiation-field enlargement control apparatus 65 outputs or stops a control signal Sig1. By increasing the number of pedestals 36 of a blade 37, the number of selectable depths of SOBP can be increased. For example, the RMW 35a has two blades 37a and 37b; each of the blades 37a and 37b has nine pedestals 36a through 36i. In this case, the angle range of each of the blades 37a and 37b is 180°; the angle range of each pedestal is 20°, as is the case with Embodiment 5. It may be allowed that there exists only a single blade 37 and the respective thicknesses of the pedestals 36 of the RMW 35 are different from one another. It may be allowed that also in an embodiment in which the RMW 35 is utilized, the respective thicknesses of the pedestals 36 of the RMW 35 are different from one another. Because having a plurality of RMW apparatuses 66a and 66b whose respective numbers of selectable depths of SOPB are different from each other, the depth-direction irradiation field enlargement apparatus 3d according to Embodiment 6 can form a wider range of depth of SOPB than the depth-direction irradiation field enlargement apparatus 3c according to Embodiment 5. Accordingly, the particle beam irradiation apparatus 58 having the depth-direction irradiation field enlargement apparatus 3d can form and irradiate more columnar irradiation fields than the particle beam irradiation apparatus 58 according to Embodiment 5 and hence can efficiently perform multi-port irradiation onto the diseased site 40. FIG. 13 is a configuration diagram illustrating a columnar-irradiation-field generation apparatus according to Embodiment 7 of the present invention. A columnar-irradiation-field generation apparatus according to Embodiment 7 is different from the columnar-irradiation-field generation apparatus 4a having the depth-direction irradiation field enlargement apparatus 3c according to Embodiment 5 in that the energy changing apparatus 2 (2a) and the depth-direction irradiation field enlargement apparatus 3c are integrated therein. The columnar-irradiation-field generation apparatus 4c is provided with range shifters 9a and 9b; RMW apparatuses 66a and 66b; deflection electromagnets 5 and 6 included in a pair of upstream deflection electromagnets that moves the position, of the charged particle beam 1, in the range shifters 9a and 9b and the RMW apparatuses 66a and 66b through which the charged particle beam 1 passes; a first deflection-electromagnet power source 20 that energizes the pair of upstream deflection electromagnets; deflection electromagnets 7 and 8 included in a pair of downstream deflection electromagnets that returns the charged particle beam 1 that has passed through the range shifters 9a and 9b and the RMW apparatuses 66a and 66b onto the original orbit; a second deflection-electromagnet power source 21 that energizes the pair of downstream deflection electromagnets; and a change control apparatus 30 that calculates the amount of movement, of the orbit of the charged particle beam, that is caused by the pair of upstream deflection electromagnets, based on an energy command value inputted from the irradiation control apparatus 33, and transmits an energization current value to the first deflection-electromagnet power source 20. The change control apparatus 30 also controls the second deflection-electromagnet power source 21. In addition, the change control apparatus 30 is provided also with the function of the irradiation-field enlargement control apparatus 65 according to Embodiment 5. The range shifter 9a is disposed at the upstream side of the RMW apparatus 66a in such a way as to be situated between the rotation axle 64a of an RMW 35a and the outer circumference of the RMW 35a. The range shifter 9b is disposed at the upstream side of the RMW apparatus 66b in such a way as to be situated between the rotation axle 64b of an RMW 35b and the outer circumference of the RMW 35b. The operations of the apparatuses are the same as those in Embodiments 1 and 5; thus, explanations therefor will not be repeated. The range shifters 9a and 9b have the same shape and are formed of the same material; in the foregoing example, the RMW 35a of the RMW apparatus 66a and the RMW 35b of the RMW apparatus 66b are different from each other in terms of the number of selectable depths of SOPB. As explained in Embodiment 6, the RMW 35a of the RMW apparatus 66a can have more selectable depths of SOPB than the RMW 35b of the RMW apparatus 66b. Because having a plurality of RMW apparatuses 66a and 66b whose respective numbers of selectable depths of SOPB are different from each other, the columnar-irradiation-field generation apparatus 4c according to Embodiment 7 can form a wider range of depth of SOPB than the depth-direction irradiation field enlargement apparatus 3c according to Embodiment 5. Accordingly, the particle beam irradiation apparatus 58 having the depth-direction irradiation field enlargement apparatus 3d can form and irradiate more columnar irradiation fields than the particle beam irradiation apparatus 58 according to Embodiment 5 and hence can efficiently perform multi-port irradiation onto the diseased site 40. The columnar-irradiation-field generation apparatus 4c according to Embodiment 7 can perform control also in such a way that when the columnar irradiation fields 44 and 45 are formed, the emission and the stop of the charged particle beam 1 are not repeated. For convenience, this example of columnar-irradiation-field generation apparatus will be referred to as a columnar-irradiation-field generation apparatus 4d, in order to distinguish it from the columnar-irradiation-field generation apparatus 4c, explained above. The emission and the stop of the charged particle beam 1 are not repeated when the columnar irradiation fields 44 and 45 are formed, so that there can be performed irradiation of the charged particle beam 1, which is suitable for respiration-synchronized irradiation. For example, the number of pedestals 36 of the RMW 35a is made to be the same as that explained in Embodiment 6, and the number of pedestals 36 of the RMW 35b is made to be the same as that explained in Embodiment 5. When the columnar irradiation fields 44 and 45 are formed, the charged particle beam 1 is made to pass through the pedestal 37 of the RMW 35a or the RMW 35b until the dose is satisfied. As a result, there exists only a single depth of SOBP (SOBP depth a) when the charged particle beam 1 passes through the RMW 35a, and there exists only a single depth of SOBP (SOBP depth b) when the charged particle beam 1 passes through the RMW 35b. On top of that, it is made possible to make SOBP depth b wider than SOBP depth a. Additionally, in the case where the columnar irradiation fields 44 and 45 are formed always without repeating the emission and the stop of the charged particle beam 1, the change control apparatus 30 is not required to generate the control signal Sig1; therefore, the configuration of the change control apparatus 30 can be simplified. The columnar-irradiation-field generation apparatus 4d according to Embodiment 7 changes the energy of the charged particle beam 1 to desired energy, through two kinds of depths of SOBP; thus, two kinds of columnar irradiation fields can have desired ranges. The emission and the stop of the charged particle beam 1 are not repeated when the columnar irradiation fields 44 and 45 are formed, so that there can be performed irradiation of the charged particle beam 1, which is suitable for respiration-synchronized irradiation. In order to line up many kinds (more than two) of depths of SOBP, it is only necessary to arrange the range filters 9 and the RMW apparatuses 66, the number of each of which corresponds to the number of the kinds of depths of SOBPs. In each of the columnar-irradiation-field generation apparatus 4c and 4d according to Embodiment 7, there are not provided the pair of upstream electromagnets and the pair of downstream deflection electromagnets for each of the set of the range filter 9a and the RMW apparatus 66a and the set of the range filter 9b and the RMW apparatus 66b, but there is provided only one set of the pair of upstream electromagnets and the pair of downstream deflection electromagnets; therefore, compared with the columnar-irradiation-field generation apparatus 4a according to Embodiment 1, the length of the apparatus in the irradiation direction (Z direction) of the charged particle beam 1 can be shortened. In the particle beam irradiation apparatus (refer to FIG. 1) having the columnar-irradiation-field generation apparatus 4c or 4d according to Embodiment 7, multi-port irradiation can be implemented based on a treatment plan corresponding to the treatment plan created by the treatment planning apparatus described in Embodiment 1; therefore, as is the case with Embodiment 1, the irradiation flexibility in the depth direction can be raised, without utilizing a bolus. As a result, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. Heretofore, the particle beam irradiation apparatuses according to Embodiment 1 through 7 have been explained with a case where the energy of the charged particle beam 1 is changed in the columnar-irradiation-field generation apparatus 4. However, the energy of the charged particle beam 1 can also be changed by changing the parameters for the synchrotron 54. In this embodiment, there will be explained an example where the columnar irradiation fields 44 and 45 are generated by combining the parameters for the synchrotron 54 with the depth-direction irradiation field enlargement apparatus 3. FIG. 14 is a configuration diagram illustrating a particle beam irradiation apparatus according to Embodiment 8 of the present invention. A particle beam irradiation apparatus 60 according to Embodiment 8 is different from the particle beam irradiation apparatuses described in Embodiments 1 through 7 in that the columnar irradiation fields 44 and 45 are generated by making the synchrotron 54 change the energy of the charged particle beam 1, without providing the energy changing apparatus 2 in the columnar-irradiation-field generation apparatus 4. A columnar-irradiation-field generation apparatus 4 (4e) of the particle beam irradiation apparatus 60 has the depth-direction irradiation field enlargement apparatus 3. The depth-direction irradiation field enlargement apparatus 3 is one of the depth-direction irradiation field enlargement apparatuses 3a, 3b, 3c, and 3d, described above. The irradiation control apparatus 33 outputs an energy command value to the synchrotron 54, which is an accelerator, so that the columnar irradiation fields 44 and 45 are formed at the depth-direction positions thereof planned in a treatment plan. In response to the energy command value, the synchrotron 54 changes the energy of the charged particle beam 1 in accordance with the energy command value. After acquiring predetermined energy, the charged particle beam 1 enters the particle beam irradiation apparatus 60 by way of an ion beam transport system 59. The columnar-irradiation-field generation apparatus 4 (4e) changes the energy of the charged particle beam 1 so that a predetermined depth of SOBP planned in a treatment plan is achieved; predetermined columnar irradiation fields 44 and 45 are formed at a predetermined position in a diseased site 40. In the particle beam irradiation apparatus 60 according to Embodiment 8, multi-port irradiation can be implemented based on a treatment plan corresponding to the treatment plan created by the treatment planning apparatus described in Embodiment 1; therefore, as is the case with Embodiment 1, the irradiation flexibility in the depth direction can be raised, without utilizing a bolus. As a result, there can be solved the problem of excess irradiation in IMRT by a particle beam therapy system. The particle beam irradiation apparatus 60 demonstrates the effect of the depth-direction irradiation field enlargement apparatuses 3a, 3b, 3c, and 3d, utilized in the columnar-irradiation-field generation apparatus 4 (4e). Embodiment 9 of the present invention is a particle beam therapy system provided with the particle beam irradiation apparatus described in each of Embodiments 1 through 8. FIG. 15 is a schematic configuration diagram illustrating a particle beam therapy system according to Embodiment 9 of the present invention. A particle beam therapy system 51 includes an ion beam generation apparatus 52, an ion beam transport system 59, and particle beam irradiation apparatuses 58a and 58b (60a and 60b). The ion beam generation apparatus 52 includes an ion source (unillustrated), a prestage accelerator 53, and a synchrotron 54. The particle beam irradiation apparatus 58b is provided in a rotating gantry (unillustrated). The particle beam irradiation apparatus 58a is provided in a treatment room where no rotating gantry is installed. The function of the ion beam transport system 59 is to achieve communication between the synchrotron 54 and the particle beam irradiation apparatuses 58a and 58b. A portion of the ion beam transport system 59 is provided in the rotating gantry (unillustrated), and in that portion, there are included a plurality of deflection electromagnets 55a, 55b, and 55c. A charged particle beam, which is a particle beam such as a proton beam generated in ion source, is accelerated by the prestage accelerator 53 and enters the synchrotron 54. The particle beam is accelerated to have predetermined energy. The charged particle beam launched from the synchrotron 54 is transported to the particle beam irradiation apparatuses 58a and 58b (60a and 60b) by way of the ion beam transport system 59. The particle beam irradiation apparatuses 58a and 58b (60a and 60b) each irradiate a charged particle beam onto a diseased site (unillustrated) of a patient. In the particle beam therapy system 51 according to Embodiment 9, the particle beam irradiation apparatus 58 (60) is operated based on a treatment plan generated by the treatment planning apparatus described in Embodiment 1, and a charged particle beam is irradiated onto a diseased site of a patient; therefore, the problem of excess irradiation in IMRT by a particle beam therapy system can be solved by raising the irradiation flexibility in the depth direction, without utilizing a bolus. The particle beam therapy system 51 according to Embodiment 9 irradiates a beam having a columnar dose distribution; therefore, compared with irradiation of a beam having a spot-like distribution, the particle beam therapy system 51 has an advantage in that the irradiation time is shortened. Moreover, multi-port irradiation can be performed; therefore, in the case where irradiation is implemented onto the same diseased site, the damage to the body surface, which is a normal tissue, can be reduced, whereby irradiation can be prevented from being preformed onto a risk site (such as a spinal cord, an eyeball or the like), onto which a particle beam should not be irradiated. Furthermore, the particle beam therapy system 51 according to Embodiment 9 has an advantage that multi-port irradiation can remotely be performed. Remote multi-port irradiation, which does not require that an engineer or the like enters a treatment room so as to operate the rotating gantry, means that the direction of irradiation onto a diseased site is changed among many directions remotely from the outside of the treatment room and then a particle beam is irradiated. As described above, the particle beam therapy system according to the present invention has a simple irradiation system that requires neither an MLC nor a bolus; therefore, neither bolus replacement work nor MLC-shape confirmation work is required. As a result, there is demonstrated an effect that remote multi-port irradiation can be performed and the treatment time is considerably shortened. Additionally, as the columnar-irradiation-field generation apparatus 4 having the energy changing apparatus 2 and the depth-direction irradiation field enlargement apparatus 3, there can be utilized the energy changing apparatus 2b described in Embodiment 2 or the depth-direction irradiation field enlargement apparatus 3b described in Embodiment 3. Heretofore, in Embodiments 5 through 7, there has been explained an example where in order to form a plurality of depths of SOBP, the depth-direction irradiation field enlargement apparatus makes the RMW 35 rotate at a predetermined constant speed and repeats the emission and the emission stop of the charged particle beam 1 in such a way that the charged particle beam 1 passes through only selected pedestals. There exists another way to form a plurality of depths of SOBP by use of the RMW 35. For example, there will be explained a case where there is formed SOBP depth 1, which is a depth of SOBP when the pedestals 36e and 36f are selected. As the motor 62, a servo motor or a stepping motor is utilized. The position of the RMW 35 is set in such a way that the charged particle beam 1 passes through the pedestal 36f, and then irradiation of the charged particle beam 1 is started. After a certain time elapses, the motor 62 sets the position of the RMW 35 in such a way that the charged particle beam 1 passes through the pedestal 36e. After a certain time elapses, the motor 62 sets the position of the RMW 35 in such a way that the charged particle beam 1 passes through the pedestal 36f. By changing the positions of the RMW 35 in such a way that the charged particle beam 1 shuttles between the positions of the pedestal 36e and 36f in a constant cycle, SOBP depth 1 can be formed. In the case where there is formed SOBP depth 5, which is a depth of SOBP when the pedestals 36a through 36f are selected, it is only necessary to change the position of the RMW 35 in such a way that the charged particle beam 1 shuttles between the positions of the pedestals 36a and 36f in a constant cycle. In addition, there may be repeated the procedure in which the charged particle beam 1 is stopped every constant time and then the position, of the pedestal 36, through which the charged particle beam 1 passes through is changed, and after that, the charged particle beam 1 is emitted. The procedure, in which the charged particle beam 1 is not stopped and the position of the RMW 35 is changed in such a way that the charged particle beam 1 shuttles between the positions of the pedestal 36a and 36f, can be applied to respiration-synchronized irradiation. Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this is not limited to the illustrative embodiments set forth herein.
043022863	abstract	A reactor vessel in-service inspection assembly (17) having an improved positioning device (80) for properly and repeatedly locating the inspection transducers (75) of the assembly within a hollow portion of the reactor vessel cavity. An acoustic transducer of the positioning device of this invention is affixed to the positioning arm (40) of the inspection transducers (75). The positioning transducer is operable to generate and simultaneously, radially direct acoustic signals around the circumference of the hollow portion of the vessel cavity and receive the signals reflected off of the cavity walls at a location within the hollow cavity. Means are provided for monitoring the received signals as a function of time. The in-service inspection assembly transducer positioning arm is arranged to automatically move in response to the monitored difference in the time of reception of the received signals to locate the positioning transducer at a preestablished location within the hollow portion of the reactor cavity.
	abstract	Apparatus for performing electron radiation therapy on a breast cancer patient preferably includes an intraoperative electron radiation therapy machine, an intraoperative electron radiation therapy collimator tube connected to the intraoperative electron radiation therapy machine, and a plurality of filters made of a material having substantially the same density as human breast tissue for placement between the machine and the patient to change the energy of a monoenergetic beam after the beam has left the machine, allowing a filter to be chosen to reduce the energy traveling through the tube to a desired amount of energy to treat the patient. A method of controlling the amount of energy to reach a breast cancer patient undergoing electron radiation therapy includes selecting a filter made of a material having substantially the same density as human tissue and placing the filter between an intraoperative electron radiation therapy machine and a breast cancer patient to change the energy of a monoenergetic beam after it has left the machine, the filter being chosen to reduce the energy traveling from the machine to a desired amount of energy to treat the patient.
059600500	claims	1. A method for determining the absolute value of fission flux of a prime fuel-bearing specimen containing Uranium 235 inserted into a test holder of a nuclear reactor, said method comprising: inserting into said test holder of said nuclear reactor at least one prime specimen, a plurality of bulk water channels and at least two thermocouple test specimens, said thermocouple test specimens being positioned at the same level in said test holder and comprising first and second outer clads, a central backclad and first and second fuel fillers disposed between respective outer clads and said backclad; determining the temperature of said thermocouple test specimens and said bulk water channels, the gamma scan count ratios for said thermocouple test specimens and said at least one prime specimen, the thicknesses of said outer clads, said fuel fillers and said backclad of said thermocouple test specimens, and the water channel heat transfer coefficient of the thermocouple test specimens; calculating, using the temperatures of said thermocouple test specimens, the ratio of the gamma scan counts of said thermocouple test specimens, the temperature of the bulk water channels, the thicknesses of said outer clads, said fuel fillers and said backclad of said thermocouple test specimens, and said surface water channel heat transfer coefficient, the absolute value of the fission heat fluxes for the thermocouple test specimens; and calculating, using the absolute value of the fission heat fluxes for the thermocouple test specimens and the gamma scan ratio for said at least one prime specimen, the absolute value of the fission heat flux for the prime specimen. inserting into said test holder a specimen assembly comprising a plurality of bulk water channels, at least one prime specimen comprising a prime fuel filler disposed between first and second prime clads, and at least two thermocouple specimens positioned at the same level as each other in said test holder, said thermocouple specimens comprising first and second outer clads, a central backclad and first and second fuel fillers disposed between respective outer clads and said backclad; determining the temperature of said thermocouple test specimens and said bulk water channels, the gamma scan count ratios for said thermocouple test specimens and said at least one prime specimen, the thicknesses of said outer clads, said fuel fillers and said backclad of said thermocouple test specimens, the surface water channel heat transfer coefficient of the thermocouple test specimens, the reactor lobe power, and axial factor for gamma heat; using the temperatures of said thermocouple test specimens, the ratio of the gamma scan counts of said thermocouple test specimens, the temperature of the bulk water channels, the thicknesses of said outer clads, said fuel fillers and said backclad of said thermocouple test specimens, said surface water channel heat transfer coefficient, the reactor lobe power, and axial factor for gamma heat, to calculate the absolute value of the fission heat fluxes for the thermocouple test specimens; and using the absolute value of the fission heat fluxes for the thermocouple test specimens and the gamma scan ratio for said at least one prime specimen, to calculate the absolute value of the fission heat flux for the prime specimen. 2. A method of claim 1 further comprising determining the reactor lobe power and axial factor for gamma heat and using the lobe power and axial factor so determined to separate fission heat from total heat in determining the absolute value of the fission heat flux for said thermocouple test specimens. 3. A method according to claim 1 wherein determining said water channel heat transfer coefficient comprises determining a measured flow heat rate and deriving said water channel heat transfer coefficient. 4. A method for determining the absolute value of fission flux of a prime fuel-bearing specimen containing Uranium 235 inserted into a test holder of a nuclear reactor, said method comprising: 5. A method according to claim 4 wherein said prime specimen is disposed between a pair of said plurality of water channels, and each of said thermocouple test specimens is separately disposed between a pair of said plurality of water channels.
060524308	claims	1. A movable controlled collimator having a plurality of movable collimator leaves, comprising: a plurality of movable leaves configured to delimit a radiation beam path to define a radiation field on an object, said radiation field including a static region and a margin region; and a control processor configured to move one or more of said plurality of movable leaves from a first predetermined position to a second predetermined position at a constant velocity over said margin region of said field. generating a radiation beam having a beam path from a radiation source to the patient; delimiting said beam path by adjusting one or more of a plurality of collimator leaves to define a corresponding radiation field having a static region and a margin region at the patient; and changing said beam path by moving a predetermined number of said collimator leaves at a constant velocity over said margin region. a radiation source for generating a radiation beam defining a source beam path to said patient; a collimator having a plurality of movable leaves configured to delimit said source beam path, to define a radiation field at the patient, said radiation field including a static region and a surrounding region; and a processor configured to move a predetermined number of the plurality of leaves at a constant velocity within said surrounding region during application of the radiation beam. 2. A movable controlled collimator according to claim 1, wherein said first predetermined position is relatively closer to a center of said beam path than said second predetermined position. 3. A movable controlled collimator according to claim 2, wherein said control processor is configured to begin moving the predetermined number of collimator leaves from said first predetermined position to said second predetermined position a predetermined time after a beginning of the application of the radiation field. 4. A movable controlled collimator according to claim 3, wherein said control processor is configured to move said predetermined number of collimator leaves from said first predetermined position to said second predetermined position upon the beginning of the application of the radiation field. 5. A movable controlled collimator according to claim 3, wherein said control processor is configured to move said predetermined number of collimator leaves a predetermined time after application of a predetermined number of monitor units of radiation, according to the formula: ##EQU3## wherein x is the distance over which the at least one of the plurality of leaves should move and .vertline.DMU/dx.vertline. is the absolute value of a slope of an intensity profile the leaf can deliver. 6. A movable controlled collimator according to claim 1, wherein said second predetermined position is relatively closer to a center of said beam path than said first predetermined position. 7. The radiation treatment apparatus of claim 6, wherein said control processor is configured to move said predetermined number of collimator leaves from an initial position defined by the relation y+z, wherein y is the static field leaf position, and z is the size of the sloped region of the intensity profile. 8. The radiation treatment apparatus of claim 6, wherein said control processor is configured to begin moving said at least one of said collimator leaves from an initial position defined by the relation y+b, wherein y is the static field leaf position, and b is [total MU's/(DMU/dx)]. 9. A method for shaping a cumulative therapeutic radiation exposure to a patient, comprising: 10. A method for shaping a cumulative therapeutic radiation exposure to a patient, according to claim 9, wherein said moving step comprises moving said predetermined number of collimator leaves from a first predetermined position to a second predetermined position, said first predetermined position being relatively closer to a center of said beam path than said second predetermined position. 11. A method for shaping a cumulative therapeutic radiation exposure to a patient, according to claim 10, further comprising waiting to begin moving the predetermined number of collimator leaves from said first predetermined position to said second predetermined position a predetermined time after a beginning of the application of the radiation beam. 12. A method for shaping a cumulative therapeutic radiation exposure to a patient, according to claim 10, further comprising moving said predetermined number of collimator leaves from said first predetermined position to said second predetermined position upon the beginning of the application of the radiation field. 13. A method for shaping a cumulative therapeutic radiation exposure to a patient, according to claim 11, including moving said predetermined number of collimator leaves a predetermined time after application of a predetermined number of monitor units of radiation, according to the formula: ##EQU4## wherein x is the distance over which the at least one of the plurality of leaves should move and .vertline.DMU/dx.vertline. is the absolute value of a slope of an intensity profile the leaf can deliver. 14. A method for shaping a cumulative therapeutic radiation exposure to a patient, according to claim 9, wherein said moving step comprises moving said predetermined number of collimator leaves from a first predetermined position to a second predetermined position, said first predetermined position being relatively farther from a center of said beam path than said second predetermined position. 15. A method for shaping a cumulative therapeutic radiation exposure to a patient, according to claim 14, including moving said predetermined number of collimator leaves from an initial position defined by the relation y+z, wherein y is the static field leaf position, and z is the size of the sloped region of the intensity profile. 16. A method for shaping a cumulative therapeutic radiation exposure to a patient, according to claim 14, including moving said at least one of said collimator leaves from an initial position defined by the relation y+b, wherein y is the static field leaf position, and b is [total MU's/(DMU/dx)]. 17. A radiation treatment apparatus for providing therapeutic radiation to a patient, comprising:
046577327	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention applies the principle of redundant design in order to seal a primary loop integrated into a prestressed concrete pressure vessel in a failure-safe manner. The prestressed concrete pressure vessel has two redundant seals, namely, a metal liner and a concrete body, which acts as an effective flow limitation. A precondition is that the radioactivity passing through the concrete body must be less than the value permitted for the installation in view of the environment. If this is not the case, the reactor must be shut down as a consequence of a "liner leak". If the condition is satisfied, the reactor may continue in operation, as the redundant seal of the concrete body is failure-safe. In the case of a leak of the inner cover of one of the closure devices, the escaping primary gas is discharged through a filter system and exhaust stack into the environment, while the fission products are retained in the filter system. In the space between the inner and outer covers, therefore, no appreciable excess pressure can be built up, so that the outer cover is failure-safe eve in relation to the sealing function. The outer cover, forming the fourth barrier, is thus comparable to the safety housing of the above-described nuclear reactor installation with a steel reactor pressure vessel. As radioactivity cannot escape into the environment from the primary loop through the prestressed concrete pressure vessel, or the closure devices of the passages, a tight safety housing is no longer necessary, and the tasks of containing the primary gas in a failure-safe manner and protecting the high temperature reactor against outside effects may be performed by the concrete pressure vessel alone. The additional construction effort required is relatively small, consisting essentially of the closure devices with the exhaust of the intermediate spaces. The invention thus makes possible the construction of a high temperature reactor in a highly economical manner, as no safety-associated reactor protection building is required. It is advantageous to locate the pipelines for the removal of primary gas leakages, to their connection with the exhaust stack, extensively in the concrete of the reinforced concrete pressure vessel, in order to contribute to the reduction of the risk potential of said pipelines, and for environmental reasons. The filter systems for the retention of fission products may also be installed within the walls of the prestressed concrete pressure vessel, thereby serving the same purpose. In order to provide securement against external catastrophes, such as an airplane collision, the prestressed concrete pressure vessel may be equipped with an appropriately designed protective installation. This may consist, for example, of a concrete building which simultaneously serves as the architectonic enclosure of the installations of the nuclear reactor. As this building is not charged with radioactivity from the primary loop, it may be structurally simple. A preferred embodiment of the invention can be seen with reference to the drawing. A cylindrical prestressed concrete pressure vessel 1 comprises a center cavity 2, which is clad with a metal liner 3. In the cavity 2, a high temperature reactor 4 is arranged, the core thereof comprising a pile of spherical fuel elements. The fuel elements consist of coated fissionable material particles embedded in a graphite matrix. The graphite matrix and the coating represent a first and a second barrier against the release of fission products. A cooling gas, e.g., helium, flows from top to bottom through the pile, as indicated by arrows in the figure. It is surrounded on all sides by a reflector 5, which is followed below by a hot gas collector space 6. The hot gas collector space is connected by the hot gas channel 7 with a plurality of steam generators 8 arranged about the high temperature reactor 4 in the cavity 2. Several circulating blowers 9 convey the cold cooling gas back into the reactor core. The reflector 5 is surrounded by a thermal shield 10, which also defines the guides for the return of the cold cooling gas. The prestressed concrete pressure vessel 1 comprises several large passages 11 in its roof area, each of which is closed off by a closure device 12. The circulating blowers 9 are arranged in part in said passages, thereby serving the purpose of installation and disassembly of the steam generators 8, and of other reactor components. Each closure device consists of two steel covers 13 and 14 arranged above each other, of which the inner cover 13 forms the seal for the primary gas. Between the two covers 13 and 14 of each closure device 12, an intermediate space 15 is present, and to which a pipeline 16 is connected. This pipeline, which is located for the most part in the concrete of the concrete pressure vessel 1, is connected through a filter system 17 to an exhaust stack 18. The filter system provides for the retention of fission products. To reduce the potential danger, in addition to the pipelines 16, the filter systems 17 are also arranged in the wall of the prestressed concrete pressure vessel 1. In place of the protective reactor building usually provided, and which forms the outermost barrier against the release of fission products, the instant invention provides for the prestressed concrete pressure vessel 1 as a barrier system. The liner thereof acts as a third barrier, and the concrete body, which provides for an extremely tight flow limitation, acts as the fourth and outermost barrier. The prestressed concrete pressure vessel thus has two redundant seals. In the area of the passages 11, the third and the fourth barriers comprise inner covers 13 and outer cover 14 of closure devices 12. In the case of leakage through the inner covers 13 into intermediate spaces 15, the outer covers 14, which are dimensioned for full design pressure, are not stressed appreciably due to the exhausting of the intermediate space through the pipelines 16, thus, they are failure safe as regards their sealing function. There is no need, consequently, for a tight protective reactor building.
050948091	claims	1. Device for obturating and retaining a sealed closure plug (3) of a steam generator tube (1) comprising a tubular casing (4) closed at one end of said casing by a sealed base (5) engaged into said one end of said tube (1) in such a manner that said base (5) is disposed within said tube (1) and a core (10) traversed by a threaded bore (10') at a central part of said core, and engaged within said casing (4) in order to effect blocking of said plug (3) in said tube (1) by diametral expansion of said casing (4), said device further comprising a threaded rod (11a; . . .) adapted to be screwed into said threaded bore (10') and solid, at one end of said threaded rod with a blocking element (11b; . . .) having an external diameter greater than a diameter of said threaded rod and being adapted to come into engagement in an end of said casing (4) opposite said one end when said threaded rod is screwed into said core (10), and comprising means cooperating with the end of said casing to block said obturating device against rotation and/or translation. 2. Obturating device according to claim 1, constituted in the form of a screw having a screw head (11b) which constitutes a blocking element adapted to come into engagement in a bore (7) of said casing (4) of said plug, blocking against rotation and translation of said obturating device being effected by junction weld points (13) between said screw head (11b) and said casing (4) at the location of said bore (7). 3. Obturating device according to claim 1, wherein said blocking element (21b) comprises an annular throat (23) in its part of junction with said rod (21a), a supporting collar (22) at its end opposite the threaded rod (21a) and an elastic ring (25) engaged in said throat (23) and adapted to retract by elasticity in radial directions for introduction of said ring into a bore (7) of said casing (4) located at an end of said plug opposite said base (5), during screwing of said threaded rod (21a) into said bore (10') of said core (10) and its diametral expansion in a diametrally enlarged part (8) of said bore (7). 4. Obturating device according to claim 1, wherein said blocking element (21'b) is separated from said threaded rod (21'a) by a shoulder on which there is placed in abutment an elastic ring (25') which is adapted to be retracted in radial directions in order to permit introduction of said blocking element (21'b) into a bore (7') opening at an end of said casing (4') opposite its base (5'), during screwing of said threaded rod (21'a) into said threaded bore (10') of said core (10), said elastic ring (25') being received, on completing screwing of said rod (21'a), in a diametrally enlarged part (8') of said bore (7') of said casing (4'). 5. Obturating device according to claim 4, wherein the ring (25') has the shape of a torus of square cross-section. 6. Obturating device according to claim 1, wherein the blocking element (31b) is constituted by a tubular element comprising axial slits (33) delimiting radially deformable elastic plates (34) comprising ends opposite said threaded rod (31a) which are constituted by abutment lugs projecting radially towards the exterior, said elastic plates (34) being clamped in such a manner as to bring them close to one another during screwing of said rod (31a) into said core (10) and released on completing screwing, whereby end lugs of said elastic plates (34) come into a position of blocking of said obturating device, in a throat (8) in an internal bore of said casing (4). 7. Obturating device according to claim 1, wherein said blocking element (41b) is a deformable thin ferrule having an external diameter smaller than the diameter of said internal bore (7) of said casing (4) at an end of said bore opposite said base (5), blocking of said obturating device (41) against translation occurring by diametral expansion towards the exterior of said deformable ferrule (43), within a throat (8) constituting an enlarged part of said bore (7), within said casing (4). 8. Obturating device according to claim 1, in the shape of a screw (51), a head (51b) of said screw and a part of said threaded rod (51a) being traversed by axial slits (53) delimiting four branches deformable elastically in radial directions, and entirely separated, over an entire length of said head (51b) and over a part of a length of said threaded rod (51a), as well as a collar (54) projecting radially in a junction zone between said threaded rod (51a) and said head (51b) and means (56) for gripping said deformable branches of said screw, in order to effect radial retraction of said head (51b) during screwing of said threaded rod (51a) into said core (10), release of said elastic branches of said screw after screwing into said core (10) enabling blocking of said screw by introduction of said collar (54) into a throat (8) within said bore of said casing (4). 9. Obturating device according to claim 1, in the shape of a screw (61), a head (61b) of said screw and a part of said threaded rod (61a) being traversed by axial slits (63) delimiting four branches deformable elastically in radial directions, and entirely separated, over an entire length of said head (61b) and over a part of a length of said threaded rod (61a), as well as a collar (64) projecting radially in a junction zone between said threaded rod (61a) and said head (61b) and spacing means (66) introduced axially into a bore (67) at a central part of said screw (61), between said elastic branches of said screw, said collar (64) having an external diameter less than an internal diameter of said bore (7) of said casing (4) in its part opposite said base (5) in order to permit screwing of said threaded rod (61a) into said screw (10), blocking of said screw (61) constituting said obturating device being effected by introduction of said device (66) for spacing said elastic branches in such a manner as to introduce said collar (64) into an enlarged-diameter throat (8) machined within said bore of said casing (4). 10. Obturating device according to claim 9, wherein said central bore (67) of said screw (61) comprises a frusto-conical part (67a), and wherein said spacing device (66) has an external surface of frusto-conical shape corresponding to the shape of said frusto-conical part (67a) of said bore of said screw (61), spacing of said branches of said screw (61) being obtained by axial thrust on said spacing device (66). 11. Obturating device according to claim 1, wherein said threaded rod (71a) and said blocking element (71b) comprise an axial blind bore (73) traversing said blocking element (71b) over its entire axial length, a base of said blind bore (73) being located adjacent an end of said threaded rod (71a) opposite said blocking element (71b), wherein the screw pitch of the threaded rod (71a) is smaller than the screw pitch of the threaded bore (10') of the expander core (10), and wherein the blocking element (71b) comprises, at its end opposite the threaded rod (71a), a radially projecting collar (72) adapted to come into abutment on the end of said casing (4), said obturating device (71) further comprising means (73') for fixing a tool for axial extension of said threaded rod (71a), during the screwing thereof, into said threaded bore (10') of said core (10). 12. Obturating device according to claim 1, wherein the element for blocking said threaded rod (81a) comprises: (a) an end part (81b) of said threaded rod (81a) in which there is machined a cavity (83) for a tool for screwing and unscrewing said threaded rod (81a) and which is extended axially by a deformable thin ferrule (84); and (b) a nut (82) having a threaded external surface adapted to be screwed into a threaded bore (7) of said casing (4) of the plug constituting the end part of said bore of said casing (4) opposite said base (5), an internal bore having a diameter greater than a diameter of said end part (81b) of said rod (81a), a supporting collar (86) on an end of said casing (4) opposite said base (5) and at least one crimping internal recess (85) projecting radially towards the exterior in relation to an internal bore of said nut (82), in its part traversing said collar (86), screw pitches of said threaded rod (81a) and of said nut (82) being different and said nut (82) being screwed into said threaded bore (7) after screwing of said threaded rod (81a) into said threaded bore (10') of said core (10), in such a manner that the end part (81b) of said threaded rod (81a) is introduced into the internal bore of said nut (82) by pushing-back of said ferrule (84) into said internal recess (85). 13. Device according to claim 1, wherein said threaded rod (105, 105') has at least one transverse orifice (112, 120, 121) perpendicular to its axis (111) and opening out at either side of said rod (105, 105') and in which is engaged a braking piece (115, 122, 123) which comes into contact by means of end parts with flights of the internally threaded hole (103') of said core (103) during screwing of said threaded rod (105, 105') into said core (103). 14. Device according to claim 13, wherein said orifice (112, 120, 121) has an axial direction corresponding to a diameter of the cross-section of said rod (105, 105'). 15. Device according to claim 13, wherein said orifice (112, 120, 121) and the corresponding braking piece (115, 122, 123) have circular cross-sections. 16. Device according to claim 13, wherein said braking piece (115, 122, 123) is made of a material having a hardness substantially lower than a hardness of material forming said core (103). 17. Device according to claim 13, wherein said braking piece (115, 122, 123), in its axial direction corresponding to an axial direction of said orifice (112, 120, 121) of said rod (105, 105') is longer than the thread-bottom diameter of said threaded rod (105, 105'). 18. Device according to claim 13, wherein said rod (105') has two successive orifices (120, 121) which are spaced in an axial direction of said rod and in each of which orifices a corresponding braking piece (122, 123) is engaged. 19. Device according to claim 18, wherein said braking piece (122) engaged in an orifice (120) of said rod (105') located nearest to an end of said rod adjacent a bottom (102) of said plug is shorter than said braking piece (123) engaged in the orifice (121) located nearest to an end of said rod (105') integral with its widened part (106, 107) engaged for fastening said rod (105') in the orifice of said casing (101).
	claims	1. A method of diagnostic imaging comprising the steps of:comparing a position of a subject in a scanning bay relative to a reference position;determining a region of maximum attenuation of the subject from the comparison;automatically adjusting an attenuation characteristic of an attenuation filter based on the determined region of maximum attenuation of the subject; andimaging the subject. 2. The method of claim 1 further comprising determining a size and an elevation of the subject within the scanning bay. 3. The method of claim 2 further comprising adjusting the attenuation characteristic of the attenuation filter according to the size and the elevation of the subject. 4. The method of claim 1 further comprising automatically adjusting the elevation of the subject within the scanning bay to optimize radiation exposure to the subject. 5. The method of claim 1 further comprising acquiring data from at least one scout scan to determine the position of the subject in the scanning bay. 6. The method of claim 5 further comprising determining at least one of a size, a shape, and a centering of the subject from the at least one scout scan. 7. The method of claim 5 wherein the step of acquiring data from at least one scout scan includes acquiring a flux trend of the scout scan and wherein the step of adjusting an attenuation characteristic of an attenuation filter includes adjusting a filter position according to the flux trend. 8. The method of claim 7 wherein the step of adjusting an attenuation characteristic of an attenuation filter includes at least one of:adjusting a position of the attenuation filter to avoid flux rates beyond a threshold rate; andadjusting a position of the attenuation filter according to a flux rate of a central region of the subject. 9. The method of claim 1 wherein the step of adjusting an attenuation characteristic of an attenuation filter includes configuring an imaging filter to provide an optimal dose profile of high frequency electromagnetic energy to the subject. 10. The method of claim 1 further comprising modulating a high frequency electromagnetic energy projection source at least according to the position of the subject in the scanning bay. 11. The method of claim 1 further comprising performing at least one orthogonal scout and performing centroid calculations to determine a center of the subject. 12. The method of claim 1 further comprising determining a diameter of the subject and an optimum bowtie filter opening for the diameter of the subject. 13. The method of claim 1 further comprising determining a contour of the subject and the position of the subject in the scanning bay according to feedback from at least one of a laser sensor and a sonic sensor. 14. The method of claim 13 further comprising determining an area of the subject from the contour of the subject. 15. The method of claim 1 further comprising determining a position of the subject in three dimensions. 16. A computer readable storage medium having stored thereon a computer program representing a set of instructions which, when executed by at least one processor, causes the at least one processor to:receive feedback regarding a position of maximum attenuation of a subject to be scanned;determine a value of mis-centering of the subject to be scanned from the position of maximum attenuation relative to an isocenter of an x-ray beam;adjust at least one of an attenuation filter configuration and a subject position based on the value of mis-centering; andacquire radiographic diagnostic data from the subject. 17. The computer readable storage medium of claim 16 wherein the at least one processor is further caused to repeatedly receive position information about the attenuation filter during the acquisition of radiographic diagnostic data from the subject. 18. The computer readable storage medium of claim 16 wherein the at least one processor is further caused to determine a desired tube current modulation in a first, a second, and a third direction with respect to a desired image noise and dynamically adjust a tube current based on the desired tube current modulation. 19. The computer readable storage medium of claim 16 wherein the at least one processor is further caused to determine a center of mass of the subject and determine a distance of the center of mass from isocenter. 20. The computer readable storage medium of claim 19 wherein the at least one processor is further caused to determine a centering error from the distance of the center of mass of the subject from isocenter. 21. The computer readable storage medium of claim 20 wherein the at least one processor is further caused to adjust a projection area according to the determined centering error. 22. The computer readable storage medium of claim 16 wherein the at least one processor is caused to adjust the position of the subject by adjusting an elevation of the subject. 23. The computer readable storage medium of claim 16 wherein the at least one processor is further caused to determine an optimum opening of the attenuation filter to optimize the acquisition of radiographic diagnostic data from the subject while reducing dosage of electromagnetic energy projected toward the subject. 24. A tomographic system comprising:a rotatable gantry having a bore centrally disposed therein;a table movable within the bore and configured to position a subject for tomographic data acquisition within the bore;a high frequency electromagnetic energy projection source positioned within the rotatable gantry and configured to project high frequency electromagnetic energy toward the subject;a detector array disposed within the rotatable gantry and configured to detect high frequency electromagnetic energy projected by the projection source and impinged by the subject;an attenuation filter positioned between the high frequency electromagnetic energy projection source and the subject; anda computer programmed to:determine a region of maximum attenuation of the subject; andadjust at least one of an attenuation characteristic of the attenuation filter and a table position such that a region of minimum attenuation of the attenuation filter is aligned with the region of maximum attenuation of the subject. 25. The tomographic system of claim 24 wherein the computer is further programmed to determine a mean high frequency electromagnetic energy at a central portion of the subject with respect to a desired image noise, and dynamically adjust a tube current to maintain the desired mean high frequency electromagnetic energy at at least one of the central portion of the subject and an edge portion of the subject. 26. The tomographic system of claim 24 wherein the computer is further programmed to adjust the attenuation characteristic to reduce noise. 27. The tomographic system of claim 24 wherein the attenuation filter is a bowtie filter having multiple filtering elements dynamically positioned within an x-ray path. 28. The tomographic system of claim 24 wherein the computer is further programmed to perform an imaging scan. 29. The tomographic system of claim 28 wherein the computer is further programmed to sense a maximum edge x-ray flux and determine whether the maximum edge x-ray flux is within a selected range. 30. The tomographic system of claim 29 wherein the computer is further programmed to adjust a configuration of the attenuation filter to maintain the maximum edge x-ray flux.
	summary
	abstract	A SPECT apparatus has a two-dimensional detector that detects radiations from RIs in a patient via a collimator. A correction processing unit corrects plural two-dimensional projection distributions with different projection angles, which are detected by the detector, on a three-dimensional frequency space according to plural correction functions corresponding to plural distances, respectively. Consequently, a fall in spatial resolution having dependency on distances between the respective RIs and the detector is reduced. A reconfiguring unit reconfigures a three-dimensional RI distribution from the plural two-dimensional projection distributions corrected.
	abstract	The invention is directed to a purifying device for sludge under water and a method for operating the same. The device includes a main fixing frame having an accommodating portion assess to the outside, a hollow liquid container in the accommodating portion, wherein the liquid container is provided with a liquid-flow hole and at least a backwash hole, multiple filters on the liquid container, and a pump connected to the liquid-flow hole at the liquid container through a liquid pipeline. The method includes steps: moving the liquid container having the filters to an area having a liquid to be filtered; leading the liquid to flow into the liquid container through the filters filtering out solid particles contained in the liquid; and leading a fluid to flow into the liquid container such that the filters can be backwashed accompanying with an external cleaning device if the filters are clogged.
053234286	abstract	In order to reduce the time and difficulty of disassembling a seal arrangement which includes a Grayloc flange, in a cramped radioactive environment, the Grayloc hub is modified to include a step bore which receives a seal arrangement and a retaining nut which presses the seal into engagement with an inner wall portion of the hub and outer wall portion of an ICI (in core instrument) supporting column. A loading ring is threaded onto a portion of the column. Bolts associated with the ring are screwed down onto a belleville washer which is disposed between the loading ring and the top of the retaining nut for maintaining a desired amount of load on the seals irrespective of thermal variations.
	claims	1. A method of directing charged particle beams in a charged particle beam system, comprising:applying a first deflection signal to a first stage deflector, the first deflection signal corresponding to a first dwell point; andapplying a second signal to a second stage deflector, the second deflection signal corresponding to the first dwell point and being delayed with respect to the first deflection signal, in which the delay is approximately equal to the transition time of the electronics plus the time required for a charged particle to pass from the exit of the first deflector stage to the exit of the second deflector stage. 2. A method of directing charged particle beams in a charged particle beam system, comprising:applying a first deflection signal to a first stage deflector, the first deflection signal corresponding to a first dwell point; andapplying a second signal to a second stage deflector, the second deflection signal corresponding to the first dwell point and being delayed with respect to the first deflection signal, in which the delay is approximately equal to the transition time of the electronics plus the time required for a charged particle to pass from the center of the first deflector stage to the center of the second deflector stage. 3. A method of directing charged particle beams in a charged particle beam system, comprising:applying a first deflection signal to a first stage deflector, the first deflection signal corresponding to a first dwell point; andapplying a second signal to a second stage deflector, the second deflection signal corresponding to the first dwell point and being delayed with respect to the first deflection signal, in which the delay is determined so as to increase the actual dwell time at each dwell point by compensating at least in part for charged particles that are in flight when the first deflection signal changes. 4. A method of directing charged particle beams in a charged particle beam system, comprising:applying a first deflection signal to a first stage deflector, the first deflection signal corresponding to a first dwell point;applying a second signal to a second stage deflector, the second deflection signal corresponding to the first dwell point and being delayed with respect to the first deflection signal; andapplying a blanking signal to a blanking electrode and incorporating into the deflector signals a delay caused by the ion travel time from blanker to the deflector. 5. A charged particle beam system comprising:a source of particles;a first stage charged particle deflector;a second stage charged particle deflector;a voltage source for applying signals to the first and second stage deflectors; anda memory storing computer readable instructions that when executed cause the system to apply the second stage detector signal corresponding to a first dwell point at a different time than the first stage deflector signal for the same dwell point, the time difference between the application of the second stage deflector signal and the application of the first stage deflector signal is determined to increase the actual time during which the beam impacts on a previous dwell point to which it was directed. 6. A method of directing charged particle beams in a charged particle beam system, comprising:applying a first deflection signal to a first stage deflector, the first deflection signal corresponding to a first dwell point; andapplying a second signal to a second stage deflector, the second deflection signal corresponding to the first dwell point and being delayed with respect to the first deflection signal, in which the delay is determined to increase the actual time during which the beam impacts on a previous dwell point to which the beam was directed. 7. The method of claim 6 further comprising applying a third signal to a third stage deflector, the third deflection signal corresponding to the first dwell point and being delayed with respect to the second deflection signal. 8. The method of claim 6 further comprising applying one or more additional deflection signals to one or more additional deflectors. 9. The method of claim 6 in which the charged particle beam is a focused ion beam. 10. The method of claim 6 in which the charged particle beam is an electron beam. 11. A method of directing charged particle beams in a charged particle beam system, comprising:applying a first deflection signal to a first stage deflector, the first deflection signal corresponding to a first dwell point; andapplying a second signal to a second stage deflector, the second deflection signal corresponding to the first dwell point and being delayed with respect to the first deflection signal, in which the delay is programmed to a value between 0 and three times the pixel rate. 12. The method of claim 11 in which the delay is programmed to a value between one half and three halves the pixel rate. 13. The method of claim 11 further comprising applying a third deflection signal to a third stage deflector, the third deflection signal corresponding to the first dwell point and being delayed with respect to the second deflection signal. 14. The method of claim 11 further comprising applying one or more additional deflection signals to one or more additional deflectors. 15. The method of claim 11 in which the charged particle beam is a focused ion beam. 16. The method of claim 11 in which the charged particle beam is an electron beam. 17. A charged particle beam system comprising:a source of particles;a first stage charged particle deflector;a second stage charged particle deflector;a voltage source for applying signals to the first and second stage deflectors, the system being programmed to apply the second stage deflector signal corresponding to a first dwell point at a different time than the first stage deflector signal for the same dwell point, the time difference between the application of the second stage deflector signal and the application of the first stage deflector is determined to increase the actual time during which the beam impacts on a previous dwell point to which it was directed. 18. The apparatus of claim 17 further comprising a memory storing computer instructions, the instructions including a program controlling the voltage source. 19. The apparatus of claim 18 in which the memory stores computer instructions to delay the application of the second stage deflector signal by an amount corresponding approximately to the time of flight of a charged particle through a part of the system. 20. The charged particle beam system of claim 17, in which the system is programmed to apply the second stage deflector signal corresponding to a first dwell point at a different time than the first stage deflector signal for the same dwell point, the time difference between the application of the second stage deflector signal and the application of the first stage deflector signal is approximately equal to the transition time of the electronics plus either the time required for a charged particle to pass from the exit of the first deflector stage to the exit of the second deflector stage or time required for a charged particle to pass from the center of the first deflector stage to the center of the second deflector stage. 21. The charged particle beam system of claim 17, in which the system is programmed to apply a blanking signal to a blanking electrode and incorporate into the deflector signals a delay caused by the ion travel time from blanker to the deflector.
	summary
	description	Not Applicable. The subject technology generally relates to coherent matterwave beams and, in particular, relates to systems and methods for generating coherent matterwave beams. Coherent massless particle beams such as lasers have been successful and spawned many disruptive technologies. A massive counterpart to lasers, namely coherent matterwave beams, may hold the promise of similar and even more revolutionary technologies. Generating massive coherent beams, however, has been elusive. A major obstacle in producing coherence in matterwaves is to change the phase of beam particles without modifying the energy of the particles. Conventional phase modifying effects may lead to a change in the energy, thus modifying the wavelength of the particles and making it difficult to synchronize the particles for coherence. While coherence for photons may be achieved through photon emission enhancement via resonance, a similar technique for massive particles (e.g., particles with mass) may not work because the velocity of the massive particles is a function of the wavelength. The speed of photons is the speed of light, regardless of the energy. This dependence of the energy on the speed of the particles may make it difficult for massive particles to become coherent unless a way is found for changing the massive particle phase without changing the energy. According to various aspects of the subject technology, a directed beam of low-entropy coherent massive particles similar to laser beams may be produced, but with concentrations millions of times higher than any intense laser beams currently available. Furthermore, unlike laser beams or the Bose-Einstein condensate (BEC) (e.g., a form of coherent matterwave), the subject technology may produce coherent matterwaves that allow both Fermions and Bosons to achieve coherence. According to various aspects of the subject technology, a system for generating a coherent matterwave beam is provided. The system comprises a plurality of beam generating units disposed. Each of the plurality of beam generating units is configured to generate a stream of charged particles. The system also comprises a magnetic field generator configured to expose the plurality of streams to a magnetic field such that (i) the charged particles of the plurality of streams undergo phase synchronization with one another in response to a vector potential associated with the magnetic field and (ii) the plurality of streams is directed along one or more channels to combine with one another and produce a coherent matterwave beam. According to various aspects of the subject technology, a method for generating a coherent matterwave beam is provided. The method comprises generating a plurality of streams of charged particles. The method also comprises exposing the plurality of streams to a magnetic field such that (i) the charged particles of the plurality of streams undergo phase synchronization with one another in response to a vector potential associated with the magnetic field and (ii) the plurality of streams is directed along the same direction to combine with one another and produce a coherent matterwave beam. According to various aspects of the subject technology, a system for generating a coherent matterwave beam is provided. The system comprises a housing having one or more channels. The system also comprises at least one beam generating unit disposed within the housing. The at least one beam generating unit is configured to generate a stream of charged particles. The charged particles are generated with the same non-zero kinetic energy as one another. The charged particles comprise Fermions. The system also comprises a magnetic field generator configured to expose the stream to a magnetic field such that (i) the charged particles of the stream, in response to a vector potential associated with the magnetic field, undergo phase synchronization with one another without exchanging energy with one another and (ii) the stream is directed along the one or more channels to produce a coherent matterwave beam. Additional features and advantages of the subject technology will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the subject technology. The advantages of the subject technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. In the following detailed description, numerous specific details are set forth to provide a full understanding of the subject technology. It will be apparent, however, to one ordinarily skilled in the art that the subject technology may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the subject technology. According to various aspects of the subject technology, intense directed coherent matterwave beams of particles for Bosons (e.g., particles with integer spins) or Fermions (e.g., particles with half-integer spins), neutral or charged, may be produced. The energy stored in these beams may have virtually zero-entropy, allowing for experimenting with physics in unexplored territories. Coherence in matterwaves, and in particular in Fermions, may be beyond the reach of conventional technologies unless the temperature can be reduced to near-zero. However, even this approach may only work for Bosons using the conventional technologies. Aspects of the subject technology may produce coherence for Bosons, as well as for Fermions, while obviating the use of cryogenics or other technology to implement near-zero temperatures. Thus, room temperature coherence for Bosons, as well as for Fermions, may be produced. According to certain aspects, the Aharonov-Bohm (AB) effect may be used as a stipulant under a noise-seeded resonance condition to induce coherence in matter waves. The AB effect is a demonstrated quantum mechanical effect that can modify a physical system solely through its geometrical parameters, without exchanging any physical quantity. According to the AB effect, the angular phase of a particle inside a vector potential can change even if there are no forces or fields acting on the particle, as shown in FIG. 5. The AB effect was predicted in 1959 by Aharonov and Bohm and physically demonstrated by Tonomura in 1986. In the demonstration, a beam of charged particles is split into two coherent beams, where one beam travels through a field-free vector potential and the other beam travels straight. When the two beams recombine, an interference pattern is observed, which shows that the phase of the beam that went through the field-free potential has been shifted. Laser technologies involve forcing equal energy photons to have the same phase. With random phase, the field energy available at any point may be proportional to the number of photons N present at that point. When the photons are all at the same phase, the energy available in the field may become redistributed in such a way that the energy available at any point becomes proportional to the square of the number of the photons (N2) present at that point. This phase unification known as coherence may make it possible to assign a single and simple wave function to a large number of photons N, and provide for a local field energy that scales with N2. By doing so, a single wave whose amplitude is simply N times the amplitude of a single photon wave may be achieved, with energy that is N2 times the energy of a single photon. Fortunately, this dramatic energy enhancement due to phase synchronization of photons is not limited to electromagnetic waves alone. Rather, it is a property of wave phenomena and may be applicable to all kinds of waves. According to quantum mechanics, particles may be waves (e.g., De Broglie's waves) and may be subject to this phase coherence. However, creating coherence among particle waves (e.g., matterwaves) may not be as easy as it is for photon waves, and so far, using conventional technologies, the only achievable coherent matterwave has been at near absolute zero temperatures, and for a very small number of particles (e.g., in the order of thousands or millions of particles) and only for Bosons. Matterwave coherence for streaming particles (e.g., beams) may open the door to many new technologies and many potential new applications. Matterwave particles carry mass, and thus the potential for concentrating energy to densities far beyond what massless photons are capable of may be much higher. Furthermore, coherent matterwaves may allow Fermions (e.g., electrons) as well as Boson (e.g., photons) to achieve coherence. Examples of applications for coherent matterwave beams may include single bath thermal energy extraction, ultra-sensitive accelerometers and interferometric tracking of air/space crafts, a more accurate alternative to global positioning systems, matterwave projectiles and missiles, directed energy weapons, matterwave optics and cloaking, matterwave emission and propulsion, matterwave solitons, high-energy collision, high precision matter optics, atomic clocks, tests of physics constants, and other suitable applications. Unlike lasers, where resonance may be the agent in phase modification for coherence, resonance alone may not modify the phase of massive particles without exchanging energy with them. Exchanging energy can destroy the monochromaticity needed for coherence. According to aspects of the subject technology, the AB effect (e.g., a phase modifying process without energy exchange) can be used to modify the phase of massive particles and make the massive particles coherent. With the AB effect, the phase of the massive particles may be shifted without exchanging energy with the massive particles. According to the least action principle, a physical system can evolve until the system's available energy reaches a minimum (or a maximum). The system may be stable when the minimum in the energy is reached. A system of weakly coupled oscillators may self-organize because the energy exchanged may be minimized when constituents move in harmony (e.g., in phase). It is not complex to show mathematically that when a random oscillator joins an organized crowd, its phase may move gradually towards the phase of the crowd. This exchange of energy to achieve coherence, however, may only work for macroscopic systems. To achieve coherence in particles, the particles' De Broglie phase may need to be modified without exchanging energy. Exchanging energy modifies the De Broglie's wavelength (frequency), thereby making it difficult to synchronize. Since the AB effect is a quantum mechanical effect that can affect matter without causing the exchange of any physical quantity, the AB effect may be used to change the phase of massive particles and produce coherent matterwave beams. Furthermore, AB-induced coherence for the production of matterwaves does not differentiate between Bosons and Fermions. In contrast, the conventional approach for producing coherent matter, the Bose-Einstein condensate, only works for Bosons, and only at very low temperatures (e.g., near-zero temperatures). Coherence can be more easily achieved under the influence of resonance. In a noise grown resonance, a cavity can be filled with many waves of different wavelengths. Of this multitude of waves, a few may happen to have the right wavelength and the right phase to resonate. As a stipulant acts on these waves in the cavity, more resonantly correct waves may join the resonance and the superposed (e.g., coherent) wave may grow. The unfit waves, which do not have the proper wavelength and the proper phase to join the resonance, may wither and eventually disappear (e.g., transfer the last of their energy to the resonant waves through collision and die out). According to certain aspects, interconnected micro-cavities may be filled with particles (e.g., atoms, molecules, etc.) and the AB effect may be used to grow resonance, and consequently coherence in the matterwaves in each cavity. Resonance, like self-coherence, can be achieved by itself under proper conditions. However, the process may be slow and may utilize sub-nanometer cavities to grow. Overmoded resonances may be possible in larger (e.g., a few nanometers) cavities but that introduces multiple phases and may be subject to more de-coherence. The AB effect can speed up the process for achieving coherence by inducing a phase shift of proper sign. As illustrated in FIG. 5, the AB effect may produce a shift in the same direction as the motion of a wave: Δϕ = ± e h ⁢ ∫ C D ⁢ A · ⅆ s where Δφ is the phase shift, e is the fundamental electric charge, h is the Planck's constant, A is the vector potential, and ds is the element of the area. This means that two waves that move in opposite directions (e.g., like a wave and its reflection) may have their phases shifted in opposite directions, which may be favorable to producing a new phase closer to the phase of the bunch. Due to Maxwellian distribution in a thermal motion, about half of the particles on the average may move in one direction while the other half may move in the opposite direction, a natural setting for AB enhanced self-induced coherence. This AB boost in coherence may not only speed up the process for achieving coherence, it may also help keep the number of modes down by encouraging only certain modes to grow. Elastic scattering may also cause a phase shift in the wave function of the particles. However, by controlling the density and the pressure, that effect can be kept at a minimum. FIG. 1 illustrates an example of system 100 for generating coherent matterwave beam 112, in accordance with various aspects of the subject technology. System 100 comprises housing 102 having channels 104. System 100 also comprises beam generating units 106 disposed within housing 102. Each beam generating unit 106 may be configured to generate a stream of charged particles 108 (e.g., electrons). System 100 also comprises a magnetic field generator 140 configured to expose streams 108 to a magnetic field B such that (i) the charged particles of streams 108 undergo phase synchronization with one another in response to a vector potential associated with the magnetic field B and (ii) the streams 108 are directed along channels 104 to combine with one another and produce coherent matterwave beam 112. According to certain aspects, the streams of massive particles 108 may be produced under the influence of a diode-like external electric field in a mesh of beam generating units 106 (e.g., microscopic sized cavities). After being accelerated in the electric field to the desired energy, the streams may be exposed to an external magnetic vector potential, where the phases of the particles may be modified elastically and brought to a common value (e.g., coherence), under the global influence of the least action principle that tends to minimize the overall potential energy of system 100 through synchronization. This is a quantum mechanical counterpart to the well-known phenomena of self-organization observed naturally in various systems including physical systems, such as magnetic domains, as well as biological systems, such as fish, birds, bees, etc. This process produces low-entropy coherent matterwaves with potentials unprecedented in condensed energy technologies. Beam generating units 106 may also be linked to each other through apertures in the walls of beam generating units 106. The apertures provide a coupling between the cavities of beam generating units 106 that cause phase synchronization across the cavities. Phase synchronization within the cavities may be a consequence of the AB effect. In a few hundred nanoseconds, depending on the strength of the magnetic field B and the size of the cavities, a mass of coherent particles may be streaming in the entire mesh to produce coherent matterwave beam 112. FIG. 1 illustrates a top view of one layer of system 100. System 100 may also comprise multiple stacked layers, but one layer may be adequate in most cases. Each layer may be a housing 102, which can be approximately 10 microns long, 1 micron wide, and 0.1 microns thick. However, housing 102 may comprise other suitable dimensions greater than or less than these dimensions. The magnetic field B may be perpendicular to the electric field of each beam generating unit 106. It can be either perpendicular to the plane of view, or parallel to it. One beam generating unit 106 or hundreds of beam generating units 106 may be disposed in housing 102, for example. According to certain aspects, housing 102 may be a vacuum housing. Thus, the streams of charged particles 108 may be generated in a vacuum. Housing 102 also comprises channels 104. Although four channels 104 are shown, housing 102 may comprise more or less channels. For example, housing 102 may comprise at least 100 channels. System 100 also comprises an electric field generator having main cathode 114, main anode 116, and voltage source 118. Beam generating units 106 are disposed between main cathode 114 and main anode 116. Channels 104 are aligned with main cathode 114 and main anode 116. The electric field generator may generate an electric field between main cathode 114 and main anode 116. In one example, the electric field generator may be connected to each of the beam generating units 106 so that each of the beam generating units 106 may generate its own electric field and stream of charged particles 108. FIG. 2 illustrates an example of beam generating unit 106, in accordance with various aspects of the subject technology. Beam generating unit 106, for example, may comprise a diode. Beam generating unit 106 comprises cavity 126 formed within cathode wall 120, anode wall 122, and one or more intermediate walls 124, which joins cathode wall 120 and anode wall 122. Cathode wall 120, for example, may comprise a cathode, and anode wall 122 may comprise an anode. Cathode wall 120 and anode wall 122 are opposite one another. Cathode wall 120 and anode wall 122 are perpendicular to channels 104, while the one or more intermediate walls 124 are parallel to channels 104. Cathode wall 120 may be connected to main cathode 114, and anode wall 122 may be connected to main anode 116. Thus, beam generating unit 106 may generate stream of charged particles 108 as well as electric field 130 between cathode wall 120 and anode wall 122. For example, beam generating unit 106 may generate stream of charged particles 108 using dielectric barrier discharge. However, other suitable methods known to those of ordinary skill in the art may be used for generating the stream of charged particles 108. The charged particles may be emitted from cathode wall 120 to anode wall 122. According to certain aspects, the charged particles of stream 108 may be generated with substantially the same non-zero kinetic energy as one another, which may allow the charged particles to achieve coherence with one another. In contrast to conventional technologies, where particles of coherent matterwaves such as the Bose-Einstein condensate achieve the same kinetic energy relying on cryogenics (e.g., making the kinetic energy zero so that the particles have the same zero kinetic energy), aspects of the subject technology may produce coherent matterwaves in which the charged particles of the coherent matterwaves exhibit the same non-zero kinetic energy without the use of cryogenics. According to certain aspects, in order to minimize collisions between the charged particles of stream 108 with one another, a length of beam generating unit 106 (e.g., the length between cathode wall 120 and anode wall 122) may be less than a mean free path of the charged particles of stream 108. The mean free path may be an average distance that a particle may travel before colliding with another particle. Thus, because the length of beam generating unit 106 is less than the mean free path of the charged particles of stream 108, collisions between the charged particles may be minimized. Beam generating unit 106 further comprises channel opening 128 connecting cavity 126 to channels 104. Channel opening 128 may be parallel to channels 104 and/or one or more intermediate walls 124, and is formed between cathode wall 120 and anode wall 122. According to certain aspects, the magnetic field B is perpendicular to electric field 130. Thus, stream 108, which is generated within cavity 126, may be bent and directed to outside of cavity 126 through channel opening 128 to channels 104. By directing stream 108 to channels 104, stream 108 may be combined with other streams of charged particles to produce coherent matterwave beam 112. Beam generating units 106 may be aligned in one or more rows. For example, as shown in FIG. 1, beam generating units 106 are aligned in three rows between four channels 104. In some aspects, adjacent beam generating units 106 may share at least one of cathode wall 120 and anode wall 122 with one another to conserve space. The shared wall may comprise an aperture for linking the cavities of the adjacent beam generating units 106. The aperture may allow not only the charged particles within one cavity to be synchronized with one another, but also the charged particles from one cavity to be synchronized with the charged particles of another cavity. In some aspects, apertures may be used (e.g., formed on cathode wall 120 and/or anode wall 122) to link the charged particles along an entire row of beam generating units 106. In some aspects, channel openings 128 of adjacent beam generating units 106 may connect to different channels 104. For example, a beam generating unit 106 of a particular row may have a channel opening 128 that connects to channel 104 beneath the row, while an adjacent beam generating unit 106 may have a channel opening 128 that connects to a channel 104 above the TOW. According to various aspects of the subject technology, the magnetic field B may bend each stream of charged particles 108 within a respective cavity 126 into a respective channel 104. In this regard, the streams 108 may further combine with one another in the channels 104 to produce coherent matterwave beam 112. The charged particles of streams 108 may undergo phase synchronization with one another in response to a vector potential associated with the magnetic field B. While the streams 108 are in the channels 104, the charged particles of the streams may undergo further phase synchronization with one another to form coherent matterwave beam 12. In some aspects, the charged particles may undergo phase synchronization with one another utilizing the AB effect. For example, the charged particles may undergo phase synchronization with one another without exchanging energy with one another. According to certain aspects, the magnetic field B may be about 100 gauss. However, the magnetic field B may be lower or higher depending on the configuration of beam generating units 106, the desired size of coherent matterwave beam 112, the application of coherent matterwave beam 112, etc. According to certain aspects, system 100 may produce coherent matterwave beam 112 without using cryogenics. Furthermore, the charged particles of the coherent matterwave beam 112 may comprise not only Bosons, but also Fermions. While conventional technologies may produce coherent matterwaves in the form of the Bose-Einstein condensate, which may comprise a low number of particles (e.g., hundreds of thousands of particles to a million particles), coherent matterwave beam 112 may comprise many more particles (e.g., at least one billion charged particles). The physics and the mathematics of self-induced coherence may be complex. Rather than presenting a quantum mechanical model, a macroscopic model of coherence such as the Kuramoto model may be used to describe aspects of the subject technology. With AB-induced self-coherence, some simplifying assumptions can be made to make the mathematics more manageable. A numerical approach may be possible based on these assumptions. Even though a dynamical time-evolving solution to the state function for AB synchronization of matterwaves may be difficult to obtain, characteristic times, major viability criteria, and effectiveness measures can be worked out. The characteristic time-to-synchronization, viability, and effectiveness is discussed herein. The mean free path of the particles desired to be synchronized may be important to consider. Inter-Oscillator Coupling and Analysis An approach to inter-oscillator coupling analysis may be based on oscillators (e.g., particles) being weakly coupled to each other, and the strength of the coupling may be inversely proportional to the distance between the oscillators. A thorough analysis may require that every oscillator influence and be influenced by every other oscillator. Implementing this requirement however can lead to unmanageable mathematics. A non-complex approximation may assume each oscillator is coupled to the nearest set of oscillators (e.g., a shell of nearest neighbors). In this analysis, it can be assumed that each oscillator is coupled to at least four sets (e.g., shells) of nearest neighbors, as illustrated in FIG. 3. In particular, FIG. 3 is a schematic drawing of the coupling between neighboring particles 302, in accordance with various aspects of the subject technology. To avoid clutter, not all links between particles 302 are shown. Collision Frequency and Mean Free Path According to certain aspects, the mean free path in a plasma of pressure p and temperature T may be given byλ=kBT/(21/2πd2p), where d is the effective interaction diameter of the particles. Assuming a spherical shape, the effective cross-section for the collision may be πd2. Assuming atmospheric pressure and ambient temperature, the effective cross-section for electrons may be roughly 3×10−24 m2, so that the mean free path λ may be approximately 9.3×10−3 m. At room temperature (e.g., 100 km/s for electrons), the characteristic time tc between collisions may be approximately 100 ns. However, the distance between the cathode and the anode (AK gap) may be 0.1 mm, which is roughly 100 times shorter than the mean free path. This means that the electrons may hit the anode long before they would have a chance to collide with one another and thermalize (e.g., called “ballistic transport”). With the geometry of the subject technology, thermalization may not be an issue, and if a partial vacuum is introduced into system 100 for example, the mean free path can be increased to several centimeters, allowing for larger cavities and more extended AK gaps (e.g., about 1 mm). Characteristic Time to AB Induced Coherence According to the least action principle, system constituents (e.g., charged particles) undergoing dynamical evolution may select paths that minimize (or maximize) the action. Action (e.g., in tensor form) may be defined as the time integral of the Lagrangian along a path connecting two fixed points: ⁢ S ⁢  q ⁡ ( t )  = ∫ t 1 t 2 ⁢ L ⁡ [ q ⁡ ( t ) , q . ⁡ ( t ) , t ] ⁢ ⅆ t ℒ κ = ∑ f ⁢ f _ ⁡ ( ⅈ ⁢ ϕ . - m f ) ⁢ f - 1 4 ⁢ A μ ⁢ ⁢ v ⁢ A μ ⁢ ⁢ v - 1 2 ⁢ W μ ⁢ ⁢ v + ⁢ W - μ ⁢ ⁢ v + m W 2 ⁢ W μ + ⁢ W - μ - 1 4 ⁢ Z μ ⁢ ⁢ v ⁢ Z μ ⁢ ⁢ v + 1 2 ⁢ m Z 2 ⁢ Z μ ⁢ Z μ + 1 2 ⁢ ( ∂ μ ⁢ H ) ⁢ ( ∂ μ ⁢ H ) - 1 2 ⁢ m H 2 ⁢ H 2 Although a thorough quantum mechanical analysis of AB induced coherence using least action principle for finding the characteristic time T may be a major undertaking and may be possible only through a numerical approach, implementing a major simplifying assumption for aspects of the subject technology may make it possible to estimate T with reasonable accuracy. Since the electrons may be confined to move from the cathode to the anode under the influence of the diode potential, the paths the electrons take may be assumed to be straight lines connecting the cathode to the anode. Synchronization Rate and Characteristic Times The characteristic time T may be a function of the synchronization rate. The classical version of a synchronization process may be used, and according to the Kuramoto model (or an Ising model), the synchronization rate, dq/dt, may be given bydθi/dt=ωi+σKij sin(θj−θi), i=1,2, . . . N, where θ is the relative phase, the tensor σK is the strength of the synchronizing agent and N is the number of the particles. Notice that the rate relaxes as the phase of individual particles approaches the common phase and sin(δθ) approaches zero. This may guarantee accumulation in phase space, which may be important in synchronization. The Kuramoto model, and other classical analyses, may start out with a Hamiltonian, calculate the density of particles with the phase in a certain range, and solve for the evolution as a function of time. A quantum mechanical approach may follow the same path, but through 2nd quantization: H tot = ∑ j = e , h ⁢ ( P -> j + q j ⁢ A -> j ) ⁢ 1 2 ⁢ m j ⁢ ( P -> j + q j ⁢ A -> j ) + V c ⁡ ( r -> e - r -> h ) + ∑ j = e , h ⁢ V j ⁡ ( r -> j ) - eEz e + eEz h , The classical formula may be assumed to be a good approximation at this point. Numerical approach for quantum mechanical analysis may be possible. Prior to synchronization, the electron phases in the ensemble may be random, as shown in FIG. 4A. FIGS. 4A and 4B illustrate an example of the distribution of phases before (FIG. 4A) and during (FIG. 4B) synchronization, in accordance with various aspects of the subject technology. Under the influence of the AB effect and depending on the value with respect to a peak or a trough, the phases either may advance or retreat until they all converge on one value. Once synchronization takes hold, the phases may shift together and a steady state may be reached. Based on the Kuramoto model, for very large N, the synchronized particle density may be given by ρ = δ ⁡ ( θ - ψ - arcsin ⁡ ( ω Kr ) ) , where ψ is the average phase and δ is an inverse measure of noise in the system. The dynamics of the Kuramoto model for synchronization may be given bydθi/dt=ωi+(K/N)sin(θj−θi) i=1,2, . . . N. According to the Kuramoto model, there may be a critical coupling-gain parameter Kc below which synchronization is not possible. If we define an order parameter r asreiφ=(1/N)Σj=1,Neiθj, where r is a function of time, r may be less than one as t goes to infinity for super-critical K. By taking the derivative of this equation with respect to time and based on some algebra, it can be shown that, when frequencies are the same, r may be constant and less than 1, as illustrated below:reiφ=(1/N)Σj=1,Neiθj d/dt(reiφ)=(1/N)Σj=1,Nd/dt(eiθj)(dr/dt)eiφ+ir(dφ/dt)eiφ=(1/N)Σj=1,N(dθ/dt)eiθj (dr/dt)eiφ+ir(dφ/dt)eiφ=(idθ/dt)j/N)Σj=1,Neiθj (dr/dt)eiφ+ir(dφ/dt)eiφ=i(dθj/dt)reiφ,dθ/dt=ωdr/dt+ir(dφ/dt)=irω, but dφ/dt=ωdr/dt=0.r=constant This shows that for monochromatic beams, the critical coupling-gain may be zero. Thus, such a system may always synchronize. According to Chopra and Spong, a synchronization rate may be given byΔφ=e−(βt/2), where β is the magnetic coupling constant, and may be given byβ=φ2mv/(2hcμ0)d. φ is the elementary magnetic charge (h/e), v is the velocity of the charged particles, h is the Planck constant, c is the speed of light, μ0 is the magnetic constant, and d is the lateral extent of the particle beam. Upon substituting for these constants and the geometrical/kinematical parameters for the beam at 1 Tesla, the value of β is 1.02×109 s−1, which means it can take 4 ns for Δφ to reduce two e-fold. So the characteristic time for synchronization may be approximately 4 ns. A challenge to phase synchronization of matter particles is to keep every particle at the same energy (e.g., same wavelength) and shift the phase without changing the energy. Conventional methods lower the temperature to near absolute zero (e.g., to guarantee monochromaticity) and work with a small number of particles. These methods require cryogenics, only work for Bosons, and do not produce streaming beams (only a stationary blob). For these reasons, intense streaming beams of coherent massive particles have not been produced. Use of cryogenics for monochromatization may be cumbersome and inconsistent with beaming, as cryogenics may involve the particles being brought to the ground (zero) level energy for synchronization. There is no easy way to synchronize Fermions even with cryogenics because of Pauli's exclusion principle that forbids putting identical particle in the same state. The Fermions may not get close enough to each other to affect the proper interaction needed for synchronization. The total number of synchronized particles may also be limited because of the need for trapping the particles prior to cooling and synchronization. There may not be a steady flow of new particles brought in. According to various aspects of the subject technology, using the AB effect for coherence induction and using coherence growth in microcavities that combine resonance with coherence may allow the foregoing obstacles to be overcome, thereby paving the road for the production of an energetic intense beam of coherent matterwaves. Because the AB effect is a phase-shifting process that does not change the energy of the particles, coherence can be achieved while keeping the wavelength the same for all particles. The number of particles may not be limited because new particles may be constantly emitted from the cathode while upstream particles may undergo synchronization. The diode action of cavity walls may accelerate the particles to a fixed energy. Coherent beams of energetic particles may be produced at any kinetic energy by adjusting the electrode potential across the cathode wall and the anode wall (e.g., AK gap). This approach may work for Fermions as well as for Bosons without discriminating effects. The particles need not be in the same state to synchronize. Room temperature matterwave coherence may be beyond the reach of conventional technology. In contrast, aspects of the subject technology achieve room temperature matterwave coherence that is suitable for Bosons as well as Fermions. According to certain aspects, particles interact globally (e.g., are aware of each other) without energy exchange, and phases of the particles are shifted without energy exchange. In this approach, the magnetic vector potential may establish the universal energy-free link between particles and the AB effect may guarantee the energy-free phase shift. The foregoing description is provided to enable a person skilled in the art to practice the various configurations described herein. While the subject technology has been particularly described with reference to the various figures and configurations, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology. There may be many other ways to implement the subject technology. Various functions and elements described herein may be partitioned differently from those shown without departing from the scope of the subject technology. Various modifications to these configurations will be readily apparent to those skilled in the art, and generic principles defined herein may be applied to other configurations. Thus, many changes and modifications may be made to the subject technology, by one having ordinary skill in the art, without departing from the scope of the subject technology. It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Some of the steps may be performed simultaneously. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. Terms such as “top,” “bottom,” “front,” “rear” and the like as used in this disclosure should be understood as referring to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference. Thus, a top surface, a bottom surface, a front surface, and a rear surface may extend upwardly, downwardly, diagonally, or horizontally in a gravitational frame of reference. A phrase such as “an aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. An aspect may provide one or more examples of the disclosure. A phrase such as an “aspect” may refer to one or more aspects and vice versa. A phrase such as an “embodiment” does not imply that such embodiment is essential to the subject technology or that such embodiment applies to all configurations of the subject technology. A disclosure relating to an embodiment may apply to all embodiments, or one or more embodiments. An embodiment may provide one or more examples of the disclosure. A phrase such an “embodiment” may refer to one or more embodiments and vice versa. A phrase such as a “configuration” does not imply that such configuration is essential to the subject technology or that such configuration applies to all configurations of the subject technology. A disclosure relating to a configuration may apply to all configurations, or one or more configurations. A configuration may provide one or more examples of the disclosure. A phrase such as a “configuration” may refer to one or more configurations and vice versa. Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. All structural and functional equivalents to the elements of the various configurations described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.
	description	Table I is a listing of absorbing layer thicknesses. Referring now to FIG. 1, the essential principle of operation for the devices of the present invention is illustrated. FIG. 1 is a conceptual cross section view of a single neutron detector comprising a means for detecting neutrons 10 stacked on an absorbing layer 11. The absorbing layer 11, being composed of a first material that absorbs protons, such as titanium, is stacked on a hydrogenous substrate 12. Hydrogenous substrate 12 is composed of a second material having hydrogen atoms interacting with an unknown source of neutrons, indicated by box 13. When a single neutron detector is placed in a field of a neutron spectrum, the incident neutrons, indicated by arrow 14, from suspected neutron source 13 interact with hydrogen atoms within hydrogenous substrate 12. This interaction produces proton recoils that travel in fairly straight lines, one of which is indicated by arrow 15, through the absorber layer 11 and the detector means 10. Scattered neutrons, indicated by arrow 16, are deflected away from the hydrogenous substrate 12. Detector means 10 is connected to a data processing means, indicated by box 17, and a ground 18. The data processing means 17 includes a means for proton distribution. Using several detector means 10 with each absorbing layer 11 having a different thickness allows protons with energies and corresponding ranges greater than the thickness of a particular absorbing layer 11 to reach detector means 10 and produce proton counts. The amount of absorber layers 11 and their thickness can be selected to correspond to ranges of protons from a low value for 1 MeV and larger thicknesses of 250 MeV. Hydrogenous substrate 12 converts part of the kinetic neutron energy to energy of the recoil protons 15 and the detector means 10 detects protons passing through the absorbing layer 12. This approach is demonstrated by considering the energy transfer behavior of neutrons and protons. The maximum energy a neutron of energy En can transfer to a proton Ep (max) equals En (1,2). For this example, assume an absorbing layer 11 thickness of d. For monoenergetic neutrons (En), the number of recoil protons reaching detecting means 10 and producing proton counts decreases as energy En decreases. The number of protons will eventually equal zero when the range of maximum energy recoil protons becomes smaller than d. Recoil particles due to elastic scattering do occur in the higher atomic number non-hydrogenous absorber but, except for very high En, they do not contribute to the counts due to their small range and the unfavorable quantum energy transfer in elastic scattering. Having a system with K units, each with a different d and exposing them to a neutron spectrum, one obtains data which consist of K counts or count rate values Ci(di) i=1, 2, . . . K where for dixe2x88x921 less than di less than di+1, Cixe2x88x921 (dixe2x88x921 greater than Ci greater than Ci+1. From these numbers one can unfold the incident spectrum of neutrons. The detector means 10 can be of any shape or configuration and can be any type of solid state device. The inventors herein have employed a depleted n/p diode used to measure alpha particles, which was relatively insensitive to beta particles because of their low LET (Linear Energy Transfer) values as a detector means 10. Spectroscopic grade detectors are not required for this device since only event counting is required and data describing the energy spectrum are not needed. In considering the thicknesses of absorbing layers 11 and the ranges of protons to be measured, an energy range of 1 to 250 MeV was selected to match the expected neutron spectrum distribution. One solution to achieve this objective is to fabricate an instrument that converts a distribution of neutrons to one of recoil protons, which are charged particles that can be easily courted. By employing 12 detector means 10 within a given chamber, the recoil protons are essentially sorted into 12 bins where they can be readily counted. Said absorber layers 11 can be constructed of aluminum for detecting the lower energy levels or tantalum for the higher values. The hydrogenous substrate 12 for each detector means 10 could be constructed of polyethylene. The data processing means 17 and its means for proton distribution provides a hitherto unavailable capability to determine a proton distribution pattern to construct a neutron spectrum indicating the spectrum of neutrons from an unknown source of neutrons 13. In operation, results of a spectral measurement are a set of pairs from the detector means 10 and the absorbing layer 11 that allows protons with energies and corresponding ranges greater than the absorbing layer 11""s thickness to reach the detector means 10 and produce proton recoil counts. One data processing means 17 successfully employed by the present inventors is a 3-dimensional Monte Carlo Adjoint Transport code, NOVICE, which is described in Jordan, T., xe2x80x9cNovice, A Radiation Transport and Shielding Codexe2x80x9d, Experimental and Mathematical Physics Consultant, Report EMP. L 82.001, Jan. 1982. FIG. 2 is a chart showing plots of counts in the detector versus proton energy with different thicknesses indicated as a parameter on the curves, and these results were obtained using the NOVICE program and a flat spectrometer 20 depicted in FIG. 6, which will be described below. The FIG. 2 plots are counts in the detector versus proton energy with the aluminum and tantalum thicknesses indicated as a parameter on the curves. In this preliminary assessment of the feasibility of neutron monitor with multiple neutron detectors, an incident neutron spectrum and the subsequent unfolding software were not included in the code""s run the proton recoil spectrum was assumed to exist in the converser material of hydrogenous substrate 12. The separation or resolution of proton energy shown in FIG. 2 provides useful information about detecting 12 ranges of neutron energy. The flat configuration of monitor 20, depicted in FIG. 6, along with the use of tantalum for the absorber layers 11 and for the chamber 21 make it too heavy for spacecraft or other airborne applications. Using a data processing device with the NOVICE computer software to analyze the monitor revealed other more useful potential configurations for neutron spectrometers, which were modeled and analyzed by the computer. One configuration suggested by the FIG. 2 NOVICE results is a pentagon dodecahedron, which allows for a full measurement range because of its 12 surfaces, each supporting a detector-absorber pair with different absorber layer thicknesses. FIGS. 3A and 3B, are perspective drawings depicting a detector means 41 stacked on a pentagonal absorbing layer 42 and a dodecahedron neutron spectrometer monitor 40, respectively. Referring now to FIG. 3A, which depicts a perspective view of a neutron detector comprising a detector means 41 stacked on an absorbing layer 42. Absorbing layer 42 is composed of a first material that absorbs protons, such as titanium in this embodiment, or tantalum or aluminum in other embodiments. By placing this assembly on an appropriate hydrogenous substrate, a neutron detector is provided. Referring now to FIG. 3B, dodecahedron neutron spectrometer monitor 40 is depicted with 11 of 12 of the absorbing layers 42 with varying thicknesses stacked on a surface facet of a solid dodecahedron substrate 43, which provides the hydrogenous substrate. Dodecahedron substrate 43 is shown partially exposed without one absorbing layer for illustrative purposes. FIG. 4 is a front view drawing of the dodecahedron neutron spectrometer monitor 40 with all absorbing layers 51-62, respectively, covering each of the 12 facets of substrate 43 and representative dimensions. For the sake of clarity, only one detector means 42 is shown stacked on absorbing layer 54, with 11 other detector means 42 for the other 11 absorbing layers 51-53 and 55-62, respectively, not shown. Each of the 12 absorbing layers 51-62 are constructed with a varying thickness and are stacked on a surface facet of the solid dodecahedron substrate 43. Substrate 43 is composed of a hydrogenous material, such as polyethylene, having hydrogen atoms and functions as a neutron converter when interacting with said absorbing layers 51-62 in the presence of an unknown energy distribution, indicated by box 44, which emits incident neutrons, indicated by arrow 63. In operation, said hydrogenous substrate 43 converts said neutrons to recoil protons and each of said detector means 42 detects recoil protons passing through each absorbing layer 51-62, respectively. Each absorbing layer 51-62, respectively has a different thickness, as depicted in FIG. 5, to absorb neutron energies from 1 to 250 MeV. Returning now to FIG. 4, the hydrogenous substrate 43 is housed in a concentrically hollow spherical chamber, indicated by broken line 45. Each detector means 42 is coupled to a means for data processing, indicated by box 415, outside the spherical chamber 45, which provides a count of recoil protons to a means for proton distribution, not shown, residing within said data processing means 46. The means for proton distribution determines a proton distribution pattern to construct a neutron spectrum pattern indicating the spectrum of neutrons from said suspected source of neutron radiation 44. FIG. 4 also includes representative dimensions. Each absorbing layer 51-62 is pentagonally shaped in this embodiment, with each side 2.03 cm in length. Each of said detector means 42 are circular and 0.5xe2x80x3 wide and 0.015xe2x80x3 thick. Covered hydrogenous substrate 43 is 4.47 cm in height and housed concentrically within hollow spherical chamber 45. Hydrogenous substrate 43 was fabricated from a solid block of Lucite(trademark). The hollow spherical chamber 45 is composed of titanium in this embodiment with an inner diameter of 10.8 cm and a wall thickness of 2.5 cm. Each of said 12 absorbing layers 51-62 is composed of titanium, in this embodiment with a varying thickness ranging from 0.00105 cm to 2.4217 cm, as described in Table I below. The absorbing layers 51-62 may also be composed of tantalum and aluminum. Detector means 42 can be constructed from a depleted n/p diode. It should be understood to those skilled in the art that these dimensions are merely representative and numerous other choices of dimensions are possible. FIG. 5 is a perspective drawing of hydrogenous substrate 43, using lake numerals for similar structural elements, illustrating a number of absorbing layers with a varying thickness. In this drawing, covered hydrogenous substrate 43 is shown removed from the hollow spherical shell 45 to better illustrate each absorbing layer having a different thickness. Referring back to FIG. 2, which is the chart showing plots of counts in the detector versus proton energy with different thicknesses indicated as a parameter on the curves from the NOVICE program. Those plots from the FIG. 6 flat spectrometer 20, which will be described shortly, are based on using aluminum and tantalum as absorber material. These results suggested using titanium as the preferred absorber material for the FIG. 4 absorbing layers 51-62 for all energy levels, because titanium is lighter than tantalum and its neutrons do not generate nuclear interactions. Only elastic scattering takes place. The proton energy resolution from this embodiment is also relatively good. The FIG. 2 results also indicate that aluminum absorbers produced a slightly better energy resolution for the lower range of energies, 1 to 10 MeV. The size of this dodecahedron configuration is small and light in weight and very practical for a spacecraft application. In order to insure that an unknown neutron spectrum has an isotropic distribution, the spectrometer 40 can also be located at the center of a titanium sphere with a diameter of 3 inches. FIG. 6 is a perspective conceptual drawing of the flat embodiment of the present invention""s neutron spectrometer monitor 70. Monitor 70 comprises a group of the FIG. 1 neutron detector means 10 arranged in a chamber 71. As described above, having several detector means 10 stacked onto absorbing layers, not shown, each having a different thickness, allows protons with energies and corresponding ranges greater than the thickness of each absorbing layer to reach the detector means 10 and produce proton counts. FIG. 6 depicts 12 detector means 10 which correspond to 12 energy bins and thus detect protons with ranges corresponding to energies from 1 MeV up to 250 MeV. The floor of chamber 71 serves as the hydrogenous substrate. Monitor 70 is placed in proximity to an unknown source of neutrons, shown as box 76. Detecting means 10 is coupled to a means for data processing, indicated by box 77, and provides a separate count of recoil protons for each different thickness employed in the absorbing layers. The data processing means 77 transmits the count of recoil protons to a means for proton distribution, not shown, residing within the data processing means 77. The means for proton distribution determines a proton distribution pattern to construct a neutron spectrum pattern indicating the spectrum of neutrons from the suspected concentration of neutrons 76. Bulkhead output connector 72 on the chamber 71 allows correction of voltage to the detector as well as correction of output counts to counting instruments. In the flat configuration, said chamber 71 is shown in a rectangular shape, and its walls 78, lid, not shown, and unit compartments 79 can be composed of tantalum. Each detector means 10 in the egg-crate-like structure is numbered 1xe2x80x2-12xe2x80x2, respectively, to correspond with readings shown in the FIG. 2 chart. Detector means 7xe2x80x2 is depicted with representative dimensions of 2 cm in width and 2 cm in length. A gap 80 between detector means 11xe2x80x2 and 12xe2x80x2 is 0.471 cm. The thickness of each wall 78 is 1 cm and its height is about 3 cm. The chamber 71 is depicted as 15 cm in length and 5.41 cm in width. These dimensions are merely representative and numerous other choices of dimensions are possible, however, it is critical that each absorber layer is constructed with a different thickness according to the minimum and maximum energies of neutrons in the spectrum. Similarly, the materials used for constructing the absorber layers, detector means 10 and chamber 71 can also be varied according to the minimum and maximum energies of neutrons in the spectrum. It is to be understood that details concerning materials, shapes and dimensions are merely illustrative, and that other combinations of materials, shapes and dimensions can also be advantageously employed and are considered to be within the contemplation of the present invention. We also wish it to be understood that we do not desire to be limited to the exact details of construction shown and described. It will be apparent that various structural modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
	abstract	A nuclear reactor includes a nuclear reactor core comprising fissile material disposed in a reactor pressure vessel having vessel penetrations that exclusively carry flow into the nuclear reactor and at least one vessel penetration that carries flow out of the nuclear reactor. An integral isolation valve (IIV) system includes passive IIVs each comprising a check valve built into a forged flange and not including an actuator, and one or more active IIVs each comprising an active valve built into a forged flange and including an actuator. Each vessel penetration exclusively carrying flow into the nuclear reactor is protected by a passive IIV whose forged flange is directly connected to the vessel penetration. Each vessel penetration carrying flow out of the nuclear reactor is protected by an active IIV whose forged flange is directly connected to the vessel penetration. Each active valve may be a normally closed valve.
062193988	claims	1. In a nuclear reactor heated junction thermocouple level measurement system having a plurality of sensors, each sensor including both an unheated and a heated thermocouple, and a heater coil adjacent the heated thermocouple, wherein two thermocouple conductors of a first polarity are associated with each thermocouple and one thermocouple conductor of an opposite polarity is shared between the heated and unheated thermocouples, the improvement comprising: a heated junction thermocouple cable arrangement including: 2. In a nuclear reactor heated junction thermocouple level measurement system as recited in claim 1, wherein the heated junction thermocouple cable arrangement includes a separate transition conduit having a pin or socket connector at opposing ends, one connector having sixteen pins or sockets corresponding to said power conductors for each of the heater coils and a second connector having four pins or sockets for all of the heater coils such that the number of said power conductors is reduced from sixteen to four. 3. In a nuclear reactor heated junction thermocouple level measurement system as recited in claim 2, wherein said conduit includes connectors at opposing ends, one of said connectors engaging a corresponding connector of said transition conduit. 4. In a nuclear reactor heated junction thermocouple level measurement system as recited in claim 1, wherein said conduit has an outer diameter of approximately 0.55 inches. 5. In a nuclear reactor heated junction thermocouple level measurement system as recited in claim 4, wherein said cables are manufactured entirely from inorganic materials. 6. In a nuclear reactor heated junction thermocouple level measurement system as recited in claim 5, wherein said cables are insulated with a mineral oxide. 7. In a nuclear reactor heated junction thermocouple level measurement system as recited in claim 2, wherein said transition conduit is a head lift rig conduit, a containment conduit being disposed between said head lift rig conduit and a penetration connector positioned in a containment wall, said bridge conduit and said containment conduit each having connectors at opposite ends such that said head lift rig conduit engages said bridge conduit and said bridge conduit engages said containment conduit.
039708551	abstract	Positron-emitting probes that have certain features that facilitate the use f positrons for nondestructive testing of fatigued metals. The features include the use of an unfatigued substrate for supporting the positron-emitting material, electric and/or magnetic fields to concentrate the positrons on the test item, and a thin scintillator window for use with those radioactive materials that emit a positron without emitting a time-correlated gamma photon.. It should be understood that the foregoing abstract of the disclosure is for the purpose of providing a non-legal brief statement to serve as a searching-scanning tool for scientists, engineers and researchers and is not intended to limit the scope of the invention as disclosed herein nor is it intended that it should be used in interpreting or in any way limiting the scope of fair meaning of the appended claims.
042658616	description	The following example further illustrates this invention. EXAMPLE 1316 gms of calcium carbonate obtained from the precipitation of uranium recovery leach was dissolved in 1.54 liters of concentrated HCl. The pH was adjusted with the same calcium carbonate to 3. There were 854 gms of CaCO.sub.3 per liter of solution. The solution was filtered and contacted with 0.3 M DEPHA-0.075 M TOPA in kerosene in various ratios of organic to aqueous. The concentration of uranium in the initial solutions was 3.9 gms/l. The phases were permitted to separate and a sample of the CaCl.sub.2 solution was analyzed for uranium. The following results were obtained: ______________________________________ Uranium in Solution Organic-Aqueous After Extraction Uranium Ratio (gms/l) Extracted (%) ______________________________________ 0.5 0.0064 >99 0.33 0.0063 >99 0.25 0.053 98.6 ______________________________________ 0000 150 ml of the CaCl.sub.2 solution was contacted with 6.7 ml of a 2.5 M solution of ammonium sulfate and 17.4 ml of a 1 M solution of barium chloride. The precipitate was weighed and the radium remaining in a 40 ml sample of the solution was determined. The remaining solution was again contacted with 2.5 M ammonium sulfate and 1 M barium chloride and the procedure repeated. A third contact was also made. The following table gives the results: ______________________________________ Vol- Start- ume Final Weight Dila- ing of Volume of Vol- of Pre- tion Vol BaCl.sub.2 (NH.sub.4).sub.2 SO.sub.4 ume cipitate Fac- Radium (ml) (ml) (ml) (ml) (gms) tor (pici/l) ______________________________________ Feed -- -- -- -- -- 2.35 .times. 10.sup.5 150 17.4 6.98 174.38 8.986 1.16 1.49 .times. 10.sup.4 134 15.6 6.2 155.8 6.3699 1.35 500 .+-. 100 100 11.6 4.7 116.3 4.1977 1.57 100 ______________________________________ The dilution factor is the amount that the sample was diluted by the addition of the ammonium sulfate and barium chloride solutions. The table shows that the invention successfully reduced the level of radium in the solution to levels tolerable for release into the environment.
050330730	claims	1. A system for radiographically inspecting a predetermined area of relatively stationary object positioned at a selected location, comprising: a source of radiation operative to transmit along a radiation path toward the selected location a fixed position radiation beam having a cross-sectional area at least corresponding to the predetermined inspection area; detection means, having a detection area at least corresponding to the predetermined inspection area disposed in a fixed position in the radiation path in alignment with the fixed position radiation beam; scanning point selection means, disposed in the radiation path between the radiation source and detection means, for sequentially selecting and transmitting a plurality of selected portions of the cross-sectional area of the fixed position radiation beam striking in sequence a corresponding plurality of portions of the detection area of the detection means in both the length and width dimension, each said selected portion of the cross-sectional area of the fixed position radiation beam corresponding to a pencil beam of radiation, the selected plurality of portions of the cross-sectional area of the radiation beam and the corresponding portions of the detection means, each having both a width dimension and a length dimension substantially greater than the cross-sectional area of each pencil beat at the selected location, said detection means being responsive to each said selected portion of the fixed position radiation beam striking a corresponding portion of the detecting area for generating signals corresponding to radiation interactive with a corresponding portion of the predetermined inspection area of an object at the selected location; position encoder means responsive to said scanning point selection means for determining the position of each selected portion of the fixed position radiation beam; data processing means responsive to said position encoder means and said detecting means for processing the signals generated by the detected means; and display means governed by said data processing means for generating a radiographic image of the predetermined area of the object. a first rotating disk having a spirally-shaped aperture, disposed in the radiation path between the radiation source and the detection means, for sequentially selecting and transmitting spirally-shaped portions of the cross-sectional area of the fixed position radiation beam along the path in the direction toward the selected location; and a second rotating disk having an opposite spirally-shaped aperture, disposed in the radiation path in alignment with said first rotating disk between said first rotating disk and the detecting means, for sequentially selecting from said spirally-shaped portions, and for transmitting to the selected location, said selected portions of cross-sectional area each corresponding to a said pencil beam of radiation. means for selecting the intensity of the radiation source in accordance with the selected element. a first rotating disk having a spirally-shaped aperture, disposed in the radiation path between the radiation source and the detection means, for sequentially selecting and transmitting spirally-shaped portions of the cross-sectional area of the fixed position radiation beam along the path in the direction toward the selected location; and a second rotating disk having an opposite spirally-shaped aperture, disposed in the radiation path in alignment with said first rotating disk between said first rotating disk and the detecting means, for sequentially selecting from said spirally-shaped portions, and for transmitting to the selected location, said selected portions of cross-sectional area each corresponding to a said pencil beam of radiation. transmitting a fixed position radiation beam having a cross-sectional area at least corresponding to the predetermined inspection area along a radiation path in a direction toward the selected location; selecting sequentially a plurality of portions from the cross-sectional area of the fixed position radiation beam and transmitting the selected portions along the radiation path to the selected location, each said selected portion of the cross-sectional area of the fixed position radiation beam corresponding to a pencil beam of radiation, said plurality of portions having both a length and width dimension substantially greater than the cross-sectional area of each pencil beam; detecting each of the selected portions of the fixed position radiation beam striking corresponding portions of the predetermined inspection area of an object at the plurality of selected locations and generating signals in response to the radiation striking the corresponding portions said plurality of locations having both a length and width dimensions substantially greater than the cross-sectional area of each pencil beam; determining the position of each selected portion of the fixed position radiation beam; processing the signals generated in response to the radiation striking the corresponding portions; and generating a radiographic image of the predetermined area of the object. sequentially selecting and transmitting selected spirally-shaped portions of the cross-sectional area of the fixed position radiation beam along the radiation path in the direction toward the selected location; and sequentially selecting from said spirally-shaped portions, and transmitting to the selected location portions of cross-sectional area each corresponding to a said pencil beam of radiation. a source of radiation operative to transmit along a radiation path, toward the selected location, a fixed radiation beam of a selected energy intensity having a cross-sectional area at least corresponding to the predetermined inspection area; detection means, having a detection area at least corresponding to the predetermined inspection area, disposed in the radiation path in alignment with the fixed radiation beam; scanning point selection means including a first rotatable disk having a spirally-shaped aperture, disposed in the radiation path between the radiation source and the detection means, said disk being rotatable a distance corresponding to a width of the aperture at the end of a predetermined time period for sequentially selecting and transmitting spirally-shaped portions of the cross-sectional area of the fixed radiation beam along the path in the direction toward the selected locations; and a second rotatable disk having an opposite spirally-shaped aperture disposed in the radiation path in alignment with said first rotatable disk between said first rotatable disk and the detection means, and being completely rotatable during the predetermined time period for sequentially selecting from said spirally-shaped portions and for transmitting to the selected location, said selected portions of cross-sectional area each corresponding to a said pencil beam of radiation, said time period being pre-selected in accordance with the selected energy intensity; said detection means being responsive to each said selected portion of the fixed radiation beam striking a corresponding portion of the detecting area for generating signals corresponding to radiation interactive with a corresponding portion of the predetermined inspection area of an object at the selected location; position encoder means responsive to said scanning point selected means for determining the position of each selected portion of the fixed radiation beam; data processing means responsive to said position encoder means and said detection means for processing the signals generated by the detection means; and display means governed by said data processing means for generating a radiographic image of the predetermined area of the object. means for selecting the intensity of the radiation source in accordance with the selected element. a source of radiation operative to transmit along a radiation path, toward the selected location, a fixed radiation beam having a cross-sectional area at least corresponding to the predetermined inspection area; detection means, having a detection area at least corresponding to the predetermined inspection area, disposed in the radiation path in alignment with the fixed radiation beam; scanning point selection means including a first disk having an elongate aperture, disposed in the radiation path between the radiation source and detection means, said first disk being rotatable at the end of a predetermined time period, a distance corresponding to a width of the elongate aperture, and a second disk having an elongate aperture with a predetermined orientation relative to the first disk, said second disk being rotatable completely during the predetermined time period, for sequentially selecting and transmitting selected portions of the cross-section area of the fixed radiation beam striking in sequence corresponding portions of the detection area of the detection means, each said selected portion of the cross-section area of the fixed radiation beam corresponding to a pencil beam of radiation, said detection means being responsive to each said selected portion of the first radiation beam striking a corresponding portion of the detecting area for generating signals corresponding to radiation interactive with a corresponding portion of the predetermined inspection area of an object at the selected location; position encoder means responsive to said scanning point selection means for determining the position of each selected portion of the first radiation beam; data processing means responsive to said position encoder means and said detection means for processing the signals generated by the detection means; and display means governed by said data processing means for generating a radiographic image of the predetermined area of the object. means for selecting the intensity of the radiation source in accordance with the selected element. transmitting a radiation beam along a radiation path in a first direction toward the selected inspecting location, the beam having a cross-sectional area corresponding at least to the predetermined area of the inspecting location; sequentially selecting a plurality of portions of the cross-sectional area of beam of radiation and transmitting the selected portions to the selected location, each said selected portion of the cross-sectional area of the fixed radiation beam corresponding to a pencil beam of radiation, and the plurality of portions of the cross-sectional area of the radiation beam having both a length and width dimension substantially greater than the pencil beam; backscattering radiation in a second direction along the radiation path, opposite the first direction, through the object at the selected location; detecting each of the plurality of selected portions of the first radiation travelling through an object at the inspecting location and backscattered in the second direction, and detecting second radiation interacting with the object and backscattered in the second direction, the plurality of portions of the inspection area having both a length and width dimension greater than one pencil beam; generating signals in response to the detected radiation; and processing the response signals for the sequentially selected area portions of the inspecting location to obtain a radiographic representation of the object at the inspecting location. 2. The system of claim 1 further comprising filtering means fixedly disposed in the radiation path between the radiation source and the scanning point selection means for determining the identity of at least a grouping of atomic elements. 3. The system of claim 1 wherein the scanning point selection means comprises: 4. The system of claim 2 wherein the filtering means comprises a fixed member composed of a selected atomic element having an area corresponding to at least the total radiation beam area; and 5. The system of claim 3, wherein said detection means includes a detection device wherein said radiation source and the detection device are disposed with the selected location therebetween. 6. The system of claim 3, wherein said detection means includes a defection device disposed in the radiation path between said radiation source and the selected location. 7. The system, of claim 3, wherein said detection means comprises a first detector device and a second detector device responsive to each of the selected portions of the fixed position radiation beam, said first detector device being positioned such that said first detector device and said radiation source are disposed with the selected location therebetween, said second detector device being disposed between said radiation source and the selected location. 8. The system of claim 4 wherein the scanning point selection means comprises: 9. The system of claim 7, further comprising filtering means for determining the identity of at least a grouping of atomic elements disposed between the radiation source and selected location second detection device. 10. The system of claim 8, wherein said first and second rotating disks are comprised of a material having a high atomic number, and wherein said spirally-shaped apertures of said first and second rotating disks are shaped in the form of spiral parabolic curves respectively represented by the equations in polar coordinates: ##EQU3## where a represents a constant, .theta. represents the polar angle in radian measure from the horizontal axis, and R.sub.1 and R.sub.2 represent the radius vector of disks, the first and second, rotating respectively. 11. The system of claim 3, wherein said first and second rotating disks are comprised of a material having a high atomic number, and wherein said spirally-shaped apertures of said first and second rotating disks are shaped in the form of spiral Archimedian curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times..theta., and EQU R.sub.2 =a.times.(.pi.-.theta.), 12. The system of claim 8 wherein said first and second rotating disk are comprised of a material having a high atomic number, and wherein said spirally-shaped apertures of said first and second rotating disks are shaped in the form of spiral Archimedian curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times..theta., and EQU R.sub.2 =a.times.(.pi.-.theta.), 13. The system of claim 3, wherein said first and second rotating disks are comprised of a material having a high atomic number, and wherein said spirally-shaped apertures of said first and second rotating disks are shaped in the form of spiral quadradic curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times..theta..sup.2, and EQU R.sub.2 =a.times.(.pi.-.theta.).sup.2, 14. The system of claim 8 wherein said first and second rotating disks are comprised of a material having a high atomic number, and wherein said spirally-shaped apertures of said first and second rotating disks are shaped in the form of spiral quadradic curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times..theta..sup.2, and EQU R.sub.2 =a.times.(.pi.-.theta.).sup.2, 15. The system of claim 3, wherein the system further comprises an image memory, responsive to said data processing means, for storing the signals processed by said data processing means, said display means being responsive to the signals stored by said image memory to generate the radiographic image of the predetermined area of the object. 16. The system of claim 8 wherein the system further comprises an image memory, responsive to said data processing means, for storing the signals processed by said data processing means, said display means being responsive to the signals stored by said image memory to generate the radiographic image of the predetermined area of the object. 17. A method for radiographically inspecting a predetermined area of relatively stationary object positioned at a selected location comprising the steps of: 18. The method of claim 17 wherein the step of sequentially selecting and transmitting the portions from the cross-sectional area of the first radiation beam comprises the substeps of: 19. The method of claim 17 wherein the method further comprises the step of storing the processed signals for generating a radiographic image of the predetermined area of the object. 20. A system for radiographically inspecting a predetermined area of a relatively stationary object positioned at a selected location, comprising: 21. The system of claim 20 further comprising filtering means disposed in the radiation path between the radiation source and the detection means for determining the identity of at least a grouping of atomic elements, and wherein the filtering means includes a member composed of a selected atomic element having an area corresponding to at least the radiation beam area; and 22. A system for radiographically inspecting a predetermined area of a relatively stationary object positioned at a selected location, comprising: 23. The system of claim 22, further comprising filtering means disposed in the radiation path between the radiation source and the detection means for determining the identity of at least a grouping of atomic elements; and wherein the filtering means includes a member composed of a selected atomic element having an area corresponding to at least the radiation beam area. 24. The system of claim 22 further comprising filtering means disposed in the radiation path between the radiation source and the detection means for determining the identity of at least a grouping of atomic elements. 25. The system of claim 24 wherein the filtering means comprises a member composed of a selected atomic element having an area corresponding to at least the radiation beam area; and 26. The system of claim 22 wherein said first and second disks are comprised of a material having a high atomic number, and wherein said apertures of said first and second disks are shaped in the form of spiral parabolic curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times.0, and EQU R.sub.2 =a.times.(.pi.-0), 27. The system of claim 22 wherein said first and second disk are comprised of a material having a high atomic number, and wherein said aperture of said first and second rotating disks are shaped in the form of spiral Archimedian curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times.0, and EQU R.sub.2 =a.times.(.pi.-0), 28. The system of claim 24 wherein said first and second disks are comprised of a material having a high atomic number, and wherein said apertures of said first and second rotating disks are shaped in the form of spiral Archimedian curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times.0, and EQU R.sub.2 =a.times.(.pi.-0), 29. The system of claim 22 wherein said first and second rotating disks are comprised of a material having a high atomic number, and wherein said spirally-shaped apertures of said first and second rotating disks are shaped in the form of spiral quadradic curves respectively represented by the equation in polar coordinates: EQU R.sub.1 =a.times.0.sup.2, and EQU R.sub.2 =a.times.(.pi.-0).sup.2, 30. The system of claim 24 wherein said first and second rotating disks are comprised of a material having a high atomic number, and wherein said spirally-shaped apertures of said first and second rotating disks are shaped in the form of spiral quadradic curves respectively represented by the equations in polar coordinates: EQU R.sub.1 =a.times.0.sup.2, and EQU R.sub.2 =a.times.(.pi.-0).sup.2, 31. The system of claim 22, wherein the system further comprises an image memory, responsive to said data processing means, for storing the signals processed by said data processing means, said display means being responsive to the signals stored by said image memory to generate the radiographic image of the predetermined area of the object. 32. The system of claim 24 wherein the system further comprises an image memory, responsive to said data processing means, for storing the signals processed by said data processing means, said display means being responsive to the signals stored by said image memory to generate the radiographic image of the predetermined area of the object. 33. The system of claim 22, wherein said radiation source includes means operative to transmit radiation of a selected energy intensity, and wherein said first disk is rotatable a distance corresponding to a width of the aperture at the end of a predetermined time period, and said second disk is rotatable completely during a predetermined time period, said time period being preselected in accordance with the selected energy intensity. 34. The system of claim 33 wherein the energy intensity is selected in accordance with the selected element. 35. A method for radiographically inspecting a predetermined area of a relatively stationary object, disposed at a selected location along a radiation path, comprising the steps of:
050698273	summary	The present invention relates to a process for dissolving a refractory compound of plutonium which it is difficult to dissolve, namely plutonium dioxide. It more particularly applies to the dissolving of said compound present in solid waste and in particular in organic waste. One of the main problems which is frequently encountered in nuclear installations is the recovery of the plutonium in the form of PuO.sub.2, which is substantially insoluble in acid solutions. This compound is more particularly present in solid waste resulting either from the production of nuclear fuel elements, or from the processing of irradiated nuclear fuels. Such waste can be constituted by ash resulting from incineration at 800.degree. to 900.degree. C. of highly plutonium contaminated combustible waste in which the plutonium is in oxide form. Other waste is constituted by laboratory waste, particularly organic material waste, such as plastic and cellulose material waste contaminated by plutonium in the form of oxide which it is difficult to dissolve. Hitherto four methods have been used for dissolving plutonium dioxide. The first method consists of maintaining the plutonium in the tetravalent state during its dissolving. One process is based on the catalytic action of fluoride ions and the formation of a complex anion PuF.sup.3+ making it possible to solubilize the plutonium in a nitric solution. This dissolving can be accelerated by adding a silver compound which oxidizes the complex ion PuF.sup.3+ and thus regenerates the F.sup.- ions. This process is more particularly described in U.S. Pat. Nos. 3,976,775 and 4,069,293. This process suffers from the disadvantage of requiring the use of corrosive reagents and of producing fluorinated effluents, whose treatment causes problems. Moreover, when the plutonium is present in reducing organic waste, the latter can be oxidized by Ag.sup.2+ ions, which no longer fulfil their function of accelerating the plutonium oxide dissolving reaction. Thus, this process is not very suitable for the treatment of organic waste. Another possible way of dissolving plutonium whilst maintaining it in the tetravalent state is to transform it into plutonium sulphate by the action of concentrated sulphuric acid at a high temperature of approximately 250.degree. C. and as is described by B. Stojanik et al in Radiochimica Acta, 36, pp 155-157, 1984. Thus, this process suffers from the disadvantage of requiring the use of high temperatures and concentrated acid solutions. Moreover, it does not permit the complete dissolving of PuO.sub.2, when the latter has been exposed to high temperatures. The second procedure for dissolving plutonium dioxide consists of oxidizing dissolving in which the plutonium is brought into the soluble state by oxidizing at valence VI. This can be obtained by using a powerful oxidizing agent such as the ion Ag.sup.2+ and as is described in European patents 160 589 and 158 555. This procedure is very interesting because it makes it possible to obtain high dissolving rates. However, it is not very suitable for the treatment of organic waste having reducing properties because, in this case, the reducing organic materials can be oxidized by the Ag.sup.2+ ions, which can therefore no longer participate in the dissolving reaction. This reduces the effectiveness of the process and greatly increases the waste treatment time, which constitutes a handicap for the performance of this type of treatment on an industrial scale. A third plutonium dioxide dissolving procedure consists of treating the plutonium dioxide by a concentrated 6M hydroiodic acid solution brought to the boiling temperature and as is described in U.S. Pat. No. 4,134,960. However, in such a process, the dissolving rate is relatively low and the effluent obtained is difficult to treat. A fourth procedure based on the reduction of plutonium described in FR-A-2 553 560 consists of dissolving the plutonium dioxide in a nitric solution brought to boiling point and which contains uranium IV and hydrazine. Thus, in this process, the stabilization of the uranium IV by hydrazine is necessary. In addition, a hydrazine depletion at the end of dissolving can lead to an autocatalytic oxidation of the uranium IV excess, i.e. an explosive reaction making its performance on an industrial scale difficult. Thus, the presently known processes do not make it possible to ensure under good conditions the dissolving of a refractory compound of plutonium, such as plutonium dioxide and which is present in waste having reducing properties. The present invention specifically relates to a process for the reducing dissolving of plutonium dioxide, which obviates this disadvantage. This process consists of contacting the plutonium dioxide with a hydrazine-free, acid aqueous solution, which contains a reducing agent, whose redox potential is below +3.5 V/ENH in order to reduce the plutonium and to dissolve the same. The inventive use of reducing agents having a potential below +0.5 V/ENH makes it possible to carry out the reduction of the plutonium from valence IV to valence III and thus solubilize the same in the acid solution. Thus, the standard potential of the transformation ##STR1## is E.sub.o =0.544 V/ENH at 25.degree. C. and E.sub.o =0.487 V/ENH at 85.degree. C. Moreover, the use of reducing agents having a redox potential below +0.5 V/ENH make it possible to obtain said transformation. Thus, contrary to what is indicated in FR-A-2 553 560, the ferrous ion Fe.sup.2+, whose redox potential is equal to +0.77 V/ENH is not suitable for carrying out this transformation. Examples of suitable reducing agents are Cr.sup.2+, U.sup.4+, U.sup.3+, Eu.sup.2+, V.sup.3+, V.sup.2+, Ti.sup.3+ and Ti.sup.2+. According to the invention, the reducing agent is chosen in such a way as to obtain a favourable dissolving kinetics as a function of the solution and operating conditions used. According to a first embodiment of the inventive process, the reducing agent is present in the acid aqueous solution in a quantity adequate to reduce all the plutonium to be dissolved. When the reducing agent is one of the aforementioned ions, it can be introduced in the form of a soluble salt, e.g. sulphate. It is also possible to introduce it in solution in oxidized form and to reduce the solution, e.g. by electrochemistry or by zinc amalgam. When the oxidation reaction of the reducing agent only uses a single electron, it is necessary for the molar concentration in the reducing agent of the solution to at least be equal to the molar concentration of the plutonium to be dissolved. If the oxidation reaction of the reducing agent uses several electrons, the molar concentrations of the reducing agent can be lower. This embodiment of the process can be used when there are only small plutonium quantities to be dissolved. However, in the case of relatively large quantities, it is preferable to regenerate the reducing agent in solution to limit the reducing agent quantities used. According to a second embodiment of the inventive process, the reducing agent in solution is regenerated by electrolysis. This can be carried out by using the oxidizing dissolving installations described in European patents 158 555 and 160 589, where the oxidizing agent Ag.sup.2+ is regenerated by electrolysis. In the invention, regeneration takes place on the cathode and the anode and cathode compartments are reversed as compared with what is used in installations for oxidizing dissolving. In this second embodiment of the inventive process, the reducing agent concentration in the solution is generally 0.02 to 0.2 mol/l. The acid aqueous solutions used for dissolving can be of different types, the only condition being that the acid is compatible with the chemical species which can occur in solution and in particular with the plutonium and reducing agent. For example, it is possible to use sulphuric acid, preferably at a molar concentration of 0.5 to 7 mol/l. It would also be possible to use formic acid. It is preferable to avoid using nitric acid due to possible reactions between the nitrous acid and the reducing agent, particularly in the case of U(IV). On regenerating the reducing agent by electrolysis, the plutonium to be dissolved, optionally included in waste in the presence of the dissolving solution is brought into the cathode compartment of an electrolyzer having an anode and a cathode. The reducing agent can be introduced in oxidized form and can be generated at the start of the reaction by applying an adequate potential difference to reduce its oxidized form. Preferably, the solution is vigorously stirred, on the one hand to facilitate exchanges between the solution and the cathode and on the other in order to perfectly impregnate the plutonium dioxide or the waste containing the same with the solution. In this way the reactions are accelerated and in particular the reduction of the oxidized species of the reducing agent, because the reducing kinetics are mainly dependent on the speed at which the ions to be reduced can reach the cathode. Generally, the potential difference is applied in such a way as to impose a constant current in the cell, which permits the permanent regeneration of the reducing agent. The material from which the cathode is made must comply with the electrochemical properties of the reducing agent and have adequate mechanical and chemical characteristics to remain unimpaired under the adopted operating conditions. When the regeneration of the reducing agent takes place at a potential higher than that of the reduction of the solution, the cathode can be made from platinum. In the case of more powerful reducing agents requiring a high cathode overvoltage, it is possible to use an electrode having a solid copper support covered with gold, whereby it is amalgamed by soaking in mercury. Thus, such an electrode roughly has the cathode overvoltage of mercury due to the use of gold amalgam as the electro-active material. The copper support contributes to the rigidity of the electrode. The use of such an electrode is particularly suitable for the regeneration of powerful reducing agents such as Cr.sup.2+, U.sup.4+, U.sup.3+, Eu.sup.2+, V.sup.2+, Ti.sup.3+ and Ti.sup.2+. In order to improve the efficiency of electrolysis, as well as the reaction rate between the reducing agent and the plutonium compound, it is preferable to work at a temperature above ambient temperature, e.g. at 50.degree. to 100.degree. C. Moreover, when the reducing agent used reacts with the oxygen, the cathode compartment is placed under an inert atmosphere to prevent said reaction. A condenser is also added to the cathode compartment in order to limit the vaporization of the solution. Other features and advantages of the invention can be better gathered from reading the following examples concerning the performance of the inventive process and which are obviously given in an illustrative and non-limitative manner. Comparative examples 1 and 5 reveal the advantages provided by the inventive process.
	summary
043671845	claims	1. A process for forming nuclear reactor fuel comprising the steps of: sintering microspheres containing uranium dioxide and free carbon in an atmosphere consisting essentially of an inert gas and carbon monoxide at such carbon monoxide concentration and at such temperature that high density microspheres consisting essentially of uranium dioxide and uranium oxycarbide are formed; and sintering said uranium dioxide/uranium oxycarbide microspheres in an atmosphere consisting essentially of an inert gas and carbon monoxide at such carbon monoxide concentration and at such temperature that microspheres having a density of about 10.2 to 11.0 g/cm.sup.3 and consisting essentially of about 1-30 mole percent uranium dicarbide and 70-99 mole percent uranium dioxide are formed. 2. The process of claim 1 wherein said microspheres containing uranium dioxide and free carbon are sintered at a temperature of about 1550.degree. C. in an atmosphere consisting of less than 1.2 mole percent carbon monoxide, and said microspheres containing uranium dioxide and uranium oxycarbide are sintered at a temperature of about 1550.degree. C. in an atmosphere consisting of more than 1.9 mole percent carbon monoxide. 3. The process of claim 2 wherein said microspheres containing uranium dioxide and free carbon are sintered in an atmosphere consisting of about 0.5 to 1 mole percent carbon monoxide, and said microspheres containing uranium dioxide and uranium oxycarbide are sintered in an atmosphere consisting of about 3 mole percent carbon monoxide. 4. The process of claim 3 wherein said microspheres containing uranium dioxide and free carbon and said microspheres containing uranium dioxide and uranium oxycarbide are each sintered for about 4 hours under the stated conditions. 5. Nuclear reactor fuel microspheres consisting essentially of about 1-30 mole percent uranium dicarbide and 70-99 mole percent uranium dioxide and having a density in the range of about 10.2-11.0 g/cm.sup.3.
	summary
040640027	claims	1. An emergency core cooling system for a nuclear reactor comprising a pressure vessel hermetically sealed by a closure head, a reactor core in the pressure vessel and an inlet and outlet for circulating coolant through the reactor core; emergency coolant means including at least one accumulator having a pressurized neutron absorber material therein; an outlet on said accumulator connected with the closure head for discharging said absorber material into the pressure vessel; flow restricting means between said accumulator and closure head which permits flow of absorber material only from the accumulator toward the reactor, said flow restricting means being held closed by the pressure of coolant in said reactor, the arrangement being such that when the reactor coolant pressure drops below the accumulator pressure, neutron absorber material flows from the accumulator into the pressure vessel; and means in said pressure vessel for conducting the neutron absorber material from the accumulator to the top of said core for distribution downwardly therethrough for carrying away heat generated in the core; said conducting means comprising piping supported by the closure head, said piping being arranged to extend from the accumulator outlet to a plenum chamber under the closure head, thereby providing an avenue for the discharge of absorber material from the accumulator into the plenum chamber; means communicating with the plenum chamber and top of said core for conducting the absorber material to the core; said piping extending from the accumulator outlet further being connected to downcomer tubing supported in the pressure vessel and having openings which discharge said absorber material directly on to the reactor core, thereby permitting it to flow in and between fuel assemblies in the core; a connector connecting said piping and downcomer tubing, said connector being designed to allow for lateral displacement of the tubing and piping after the closure head is mounted on the pressure vessel; high and low liquid level sensors in said accumulator; valve means in said piping connected to the accumulator outlet; and means connecting said sensors with said valve means in the piping which are operable to close said valves when the absorber material level in the accumulator rises or falls respectively to predetermined levels.
043364608	abstract	A cask for containing spent nuclear fuel during transport. The cask has a pair of multiple element trunnions disposed on opposite sides of the cask adjacent the top thereof. The multiple elements of the trunnions provide separate and independent load paths for lifting the cask. The trunnions are removable and disassemblable to permit inspection of each element. Disposed on the ends of the cask are convex impact limiters for reducing forces applied to the cask in a collision. Apparatus engageable with the trunnions for lifting the cask thereby comprise a pair of multiple element laminated plates engageable with a crane hook. A pair of multiple element straps have ends selectively engageable with the plates and ends selectively engageable with the trunnions of the cask.
047913037	description	DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention is directed to both apparatus and methods for the utilization of cold plasma techniques in laminating at least two polymeric sheets, without the use of any substantial heat which might cause a degradation of the structure of such polymeric sheets and thus result in a diminution of the physical properties and desirable characteristics thereof, and also without the use of any separate adhesive material. The cold plasma reactor methods and apparatus of the present invention are specifically directed to activating the surface of a first sheet of polymeric film material to form free radicals thereon for effecting adhesion with a second sheet of polymeric sheet material. The cold plasma reactor apparatus of the present invention in a broad embodiment thereof comprises cold plasma generating cathode and anode respectively disposed is spaced proximity with the first sheet of polymeric material. Means are providing for flowing a stream of a cold plasma generateable gaseous medium past the cold plasma generating cathode. In addition thereto, sheet transporting means for effectuating relative movement between the cathode and the treated surface of the first sheet of polymeric film material for exposing a substantial portion of the surface of such first sheet to such cold plasma is further provided. Such cold plasma reactor includes cathode means which are disposed and spaced at a selected distance from one side of the first sheet of polymeric material. In such embodiments, the accompanying anode is disposed also in selected spaced array from the opposite side of such first sheet, and in certain preferred embodiments in contact with such opposite side thereof. In these preferred embodiments, the cathode comprises a pair of conductive cathode bodies projecting towards the adjacent surface of the first sheet. Such conductive cathode bodies may preferably comprise a pair of elongated elements which extend in a longitudinal direction. Such elongated pair of cathode bodies are preferably disposed substantially parallel to each other along the longitudinal extent thereof. The conductive cathode bodies as described hereinabove have a substantially sharp terminal edge facing the surface of the first sheet of polymeric material to be treated with the cold plasma. Each of such pair of upwardly projecting cathode bodies is also preferably substantially thin, and in preferred embodiments such conductive cathode bodies may comprise a plurality of razor blade bodies disposed end-to-ed and with the sharpened edge portion thereof disposed upwardly and toward such surface of such first sheet. The means for flowing a stream of the cold plasma generatable gaseous medium is disposed in preferred embodiments to provide flow of such gas in a stream between the pair of conductive cathode bodies. The above means for effectuating relative movement between the cathode and the treatment surface of the first sheet preferably comprises at least one conductive roller disposed opposite the cathode. The conductive roller extends in a longitudinal direction, and in such preferred embodiments the conductive roller also comprises the anode. Also included in preferred embodiments of the cold plasma reactor apparatus of the present invention is a cathode housing means for defining a cold plasma containing chamber. Such cold plasma containing chamber has the cathode disposed therein. Such cathode housing defines the cold plasma containing treatment chamber, and which treatment chamber extends longitudinally, and essentially parallel with the longitudinal dimension of the conductive anodic roller. Thus, the cold plasma containing, or treatment, chamber is defined by such cathode housing walls and is formed of an insulator material, and has a mouth at one end thereof for disposition of the first sheet of polymeric material thereacross to form a substantial relative seal of the chamber by means of the first sheet of polymeric material. Although such relative seal in preferred embodiments is sufficient to permit some pressurization of such chamber, other alternative embodiments do not require a seal, but rather comprehend such polymeric material as constituting a not substantially sealing cover means for the end of such chamber. In such preferred embodiments, the first sheet of polymeric material is transported across the mouth of the cold plasma containing chamber while simultaneously substantially maintaining the relative seal on such chamber to prevent substantial loss of cold plasma from the cold plasma containing chamber, and wherein the treatment surface of the first sheet of polymeric film material faces the cathode within the chamber and is accordingly exposed to such gaseous cold plasma. At least one, and preferably two, non-conductive roller(s) are disposed in spaced array from the conductive roller to assist in effectuating such relative movement between the cathode and the treatment surface of the first sheet of polymeric material in preferred embodiments by functioning as a transporting roller for such first sheet. Such non-conductive rollers are each disposed in spaced array generally on opposite sides of the conductive roller to assist in such relative movement, and in particular to form an ingress roller and an egress roller for transporting such polymeric sheet into such cold plasma reactor, across the cold plasma containing chamber, and out of such cold plasma reactor. In such preferred embodiments, each of the non-conductive rollers is disposed for contact with one surface of the first sheet of polymeric material, and preferably the treatment surface, and the conductive roller is disposed for contact with the opposite surface thereof. In the above preferred embodiments, the cathode bodies are carried by a cathode frame. Means for flowing a stream of the cold plasma generatable gaseous medium between the pair of elongated conductive cathode bodies comprises a plurality of substantially evenly spaced gaseous medium inlets disposed in longitudinal array in the cathode frame. Such evenly spaced gaseous inlets open within a longitudinally extending trough formed in the cathode frame and between the longitudinally extending, elongated, and evenly spaced cathodes. Thereby, such cathodes in conjunction with the associated trough spaced therebetween function together to maintain the pressure of the gaseous medium at a substantially equal level over the longitudinal dimension of the elongated cold plasma containing chamber. Also, in preferred embodiments of the cold plasma reactor apparatus of the present invention, pressurization means for pressurizing the cold plasma containing chamber are provided. Such pressurization means may preferably comprise means for substantially providing continuous gas flow to the cold plasma containing chamber. Means for substantially continuously removing gas from the cold plasma containing chamber to provide a constant flow thereof are also provided. Such means further function substantially to diminish leakage of the gas from the chamber, and may further function to reclaim such gaseous medium for reuse. The above cathode frame further includes at least one internal channel extending longitudinally along the length thereof for supplying gas to the plurality of gaseous inlets which are substantially evenly spaced along the length of the cathode frame. Such cathode frame is dimensioned to fit snugly and removably within the cathode housing along the respective longitudinal dimensions thereof. In such preferred embodiments, such cathode housing defines the cold plasma containing chamber and includes a longitudinally extending slot in the wall thereof opposite the first sheet, into which slot the longitudinally extending pairs of cathodes are disposed to project into the cold plasma containing chamber, and to provide the gaseous medium to such cold plasma containing chamber from the trough disposed between the pair of elongated cathode bodies. As set forth in the description hereof, the above cold plasma reactor apparatus provides examples of apparatus suitable for carrying out the cold plasma techniques and methods of the present invention for laminating at least two polymeric sheets into a composite having improved and/or hybrid properties. Such methods comprise in certain broad embodiments thereof the steps of first providing a first sheet of polymeric material; next, exposing the surface of the first sheet of polymeric material to cold plasma to activate the surface thereof; and finally, disposing such activated surface of the first sheet into intimate proximity with the second sheet of polymeric material and pressing such first sheet and second sheets together to effect adhesion therebetween, to form a laminated composite in the absence of any substantial heating of either of such sheets and without application to either of such sheets of a separate adhesive. In the inventive cold plasma methods of the present invention, such first and second and/or further polymeric sheets may be composed of different polymeric materials. At least one of such first sheet and such second sheet may be maintained in rolled form prior to such laminating to form such composite. After such laminating, such laminating composite is preferably also wound into rolled form for convenience of transportation and storage. The cold plasma utilized in the methods of the present invention preferably comprises cold argon plasma. Such cold argon plasma is generated in preferred embodiments by application to a gaseous mixture of approximately at least one percent to two percent argon, or other inert gas, in air of an electromagnetic energy discharge of at least approximately 180,000-500,000 volts, such gaseous mixture preferably comprising a stream of such gaseous material and which preferably comprises argon. The cold plasma utilized in the methods of the present invention is generated by application of electromagnetic energy of a frequency in the radio wave length to the inert gas. Such radio frequency discharge is carried out at approximately the frequency of 12.56 megaHertz. The cold plasma is also preferably maintained at a selected pressure of approximately at least 1.1 Torr during such treatment by such cold plasma of such first sheet. In some preferred embodiments of the method of the present invention, the pressure of the cold plasma and the voltage applied thereto may be individually controlled and maintained in proportional relationship to each other. In such methods, there may be preferably an inverse proportional relationship between the pressure of the cold plasma and the voltage applied thereto. Such inverse proportional relationship may be controlled automatically, such as for example by means of an adiabatic pressure valve, examples of which are known to those skilled in the pressure valve arts. In certain preferred embodiments, the first sheet of polymeric material in such improved methods of the present invention is exposed to the cold plasma for a period of approximately less than approximately 5.0 milliseconds. Such first sheet is run through such cold plasma treatment chamber at a rate of approximately 500 feet per second. In the improved methods of the present invention, the cold plasma is generated by means of application of energy of a selected frequency to a gas wherein such gas has a flow rate of approximately at least 10 milliliters per second per linear meter onto the surface of such first sheet. Referring now to the drawing and to FIGS. 1 and 2 in particular, wherein illustrative embodiments of the cold plasma apparatus generally 10 are shown, left side end plate 12 includes therein the three axes of rotation 14, 16, 18 for the respective journals for rollers 20,22,24, as shown in FIG. 2. In particular, conductive roller 20 comprising the anode is disposed between the two non-conductive rollers 22,24. FIG. 1 further depicts the cover plate 26 for the electrical terminal 28, and which is secured by means nylon cap screws 30, and stainless steel cap screws 32. Such cover plate 26 is disposed generally between such non-conductive roller axes 14,18. FIG. 1 further shows the reactor covers 34,36 which are hemispherically shaped in cross-section with ingress and egress openings 38,40 respectively located at the bottom and top respectively thereof, and with such reactor covers 34,36 maintained and secured thereon by means of thumb screws 42. Tapped screw holes 43 are provided for securing reactor apparatus 10 to externally associated frame and support means (not shown) for positioning in proper relationship with the various rolls of sheet material stock and the roller(s) for the composite laminate in its various stages of formation. FIG. 2 shows left side and right side end plates 12,44, which hold means thereon for journaling for rotation the pair of non-conductive rollers 22,24 disposed on either side of the conductive anodic roller 20. The respective end portions 46,48 of anodic roller 20 include spring-loaded electrical clips 50,51 for contacting commutator rings 52,54 to provide electrical contact between the power source (not shown) and the commutator rings 52,54 disposed at each respective end 46,48 and around the conductive, anodic roller 20. Such electrical clips 50,51 are secured by means of thumb screws 56,58 to a removable electrical clip support bar 53 which extends longitudinally across the length of reactor apparatus 10, as shown in FIG. 2 and in cross section as shown in FIG. 6. FIG. 2 further illustrates spring-loaded grips 60,62 for holding such clip support bar 53, the structure and functioning of which are shown in greater detail in FIG. 7, as described, infra. FIG. 3 shows electrical terminal 28 connected to electrical contact 64 and to spring 66 for insuring contact with cathode contact 70 which is connected to the cathode generally 80 by means of cathode connector plates 82. Cathode 80 is supported by a longitudinally extending cathode frame 84 having supported thereon the longitudinally extending conductive cathode bodies 86,87 comprising a plurality of end-to-end positioned, upwardly directed razor blade bodies, the sharp edges of which are disposed in proximity to such conductive roller 20 and forming a treatment chamber 88 therebetween, as depicted more particularly in FIG. 6. In the jogged right hand portion of FIG. 3 generally 90, securement means in the form of cathode bolts 92 for securing such razor blade cathodes 86 to such cathode frame 84 are shown. Cover bar 83 and shim 85 in FIGS. 3,4,5 and 6 are secured to and under cathode frame 84 by bolts 85, and to cathode holder 100 by bolts 87, as shown in FIG. 5, to hold cathode bodies 86 in functional position. In FIG. 4 gas inlet 94 for supplying the gaseous medium from an external source (not shown to) longitudinally disposed gaseous supply conduit 96 is shown for in turn providing the gaseous plasma medium to gaseous inlets 98 in cathode holder 84 which also carries such cathode bodies 86. Such gaseous inlets serve to uniformly distribute such gaseous medium upwardly into the cold plasma chamber 88, as shown by the path of Arrows B,B in FIGS. 3 and 4. FIGS. 5 and 6 depict cathode holder 100 of the cold plasma reactor apparatus 10 which contains means for continuously removing the gaseous cold plasma from reactor appaaratus 10 in the path as shown at Arrows C,C in FIGS. 5 and 6 through vacuum outlet 102. In particular, cathode holder 100 includes downwardly directed gaseous medium exhaust channels 101,101, which in turn feed into horizontally directed gas exit passages 103,103 eventually to exit reactor 10 through vacuum outlet 102. Exit passages 103,103 lead into and communicate with a single exhaust collection chamber 93 defined by an end cap 95 covering an aperture cut into right side end plate 44, which end cap 75 is secure to end plate 44 by bolts 97. Such cathode holder 100 is secured to each end plate 12,44 by means of screws 104, as shown in FIG. 5. As shown particularly in FIG. 6, cathode housing 100 includes upwardly extending walls 108 for defining cold plasma containing chamber 88. Such cold plasma containing chamber 88 has the cathode bodies 86 disposed therein. Such cathode housing 100 thus defines the cold plasma containing treatment chamber 88, and which treatment chamber 88 extends longitudinally, and essentially parallel with the longitudinal dimension of conductive roller 20 as shown in FIGS. 3-5. Cold plasma containing, or treatment, chamber 88 comprising housing walls 108 formed of an insulator material has a mouth at one side thereof, which is the tope side as shown in the embodiment of FIG. 6, for disposition of the first sheet 106 of polymeric material thereacross to form a substantial relative sealing of chamber 88 by means of the first sheet 106 of polymeric material covering and disposed across such mouth of chamber 88. In such preferred embodiments, the first sheet 106 of polymeric material is transported across the mouth of cold plasma containing chamber 88 in the direction of Arrows A,A while simultaneously substantially maintaining the seal on such chamber 88 to prevent substantial loss of cold plasma from the cold plasma containing chamber 88, and wherein the treatment surface 105 of the first sheet 106 of polymeric film material faces cathode bodies 86 within chamber 88 and is exposed to such gaseous cold plasma. As shown in FIG. 6, each of non-conductive rollers 22,24 is disposed is spaced array from conductive roller 20 to assist in effectuating such relative movement between cathode bodies 86 and the treatment surface 105 of the first sheet 106 of polymeric material in preferred embodiments by functioning as a transporting roller for such first sheet 106. Such non-conductive rollers 22,24 are each disposed in spaced array generally on opposite sides of conductive roller 20 to assist in such relative movement and in particular to form an ingress roller 24, and an egress roller 22 for transporting such polymeric sheet 106 into such cold plasma reactor 10 at ingress 38 across the cold plasma containing chamber 88, and out of such cold plasma reactor 10 at egress 40. As shown in FIG. 6, in such preferred embodiments each of non-conductive rollers 22,24 is disposed for contact with treatment surface 105 of the first sheet 106 of polymeric material, and conductive roller 20 is disposed for contact with the opposite surface 107 thereof. In the above preferred embodiments as shown in FIG. 3, cathode bodies 86 are attached to, and carried and supported by cathode frame 84. Means for flowing a stream of the cold plasma generatable gaseous medium between the pair of elongated conductive cathode bodies 86,86 as shown best in FIG. 6 comprises a plurality of substantially evenly spaced gaseous medium inlets 98,98 as shown in FIGS. 3-4, and which are disposed in upwardly directed longitudinal array in cathode frame 84. Such evenly spaced gaseous inles 98 open within a longitudinally extending trough 112 formed in cathode frame 84 and between the longitudinally extending, elongated, and evenly spaced cathode bodies 86. Thereby, because off such uniform dimensions and spacing, such cathode bodies 86 in conjunction with associated trough 112 spaced therebetween function together to maintain a uniform volume for such gaseous medium and thereby to maintain the pressure of the gaseous medium at a substantially equal level over the longitudinal dimension of the elongated cold plasma containing chamber 88. Also, in preferred embodiments of the cold plasma reactor apparatus 10 of the present invention, pressurization means for pressurizing the cold plasma containing chamber are provided. Such pressurization means may preferably comprise means for substantially providing continuous gas flow to the cold plasma containing chamber 88 as shown in FIG. 4 by means of gaseous medium inlet 94. Means for substantially continuously removing gas from cold plasma containing chamber 88 to provide a constant flow thereof are also provided as shown in FIGS. 5-6. Such means further function substantially to diminish leakage of the gas from the chamber, and may further function to reclaim such gaseous medium for reuse. Cathode frame 84 further includes at least one internal channel comprising gaseous supply conduit 96 extending longitudinally along the length thereof for supplying such gaseous plasma medium to the plurality of gaseous inlets 98 which are substantially evenly spaced along the length of cathode frame 84. Such cathode frame 84 is dimensioned to fit snugly and removably within the cathode housing 100 as shown in FIG. 6 along the respective longitudinal dimensions thereof. In such preferred embodiments, such cathode housing 100 defines the cold plasma containing chamber 88 and includes a longitudinally extending slot 114 in the wall thereof opposite first sheet 106 into which slot the longitudinally extending pairs of cathode bodies 86,86 are disposed to project into the cold plasma containing chamber 88, and to provide the gaseous medium to such cold plasma containing chamber 88 from trough 112 disposed between the pair of elongated cathode bodies 86,86. Referring now to FIG. 7, the anti-rotational mechanism for preventing rotation of the journal for non-conductive roller 22 is depicted, and comprises a non-rotational pin 116 which interconnects rotational journal holder 118 with left side end plate 12. As depicted, roller bearings 120 are disposed on non-conductive roller 22 for rotation thereof about shaft 122. FIG. 8 depicts the grip and locking mechanism for the contact springs 50 and includes a slideable grip 60 which is slideable within slot 61 and is connected by screws 63,63 to a locking bar 65 as disposed within right side end plate 44 and as urged by coil spring 67. Thus, the functioning of grip 60 is to permit removal of bar 53 which functions to hold contact springs 50,51. The above methods and apparatus may be utilized in several variations and alternative embodiments. Specifically, the above laminate may comprise two layers, one of which comprises a sealant layer, and the other which comprises a barrier layer. Such sealant layer may comprise a polyolefin, such as for example polyethylene. The barrier layer may comprise polyvinyledine chloride, polyvinyl alcohol, polyacrylonitrile, etc. In other embodiments, the barrier layer may be sandwiched between two such sealant polymer layers. Also in yet other embodiments of the invention hereof, such laminate may form a primary web, which may then be further joined to a secondary and non-laminated web. In yet other embodiments, the above laminate may be joined on both sides thereof by separate secondary non-laminated webs. In the above embodiments, the secondary web may comprise a heavier gauge plastic sheet, such as high density polyethylene, polyvinyl chloride, polyacrylonitrile, polyethylene teraphthalate, nylon, polyurethanes, polystyrenes, polyvinylidene chloride, acrylonitrile, and/or other suitable polymers. Other gases useful for generating such cold plasma may comprise nitrogen, helium, xenon, krypton, neon, and/or other inert gases. Various different materials may be utilized as and for the elements of the cold plasma reactor apparatus of the present invention. The conductive roller may preferably comprise stainless steel. The contact springs and the commutator rings may comprise phosphor bronze. The various thumb screws may be formed from brass or nylon. The plate cover may also preferably comprise stainless steel, as does the compression spring. The connector screws may comprise stainless steel, brass, etc. The cathode bodies may preferably comprise one half of double-edged stainless steel razor blades, and preferably with platinum coating, as produced, for example, under the Schick.RTM. trademark by Warner Lambert Company of Morris Plains, New Jersey. Most of the non-conductive structural materials, such as the right and left side end plates, the non-conductive rollers, the cathode frame, the cathode housing, etc. may be formed from a high density polymeric material sold under the trademark Delrin.RTM. produced by E. I. Dupont Company of Wilmington, Del. The ball bearings contained within the journal for the non-conductive rollers preferably comprise a nonmetallic material, such as nylon orfoss. The male connector for the gas input is preferably formed from black polyethylene, as is the male connector for the vacuum suction. Cap screws and other screws which are not subjected to large amounts of force may be formed of nylon. The basic and novel characteristics of the improved methods and apparatus of the present invention will be readily understood from the foregoing disclosure by those skilled in the art. It will become readily apparent that various changes and modifications may be made in the form, construction and arrangement of the improved apparatus of the present invention, and in the steps of the inventive methods hereof, which various respective inventions are as set forth hereinabove without departing from the spirit and scope of such inventions. Accordingly, the preferred and alternative embodiments of the present invention set forth hereinabove are not intended to limit such spirit and scope in any way.
	description	The present disclosure relates to a neutron sealed source which holds cermet wire sources, such as Californium-252/Palladium wires, in separate blind apertures within a stainless steel block, thereby rejecting internally generated fission and decay heat from the cermet wire sources through the stainless steel block. In the prior art, it is known to use Californium-252 as a neutron source to provide stable initiation of the nuclear chain reaction during the start up of nuclear reactors. This provides for a more predictable, safe and reliable start up than relying solely on spontaneous fission or delayed fission within the reactor fuel rods. Such a neutron source increases the neutron flux and thereby the fission reaction rate in the reactor thereby allowing the reactor to be initially started even in an otherwise subcritical state. Additionally, such a known neutron source within the reactor during start up allows for the testing of neutron flux detectors. In the prior art, a plurality of cermet wires comprising Californium-252 and Palladium are loosely placed inside a single source cavity and then the source capsule is welded shut, as shown in FIGS. 1 and 2. These source capsules are typically placed throughout the reactor core. However, in such a configuration, the cermet Wires may touch each other. Such a configuration may result in heat from both fission and decay which is high enough to melt the cermet wires during operation within a nuclear reactor thereby risking capsule integrity. It is therefore an object of the present disclosure to provide a neutron source, using Californium-252 or similar isotopes, which can reject the heat generated in the neutron source during operation in a nuclear reactor, from both fission and decay, and avoid or minimize melting of the source which would risk capsule integrity. This and other objects are attained by providing a neutron sealed source wherein a stainless steel block, insert, or similar structure is provided with a plurality of compartments or blind apertures, each for receiving a length of Californium-252/Palladium cermet wire or other neutron source. A typical embodiment would include four such compartments or blind apertures, but it is envisioned that more or less compartments or blind apertures may be used for various applications. The stainless steel block, or similar structure, after receiving the plurality of lengths of Californium-252/Palladium cermet wire or other neutron source, is welded or otherwise sealed within a capsule structure. Referring now to the drawings in detail, wherein like numerals indicate like elements through the several views, one sees that an embodiment of the sealed neutron source 10 of the present disclosure is illustrated in FIGS. 3-10. The encapsulation in an exemplary embodiment may be firmed from stainless steel bar, type 304L, condition A (annealed), hot or cold finished, UNS 30403, whereas the active source is typically formed from cermet wires (formed by compacting and sintering a metal and a ceramic) containing Californium-252/Palladium in the chemical form of Pd/Cf2O3 (Californium (III) oxide). Those skilled in the art will recognize a range of equivalents. In particular, alternative materials for the encapsulation are nickel, titanium and zirconium. As shown in FIGS. 3-6, the sealed neutron source 10 includes inner integrated cylindrical insert 12 with a relatively solid cylindrical block portion 14 with a closed external end 15. The cylindrical walls 16 of cylindrical block portion 14 extend past cylindrical block portion 14 thereby forming hollow cylindrical lid seat portion 18 adjacent to the cylindrical block portion 14 and further forming open end 19. The exterior portion of cylindrical walls 16 adjacent to open end 19 may include a circumferential chamfered portion 21 of slightly reduced diameter. The inner integrated cylindrical insert 12 thereby forms a first or inner capsule structure. As best shown in FIGS. 5 and 6, four blind apertures 20, 22, 24, 26 are bored or otherwise formed in cylindrical block portion 14 at rotationally symmetric locations (that is, in the case of four blind apertures, spaced ninety degrees apart rotationally, as shown in FIG. 5). The blind apertures 20, 22, 24, 26 are typically parallel with each other, and co-extensive with each other (i.e., longitudinally aligned with each other and of equal depth). The blind apertures 20, 22, 24, 26 form compartments which are separated from each other by the material of the cylindrical block portion 14. As shown in FIGS. 3 and 4, in the fully assembled configuration, active sources, such as cermet wires 200, typically of Californium-252/Palladium (in the form Pd/Cf2O3), are placed within the blind apertures 20, 22, 24, 26. The cermet wires 200 are prevented from touching each other by the material of cylindrical block portion 14. Additionally, during operation, the cylindrical block portion 14 serves as a heat sink for fission heat and decay heat from the cermet wires 200. The material of cylindrical block portion 14, as best illustrated in FIG. 4, acts as a separator for the cermet wires 200 within the apertures or compartments 20, 22, 24, 26 as well as a heat sink. Typical dimensions of the cermet wires 200 are a length of 8.85 millimeters and a nominal diameter of 1.22-1.27 millimeters. Cermet wires 200 may have a slightly oval cross section and may have a typical activity loading of 20 milligrams per millimeter. Dimensions for an embodiment of the blind apertures 20, 22, 24, 26 are a total depth of 11.5 millimeters and a nominal diameter of 1.65 millimeters. Dimensions for an embodiment of the inner integrated cylindrical insert 12 are 14.20 millimeters in length and 6.0 millimeters in diameter. However, those skilled in the art will recognize that other dimensions may be preferable for different applications. As shown in FIGS. 7 and 8, an internal lid 30 includes a transverse circular plate-like portion 32 with longitudinal extending walls 34 extending around the periphery thereof for welding or otherwise sealing against the interior of cylindrical walls 16 when positioned or seated within hollow cylindrical lid seat portion 18 adjacent to the cylindrical block portion 14, after insertion of the cermet wires 200 into apertures 20, 22, 24, 26. As shown in FIG. 3, the outer cylindrical capsule 40 includes outer cylindrical walls 42 with an open end 44 and a closed end 46. The outer cylindrical capsule 40 forms a second or outer capsule structure, which is concentrically outward from the inner integrated cylindrical insert 12. The exterior portion of cylindrical walls 42 adjacent to open end 44 may include a circumferential chamfered portion 45 of slightly reduced diameter. The inner integrated cylindrical insert 12, including the cermet wires 200 and the internal lid 30, is inserted into the open end 44 of outer cylindrical capsule 40 so that internal lid 30 is urged against the closed end 46 of the outer cylindrical capsule 40. The closed external end 15 of solid cylindrical block portion 14 is positioned inwardly adjacent from the open end 44 of outer cylindrical capsule 40, thereby providing a cylindrical space or seat to receive outer lid 50 which is welded or otherwise scaled in place with respect to the interior of the outer cylindrical walls 42 inwardly adjacent from open end 44 and adjacent to closed external end 15 of inner integrated cylindrical insert 12, Outer lid 50 includes a transverse circular plate-like portion 52 with longitudinal extending walls 54 extending around the periphery thereof for engaging against the interior of outer cylindrical walls 42. Dimensions for an embodiment of the outer cylindrical capsule 40 are 17.20 millimeters in length and 7.825 millimeters in diameter. However, those skilled in the art, will recognize that other dimensions may be preferable for different applications. In operation, sealed neutron sources 10, typically surrounded by cladding (typically, but not limited to, zirconium, not shown) and configured as a start-up rod, are typically placed in regularly spaced positions among the fuel rods of a nuclear reactor which is being started up. In some applications, a mixture of ninety percent helium and ten percent air may be placed between the cladding (not shown) and the sealed neutron sources 10. The neutrons emanating from the Californium-252 initiate or increase the fission chain reaction within the fuel rods of the nuclear reactor. Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby.
050911465	abstract	In a fuel bundle for a boiling water reactor having one or more part length rods in the two phase region, a steam vent tube is introduced overlying the part length rods. The fuel bundle includes a lower tie plate for admitting water moderator and supporting a plurality of fuel rods in upstanding side-by-side relation, an upper tie plate for permitting water and steam to be discharged from the top of the fuel bundle and maintaining the fuel rods in upstanding side-by-side relation, a surrounding fuel channel for confining moderator flow along a path over the fuel rods and between the tie plates, and dispersed vertically intermittent spacers for maintaining the fuel rods in their designed side by side relation. One or more fuel rods extends from the lower tie plate vertically less than the full length to the upper tie plate ending interior of the fuel bundle at a disposition where the upper end of the part length rods is braced in the vertical position by a spacer. At least one of these partial length rods is provided with an overlying steam vent tube. This steam vent tube has openings and devices distributed along its length to encourage steam flow interior of the tube and remove liquid flow from the interior of the tube. The steam flow within the vent tube eliminates the interface drag between the steam interior of the tube and the surrounding water steam mixture. The presence of the steam vent tube as a high velocity steam escape path enables remaining portions of the fuel bundle to contain a higher liquid moderator fraction with flatter axial voids and power distributions during the operating state of the fuel bundle. The presence of high velocity escaping steam combined with distributed apertures along the length of the steam vent tube promotes resistance to fluid oscillations within the fuel bundles. Variations of steam vent tubes are disclosed including steam vent tubes overlying multiple clustered part length rods. There results a fuel bundle design in which the entire upper cross section of the fuel bundle is devoted to steam generation and coolant outflow.
	description	This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-301577 filed on Nov. 7, 2006, the entire contents of which are incorporated herein by reference. The present invention relates to a reflector control type fast reactor that controls a reactivity of a reactor core by vertically moving a reflector. FIG. 5 shows an example of a conventional fast reactor 1 disclosed in Japanese Patent Registration No. 3126524. As shown in FIG. 5, the conventional fast reactor 1 includes a reactor vessel 7 in which the fast reactor 1 is accommodated, and a reactor core 2 disposed in the reactor vessel 7 and loading thereon a fuel assembly. The reactor core 2 has generally a cylindrical shape. An outer circumference of the reactor core 2 is surrounded by a core barrel 3 that protects the reactor core 2. A reflector 4 is arranged outside the core barrel 3. The reflector 4 is connected to a reflector drive unit 12 through a drive shaft 11. The reflector 4 is capable of vertically moving around the reactor core by the reflector drive unit 12 so as to control a reactivity of the reactor core 2. Disposed outside the reflector 4 is a partition wall 6 surrounding the reflector 4 and forming an inner wall of a channel for a coolant 5. The channel for the coolant 5 is formed in a gap between the reactor vessel 7 and the partition wall 6. In the channel for the coolant 5 between the reactor vessel 7 and the partition wall 6, there is disposed a neutron shielding member 8 that surrounds the reactor core 2. The reactor core 2, the core barrel 3, the partition wall 6, and the neutron shielding member 8 are all placed on and supported by a reactor-core support plate 13. FIG. 6 shows an example of the structure of the reflector 4 disclosed in Japanese Patent Registration No. 3126502. The reflector 4 includes a neutron reflecting part 4a and a cavity part 4b integrally disposed on an upper portion of the neutron reflecting part 4a. The cavity part 4b is formed of a housing. An inside of the housing is filled with a gas 41 whose neutron reflecting ability is inferior to that of a coolant 5, or is maintained in a vacuum condition. Owing to the cavity part 4b, a reactivity can be suppressed, as compared with a case in which an outside of a core barrel 3 is covered with the coolant 5. Thus, enrichment of fuel can be increased, whereby a reactivity life of a reactor core 2 can be elongated. A reflector drive unit 12 is connected to an upper portion of the neutron reflecting part 4a through a drive shaft 11. In FIG. 6, the same parts as those in FIG. 5 are shown by the same reference numbers. A temperature of the coolant 5 in the fast reactor 1 is between about 350° C. and about 500° C. To be specific, the temperature of the coolant 5 is about 500° C. near the reactor core 2 inside the core barrel 3, and is about 350° C. near the neutron shielding member 8 outside the partition wall 6. Namely, the temperature of the coolant 5 near the core barrel 3 and the temperature of the coolant 5 near the partition wall 6 vary by about 150° C. In addition, since the coolant 5 is heated from about 350° C. to about 500° C, the temperature of the coolant 5 inside the core barrel 3 axially varies by about 150° C. In the neutron reflecting part 4a and the cavity part 4b of the reflector 4, since the temperature significantly varies in both the radial and the axial directions, the reflector 4 may be deformed by a thermal expansion difference. The deformed reflector 4 may come into contact with the core barrel 3 and/or the partition wall 6, when the reflector 4 is dropped down in order to urgently shut down the fast reactor 1. In this case, the reflector 4 may fail to fall down within a predetermined period of time. In addition, because of the temperature difference of the reflector 4, there is a possibility that a thermal stress and/or a creep generate in the reflector 4 to damage the neutron reflecting part 4a and/or the cavity part 4b of the reflector 4. The present invention has been made in view of the above circumstances. The object of the present invention is to provide a reliable fast reflector control type fast reactor having a reflector that is difficult to be deformed by a thermal expansion and/or a thermal stress, and thus has an excellent structural robustness. The present invention is a reflector control type fast reactor comprising: a reactor vessel accommodating therein a coolant; a reactor core disposed in the reactor vessel and immersed in the coolant; and a reflector that vertically moves for adjusting leakage of neutrons generated from the reactor core to control a reactivity of the reactor core, the reflector including a neutron reflecting part disposed on an outside of the reactor core in a vertically movable manner, and a cavity part positioned above the neutron reflecting part, the cavity part having a neutron reflecting ability lower than that of the coolant; wherein the neutron reflecting part is formed of a plurality of metal plates that are stacked on each other, and each of the metal plates has a plurality of coolant channels through which the coolant flows. The present invention is the reflector control type fast reactor wherein the number of the coolant channels in each of the metal plates per unit area increases from a side of the reactor vessel to a side of the reactor core. The present invention is the reflector control type fast reactor wherein the cavity part includes a frame, and a plurality of sealable containers of a box shape that are held in the frame. The present invention is the reflector control type fast reactor wherein the frame is formed of a plurality of frame units, and the respective frame units are connected to each other by a bolt. The present invention is the reflector control type fast reactor wherein the respective sealable containers are fitted to the adjacent sealable containers to be vertically connected to each other, or are fitted in an intermediate rib of the frame to be vertically connected to each other. The present invention is the reflector control type fast reactor wherein a resilient member(s) is (are) disposed between an upper end of the uppermost sealable container in the frame and an upper end of the frame, and/or between a lower end of the lowermost sealable container in the frame and a lower end of the frame. The present invention is the reflector control type fast reactor wherein a reflector drive unit is connected to an upper portion of the cavity part via a universal joint and a drive shaft, and the neutron reflecting part is connected to the cavity part via a universal joint. The present invention is the reflector control type fast reactor wherein a gap is formed between the neutron reflecting part and the cavity part. The present invention is the reflector control type fast reactor wherein a volume of the neutron reflecting part excluding the coolant channels is between 80% and 95% of a total volume of the neutron reflecting part. The present invention is the reflector control type fast reactor wherein a volume of a structural member constituting the cavity part is not less than 10% of a total volume of the cavity part. According to the present invention, with the use of a reflector including a neutron reflecting part that is formed by stacking a plurality of metal plates each having a plurality of coolant channels through which a coolant flows, there can be obtained the reflector which is difficult to be deformed by a thermal expansion and/or a thermal stress, and thus has an excellent structural robustness. Therefore, a reliable fast reflector control type fast reactor can be obtained. A first embodiment of a fast reactor 1 according to the present invention is described below with reference to the drawings. FIG. 1 and FIGS. 2(a) to 2(f) show the first embodiment of the present invention. As shown in FIG. 1, the fast reactor 1 includes: a reactor vessel 7 accommodating a coolant 5; a reactor core 2 disposed in the reactor vessel 7 and immersed in the coolant 5; and a reflector 4 disposed on an outside of the reactor core 2 in a vertically movable manner. The reflector core 4 vertically moves for adjusting leakage of neutrons from the reactor core 2 so as to control a reactivity of the reactor core 2. As shown in FIGS. 2(e) and 2(f), the reflector 4 has a neutron reflecting part 4awhose neutron reflective ability is higher than that of the coolant 5, and a cavity part 4b positioned above the neutron reflecting part 4a, the cavity part 4b having a neutron reflective ability lower than that of the coolant 5. FIG. 2(e) is a front view of the reflector 4 when viewed from a front side. FIG. 2(f) is a side view of the reflector 4 when viewed from a lateral side. FIG. 2(d) is a plan view of the reflector 4 when viewed from an upper side. As described above, since the neutron reflective ability of the neutron reflecting part 4a is higher than the neutron reflective ability of the coolant 5, a reaction of the reactor core 2 can be activated. Specifically, the neutron reflecting part 4 can reflect neutrons that have been released by a nuclear fission in the reactor core 2, so that the nuclear fission continues in the reactor core 2. On the other hand, since the neutron reflective ability of the cavity part 4b is lower than the neutron reflective ability of the coolant 5, neutrons that have been released by a nuclear fission in the reactor core 2 can transmit through the cavity part 4. Thus, a reaction of the reactor core 2 can be restrained. Therefore, a reactivity life of the reactor core 2 can be elongated. As shown in FIGS. 2(e) and 2(f), the neutron reflecting part 4a is formed of a plurality of metal plates 37 that are stacked on each other. As shown in FIG. 2(c), each metal plate 37 is equipped with a plurality of coolant channels 36 through which the coolant 5 flows. The number of the coolant channels 36 per unit area increases from a side of the reactor vessel 7 to a side of the reactor core 2. FIG. 2(c) is a cross-sectional view of the metal plate 37 of the neutron reflecting part 4a. As shown in FIG. 1, a core barrel 3 is disposed on an outside of the reactor core 2. As also shown in FIG. 1, the reactor vessel 7 is covered with a guard vessel 9. A fuel assembly 32 is loaded in the reactor core 2. As shown FIG. 1 and FIGS. 2(e) and 2(f), a drive shaft 11 is connected to an upper portion of the cavity part 4b via a universal joint 44u and a joint 35. A reflector drive unit 12 is connected to an upper end of the drive shaft 11. The neutron reflecting part 4a is connected to the cavity part 4b via a universal joint 44l. As shown in FIG. 1, an upper end periphery of the drive shaft 11 is covered with an upper plug 10. As shown in FIG. 1, disposed on an outside of the reflector 4 is a partition wall 6 that surrounds the reflector 4 and forms an inner wall of a channel for the coolant 5. The reactor vessel 7 disposed on an outside of the partition wall 6 to be spaced apart therefrom forms an outer wall of the channel for the coolant 5. In the channel for the coolant 5, a neutron shielding member 8 is arranged to surround the reactor core 2. The reactor core 2, the core barrel 3, the partition wall 6, and the neutron shielding member 8 are all placed on and supported by a reactor-core support plate 13. The reactor-core support plate 13 is supported from below by a reactor-core support table 34 fixed on an inner periphery of the reactor vessel 7. As shown in FIG. 1, a drive unit for reactor shut-down rod 27 is disposed on an upper surface of the upper plug 10. A downwardly extending reactor shut-down rod 26 is connected to the drive unit for reactor shut-down rod 27. The drive unit for reactor shut-down rod 27 and the reflector drive unit 12 are covered with an accommodating dome 28. The accommodating dome 28 is located on a seat 31. As shown in FIG. 1, disposed in the reactor vessel 7 are an electromagnetic pump 14 for circulating the coolant 5, and an intermediate heat exchanger 15 for exchanging a heat of the coolant 5 in the reactor vessel 7. To an upper portion of the reactor vessel 7, there are connected an inlet nozzle 18 for introducing the coolant 5 into the reactor vessel 7, and an outlet nozzle 19 for introducing the coolant 5 to an outside of the reactor vessel 7. As shown in FIGS. 2(c), 2(e), and 2(f), the respective metal plates 37 are arranged in position by a plurality of pins 38 such that the coolant channels 36 pass through the metal plates 37. The metal plates 37 are connected to each other by vertically extending connecting rods 39. On the other hand, as shown in FIGS. 2(a) and 2(b), the cavity part 4b has a frame 42 constituted by beams and plates, and a plurality of sealable containers 40 of a box shape held in the frame 42. An inside of each sealable container 40 may be filled with a gas 41 whose neutron reflective ability is inferior to that of the primary coolant 5, or may be maintained in a vacuum condition. In FIGS. 2(e) and 2(f), the sealable containers 40 are arranged in two columns and five levels, i.e., the ten sealable containers 40 are laid and held in the frame 42. FIG. 2(a) is a perspective view of the sealable container 40, and FIG. 2(b) is a cross-sectional view of the cavity part 4b. As described above, not limited to the gas 41 whose neutron reflective ability is inferior to that of the primary coolant 5, each sealable container 40 may be filled with a metal, such as boron, hafnium, and tantalum, whose neutron reflective ability is inferior to that of the primary coolant 5, or a compound of these metals. As shown in FIGS. 2(e) and 2(f), a resilient member 43 is disposed between an upper end 40u of each uppermost sealable container 40 arranged in the frame 42 and an upper end 42u of the frame 42. A coil spring, a disc spring, or a flat spring may be used as the resilient member 43. In FIGS. 2(e) and 2(f), a load acting on the sealable containers 40 from the resilient member 43 is small. Since a load for suspending the neutron reflecting part 4a acts on the frame 42, a load acting on the sealable containers 40 is sufficiently small. Thus, a mechanical load acting on the sealable containers 40 excluding an external pressure exerted by the primary coolant 5 can be suppressed, to thereby ensure a robustness of each sealable container 40. As shown in FIGS. 2(e) and 2(f), the resilient member 43 is disposed between the upper end 40u of the uppermost sealable container 40 in the frame 42 and the upper end 42u of the frame 42. However, not limited thereto, the resilient member 43 may be disposed between a lower end of the lowermost sealable container 40 in the frame 42 and a lower end of the frame 42. As shown in FIGS. 2(e) and 2(f), a gap G is formed between the neutron reflecting part 4a and the cavity part 4b. Thus, the coolant 5, which has flown from below the neutron reflecting part 4a of the reflector 4 into the coolant channels 36 in the neutron reflecting part 4a, can flow outward of the neutron reflecting part 4a through the gap G. The universal joint 44l is mounted on a central portion of the gap G. The neutron reflecting part 4a has a function of controlling a reactivity of the reactor core 2, by preventing leakage of neutrons from the reactor core 2. However, if the neutron reflecting part 4a includes too many coolant channels 36 whereby a volume of the neutron reflecting part 4a excluding the coolant channels 36 is not more than 80% of a total volume of the neutron reflecting part 4a, leakage of neutrons cannot be satisfactorily prevented. Thus, it is preferable that the volume of the neutron reflecting part 4b excluding the coolant channels 36 is between 80% and 95% of the total volume of the neutron reflecting part 4a. Since the neutron reflective ability of the cavity part 4b is lower than that of the coolant 5, the cavity part 4b can more effectively suppress a reactivity of the reactor core 2, as compared with a case in which the reactor core 2 is covered with the coolant 5. However, when a volume of a structural member constituting the cavity part 4b is not less than 10% of a total volume of the cavity part 4b, the neutron reflective ability is increased so that the cavity part 4b cannot satisfactorily exert its function. Thus, it is preferable that the volume of the structural member constituting the cavity part 4b is not more than 10% of the total volume of the cavity part 4b. Next, an operation of the embodiment as constituted above is described. At first, the coolant 5 flows into the reactor vessel 7 through the inlet nozzle 18 (see, FIG. 1). Then, the coolant 5 moves downward in the reactor vessel 7 to flow into the reactor core 5 by a driving force of the electromagnetic pump 1 (see, FIG. 1). The coolant 5, which has flown into the reactor core 2, absorbs the heat generated by a nuclear fission of the fuel assembly 32 in the reactor core 2, and then the coolant 5 is heated (see, FIG. 1). At this time, the reflector 4 is vertically driven by the reflector driving unit 12 to adjust leakage of neutrons from the reactor core 2, so as to control a reactivity of the reactor core (see, FIG. 1). The neutron reflecting part 4a interacts neutrons generated from the reactor core 2 to generate a γ heat. As shown in FIGS. 2(e) and 2(f), since the neutron reflecting part 4a is formed by stacking the metal plates 37, a thermal expansion and/or a thermal stress generated in the respective metal plates 37 can be dispersed. Thus, distortion of the overall neuron reflecting part 4a can be suppressed. As shown in FIGS. 2(e) and 2(f), the drive shaft 11 and the cavity part 4b are connected to each other through the universal joint 44u, and the cavity part 4b and the neutron reflecting part 4a are connected to each other through the universal joint 44l, whereby an articulated structure is provided. Thus, it is possible to restrain warping which may be caused by a thermal expansion because of temperature difference in the radial direction and the vertical direction of the reactor. Therefore, deformation of the neutron reflecting part 4a and the cavity part 4b can be more effectively prevented. As shown in FIGS. 2(e) and 2(f), the resilient members 43 are disposed between the upper ends 40u of the uppermost sealable containers 40 in the frame 42 and the upper end 42u of the frame 42. Thus, it is possible to absorb a vertical thermal expansion difference between the frame 42 and the sealable containers 40, and a vertical displacement of the sealable containers 40 caused by a thermal expansion of the gas in the sealable containers 40. Then, the coolant 5 heated in the reactor core 2 raises on an inner peripheral side of the partition wall 6 to reach the intermediate heat exchanger 15 (see, FIG. 1). At this time, the coolant 5 passes through the coolant channels 36 in the metal plates 37 of the neutron reflecting part 4a (see, FIGS. 1 and 2(c)). Thus, the coolant 5 cools the γ heat generated by the interaction of the neutrons and the neutron reflecting part 4a, so that a material temperature of the neutron reflecting part 4a can be lowered. As a result, it is possible to prevent deformation of the neutron reflecting part 4a caused by a thermal expansion difference. As shown in FIG. 2(c), the number of coolant channels 36 in each metal plate 37 per unit area increases from the side of the reactor vessel 7 to the side of the reactor core 2. Thus, the γ heat mainly generated near the reactor core 2 can be effectively cooled, so that the temperature of the whole metal plate 37 can be made uniform. As a consequence, deformation of the metal plate 37 caused by a thermal expansion difference can be restrained. Then, the heat of the coolant 5 is exchanged, so that the coolant 5 is cooled (see, FIG. 1). The secondary coolant that has been thermally exchanged becomes vapor to rotate a turbine (not shown) so as to generate electricity. Then, the cooled coolant 5 is moved by a driving force of the electromagnetic pump 14 to be discharged outside through the outlet nozzle 19 (see, FIG. 1). The thus discharged coolant 5 is again allowed to flow through the inlet nozzle 18 to repeat circulation. As shown in FIGS. 2(e) and 2(f), the neutron reflecting part 4a is formed of the stacked metal plates 37 that are connected to each other simply by the pins 38 and the connecting rods 39. Thus, in accordance with a circumstance where the neutron reflecting part 4a is used, the number of metal plates 37 can be suitably adjusted to thereby achieve manufacturing facility. As described above, the drive shaft 11 and the cavity part 4b are connected to each other through the universal joint 44u, and the cavity part 4b and the neutron reflecting part 4a are connected to each other through the universal joint 44l, whereby an articulated structure is provided (see, FIGS. 2(e) and 2(f)). Thus, when the fast reactor 1 is urgently shut down, if the reflector 4 comes into contact with the core barrel 3 and the partition wall 6, the neutron reflecting part 4a and the cavity part 4b can be readily inclined due to the provision of the universal joints 44l and 44u. Therefore, the reflector 4 can be dropped down within a predetermined period of time. As shown in FIGS. 2(a) to 2(f), the cavity part 4b includes the independent sealable containers 40. Thus, even if one of the sealable containers 40 is cracked or the like to invite leakage of the coolant 5 into the sealable container 40 so that the low neutron reflecting ability of the sealable container 40 cannot be maintained, influences on the reaction controllability for the reactor core 2 can be held to a minimum. Next, a second embodiment of the present invention is described with reference to FIGS. 3(a) to 3(d). In the second embodiment shown in FIGS. 3(a) to 3(d), a frame 42 is composed of a plurality of frame units 42a which are connected to each other by bolts 46. Other structures of the second embodiment are substantially the same as those of the first embodiment shown in FIG. 1 and FIGS. 2(a) to 2(f). In the second embodiment shown in FIGS. 3(a) to 3(d), the same parts as those in the first embodiment shown in FIG. 1 and FIGS. 2(a) to 2(f) are shown by the same reference numbers, and the detailed description thereof is omitted. FIG. 3(b) is an enlarged view of an upper end area of a cavity part 4b. FIG. 3 (d) is an enlarged view of a lower end area of the cavity part 4b. FIG. 3(c) is an enlarged view of an intermediate portion between the upper end and the lower end of the cavity part 4b. The frame 42 shown in FIGS. 3(a) to 3(d) has to have a strength sufficient for holding sealable containers 40. Since the frame 42 of the cavity part 4b is positioned near the reactor core 2, the frame 42 is prone to undergo swelling and/or degradation in toughness of material, under the influence of radiations. Thus, it is generally to use, as a material of the frame 42, chromium-molybdenum steel, in particular, 9Cr-1Mo steel or 9Cr-1Mo-V steel obtained by improving the 9Cr-1Mo steel, which material is excellent in high-temperature strength and radio-resistance. The frame 42 is generally manufactured by welding. However, since the chromium-molybdenum steel is a material that can be easily cracked during welding, there is a possibility that the frame 42 manufactured by welding has a degraded strength, and, in consequence, the frame 42 is broken. In addition, when the frame 42 is manufactured by welding, the frame 42 has to be subjected to a preheating process before welding and a heating process after welding, which results in increase in manufacturing cost and equipment cost of the frame 42. On the other hand, the frame 42 of the present invention is manufactured by connecting the respective frame units 42a by the bolts 46. Thus, a strength of the frame 42 can be improved, while increase in manufacturing cost and equipment cost can be inhibited. Further, since the respective frame units 42a are connected by the bolts 46, it is easy to disassemble, check, and exchange the frame 42. Next, a third embodiment of the present invention is described with reference to FIG. 4A. In the third embodiment shown in FIG. 4A, sealable containers 40 are fitted in intermediate ribs 42m of a frame 42 to be vertically connected to each other. Other structures of the third embodiment are substantially the same as those of the first embodiment shown in FIG. 1 and FIGS. 2(a) to 2(f)). In the third embodiment shown in FIG. 4A, the same parts as those in the first embodiment shown in FIG. 1 and FIGS. 2(a) to 2(f) are shown by the same reference numbers, and the detailed description thereof is omitted. In FIG. 4A, the sealable containers 40 are fitted in the intermediate ribs 42m of the frame 42 to be vertically connected to each. More specifically, each intermediate rib 42m of the frame 42 is provided with an opening 42p. Each sealable container 40 is provided with an upper projection 40a disposed on an upper end thereof, and a lower projection 40b disposed on a lower end thereof. By fitting the upper projection 40a and the lower projection 40b of the sealable container 40 in the openings 42p of the intermediate ribs 42m, the sealable containers 40 are vertically connected to each other. Due to this structure, not only a vertical movement of the sealable containers 40 but also a horizontal movement thereof can be suitably restricted. There is a possibility that, when a reflector 4 is installed, when a reactor is operated, and when the reactor is urgently shut down, for example, the reflector 4 excessively vibrates and swings. However, collision of the sealable containers 40 and contact of the sealable containers 40 with a core barrel 3 and a partition wall 6 can be prevented. Consequently, breakage of the sealable containers 40 can be prevented. (Modification) Next, a modification of the third embodiment of the present invention is described with reference to FIG. 4B. In the modification of the third embodiment shown in FIG. 4B, sealable containers 40 are fitted to the adjacent sealable containers 40 to be vertically connected to each other. Other structures of the third embodiment are substantially the same as those of the first embodiment shown in FIG. 1 and FIGS. 2(a) to 2(f)). In the modification of the third embodiment shown in FIG. 4B, the same parts as those in the first embodiment shown in FIG. 1 and FIGS. 2(a) to 2(f) are shown by the same reference numbers, and the detailed description thereof is omitted. In FIG. 4B, the sealable containers 40 are fitted to the adjacent sealable containers 40 to be vertically connected to each other. More specifically, each sealable container 40 is provided with an upper projection 40a disposed on an upper end thereof, and a lower recess 40p disposed in a lower end thereof. The upper projection 40a of the sealable container 40 is fitted in the lower recess 40p of the upwardly adjacent sealable container 40, and the lower recess 40p of the sealable container 40 is fitted to the upper projection 40a of the downwardly adjacent sealable container 40. Also due to this structure, not only a vertical movement of the sealable containers 40 but also a horizontal movement thereof can be suitably restricted. There is a possibility that, when a reflector 4 is installed, when a reactor is operated, and when the reactor is urgently shut down, for example, the reflector 4 excessively vibrates and swings. However, collision of the sealable containers 40 and contact of the sealable containers 40 with a core barrel 3 and a partition wall 6 can be prevented. Consequently, breakage of the sealable containers 40 can be prevented.
	summary
046738142	claims	1. A container for receiving and safely storing radioactive materials or other materials damaging to living organisms such as vitrified radioactive fission products or irradiated nuclear reactor fuel elements, the container comprising: a vessel for receiving the materials to be stored therein, the vessel including a base and a wall extending upwardly from said base, said wall terminating in a circular rim defining the opening of the vessel through which the materials to be stored therein are passed, said wall defining an inner wall surface having an upper surface portion diverging outwardly away from the remainder of said inner wall surface to define a conical seating surface communicating with said rim; a sealing cover pressable into said vessel thereby exerting a radial force thereagainst and closing off the latter from the ambient, said cover having a massive unyielding peripheral portion defining an outer peripheral surface for engaging said vessel seating surface when the sealing cover is pressed into said vessel, said peripheral surface converging toward the interior of said vessel to define a conical surface having a taper corresponding to the taper of said vessel seating surface whereby said conical surfaces coact to provide a seal fit between said vessel and said sealing cover; said wall of said vessel having a thickness at said conical sealing surface thereof selected to permit said wall to respond to said radial force to fit approximately evenly to said conical surface of said cover thereby contributing to the integrity of said seal fit; said conical surface being smooth and uninterrupted so as to unrestrictingly receive said cover thereagainst as the latter is pressed downwardly into said vessel so as to permit development of said radial force fit; and, a weld joining said sealing cover to said vessel, said weld being in the form of a fused-mass joint extending around the entire periphery of said sealing cover. a vessel for receiving the materials to be stored therein, the vessel including a base and a wall extending upwardly from said base, said wall terminating in a circular rim defining the opening of the vessel through which the materials to be stored therein are passed, said wall defining an inner wall surface having an upper surface portion diverging outwardly away from the remainder of said inner wall surface to define a conical seating surface communicating with said rim; a sealing cover pressable into said vessel thereby exerting a radial force thereagainst and closing off the latter from the ambient, said cover having a massive unyielding peripheral portion defining an outer peripheral surface for engaging said vessel seating surface when the sealing cover is pressed into said vessel, said peripheral surface converging toward the interior of said vessel to define a conical surface having a taper corresponding to the taper of said vessel seating surface whereby said conical surfaces coact to provide a seal fit between said vessel and said sealing cover; said wall of said vessel having a thickness at said conical sealing surface thereof selected to permit said wall to respond to said radial force to fit approximately evenly to said conical surface of said cover thereby contributing to the integrity of said seal fit; said conical surface being smooth and uninterrupted so as to unrestrictingly receive said cover thereagainst as the latter is pressed downwardly into said vessel so as to permit development of said radial force fit; the upper portion of said cover outer peripheral surface diverging away from the remainder thereof to define a cylindrical surface, said cylindrical surface and said conical seating surface conjointly defining an annular groove of wedge-shaped section for receiving a bevel weld therein; said cover further having a top peripheral edge contiguous with said cylindrical surface thereof; and said top peripheral edge and the portion of said conical seating surface of said vessel above the level of said top peripheral edge conjointly defining an annular fillet for receiving a fillet weld therein. a first portion defining an annular bevel weld filling in said annular groove of wedge-shaped section; and, a second portion defining an annular fillet weld disposed in said fillet conjointly defined by said top peripheral edge of said cover and the remainder of said conical seating surface of said vessel above said bevel weld. a vessel for receiving the materials to be stored therein, the vessel including a base and a wall extending upwardly from said base, said wall terminating in a circular rim defining the opening of the vessel through which the materials to be stored therein are passed, said wall defining an inner wall surface having an upper surface portion diverging outwardly away from the remainder of said inner wall surface to define a conical seating surface communicating with said rim; a sealing cover pressable into said vessel thereby exerting a radial force thereagainst and closing off the latter from the ambient, said cover having a massive unyielding peripheral portion defining an outer peripheral surface for engaging said vessel seating surface when the sealing cover is pressed into said vessel, said peripheral surface converging toward the interior of said vessel to define a conical surface having a taper corresponding to the taper of said vessel seating surface whereby said conical surfaces coact to provide a seal fit between said vessel and said sealing cover; said wall of said vessel having a thickness at said conical seating surface thereof selected to permit said wall to respond to said radial force to fit approximately evenly to said conical surface of said cover thereby contributing to the integrity of said seal fit; said conical surface being smooth and uninterrupted so as to unrestrictingly receive said cover thereagainst as the latter is pressed downwardly into said vessel so as to permit development of said radial force fit; the upper portion of said cover outer peripheral surface diverging away from the remainder thereof to define a cylindrical surface, said cylindrical surface and said conical seating surface conjointly defining an annular groove of wedge-shaped section; said cover further having a top peripheral edge contiguous with said cylindrical surface thereof; and said top peripheral edge and the portion of said conical seating surface of said vessel above the level of said top peripheral edge conjointly defining an annular fillet; and, weld means for joining said cover to said vessel about the periphery of said cover, said weld means including: a first portion defining an annular bevel weld filling in said annular groove of said wedge-shaped section; and, a second portion defining an annular fillet weld disposed in said fillet conjointly defined by said top peripheral edge of said cover and the remainder of said conical seating surface of said vessel above said bevel weld. conically widening the inner bore of the vessel at the end thereof at said opening to define a clear uninterrupted conical seating surface; turning the outer peripheral surface of the cover to have a conical surface having the same taper as the taper of said seating surface; turning the upper portion of said outer peripheral surface to define a cylindrical surface; pressing said cover down onto said conical seating surface to exert a radial force thereagainst so as to cause said wall to respond and fit approximately evenly to said conical surface of said cover thereby contributing to the integrity of said seal fit; said cover being pressed downwardly to a depth below the rim of said vessel after filling said vessel with the materials to be stored thereby defining an annular groove of wedge-shaped section; joining the cover to said vessel by means of a gas-shielded arc weld while maintaining an equalization of pressure between the interior of the container and the ambient, the flow of shielding gas being directed from above into the annular gap of wedge-shaped section and the weld having a first portion defining an annular bevel weld filling in said annular groove of wedge-shaped section; and, a second portion defining an annular fillet weld disposed in the fillet defined by the top peripheral edge surface of the cover and the remainder of the conical seating surface of the vessel above the bevel weld; and, discontinuing the maintenance of said equalization of pressure after completing the welding step. 2. The container of claim 1 wherein: said sealing cover has an upper edge communicating with said sealing cover peripheral surface, said upper edge being disposed beneath said rim; and said weld being a fillet weld mutually joining said rim and said upper edge. 3. The container of claims 1 or 2 wherein: the upper portion of said cover outer peripheral surface diverges away from the remainder thereof to define a cylindrical surface, said cylindrical surface and said conical seating surface conjointly defining an annular groove of wedge-shaped section for receiving at least a portion of said weld therein. 4. The container of claim 3 comprising: a valve mounted on the sealing cover so as to be accessible outside of the container, said valve communicating with the interior of said vessel and having test-gas connection means connectable to a source of test gas. 5. The container of claim 4 wherein: said sealing cover has a projection extending upwardly therefrom, said projection having a recess formed therein for accommodating said valve. 6. The container of claim 5 comprising: a plug engageable with said projection for closing off said recess. 7. The container of claim 5, said projection having a cylindrical configuration and having a thread formed on the PG,14 lower end thereof; and, said sealing cover having a central threaded bore formed therein for threadably engaging said cylindrical projection. 8. The container of claim 7 wherein: the projection is further configured as a knob. 9. A container for receiving and safely storing radioactive materials or other materials damaging to living organisms such as vitrified radioactive fission products or irradiated nuclear reactor fuel elements, the container comprising: 10. The container of claim 9 comprising: weld means for joining said cover to said vessel about the periphery of said cover, said weld means including: 11. A container for receiving and safely storing radioactive materials or other materials damaging to living organisms such as vitrified radioactive fission products or irradiated nuclear reactor fuel elements, the container comprising: 12. A method for tightly sealing a container for receiving and safely storing radioactive materials or other materials damaging to living organisms such as vitrified radioactive fission products or irradiated nuclear reactor fuel elements, the container including a vessel having a circular opening and a cover seated in said opening, the method including the steps of:
055915647	summary	TECHNICAL FIELD OF THE INVENTION The present invention relates to techniques for manufacturing semiconductor devices and, more particularly, to techniques for forming patterned features on a semiconductor device. BACKGROUND OF THE INVENTION Photolithography is a common technique employed in the manufacture of semiconductor devices. Typically, a semiconductor wafer is coated with a layer of light sensitive resist material (photoresist). Using a patterned mask or reticle, the wafer is exposed to projected light from an illumination source, typically actinic light, which manifests a photochemical effect on the photoresist, which is ultimately (typically) chemically etched away, leaving a pattern of photoresist "lines" on the wafer corresponding to the pattern on the mask or reticle. The patterned photoresist on the wafer is also referred to as a mask, and the pattern in the photoresist mask replicates the pattern on the image mask (or reticle). As used in the main, hereinafter, with respect to semiconductor lithography, the term "upstream" means towards the illumination or radiation source, and "downstream" means away from the illumination source (or, towards the wafer). For example, a lens in the illumination path of photolithographic apparatus has an upstream side facing the illumination source and a downstream side facing away from the illumination source. FIG. 1 shows a simplified prior-art photolithographic apparatus 110 for exposing a semiconductor wafer (W), more particularly a coating thereon (e.g., photoresist), to light. An optical path is defined from left to right in FIG. 1, as viewed. Prior to exposure, the semiconductor wafer (W) typically receives on its front surface a layer of photoreactive material (not shown), such as photoresist. A light source 112 emits actinic light, and may be backed up by a reflector 114. Light emitted by the light source typically passes through a uniformizer 116, such as a "fly's eye" lens or a light pipe. Light exiting the uniformizer 116 is represented by rays 118a, 118b, and 118c, and passes through a condenser lens 120. The ray 118b represents the optical axis of the photolithographic apparatus. The light source 112, reflector 114, uniformizer 116 and condenser lens 120 form what is termed an "illuminator", which is often detachable as a unit from the photolithographic apparatus. An image mask 122 ("M") is disposed "downstream" of the condenser lens 120, at the focal plane (point) thereof. One type of image mask used in the photolithography process is a chromed glass or quartz plate bearing the pattern to be projected onto the photoresist layer. Light is projected through the image mask, and those areas of the image mask which are not chromed allow the light to expose the photoresist, while those areas of the image mask which are chromed prevent the light from exposing the photoresist. The exposed areas of the photoresist typically resist chemical etching, while the unexposed areas can readily be removed, leaving a pattern of photoresist on the surface of the wafer. Further downstream along the light path, the rays diverge from the mask 122, and pass through a "taking" (imaging) lens 124. Because of its imaging function, the taking lens 124 must be of relatively high quality as compared with the condenser lens 120. The mask 122 is disposed at a common focal point of the two lenses 120 and 124. A semiconductor wafer (W) is disposed at the "downstream" focal plane, or image plane, of the taking lens 124. Those areas of the mask (or reticle) which are not chromed allow the light to expose a photoreactive layer (e.g., photoresist) on the surface of the wafer (W), while those areas of the mask which are chromed (or otherwise opaquely patterned) prevent the light from exposing the photo-reactive layer. The photoreactive layer is typically a photoresist material. The exposed areas of the photoresist resist chemical etching and, in subsequent processing, are used to form defined features on the wafer (such as on a layer of polysilicon underling the photoresist). The resist materials used in photolithography are typically organic. Typical resist materials for visible light photolithography include mixtures of a casting solvent, such as ethyl lactate, and novolac resin (diazoquinone). Inasmuch as the light passing through the image mask (reticle) has an inherent characteristic that induces photochemical activity in the photoresist material, such radiation (e.g., light) is termed "actinic". In current photolithographic apparatus, light having at least a substantial visible content is typically employed. Visible light has a frequency on the order of 10.sup.15 Hz (Hertz), and a wavelength on the order of 10.sup.-6 -10.sup.-7 meters. The following terms are well established: 1 .mu.m (micrometer) is 10.sup.-6 meters; 1 nm (nanometer) is 10.sup.-9 meters; and 1 .ANG. (Angstrom) is 10.sup.-10 meters. Among the problems encountered in photolithography are non-uniformity of source illumination and point-to-point reflectivity variations of photoresist films. Both of these features of current photolithography impose undesirable constraints on further miniaturization of integrated circuits. Small and uniformly sized features are, quite evidently, the object of prolonged endeavor in the field of integrated circuit design. Generally, smaller is faster, and the smaller the features that can be reliably fabricated, the more complex the integrated circuit can be. With regard to uniformity of source illumination, attention is directed to commonly-owned U.S. Pat. No. 5,055,871, issued to Pasch. As noted in that patent, non-uniformities in the illuminating source will result in non-uniformities of critical dimensions (cd) of features (e.g., lines) formed on the semiconductor device, and the illumination uniformity of photolithographic apparatus will often set a limit to how small a feature can be formed. There usually being a small "error budget" associated with any integrated circuit design, even small variations in illumination intensity can be anathema to the design goals. With regard to reflectivity of photoresist films, it has been observed that minor thickness variations in a photoresist film will cause pronounced local variations in how efficiently the illuminating light is absorbed (actinically) by the photoresist film, which consequently can adversely affect the uniformity of critical dimensions (cd) of features (such as polysilicon lines or gates) sought to be formed in a layer underlying the photoresist. This problem is addressed in commonly-owned, copending U.S. patent application No. 07/906,902, filed Jun. 29, 1992 by Michael D. Rostoker, which discussed techniques for applying a substantially uniform thickness layer of photoresist, and which is incorporated by reference herein. Another, more serious problem with photolithography is one of its inherent resolution. The cd's of the smallest features of today's densest integrated circuits are already at sub-micron level (a "micron" or ".mu.m" is one millionth of a meter). Such features are only slightly larger than a single wavelength of visible light, severely pushing the limits of the ability of visible light techniques to resolve those features. As integrated circuit features become smaller, the demand for more nearly "perfect" optical components increases. At some point, however, such optics become impractical and inordinately expensive, or even impossible to produce. Although the resolving power of light, vis-a-vis submicron semiconductor features, is being stretched to its limit, the ability to etch (wet, dry, chemical, plasma) features on a semiconductor wafer is not limited by wavelength. As is well known, ultraviolet light (UV) is slightly higher (in frequency) on the electromagnetic spectrum than visible light. Typically, ultraviolet light has a frequency on the order of 10.sup.15 -10.sup.17 Hz, and has a wavelength on the order of 10.sup.-7 -10.sup.-8 meters. Ultraviolet light is known to be actinic, for example with respect to skin pigmentation. Due to its shorter (than visible light) wavelength, ultraviolet light would seem to hold promise for increased resolution in integrated circuit photolithography. However, it is difficult to find reliable, fluent sources of UV (typically vacuum UV) light. Further, the performance of present day optics begins to degrade substantially at around 190 nm (1.9.times.10.sup.-7 meters; which is towards the top of the visible light spectrum), and is not well suited for focusing UV light. In contrast to visible light, X-rays have a much shorter wavelength. Typically, X-rays have a frequency on the order of 10.sup.17 -10.sup.20 Hz, and have a wavelength on the order of 10.sup.-8 -10.sup.-11 meters. Evidently, due to their shorter wavelength, X-rays have the inherent capability of providing better resolution than visible light. However, as with UV sources, there are some problems with obtaining reliable emission sources that exhibit good fluence. The best (most intense) X-ray sources (e.g., X-ray tubes) produce X-rays in the range of 1-10 .ANG. in wavelength, with a nominal output spectrum between 2 .ANG. and 6 .ANG. in wavelength. Gamma-rays exhibit an even shorter wavelength than X-rays. Typically, Gamma-rays have a frequency on the order of 10.sup.19 -10.sup.22 Hz, and have a wavelength on the order of 10.sup.-10 -10.sup.-12 meters. Evidently, Gamma-rays provide the potential for even better resolution than X-rays. Furthermore, gamma-ray sources providing intense streams of fluent emission are readily available, such as in the form of Cobalt-60. In the absence of the novel viable gamma-ray and X-ray semiconductor-processing techniques disclosed herein, various techniques for "stretching" the resolution of UV and visible light techniques have been contemplated. One such technique provides a method of forming short-channel polysilicon gates (0.6 .mu.m polysilicon feature size). (See, for example, U.S. Pat. No. 5,139,904, issued Aug. 18, 1992 to Auda et al.) This method employs a technique of laying down a layer of conventional photoresist over a polysilicon layer and patterning the photoresist to "normal" dimensions (greater than the ultimately desired 0.6 .mu.m dimension). The photo-resist pattern is then uniformly eroded in all dimensions using an isotropic (non-directional) RIE (reactive ion etching) etch process. The size of features in the photo-resist pattern is carefully monitored during the etch process. When the pattern features are eroded to the desired size, the etch process is stopped. An anisotropic (highly directional) etch process is used to etch away portions of the underlying polysilicon outside of the "shadow" of the eroded photo-resist pattern (relative to a generally vertical etch direction). While this technique may be employed to produce small polysilicon structures, it has the same limitations as conventional photolithography with respect to line-to-line spacing. Because the photoresist is initially patterned to "conventional" dimensions, it is not possible with such "stretched" techniques to space pattern features substantially closer with sufficient resolution than is ordinarily possible with conventional photolithography. DISCLOSURE OF THE INVENTION It is therefore an object of the present invention to provide improved techniques for fabricating semiconductor devices. It is another object of the present invention to provide improved techniques for forming ultra-fine features on a semiconductor device. It is another object of the present invention to provide techniques for forming features on a semiconductor device which are not limited by the resolving power of light. It is another object of the present invention to provide wafer processing techniques which yield improved critical dimensions (cd's) in semiconductor features. It is another object of the present invention to provide techniques capable of resolving smaller features (such as polysilicon or metal lines). It is another object of the present invention to provide near-field afocal techniques for processing semiconductor wafers. It is another object of the present invention to provide X-ray lithographic techniques. It is another object of the present invention to provide gamma ray lithographic techniques. It is another object of the present invention to provide means for "shuttering" gamma rays or X-rays. As used herein, the term "lithography" refers to any technique which is employed to define features on a semiconductor wafer, for example patterning photoresist overlying a layer that will subsequently be etched. Generally, all of the lithography techniques discussed hereinbelow employ some form of illumination (or radiating) source. According to the invention, lithography is performed on a semiconductor device using electromagnetic energy of shorter, or of substantially shorter wavelength, than visible or UV light. In one embodiment of the invention, X-rays are used as the illumination (radiation) source. According to an aspect of the invention, Beryllium is used as transparent image mask substrate for imaging X-rays onto a semiconductor wafer. Beryllium has excellent transparency to X-rays, and since it is a metal itself, carriers and opaque masking materials can be readily provided which have similar expansion coefficients, resulting in relatively low distortion of the mask. According to various aspects of the invention, Gold, Tungsten, Platinum, Barium, Lead, Iridium, or Rhodium are used as opaque mask materials to be deposited over a Beryllium substrate (image mask). All of these materials exhibit excellent opacity to X-rays. Further, these materials exhibit adequate adhesion to Beryllium (the image mask substrate) and adequate environmental robustness for utility as lithographic image masks. The resulting image mask (beryllium substrate with a pattern of opaque lines on a surface thereof) is suitably employed for "near field" lithography. By "near field" it is meant that the process is afocal, and by spacing the image mask close to the semiconductor wafer there is limited opportunity for the radiation passing through the image mask to spread. In another embodiment of the invention, Gamma-rays are used as the lithographic illumination source. According to an aspect of the invention, "base" organic resist materials applied to the semiconductor die (wafer) are doped either with organic or with inorganic materials (dopants) which exhibit high absorptivity to gamma-rays, to enhance the sensitivity of the resist material. Preferably, the dopant is inorganic. Examples of organic dopants include polystyrene, phenolformaldehyde, polyurethane, etc.. Examples of inorganic dopants include bromine, chromium, tantalum, gold, platinum, palladium, lead, barium, boron, aluminum and magnesium. The dopants are highly reactive to incident gamma radiation, and produce secondary photon emissions of a different wavelength (longer) than that of the incident gamma rays. The organic resist base, which is not ordinarily reactive to gamma radiation, is however highly absorptive of these secondary emissions (from the dopants), which are actinic with respect to the organic resist base, thereby causing the resist base to become chemically converted. The high cross-section (absorptivity) of the organic resist base to the secondary emissions also limits the amount of "blooming" (spreading) inherent in the secondary emissions. According to another aspect of the invention, an organic resist material has an absorptive (to gamma radiation) film of material disposed on a surface thereof. The film atop the photoresist is organic or inorganic, preferably inorganic, and provides secondary emissions (photons) which convert the underlying photoresist. The film is termed a "secondary resist layer". Examples of organic resist materials suitable for the secondary resist layer include polystyrene, phenolformaldehyde, polyurethane, etc.. Examples of inorganic secondary resist materials suitable for the secondary resist layer include bromine, chromium, tantalum, gold, platinum, palladium, lead, barium, boron, aluminum and magnesium. The secondary resist layer, when exposed to gamma radiation, produces secondary photon emissions of a different wavelength (longer) than that of the incident gamma rays. The underlying organic resist material is highly absorptive of these secondary emissions, which are actinic with respect to the organic resist, causing it to become chemically converted. The high cross-section (absorptivity) of the underlying organic resist to the secondary emissions, and its close juxtaposition to the overlying secondary resist film, limit the amount of "blooming" (spreading) that would otherwise be expected to be experienced. Other combinations of organic resist bases (or layers) either doped with high cross-section (to gamma radiation) dopants or underlying more absorptive (to gamma radiation) layers are disclosed and otherwise contemplated. Other aspects of the invention are directed to direct-write, afocal, lithography techniques and to means for directing, concentrating, collimating and shuttering beams of radiative energy. According to the invention, a broad incident beam of radiation can be concentrated and collimated, providing a very narrow, very intense beam of radiation (such as X-ray or gamma radiation) useful over a short range of distances as by means of a hollow, horn-shaped (e.g., conical) afocal concentrator (described extensively hereinafter). The afocal concentrator has a tapered section and a cylindrical section. The tapered section has a broad mouth at one end and a narrow opening at an opposite end. The cylindrical section has a diameter equal to that of the narrow opening, and is formed continuously therewith. A broad incident beam of radiation enters the mouth of the tapered portion and is concentrated in the tapered portion and is collimated in the cylindrical portion to provide a collimated, intense output beam that can be directed onto a semiconductor wafer. In order to produce patterns on the wafer, either the collimator or the wafer is moved (in two axes). Preferably, the wafer would moved and the concentrator would be fixed in position. According to various aspects of the invention, the concentrator may have any of various tapered forms, including a linear, cone-shaped taper, an exponential taper, or some combination thereof. In any case, the inner surface of the afocal concentrator is highly reflective of the incident radiation. According to various other aspects of the invention, the afocal concentrator may be used to collimate (thereby intensify) any of various forms of radiation, including gamma radiation, X-ray radiation, UV light, and visible light. In the main hereinafter, the utility of the collimator for very short wavelength radiation that cannot be focused by conventional optics is discussed. According to other aspects of the invention, the reflective inner surface (bore) of the afocal concentrator is formed of aluminum, nickel, or chromium. The entire collimator can be formed of a single material, or its bore can be plated. According to the invention, a surface acoustic wave (SAW) device operating as a shallow angle scattering surface, can act as a shutter for X-ray or gamma-ray radiations. In the context of the present invention, such a shutter would controllably allow/prohibit the downstream (towards the wafer, or towards the concentrator) passage of radiation from a fluent, continuous source of radiation. A thin, reflective film of, for example, aluminum, nickel, or chromium, is disposed over the surface of a Surface Acoustic Wave (SAW) device. When the SAW device is not activated, the reflective surface is substantially planar, and reflects incident radiation at an angle equal and opposite to its angle of incidence. This beam, the position of which is highly predictable, can be used to pattern a layer (e.g., photoresist) on a semiconductor wafer. A tightly collimated beam approaching the surface of the SAW (such as from the aforementioned collimator) at a known shallow angle, will be reflected off of the reflective surface of the unactivated SAW device at a predictable angle. When the SAW device is activated, however, the surface of the SAW device becomes distorted and deflects or scatters the incident beam. By providing a beam stop or an aperture and positioning it such that radiation from the incident beam will pass the beam stop (or aperture) only when reflected at an angle corresponding to its reflection off of the planar surface of the unactivated SAW device, an effective shutter is formed. Hence, the planar and distorted surface of the SAW device, in combination with a knife-edge, opaque beam stop or aperture, effectively functions as a shutter, turning an incident beam ON and OFF, respectively, particularly for very short wavelength radiation (e.g., X-rays or Gamma rays). It is not necessary, according to the invention that the incident beam be "cleanly" reflected in any particular direction when the SAW device is activated (distorted surface). It is only necessary that the reflected beam be reflected from the SAW device anywhere other than past the beam stop or aperture when the SAW device is activated. In a similar manner, a magnetostrictive device may be employed instead of a SAW device, in combination with a beam stop or aperture, to form an effective shutter mechanism. Again, the surface of the magnetostrictive device can selectively be made planar, to reflect incident radiation past a beam stop or aperture, or it can be made non-planar, to divert incident radiation from passing the beam stop or aperture. As with the SAW device, the magnetostrictive device is coated with a material that is highly reflective vis-a-vis the incident radiation. In either case, namely employing a SAW device or a magnetostrictive device, the reflective element acts as a "surface distortion device" for the purposes of the present invention. Other devices whose surfaces may selectively be distorted may be employed, in combination with a beam stop or aperture, to achieve a similar shuttering function. According to various other aspects of the invention, the Surface Acoustic Wave or magnetostrictive shutter may be used to shutter radiation of a variety of wavelengths, including gamma-rays, X-rays, UV light, etc.. In the main hereinafter, the utility of these surface distortion devices in conjunction with nonvisible radiation is discussed. Further, according to the invention, direct-write gamma-ray lithographic apparatus is provided. An omni-directional radiation source provides a source of intense gamma-ray radiation. A suitable radiation source is a Cobalt-60 pellet which passively (without any external power) radiates intense, fluent (e.g., steady, not varying or intermittent) gamma-ray radiation. A reflector (similar to the reflector 114 discussed with respect to FIG. 1, above) may be employed behind the Cobalt-60 pellet to improve the directionality and intensity of the emissions from the pellet. Gamma-ray radiation from the gamma-ray radiation source enters (is incident to) a shutter device, such as the SAW or magnetostrictive-based shutter devices described above. The shutter device serves to selectively gate (block or pass) the incident beam, resulting in a controlled gamma-ray beam. The controlled gamma-ray beam enters the mouth of an afocal concentrator, such as that described above and in greater detail with respect to FIG. 4 et seq.. The afocal concentrator narrows, intensifies and collimates the controlled beam to provide a collimated beam. A semiconductor wafer is positioned a distance from the output of the afocal concentrator such that the collimated beam impinges upon the surface thereof. The surface of the wafer is coated with a layer of gamma-sensitive resist, such as that described above. Preferably, the wafer is mounted to a movable carriage, by which means the wafer may be positioned such that the collimated beam may be caused to impinge on any point on the resist layer, to form a pattern in the resist layer for further processing (e.g., chemical etching). This is referred to as "direct write" lithography. The on/off state of the collimated beam may be effectively controlled by selectively activating and de-activating the shutter device. Preferably, the distance between the wafer and the output of the afocal concentrator is approximately 5 .mu.m. Even if the collimated beam of gamma radiation is not perfectly collimated, by positioning the wafer so close to the output of the collimator, there is not much opportunity for the collimated beam to spread out. In an alternate embodiment of the direct-write gamma-ray lithography apparatus described hereinabove, the positions of the shutter device and the afocal concentrator are reversed. In other words, the gamma radiation would be collimated, then shuttered, then caused to impinge on a semiconductor wafer. Other objects, features and advantages of the invention will become apparent in light of the following description thereof.
	abstract	An ECP sensor includes a tubular ceramic probe having a closed tip at one end packed with a metal and metal oxide powder. A metal support tube receives an opposite end of the probe, and is joined thereto by a braze joint therewith. An electrical conductor extends through the support tube and probe, and has an end buried in the powder for electrical contact therewith. A ceramic band bridges the probe and tube at the joint for sealing thereof.

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