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claims | 1. An ion implanting apparatus for implanting ionized impurities into a semiconductor substrate, the ion implanting apparatus comprising: an ionization unit operative to produce an ion beam; an analyzer unit connected to said ionization unit downstream thereof in the apparatus such that the ion beam produced by the ionization unit passes through the analyzer unit, said analyzer unit operative to discriminate ions that are to be implanted into the substrate; an implanting chamber connected to said analyzer unit downstream thereof in the apparatus and in which the ions are implanted into the substrate; a vacuum unit including a vacuum pump connected to said analyzing unit so as to create a vacuum within the analyzing unit; a vacuum gauge connected to said analyzing unit so as to measure the level of the vacuum within the analyzer unit; and a magnetic field shield comprising a plurality of magnetic field shielding plates extending around said vacuum gauge, and dielectric material interposed between said magnetic field shielding plates, whereby the vacuum gauge is shielded from an external magnetic field. 2. The ion implanting apparatus of claim 1 , wherein said vacuum gauge is a cold cathode ion gauge comprising an anode, a cathode spaced from said anode, and a permanent magnet oriented to generate a magnetic field whose field lines extend between said anode and said cathode. claim 1 3. The ion implanting apparatus of claim 1 , wherein said magnetic field shielding plates are cylindrical and concentric. claim 1 4. The ion implanting apparatus of claim 1 , wherein said magnetic field shield is a cylindrical member. claim 1 5. The ion implanting apparatus of claim 1 , wherein said plurality of magnetic field shielding plates comprise a first magnetic field shielding plate encircling said vacuum gauge, a second magnetic field shielding plate encircling said first magnetic field shielding plate, and a third magnetic field shielding plate encircling second magnetic field shielding plate, and said dielectric material is interposed between the first and third magnetic field shielding plates and between the second and third magnetic field shielding plates. claim 1 6. The ion implanting apparatus of claim 1 , wherein said analyzer unit comprises a magnet. claim 1 7. The combination of a vacuum gauge for use in measuring the level of a vacuum within an analyzer unit of an ion implanting apparatus, and a magnetic field shield for the vacuum gauge, wherein said vacuum gauge comprises a permanent magnet, and said magnetic field shield comprises a plurality of magnetic field shielding plates each extending around said vacuum gauge, and dielectric material interposed between said magnetic field shielding plates. 8. The combination of claim 7 , wherein said vacuum gauge is a cold cathode ion gauge and further comprises an anode and a cathode spaced from said anode, and said permanent magnet is oriented to generate a magnetic field whose field lines extend between said anode and said cathode. claim 7 9. The combination of claim 7 , wherein said magnetic field shielding plates are cylindrical and concentric. claim 7 10. The combination of claim 7 , wherein said magnetic field shield is a cylindrical member. claim 7 11. The combination of claim 7 , wherein said plurality of magnetic field shielding plates comprise a first magnetic field shielding plate encircling said vacuum gauge, a second magnetic field shielding plate encircling said first magnetic field shielding plate, and a third magnetic field shielding plate encircling second magnetic field shielding plate, and said dielectric material is interposed between the first and third magnetic field shielding plates and between the second and third magnetic field shielding plates. claim 7 |
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043483534 | claims | 1. A nuclear reactor fuel assembly duct-tube-to-inlet-nozzle attachment system, comprising: (a) a nuclear reactor fuel assembly inlet nozzle having an upper end (11) with a generally equilateral polygonal top section (12) and a generally cylindrical bottom section (14), said top section (12) and said bottom section (14) being coaxially interconnected, said top section (12) with each of its sides having an external recess (13) and said bottom section (14) having an outside threaded portion (15); (b) a nuclear reactor fuel assembly duct tube having a generally equilateral polygonal lower end (21), the lower end's (21) polygon shape being similar to the inlet nozzle upper end top section's (12) polygon shape, said lower end (21) with each of its sides having an outwardly-extending protrusion (24), after which each side terminates in a deflectable locking tab (22), said locking tabs (22) slidable over said top section (12) to said recesses (13), each of said locking tabs (22) ending in an inwardly-extending, recess-matching flange (23), said flanges (23) coaxially surrounding and engaging said recesses (13) for attachment of said duct tube's lower end (21) to said inlet nozzle's upper end (11); (c) a retaining collar (30) having a flange-restraining, protrusion-engaging, generally equilateral polygonal top segment (31) and a generally cylindrical bottom segment (32), said top segment (31) and said bottom segment (32) being coaxially interconnected, the top segment's (31) polygon shape being similar to the inlet nozzle upper end top section's (12) polygon shape, said top segment (31) slidable over said locking tabs (22) to said protrusions (24) when said flanges (23) engage said recesses (13) during said attachment, said bottom segment (32) slidable over said bottom section (14) to above only part of the outside threaded portion (15), said collar's top segment (31), during said attachment, engaging said protrusions (24), and surrounding and restraining said flanges (23) in said recesses (13); and (d) a locking nut (40), engageable with said retaining collar's bottom segment (32), having an inside threaded portion (41) engageable with said outside threaded portion (15) to secure said retaining collar's top segment (31) against said duct tube lower end's protrusions (24) during said attachment. 2. The system of claim 1, wherein the generally equilateral polygon is a generally equilateral hexagon. 3. The system of claim 2, wherein said recesses (13) together have a generally orthogonally transverse, annular groove shape. 4. The system of claim 3, wherein the width of each of said locking tabs (22) is generally equal to the width of one of said top section's (12) sides. 5. The system of claim 4, wherein the width of each of said flanges (23) is equal to the width of one of said locking tabs (22). 6. The system of claim 5, wherein said locking tabs (22) are generally coaxially aligned with said duct tube during said attachment, and wherein each of said flanges (23) is generally perpendicular to its said locking tab (22). 7. The system of claim 6, wherein said protrusions (24) together have a generally orthogonally transverse, annular band shape. 8. The system of claim 7, wherein said locking tabs (22) are outwardly disposed and resiliently deflectable, and wherein said flanges (23) are slidable, without locking tab deflection, over said top section (12) to and from said recesses (13) during attaching and removing of said duct tube and said inlet nozzle shield. 9. The system of claim 8, also including means for preventing the backing off of said locking nut (40) during said attachment. |
058898310 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the single figure of the drawing, there is seen a containment 1 of a nuclear power station that is not represented in greater detail. The containment 1 has a central electrode 2 for igniting hydrogen contained in a hydrogen/air mixture. The central electrode 2 is connected to a high-voltage source 4. The high-voltage source 4 is constructed as a high-frequency high-voltage source for generating a high voltage of more than a disruptive discharge voltage of air with a frequency of more than 1 kHz. The disruptive discharge voltage of air is determined from the frequency-dependent disruptive field strength of air and the dimensions of the containment 1. A number of internal parts 6 are disposed inside the containment 1. In this case, the internal parts 6 include a reactor core and further operating and maintenance devices. In the event of an accident situation, be it ever so improbable, hydrogen gas can be released inside the containment 1. This released hydrogen is ignited in order to prevent the formation of an explosive gas mixture. The central electrode 2 which is connected to the high-voltage source 4 is activated for this purpose. For this purpose, the high-voltage source 4 generates a high voltage of more than the disruptive discharge voltage of air, referring to the internal dimensions of the containment, 1. This high voltage causes discharges of the central electrode 2 in the form of lightning flashes 8. In this configuration, each internal part 6, or also another structural part such as, for example, the wall of the containment 1, can function as a counter-electrode. Due to the chaotic nature, that is to say the statistical occurrence, of the lightning flashes 8, after even a short time the entire volume inside the containment 1 is penetrated by the lightning flashes 8. The released hydrogen is thereby ignited in the entire volume inside the containment 1, thus reliably preventing a critical limiting value for the hydrogen concentration in the entire volume inside the containment 1 from being exceeded. In order to generate a preferred direction of the lightning flashes 8, a number of counter-electrodes 10 are disposed in a subregion or subspace inside the containment 1, in which it is necessary to expect the release of hydrogen gas with a relatively high probability. This subregion that is detected as a possible hydrogen source is thus penetrated by lightning flashes 8 particularly frequently, with the result that the hydrogen released there is ignited in a particularly reliable manner. |
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description | The present application is a National Stage Application of International Application No. PCT/EP2010/057681 entitled “Connection Device For A System For Filling Jars For The Production Of Nuclear Fuel” filed Jun. 2, 2010, which claims priority of French Patent Application No. 0953627, filed Jun. 2, 2009, the contents of which are incorporated herein by reference in their entirety. The present invention relates to a device for filling jars with materials intended for the manufacture of nuclear fuel, in particular for the manufacture of MOX pellets (mixture of PuO2 and UO2). MOX pellets are manufactured as follows: the various materials to be used in the manufacture of the pellets are stored separately in the form of powder. These materials are UO2, PuO2 and chamotte. This mixture of powders is then compressed so as to form pellets, which will subsequently be subject to a fritting step. The mixture is then produced in jars. To do so, a given quantity of chamotte is placed in the jar, and then a given quantity of PuO2 and finally a given quantity of UO2, although the UO2 can be put in the jar before the PuO2. The quantities placed in the jar are measured by weighing. Handling of plutonium and uranium oxide powders requires great precautions due to their toxicity. In particular, when powders pour out they tend to disperse. It is therefore necessary to confine them. Filling is undertaken in a glove box to prevent any risk of the powder escaping. However, it is necessary, as far as possible, to prevent contaminating the systems positioned in the glove box, and the outer surface of the jar, since the latter will be carried elsewhere for the manufacture of the pellets. A connection device is placed between the tanks and the jar. Vibrating chutes are generally used to convey the powder from the tanks to the filling device. The vibrations are then transmitted to the filling device. Consequently, in order not to disturb the measurements by weighing, contact between the filling device and the jar is avoided. Existing filling devices then include a filling tube penetrating into the neck of the jar, avoiding any contact with the latter in order not to distort the measurements of the weigh scale, and implement dynamic confinement of the powders, i.e. continuous suction in the space between the neck of the jar and the filling tube, in order to collect any powders which might escape. The device is complex. It requires very accurate positioning in order to prevent contact with the jar, whilst ensuring that there is very little clearance, of the order of a few mm. In addition, this continuous suction is obtained by a suction system using filters, which naturally become soiled over time. These filters must be changed regularly in order to maintain confinement efficiency, thus forming nuclear waste which must be managed. It is consequently one aim of the present invention to provide a system for filling a container with powder for the production of nuclear fuel, implementation of which provides safe and accurate dosing of the quantities of powder, and reduces the waste. The aim previously set out is obtained by a device to connect a container with powders containing a cylindrical pipe intended to be placed opposite a filling orifice of the container without contact with the edges of the orifice, where a ring comes into contact with the edge of the orifice in a tight fashion, where the said ring surrounds the filling pipe in tight fashion, and which moves relative to the latter. The ring is mechanically disengaged from the filling pipe in order not to disturb the weighing during the filling. Only the seal ring must then be taken into account when weighing. This device provides a tight confinement requiring no suction system. Consequently, no filter is used. Waste generation is therefore eliminated. In addition, this device does not require great positioning accuracy relative to the container. Risks of error in producing the mixture are consequently small. In other words, a static seal is produced between the connection device and the container, providing a safe and robust system. The subject-matter of the present invention is therefore mainly a tight connection device between a system for feeding powdery or granular materials for the manufacture of nuclear fuel and a container fitted with a filling orifice, where the said device includes: a stationary connection portion intended to be connected to the feed system, a connection portion which moves relative to the stationary connection portion intended to be connected to the container's filling orifice, where the moving connection portion includes in the area of one downstream end at least one seal to produce a tight connection by contact with the contours of the filling orifice, and where the downstream end of the moving connection portion is connected to the stationary connection portion by tight and flexible means, so as to provide a mechanical disengagement between the downstream end of the moving connection portion and the stationary connection portion. The stationary connection portion can form a hopper for collecting materials, in which the moving connection portion includes a supporting ring assembled in sliding and tight fashion around the stationary pipe and a seal ring forming the downstream end of the moving connection portion, where the seal ring is intended to come into tight contact with the contour of the filling orifice, where the seal ring and the supporting ring are connected by a tight bellows providing the mechanical disengagement between the stationary connection portion and the downstream end of the moving connection portion. Advantageously, the tight connection device according to the invention includes means to limit the movement of the seal ring away from the supporting ring, where the said means are active when the seal ring is not in contact with the contour of the filling orifice, and are inactive when the seal ring is in contact with the contour of the filling orifice. The means of limitation include, for example, radial pins and a shoulder upstream from the pins such that, when the seal ring comes into contact with the contour of the filling orifice the shoulder and the pins separate. The device can also include means to cause the supporting ring to slide axially relative to the stationary connection portion, for example means of the electric jack type. The sealing means supported by the seal ring are, for example, formed by a lip seal assembled in a groove. The bellows is advantageously assembled on the supporting ring by means of a mounting flange, and the upstream and downstream ends of the bellows are attached to the mounting flange and to the seal ring, respectively, by means of clamp connections. It is therefore easy to replace the bellows. The mounting flange is, for example, secured axially to the supporting ring by a bayonet system. The supporting ring is advantageously extended by a pipe conveying in the direction of the seal ring, guiding the powder as far as the container's filling orifice, and protecting the bellows. There can also be sealing means between the conveyance pipe and the collecting hopper to provide sealed sliding. The supporting ring can include a vent ring, communicating with the interior of the container by a passage demarcated between the bellows and the conveyance pipe. Another subject-matter of the present invention is a filling system including powder feed pipes, a tight connection device according to the present invention, and a weighing device supporting the container, where the feed pipes are connected to the stationary connection portion. The feed pipes are advantageously of the vibrating chute type. Vibrating chutes can be operated so as to deliver the materials at high speed at the start of the filling, and then to deliver the materials at slower speeds when the delivered quantity is close to the desired quantity. The weighing system is advantageously able to be positioned close to the filling orifice of the container of the tight connection device. Another subject-matter of the present invention is a method for filling a container by means of the system for filling a container according to the present invention, including the following steps: positioning of the container beneath the connection device, weighing of the container, bringing the tight connection device close to the container's filling orifice, bringing the seal ring into contact with the contour of the filling orifice in order to make a tight connection, weighing of the assembly formed by the container and the seal ring, arrival of the material or materials. Between each filling by a material, the seal ring is advantageously separated from the contour of the filling orifice and the container with its content is weighed. A unit for manufacturing nuclear fuel includes a system for filling a jar including a dosing module including several pipes for conveying powder as far as a device for connection to a jar. The jar is positioned on a scale and the various dosings are accomplished by weighing the jar. When a mixture of powder is produced the filled jar is replaced by an empty jar. In FIG. 2A an example embodiment of a connection device 2 according to the present invention can be seen, positioned above a container 4 in which the mixture will be produced. Container 4 is generally called a jar. The description will use as an example the production of a mixture of PuO2 powders and UO2 powders. However, the present invention applies to all types of powder. Powder, in the present application, is understood to mean a material in granular or particular form, the size of which may attain, for example, approximately 1 mm. Jar 4 includes a filling orifice 6 lined with a neck 8. Connection device 2 represented in FIGS. 1, 2A and 2B, is intended to be positioned between an area through which the various powders (not represented) are conveyed, this area being upstream from the connection device and jar 4. Connection device 2 roughly has a lengthways axis X. Lengthways axis X is roughly aligned in the flow direction of the powders. Jar 4 also has a lengthways axis; the jar is positioned under the device such that its axis is roughly the same as axis X. According to the present invention, the connection device includes a portion I intended to be on the side of the powder arrival area, called the upstream portion, intended to be stationary relative to the installation, and a portion II on the side of jar 4, called the downstream portion, intended to be moved. Upstream portion I includes a collecting hopper 10 of axis X, a first lengthways end of which 10.1 is intended to be positioned on the side of the powder conveyance area, and a second lengthways end 10.2 intended to guide the powders towards the jar. Downstream portion II is positioned around hopper 10 and is able to move along axis X. Downstream portion II forms a mobile rig consisting of a first part 12 forming a support and a second part 14 intended to come into contact with neck 8 of jar 4. First part 12 includes an upstream lengthways end 12.1 and a downstream lengthways end 12.2. Downstream lengthways end 12.2 is intended to be positioned opposite filling orifice 6 and to guide the powder to this orifice 6. First part 12 includes a supporting ring 18 which is extended by a pipe 16 aligned with hopper 10. The movement of supporting ring 18 and of conveyance pipe 16 relative to the hopper is advantageously facilitated by a ball-bearing runner 19. First part 12 includes, in the area of its downstream end, stop elements 22 protruding radially inwards. In the represented example, these stop elements are formed by pins 24 extending radially inwards. First part 12 may also include a ventilating aperture made in supporting ring 18 in the area of the upstream end of pipe 16. If the diameter of hopper 10 is sufficiently large there is no risk of the passage being obstructed, since the gases present in the jar pass into the hopper. In this case the device is completely tight. Downstream end 10.2 of collecting hopper 10 includes an external shoulder 27 cooperating with a radial surface 29 of supporting ring 18, protruding inwards, so as to form an axial stop for the movement of first part 12. In addition, this contact forms a metal-on-metal seal. Radial surface 29 is supported by a removable ring allowing the first part to be assembled on collecting hopper 20. Second part 14 has the rough shape of a ring and is intended to be moving along axis X relative to first part 12. Ring 14 includes in the area of its downstream end a support face 28 intended to be pressed against the flat face of neck 8 of jar 6. This support face 28 includes means 30 making a tight contact between support face 28 and the neck of the jar. These means 30 are formed, in the represented example, by a lip seal assembled in a groove made in support face 28. Seal ring 14 includes a shoulder 32 protruding radially outwards upstream from pins 24, cooperating with pins 24 so as to form axial stop means of ring 14 relative to support 12, when seal ring 14 is no longer resting on jar neck 8. The internal passage 36 of seal ring 14 is fitted, in the area of its downstream end, with a nose 38 of tapered shape so as to divert the powder towards the axis of the pipe, and to protect lip seal 30. There are sealing means 40 between collecting hopper 10 and first part 12. In the represented example this is a joint assembled in the inner face of pipe 16, which rubs against the outer face of hopper 10. Joint 40 is such that it tolerates the friction due to the sliding of conveyance pipe 16. In addition, there are sealing means 42 between first part 12 and second part 14. Sealing means 42 are such that they provide a mechanical disengagement between supporting ring 12 and seal ring 14 and, more specifically, between collecting hopper 10 and seal ring 14 in contact with the jar. Indeed, the powders are generally conveyed by means of vibrating systems, of the vibrating chute type, but these vibrations distort the weighing operations. By virtue of the invention these vibrations are not transmitted to the ring, and consequently are not transmitted to jar 4. In the represented example the sealing means 42 are formed by a flexible bellows extending lengthways between the upstream face of ring 14 and the downstream face of the radial projection of supporting ring 18. Bellows 42 has the advantage that it folds when the second portion II is in the upper position, and therefore that it does not hinder the relative movement of the first and second parts. The bellows shape has the advantage that it has a remanence which does not fluctuate greatly over time, i.e. the effort which it applies to the jar and therefore to the scale is roughly constant over time. This effort may therefore the deduced when measuring. Conversely, a sleeve made from a flexible and compressible material may have a varying remanence, which may cause the support effort on the jar to vary, and therefore the weighing operation to be distorted. It could be decided to use a flexible element of tubular shape, or one having another section, where this element is chosen such that it does not influence the weighing operation. In FIG. 3 bellows 42 can be seen with ring 14 and a mounting flange on the first part. Bellows 42 is assembled by a first upstream end on a mounting flange 46 by means of a clamp connection 48, and the second downstream end on seal ring 14 by means of a clamp connection 50. The connection of bellows 42 by a downstream end to seal ring 14 is particularly advantageous, since it enables the bellows to be used as a restraint device for the seal ring. Indeed, if it is only the bellows which restrains seal ring 14, the displacement of seal ring 14 is at most equal to the unfolded length of the bellows. The travel of the seal ring is therefore limited, and compatible with operation of the device. Mounting flange 46 is itself secured on the first part. A joint is interposed between mounting flange 46 and supporting ring 18. Mounting flange 46 may advantageously be secured and disengaged easily from the first part, thus enabling easier replacement of the bellows. In the represented example the securing means are of the bayonet type. The first part includes snugs 52 formed from a rod and a head protruding from the downstream face of the first part, and assembly ring 46 includes apertures 54, including a section of lesser width close to that of the diameter of the rod, and a section of greater width close to the diameter of the head to enable them to be inserted into the aperture. For assembly, the snugs need merely be inserted into the sections of greater width, and then the attachment flange 46 pivoted relative to first part 12 on its axis, so as to position the catches in the sections of smaller width. Bellows 42 is then secured axially to first part 12. To replace bellows 42, the mounting flange need merely be pivoted in the reverse direction relative to the first part. The use of clamp connections has the advantage that they are simple and rapid to handle, and they provide safe tightening. However, other fasteners may be used. The bellows advantageously includes at its lengthways ends lugs 56 radially protruding outwards for assembly of the bellows. These lugs 56 enable bellows 42 to be stretched out in order that it may be put in position in the housings of the interfacing parts. The presence of these lugs 56 facilitates assembly of bellows 42, with the stipulation that it is undertaken remotely with over-gloves and gloves. It may be arranged that the rings are assembled in loops in the lugs, in order to prevent the rings falling in the glove box during assembly. Conveyance pipe 16 advantageously extends over the entire length of the deployed bellows, protecting the latter from excessive contact with the powder, and preventing the powder from remaining trapped in the pleats of the bellows. Nuclear fuel powders are very aggressive, notably for synthetic materials such as those used for manufacturing bellows and gasket seals. It is consequently preferable to reduce direct contact between the bellows and the powder. Pipe 16 advantageously reduces this contact. In addition, if there is a ventilating aperture, a ventilation pipe 44 is formed between conveyance pipe 16 and bellows 42 as far as the ventilating aperture. Mounting flange 46 advantageously protects the upstream end of bellows 42 against the powder. In a similar manner, seal ring 14 covers the downstream end of the bellows joint and is interposed between the powder and the joint. Means are also included to dock ring 14 on the neck of the jar. Jar 4 is advantageously brought close to seal ring 14. Indeed, the scale on which jar 4 is positioned habitually includes means to raise the jar. Thus, the connection device is simplified and uses the pre-existing means. In FIG. 2A mechanical means 56 can be seen, of the electric jack type, to lower and raise the second portion II. It is also possible to envisage both lowering the second portion II and raising the jar. We shall now explain the positioning of connection device 2 on neck 8 of the jar if connection device 2 according to the present invention is moved. Jar 4 is put in position beneath connection device 2. The second portion II is lowered relative to collecting hopper 10. Supporting ring 18 and conveyance pipe 16 thus slide along hopper 10, with joint 40 rubbing on the inner face of pipe 16, and providing the seal. The seal ring approaches neck 8 of jar 4. After a certain travel, the support face of seal ring 16 comes into contact with the neck of the jar. Supporting ring 18 continues its travel until pins 24 disengage from shoulder 32 of seal ring 16. Seal ring 16 is then released; it rests on the neck and its weight presses lip seal 30, under the effect of gravity, on to neck 8 of the jar, giving a tight contact, as can be seen in FIGS. 2A and 2B (where the seal is pressed tight). In FIG. 1 lip seal 30 is in its unpressed state. At that moment connection device 2 is deployed and produces a tight contact between the powder feed area and jar 4. The system is ready for filling jar 4. It is not necessary for the connection device to be completely deployed, i.e. for first part 12 to be in an extreme lowered position, as represented in FIGS. 2A and 2B. Indeed, the sealing between the device and the jar occurs due to the weight of seal ring 14. However, a check is made that first part 12 is resting on collecting hopper 10, or more specifically that surfaces 27 and 29 are in contact, in order to guarantee repeatability of the bellows' pressing value, thus guaranteeing an effort due to the remanence of the bellows which is identical in each docking operation. In addition, this metal-on-metal contact provides an additional seal. During filling the powder flows into collecting hopper 10, and then into conveyance pipe 16 and reaches neck 8 of the jar. The air contained in the jar is evacuated through the vent passage, or passes into the hopper. The powder flow occurs in a sealed fashion by virtue of lip seal 30, which is pressed on to neck 8 of the jar, by virtue of bellows 42 between supporting ring 18 and seal ring 14, and joint 40 between hopper 10 and supporting ring 18. Confinement of the powder is achieved without using a suction system. Consequently, the problem of the management of the soiled filters is no longer posed. In addition, there is no risk of the seal malfunctioning since it is obtained by static elements. In addition, the powder feed is generally obtained by means of vibrating chutes (not represented). Due to the mechanical disengagement between collecting hopper 10 and jar 4 obtained by virtue of the bellows, the vibrations produced are not transmitted to the jar, nor therefore to the scale. The weighing steps are not distorted. Moreover, the relative positioning of jar 4 and of connection device 2 does not require great accuracy. All that is required is for the pins to disengage relative to the shoulder. The device according to the present invention therefore provides great operational safety and is easy to maintain. The jar is removed by lifting first part 12 which, after a certain length of travel, meets pins 24, which raises seal ring 16, and the latter is separated from the neck of the jar. The lifting of first part 12 can occur over a long travel length, enabling the seal ring of the jar to be removed sufficiently far; the jar can then easily be withdrawn from the scale and be removed by a conveyor. The cooperation of pins 24 and shoulder 32 advantageously enables seal ring 14 to be supported when seal ring 14 is not resting on neck 8 of the jar. However, it could be envisaged to use tight bellows 42 to support seal ring 14. This has the advantage of simplifying connection device 2. However, in this case, bellows 42 is subject to traction stress during all the resting phases, which may reduce its lifetime. We shall now explain a step of filling of a jar with the goal of manufacturing MOX pellets. The mixture used to manufacture MOX pellets includes PuO2, UO2 and chamotte. A filling operation includes the following steps: weighing of jar 4 when empty, lowering of moving portion II until the seal ring is resting on neck 8 of the jar, and until pins 24 are separated from shoulder 32, weighing of the assembly formed by empty jar 8 and seal ring 14, filling with chamotte; the quantity of chamotte placed in the jar is simultaneously weighed, raising of portion II in such a way as to separate seal ring 14 from neck 8 of the jar, weighing of jar 4 containing the chamotte; if the mass of chamotte matches the desired value, one then changes to filling with PuO2 and UO2; otherwise the mass of chamotte is adjusted, and seal ring 14 is put back in place, after this the seal ring is put back in place on the neck of the jar, PuO2 or UO2 is then added; the quantity of oxide placed in the jar is simultaneously weighed, portion II is once again raised in such a way as to separate seal ring 14 from neck 8 of the jar, the jar containing the chamotte and the oxide is weighed; if the mass of oxide matches the desired value, one then changes to filling with the other oxide; otherwise the mass of the said oxide is adjusted, and seal ring 14 is put back in position, seal ring 14 is put back in position on the neck of the jar; the last oxide is placed in the jar; and the quantity of oxide placed in the jar is simultaneously weighed, portion II is once again raised in such a way as to separate seal ring 14 from jar 4, jar 4 containing the chamotte and the oxides is weighed; if the mass of the other oxide matches the desired value filling is terminated; otherwise the mass of the said oxide is adjusted, putting seal ring 14 back in position. As mentioned above, the powders are generally conveyed from their tank as far as the connection device by means of vibrating conveyors, known as vibrating chutes. In order to match the filling rates and also to guarantee the dosing accuracies, the vibrating chutes are operated at high speed, to deliver a mass of powder M′=M−Λ, where M is the mass of powder desired and Λ is a small mass of missing powder. When the scale detects that mass M′ is reached, the conveyor control system reduces the speed, which changes to a medium speed, and then to a low speed, until the scale detects that mass M has been reached. At that moment the vibrating chute is stopped. This cycle of control of a vibrating chute is similar for each vibrating chute connecting the tanks of chamotte, PuO2 and UO2 to the collecting hopper. Maintenance of the connection device is simplified. It is therefore easy to replace bellows 42. Indeed, one need merely disengage assembly flange 46 from first part 12 by rotating it, and then separate seal ring 14 and assembly flange 46 from bellows 42 by removing clamp connections 48, 50. Preferentially, before disengaging flange 46 from first part 12, flange 46 and seal ring 14 are secured after having been brought close to one another, for example along a transverse axis. Bellows 42 is compressed and there is no danger of it being damaged by elongation under the load of seal ring 30. Bellows 42 is then managed as radioactive waste, and seal ring 14 and assembly flange 46 are reassembled on a new bellows 42, which is then put into position in the connection device. The axial stop means between first part 12 and seal ring 14, in the represented example, are simple to produce and of reliable operation. However, more elaborate stop means may be used, involving for example the moving of parts. |
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claims | 1. A nuclear fuel rod cladding in a nuclear reactor having a coolant flowing therein, the nuclear fuel rod cladding comprising:a base ceramic composite structured to form a shape that has an interior surface, an exterior surface, and an inner cavity, comprising:a ceramic matrix; anda plurality of ceramic fibers;nuclear fuel positioned within the inner cavity of the base ceramic composite; anda coating composition comprising a zirconium component composed of zirconium alloy deposited on the exterior surface of the base ceramic composite to form a coating thereon, which is in contact with the coolant, wherein the coating has a thickness from about 0.004 to about 0.006 inches. 2. The cladding of claim 1, wherein the ceramic matrix is composed of material selected from the group consisting of silicon carbide and silicon carbide-containing material. 3. The cladding of claim 1, wherein the plurality of ceramic fibers is composed of a material selected from the group consisting of silicon carbide and a silicon-carbide containing material. 4. The cladding of claim 1, wherein the plurality of ceramic fibers is selected from the group consisting of individual fibers, woven fibers and braided fibers. 5. The cladding of claim 1, wherein the ceramic composite is in the shape of a cylindrical tube. 6. A nuclear fuel rod cladding for a nuclear reactor, the nuclear fuel rod cladding comprising:a ceramic composite tube comprising a silicon carbide matrix and a plurality of silicon carbide fibers; anda coating deposited on an exterior surface of the ceramic composite tube, wherein the coating comprises zirconium alloy and a thickness in a range of about 0.004 to about 0.006 inches, wherein the coating is configured to contact a coolant in the nuclear reactor. 7. The nuclear fuel rod cladding of claim 6, wherein the nuclear fuel rod cladding comprises a thickness in a range of 100 microns to 600 microns. 8. The nuclear fuel rod cladding of claim 6, wherein the nuclear fuel rod cladding consists of the ceramic composite tube and the coating. 9. The nuclear fuel rod cladding of claim 6, wherein the coating has been deposited by arc spray, liquid phase spray, plasma spray, cold spray, or laser deposition. 10. The nuclear fuel rod cladding of claim 6, wherein the coating is configured to provide a hermetic seal on the exterior surface of the ceramic composite tube. 11. The nuclear fuel rod cladding of claim 6, wherein the coating is configured to preclude coolant in the nuclear reactor from contacting the ceramic composite tube. 12. The cladding of claim 6, wherein the cladding comprises a thickness from 100 microns to 600 microns. |
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claims | 1. An ion implantation method comprising:proceeding an ion implantation scan pass to form a plurality of parallel ion implantation scan lines on a substrate, wherein said ion implantation scan pass is to form an ion implantation scan line parallel to a first direction via an ion beam, and then to shift said ion beam with a scan pitch along a second direction, which is on the plane of said substrate and is perpendicular to said first direction, and then to form another ion implantation scan line via said ion beam along the reverse direction of said first direction, and then to repeat the procedure to form said plurality of parallel ion implantation scan lines on said substrate;rotating said substrate by 180/n degree, shifting said ion beam with an interlace pitch T/2 n along said second direction and repeating one time of said ion implantation scan pass, wherein n is a positive integer equal to or larger than 2 and T is said scan pitch; andrepeating the step of rotating said substrate, the step of shifting said ion beam and the step of proceeding said ion implantation scan pass for 2 n−1 times to form interlaced and non-overlapped ion implantation scan lines on said substrate. 2. An ion implantation method according to claim 1, wherein the step of shifting said ion beam with said scan pitch is to move said substrate. 3. An ion implantation method according to claim 1, wherein the step of shifting said ion beam with said scan pitch is to move said ion beam. 4. An ion implantation method according to claim 1, wherein the step of shifting said ion beam with said interlace pitch is to move said substrate. 5. An ion implantation method according to claim 1, wherein the step of shifting said ion beam with said interlace pitch is to move said ion beam. 6. An ion implantation method according to claim 1, wherein said integer n is equal to 2. 7. A ion implantation method comprising:proceeding first time of an ion implantation scan pass to form a plurality of parallel ion implantation scan lines on a substrate, wherein said ion implantation scan pass is to form an ion implantation scan line parallel to a first direction via an ion beam, and then to shift said ion beam with a scan pitch along a second direction, which is on the plane of said substrate and is perpendicular to said first direction, and then to form another ion implantation scan line via said ion beam along the reverse direction of said first direction, and then to repeat the procedure to form said plurality of parallel ion implantation scan lines on said substrate;rotating said substrate by 90 degree and shifting said ion beam with an interlace pitch T/4 along said second direction, wherein T is said scan pitch;proceeding second time of said ion implantation scan pass;rotating said substrate by 90 degree and shifting said ion beam with said interlace pitch along said second direction;proceeding third time of said ion implantation scan pass;rotating said substrate by 90 degree and shifting said ion beam with said interlace pitch along said second direction; andproceeding forth time of said ion implantation scan pass to form perpendicularly interlaced and non-overlapped ion implantation scan lines on said substrate. 8. An ion implantation method according to claim 7, wherein the step of shifting said ion beam with said scan pitch is to move said substrate. 9. An ion implantation method according to claim 7, wherein the step of shifting said ion beam with said scan pitch is to move said ion beam. 10. An ion implantation method according to claim 7, wherein the step of shifting said ion beam with said interlace pitch is to move said substrate. 11. An ion implantation method according to claim 7, wherein the step of shifting said ion beam with said interlace pitch is to move said ion beam. |
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051030950 | summary | BACKGROUND OF THE INVENTION This invention relates to scanning probe microscopes and, more particularly, in a scanning probe microscope having a probe wherein the relationship between the probe and a sample to be scanned is defined by three legs, to the improvement to allow tilt between the probe and the sample to be adjusted comprising, each of the three legs including adjusting means for adjusting a length thereof; and, tilt control means attached to the adjusting means for independently adjusting the length of selected ones of the three legs. Scanning probe microscopes (SPMs) are instruments that provide high resolution information about the properties of surfaces. One common use of these devices is imaging, and some types of SPM have the capability of imaging individual atoms. Along with images, SPMs can be used to measure a variety of surface properties, over the range from a few angstroms to hundreds of microns. For many applications, SPMs can provide lateral and vertical resolution that is not obtainable from any other type of device. The first type of SPM developed was the scanning tunneling microscope (STM). The STM places a sharp, conducting tip near a surface. The surface is biased at a potential relative to the tip. When the tip is brought near the surface, a current will flow in the tip due to the tunneling effect. Tunneling will occur between the atom closest to the surface in the tip and the atoms on the surface. This current is a function of the distance between the tip and the surface, and typically the tip has to be within 20 angstroms of the surface for measurable current to be present. An STM has a mechanism to scan the tip over the surface, typically in a raster pattern. While the tip is scanned over the surface, the tip is kept at a constant distance above surface features by means of a feedback loop employing the tunneling current and a vertical position controlling mechanism. The feedback loop adjusts the vertical position of the tip to keep the tunneling current, and thus the distance, constant. The vertical position of the tip is determined from the control signals applied to the vertical position controlling mechanism. The vertical position, as a function of horizontal scan position, produces a topographic map of the surface. STMs can easily image individual atoms, and can also be used for highly accurate surface measurements on larger scales, up to a few hundred microns. STMs also may be used for data other than topographic images. One alternative operation of an STM is to hold the tip stationary while varying the bias voltage applied to the sample and monitoring the tunneling current, thus measuring local current/voltage characteristics of the surface. STMs require a conducting sample surface for operation. Non-conducting surfaces may be coated with a thin conducting material such as gold or, in some cases, non-conducting materials a few atoms thick lying on a conducting surface may be imaged. Another SPM, the atomic force microscope (AFM), similarly scans a tip across a surface. The tip in this case is mounted on the free end of a lever or cantilever which is fixed at the other end. The tip is brought to a surface such that the force interaction of the tip with the surface causes the cantilever to deflect. An AFM may be operated such that the Van der Waals attractive force between the tip and surface are near equilibrium with the repulsive force, or at larger cantilever deflections where the repulsive force, dominates. A feedback loop employing the cantilever deflection information and the tip vertical position is used to adjust the vertical position of the tip as it is scanned. The feedback loop keeps the deflection, and thus the force, constant. The tip vertical position versus horizontal scan provides the topographic surface map. In this mode, the forces on the surface can be made very small so as not to deform biological molecules. AFMs can also be operated in a mode where the repulsive force deflects the cantilever as it scans the surface. The deflection of the tip as it is scanned provides topographic information about the surface. AFMs may also be operated in a non-contact mode where the cantilever is vibrated and the Van der Waals interaction between the tip and surface affects the vibration amplitude. AFMs have a means to detect the small movements of the cantilever. Several means for cantilever motion detection have been used with the most common method employing reflected light from the cantilever. The deflection of a light beam due to the cantilever motion may be detected, or the movement of the cantilever can be used to generate interference effects which can be used to derive the motion. Like an STM, AFMs can image individual atoms; but unlike an STM, AFMs can be used for non-conducting surfaces. AFMs may also be used for measurements such as surface stiffness. Other SPMs may use different probing mechanisms to measure properties of surfaces. Probing devices have been developed for such properties as electric field, magnetic field, photon excitation, capacitance, and ionic conductance. Whatever the probing mechanism, most SPMs have common characteristics, typically operating on an interaction between probe and surface that is confined to a very small lateral area and is extremely sensitive to vertical position. Most SPMs possess the ability to position a probe very accurately in three dimensions and use high performance feedback systems to control the motion of the probe relative to the surface. The positioning and scanning of the probe is usually accomplished with piezoelectric devices. These devices expand or contract when a voltage is applied to them and typically have sensitivities of a few angstroms to hundreds of angstroms per volt. Scanning is implemented in a variety of ways. Some SPMs hold the probe fixed, and attach the sample to the scanning mechanism while others scan the probe. Piezoelectric tubes have been found to be the best scanning mechanism for most applications. These tubes are capable of generating three dimensional scans. They are mechanically very stiff, have good frequency response for fast scans, and are relatively inexpensive to manufacture and assemble. Such scanners are used in a commercial STM sold by the assignee of this application, Digital Instruments, Inc., under the trademark NanoScope. These scanners are made in various lengths, the larger ones having larger scan ranges. As can be appreciated, SPMs are extremely useful research tools, allowing for information of higher resolution to be obtained more conveniently than previously possible. Some aspects of SPM performance require improvement, however, in order for SPMs to become more practical for applications requiring less operator interaction, accurate repeatable measurements for larger scale samples, and high throughput. In the scanning probe microscope, the piezoelectric scanners typically have ranges of a few microns, so the sample must be brought close to the probe with some kind of mechanical arrangement in order for the probing of the surface to occur. Presently, these arrangements include moving the sample straight toward the probe with a screw or piezoelectric inchworm, or tilting the scanner support to bring the probe toward the surface. A prior art scanning probe microscope, which is most representative of scanning tunneling microscopes, is illustrated in FIG. 1 where it is generally indicated as 10. In this device, a scanner 12 rests on two fixed supports 14 and one movable support 16 attached to a base 18. The fixed supports 14 can be hand adjusted while the movable support 16 is motor driven and allows for automatic final approach. The scanner 12 must be hand adjusted and leveled; so, the probe 20 must be placed very near the sample 22 by eye, usually using an optical microscope, before the automatic approach is engaged. This procedure is not difficult; but, requires an operator to prepare each new probe site by hand. Other prior art SPMs utilize systems that translate the scanner toward the sample with a motion parallel to its axis. These systems may be operated with less operator participation; but, have no flexibility to adjust for sample tilt. In many instances and for several reason, it would be useful to have the ability to control the tilt of the scanner with respect to the sample independent of positioning the probe vertically. One reason is related to the errors caused by non-linear behavior of the piezoelectric scanning elements. Piezoelectric non-linearity is a well known source of error in the art, and can affect SPM data in many ways. For large scans, one non-linear error is related to tilt between the probe and the sample. It is extremely difficult to mount a sample such that, on the scale of SPM measurements, there is not some tilt between the sample and probe. For large scans, the cumulative non-linearity errors due to the scanner make a tilted flat surface appear bowed. As one useful application of SPMs for larger scale samples is surface dimensional measurements, the distortion of a tilted sample is a serious problem. The tilt may be on only part of the sample, so having a flat sample holder will not solve this problem. What is needed is a scanner which minimizes this distortion by having the scanner able to be tilted with respect to the sample, thereby allowing compensation for an effect that otherwise decreases the utility of the instrument. On the other hand, in the scanning of surfaces which have very steep features, such as the surface of an integrated circuit, it is useful to have a known tilt between the probe and sample. Given a tapered probe 20, such as an etched tungsten probe in the case of an STM, the probe 20 will have some angle for its profile, as indicated by the arrows in FIG. 2. If the probe 20 is perpendicular to the bottom of a groove 23 as depicted in that figure, it can be seen that it is impossible to scan all the way to the edge of the groove 23 as the side of the probe 20 will hit the side of the groove 23 before the scanning point of the tip. Thus, in order to scan to the edge of the groove 23, one must tilt the scanner (and therefore the probe 20) with respect to the sample 22 by an angle which is greater than the tip profile angle as depicted in FIG. 3. A lesser tilt would, of course, improve the situation but not completely solve it. As shown, the tilting allows the tip of the probe 20 to travel down the sidewall and determine its profile. The scanner and probe 20 would be tilted in the opposite direction in order to image the other side of the groove 23. The images of the tilted surfaces could then be patched together with the computer to construct a proper image reflecting the true surface topology of the entire groove 23. A similar procedure could be used for any very steep feature, such as a step or bump. As will be seen, this unique method is possible with the present invention as described hereinafter. Not only would it be desirable to be able to tilt the scanner with respect to the sample in a controlled manner in order to remove tilt or create known tilts; but, it would be desirable also to be able to automatically approach the sample with the scanner in a straight line fashion over a long range so that there is no need to manually place the tip near the surface with a microscope or magnifier. Most desirable would be to have both of these abilities in a single device as it is not practical to approach a new sample or a new sample section automatically without some means to adjust the tilt. These abilities along with the ability to translate a large sample underneath the probe, or the ability to automatically sequence a series of samples to the probe would allow SPMs to be used for totally automatic inspection and characterization of either large area samples or multiple samples. Such capabilities would make SPMs much more useful for industrial applications such as imaging magnetic disks or integrated circuit wafers. Wherefore, it is an object of this invention to provide a scanning probe microscope head which has both vertical motion and tilt motion. It is another object of this invention to provide a scanning probe microscope head which can be used conveniently in SPMs that will have the capability for large samples, fully automated operation, and multiple samples. Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it. SUMMARY The foregoing objects have been achieved in a scanning probe microscope having a probe wherein the relationship between the probe and a sample to be scanned is defined by three legs, by the improvement of the present invention to allow tilt between the probe and the sample to be adjusted comprising, each of the three legs including adjusting means for adjusting a length thereof; and, tilt control means attached to the adjusting means for independently adjusting the length of selected ones of the three legs. In the preferred embodiment, each adjusting means comprises, an outer leg connected to the scanner; a threaded inner leg threadedly disposed within the outer leg, the inner leg having an outer end contacting a supported area adjacent a portion of the sample to be scanned; and, means for rotating the inner leg within the outer leg whereby the inner leg is threaded into and out of the outer leg to change a combined length of the inner leg and the outer leg. The preferred means for rotating the inner leg within the outer leg comprises a motor drive connected to the inner leg. The preferred motor drive comprises a DC motor with a reduction transmission connected between the DC motor and the inner leg. In one embodiment, the three legs, the adjusting means, and the tilt control means are located in a base with the legs facing upward and the piezoelectric scanner sits on the three legs. In another embodiment, the three legs, the adjusting means, and the tilt control means are disposed in combination with the piezoelectric scanner as part of a stand-alone head with the legs facing downward and the head sits on the three legs over (or on) a sample to be scanned. In one variation of this embodiment, there is a sample holding structure having an upper surface upon which the head sits, the upper surface having an opening therethrough through which the piezoelectric scanner can pass into an interior of the box to place the probe in contact with a surface of a sample disposed thereunder; and, sample holding and positioning means are disposed in the interior of the structure for holding a sample and for positioning selected areas of a surface of the sample under the probe of the scanner to be scanned thereby. In another variation of this embodiment there are, a sample holding member positioned over the stand-alone head and having a lower surface against which the head rests, the member having a plurality of openings therethrough through which the probe of the scanner can pass to place the probe in contact with a surface of a sample disposed within selected ones of the opening; a plurality of holding and positioning means removeably disposed in respective ones of the openings for holding individual samples and for positioning a surface of a sample held thereby over the probe of the scanner to be scanned thereby; and, indexing means for selectively positioning respective ones of the openings over the probe. Preferably in this latter variation, the sample holding member comprises a disk mounted for rotation about a shaft in a horizontal plane; the openings comprise a plurality of shouldered bores through the disk located at spaced scanning stations of the disk; and, the plurality of sample holding and positioning means comprises a plurality of disk-shaped inserts having a bottom surface for carrying a sample to be scanned whereby the inserts may be dropped into the bores from above to rest on shoulders of the bores. This latter variation may also include means for lowering the stand-alone head while the indexing means is selectively positioning a respective one of the openings over the probe and for raising the stand-alone head after the indexing means is through selectively positioning the respective one of the openings over the probe. This could, of course, also be accomplished in an inverted configuration wherein the head is above the samples. The probe can be fixed with the sample being mounted on a device wherein the orientation between the sample and the probe is determined by three legs on the device. |
claims | 1. A test system, comprising:a storage system configured to store first test data for a first individual component and second test data for a second individual component, wherein the first and second components occupy corresponding locations on different wafers; anda composite analysis element configured to analyze the first test data and the second test data for common characteristics. 2. A test system according to claim 1, wherein the composite analysis element is configured to compare a summary value for the first and second test data to a threshold. 3. A test system according to claim 2, wherein the threshold is a dynamic threshold based on the test data. 4. A test system according to claim 2, wherein the summary value is determined according to a number of test data for corresponding components to satisfy a criterion. 5. A test system according to claim 1, wherein the composite analysis element is configured to compare the first test data and the second test data to a threshold. 6. A test system according to claim 5, wherein the threshold is calculated based on the first test data and the second test data. 7. A test system according to claim 1, wherein the common characteristics comprise data values meeting at least one threshold. 8. A test system according to claim 1, wherein the composite analysis element is configured to generate composite data according to the test data having the common characteristics. 9. A test system according to claim 8, wherein the composite analysis element is configured to accord a designated treatment to composite data within a designated zone. 10. A test system according to claim 9, wherein the composite analysis element is configured to at least one of ignore and accord a lower significance to the composite data within the designated zone. 11. A test system according to claim 8, wherein the composite analysis element is configured to perform a spatial analysis on the composite data. 12. A test system according to claim 8, wherein the composite analysis element is configured to accord a significance to a selected composite data point based on values of nearby composite data points. 13. A test system according to claim 12, wherein the significance accorded to the selected composite data point is adjusted by a first amount if a first nearby composite data point is at a first position relative to the selected composite data point and by a second amount if the first nearby composite data point is at a second position relative to the selected composite data point. 14. A test system according to claim 8, wherein the composite analysis element is configured to remove a cluster of composite data points from the composite data. 15. A test system according to claim 14, wherein the composite analysis element is configured to remove the cluster of composite data points only when the cluster is smaller than a selected size. 16. A test system according to claim 8, wherein the composite analysis element is configured to merge the composite data with another set of data. 17. A test system according to claim 16, further comprising an output element configured to generate a composite map including the merged composite data. 18. A test system, comprising:a storage system configured to store test data for at least two sets of components, including test data for individual components, wherein:components from each set of components correspond to components in other sets of components; andthe corresponding components occupy corresponding locations on different wafers; anda composite analysis element configured to analyze the test data for at least two individual corresponding components for common characteristics. 19. A test system according to claim 18, wherein the composite analysis element is configured to compare a summary value for at least one test datum for one or more corresponding components to a threshold. 20. A test system according to claim 19, wherein the threshold is a dynamic threshold based on the test data. 21. A test system according to claim 19, wherein the summary value is determined according to a number of test data for corresponding components to satisfy a criterion. 22. A test system according to claim 18, wherein the composite analysis element is configured to compare the test data from different datasets to a threshold. 23. A test system according to claim 22, wherein the threshold is calculated based on the test data. 24. A test system according to claim 18, wherein the common characteristics comprise data values meeting at least one threshold. 25. A test system according to claim 18, wherein the composite analysis element is configured to generate composite data according to the test data having the common characteristics. 26. A test system according to claim 25, wherein the composite analysis element is configured to accord a designated treatment to composite data within a designated zone. 27. A test system according to claim 26, wherein the composite analysis element is configured to at least one of ignore and accord a lower significance to the composite data within the designated zone. 28. A test system according to claim 25, wherein the composite analysis element is configured to perform a spatial analysis on the composite data. 29. A test system according to claim 25, wherein the composite analysis element is configured to accord a significance to a selected composite data point based on values of nearby composite data points. 30. A test system according to claim 29, wherein the significance accorded to the selected composite data point is adjusted by a first amount if a first nearby composite data point is at a first position relative to the selected composite data point and by a second amount if the first nearby composite data point is at a second position relative to the selected composite data point. 31. A test system according to claim 25, wherein the composite analysis element is configured to remove a cluster of composite data points from the composite data. 32. A test system according to claim 31, wherein the composite analysis element is configured to remove the cluster of composite data points only when the cluster is smaller than a selected size. 33. A test system according to claim 25, wherein the composite analysis element is configured to merge the composite data with another set of data. 34. A test system according to claim 33, further comprising an output element configured to generate a composite map including the merged composite data. 35. A method for testing semiconductors, comprising:obtaining at least two datasets of test data for at least two sets of components, wherein:a first component in a first set corresponds to a second component in a second set; andthe first and second components occupy corresponding locations on different wafers; andanalyzing the test data for the individual corresponding first and second components for common characteristics. 36. A method for testing according to claim 35, wherein analyzing the test data comprises comparing a summary value based on test data for multiple components to a threshold. 37. A method for testing according to claim 36, wherein the threshold is a dynamic threshold based on the test data. 38. A method for testing according to claim 36, wherein the summary value is determined according to a number of test data for corresponding components to satisfy a criterion. 39. A method for testing according to claim 35, wherein the composite analysis element is configured to compare the test data from different datasets to a threshold. 40. A method for testing according to claim 39, wherein the threshold is calculated based on the test data. 41. A method for testing according to claim 35, wherein the common characteristics comprise data values meeting at least one threshold. 42. A method for testing according to claim 35, further comprising generating composite data according to the test data having the common characteristics. 43. A method for testing according to claim 42, wherein generating composite data includes according a designated treatment to composite data within a designated zone. 44. A method for testing according to claim 43, wherein according the designated treatment includes at least one of ignoring and according a lower significance to the composite data within the designated zone. 45. A method for testing according to claim 42, further comprising performing a spatial analysis on the composite data. 46. A method for testing according to claim 42, further comprising according a significance to a selected composite data point based on values of nearby composite data points. 47. A method for testing according to claim 46, wherein the significance accorded to the selected composite data point is adjusted by a first amount if a first nearby composite data point is at a first position relative to the selected composite data point and by a second amount if the first nearby composite data point is at a second position relative to the selected composite data point. 48. A method for testing according to claim 42, further comprising removing a cluster of composite data points from the composite data. 49. A method for testing according to claim 48, wherein removing the cluster includes removing the cluster of composite data points only when the cluster is smaller than a selected size. 50. A method for testing according to claim 42, further comprising merging the composite data with another set of data. 51. A method for testing according to claim 50, further comprising generating a composite map including the merged composite data. |
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description | This application is a divisional of U.S. application Ser. No. 13/786,643, filed Mar. 6, 2013, the contents of which are incorporated herewith. This disclosure generally relates to systems and methods for storing and managing nuclear spent fuel. Spent fuel pools provide long term decay heat removal from fuel that has been recently discharged from a nuclear reactor. A recently discharged nuclear core typically represents the largest source of heat generation in a spent fuel pool. In the event of a complete loss of power to the nuclear power plant, cooling systems for the spent fuel pool may not be available to remove the fuel's decay heat. For prolonged nuclear plant station blackout conditions with recently discharged fuel, the potential exists to boil off all of the water in the spent fuel pool thereby overheating and subsequently damaging the spent fuel bundles. This may result in a radioactive release to the environment. This disclosure describes technologies related to systems, apparatus, and methods for handling, storing, and otherwise managing spent fuel rods from a nuclear reactor. In one general implementation, a spent nuclear fuel rod canister includes a submersible pressure vessel including a casing that defines an interior cavity, the casing including a corrosion resistant and heat conductive material with a thermal conductivity of above about 7.0 watts per meter per kelvin; and a rack enclosed within the interior cavity and configured to support one or more spent nuclear fuel rods. A first aspect combinable with the general implementation further includes a first hemispherical enclosure coupled to the casing at a top end of the casing. In a second aspect combinable with any of the previous aspects, the first hemispherical enclosure includes a radiussed interior surface that defines a top portion of the interior cavity. A third aspect combinable with any of the previous aspects further includes a second hemispherical enclosure coupled to the casing at a bottom end of the casing. In a fourth aspect combinable with any of the previous aspects, the second hemispherical enclosure includes a radiussed interior surface that defines a bottom portion of the interior cavity. A fifth aspect combinable with any of the previous aspects further includes a riser that defines a fluid pathway through the riser between a top portion of the interior cavity and a bottom portion of the interior cavity. A sixth aspect combinable with any of the previous aspects further includes an annulus defined between the riser and the casing. A seventh aspect combinable with any of the previous aspects further includes a fuel basket positioned in the interior cavity between the riser and the bottom portion of the interior cavity. In an eighth aspect combinable with any of the previous aspects, the fuel basket includes a spent nuclear fuel rod rack. In a ninth aspect combinable with any of the previous aspects, the fuel basket includes a perforated support plate adjacent a bottom surface of the rack, the fluid pathway fluidly coupled to the bottom portion of the interior cavity through the perforated support plate. A tenth aspect combinable with any of the previous aspects further includes a heat exchanger attached to the casing of the pressure vessel. In an eleventh aspect combinable with any of the previous aspects, the heat exchanger includes at least one conduit that is at least partially disposed exterior to the casing and is in fluid communication with the interior cavity. In a twelfth aspect combinable with any of the previous aspects, the corrosion resistant material includes a high radioactivity conduction material. In a thirteenth aspect combinable with any of the previous aspects, the vessel is free of any radiation shielding material. In another general implementation, a spent nuclear fuel rod management system includes a spent fuel pool containing a heat transfer liquid; and a plurality of spent fuel canisters, where each of the canisters includes a submersible pressure vessel including a casing defining an interior cavity at least partially filled with a liquid coolant; a rack enclosed within the interior cavity; and one or more spent nuclear fuel rods supported in the rack. In a first aspect combinable with the general implementation, the liquid coolant includes water. In a second aspect combinable with any of the previous aspects, the heat transfer fluid includes at least one of water or ambient air. In a third aspect combinable with any of the previous aspects, the heat removal rate of each canister is between about 0.3 MW and 0.8 MW. In another general implementation, a method of dissipating decay heat generated by a spent nuclear fuel rod includes loading at least one spent nuclear fuel rod in a spent fuel canister that includes an inner cavity, the interior cavity at least partially filled with a fluid coolant; submerging the spent fuel canister in a heat transfer fluid contained in a spent fuel pool; transferring decay heat from the spent nuclear fuel rod to the fluid coolant; and transferring the decay heat from the fluid coolant to the heat transfer fluid in the spent fuel pool. In a first aspect combinable with the general implementation, a rate at which heat is transferred from the spent fuel rod is at Past as great as a rate at which the spent nuclear fuel rod produces decay heat. A second aspect combinable with any of the previous aspects further includes circulating the fluid coolant within the interior cavity of the spent fuel canister via natural circulation. A third aspect combinable with any of the previous aspects further includes exposing an exterior surface of the spent fuel the canister to ambient air. A fourth aspect combinable with any of the previous aspects further includes based on the exposure to ambient air, phase changing a portion of the fluid coolant from a liquid to a gas in the spent fuel canister; and phase changing the gas hack to a liquid condensate on an interior surface of the spent fuel canister based at least in part on heat transfer between the gas and the ambient air. A fifth aspect combinable with any of the previous aspects further includes circulating at least a portion of the liquid condensate on the interior surface to a pool of the fluid coolant in a bottom portion of the canister. In another general implementation, a method of managing spent fuel rods includes removing a first batch of spent fuel rods from a nuclear reactor; at a first time, installing the first batch of spent fuel rods in a spent fuel canister, the first batch of spent fuel rods generating decay heat at a first decay heat rate; submerging the spent fuel canister in a heat transfer fluid to remove decay heat from the first batch of spent fuel rods; removing decay heat from the first batch of spent fuel rods using the spent fuel canister for a time period at a rate greater than the first decay heat rate; at a second time subsequent to the first time, installing a second batch of spent fuel rods in the spent fuel canister, the second batch of spent fuel rods generating decay heat at a second decay heat rate greater than the first decay heat rate; and removing decay heat from the first and second batch of spent fuel rods at a rate at least as great as a sum of the first and second decay heat rates. In a first aspect combinable with the general implementation, installing the first batch of spent fuel rods in a spent fuel canister includes installing the first batch of spent fuel rods in a spent fuel canister directly from the nuclear reactor. A second aspect combinable with any of the previous aspects further includes removing at least a portion of the first batch of spent fuel rods; and installing the portion in a dry cask. Various implementations described in this disclosure may include none, one, some, or all of the following features. For example, decay heat removal from spent nuclear fuel may be achieved through a canister into a pool rather than directly to a pool, thereby increasing an ease of handling of spent nuclear fuel and providing an additional safety barrier to fission product release. Further, in the case of loss of pool liquid or loss of recirculation of pool liquid (e.g., water), such as, due to a loss of power incident, decay heat removal from spent nuclear fuel may be achieved through the canister to ambient air. The decay heat removal rate may be substantially similar or identical to that achieved to the pool during normal operating conditions. In some implementations, a desired decay heat removal may be achieved without any operator action or power needed. The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. FIG. 1 is a block diagram illustrating a technique of managing spent fuel 104 from one or more nuclear reactors 152 in a nuclear reactor power system 150. The technique involves removing spent nuclear fuel rods 104 from nuclear reactors 152 and transferring the spent fuel rods 104 to a spent fuel management system 154 that facilitates removal of residual decay heat produced by the spent fuel rods 104. Spent fuel management system 154 includes multiple spent fuel canisters 100 submerged in a spent fuel pool 156 filled with fluid 158. Fluid 158 provides a heat sink for receiving and dissipating the decay heat from spent fuel rods 104. As described in detail below, canisters 100 can be configured to operate passively, e.g., without operator intervention or supervision, under both normal and abnormal emergency conditions. In some examples, canisters 100 provide a long term decay heat removal solution for spent fuel rods 104. For example, canisters 100 can be capable of achieving a substantially constant heat removal rate (e.g., a heat removal rate of about 0.3 MW, 0.4 MW, or 0.8 MW) in various normal and abnormal operating conditions. The number of nuclear reactors 152 and canisters 100 in FIG. 1 are not indicative of any particular implementation or implementation, and are depicted for illustrative purposes only. With respect to nuclear reactors 152, a reactor core 20 is positioned at a bottom portion of a cylinder-shaped or capsule-shaped reactor vessel 70. Reactor core 20 includes a quantity of nuclear fuel rods (e.g., fissile material that produces a controlled nuclear reaction) and optionally one or more control rods (not shown). In some implementations, nuclear reactors 152 are designed with passive operating systems employing the laws of physics to ensure that safe operation of the nuclear reactor 152 is maintained during normal operation or even in an emergency condition without operator intervention or supervision, at least for some predefined period of time. A cylinder-shaped or capsule-shaped containment vessel 10 surrounds reactor vessel 70 and is partially or completely submerged in a reactor pool, such as below waterline 90, within reactor bay 5. The volume between reactor vessel 70 and containment vessel 10 may be partially or completely evacuated to reduce heat transfer from reactor vessel 70 to the reactor pool. However, in other implementations, the volume between reactor vessel 70 and containment vessel 10 may be at least partially filled with a gas and/or a liquid that increases heat transfer between the reactor and containment vessels. In a particular implementation, reactor core 20 is submerged within a liquid, such as water, which may include boron or other additives, which rises into channel 30 after making contact with a surface of the reactor core. The upward motion of heated coolant is represented by arrows 40 within channel 30. The coolant travels over the top of heat exchangers 50 and 60 and is drawn downward by density difference along the inner walls of reactor vessel 70 thus allowing the coolant to impart heat to heat exchangers 50 and 60. After reaching a bottom portion of the reactor vessel, contact with reactor core 20 results in heating the coolant, which again rises through channel 30. Although heat exchangers 50 and 60 are shown as two distinct elements in FIG. 1, heat exchangers 50 and 60 may represent any number of helical coils that wrap around at least a portion of channel 30. Normal operation of the nuclear reactor module proceeds in a manner wherein heated coolant rises through channel 30 and makes contact with heat exchangers 50 and 60. After contacting heat exchangers 50 and 60, the coolant sinks towards the bottom of reactor vessel 110 in a manner that induces a thermal siphoning process. In the example of FIG. 1, coolant within reactor vessel 70 remains at a pressure above atmospheric pressure, thus allowing the coolant to maintain a high temperature without vaporizing (e.g., boiling). As coolant within heat exchangers 50 and 60 increases in temperature, the coolant may begin to boil. As the coolant within heat exchangers 50 and 60 begins to boil, vaporized coolant, such as steam, may be used to drive one or more turbines that convert the thermal potential energy of steam into electrical energy. After condensing, coolant is returned to locations near the base of heat exchangers 50 and 60. FIGS. 2A-2C illustrate schematic views of an example implementation of a spent fuel canister 200 operating in normal conditions having one stack or two stacks of spent fuel rods. Canister 200 includes a submersible vessel 202 that contains spent fuel rods 204 and coolant 206 surrounding the spent fuel rods 204. As shown schematically in FIG. 2A, canister 200 (filled to a coolant level 201) is supported in a spent fuel pool 256 filled with fluid 258 (e.g., water or some other suitable coolant). In some implementations, the fluid 258 in spent fuel pool 256 (filled to fluid level 203) is continuously or intermittently circulated by pumps or other hardware to improve heat transfer between vessel 202 and the fluid 258. Circulation of the fluid 258, in some aspects may increase the effectiveness of convective heat transfer between the canister 200 and the fluid 258. Vessel 202, in the example implementation, facilitates the dissipation of decay heat from multiple spent fuel rods 204. In this example, vessel 202 is an elongated capsule-shaped container, having a cylindrical main body with two elliptical or hemispherical heads on either end (e.g., the top head 205 and the bottom head 207). The shape of vessel 202, in this example provides a relatively large amount of available surface area (e.g., relative to the available volume) to facilitate convective heat transfer with both the coolant 206 contained within the vessel 202 and the fluid 258 surrounding the vessel 256 in the spent fuel pool 256. The shape of the vessel 202 also may facilitate gravity driven natural circulation of the contained coolant 206. In some examples, vessel 202 defines an outer diameter of between about 7 and 12 ft. and a length of about 72 D. In some examples, vessel 202 defines a surface area of about 1600 ft.2 Vessel 202 can be sized to lengths and diameters that can be accommodated in typical commercial nuclear spent fuel pools (e.g., 30 to 50 ft. in length). Vessel 202, in this example, is hermetically sealed and capable of pressurization to a specified design limit (e.g., 400-500 psia). As discussed below, the design limit pressure of vessel 202 may be particularly significant to vessel heat removal in abnormal operating conditions. The cylindrical shell or casing 208 of vessel 202, in this example, is a thin-walled construction fashioned from a corrosion resistant and heat conductive material (e.g., steel). In general, cylindrical shell 208 conducts heat and withstands pressure, thermal, radiation, and seismic induced stresses. The cylindrical shell 208 can be fabricated using materials approved for use in nuclear reactor pressure vessels. For example, in some implementations, cylindrical shell 208 includes a steel base material such as SA302 GR B, SA533 GR B, Class 1, SA 508 Class 2, or SA 508 Class 3 that may be clad with TYPE 308L, 309L TYPE 304 austenitic stainless steel. Other base materials can be implemented such as 161MnD5, 20MnMoNi55, 22NiMoCr3 7, 15Kh2MFA(A), 15Kh2NMFA(A) with Sv 07Kh25N13 and/or Sv 08Kh19N10G2B austenitic cladding. In some examples, cylindrical shell 208 does not provide any shielding to block or otherwise inhibit potentially harmful radiation generated by spent fuel rods 204. However, in some other examples, cylindrical shell 208 is provided with radiation shielding. Cylindrical shell 208 can be fabricated using rolled plate or ring forgings. The wall thickness of cylindrical shell 208 can be between about 1.5 and 4.5 inches. In any event, the material and thickness of cylindrical shell 208 provides sufficient strength to withstand stresses associated with the design limit pressurization. Spent fuel rods 204 are secured in place near the bottom of vessel 202 inside the riser channel 216 and supported by a lower support plate 214 (e.g., as also shown in FIG. 29) and lower support structure 211. As shown, the lower support plate 214 and riser channel 216 form a “basket” which cradles spent fuel rods 204 and facilitates natural circulation of coolant 206. In this example, fuel barrel support/shield 210 includes a fuel barrel and radiation shield that supports a plurality of individual racks 212. It is attached to lower support plate 214 and channel riser 216. Channel riser 216 is supported by upper support ring 218 and upper support structure 213. Racks 212 receive respective spent fuel rods 204 and maintain them in a relatively stable, e.g., non-critical, condition. For example, racks 212 can be fashioned from a material that includes a neutron absorber (e.g., boron) to inhibit criticality events. FIG. 2A shows a single stack of spent fuel 204 whereas FIG. 2C shows a double stack of spent fuel 204. FIG. 3A shows a first example fuel barrel support/shield structure 310a with a particular number (e.g., 37) of available racks 312a to accommodate respective spent fuel rods. FIG. 3B shows a second example fuel barrel support/shield structure 310b with another number (e.g., 97) of fuel accommodating racks 312b. Support structure 310b is significantly larger than support structure 310a, and therefore may require a larger vessel. For example, support structure 310a can be incorporated in a vessel having a 7 ft. outer diameter, while support structure 310b can be incorporated in a vessel having a 12 ft. outer diameter. The racks can be arranged to accommodate a wide variety of fuel types such as those typical of boiling water reactors (e.g., 8×8, 9×9, or 10×10 fuel assemblies) or the larger pressurized water reactor fuel assemblies (e.g., 17×17 fuel bundles). In these illustrations, racks 312a and 312b are rectilinear in cross-section defining an open area of about 11 and 28 ft2 respectively. Of course, other suitable shapes (e.g., circular, hexagonal, triangular, etc.) sizes can also be implemented. Further, as shown, racks 312a and 312b are arranged in a symmetrical, tightly packed honeycomb configuration. In some examples, this geometric configuration is provided for the dual purposes of heat removal and criticality mitigation. However, other suitable configurations can also be effectively implemented. For instance, racks 312a and 312b can be spaced apart from one another (as opposed to tightly packed), or arranged in some other symmetrical configuration quadrilateral configuration), as opposed to a honeycomb shape. Turning back to FIG. 2A, upper support ring 218 and lower support plate 214 forms the base of support for the riser channel 216. In addition, lower support plate 214 may have sufficient strength to bear the weight of spent fuel rods 204. Lower support plate 214 allows coolant 206 to flow upward past spent fuel rods 204 for convective heat transfer from the spent fuel rods 204 to the coolant. For example, lower support plate 214 can include small perforations or large openings that allow naturally circulating coolant 206 to flow up through the support plate and past spent fuel rods 204. The illustrated riser 216 extends upward from lower support plate 214 to surround the fuel barrel support/shield 210 and the spent fuel rods 204 supported in racks 212. As shown, riser 216 extends from a point near the top of the lower support plate 214 to the top of the upper support ring 218, a point that is approximately halfway to the vessel's upper head flange 219. For example, riser 216 can have a height of about 30 ft. In some examples, riser 216 is cylindrical in shape with a rounded shaped exit, so as to reduce form losses in the naturally circulating coolant 206. The example riser 216 defines a hollow bore 220 that serves to direct coolant 206 upward through the interior of vessel 202, and a narrow annulus 222 that directs coolant downward along the inner wall of vessel 202. Upper support ring 218 peels radially inward from the cylindrical shell 208 to the top of riser 216. Similar to support plate 214, upper support ring 218 also includes perforations or large openings that allow naturally circulating coolant 206 to pass downward through the upper support ring 218 and through annulus 222. Vessel 202 may initially be filled with an amount of liquid coolant 206. In particular, the vessel 202 is filled with at least enough coolant 206 to place the liquid level 201 above the top of the upper support ring 218. In some examples, vessel 202 is filled with about 35 m3 of liquid coolant 206. The coolant can include water and/or some additional type of coolant. For instance, coolant 206 under natural circulation conditions may generate a convective heat transfer coefficient of between about 1000-2500 (W/m2K on the inside surface of cylindrical shell 208. Coolant 206 can be engineered to undergo a liquid-to-gas phase change under certain conditions (e.g., when convective heat transfer to the ambient fluid 258 in the spent fuel pool 256 has significantly decreased) to maintain the heat removal rate at a substantially constant level in abnormal operating conditions, as explained in detail below. In operating under normal conditions as shown in FIG. 2A (e.g., no loss of power or loss of fluid 258) vessel 202 is submerged in the spent fuel pool fluid 258. Natural circulation of the coolant 206 inside of vessel 202 is established by the buoyancy force generated as a result of the density and elevation differences between hot coolant 206 in contact with the spent fuel 204 and cooler coolant 206 in annulus 222. That is, when coolant 206, in contact with the spent fuel 204, is heated by the decay heat emanating from spent fuel rods 204, the coolant 206 becomes less dense and begins to rise. The rising coolant 206 is directed upward through racks 212 holding spent fuel rods 204. As the coolant 206 flows up past the spent fuel rods 204, it receives even more heat, which makes it continue to flow upward. Riser 216 directs the heated coolant 206 upward through bore 220, away from spent fuel rods 204 and toward the exit of the channel riser 216 near the top of the upper support ring 218. Coolant 206 emerging from riser 216 is cooled down through convective heat transfer with the inner surface of vessel 202. The heat is conducted through the wall of vessel 202 then transferred by convection to the spent fuel pool fluid 258. The cooled coolant 206 becomes denser and is therefore drawn downward by gravity. The sinking coolant 206 is directed trough the perforated upper support ring 218 of support structure 210 and through annulus 222, through the perforated lower support plate 214 and ultimately returning to the lower head 207 of vessel 202. FIG. 4 illustrates a schematic view of an example implementation of spent fuel canister 200 operating in abnormal conditions. In some implementations, spent fuel canister 200 is designed to operate in abnormal operating conditions, while maintaining a substantially constant rate of decay heat removal. In some aspects, the abnormal operating condition is an emergency situation where spent fuel pool 256 has been drained or the fluid 258 has evaporated (as shown in FIG. 4). However, other types of abnormal operating conditions may also occur (e.g., loss of fluid circulation in the spent fuel pool 256). In such abnormal operating conditions, an amount of convective heat transfer between vessel 202 and the surrounding ambient environment may be significantly reduced. The reduced rate of heat transfer ultimately causes liquid coolant 206 in contact with the spent fuel 204 to undergo a liquid-to-gas phase change. A low density, two-phase coolant mixture 206c rises up through the spent fuel 204 and exits the top of the riser channel 216. At the top of the riser 216, the gas phase coolant 206a and the liquid phase coolant 206b separate from the two-phase coolant 206c by gravity. The liquid phase coolant 206b travels downward through the perforated upper support ring 218 into the annulus 222. The gas phase coolant 206a continues to travel upward in the vessel 202 to the upper head 205. When the gas phase coolant 206a comes in contact with the inside wall of the vessel 202, it exchanges heat with the wall to produce a condensate 206d. The condensate 206d may be in the form of a liquid film or droplets that travel downward along the inside wall of the vessel 202. The condensate 206d collects in the region above the upper support ring 218 and mixes with the downward flowing liquid coolant 206b. The condensate 206d and the liquid phase coolant 206b travel downward through the annulus, through the perforated lower support plate 214 and lower head 207 plenum and back upward through the spent fuel racks 212. In this example, the canister can transition from liquid cooling (e.g., water) to air cooling in the spent fuel pool 256 without the need for operator actions or external power. As noted above, the heat removal rate of the air cooled canister 200 may be substantially equal to that of the liquid cooled canister 200. In particular, the liquid-to-gas phase change may cause the inner cavity of vessel 202 to pressurize. Pressurization of vessel 202 increases the saturation temperature within the vessel 202, and thus raises the temperature of its outer surface. The increased outer surface temperature of vessel 202 increases both the thermal radiation heat transfer rate to the surroundings and the free convection heat transfer rate with the ambient air 260 (as opposed to liquid 258 in the spent fuel pool during normal operating conditions) to a point where the overall heat removal rate of canister 200 is acceptable. For example, the large surface area and high surface temperature of vessel 202 may be sufficient to remove heat from the canister 200 to the ambient air 260 at substantially the same rate as with the fuel pool fluid 258. FIGS. 5A-5B illustrate schematic views of an example implementation of a spent fuel canister 400 that includes an external heat exchanger 424 and is operating in normal conditions. As shown, heat exchanger 424 includes a horizontal upper tube header 223a and a horizontal lower tube header 223b joined together by a series of c-shaped vertical heat exchanger tubes 226. The heat exchanger tubes can be 2 to 4 inches in diameter and 15-20 feet in length. The upper tube header 223a, in this example, is connected to cylindrical shell 208 below the coolant level 201 and above the upper support ring 218 by header conduit 225a. The lower tube header 223b is connected to annulus 222 by header conduits 225b. In some examples, header conduits 225a and 225b are sloped such that liquid flowing through the conduits is always in the downward direction. The heat exchanger 424 is designed to withstand hill pressure and temperatures during normal and abnormal conditions. As shown in FIG. 5A, during normal conditions, hot liquid coolant 206 rises through the bore 220 to the outlet of the riser 216. Approximately half of the liquid coolant 206 enters the upper header conduits 225a into heat exchanger 424 where it transfers heat to the spent fuel pool fluid 258. The remaining half of the liquid coolant travels through the perforated upper support ring 218 into the annulus 222 where it transfers heat to the spent fuel pool fluid 258 by convection and conduction heat transfer through the vessel 202 walls. The flow paths for the coolant 206, in this example, are established by natural circulation created by the buoyancy force established by the density difference of the coolant in the bore 220 and the annulus 222 and the relative elevation of their thermal centers. FIG. 5C illustrates a schematic view of an example implementation of a spent fuel canister 400 that includes an external heat exchanger 424 and is operating in abnormal conditions. In this example, although similar to that illustrated in FIG. 4, the addition of heat exchanger 424 provides additional surface area for natural circulation cooling. Convection heat transfer inside the tubes can increase the heat removal rate capacity of the canister thereby reducing the overall height of the canister. In the present example, a sixty-five tube heat exchanger of 16 ft. tube length can reduce the canister height by at about 30% (e.g., from 72 feet to 50 feet) while rejecting the same amount of heat, 0.35 MW to the ambient air 206. In some examples, heat exchanger 424 is a sixty-five tube heat exchanger or an approximately 150 tube heat exchanger. The number and lengths of heat exchanger tubes 226 can be selected to provide a wide range of desired heat removal rates. FIGS. 6A-6B illustrate schematic views of another example implementation of a spent fuel canister 500 that includes an external heat exchanger 525 and is operating in normal conditions. As shown, heat exchanger 524 includes a horizontal upper tube header 223a, a horizontal lower tube header 223b joined together by a series of c-shaped vertical heat exchanger tubes 226. The heat exchanger tubes can be 2 to 4 inches in diameter and 15-20 feet in length. In the illustrated example, the heat exchanger 525 is connected to cylindrical shell 208 between the level 201 and the upper support ring 218 by header conduit 225a. The lower tube header 223b is connected to annulus 222 by header conduits 225b. Header conduits 225a and 225b are sloped such that liquid flowing through the conduits is always in the downward direction. The heat exchanger 524, in some aspects, is designed to withstand full pressure and temperatures during normal and abnormal conditions. During normal conditions, the heat transfer mechanism may be identical or substantially similar to the same as those described for FIG. 2A. FIG. 6C shows canister 500 operating under abnormal conditions, rejecting heat to ambient air 206. The liquid phase coolant behaves as described previously for FIG. 4. However, because heat exchanger 524 is connected to the gas phase region of the canister, (e.g., through riser 216) a portion of the gas phase coolant 206a is condensed inside the heat exchanger tubes. This creates a low pressure region inside the tubes 526 which draws additional gas phase coolant 206a into the tubes. The condensate 206d inside the tubes 526 falls by gravity through the tubes 526 into the cylindrical shell. The condensate mixes with the two-phase coolant 206c in the region above the upper support ring 218. The liquid phase coolant 206b travels downward by gravity through the perforated upper support ring 218 into the annulus 222, through the perforated lower support plate 214, through the plenum formed by the lower head 207. It flows upward through the spent fuel racks 212 thereby cooling the spent fuel 204. Another implementation of the present disclosure features various methods of dissipating decay heat generated by a spent fuel rod. FIG. 7 illustrates an example method 700 for dissipating decay heat. The method includes, at step 702, submerging a spent fuel canister in a heat transfer fluid contained in a spent fuel pool. As described above, the spent fuel canister can include a cylindrical shell defining an interior cavity which contains the spent fuel rod. At step 704, decay heat is transferred from the spent fuel rod to liquid coolant contained within the canister. In some implementations, the coolant is circulated within the canister via natural circulation to facilitate heat transfer. At step 706, the decay heat is transferred from the coolant, through a wall of the canister, to the heat transfer fluid of the spent fuel pool. A rate at which heat is transferred from the spent fuel rod is at least as great as orate at which the spent fuel rod produces decay heat. Method 700 can also optionally include, at step 708, exposing the canister to ambient air due to a loss of spent fuel pool fluid. At step 710, based on the exposure to ambient air, a portion of the coolant inside the canister is phase changed from a liquid to a gas. At step 712, heat is transferred, through a wall of the canister, from the gas phase coolant to the ambient air. At step 714, the gas phase coolant is condensed back to a liquid and circulated (e.g., via natural circulation) within the canister. Yet another implementation of the present disclosure features various methods of managing spent fuel rods by cycling them through spent fuel canisters. FIG. 8 illustrates an example method 800 for managing spent fuel rods. The method includes, at step 802, removing a first batch of spent fuel rods from a nuclear reactor. At step 804, the first batch of spent fuel rods is installed in a spent fuel canister (e.g., spent fuel canister 100) at a first time (T1). At step 806, the spent fuel canister is submerged in a heat transfer fluid (such as contained in spent fuel pool 156). At step 808, the canister is used to remove decay heat from the first batch of spent fuel rods for a time period (T). At step 810, a second batch of spent fuel rods is installed within the spent fuel canister at a second time (T2). The heat removal rate of the spent fuel canister is at least as great as the combined decay heat rate of the first and second batches of spent fuel rods at T2. As discussed in context of the first and second examples below, the example method of FIG. 8 can be used to continuously manage spent fuel from a nuclear reactor. In some aspects, an example spent fuel management system (e.g., spent fuel management system 154) that includes a spent fuel pool and multiple spent fuel canisters according to the present disclosure (e.g., spent fuel canister 100, 200, 400, and/or 500) manages spent fuel from nuclear reactors (e.g., 1-12 nuclear reactors 152) each effectively refueled once every twenty-four months, with a spent fuel batch of one-half core, approximately 18 fuel assemblies being removed every two months. Each batch of spent fuel produces approximately 0.2 MW of decay power after twenty days, and 0.1 MW of decay power after six months. Spent fuel that has decayed for six months can be discharged from the spent fuel canisters into, for example, a typical liquid coolant filled, non-pressurized, spent fuel pool. After an additional period of cooling, for example 5-10 years, the spent fuel can be discharged to a dry cask. In this example, there is sufficient liquid coolant 158 in the spent fuel pool 156 to provide 20 days of cooling before transitioning to cooling by ambient air. The system includes two spent fuel canisters, each capable of achieving at least 0.5 MW of decay heat removal when fully immersed in spent fuel pool coolant 158 and 0.35 MW decay heat removal after the 20 day transition cooling period. Table 1 below illustrates an example linear sequence for canister loading and unloading to accommodate spent fuel from the nuclear reactor. In Table 1, “T” is in months and “B#” represents a particular batch of spent fuel. A “+” indicates that the batch is loaded into the canister and a “−” indicates that the batch is removed. TABLE 1Canister #T = 0T = 2T = 4T = 6T = 8T = 10Canister 1+B1+B3−B10.35 MW0.5 MW+B50.5 MWCanister 2+B2+B4−B20.35 MW0.5 MW+B60.5 MWCanister #T = 12T = 14T = 16T = 18T = 20T = 22T = 24Canister 1−B3−B5−B7−B9+B7+B9+B11+B130.5 MW0.5 MW0.5 MW0.5 MWCanister 2−B4−B6−B8+B8+B10+B120.5 MW0.5 MW0.5 MW In the example sequence presented in Table 1, all of the spent fuel batches would have decayed for eight months prior to discharge. This approach, in some aspects, eliminates the potential risks associated with having higher power density spent fuel placed directly next to lower power density spent fuel. The higher power density spent fuel presents the greater risk of zirconium cladding ignition in air in the event of a loss of spent fuel pool water 158 which could potentially ignite the lower power density spent fuel. In another example spent fuel management system, the system may manage spent fuel from nuclear reactors (e.g. 1-12 nuclear reactors 152) each effectively refueled once every twenty-four months, with a spent fuel batch of one-half core being removed every two months. Each batch of spent fuel provides 0.2 NM of decay power after twenty days, and 0.1 MW of decay power after six months. Spent fuel that has decayed for six months can be discharged from the spent fuel canisters into, for example, a typical liquid coolant filled, non-pressurized, spent fuel pool. After an additional period of cooling, for example 5-10 years, the spent fuel can be discharged to a dry cask. The system includes a single spent fuel canister capable of achieving at least 0.65 MW decay heat removal when fully immersed in spent fuel pool coolant 158 and 0.45 MW decay heat removal after the 20 day transition cooling period. Table 2 below illustrates a linear sequence for canister loading and unloading to accommodate spent fuel from the nuclear reactor using the larger spent fuel canister. TABLE 2Canister #T = 0T = 2T = 4T = 6T = 8T = 10Canister 1+B1+B2+B3−B1−B2−B30.35 MW0.5 MW0.65 MW+B4+B5+B60.65 MW0.65 MW0.65 MWCanister #T = 12T = 14T = 16T = 18T = 20T = 22T = 24Canister 1−B4−B5−B6−B7−B8−B9−B10+B7+B8+B9+B10+B11+B12+B130.65 MW0.65 MW0.65 MW0.65 MW0.65 MW0.65 MW0.65 MW Note that this larger spent fuel canister, in some aspects, provides sufficient space to accommodate a six month discharge of the spent fuel batches. In another example spent fuel management system, the system may manage spent fuel from a single nuclear reactor effectively refueled once every forty-eight months, with a spent fuel hatch of one-full core (e.g. 37 assemblies) being removed and replaced. Each batch of spent fuel produces 0.4 MW of decay power after twenty days and 0.2 MW of decay power after six months. Spent fuel that has decayed for six months can be discharged from the spent fuel canisters into, for example, a typical liquid coolant filled, non-pressurized, spent fuel pool. After an additional period of cooling, for example 5-10 years, the spent fuel can be discharged to a dry cask. The system includes a single spent fuel canister capable of achieving at least 0.85 MW decay heat removal when fully immersed in spent fuel pool coolant 158 and 0.6 MW decay heat removal after the 20 day transition cooling period. Table 3 below illustrates a linear sequence for canister loading and unloading to accommodate spent fuel from the nuclear reactor using the larger spent fuel canister. TABLE 3Canister #T = 0T = 4 yrsT = 8 yrsT = 12 yrsT = 16 yrsT = 18 yrsT = 24 yrsCanister 1+B1+B2−B1−B2−B3−B4−B50.7 MW0.85 MW+B3+B4+B5+B6+B70.85 MW0.85 MW0.85 MW0.85 MW0.85 MW The use of terminology such as “front,” “back,” “top,” “bottom,” “over,” “above,” and “below” throughout the specification and claims is for describing the relative positions of various components of the system and other elements described herein. Similarly, the use of any horizontal or vertical terms to describe elements is for describing relative orientations of the various components of the system and other elements described herein. Unless otherwise stated explicitly, the use of such terminology does not imply a particular position or orientation of the system or any other components relative to the direction of the Earth gravitational force, or the Earth ground surface, or other particular position or orientation that the system other elements may be placed in during operation, manufacturing, and transportation. A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, advantageous results may be achieved if the steps of the disclosed techniques were performed in a different sequence, if components in the disclosed systems were combined in a different manner, or if the components were replaced or supplemented by other components. Accordingly, other implementations are within the scope of the following claims. |
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summary | ||
claims | 1. A method for dismantling a steam generator or heat exchanger, said steam generator or heat exchanger including a plurality of primary circuit tubes having an interior with a contaminated inner tube surface, wherein one or more of said tubes are sealed with a plug at both tube ends, the method comprising the steps of:a) opening one or both ends of each sealed tube by creating an opening in the respective plug or by removing the respective plug;b) introducing a viscous polymer which will cure inside the tube into the initially sealed and now opened tube or tubes, said polymer filling the tube across the full tube cross-section at least in a region of the tube ends and immobilizing contaminations in the filled portion inside the tube;c) curing the polymer, then detaching the tubes provided with the polymer, the detached tubes being sealed by the cured polymer;d) sorting out the detached tubes provided with the polymer. 2. The method according to claim 1, characterized in that the viscous polymer is a cross-linking polymer which performs cross-linking through polyaddition and comprises, a silicone and/or polyurethane and/or epoxy resin. 3. The method according to claim 1, characterized in that the interior of the tube is filled completely with the polymer, or the interior of the tube is filled with the polymer in a region from each tube end up to 0.5 meters beyond a tube sheet. 4. The method according to claim 1, characterized in that the polymer is introduced using one or more lines, wherein a line is inserted into the tube through an opened tube end or a respective line is inserted through each respective opened tube end of a tube. 5. The method according to claim 4, characterized in that the tubes are U-shaped tubes both ends of which end in a tube sheet, wherein a line is inserted through one of the opened tube ends and is then led to the turning point of the U-shaped tube, and wherein the polymer is then injected into the tube through the line, while the line is being retracted from the tube until the interior of the corresponding half of the tube is filled with polymer. 6. The method according to claim 4, characterized in that the tubes are U-shaped tubes both ends of which end in a tube sheet, wherein a line is inserted into the tube through one of the opened tube ends and is then led into the tube as far as about 0.5 meters beyond the tube sheet, and wherein the polymer is then injected into the tube through the line, while the line is being retracted from the tube until the corresponding portion of the tube is filled with polymer. 7. The method according to claim 5, characterized in that simultaneously with, or subsequently to, the injection of the polymer into the corresponding half of the U-shaped tube, the second half is filled with polymer through another opened tube end in a like manner. 8. The method according to claim 1, characterized in that prior to opening the sealed tubes, all tubes which are not provided with plugs are decontaminated, through mechanical or chemical cleaning processes. 9. The method according to claim 1, characterized in that the openings in the plugs are created by drilling. 10. The method according to claim 1, characterized in that the detaching of the tubes provided with the polymer also involves detaching the open tubes which are not provided with plugs and subsequently sorting out the tubes provided with polymer. 11. The method according to claim 1, characterized in that the tubes provided with polymer and/or the open tubes not provided with plugs are detached directly at or near a tube sheet or at the level of a tube sheet, said detaching being performed along a provided separation line (A). 12. The method according to claim 3, characterized in that the tubes completely filled with polymer are segmented into multiple pieces, said segmenting being performed through cutting and/or sawing and/or thermal separation processes. 13. The method according to claim 1, characterized in that the detached and sorted tubes provided with the polymer are treated and/or disposed of as radioactive waste, and/or the open tubes not provided with plugs are treated and/or disposed of as less radioactive waste or non-radioactive waste after dismantling. 14. The method according to claim 1 wherein the steam generator or heat exchanger is a steam generator or heat exchanger of a nuclear power plant. 15. The method according to claim 6, characterized in that simultaneously with, or subsequently to, the injection of the polymer into the corresponding portion of the U-shaped tube, the second portion of the tube is filled with polymer through the second opened tube end in a like manner. 16. The method according to claim 8 characterized in that prior to opening the sealed tubes, all tubes which are not provided with plugs are decontaminated through abrasive processes or through scavenging processes using solvents. 17. The method according to claim 9, characterized in that the openings in the plugs are created by a two-stage drilling process to avoid loose pieces. 18. The method according to claim 11, characterized in that the tubes provided with polymer and/or the open tubes not provided with plugs are detached directly at or near a tube sheet or at the level of a tube sheet by sawing. 19. The method according to claim 11, characterized in that the provided separation line (A) is orthogonal to the vertically extending tubes. 20. The method according to claim 3, characterized in that the tubes completely filled with polymer are segmented into multiple pieces after detachment. |
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051456362 | claims | 1. A method of producing a rhenium-188 radionuclide generator, comprising: irradiating a water soluble irradiation target selected from the group consisting of sodium tungstate and lithium tungstate, reacting the irradiated target with an aqueous zirconium solution to obtain an insoluble zirconium tungstate gel, and disposing the zirconium tungstate in an elutable container to obtain the rhenium-188 radionuclide generator. 2. The method of claim 1 wherein the irradiation target is sodium tungstate. 3. A method of producing rhenium-188 comprising irradiating a water soluble irradiation target selected from the group consisting of sodium tungstate and lithium tungstate, reacting the irradiated target with an aqueous zirconium solution to obtain an insoluble zirconium tungstate gel, disposing the zirconium tungstate in an elutable container and eluting the gel to recover rhenium-188. 4. The method of claim 3 wherein the irradiation target is sodium tungstate. |
claims | 1. An illumination system comprising:a source of light having a wavelength of less than or equal to 193 nm; andan optical element in a path of said light, having a first raster element, a second raster element, a third raster element and a fourth raster element situated thereon,wherein said second raster element is adjacent to said first raster element, and located a first distance from said first raster element,wherein said fourth raster element is adjacent to said third raster element, and located a second distance from said third raster element, andwherein said second distance is different from said first distance. 2. The illumination system of claim 1, further comprising:a first local coordinate system defined by a first x-axis, a first y-axis, and a first z-axis that are perpendicular to one another, wherein said first distance and said second distance are in a direction of said first y-axis;a second local coordinate system defined by a second x-axis, a second y-axis, and a second z-axis that are perpendicular to one another;a first plane that includes said first y-axis and said second y-axis; anda field plane in a path of said light, downstream from said optical element, wherein said field plane is perpendicular to said first plane, and includes said second x-axis and said second y-axis. 3. The illumination system of claim 1, further comprising:a field plane in a path of said light, downstream from said optical element;a first local coordinate system defined by a first x-axis, a first y-axis, and a first z-axis that are perpendicular to one another, wherein said first y-axis is situated on said optical element; anda second local coordinate system defined by a second x-axis, a second y-axis, and a second z-axis that are perpendicular to one another, wherein said second y-axis is situated in said field plane,wherein said light includes a set of light bundles that impinges on said optical element along said first y-axis, and said illumination system directs said set of light bundles to illuminate a portion of said field plane along said second y-axis. 4. The illumination system of claim 1, further comprising:an optical field element in said light path, upstream of said optical element, having a plurality of field raster elements onto which a beam of said light impinges, and thus partitions said light into a plurality of individual light bundles that form a plurality of secondary light sources. 5. The illumination system of claim 4,wherein said first raster element is a first pupil raster element, said second raster element is a second pupil raster element, said third raster element is a third pupil raster element, and said fourth raster element is a fourth pupil raster element,wherein said plurality of field raster elements includes a first field raster element, a second field raster element, a third field raster element and a fourth field raster element,wherein said plurality of individual light bundles includes a first light bundle, a second light bundle, a third light bundle and a fourth light bundle, andwherein said first pupil raster element receives said first light bundle from said first field raster element, said second pupil raster element receives said second light bundle from said second field raster element, said third pupil raster element receives said third light bundle from said third field raster element, and said fourth pupil raster element receives said fourth light bundle from said fourth field raster element. 6. The illumination system of claim 5, further comprising an optical component that images said secondary light sources into tertiary light sources in an exit pupil of said illumination system. 7. The illumination system of claim 6, wherein said plurality of pupil raster elements are arranged to compensate for a distortion of said optical component, such that said tertiary light sources have a regular distribution. 8. The illumination system of claim 6, wherein said plurality of pupil raster elements are situated such that said tertiary light sources are arranged on parallel lines. 9. The illumination system of claim 6, wherein said plurality of pupil raster elements are arranged such that said tertiary light sources are arranged on a grid. 10. The illumination system of claim 6, wherein said tertiary light sources are located inside a circle. 11. The illumination system of claim 6, wherein said tertiary light sources are located inside a circle with a mid-obscuration. 12. The illumination system of claim 6, wherein said optical component comprises a mirror. 13. The illumination system of claim 12, wherein said mirror is a grazing incidence mirror. 14. The illumination system of claim 12, wherein said mirror is a normal incidence mirror. 15. The illumination system of claim 4,wherein said plurality of field raster elements are arranged in rows, andwherein at least one of said plurality of rows is displaced relative to an adjacent row. 16. The illumination system of claim 1, wherein said raster elements are arranged on a distorted grid. 17. The illumination system of claim 1,wherein said first raster element, said second raster element, said third raster element, and said forth raster element are four of a plurality of pupil raster elements, andwherein said plurality of pupil raster elements are arranged in arc-shaped rows. 18. A projection exposure system comprising:a support for holding a mask;a support for holding a light sensitive object;the illumination system of claim 1 to illuminate said mask; anda projection lens to image said mask onto said light sensitive object. 19. The projection exposure system of claim 18, wherein said projection exposure system scans said mask in a direction of said second y-axis. 20. A method, comprising employing the projection exposure system of claim 18 to produce a micro electronic device having a structure defined by said mask. 21. An illumination system, comprising:a source of light having a wavelength of less than or equal to 193 nm;a first optical element in a path of said light, having a plurality of field raster elements;a second optical element in said path, downstream of said first optical element, having a plurality of pupil raster elements;wherein said plurality of pupil raster elements receive said light from said plurality of field raster elements, andwherein said plurality of pupil raster elements are arranged in an irregular pattern on said second optical element. 22. The illumination system of claim 21,wherein said plurality of pupil raster elements are arranged in a plurality of rows that includes a first row, a second row adjacent to said first row, and a third row adjacent to said second row,wherein said second row is spaced from said first row by a first distance, and said third row is space from said second row by a second distance, andwherein said second distance is different from said first distance. 23. the illumination system of claim 21,wherein said plurality of pupil raster elements comprises a first pupil raster element, a second pupil raster element, a third pupil raster element and a fourth pupil raster element,wherein said second pupil raster element is adjacent to said first pupil raster element,wherein said fourth pupil raster element is adjacent to said third pupil raster element,wherein said second pupil raster element is situated a first distance from said first pupil raster element,wherein said fourth pupil raster element is situated a second distance from said fourth raster element, andwherein said second distance is different from said first distance. 24. An illumination system, comprisinga source of light source having a wavelength of less than or equal to 193 nm;a first optical element having a plurality of field raster elements that receive said light from said source and provide a plurality of secondary light sources;a second optical element having a plurality of pupil raster elements that receive said light from said plurality of field raster elements, and redirect said light; andan optical component that receives said light from said second optical element, and images said secondary light sources into a plurality of tertiary light sources in an exit pupil of said illumination system,wherein said plurality of pupil raster elements are arranged to compensate for a distortion of said optical component, such that said tertiary light sources have a regular distribution. 25. The illumination system of claim 24, wherein said plurality of pupil raster elements are situated such that said tertiary light sources are arranged on parallel lines. 26. The illumination system of claim 24, wherein said plurality of pupil raster elements are situated such that said tertiary light sources are arranged on a grid. 27. The illumination system of claim 24, wherein said tertiary light sources are located inside a circle. 28. The illumination system of claim 24, wherein said tertiary light sources are located inside a circle with a mid-obscuration. 29. The illumination system of claim 24, wherein said optical component comprises a mirror. 30. The illumination system of claim 29, wherein said mirror is a grazing incidence mirror. 31. The illumination system of claim 29, wherein said mirror is a normal incidence mirror. |
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claims | 1. A method of separating amorphous iron oxides from a sample of nuclear reactor corrosion products, comprising the steps of:(a) obtaining a water sample containing the corrosion products from the nuclear reactor coolant loop;(b) filtering said water sample containing corrosion products to separate granules containing radioactive iron oxides from the water;(c) applying ultrasonic vibration and an acid liquor mixture comprising a first acid liquor selected from a group consisting of nitric acid, sulfuric acid, carbonic acid and hydrofluoric acid and having a concentration between 0.01 M and 5M and a second acid liquor selected from a group consisting of nitric acid, sulfuric acid, carbonic acid and hydrofluoric acid and having a concentration between 0.05M and 3M to the granules containing radioactive iron oxides to obtain a solution containing amorphous radioactive iron oxides and undissolved crystalline radioactive iron oxides and then separating said solution from the granules containing crystalline radioactive iron oxides by filtering;(d) quantitatively analyzing the solution with amorphous radioactive iron oxides with inductively coupled plasma (ICP) to obtain a concentration of amorphous iron oxides in the solution;(e) quantitatively analyzing the granules containing crystalline radioactive iron oxides with X-ray diffraction (XRD) to obtain a weight percentage of crystalline radioactive iron oxides in each granule; and(f) dissolving said granules containing crystalline radioactive iron oxides with aqua regia to obtain a solution containing crystalline radioactive iron oxides and quantitatively analyzing the solution containing crystalline radioactive iron oxides with ICP quantitative analysis to obtain a concentration of crystalline iron oxides in the solution, wherein said granules containing crystalline radioactive iron oxides have granular sizes bigger than 0.45 micrometer (μm); and wherein said acid liquor mixture and said aqua regia have concentrations between 0.01M and 5M. 2. The method according to claim 1, wherein, in step (a), said water sample is obtained at a port selected from a group consisting of a condensate demineralizer (CD) inlet, a CD outlet and a feed water (FW) port. 3. The method according to claim 1, wherein said first acid liquor and said second acid liquor are mixed at a ratio of 20%˜99%:1%˜80%. 4. The method according to claim 1, wherein said acid liquor mixture has a pH value of pH0.01 to pH2.0. 5. The method according to claim 1, wherein, in step (c), said acid liquor mixture is added at a temperature of 40 Celsius degrees (° C.) to 100° C. for 5 to 60 minutes. |
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summary | ||
description | This application is related to a pending U.S. patent application entitled, “Length-of-the-Curve Stress Metric for Improved Characterization of Computer System Reliability,” by inventors Kenny C. Gross, Keith A. Whisnant, and Ayse K. Coskun, having Ser. No. 11/787,533, now U.S. Pat. No. 7,483,816 and filing date Apr. 16, 2006, which is hereby incorporated by reference. 1. Field of the Invention The present invention relates to techniques for testing computer systems. More specifically, embodiments of the present invention relate to a technique for determining an optimal stress test or combination of stress tests to characterize computer-system reliability. 2. Related Art Many precursors of component failures in computer systems, as well as the associated failure mechanisms, can only be determined by applying a stressful load onto the computer systems. For example, the stressful load may be applied for a period of time (typically, between a few hours and 24 hrs) in an attempt to trigger a fault. This technique is often used during root-cause analysis (RCA) and to confirm intermittent failures in computer systems that are returned by customers. Typically, a variety of stress tests are used for these purposes, each of which applies a different load, and thereby stresses different components in a given computer system. During many of these stress tests, such as during an RCA for problems on system boards, the underlying effect of interest is temperature dynamics, which can trigger subtle failure mechanisms that cause intermittent failures. For example, these failure mechanisms may include: solder fatigue, interconnect fretting, delamination of bonded components, stresses caused by non-coplanarity of stacked components, and/or deterioration of connectors. Some stress tests are known to cause the temperatures of processors (or processor cores) and ASICs to go up significantly (for example, by 6-12 C). Moreover, temperature cycling accelerates the aforementioned failure mechanisms even more, because many of these failure mechanisms are associated with the cumulative effect of temperature cycling and temperature gradients in the computer systems. Unfortunately, existing stress tests do not efficiently increase the occurrence of many of the failure mechanisms that affect computer systems. Moreover, for a given stress test and/or failure mechanism, the optimal test conditions for a given computer system are typically not known. Consequently, stress tests are often performed for a long time or on a large population of suspected computer systems in an attempt to trigger sufficient failures to enable proper RCA. Hence, what is needed is a technique for characterizing stress tests to determine the optimal stress test and/or combinations of stress tests, as well as the associated test conditions, without the above-described problems. One embodiment of the present invention provides a system for selecting tests to exercise a given computer system. During operation, the system tests the given computer system using a set of tests, where a given test includes a given load and a given cycling time selected from a range of cycling times. Moreover, for the given test, the system monitors a stress metric in the given computer system. Additionally, the system selects at least one of the tests from the set of tests to exercise the given computer system based on the monitored stress metric. In some embodiments, the given cycle time for the given load can include an idle time, during which the given load is not executed. In some embodiments, the given load includes an application. Moreover, the application may be configured to stress a portion of the given computer system, which can include: a processor, memory, an application-specific integrated circuit, an input/output interface, and/or a disk drive. In some embodiments, the selected test corresponds to the worst-case monitored stress metric. Moreover, the selected test may be used during reliability or failure-analysis testing of the given computer system. In some embodiments, tests are selected for different types of computer systems, and where a given selected test is subsequently used for a given type of computer system. In some embodiments, the stress metric includes thermal dynamics of the given computer system. Moreover, the stress metric may be determined from temperature samples measured at different locations in the given computer system. Additionally, in some embodiments at least some of the temperature samples are multiplied by an associated weight when determining the stress metric. In some embodiments, the determination of the stress metric involves: computing a length of a line between adjacent temperature samples, where the line includes a component that is proportionate to a difference between values of the adjacent temperature samples and a component that is proportionate to a time interval between the adjacent temperature samples; and adding the computed length to a cumulative length variable, which is used as the stress metric. Moreover, the computed length may be adjusted based on a function of the magnitude of the adjacent temperature samples. For example, the adjustment may involve multiplying the length of the lines by an associated weight. In some embodiments, computing the length of the line between adjacent temperature samples involves computing √{square root over (|S1−S2|2+t2)}, where S1 and S2 are magnitudes of the adjacent temperature samples and t is the magnitude of the time interval between the adjacent temperature samples. In some embodiments, the temperature samples are measured at pre-determined time intervals. Another embodiment provides a method including at least some of the above-described operations. Another embodiment provides a computer program product for use in conjunction with the system. Table 1 provides stress-test combinations and associated cycling times for use in selecting tests to exercise a computer system. Note that like reference numerals refer to corresponding parts throughout the drawings. The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. Embodiments of a system, a method, and a computer program product (i.e., software) for use with the system are described. These systems and processes may be used to determine an optimal combination of stress tests and associated cycling times for a given computer system. In particular, while there are a wide variety of stress tests, selecting the appropriate stress test(s) and test conditions for a particular failure mechanism, type of computer, or even for a given application (such as one that is I/O intensive versus one that is processor intensive) that is to execute on the given computer is often ad hoc. Consequently, the stress test(s) used during qualification, ‘burn-in,’ and/or RCA is often sub-optimal, and therefore, often does not achieve the worst-case thermal dynamics in the given computer system. In the discussion that follows, different combinations of stress tests and associated cycling times (e.g., how long they are run) are used in conjunction with a stress metric to identify the optimal stress test (or combination of stress tests), including the test conditions (such as the cycling time). In some embodiments, the stress metric is based on system-telemetry measurements in the given computer system, such as temperature measurements. Moreover, data obtained in these temperature measurements may be analyzed to generate a cumulative length-of-curve (LOC) value, which summarizes the thermal dynamics during a given stress test. Note that system-telemetry data and the results of the stress tests may be received and transmitted over a network, such as: the Internet or World Wide Web (WWW), an Intranet, a local area network (LAN) (such as IEEE 802.11 or WiFi), a wide area network (WAN) (such as IEEE 802.16 or WIMAX), a metropolitan area network (MAN), a satellite network, a wireless network (such as a cellular telephone network), an optical network, and/or a combination of networks or other technology enabling communication between computing systems or electronic devices. We now describe embodiments of a system, a method, and software for selecting stress tests to exercise the given computer system. For rapid RCA of a wide class of failure mechanisms in computer systems, escalation engineering teams have traditionally executed stress tests (which are also referred to as loads or exerciser scripts) onto the suspect computer systems in an effort to accelerate the intermittent failure mechanism so that the failure mode can be reproduced and the root cause can be established. In general, given an available group of stress tests, such as those provided in a Validation Test Suite, the selection of the stress test(s) to run is often based on anecdotal success stories or subjective personal preference(s). For example, a particular stress test that worked well in identifying an earlier failure mechanism may be used to try to identify an as-yet-unknown failure mechanism. Unfortunately, quantitative metrics of the relative effectiveness of the various stress tests, which can be used pick the best one(s) or to determine how best to use the various stress tests, are typically not available. Moreover, a wide variety of fundamental questions associated with stress tests remain unanswered. For example: If a given stress test is cycled on and off with a cycling period or time of P minutes, is the resulting stress level (in terms of the resulting thermal dynamics) larger than if this stress test were run continuously for X hours? If the cycling period P were made shorter or longer, does the stress level increase? If two stress tests are executed simultaneously or concurrently, is the stress level larger than if either stress test is run alone? If three stress tests are executed simultaneously or concurrently, is the stress level larger than that achieved by running either one alone, or by running different combinations of stress tests? If these stress tests are cycled simultaneously or concurrently with cycling periods or times P1, P2, and P3, are there optimal values for these cycling times to produce a maximum thermal-dynamic stress level on system boards in the given computer system (for example, during RCA analysis)? In the discussion that follows, a systematic parametric technique is provided. This technique leverages continuous system-telemetry data to answer these questions and, for an arbitrary computer system (such as a server), to identify the optimal combination of available stress tests or exercisers and cycling times or periods that produce the maximal thermal-dynamic stress levels. Note that this optimal combination may be used to: enhance RCA of suspect computer systems during stress testing; improve accelerated lifetime studies of computer systems (such as servers) during qualification testing; improve burn-in testing; shorten testing times, which can lead to higher throughput at repair centers and remanufacturing facilities. In particular, the cumulative LOC value, which measures the degree of thermal cycling during dynamic load variations in the given computer system, is used as a figure of merit to compare the various stress tests. Note that if the given stress test causes temperatures to fluctuate, the cumulative LOC value is larger. Moreover, if the peak-to-peak amplitudes are greater, the cumulative LOC value is even higher. Additionally, if the frequency of temperature variations is higher, the cumulative LOC value goes up even faster. Moreover, a parametric sensitivity investigation is performed, which iteratively varies multitude parameters that are known to produce thermal stress in computer systems, including: permutations of stress tests or load types (such as processor tests or bus tests, which generate the highest temperatures for the processor(s) and/or ASICs.); and permutations of cycling times, which are plateau levels during which a given stress test or load type is held at full intensity. In this way, the optimal stress test or combinations of stress tests (i.e., the stress test(s) that corresponds to the worst-case monitored stress metric, such as the worst-case cumulative LOC value) for the given computer system or, more generally, for a type of computer system or platform can be identified. Note that this optimal stress test or combination of stress tests may be subsequently used during reliability or failure-analysis testing of the given computer system. In some embodiments, the given stress test or load type includes an application. Moreover, the application may be configured to stress a portion of the given computer system, which can include: a processor, memory, an ASIC, an I/O interface, and/or a disk drive. Additionally, stress tests may be selected for different types of computer systems, where a given selected stress test is subsequently used for a given type of computer system. We now describe embodiments of system-telemetry monitoring in the given computer system. FIG. 1 illustrates an embodiment 100 of a computer system 110, which can be the given computer system. Computer system 110 includes processor(s) (or processor cores) 116, memory 112, and peripherals 118. Note that processor(s) 116 can be any type of processor(s) that executes program code. Memory 112 contains data and program code for processor(s) 116 and is coupled to processor(s) 116 through bus 114-1, which provides a communication channel between processor(s) 116 and memory 112. Moreover, peripherals 118 can be any type of peripheral components, such as video cards, interface cards, or network cards. Note that bus 114-2 provides a communication channel between processor(s) 116 and peripherals 118. Although we use computer system 110 for the purposes of illustration, embodiments of the present invention can be applied to other systems, such as: desktop computers, workstations, embedded computer systems, laptop computer systems, servers, networking components, peripheral cards, handheld computing devices, automated manufacturing systems, and many other computer systems. Moreover, embodiments of the present invention can be applied to individual chips, components comprised of multiple chips, field-replaceable units (FRUs), or entire systems. In some embodiments, computer system 110 includes telemetry system 122. This telemetry system is coupled through a telemetry harness to a number of sensors, such as sensor 120, on components in computer system 110. Telemetry system 122 uses the sensors to sample system performance metrics, which can then be used to determine the performance of the associated components and/or the computer system 110. For example, telemetry system 122 can sample physical system performance metrics, such as: temperatures, relative humidity, cumulative or differential vibrations, fan speed, acoustic signals, currents, voltages, time-domain reflectometry readings, and/or miscellaneous environmental variables. In some embodiments, the sensors, such as temperature sensors, are sampled or measured at pre-determined time intervals. Moreover, telemetry system 122 can separately or additionally use software sensors to sample software system performance metrics, such as: system throughput, transaction latencies, queue lengths, load on the processor(s) 116, load on the memory 112, load on the cache, I/O traffic, bus saturation metrics, FIFO overflow statistics, and/or various other system performance metrics gathered from software. Note that in some embodiments computer system 110 includes fewer or additional components. Moreover, two or more components may be combined into a single component and/or a position of one or more components may be changed. We now describe embodiments of processes for selecting tests to exercise the given computer system. FIG. 2A presents a flow chart illustrating an embodiment of a process 200 for selecting tests to exercise a given computer system, which can be implemented by the system. During operation, the system tests the given computer system using a set of tests (210), where a given test includes a given load and a given cycling time selected from a range of cycling times. Moreover, for the given test, the system monitors a stress metric in the given computer system (212). Additionally, the system selects at least one of the tests from the set of tests to exercise the given computer system based on the monitored stress metrics (214). FIG. 2B presents a flow chart illustrating an embodiment of a process 230 for selecting tests to exercise the given computer system, which can be implemented by system. During operation, the given computer system executes a series of stress tests covering all possible unique permutations of stress tests and cycling times (240). Next, the system acquires and aggregates appropriate temperature signals (242) in the given computer system. Using each of the monitored temperature signals, the system calculates the cumulative LOC value for each combination of stress tests and cycling times (244). Then, the system identifies the optimal stress test or combination of stress tests based on the cumulative LOC values (246). In an exemplary embodiment, the given computer system executes a systematic matrix of permutations on combinations of the three stress tests that generate the highest temperatures for the processor and/or ASIC, in conjunction with a range of associated cycle times P1, P2, P3 (which can include idle, i.e., the given stress test is not performed). While these combinations are executed, telemetry system 122 (FIG. 1) collects temperature data in the given computer system. Next, the system analyzes this data to generate corresponding cumulative LOC values, the largest of which identifies the optimal stress-test combination (including the associated cycling times), i.e., the combination that results in the maximum thermal dynamics that can be achieved for the given computer system. Note that there is an intuitive temptation to use the minimum cycling time as much as possible in an attempt to increase the frequency of thermal fluctuations. However, because of thermal inertia, there is a limit to how fast the actual temperature inside the given computer system will cycle. Using system-telemetry data, the point at which diminishing returns occur, e.g., the point at which a further reduction in the cycling time starts produces smaller amplitude temperature cycles, for a given stress test can be determined. Table 1 lists various stress-test combinations and associated cycling times for use in selecting tests to exercise the given computer system. Note that the optimal combination is number 46, with a P1 of 20 minutes for stress test A (Linpack), a P2 of 30 minutes for stress test B (Bus Test), and a P3 of 30 minutes for stress test C (CPU Test). Also note that the ‘idle’ label indicates that a given stress test in a given combination is not performed. TABLE 1Stress Test AStress Test BStress Test CCumulativeCom-Cycling TimeCycling TimeCycling TimeLOCbinationP1 (minutes)P2 (minutes)P3 (minutes)Value130IdleIdle64.49220IdleIdle65.46310IdleIdle69.484Idle30Idle81.125Idle20Idle80.846Idle10Idle65.107IdleIdle3063.328IdleIdle2063.239IdleIdle1069.2103030Idle80.98113020Idle81.07123010Idle69.63132030Idle81.58142020Idle76.76152010Idle72.98161030Idle88.02171020Idle79.64181010Idle69.021930Idle3066.022030Idle2065.562130Idle1065.612220Idle3066.162320Idle2064.452420Idle1064.142510Idle3064.352610Idle2064.112710Idle1070.2628Idle303081.7229Idle302080.6230Idle301079.4931Idle203077.2932Idle203077.9533Idle203079.0434Idle103073.4835Idle103074.5736Idle103073.943730303073.133830302072.583930301074.854030203077.564130202075.654230201074.724330103073.144430102073.744530101077.254620303089.834720302068.14820301065.54920203063.975020202064.425120201064.055220103064.435320102064.085420101064.005510303065.195610302063.695710301065.625810203065.785910202064.166010201064.386110103064.396210102064.886310101063.86 We now describe the determination of cumulative LOC values from system-telemetry temperature data. Embodiments of the present invention use samples of a system performance metric to generate a stress metric that provides a continuous quantitative indicator of the cumulative stress that a computer chip, component, FRU, or computer system has experienced during a given combination of stress tests. (In order to simplify the following description, we refer to computer chips, components, or FRUs as ‘computer system components.’) This cumulative stress metric or LOC value provides a measure of the thermal stress during the given combination of stress tests. Although in the following discussion, temperature is used as a parameter in computing the cumulative LOC value, in alternative embodiments, other parameters can be monitored using the LOC technique. For example, the LOC technique can be used to monitor physical performance parameters such as: relative humidity, cumulative or differential vibrations, fan speed, acoustic signals, currents, voltages, time-domain reflectometry readings, and/or miscellaneous environmental variables. Similarly, the LOC technique can be used to monitor software performance metrics such as: system throughput, transaction latencies, queue lengths, the load on the processor(s) 116 (FIG. 1), the load on the memory 112 (FIG. 1), the load on the cache, I/O traffic, bus saturation metrics, FIFO overflow statistics, and/or various other system performance metrics gathered from software. Furthermore, the LOC technique can be used to monitor combined system performance parameters, such as a computer-system temperature in combination with the load on the processor(s) 116 (FIG. 1). Assuming that data is collected from temperature sensors with a sampling interval of t, a differential LOC value for two consecutive temperature measurements T1 and T2 is computed as:Differential LOC Value=√{square root over (|T1−T2|2+t2)}. As discussed below, the computed length may be adjusted based on a function of the magnitude of the adjacent temperature samples. For example, the adjustment may involve multiplying the length of the lines by an associated weight. In particular, because higher temperatures increase the thermal stress experienced by the given computer system (or by components in the given computer system), at least some of the differential LOC values can be adjusted to differentiate between different temperature offsets by multiplying the differential LOC value by a weight factor (W). In some embodiments, an exponential function is used for W. This reflects the fact that computer systems experiencing temperatures higher than critical thresholds experience more severe stress (and potentially immediate damage). For example, the function used for computing the Win the following sections is:W=e0.1(T1.01−373)+1,where T is the temperature in Kelvin. In some embodiments, while computing W for T1 and T2, the average T=(T1+T2)/2 is computed. Thus, the weighted differential LOC value is the product of the differential LOC value and W. (Note that the t2 term in the equation for the differential LOC value can be multiplied by its own separate weight factor W′, which can be used to adjust the relative contributions of T1−T2 and t to the differential LOC value.) In an exemplary embodiment, W remains near 1 until the temperature reaches approximately 330° K (57° C.), at which point W begins to increase in value. Moreover, above approximately 360° K (87° C.), W may increase very rapidly in value. FIG. 2C presents a flow chart illustrating an embodiment of a process 260 for determining a differential LOC value, which can be implemented by the system. During operation, the system sets the LOC counter to zero and obtains an initial temperature sample from a telemetry system (270). Next, the testing system obtains a second temperature sample from the telemetry system after a predetermined delay (272). In some embodiments, the pre-determined delay is seconds, while in other embodiments the pre-determined delay is another increment of time, such as: a millisecond, a pre-determined number of seconds, an hour, and/or a day. For example, the system may obtain the initial temperature sample at time T=(N)s and then may obtain the next temperature sample at time T=(N+1)s. Then, the system computes a differential LOC value between the temperature samples (274), and optionally scales the differential LOC value using a weighting factor (276). Additionally, the system adds the differential LOC value (with or without the scaling) to the LOC counter (278). This sequence of computations generates a cumulative LOC value for the given computer system (or a component in the given computer system) as a function of time. After adding the differential LOC value to the LOC counter, the system returns to operation 272 to obtain the next sample from the telemetry system after a predetermined delay. Then, the system repeats the LOC-computation process using the newly collected sample. For example, if the first to samples were T1 and T2, the system collects a new sample T3 and computes the next differential LOC value using samples T2 and T3. Note that in some embodiments of processes 200 (FIG. 2A), 230 (FIG. 2B), and/or 260 there may be additional or fewer operations. Moreover, the order of the operations may be changed, and two or more operations may be combined into a single operation. FIG. 3A presents a graph 300 illustrating an embodiment of differential LOC values ΔT 310 for a system board as a function of time 312 (in minutes). These differential LOC values correspond to temperature changes between sampling times during a sequence of different stress-test combinations and cycling times. Moreover, FIG. 3B presents a graph 350 illustrating an embodiment of cumulative LOC values Σ(ΔT) 360 as a function of time 312 (in minutes). In graph 350, the cumulative LOC values Σ(ΔT) 360 increase approximately linearly to a value around 4650. We now describe embodiments of a computer system that can implement one or more of the aforementioned processes. FIG. 4 presents a block diagram illustrating an embodiment of computer system 400, such as the system. Computer system 400 includes: one or more processors (or processor cores) 410, a communication interface 412, a user interface 414, and/or one or more signal lines 422 coupling these components together. Note that the one or more processors 410 may support parallel processing and/or multi-threaded operation, the communication interface 412 may have a persistent communication connection, and the one or more signal lines 422 may constitute a communication bus. Moreover, the user interface 414 may include: a display 416, a keyboard 418, and/or a pointer 420, such as a mouse. Memory 424 in the computer system 400 may include volatile memory and/or non-volatile memory. More specifically, memory 424 may include: ROM, RAM, EPROM, EEPROM, flash, one or more smart cards, one or more magnetic disc storage devices, and/or one or more optical storage devices. Memory 424 may store an operating system 426 that includes procedures (or a set of instructions) for handling various basic system services for performing hardware dependent tasks. Moreover, memory 424 may also store communications procedures (or a set of instructions) in a communication module 428. These communication procedures may be used for communicating with one or more computers, devices and/or servers, including computers, devices and/or servers that are remotely located with respect to the computer system 400. Memory 424 may also include one or more program modules (or a set of instructions), including testing module 430 (or a set of instructions), telemetry module 432 (or a set of instructions), and/or analysis module 436 (or a set of instructions). Testing module 430 may instruct the given computer system to perform one or more combinations 438 of stress tests, such as combination A 440-1 and/or combination B 440-2. These stress tests may be performed for different cycling times 442, such as cycling time A 444-1 and/or cycling time B 444-2. During the testing, telemetry module 432 may collect telemetry data 434, such as temperature as a function of time, from sensors in the given computer system. Moreover, analysis module 436 may analyze this telemetry data to determine stress metrics, such as differential LOC values and/or cumulative LOC values, that are used to identify the optimal combination of stress tests for the given computer system. In some embodiments, at least some of the differential LOC values are weighted using optional weights 446. Instructions in the various modules in the memory 424 may be implemented in a high-level procedural language, an object-oriented programming language, and/or in an assembly or machine language. The programming language may be compiled or interpreted, i.e, configurable or configured to be executed by the one or more processors 410. Although the computer system 400 is illustrated as having a number of discrete components, FIG. 4 is intended to be a functional description of the various features that may be present in the computer system 400 rather than as a structural schematic of the embodiments described herein. In practice, and as recognized by those of ordinary skill in the art, the functions of the computer system 400 may be distributed over a large number of servers or computers, with various groups of the servers or computers performing particular subsets of the functions. In some embodiments, some or all of the functionality of the computer system 400 may be implemented in one or more ASICs and/or one or more digital signal processors DSPs. Computer system 400 may include fewer components or additional components. Moreover, two or more components may be combined into a single component and/or a position of one or more components may be changed. In some embodiments, the functionality of computer system 400 may be implemented more in hardware and less in software, or less in hardware and more in software, as is known in the art. We now discuss data structures that may be used in the computer systems 100 (FIG. 1) and/or 400 (FIG. 4). FIG. 5 presents a block diagram illustrating an embodiment of a data structure. This data structure may include combinations 510 of stress tests. More specifically, a given instance of the combinations 510, such as combination 510-1, may include one or more stress tests 512 and associated cycling times 514. Note that that in some embodiments of data structure 500 there may be fewer or additional components. Moreover, two or more components may be combined into a single component, and/or a position of one or more components may be changed. While the preceding discussion has described selecting an optimal stress test(s) and/or combination of stress tests for the given computer system, in other embodiments this technique is used to select the optimal stress test or combination of stress tests for one or more components in the given computer system and/or one or more applications that execute on the given computer system. Moreover, in some embodiments, the system is the given computer system, i.e., the given computer system is used to determine the optimal stress test(s) and/or combinations of stress tests, and to perform self-testing and/or diagnostics. The foregoing descriptions of embodiments of the present invention have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims. |
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052326551 | summary | BACKGROUND OF THE INVENTION The invention relates to nuclear fuel assemblies, and more particularly to fuel assemblies comprising a skeleton that constitutes the structure of the assembly and that holds a bundle of fuel elements at nodes in a regular array. Such assemblies are used, in particular, in reactors that are cooled and moderated by light water. The skeleton then comprises two end pieces interconnected by guide tubes which carry grids that are distributed along the guide tubes and that retain the fuel elements at the nodes of the array. The guide tubes are designed to receive elements belonging to absorbent clusters for controlling the reactivity and/or to clusters for varying the energy spectrum of neutrons. To attenuate the shock caused by the clusters dropping in the event of an emergency stop of the reactor, the guide tubes are often designed to act as hydraulic dampers by providing them with bottom plugs that are formed with respective narrow passages. Such a plug may also be used to receive the guide tube to the lower end piece (FR-A-2,469,777). In general, the end pieces are made of a material having high mechanical properties, such as stainless steel or one of the alloys known under the name Inconel, while the guide tubes are made of a zirconium base alloy. Consequently, it is difficult to secure the tubes to the end pieces directly by welding. In addition, it is desirable for the connection of the guide tubes to at least one of the end pieces to be easily disassembled and reassembled so as to allow faulty elements to be replaced. SUMMARY OF THE INVENTION It is an object of the invention to provide an assembly skeleton of the above-defined kind in which connection means can be made in a manner that is relatively simple and of acceptable cost. To this end, the present invention provides, in particular, a skeleton comprising two end pieces interconnected by guide tubes, in which the connection means between each guide tube and the lower end piece comprise a peg formed with a coolant flow hole, having a top portion fixed in the guide tube and a projecting bottom portion, which has a downwardly facing shoulder for bearing on the lower end piece, which passes through a passage formed in the lower end piece, and which is divided into a plurality of resilient fingers each having an upwardly facing shoulder for catching on the bottom end piece. Advantageously, the end portion of the peg beyond the upwardly facing shoulder tapers so that a vertical thrust exerted on the guide tube causes the resilient fingers to move toward one another, thereby enabling the peg to be inserted until its fingers snap into place. The passage through the end piece is constituted by a simple cylindrical machined hole which may open at its top end via a chamferin to facilitate peg insertion. In order to ensure that the fingers are sufficiently resilient and that they retain their resilience under irradiation, the peg is advantageously made of a material having proven mechanical properties, such as Inconel 718. The peg can then be fixed to the guide tube, which is generally made of a zirconium-based alloy, by circularly crimping the guide tube into a groove formed in the peg. To avoid any danger of undesirable peg release, e.g., in the event of a reduction in resilience, means may be provided for installing after snap fastening to prevent the fingers moving towards one another. These means may be constituted, in particular, by a locking ring received in a groove in the peg and having its ends inserted in the slots between the fingers. The connection between the guide tubes and the upper end piece may be implemented by any conventional means, e.g., a connection using threaded sockets of the kind described in French Patent Application No. 7923312 or a connection by crimping the top portion of the guide tube in a recess in the upper end piece, with locking by means of a force fit ring. |
047568666 | abstract | A method and apparatus for detecting concentrations of nitrogen between 20% and 30% by weight such as is common in explosives is disclosed. A microtron having an output electron beam at a level below 45 MeV is targeted onto a typically tungsten target to provide gamma radiation levels. Deflection magnets adjacent to the target deflect the electron beam of the microtron to cause it to scan. Articles placed on a container containing suspect nitrogen are systematically scanned and output gamma radiation of 511 keV detected from nitrogen. Nitrogen concentrations and consequently expected concealed explosives are easily mapped in two or three dimensions, quantitatively. |
063305259 | claims | 1. An apparatus for diagnosing a power system which includes a rotating machine, the apparatus comprising: process sensors for generating process variables, said process sensors including: an input/output device in communication with said process sensors for receiving process variables from said process sensors; and a computing device in communication with said input/output device, said computing device having a memory, said memory for storing data from said input/output device, said computing device for receiving original data including tables of machine geometry, machine installation parameters, original performance curves and fluid properties of said pumped product, said computing device for comparing said process variables with said original data and for generating an output based upon said comparison. a rotating machine vibration sensor mounted on the rotating equipment for determining vibration of the rotating machine, said vibration sensor in communication with said input/output device for providing condition monitoring variables thereto; and said computing device for comparing said condition monitoring variables with said original data for diagnosis of rotating equipment degradation and for generating an output based upon said comparison. a gear box vibration sensor mounted on a gear box for determining gear box vibration; and a motor supply sensor mounted on electrical power supply service for determining electrical power to a motor; an alignment sensor mounted on the motor for determining coupler alignment; a torque sensor mounted on a shaft of said rotating machine, said torque sensor in communication with said input/output device for providing said computing device with torque data; an angular velocity sensor mounted on a shaft of said rotating machine, said angular velocity sensor in communication with said input/output device for providing said computing device with angular velocity data for computing input power to the rotating machine, speed of the rotating machine, and rotating machine efficiency. an inlet pressure sensor positioned proximate an intake of the rotating machine for determining rotating machine inlet pressure; and a temperature sensor positioned upstream or downstream of the rotating machine for determining temperature of a process fluid. 2. An apparatus according to claim 1, including machine sensors for generating condition monitoring variables, said machine sensors comprising: 3. The apparatus according to claim 2, wherein said machine sensors further comprise: 4. The apparatus according to claim 2, wherein said machine sensors further comprise a rotating machine seal leakage sensor mounted proximate a shaft seal on the rotating machine for detecting seal leakage, said rotating machine seal leakage sensor for providing condition monitoring variables to said input/output device for providing said computing device with condition monitoring variables. 5. The apparatus according to claim 2, wherein said machine sensors further comprise an oil contamination sensor mounted in a gearbox or on an oil sump for detecting oil contamination, said oil contamination sensor for providing conditioning monitoring variables to said input/output device for providing said computing device with condition monitoring variables. 6. The apparatus according to claim 2, wherein said machine sensors further comprise a viscosity degradation sensor mounted proximate a gearbox for detecting oil viscosity degradation, said viscosity degradation sensor for providing condition monitoring variables to said input/output device for providing said computing device with an oil condition monitoring variable. 7. The apparatus according to claim 2, wherein said machine sensors further comprise a dynamic sensor mounted on a pump casing for measuring pressure noise in said pump casing for providing condition monitoring variables to said input/output device for providing said condition monitoring variables to said computing device for diagnosing pump recirculation and cavitation. 8. The apparatus according to claim 2, further comprising a valve position sensor mounted on said control valve and in communication with said input/output device, said valve position sensor for determining a position of a shaft of said control valve. 9. The apparatus according to claim 2, wherein said machine sensors further comprise an corrosion sensor mounted on a rotating machine casing for measuring the degradation of the rotating machine casing from corrosion, pump cavitation or erosion, said corrosion sensor in communication with said input/output device for providing condition monitoring variables thereto. 10. The apparatus according to claim 2, wherein said machine sensors further comprise an ultrasonic thickness sensor mounted on a rotating machine casing for measuring the degradation of the rotating equipment casing from corrosion, pump cavitation or erosion, said ultrasonic thickness sensor in communication with said input/output device for providing condition monitoring variables thereto. 11. The apparatus according to claim 2, wherein said machine sensors are integrated with said input/output device and said computing device for comparing measured performance signatures of the rotating machine at a second time with an original condition signature at a first time, for diagnosing degradation of the rotating machine. 12. The apparatus according to claim 2, wherein said machine sensors further comprise: 13. The apparatus according to claim 2, wherein said computing device serves as a host, said host in communication with a controller proximate the rotating machine for controlling the rotating machine, said microcontroller having firmware for providing control set point to said rotating machine. 14. The apparatus according to claim 2, wherein said computing device is positioned proximate a rotating machine, said computing device for providing a control set point for said rotating machine. 15. The apparatus according to claim 2, further comprising a communication port for importing condition monitoring variables from a portable handheld data logging device. 16. The apparatus according to claim 2, further comprising a process variable digital bus in communication with networked intelligent devices. 17. The apparatus according to claim 2, further comprising a monitoring system digital bus in communication with intelligent network devices with a computing device for collecting said condition monitoring variables. 18. The apparatus according to claim 2, further comprising condition monitoring subsystems for the rotating machine, said condition monitoring subsystems interfaced with the computing device via standard communication network interfaces for transmitting subsystem data over a standard communication network. 19. Apparatus according to claim 18, further comprising an external processed data storage device for storing the subsystem data wherein the apparatus is a network client having a memory database for storing data from a networked rotating machine subsystem. 20. The apparatus according to claim 2, further comprising a co-processor in communication with said computing device for providing spectral signal reduction of said condition monitoring variables from said vibration sensor, said motor vibration sensor, said dynamic pressure sensor and said bearing vibration sensor. 21. An apparatus according to claim 1, wherein said process sensors further comprise: 22. The apparatus according to claim 1, further comprising an alert device for indicating when undesirable equipment conditions occur. 23. The apparatus according to claim 22, further comprising a contact closure for shutting down the apparatus when said alert device indicates an undesirable equipment condition. 24. An apparatus according to claim 1, further comprising a final control element, said final control element responsive to said output for adjusting the rotating machine and motor system for operating the rotating machine in a recognized recommended operating design regime. 25. An apparatus according to claim 24 wherein said final control element is a control valve downstream of said rotating machine for regulating back pressure. 26. An apparatus according to claim 24, wherein said final control element is a variable speed drive coupled to the motor, said variable speed drive for adjusting motor speed. 27. The apparatus according to claim 1, further comprising a real time clock in communication with said computing device for time stamping process variables and said original data for time based comparison. 28. The apparatus according to claim 1, further comprising a display for representing a performance signature at a first time and a second time. 29. The apparatus according to claim 1, further comprising a co-processor with a spectral analysis engine for processing signals from frequency domain sensors. 30. The apparatus according to claim 1, further comprising a network communication port in communication with said input/output device, said network communication port for communicating said output to a network. 31. An apparatus according to claim 1, further comprising a communication device for communicating data from said computing device to a networked host. 32. The apparatus according to claim 1, wherein said computing device is powered by and communicates over two wires. 33. The apparatus according to claim 1, wherein said computing device is powered by and communicates with either 3-wire or 4-wire networks. 34. The apparatus according to claim 1 including multiplexer inputs in order to diagnose more than one said rotating machine. |
050826034 | abstract | A method of treatment of a high-level radioactive waste containing platinum group elements is provided in which boron and a boron compound is added to a calcined material of the high-level radioactive waste in an amount of 0.5 to 10% by weight in terms of boron as a simple substance, and the resultant mixture is heated at a temperature of about 1000.degree. C. or above under a reduction condition to melt the mixture and to alloy the platinum group elements present in the calcined material with boron. A layer of the resultant platinum group element alloys is then separated and recovered from a layer of residual oxides through sedimentation. The layer of the residual oxides is solidified to form a highly volume-reduced high-level radioactive solidified waste. |
063174774 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to sealing a space between adjacent plates or ledges. In particular, the invention relates to sealing the space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal to provide a temporary water barrier between the refueling canal and the reactor vessel during refueling operations. 2. Description of the Related Art The conditions giving rise to the problems solved by the present invention are commonly found in nuclear reactor power plants. In particular, the refueling process in pressurized water reactors must be performed under approximately 25 feet of water in a refueling canal above the reactor vessel, while the reactor vessel cavity under the canal must be maintained dry. During normal power operation the refueling canal is dry and, with the vessel cavity, forms a single large enclosure. Typically, a portion of the floor of the refueling canal forms a ledge opposite a flange attached to the upper portion of the reactor vessel. The ledge and flange provide sealing surfaces on which prior art canal sealing interfaces were effected. Conventional refueling pool seals are of two general types: temporary and permanent. Temporary seals typically comprise a ring plate having an outside diameter of about 25 feet and a width of from 1 to 3 feet. Compression elastomer seals carried on the underside of the ring plate rested on the flange and ledge. The ring plate was bolted down to the flange and ledge to compress the seals and form a watertight fit. Another temporary seal was developed having a rigid plate bridging the annular space to be sealed, and a pair of inflatable seals positioned between the reactor vessel flange and the rigid plate, and between the rigid plate and the ledge of the refueling canal. This arrangement is disclosed, for example, in U.S. Pat. No. 4,908,179, which issued to Robert H. Brookins on Mar. 13, 1990, and was assigned to Combustion Engineering, Inc., assignee of the present application. These temporary seal arrangements are relatively difficult and time consuming to install, thereby resulting in an undesired amount of occupational radiation exposure. Permanent seal arrangements have been developed that remain in place during normal power operation and during refueling. An example of a permanent refueling pool seal is disclosed in U.S. Pat. No. 5,102,612, which issued to Michael S. McDonald et al. on Apr. 7, 1992, and was assigned to Combustion Engineering, Inc., assignee of the present application. This permanent seal comprises annular deck sections supported on spaced ribs around the annular space to be sealed. The inside and outside diameters of the deck sections are welded to flexible membranes to make a watertight seal between the reactor vessel flange and the ledge of the refueling pool cavity. The deck sections include openings with removable seal covers. These openings provide reactor cavity cooling air flow and an access path to the reactor vessel cavity and external core detectors when the seal covers are removed. However, removal of the seal covers to establish a ventilation path from the reactor cavity during plant operation is time consuming, thereby resulting in an undesired amount of occupational radiation exposure. SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved seal assembly for establishing a temporary water barrier between a refueling canal and a reactor vessel during refueling with a minimal amount of occupational radiation exposure. It is a further object of the present invention to provide an improved seal assembly that can be quickly installed for sealing the space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal during refueling, and can be quickly removed to establish a ventilation path from the reactor cavity during normal plant operation. It is a further object of the present invention to provide an improved seal assembly that uses an inflatable seal to establish a primary sealing interface, and an annular support structure that supports the inflatable seal and provides a leak limiting function in the event the inflatable seal fails. It is a further object of the present invention to provide an improved seal assembly having a permanently installed closure plate with a plurality of access ports. and a ventilation path that permits adequate ventilation of the reactor cavity without the removal of seal covers from the access ports. To achieve these objects, the present invention provides a seal assembly for sealing a space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal to provide a temporary water barrier during refueling operations. The seal assembly includes an annular closure plate having an outer portion secured to the surrounding ledge and an inner portion supporting a first sealing surface. A second sealing surface opposing the first sealing surface is formed on or secured to the annular flange of the reactor vessel. An annular space between the first and second sealing surfaces provides a ventilation path from the reactor cavity during normal plant operation. The annular space is sealed by an inflatable seal during refueling operations to provide a water barrier between the refueling canal and the reactor cavity. The inflatable seal is secured to and supported by an annular support structure that straddles the annular space. The annular support structure provides a structure for handling the inflatable seal during installation and removal. The annular support structure also provides a leak limiting function in the event the inflatable seal is pulled or pushed through the annular space or otherwise fails to seal the annular space. The inflatable seal is secured to the annular support structure in a manner that allows independent movement of the seal to conform to irregularities in the sealing surfaces. The closure plate has a plurality of normally closed access ports that permit access to the external core detectors and the reactor vessel cavity. The access ports need not be opened during normal plant operation since the annular space provides sufficient ventilation for the reactor vessel. According to a broad aspect of the present invention, a seal assembly is provided for sealing an annular space between two adjacent annular surfaces. The seal assembly comprises an inflatable annular seal, and an annular support structure connected to and supporting the inflatable seal. The annular support structure has a generally rigid structure that straddles the annular space to be sealed and engages the surfaces on both sides of the annular space. The annular support structure provides a means for handling the inflatable seal during installation and removal and provides a leak limiting structure in the event the inflatable seal fails. The inflatable seal has a plurality of threaded inserts embedded in an upper surface of the seal. The annular support structure has a plurality of slotted openings or retainers through which shoulder bolts extend to engage the threaded inserts for connecting the annular support structure to the inflatable seal. This mounting arrangement allows the inflatable seal to move vertically and transversely relative to the annular support structure to facilitate self alignment of the inflatable seal within the annular space. The inflatable seal is an annular elastomer structure having an upper wedge portion and a lower tubular portion. The lower tubular portion is expandable when pressurized to engage lower edges of the surfaces on each side of the annular space to form a secondary seal. The upper wedge portion is drawn into engagement with upper edges of the surfaces on each side of the annular space to form a primary seal when the tubular portion is further pressurized. According to another broad aspect of the present invention, a method is provided for sealing a space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal to provide a temporary water barrier during refueling operations. The method comprises the steps of: providing first and second sealing surfaces secured to the surrounding ledge and annular flange, respectively, whereby an annular space between the first and second sealing surfaces provides a ventilation path from the reactor cavity during plant operation; securing an inflatable seal to a generally rigid annular support structure having inner and outer sides; placing the annular support structure over the annular space with the inner and outer sides straddling the annular space and the inflatable seal positioned within the annular space; and inflating the inflatable seal to engage the first and second sealing surfaces and seal the annular space. The method also comprises the step of removing the temporary water barrier by lifting the annular support structure together with the inflatable seal attached thereto from the annular space. With the inflatable seal removed, the annular space provides sufficient ventilation from the reactor cavity during plant operation without removing any other structures. Numerous other objects of the present invention will be apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of the present invention, simply by way of illustration of one of the modes best suited to carry out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various obvious aspects without departing from the invention. Accordingly, the drawings and description should be regarded as illustrative in nature and not restrictive. |
summary | ||
abstract | The invention relates to a material for neutron shielding and for maintaining sub-criticality, and a process for preparation of this material and applications of the said material. |
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053295633 | claims | 1. A tool for unlatching control rods from a control rod drive, comprising: a rotatable adapter member; an actuator disc operatively connected with the rotatable member so that rotation of said rotatable adapter member induces rotation of said actuator disc, said actuator disc having an elongate slot formed therein; and an actuator shaft having a crank at a first end and a cam-like member at a second end, said crank being received in said elongate slot so that rotation of said actuator disc induces said actuator shaft to rotate and cause said cam-like member to rotate through a predetermined angle. first and second arms which extend down along opposite sides of said control rod from a cross-member which is seatable on the top of said control rod; first and second actuator rods which are supported on said first and second arms; first and second cam-like members which are fixed to said first and second actuator rods, respectively; a rotatable drive input member, rotatably mounted on said cross member; and crank means operatively interconnecting said input member with said first and second actuating rods, for selectively inducing said first and second actuator rods to rotate and to induce said first and second cam-like members to engage and lift said unlatching handle. 2. A tool as set forth in claim 1, wherein said actuator disc is threadedly received on a threaded portion of said rotatable adapter member so that upon a given resistance to the rotation of said actuator shaft being produced, said actuator disc threads its way along said threaded portion of said adapter member, said actuator shaft being adapted so that when said actuator disc threads its way in a first predetermined direction, said actuator shaft is axially displaced to move the cam to lift an unlatching handle of a predetermined apparatus. 3. A tool for use in a nuclear reactor and which can be lowered onto an essentially cruciform cross-section control rod having a lift handle at the top and an unlatching handle arranged near the bottom, said control rod being releasably connected with a control rod drive by a connection mechanism which is operatively connected with said unlatching handle, said tool comprising: 4. A tool as set forth in claim 3, further comprising third and fourth cam-like members, said third and fourth cam-like members being fixed to said first and second actuator rods, respectively, and arranged to engage said lifting handle when said first and second cam-like members engage said unlatching handle. 5. A tool as set forth in claim 4, wherein said first and second cam-like members are splined to said first and second actuator shafts, respectively so as to be slidable along predetermined portions of said first and second actuator shafts, said first and second cam-like members being biased by first and second springs to slide toward the upper ends of said predetermined portions. 6. A tool as set forth in claim 3, wherein said crank means comprises an actuator disc which is operatively connected with said rotatable drive input member, and crank portions which are formed at the upper ends of said first and second actuator rods and which are received in elongate slots formed in said actuator disc. 7. A tool as set forth in claim 6, wherein said crank portions are formed with enlarged portions which are larger in diameter than the width of the elongate slots formed in said actuator disc and which therefore enable the actuator disc to pull the first and second actuating rods to induce said cams to lift said unlatching handle when said actuator disc is axially displaced along said rotatable drive input member by operative connection established therebetween. |
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061817724 | abstract | A grid enclosure for an X-ray cassette has a rugged construction, and is easy to us efficient in operation, with open corners therein to achieve the desired protection of an X-ray cassette. |
description | This application is a divisional of U.S. patent application Ser. No. 11/244,450, filed Oct. 6, 2005, which is a divisional of U.S. Pat. No. 6,981,404, filed Mar. 15, 2004, which is a continuation-in-part of U.S. Pat. No. 6,725,706, filed Mar. 14, 2002, and claims priority from and incorporates by reference U.S. Provisional application Ser. No. 60/276,780, filed Mar. 16, 2001 and U.S. Provisional application Ser. No. 60/314,859, filed Aug. 24, 2001. The present invention relates to tubes in chemical reactors, and, in particular, devices and methods for measuring the back pressure in the tubes and for blowing dust out of the tubes. Many chemical reactors use a catalyst as part of the reaction process. The catalyst material frequently is coated onto or contained in a substrate which is packed in tubes within the reactor. The reactants flow through the tubes and out the open ends of the tubes, reacting in the presence of the catalyst to form the products of the reaction. It is desirable to be able to measure the packing of catalyst within the tube in order to determine whether the tube will function properly. Ideally, the catalyst packing in all the tubes will be very close to the same. However, in reality, there is a variation in packings which adversely affects the efficiency of the reaction by providing for different residence times in different tubes. In order to assess the catalyst packing, a constant flow rate test gas is injected into the tubes, and the back pressure is measured, with the back pressure being proportional to the packing density. Higher densities produce higher back pressures, and lower densities produce lower back pressures. High back pressures can also indicate problems other than high packing density, such as dust, fines, obstructions in tubes, and the presence of foreign material. Low back pressures can also indicate problems other than low packing density, such as bridging. The goal is to measure the back pressure on each tube and determine which tubes require corrective action. Then, once the appropriate corrective action has been taken, the corrected tubes can be retested. Measurements may be taken when the tubes are first loaded with catalyst, in order to ensure that they are properly loaded, as well as periodically during the operation of the reactor, such as during normal maintenance shut-downs, and after cleaning. However, the devices and methods that have been used in the past have been labor intensive and time consuming, their accuracy has depended largely upon the skill of the operator, and they have yielded data that is not readily usable. In order to obtain a seal between the test device and the chemical reactor tube, the operator has typically inserted a stopper into the tube. Weldments and obstructions at the top of the tube can interfere with the ability to obtain a good seal, and failure of the operator to maintain the device in a vertical orientation may also interfere with the ability to obtain a good seal. The operator typically must keep track of his position manually, and the data that is obtained is typically written down on a notepad by a second person, sometimes with the person who takes the measurements shouting over the noise of the plant to the person writing down the results. Also, the tubes are typically measured one at a time, requiring many workers and a long shut-down time. With typical prior art methods, it is difficult to keep track of all the measurements, since there may be as many as 35,000 tubes to be measured in a reactor, and transferring data from the many notepads is slow and provides an opportunity for errors. In order to display the progress of the measurement process, the operators usually put colored caps on the tubes as they are measured, which is time-consuming. The present invention provides a device and method that improves the ability to measure the back pressure in tubes, making the process much more accurate, faster, less labor intensive, more efficient, safer, less dependent on the skill of the worker, and yielding more accurate and more useful results. In a preferred embodiment, the measuring device uses an inflatable, conforming seal, which provides a good seal between the measuring device and the chemical reactor tubes, even when weldments or other obstructions are present. Also, in a preferred embodiment, the measuring device measures multiple tubes at once rather than measuring only one tube at a time. Also, in a preferred embodiment, measurements are stored at the measuring device, are transmitted electronically to a remote computer, and are displayed graphically in real time at a remote display, such as in the control room, including indications of which tubes are within predetermined specifications and which are not. The visual display helps the plant engineer determine which tubes require corrective action and may permit the elimination of the time-consuming prior art process of putting caps on all the tubes as the measurements are being taken. Preferred embodiments of the present invention also permit automated handling of the data and prompt statistical analysis and cost-effectiveness analysis of the measurement data in order to help the plant engineer make quick decisions about corrective actions to be taken. The measurements that have been taken with a prototype device made in accordance with the present invention are so accurate that the engineers can begin to recognize what particular variations in pressure drops mean—for example, one pressure drop indicates that a foam pig accidentally has been left in the tube after cleaning, while another indicates that an extra clip has been inserted to retain the catalyst. In addition, in a preferred embodiment of the invention, a device and method are provided to remove dust from the tubes by blowing gas through them. The gas used in the preferred embodiments as described herein may be air, nitrogen, or some other gas. FIG. 1 is a schematic view of a chemical reactor 10, including a plurality of tubes 12, which hold catalyst. The tubes 12 extend downwardly from an upper plate (or tube sheet) 11 and are open on the bottom, except for clips (not shown), which may be used to prevent the catalyst from falling out the bottom of the tubes. A manway 14 provides access for workers to get into the reactor 10. A worker 16 is shown inside the reactor 10, measuring the back pressure in the catalyst tubes 12. In other reactors, the top may be fully removable, providing improved access. FIG. 2 shows the worker 16 standing on the plate 11 and operating a hand-held wand 18, which measures the back pressure in the tubes 12. The details of the wand 18 are shown better in FIG. 4. The wand includes a handle 28, a wand body 26, and a plurality of injector tubes 30 rigidly mounted together to form a single portable unit which is sufficiently rigid that the injector tubes can be inserted simultaneously into their respective reactor tubes simply by picking up the wand 18 by the handle 28, aligning the wand 18 with the group of reactor tubes to be measured, and then lowering the wand's handle 28 so that all the injector tubes 30 enter into respective reactor tubes 12 at once. When the wand 18 is inserted into a bank of ten tubes in the plate 11, it is self-supporting and rests on the plate 11. The wand 18 is connected to a gas line 20 and communicates with a remote computer 22 through a power and data module 24. In this particular embodiment, the gas line 20 is the plant air supply. The power and data module 24 may supply the power to the computer 22 and to the hand-held wand 18. However, the wand 18 preferably operates on battery power, and the computer 22 preferably operates on a battery or is plugged into a regular alternating current outlet. The wand 18 communicates with the power and data module 24 in real time by means of radio signals, but other means for transmitting data to the computer 22 could be used, such as hard wiring the wand 18 to the power and data module 24 or downloading data from the wand 18 onto a portable medium such as a disk, which can then be carried to the remote computer 22. The remote computer 22 may be located in the control room or in some other convenient location. Also shown in FIG. 2 is a target 25, which is used by a laser measuring device 27 on the wand 18 to determine the position of the wand 18 in order to confirm which tubes 12 are being measured. The target 25 preferably is placed in the first tube 12 of a row, and serves as a reference point, as will be described later. While the target 25 has proven to be a convenient reference point for making measurements, other reference points could be used, such as the side wall of the reactor, for example. The location of the laser measurement device 27 is best seen in FIG. 4. FIG. 4 shows that the laser measuring device 27 is fixed relative to the injector tubes 30 by being affixed to the wand. As a result, the distance measured by the laser to the reference point also establishes the position of each of the injector tubes 30 relative to the reference point. Thus, when the injector tubes 30 are placed in their respective receptacles, the reactor tubes 12 can be identified automatically based on the distance measured by the laser. So the injector tubes 30 are not only used to inject fluid but also function as probes which locate the tube positions. FIG. 3 is a plan view of the plate 11. This plan view is also a portion of the screen display that is shown on the display screen of the computer 22 to visually indicate the tubes that are being measured, as shown in FIG. 12. Prior to using the wand 18 in the reactor 10, a layout of the tubes is obtained and is made available to the computer 22 and to the controller 32 for the wand 18. This layout is shown graphically as in FIG. 3. As the wand 18 is being used, the data from the wand 18 is stored at the wand 18 and is transmitted to the computer 22. This data is displayed on the screen of the computer 22 or other graphic interface, as will be explained later. FIG. 4 is a front schematic view of the wand 18. The wand 18 includes a hollow wand body 26 (see FIG. 5), with a hollow handle 28 at its upper end and a plurality of injector tubes 30 at its lower end. The wand 18 receives regulated pressurized gas (such as air, nitrogen, or another gas) through a gas line 20. The wand 18 defines two different gas paths for each injector tube 30a test gas path and an inflation gas path. The test gas path provides the gas that passes through the injector tube 30 into the respective chemical reactor tube 12 for testing the chemical reactor tube. The inflation gas path provides the gas that is used to inflate the seal on the injector tube 30 so that the injector tubes 30 of the wand 18 seal against the interior of the respective chemical reactor tubes 12. As shown in FIG. 9, each of the injector tubes 30 includes a hollow tubular member 52 defining an internal gas flow path 54 with an open bottom outlet through which the test gas passes into the respective chemical reactor tube 12. A gas-impermeable, elastic sleeve 56 is mounted over the tubular member 52 and is sealed against the tubular member 52 by means of upper and lower ferrules or clamps 58. A recess 60 is formed in the outer surface of the tubular member, and that recess 60 receives an inflation tube 62. The depth of the recess 60 preferably is the same as the thickness of the inflation tube 62 at the upper ferrule or clamp 58, so that a good seal is formed there. The inflation tube 62 forms an inflation gas path that allows gas to be injected between the outer surface of the tubular member 52 and the inner surface of the sleeve 56 in order to inflate the sleeve 56. The inflation tube 62 preferably is welded, adhered, or otherwise secured to the tubular member 52. The bottom of the tubular member 52 is threaded, and this particular tubular member 52 receives a frustro-conical guide member 80 on its threaded end, which helps guide the injector tube 30 into the chemical reactor tube 12. FIGS. 4-10 show the main components of the wand 18. Mounted on the wand 18 is a main wand control box 34, which houses the main controls for the wand 18. An antenna 37 projects out of the control box 34. Below the main wand control box 34 is a secondary control box 35. A conduit 39 houses wires and a measuring tube 74A that extend between the control boxes 34, 35. A manual shut-off valve 36 can be used to shut off the flow of gas through the wand body 26. An inflation gas pressure regulator 38 regulates the pressure of gas going to the inflation tubes 62. An inflation path solenoid valve 42 (see FIG. 8) opens and closes the gas flow to the inflation tubes 62. An inflation path manifold 44 (see FIG. 7) distributes the incoming inflation gas to a plurality of hose fittings 46, which connect to hoses 48, which lead to the inflation gas paths 62 of the injector tubes 30. In this particular embodiment, there are eleven injector tubes—ten injector tubes 30 mounted on a frame member 50, and the eleventh injector tube 30A is on a freely-movable umbilical wand 18A, generally for use in locations that are not accessible by the larger wand 18. The umbilical wand 18A can be used independently of the ten other injector tubes 30, so the ten tubes 30 can be inserted into reactor tubes when the umbilical wand 18A is in use, or they can be completely out of the reactor tubes when the umbilical wand 18A is in use. There is a cushion 83 on the bottom of the frame member 50 to help absorb the impact as the injector tubes 30 of the wand 18 are inserted into the chemical reactor tubes 12. It is preferred that a separate inflation path solenoid valve 42A be provided for the umbilical seal 30A, as shown in the schematic of FIG. 21. Referring to FIG. 8, the test gas passes through the shut-off valve 36, through the main pressure regulator 40, and to the main manifold 64, which distributes the test gas to a plurality of needle valves or other constant flow devices 66, such as sonic nozzles, orifice plates, or precision orifices. A Nozzle or orifice can be used to obtain and maintain a constant gas flow rate while back pressure testing. Back pressure testing may be used for various purposes, such as to verify that the packing density of catalyst is proper or to determine, that a tube is empty after it has been cleaned. Tubes can be difficult to completely clean along their entire length and are typically cleaned by water blasting, sand blasting, passing a compliant material through them such as a piece of foam propelled by compressed air, or by wire brushing or passing a wire brush along the tube length using compressed air. Constant gas flow of the test gas is achieved by operating each nozzle or orifice in such a manner that its sonic coefficient is maintained. A sonic condition is said to be achieved and maintained if the ratio of downstream absolute pressure to upstream absolute pressure through the nozzle or orifice is less than its sonic coefficient. Then the flow through the nozzle or orifice should be sonic and should provide a constant flow rate. This permits the back pressure measurement to be used to indicate the degree of obstruction, from an open tube, to a tube packed with catalyst, up to a certain maximum back pressure at which the sonic coefficient is no longer satisfied. The flow rate is accordingly designed to ensure that the regulator mounted on the wand body, its adjusted setting, and the orifice or nozzle opening are all coordinated for a specific flow rate through the tube under test up to a maximum back pressure. From each constant flow device 66, the test gas passes through a respective T 68, and through the internal path 54 of the respective tubular member 52 into the respective chemical reactor tube 12. Another T fitting 70 is located just above each tubular member 52, and a measurement tube 72 extends from each fitting 70 to its respective inlet at the multiplex manifold at the multiplex valve 74. The outlet of the multiplex valve 74 is connected to a pressure sensor 76. A pressure switch 78 is in communication with each measurement tube 72, and, if the pressure in the line exceeds a predetermined limit, the pressure switch 78 closes and prevents the channel of the multiplex valve 74 corresponding to that measurement tube 72 from opening, thereby preventing gas communication with the digital pressure sensor 76. This protects the pressure sensor 76 from being damaged by exposure to high pressure gas. When the wand 18 is being used to test a plurality of chemical reactor tubes 12, the test gas flows continuously through the tubular members 52 into the chemical reactor tubes 12, and the multiplex valve 74 goes through a cycle by which it puts each of the measurement tubes 72 in gas communication with the pressure sensor 76, one at a time. In this manner, a single pressure sensor 76 is used to measure the back pressure in all the injector tubes 30 of the wand 18. Since the gas flow entering the chemical reactor tubes 12 through the injector tubes 30 has been carefully regulated by the flow control devices 66 to establish a pressure drop across the flow control devices 66 and a constant gas flow to the tubes 12, the back pressure that is generated in each chemical reactor tube 12 is in proportion to the flow resistance produced by the catalyst in that chemical reactor tube 12. That resistance, in turn, is proportional to the density with which the catalyst is packed (which is to be assessed by the testing operation). As the chemical reactor tube 12 becomes more and more packed, the back pressure approaches the pressure on the supply side of the flow control device 66. It will be noted that at least the injector tubes 30 at the ends of the wand 18 and on the umbilical injector tube 30A have tapered end pieces 80, which help in guiding the wand 18 into the chemical reactor tubes 12 to be tested. Of course, tapered ends 80 could be provided for all the injector tubes 30 if desired. In this embodiment; the injector tubes 30 are arranged; linearly, with an equal spacing between the injector tubes 30. However, other arrangements, such as a triangular array of injector tubes 30 could be provided if desired. The spacing between the injector tubes 30 can be adjusted, and different diameter injector tubes 30 may be used, depending upon the configuration of the reactor, as will be described later. There is an interlock switch 82 on an adjustable position clip (see FIG. 5) which projects downwardly from behind the frame member 50. The purpose of the switch 82 is to ensure that the injector tubes 30 are inserted all the way into the chemical reactor tubes 12, and the switch 82 is contacting the plate 11, before the sleeves 56 can be inflated. When the interlock switch 82 closes, and the start switch 109 is depressed, the central processor 32 causes the inflation path solenoid valve 42 to open and initiates inflation of the sleeves 56. In this embodiment, the switch 82 signals the central processor 32 in the control box 34, which, in turn, closes a relay which opens the inflation path solenoid valve 42, allowing gas to pass through the inflation path manifold 44 to inflate the injector tubes 30. The switch 82 protects the sleeves or bladders 56 against overinflation by preventing them from inflating unless they are inside the chemical reactor tubes 12 to be tested. The umbilical injector wand 18A (shown best in FIG. 10) includes an injector tube 30A that is essentially the same as the other ten injector tubes 30, except that it is not fixed onto the main frame 50. Instead, as shown in FIG. 5, it is connected to a longer gas inlet hose 84 and has a longer measuring tube 72A and longer inflation tube 62, so that it can be held in the operator's hand and inserted individually into one of the chemical reactor tubes 12. This is helpful in the event that some of the chemical reactor tubes 12 are not accessible by the regular bank of injector tubes 30. The umbilical injector tube 30A also includes a tubular member 52 defining an internal path 54, and a sleeve 56 and an inflation tube 62, which is used to inflate the sleeve 56. At the top of the body of the umbilical wand 18A is a frame member 85, and a handle 86 is mounted onto the frame member 85. Projecting downwardly from the bottom of the frame member 85 is an interlock switch 82A, which serves the same function as the interlock switch 82 on the main frame 50, ensuring that the umbilical injector tube 30A is inserted into the chemical reactor tube 12 and the switch 82A is depressed against the plate 11 before the solenoid valve 42A is activated so that the sleeve 56 can be inflated. There is also a start switch 88 on the rear surface of the frame member 85, which the operator uses to initiate a test using the umbilical wand 18A. The tubular member 52 of the umbilical injector tube 30A mounts onto its frame member 85 in the same mariner that the other injector tubes 30 mount onto their frame member 50, as will be described later. A holster 90 (see FIG. 10) mounts on the main wand 18 to hold the umbilical injector tube 30A when the umbilical wand 18A is not in use. When the umbilical injector tube 30A is inside the holster 90, its sleeve 56 is enclosed and contained by the holster 90. FIG. 11 is a view looking down on the control box 34 of the wand 18. The control box 34 includes a display 92 as well as a number of controls, the display 92 in this example is indicating R:7; T:1, which tells the operator that the wand 18 is measuring the chemical reactor tubes 12 in row 7, beginning with tube 1. The display 92 in this view also includes ten pressure readings, which indicate the back pressure in tubes 1-10 of row 7. In the upper left corner is a stop button 94, which can be used to shut off the gas supply to the inflation tubes 62 and stop the measurement. Below that is a keyed switch 96, which is used for initializing and calibrating the unit. Next is a switch 98 that switches the unit between automatic and manual modes. Next is a switch 100 which permits the worker to alternate between viewing the measurements for the current set of chemical reactor tubes 12 and for the previous set of chemical reactor tubes 12. Next is a “find” button 102, which, when pushed, uses the laser measuring device 27 to take a distance measurement relative to the target 25 to determine which group of chemical reactor tubes 12 is being measured. When the “find” button 102 is depressed, it also includes a light 102A, which lights up (see electrical schematic of FIG. 21). Next is a “first tube” button 104, which is depressed to indicate that the wand 18 is at the first tube in the particular row. This button also includes a light 104A (see FIG. 21), which lights up when the button is depressed. Next is a toggle switch 106 for increasing or decreasing the tube number on the display 92, and above that is a toggle switch 108 for increasing or decreasing the row number on the display 92. A “start” button 109 is located on the handle 28A of the wand 18 (see FIGS. 5 and 6), and is depressed by the worker to begin the sequence for measuring a group of chemical reactor tubes 12. It should be noted that it would be possible to provide devices that include only some of the elements that have been shown here, not requiring all of those elements. For example, it would be possible to provide a device that includes a measurer, such as the laser measurer described above, a couple of probes shaped like the injector tubes 30, that would be inserted into reactor tubes 12, and an on-board computer in which is stored a “list to fix”. An operator could then use this device to locate the tubes that were found to need work during the test, for example using the device to locate tubes that need to be capped or marked accordingly for specific corrections such as adding some catalyst or removing the tube contents and refilling with catalyst. FIGS. 3, 12, 12A, and 12B show an example of the graphic display that is available at the remote laptop computer 22. The data that is input into the laptop 22 and the central processor 32 prior to the test preferably also includes information as to which tube locations actually are taken up by thermocouples or actually house supporting structure or mechanical plugs rather than tubes. If so, this is shown on the screen even before any measurements are taken (as well as afterwards). For example, thermocouples may be shown in orange, while support structure may be shown in black. It should be noted that the modem 24 and computer 22 may be receiving data from several wands 18 at once. The initial layout specifies a row and tube number for every tube position, so that the data that comes in can be associated with a particular position on the stored layout. As measurements are taken by the wand (or wands) 18, the data, including row and tube number location as well as the back pressure readings and the wand identifier are transmitted electronically back to the modem 24 and are displayed at the computer screen 22 in real time. In this embodiment, the data is transmitted from the antenna 37 on the control box 34 to the antenna on the remote modem 24, but the data could be transmitted through wires, through an internet connection, or through other known transmission means. The data which is stored at the wand 18 could also be downloaded later to the remote computer 22. The linked data transmitted from the want is graphically displayed in pictorial format at the remote computer 22, as shown in FIGS. 3, 12, 12A, and 12B. The view of FIG. 3 showing the chemical reactor tubes 12 will indicate the tubes in various colors as they are measured, depending upon whether they have passed the preset criteria for the test. For example, if the tube back pressure measurement is within the specifications for that reactor, then that tube will show up in green on the screen. If the tube fails high, it will show up in red. If it fails low, it will show up in yellow. If the tube back pressure is so high that it is considered plugged, it will show up in dark gray. If the tube back pressure is so low that it is considered open, it will show up in white. Untested tubes show up as a gray ring with a black dot in the center. Of course, this proposed color scheme could be altered by the user if desired, as long as the color usage is consistent. It should also be noted that separate data sets may be kept for various conditions of the reactor, such as for measurements taken after cleaning out the tubes, after filling the tubes, after blowing down the tubes, after operation of the reactor for a period of time, for sample measurements that may be taken to establish the test specifications, and for measurements taken after various corrective actions are taken. Also, these data sets may be stored during the life of the reactor, providing the plant engineer with valuable historic information about the reactor. The person viewing the computer screen may choose to zoom in on a particular section of the reactor, if desired. If the person viewing the screen wants information about a particular chemical reactor tube 12, he moves his cursor over that tube in the portion of the screen shown in the graphic of FIG. 3, and the information for that tube will appear in the portion of the screen shown in FIG. 12A. For example, the sample shown in FIG. 12A indicates that we are viewing the information for row #12, tube #12. The display indicates the pressure in the most recent test, the status of the tube, the wand 18 which took the measurement, and the date, time, and operator for that measurement. There is also a graphic indicator in the upper right of the screen of FIG. 12A, with rings of color indicating the status of this tube in previous measurements and in the current measurement. The circle 112 includes an outer band 114, which has a color indicating which wand 18 took the most recent measurement prior to correction. Just inside the outer band 114 is a large color field 116, which indicates by color the results of the most recent test prior to correction. Then there is an inner band 118, which indicates by color which wand took the most recent test after correction. Inside the inner band 118 is another color field 120, which indicates by color the results of the most recent test after correction, and the number 122 inside that field 120 represents the number of times the tube has been retested during the correction process. So, in this case, if the outermost band 114 is blue, that indicates that the blue wand conducted the most recent test prior to making corrections. If the color field 116 just inside the outer band is red, that indicates that the tube failed high on the most recent test prior to correction. If the inner band 118 is also blue, that indicates that the same wand conducted the most recent test during the correction process, and if the small inner color field 120 is green, that indicates that the tube has now passed. The number “2” inside the color field 120 indicates that this tube has been retested twice during the correction process. The original test data are not shown in this icon, but they are stored and can be retrieved as desired. Since the display for any particular tube in FIG. 3 is too small to include all this detail, it will, by default, simply show the color indicating the results of the most recent test. However, if the plant engineer wanted to view the display of FIG. 3 for any historic data set, he could obtain that as well. The portion of the display shown in FIG. 12A also indicates the row and tube, the pressure measured for that tube, the last status as of the previous measurement (if any), the wand number, date, time, and operator for the measurement. Below the data for that particular tube is data about the test in general—the total number of tubes, the number of tubes tested, the percent completed, and statistical information. The plant engineer may access the complete information for any tube simply by pointing to the particular tube on the display of FIG. 3 with the cursor, or he may input the particular tube and row number, or he may run a “list to fix” report or other report, pick up the tubes with problems from that report, and may access the data about those tubes by clicking on them in the report. FIG. 12B shows additional data that is presented on the computer screen. This portion provides the specifications for what pressure would be considered a failure on the high side, what pressure would be considered a failure on the low side, what pressure would indicate that the tube is plugged, and what pressure would indicate that the tube is open. It also indicates how many tubes met those criteria, and what those tubes' failure costs in terms of lost production, wasted reactants, and so forth. There is also an analysis of the number and percentage of tubes that met the criteria for being within the specifications for each test. In addition to the data shown in these figures, the computer 22 generates a “list to fix”, which is a prioritized list of which tubes should be corrected and what should be done to correct them, based oh the criteria that have been set, such as cost or pressure criteria. Of course, once the data has been acquired, the information displayed in these screens can be varied, depending upon what the user wants. For example, the plant engineer may wish to display the “list to fix”, indicating in order of priority which chemical reactor tubes 12 should be plugged, which tubes should be blown down, which tubes should be re-loaded with catalyst, and so forth. The plant engineer may set his own criteria, which the computer 22 will use to establish the “list to fix”, prioritizing the list based on the criteria that have been established by the plant engineer. The criteria that are established to set the specifications for what is a failure on the high side or the low side and what is “plugged” or “open” may be; specific pressure readings, or they may be based on a statistical analysis of the data. As more data is collected, and as the plant engineer has more experience with the actual pressure data, actual production data, and actual costs, the specifications for determining which tubes pass and which tubes have the highest priority for corrections, and the way the data is used may become much more sophisticated. The information provided by this arrangement, the speed with which it is delivered, its accuracy, as well as the way it is presented, make it very useful for the plant engineer. The plant engineer now has a way of determining the cost of out-of-specification tubes and the ability to pinpoint them and correct them promptly during the plant shut-down, when time is of the essence. He then can adjust his specification criteria and cost information based on experience. Since the wand reports each tube's measurements back to the computer 22, the plant engineer knows for certain, as the test is being conducted, that the equipment tubes 12 have been tested. This system provides a quality control check on the installers of catalyst. This device and method provide a tremendous amount of useful information in very user friendly format that the plant engineer has never had before. In a variety of ways, it helps the plant engineer make better decisions to improve the efficiency of the plant. In the prior art, each chemical reactor tube 12 was capped in a certain color as the testing process was proceeding in order to provide a visual indication of the test results and the progress of the test. If desired, a detachable tube capping guide 33 (shown in FIG. 2) may be plugged into the control box 35, including ten rows of lights, with three different colors of lights 33A for each injector tube 30, to indicate by the color of light that is lit up by the central processor 32 whether that tube failed high, failed low, or passed the test criteria. The operator could then use that guide to place the appropriate color of cap onto each tube as the measurements progress. However, it is expected that the visual data provided at the computer 22 will be so much more helpful than were the prior art caps that plant engineers will find the capping step to be unnecessary and will decide to save money by eliminating the use of caps in tests that use the wand 18. In addition, a simulation package may be provided to the plant engineer prior to taking measurements, to give the plant engineer experience in making decisions about corrective actions to be taken before the measurements are even taken. This may help the plant engineer make quick decisions during the plant shut-down, when time is especially valuable. FIG. 13 shows schematically the laser measurement device 27 on the wand 18 measuring a distance back to a target 25, which is mounted in the first tube 12 of the row of chemical reactor tubes 12 being measured. The laser measurement device 27 shines a light onto the reflector portion 110 of the target 25, and the light is reflected back to the device 27, establishing a distance measurement from the wand to the target, which is converted by the microcomputer 32 to a tube number. The software also permits the operator to put the flag into a different chemical reactor tube 12 other than the first tube and to instruct the central processor 32 to compensate accordingly, so that the central processor 32 always indicates the correct position of the wand 18. As shown in FIGS. 15 and 16, the target 25 has two legs 111, which fit into two adjacent chemical reactor tubes 12 in a row. One of the legs 111 preferably is mounted in a slot in order to permit adjustment of the spacing between the legs 111 to fit the spacing between chemical reactor tubes 12 in a particular reactor. When the first tubes in a row are being measured, there is no reflector present, and the operator simply presses the “first tube” button 104 on the control panel to indicate that the first injector tube 30 on the wand 18 is being inserted into the first chemical reactor tube 12 in that row. When the operator removes the wand 18 from the first group of tubes, he inserts the reflector 110, and thereafter the display 92 on the control box 34 automatically indicates the tube position being measured based on the distance measurement from the laser measurement device 27. After the wand 18 has measured the end of a row, the display 92 automatically increases the row number in preparation for measuring the next row. FIG. 17 shows a wand 18 that has been reconfigured for use in blowing down the chemical reactor tubes 12. (While it is possible to use the wand 18 in its initial configuration to blow down tubes, the flow control devices 66 may prevent a high enough volume of gas from flowing through to be effective for blowing down the chemical reactor tubes 12 to remove dust. In that case, this reconfiguration may be used.) While there is still a gas inlet at the handle 28 in order to inflate the sleeves 56, anew gas inlet 124 has been provided to supply high volume gas for blowdown. This new gas inlet 124 feeds the main manifold 64, but the flow control devices 66 have been removed from the line, so that the gas simply flows straight through the main manifold 64 and through the lines 84, through the internal paths 54 of the tubes 52, and into the chemical reactor tubes 12. This permits a high volume of gas to be supplied into the chemical reactor tubes 12 to blow them down, removing dust. The operator may choose not to take pressure measurements during the blow-down operation, or the wand may be configured not to take pressure measurements during blow-down, if desired. However, the display 92 on the control panel of FIG. 11 will show which chemical reactor tubes 12 are being blown down, and the data may be transmitted to the laptop computer 22, indicating which tubes are being blown down, which wand 18 is being used, and the time and date of the procedure. The visual display 92 then will show the chemical reactor tubes 12 that have been blown down by indicating those tubes in a special color. This provides quality control, so the plant engineer can confirm that the tubes actually have been blown down. While the wand 18 can be converted back and forth from the measurement mode to the blowdown mode, with the configurations shown here, it takes time to make the conversion. Therefore, it may be preferable simply to provide two different types of wands-one for taking measurements and one for blowdown. Alternatively, a valving arrangement may be provided to permit conversion from one mode to the other simply by opening and closing valves to open and close the different pathways that are used for the different operations, preferably bypassing the flow control devices 66 and closing the flow through the measurement tubes 72 during the blow down operation. Or, if sufficient gas flow can be achieved in the normal measurement arrangement to accomplish effective blowdown, then the original configuration of the wand may be used, and the wand's central processor 32 may simply provide for a delay in taking measurements, so that the test gas is first used for blowdown and then for taking measurements. In the blowdown mode of FIG. 17, the control box 34 continues to function, using the laser measurement device 27 and target 25 to determine the chemical reactor tubes 12 that are being blown down and sending that information to the remote computer 22. FIG. 8A shows the gas flow arrangement for the blowdown mode of FIG. 17. In that arrangement, the inflation gas route is the same as in the measurement mode. However, instead of the regular test gas route, the test gas used for blowdown simply goes through a valve, and then through the main manifold 64 to all the tubular members 52. FIGS. 18-20 show a test stand 126 used to calibrate the wand 18 for taking back pressure measurements. The stand 126 includes a frame member 128, which is supported on base frame members 130 by means of uprights 132. Several calibration tubes 134 are mounted on the frame member 128. As shown in FIG. 18A, the frame member 128 has a substantially U-shaped cross-section and includes lips 129 that project inwardly toward the base 131 of the U. Straps 133 have T-shaped ends, including hooked portions 135, which fit into the recesses 137 formed in the frame member 128. The straps 133 preferably are assembled onto, the frame member 128 by sliding them in from the end, and their shape, in cooperation with the shape of the frame member 128, restricts their movement relative to the frame member to linear movement along the frame member 128. A plastic end piece 138 is placed over the end of the calibration tube 134, and the straps 133 are clamped together around the end piece 138 and calibration tube 134 by means of bolts 140 and nuts 142, with the bolts 140 extending through holes 144 in the straps 133. This mounting arrangement allows the position of the calibration tube 134 to be adjusted along the length of the frame member 128 by sliding the straps 133 linearly along the frame and then to be fixed in place once the bolts 140 are tightened. The uprights 132 are secured to the frame members 128, 130 in the same manner that the calibration tubes 134 are mounted onto the frame member 128, and the injector tubes 30 are secured onto the frame 50 of the wand 18 in the same manner as well. This permits adjustment of the positions of the injector tubes 30 along the frame members, and it permits different sizes of injector tubes 30 to be used on the same frame member 50. In this manner, the wand 18 can be reconfigured for measuring different reactors, having different tube diameters and different tube spacings. Each of the calibration tubes 134 is closed at the bottom, except for a precision orifice 136 (see FIG. 20), which imitates the effect of the packing in the open-ended chemical reactor tubes 12. In order to calibrate the wand 18, the injector tubes 30 are inserted into the calibration tubes 134, gas is sent through the inflation path to seal the injector tubes 30 against the inside of the calibration tubes 134, and then gas is sent through the test path, and aback pressure reading is taken for each chemical reactor tube 12. The central processor 32 then generates correction factors as needed for each injector tube 30 in order to correct for any variations in the measurements, and these correction factors are used by the central processor 32 as the chemical reactor tubes 12 in a reactor are measured, in order to standardize the measurements from one injector tube 30 to another. FIGS. 21 and 22 are an electrical schematic of the wand 18, showing the inputs and outputs to and from the central processor 32, which have already been described. There is a direct current power connection to the control box 34 of the wand 18, which may come from the remote power and data module 24 or from another power source. Measurements taken by the wand 18 may be transmitted through a modem and antenna 37 on the wand 18 to the antenna on the remote power and data module 24, or they may be transmitted through another means, as discussed earlier. Of course, this arrangement also permits the wand 18 to receive instructions or data from a remote source as well. The power and data module 24 communicates with the laptop computer 22. Alternatively, the data may simply be stored in the wand 18 and later downloaded to the remote computer 22. FIG. 23 shows the additional controls that are added for the blowdown mode as shown in FIG. 17. These controls take their power from the main control box 34 for the wand 18 through a power cord 146, and the valve 148 which opens a gas path from the inlet 124 to the main manifold 64 is only opened after the seals 56 are inflated. In a typical setting, the wand 18 (or several wands 18) would be prepared with injector tubes 30, 30A having the correct diameters and spacings for the reactor to be measured. The configuration of the reactor, including the locations of the chemical reactor tubes 12 would be loaded into the wand central processor 32 and into the laptop computer 22. Then, the wands 18, power and data module 24, laptop computer 22, and calibration or test stand 126 would be transported to the site. If blowdown is to be done first, then the wands 18 may be configured for blowdown, or special blowdown wands may be used if needed. The workers would then go along the plate 11, blowing down all the chemical reactor tubes 12. The workers would take their wands 18 to the end of a row, would use the toggle switch 108 if needed to make sure the display 92 is indicating the correct row, would insert the injector tubes 30 into the first group of chemical reactor tubes 12 in the row, and would push the “first tube” button 104, to indicate that the first tube is being measured. Then, the worker would push the “start” button 109 on the handle 28A. If the switch 82 is depressed, indicating that the wand 18 has been properly inserted into the chemical reactor tubes 12, then, when the “start” button 109 is pushed, the central processor 32 would open the solenoid valve 42 for the tube seals, inflating the sleeves 56 to seal against the inside of the chemical reactor tubes 12. The test gas would be flowing through the injector tubes 30 continuously. Once the first group of chemical reactor tubes 12 has been blown down, the worker would move to the next group of ten (or whatever number is provided on the wand) and would insert the target 25 into the first two tubes of the row so that the laser measuring device 27 could automatically measure the distance from the wand 18 to the target 25, thereby automatically determining which chemical reactor tubes 12 are being blown down. The central processor 32 would transmit this information electronically to the power and data module 24, telling it which wand 18 is being used, the time and date, and which chemical reactor tubes 12 are being blown down. (The identification of the worker who is using the wand 18 is expected to be in the set-up information that is input into the computer 22 before the test and therefore would hot have to be transmitted.) The power and data module 24 would, in turn, transmit this information to the laptop computer 22, so the plant engineer could see in real time on the computer screen the chemical reactor tubes 12 being blown down. If the wand 18 does not have to be reconfigured for blow-down, then the workers may perform the blow-down and the back-pressure measurement in one step, inserting the wand 18 into a bank of reactor tubes 12, blowing down the tubes, and then measuring the back pressure in the tubes before moving on to the next group of reactor tubes 12. Before measurements are taken, the wands 18 would be configured for taking measurements and would be calibrated at the test stand 126. Again, each worker would take his wand 18 to the beginning of a row of chemical reactor tubes 12 to be measured and would insert the injector tubes 30 into the chemical reactor tubes 12. He would then use the row toggle switch 108 to make sure the correct row is showing on the display 92 and would then press the “first tube” button 104. Then, he would push the “start” button 109. If the switch 82 indicates that the injector tubes 30 are properly inserted into the chemical reactor tubes 12, the central processor 32 would open the solenoid valve 42 to inflate the seals oh the injector tubes 30. Then, the central processor 32 would open the multiplex valve 74, one channel at a time, permitting the pressure sensor 76 to measure the back pressures in the measurement tubes 72 one at a time, until the back pressure for all the injector tubes 30 has been measured, stored at the wand 18, and transmitted to the power and data module 24. Once the first group of chemical reactor tubes 12 has been measured, the worker would move to the next group (of ten tubes in this arrangement) and would insert the target 25 in the first tube. Thereafter, the central processor 32 will automatically keep track of which chemical reactor tubes 12 are being measured, with the operator simply pressing the “start” button 109 each time a group of chemical reactor tubes 12 is to be measured, thereby causing the wand 18 to take the distance and pressure measurements and transmit the data for each chemical reactor tube 12 to the power and data module 24. If the worker comes to an obstacle or to the end of a row, he will put his tenth (or last) injector tube 30 into the last tube before the obstacle or the last tube at the end of the row, and may re-measure some of the chemical reactor tubes 12 that have already been measured. If the worker comes to a chemical reactor tube 12 that cannot readily be reached by the whole wand 18, he may choose to use the umbilical wand 18A. This works in the same manner as the regular measurements, except that the worker would use the switch 98 to put the wand 18 into the manual mode and would use the toggle switches 106, 108 to be sure the correct tube row and tube number are being indicated. Then he would press the “start” switch 88 on the umbilical wand 18A, and, if the interlock switch 82A is closed, indicating that the injector tube 30 is fully inserted into the chemical reactor tube 12 to be tested, a measurement will be taken. Adjustments for Changed Conditions Since testing a reactor with as many as 30,000 chemical reactor tubes 12 can take a number of hours, even when using multiple wands 18 at the same time, changes in ambient conditions and in gas supply conditions during the test period can affect the pressure measurements. These changes may be corrected for based on the gas law pv=nrT. Changes in the ambient environment and in the gas supply that may be measured and adjusted for include: supply gas temperature, supply gas pressure, discharge gas temperature, barometric pressure, and ambient temperature. Also, chemical reactor tube 12 temperature changes may be considered and corrected for based on Darcy's equation. These pressure and temperature changes may be measured during the vessel testing period, and corrections to the pressure measurements may be made to assure that the results reflect a standard: condition of pressure, temperature and flow as initially calibrated, such that all pressure results correlate to the standard condition established when testing began. This is an especially important consideration if testing must be interrupted for an unrelated plant emergency or for inclement weather. Since these parameters generally change slowly over time, they can be measured with each and every use of the wand or at specified periods during the testing process. These measurements can be made on or off the wand 18 and applied to the raw pressure measurements or stored in the memory of the wand 18 or of the host computer 22 for later analysis. FIGS. 24-26 are schematics showing how the devices described above can be used for blowing down and measuring a tube 12 in which there is an axially-oriented obstruction, such as a hollow sleeve 15 containing a plurality of thermocouples, extending along the central axis of the tube 12. The thermocouples measure the temperature at various points inside the tube 12, and a portion 15A of the hollow sleeve projects out one end of the tube 12, either out the top, as shown in FIGS. 24 and 26, or out the bottom, as shown in FIG. 25, housing the leads from the thermocouples. Since the temperature measurements taken by the thermocouples are used to control the reactor, it is very important that the conditions in the tubes 12 containing the hollow sleeves 15 housing the thermocouples are as close as possible to the conditions in the regular tubes 12. However, it is more difficult to load catalyst into a tube 12 that contains an axial obstruction such as the hollow sleeve 15, because the sleeve 15 interferes with the ability of the catalyst pellets to pass into and along the tube 12. The tube test device 18 may be used while loading a tube 12, especially a tube 12 containing a sleeve 15 or other obstruction, in order to help ensure that the tube 12 is properly loaded with catalyst. In those situations, the umbilical wand 18A is used at the end of the tube 12 opposite the projecting portion 15A of the hollow sleeve 15. Since the center of the injector tube 30A is hollow, the injector tube 30A easily fits over the end of the hollow sleeve 15 and seals against the inside of the tube 12 in the normal manner. FIG. 24 shows a worker 200 loading catalyst 202 into the top of the tube 12, while another worker 210 is at the bottom of the tube 12, measuring the back pressure in the tube 12 during the loading process. The worker 210, who is taking the measurements using the umbilical 18A, may radio the worker 200, who is doing the loading, to let him know what the back pressure is as the catalyst is being loaded. The worker 200 who is loading the catalyst will regularly measure the distance from the upper plate 11 to the catalyst level in the tube 12 by some known means, such as by inserting a tape measure or a measuring stick down into the tube 12 until it abuts the catalyst 202. He then uses the back pressure reading to determine whether the catalyst 202 is properly loaded for that depth. This helps train the worker 200 to load the catalyst properly, and, if there is a bridging or other problem, the catalyst can be removed and the filling can be restarted at an early stage, as soon as the problem is detected, rather than waiting until the tube is completely filled and fails a test. Various measurements may be taken at various heights to ensure that the catalyst density is correct throughout the tube 12. While the workers 200, 210 are shown here using radios to talk with each other and to transmit the pressure readings verbally, it is understood that the pressure readings, as well as other information, may be transmitted directly from the tube test device 18 to another type of receiver such as a laptop computer 22, as described earlier. If the projecting end 15A of the hollow sleeve 15 extends out the bottom of the tube 12, as shown in FIG. 25, then the person 210 who is taking the pressure measurements as well as the person 200 who is loading the catalyst 202 would be on top of the top plate 11, and they might in fact be the same person. The umbilical wand 18A may also be used for blowing down a tube 12 containing a thermocouple 15, as shown in FIGS. 25 and 26. In this case, the umbilical wand 18A is preferably on a modified blowdown device, such as the device shown in FIG. 17. The modified device need not be equipped to take pressure measurements and may be equipped to permit the flow of gas at higher pressures than the original device. As shown in FIG. 25, the worker 200, who is standing on the top plate 11, has inserted, the umbilical injector tube 30A into the top of the tube 12, surrounding the top end of the hollow sleeve 15 containing the thermocouples, and has sealed the injector tube 30A against the inside surface of the tube 12. He then blows air through the umbilical 18A and through the injector tube 30A to blow dust out the bottom of the tube 12. The worker 210 at the bottom of the tube 12 uses a vacuum hose 212 to vacuum out the dust 214. Typically, the dust would be allowed to accumulate at the bottom, and then the worker 210 would come along and vacuum it up after the blowdown is completed. FIG. 26 shows the same procedure as FIG. 25, except that, since the projection 15A from the hollow sleeve 15 housing the thermocouples extends out the top of the tube, the positions of the workers are reversed. The worker 200, who is blowing down the tube 12 is at the bottom of the tube 12, and the worker 210, who is vacuuming out the dust 214, is on top of the top plate 11. In this case, the vacuuming is done simultaneously with the blowdown in order to prevent the dust 214 from falling into other tubes and contaminating them. The embodiments described above are intended simply as examples of devices and methods in accordance with the present invention. It will be obvious to those skilled in the art that a wide variety of modifications may be made to the embodiments described above without departing from the scope of the present, invention. |
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050376055 | abstract | A nuclear fuel assembly with a debris filter. The lower end fitting of the fuel assembly has a stamped plate attached thereto that serves as a debris filter immediately upstream of the fuel rods. The stamped plate is provided with a plurality of flow holes in a size and pattern that provides filtration of debris damaging to the fuel rods while maintaining adequate coolant flow through the fuel assembly. |
048287911 | summary | CROSS REFERENCE TO RELATED APPLICATIONS Reference is hereby made to the following copending patent applications dealing with related subject matter and assigned to the assignee of the present invention: 1. "Debris Trap For A Pressurized Water Nuclear Reactor" by John F. Wilson et al, assigned U.S. Ser. No. 672,040 and filed Nov. 16, 1984. 2. "Fuel Assembly Bottom Nozzle With Integral Debris Trap" by John F. Wilson et al, assigned U.S. Ser. No. 672,041 and filed Nov. 16, 1984. 3. "Wire Mesh Debris Trap For A Fuel Assembly" by William Bryan, assigned U.S. Ser. No. 679,511 and filed Dec. 7, 1984. 4. "Debris-Retaining Trap For A Fuel Assembly" by John A. Rylatt, assigned U.S. Ser. No. 720,109 and filed Apr. 4, 1985. 5. "Bottom Grid Mounted Debris Trap For A Fuel Assembly" by Harry M. Ferrari et al, assigned U.S. Ser. No. 763,737 and filed Aug. 8, 1985. 6. "Nuclear Fuel Assembly Debris Filter Bottom Nozzle" by John M. Shallenberger et al, assigned U.S. Ser. No. 046,219 and filed May 5, 1987. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactors and, more particularly, is concerned with a debris resistant bottom nozzle in a nuclear fuel assembly. 2. Description of the Prior Art During manufacture and subsequent installation and repair of components comprising a nuclear reactor coolant circulation system, diligent effort is made to help assure removal of all debris from the reactor vessel and its associated systems which circulate coolant therethrough under various operating conditions. Although elaborate procedures are carried out to help assure debris removal, experience shows that in spite of the safeguards used to effect such removal, some chips and metal particles still remain hidden in the systems. most of the debris consists of metal turnings which were probably left in the primary system after steam generator repair or replacement. In particular, fuel assembly damage due to debris trapped at the lowermost grid has been noted in several reactors in recent years. Debris enters through the fuel assembly bottom nozzle flow holes from the coolant flow openings in the lower core support plate when the plant is started up. The debris tends to become lodged in the lowermost support grid of the fuel assembly within the spaces between the "egg-crate" shaped cell walls of the grid and the lower end portions of the fuel rod tubes. The damage consists of fuel rod tube perforations caused by fretting of debris in contact with the exterior of the tube. Debris also becomes entangled in the nozzle plate holes and the flowing coolant causes the debris to gyrate which tends to cut through the cladding of the fuel rods. Several different approaches have been proposed and tried for carrying out removal of debris from nuclear reactors. Many of these approaches are discussed in U.S. Pat. 4,096,032 to Mayers et al. Others are illustrated and described in the first five U.S. patent applications cross-referenced above. While all of the approaches described in the cited patent and patent applications operate reasonably well and generally achieve their objectives under the range of operating conditions for which they were designed, a need still exists for a fresh approach to the problem of debris filtering in nuclear reactors. The new approach must be compatible with the existing structure and operation of the components of the reactor, and at least provide overall benefits which outweigh the costs it adds to the reactor. SUMMARY OF THE INVENTION The present invention provides a debris resistant bottom nozzle in a fuel assembly designed to satisfy the aforementioned needs. The bottom nozzle of the present invention includes a substantially solid flat plate having spaced cut-out regions aligned directly above inlet holes of the lower core plate and open criss-cross structures fixed to the plate and extending across the regions. The criss-cross structures define individual openings small enough in cross-sectional size to filter out debris of damaging-inducing size which otherwise collects primarily in the sections of the fuel assembly between the bottom nozzle and the lowermost grid and in the unoccupied spaces of the lowermost grid and causes fuel rod fretting failures. The criss-cross structures also have structural portions which support the lower ends of guide thimbles aligned with these regions of the bottom nozzle plate. Accordingly, the present invention is directed to a debris resistant bottom nozzle useful in a fuel assembly for a nuclear reactor wherein the fuel assembly includes a plurality of nuclear fuel rods, at least a lowermost grid supporting the fuel rods in an organized array and having unoccupied spaces defined therein allowing flow of liquid coolant therethrough. The debris resistant bottom nozzle is disposed adjacent to and below the grid and below lower ends of the fuel rods. The bottom nozzle comprises: (a) support means adapted to rest on the lower core plate of the nuclear reactor; (b) a plate fixed on the support means and being of a substantially solid configuration with a plurality of spaced cut-out regions therein adapted to align directly above inlet holes in the lower core plate; and (c) a plurality of open separate criss-cross structures, each of the criss-cross structures fixed to the plate and extending across one of the cut-out regions therein. The criss-cross structures define individual openings small enough in cross-sectional size to filter out debris of damage-inducing size which otherwise collects in unoccupied spaces of a lowermost grid of the fuel assembly, but large enough in size to let pass debris of nondamage-inducing size which otherwise passes through the unoccupied spaces of the lowermost grid. More particularly, each of said cut-out regions is approximately of the same size as each of the inlet holes in the lower core plate. Also, at least one guide thimble lower end supporting structure is provided, extending into the cut-out region and fixed to the plate and cross-cross structure. In one embodiment, the cross-cross structure is in the form of a plurality of interleaved straps forming an open grid structure. In another embodiment, the cross-cross structure is in the form of a plurality of interconnected crossed wires forming an open mesh structure. Optionally, at least one pressure drop reducing flow hole can be defined in the plate at a location spaced from the cut-out regions. These and other advantages and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings . |
claims | 1. An apparatus for translating a payload comprising:a body for supporting the payload, the body comprising a cavity for receiving the payload, the body comprising;an annular ring plate having an inner surface forming the cavity about an axis for receiving the payload;an upper plate having an opening, the upper plate connected to a top end of the annular ring plate and extending radially outward from the annular ring plate; anda lower plate having an opening, the lower plate connected to a bottom end of the annular ring plate and extending radially outward from the annular ring plate;the openings of the upper and lower plates in axial alignment with the cavity and each other; anda plurality of support members for supporting the payload, the support members extending radially inward into the cavity;a plurality of rollers movable between a retracted position and an extended position, the plurality of rollers located radially outside of the cavity;wherein when the rollers are in the extended position, the rollers contact a ground surface and the body does not contact the ground surface; andwherein when the rollers are in the retracted position, the rollers do not contact a ground surface and the body contacts the ground surface. 2. The apparatus of claim 1 wherein each of the plurality of rollers is connected to a jack, wherein the jacks move the rollers between the retracted position and the extended position. 3. The apparatus of claim 2 further comprising two sliding plates that prevent the rollers from pronating or supinating when the apparatus is in motion. 4. The apparatus of claim 1 further comprising a plurality of shims for adjusting a height of the apparatus. 5. An apparatus for translating a cask comprising:a body comprising:a ring, plate having an inner surface forming a cavity about an axis for receiving the cask;an upper plate having an opening, the upper plate connected to the ring plate and extending radially outward from the ring plate, the opening of the upper plate in axial alignment of the cavity; anda lower plate connected to a bottom end of the ring plate and extending radially outward from the ring plate;a plurality of support members for supporting the cask, the support member connected to the bottom end of the ring plate and extending radially inward into the cavity, the support members being non-movable with respect to the body; anda plurality of rollers for translating the apparatus. 6. The apparatus of claim 5 wherein the support members are arranged in a circumferentially spaced-apart manner about the axis. 7. The apparatus of claim 6 wherein each of the support members comprises a contact plate and at least one L-shaped support plate, the L-shaped support plate having, a portion extending radially inward into the cavity, the contact plate connected to the portion of the L-shaped support plate extending into the cavity. 8. The apparatus of claim 7 wherein the ring plate further comprises a plurality of cutouts, the portions of the L-shaped support plates extending into the cavity through the cutouts in the ring plate. 9. The apparatus of claim 8 wherein each of the support members comprises three L-shaped support plates. 10. The apparatus of claim 5 further comprising a plurality of reinforcement plates extending from the outer surface of the ring and connected to a bottom surface of the upper plate and a top surface of the lower plate. 11. The apparatus of claim 5 further comprising a plurality of removable shims for adjusting a height of the apparatus. 12. The apparatus of claim 5 wherein the ring plate is a single annular plate structure. 13. The apparatus of claim 12 further comprising two plates that prevent the rollers from pronating or supinating when the apparatus is in motion. 14. The apparatus of claim 5, wherein the rollers are movable between a retracted position and an extended position; wherein when the rollers are in the extended position, the rollers contact a ground surface and the body does not contact the ground surface; and wherein when the rollers are in the retracted position, the rollers do not contact a ground surface and the body contacts the ground surface. 15. The apparatus of claim 5, wherein the rollers comprise a first pair of rollers and a second pair of rollers, the first and second pairs of rollers located radially outside of the cavity, the second pair of rollers located, on an opposite side of the cavity than the first pair of rollers. 16. The apparatus of claim 1 wherein the upper plate does not extend radially inward into the cavity. 17. The apparatus of claim 1 wherein the annular ring plate extends through the openings of the upper and lower plates. 18. The apparatus of claim 5 wherein the cavity and the openings of the upper and lower plates define an axial passageway that extends through an entirety of the body. 19. The apparatus of claim 5 wherein the ring plate extends through the opening of the upper plate. 20. An apparatus for translating a cask comprising:a body comprising:a ring plate having an inner surface forming a cavity about an axis for receiving the cask;an upper plate having an opening, the upper plate connected to the ring plate and extending radially outward from the ring plate, the opening of the upper plate in axial alignment of the cavity; anda lower plate connected to a bottom end of the ring plate and extending radially outward from the ring plate;at least one contact plate connected to the bottom end of the ring plate by a plurality of support plates, the contact plate located within the cavity and being non-movable with respect to the body; anda plurality of rollers for translating the apparatus. |
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abstract | A method of detecting an engine malfunction such as a misfire includes determining engine speed values at each of a plurality of measurement angular positions, heterodyning the engine speed values with sine and cosine functions indexed in the angular domain, passing the heterodyned results through a low pass filter, and computing the resulting magnitude from the resulting two vectors. An apparatus for detecting an engine malfunction, such as a misfire, includes an engine speed analyzer, a multiplier, and a low pass filter. |
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description | This application is a divisional of U.S. patent application Ser. No. 10/441,818, titled “BATCH TARGET AND METHOD FOR PRODUCING RADIONUCLIDE”, filed May 20, 2003, now U.S. Pat. No. 7,127,023, which claims the benefit of U.S. Provisional Patent Application Ser. Nos. 60/382,224 and 60/382,226, both filed May 21, 2002, the disclosures of all of which are incorporated herein by reference in their entireties. The present invention relates generally to radionuclide production. More specifically, the invention relates to apparatus and methods for producing a radionuclide such as F-18 using a thermosyphonic beam strike target. Radionuclides such as F-18, N-13, O-15, and C-11 can be produced by a variety of techniques and for a variety of purposes. An increasingly important radionuclide is the F-18 (18F−) ion, which has a half-life of 109.8 minutes. F-18 is typically produced by operating a cyclotron to proton-bombard stable O-18 enriched water (H218O), according to the nuclear reaction 18O(p,n)18F. After bombardment, the F-18 can be recovered from the water. For at least the past two decades, F-18 has been produced for use in the chemical synthesis of the radiopharmaceutical fluorodeoxyglucose (2-fluoro-2-deoxy-D-glucose, or FDG), a radioactive sugar. FDG is used in positron emission tomography (PET) scanning. PET is utilized in nuclear medicine as a metabolic imaging modality employed to diagnose, stage, and restage several cancer types. These cancer types include those for which the Medicare program currently provides reimbursement for treatment thereof, such as lung (non-small cell/SPN), colorectal, melanoma, lymphoma, head and neck (excluding brain and thyroid), esophageal, and breast malignancies. When FDG is administered to a patient, typically by intravenous means, the F-18 label decays through the emission of positrons. The positrons collide with electrons and are annihilated via matter-antimatter interaction to produce gamma rays. A PET scanning device can detect these gamma rays and generate a diagnostically viable image useful for planning surgery, chemotherapy, or radiotherapy treatment. It is estimated that the cost to provide a typical FDG dose is about 30% of the cost to perform a PET scan, and the cost to produce F-18 is about 66% of the cost to provide the FDG dose derived therefrom. Thus, according to this estimate, the cyclotron operation represents about 20% of the cost of the PET scan. If the cost of F-18 could be lowered by a factor of two, the cost of PET scans would be reduced by 10%. Considering that about 350,000 PET scans are performed per year, this cost reduction could potentially result in annual savings of tens of millions of dollars. Thus, any improvement in F-18 production techniques that results in greater efficiency or otherwise lowers costs is highly desirable and the subject of ongoing research efforts. At the present time, about half of the accelerators such as cyclotrons employed in the production of F-18 are located at commercial distribution centers, and the other half are located in hospitals. The full production potential of these accelerators is not realized, at least in part because current target system technology cannot dissipate the heat that would be produced were the full available beam current to be used. About one of every 2,000 protons stopping in the target water produces the desired nuclear reaction, and the rest of the protons simply deposit heat. It is this heat that limits the amount of radioactive product that can be produced in a given amount of time. State-of-the-art target water volumes are typically about 1-3 cm3, and typically can handle up to about 500 W of beam power. In a few cases, up to 800 W of beam power has been attained. Commercially available cyclotrons capable of providing 10-20 MeV proton beam energy, are actually capable of delivering twice the beam power that their respective targets are able to safely dissipate. It is proposed herein that, in comparison to conventional targets, if target system technology could be developed so as to tolerate increased beam power by a factor or two or more, the production of F-18 could at the least be potentially doubled, and the above-estimated cost savings could be realized. In most conventional batch target systems, a target volume includes a metal window on its front side in alignment with a proton beam source, and typically is partially filled with target water from the bottom thereof to a level at or above that of the beam strike. If beam power were applied to a completely filled conventional target, boiling in the target volume would cause a very rapid rise in pressure due to the sudden appearance of vapor bubbles. As a result, target pressure will dramatically increase, thereby causing the window to plastically deform until it ruptures or otherwise fails. Thus, the conventional target is typically incompletely filled and sealed such that the mass of water therein is fixed. As a result, the conventional target is limited to a single optimum beam power level that prevents destruction, and this optimum power level does not correspond to the most efficient production of radionuclides for the given target system and beam source and for all beam power levels. In addition, because the bottom of the conventional target is sealed, the target water expands upwardly when heated into a reflux chamber, thereby reducing the vapor space available for heat transfer. Moreover, such conventional targets have the disadvantage of introducing pressurizing gas molecules other than water vapor into the target volume, which can be potentially contaminating and which impedes heat transfer efficiency. An opposite approach to reducing the cost of F-18 production is to use a low-energy (8 MeV), high current (100-150 mA) proton beam, as disclosed in U.S. Pat. No. 5,917,874. A cooled target volume is connected to a top conduit and a bottom conduit. A front side of the target is defined by a thin (6 μm) foil window aligned with the proton beam generated by a cyclotron. The window is supported by a perforated grid for: protection against the high pressure and heat resulting from the proton beam. The target volume is sized to enable its entire contents to be irradiated. A sample of O-18 enriched, water to be irradiated is injected into the target volume through the top conduit instead of from the bottom. The resulting F-18 is discharged through the bottom conduit by supplying helium through the top conduit. Such target systems as disclosed in U.S. Pat. No. 5,917,874, deliberately designed for use in conjunction with a low-power beam source, cannot take advantage of the full power available from commercially available high-power beam sources. It would therefore be advantageous to provide a new batch target device and associated radionuclide production apparatus and method that are compatible with the full range of beam power commercially available and are characterized by improved efficiencies, performance and radionuclide yield. According to one embodiment, an apparatus for producing a radionuclide comprises a target chamber, a particle beam source, and a lower liquid conduit. The target chamber comprises a beam strike region for containing a liquid and a condenser region for containing a vapor. The condenser region is disposed above the beam strike region in fluid communication therewith for receiving heat energy from the beam strike region and transferring condensate to the beam strike region. The particle beam source is operatively aligned with the beam strike region for bombarding the beam strike region with a particle beam. The lower liquid conduit fluidly communicates with the beam strike region for transferring liquid to and from the beam strike region during bombardment. A method is disclosed herein for producing a radionuclide, according to the following steps. A target chamber is filled with a target fluid including a target material. The target chamber is pressurized. A lower region of the target chamber is bombarded with a particle beam. The target fluid becomes heated and expands into a lower liquid conduit communicating with the lower region, and a vapor space is created in an upper region of the target chamber contiguous with the lower region to establish a self-regulating evaporation/condensation cycle. It is therefore an object of the invention to provide an apparatus and method for producing a radionuclide. An object of the invention having been stated hereinabove, and which is addressed in whole or in part by the present disclosure, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. As used herein, the term “target material” means any suitable material with which a target fluid can be enriched to enable transport of the target material, and which, when irradiated by a particle beam, reacts to produce a desired radionuclide. One non-limiting example of a target material is 18O (oxygen-18 or O-18), which can be carried in a target fluid such as water (H2 18O). When O-18 is irradiated by a suitable particle beam such as proton beam, O-18 reacts to produce the radionuclide 18F (fluorine-18 or F-18) according to the nuclear reaction O-18(P,N)F-18 or, in equivalent notation, 18O(p,n)18F. As used herein, the term “target fluid” generally means any suitable flowable medium that can be enriched by, or otherwise be capable of transporting, a target material or a radionuclide. One non-limiting example of a target fluid is water. As used herein, the term “fluid” generally means any flowable medium such as liquid, gas, vapor, supercritical fluid, or combinations thereof. As used herein, the term “liquid” can include a liquid medium in which a gas is dissolved and/or a bubble is present. As used herein, the term “vapor” generally means any fluid that can move and expand without restriction except for a physical boundary such as a surface or wall, and thus can include a gas phase, a gas phase in combination with a liquid phase such as a droplet (e.g., steam), supercritical fluid, or the like. Referring now to, FIG. 1, a target device or assembly, generally designated TA, is illustrated in accordance with an exemplary embodiment. Target assembly TA generally comprises a target body 12, a window body or flange 14 secured to the front side (beam input side) of target body 12, a front body or flange 16 secured to the front side of window flange 14, and a back body or flange 18 secured to the back side of target body 12. As appreciated by persons skilled in the art, the various body or flange sections of target assembly TA can be secured to each other by any suitable means, such as by using appropriate fastening members such as threaded bolts. Target body 12 in one non-limiting example is constructed from silver. Other suitable non-limiting examples of materials for target body 12 include nickel, titanium, copper, gold, platinum, tantalum, and niobium. Target body 12 defines or has formed in its structure a target chamber, generally designated T; an upper target conduit (or upper liquid conduit, upper fluid conduit, or upper conduit) 22 fluidly communicating with target chamber T; an upper target port 22A generally disposed at an outer surface 12A of target body 12 and fluidly communicating with upper target conduit 22; a lower target conduit (or lower liquid conduit, lower fluid conduit, or lower conduit) 24 fluidly communicating with target chamber T; and a lower target port 24A generally disposed at outer surface 12A of target body 12 and fluidly communicating with lower target conduit 24. As also shown in FIG. 2, in one exemplary embodiment, target chamber T has a generally L-shaped cross-sectional volume between a target front side 32A and a target back side 32B thereof. The lower leg of this L-shape terminates at a beam strike section 34 of target front side 32A for receiving a particle beam PB (FIG. 1). Some additional details of target body 12 are shown in the partially schematic view of FIG. 4, which illustrates target body 12 from its front side. A pressure transducer PT is installed in a bore 34 of target body 12 in fluid communication with lower target conduit 24 and in electrical communication with an electrical cable 36 for sending pressure measurement signals to reading instrumentation external to target body 12. This fitting 36 is suitable for connection to a pressure transducer, as schematically represented by an arrow PT. A fluid passage 38 interconnects lower target conduit 24 with an expansion chamber EC. Expansion chamber EC fluidly communicates with a fitting 42 mounted externally to target body 12, to which an extension 44 of expansion chamber EC can be connected. As further shown in FIGS. 1 and 2, in the operation of target chamber T, the interior of target chamber T is virtually partitioned into a boiler or evaporator region (also termed a beam strike region or, more generally, a lower region), generally designated BR, and a condenser region (or, more generally, an upper region), generally designated CR. Condenser region CR is disposed above, but is contiguous with, boiler region BR. Boiler region BR fluidly communicates with lower target conduit 24, and condenser region CR fluidly communicates with upper target conduit 22. During operation of target assembly TA, as described in more detail hereinbelow, boiler region BR is generally defined by a volume of target liquid, generally designated TL (i.e., liquid-phase target fluid), residing in target chamber T, and condenser region CR is generally defined by a void or space containing target vapor, generally designated TV, above target liquid TL. The virtual partition or boundary between boiler region BR and condenser region CR is thus generally defined by a liquid surface LS of target liquid TL present in target chamber T at any given time. Target liquid surface LS is schematically depicted by a shaded area in FIG. 2. Due to the thermodynamics occurring within target chamber T during operation, the level or elevation of target liquid surface LS is variable. Owing to the variable or virtual partitioning of target chamber T into boiler region BR and condenser region CR, target chamber T can be characterized as a thermosyphon. The thermosyphonic design of target chamber T illustrated herein, however, is unlike most conventional thermosyphons. As appreciated by persons skilled in the art, a conventional thermosyphon typically includes physically distinct upper and lower chambers serving as a condenser and a boiler, respectively, which usually are fluidly interconnected by a liquid line and a vapor line. By contrast, the thermosyphonic design of target chamber T disclosed herein comprises condenser region CR that is physically contiguous with or adjoined to boiler region BR, and thus does not require liquid and vapor lines. Moreover, unlike other conventional thermosyphons and heat pipes that have an essentially single interior volume, target chamber T includes lower target conduit 24 that allows liquid to shift in and out of target chamber T in response to cooling and heating, respectively. Conventional thermosyphons are described in, for example, Lock, G. S. H., The Tubular Thermosyphon, Oxford University Press (1992); Ramaswamy et al., “Performance of a Compact Two-Chamber Two-Phase Thermosyphon: Effect of Evaporator Inclination, Liquid Fill Volume and Contact Resistance”, Proceedings of the 11th International Heat Transfer Conference, Volume 2, Pages 127-132 (1998); Joshi et al., “Design and Performance Evaluation of a Compact Thermosyphon”, THERMES 2002, Pages 251-260 “Pages 1-10” (2002); Ramaswamy et al., “Thermal Performance of a Compact Two-Phase Thermosyphon: Response to Evaporator Confinement and Transient Loads”, J. Enhanced Heat Transfer, Volume 6, Number 2-4, Pages 279-288 (1999); and Beitelmal et al., “Two-Phase Loop: Compact Thermosyphon”, Hewlett Packard Company, Pages 1-22 (2002). In one exemplary embodiment, the internal volume provided by target chamber T can range from approximately 1.5 to approximately 5.0 cm3, and the diameter of beam strike section 34 can range from approximately 0.8 to approximately 1.8 cm3. In one exemplary embodiment, during the operation of target assembly TA, the volume of condenser region CR can range from approximately 0.8 to approximately 2.5 cm3, and the ratio of the respective volumes of condenser region CR to boiler region BR can range from approximately 0.5:1 to approximately 2:1. As shown in FIG. 1, a target window W is interposed between target body 12 and window flange 14 and defines beam strike section 34 of target chamber T. Target window W can be constructed from any material suitable for transmitting a particle beam PB while minimizing loss of beam energy. A non-limiting example is a metal alloy such as the commercially available HAVAR® alloy, although other metals such as titanium, tantalum, tungsten, gold, and alloys thereof could be employed. Another purpose of target window W is to demarcate and maintain the pressurized environment within target chamber T and the vacuum environment through which particle beam PB is introduced to target chamber T at beam strike section 34. The thickness of target window W is preferably quite small so as not to degrade beam energy, and thus can range, for example, between approximately 0.3 and 30 μm. In one exemplary embodiment, the thickness of target window W is approximately 25 μm. Referring now to FIGS. 1 and 3, window flange 14 in one non-limiting example is constructed from aluminum. Other suitable non-limiting examples of materials for window flange 14 include gold, copper, titanium, and tantalum. Window flange 14 defines a window bore 14A generally aligned with target window W and beam strike section 34 of target chamber T. In one advantageous embodiment, a window grid G is mounted within window bore 14A and abuts target window W. Window grid G is useful in embodiments where target window W has a small thickness and therefore is subject to possible buckling or rupture in response to fluid pressure developed within target chamber T. Window grid G can have any design suitable for adding structural strength to target window W and thus preventing structural failure of target window W. In one embodiment, window grid G is a grid of thin-walled tubular structures adjoined in a pattern so as to afford structural strength while not appreciably interfering with the path of particle beam PB. In the advantageous embodiment illustrated in FIGS. 1 and 3, window grid G comprises a plurality (e.g., seven, or more or less) of hexagonal or honeycomb-shaped tubes 42. In one embodiment, the depth of window grid G along the axial direction of beam travel can range from approximately 1 to approximately 4 mm, and the width between the flats of each hexagonal tube 42 can range from approximately 1 to approximately 4 mm. In other embodiments, additional strength is not needed for target window W and thus window grid G is not used. Referring again to FIG. 1, front flange 16 in one non-limiting example is constructed from aluminum. Other suitable non-limiting examples of materials for front flange 16 include copper and stainless steel. Back flange 18 likewise can be constructed from aluminum or other suitable materials as previously described. Front flange 16 defines a particle beam introduction bore 46 generally aligned with window grid G, target window W and beam strike section 34 of target chamber T. A particle beam source PBS of any suitable design is provided in operational alignment with particle beam introduction bore 46. The particular type of particle beam source PBS employed in conjunction with the embodiments disclosed herein will depend on a number of factors, such as the beam power contemplated and the type of radionuclide to be produced. For example, to produce the 18F−ion according to the nuclear reaction 18O(p,n)18F, a proton beam source is particularly advantageous. Generally, for a beam power ranging up to approximately 1.5 kW (for example, a 100-μA current of protons driven at an energy of 15 MeV), a cyclotron or linear accelerator (LINAC) is typically used for the proton beam source. For a beam power typically ranging from approximately 1.5 kW to 15.0 kW (for example, 0.1-1.0 mA of 15 MeV protons), a cyclotron or LINAC adapted for higher power is typically used for the proton beam source. For the thermosyphonic target chamber T specifically disclosed herein, a cyclotron or LINAC operating in the range up to 1.5 kW is recommended for use as particle beam source PBS. In another example, the beam power ranges from approximately 0.5 kW to approximately 1.5 kW. In another example, the beam power ranges from approximately 0.5 kW to approximately 4.0 kW. As further shown in FIG. 1, target assembly TA includes a coolant circulation device or system, generally designated CCS, for transporting any suitable heat transfer medium such as water through various structural sections of target assembly TA. A primary purpose of coolant circulation system CCS is to enable heat energy transferred into target chamber T via particle beam PB to be carried away from target assembly TA via the circulating coolant. Coolant circulation system CCS can have any design suitable for positioning one or more coolant conduits, and thus the coolant moving therethrough, in thermal contact with one or more inner structures of target assembly TA that define target chamber T. In the illustrated embodiment, coolant circulation system CCS comprises a coolant inlet bore 52 formed in back flange 18; a back plenum 54 formed in back flange 18; a target back structure 56 disposed at an interfacial region of back flange 18 and target body 12; a front plenum 58 formed in front flange 16; one or more coolant passages such as passages 62A and 62B formed through the axial thickness of target body 12 and disposed radially outwardly of target chamber T between back plenum 54 and front plenum 58; and a coolant outlet bore 64 formed in front flange 16. In addition, coolant circulation system CCS fluidly communicates with a cooling device or system CD of any suitable design (including, for example, a motor-powered pump, heat exchanger, condenser, evaporator, and the like). Cooling systems based on the circulation of a heat transfer medium as the working fluid are well-known to persons skilled in the art, and thus cooling device CD need not be further described herein. It can be seen from the various flow path arrows in FIG. 1 that coolant flows from cooling device CD to coolant inlet bore 52, target back structure 56, back plenum 54, coolant passages 62A and 62B and others if provided, front plenum 58, coolant outlet bore 64, and then returns to cooling device CD. Target back structure 56 includes a profiled surface 56A designed to split the flow of incoming coolant to upper and lower sections of target assembly TA and to prevent stagnation of the coolant flow. As shown in FIG. 3, a plurality of coolant passages including passages 62A and 62B can be provided in a pattern designed to optimize heat transfer. Referring now to FIG. 4, an example of a radionuclide production apparatus or system, generally designated RPA, is schematically illustrated for interacting with target assembly TA. In FIG. 4, the beam side of target assembly TA (i.e., the view of the front side of target body 12) is illustrated. In addition to target assembly TA, radionuclide production apparatus RPA generally comprises an enriched target fluid supply reservoir R; a pump P for transporting the target material carried in a target fluid; and a pressurizing gas supply source GS. Radionuclide production apparatus RPA further comprises various vents VNT1, VNT2, and VNT3 to atmosphere; valves V1-V10; pressure regulators PR1, PR2, and PR3; and associated fluid lines L1-L13 as appropriate. Although not specifically shown, one or more additional pressure regulators are installed in appropriate gas supply lines to enable pressurized gas supply source GS to deliver a suitable gas at a relatively high pressure (e.g., 500 psig or thereabouts), indicated by a gas line HP, to valve V9, and a suitable gas at a relatively low pressure (e.g., 30 psig or thereabouts), indicated by a gas line LP, to a manifold M and thus valves V5, V6, and V7. A radiation-shielding enclosure E, a portion of which is depicted schematically by dashed lines in FIG. 4, defines a vault area, generally designated VA, which houses the potentially radiation-emitting components of radionuclide production apparatus RPA. On the other side of enclosure E is a console area, generally designated CA, in which the remaining components as well as appropriate operational control devices (not shown) are situated, and which is safe for users of radionuclide production apparatus RPA to occupy during its operation. Also external to vault area VA is a remote, downstream radionuclide collection site or “hot lab” HL, for collecting and/or processing the as-produced radionuclides into radiopharmaceutical compounds for PET or other applications. Enriched target fluid supply reservoir R can be any structure suitable for containing a target material carried in a target medium, such as the illustrated syringe-type body. Pump P can be of any suitable design, such as MICRO π-PETTER® precision dispenser available from Fluid Metering, Inc., Syosset, N.Y. Pressurizing gas supply source GS can be any suitable source, such as a tank, compressor, or the like for delivering a suitable gas that is inert to the nuclear reaction producing the desired radionuclide. Non-limiting examples of a suitable pressurizing gas include helium, argon, and nitrogen. In the exemplary embodiment illustrated in FIG. 4, valves V1, V2 and V3 are three-position ball valves actuated by gear motors and are rated at 2500 psig. For each of valves V1, V2 and V3, two ports A and B are alternately open or closed and the remaining port C is blocked. Hence, when both ports A and B are closed, fluid flow through that particular valve V1, V2 or V3 is completely blocked. Remaining valves V4-V10 are solenoid-actuated valves. Other types of valve devices could be substituted for any of valves V1-V10 as appreciated by persons skilled in the art. Pressure regulators PR1, PR2, and PR3 are set by way of example to 0.5, 5, and 15 psig, respectively, to provide relatively low-, medium-, and high-pressure when desired. Fluid lines L1-L13 are sized as appropriate for the target volume to be processed in target chamber T, one example being 1/32 inch I.D. or thereabouts. The fluid circuitry or plumbing of radionuclide production apparatus RPA according to the embodiment illustrated in FIG. 4 will now be summarized. Fluid line L1 interconnects target material supply reservoir R and the inlet side of pump P for conducting the target fluid enriched with the target material. Fluid line L2 interconnects the outlet side of pump P and port A of valve V3 for delivering the enriched target fluid. Fluid line L3 is a delivery line for delivering as-produced radionuclides to hot lab HL from port B of valve V3. In one embodiment, delivery line L3 is approximately 100 feet in length. Fluid line L4 is a transfer line interconnected between valve V3 and lower target port 24A, for alternately supplying the enriched target fluid to target chamber T or delivering the target fluid carrying the as-produced radionuclides from target chamber T. Fluid line L5 interconnects upper target port 22A and port B of valve V1. In operation, fluid line L5 receives excess target fluid from target chamber T, receives vapor from target chamber T during depressurization, or conducts pressurizing gas to target chamber T from fluid line L6. Fluid line L6 interconnects fluid line L5 and valve V2, and in operation either receives excess target fluid from fluid line L5 or conducts pressurizing gas to fluid line L5. Fluid line L7 interconnects port B of valve V2 and enriched target fluid supply reservoir R, and is primarily used to recirculate enriched target fluid back to supply reservoir R during the loading of target chamber T and thereby sweep away bubbles in the lines. Continuing with FIG. 4, fluid line L8 interconnects port A of valve V2 and fluid line L9 for conducting pressurizing gas to valve V2. Fluid line L9 includes “T” intersections for fluidly communicating with pressure regulators PR1, PR2 and PR3. Fluid line L10 is an expansion or depressurization line interconnecting expansion chamber EC of target assembly TA with vent VNT1, and is employed for gently or slowly depressurizing target chamber T according to a method disclosed herein. For this purpose, in one embodiment, fluid line L10 has an inside diameter of 0.010 inch or thereabouts and is 100 feet in length. Fluid line L11 interconnects fluid line L10 and valve V1 and can conduct pressurizing gas to vent VNT3 through valve V1. A portion of fluid line L11 is employed to conduct a pressurizing gas to target chamber T from high-pressure gas line HP. Fluid line L12 interconnects port A of valve V1 and vent VNT3. Fluid line L13 interconnects valve V4 and vent VNT2. Manifold M interconnects pressurizing gas supply source GS and valves V5, V6 and V7 for selectively conducting pressurizing gas from pressurizing gas supply source GS to fluid lines L9 and L8 through pressure regulator PR1, PR2 or PR3. The following four Tables provide the control sequences and ON/OFF states of valves V1-V10 and pump P during load, beam run, delivery, and standby steps, respectively, which occur during the operation of radionuclide production apparatus RPA. In each step, components are turned ON in the order shown. In the case of multi-port valves V1-V3, the specific port A or B of that valve V1, V2 or V3 that is open is indicated. It will be noted that for each event listed, those valves V1-V10 and pump P not specifically listed are in their OFF positions. All components are turned OFF between steps. Finally, as appreciated by persons skilled in the art, time delays and pressure interlocks are variables that can be determined for specific applications of radionuclide production apparatus RPA. TABLE 1LOAD TARGET MATERIAL SEQUENCECOMPONENTS ONEVENTV4, V2-A, V1-BVent to atmosphere.V2-B, V3-A, PPump target fluid up through target. TABLE 2RUN BEAM SEQUENCECOMPONENTS ONEVENTV9Pressurize target.Leak check.V9Beam on target, then beam off at end.Leak check. TABLE 3DELIVERY SEQUENCECOMPONENTS ONEVENTV1-B, V10Equalize pressure, slow depressurize.V1-B, V8, V4Vent to atmosphere.V3-BGravity drain into delivery line.V3-B, V2-ALow pressure on upper target port.V3-B, V8, V5Low pressure on expansion chamber top.V3-B, V1-B, V2-A, V6Medium pressure delivery.V3-B, V1-B, V2-A, V7High pressure delivery. TABLE 4STANDBY AFTER DELIVERY COMPLETECOMPONENTS ONEVENTV4, V2-A, V1-BVent to atmosphere, then all off. The operation of target assembly TA and radionuclide production apparatus RPA will now be described, with primary reference being made to FIGS. 1 and 4 and Tables 1-4. As indicated by the Tables hereinabove, the method can generally be divided into four main steps or sequences of steps: (1) loading enriched target fluid into target chamber T, (2) applying a particle beam to target chamber T, (3) delivering the resultant radionuclide to a downstream site such as hot lab HL, and (4) initiating a post-delivery standby procedure. In preparation of radionuclide production apparatus RPA and its target assembly TA for the loading of target chamber T and subsequent beam strike, the fluidic system is vented to atmosphere by opening valve V4, port A of valve V2, and port B of valve V1. Also, a target fluid enriched with a desired target material is loaded into reservoir R, or a pre-loaded reservoir R is connected with fluid lines L1 and L7. Port B of valve V2 and port A of valve V3 are then opened, thereby establishing a closed loop through pump P, valve V3, target chamber T, valve V2, and reservoir R. Pump P is then activated, whereupon the enriched target fluid is transported to target chamber T via lower target conduit 24, completely filling target chamber T (in effect, both boiler region BR and condenser region CR) from the bottom. During the loading of target chamber T, the enriched target fluid is permitted to fill upper target conduit 22 and flow back through valve V2 and reservoir R, ensuring that any bubbles in the closed loop are swept away. Once charged in this manner, target chamber T is effectively sealed off at the top by closing port B of valve V2. Target chamber T is pressurized from the bottom by opening valve V9 and delivering a high-pressure gas through expansion chamber EC, fluid passage 38, and lower target conduit 24. A system leak check can then be performed by any suitable technique known to persons skilled in the art. At this stage, target chamber T is ready to receive particle beam PB. Particle beam source PBS (FIG. 1) is then operated to emit a particle beam PB through particle beam introduction bore 46, the openings defined by window grid G, and target window W at beam strike section 34 of target chamber T in alignment with boiler region BR. Irradiation by particle beam PB of enriched target liquid TL (FIG. 1) in target chamber T causes heat energy to be transferred to target liquid TL, thereby initiating a thermosyphonic evaporation/condensation cycle within target chamber T. Due to the presence of lower target conduit 24 and the fact that the top of target chamber T and its upper target conduit 22 are effectively sealed, the heating of target liquid TL causes thermal expansion of target liquid TL into lower target conduit 24. Thus, some of target liquid TL is forced out of the bottom of target chamber T into cooled lower target conduit 24 and expansion chamber EC prior to the onset of boiling, against the pressure head maintained by the pressurizing gas supplied to target assembly TA. As shown in FIG. 1, sufficient heat is added to boil target liquid TL in target chamber T, thereby forming bubbles that rise due to buoyancy effects. These events create a vapor void or space in the upper confines of target chamber T, thereby defining a condenser region CR above, yet contiguous with, a generally distinct boiler region BR in target chamber T. As described previously, boiler region BR and condenser region CR are generally demarcated by a liquid surface LS (FIG. 1). As heating increases, condenser region CR enlarges, and the vapor therein condenses on those portions of the metal surfaces of target chamber T that are exposed to the vapor space. The resulting liquid-phase droplets and/or films F then run down the exposed surfaces to return to the liquid-phase volume contained in boiler region BR. It can thus be seen that target chamber T, operating as a thermosyphon, drives an evaporation/condensation cycle that is very efficient and self-regulating. At low beam power, target chamber T is completely or nearly filled with liquid-phase target fluid, and heat transfer occurs by way of natural convection cooling patterns. As the beam power increases, target chamber T self-regulates the cycle by increasing the vapor space until there is adequate condenser surface area to remove the excess heat energy introduced by particle beam PB. The process is quite dynamic at high beam power, with target fluid constantly cycling in and out at the bottom of target chamber T and moving up and down in expansion chamber EC. Target chamber T reaches the limit of its performance when sufficient beam power is applied to allow the vapor space to lower liquid surface LS toward the point where particle beam PB starts passing through vapor at the top of the beam strike area and into target back structure 56. The vapor in expansion chamber EC then starts to oscillate up and down, breaking up the target fluid column therein into gas/liquid interfaces. The self-regulating performance and depth of target chamber T prevent particle beam PB from ever passing through to target back structure 56, which is undesirable from a radionuclide production standpoint. If target chamber T is operated at any point below this maximum power limit, and particle beam PB is then removed or its intensity reduced, the target fluid cools rapidly, the vapor condenses, and target chamber T again becomes filled to the top with liquid-phase target fluid as the contents of expansion chamber EC flow back through lower target port 24A (the original condition). The size of condenser vapor volume is thus maintained in proportion to the beam power. Moreover, foreign gas molecules impeding target vapor transport are avoided. In the operation of thermosyphonic target chamber T, an important consideration is the depth (the dimension from its front side to back side) of target chamber T. The depth of target chamber T should be sufficient to accommodate density reduction due to the vapor bubbles generated in and rising up through the beam strike due to boiling at any power level. Calorimetry data has been acquired in the course of experimental testing of prototypes of target assembly TA disclosed herein, using the CS-30 cyclotron at Duke University, Durham, N.C. The measurements indicated that a linear increase of target depth is required to compensate for vapor bubble density reduction with increasing beam current. For example, for 22 MeV protons on 30 atm water, the target depth required increased from 5 mm at 10 μA where boiling just begins, to 10 mm at 40 μA. The beam generated by the CS-30cyclotron is quite concentrated, about 3-4 mm at full width half-maximum (FWHM). The target depth required for other cyclotrons with other energies and beam optics might vary considerably. The depth required is also a strong function of the ability of a particular target to efficiently remove heat deposited by the beam. Referring to FIG. 2, an exemplary depth through boiler region BR between beam strike section 34 and back side 32B of target chamber T can range from approximately 0.2 to 12.0 cm although the invention is not limited solely to this range. Calorimetry data was also studied to assess heat removal partitioning between target back structure 56, target body 12, and the collimator/degrader typically provided with particle beam source PBS. These calorimetry data were compared to the power deposited as calculated from the product of beam current and beam energy. The latter data were higher than the calorimetry data, which suggests that some heat is also removed by natural convection and radiation from the target flange components in addition to the forced convection cooling. In all cases, the heat removal by the target sides and condenser region CR was about four times that removed by target back structure 56. The nuclear effect of particle beam PB irradiating the enriched target fluid in target chamber T is to cause the target material in target fluid to be converted to a desired radionuclide material in accordance with an appropriate nuclear reaction, the exact nature of which depends on the type of target material and particle beam PB selected. Examples of target materials, target fluids, radionuclides, and nuclear reactions are provided hereinbelow. Particle beam PB is run long enough to ensure a sufficient or desired amount of radionuclide material has been produced in target chamber T, and then is shut off. A system leak check can then be performed at this time. Once the radionuclides have been produced and particle beam source PBS is deactivated, radionuclide production apparatus RPA is taken through pressure equalization and depressurization procedures to gently or slowly depressurize target chamber T in preparation for delivery of the radionuclides to hot lab HL. These procedures are designed to be gentle or slow enough to prevent any pressurizing gas that is dissolved in the target fluid from escaping the liquid-phase too rapidly and causing unwanted perturbation of the target fluid. First, port B of valve V1, and valve V10 are opened to allow vapor to vent to atmosphere via depressurization line L10 and vent VNT1. In one advantageous embodiment, depressurization line L10 has a smaller inside diameter than the other fluid lines in the system, and is relatively long (e.g., 0.010 inch I.D., 100 feet). While port B of valve V1 remains open, valve V10 is closed and valves V8 and V4 are opened to allow vapor to vent to atmosphere via vent VNT2. After equalization and depressurization, port B of valve V3 is opened to establish fluid communication between target chamber T at its lower target conduit 24 and lower target port 24A and an appropriate downstream site such as hot lab HL, and to initiate a gravity drain into delivery line L3. A sequence of pressurizing steps is then performed to cause the target fluid and radionuclides in target chamber T to be delivered through lower target conduit 24, target fluid transfer line L4, valve V3 and delivery line L3 to hot lab HL for collection and/or further processing. Port A of valve V2 is opened to establish fluid communication between fluid line L8 and upper target port 22A, such that a low pressure is applied to upper target port 22A. Valves V8 and V5 are then opened to apply a low pressure to the top of expansion chamber EC, as regulated by first pressure regulator PR1 (e.g., 0.5 psig or thereabouts). Port A of valve V1 is then re-opened and valve V6 is opened to apply a medium pressure to the top of expansion chamber EC, as regulated by second pressure regulator PR2 (e.g., 5 psig or thereabouts). Valve V7 is then opened to apply a higher pressure to the top of expansion chamber EC, as regulated by third pressure regulator PR3 (e.g., 15 psig or thereabouts). After delivery of the as-produced radionuclides is completed, radionuclide production apparatus RPA can be switched to a standby mode in which the fluidic system is vented to atmosphere by opening valve V4, port A of valve V2, and port B of valve V1. At this stage, reservoir R can be reloaded with an enriched target fluid or replaced with a new pre-loaded reservoir R in preparation for one or more additional production runs. Otherwise, all valves V1-V10 and other components of radionuclide production apparatus RPA can be shut off. The radionuclide production method just described can be implemented to produce any radionuclide for which use of target assembly TA is beneficial. One example is the production of the radionuclide F-18 from the target material O-18 according to the nuclear reaction O-18(P,N)F-18. Once produced in target chamber T, the F-18 can be transported over delivery line L3 to hot lab HL, where it is used to synthesize the F-18 labeled radiopharmaceutical fluorodeoxyglucose (FDG). The FDG can then be used in PET scans or other appropriate procedures according to known techniques. It will be understood, however, that radionuclide production apparatus RPA could be used to produce other desirable radionuclides. One additional example is 13N produced from natural water according to the nuclear reaction 16O(p,α)13N or, equivalently, H216O(p,α)13NH4+. It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the invention is defined by the claims as set forth hereinafter. |
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042344492 | description | DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1 of the drawings, there is disclosed apparatus used in the direct oxidation of liquid sodium in the presence of particulate silica to form a sodium monoxide coated silica suitable as a feed material for making glass. Although the reported runs were conducted with sodium only, it is clear to those skilled in the art that alkali metals other than sodium are applicable to the subject method as are various mixtures of alkali metals such as sodium and potassium used as a coolant in breeder reactors. In the drawing, a rotary drum reactor (calciner) 50 includes a cylindrical body portion 51 having a circular end flange 52 to which is mated an end plate 53. A plurality of openings (not shown) are evenly spaced about the flange 52 and cover 53 to receive a corresponding plurality of fasteners firmly to seal the cover 53 to the end flange 52. If desirable, a gasket (not shown) may be used intermediate the end flange 52 and the cover 53 to insure an air tight seal. A rotary seal 55 is positioned along the central axis of the end flange 52 and cover 53 and provides communication to the inside of the reactor 50, allowing the introduction of material into the rotary drum reactor during rotation thereof. At the other end of the rotary drum reactor 50 is a circular cover 56 along with another rotary seal 57, positioned axially thereof. An electrical heater 61 in the form of the usual heating wire is wrapped about the surface of the cylindrical body and is suitably connected to a source of electrical current. Insulation 62 is positioned over the electrical heater 61 so as to reduce the heat loss to the atmosphere. A roller bar 65 is a ball mill roller having an axial shaft 66 is positioned directly below the rotary drum reactor 50 in frictional contact with both the end flange 52 and cover 53 as well as the cover 56, rotation of the roller bar 65 by a motor (not shown) coupled to the shaft 66 causes rotation of the rotary drum reactor 50 and mixing of materials within the reactor. A thermocouple well 68 extends into the rotary drum reactor 50 through the seal 57 and houses a thermocouple 69 connected by means of a lead 71 to a suitable electrical connection, thereby to provide an axial temperature profile of the reaction within the rotary drum reactor 50. As may be seen, the thermocouple 69 is movable axially within the housing 68 from one end of the drum 50 to the other end to enable data to be collected incrementally along the longitudinal axis of the drum. An oxygen source 75 is connected to a valve 76 by a pipe 77, and the valve 76 is connected to a flow meter 78 by a pipe 79. An argon source 85 is connected to a valve 86 by a pipe 87, and the valve 86 is connected to a flow meter 88 by a pipe 89. A pipe 90 from the flow meter 88 is connected to and provides communication with the rotary drum reactor 50; a pipe 91 serves to connect the flow meter 78 to the inlet pipe 90 of the rotary drum reactor 50. Accordingly, both the source of oxygen 75 and the source of argon 85 are connected by the piping routes hereinbefore described to the rotary drum reactor 50. The rotary drum reactor 50 has an outlet pipe 95 extending through the seal 57 and is connected to a cyclone separator 96 having a bottoms collection plenum 97. A filter 98 is connected by a pipe 99 to the cyclone separator 96 and a pipe 100 is connected to the other end of the filter 98 to vent the filtered gases to the atmosphere, or if desired to a recycling system for further introduction into the rotary drum reactor 50. In the examples, a mixture of oxygen and argon was passed through the rotary drum reactor 50 without recirculation; however, it is contemplated that recirculation of the oxygen and diluent gas, whether it be argon or nitrogen or other suitable diluent, would be used to eliminate gas effluent carryover. The cyclone separator 96 was used to collect solid materials, that is the sodium monoxide dust, carried over by the gas stream from the rotary drum reactor 50. The rotary drum reactor 50 was fabricated from a straight 150 millimeter internal diameter (6 inch, schedule 40) pipe having a length of 0.5 meter (19 inches) with four straight 25 millimeter wide baffles running axially on the inner wall of the reactor. These baffles were not shown in the drawing. As illustrated, the gas mixture enters reactor 50 through the rotating seal 55 at the center of the end cover 53 and exits through the rotating seal 57 at the other end cover 56. The thermocouple 69 in the thermocouple well 68 allows the axial temperature distribution in the reactor 50 to be determined. During the tests, the drum 50 was rotated at a rate of between 12 and 25 rpm of the ball mill roller 65. Since one of the objects of the present invention is to produce a feed material for making satisfactory glass for storing radioactive alkali materials, the initial silica-sodium ratio in the examples was chosen to be 7 to 1 in order to yield the silicon dioxide-sodium monoxide ratio of 5 to 1 which is suitable for making a stable glass required to store radioactive materials. All of the examples reported herein started with a total initial charge of 1.3 kilograms consisting of 0.17 kilogram sodium, 1.2 kilogram silica. Two types of silica were tested, one being silica sand between 95 and 100 mesh, that is a material which passed through a 95 mesh screen and was retained on a 100 mesh screen and silica flour which passes through a 200 screen. (Unless otherwise indicated, all screen sizes are given herein as U.S. Sieve Series mesh). In preparing the materials, the silica flour was dried by baking the material at about 200.degree. C. for 7 days. The sodium and the silica were mixed manually in a glove box under a helium atmosphere by heating each of the constituent materials to about 130.degree. C. and pouring the liquid sodium into the silica while stirring the mixture until it had cooled below 80.degree. C. The sodium-silica mixture prepared in this manner was neither sticky nor gummy but was granular, dry and poured easily. Five runs are reported showing the effect of varying the oxygen concentration in the feed gas, the reaction temperature and the silica particle size. The conditions of each run are summarized in Table 1. TABLE I ______________________________________ Silica Ar Duration Run Mesh Flow, O.sub.2 Flow,.sup.a Temp., .degree.C. of Run, No. Size cm.sup.3 /s cm.sup.3 /s Max. Final min ______________________________________ 1 -200 45 9.2 (17%) 158 -- .sup.b 2 -200 27.2 14.3 (35%) 164 100 105 3 -95 +105 22.5 14.3 (39%) 212 155 96 4 -95 +105 27.2 20.3 (43%) 246 110 165 5 -200 10.0 14.3 (59%) 225 150 94 ______________________________________ .sup.a Numbers in parentheses indicate oxygen concentration in feed gas. .sup.b Terminated before completion due to excessive carryover. Referring now to table 1, in the first two runs although it was attempted to start the reaction spontaneously due to the exothermic nature of the oxidation reaction of sodium to sodium monoxide (-45 kcal molNa), it was determined that the spontaneous reaction would not occur even under oxygen pressures as high as 100 kPa (Kilonewtons per square meter) (100 kPa=14.7 psi). In all cases, it was necessary to exceed the melting temperature of sodium (97.8.degree. C.) before the reaction proceeded spontaneously. It is believed that the oxide coating protects the solid sodium from contact with oxygen; however, as the sodium melts, the oxide coating is broken and the reaction is initiated. After the reaction was initiated, the reactor temperature increased sharply to a maximum then declined slowly as the metallic sodium became less accessible and the heat loss rate exceeded the heat production rate. The temperature rose more rapidly at the oxygen-inlet end of the reactor as the high temperature peak was observed to travel axially of the reactor from the inlet end early in the run to the outlet end near the completion of the run. This progression of maximum temperature is clearly shown in FIG. 2 wherein the axial temperature profile is plotted at a variety of times during run no. 3. An important concern in the operation of a rotary drum reactor 50 of the type described or a rotary calciner is the degree of carryover of solids with the gaseous effluent. Varying degrees of solids carryover were observed during the runs, ranging from several grams in the first run to negligable amounts in the later runs, see Table 2 hereinafter set forth. As it was determined that the concentration of oxygen in the argon sweep gas had a negligible effect on the reaction rate, see Table 2, the reaction rate being controlled by the rate of oxygen flow into the reaction chamber, the argon flow rate was reduced to a very low value in the order of 10 cubic centimeters per second to reduce the solids carryover. Whether or not any inert diluent such as argon is required is not clear, except to insure that oxygen reaches all parts of the reactor vessel. In a fully commercial system, substantially all of the metallic sodium would have to be reacted to the monoxide, while in the samples tested some metallic sodium remained. In these tests, the reaction vessel was allowed to cool down rapidly near the end of the reaction. This explains the fact, as shown in Table 2, that none of the reactions were complete, in the sense that some metallic sodium remained in all of the runs. Nevertheless, the amount of elemental sodium remaining is a critical measurement in carrying out the objects of the present invention, and in order to determine same, two weighed portions of each sample were taken for analysis. One portion was used for determination of total sodium and sodium peroxide. The total sodium was determined by dissolving sodium, sodium monoxide and sodium peroxide in water, filtering the sample to remove the silica particles and thereafter titrating the solution with a standard hydrochloric acid solution. The sodium peroxide was then determined by acidifying the solution and titrating the hydrogen peroxide produced by the reaction of sodium peroxide with water with a standard potassium permanganate solution. Some silica was found to dissolve in the strongly basic solution, but it did not appear to interfere with the total sodium analysis. The second portion of the sample was heated to a temperature in the range of between about 400.degree. and about 450.degree. C. under vacuum conditions to determine the elemental sodium present by evaporative weight loss. The amount of loss by evaporation was confirmed by dissolving the residue in water and titrating the solution with a standard hydrochloric acid solution, as was done for the total sodium measurement. In all cases, the weight loss correlated well with the difference in total sodium in the untreated sample and in the residue after evaporation. The results of each run are presented in Table 2 wherein the percent of the original sodium that was converted is expressed as a combination of sodium monoxide and sodium peroxide. The quantity of sodium peroxide is given separately as a percentage of the original sodium, as is the quantity of unreacted sodium. Sodium peroxide is considered an acceptable product for incorporation into the glass. While it is of interest to know the quantity of sodium peroxide formed, its presence in no way detracts from the success of the reaction. TABLE 2 __________________________________________________________________________ Na % of Na Reacted to Run Added, Form Na.sub.2 O + Na.sub.2 O.sub.2.sup.a % of Na Remaining Carryover, No. kg Inlet Middle Outlet Inlet Middle Outlet g __________________________________________________________________________ 1 0.164 -- -- -- -- -- -- .sup.b 2 0.173 91.9 92.0 92.9 8.1 8.0 7.1 1 (7.5) (9.0) (8.8) 3 0.173 86.8 80.6 85.4 13.2 19.4 14.6 (5.5) (10.9) (4.5) 4 0.174 82.9 79.6 81.0 17.1 20.4 19.0 3.2 (7.1) (20.6) (8.8) 5 0.173 83.2 79.6 80.6 16.8 20.4 19.4 None (10.7) (8.9) (9.8) __________________________________________________________________________ .sup.a Values in parentheses are percentages of Na.sub.2 .sup.b Run terminated due to excessive material carryover. Na analyses no available. As shown in Table 2, the highest sodium conversion was achieved in run 2, in which -200 mesh silica flour was used. The oxygen input rate was low, and the maximum temperature was maintained at a relatively low 164.degree. C. The total time of the run was 105 minutes, indicating that in a continuous, large-scale process, the residence time in the reactor would be at least 120 minutes. The conditions that seem to reduce the conversion efficiency were the use of the -95 +105 silica particles, higher operating temperatures and higher oxygen feed rates. Nevertheless, when continued stirring was employed with the -95 +105 silica a satisfactory product was obtained. Since the higher oxygen feed rate results in higher operating temperatures, it is difficult to separate these effects. It is certain, however, that the larger silica particles provide larger volumes between the particles for sodium containment so that it is more difficult for the oxygen to reach all the sodium present in the charge. As seen, the direct-oxidation method using a silica carrier has been shown to achieve a more than 92% conversion of elemental sodium to the oxide when dry oxygen is used. With the addition of sufficient humidity, 100% conversion should be achievable without difficulty. The material produced, that is sodium monoxide coated silica particles having a weight ratio of silica to sodium monoxide of about 5 to 1 , would be suitable as a feed material to make a stable glass for storing radioactive waste containing alkali metal cations. Table 3 below sets forth an additional summary of the five runs presented in Tables 1 and 2. As noted, supplemental heating was necessary to initiate the reaction in both runs 1 and 2 during which time argon was passed through the system. When the temperature reached approximately 230.degree. F. (110.degree. C.) supplemental heating was stopped and the oxygen flow was started through the rotating drum reactor 50. The drum reactor 50 was turning at 25 rpm in the first run and the oxygen concentration in the gas stream was varied from between 10% to 20% by volume. The highest temperature reached in the first run was 320.degree. F. (160.degree. C.) as reported, the first run being shut down sooner than desired because of excessive carryover of the silicon dioxide and sodium monoxide particulate. TABLE 3 __________________________________________________________________________ Percent Max Total SiO.sub.2 O.sub.2 Temp. Percent Conversion Charge Particle in sweep Achieved of Na to Na.sub.2 O & Na.sub.2 O.sub.2 Run # (Kg) Size Gas (.degree.F.) Inlet Middle Outlet __________________________________________________________________________ 1 1.37 -200 10-20 316(158.degree. C.) -- a -- 2 1.37 -200 20-60 327(164.degree. C.) 92 92 92 3 1.37 +95, -105 25-40 408(209.degree. C.) 87 81 85 4 1.37 +95, -105 40 475(246.degree. C. 82 80 82 5 b 1.37 -200 60 435(224.degree. C.) 83 80 81 __________________________________________________________________________ a High argon flow and excessive solids carryover. Run stopped prematurely b Run terminated early due to seal failure. Run 2 essentially duplicated run 1 except that the drum 50 was rotated at 12 rpm. The oxygen gas concentration was varied between 20% and 60% by volume with 100% pure oxygen being run at small time intervals during the run. Again 230.degree. F. (110.degree. C.) seemed to be the temperature at which the reaction became self-sustaining. Run 3 was similar to runs 1 and 2 except that a higher reaction temperature, 392.degree. F. (200.degree. C.), was achieved by wrapping insulation on the drum body 51. The silicon dioxide-sodium charge was slightly different than in runs 1 and 2 in that -105 mesh silica was used instead of the silica flour in the previous runs. By manually stirring the silica-sodium mix until it was cool, with the Inconel sheath 68 of the thermocouple 69, it was found that the sodium monoxide coated silica particles remained separate and poured very nicely. Runs 4 and 5 show the result of an increase in the volume percent of oxygen in the sweep gas, which translates to a higher reaction temperature. As seen, in runs 5, 60% by volume of oxygen was used which generated a reaction temperature of 435.degree. F. (224.degree. C.), the run being terminated after only about 90 minutes due to the failure of a seal on the rotary drum calciner 50. It is speculated that the percentage conversion reported in Table 3 would have been much higher had the run been allowed to continue. Nevertheless, sodium monoxide coated silica product was uniform and was easily poured out of the drum reactor 50 after termination of the run and is a very easily handled material. The product from the rotary drum 50 produced in runs 4 and 5 has been fabricated into a glass having a composition similar to that given in Battelle Northwest Laboratory Report "Annual Report on the Characteristics of High-Level Waste Glasses," BNWL-2252, page 8, June 1977. ______________________________________ Component Percent by Weight ______________________________________ Na.sub.2 O-SiO.sub.2 (calciner drum 48 product) B.sub.2 O.sub.3 (as H.sub.3 BO.sub.3) 15 ZnO 29 MgO 2 CaO 6 ______________________________________ These materials were heated in a platinum crucible for 70 hours at 2012.degree. F. (1100.degree. C.) and a transparent glass was formed. Although not tried, the following starting composition also may be suitable for preparing a similar glass for storing radioactive waste material. ______________________________________ Component Percent by Weight ______________________________________ SiO.sub.2 34.1 H.sub.3 BO.sub.3 24.6 Na 7.4 ZnO 26.5 CaO 5.5 MgO 1.8 ______________________________________ In the above-listed glass, the metallic sodium is expected to react with the boric acid as the mixtures heat. The boric acid normally decomposes on heating, liberating water which will be available to react with any metallic sodium present. As seen in the foregoing, there has been disclosed a method for producing an alkali metal monoxide coated particulate material which is suitable as feed material to make glass. Also disclosed is a process for converting highly radioactive alkali metal cations into a suitable solid material for storage. It will be apparent to those skilled in the art that various modifications and alterations may be made in the processes disclosed herein without departing from the true spirit and scope of the present invention, and it is intended to cover in the claims appended hereto all such alterations and modifications. |
041750047 | abstract | This invention is directed toward a nuclear fuel assembly guide tube arrangement which restrains spacer grid movement due to coolant flow and which offers secondary means for supporting a fuel assembly during handling and transfer operations. |
abstract | A radiation shield is provided for use on patients undergoing radiotherapy treatment. The shield is made of a suitable radiation absorbing material for preventing the transmission of high energy radiation to the patient""s non-treatment areas. The device may further comprise an exterior surface layer for absorbing low energy photons. The shield is sized and shaped to conform to a patient""s anatomy and to provide the necessary amount of absorbing material closest to the beam edge while not interfering with the beam. The shield may further comprise an optional cavity located on the interior surface of the shield which may be lined with a soft compressible material for conforming to a patient""s unique anatomy. The shield may be further provided with dosimeters mounted on the exterior surface of the leading edge as well as on the interior surface of the shield. The dosimeters may be connected in a systematic manner with the linear accelerator such that the machine could be automatically switched off or warnings given if the patient is receiving too much radiation scatter dose. |
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052020851 | claims | 1. A fuel assembly comprising: a plurality of first fuel rods, a means for moderating material having a larger cross sectional area in an upper region than a lower region in an axial direction of the fuel assembly and being surrounded with the first fuel rods, and at least one second fuel rod having a lower enrichment than a cross sectional average enrichment of the fuel assembly and being arranged in locations adjacent to the lower region of the means for the moderating material, wherein a width of the horizontal cross sectional area at the lower region of said means for moderating material is so set that minimum values of both thermal neutron flux and resonance flux in a vertical direction to the axis of the fuel assembly are located in an outer region with respect to the location of said second fuel rod in the vertical direction to the axis of the fuel assembly, and wherein the enrichment of said second fuel rod is at most 0.7 of the horizontal cross sectional average enrichment of the fuel assembly. a plurality of first fuel rods, a means for moderating material surrounding with said first fuel rods, and a plurality of second fuel rods arranged at a location adjacent to said means for moderating material, the enrichment of said second fuel rod is set at most 0.7 of a horizontal cross sectional average enrichment of said fuel assembly. a plurality of first fuel rods, a means for moderating material having a larger horizontal cross sectional area at an upper region in an axial direction than the area at a lower region and being surrounded with said first fuel rods, and a plurality of second fuel rods having lower enrichment than a horizontal cross sectional average enrichment of said fuel assembly and being arranged at a location adjacent to said means for moderating material, wherein said means for moderating material comprises a water rod having a cruciform horizontal cross section occupying an area equivalent to five fuel unit cells at the lower region, and said second fuel rods are arranged at four denting locations formed by the cruciform horizontal cross section at the lower region of the water rod, and wherein the enrichment of said second fuel rods is at most 0.7 of the horizontal cross sectional average enrichment of said fuel assembly. a plurality of first fuel rods, a means for moderating material having a larger cross sectional area in an upper region than a lower region in an axial direction and being surrounded with the first fuel rods, a plurality of second fuel rods having a lower enrichment than a cross sectional average enrichment of the fuel assembly and being arranged in a location adjacent to the lower region of the means for he moderating material, and a channel box surrounding said first fuel rods, said second fuel rods, and said means moderating material, wherein a width of the horizontal cross sectional area at the lower region of said means for moderating material is so set that minimum values of both thermal neutron flux and resonance neutron flux in a vertical direction to the axis of the fuel assembly are located in an outer region with respect to the location of said second fuel rods in the vertical direction to the axis of the fuel assembly, and the wall thickness of said channel box is selected as thinner at the upper region in the axial direction than at the lower region, and as thicker at corners than any other location, and wherein the enrichment of said second fuel rods is at most 0.7 of the horizontal cross sectional average enrichment of said fuel assembly. a plurality of first fuel rods, a means for moderating material having a larger cross sectional area in an upper region than in a lower region in an axial direction and being surrounded with the first fuel rods, at least one second fuel rod having a lower enrichment than a cross sectional average enrichment of the fuel assembly an being arranged in a location adjacent to the lower region in the axial direction of the means for the moderating material, and a means for controlling neutron flux installed in a region, wherein the lower region of said means for moderating material is located, in order to locate minimum values of both thermal neutron flux and resonance neutron flux in a vertical direction to the axis of the fuel assembly at an outer region with respect to the location of said second fuel rod in the vertical direction to the axis of the fuel assembly, and wherein the enrichment of said second fuel rods at most 0.7 of the horizontal cross-sectional average enrichment of said fuel assembly. a plurality of first fuel rods; a means for moderating material having a larger cross sectional area in an upper region than in a lower region in an axial direction and being surrounded with the first fuel rods, and at least one second fuel rod having a lower enrichment than a cross sectional average enrichment of the fuel assembly and being arranged in a location adjacent to the lower region of the means for the moderating material, wherein the horizontal cross sectional area at the lower region of the means for moderating material is set so as to locate minimum values of both thermal neutron flux and resonance neutron flux in a vertical direction to the axis of the fuel assembly at an outer region with respect to the location of said second fuel rod in the vertical direction to the axis of the fuel assembly, and wherein the enrichment of said second fuel rod is at most 0.7 of the horizontal cross sectional average enrichment of said fuel assembly. a plurality of first fuel rods, a means for moderating material having a larger cross sectional area in upper region than in a lower region in an axial direction and being surrounded with the first fuel rods, and at least one second fuel rod having a lower enrichment than a cross sectional average enrichment of the fuel assembly and being arranged in a location adjacent to the lower region of the means for the moderating material, wherein the horizontal cross sectional area at the lower region of the means for moderating material is set so as to locate minimum values of both thermal neutron flux and resonance neutron flux in a vertical direction to the axis of the fuel assembly at an outer region with respect to the location of said second fuel rod in the vertical direction to the axis of the fuel assembly, wherein said fuel assemblies are loaded more in the central region than in the peripheral region, and wherein the enrichment of said second fuel rod is at most 0.7 of the horizontal cross sectional average enrichment of said fuel assembly. 2. A fuel assembly as claimed in claim 1, wherein the horizontal cross sectional area at the lower region of said means for moderating material is equivalent to a sum of horizontal cross sectional areas of at least two of said first fuel rods. 3. A fuel assembly as claimed in claim 1, wherein the enrichment of said second fuel rod is at most 0.5 of horizontal cross sectional average enrichment of said fuel assembly. 4. A fuel assembly as claimed in claim 1, wherein said second fuel rod contains natural uranium. 5. A fuel assembly as claimed in claim 1, wherein said second fuel rod is a short fuel rod arranged at a location adjacent to the lower region of said means for moderating material. 6. A fuel assembly as claimed in claim 5, wherein the axial length of effective fuel length portion of said short fuel rod is at most a half of the axial full length of an effective fuel length portion of said first fuel rod. 7. A fuel assembly as claimed in claim 1, wherein said means of moderating material is a water rod having a larger horizontal cross sectional area at the upper region than the area at the lower region. 8. A fuel assembly as claimed in claim 1, wherein a plurality of said second fuel rods is provided. 9. A fuel assembly comprising 10. A fuel assembly as claimed in claim 9, wherein said means of moderating material comprises a water rod having a uniform horizontal cross sectional area in all through the axial direction and a coolant flow path surrounding the upper region of said water rod. 11. A fuel assembly as claimed in claim 9, wherein said means of moderating material comprises a water rod having a uniform horizontal cross sectional area in all through the axial direction and a plurality of solid moderating rods surrounding the upper region of said water rod. 12. A fuel assembly as claimed in claim 9, wherein the horizontal cross sectional area of said moderating material is so set that the minimum values of both thermal neutron flux and resonance neutron flux in a vertical direction to the axis of the fuel assembly are located in an outer region with respect the location of said second fuel rod in the vertical direction to the axis of the fuel assembly. 13. A fuel assembly as claimed in claim 9, wherein the horizontal cross sectional area of said moderating material is set larger at an upper region than the area at a lower region in the axial direction, and said second fuel rods are arranged in locations adjacent to the lower region of said means for moderating material. 14. A fuel assembly as claimed in claim 9, wherein said second fuel rod contains natural uranium. 15. A fuel assembly as claimed in claim 9, wherein the enrichment of said second fuel rods is set at most 0.5 of the horizontal cross sectional average enrichment of said fuel assembly. 16. A fuel assembly comprising: 17. A fuel assembly as claimed in claim 16, wherein the enrichment of fuel in said second fuel rods is at most 0.5 of the horizontal cross sectional average enrichment of said fuel assembly. 18. A fuel assembly comprising: 19. A fuel assembly comprising: 20. A reactor core of a nuclear reactor loaded with a plurality of fuel assemblies, wherein said fuel assembly comprises: 21. A reactor core of a nuclear reactor as claimed in claim 20, wherein the reactor core has at least a central region and a peripheral region, and said fuel assemblies are arranged more in the central region than in the peripheral region. 22. A reactor core of a nuclear reactor as claimed in claim 20, wherein the reactor core has at least a central region and a peripheral region, and said fuel assemblies are loaded in the central region by three batches dispersion method and in the peripheral region by four batches dispersion method. 23. A loading method of fuel assemblies in a reactor core of a nuclear reactor having at least a central region and a peripheral region, wherein respective ones of said fuel assemblies comprise: 24. A loading method of fuel assemblies in a reactor core of a nuclear reactor as claimed in claim 23, wherein said fuel assemblies are loaded in the central region by three batches dispersion method and in the peripheral region by four batches dispersion method. |
040428273 | description | Referring specifically to FIG. 1, the basic elements of a system in accordance with the invention are illustrated. Energy for the amplification process is basically supplied by a beam generator 11. The nature of the beam generated by beam generator 11 is widely variable within the scope of the invention, it being necessary only that the beam is capable of being directed with moderately high energy density to interact with an interactant material to produce excited particles. Clearly such requirements may be met by a beam of ions, a beam of electromagnetic energy, or, perhaps, by a beam of uncharged particles. The beam from beam generator 11 is directed by a scanner indicated at 13. The scanner 13 functions to direct the beam to the interactant material with which it is to interact, and to sweep the beam at a velocity approximately equal to the velocity of light. The scanner may also take a wide variety of forms, which will naturally be determined in part by the nature of the beam produced by the beam generator 11. It should be particularly noted that the scanner 13 should not be considered only in terms of an electrostatic deflection apparatus such as in a cathode ray tube. The scanner 13 may control beam direction electrostatically, magnetically, electro-optically, or by use of any other phenomenon consistent with the nature of the beam from beam generator 11. Furthermore, the scanner 13 may form a part of and be essentially inseparable from the beam generator, as will be seen in the description of FIGS. 4 and 5 below. The scanned beam from scanner 13 is directed to interact in an evacuated enclosure 15 with an interactant material 17. Obviously, the evacuated enclosure 15 may more conveniently also enclose the scanner 13 and/or the beam generator 11, particularly in the case of an ion beam electrostatically deflected by the scanner. Enclosure 15 may in some cases be partially evacuated or even pressurized. Highly excited particles are produced by the apparatus of FIG. 1 due to the interaction of the beam and the interactant material. As a specific example, the post-interaction region in which X-radiation is amplified is shown on the downstream side of the beam from the interactant material. This is only a specific example, however; and the post-interaction region containing the excited particles may be upstream of the interactant material or within the interactant material as well. In FIG. 1, the post-interactant region contains highly excited particles, typically ions with selective inner-shell vacancies as may be produced in intermediate-energy ion-atom collisions. The highly excited particles may also be produced by intense electromagnetic radiation or by plasma techniques. A pulse control system 19 is shown, which serves to synchronize the emission of the beam from the beam generator with the scanner 13 and provide other necessary control functions. At least in the early stages of the development of systems according to the invention, it is expressed that pulse operation will be conducted at a very low duty cycle, so that the system can be considered as if producing only a single pulse. FIG. 2 shows a specific form of apparatus in accordance with the invention in detail. An enclosure 21 is provided, preferably of nonconductive material, which is evacuated by conventional apparatus (not shown). Enclosure 21 provides a drift space for an ion beam shown at 25 which is produced by a beam source 23. The beam source 23 may consist of a duoplasmatron ion source conventionally coupled with a heavy ion accelerator. In a typical case, the beam 25 will be generated with a current of 500 milliamperes and an energy of 30 kilovolts. Beam 25 is swept parallel to its axis by an electrostatic deflection system including low potential plate 27 and high potential plate 29. The pulse for causing deflection of beam 25 is provided by a high voltage pulse system 35, connected to plates 27 and 29 by leads 31 and 33, respectively. The pulse from the high voltage pulse system 35 will initially cause the beam 25 to impinge upon the plate 27 at the right end of the plate, as viewed in FIG. 2. As the high voltage pulse propagates along the transmission path provided by plates 27 and 29 at approximately the speed of light, the area of impingement of the beam 25 on plate 27 will move to the left, as explained in more detail hereinafter. A pulse control system 39 is provided to properly synchronize a pulsed output from the ion beam source 23 with a high voltage pulse from the high voltage pulse system 35. It may be noted that the illustration of the beam in FIG. 2 is not intended as a "stop action" depiction of the geometry of the beam. Rather, it shows the path of a group of particles emitted from the accelerator 23 at the same instant. This give a proper showing of the angle at which the particles strike the target and is an appropriate illustration to aid in the explanation of the calculation of the angle alpha. A stop motion illustration would not show a readily perceptible deflection of the beam because the velocity of the high-voltage pulse is so much higher than the beam particle velocities. A nearly imperceptible deflection of the beam would occur during the time that the high-voltage pulse traverses the full length of electrodes 27 and 29. A Faraday cage assembly of a conventional type employed with ion beam apparatus is shown schematically at 37. The practical realization of such a system is aided by the existing availability of major components. State of the art heavy ion sources (such as the High Voltage Engineering DP240 duoplasmatron ion source) are capable of delivering heavy ions with current values well within the range mentioned here. Furthermore, source compatability with off-the-shelf ion beam accelerators (the High Voltage model LS-4 or LS-5) means that systems available on the market may be employed for the production of the beams discussed (the focusing employed would be tailored to the desired system). The beam need only traverse distances on the order of approximately 2 meters of straight-line vacuum plumbing in the deflection scheme described. The deflection system may be loaded by discharging a suitable capacitor bank through standard ignitron switches or by means of the more recent solid dielectric switches. If the deflection plates are spaced a distance apart equal to their transverse height, the line impedance will be 377 ohms with a capacitance per unit length of 8.85 pf/meter. Thus, for a sweep of 1 meter, if potential loss of 1 part in 10.sup.4 is to be tolerated during the charging, a capacitor bank of less than 0.1 .mu.farads is sufficient. Requirements of purity and accurate thickness for foil material 42 are well within presently achievable limits. Such foils are currently being marketed as well as being readily fabricated in the laboratory by vacuum deposition. The most demanding fabrication requirement appears to be the extreme care demanded in mounting and aligning the foil in its holder. Fabrication requirements for such a holder are however within the bounds of machining capabilities in common use by manufacturers of precision optical systems. Additionally, an advantage can be had by mounting this section of the apparatus on a vibration isolation base. If one wished to avoid the alignment requirement, then design of the foil arrangement into an arrangement of several foils "back-to-back" with the subsequent small gap between them providing a region for the active medium is a quite suitable alternative. Here a greater ion beam energy may be employed and, of course, the X-ray pulse would suffer some absorption due to the possible presence of foil material along the line of sight. Integration of this system with additional system components, such as a ring cavity, could be achieved easily with standard vacuum plumbing parts with additional pumping stations as needed. The operation of the system of FIGS. 2 and 3 will be better understood by a more detailed consideration of the physical phenomenon involved in the operation. The system of FIG. 2 utilizes the beam-foil mechanism for the selective production of inner-shell vacancies. Recent investigations into the nature of the processes by which inner-shell vacancies are produced during intermediate energy (10's to 100's of KeV) collisions involving heavy ions and atoms have clearly revealed that the mechanism propounded in the "Fano-Lichten model," (Phys. Rev. Lett. 14,627 (1965)) namely the "promotion mechanism" of inner-shell electrons in the quasi-molecule formed during the collision as dictated by the exclusion principle, occurs due to level matching in the collision partners. The process may be understood in terms of the Landau-Zener theory of electron transitions at level crossings. By selecting appropriate ion-atom combinations such that inner-shell energy levels of interest match ion to atom, cross-sections for the selective production of vacancies in these shells may be obtained that are approximately given by taking for the level crossing radius a value equal to the sum of the radii of the two electronic shells involved. As an example, argon ions colliding with carbon atoms provide a match in energy between the carbon K-shell and the argon L-shell. Thus, selective vacancies may be produced in the L-shell of argon, in particular, similar collisions have revealed that for bombarding energies below .about. 80 KeV the effects of double L-shell excitation are not observed. Furthermore, in this work, it was found that at an ion energy of .about.50 KeV, the resulting X-ray spectra clearly indicated the strong predominance of the 224-eV line due to a 3s.fwdarw.2p transition. The radiative lifetime of this transition may be expected to have a maximum value of .about. 2.8 .times. 10.sup.-.sup.11 sec and fluorescent yields on the order of 1.67 .times. 10.sup.-.sup.3 may be expected from the theoretical calculations. In FIG. 2 a relatively high current heavy ion beam 25 (for example, argon ions) is produced by a suitable ion source 23, internally focused and accelerated to the energy range of interest (30 to 500 KeV) and launched into a drift tube region of axial extent of about 2 M. provided by enclosure 21. Parallel to the beam and on each side of it are two parallel plates 27 and 29 which form a transmission system for a deflection pulse which is to be applied from the downstream end of the system. These plates serve the purpose of an extended electrostatic deflection system. A high voltage pulse of 20 to 50 KV applied to this electrode arrangement travels in the upstream direction with respect to the beam (to the left in FIG. 2) at a linear rate of approximately the speed of light. At a well defined and constant distance behind this advancing wave front, the deflected stream intersects the front face plane of the slotted low potential plate 27 which supports a thin foil 42 on its rear face as seen in FIG. 3. On the back side of this foil there is created a thin layer of ions with selected inner-shell vacanices due to the collisional mechanism described above and in the literature on X-ray spectroscopy. The foil thickness, beam energy, excitation cross-sections, and excited state lifetimes are chosen to produce the population inversion for amplifying the particular X-ray wavelengths of interest. This region of excited states will have a geometrical cross-section in the plane of the foil of approximately the area of the beam intersection with the foil and it will travel in the upstream direction at a linear rate of approximately the speed of light. A substantial fraction of the excited states produced (as well as perhaps many of the unexcited ions emerging from the foil) may be obtained in an aligned condition. By supplying large beam current and control of other parameters in accordance with beam-foil spectroscopy techniques, these excited states can be produced in more than sufficient numbers to provide a significant line-of-sight amplification for a resonant X-ray pulse originating near the terminal end of the tube and proceeding along the top side of the foil in the upstream direction. Then a coherent amplification of this signal will occur and an enhanced output of directional X-radiation will be obtained on the chosen X-ray line. A discussion of specific parameter values and the calculations for determination of such values follows. As an example, consider a system in which a 30 KV argon ion beam generator launches a collimated beam parallel to the deflection plates and is subsequently deflected by a pulse such that the beam changes potential energy by 20 KeV due to motion transverse to the original beam direction. From dynamical considerations, the beam will then intersect the foil a distance of 2l.sqroot.f V.sub.bo /V.sub.d downstream from the position of the advancing wavefront. Here, l is the parallel plate separation distance, V.sub.bo the undeflected beam voltage, V.sub.d the deflection voltage, and f the fractional distance the undeflected beam is from the plate housing the foil. Thus for V.sub.bo = 30 KV, V.sub.d = 40 KV, and f = 1/2, the downstream distance is 1.2 l = 6 cm for a characteristic plate separation of 5 cm. The beam will then intersect the foil with the beam making an angle of .alpha. with the foil surface where sin .alpha. = .sqroot.20/50, since the beam energy will be 50 KeV at this point. Then .alpha. = 39 .degree.. For a carbon foil of appropriate thickness, for example, 5.mu.g/cm.sup.2, the apparent thickness to the beam will be 5.mu.g/cm.sup.2/sin .alpha., or 7.79 .mu.g/cm.sup.2. The following calculations provide an estimate of the fraction of excitations that may be expected to lead to excited states on the back side of the foil and hence the effect of parameter values on system function. As the ions traverse the foil, the number of excitations per unit time occurring in a distance between x and x + dx into the foil is Ndx/.lambda.where N = N.sbsb.o.sub.e .sup.-x.sup..lambda., N.sub.o is the number of ions incident per unit time, and .lambda. = 1/N.sub.f * is the mean free path for inner-shell excitation, .sigma.* being the cross-section for this process and N.sub.f the atomic density of the foil. The probability that these excited ions exit the back side of the foil in such a state is .about. exp [-(t.sub.b -x)/v.sub.b .tau.] .sup.. exp[-(t.sub.b -x)/.lambda.], the first factor being due to the exponential decrease in population due to spontaneous decay (both Auger and radiative) with a lifetime .tau., the ion having a speed v.sub.b, the second factor being due to subsequent atom-ion collisions leading to large angle scattering and hence loss from the excited beam. The mean free path for the latter process is taken to be that for inner-shell excitation, an approximation valid due to the screened Coulomb nature of the scattering interaction and the distance of closest approach needed for inner-shell excitations. Then the fractional excitation obtained on the exit side of the foil is ##EQU1## This ratio may be maximized by choosing t.sub.b = t.sub.bm = v.sub.b .tau. ln.sub.(1 .sub.+ .sub..lambda./v .sub..tau.). With N.sub.f .perspectiveto. 1.13 .times. 10.sup.23 atoms/cm.sup.3 for carbon, .sigma..sub.AR on.sup.* C = 0.795 .times. 10.sup..sup.-18 cm.sup.2, .tau. .perspectiveto. .DELTA.t.sub.auger = 3.84 .times. 10.sup..sup.-14 sec, and v.sub.b = 4.90 .times. 10.sup.7 cm/sec at 50 KeV primary beam energy; t.sub.bm .perspectiveto. 8.6 g/cm.sup.2 thus requiring the foil thickness specified above. The fraction of useful excitations for the selected parameter values then becomes .about. 1/8. This ratio may be improved (up to values .about. e.sup..sup.-1), by increasing the primary beam energy (consequently decreasing .lambda. and increasing v.sub.b). At 50 KeV, the range of Ar.sup.+ on C is 10.4 .+-. 2.7 .mu.g/cm.sup.2. Should this range be unsatisfactory, a small increase in energy values could easily remove any difficulty. The total number of excited states existent at any one time is N* .perspectiveto. R.sup.. .DELTA.t.sub.auger where R is the production rate. Due to the efficiency of the deflection scheme, a large number of beam particles intersect the foil per unit time. In particular, the point of intersection of the beam with the foil travels a distance of 1 meter in a time 1m/c and during this time the number of particles intersecting the foil will be the number of beam particles per meter of length, N.sub.b.sub..lambda., plus the number of beam particles that advance across an arbitrary position in the undeflected beam during this time, N.sub.b.sub..lambda. v.sub.b /c. Since in the example under consideration roughly 1/8 of these lead to useful excitations (i.e., excitations that exit the back side of the foil), then the useful production rate is ##EQU2## Utilizing state of the art duoplasmatron ion sources, 500 mA argon ion beams at 30 KV are relizable. Then R = 3.09 .times. 10.sup.20 sec.sup..sup.-1 and N* .perspectiveto. 1.19 .times. 10.sup.7 excited states. In the time .DELTA.t.sub.auger, the beam is swept a distance c t.sub.auger .perspectiveto. 1.15 .times. 10.sup..sup.-2 mm. Thus, if the beam is focused such that it intersects the foil in an ellipse of major axis 12.6 mm and a minor axis of 3 mm giving the beam a cross-sectional area of 29.8 mm.sup.2 ; this zone of interaction will be essentially static in the time interval .DELTA.t.sub.auger. During this time, the excited ions will occupy a volume of v.sub.b .DELTA.t.sub.auger .times. 29.8 mm.sup.2 where v.sub.b is the component of ion velocity perpendicular to the foil upon exiting the foil. Based on stopping power data, the ions may be expected to emerge with an energy of .about. 9 KeV at the average angle of 39.degree.. Then v.sub.b .perspectiveto. 1.32 .times. 10.sup.7 cm/sec and the volume occupied by the N* particles is .about. 1.1 .times. 10.sup..sup.-7 cm.sup.3, giving an excited density of .about. 0.79 .times. 10.sup. 14 cm.sup..sup.-3. It is interesting to note that carrying the arguments through in general leads to an expression of the form n* = I.sub.b c/8ev.sub.b v.sub.be A.sub.b, where v.sub.b is the beam speed when parallel to the deflection plates (before deflection) and v.sub.be is the beam exit speed. The density of excited states calculated here may be taken as a measure of the inverted population density since most non-excited states will containe electrons in both the upper and lower levels. Furthermore, since the radiative lifetime is .about. 2.8 .times. 10.sup..sup.-11 sec, the coherence length of the radiation (neglecting pulse shaping effects) is .about. 8.4 mm, and consequently the 12.6 mm length of active volume provided by the suggested pump geometry is sufficient for full amplification of the pulse. For a radiative decay half-life of 2.8 .times. 10.sup..sup.-11 sec, the natural line width is .DELTA..nu..sub.n .perspectiveto. 3.58 .times. 10.sup.10 Hz. At the photon energy of 224 eV, the recoil broadening is only 3.6 .times. 10.sup.8 Hz, entirely negligible. However, the Doppler broadening attributable to the spread in scattering angle should not be neglected. Since the scattering in angle closely approximates that due to a screened Coulombic interaction and the nature of the vacancy producing process is such that the probability of the process occurring rises very rapidly from zero to a fixed high value as the distance of closest approach decreases, the vacancy producing collisions may be estimated to scatter these ions into a cone of .theta..about.5.degree. with a d.theta. between 3.degree. and 4.degree. (the angular spread needed for the scattered intensity to drop by a factor if 1/e). Since the beam was incident at an angle 39.2.degree., one segment of the scattered cone will exit the foil within an angular spread from 30.7.degree. to 34.2.degree. thus leading to a spread in ion velocity in the direction parallel to the foil of 6.81 .times. 10.sup.5 cm/sec. This results in an inhomogeneous broadening of 1.23 .times. 10.sup.12 Hz. Then .DELTA..nu..sub.D /.DELTA..nu..sub.N 18 34.5. Now, the fraction of excited particles that may be expected to lie within an angular spread of 3.5.degree. from each other is .about. .psi./.pi. where cos .psi. = sin .theta./sin (.theta. + d.theta.), and thus .psi./.pi. .about. 1/3. Accordingly, if the Doppler spread calculated above is to be used, the effective population inversion should be decreased by this same factor, giving n* .perspectiveto. 2.63 .times. 10.sup.13 cm.sup..sup.-3. Although the main branching ratio implied by fluorescent yield has been considered, branching ratios due to competing radiative decay modes have been neglected. However, previous spectroscopic work tends to indicate that a single inter-combination may be reasonably well expected to predominate. Under the conditions outlined above, the negative absorption coefficient, given as ##EQU3## for an inhomogeneously broadened line of wavelength .lambda., transition coefficient A.sub.ij for i.fwdarw.j transitions, respective densities of n.sub.i and n.sub.j with statistical weights g.sub.i and g.sub.j, and inhomogeneous width .DELTA..nu..sub.D ; becomes 0.873/m thus indicating a gain in excess of 3.79dB/meter. For a line of sight amplification path of length 2 meters, single pass gain factors of .about. 5.73 would result. Such amplification will be observed by virtue of the narrow beam angle of the amplified radiation which alone will permit it to be distinguished from spontaneous emission or other background radiation. Of course, one would also wish to evaluate the spectral distribution of the amplified output, which will also distinguish it as stimulated emission-amplified. The choice of argon for the beam ions in the example explained above represents what may be considered to be a poor choice of ions with regard to the main branching ratio. In this respect the use of a neon ion beam incident on copper foil may advantageously be substituted for the above-described argon-carbon system. For neon ion-copper atom collisions, level matching between the K shell of the neon ion and the L shell of copper results in high cross sections for selective vacancy production in these shells. Furthermore, it is believed that for K vacancy production, the vacancies are almost exclusively produced in the lower-Z collision partner. The fluorescence yield for neon ion impact on copper foil is at least an order of magnitude higher than for the argon-carbon case. Hence, there is good reason to believe that a significant output of 874-eV photons may be produced from a neon-copper apparatus at least as easily as the lower energy photons which would be produced in the argon-carbon apparatus described in detail above. The neon-copper aparatus need not differ materially from the apparatus described for argon-carbon excepting, of course, in respect to the ion beam being neon, and the foil being of copper. Referring to FIGS. 4 and 5, an alternative form of apparatus is shown for impacting ions at high current densities on a foil to produce a beam-foil interaction. The apparatus of FIGS. 4 and 5 is in certain respects simpler and more practical to construct than the apparatus of FIGS. 2 and 3. In the apparatus of FIG. 4, a cylindrical enclosure 51 is filled with argon gas 53. The argon gas 53 is ionized by a radio frequency discharge in the gas. The radio frequency discharge may be produced in a conventional manner, as illustrated by the radio frequency electrodes 55 connected to a radio frequency source 57. Located coaxially in the enclosure 51 is a separate enclosed cylindrical tube 59. As may be better seen in FIG. 5, the tube structure 59 includes a thin-walled hydrocarbon tubing 61, which supports on its interior surface a thin foil of carbon which serves the same function as the foil 42 in FIG. 3. The center portion 65 of the enclosure 59 is hollow and is filled with gas, hydrogen for example. The thickness of the foil 63 will be determined in accordance with the previous discussion of FIGS. 2 and 3. The thickness of the thin-walled hydrocarbon tubing will be minimized to the extent possible, consistent with structural integrity of the element 59. The hydrogen gas fill 65 helps to prevent collapse of the tube 61. The diameter of the hollow interior 65 of enclosure 59 will be such that in operation the volume is substantially filled with the stimulated emission medium. The diameter in a typical case may be on the order of tenths of a millimeter. The length of the enclosure 59 may be about 1 meter (or less if the system gain per unit length is high). Surrounding the argon gas discharge enclosure 51 is an electric pulse apparatus including a cylindrical conductor 67 which is provided with a fast-rise traveling electrical pulse by coaxial cables 69. The coaxial cables 69 are of graduated lengths and are connected to solid dielectric switches and a pulse power supply now shown. The construction and operation of the cylindrical conductor 67 fed by the coaxial cable 69, and the dielectric switches and power supply is not described in detail because this apparatus comprises a well-known fast-rise theta-pinch sequentially triggered form of plasma apparatus, described for example by J. D. Shipman, Jr. in Applied Physics Letters 10, 3 (1967). The apparatus of FIGS. 4 and 5 causes the preionized argon plasma to be implosively collapsed on the coaxial enclosure 59 by a fast-rise theta-pinch effect. Furthermore, the pinch effect and hence the implosion wavefront travels at approximately the speed of light in the axial direction from left to right in FIG. 4. As the ion implosion reaches a particular portion of the length of the coaxial enclosure 59, the ions penetrate the hydrocarbon tubing and the thin carbon foil, whereupon the argon ions undergo selective inner-shell vacancy production and the ions thus excited create a stimulated emission amplification medium in the interior 65 of the coaxial tube 59. The active region for amplification by stimulated emission travels in synchronism with a resonant X-ray pulse traveling through the center of the coaxial tube 59, thereby producing a highly directional X-ray output from the apparatus. The calculated gain for a state-of-the-art apparatus as illustrated in FIG. 4 is 4.3dB/cm. Thus a 10 cm. theta-pinch apparatus may be predicted to produce about 40 dB gain. The output from a stimulated emission amplifying medium without resonant cavity of the sort illustrated in FIG. 4 is referred to by some as superradiance. The highly directional output would permit the apparatus of FIG. 4 to be replicated to several stages with the output of one stage serving as an input to the next. It should be noted that the apparatus of FIGS. 4 and 5 produces what is known as a beam-foil interaction in which the role of the beam is played by an implosion of a cylindrical volume of pre-ionized argon ions. Thus it will be understood that whenever the term beam is used herein, it will be understood to be used in the broadest sense, to mean a flow or pulse of particles or waves traveling at a high velocity in a controlled manner. The apparatus of FIG. 4 and FIG. 5 has been described as using argon ions in conjunction with the carbon foil, so that the description of the operation of apparatus of FIGS. 4 and 5 may be closely relate and compared with the operation of the apparatus of FIGS. 2 and 3. It should be understood, however, that with the apparatus of FIGS. 4 and 5, as well as with the apparatus of FIGS. 2 and 3, other chemical elements may be employed as partners in the beam-foil interaction. As previously described, the beam may be of neon and the foil may be of copper. Alternatively, the argon ions may be impacted on an aluminum foil material or on titanium foil to supply the desired selective inner-shell vacancy production mechanism. Utilizing the examples of FIGS. 1-5, the invention has been explained for clarity and simplicity in terms of a beam interacting with an interactant material; however, in certain forms of apparatus, this explanation needs to be modified. For example, apparatus according to the invention may employ plasma techniques wherein a cylindrical hollow plasma is implosively collapsed upon itself by the influence of an electric or magnetic field. As the opposite walls of the cylindrical plasma collide at near zero radius of the cylinder, highly excited particles are produced. These particles are capable of producing a traveling amplification region in accordance with the invention. In such apparatus, the previously described beam plus interactant material is replaced by a single plasma material. In the plasma case one might say that the plasma material serves as a swept beam which in effect interacts with itself. Accordingly, the scope of the invention should be understood to include the use of such plasma techniques for the production of a region of excited particles as being equivalent to the beams impinging on interactant materials described above in detail. Considerable aid in evaluating inversion processes to achieve particular objectives is provided by the pertinent rate equations. Although inversions might be produced by electron impact, photoionization, or recombination, only inversion due to ion-atom collisions will be treated in the following analysis. Two distinct reaction environments are considered; volume reaction and beam-foil excitation. A three-level scheme is considered. Referring to FIG. 6, there is shown an energy level diagram for Ar.sup..sup.+5. A 2p electron is promoted to a 3p level to provide an upper laser level. The lower laser level is reached by a 2p-3s transition. For volume reaction, ##EQU4## where pumping is on particles .alpha. of density N.sub..sub..alpha.G in the ground state, N.sub..sub..alpha.U in the upper state of interest, and N.sub..sub..alpha.L in the lower state of interest. N.sub..sub..alpha.G is taken as constant throughout and N.sub..sub..alpha.U =N.sub..sub..alpha.L =0 initially. Such a system has been considered for a rapidly rising pump [pump risetime << (R.sub.UL + .SIGMA..sub.j R.sub.Uj).sup..sup.-1 ] and a linearly rising pump (r.sub.GU .about.R.sub.GU t). For inner-shell vacancy production by ion-ion collisions in a high-velocity counterstreaming plasma, R.sub.GU .about.t.sub.ii *.sup..sup.-1. Depopulation of the upper level is by spontaneous and stimulated decay to the lower level, branching to other states due to Auger (and possibly Coster-Kronig) processes, further excitation and ionization by electron impact, radiative and collisional recombination, large-angle scattering of the ions of interest and further ion-ion inner-shell vacancy production. Thus, ##EQU5## Population of the lower level from the upper state includes spontaneous and stimulated decay; EQU R.sub.UL .about. t.sub.r,UL .sup..sup.-1 + t.sub.S,UL .sup..sup.-1. finally, ##EQU6## where, in addition to previously described times, depopulation of the lower level includes nonradiative decay (due to rearrangements in the M shell for the example chosen) estimated by a fluorescence yield .omega.', and an effective lifetime due to utilization of a traveling wave pump. Nonradiative decay (and perhaps shakeup decay) as well as quenching by electron impact (with the outermost electrons) of the lower level of interest may be sufficiently rapid to allow cw-type operation. Such possibilities are attractive features of pumping with an inner-shell vacancy production mechanism (in contrast to systems for which pumping is on optical-like outer shells). To compare rates, an example is chosen for which Ar.sup..sup.+5 predominates; T.sub.e .about.10eV, and consequently .sigma..sub.PI .about.2.4 .times. 10.sup..sup.-19 cm.sup.2. A competitive stimulated emission time of .about.3 .times. 10.sup..sup.-12 sec requires .alpha..about.10 cm.sup..sup.-1, and since .sigma..sub.SN .about.10.sup..sup.-16 cm.sup.2, an inversion density of .about.10.sup.17 cm.sup..sup.-3 is needed. In order for stimulated emission to predominate over nonresonant absorption, .DELTA.N/N.sub.i .gtorsim..sigma..sub.PI /.sigma..sub.SN .about.2.4 .times. 10.sup..sup.-3, and thus N.sub.i .gtorsim.4 .times. 10.sup.19 cm.sup..sup.-3 and N.sub.e .about.Z.sub.i N.sub.i .about.2 .times. 10.sup.20 cm.sup..sup.-3. For dynamical plasmas with streaming speeds of 2-3 .times. 10.sup.7 cm/sec, counterstreaming ion energies are equivalent to 30-70 keV in terms of beam-foil systems. Then the reaction time estimates given previously become relevant. It is seen that (with t.sub.r,LG .about.1.52 .times. 10.sup..sup.-10 sec) EQU R.sub.GU .about.2.85.times. 10.sup.11 sec.sup..sup.-1 ##EQU7## EQU R.sub.UL .about.t.sub.s,UL.sup..sup.-1 .about.3.times. 10.sup.11 sec.sup..sup.-1, and ##EQU8## At counterstreaming speeds of interest here, the plasma overlap increases by .about.5 .times. 10.sup..sup.-6 cm during the decay time of the upper state. Since this value is smaller than typical macroscopic denisty variation distances, the rate equations should be considered during both the pump risetime and the time of steady-state pumping. For a linearly rising pump, since b .tbd. R.sub.UL (R.sub.UL + .SIGMA..sub.j R.sub.Uj).sup..sup.-1 .about.3.3 .times. 10.sup..sup.-2 << 1 (note also that R.sub.LG +.SIGMA..sub.k R.sub.Lk .about.R.sub.UL +.SIGMA..sub.j R.sub.Uj), the equlibrium inversion density is approached in a time on the order of the plasma density risetime and is held at this value; EQU .DELTA.N.about.(N.sub..sub..alpha.U -N.sub..sub..alpha.L).sub.eq = N.sup.2.sub..sub..alpha.G .theta..sub.ii.sup..upsilon. U.sub.ir t.sub.AU (1 - t.sub.ei.sup..upsilon. /t.sub.S,UL) .about. N.sub..sub..alpha.G.sup.2 .sigma..sub.ii.sup.98 U.sub.ir t.sub.AU. this estimate indicated the inversions achievable from volume reactions. (As a matter of self-consistency, for the case chosen, .DELTA.N/N.sub..sub..alpha.G .about.N.sub..sub..alpha.G .sigma..sub.ii.sup..upsilon. .times. v.sub.ir t.sub.AU .about.2.4 .times. 10.sup..sup.-2, which, with a branching estimate of .about.0.1 discussed below, gives the assumed .DELTA.N/N.sub.i .about.2.4 .times. 10.sup..sup.-3.) Thereshold requirements for volume reaction are now EQU N.sub.i.sup.2 .sigma..sub.ii.sup..upsilon. U.sub.ir t.sub.AU .gtorsim. (1 + K.sub.v L)/.sigma..sub.s L. for the case of beam-foil excitation, consider ions incident normally on a foil of thickness .delta. (smaller than the range R of the ions in the foil material) and particle density N.sub.f. TABLE I ______________________________________ PROBABILITY OF: EXCITATION IN x TO x + dx N.sub.f .sigma.*(x)dx REACHING x WITHOUT EXCITATION exp (-.intg.x 0 N.sub.f .sigma.*(s)ds) REACHING .delta. FROM x BEFORE DECAY exp (-.intg..delta. x [v(s).tau.*(s)].sup.- 1 ds) REACHING .delta. FROM x BEFORE SECOND COLLISION exp (-.intg..delta. x N.sub.f .sigma.(s)ds) ______________________________________ Referring to FIG. 7 and the above table of probabilities, with an effective cross section for excitation .sigma..sup..upsilon., the probability for a singly excited ion emerging from the back surface of the foil per incident ion is ##EQU9## .tau..sup..upsilon. is the excitation lifetime and v.sub.i is the ion speed. Since the exponential in the integrand is small unless (.delta.-x)<v.sub.i (x).tau..sup..upsilon. (x;l ), the probability may be estimated conservatively as EQU F .gtorsim. N.sub.f .sigma..sup..upsilon. V.sub.i .tau..sup..upsilon. e.sup..sup.-N.sbsp.f.sup..sigma..upsilon..sup..delta. (1 - e.sup..sup.-.sup..delta./.sup..upsilon..sbsp.iT.sup..tau.), for which quantities are evaluated at the exit side of the foil. Fractional excitation is optimized by choosing a foil thickness of v.sub.i .tau..sup..upsilon. 1n(1+1/N.sub.f .sigma..upsilon.v.sub.i .tau..upsilon.), for which F.gtoreq.(1+1/N.sub.f .sigma..upsilon.v.sub.i .tau..upsilon.).sup..sup.-( 1.sup.+N.sbsp.f.sup..sigma..upsilon.V.sup..tau.T.upsilon.). Due to angular scattering of the excited particles into a cone with angular spread from .theta. to .theta.+d.theta. to the foil normal, only the fraction .psi./.pi., where cos.psi.=sin .theta./sin (.theta.+d.theta.), will emerge from the foil excited and having trajectories lying within an angular spread d.theta. from each other. Thus the fractional excitation considered to be of interest is of order F.psi./.pi. giving an inversion density of .about.(F.psi./.pi.)N.sub.o for an incident ion density N.sub.o. For typical ion-atom cross sections at ion speeds of interest, identifying .tau..upsilon. as the Auger lifetime of the state of interest and taking reasonable values for the angular scattering reveals that a fractional excitation F.psi./.pi., of .about.0.1 is realizable. Thus, the relevant loss mechanisms mentioned earlier are seen to be easily overcome without detailed evaluation. However, if lasing is to occur parallel to the foil surface, diffraction losses may become significant since the effective thickness of pumping is .about.V.sub.i t.sub.A, which may be quite small. Also, as previously, observed, strong requirements are now placed on the planarity of the foil. Accordingly, comparison of alternative inversion and amplification processes should include consideration of diffraction loss. Although some focusing of the radiation may occur due to the rapid variation of the index of refraction with distance normal to the surface, this effect is small. The effective loss coefficient due to diffraction is taken, in cognizance of a high reflection coeficient by the foil for soft X-rays at large angles of incidence, as ##EQU10## The threshold requirement becomes ##EQU11## some reduction of inversion density estimates due to distributions in charge states as well as distributions over excited states in the inner and outer shells is in order. Charge state distributions may, in some cases, reduce inversion estimates by no more than a factor of .about.1/2 since for dense plasmas a reasonable characterization by local thermal equilibrium or coronal equilibrium suggests the predominance of two-, and in some cases, one-charge states. For the beam-foil case, similar conclusions are in order. Assuming energy of relative motion for collisions of interest is below a realizable value, the production of a single inner-shell vacancy may be expected. Moreover, althrough the L.sub.1, L.sub.2, L.sub.3 separation is greater than the line broadening envisioned (for the argon case), the production of an L.sub.1 vacancy may be expected to be transferred to an L.sub.2,3 vacancy by Coster-Kronig transitions before or in competition with Auger decay. The violence of ion-atom collisions at intermediate energies is known to produce multiple excitations in the outer electronic shells leading to complicated Auger spectra. Apart from possible autoionizing states in the M shell that should decay early, M-shell excitations in argon will cause a spread in the 2p-3s transition of interest that may be estimated to fall within the shift of this transition between the relevant consecutive stages of ionization. A consideration of all these effects leads to the conclusion that, realistically, an order of magnitude should be sacrificed in the above estimates of inversion density (an estimate in accord with relevant Auger spectra). Moreover, it should be mentioned that omission of allowances for pumping of the lower laser level by collisions from the ground state in the rate equations is due to the violence of the ion-atom-ion collisions of interest. Extensive M-shell excitation simultaneous with the L-shell vacancy production leads to both upper and lower laser levels being appreciably shifted in energy from the case of little or no M-shell excitation, thus making direct collisional excitation of the lower level from the ground state sufficiently unlikely. TABLE II __________________________________________________________________________ Stimulated emission cross sections and threshold power densities. Dominant line- Stimulated emission.sup.a Threshold power broadening process cross section density (W/cm.sup.3) __________________________________________________________________________ Auger decay ##STR1## ##STR2## Doppler effect ##STR3## ##STR4## Ion impact ##STR5## ##STR6## __________________________________________________________________________ .sup.a All units cgs except for temperatures (eV) and wavelength (in A.degree.) A summary of threshold conditions with these more realistic estimates is given in Table III. These may be compared with the stimulated emission cross sections and thershold power densities for amplified spontaneous emission in Table II. TABLE III __________________________________________________________________________ Dominant line- broadening process Threshold requirement __________________________________________________________________________ Volume reaction Auger decay ##STR7## Doppler effect ##STR8## Ion impact ##STR9## Beam Foil Auger decay ##STR10## Doppler effect ##STR11## Ion impact ##STR12## __________________________________________________________________________ Caution must be exercised in scaling from these expressions in that K.sub..sub..nu. depends on N.sub.i. The volume-reaction case is reexamined here for threshold, as given in Table III. At the counterstreaming speeds of .about.4.4 .times. 10.sup.7 cm/sec of interest here, initially cold streaming ions will "thermalize" to a temperature .about.keV in approximately 10.sup..sup.-10 sec. Although lasing over distances of several centimeters may occur during this time, estimates of ion temperatures below .about.100 eV are probably unrealistic. Assuming that ion densities are lower than 1.4 .times. 10.sup.20 cm.sup..sup.-3, Doppler broadening is dominant for T.sub.i .about.400eV. Then, for K,L >> 1, threshold occurs for ##EQU12## independent of the axial extent of the region pumped. Here, .DELTA.N.sigma..sub.s .about.26.8 cm.sup..sup.-1 and a slight increase in ion density, by a factor of .about.1.25, provides a net gain coefficient of .about.10 cm.sup..sup.-1. In this case, N.sub.i .about.1.34 .times. 10.sup.20 cm.sup..sup.-3, and ion-impact broadening is beginning to be appreciable. (It is noted that in the Doppler limit, .DELTA.N.sigma..sub.s .about.N.sub.i.sup.2, whereas .DELTA.N.sigma..sub.s .about.N.sub.i in the ion-impact case.) Since the threshold density is independent of the length of the pumped region (because of absorption) and a slight increase of density above threshold provides large gain per unit length, pumping over distances greater than about 1 to 10 cm is seen as impractical as a result of difficulties in obtaining dense plasmas in large geometries. For beam-foil excitation, argon ions incident on a titanium foil should result in appreciable pumping. A fractional argon excitation, F.psi./.pi., of .about.0.1 is to be expected on the downstream side of the foil. For a streaming energy eV.sub.o, an effective temperature of order eV.sub.o sin.sup.2 .theta.[(cos.psi.).sup..sup.-1 1 ].sup.2 results due to angular scattering. Ignoring initial thermal spread, Doppler broadening is dominant over natural broadening. At ion speeds .about.5 .times. 10.sup.7 cm/sec, diffraction losses are considerable and threshold occurs for N.sub.o .about.3.5 .times. 10.sup.19 L.sup..sup.-1 cm.sup..sup.-3. For the limit in which ion-impact broadening is dominant, threshold appears to be independent of ion density from Table III. This conclusion is subject to the requirements .UPSILON..nu..sub.ci >.delta..nu..sub.D, however. Then ##EQU13## This requires ion densities in excess of 3 .times. 10.sup.18 cm.sup..sup.-3 and 1.4 .times. 10.sup.19 cm.sup..sup.-3, respectively, for Ar.sup..sup.+5. Thus, operation in this regime is at densities below threshold for the Doppler broadened case unless L>2.5 cm. Moreover, since the net gain coefficient in this limit is independent of ion density (.alpha..sub.eff =L.sub.c.sup..sup.-1 with L.sub.c taken from Table III), such a regime represents an upper bound on achievable gain per unit length. A traveling wave pump to provide a large L, thus allowing threshold to be reached at ion densities below that for which ion-impact broadening becomes dominant, is of considerable advantage in this case. Of interest for use in achieving stimulated emission under various of the conditions evaluated above are plasma experimental facilities recently reported in Nuclear Fusion 13, P. 458, (1973) (with possible modifications to obtain either counterstreaming or beam-foil-type behavior). The use of argon in such systems may not be necessarily the most judicious choice. From the foregoing description and explanation, it will be understood that apparatus according to present invention constitutes a notably practical apparatus for generating X-ray emission by stimulated emission of radiation, which will have the property of controlled directiveity in a high degree, as well as other useful properties associated with radiation generated by the phenomenon of stimulated emission. It will be understood that the particular examples are presented by way of illustration only, and that the scope of the invention is not limited to the particular examples described, but is rather to be determined by reference to the appended claims. |
summary | ||
046817310 | claims | 1. An improved liquid metal nuclear reactor construction comprising: (a) a nuclear reactor core having a bottom platform support structure; (b) a reactor vessel for holding a large pool of low pressure liquid metal coolant and housing said core within said pool, said vessel having an open top end, a closed bottom end wall and a continuous closed side wall interconnecting said top end and bottom end wall; (c) a containment structure surrounding said reactor vessel and having a sidewall spaced outwardly from said reactor vessel side wall and having a base mat spaced below said reactor vessel bottom end wall; (d) a central small diameter post anchored to said containment structure base mat and extending upwardly therefrom to said reactor vessel and upwardly therefrom to said reactor core so as to axially fix said bottom end wall of said reactor vessel and provide a center column support for said lower end of said reactor core; (e) annular support structure disposed in said reactor vessel on said bottom end wall thereof and extending about said lower end of said core (f) structural support means disposed between said containment structure base mat and bottom end of said reactor vessel wall and cooperating with said annular support structure and said central post for supporting said reactor vessel at its bottom end wall on said containment structure base mat so as to allow said reactor vessel to expand radially but substantially prevent any lateral motions that might be imposed by the occurrence of a seismic event; (g) a bed of insulating material disposed between said containment structure base mat and said bottom end wall of said reactor vessel and uniformly supporting said reactor vessel at its bottom end wall on said containment structure base mat so as to insulate said reactor vessel bottom end wall from said containment structure base mat and allow said reactor vessel bottom end wall to freely expand radially from said central post as it heats up while providing continuous support thereof; (h) a deck supported upon said said wall of said containment vessel above said top open end of said reactor vessel; and (i) extendible and retractable coupling means extending between said deck and said top open end of said reactor vessel and flexibly and sealably interconnecting said reactor vessel at its top end to said deck. an annular guide ring axially positioned with radial keys and keyways disposed on said containment structure and extending between its side wall and said top open end of said reactor vessel for providing lateral support of said reactor vessel top open end for limiting imposition of lateral loads on said coupling means by the occurrence of a lateral seismic event while allowing axial expansion to occur. a guard wall disposed between said reactor and containment structure side walls, said guard wall surrounding and spaced outwardly from said reactor vessel side wall and being connected at its lower end to said reactor vessel support ring adjacent the reactor vessel bottom end wall. a bottom liner disposed between said base mat of said containment structure and said bottom end wall of said reactor vessel and below said bed of insulating material. cooling means disposed in said base mat of said containment vessel for removing heat from said containment vessel and said bed of insulating material. (a) a nuclear reactor core having a bottom platform support structure; (b) a generally cylindrical reactor vessel for holding a large pool of low pressure liquid metal coolant and housing said core within said pool, said vessel having an open top end, a closed flat bottom end wall with and a continuous cylindrical closed side wall interconnecting said top end and bottom end wall; (c) a generally cylindrical concrete containment structure surrounding said reactor vessel and having a cylindrical side wall spaced outwardly from said reactor vessel side wall and having a flat base mat spaced below said reactor vessel bottom end wall; (d) a central small diameter post anchored to said containment structure base mat and extending upwardly therefrom to said reactor vessel and upwardly therefrom to said reactor core so as to axially fix said bottom end wall of said reactor vessel and provide a center column support for said lower end of said reactor core; (e) annular reinforced support structure disposed in said reactor vessel on said bottom end wall thereof and extending about said lower end of said core so as to support the periphery thereof while allowing radial expansion to occur (f) an annular support ring having a plurality of inward radially extending linear members being disposed between said containment structure base mat and bottom end of said reactor vessel wall and connected to and supporting said reactor vessel at its bottom end wall on said containment structure base mat so as to allow said reactor vessel to expand radially but substantially prevent any lateral motions that might be imposed by the occurrence of a seismic event. (g) a bed of insulating material in sand-like granular form disposed between said containment structure base mat and said bottom end wall of said reactor vessel and uniformly supporting said reactor vessel at its bottom end wall on said containment structure base mat so as to insulate said reactor vessel bottom end wall from said containment structure base mat and allow said reactor vessel bottom end wall to freely expand radially from said central post as it heats up while providing continuous support thereof; (h) a deck supported upon said side wall of said containment structure above said top open end of said reactor vessel; (i) a plurality of serially connected extendible and retractable annular bellows extending between said deck and said top open end of said reactor vessel and flexibility and sealably interconnecting said reactor vessel at its top end to said deck; and (j) an annular guide ring with axially positioned radial keys and keyways disposed on said containment structure and extending between its side wall and said top open end of said reactor vessel for providing lateral support of said reactor vessel top opened by limiting imposition of lateral loads on said annular bellows by the occurrence of a lateral seismic event while allowing axial expansion to occur. a generally cylindrical guard wall disposed between said reactor and containment vessel side walls, said guard wall surrounding and spaced outwardly from said reactor vessel side wall and being connected at its lower end to said reactor vessel support structure adjacent the vessel bottom end wall. a flat bottom liner disposed between said base mat of said containment structure and said bottom end wall of said reactor vessel and below said bed of insulating material. cooling means disposed in said base mat of said containment structure for removing heat from said containment structure and said bed of insulating material. 2. The improved reactor construction as recited in claim 1, further comprising: 3. The improved reactor construction as recited in claim 1, wherein said structural support means includes an annular support ring having a plurality of inward radially extending linear members being disposed between said containment structure base mat and said support ring of said reactor vessel and connected to and supporting said reactor vessel at its bottom end wall on said containment structure base mat. 4. The improved reactor construction as recited in claim 1, wherein said bed of insulating material is in sand-like granular form. 5. The improved reactor construction as recited in claim 4, wherein said insulating material is high density magnesium oxide particles. 6. The improved reactor construction as recited in claim 1, wherein said coupling means includes a plurality of serially connected extendible and retractable annular bellows. 7. The improved reactor construction as recited in claim 1, further comprising: 8. The improved reactor construction as recited in claim 1, further comprising: 9. The improved reactor construction as recited in claim 1, further comprising: 10. The improved reactor construction as recited in claim 9, wherein said cooling means includes a plurality of radial cooling pipes embedded in said base mat of said containment vessel and underlying said bed of insulating material. 11. An improved liquid metal nuclear reactor construction comprising: 12. The improved reactor construction as recited in claim 11, further comprising: 13. The improved reactor construction as recited in claim 11, further comprising: 14. The improved reactor construction as recited in claim 11, further comprising: 15. The improved reactor construction as recited in claim 14, wherein said cooling means includes a plurality of radial cooling pipes embedded in said base mat of said containment structure and underlying said bed of insulating material. 16. The improved reactor construction as recited in claim 11, wherein said insulating material is high density magnesium oxide particles. |
description | FIG. 1 shows diagrammatically an embodiment of a step-and-scan lithographic projection apparatus 1 in which an EUV radiation source according to the invention may be used and with which the method according to the invention may be performed. The apparatus comprises an illumination system for illuminating a mask MA and a mirror projection system for imaging a mask pattern, present in the mask, on a substrate W, for example, a semiconductor substrate which is provided with an EUV radiation-sensitive photoresist WR. The illumination system 10 shown in the left-hand part of FIG. 1 is designed in known manner in such a way that the illumination beam IB supplied by the system at the area of the ask MA has a cross-section in the form of an annular segment or a rectangle, and has a uniform intensity. The illumination system comprises, for example, three mirrors 11, 12 and 13 which are maximally reflecting for EUV radiation at, for example, a wavelength of the order of 13 nm because they have a multilayer structure of, for example, silicon layers alternating with molybdenum layers. The mask MA is arranged in a mask holder MH which forms part of a mask table MT. By means of this table, the mask can be moved in the scanning direction SD and possibly in a second direction perpendicular to the plane of the drawing, such that all areas of the mask pattern can be introduced under the illumination spot formed by the illumination beam IB. The mask table and the mask holder are shown only diagrammatically and may be constructed in different ways. The substrate W to be illuminated is arranged in a substrate holder WH which is supported by a substrate table WT, also referred to as stage. This table can move the substrate in the scanning direction SD but also in a direction perpendicular to the plane of the drawing. The substrate table is supported, for example, by a table bearing ST. For further details of a step-and-scan apparatus, reference is made by way of example to PCT patent application WO 97/33204 (PHQ 96004). For imaging the mask pattern on the substrate with a reduction of, for example, 4xc3x97, a mirror projection system 20 comprising, for example, four mirrors 21, 22, 23 and 24 is arranged between the mask and the substrate. For the sake of simplicity, the mirrors are shown as plane mirrors but actually these mirrors, as well as those of the illumination system 10, are concave and convex mirrors and the mirror projection system 20 is designed in such a way that the desired sharp image is realized at a reduction of, for example 4xc3x97. The design of the mirror projection system does not form part of the present patent application. Analogously as the mirrors of the illumination system, each mirror 21, 22, 23 and 24 is provided with a multilayer structure of first layers having a first refractive index, alternating with second layers having a second refractive index. Instead of four mirrors, the mirror projection system may alternatively comprise a different number of mirrors, for example, three, five or six. Generally, the accuracy of the image will be greater as the number of mirrors is larger, but there will be more radiation loss. Thus, a compromise will have to be found between the quality of the image and the radiation intensity on the substrate, which intensity also determines the velocity at which the substrates are illuminated and can be passed through the apparatus. Mirror projection systems having four, five or six mirrors for lithographic apparatuses are known per se. For example, a six-mirror system is described in EP-A 0 779 528. Since EBV radiation is absorbed by air, the space in which this radiation propagates must be a highly vacuum-exhausted space. Minimally, both the illumination system, from the radiation source to the mask, and the projection system, from the mask to the substrate, must be arranged in a vacuum-tight space, which is denoted by means of the envelope 16 in FIG. 1. Instead of being accommodated in the same envelope, the illumination system and the projection system may be alternatively accommodated in separate envelopes. The mask MA and the substrate W may be juxtaposed, as shown in FIG. 2, instead of opposite each other. In this Figure, the components corresponding to those in FIG. 1 have the same reference numerals or symbols. The separate mirrors of the illumination system are not shown in FIG. 2 but form part of the block 10 representing the illumination system, with which the illumination beam is given the desired shape and the uniform intensity. FIG. 2 is a plan view of a mask with a mask pattern C and a plan view of a substrate W with substrate fields, with an image of the mask pattern C being formed on each field. The mask and the substrate comprise two or more alignment marks M1 and M2, and P1 and P2, respectively, each, which are used for aligning the mask pattern with respect to the substrate or with respect to each substrate field separately before the mask pattern is projected. For checking the movements of the mask and the substrate, the lithographic projection apparatus comprises very accurate measuring systems, preferably in the form of interferometer systems IF1 and IF2. The block denoted by reference numeral 2 in FIGS. 1 and 2 comprises an EUV radiation source unit in which EUV radiation is generated by irradiating a solid medium, for example, a metal with a high-intensity laser beam. FIG. 3 is a cross-section of an embodiment of such a radiation source unit. This unit comprises a transport device 30 in the form of, for example, a supply reel 31 and a take-up reel 32 for transporting a tape 33 of, for example, metal through a vacuum source space 34. This space is connected to a pump 35, for example, a turbo pump having a power of, for example, 1000 dm3/sec, with which the space 34 can be pumped to a vacuum of 10xe2x88x924 mbar. The radiation source unit further comprises a high-power laser 40, for example, an Nd-YAG laser which supplies laser pulses at a frequency of, for example, 10 Hz and at a pulse duration of, for example, 8 ns and with an energy content of 0.45 Joule. The optical frequency of the laser radiation may be doubled in known manner so that laser radiation with a wavelength of the order of 530 nm is obtained. An excimer laser, for example a Kr-F laser emitting at a wavelength of 248 nm, may be alternatively used as a laser source. The beam 41 emitted by the laser 40 enters, through a window 43, into the wall of the source space 34. This beam is focused by a lens system 42, illustrated by a single lens element, to a radiation spot 45 in a position 46 in a plane which substantially coincides with the laser-facing surface 36 of the tape 33. The pulsed beam 42 is each time substantially focused on a part of the tape which is instantaneously at the position 46. The radiation spot 45 has a diameter of, for example, 10 xcexcm. As a result of the extremely high energy density, for example, of the order of 1021 W/m3 of the laser beam at the bombarded area on the tape, this area partly explodes so that material, for example, metal particles are repelled from the tape. The repelled particles constitute a plasma, as is indicated in FIGS. 4a and 4b. In these Figures, the reference numeral 36 denotes the bombarded surface of the tape 33 and the reference numeral 41 denotes the laser beam. The plasma is denoted by the reference numeral 47. This plasma reaches a temperature corresponding to an energy of the order of several tens of eV. Then, EUV radiation is generated at a wavelength in the range of several nm to several tens of rm. The wavelength of the generated radiation is dependent on the process parameters, such as the material of the tape 33. FIG. 4a illustrates the situation immediately after the laser beam has bombarded an area on the tape. At that instant, energy-rich ions 51 and atoms 52 are repelled from the plasma. A few moments later, hot pieces of metal 53, or clusters of metal particles, are evaporated, as is shown in FIG. 4b. For further particulars about the way and conditions in which EUV radiation is formed, reference is made to the above-mentioned article: xe2x80x9cCharacterization and control of laser plasma flux parameters for soft X-ray projection lithographyxe2x80x9d. According to the invention, the surface 36 of the tape 33 is provided with pits 37, in which the width of these pits is, for example approximately equal to the cross-section of the laser beam at the area of the tape, as is shown in FIG. 5. A cross-section in this Figure shows a small part of the tape 33 in which a pit is present. As is shown in FIG. 5, the tape may have a constant small thickness and the pit is formed by a local protuberance of the tape. The pit may alternatively have the shape of a local indentation in a thicker tape. The pits may be cylindrical or spherical. Due to this shape of the local surface of the tape which is irradiated, the plasma formed there is concentrated in a smaller volume, so that the plasma has a considerably higher density and temperature than when using a flat tape as a plasma-forming medium. Due to the higher density and temperature, the emitted EUV radiation has a considerably higher intensity than in known EUV metal plasma radiation sources. In addition to the high intensity gain, the use of the tape with pits as a plasma-forming medium provides another advantage which is not less important. Due to the pit structure, the ions 39, atoms 41 and the metal pieces 42 are also concentrated, i.e. the spatial angle at which these particles are repelled is reduced considerably. This provides the possibility to collect these particles within the source space by means of a particle collector, or receptacle 48, arranged within this space. The tape 36 may consist of various metals such as iron, tin or carbon. Instead of a metal, another solid material may be used as a medium. The requirements imposed on such a material are that it should form an EUV emitting plasma upon bombardment with a high power laser beam and can be brought to a shape which is suitable for transport through the source space. As regards the shape of the medium, there are various possibilities, as is illustrated in FIGS. 6, 7 and 8. FIG. 6 is an elevational view, in the direction of the laser beam, of the above-mentioned strip or tape 33 provided with the pits 37. When this type of tape is used, an extra provision may be made in the radiation source unit so as to ensure that a laser pulse each time impinges upon a pit. As is shown in FIG. 3, the transport device can be synchronized with the laser driver via an electronic circuit 50 comprising a delay element, so that a laser pulse is formed at the instant when a pit 37 arrives at the position 46. FIG. 7 is a perspective view of a medium in the form of a bent tape 55 which is transported through the source space in such a way that the concave side 56 faces the laser. This embodiment of the medium provides the advantage that each laser pulse automatically impinges upon a tape section of the desired concave shape. This also applies to the medium shown in FIG. 8. This medium has the shape of a concave wire 57 whose concave surface 58 must face the laser beam upon transport through the source space 34. The wall of this space is provided with one or more apertures (not shown) through which the generated EUV radiation can exit. One or more mirrors 49 for collecting, concentrating and directing the generated EUV radiation may be arranged in this space. Alternatively, such mirrors may be arranged outside the space so as yet to concentrate and direct the EUV radiation exiting from this space. The number of mirrors required is dependent on the percentage of the EUV radiation which must be collected and used and is emitted by the plasma in all directions. In the radiation source unit described, the problem may occur that the metal elements 51, 52 and 53 present in the source space 34 absorb EUV radiation which may reach other spaces in the apparatus via the apertures for passing EUV radiation. These particles may then damage the mirrors arranged in these spaces. This is an important problem, notably in lithographic projection apparatuses because a reduced reflection of the mirrors, whereby less radiation can reach the mask and notably the substrate, has a direct influence on an important performance parameter of such an apparatus, namely the rate at which substrates can be illuminated. This problem can be eliminated, or at least sufficiently reduced, by passing a flow of rare gas through the source space, parallel to the direction of movement of the medium 33. FIG. 9 shows a first embodiment of a radiation source unit in which this is realized. In this Figure, the elements corresponding to those in FIG. 3 are denoted by the same reference numerals. Furthermore, the components of the radiation source unit which are not important for the present invention are no longer shown in this Figure and subsequent Figures. In FIG. 9, the reference numeral 61 denotes the wall of a source space 60 which has the shape of, for example, a cylinder and through which the solid medium 33 is moved. This wall is provided with, for example, a narrow aperture 63 having a diameter of, for example, 2.5 mm, via which the pulsed laser beam 41 can enter the space 60. The generated EUV radiation can leave the source space 60, for example, via this aperture or other apertures (not shown) and enter a space 65. In this space, which is only shown diagrammatically and in which a high vacuum of, e.g., 10xe2x88x924 mbar is maintained by means of the vacuum pump denoted by the reference numeral 35 in FIG. 3, the EUV radiation is guided towards the mask via the mirrors of the illumination system. The space 65 may also be filled with a rare gas such as helium, or with hydrogen at a low pressure of, for example 10xe2x88x921 mbar. A flow 77, 78 of rare gas, for example helium, is introduced into the source space 60 so that the helium flow is parallel to the direction of movement of the tape 33. To this end, the source space has a tube 70 which communicates with a helium outlet, for example, in the form of a tank 73. This tube has a diameter of, for example, 5 mm. A vacuum pump 75 connected to the source space ensures that a continuous flow of helium is maintained and that the helium pressure in the source space will not exceed, for example, 10xe2x88x921 mbar. At this low helium pressure, the generated EUV radiation is not absorbed. The tape 33 is now embedded in a tubular and viscous flow of helium which has a sufficient suction power. As a result, the medium particles are enclosed within the helium column and are taken along by the helium flow and transported out of the source space. The tube 70 ensures that the helium flow is a laminar flow so that the helium gas and the medium particles present therein cannot flow back. Due to the interaction of the tape 33 with the helium flow, the desired flow profile of the helium flow may be disturbed. To prevent this, a second tube 71 connected to the helium tank 73 is preferably arranged in the source space 60, so that a second helium flow 78 is established coaxially with the first flow 77. The flow profile can be restored again by means of the second flow. Instead of helium, another rare gas may be used for draining water vapor and excess water droplets from the source space. An example of another gas is argon having larger molecules than those of helium so that an argon flow has a better suction power than helium. However, argon absorbs more EUV radiation than helium. In the choice of the gas, a compromise must be made between the minimal absorption and the maximal suction power. FIG. 10 is a cross-section of a part of a second embodiment of the radiation source unit in which a rare gas flow is used. This embodiment differs from that in FIG. 9, inter alia, in that the source space 60 has a smaller diameter, for example 5 mm, and consists of three parts. A wall 81 surrounds the lower part. The upper part is closed by the wall 82 of the tube 88 surrounding the tape 33 for the supply of the rare gas. The central part 85 of the source space, at the area of the radiation path of the laser beam 41, communicates with the ambience. At the area of this central part, the walls 81 and 82 are slightly bent outwards so that a so-called ejector configuration, or geometry, is obtained. The combination of the vacuum pump 75 and its specific wall shape at the area of the central part of the source space operates as a so-called ejector pump or jet pump. Such a pump prevents helium or other particles from leaking to the ambience of the source space because it also sucks up possible particles present in this ambience and removes them. The open central part 85 of the source space 60 only needs to have such a height that the converging laser beam 41 can enter the source space in an unhindered way. Helium gas or another rare gas is supplied from a helium inlet 73 between the tape 33 and the wall 82. This helium gas is sucked downwards by the vacuum pump 75 in the form of a laminar flow and takes along the medium particles. Due to the jet pump configuration of the source space, migration of medium particles and loss of helium gas to the high-vacuum space 65 is prevented, and this to a stronger extent than is the case in the embodiment of FIG. 9. In this way, the helium gas pressure in the space 65 may be further reduced. To be able to operate as a jet pump, the straight part of the source space 60 must have a small diameter, for example, 5 mm. Then, the laser beam must be focused substantially on the position where the plasma-forming medium passes. Then there is a greater risk that the beam radiation does not impinge upon a desired pit in this medium, as compared with the case where the laser beam is focused at some distance from said position and hence this beam has a larger diameter at this position. Moreover, when focusing the laser beam on said position, the laser radiation has a large energy density at that position. This possible problem is mitigated by the embodiment shown in FIG. 11. This embodiment also comprises a jet pump. However, the inlet tube 90 now has an annular cross-section, with the width of the ring, for example 1 mm, being considerably smaller than its internal diameter which is, for example, 10 mm. The wall portions 92 and the upper parts of the wall 81 again constitute an ejector configuration. The gas curtain supplied through the tube 90 ensures that the medium particles remain entrapped and are drained. The jet pump configuration ensures that the gas curtain moves downwards at a great velocity and prevents rare gas from leaking to the high-vacuum space 65. Since the jet tube has an annular cross-section, the source space 60 may have a relatively large diameter so that the laser beam can be focused at some distance from the position where the water droplets pass so that the risk of missing a droplet will thus become smaller. The embodiment of FIG. 11 thus combines the advantages of the embodiment of FIG. 10 with those of the embodiment of FIG. 9. For the theoretical background and details about ejector pumps, reference is made to the article xe2x80x9cExit Flow Properties of Annular Jet-Diffluser Ejectorsxe2x80x9d in Journal of the Chinese Society of Mechanical Engineers, Vol. 18, No. 2, pp. 1113-125, 1997. EUV radiation sources may not only be used in lithographic projection apparatuses but also in EUV microscopes having a very high resolving power. The radiation path of the EUV radiation in such a microscope must be in a high vacuum. To prevent the vacuum from being attacked from the radiation source and from contaminating the optical components, the invention and its various described embodiments may be used to great advantage. It has been noted hereinbefore that EUV radiation is also known as soft X-ray radiation because its wavelength is close to that of real X-ray radiation having a wavelength of the order of 1 nm or less. It has also been noted that the wavelength of the radiation generated with the described radiation sources is dependent on, inter alia, the medium used. For generating X-ray radiation, similar radiation sources, with similar problems as for generating EUV radiation may therefore be used. For this reason, the present invention may also be used to great advantage in X-ray sources and this invention also relates to these sources and apparatuses such as X-ray microscopes or X-ray analysis apparatuses, hence the use in the claims of the term extremely short-wave radiation which is understood to be EUV radiation and X-ray radiation. |
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description | This application claims the benefit of U.S. application Ser. No. 13/820,145, filed Feb. 28, 2013 and presently pending, which is a National Stage Entry of PCT/US11/53185 filed Sep. 25, 2011, which Claims Priority from Provisional Application 61/393,804, filed Oct. 15, 2010; the disclosures of which are incorporated herein by reference in their respective entireties. 1. Field of the Invention The present invention relates to a Method, Process or System for processing and treating a radioactive liquid or aqueous concentrate, such as a nuclear fuel plant stream, or liquid or aqueous concentrate containing radwaste or other forms of environmental waste. 2. Background Information It has been documented that a number of plants in North America, Asia, and Europe, particularly Eastern Europe, and in other locations around the world, have been dealing with the problem of stored radioactive concentrate fluids (or radioactive agents in solution), or historical concentrates, which have, especially in the last 20-30 years grown to great stored volumes at various plants. Therefore, radionuclide removal from nuclear power plant's liquid radwaste has become an important priority for the European Union and its member states and other countries of the world. These plants have frequently included nuclear power plants where energy obtained by nuclear fission is transformed into electricity. An example of such a plant is the Kola NPP in the Polyarnye Zori/Murmansk Region, Russian Federation. Accumulated LRW (Liquid Radioactive Waste) at this plant had, at one point, been temporarily stored in stainless steel tanks and was to have been processed in such a way as to allow safe long-term storage, haulage and final disposal of such waste. This plan had not proven to be adequately successful. The Kola NPP (Nuclear Power Plant) had operated a system for the removal of radionuclides from evaporator concentrate decantates and salt crystalline deposits. This process had consisted of an oxidation phase and a filtration phase. In their case oxidation was achieved by ozone ejection into the liquid radwaste. However, this approach did not control temperature and pH in an ideal state to further the ozone process involved, allowing it to go up to 90 degrees F. (or about 32.22 degrees C.) where soluble ozone went to about zero solubility; and, therefore, was subject to poor utilization; where it was not absorbed into water and lost as gas. The pH was not controlled in an optimum range that both prevented boron precipitation and optimized utilization of the ozone. Filtration was applied to separate (non-soluble) radioactive oxidation products from its liquid phase, but only micro-filtration rather than ultrafiltration which allowed particulate activity smaller than micro-filtration range to pass. Cobalt, silver and iron isotopes are often found in about colloidal to about the lower end of the microfiltration range. In the past some of the equipment and method approaches used in this system had been found deficient in terms of meeting the needed performance requirements and with regard to the reliability or in terms of efficiency; and in general significant improvements to this type of process have sorely been needed to address this plant and plant areas like this. Inventions the subject of patent publication in the past suffer from a number of disadvantages; and, in one or more ways, appear to have only tangential relationship to the present invention. See, for example: U.S. Pat. No. 4,894,091 to Napier et al. which teaches a process for removing metals from water including the steps of prefiltering solids from the water, adjusting the pH to between about 2 and 3, reducing the amount of dissolved oxygen in the water, increasing the pH to between about 6 and 8, adding water-soluble sulfide to precipitate insoluble sulfide- and hydroxide-forming metals, adding a flocculating agent, separating precipitate-containing floc, and postfiltering the resultant solution; and where the postfiltered solution may optionally be eluted through an ion exchange resin to remove residual metal ions. U.S. Pat. No. 7,772,451 to Enda et al. discloses what is said to be a system for chemically decontaminating radioactive material, distinguishable from the present invention in providing, in its broadest sense, for “a system for chemically decontaminating radioactive material which forms a passage for liquid to flow through, comprising: a circulation loop connected to the passage for circulating a decontamination liquid, the circulation loop comprising a decontamination agent feeder feeding the decontamination liquid that is reductive and that is an aqueous solution comprising a monocarboxylic acid (namely, “formic acid”) and a di-carboxylic acid (namely, “oxalic acid”) to the decontamination liquid; a hydrogen peroxide feeder feeding hydrogen peroxide to the decontamination liquid; an ion exchanger for separating and removing metal ions in the decontamination liquid; and an ozonizer for injecting ozone into the decontamination liquid or an oxidizer feeder feeding permanganic acid or permanganate to the decontamination liquid; and wherein the system does not contain a device for reducing trivalent iron atoms into bivalent iron atoms, and wherein any acid present in the system is an organic acid. This system, as well as that of Napier et al. just above, does not employ the present invention's process steps of Oxidation or Ozone Oxidation (I) Sorption or Powder Sorbent Isotopic Reduction (II), Solid-Liquid Separation (III), Adjustable and Configurable Ion exchange (IX) (IV), and Within Step V: Discharge of Water (Va) or Drying of resulting waste stream dissolved solids to Dry Solids (Vb). U.S. Pat. No. 5,196,124 to Connor et al. appears to involve a method for reducing the radioactive material content of fluids withdrawn from subterranean reservoirs which employs the deposition of sorbent solids within its reservoir matrix surrounding its production well to act as an in-situ filter for dissolved radionuclides present in reservoir pore waters. Though using a form of sorption application, Connor does not facilitate this use in the same manner or staging as that set forth in the present invention. It does not employ the order of steps used or the effect so obtained by Oxidation prior to sorption; or Solid-Liquid Separation, Adjustable and Configurable ion exchange, or discharge of water or drying of waste stream dissolved solids to dry solids, all after the step of sorption. See also U.S. Pat. No. 5,728,302 to Connor; engendering similar distinctions in relation to the present invention. U.S. Pat. No. 5,908,559 to Kreisler sets forth a METHOD FOR RECOVERING AND SEPARATING METALS FROM WASTE STREAMS. The 25 method involves steps, distinguishable from the present invention, where: pH of a waste stream is adjusted; a metal complexing agent is added; a particle growth enhancer is added; a flocculating agent is added resulting in a solution; the solution effluent is dewatered, preferably using a plate and frame press, resulting in a sludge and a supernatant; and metals are recovered from the sludge upon melting, drying and dewatering a filter cake with melting enhancers so as to permit selective removal of a fused metal-bearing concentrate for casting into ingots to be sold to primary smelters. U.S. Pat. No. 7,282,470 to Tucker et al., though utilizing a water soluble sorbent additive, namely sorbitol or mannitol; is otherwise dissimilar to the steps of the method of the present invention. U.S. Application No. 200910252663 of Wetherill, provides for a METHOD AND SYSTEM FOR THE REMOVAL OF AN ELEMENTAL TRACE CONTAMINANT FROM A FLUID STREAM; and includes within its steps passing a fluid stream with an elemental trace contaminant through a flow-through monolith comprising an oxidation catalyst to oxidize the elemental trace contaminant; and contacting the fluid stream comprising the oxidized trace contaminant with a sorbent free of oxidation catalyst to sorb the oxidized trace contaminant. However, it otherwise lacks the functional effect brought about by the other inclusive steps of the present invention. In the PCT publication, W02007123436 (A1) of ALEXANDROVI et al. as inventors; the disclosure appears to disclose the use of a sorbent and the use of oxidizers such as potassium permanganate. However, this process does not employ the order sequence of the 25 present invention; nor employ Solid-Liquid Separation III, Adjustable and Configurable Ion exchange (IX) IV , or Discharge of Water (Va) or Drying of resulting waste stream dissolved solids to Dry Solids (Vb), as carried out in the present invention. The Russian patent, RU 2122753 (C1) to Dmitriev, et al. appears to set forth elements within a process which consists in oxidative treatment of waste through ozonation in the presence of oxidation catalyst and/or radionuclide collector; solid-liquid separation and, further downstream, a liquid phase finally purified on selective sorbents. However, the order sequence and qualitative composition of the steps is dissimilar to the present invention; and Dmitriev does not employ Adjustable and Configurable Ion exchange (IX) (IV), and Within Step V: Discharge of Water (Va) or Drying of resulting waste stream dissolved solids to Dry Solids (Vb) in the same manner as the present invention; nor is clear from an absence of descriptive illustration as to the routing and nature of treatment to achieve radionuclide separation. It will, therefore, be understood by those skilled in these technologies that a substantial and distinguishable process and system with functional and structural advantages are realized in the present invention over the past conventional technology with regard to processing, treating, packaging and chemically affecting radwaste liquid or a concentrate fluid stored or located at or in relation to a nuclear plant. It will also be appreciated that the efficiency, flexibility, adaptability of operation, diverse utility, and distinguishable functional applications of the present invention all serve as important bases for novelty of the invention, in this field of technology. The foregoing and other objects of the invention can be achieved with the present invention's method and system. In one aspect, the invention includes a method and associated system for processing and treating a radioactive concentrate, often stored as historical aqueous concentrate, or other radwaste or forms of environmental or hazardous waste which includes the steps, designated as Roman numerals: I, II, III, IV and V as follows: Oxidation or Ozone Oxidation I, when needed for the destruction of existing chelants Sorption or Powder Sorbent Isotopic Reduction II Solid-Liquid Separation III Adjustable and Configurable Ion exchange (IX) IV, and Within Step V: Discharge of Water (Va) or Drying of resulting Liquid waste stream dissolved solids to Dry Solids (Vb). A further aspect is directed to processing and elimination of C-14. 10 method and system of treating radioactive concentrate, the Concentrate Treatment System or invention's method I (Roman Numeral One) Step of Oxidation or Ozone Oxidation or oxidation step II Step of Sorption or Powder Sorbent Isotopic Reduction III Step of Solid-Liquid Separation IV Step of Adjustable and Configurable Ion Exchange (IX) V Step of Direct Discharge of Water (Va) or Drying of resulting waste stream to Solids (Vb) and Discharge or Recycle of Water 8 wastestream or feed stream 6 stored location, container area or facility 12 recycle oxidation vessel 14 supply line for (12) 14a oxidation return line IX ion exchange 16b ozone eductor and mixing equipment 17 ozone supply line 16a ozone supply skid or module 11 ORP measurement station 18 heat exchanger 23 pump (or other equivalent conveyance energy or force) 22 oxidation recycle line 24 sorbent supply area 24a supply line from (24) 13 pH/temperature measurement area 15 chemical injection skid 19 eductor supply feed 20 sorbent treatment area (vessel or container) 38 central recycle line 21 transfer line 25 mixer 26 solids transfer line 28 solids collection tank 31 sorbent recycle line 34 filter unit 35 filter media of (34) 33 separation and settling device (and such types of equipment and means) 22A first recycle line 31A second recycle line 36A filter recycle line or third recycle line 30 pump (or other means of motive or conveyance force) 7 solids separation device 7T solids transfer line 28 solids collection tank 40 filter permeate line 42 first IX vessel 43 first IX manifold line 44 second IX vessel 45 second IX manifold line 46 third IX vessel 47 third IX manifold line 48 fourth IX vessel 51 IX effluent line 49 fourth IX manifold line 41 manifold system 50 monitor tank 53 evaporator feed line 54 evaporator unit 52 pH adjustment station 56 pH measurement station 50R recycle line of (50) 55 pump 57a line (associated with Step Va) 57b line (associated with Step Vb) 60 reuse line (selective recycle line to plant) 70 Process controls (for Remote or Computer System Operation) PLC Computer utilized within the scope and teachings of the invention, programmed to control all the major functions of the system 10 in the sequence required for safe startup, operation and shutdown of the invention's system HMI Human Machine Interface (or HMI) which is either a dedicated local screen, or on one or more remote computer screens on computers that may be located in a control room supporting use of the present invention, wherein such computers can also be located anywhere in the plant area supporting use of the present invention, or anywhere in the world when internet lines available 71 Soluble Calcium Salts 72 pH adjustment 73 pH adjustment before oxidation with ozone in step (I) 74 pH adjustment after oxidation with ozone in step (I) 75 Evacuation 76 Providing a temperature range for drying in step Vb from greater than or equal to about 100 deg. C. to a temperature of less than or equal to about 240 deg. C The following description of the preferred embodiments of the concepts and teachings of the present invention is made in reference to the accompanying Drawing figure which constitutes an illustrated example of the teachings, and structural and functional elements, of the present invention's method and system; among many other examples existing within the scope and spirit of the present invention. Referring now to the single Drawing illustration, the sole drawing figure presented in the present application (also referred to herein as the Drawing), thereof, there is illustrated by schematic means exemplary embodiments of the present invention addressing the method and system of treating radioactive aqueous concentrate, the Concentrate Treatment System or invention's method 10. In a preferred embodiment of the invention the following steps 15 are included: Oxidation or Ozone Oxidation—Step I (Roman Numeral One) Sorption or Powder Sorbent Isotopic Reduction—Step II Solid-Liquid Separation—Step III Selective or Adjustable and Configurable Ion exchange (IX)—Step IV Step V: Discharge of Water (Va) or Drying of resulting dissolved solids stream to Dry Solids V (Vb) and evaporate stream that can be either environmentally discharged or recycled for reuse. The invention can address a number of problems involving known quality of the water, proposed effluent release limits, and major waste volume reduction during reprocessing of existing stored and new concentrates, as well as a number of other substances, concentrates and fluids. The invention's method 10 can also act to remove such substances as Antimony, Cesium, Cobalt Chromium, Manganese, Iron, Silver and other contaminants. The oxidation step I (Roman numeral one) of the present invention is preferably a batch operation, though other cycles and volume orientation such as ‘continuous’ and others can be utilized, lasting from about one (1) hour to about forty-eight (48) hours. The liquid waste stream 8 is provided from a stored location, container area or facility 6. The concentrates or radioactive concentrates discussed above which have been stored for a period of years (historical waste) or recently produced are subject radwaste substances for which the present invention process can be effectively used. In a preferred embodiment of the invention the stream 8 will consist of an historical concentrate stored over the years or recently produced as discussed above in various containers or facilities. The waste stream 8 is provided or transferred from the stored location 6, containing such radioactive concentrate, often stored, without limitation as to type, as historical concentrate, or other radwaste or forms of environmental or hazardous waste, to the recycle oxidation vessel 12 by the supply line 14. The waste 8 treated by the method 10 will at least in part frequently already contain chelants such as oxalic and citric acid, EDTA, LOMI solution and others. More likely, though not always, the waste 8, the subject of treatment, will contain Oxalic & citric acid and occasionally EDTA. As indicated more fully below, these chelants or others present will he destroyed or inactivated so as not to form a part within the present method 10 of actually or specifically extracting radioisotopes and target substances from the waste 8. This is principally accomplished in the present invention with oxidation and polishing, as opposed to chelation, as set forth herein. During a contemporaneous period of time during or after the transfer, the pump 23 is started to recycle concentrate from and returning to vessel 12, and heat exchanger 18, when utilized; and the pH and temperature (pH/temperature) measurement area 13 and ORP measurement station 11 are used for measurement purposes to determine further treatment required. The suitability of pH is determined and adjustment is performed if required using the chemical injection skid 15. If antifoaming agent is required this is added using the chemical injection skid 15. The heat exchanger 18 is utilized if temperature adjustment is required to adjust the temperature to a more favorable oxidation range. Due to the increased solubility of oxygen and ozone at lower temperatures the use of cooling to maintain a lower concentrate temperature will increase the rate of oxidation as more oxidant will be dissolved and thus available for oxidation. After chemical additions the ozone which is supplied on line 17 from an ozone supply skid or module 16a goes through the ozone eductor 16b provided or communicated directly by/in ozone supply line 17 with a volume of ozone or other oxidant supplied through chemical injection skid 15. The oxidation process (I) (or ozone supply process) as manifested in the vessel 12 may also involve (be assisted or replaced by) chemicals such as permanganate (or potassium permanganate), hypochlorite (or sodium hypochlorite), perchlorate, and/or hydrogen peroxide (H202), and/or other oxidants. The Oxidation step (I) (Roman numeral one) will also involve measuring ORP and pH to monitor the status of the oxidation of the waste stream 8. In this regard, as shown by example in the Drawing figure, ORP is measured at ORP measurement station 11 on recycle to the oxidation vessel 12. In so doing the water is recycled through ozone eductor 16b to oxidize the organics and metals in the wastewater from the vessel 12 and thru chiller 18 to maintain a lower temperature for better solubility of ozone using pump 23 or other equivalent conveyance energy or force. It is a teaching of the present invention that the destruction of chelants, such as, for example, EDTA, citric: acid, oxalic acid and others; is necessary within the invention's process to release activity so that this dissolved activity can be removed in a concentrated solid form, and the aqueous phase can be either environmentally released or recycled. As indicated below the stream 8 is communicated or transferred through supply line 22; which, in so doing, provides for transfer of the stream 8 as an oxidized solution from vessel 12 to sorbent treatment area 20. Separation of treatment to a second vessel provides for both increased system throughput and prevents possible sorbent residues from being oxidized by subsequent oxidation treatments that may result in formation of intermediate chemicals that are both difficult to oxidize and that prevent proper sorbent removal in the sorption step II (Roman numeral two). The pH of the solution to be treated is an important factor in utilization of the ozone in preferred embodiments of the present invention. In the oxidation step I (Roman numeral one), involving the destruction of chelant the pH should preferably be below about 12.5 and more preferably less than (<) about 12 for oxidation of chelants. Higher pH values provide poor utilization of the ozone in oxidation of chelants. Starting pH may be higher if other organics are present and when oxidized reduce the pH to the preferred value prior to the oxidation of the chelants. Otherwise an acid compatible with the system should be added to adjust the pH to this value prior to the start of oxidation of the chelants, if present. The pH has a large effect on the required ORP to meet the required final oxidation. During the period of initial oxidation of the typical chelants in the concentrate the pH does not change appreciably as chelant structure is broken into smaller chemical components that are not chelating in nature. When the organic from the chelant has been destroyed the pH again begins to lower indicating the production of CO2. At this time the oxidation is often sufficiently complete to permit precipitation of cobalt and other metals and release of other isotopes for removal either by sorbents or selective ion exchange. With regard to pH controls and Oxidation step I in the present invention, pH control is essential for solubility of some constituents and provides for optimum oxidation. The solubility of some constituents is very sensitive to pH; therefore, either a minimum or maximum pH may be maintained to prevent precipitation of a salt that is not required to be precipitated prior to final discharge or drying. The oxidation process also has an optimum pH target to minimize usage of the oxidant and maximize the rate of oxidation of a given chemical specie. In the method 10 of the invention pH may be adjusted at various points in the oxidation to minimize time without getting outside the solubility range. The oxidation of the chelants is often very slow at a pH outside the optimum range. The pH adjustment may be delayed until low molecular organics and more easily oxidized organics are oxidized so as to shift the pH range into more optimum ranges without chemical addition. Therefore, pH monitoring versus ORP levels during oxidation is essential to know when to add pH adjustment chemicals. A continuous extended period with no pH change but increasing oxidation may indicate entry into the chelant oxidation process, especially when ORP changes slow to a relatively steady increase with no constant decrease in pH. This will normally occur in about the +300 to +1000 mV ORP range depending upon pH. Therefore, as shown by example in the Drawing, if the pH 25 at pH/temperature measurement area 13 is greater than a pH of 12 then the pH should be lowered through the addition of suitable acids at chemical injection skid 15. Also, in the present invention pH is an indicator when the oxidation of chelants into smaller components is nearing completion, and as oxidation of the smaller components to CO2 begins to lower the pH which has been nearly constant during breaking of the 5 chelants. The breaking of chelants into smaller pieces which no longer can chelate the metals occurs preferentially to oxidation of most of the pieces. This chelant oxidation process is indicated by little or no change in pH. Once a change of about 0.01 to about 0.1 pH unit has occurred greater than (>) about 99.9% of the chelant has already occurred and the radioisotopes can be removed by filtration, sorbents (Step II) and Adjustable and Configurable ion exchange (Step IV). In a related aspect of the invention the oxidation return line 14a supplies a recycle volume which comes through the heat exchanger 18 to lower the temperature of the recycle volume to a preferred temperature of below about 80 degrees F. (or about 26.67 degrees C.), but preferably closer to about 60 degrees F. (or about 15.56 degrees C.) when possible, before entering the supply line 14 directly or through eductor supply feed 19 and continuing back to the vessel 12 as illustrated schematically in the Drawing. In this manner ozone can be more ideally utilized in lines before and in vessel 12. The waste stream 8 is pumped, for example by pump 23, or otherwise communicated in oxidation recycle line 22, in a batch sequence, to the recycle sorbent area, vessel or container 20. As shown in the Drawing, line 22 leads to transfer line 21. Transfer line 21, therefore, constitutes a short connector line between oxidation recycle line 22 and central recycle line 38, such that line 38 communicates recycle all the way to the recycle sorbent area or vessel 20. In the sorbent area 20 sorbent substances are added from the sorbent supply area 24 through the supply line 24a, or other means of transfer or communication, and mixed well using mixer 25, or equivalent stirring or mixing means, with the waste stream 8 in the area 20. A number of sorbent substances or materials, and particularly those powdered sorbents preferred for use in the present invention, are available and known in the art which can be utilized in step II. The sorbent could also include ion exchange media especially in a finer mesh size that may not be practical for column polishing. Generally speaking, a sorbent is defined as a substance that has the property of collecting molecules of another subject substance (which, itself, may be mixed with yet further substances not sought for collection) by sorption or by taking up and holding the subject substance by either adsorption or absorption. Sorbents in the present invention are utilized to remove a large percentage of the radioisotopes or other undesirable contaminants rather than using selective ion exchange materials as these sorbents are at least about 10 to 100 times more volume efficient than selective IX materials so that waste volumes for disposal are significantly reduced, thus lowering operating costs. Sorbent substances are chosen and mixed in the container 20 such that the stream 8 is placed in a chemical orientation for ionic removal and such that ionic bonding is formed for longer hold-up in this area when needed. The powdered, granular, liquid ionic flocculent and other forms of sorbents are such that they constitute ion exchange material acting as an absorbent and forming ionic bonds and early-stage particulate. Additionally, in preferred embodiments, precipitate and chemically sorbent solids which are formed in the recycle sorbent vessel 20 are transferred or communicated on/in the solids transfer line 26 to the solids collection tank 28. This process may be repeated sequentially with additional sorbents when needed; i.e., one or more sorbents may be added to the sorbent container 20 in a manner selected to address sorbency-targeting of one or more selected element substances. Such adding of individual sorbents, when chosen, creates a sequential adding of sorbents and sorbent addition strategy to best target element substances in the sorbent container 20 during related or contemporaneous time periods while such element substances are present in the sorbent container 20 and being processed. The waste stream 8, as treated in the container or area 20, is then pumped or otherwise communicated on the supply line 31 to the subsystem carrying out solid-liquid separation step III, as illustrated schematically in the Drawing. Solids are typically separated using a combination of centrifugal separation and settling (33) and filtration (34). Hydrocyclones, and such like means, are a preferred method for initial separation of sorbents followed by ultrafiltration to remove very fine or colloidal solids. Centrifugal separation is particularly effective at concentrating the solids for disposal. However, it will be understood that other similar means may be used to carry out the same functional purpose. The filter unit 34, to which the stream 8 is provided by supply line 31; is illustrated representationally as showing an ultrafiltration setup having at least one media or membrane sub-unit. In a preferred embodiment of the invention one or more Tubular Ultrafilter Membranes are utilized although the ultrafiltration employed does not have to be tubular in nature and one or more of such units can be employed. An example of a preferred ultrafiltration unit is the TUF™ System from Diversified Technologies Systems, Inc., in Knoxville, Tennessee. The TUF™ System; i.e., the “Tubular UltraFiltration” System, filters the waste stream 8 to less than about 0.05 micron, and is capable of removing virtually 100% of suspended solids, metal complexes, and most colloidal material from the stream by passing it through a series of cross-flow membranes. As indicated, other types of cross-flow membranes and media can be utilized. Additionally, in a preferred embodiment, the separation and settling device 33, and these types of centrifugal equipment and devices such as a hydrocyclone, can be used in the present method 10 to remove sorbent materials in advance of the filter unit 34 (or ultrafiltration units), to get such solids back out once they had been introduced in the sorption step II. As illustrated in the Drawing regarding respective recycle lines in preferred embodiments thereof: first recycle line 22A, second recycle line 31A and third recycle line 36A; are provided as a part of the invention's method 10 in preferred embodiments. Thus, in a preferred embodiment of the invention's method 10 the sorbent treatment area (vessel or container) 20 has three possible recycle paths: first, second and third recycles; depending upon the operation required in the system. The first recycle line 22A before the separation and settling device 33 allows mixing of the sorbent without removal of solids thus utilizing sorbent that may settle into line 31 and assist mixing. The second recycle line 31A provides for removal of sorbents or other solids without filtration. This may be utilized when current sorbent should be removed prior to a subsequent sorbent that is to be added. The third recycle line 36A can utilize both the separation and settling device 33 and the filter unit 34 with the reject being returned through recycle line 36A and line 38 to sorbent treatment area 20 for further processing, with pump 30 providing the motive force. Line 38 can comprise several grouped respective lines for use in different directions as needed. Therefore, if there are no solids present there is no need to remove solids prior to sorbent treatment (20) in the concentrate stream 8 and only one sorbent is utilized in the sorbent treatment area or vessel 20, the first and third recycles (respective lines 22A and 36A) being utilized. If solids are to be removed from initial concentrate stream 8 or if at least two (2) separate sorbent treatment cycles are utilized in the sorbent treatment area or vessel 20; i.e., the first sorbent is removed before utilizing the second (or respective additional) sorbent for absorption of targeted element substances; then the second (2nd) recycle (line 31A) is employed additionally. The separation and settling device 33 can be any of a number of centrifugal separators; for example, units such as a hydrocyclone which is preferred in the embodiments just discussed herein, or a centrifuge or other similar or equivalent type of equipment or other equipment accomplishing a separation function. In the preferred embodiment illustrated in the Drawing, a further separation and settling device 7 (such as a hydrocyclone or equivalent separation means) is utilized on supply line 14 shortly after leaving stored container area 6 in a sub-step to process and remove solids which are then communicated directly to, or on/in solids transfer line 7T, to the solids collection tank 28. Solids may be removed using solids separator 7, preferably a hydrocylone, during this transfer to decrease the consumption of oxidant, decrease the time for oxidation and eliminate the possibility of release of radioactive isotopes from the solids that later must be removed. In related preferred embodiments of the invention's method 10, and in the case of the third recycle line 36A, portions of the stream 8 on the rejected side of the filter media 35 are recycled back along the recycle line 36A and the central recycle line 38 to the sorbent treatment area or vessel 20 as illustrated by example in the Drawing illustration. Recycle of the stream 8 through the tubular ultrafilter cleans the membranes resulting in extended membrane life and less maintenance. Portions of the waste stream 8 on the permeate side of the filter media 35 in the filter unit 34, in the Solid-Liquid Separation step III, are communicated directly to the filter permeate line 40. The line 40 communicates such portions of the waste stream 8, exiting the filter unit 34 to ion exchange units (in preferred embodiments of the invention) comprising the method's (10) Adjustable and Configurable Ion Exchange (IX) step IV. The ion exchange (IX) vessel units, which can number one (1) or more, are shown representationally by example connected in series by manifold lines as illustrated in the Drawing in connecting and affording the ion exchange (IX) units selective, adjustable and configurable bypass options in transporting the stream 8 in relation to one another in an exemplar alignment as follows: the 25 first IX vessel 42, the first IX manifold line 43, the second IX vessel 44, the second manifold line 45, the third IX vessel 46, the third manifold line 47, the fourth IX vessel 48 and the fourth manifold line 49. The first IX vessel 42 is supplied with the stream 8 from the filter permeate line 40; and the last (fourth) IX vessel 48, in this case shown by example in the Drawing, is connected to the IX effluent line 51. The manifold lines 43, 45, 47 and 49, functionally manifested as the manifold system 41, is installed and positioned, and functions within the Adjustable and Configurable ion exchange (IX) step IV, such that the manifold lines 43, 45, 47 and 49 extend and connect to the respective IX vessels 42, 44, 46 and 48, as well as communicating with the filter permeate line 40 and the IX effluent line 51; as 10 illustrated by example in the Drawing. Each of the manifold lines; 43, 45, 47 and 49 can also be regarded functionally and structurally in the present invention as an influent/effluent header with bypass connection line. Each of the manifold lines (43, 45, 47 & 49), which can also be described as influent/effluent manifold lines, consists of 15 an H-shaped (i.e., configuration of the alphabetical letter “H” when viewed from at least one axis of sight) piping structure that has valves on piping running into (influent) and out (effluent) of the vessel. These are normally in an open position when the vessel is in service. A valve is also located on the cross piping between the influent and effluent and is called the bypass valve. The bypass valve is normally closed during vessel use. If the vessel is to be bypassed the bypass valve is opened and the influent and effluent valves are closed thus bypassing flow to the vessel, and facilitating the selection and adjustable or configurable alignment of those vessels to be specifically employed during this step when in use in the field. Thus, collectively, the manifold system 41 permits the ionic exchange (IX) vessels (as shown in this example of the present invention as 42, 44, 46 and 48) to be entered into flow path or removed without changing piping. Thus media in the vessels will not be exposed to wastewater that does not require further removal of a given isotope; or, when completely expended, can be removed from the flow path for media removal in step IV. It will be appreciated that elements of the manifold system 41 can be positioned, structured and/or connected to accommodate any number of vessel units utilized in the Adjustable and Configurable ion exchange (IX) step IV, and that a number of different means and structural orientations and positions can be utilized in carrying out the method's bypass function in relation to the IX vessel units utilized to carry out step IV and the selection choice of those IX vessels (for example 42, 44, 46 and/or 48) to actually be used in step IV when the system (10) is in operation in the field. It will also be appreciated that a number of IX arrays, sequences and connections can be utilized in the equipment carrying out the ion exchange (IX) step IV. One such arrangement in a preferred embodiment of the invention employs the equipment illustrated in the Drawing. The ion exchange step IV can employ media addressing additional removal to that of Cesium. It can clear water of all Cobalt and other targeted isotopes, such as media to address any Antimony, Cesium and other isotopes. It will be understood that a number of substances in media can be employed including, but not limited to, bead resin, zeolite and others. The fifth overall step (V) of the present invention's method; involving Discharge of Water Va or Drying of resulting dissolved solids to Dry Solids Vb, as illustrated by example in the Drawing figure; involves communicating the resulting stream 8 from the 4th IX vessel 48, last IX vessel in the selected array of such units (in the exemplar case, the fourth IX vessel 48) or the last of such units utilized or chosen; to the IX effluent line 51 leading, or directly, to the monitor tank 50. The various chemicals remaining in the water (i.e. for example: sodium borate, sodium sulfate, permanganates, nitrates and chlorides) represent the dissolved solids. The water which has had the radioisotopes removed must be analyzed for isotopic content before being released to the environment to assure that discharge limits are met; so the water is held in the monitor tank 50 before either being discharged or sent to the evaporation step Vb. Clean, environmentally suitable, discharged water therein, and in preferred embodiments so confirmed by analysis, can, therefore, be released and discharged Va to the environment. This process is capable of releasing to the environment essentially about 100% of the dissolved concentrate. An alternative pathway of the discharged stream in the tank 50 can be transferred or communicated by evaporator feed line 53 to the evaporator unit 54 for drying of dissolved solids (Vb), producing non-radioactive industrial disposal solid waste material and dischargeable evaporate condensate and release of the vapor to the atmosphere. In so doing, the overall temperature range in step Vb will be from greater than or equal to about 100 deg. C. to a temperature of less than or equal to about 240 deg. C. In the present invention it is preferred to utilize a center temperature of greater than or equal to about 100 deg. C. for general water removal; and a temperature range of greater than about 100 deg. C to about 240 deg. C. for water of hydration removal. In the present method 10 an example of preferred equipment utilized to carry out evaporation in the unit 54 is the DrumDryer™ manufactured by Diversified Technologies Services, Inc., Knoxville, Tenn./USA, which minimizes the volume of the dried product by producing a dense hard product with minimal voids. A number of other types of means and equipment can also be used to carry out the evaporation function of the evaporator unit 54. The evaporate is very high quality water produced from the evaporator unit 54 which is devoid of dissolved solids. The evaporate from the evaporator unit 54 is conveyed or sent by line 57b to be discharged to the environment as part of Step Va on line 57a or optionally or selectively recycled to the plant by reuse line 60 or other means which may occur in some applications. The pH can also be a valuable tool in optimizing the rate of drying and minimizing the final dried volume. For example, in the presence of boron a pH of greater than about 12 is desirable to maximize solubility of boron prior to precipitation with optimum pH of about 12.5 to about 13. The higher pH maximizes the solubility of the boron thus preventing premature precipitation resulting in poor heat transfer. This maximizes the heat transfer of the liquid from the heating surfaces even though the liquid becomes very viscous. Therefore, when evaporation is finally minimized as the solution approaches solubility at the elevated temperature, simple removal of heat causes the thick solution to crystallize as the temperature lowers. All remaining water is chemically bound in the crystalline structure. Accordingly, in a preferred embodiment of the invention, the concentrate with a majority of boron prior to drying should be increased to maximize solubility before entry into the evaporator unit 54 to maximize drying efficiency. Caustic is added through pH adjustment station 52 to reach desired pH value at pH measurement station 56 during recycle on transfer line 50R with pump 55. In the case of sulfate systems the pH may need to be adjusted to the acid side to obtain the same effect. The elevated pH also minimizes nucleate boiling that causes spattering which results in salt buildup in the fill head. Additionally, preferred embodiments of the present invention's method 10 include process controls 70 for remotely carrying out functional steps and sub-steps of the invention by computer and electronic means. Therefore, the operation of the invention 10 can normally be conducted remotely and often under automatic computer control to minimize radiological exposure and minimize operator time demands. The potential dose of some of these components can cause dangerous exposure to personnel. Although shielding can minimize exposure long-term exposure is still a concern. Thus, remote operations for most activities can be employed in preferred embodiments by the invention 10. The use of automated valves, remote controlled motors and feeders, sensors with remote displays and connections to process logic controller or PLC are therefore encompassed within the invention's method 10. Also, these controls can activate and control oxidation monitoring and completion, sorbent addition, level, volume and weight, pressure on filtration, and evaporation. The PLC is a computer programmed to control all the major functions of the system in the sequence required for safe startup, operation and shutdown of the invention's system. This minimizes the operators that must monitor the system and nearly eliminates operator radiological exposure. The PLC is also a better means of optimizing system operation through programmed analogs that would otherwise be more difficult for operators to implement, requiring extensive training. The PLC monitors parameters every few seconds and is able to recognize and correct operational problems, send warning and alarms and safely shutdown the system. Optimization of operations can occur by changing pump speeds, valve positions, and addition of chemicals for pH or foaming problems. The PLC is interfaced by use of a Human Machine Interface or HMI which utilizes a dedicated local screen or one or more remote computer screens on computers that may be located in a control room. Such computers can also be located anywhere in the plant or world through internet connections. This permits supervisors, management and equipment supplies to remotely monitor the system for proper operation and further optimization. The HMI is also capable of recording data from the system for permanent record, for trending system parameters and for generating management reports for the invention's system operation. These trends and reports can warn management of upcoming maintenance requirements. Even issues like membrane cleaning can be handled automatically between batch operations. In another included use of the present invention the removal of C-14, a radioactive isotope of Carbon, thought or known to exist in the subject wastestream (8), in a preferred embodiment of the present invention is accomplished before the attainment of the final dried product by chemical treatment in the sorbent vessel, or the environment of step (II) through the addition of a soluble calcium salt 71, including CaCl2, Ca(NO3)2, and other such salts; probably in liquid form (but not required); that results in the precipitation of calcium carbonate finally being removed with other sorbent solids. Removing C-14 important as a use of the present invention, and objective thereof, in that a very limited amount of C-14 is permitted to be present in the DrumDryer or drying solids in step Vb of the invention to obtain free release to the environment (under existing environmental regulations). Typical C-14 isotope and Citric Acid (and other chelants and organics) are known to exist in waste waters of nuclear facilities in concentration or levels greater than would be an acceptable by those skilled in the art at least in areas such as Russia (e.g., Russian designed VVER), Slovakia and other countries. C-14 can come from almost any organic present in the primary water that passes through the reactor during the fission reactions. In the present invention the use of Ozone in the present invention destroys all the organics. As it has been determined that citric acid and oxalic acid are chelants that hold Cs, Co, Sb and others in solution it must be destroyed to release the isotopes. Generally speaking, C-14 requires special analytical techniques to identify its presence, and C-14 is one of a number of other substances that might be a part of the incoming wastestream, which are not easily identified using normal gamma, beta and alpha analysis; but, are understood by those skilled in certain areas of the world to often be a radwaste constituent. However, when the presence of such a substance is suspected or known the present invention can be utilized to remove them. For example, in the U.S. the presence of C-14 may not be inherently understood by one skilled in the art, as the U.S. does not normally use C-14 substances, while countries like Russia and Slovakia, responsive to organizations like the EU, or other countries, might well use these substances in the primary water of a NPP or similar Boron wastestream. The fact that countries such as Russia and Slovakia may have to account for C-14, or other such substances, and the effect that it would have on overall processing, is, thus, considered an additional use to be indicated within the scope of the present invention when this occurs in the NPP original wastestream addressed by the present invention. The removal of C-14 in the Ozone Recycle Vessel, or as a part of step (I), is an alternate method utilized in the present invention, by first lowering the pH (or applying a pH adjustment) 72 to a range of about 5 to about 7, or about, or approximately, 6 where solubility of CO2 is minimized and carbonic acid is not readily formed. The pH adjustment can be made either before 73 or after 74 oxidation with ozone in step (I) that destroys the organic containing the C-14. Preferable pH adjustment would be before oxidation due to immediate release to the gaseous phase where some C-14 would be swept out with the oxygen and unreacted ozone. The lower pH may also aide the rate and efficiency of ozone oxidation. After the ozonation is complete the vessel would be subjected to evacuation 75 to a preferred vacuum level range of about 18 in. to about 28 in. Hg vacuum, or lower than about 20 in. Hg, or a range of about 20 in. Hg to a range of about 28 in. Hg; if needed, to cause the CO2 to effervesce from the liquid along with oxygen and ozone, thus removing C-14 from the liquid. It has the added benefit of also removing ozone and oxygen from the liquid thus potentially eliminating the step of passing the liquid through a carbon bed to destroy the ozone. A flow through degassifier which operates with vacuum could also be utilized in evacuation 75 instead of directly applying vacuum to the vessel. The degassifier uses a gas permeable membrane and the vacuum is applied on the gaseous side of the membrane. As a part of step 72 (73 and 74), the pH must then returned to an acceptable level after evacuation 75 to reconvert the boric acid to sodium borate so that any dissolved boric acid/sodium borate is not removed in the following process step. The water or wastestream could be provided as boric acid or as sodium borate depending upon the type of plant or facility involved. If the sodium borate is the feed source, the pH must be lowered to 5-7 in order to be at a pH that will release the generated carbon dioxide to the atmosphere as gas rather than convert the carbon dioxide to bicarbonate or carbonate at higher pH. At a lower pH than 5 the carbon dioxide is converted to carbonic acid that increases the solubility of carbon dioxides. Sodium borate is much more soluble than boric acid. The solubility curve for boron reaches a minimum around a pH of 7. This means that some boron will likely precipitate out at a pH of 6. To prevent removal of the boron with the precipitating sorbents the pH must be raised back to a pH greater than (>) 11-12 to resolubilize the boron as sodium borate. The addition of sodium or potassium hydroxide quickly dissolves the boric acid as sodium or potassium borate. While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. |
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056688458 | summary | BACKGROUND OF THE INVENTION The present invention relates to a computed-tomography (CT) apparatus for acquiring a cross-sectional image of an object by use of X-rays, ultrasonic waves or the like, and more particularly to such a CT apparatus suitable for use as a medical diagnosis apparatus. In recent years, CT apparatuses for acquiring cross-sectional images of objects have widely been used especially as medical diagnosis apparatuses for diagnosing patients. Such apparatuses include an X-ray CT apparatus which uses X-rays, a radiography isotope (RI) CT, ultrasonic CT and image intensifier (I.I) CT apparatuses in which the measurement of projection data is made from the circumferential directions of an object around the object to reconstruct an image, and so forth. In a general X-ray or other type CT apparatus, a time for measuring an object at a predetermined slice position through the scan of the entire circumference of the object (or so-called 360.degree. one-slice measurement time) differs according to a plurality of measurement modes which can be changed. Usually, this measurement time is 1 to 9 seconds. Therefore, it is general that an operator of the apparatus selectively uses the optimum measurement mode in accordance with the size of an object, a part to be subjected to diagnosis or the purpose of diagnosis. If a motion such as the motion of an object or the motion of internal organs of the object occurs during the above-mentioned measurement time, artifacts called motion artifacts are generated due to this motion. Owing to the artifacts, an accurate diagnosis from the acquired cross-sectional image becomes difficult. The well known method for solving such a technical problem is a measurement data correcting method disclosed by, for example, U.S. Pat. No. 4,580,219 issued on Apr. 1, 1986 and entitled "METHOD FOR REDUCING IMAGE ARTIFACTS DUE TO PROJECTION MEASUREMENT INCONSISTENCIES". This correction method is generally called bowel gas correction. The bowel gas correction method will now be explained briefly by use of FIG. 6. In a usual CT apparatus, a measurement start position of a scanner is fixed beforehand at a predetermined position. The scanner starts the measurement from the predetermined measurement start position and makes a 360.degree. scan over the entire circumference of an object to obtain projection data of the object. A measurement end position assumes the same position as the measurement start position. Therefore, the first image and the last image will be consistent with each other if there is no motion of the object during an interval between the measurement start and end positions. In the actual measurement, however, when the object moves during the measurement interval, discontinuities are generated between measurement data at the measurement start and end positions. Owing to the discontinuities of measurement data, inconsistencies called misregistration differences appear between the projection data measurement start and end positions. The inconsistencies cause the generation of motion artifacts after image reconstruction. For such circumstances, data correction called bowel gas correction is made in order that the continuity of data in a predetermined rotation angle range (hereinafter referred to as correction region A) near each of the measurement start and end positions is improved even if any motion of the object is involved. In general, the same result is given by CT projection data obtained by measuring an object from directions which are different by 180.degree.. In the bowel gas correction, the contribution of projection data to the reconstruction of a cross-sectional image is modified. More particularly, the contributions of projection data near the measurement (or scan) start position and projection data near the measurement end position providing the cause of artifacts are reduced while the contributions of projection data near a position opposite to the measurement start position with 180.degree. therebetween and projection data near a position opposite to the measurement end position with 180.degree. therebetween are increased. Namely, the cross-sectional image of one slice is generated by assigning a weight smaller than 1 to projection data in the predetermined rotation angle range (or the correction region A in FIG. 6) and assigning a weight greater than 1 to projection data in a rotation angle range (hereinafter referred to as correction region B) opposite to the correction region A. The correction regions A and B are positioned opposite to each other and have the same rotation angle range. The weight takes the smallest value (zero) at the measurement start position and the measurement end position and is gradually increased with the increase of a distance from the measurement start position and the measurement end position. Also, the weight takes the greatest value at the middle portion of the correction region B opposite to the measurement start position and the measurement end position and is gradually decreased with the increase of a distance from the correction region B. The case where no bowel gas correction is made corresponds to the case where the same weight (1.0) is used at any position, as shown by dotted line in FIG. 6. In a medical diagnosis CT apparatus such as X-ray CT apparatus, a measurement method is generally performed in which a contrast agent is injected into a blood vessel to emphasize constrastive differences between various tumors and normal tissues, thereby facilitating the diagnosis of a patient. In this method, the contrast agent flows away as the blood circulates. Therefore, the timing of injection of the contrasting agent and the timing of start of measurement provide important factors for accurate diagnosis. Particularly, in the tomographic imaging of a patient with an impediment in consciousness or an infant, an operator starts the measurement at a timing when the object has no motion. In such cases, the concurrency of a measurement start instruction (or operation) by the operator and the start of measurement by the diagnosis apparatus is an important task for the purpose of providing a cross-sectional image which has a high diagnostic value. Under such backgrounds, a continuously rotatable scanner having, for example, a slip ring mounted thereon has recently been used widely. In such a scanner, the measurement start position can be set freely. Therefore, it is possible to improve the concurrency of an operator's desired measurement start timing and the start of measurement by the diagnosis apparatus, thereby shortening a time for a series of measurements. SUMMARY OF THE INVENTION FIGS. 7A, 7B, 7C and 7D show the examples of cross-sectional images of a human belly subjected to bowel gas correction. As shown, linear artifacts 20 appear in the image. A plurality of short lines designated by reference numeral 21 are background noises. In the cases of FIGS. 7A and 7B, the correction region A (see FIG. 6) for bowel gas correction is set to be wide as compared with that in the cases of FIGS. 7C and 7D. As the correction region A becomes wider, the continuity between data near the measurement start position and data near the measurement end position is improved. Accordingly, the artifacts 20 in the image of FIG. 7A are reduced as compared with those in the image of FIG. 7C and therefore give a reduced influence on the diagnosis of the image of internal organs. On the contrary, in the case of FIG. 7C in which the correction region A is narrow, the artifacts 20 appear strongly in the image. However, in the case where the correction region A is set to be wide, the background noises 21 appear strongly in the image, as apparent from FIG. 7B. On the contrary, in the case where the correction region A is set to be narrow, the background noises 21 are weakened, as apparent from FIG. 7D. The reason why the background noises are increased when the correction region for bowel gas correction is wide, is that the range of data giving no contribution to image generation is increased due to the correction, thereby deteriorating the efficiency of utilization of X-rays with the relative increase of the background noises. Consequently, the bowel gas correction involves a problem that the suppression of artifacts is accompanied by the increase of background noises. In the conventional CT apparatus, a cross-sectional image obtained through measurement from an axial direction having a large attenuation of radiation is characterized in that conspicuous background noises appear along that axial direction. FIG. 8 shows projection data 24 which is obtained by irradiating an elliptic object 22 with X-rays emitted from an X-ray source suited at a position 23 on the x axis and projection data 26 which is obtained by irradiating the object 22 with X-rays emitted from an X-ray source suited at a position 25 on the y axis. As apparent from FIG. 8, the thickness of the object 22 is large in the x-axis direction and hence the attenuation of X-rays in the x-axis direction is larger than that in the y-axis direction. In this case, background noises will be conspicuous in the image data obtained through the measurement from the x-axis direction. If a direction having a large attenuation (such as the x-axis direction in the above example) coincides with a measurement start position by chance, the bowel gas correction will cause a further increase of background noises. In an image having a low contrast, the background noises make the diagnosis difficult. In addition, artifacts are an obstacle to the diagnosis. In medical diagnosis apparatuses for making the diagnosis of patients for the purpose of medical diagnosis, a variety of combinations may be employed in accordance with the shapes of objects such as patients and the measurement conditions. Therefore, it is desired to acquire a high-quality cross-sectional image by setting the optimum bowel gas correction region for all the combinations while synthetically considering merits and demerits based on the shapes of objects and the measurement conditions. In the practical state of the conventional CT apparatus, however, it is difficult to satisfy such a requirement. The present invention has been completed on the basis of the present inventors knowledge of the bowel gas correction in the prior art and the relationship between background noises and an object as mentioned above. ACT apparatus according to the present invention provides an image in which the increase of background noises necessarily associated with the bowel gas correction is reduced to the possible minimum while the motion artifact correction effect based on the bowel gas correction is maintained to the optimum and the shape of an object and the difference in attenuation depending on the axial direction of the object are taken into consideration. One object of the present invention is to provide a CT apparatus which can provide a high-quality cross-sectional image necessary for accurate diagnosis of a patient in the capacity of a medical diagnosis apparatus. ACT apparatus according to the present invention realizes the concurrency of the operation of measurement start by an operator and the actual measurement start. In the above-mentioned continuously rotatable scanner having a slip ring mounted thereon, the operation of measurement start by the operator substantially coincides with the actual measurement start. However, in a scanner based on a control method in which the operation of measurement start is performed from a certain fixed position, there may occur a situation in which a measurement instruction is issued by an operator when the scanner has already passed the measurement start position. In this case, there is generated a time delay until the scanner reaches the measurement start position again. In a measurement mode in which a long measurement (or scan) time is set for one slice, not only such a time delay but also the variations of a time from the timing of measurement instruction issuance until the actual measurement start are dominant problems in making the quantitative analysis of an image. Therefore, another object of the present invention is to provide a CT apparatus which can provide a high-quality cross-sectional image by minimizing a time delay from the designation of measurement start by an operator until the actual measurement start irrespective of the lengths of scan times determined by measurement modes which may be employed in a scanner based on a control method with the operation of measurement start performed from a fixed position. In a CT apparatus according to an embodiment of the present invention, the scan is started from a direction having a small attenuation of radiation to acquire a cross-sectional image of an object in which background noises and motion artifacts are suppressed to the possible minimum. In the CT apparatus of this embodiment, one of rotation positions of a scanner having a smaller attenuation of radiation is determined. The operation of the scanner is controlled so that the scan is started from the determined rotation position having the smaller attenuation. Individual weights are assigned to projection data in a predetermined rotation angle range including the vicinity of a scan start rotation position of the scanner and the vicinity of a scan end rotation position thereof and projection data in a rotation angle range opposite to the predetermined rotation angle range, respectively. The projection data assigned with the weights and projection data assigned with no weight are used to determine corrected data for the entire circumference of the object, thereby generating a cross-sectional image of the object on the basis of the corrected data. In a CT apparatus according to another embodiment of the present invention, the range of a correction region is changed in accordance with a scan start position. If the scan start position is not suited in a small attenuation of radiation, the correction region is narrowed to optimize the effect of suppression of background noises and artifacts. In the CT apparatus of this embodiment, one of rotation positions of a scanner having a smaller attenuation of radiation is determined. Further, a scan start rotation position of the scanner is detected. In the case where the detected scan start rotation position is not suited in the rotation position having the smaller attenuation, a predetermined rotation angle range including the vicinity of a scan start rotation position of the scanner and the vicinity of a scan end rotation position thereof is narrowed. Individual weights are assigned to projection data in the predetermined rotation angle range and projection data in a rotation angle range opposite to the predetermined rotation angle range, respectively. The projection data assigned with the weights and projection data assigned with no weight are used to determine corrected data for the entire circumference of an object, thereby generating a cross-sectional image of the object on the basis of the corrected data. In a CT apparatus according to a further embodiment of the present invention, a delay corresponding to a time from the operation of scan (or measurement) start by an operator until the actual scan start and the variations of such a time are minimized by setting a plurality of scan start positions on the locus of scan rotation of the scanner. In the CT apparatus of this embodiment, a plurality of scan start positions are detected during the rotation of the scanner. The actual scan is started from a scan start position which is first detected from the point of time when a scan start signal is issued. |
description | The field of the disclosure relates generally to liquid handling systems and, more particularly, to systems and methods for dispensing discrete volumes of radioactive liquids. Radioactive material is used in nuclear medicine for diagnostic and therapeutic purposes by injecting a patient with a small dose of the radioactive material, which concentrates in certain organs or regions of the patient. Radioactive materials typically used for nuclear medicine include Germanium-68 (“Ge-68”), Strontium-87m, Technetium-99m (“Tc-99m”), Indium-111m (“In-111”), Iodine-131 (“I-131”) and Thallium-201. In the U.S., production of radiopharmaceuticals is regulated by the Current Good Manufacturing Practice (cGMP) regulations for human pharmaceuticals. During cGMP pharmaceutical (and other) manufacturing, it is sometimes desirable to accurately dispense low quantity target volumes of hazardous substances, such as radioactive liquids, from a source container into a clean destination container. For example, in the production of radiopharmaceuticals used in diagnostic imaging, a relatively large quantity of the radiopharmaceutical may be prepared in a source vial. In some applications, it is desirable to transfer the radiopharmaceutical from the source vial into a relatively clean vial, for example, for shipment to an end user. At least some known methods of transferring radioactive liquid from a source vial to a destination vial provide less than optimal accuracy and consistency, and/or expose the operator to nuclear radiation. Accordingly, a need exists for a radioactive material handling system that provides improved accuracy and precision in transferring radioactive liquids, and reduces operator exposure to radiation. This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. In one aspect, a system for dispensing radioactive liquids includes a radiation containment chamber including an enclosure constructed of a radiation shielding material, and a liquid dispensing apparatus at least partly disposed in an interior of the enclosure. The liquid dispensing apparatus includes a support arm rotatable about a rotation axis, an actuator operatively connected to the support arm and configured to at least one of rotate the support arm about the rotation axis and displace the support arm in a direction parallel to the rotation axis, and a pipette assembly mounted to the support arm. The pipette assembly includes a pipette tip defining an opening through which liquids are aspirated and dispensed, a piston, and a stepper motor operatively connected to the piston to control linear displacement of the piston. In another aspect, an apparatus for dispensing radioactive liquids includes a support arm rotatable about a rotation axis, an actuator operatively connected to the support arm and configured to at least one of rotate the support arm about the rotation axis and displace the support arm in a direction parallel to the rotation axis, and a pipette assembly mounted to the support arm. The pipette assembly includes a pipette tip defining an opening through which liquids are aspirated and dispensed, a piston, and a stepper motor operatively connected to the piston to control linear displacement of the piston. The apparatus is free of radiation-sensitive electronics. In yet another aspect, a method of dispensing radioactive liquid using a dispensing apparatus including a pipette assembly mounted on a rotatable support arm is provided. The pipette assembly includes a pipette tip, a piston, and a stepper motor operatively connected to the piston. The method includes positioning the pipette assembly above a first vial using the support arm, aspirating a volume of radioactive liquid from a first vial by displacing the piston in a first direction using the stepper motor, rotating the support arm to position the pipette assembly above a second vial, and dispensing at least a portion of the volume of radioactive liquid into the second vial by displacing the piston in a second direction opposite the first direction using the stepper motor. Various refinements exist of the features noted in relation to the above-mentioned aspects. Further features may also be incorporated in the above-mentioned aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments may be incorporated into any of the above-described aspects, alone or in any combination. Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. Example systems and methods of the present disclosure facilitate dispensing small volumes of liquids (e.g., from 0.1 microliters (μL) up to 10 milliliters (mL)), while eliminating human error typically associated with manual dispensing. Embodiments of this disclosure are particularly suitable for dispensing small volumes of radioactive liquids, and facilitate dispensing such liquids safely, cleanly, accurately, and precisely. In particular, embodiments of the present disclosure facilitate automating the transfer of radioactive liquids from a source vial to a destination vial while avoiding or minimizing operator whole-body and extremity radiation exposure. FIG. 1 is a schematic view of a system for dispensing liquids, indicated generally by reference numeral 100. Although the system 100 is described herein with reference to dispensing and transferring radioactive liquids, the system is not limited to dispensing radioactive liquids and may be used to dispense, transfer, or otherwise handle other liquids. The system 100 generally includes a liquid dispensing apparatus 102 enclosed within the interior of a shielded nuclear radiation containment chamber 104, also referred to herein as a “hot cell”, and a computing device or controller 106 connected to the liquid dispensing apparatus 102 by a suitable communication link (e.g., a wired connection). The liquid dispensing apparatus 102 and the controller 106 are connected to a suitable power supply. Suitable power supplies include, for example and without limitation, a 120V AC power supply. As described further herein, the liquid dispensing apparatus 102 is configured to transfer precise amounts of radioactive liquids from one vial to another vial in response to control signals received from the controller 106. The liquid dispensing apparatus 102 is enclosed within the containment chamber 104 to shield operators and radiation-sensitive electronics of the controller 106 from nuclear radiation emitted by radioactive materials within the containment chamber 104. The containment chamber 104 generally includes an enclosure 108 constructed of nuclear radiation shielding material designed to shield the surrounding environment from nuclear radiation. The enclosure defines an interior in which the liquid dispensing apparatus is positioned. Suitable shielding materials from which the containment chamber 104 may be constructed include, for example and without limitation, lead, depleted uranium, and tungsten. In some embodiments, the containment chamber 104 is constructed of steel-clad lead walls forming a cuboid or rectangular prism. Further, in some embodiments, the containment chamber 104 may include a viewing window constructed of a transparent shielding material. Suitable materials from which viewing windows may be constructed include, for example and without limitation, lead glass. With additional reference to FIG. 2, the liquid dispensing apparatus 102 generally includes a pipette assembly 202 mounted to a support frame 204, a source vial 206 (generally, a first vial), a destination vial 208 (generally, a second vial), and a dual-motion actuator 210 operatively connected to the pipette assembly 202 for positioning the pipette assembly 202 relative to the source vial 206 and the destination vial 208. In the illustrated embodiment, the support frame 204 includes a base 212, a column 214 extending vertically upwards from the base 212, and a support arm 216 rotatably mounted at the top of the column 214 for rotation about a rotation axis 218. The column 214 has a tubular construction defining an interior 220 of the support base 212. In the example embodiment, the dual-motion actuator 210 is positioned within the interior 220 of the column 214. The support arm 216 is mounted at the top of the column 214, and is configured to rotate about the rotation axis 218 under the control of the dual-motion actuator 210. More specifically, as shown in FIG. 3, the support arm 216 is operatively connected to the dual-motion actuator 210 at the top of the column 214 by a compression fitting (e.g., a machined hole extending through the support arm 216), a set screw 302, and a locknut 304. In other embodiments, the support arm 216 may be operatively connected to the dual-motion actuator 210 by any other suitable connection means that enables the liquid dispensing apparatus 102 to function as described herein. The support arm 216 extends radially outward from the top of the column 214 to opposing first and second ends 222, 224. The pipette assembly 202 is connected to the support arm 216 at the first end 222. In the example embodiment, the support arm 216 also includes a counterweight or counterbalance 226 connected at the second end 224 of the support arm 216 to maintain the support arm 216 in a horizontal orientation and facilitate smooth rotation about the rotation axis 218. Components of the support frame 204, including, but not limited to, the base 212, the column 214, and the support arm 216, may be constructed from materials having a high tolerance to gamma and beta radiation. Suitable materials from which components of the support frame 204 may be constructed include, for example and without limitation, acrylic, polyvinylchloride (PVC), and polycarbonate. “High tolerance to gamma and beta radiation” means that the material can withstand a dose of at least 4 megarads (Mrads) of radiation without experiencing significant damage. Acrylic experiences significant damage at a radiation dose of about 5 Mrads, PVC experiences significant damage at a radiation dose of about 50 to 100 Mrads, and polycarbonate experiences significant damage at a radiation dose in excess of 100 Mrads. The dual-motion actuator 210 is configured to control a vertical and rotational position of the support arm 216 and, consequently, a vertical and rotational position of the pipette assembly 202. More specifically, the dual-motion actuator 210 is configured to rotate the support arm 216 about the rotation axis 218, and to displace (e.g., raise and lower) the support arm 216 in a direction parallel to the rotation axis 218 (i.e., a vertical direction). In the example embodiment, the dual-motion actuator 210 includes a first stepper motor 110 (shown in FIG. 1) that controls rotation of the support arm 216, and a second stepper motor 112 (shown in FIG. 1) that controls the vertical position of the support arm 216 and, consequently, the vertical position of the pipette assembly 202. In the example embodiment, the first stepper motor 110 is operatively connected to the support arm 216 via a rotatable shaft 114 that protrudes from a top of the column 214. The rotatable shaft 114 is received within the compression fitting and secured to the support arm 216 by the set screw 302 and the locknut 304. Operation of the first stepper motor 110 causes the shaft 114 to rotate, and thereby rotate the support arm 216 about the rotation axis 218. The second stepper motor 112 is operatively connected to the support arm 216 (e.g., via the rotatable shaft 114). Moreover, the second stepper motor 112 is connected to the support arm 216 through a linear actuator (not shown) such that operation of the second stepper motor 112 raises and lowers the support arm 216 (and, consequently, the pipette assembly 202). In some embodiments, the shaft 114 is connected to the first stepper motor 110 by a spline joint to enable the shaft 114 to maintain engagement with the first stepper motor 110 while being raised and lowered by the second stepper motor 112. The rotational direction and speed of the first and second stepper motors 110, 112 are controlled by the controller 106 such that the dual-motion actuator 210 selectively controls a rotational position and vertical height of the support arm 216 and the pipette assembly 202. The first and second stepper motors 110, 112 may have any suitable stepper motor construction that enables the liquid dispensing apparatus 102 to function as described herein. Generally, each of the first and second stepper motors 110, 112 includes a plurality of motor windings or coils and a rotor that rotates in response to the motor windings being sequentially energized. Rotation of the rotor occurs in discrete, equal steps or angular distances, the number of steps generally corresponding to the number of times the motor windings are energized. In this way, the first and second stepper motors 110, 112 can be rotated and/or held at a desired position without the use of position feedback sensors. In the example embodiment, the first and second stepper motors 110, 112 do not include any electronics, such as position feedback sensors (e.g., resolvers, encoders, or optical sensors). One example of a suitable actuator suitable for use as the first and/or second stepper motors 110, 112 includes the Haydon™ dual motion linear actuator model LR43MH4R-2.33-940, available from Haydon Kerk Motion Solutions. The pipette assembly 202 is disposed at the first end 222 of the support arm 216, which is operatively connected to the dual-motion actuator 210. The vertical height and rotational position of the support arm 216 and, consequently, the pipette assembly 202, are controlled by operation of the dual-motion actuator 210. In this way, the pipette assembly 202 can be rotated into different rotational positions relative to the rotation axis 218, for example, above the source vial 206, above the destination vial 208, or in a home position in between the source and destination vials 206, 208. Additionally, the pipette assembly 202 can be raised and lowered relative to the source vial 206 and the destination vial 208. With additional reference to FIG. 4, the pipette assembly 202 is configured to aspirate and dispense discrete volumes of liquid to effect liquid transfer between the source vial 206 and the destination vial 208. The pipette assembly 202 includes a pipette body 402, a pipette tip 404 connected to the pipette body 402, and a linear actuator 406 operatively connected to the pipette body 402. FIG. 5 is an exploded view of the pipette body 402. As shown in FIG. 5, the pipette body 402 includes a plunger or piston 502 that reciprocates within a piston chamber 504 defined by a piston housing 506 of the pipette body 402. The piston 502 includes an annular seal 508 that seals against a cylindrical sidewall 510 of the piston housing 506 to prevent fluid flow past the piston 502. Linear movement of the piston 502 within the piston chamber 504 generates pressure differentials that allow liquids to be aspirated into and dispensed from the pipette tip 404. In the example embodiment, the pipette body 402 also includes a piston guide 512, a piston mount 514, and a spring 516 connected between the piston guide 512 and the piston mount 514. The piston guide 512 engages a stem 518 of the piston 502 to maintain alignment of the piston 502 within the piston chamber 504. The piston guide 512 is connected to a first end 520 of the piston housing 506 by a suitable fastening mechanism, such as a threaded connection. The piston mount 514 is operatively connected to the piston 502 (e.g. via the piston stem 518), and is accessible from the exterior of the pipette body 402 to enable manipulation of the piston 502. The spring 516 is compressed between the piston mount 514 and the piston guide 512, and biases the piston mount 514 and the piston 502 towards a fully retracted position. Examples of commercially available pipette bodies suitable for use with the liquid dispensing apparatus 102 include, without limitation, the pipette body of an Eppendorf Reference® 2 manual pipette, sold by Eppendorf AG, Germany. The pipette tip 404 is removably connected to a second, lower end 522 of the piston housing 506, and defines an interior volume 408 that is in fluid communication with the piston chamber 504. The pipette tip 404 includes a first, connection end 410 connected to the lower end 522 of the piston housing 506, and a second end 412 distal from the first end 410 that defines an opening 414 through which liquids are aspirated and/or dispensed. In the example embodiment, the pipette tip 404 is conically shaped such that the cross-section of the pipette tip 404 gradually and continuously decreases from the first end 410 to the second end 412 of the pipette tip 404. In some embodiments, the pipette tip 404 is designed to be disposed following one or more liquid transfer processes described herein. The pipette body 402 and/or the pipette tip 404 may be interchanged with other pipette bodies and pipette tips to vary the dispensing capacity of the liquid dispensing apparatus 102. In some embodiments, for example, the capacities of pipette body 402 and the pipette tip 404 are such that the liquid dispensing apparatus 102 can be set (e.g., using the controller 106) to accurately deliver (i.e., aspirate and/or dispense with a single piston stroke) liquid volumes from 100 μL up to 5,000 μL, such as from 500 μL up to 5,000 μL. In other embodiments, the capacities of pipette body 402 and the pipette tip 404 are such that the liquid dispensing apparatus 102 can be set to deliver liquid volumes as low as 0.1 μL and as high as 10 mL. The linear actuator 406 is connected to the pipette body 402, and is configured to control linear displacement of the piston 502 within the piston chamber 504 to control a volume of liquid aspirated and/or dispensed by pipette assembly 202. In the example embodiment, the linear actuator 406 includes a third stepper motor 416 that drives a rod 602 (shown in FIG. 6) along a linear path via a linkage mechanism (not shown) that converts rotational motion of the motor into linear motion. Suitable linkage mechanisms for connecting the third stepper motor 416 to the rod 602 include, for example and without limitation, rack and pinion assemblies and leadscrew assemblies. The third stepper motor 416 may have any suitable stepper motor configuration that enables the liquid dispensing apparatus 102 to function as described herein. For example, the third stepper motor 416 may have the same configuration as the first stepper motor 110 and/or the second stepper motor 112. The linear actuator 406 is operatively connected to the piston 502 by the rod 602. In particular, as shown in FIG. 6, the rod 602 protrudes from a lower end 604 of the linear actuator 406 and engages the piston mount 514. Operation of the third stepper motor 416 causes the rod 602 to move linearly upward or downward, and to linearly displace the piston mount 514 and the piston 502. This in turn causes the piston 502 to create a positive or negative pressure differential within the piston chamber 504, allowing liquids to be dispensed or aspirated, respectively, through the pipette tip opening 414. In the illustrated embodiment, the pipette assembly 202 also includes a connector 606 to connect the pipette body 402 with the linear actuator 406, and to align the piston 502 of the pipette body 402 with the linear actuator rod 602. The connector 606 has a cylindrical opening 608 defined therein that extends from a top of the connector 606 to a bottom of the connector 606. A portion of the linear actuator 406 is positioned within the cylindrical opening 608 at the top of the connector 606 and is secured to the connector 606 by suitable connection means. In the illustrated embodiment, the connector 606 is connected to the linear actuator 406 by a pair of diametrically opposed set screws 610 that extend through the sides of the connector 606 and engage the linear actuator 406 within the cylindrical opening 608. A portion of the pipette body 402 is received in the cylindrical opening 608 at the bottom of the connector 606 to connect the pipette body 402 to the connector 606. In some embodiments, the pipette body 402 is removably connected to the connector 606 such that the pipette body 402 can be interchanged with other pipette bodies having different configurations (e.g., different volumes). Suitable means for removably connecting the pipette body 402 to the connector 606 include, for example and without limitation, one or more detents, a bayonet connection, and a threaded connection. In the illustrated embodiment, the pipette assembly 202 also includes a pipette tip retaining clip 418 (shown in FIG. 4) to maintain the connection between the pipette body 402 and the pipette tip 404. The retaining clip 418 inhibits the pipette tip 404 from being unintentionally dislodged or otherwise disconnected from the pipette body 402 during operation. In the example embodiment, the retaining clip 418 is positioned at the second end 522 of the piston housing 506 (shown in FIG. 5), and applies a clamping force to the pipette tip 404 against the second end 522 of the piston housing 506. Referring to FIGS. 7 and 8, the source vial 206 and the destination vial 208 are housed within a source vial assembly 702 and a destination vial assembly 704, respectively. As shown in FIG. 8, the source vial assembly 702 includes the source vial 206, a vial holder 802, a liquid retaining disc 804, and a radiation shield 806 that at least partially encloses the source vial 206, the vial holder 802, and the liquid retaining disc 804. In the example embodiment, the source vial 206 is constructed of glass. In other embodiments, the source vial 206 may be constructed from materials other than glass. Further, in the example embodiment, the source vial 206 is a conical-bottom vial. That is, the source vial 206 has a conically-shaped bottom 810. The use of vials having conically-shaped bottoms facilitates transferring liquids through the liquid dispensing apparatus 102 by facilitating removal of nearly all liquid from the vial while preventing occlusion of the pipette tip opening 414 during aspiration. The vial holder 802 defines a vial chamber 812 in which the source vial 206 is positioned. The vial holder 802 has a leak-tight construction to prevent or inhibit liquids from leaking out of the vial holder 802. Suitable materials from which the vial holder 802 may be constructed include, for example and without limitation, polyactic acid (PLA). In some embodiments, each vial holder 802 is designed for use with a specific vial such that the bottom 810 of the vial, when positioned within the vial holder 802, is positioned at a predetermined height relative to another component of the liquid dispensing apparatus 102, such as the base 212 or the pipette tip 404. In one embodiment, for example, each vial holder 802 includes a spacer 814 that positions the bottom of the vial at a predetermined height relative to the pipette tip 404 when the pipette tip 404 is in a fully lowered position. Further, in some embodiments, the vials 206, 208 and/or the vial holders 802 may be interchanged with other vials and vial holders to maintain the bottom of the vials at a consistent height. The liquid retaining disc 804 is connected proximate the top of the vial holder 802, and extends radially outward therefrom to an annular lip 816. The lip 816 extends upward to retain liquids on the liquid retaining disc 804. In some embodiments, the liquid retaining disc 804 is configured to contain up to 5 mL of liquid. Suitable materials from which the liquid retaining disc 804 may be constructed include, for example and without limitation, polyurethane. The radiation shield 806 is constructed of suitable radiation shielding material, including, for example and without limitation, lead, depleted uranium, and tungsten. In the example embodiment, the radiation shield 806 is a cylinder having a closed bottom end and an open top end in which the vial holder 802 and liquid retaining disc 804 are received. In other embodiments, the radiation shield 806 may have any suitable configuration that enables the liquid dispensing apparatus 102 to function as described herein. Although not shown in FIG. 8, the destination vial assembly 704 has the same construction and configuration as the source vial assembly 702. For example, the destination vial assembly 704 includes a vial (i.e., the destination vial 208), a vial holder, a liquid retaining disc, and a radiation shield. In the illustrated embodiment, the source vial assembly 702 and the destination vial assembly 704 are secured to the support frame 204 by a bracket or brace 706. In the example embodiment, each of the source vial assembly 702 and the destination vial assembly 704 are secured to the base 212 of the support frame 204 by a respective brace 706. In the example embodiment, each brace 706 includes a band 708 shaped complementary to the outer contour of a corresponding vial assembly. The band 708 includes a pin collar 710 disposed at each end of the band 708. Each pin collar 710 is sized and shaped to receive a pin 712 therein. The band 708 has a suitable length and shape such that the pin collars 710 are positioned relative to one another so as to simultaneously align with respective pin holes 714 defined by the support frame base 212. A pin 712 extends through each collar 710 and its associated pin hole 714 to secure the brace 706 to the support frame 204, and thereby secure a corresponding vial assembly to the support frame 204. In some embodiments, the band 708 has a rigid construction such that the band 708 maintains its general shape in the absence of an applied force. That is, the band 708 does not bow or sag under its own weight. In some embodiments, for example, the band 708 is constructed from metal or rigid plastic. Further, in some embodiments, components of the brace 706 may be formed as a single, integral unit. In some embodiments, for example, the band 708, pin collars 710, and pins 712 are formed as a single, integral unit (e.g., from welded stainless steel). In the example embodiment, the support frame 204 also includes a pipette tip receptacle 716 connected to the base 212. In example embodiment, the pipette tip receptacle 716 is a 20 mL syringe barrel removably connected to the base 212. In some embodiments, the pipette tip receptacle 716 may be sealed (e.g., with a luer plug) to retain liquid spills. Further, in some embodiments, the pipette tip 404 may be positioned within the pipette tip receptacle 716 between liquid transferring processes. In the example embodiment, the pipette tip receptacle 716 is located between the source vial 206 and the destination vial 208, and extends at least partially into a hole 718 defined by the base 212. The pipette tip receptacle 716 may be removed from the hole 718 and discarded using, for example, telemanipulators. Further, in some embodiments, the pipette tip 404 may be ejected (i.e., disconnected) from the pipette body 402 into the pipette tip receptacle 716 to facilitate disposal of the pipette tip 404 while controlling contamination that might be present on the pipette tip exterior. In some embodiments, the liquid dispensing apparatus 102 does not include any (i.e., is free of) radiation-sensitive electronics. In some embodiments, for example, each of the stepper motors 110, 112, 416 contains no electronics, and control is achieved by adjusting stator current via the controller 106 (e.g., via stepper drives) located outside the radiation containment chamber 104. In such embodiments, the stepper motors 110, 112, 416 do not include any position sensors or feedback sensors or devices, such as encoders, that are sensitive to radiation. As used herein, the term radiation-sensitive electronics refers to electronic components, such as sensors, that are susceptible to damage, reduced performance, or reduced functionality resulting from exposure to nuclear radiation (e.g., gamma and beta radiation). Examples of radiation-sensitive electronics include, but are not limited to, encoders, optical sensors (e.g., fiber optic sensors, reflective light sensors, photo-optic sensors), proximity sensors (e.g., capacitive or inductive based sensors), and processors. The absence of radiation-sensitive electronics, such as those used in other liquid handling systems, facilitates operation of the liquid dispensing apparatus 102 in high radiation environments. In some embodiments, for example, the liquid dispensing apparatus 102 is capable of operating for extended periods of time in a high radiation environment, such as within the radiation containment chamber 104. In some embodiments, for example, the liquid dispensing apparatus 102 is capable of operating within a high radiation area and even a very high radiation area for at least 10 cumulative hours, for at least 20 cumulative hours, for at least 30 cumulative hours, for at least 50 cumulative hours, for at least 100 cumulative hours, for at least 200 cumulative hours, for at least 300 cumulative hours, for at least 500 cumulative hours, and even up to 1,000 cumulative hours. As used herein, the term “high radiation area” means an area in which radiation levels from radiation sources external to an individual's body would result in an individual receiving a dose equivalent in excess of 0.1 rem (1 mSv) in 1 hour at 30 centimeters from the radiation source or 30 centimeters from any surface that the radiation penetrates. As used herein, the term “very high radiation area” means an area in which radiation levels from radiation sources external to an individual's body would result in an individual receiving an absorbed dose in excess of 500 rads (5 grays) in 1 hour at 1 meter from a radiation source or 1 meter from any surface that the radiation penetrates. Further, in some embodiments, the liquid dispensing apparatus 102 is capable of operating in a radioactive field equal to 5 million millirem per hour (mrem/hr) for at least 10 cumulative hours, for at least 20 cumulative hours, for at least 30 cumulative hours, for at least 50 cumulative hours, for at least 100 cumulative hours, for at least 200 cumulative hours, for at least 300 cumulative hours, for at least 500 cumulative hours, and even up to 1,000 cumulative hours. In some embodiments, the liquid dispensing apparatus 102 includes one or more mechanical switches that provide an indication of the position of the pipette assembly 202 relative to the support frame 204. Suitable mechanical switches include, for example and without limitation, electrical contacts that complete or close an electrical circuit when the contacts are engaged. In this embodiment, the liquid dispensing apparatus 102 includes a first mechanical switch 420 (shown in FIG. 4) and a second mechanical switch 228 (shown in FIG. 2). The first mechanical switch 420 is located proximate the linear actuator 406, and is activated or switched (e.g., electrical contacts are engaged with one another) when the linear actuator rod 602 is in a fully retracted position. The second mechanical switch 228 is located between the support arm 216 and the top of the column 214, and diametrically opposite to the pipette tip receptacle 716. The second mechanical switch 228 is activated or switched when the pipette assembly 202 is in a fully lowered position. The first and second mechanical switches 420 and 228 are connected to the controller 106. The controller 106 may determine whether one or more operations should or should not be performed based on the status of the first mechanical switch 420 and/or the second mechanical switch 228. For example, the controller 106 may determine that an aspiration or dispense operation should not be performed when the second mechanical switch 228 is activated. As noted above, the controller 106 is connected to the liquid dispensing apparatus 102 to control operation thereof. In particular, the controller 106 is connected to each of the first stepper motor 110, the second stepper motor 112, and the third stepper motor 416 to output control signals to each of the motors and control operation thereof. In some embodiments, the controller 106 includes or is connected to the stepper motors 110, 112, 416 through one or more suitable stepper drivers configured to output and/or regulate the supply of current supplied to the stepper motors. In some embodiments, for example, control signals generated by the controller 106 are translated or converted into a suitable current waveform by a stepper driver to achieve a desired number of motor steps. FIG. 9 is a block diagram of the controller 106. The controller 106 includes at least one memory device 910 and a processor 915 that is coupled to the memory device 910 for executing instructions. In this embodiment, executable instructions are stored in the memory device 910, and the controller 106 performs one or more operations described herein by programming the processor 915. For example, the processor 915 may be programmed by encoding an operation as one or more executable instructions and by providing the executable instructions in the memory device 910. The processor 915 may include one or more processing units (e.g., in a multi-core configuration). Further, the processor 915 may be implemented using one or more heterogeneous processor systems in which a main processor is present with secondary processors on a single chip. As another illustrative example, the processor 915 may be a symmetric multi-processor system containing multiple processors of the same type. Further, the processor 915 may be implemented using any suitable programmable circuit including one or more systems and microcontrollers, microprocessors, programmable logic controllers (PLCs), reduced instruction set circuits (RISC), application specific integrated circuits (ASIC), programmable logic circuits, field programmable gate arrays (FPGA), and any other circuit capable of executing the functions described herein. In this embodiment, the processor 915 controls operation of liquid dispensing apparatus 102 by outputting control signals to each of the first, second, and third stepper motors 110, 112, 416. The memory device 910 is one or more devices that enable information such as executable instructions and/or other data to be stored and retrieved. The memory device 910 may include one or more computer readable media, such as, without limitation, dynamic random access memory (DRAM), static random access memory (SRAM), a solid state disk, and/or a hard disk. The memory device 910 may be configured to store, without limitation, application source code, application object code, source code portions of interest, object code portions of interest, configuration data, execution events and/or any other type of data. In this embodiment, the controller 106 includes a presentation interface 920 that is connected to the processor 915. The presentation interface 920 presents information, such as application source code and/or execution events, to a user 925, such as a technician or operator. For example, the presentation interface 920 may include a display adapter (not shown) that may be coupled to a display device, such as a cathode ray tube (CRT), a liquid crystal display (LCD), an organic LED (OLED) display, and/or an “electronic ink” display. The presentation interface 920 may include one or more display devices. In this embodiment, the presentation interface 920 displays a graphical user interface for receiving information from the user 925, such as a target dispense or transfer volume. The controller 106 also includes a user input interface 930 in this embodiment. The user input interface 930 is connected to the processor 915 and receives input from the user 925. The user input interface 930 may include, for example, a keyboard, a pointing device, a mouse, a stylus, a touch sensitive panel (e.g., a touch pad or a touch screen), a gyroscope, an accelerometer, a position detector, and/or an audio user input interface. A single component, such as a touch screen, may function as both a display device of the presentation interface 920 and the user input interface 930. In this embodiment, the user input interface 930 receives an input associated with a target transfer volume of liquid to be transferred from the source vial 206 to the destination vial 208 including, for example and without limitation, a volume of liquid in milliliters. The presentation interface 920 and the user input interface 930 may be collectively referred to as an operator interface or a human-machine interface (HMI). In this embodiment, the controller 106 further includes a communication interface 935 connected to the processor 915. The communication interface 935 communicates with one or more remote devices, such as the liquid dispensing apparatus 102. In operation, the liquid dispensing apparatus 102 transfers radioactive liquid from the source vial 206 to the destination vial 208 in response to control signals received from the controller 106. Specifically, in this embodiment, the controller 106 (specifically, the processor 915) receives an input (e.g., from the user 925 via the user input interface 930) associated with a target transfer volume to be transferred from the source vial 206 to the destination vial 208. The controller 106 controls operation of the first stepper motor 110 and the second stepper motor 112 (e.g., by controlling the supply of current to the first and second stepper motors 110, 112) to position the pipette assembly 202 over the source vial 206, and to the lower the pipette assembly 202 such that the pipette tip 404 is submerged in radioactive liquid within the source vial 206. Specifically, in this embodiment, the controller 106 determines a number of steps by which each of the first stepper motor 110 and the second stepper motor 112 need to be rotated to position the pipette assembly 202 in a position in which the pipette tip 404 is submerged in radioactive liquid within the source vial 206, also referred to as an aspiration position. The controller 106 may determine the number of steps, for example, by determining a difference in height and rotational position between a current position of the pipette assembly 202 and the desired aspiration position. Based on the differences in height and rotational position, the controller 106 may determine the number of steps using look-up tables, formulas, algorithms, or other instructions (e.g., stored in the memory device 910) that correlate a motor step of the first stepper motor 110 to an incremental rotational distance, and a motor step of the second stepper motor 112 to an incremental vertical distance. In some embodiments, the controller 106 determines a difference in height and/or rotational position of the current position of the pipette assembly 202 and a desired position of the pipette assembly 202 (e.g., an aspiration or dispense position) by tracking or logging the position of the pipette assembly 202 based on previous control signals output to the first stepper motor 110, the second stepper motor 112, and/or the third stepper motor 416. Additionally, in this embodiment, the controller 106 outputs a control signal to each of the first stepper motor 110 and the second stepper motor 112 based on the determined number of steps. The control signal may be output as or converted to (e.g., by a stepper drive) a current waveform that energizes the windings of the stepper motors in a desired sequence and a desired number of times that corresponds to the determined number of steps. In response to the control signals, the first stepper motor 110 and the second stepper motor 112 rotate, thereby rotating and vertically displacing, respectively, the support arm 216 such that the pipette assembly 202 is positioned in the desired position. In this embodiment, the controller 106 also controls operation of the linear actuator 406 via the third stepper motor 416 (e.g., by controlling the supply of current to the third stepper motor 416) to control aspiration and dispensing operations. Specifically, in this embodiment, the controller 106 determines, based on an input associated with a target transfer volume, a number of steps by which the third stepper motor 416 needs to be rotated to displace the piston 502 a distance that results in the target transfer volume being aspirated and/or dispensed by the pipette assembly 202. The controller 106 (specifically, the processor 915) may determine the number of steps for the third stepper motor 416, for example, using look-up tables, formulas, algorithms, or other instructions (e.g., stored in the memory device 910) that correlate a number of steps of the third stepper motor 416 to a resulting piston displacement and/or a volume of liquid aspirated or dispensed by the pipette assembly 202. Additionally, in this embodiment, the controller 106 outputs a control signal to the third stepper motor 416 based on the determined number of steps. The control signal may be output as or converted to (e.g., by a stepper drive) a current waveform that energizes the windings of the third stepper motor 416 in a desired sequence and a desired number of times that corresponds to the determined number of steps. In response to the control signals, the third stepper motor 416 rotates, causing actuation of the linear actuator 406 and displacement of the rod 602 and the piston 502. Displacement of the piston 502 generates a positive or negative pressure differential within the piston chamber 504, resulting in liquid being aspirated or dispensed from the pipette tip 404. Following aspiration, the controller 106 controls operation of the first stepper motor 110, the second stepper motor 112, and the third stepper motor 416 to position the pipette assembly 202 over the destination vial 208 and dispense the target transfer volume into the destination vial 208. The controller 106 may control the first, second, and third stepper motors 110, 112, 416 in the same manner described above with reference to the aspiration procedure. In some embodiments, the pipette body 402 and/or the pipette tip 404 may exhibit a non-linear response or relationship between the number of steps by which the third stepper motor 416 is rotated and the volume of liquid aspirated or dispensed by the pipette assembly 202 over the full usable dispensing range (i.e., capacity) of the pipette assembly 202. In such embodiments, discrete volume ranges may be identified and stored in the controller 106 (specifically, in the memory device 910), and different factors, coefficients, formulas, and/or algorithms may be assigned to each range to facilitate determining the number of steps by which the third stepper motor 416 needs to be rotated to achieve target liquid volumes across the entire dispensing range of the pipette assembly 202. In some embodiments, for example, the controller 106 determines separate equations, such as linear equations, for discrete segments of a target dispense volume/motor steps curve. FIG. 10 is a plot of an example target transfer volume/motor steps curve 1002 for the pipette assembly 202. The curve 1002 illustrates an example relationship between the target transfer volume for the pipette assembly 202 and the corresponding number of steps for third stepper motor 416 needed to aspirate or dispense the target transfer volume. As shown in FIG. 10, the curve 1002 includes three discrete volume ranges: a first volume range 1004 from 0.1 to 0.3 mL, a second volume range 1006 from 0.3 mL to 1.0 mL, and a third volume range 1008 from 1.0 mL to 5.0 mL. The curve 1002 may be stored in the controller 106 (specifically, in the memory device 910), and/or the controller 106 (specifically, the processor 915) may determine different equations or algorithms for each of the volume ranges 1004, 1006, 1008 to determine the number of steps by which the third stepper motor 416 should be rotated. In this embodiment, for example, the controller 106 determines a different linear equation for each of the first volume range 1004, the second volume range 1006, and the third volume range 1008, and uses the linear equations in combination with an input target transfer volume to determine the number of steps by which the third stepper motor 416 should be rotated to achieve the target transfer volume. Accounting for the non-linear response of the pipette assembly 202 as described herein facilitates accurately aspirating and dispensing target transfer volumes over the full usable dispensing range (i.e., capacity) of the pipette assembly 202. In some embodiments, for example, the liquid dispensing apparatus 102 is capable of dispensing liquid with a single piston stroke over a range of 100 μL to 5,000 μL within +/−5.0% of a target dispense volume, within +/−3.0% of a target dispense volume, within +/−2.5% of a target dispense volume, within +/−2.0% of a target dispense volume, within +/−1.5% of a target dispense volume, and even within +/−1.0% of a target dispense volume. Additionally, in some embodiments, the liquid dispensing apparatus 102 is capable of dispensing liquid with a single piston stroke within +/−1.0% of a target volume over a range of 500 μL to 5,000 μL, over a range of 300 μL to 5,000 μL, over a range of 200 μL to 5,000 μL, and even over a range of 100 μL to 5,000 μL. In some embodiments, the controller 106 further controls the liquid dispensing apparatus 102 (e.g., by controlling the supply of current to each of the stepper motors 110, 112, 416) to reduce or minimize errors in liquid dispensing and facilitate more accurate, precise dispense volumes. In some embodiments, for example, the controller 106 controls the height of the pipette tip 404 relative to the bottom of the source vial 206 during aspiration to maintain spacing between the pipette tip 404 and the bottom of the source vial 206. This facilitates preventing occlusion of the pipette tip opening 414 during aspiration, which might otherwise result in errors in the volume of liquid aspirated. The controller 106 controls the height of the pipette tip 404 by controlling the supply of current to the second stepper motor 112, which adjusts the height of the support arm 216 and, consequently, the pipette assembly 202. Additionally, in some embodiments, the controller 106 controls the height of the pipette tip 404 to aspirate a target volume of liquid by performing a plurality of partial aspirations at different elevations or depths within the source vial 206. In one embodiment, for example, the controller is configured to control the second stepper motor 112 to position the pipette tip 404 at a first height, to control the third stepper motor 416 to displace the piston 502 and aspirate a first volume of radioactive liquid from the source vial 206 while the pipette tip 404 is positioned at the first height, to further control the second stepper motor 112 to position the pipette tip 404 at a second height lower than the first height, and to further control the third stepper motor 416 to displace the piston 502 and aspirate a second volume of radioactive liquid from the source vial 206 while the pipette tip 404 is positioned at the second height. Performing partial aspirations at multiple different heights or submersion depths within the source vial 206 facilitates preventing liquid overflows from the source vial 206 that might otherwise occur if the pipette tip 404 were moved directly to the bottom of the source vial 206 at the beginning of aspiration. Additionally, performing partial aspirations at different heights facilitates reducing or minimizing the amount of liquid forced into the pipette tip 404 during submersion by limiting the submersion depth of the pipette tip and the resulting pressure differential across the pipette tip opening 414. In some embodiments, the controller 106 also controls the aspiration rate of the pipette assembly 202 at a slow, steady aspiration rate to ensure the entire target volume is aspirated with minimal turbulence. For example, the controller 106 may control the rate of piston displacement during aspiration by controlling the supply of current to the third stepper motor 416, which controls the speed of the third stepper motor 416 and, consequently, the rate of piston displacement. In some embodiments, for example, the controller 106 controls the rate of piston displacement at a displacement rate of between 7 seconds to 10 seconds per full piston stroke. Additionally, in some embodiments, the controller 106 controls removal of the pipette tip 404 from the source vial 206 to reduce or minimize errors in liquid dispensing. In some embodiments, for example, the controller 106 maintains the pipette tip 404 within the source vial 206 for a predetermined or preset delay time following aspiration to ensure aspiration is complete prior to withdrawing the pipette tip 404 from the source vial 206. Suitable delay times following aspiration include, for example and without limitation 1 second, 2 seconds, 3 seconds, 5 seconds, and 10 seconds. In some embodiments, the controller 106 also controls the rate at which the pipette tip 404 is withdrawn from the liquid within the source vial 206 by controlling the supply of current to the second stepper motor 112. In some embodiments, for example, the controller 106 removes or withdraws the pipette tip 404 from the source vial 206 following aspiration at a rate of about 4 seconds from a fully lowered position to a fully raised position. Controlling the rate at which the pipette tip 404 is removed from the source vial liquid allows surface tension of the liquid to eliminate or reduce liquid pooling on the outside of the pipette tip 404, which might otherwise drip down and be dispensed with the liquid inside the pipette tip 404. In some embodiments, the controller 106 also controls insertion of the pipette tip 404 into the destination vial 208 to reduce or minimize errors in liquid dispensing. In some embodiments, for example, the controller 106 lowers the pipette tip 404 below the opening of the destination vial 208 prior to dispensing any liquid to prevent or inhibit liquid from being dispensed outside the destination vial 208. Additionally, in some embodiments, the controller 106 controls the piston displacement rate during liquid dispensing into the destination vial 208 to facilitate the use of surface tension to eliminate liquid pooling on the inside of the pipette tip 404 walls. Specifically, in some embodiments, the controller 106 decelerates the piston 502 near the end of a liquid dispensing process (e.g., by controlling the supply of current to the third stepper motor 416). Additionally, in some embodiments, if an incomplete dispense condition is detected, the controller 106 automatically flushes liquid within the pipette tip 404 back into the source vial 206, and then automatically wets the interior surface of the pipette tip 404 to eliminate interior surface drops that might otherwise increase subsequent dispensing error. Embodiments of the systems and methods described herein provide several advantages over known liquid handling systems. In particular, embodiments of the systems and methods facilitate accurately transferring precise amounts of radioactive liquid between a source vial and a destination vial, while avoiding or minimizing operator exposure to nuclear radiation. For example, embodiments of the systems and methods described herein use a pipette assembly to transfer liquid between the source vial and the destination vial. Use of a pipette assembly to aspirate and dispense liquids provides several advantages over other liquid transfer mechanisms, such as peristaltic, syringe, or rotary piston pumps. For example, virtually no liquid is lost in the pipetting process because there are no tubes or other lines in which the liquid may otherwise collect or be trapped. Additionally, no pump calibration is required, thereby avoiding time, effort, and measurement instrumentation complexity (e.g. weight measurement) associated with peristaltic pump calibration. Further, unlike rotary piston pumps, the pipette tips used in pipette assemblies can be pre-sterilized and disposed with each use to minimize contamination and cross-contamination between batches. Additionally, embodiments of the liquid dispensing apparatus described herein facilitate the use of pipette assemblies to transfer liquids, while avoiding drawbacks commonly associated with the use of pipettes, such as variation in operator pipetting technique, which can adversely affect dispensing precision and accuracy. Examples of variation in pipetting technique include pipette tip angle, pipette aspiration volume, speed of pipette aspiration, duration of pause after aspiration, speed of pipette withdrawal from liquid, dispense speed, and completion of blow-out without tip ejection. Additionally, manual dispensing requires physical access to the equipment, which may result in operator exposure to radioactive environments. Experimental testing was conducted on a liquid dispensing apparatus having substantially the same configuration as the liquid dispensing apparatus 102. The experimental testing included five different test runs. In each test run, 20 different target dispense volumes were assigned to the liquid dispensing apparatus ranging from 0.1 mL to 5.0 mL. Under the control of a controller, such as the controller 106, the liquid dispensing apparatus transferred 20 different liquid volumes from a source vial to a destination volume based on the target dispense volumes. The first test run was conducted without wetting the inside of the pipette tip. In the second test run, the interior of the pipette tip was wetted prior to liquid being transferred with the pipette tip. Following the second test run, the pipette tip was replaced with another pipette tip having substantially the same configuration. The pipette tip was not wetted in the third test run, and the pipette tip was wetted in the fourth test run. Following the fourth test run, the pipette body was replaced with a pipette body having substantially the same configuration. The fifth test run was then carried out with the new pipette body by wetting the pipette tip prior to liquid being transferred with the pipette tip. Each test run was performed using the pipette body from an Eppendorf Reference® 2 manual pipette and a pipette tip having a capacity rating of 0.5 mL to 5.0 mL. Following completion of the test runs, the actual dispense volumes were compared to the target dispense volumes, and percentage differences were calculated for each target dispense volume. The results of test runs 1-4 are listed below in Table 1, and the results of test run 5 are listed below in Table 2. TABLE 1Results of Test runs 1-4Target DispenseFirstSecondThirdFourthVolume (mL)Test Run% DiffTest Run% DiffTest Run% DiffTest Run% Diff0.1000.1022.00%0.1033.00%0.1011.00%0.099−1.00%0.2000.2000.00%0.20.00%0.197−1.50%0.20.00%0.3000.3020.67%0.3031.00%0.3010.33%0.295−1.67%0.4000.4020.50%0.398−0.50%0.394−1.50%0.399−0.25%0.5000.496−0.80%0.5010.20%0.495−1.00%0.497−0.60%0.6000.592−1.33%0.597−0.50%0.596−0.67%0.596−0.67%0.7500.745−0.67%0.745−0.67%0.745−0.67%0.745−0.67%0.9000.896−0.44%0.898−0.22%0.896−0.44%0.897−0.33%1.0000.999−0.10%0.994−0.60%0.99−1.00%0.997−0.30%1.1001.089−1.00%1.092−0.73%1.095−0.45%1.098−0.18%1.2501.243−0.56%1.248−0.16%1.24−0.80%1.247−0.24%1.5001.489−0.73%1.496−0.27%1.491−0.60%1.492−0.53%2.0001.992−0.40%1.997−0.15%1.991−0.45%1.992−0.40%3.0002.983−0.57%2.985−0.50%2.984−0.53%2.987−0.43%4.0003.979−0.52%3.985−0.38%3.977−0.58%3.988−0.30%4.2504.230−0.47%4.231−0.45%4.235−0.35%4.233−0.40%4.5004.484−0.36%4.491−0.20%4.483−0.38%4.489−0.24%4.7504.726−0.51%4.736−0.29%4.727−0.48%4.733−0.36%4.9004.888−0.24%4.894−0.12%4.882−0.37%4.886−0.29%5.0004.980−0.40%4.987−0.26%4.967−0.66%4.984−0.32% TABLE 2Results of Test Run 5Target Dispense Volume (mL)Fifth Test Run% Diff0.1000.098−2.00%0.2000.2021.00%0.3000.3031.00%0.4000.4020.50%0.5000.491−1.80%0.6000.599−0.17%0.7500.7520.27%0.9000.897−0.33%1.0000.999−0.10%1.1001.1010.09%1.2501.2510.08%1.5001.493−0.47%2.0001.992−0.40%3.0002.984−0.53%4.0003.987−0.32%4.2504.242−0.19%4.5004.499−0.02%4.7504.735−0.32%4.9004.898−0.04%5.0004.998−0.04% As shown in the above tables, the liquid dispensing apparatus maintained a dispense tolerance better than +/−5.0% over the entire dispense range of 0.1 mL to 5.0 mL for each of the test runs. Additionally, the liquid dispensing apparatus maintained a dispense tolerance better than +/−2.0% over the dispense range from 0.5 mL to 5.0 mL for each of the test runs. Additionally, in at least two of the test runs (test runs three and four), the liquid dispensing apparatus maintained a dispense tolerance better than +/−2.0% over the entire dispense range of 0.1 mL to 5.0 mL. Dispense accuracy and precision were not substantially affected by wetting, changes in pipette tips, or changes in pipette bodies. When introducing elements of the present invention or the embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. |
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abstract | A method for the separation of the rare-earth fission product poisons comprising providing a spent nuclear fuel. The spent nuclear fuel comprises UO2 and rare-earth oxides, preferably Sm, Gd, Nd, Eu oxides, with other elements depending on the fuel composition. Preferably, the provided nuclear fuel is a powder, preferably formed by crushing the nuclear fuel or using one or more oxidation-reduction cycles. A compound comprising Th or Zr, preferably metal, is provided. The provided nuclear fuel is mixed with the Th or Zr, thereby creating a mixture. The mixture is then heated to a temperature sufficient to reduce the UO2 in the nuclear fuel, preferably to at least to 850° C. for Th and up to 600° C. for Zr. Rare-earth metals are then extracted to form the heated mixture thereby producing a treated nuclear fuel. The treated nuclear fuel comprises the provided nuclear fuel having a significant reduction in rare-earths. |
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047055774 | claims | 1. Process for producing a plate-shaped high power nuclear fuel element containing lowenrichment uranium as fissionable material, the low-enrichment uranium containing 5 to 20 percent by weight uranium.sup.235, the fuel element essentially comprising a UAl.sub.4 plate provided with an aluminum sheath of an Al alloy and impurities inherent in the manufacturing process, comprising the following steps: (a) intimately mixing (1) a powder of low enrichment uranium metal or uranium compound U.sub.6 Fe, with the uranium in the metal or compound being 5 to 20 percent by weight U.sup.235, the powder having a particle size in the range from 0.1.mu. to 90.mu. with (2) aluminum powder having a particle size in the range from 0.1.mu. to 100.mu. in a weight ratio range of uranium to aluminum between 1.1 U:1 Al and 2.2 U:1 Al; (b) prepressing the mixture in step a) at a pressure in the range from 300 MPa to 500 MPa at room temperature to form a plate; (c) inserting said plate into an Al picture frame or a picture frame of an Al alloy and welding the plate to said frame in vacuo or inert gas argon; (d) rolling the picture frame in three roll passes, a reduction in thickness of about 1 mm occurring in each of the first and second passes, and a reduction in thickness by about 15% occurring during the third pass, at a temperature of 800.degree..+-.25.degree. K.; and (e) inserting the plate in the frame after the third roll pass between two Mo sheets, one Mo sheet being at the underside of the plate, inserting the framed plate together with the Mo sheets in a clamping device, and subsequently heat treating the clamped plate at 800.degree..+-.25.degree. K. for a duration of at least 75 hours in order to form a plate consisting essentially of UAl.sub.4 and other uranium-aluminum compounds and containing at least 50 weight % UAl.sub.4 based on the weight of the plate. 2. Process according to claim 1, wherein in step (a) the low enrichment uranium is in the form of the uranium compound U.sub.6 Fe. |
060841494 | claims | 1. A method for treating hazardous substances and removing such hazardous substances generated during incineration at high temperature and under high pressure comprising the steps of: applying high frequency waves for melting and thermal drying said hazardous substances resulting in a residual material; applying agents to said residual material after said high-frequency melting treatment, said agents being selected from the group consisting of 2-naphthol-4-sulfonic acid salt, derivatives of the above-mentioned naphthol, and 1-naphthylamine-4-sulfonic acid. 2. The method of claim 1 wherein specific metals and metal oxides are used after said high-frequency melting for treating gas released thereby and are selected from the group consisting of magnesium, fine powder of pure iron and zeolite. |
039309410 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows part of a cladding tube 1 of a fuel element 2. A plurality of fin rows 3 are provided on the outer tube surface at right angles to the axial direction 4 of the fuel element 2. Each fin row 3 (of which only two are designated) with the reference numeral is constituted of single fins 5. The individual fins 5 are circular segments of a square, rectangular or trapezoidal cross section or have a rhombic shape, respectively. The individual fins 5 of single fin rows 3 are offset relative to each other. This means that any gap between two fins of a given fin row is flanked on both sides by two fins belonging to the two fin rows that are immediately adjacent the given fin row. In this manner meandering passages are obtained. The fins of every other row are always located on the same generatrix of the fuel element 2. The distance x (e.g., x = 1.6 mm) between the fin rows 3 is twice the fin height h (h= 0.8 mm), so that the unobstructed clearance between two fins 5 that are in alignment parallel to the axis of the tube 1 is four times the height h. The width b of the fins 5 in this embodiment is 3 mm. The thickness d of the fins 5 is measured parallel to the axis of the cladding tube 1. FIG. 2 is a sectional view of the fuel element 2 showing the individual fins 5 of one of fins. The clearance e between the fins 5 is 2.9 mm in this example, thus slightly smaller than the width b of the fins, which is 3.0 mm in this embodiment. FIG. 3 is a diagram illustrating the roughness parameter R (h.sup..sup.+) as a function of the so-called dimensionless roughness height h.sup..sup.+ = h/d.sub.h .sup.. Re .sup.. .sqroot. f/2. Two curves 6 and 7 are plotted, curve 7 showing a measured result with offset roughnesses and curve 6 indicating a measured result with the values of p/h = 9.9 and h/b = 1.68. Evidently, much smaller values of R (h.sup..sup.+) are achieved with offset roughnesses, as is shown in curve 7. FIG. 4 shows a diagram illustrating the ratios St.sub.R /St.sub.o as a function of f.sub.R /f.sub.o of the offset fins according to curve 8 as compared with circumferential fins with different cross sections. These are curves 9, 10, 11, 12 and with the respective values of p/h = 9.9; 10.0; 47.2; 8.0 and 4.1 and the values for h/b = 1.68; 1.0; 1.7; 2.45 and 1.55. These measurements were performed in a rod bundle with the values of p.sub.R /d = 1.4; Re = 10.sup.5 ; f.sub.o = 4.55 .times. 10.sup..sup.-3 and St.sub.o = 2.8 .times. .sup..sup.-.sup.3. It is evident that the shape of roughness according to the present invention greatly improves the heat transfer coefficient. FIG. 5 is a diagram illustrating the ratio (St.sub.R /St.sub.o).sup.3 /f.sub.R /f.sub.o as a function of f.sub.R /f.sub.o. Again, a rod bundle with the same data as those shown in FIG. 4 has been used. Curve 14 again shows measured results with the offset roughness elements according to the present invention, while curves 15, 16, 17, 18 and 19 indicate the parameters p/h and h/b as curves 9 to 13 according to FIG. 4. This makes it particularly clear that the shape of roughness according to the present invention furnishes optimum results. The rod bundle investigated with the fuel element 1 was fabricated by the spark erosion technique. However, it can also be made as an opposed thread by cutting in such a way that a shape of roughness can be generated in which the webs have not a rectangular but a rhombic shape. |
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abstract | To provide a method of controlling a turbine equipment and a turbine equipment capable of carrying out a starting operation of controlling a load applied to a speed reducing portion while complying with a restriction imposed on an apparatus provided at a turbine equipment. The invention is characterized in including a speed accelerating step (S1) of increasing a revolution number by driving to rotate a compressing portion and a turbine portion by a motor by way of a speed reducing portion, a load detecting step (S2) of detecting a load applied to the speed reducing portion by a load detecting portion, and a bypass flow rate controlling step (S3) of increasing a flow rate of a working fluid bypassed from a delivery side to a suction side of the compressing portion when an absolute value of the detected load is equal to or smaller than an absolute value of a predetermined value and reducing the flow rate of the bypassed working fluid when equal to or larger than the absolute value of the predetermined value. |
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claims | 1. An X-ray irradiator for providing a uniform dose of X-ray beam irradiation, said irradiator comprising in combination; a) a chamber for mounting items to be irradiated; b) an X-ray tube mounted to irradiate said items; and c) a collar of a low Z high density material mounted adjacent said chamber so as to reflect X-rays from said tube onto said items. 2. An X-ray irradiator for providing X-ray beams to irradiate items, said irradiator comprising in combination, a) a chamber for containing said items; b) first and second X-ray tubes mounted to provide irradiation to opposite surfaces of said items; and c) a collar of low Z high density material mounted around a cannister to reflect X-rays from said tubes to said items; d) the irradiation of said tubes, and the reflected irradiation from said collar effectively combining to provide total uniform irradiation to said items. 3. An X-ray irradiator as in claim 2 wherein said X-ray tubes each provide a beam of radiation to fully cover the area of said chamber. claim 2 4. An X-ray irradiator for providing a uniform dose of X-ray beam irradiation to blood product transfusion bags, said irradiator comprising in combination, a) a chamber for mounting said transfusion bags; b) X-ray tubes mounted on opposed sides of said chamber; said tubes providing X-ray beams of radiation to said bags from opposite sides of said bags; c) said tubes each providing radiation at a same selected energy level to said bags to thereby provide a total radiation energy to said bags which is substantially uniform throughout each of said bags; and d) a collar of a low Z high density material mounted around a cannister to further reflect X-rays onto said bags. 5. An X-ray irradiator as in claim 4 wherein a cannister is mounted in said chamber, said cannister being dimensioned to contain said bags, and said cannister being of a plastic material which absorbs minimal X-ray energy. claim 4 6. A system as in claim 4 wherein said X-ray tubes are each mounted on opposite sides of said chamber and the same distance from the respective facing surface of said chamber. claim 4 7. A system as in claim 5 wherein up to three bags can be mounted in said cannister providing a large increase in the efficiency of said system. claim 5 8. A system as in claim 5 wherein said chamber and said cannister are both circular and said cannister is mounted within said chamber to have its exterior circular surface in abutting relation within the inner circular surface of said chamber. claim 5 9. A method for providing a uniform dose of X-ray beam irradiation to blood products transfusion bags, said method comprising in combination, a) mounting said bags in an irradiation chamber; b) irradiating said bags from opposite sides of said bags at a same selected energy level to said bags to thereby provide a radiation energy to said bags which is substantially uniform throughout said bags; and d) reflecting said X-rays from a low Z high density material mounted around a cannister and directing said X-rays onto said bags, thereby operatively combining the X-ray energies from said opposite sides and the reflected X-ray energy into a total effective irradiation for said bags. |
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047708417 | abstract | Disclosed are methods and apparatus for the control of dynamic systems, more particularly complex dynamic systems and especially those systems exhibiting minimum phase behavior. The method utilizes observer theory to estimate the state variables of the system. Based in part upon the estimated values of the state variables, a pseudo or compensated output for the system is generated. This compensated output represents the steady state asymptote of the actual system output without the unstable or transient system responses. The actual outputs are then controlled by controlling the compensated output.. According to another embodiment, a bounded output may also be generated from the state variable estimates. This bounded output represents the minimum and/or maximum excursion that the actual output takes in its approach to the steady state value represented by the compensated output. This bounded output is then used to control the system so as to prevent the actual output from crossing any predetermined system limits. |
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043953816 | summary | BACKGROUND OF THE INVENTION In industrial technology, there are certain cases where a confinement building is required in order to isolate, from the outside world, certain installations which are dangerous owing to the fact that they are liable to emit pollutants, especially radioactive products, which, to comply with the safety standards, must not simply be discharged into the atmosphere. This is particularly true of nuclear reactors, to which reference will be made exclusively hereinafter, although it should be realised that this example is entirely non-restrictive and that this invention covers confinement enclosure in general for all installations capable of releasing dangerous products either temporarily or permanently. Nuclear reactors are generally sited inside confinement enclosures designed to maintain a satisfactory level of leaktightness against radioactive products liable to escape from the primary circuit of the reactor during certain incidents, especially incidents which put the interior of the enclosure under pressure. In some constructions, this leaktight seal is obtained, in particular, by means of an impermeable membrane applied to the inside of the reinforced or prestressed concrete wall; in other constructions, it has been proposed to construct the enclosure with no membrane but with a double wall, with an intermediate space between the two walls serving to collect the gases, liquids and aerosols liable to pass through the inner or outer walls at a moderate rate of flow; the two walls are independent over their full height above ground level. This arrangement ensures excellent confinement in the case of the accidents for which it is designed, but on the one hand it requires the use of special equipment at the moment when an accident occurs, which means that stringent precautions must be taken to ensure reliability, and on the other hand the arrangement does not make the best use of the materials as regards resistance to extreme loads. In fact, if the internal pressure increases to the point of causing cracking or fracture of the inner enclosure, the outer enclosure may be subjected to the full pressure within the confinement enclosure, and it will be appreciated that the resistance of the two independent walls in series is finally only as great as that of the stronger wall. For dynamic impact due to seismic shocks or impact from projectiles originating from inside or outside, better resistance is again generally obtained by using the entire mass of materials used in the construction of the walls to form a single thick enclosure. From this point of view, confinement enclosures have already been proposed consisting of a single wall of reinforced concrete, more particularly prestressed concrete, characterised by the existence of a drainage network within the wall itself; this is the case particularly in Luxembourg patent 33.557 amd U.S. Pat. Nos. 3,320,969 and 3,778,948. In these known solutions, this drainage network usually consists of a set of holes in the form of parallel tubular channels produced during the casting of the concrete, with their openings arranged close enough together to ensure that any accidental crack will necessarily meet one of the channels or its porous surroundings, if any, thus enabling the pollutant phase to be drained off accordingly. The holes in the form of tubular channels are theoretically arranged in random directions inside the body of the wall, even though, for practical reasons, it is more convenient to make them vertical or horizontal; these two latter systems may, moreover, coexist, possibly comprising junction points. Sometimes there is advantageously provided within the wall of the enclosure a special permeable layer, e.g. of porous concrete, in which the drainage channels are located, thus increasing the efficiency of the arrangement; occasionally, also, inclusions of permeable strips consisting of tubes filled with gravel which connect the drainage channels of one of the horizontal or vertical systems to one another are provided during the casting of the concrete. The known drainage networks provided in confinement enclosures are generally linked to a system for sucking escaped substances through external filters; the fluid circulating in the drainage network is usually gaseous and both the internal, possibly pollutant, gaseous phase and the outer air which would tend to pass through the wall of the enclosure which is assumed to be cracked following an accident occurring either internally or externally are drained into the said network, which has been put under vacuum by means of an extractor fan and a filter located outside the enclosure. This gaseous phase is filtered and then ejected into the outer atmosphere. However, in all these known systems, it is necessary to use suction systems or mechanical vacuum systems on which the safety of the installation depends, in the last analysis, and which cannot therefore ensure total reliability. BRIEF SUMMARY OF THE INVENTION This invention relates to a confinement enclosure provided with a drainage network which obviates the disadvantage mentioned above, whilst combining the advantages of the solidity of a single thick wall with those of a means of collecting leakages in an intermediate layer situated inside the body of the wall. This confinement enclosure is essentially characterised in that its drainage network is under pressure and that it can function to the limit entirely passively without the need for any external energy source, thus making it remarkably reliable in the case of accidents. The confinement enclosure according to the invention may take the form of one of two main distinct embodiments. In the first embodiment, the drainage network is simply connected to passive filters located within the enclosure; in this way, using very simple, safe means, adequate protection is obtained against the statistically fairly common event of an accident resulting in pollution of the inside of the enclosure accompanied by excess pressure therein: this excess pressure is then sufficient to cause the major portion of the polluted internal gaseous phase to escape outside through the filters and drainage system; in other words, the installation itself forces all the dangerous gaseous fluid liable to escape to pass through the passive filters, without the need for any pumping or suction apparatus. In the second embodiment of the drainage network, the fluid circulating therein is a liquid under hydrostatic pressure, usually water. This water under pressure thus constitutes an actual damming layer in the body of the wall of the enclosure and flows both inwards and outwards in the case of severe cracking of the wall, thus preventing the dangerous internal medium from escaping. In practice, this result is obtained by dividing the drainage network into a plurality of independent zones or sub-groups each of which is connected to at least one water reservoir located at a higher level than that of the corresponding zone; in this case, one particular zone may be constituted by the frame of the confinement wall itself. |
047730870 | summary | BACKGROUND AND SUMMARY OF THE INVENTION The invention is in the field of x-ray machines, such as those used for chest radiography and shadowgraphic radiography of other parts of a patient's body or of an inanimate object. Its main object is to improve image quality, for example by ensuring that just the right amount of radiation is used to accomplish a desired image characteristic, be it a desired image density or contrast or signal-to-noise (S/N) ratio or some other characteristic. For example, in imaging both lungs and mediastinum in a single picture, just the right amount of radiation can be delivered to achieve the required diagnostic content. The receptor can be conventional x-ray film or it can be some other receptor, such as a digital or a digitized receptor. The advantages of the invention include, in the case of film receptors, overcoming sensitometric limitations and, in the case of both film and digital receptors, control of S/N degradation from transmitted primary field variations, control of both the noise degradation and the nonlinear effects of scattered radiation, regaining low spatial frequency information lost initially by equalization, and reduction of exposure period and scanning artifacts. Shadowgraphic radiography has been widely used for many decades, and has long-recognized inherent limitations. For example, chest radiography is probably the most frequently performed x-ray examination in a typical radiology department, and tens of millions of chest x-rays are taken annually in this country alone. However, in spite of its clinical importance it is far from being a technically consistent procedure and is subject to large variations in image quality, sometimes with imperfections in clinical results. One reason is that the posterior-anterior and lateral projections of the chest pose significant challenges. The presence of scattered radiation reduces film contrast, even when anti-scatter grids are used or an effort is made to reduce the scatter component by the use of air gap techniques or sophisticated anti-scatter grid designs. Scanning slit devices have also been used, bringing about significant contrast improvement in imaging the head, abdomen, chest and breast. Another inherent limitation in conventional chest radiography arises from the wide variation in patient x-ray thickness (meaning attenuation along a given raypath) between the lung field and the relatively thick mediastinal, retrocardiac and diaphragmatic portions, which produces a large variation in receptor exposure. One aspect of this is sensitometric, in that it may not be possible to achieve proper density or contrast at the portions of the image which may be of interest. Another deals with S/N ratios, in that the radiation reaching some portions of the receptor may be too little, in which case the S/N ratio can be too low, and that reaching other portions may be more than enough, in which case the patient would be exposed to more radiation than needed. Efforts to improve the exposure range of radiographic film with wide latitude films offer a wider exposure range, however at the expense of contrast in the lung fields, and with reduced signal-to-noise ratio over the thicker, underexposed portions. One approach to rectify these exposure problems is through the use of portal x-ray compensation filters shaped to match the contour of the lung fields and preferentially attenuate the pre-patient x-ray beam over the lungs, resulting in a more uniform film exposure. The obvious limitation is the difficulty of designing a filter to match the large variations in lung contour and patient thickness expected in a typical patient population. The so-called unsharp mask technique addresses this limitation by using a tailored optical filter for each patient, to be used in the film cassette during exposure. While these techniques can produce images with improved contrast uniformity, they can be time consuming and prone to misregistration artifacts in their clinial application. Digital radiography using arrays of detectors having wide dynamic range represents another imaging technique which offers good scatter rejection, image contrast control, and a potential for image data manipulation using temporal subtraction and multiple imaging techniques. However, in the systems known to the inventor herein these improvements are gained at the expense of spatial resolution, x-ray tube heat loading increase and an increased system complexity and cost. Significant improvements have been made through the use of scanning equalization radiography using both prepatient and post-patient collimation to reduce scatter and a feedback technique to modulate a scanned x-ray beam. See, e.g.: Plewes, D. B., Computer-Assisted Exposure In Scanned Film Radiography, Proceedings International Workshop On Physics And Engineering In Medical Imaging, March 1982, pp. 79-85; Wandtke, J. C. and Plewes, D. B., Improved Chest Radiography With Equalization, RadioGraphics, Vol. 3, No. 1, March 1983, pp. 141-154; Plewes, D. B., A Scanning System For Chest Radiography With Regional Exposure Control: Theoretical Considerations, Med. Phys. 10(5), September/October 1983, pp. 646-654; Plewes, D. B. and Vogelstein, E., A Scanning System For Chest Radiography With Regional Exposure Control: Practical Implementation, Med. Phys. 10(5), September/October 1983, pp. 655-663; Plewes, D. B. and Vogelstein, E., Exposure Artifacts In Raster Scanned Equalization Radiography, Med. Phys. 11(2), March/April 1984, pp. 158-165. The contents of said publications are hereby incorporated by reference in the specification as though fully set forth herein. Despite the significant progress made in the past in improving image quality, it is believed that room remains for improvement. In an effort to meet at least some aspects of this need, one of the features of this invention is to reduce signal-to-noise ratio variations in the x-ray image. One way of doing this in accordance with the invention is by measuring both post-patient scatter and post-patient primary radiation and using the results in a feedback loop controlling the pre-patient x-ray beam. One benefit is that the patient tends to be exposed only to the amount of radiation needed to produce an image of a given quality. Another is an overall improvement in image quality. It has been proposed in the past, in the context of CT scanners, to ensure adequate signal-to-noise ratio by concurrently monitoring the integrated radiation from all of the detectors for a given x-ray pulse and ending the pulse only when all detectors have received at least a threshold quantity of radiation believed sufficient for an adequate signal-to-noise ratio. See U.S. Pat. No. 4,260,894. One of the many differences between this prior art proposal and this aspect of the invention disclosed and claimed here is that in the invention here each spot of the x-ray receptor should receive only the radiation sufficient for a selected signal-to-noise ratio, while in the prior art proposal it is only ensured that each CT detector would receive no less than the amount of radiation needed for a satisfactory signal-to-noise ratio (but in fact many detectors are likely to receive more, and thus expose the patient to more radiation than needed). Other proposals for modulating the pulse width of the pre-patient x-ray beam to achieve uniform film darkening are discussed in the publications authored or co-authored by Dr. Plewes, the inventor herein, cited above. Another feature of the invention disclosed and claimed here is improving image quality by dynamically modulating each of the pre-patient intensity and pre-patient hardness of the x-ray beam on the basis of intermittent post-patient beam measurements made at selected positions of the beam relative to the patient and at a selected low beam intensity. It is generally desirable to use high KV (harder) radiation to reduce the dynamic range requirements on the receptor but to use low KV (softer) radiation in certain parts of the body (e.g., the lungs) to increase contrast. It is also generally desirable to use high intensity radiation through highly attenuating parts of the body (e.g., bone), so as to get sufficient radiation to the receptor, but low intensity through low attenuation parts of the body (e.g., lungs and soft tissue) to increase contrast. In this aspect of the invention disclosed and claimed herein, a very short pulse of low energy radiation and a very short pulse of high energy radiation are used at each selected beam position while scanning the patient. The relative amounts of bone and soft tissue along each beam are determined from those short pulses, and the best combination of intensity and hardness for that beam position is found and the x-ray tube is energized accordingly. It has been proposed in the prior art (see U.S. Pat. No. 4,032,784) to control both the x-ray tube current and voltage in a raster scan x-ray machine so as to improve the picture and reduce radiation exposure. The patent proposes dynamically varying beam intensity to have high intensity through highly attenuating parts of the body and low intensity otherwise, and concurrently dynamically varying KV to have harder (shorter wavelength) radiation through high attenuation parts of the body and softer x-rays otherwise. However, the prior art patent proposes deriving the control signal from the output of the detector in the normal scanning operation rather than from short preliminary bursts of radiation. Another, similar prior art proposal is U.S. Pat. No. 2,962,594. Another nonlimiting aspect of the invention relates to ensuring constant line velocity when raster scanning a patient through the use of a special, curved slit, rotating pre-patient collimator. While it is possible to use linearly moving collimator apertures (or an x-ray tube) to ensure constant line velocity (and thus facilitate modulation techniques) it is mechanically more efficient to use a rotating collimating aperture. This, however, introduces variation in the beam velocity within a raster scan line and complicates beam modulation. A single x-ray beam can be raster scanned in overlapping scan lines to produce an x-ray image. This, however, must take several seconds, which can lead to motion artifacts. In order to reduce scanning time, and hence motion artifacts, another feature of this invention is to use a segmented fan beam scanned across the patient in a direction transverse to the plane of the fan. In accordance with a nonlimiting aspect of the invention, the fan segments are individually dynamically modulated to improve the image and reduce patient dosage. While there have been prior art proposals for using fans segmented by pre-patient or post-patient collimators, or both, as for example in the so-called localizer mode of CT scanners, and shaped collimators can be used to vary the pre-patient attenuation as between fan segments, the invention disclosed and claimed herein adds the benefit of dynamically and individually modulating the segments through a feedback loop. There are at least two general application of equalization at this time, namely to x-ray film (nonlinear systems) and to wider dynamic range receptors, such as digital or digitized receptors. Especially for wider dynamic range receptors, the invention offers benefits such as control of signal/noise degradations from transmitted primary field variations, control of both the noise degradation and the nonlinear effects of scattered radiation, regaining low spatial frequency information lost by equalization and reduction of exposure period and of scanning artifacts. With respect to control of signal/noise degradations from transmitted primary field variations, the objective is to maintain an approximately constant noise structure throughout the image, which implies approximately constant receptor exposure. Both primary and scattered radiation are important, and thus in accordance with the invention control can be maintained of both the noise degradation and the nonlinear effects of scattered radiation. While it is possible to use very narrow beam widths (e.g., 1 mm or less) to reduce scatter contamination, this may not be clinically practical because it places a severe load on the X-ray tube, as most of the radiation is blocked by the collimator. A more practical approach is to use a scanning beam which is a few cm wide, which cuts the X-ray tube load requirements but also increases scatter. Beam equalization in accordance with the invention offers two benefits in this respect. First, since the primary radiation levels at the receptor can be maintained approximately constant, the scatter/primary ratios will tend to be nearly constant. This can allow a measurement of scatter by looking beside the primary beam to be a good approximation of the full scatter profile. Thus, in accordance with the invention the scatter field can be measured while scanning to generate an approximate scatter field map which later can be subtracted from the initial image. This can make the scatter data more suitable for dual energy imaging and image processing techniques, which tend to be particularly sensitive to scatter contamination. This approach can allow a good approximation of the correction needed to account for the nonlinear effects of scatter, although the noise due to scatter would still be present. A second aspect of this approach is to use the scatter measurements made during the scan to adjust the x-ray tube output to compensate for the noise degradation from scatter. With respect to regaining low spatial frequency information lost by equalization, it should be clear that one of the reasons equalization achieves improved images is that it rejects low frequency subject contrast. For example, the contrast between the mediastinum and the lung field is nearly eliminated by equalization. While this is useful in many, if not most, clinical situations, it can be troublesome in those where disease is manifest by low contrast variations that are diffuse and without sharp edges. Pneumothorax is a case in point. In this regard, the digital application of equalization can be particularly useful, because a record can be made during the scan of the spatial distribution of patient exposure. This information can then be used to correct the recorded data set to regain the lost low frequency information that would have been present in the uncorrected, equalized image. A simpler but less accurate way to do this is to normalize the measurements made for a one dimensional scan of the x-ray beam across the patient. If a fan beam is used, it is preferable to orient it vertically, i.e., to have its plane parallel to the mediastinum. Another way is to normalize the measurements for a two-dimensional scan. Here the two-dimensional distribution can maintain more accurately the noise uniformity over the image. With respect to reduction of exposure period and scanning artifacts, a digital receptor can reduce the need for overlapping the scanning beams and thereby significantly reduce the exposure period. This can be done without very precise mechanical scan line registration, which is essential with film in order to prevent scan line artifacts, because with a digital receptor the line spacing can be made periodic and the scan line artifacts can be numerically filtered out. Thus, in the case of digital receptors the features of the invention discussed above can lead to equalized images which are substantially free from scanning artifacts, can be produced in short exposure periods (e.g., of the order of 35-50 mS) to reduce motion blurring, can exhibit all desired low frequency structures and this can be applied to both one-dimensional and two-dimensional equalization systems, can have an approximately constant SN ratio, and can be free of significant scatter contamination. These and other aspects of the invention are explained in greater detail in connection with the figures described below. |
063079178 | claims | 1. A soller slit comprising a plurality of metal foils and a plurality of spacers, the plurality of said spacers being laminated alternatively with the plurality of said metal foils to support one end portions of said metal foils with a space between adjacent metal foils. the other end portions of said metal foils being opened. said soller slit includes a plurality of metal foils and a plurality of spacers, the plurality of said spacers being laminated alternatively with the plurality of said metal foils to support one end portions of said metal foils with a space between adjacent metal foils, the other end portions of said metal foils being opened, and wherein said the other end portions of said metal foils are arranged in contact with or in the vicinity of a surface of said specimen. said soller slit includes a plurality of metal foils and a plurality of spacers, the plurality of said spacers being laminated alternatively with the plurality of said metal foils to support one end portions of said metal foils with a space between adjacent metal foils, the other end portions of said metal foils being opened, and wherein said the other end portions of said metal foils are arranged in contact with or in the vicinity of a surface of said monochromator. 2. A soller slit as claimed in claim 1, wherein each said spacer has a center portion protruding forward and both side portions being behind. 3. A soller slit as claimed in claim 2, wherein said center portion of said spacer takes in the form of an apex of a mountain. 4. An X-ray apparatus comprising an X-ray source for generating X-rays, an X-ray detector for detecting X-rays diffracted by a specimen after being generated from said X-ray source, and a soller slit, wherein 5. An X-ray apparatus comprising an X-ray source for generating X-rays, an X-ray detector for detecting X-rays diffracted by a specimen after being generated from said X-ray source, a monochromator for making X-rays generated by said X-ray source or X-rays diffracted by said specimen monochromatic, and a soller slit, wherein |
048790907 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, as previously noted, FIGS. 1 and 2 are schematic views of vanes. FIG. 1 is a prior art type of vane 1 with a weld nugget 2 and opening 3. Arrows illustrate the flow obtained. FIG. 2 illustrates the flow obtained when the same test is performed on a vane 4 without a weld nugget or opening, but with the weld nugget 5 "shielded" by the full vane 4 and by the thickness of the strips 6 and 7. The weld nugget 5 lies substantially within the transverse confines of the strips 6 and 7 in the case of a grid structure provided in accordance with the principles of the invention. FIG. 3 shows a nuclear reactor fuel assembly 10 comprising an array of fuel rods 12 held in spaced relationship with each other by grids 14 spaced along the fuel assembly length. Fuel assembly 10 includes, extending longitudinally therethrough, guide tubes 16. Control rods 50, in the form of neutron absorber elements, move within guide tubes 16; such control rods serving as a means for regulating the thermal output power of the reactor. The fuel assembly also includes a plurality of fuel rods 12. Each fuel rod 12 comprises a hermetically sealed elongated tube, known in the art as the cladding, which contains a fissionable fuel material, such as uranium, in the form of pellets. As may best be seen from FIG. 3, the individual fuel rods 12 are supported in the fuel assembly by means of a plurality of spacer grids 14, such that an upwardly flowing liquid coolant may pass along the fuel rods thus preventing overheating and possible melting through of the cladding. In the manner well-known in the art, the coolant, after passing through the reactor core and being heated through contact with the fuel rods, will be delivered to a heat exchanger and the heat extracted from the circulating coolant will be employed to generate steam for driving a turbine. As noted, and as may be seen from FIG. 3, the positioning and retention of the fuel rods in fuel assembly 10 is accomplished through use of a plurality of the spacer grids 14. All or several of the spacer grids 14 may be of the improved design depicted in FIGS. 4-12. It is to be noted that due to differential expansions which will not be described herein, when the reactor is running hot, the spacing between the fuel assemblies will be larger than under cold conditions. The aforementioned spacing includes the clearance left between fuel assemblies to accommodate thermal and irradiation induced growth. Under a seismic load, the fuel assemblies could, with this spacing, move about and impact against each other and against the walls of the core shroud. Such impacts could, if sufficiently strong, cause the permanent distortion of the fuel assembly spacer grids of the prior art, could also cause bending of the guide tubes and could result in damage to the cladding of individual fuel assemblies through varying the coolant flow characteristics of the fuel assembly or otherwise. Additionally, seismically induced stresses could exceed the elastic limit of the integral grid assembly springs of the prior art fuel assemblies, this being particularly true for those springs in the outer rows of the fuel assemblies. With reference now jointly to FIGS. 4-12, each of the zircaloy spacer grids 14 support and align the fuel rods 12 through the establishment of six points of contact therewith. Thus, as depicted in FIG. 4, each of the fuel rods 12 is contacted by a pair of generally transversely oriented springs 20,22 which respectively urge the fuel rod against oppositely disposed stop members 20' and 22' in each sector or cell of the grid. The stop members 20' and 22' will customarily be provided in pairs with the individual stops of each pair being respectively vertically above and below a plane through the point of contact of the springs 20,22 with the cladding of fuel rod 12. Thus, considering fuel rod 12, this element is urged by means of springs 20 and 22 against pairs of arches 20' and 22' formed respectively on upper strip members 46 and lower strip members 46'. The spacer grid 14 is assembled by interweaving of the internal strip members 46 and 46'. The ends of the strip members 46, 46' may be engaged in slots 30 provided in the spacer grid perimeter strip 32. Welds are formed at all points of the intersection within the spacer grid and the ends of the strip members 46,46' are either welded into the slots 30 in perimeter strip 32 or are butt welded to the perimeter strip. When compared to the prior art, the spacer grid 14 of the present invention has a longer internal strip to perimeter strip weld because the slots 30 run the full transverse width of the perimeter strip 32 exterior plane and thus provide greater strength. Referring to FIG. 5, perimeter strip 32 is provided with cutouts or "windows" 34 in regions corresponding to alternate sectors of the outer row of the spacer grid. These "windows" which are of smaller dimensions when compared to the windows of the prior art perimeter strips, such as shown in U.S. Pat. No. 3,607,640, enhance grid strength while maintaining coolant flow to the outer row of fuel rods. The perimeter strip 32 is also stamped so as to form, in sectors which alternate with the sectors provided with "windows" 34, inwardly extending integral springs 36. As may be seen from FIG. 4 by reference to fuel rod 12, each of the springs 36 cooperates with an internal spring 36' on a grid internal strip member to support and align a fuel rod of the outer row of the fuel assembly. The perimeter strip 32 may also be provided, above and below each of the windows 34, with inwardly extending dimples 38. Dimples 38, in the manner known in the art, enhance the rigidity of perimeter strip 32. Restated, the presence of dimples 38 increases the resistance of strip 32 to bending in response to a force component directed along the length of the perimeter strip. Additionally, as may be seen in the case of fuel rod 12, dimples 38 function as stops or arches against which the fuel rod will be urged by the internal springs 20 and 22, integral with the strip members 46 and 46'. The dimples 38 must be provided above and below each of the perimeter strip "windows" 34. Additional parts of dimples 39 may also be provided in the perimeter strip sectors which have the integral springs 36 formed therein. In the interest of facilitating understanding of the drawing, the dimples 39 have not been shown in FIG. 3. When employed, dimples 39 will not extend into the fuel assembly sector as far as the fuel rod contacting springs 36. The dimples 39 will thus function as backup arches to prevent the elastic limit of springs 36 from being exceeded should the fuel assembly be subjected to vibration in excess of that encountered during normal operation. The pairs of dimples 39, if provided, will also enhance the rigidity of perimeter strip 32. The perimeter strip 32 is also provided, above and below each of the windows 34, with an inwardly ridged horizontal rib 40, as may best be seen from joint consideration of FIGS. 5 and 6. Ribs 40, in the manner known in the art, also enhance the rigidity of the perimeter strip 32. The presence of the ribs 40 increases the section modulus of the perimeter strip and results in increased resistance to bending compared to a flat non-ribbed perimeter strip or a strip provided with a plurality of irregularities. The valleys or slots defined by tabs 44 of the serrated upper and lower edges of perimeter strip 32 function as partial lead-in tabs for the fuel rods 12 which facilitate their insertion; the bases of the slots are aligned with the center of the windows 34 and springs 36 in the perimeter strip 32. The tabs 44 function as anti-hangup devices; these tabs 44 preventing the hanging or interference between adjacent fuel assemblies during refueling. Interior strips 46,46' are provided with large unslotted sections which are kept free of large windows 34 or cutouts 33 and only contain one arch 20' or 22' in the section as can best be seen in FIGS. 7 and 8. The wide unslotted section with a minimum of windows 34 or cutouts 33 provides a larger load path than grids of prior art, which increases the resistance to bending of the strip and thus the strength of the grid. Strip slots 48 may also be tapered at the ends to facilitate the welding at the intermediate locations. The presence of intermediate welds increases the resistance to bending the strip and thus the strength of the grid. To summarize the significant features of the spacer grid of FIGS. 4-12, the perimeter strip 32 is, when compared to the prior art, wider and contains stiffening dimples 38,39. The perimeter strip 32 of the spacer grid is also characterized by inwardly ridged horizontal upper and lower ribs 40 which also add to the stiffness of the strip. The connection between the perimeter strip 32 and the internal strip members 46,46' is defined by a weld seam of increased length along slot 30, when compared to prior art spacer grids, and the serrated upper and lower edges of the perimeter strip define anti-hangup tabs 44 and fuel rod lead-in features. Interior strips 46,46' have been provided with large unslotted sections which have been kept free of windows and any unnecessary cutouts. Also, intermediate welds may be associated with the grid interior strip to increase its rigidity and strength. Tests have shown that the spacer grid of FIGS. 4-12 exhibits an improvement in impact strength and this increase in impact strength has been achieved with essentially no degradation in performance, perturbation in enrichment, or added resistance to coolant flow, i.e., no increase in pressure drop across the fuel assembly and with little change in the cost of fabrication of the grid. In assembling a fuel assembly, an array of control rod guide tubes 16, FIG. 3, having control rods 50 adapted for slidable longitudinal movement therein, are positioned to extend axially through selected sectors in the grids 14 and are thereupon welded to grid tabs or strip walls to form the fuel assembly skeleton structure. Opposite ends of the guide tubes 16 are attached to top and bottom end fittings 52 and 54 using a unique threaded fastener. Reference to the plan view of FIG. 4 illustrates the relative disposition of fuel rods 12 and guide tubes 16 and, particularly, how the fuel rods are held in a relatively immovable position in each grid. Each fuel rod 12 is biased by a spring 20 and 22 into engagement with arches 20' and 22' formed on the grid strip walls, and, as shown, project inwardly into each sector or cell 24. This construction serves to preclude axial movement of the fuel rods 12 in their grids 14 during the time the fuel assembly is being moved or transferred from one location to another. The arches are impressed in the strips 46,46' and dimples may be impressed in the peripheral strip 32 during the strip punching and stamping operation. After the appropriate grid strips 46,46' and 32 are assembled into the form of a grid 14, the arches project into each sector, except the sectors having control rod guide tubes 16, from two adjacent walls as shown in FIGS. 4 and 12. As shown in FIG. 12, the intersecting strips 46,46' are welded together at each junction with the weld nugget being designated 26. At each intersecting joint of the strips where a mixing vane is desired, there is provided a solid mixing vane 28 containing a longitudinally disposed slot 48. These mixing vanes are disposed so as to provide the desired directional flow of the fluid coolant as explained heretofore. Each vane shields a small opening or window 35 which, according to the preferred embodiment, is formed under the bottom end in each vane and directly above and adjacent to the junction of the intersecting strips. While the windows 35 are shown as oval, other shapes and configurations, such as rectangular, semi-circular, square, etc. can be employed. It is also possible to locate the window 35 and weld nugget 26 at different elevations within the grid 14. The function of the window 35 in each case is to create material and provide clearance for welding the strips 46,6' together. The placement of the weld 26, shielded by the vane 28, substantially eliminates flow separation on the downstream side of the mixing vane. This results in an improvement of the vane's fluid mixing capability between subchannels and rod heat transfer ability downstream of the vanes. The intersecting joints are formed in the usual manner by providing strips 46,46' with complementary slots 48 which are oriented as shown in FIGS. 7-11 for engagement. Slots 48 may be tapered at their ends if intermediate welds are required for additional grid strength. The vane strips 46,46' are provided with an integrally formed vane 28. The vane strips 46,46' have formed therewith in the area where the window 35 is to be provided, a consumable weld tab 60,60' complementary to the shape of the window. The complementary spacer strip 46,46' is provided at its edge with a consumable weld tab 60 similar to consumable weld tab 60', only being unslotted which comprises a continuation of the slot 48 continuation line by virtue of the orientation of the consumable weld tab directly over the slot 48. These strips, when intersected as illustrated in FIG. 10, have their tabs similarly intersected. These tabs are made of a material such as zircaloy or Inconel which is consumed during the welding of the joints. The consumable weld tabs 60,60',62,62' are dissolved to form the weld nugget 26 as best illustrated in FIG. 11. The consumable weld tabs are integral with the intersecting strips 46,46' which are made of the same material. By shielding the upper grid intersect welds 26 by the novel vane design, its reactor performance has been increased. FIGS. 1 and 2 show two different vane designs in operation. FIG. 2 illustrates the flow patterns seen when the shielded vane is employed. Flow separation on the downstream side of the mixing vane is minimized, thus improving the fluid mixing and rod heat transfer capability of the vanes. These conditions would include all anticipated flows during normal and transient core operations. By eliminating or at least reducing fluid separation, the pressure losses of the grid spacer 14 which are normally attributable to fluid friction and acceleration can be reduced, the directional movement of the fluid from one subchannel to another is improved, and the flow pattern generated by the vanes is more effective in cooling the rods. With the present invention, the fluid streamlines on the downstream surface of the mixing vane will assume a trajectory which is similar in many ways to a frictionless flow pattern. This advantage can be seen by looking at FIG. 1 which illustrates a typical prior art mixing vane which has a window at the spacer strip intersection joint. As shown, the flow streamlines have pressure differentials which result from acceleration differences between the flow on the upstream side, downstream side, and around the weld nugget thereby causing flow separation on the downstream side of the vane. This in turn reduces the extent of fluid directional change on the downstream side which is desired for purposes of obtaining uniform cooling of the fuel rods and subchannel mixing. It will be appreciated from the foregoing description that a novel and improved nuclear fuel grid spacer 14 for a nuclear fuel reactor has been disclosed and enjoys significant advantages over conventional spacers as discussed heretofore. |
047566566 | claims | 1. Sectional apparatus for remotely handling a device in an irradiated underwater environment, said apparatus comprising: an elongated structure including one or more elongated structural sections; each of said sections carrying a control line segment, each of said sections including first and second coupling means respectively mounted at opposite ends thereof, all of said first coupling means being substantially identical to one another, all of said second coupling means being substantially identical to one another, each of said first coupling means being mateable and connectable with each of said second coupling means for interconnecting said sections and the control line segments thereof in end-to-end relationship to form said structure with said control line segments cooperating to form a control line, said second coupling means at one end of said structure being connectable to the associated device for support thereof and for connecting said control line thereto; and support means including said second coupling means connected to said first coupling means at the other end of said structure, said support means including means for connecting said control line to associated control means for controlling the operation of the device. 2. The sectional apparatus of claim 1, wherein each of said structural sections is tubular in shape. 3. The sectional apparatus of claim 2, wherein each of said control line segments is disposed within the corresponding tubular section. 4. The sectional apparatus of claim 1, wherein said structure includes sections of different lengths. 5. The sectional apparatus of claim 1, wherein said support means is adapted to be suspended from an associated support mechanism. 6. The sectional apparatus of claim 1, wherein each of said control line segments comprises a hydraulic fluid conduit. 7. The sectional apparatus of claim 1, wherein each of said sections includes two of said control line segments arranged in parallel relationship. 8. Sectional apparatus for remotely handling a device in an irradiated underwater environment, said apparatus comprising: an elongated structure including one or more elongated structural sections each having first and second attachment flanges respectively fixed to the opposite ends thereof, each of said sections including first and second coupling means respectively mounted on said first and second attachment flanges, each of said first coupling means including an internally threaded opening in said first attachment flange, each of said second coupling means including a bolt carried by said second attachment flange and extending through an opening therein, said bolt being reciprocatively movable axially between a coupling position projecting through and outwardly beyond said second attachment flange and a retracted position wherein no part thereof projects outwardly beyond said second attachment flange, said bolt in the coupling position thereof being adapted for threaded engagement in said opening in said first attachment flange of an adjacent structural section for interconnecting said sections in end-to-end relationship to form said structure, and bias means resiliently urging said bolt toward the retracted position thereof; said second coupling means at one end of said structure being connectable to the associated device for support thereof; and support means including said second coupling means connected to said first coupling means at the other end of said structure. 9. The sectional apparatus of claim 8, wherein each of said second coupling means includes two of said bolts and each of said first coupling means includes two of said internally threaded openings for respectively threadedly receiving said bolts. 10. The sectional apparatus of claim 8, wherein each of said structural sections further comprises retaining means for limiting movement of said bolt toward the retracted position thereof. 11. The sectional apparatus of claim 8, wherein said bias means comprises a helical compression spring disposed coaxially with said bolt. 12. The sectional apparatus of claim 8, wherein each of said structural sections further comprises guide means for guiding movement of adjacent sections accurately into position for engagement of said bolt in said internally threaded opening. 13. The sectional apparatus of claim 12, wherein said guide means comprises guide pins projecting from each of said first attachment flanges and guide holes formed in each of said second attachment flanges for respectively receiving said guide pins. 14. The sectional apparatus of claim 13, wherein said guide holes and said guide pins are arranged asymmetrically for cooperation in only one orientation. 15. Sectional apparatus for remotely handling a device in an irradiated underwater environment, said apparatus comprising: an elongated structure including one or more elongated tubular sections; each of said sections carrying a control line segment, each of said sections having first and second attachment flanges respectively fixed to the opposite ends thereof, each of said sections including first and second coupling means respectively mounted on said first and second attachment flanges, each of said first coupling means including an internally threaded opening in said first attachment flange, each of said second coupling means including a bolt carried by said second attachment flange and extending through an opening therein, said bolt being movable axially between a coupling position projecting through and outwardly beyond said second attachment flange and a retracted position wherein no part thereof projects outwardly beyond said second attachment flange, said bolt in the coupling position thereof being adapted for threaded engagement in said opening in said first attachment flange of an adjacent structural section for interconnecting said sections in end-to-end relationship to form said structure, and bias means resiliently urging said bolt toward the retracted position thereof; each of said control line segments including first and second connecting means respectively fixed to the opposite ends thereof, all of said first connecting means being substantially identical to one another, all of said second connecting means being substantially identical to one another, each of said first connecting means being mateable and connectable with each of said second connecting means for cooperation to form a control line when said tubular sections are interconnected; said second coupling means and said second connecting means at one end of said structure being connectable to the associated device for support thereof and for connecting said control line thereto; and support means including said second coupling means connected to said first coupling means at the other end of said structure, said support means including means for connecting said control line to associated control means for controlling the operation of the device. 16. The sectional apparatus of claim 15, wherein each of said control line segments comprises a hydraulic fluid conduit. 17. The sectional apparatus of claim 15, wherein said first and second connecting means respectively comprise male and female quick-connect/disconnect fittings. 18. The sectional apparatus of claim 17, wherein each of said fittings includes a normally-closed valve adapted to be opened upon interconnection with an associated fitting. 19. The sectional apparatus of claim 15, wherein each of said tubular sections further comprises means for supporting and positioning said control line segment in said tubular section. 20. The sectional apparatus of claim 15, wherein each of said tubular sections has a plurality of openings therein to permit the flow of water therethrough. |
description | X-rays are commonly used in medical and dental imaging techniques for examining living things, as well as in internal examination of objects in materials analysis and other fields. X-rays are commonly passed through the object to be imaged, such as a person or a metal casting, and the X-rays that are not absorbed and pass through the object are recorded on a medium, such as a photographic film or a semiconductor detector. X-rays generally travel in straight lines directly between an X-ray source, through the object to be imaged, and to the detector. However, the clarity and resolution of the image may be degraded by X-rays that have a distorted or bent path, due to being scattered or deflected away from the usual straight path rather than simply being absorbed, for example, being scattered by a bone. In this case any particular portion of the X-ray detector will record some X-rays that have not travelled to the detector in a straight line, which will represent a source of ‘noise’, degrading the signal to noise ratio (S/N) of the image. The ‘noise’ may reduce the sharpness of the image and result in an image that does not provide a clear view of the features to be imaged. A method of reducing the number of X-rays that do not travel directly from the X-ray source to the detector includes the use of thin sheets of an X-ray opaque material such as lead, separated by sheets of an X-ray transparent (also referred to as X-ray lucent) material such as aluminum, to form a structure similar to a Venetian Blind. This structure reduces the number of X-rays that travel to the detector with greater than a specific blocking angle to the vertical lead sheets, where the blocking angle is determined by a ratio between the height (or depth D) of the vertical lead sheets and the separation (L) between the vertical sheets (i.e., an L/D ratio). The thickness of the lead sheets must also be great enough to block X-rays of the energy level being used. It is to be understood that since the lead/aluminum sheet method uses lead sheets to form a linear array, the blocking angle is only applicable in the direction perpendicular to the linear array, and that it would require a second such linear array placed on top of the first, and rotated ninety degrees relative to the first linear array, to form a grid pattern to obtain a general X-ray anti-scatter device. In general, the grid is placed somewhere between the object to be examined and the detector. Unfortunately, there are deficiencies with the known methods of reducing the incidence angle of X-rays and blocking X-rays that have been scattered. These deficiencies include excess weight and cost, decreased durability, increased X-ray dose, and the formation of image artifacts on the detectors due to the anti-scatter grid itself blocking X-rays. For example, in order to obtain a L/D ratio sufficient to block most off-axis X-rays using the lead and aluminum sheet structure discussed above, the height of the lead sheets may need to be fifty times the distance between adjacent lead sheets. Such a structure is difficult to fabricate and greatly increases the weight of the X-ray anti-scatter grid needed to reduce the number of non-vertical X-rays reaching the detector and improving image contrast. An X-ray anti-scatter device that addresses the problems of the prior art includes an X-ray transparent dielectric material having a set of X-ray opaque tubes, where each of the X-ray opaque tubes has an axial orientation, an outside width and an inside width. In an embodiment the wall thickness of the X-ray opaque tubes is selected to obtain what is known as an X-ray open area ratio of greater than 80%. In an embodiment inside width or diameter of the X-ray opaque tubes and the length of the tubes, as determined by the thickness of the X-ray transparent dielectric material, results in a tube length to width ratio of greater than 100/1, which results in excellent blocking of off-axis X-rays. In an embodiment the X-ray transparent dielectric material is formed of borosilicate glass, which is inexpensive and easy to form into thin strong tubes, and the X-ray opaque tubes are formed of tungsten, which has excellent X-ray stopping power, with the tungsten as a layer inside a hollow capillary tube extending the length of the tube. In an embodiment each X-ray opaque tube is directed towards a point a selected distance away from the dielectric layer with either a curved surface or with a flat plane surface. In an embodiment the dielectric material is formed by a set of connected straight hollow open ended tubes, each tube including a layer of X-ray opaque material covering an inside surface. A method of forming an X-ray anti-scatter device may include forming a block having a desired shape, such as a rectangular solid, from a set of connected parallel straight hollow capillary tubes made of an X-ray transparent dielectric material, such as glass or plastic. One embodiment forms the block by heat drawing glass tubes into thin walled narrow diameter capillary tubes, and then heat fusing the capillary tubes together in the desired shape. Ensuring that the ends of the capillary tubes are open, and forming a layer of an X-ray opaque material on the inside surface of each one of the capillary tubes. In an embodiment the X-ray opaque layer may be formed by alternating layers of alumina and tungsten, and the overall composition of the X-ray opaque layer may be varied from the bottom to the top by changing the relative thickness of the alternating layers. The alternating layers may be formed by an atomic layer deposition (ALD) method or a chemical vapor deposition (CVD method or a combination of the two methods. The X-ray opaque layer composition may vary from a composition near the bottom selected for thermal stress relief or coefficient of thermal expansion (CTE) matching with the X-ray transparent dielectric material, to an essentially pure layer of tungsten at the top for maximum X-ray stopping power. An X-ray imaging system using the anti-scatter device may include an X-ray source, a location for placing an object to be imaged, such as a human patient, the anti-scatter grid, and an X-ray detector and recording system. In an embodiment the X-ray imaging device may include a scintillating material attached to the X-ray anti-scatter device and a solid state imaging device attached to the scintillating material, for an integrated device. FIG. 1 is a side view of six representative rows of X-ray transparent dielectric tubes 102 aligned in a parallel arrangement prior to forming an attachment, where the gap between the tubes 102 is intended to show that each tube is a separate and unattached tube, such as any sort of glass tube or plastic tube. The gap shown between the tubes 102 may not exist in all situations where, for example, the tubes 102 may be physically bound together by a clamp for handling purposes. It should be noted that the tubes 102 are formed of materials that are X-ray transparent, and the tubes 102 are not necessarily transparent at visible light wavelengths. The definition of X-ray transparent, as used herein, is a substantial percentage of incident X-rays at a specific X-ray energy will not be absorbed or deflected in the material, and will pass directly through the material thickness. Another substantially equivalent term for X-ray transparent may be X-ray lucent. A thickness of a material may be said to be X-ray transparent if 90% of incident radiation is transmitted, as compared to transmission without the material. Each X-ray transparent dielectric tube 102 will have a length L that will in part determine the overall thickness of an eventual X-ray transparent dielectric layer. The tubes 102 may be formed by heat drawing standard hollow glass tubes into thinner and longer form, by methods well known in the art, into capillary tubes having a desired diameter and wall thickness. The heat drawing process may be repeated as many times as needed to obtain the diameter required. Smaller diameter tubes may result in X-ray anti-scatter grids having superior image improvement properties. Tubes may also be formed of plastic. FIG. 2 is top view of the arrangement of the X-ray transparent dielectric tubes of FIG. 1, showing six rows of six X-ray transparent dielectric material tubes 202 forming a 6×6 matrix of tubes. In general, an anti-scatter grid would comprise thousands of such tubes. The gaps between the tubes 202 again indicate that the individual tubes 202 are not connected to each other. Each tube 202 has an outer diameter OD and an inner diameter ID. FIG. 3 is a top view of the arrangement of FIG. 2 after a process of attachment, for example heat fusing a bundle of glass capillary tubes 302 into a rectangular block 304 as shown. Any sort of shape may be formed as desired for the eventual device, and not simply the block shown. Further, the arrangement of the tubes may be of a different orientation than the square pack array shown, and may include a denser hexagonal close pack arrangement, or other well known arrays. Since the X-ray transparent tubes 302 have been fused together and attached, there is no longer any gap shown between the individual tubes 302, although there may still be a gap 306 at the intersection of four X-ray transparent tubes, or the shown gap 306 may be filled, or the tube shape altered. The X-ray transparent tubes 302 still have an outer dimension OD and an inner dimension ID, but the cross section of the X-ray transparent tubes may not be circular as shown, but may form a hexagonal array with a circular inside shape, or an oval shape, or other shapes depending upon the process used in forming the X-ray transparent material. FIG. 4 is a perspective view of the arrangement of FIG. 3, showing the X-ray transparent tubes 302 of FIG. 3 fused together and compressed in one dimension to form an array of oval or elliptical shaped holes 402 in a block of X-ray transparent material 404. The holes 402 are generally cylindrical channels in the X-ray transparent material that traverse the material 404 from the shown front surface to the not shown back surface on the opposite side. The holes 402 do not need to be elliptical as shown and may be circular, or hexagonal or other shapes. It should be noted that the relative sizes and separations of the holes 402 in the figure are to illustrate the formation, and in general the holes 402 will have smaller separation distances than shown. In the shown embodiment the gaps 306 of FIG. 3 at the intersection of four of the tubes 302 have been filled by the flow of the glass during the fusing process, but this is not necessary and the presence of spaces such as the gaps 306 of FIG. 3 will not affect the X-ray anti-scatter device significantly. In this embodiment the X-ray transparent material 404 has been formed by the fusing of the glass capillary tubes 302 of FIG. 3. A similar type device may be formed using plastic or other materials. While the described embodiment illustrates a flat micro-channel plate formed of numerous thin tubes, a micro-channel plate may also be formed using other methods. For example, the arrangement of FIG. 4 may be formed by electrochemical oxidation and directional etching in layers of metallic materials or metallic oxide layers, such as anodic aluminum oxide layers. FIG. 5 is a perspective view of the arrangement of FIG. 4 after an X-ray opaque material is deposited on an inside surface of the hole 402 of FIG. 4, where the X-ray opaque material forms a layer 508 that has a thickness T. The thickness T is selected depending upon the material forming the X-ray opaque layer 508, and is selected to be thick enough to substantially absorb all incident X-rays having a specified energy. For example, the X-ray anti-scatter device may be designed to block off-axis X-rays having an energy of 25 KeV, as may be used in mammography procedures, and have the X-ray opaque material layer formed of tungsten (W) having a thickness of 800 nanometers to block 90% of the incident X-rays. If another X-ray blocking material such as lead (Pb) is used, the layer 508 may be thinner or thicker than the comparable tungsten layer. The X-ray opaque layer 508 may extend substantially the entire length L of channel 402 from FIG. 4 in the X-ray transparent material 504, but this may not be required for proper operation of the X-ray anti-scatter device. The ratio of the length L versus the inner dimension ID of the tube formed by the X-ray opaque layer 508 helps determine the percentage of undesirable off-axis X-rays that will traverse the opaque material and reach the X-ray detector that forms the image. A larger ratio improves the image quality. It should again be noted that in general the spacing between the X-ray opaque layers 508 is smaller than shown in the figures. It should also be noted that the X-ray opaque material layer 508 will not be separated from the x-ray transparent material 504 as shown in the figure. The figure shows a gap in order to make clear that the X-ray opaque layer 508 is different from the X-ray transparent material 504 of the block. FIG. 6 is a side view of a set of focused X-ray tubes, in which the X-ray opaque tubes 608 include X-ray transparent channels, for example air, that are each directed towards a focus point F. The point F may represent an X-ray source in an X-ray imaging system. The X-ray opaque tubes 608 may be an X-ray opaque material layer on an X-ray transparent material tube, as shown in FIG. 5, and the X-ray opaque tubes 608 may be separated by an X-ray transparent material 604, which may be formed by fusing the tubes 302 shown in FIG. 3, or by other well-known methods. The X-ray opaque tubes 608 may have a constant diameter as shown, or the forming process may cause the channels in the X-ray transparent material 604 to change in diameter. The X-ray anti-scatter device shown in the figure has a curved surface 610 formed by the connected open ends of the X-ray opaque tubes 608. The surface 610 may be a concave surface as shown in the figure, but the invention is not necessarily so limited, and many different surface shapes may be used depending upon the application for which the X-ray anti-scatter device is intended. In the case of a point source X-ray generator, such as may be used in mammography or dental X-rays, the illustrated concave shape with the X-ray source at the location F may be a preferred arrangement. The X-ray anti-scatter device shape shown may be difficult to handle, aim and store, which may be addressed with a simple light carrying structure made of organic foam, or other X-ray transparent material, having a cut out portion shaped to match and hold the device shape. The cut out portion may also have an insert placed on top of the X-ray anti-scatter device since the foam is X-ray transparent and will not impact the operation of the X-ray anti-scatter device. Such a foam carrying apparatus may also protect the X-ray anti-scatter device from impacts which may damage the glass tube structure. FIG. 7 is another side view of a set of focused X-ray tubes with the tops of the X-ray opaque tubes 708 located in a plane formed of the X-ray transparent material 704, with the X-ray opaque tubes 708 each aligned with a focal point F. It should be noted that the open tops of the X-ray opaque tubes 708 do not need to be in physical contact as shown in the figure, but rather may be placed throughout the material 704. Close placement of the X-ray opaque tubes 708 may be desirable to reduce the number of off-axis X-rays that can pass between the X-ray opaque tubes 708, and thus reduce the eventual X-ray image quality. The arrangement shown in FIG. 7 may be preferred over the arrangement shown in FIG. 6 due to what may be considered a more compact and easily handled shape of the X-ray anti-scatter device. The shape of the X-ray anti-scatter device shown in the figure may be obtained by a controlled thermal slumping process on a curved section cut out of a block such as shown in FIG. 5, or thermal slumping of the arrangement of FIG. 6, or by other methods known in the art. Different methods of formation may result in variations in the channel diameter and thus in the configuration of the X-ray opaque tubes 708 and the X-ray transparent material 704 from the features illustrated in FIG. 7. FIG. 8 is a flowchart of a method of forming the arrangement shown in FIG. 5, using an example process having boro-silicate glass tubes as the X-ray transparent material and tungsten as the X-ray opaque material. As is well known, a glass tube subjected to a proper amount of heat and drawing pressure may be reduced from an original diameter to a selected smaller diameter, which is accompanied by increasing tube length in proportion to the reduction in width. By repetition of the heat drawing process a capillary tube of desired dimensions may be obtained. By bundling parallel lengths of the capillary tubes together and thermally fusing the glass walls of the tubes together, arrays of capillary tubes may be formed in many desired shapes, such as blocks or plates. The plates may be formed from the blocks by separating selected length sections from the block perpendicular to the direction of the capillary tubes. At step 802 a block of capillary tubes is formed having the desired dimensions, for example as shown in FIGS. 1 through 4. This step includes the heat forming of the boro-silicate glass tubes into capillary tubes having the correct dimensions, forming a block having a desired shape by parallel placement of a set of capillary tubes, and heat fusing the capillary tubes into a single block of X-ray transparent material having a set of cylindrical holes. At step 804 the block is separated into plates having a selected thickness, where the set of cylindrical holes pass through a thinnest plate thickness. The plates may be separated from the block by cutting, sawing, laser, or other known methods. Sawing may include using a wire saw, a radius saw, or other methods. Step 804 produces a plate having open ended tubes extending through the plate thickness. The ends of the tubes may be ground or polished to remove excessively rough surfaces and glass defects by use of grinding wheels, polishing wheels, chemical mechanical polishing (CMP), or other methods known in the art. In an embodiment, the plates have a thickness that determines the length of the capillary tubes L, where L is at least 50 times larger than an inside diameter of the capillary tubes. In the finished X-ray anti-scatter device this ratio increases the number of undesirable off-axis X-rays that reach the X-ray imaging device. At step 806 a layer of X-ray opaque material, such as tungsten (W) or a composite layer including tungsten, is formed inside each of the capillary tubes. The tungsten layer should have a thickness sufficient to block a majority of incident X-rays having a selected energy, or less. The tungsten layer should coat essentially the entire length L of the capillary tubes with the desired thickness. The coating of long narrow tubes having aspect ratios of 50 to 1, or greater, as described with reference to the capillary tubes of step 804, may require the use of Atomic Layer Deposition (ALD) methods, or Chemical Vapor Deposition (CVD) methods that have growth characteristics and features in common with ALD methods. ALD methods of layer deposition are known, as are CVD methods that incorporate some ALD features. ALD methods are known to provide very controllable thickness and composition layers, which have highly conformal layer characteristics in areas having high aspect ratios. The high aspect ratio coverage possible using ALD methods may be useful for X-ray anti-scatter devices, since high aspect ratios result in better image quality. However, ALD is a slow and expensive method of layer deposition. It is also known that metals, such as tungsten, have a coefficient of thermal expansion (CTE) that is much greater than found in dielectric materials, such as boro-silicate glass or plastic. A layer of tungsten in a boro-silicate glass tube subjected to thermal cycling may delaminate or form flakes of tungsten, either of which may damage the efficiency of the X-ray anti-scatter device. It would be desirable to provide an X-ray opaque layer that has a CTE that is closer to the CTE of glass, or a layer that has thermal stress relief layers. In an embodiment, the X-ray opaque layer includes a first layer directly on the glass that consists of aluminum oxide having a first thickness. A second layer formed on the first layer consists of tungsten having a second thickness. Subsequent alternating layers of aluminum oxide and tungsten having selected thicknesses form a composite layer having an overall thickness sufficient to block most X-rays of less than a selected energy. The composite layer may have a composition that grades smoothly from essentially entirely aluminum oxide near the glass tube, to essentially entirely tungsten as the distance from the glass increases. The composition may be varied by adjusting the thickness of the aluminum oxide and tungsten layers in the composite layer. At step 808 the tungsten layer that may have formed on the block outside of the capillary tubes may be removed. While it is important that the X-ray transparent channels are clear, an X-ray opaque coating on the face of the plate will reduce the total number of X-rays that reach the imaging system, whether or not the X-rays are on or off-axis. This may require an increase in the total number of X-rays produced for a given image and increase X-ray exposure time and cost. If the excess X-ray opaque material is not a problem, then step 808 may be deleted and the process goes to step 810. At step 810 the finished flat plate forming an X-ray anti-scatter device may be formed into a focused device such as shown in FIG. 6 or FIG. 7 if desired. The use of focused devices allows greater aspect ratios for the X-ray transparent channels to be used, which results in better image quality. This is because in a device having parallel anti-scatter tubes such as shown in FIG. 5, only the tubes in the center directly facing the X-ray source will have the on-axis X-rays travel exactly parallel to the tube axis. Therefore, as the distance from the center of the plate increases the number of on-axis X-rays that hit the sides of the tubes and are absorbed increases, and the image strength is reduced unnecessarily. This may be a problem with X-ray anti-scatter devices that are either very large, such as would be used in a whole chest X-ray procedure, or are very close to the X-ray source. However, for X-rays on small areas, such as a finger or a hand, the use of flat X-ray anti-scatter devices may be desired for the reduced cost and ease of handling. For small area X-ray anti-scatter devices this step may be deleted and the process goes to the end at step 812. FIG. 9 is a schematic of an imaging system using an X-ray anti-scatter grid, in accordance with some embodiments described herein. The X-ray imaging system includes an X-ray source 902 that generates X-rays having a desired energy that may depend upon the thickness and density of the object to be examined 904. The X-rays travel in straight lines as shown by representative rays shown by the dashed arrows. The object to be examined 904 may be a patient having a chest X-ray, or the engine block of an internal combustion engine, or any of many other objects that may require an internal image. X-rays that pass directly thru the object 904 are passed thru the X-ray anti-scatter device 906, and imaged at the X-ray detector. X-rays that are deflected, such as the dashed arrow labeled 912, are too far off-axis to pass thru the X-ray anti-scatter device 906, and are absorbed by the X-ray opaque layer. The X-ray detector 908 may be a scintillating material 908 that emits visible light when absorbing an X-ray. The visible light may then be detected and recorded as an image by the imager 910, which may be a CMOS imager, a CCD imager, photo sensitive film or other well-known optical imagers. Alternatively, the detector 908 and the imager 910 may be replaced by X-ray sensitive film. In an embodiment, the X-ray imaging system includes the X-ray anti-scatter device 906 directly attached to the scintillator 908, which is attached to the imager 910 in an integrated package. This improves the ease of use of the X-ray imaging system and is not practical with known X-ray anti-scatter devices, which are too bulky and heavy to integrate with the detectors. The disclosed X-ray anti-scatter device improves image resolution over the prior art, and reduces the cost and weight of prior art devices. The reduced thickness of the X-ray opaque layers made possible by the disclosed methods reduces what are known as image artifacts due to the thickness of the prior art lead sheet X-ray opaque layers. The artifact problem is addressed in the prior art by mechanisms that slowly move the X-ray anti-scatter grid randomly during the course of the X-ray exposure. While various embodiments of the invention have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. |
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abstract | A method for detecting a mass density image of an object. An x-ray beam is transmitted through the object and a transmitted beam is emitted from the object. The transmitted beam is directed at an angle of incidence upon a crystal analyzer. A diffracted beam is emitted from the crystal analyzer onto a detector and digitized. A first image of the object is detected from the diffracted beam emitted from the crystal analyzer when positioned at a first angular position. A second image of the object is detected from the diffracted beam emitted from the crystal analyzer when positioned at a second angular position. A refraction image is obtained and a regularized mathematical inversion algorithm is applied to the refraction image to obtain a mass density image. |
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055090397 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1A-1B illustrate a manual nuclear fuel pellet collating and measuring station 2 and include, respectively, a front X-axis view and a side Y-axis view of an X-Y positioning table 4 utilizing a measuring arm 6. An operator uses the station 2 to assemble various columnar pellet stack segments 8 in a variety of stack configurations. The station 2 further includes a measuring device 10. The measuring device 10 responds to X-Y positions of the measuring arm 6 and has a linear scale 114 which, in the exemplary embodiment, is capable of measuring pellet stack segments 8, which are up to 23 inches in length, with a resolution of.+-.0.004 inch. Referring now to FIG. 1C, a plurality of nuclear fuel pellets 12 are positioned on an input tray 14. The manual collating process generally includes handling of a plurality of pellet input and output trays, such as the exemplary pellet input tray 14 and an exemplary pellet output tray 16, pellet manipulation to assemble the pellet stack segments 8, data entry and data manipulation (e.g., stack weight, stack length, pellet tray identification and operator identification) in a data collection computer 110 (see FIG. 3), and data transactions with an historical data collection computer (RAMS) 118 (see FIG. 3). The pellet stack segments 8 are measured on the input tray 14 and then are transferred to the output tray 16. The exemplary input tray 14 includes 25 parallel triangular grooved rows 20 for holding individual pellet stack segments 8. A comb type reference stop 22 is used to block transfer of the pellet stack segments 8 from the input tray 14 to the output tray 16 during length measurements. Later, the stop 22 is moved in order to transfer the stack segments 8 to the output tray 16. Referring now to FIGS. 1C-2A, the measuring arm 6 includes an attached cylindrical measuring probe 24. The measuring arm 6 and the attached probe 24 are moved into an X-Y position, above the input tray 14, at an end 26 of an individual pellet stack segment 8. A measuring head 28 is attached to the measuring arm 6 by a pair of levers 38 and is moveable in a vertical Z-direction by a handle 32. The handle 32 is attached to an end 33 of a lever 34 which pivots about a hinge 36. For simplicity, operation of only one of the levers 38 is described below, it being understood that the other lever 38 operates in a similar manner. As shown in FIGS. 1D and 1E, the lever 34, in turn, is pivotally connected to the lever 38 at an end 40 thereof. The lever 38 is pivotally connected at another end 42 to the measuring head 28. FIGS. 1D and 1E show the measuring head 28 in a lowered position and a raised position, respectively. The cylindrical probe 24 has a diameter approximately the same as a diameter of the nuclear fuel pellets 12. The probe 24 may be lowered into an individual row 20 of the input tray 14 adjacent the stop 22, or adjacent the end 26 of a segment 8. As will be explained in greater detail with FIGS. 3 and 5 below, length measurements include, first, a zero length calibration, where probe 24 of measuring arm 6 is positioned against the stop 22; second, a series of pellet stack segment length measurements at the end 26 of each segment 8; and third, a zero length measurement which verifies the first length calibration. Referring to FIGS. 1D and 2A, an exemplary automatic pellet stack length recording switch 50 includes the cylindrical probe 24, a slider block 44, a spring 46, a generally rectangular spacer 48, a fiber optic sensor trip screw 52, two fiber optic reflectors 54,56, a sensor mount 58, two fiber optic cables 60 and a fiber optic sensor 102 (see FIG. 3). The generally inverted-U-shaped measuring head 28 has two legs 27,29 and is connected to the measuring arm 6 by a central rod 30. The rod 30 is attached to a central mounting hole 31 (see FIG. 2C) of the measuring head 28. As discussed above, the rod 30 and the attached measuring head 28 are movable in the vertical Z-direction. As shown in FIG. 2A, whenever the measuring head 28 is lowered by the handle 32 (see FIG. 1D), a washer 35 attached to an end of the rod 30 compresses a spring 37 until the washer 35 contacts a shoulder of a spacer 39 within the measuring arm 6. Otherwise, the measuring head 28 is normally raised under the influence of the spring 37. Two central cylindrical bores 66,68 are bored through the two legs 27,29, respectively, along a longitudinal axis of the measuring head 28. The sensor mount 58 has an oblong-shag opening 72 which is open along the longitudinal axis of the central bores 66,68. A longitudinal axis of the oblong-shaped opening 72 is perpendicular to the longitudinal axis of the bores 66,68. Referring now to FIGS. 2A-2C, the measuring head 28 has two sets of off-center cylindrical bores 82-82A,84-84A bored through the two legs 27,29, respectively, along a longitudinal axis. The slider block 44 has two off-center cylindrical bores 86,86A. Similarly, the sensor mount 58 has two off-center holes 75,75A. The holes 75,75A of the sensor mount 58 and the bores 86,86A of the slider block 44 are positioned on the longitudinal axis of the bores 82-84,82A-84A, respectively, of the measuring head 28. The sensor mount 58 is attached by two set screws 70 to two pins 76,78. The pins 76,78 pass through the bores 82A-84A,82-84, respectively, of the measuring head 28. The two pins 76,78 slidably support the slider block 44 within a cut out 80 between the legs 27,29 of the measuring head 28. For simplicity, operation of only pin 78 is described below, it being understood that the other pin 76 operates in a comparable manner. Similarly, only one of the bores 86 of the slider block 44 and only one of the holes 75 of the sensor mount 58 are described below. The pin 78 is fixedly attached using a set screw 70A within the bore 82 of the leg 27 of the measuring head 28 and using the set screw 70 within the hole 75 near the side 62 of the sensor mount 58. The pin 78 passes through the off-center hole 59 of the spacer 48 and is fixedly attached using a set screw 70B at an end 67 of the spacer 48. Two cylindrical beatings 87 within opposite halves of the bore 86 surround the pin 78 which slidably supports the slider block 44. Two retaining rings 88, near the opposite ends of the bore 86, hold the bearings 87 in place within the bore 86. Two bushing seals 90 seal the ends of the bore 86. The off-center bores 82,84,86 and the off-center hole 75 are parallel with the central bores 66,68 of the measuring head 28. In this manner, movement of the measuring head 28, with respect to the slider block 44, is along the longitudinal axis of the central bores 66,68. The slider block 44 also has a central cylindrical bore 92 and a counter-bore 91 which are positioned on the longitudinal axis of the central bores 66,68 of the measuring head 28. The trip screw 52, having a threaded head 51 and a shaft 53, is threadably attached by the head 51 within the bore 92. The shaft 53 of the trip screw 52 protrudes into the bore 68 of the measuring head 28. A set screw 49 is threadably attached within the bore 92 and is axially positioned next to the head 51 of the trip screw 52. As will be described more fully below, the trip screw 52 has an adjustable position within the bores 68,91,92. The generally rectangular spacer 48 includes a central hole 55, two off-center holes 57,59 which are on opposite sides of the central hole 55, two longitudinal surfaces 61,63, and two end surfaces 65,67. The longitudinal surface 63 is adjacent the leg 29 of the measuring head 28. The central hole 55 is positioned on the longitudinal axis of the central bores 66,68. The hole 55 and the bore 68 have diameters which are larger than a diameter of the shaft 53 of the trip screw 52. The shaft 53 freely passes through the hole 55 without contacting the spacer 48. Furthermore, the shaft 53 freely passes through the bore 68 and enters the opening 72 without contacting the sensor mount 58. As described above, the spacer 48 is attached to the pins 76,78 by set screws 70B through the end surfaces 65,67, respectively. Continuing to refer to FIGS. 2A-2C, the spring 46 is positioned around the shaft 53 of the trip screw 52 and within the counter-bore 91 of the slider block 44. The spring 46 has an end which abuts an inner surface 93 of the counter-bore 91 and another end which abuts the surface 61 of the spacer 48. The spring 46 is selected to provide a predetermined compression force to resist a movement of the measuring head 28 and the spacer 48 toward the slider block 44. The surface 61 of the spacer 48 provides an end stop for movement of the spacer 48 toward the slider block 44. The cylindrical probe 24 is affixed to a lower grooved alignment surface 25 of the slider block 44 by two set screws 70C. As will be described in greater detail below, an operator moves the measuring arm 6, in order that the probe 24 contacts and compresses an end 26 of a pellet stack segment 8 (see FIG. 1C). In this manner, the combination of the measuring arm 6, measuring head 28, spacer 48, spring 46, slider block 44 and probe 24 are used to apply a compression force to the end 26 of the pellet stack segment 8 for each length measurement. After a compression force is applied by the probe 24, in response to operator movement of the measuring arm 6, the measuring head 28 and the spacer 48 move left, with respect to the slider block 44 of FIG. 2A, and compress the compression spring 46. In the same manner, the sensor mount 58 also moves left with respect to the shaft 53 of the trip screw 52. Before the predetermined compression force is applied, and before the spacer 48 contacts the slider block 44, the shaft 53 enters the opening 72 of the sensor mount 58. In the event that a compression force greater than the predetermined compression force is applied, the spacer 48 contacts the slider block 44. This restricts any further motion of the measuring head 28 toward the slider block 44. Two protective tubes 94 (see FIG. 1D) and 96 are routed along a side of the measuring arm 6 and each contain the fiber optic cable 60. Sufficient slack is provided in the cables 60 to permit a full range of vertical motion of the measuring head 28. The fiber optic cables 60 terminate in the fiber optic reflectors 54,56. The fiber optic reflectors 54,56 are secured within the sensor mount 58 using two set screws 70D. As will be discussed more fully with FIGS. 3-4, a beam of light originates in the fiber optic sensor 102 (see FIG. 3). The light beam passes through the fiber optic cable 60 within tube 94 and is reflected perpendicular to the longitudinal axis of the bores 66,68 by the reflector 54 (see FIG. 1D) within the opening 72 of the sensor mount 58. Within the opening 72, the light beam passes to the corresponding reflector 56 which reflects the light beam into the fiber optic cable 60 within tube 96. Finally, the light beam is received by the fiber optic sensor 102. Whenever the predetermined compression force is applied, the shaft 53 of the trip screw 52 enters the opening 72 and breaks the light beam. The fiber optic sensor 102 detects the broken light beam, which signifies that the measuring head 28 is properly positioned. In turn, an output 103 (see FIG. 3) of the sensor 102 triggers a length measurement. It being understood that the invention is applicable to other types of position sensors (e.g., a proximity switch, a limit switch, etc.). The trip screw 52 is adjusted, in order that the shaft 53 of the trip screw 52 breaks the light beam whenever the predetermined compression force is applied. The set screw 49 is inserted through the bore 66 of the measuring head 28 and is threadably attached within the bore 92 of the slider block 44. The set screw 49 is adjacent the head 51 of the trip screw 52, in order to prevent any back-off of the trip screw 52 within the bore 92 of the slider block 44. The manual measuring system 150 of FIG. 3 includes a local control panel 100 and an exemplary data collection computer, such as conventional personal computer (PC) 110. The local control panel 100 is interconnected with the fiber optic sensor 102, a foot switch 104, two manual switches 106, and the linear scale 114. The PC 110 is interconnected by standard RS-232 interfaces 110a-1 10c with a weight scale 112, the linear scale 114, and the historical computer (RAMS) 118, respectively. The PC 110 is further interconnected by an interface, such as the exemplary keyboard interface 110d with a barcode scanner 116. The two manual switches 106 are used for selecting an automatic or a manual mode of operation (AUTO/MAN) and for manually activating an output of the interface 110b of the linear scale 114 (MANUAL TRANSMIT LENGTH). The PC 110, in order to determine a length of a stack segment, prompts the operator to conduct a series of length measurements. The first measurement is the zero length measurement at the stop 22 (see FIG. 1C). Using interface 110b, the PC 110 instructs the linear scale 114 to calibrate a "zero length" using this zero length measurement. The second measurement is one of the stack segment length measurements at the end 26 of each segment 8 (see FIG. 1C). After all of the stack segment length measurements are completed, a final zero length measurement is performed at the stop 22 in order to verify that the linear scale 114 returns a "zero length" within a predetermined tolerance. FIG. 4 is a circuit diagram of the local control panel 100. Power for the local control panel 100 is provided by a suitable alternating current power source (VAC) 120 on power leads 121,122. The POWER ON status of the power source 120 is indicated by a lamp 123 connected across the power leads 121,122. A dual switch 124 for selecting an automatic (AUTO) or a manual (MAN) operation mode of local control panel 100 includes two individual switches 124a, 124b. Whenever switch 124a is in the automatic position, terminal 125, which is connected to power lead 121, is connected to terminal 127, and the automatic status of panel 100 is indicated by a lamp 126 through a circuit to power lead 122. A relay coil (R1) 130 is connected between power lead 122 and a contact 128 of the foot switch 104. The contact 128 is connected between the coil 130 and terminal 127. Whenever switch 124a is in the automatic position, power lead 121 and terminal 125 are connected to terminal 127, and the closure of foot switch contact 128 energizes the coil 130 through a circuit to power lead 122. On the other hand, whenever switch 124a is in the manual position, terminal 127 is disconnected from power lead 121, the lamp 126 is extinguished to signify the manual mode of panel 100, the foot switch contact 128 is disabled, and power to the coil 130 is disconnected. Whenever switch 124b is in the automatic position, terminal 129 is connected to terminal 131, and a relay contact (TDR1) 132 is connected across terminals 136,137 for presentation to a transmit enable input of linear scale 114. Whenever terminals 136,137 are interconnected (e.g., whenever contact 132 is closed in the automatic mode of panel 100), linear scale 114 transmits an RS-232 message representative of a length measurement of stack segment 8 (see FIG. 1C). On the other hand, whenever switch 124b is in the manual position, terminal 129 is connected to terminal 133, and a manual transmit length switch 134 is connected across terminals 136,137 for presentation to the transmit enable input of linear scale 114. Accordingly, length measurements may be requested in the manual mode of operation by closing switch 134, and may be requested in the automatic mode of operation whenever contact 132 is closed. An alternating-to-direct current power supply (VAC/DC) 138 generates a direct current (DC) voltage at terminals 139,140 from the AC voltage of power leads 121,122. In the exemplary embodiment, a 120 VAC to+24 VDC power supply is utilized. Terminals 139,140 provide DC power and ground, respectively, to fiber optic sensor 102. The output 103 of the fiber optic sensor 102 is suitable for energizing a DC relay coil (R2) 144 whenever the light beam associated with the sensor 102 is broken. Whenever the light beam is broken, output 103 is driven to the DC ground reference of terminal 140. In this manner, a circuit is formed between DC power terminal 139, a relay contact (R1) 142, coil 144, output 103 and DC ground terminal 140. In other words, in the automatic mode, whenever the light beam is broken and foot switch contact 128 is closed, then relay coil (R1) 130 is energized, contact 142 is closed and relay coil (R2) 144 is energized. A relay contact (R2) 148 is driven by coil 144 and is interconnected with a time delay relay (TDR1) 146. The exemplary time delay relay 146 has an adjustable time delay range of 0.1 through 10 seconds on deenergization. On the other hand, the relay 146 generally has no delay on energization. In the automatic mode, whenever foot switch contact 128 is closed, coil 130 is energized and contact 142 is closed. Then, whenever the light beam is broken, coil 144 is energized, contact 148 is closed, time delay relay 146 is energized and contact 132 is closed. In this manner, terminals 136,137 are interconnected and linear scale 114 outputs a length measurement, in the automatic mode, whenever the operator depresses foot switch 104 and the light beam is broken, which signifies that the measuring head 28 (see FIG. 2A) is properly positioned. The exemplary adjustable time delay of 0.1 to 10 seconds maintains contact 132 in a closed state for the adjusted time delay. This ensures that spurious length measurements are not provided in the event of contact bounce in contacts 128,142,148, or in the event the light beam is only partially broken. Referring now to FIGS. 1C, 3 and 5, PC 110 executes a software routine, in order to determine length measurements of individual pellet stack segments 8. At step 180, the PC 110 prompts the operator and reads various stack building requirements from operator entry. Then, at step 182, the stack building requirements are transferred to RAMS 118. Also, a data base in RAMS is accessed in order to identify the appropriate set of input trays 14. Next, at step 184, based on the stack building requirements, the PC 110 prompts the operator to begin building up to 25 stacks. At step 186, the PC 110 prompts the operator to begin to measure the stack segment lengths. Next, at step 187, the operator is prompted to perform a zero length calibration at stop 22 in order to calibrate the linear scale 114. At step 188, the operator is prompted to perform up to 25 length measurements at the end 26 of each of the pellet stack segments 8 on the input tray 14. Then, at step 189, the operator is prompted to perform a zero length measurement which verifies the first zero length calibration. A test, at step 190, determines whether the zero length measurement is within a predetermined tolerance value. If not, then the length measurements are discarded at step 192 and step 186 is repeated in order to prompt the operator to repeat the stack segment length measurements. Otherwise, if the zero length measurement is within the predetermined tolerance value, the length measurements are accepted and saved at step 194. At step 196, the PC 110 determines whether all of the stacks are completed based on a comparison of the length measurements with the stack building requirements. If the stacks have not been completely built and measured, then step 184 is repeated in order to prompt the operator to continue building the stacks. Otherwise, when the stacks are completed, a confirmation which signifies that the stack building procedure is finished is transferred to RAMS 118 at step 198 before the software routine exits. 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 arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
summary | ||
abstract | A system and method for drying cavities loaded with spent nuclear fuel is devised. The invention utilizes a non-intrusive procedure that is based on monitoring the dew point temperature of a non-reactive gas that is circulated through the cavity. In one aspect, the invention is a system for drying a cavity loaded with spent nuclear fuel comprising: a canister forming the cavity, the cavity having an inlet and an outlet; a source of non-reactive gas; means for flowing the non-reactive gas from the source of non-reactive gas through the cavity; and means for repetitively measuring the dew point temperature of the non-reactive gas exiting the cavity. |
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050248049 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT More particularly, there is schematically shown in FIG. 1 a pressurizer 20 employed in a pressurized water nuclear power plant for reactor coolant pressure regulation. A manifold 22 is supported above the pressurizer 20 as part of a relief and safety valve system (not shown) for the pressurizer 20. The relief and safety valves and associated piping (not shown) which is connected to nozzles (not shown) on top of the pressurizer 20, to the manifold 22, to the valves and to an overflow vessel (not shown) are supported on the manifold 22. The relief and safety valve system 23 can include valves and piping, for example, like that shown in the drawings of referenced U.S. Pat. No. 4,426,350. A valve support system 24 is arranged in accordance with the invention to support the manifold 22 and the rest of the valve system 23. As set forth in U.S. Pat. No. 4,426,350, it is arranged to provide certain basic objectives including valve support against steam outflow discharge forces, system integrity against earthquake forces transmitted from ground-based structure, limited space layout of system consistent with facilitated valve maintenance and limited radiation exposure time, cost economy, and modularization that facilitates field assembly. It is highly desirable that a pressurizer relief and safety valve support system be structured simply with operating characteristics that meet safety and performance requirements while achieving better manufacturing economy and enhanced service accessibility for vessel weld inspections and other servicing requirements. The valve support system 24 is characterized with such improvement in accordance with the invention. The valve support system 24 includes a plurality of supporting lug pairs 26A, 26B, 26C and 26D welded to and equally spaced about a sidewall 28 of the pressurizer vessel 20 below the horizontal reference plane 32 where the sidewall 28 is welded to a dome 30 of the pressurizer 20. Generally, the force and moment loading of the valve and valve support systems is carried by the support lugs. However, as a result of the operation of the invention, the support lugs carry significantly less stress and therefore can be substantially downsized as compared to the prior art. The valve system 23 is supported above the lugs 26A-26D by respective columnar supports 34A-34D which are preferably V-structured. Thus, each columnar support (FIG. 2) includes a top crossbar 36 and a pair of diagonal columns 38 and 40 that extend upwardly from a base 42 in a V-shape. The columnar supports are simpler in structure than prior art schemes to provide greater service accessibility yet safety and performance requirements are met as well or better than such requirements are met by the prior art. The support column simplification is achieved at least partly because of the improved structural support enabled by application of the invention. The crossbar 36 and the columns 38 and 40 are preferably formed from tubular stainless steel with sufficient specifications to carry the loading involved with substantial safety margin. These elements are welded together as indicated by the reference characters 44, 46, and 48 and to the base 42 as indicated by 50. As shown in FIGS. 2-7, each support crossbar 36 is secured to the manifold 22 by collars 52, 54, and 56 having upper members respectively welded to the bottom side of the manifold 22. Generally, the inner collar 54 withstands horizontal loading along the crossbar axis. The two outer collars 52 and 56 withstand vertical loading while allowing for differential thermal expansion of the manifold 22 and the support crossbar 36, i.e. sliding movement of the crossbar 36 relative to the outer collars 52 and 56. The outside collars 52 and 56 are each provided with a first fixed collar member 51 welded to the underside of the manifold 22 and a second collar member 53 that is bolted to the collar member 51 to secure the inwardly located columnar support crossbar 36 in place. The collar 54 is located between the outer collars 52 and 56 and similarly includes a fixed collar member 55 welded to the underside of the manifold 22 and a second collar member 57 that is bolted to the collar member 55. Respective web members 47 and 49 strengthen the securance of the collar members 51 and 55 to the manifold 22. During assembly, the crossbar 36 is located against the three fixed collar members 51 and 55 and the three collar members 53 and 57 are bolted to the fixed collar members 51 and 55 to lock the crossbar 36 against vertical movement while permitting outward swinging movement of the columnar support 34 and while permitting sliding horizontal expansionary or contractive movement of the crossbar 36 relative to the outside collars 52 and 56. With crossbar/collar assembly completed, collar stops 54A and 54B are preferably welded to the crossbar 36 on opposite sides of the inner collar 54 to lock the crossbar 36 against unitary sliding horizontal movement relative to the collars 52, 54 and 56. With this arrangement, basis support functions are realized while subsequent columnar support disassembly is facilitated, i.e. the three collar members 53 and 57 are unbolted and the crossbar can be lowered and free from its secured position. The base portion 42 of each columnar support preferably includes a base plate 58 that is welded to the bottoms of the diagonal columns 38 and 40 as previously indicated. A base block 59 is also provided with a plate 60 that is securely bolted to the base plate 58. If necessary, shim plates can be disposed between the plates 58 and 60 prior to plate securance to take up dimensional differences. The columnar base portion 42 is secured to the vessel lug pair by a structural pin 62. During valve support system assembly, the pin 62 is inserted through a first lug member 63 of the vessel lug pair, then through an opening 64 in the support base block 59, and finally through the second lug member 65 of the vessel lug pair. A pair of clamp units 66 are secured by bolts and nuts 68 in respective grooves 70 and 72 which respectively lie outside the lug members 63 and 65. With the pin 62 thus locked in place, the columnar support 34 is held substantially upright with the base block 59 against the vessel wall and it is further held against horizontal displacement by the lug members 63 and 65 and the pin 62. When all four of the columnar supports 34 are locked onto the vessel lug pairs, the valve system manifold 22 is disposed on the columnar supports 34 and the collars 52, 54 and 56 are secured about the support crossbars 36. Thereafter, the valves and piping and other apparatus may be installed to complete the supported relief and safety valve system 23. Once the nuclear power plant has been placed in operation and is thereafter shut down for servicing, servicing of the valve system 23 and weld inspection access to the vessel wall and dome are facilitated by the reduced obstruction presented by the relatively simplified valve support system structure and especially by a swingout capability of the individual columnar supports 34. Thus, as shown in FIG. 2 for the support 34C, the columnar support can be swung outwardly and upwardly once the pin clamps 66 and the pin 62 have bee disassembled. Swing out action is easily achieved because of the rotative relationship of the crossbar 36 to its bearing support collars 52, 54 and 56. As previously noted, the columnar support can even be completely removed if desired. Normally, the columnar supports 34 would be swung away from the vessel wall and done one at a time. While each support is suitably held in its swing out position, unobstructed access is provided for service personnel to make vessel weld inspections over the uncovered nearby vessel surface area, i.e. the vessel surface over about the one quarter of the vessel periphery uncovered by the swung out columnar support. In addition, unobstructed service access is provided to the underside of the valves and piping. Overall, the invention results in reduced time and labor for assembly, disassembly and service and in reduced radiation exposure to service personnel. Just as importantly, reduced loading is applied to the vessel lugs thereby enabling the use of smaller lugs with reduced stressing of the vessel wall. Further, greater flexibility is provided for making adjustments needed during installation to take up structural dimensional variations from system to system. The principles of force interaction which characterize the operation of the invention and lead to many of the described improvements are graphically, illustrated by the free body diagrams in FIGS. 8-11. In FIG. 8, a diagrammatic representation is shown for the valve system and its support structure and the manner in which basic forces are applied to the supports. Thus, the valve system manifold 22 is shown on its columnar supports 34A-34D. Reference axes X, Y and Z are also shown. As indicated, the manifold 22 may apply translated horizontal forces Hx and/or Hz (resulting from valve thrust) to the columnar supports. Vertical force V may also be applied by the manifold 22 to the columnar supports in the direction of the Z-axis. FIG. 10 shows one of the manifold supports and the supporting relationship it has to the manifold and its supporting lug pair 26. Thus, the support crossbar 36 is rigidly connected to the manifold at its midpoint G but is free to contract and expand in the horizontal direction outwardly from the crossbar midpoint (crossbar sliding in the collar end supports). As shown, the ends of the crossbar 36 are rigidly held against vertical movement, but are supported for limited parallel horizontal swinging movement relative to the manifold 22 and further for outward swinging movement of the columnar support from the plane of the drawing for pressure vessel maintenance as previously described. At the base of the columnar support, the lug pair 26 holds the columnar support fixed against horizontal forces Hx or Hz as the case may be as well as vertical forces V, but the columnar support can swing outwardly from the plane of the drawing (about the pin 62). FIGS. 9 and 11 illustrate all of the supporting lugs together and the application of manifold forces to them. With reference to FIG. 11, vertical force V is taken by all four columnar supports 34A-34D and transferred taken by al four columnar to all of the lugs 26A-26D. Horizontal force Hx is taken by crossbar midpoint G (of support 34B or 34D) and transferred by diagonal columns 38 and 40 to the lug pair 26B or 26D. A vertical manifold movement Mv in a vertical plane along the X-axis is taken by a vertical reaction of supports 34A and 34C with 34A in compression and 34C in tension for the illustrated moment. A horizontal thrust Hz is taken by a horizontal reaction of supports 34A and 34C. The supports 34B and 34D similarly react for a horizontal thrust Hx or a vertical movement Mv in a plane along the Z-axis. Generally, the columnar supports rigidly withstand vertical moments or horizontal forces without bending or tilting and thus react to applied forces with tension or compression. For example, the moment Mv in FIG. 11 produces tension in the support 34C and the diagonal 40 of the support 34B, and it produces compression in the support 34A and the diagonal 38 of the support 34B. As a consequence of the avoidance of support bending, the manifold 22 is always held in a horizontal plane. In contrast, the prior art typically involves the application of bending moments to the supports with resulting support deflection and manifold tilting. In turn, the bending moments are transferred to the supporting lugs, where excessive lug loading occurs as a result of the twisting action applied to the lugs. As shown for the lug pairs 26A and 26C, radial thermal growth of the pressure vessel in the X direction results in outward movement of the lug pairs with the associated columnar support pivoting about the lug pin without obstruction. Lug pairs 26B and 26D react similarly for radial pressure vessel thermal growth in the Y direction. In FIG. 9, the lug pairs 26B and 26D react rigidly against horizontal forces Hx. Similarly, for horizontal forces Hz, the lug pairs 26A and 26C rigidly prevent system displacement. All four lug pairs react rigidly against moments or forces in vertical planes. From a support performance standpoint, the invention accordingly employs a relatively simplified valve system support structure which reacts very efficiently and effectively to manifold load forces and thermal growth forces so that significantly reduced loading is applied to the supporting lugs. Thus, structural advantages are realized in addition to vessel maintenance and other operating advantages. Particularly, vertical forces are taken in the middle of the lug pin at a point so close to the pressure vessel wall that the forces applied to the lugs are essentially shear forces with no significant bending moment on the lugs. Horizontal forces are applied against one lug member of the lug pair from the base of the columnar support through a washer (not specifically indicated). Thereafter, the horizontal forces are transferred to the retaining ring for that lug member and then to the pin and through the pin to the retaining ring at the opposite end of the pin and finally to the other lug member. The lug members thus share in the reaction to horizontal forces which are applied thereto essentially as shear forces. Since the columnar supports undergo no bending moments in accordance with the operation of the invention, no bending moments are applied to the lugs and lug twisting is avoided. As shown in prior art FIG. 12, twisting of lugs 26A typically occurs as indicated by dotted lines 26T under applied manifold horizontal forces or vertical moments. Reduced lug loading is thus achieved through avoidance of lug bending moments and the transference of load forces to the lugs as shear forces. |
claims | 1. A nuclear fuel assembly comprising: a fuel bundle having a plurality of fuel rods; a fuel rod support structure including a lower tie plate having an inlet nozzle, a lower tie plate grid and a transition structure for receiving coolant entering said nozzle and flowing coolant through said transition structure to said lower tie plate grid; said lower tie plate grid including a plurality of spaced bosses defining holes sized for receiving lower ends of said fuel rods within the holes of said bosses; said lower tie plate grid further including webs interconnecting said bosses to define with said bosses a plurality of flow openings through the lower tie plate grid for flowing coolant through said tie plate grid, said webs having upper edges recessed below upper edges of said bosses; a flat filter plate extending in a plane overlying the lower tie plate grid and disposed on upper edges of said bosses and spaced from said upper edges of said webs to define spaces therebetween, said flat filter plate having a plurality of spaced holes therethrough in registration with the holes in said bosses and bounded by a peripheral margin generally corresponding to a peripheral margin of the lower tie plate grid, said filter plate having a plurality of apertures therethrough spaced from said filter plate holes and in registration with the flow openings between said bosses and said webs and with the spaces between said filter plate and the upper edges of said webs for flowing coolant therethrough, the area of each said aperture being smaller than the area of each said hole through said filter plate and the ratio of the total number of apertures to the total number of said holes through said filter plate being in excess of ten; and a predetermined number of said fuel rods having end plugs received in said registering holes of said filter plate and said bosses and engaging said filter plate about the margins of said holes therethrough to position and maintain the filter plate against the ends of the bosses of the lower tie plate grid. 2. An assembly according to claim 1 wherein the ratio of the total number of apertures to the total number of said holes through said filter plate is in excess of fifteen. claim 1 3. An assembly according to claim 1 wherein the cross-sectional area of each said hole through said filter plate is at least fifteen times the cross-sectional area of each said aperture. claim 1 4. An assembly according to claim 1 wherein the cross-sectional area of each said hole through said filter plate is at least twenty times the cross-sectional area of each said aperture. claim 1 5. An assembly according to claim 1 wherein said end plugs of said predetermined number of fuel rods are smooth-sided and rest in registering holes holding down the debris filter plate. claim 1 6. An assembly according to claim 1 wherein said plurality of fuel rods includes tie rods having threaded end plugs for threaded engagement in threaded registering holes of said bosses to secure said fuel bundle to said lower tie plate, said threaded end plugs being spaced from margins of the holes about said filter plate in final securement thereof to said lower tie plate. claim 1 7. An assembly according to claim 1 wherein said filter plate apertures form an open area through said filter plate of approximately at least 30% of the area of said filter plate. claim 1 8. An assembly according to claim 1 wherein the ratio of the total number of apertures to the total number of said holes through said filter plate is in excess of fifteen, the cross-sectional area of each said hole through said filter plate being at least fifteen times the cross-sectional area of each said aperture. claim 1 9. An assembly according to claim 1 wherein said end plugs of said predetermined number of fuel rods are smooth-sided and rest in registering holes holding down the filter plate, said plurality of fuel rods including tie rods having threaded end plugs for threaded engagement in threaded registering holes of said bosses to secure said fuel bundle to said lower tie plate, said threaded end plugs being spaced from margins of the holes about said filter plate in final securement thereof to said lower tie plate. claim 1 10. An assembly according to claim 9 wherein the cross-sectional area of each said hole through said filter plate is at least fifteen times the cross-sectional area of each said aperture. claim 9 11. An assembly according to claim 9 wherein said filter plate apertures form an open area through said filter plate of approximately at least 30% of the area of said filter plate. claim 9 12. An assembly according to claim 9 wherein the ratio of the total number of apertures to the total number of said holes through said filter plate is in excess of fifteen, the cross-sectional area of each said hole through said filter plate being at least fifteen times the cross-sectional area of each said aperture. claim 9 13. A nuclear fuel assembly comprising: a fuel bundle having a plurality of fuel rods; a fuel rod support structure including a lower tie plate having an inlet nozzle, a lower tie plate grid and a transition structure for receiving coolant entering said nozzle and flowing coolant through said transition structure to said lower tie plate grid; said lower tie plate grid including a plurality of spaced bosses defining holes sized for receiving lower ends of said fuel rods within the holes of said bosses; said lower tie plate grid further including webs interconnecting said bosses to define with said bosses a plurality of flow openings through the lower tie plate grid for flowing coolant through said tie plate grid, said webs having upper edges recessed below upper edges of said bosses; a flat filter plate extending in a plane and disposed on upper edges of said bosses and spaced from said upper edges of said webs to define spaces therebetween, said flat filter plate having a plurality of spaced holes therethrough in registration with the holes in said bosses and bounded by a peripheral margin generally corresponding to a peripheral margin of the lower tie plate grid, said filter plate having a plurality of apertures therethrough in registration with the flow openings between said bosses and said webs and with the spaces between said filter plate and the upper edges of said webs for flowing coolant therethrough, the cross-sectional area of each said filter plate hole being at least fifteen times the cross-sectional area of each said aperture through said filter plate and the ratio of the total number of apertures to the total number of said holes through said filter plate being in excess of ten; and a predetermined number of said fuel rods having end plugs received in said registering holes of said filter plate and said bosses. 14. An assembly according to claim 13 wherein the cross-sectional area of each said hole through said filter plate is at least fifteen times the cross-sectional area of each said aperture. claim 13 15. An assembly according to claim 13 wherein said filter plate apertures form an open area through said filter plate of approximately at least 30% of the area of said filter plate. claim 13 16. An assembly according to claim 13 wherein the ratio of the total number of apertures to the total number of said holes through said filter plate is in excess of fifteen. claim 13 17. An assembly according to claim 13 wherein said end plugs of said predetermined number of fuel rods are smooth-sided and rest in registering holes holding down the filter plate. claim 13 18. An assembly according to claim 13 wherein said plurality of fuel rods includes tie rods having threaded end plugs for threaded engagement in threaded registering holes of said bosses to secure said fuel bundle to said lower tie plate, said threaded end plugs being spaced from margins of the holes about said filter plate in final securement thereof to said lower tie plate. claim 13 19. An assembly according to claim 13 wherein said filter plate apertures form an open area through said filter plate of approximately at least 30% of the area of said filter plate. claim 13 20. An assembly according to claim 3 wherein said end plugs of said predetermined number of fuel rods are smooth-sided and rest in registering holes, said plurality of fuel rods including tie rods having threaded end plugs for threaded engagement in threaded registering holes of said bosses to secure said fuel bundle to said lower tie plate, said threaded end plugs being spaced from margins of the holes about said filter plate in final securement thereof to said lower tie plate. claim 3 21. An assembly according to claim 20 wherein the cross-sectional area of each said hole through said filter plate is at least fifteen times the cross-sectional area of each said aperture. claim 20 22. An assembly according to claim 20 wherein said filter plate apertures form an open area through said filter plate of approximately at least 30% of the area of said filter plate. claim 20 23. An assembly according to claim 20 wherein the ratio of the total number of apertures to the total number of said holes through said filter plate is in excess of fifteen. claim 20 |
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abstract | A radiation source includes an anode and a cathode for creating a discharge in a vapor in a space between anode and cathode and to form a plasma of a working vapor so as to generate electromagnetic radiation. The cathode defines a hollow cavity in communication with the discharge region through an aperture that has a substantially annular configuration around a central axis of said radiation source so as to initiate said discharge. A driver vapor is supplied to the cathode cavity and the working vapor is supplied in a region around the central axis in between anode and cathode. |
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claims | 1. A water injection device that injects water into a reactor containment vessel, the device comprising:a flow path through which cooling water is supplied;a disk that closes the flow path;a swing arm that is connected to the disk and performs closing and opening of the flow path by the disk; anda weight that is connected to the swing arm via a swing lever, whereinthe weight is supported by a support member made of a low melting point alloy,the swing arm has one end which is rotatably supported by a body of the water injection device and another end which is rotatably connected to the swing lever,an end portion of a side opposite to an end portion which is connected to the swing arm of the swing lever is connected to the weight via a wire, andthe low melting point alloy is an alloy that is in a solid state at a temperature lower than 200° C. and is in a liquid state at 260° C. 2. The water injection device according to claim 1,wherein the flow path is closed by the disk by a connection portion between the swing arm and the swing lever being supported by an arm rotatably provided with respect to the body of the water injection device. 3. The water injection device according to claim 1,wherein the disk is seal welded to a body of the water injection device using a metal material having a melting point lower than that of the low melting point alloy constituting the support member. 4. The water injection device according to claim 1, wherein the support member melts due to the temperature rise of the surrounding environment of the water injection device, the weight falls, the disk is released due to the fall of the weight, and water is injected into the reactor containment vessel. 5. The water injection device according to claim 1, wherein the low melting point alloy constituting the support member is an alloy including Sb: 8.0 mass % to 12.5 mass %, Ag: 0 to 6.0 mass %, and Cu: 0 to 1.5 mass %. 6. The water injection device according to claim 5, wherein the low melting point alloy constituting the support member is an alloy further including Sn. |
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claims | 1. A projection objective for use in short wavelength microlithography to image an object onto a wafer plane, comprising: a first mirror (S 1 ), a second mirror (S 2 ), a third mirror (S 3 ), a fourth mirror (S 4 ), and a fifth mirror (S 5 ) such that the projection objective comprises a first subsystem and a second subsystem and wherein the object is imaged by a first subsystem, formed of the first mirror, the second mirror, and the third mirror (S 1 , S 2 , S 3 ) with an imaging ratio (xcex2) less than 0, into a real intermediate image (Z), and wherein a second subsystem, formed of the fourth mirror and the fifth mirror (S 4 , S 5 ), images the intermediate image as a real system image in the wafer plane. 2. The projection objective of claim 1 , wherein claim 1 NAxe2x89xa7 0.10, Wxe2x89xa7 1.0 mm, Axe2x89xa6 24 xcexcmxe2x88x92129 xcexcm(0.20 xe2x88x92NA )xe2x88x922.1 [xcexcm/mm](2 mmxe2x88x92 W ). the first mirror (S 1 ), the second mirror (S 2 ), the third mirror (S 3 ), the fourth mirror (S 4 ), and the fifth mirror (S 5 ) are arranged such that the image-side numerical aperture (NA) is the arc-shaped field width (W) at the wafer plane lies in the range of and the peak-to-valley deviation (A) of the aspheres in comparison to the best-fitting sphere in the used area is limited on all mirrors by 3. The projection objective of claim 1 , wherein claim 1 AOI xe2x89xa622xc2x0xe2x88x922xc2x0(0.20 xe2x88x92NA )xe2x88x92[0.3xc2x0/mm](2 mmxe2x88x92 W ), the first mirror (S 1 ), the second mirror (S 2 ), the third mirror (S 3 ), the fourth mirror (S 4 ), and the fifth mirror (S 5 ) are arranged such that the image-side numerical aperture (NA) is at least 0.10, the image-side width of the arc-shaped field (W) at the wafer plane is at least 1.0 mm, and the angle of incidence (AOI) on all mirrors are in the range: xe2x80x83where the angle of incidence is measured for any given mirror relative to the surface normal of that mirror. 4. The projection objective of claim 1 , wherein claim 1 the first mirror (S 1 ), the second mirror (S 2 ), the third mirror (S 3 ), the fourth mirror (S 4 ), and the fifth mirror (S 5 ) are arranged such that the image-side numerical aperture (NA) is at least 0.10, and an object plane, where the object is located, is within the structural space of a mirror system consisting of the first mirror, second mirror, third mirror, fourth mirror and fifth mirror. 5. The projection objective according to claim 1 , wherein the first subsystem is disposed near the object and that the second subsystem is disposed near the wafer plane. claim 1 6. The projection objective according to claim 4 , wherein the mirrors are arranged in such a way that there is sufficient lateral structural space provided for a scan of the object plane so that an obscuration-free beam path is achieved. claim 4 7. The projection objective according to claim 4 , wherein the mirrors are arranged in such a way that there is sufficient axial structural space for a scan of the object plane so that an obscuration-free beam path is achieved. claim 4 8. The projection objective according to claim 1 , wherein the fourth mirror and the fifth mirror have substantially the same radii (R). claim 1 9. The projection objective according to claim 8 , wherein the distance between the fourth mirror and the fifth mirror is approximately claim 8 10. The projection objective according to claim 1 , wherein the mirror surfaces are arranged on surfaces which exhibit rotational symmetry with respect to a principal axis (PA). claim 1 11. The projection objective according to claim 1 , further comprising an aperture stop (B) arranged on the body of the first mirror (S 1 ). claim 1 12. The projection objective according to claim 1 , wherein the aperture stop lies between the first mirror and second mirror so that it is freely accessible. claim 1 13. The projection objective according to claim 1 , wherein at least four mirrors are aspherical. claim 1 14. The projection objective according to claim 13 , wherein all mirrors are aspherical. claim 13 15. The projection objective according to claim 1 , wherein the imaging ratio (xcex2) of the first subsystem is between xe2x88x920.5 and xe2x88x921.0. claim 1 16. The projection objective according to claim 1 , wherein the rms wavefront error of the objective is at most 0.07 xcex over an entire image field. claim 1 17. The projection exposure apparatus with a microlithography projection objective according to claim 1 , further comprising an illumination device for illuminating an arc-shaped field. claim 1 |
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description | This application claims the benefit of Korean Patent Application No. 10-2007-0080268 filed with the Korea Intellectual Property Office on Aug. 9, 2007, the disclosure of which is incorporated herein by reference. 1. Field of the Invention The present invention relates to an apparatus for forming a nano pattern; and, more particularly, to an apparatus for forming a nano pattern uniformly at a low cost and a method for forming the nano pattern using the same. 2. Description of the Related Art Generally, a nano-patterning technique has been widely used in a semiconductor field such as circuit design, and so on, as a technique for forming a fine structure shape below 100 nm on a desired substrate. In the nano-patterning technique, because patterns to be formed are very fine in comparison with the substrate on which the patterns are formed, a method for uniformly fabricating patterns with a desired shape on the wide substrate is becoming a key issue. The nano-patterning technique is mainly divided into a nano imprinting method and a holographic lithography according to a principle of forming the patterns. The nano imprinting method is a method of transferring a previously formed master shape to a substrate by using a mechanical principle similarly to a method of imprinting a stamp, wherein a pattern is formed by coating UV curable resin on a substrate, imprinting a master with a pattern thereon and curing the resin through UV rays. Therefore, the nano printing method has an advantage of obtaining the uniform shape on a region with the same size as the master only if the desired shape is formed on the master according to the principle of transferring the shape of the master to the substrate, and thus it is appropriate for mass-production of the same shape. However, if a desired pattern is changed, the master should be newly fabricated to match with the changed pattern and further a fabrication cost of the master is very high, thereby deteriorating flexibility. Further, because the master should be periodically washed according to a characteristic of a process, the master should be replaced after producing a predetermined number of patterns, and equipment for nano imprinting is also very high, a process cost is greatly increased. The holographic lithography is a method of transferring an interference pattern generated due to interference of a laser beam to a substrate by using an optical principle. This method has an advantage of improving flexibility by easily changing a period of the desired pattern through the controlling of an angle of a coherent beam without requiring the mask for forming the pattern. However, this method is not suitable for forming the uniform patterns over a wide area since a size of the beam is less than 1 mm according to a characteristic of a laser and a region on which the pattern is fabricated is very narrow. Hence, for fabricating the pattern over the wide area through the holographic lithography, two methods, i.e., a beam expansion method and a beam scanning method, are currently used. The beam expansion method, one of the most widely used methods, is a method of producing a pattern by expanding a small laser beam to a predetermined size by using a lens and has an advantage of widening an area on which the pattern is produced by adding an optical unit for beam expansion in a general holographic lithography system. However, since this method merely expands the laser beam, it has a drawback that uniformity of the pattern is deteriorated as the pattern becomes more distant from a center of the beam according to a characteristic of the laser beam with Gaussian beam intensity distribution. That is, while the beams pass through the beam expansion unit, diameters of the beams are increased so that the beams meet on a substrate to form an interference pattern, wherein the uniformity of the formed interference pattern tends to be reduced as the interference pattern gets away from a central part of the substrate according to the characteristic of the laser beam, and thus the pattern is hardly impressed on a position apart from the central part at a predetermined distance. Accordingly, to obtain the uniformity over a wide range, the beam should be expanded, but the intensity of the beam is reduced and an exposure time is extended, whereby the contrast of the interference pattern is deteriorated according to a characteristic of an interferometer which is sensitive to vibration and disturbance to prevent the pattern from being formed. The beam scanning method is a method of fabricating a pattern over a wide area by scanning the entire surface of a substrate with a small laser beam and has an advantage of fabricating a very uniform pattern over the wide area, meanwhile, because many hours are required to perform the scanning over the wide area and a precise stage and a feedback system for scanning are needed to maintain an interference pattern during scanning, the beam scanning method is not economical. That is, in case of the beam scan type, because a beam generated from the laser is directly used without installing an additional beam expansion unit, the formed pattern is very small and therefore in order to form the pattern on the entire surface of the substrate, the substrate is put on a stage for precisely controlling the substrate and scanned with the laser beam. Accordingly, the beam scan type has an advantage of forming the very uniform patterns on the entire surface of the substrate, but it has disadvantages of needing the very high cost precise stage and feedback control system for beam scanning and increasing a time of fabricating the pattern. The present invention has been invented in order to overcome the above-described problems and it is, therefore, an object of the present invention to provide an apparatus for forming a nano pattern and a method for forming the nano pattern using the same capable of fabricating a fine pattern with piecewise uniformity over a wide area at a low cost in a short time by combining advantages of the beam expansion method and the beam scanning method. The object of the present invention can be achieved by providing an apparatus for forming a nano pattern including a laser for generating a beam; a beam splitter for splitting the beam from the laser into two beams with the same intensity; variable mirrors for reflecting the two beams split by the beam splitter to a substrate; beam expansion units for expanding diameters of the beams by being positioned on paths of the two beams traveling toward the substrate; and a beam blocking unit, installed on an upper part of the substrate, transmitting only a specific region expanded through the beam expansion unit and blocking a remaining region. And, the apparatus for forming the nano pattern may further include a substrate transfer device for transferring the substrate vertically and horizontally by being provided on a lower part of the substrate and the beams can be uniformly irradiated over the entire surface of the substrate through the substrate transfer device. Further, the apparatus for forming the nano pattern may further include reflection mirrors for changing the paths of the beams generated from the laser between the laser and the beam splitter and the paths of the beams can be variously changed by controlling the number of the reflection mirrors. The beam blocking unit is constructed to transmit only a central region of the expanded beams and block a remaining region beyond the central region, that is, the regions where the intensity of the beams is remarkably reduced. Further, the object of the present invention can be achieved by providing a method for forming a nano pattern including the steps of: generating a beam through a laser; splitting the beam into two beams with the same intensity through a beam splitter; directing the two beams to a substrate through variable mirrors; expanding diameters of the beams through beam expansion units respectively positioned on paths of the beams traveling toward the substrate; and illuminating the substrate by transmitting a central region of the expanded beams through a beam blocking unit provided on an upper part of the substrate. At this time, the substrate is coated with UV curable resin and the region where the beams are irradiated may remain in a developing solution or be removed according to the kind of the UV curable resin. And, the method may further includes a step of: changing the path of the beam generated from the laser through at least one reflection mirror and the path of the beam may be variously changed according to the number of the reflection mirrors. Further, the uniform beams are irradiated over the entire surface of the substrate by movement of a substrate transfer device on which the substrate is mounted and the substrate transfer device is capable of being moved vertically and horizontally. As described above, the apparatus for forming the nano pattern in accordance with the present invention is capable of forming the uniform pattern over the entire surface of the substrate in comparison with the conventional beam expansion method by transmitting only the central region of the expanded beams through the beam expansion unit, that is, only the beams of the region except the regions where the intensity of the beams is remarkably reduced, through the beam blocking unit installed on the upper part of the substrate. That is, the conventional beam expansion method has the disadvantage that the pattern is hardly formed on the position apart from the central part at the predetermined distance since the expanded beams through the beam expansion unit shows the Gaussian distribution that the intensity of the expanded beams is sharply reduced as the expanded beams gets away from the central part and all the beams contribute to forming the pattern. Meanwhile, in accordance with the present invention, it is possible to improve uniformity of the pattern formed in the region where beams are transmitted by increasing uniformity of the intensity of the beams contributing to the beam formation by blocking regions where the intensity of the beams is remarkably reduced and transmitting only the central region through the beam blocking unit and further to form the uniform fine pattern over the entire surface of the substrate by forming the pattern on a new part of the substrate on which the pattern is not formed through the movement of the substrate transfer device by the same method. Further, in accordance with the present invention, the method for forming the fine pattern has advantages of reducing a fabricating time of the pattern by using the expanded beams through the beam expansion unit and of reducing a cost without requiring the high cost precise stage and feedback control system in comparison with the conventional beam scanning method. That is, in the conventional beam scanning method, because the beam from the laser is directly used, the pattern formed on the substrate is very small and therefore in order to form the pattern on the entire surface of the substrate, the substrate is put on the precise stage for precisely transferring the substrate and scanned with the laser beam. Therefore, the beam scanning method has the disadvantages of needing the high cost precise stage and feedback control system for beam scanning and increasing the time of fabricating the pattern. Meanwhile, in accordance with the present invention, it is possible to increase the size of the pattern formed on the substrate by using the beam expansion unit and the beam blocking unit for transmitting the predetermined region of the expanded beams, to reduce the time of fabricating the pattern by forming the pattern over the entire surface of the substrate by transferring the substrate as much as the transmission region of the beams vertically and horizontally and to reduce the cost without requiring the high cost precise stage and feedback control system substrate in comparison with the beam scanning method. Hereinafter, an apparatus for forming a nano pattern and a method for forming the nano pattern using the same in accordance with the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic view showing a construction of an apparatus for forming a nano pattern in accordance with the present invention. As shown in FIG. 1, in accordance with the present invention, the apparatus for forming the nano pattern 100 includes a laser 101 for generating a beam 110, a beam splitter 104 for splitting the beam 110 into two beams 110a and 110b; variable mirrors 105a and 105b directing the two split beams 110a and 110b to a substrate 107; beam expansion units 106a and 106b for diffusing the beams by being positioned on paths of the beams traveling toward the substrate 107; and a beam blocking unit 112 for transmitting only a specific region of the beams expanded through the beam expansion units 106a and 106b. The apparatus for forming the nano pattern 100 may further include at least one mirror 102 and 103 for changing a path of the beam 110 generated from the laser 101 between the laser 101 and the beam splitter 104 and the path of the beam may be freely controlled by varying the number of the reflection mirrors 102 and 103. In accordance with one embodiment of the present invention, the path of the beam is changed twice through the two reflection mirrors 102 and 103. The beam splitter 104 splits the beam 110 received through the reflection mirrors 102 and 103 into two beams 110a and 110b with the same intensity to send the beams 110a and 110b toward the two variable mirrors 105a and 105b facing each other and the beams 110a and 110b which reach the variable mirrors 105a and 105b are reflected respectively to travel toward the substrate 107 mounted on a substrate transfer device 108. Diameters of the beams 110a and 110b reflected through the two variable mirrors 105a and 105b are expanded by passing each of the beams 110a and 110b through the beam expansion unit 106a and 106b which are positioned on paths of the beams 110a and 110b traveling toward the substrate 107 and the expanded beams meet on the substrate 107 to form an interference pattern. At this time, UV curable resin(not shown) is coated on the substrate 107 and the interference pattern is formed on the UV curable resin. And, all the expanded beams are not irradiated on the substrate 107 and only a part of the expanded beams which are transmitted through the beam blocking unit 112 provided on an upper part of the substrate 107 are irradiated on the substrate 107. That is, the beam blocking unit 112, as shown in FIG. 2, includes a transmission unit I for transmitting the beams and a blocking unit II for blocking the beams and right before the expanded beams through the beam expansion units 106a and 106b are irradiated on the substrate 107, only a central part of the expanded beams is transmitted by the beam blocking unit 112 and irradiated on the substrate 107 to form the interference pattern. At this time, because the expanded beams through the beam expansion units 106a and 106b are gathered toward the substrate 107, the beams shows a Gaussian distribution that the beams have the maximum intensity at the central part where the beams are overlapped and the intensity of the beams is sharply reduced as getting away from the central part. And, the beam blocking unit 112 blocks the beams on the regions where the intensity of the beams is remarkably reduced through the blocking unit 11 and transmits the beams on the region where the intensity thereof is almost uniformly distributed, that is, the central part through the transmission unit I. Therefore, because the beams contributing to forming the pattern on the substrate 107 have the uniform intensity in comparison with the conventional beam expansion method, the uniformity of the pattern formed within the transmission unit I region is improved. At this time, the transmission unit I region is not limited to the predetermined intensity of the beam but it is preferable to limit the transmission unit I region to a point at which the intensity of the beams is a half of the maximum. However, it is allowable to limit the region to a point at which the intensity of the beams is smaller than the half of the maximum. FIG. 3 is a plane-view showing the beam blocking unit 112 and as shown, the pattern is formed as much as the transmission unit I region by irradiating the beams on the substrate 107 positioned on a lower part of the beam blocking unit 112 through the transmission unit I formed on the beam blocking unit 112. As described above, when the pattern formation is completed on one part of the substrate 107 by using the beam blocking unit 112, a pattern is formed by the same method on another new part of the substrate 107 on which the pattern is not formed by vertically and horizontally transferring the substrate 107 as much as the beam transmission region of the beam blocking unit 112. Therefore, as shown in FIG. 1, the substrate 107 is mounted on the substrate transfer device 108 to be transferred vertically and horizontally and the patterns can be substantially formed on the entire surface of the substrate 107 by movement of the substrate transfer device 108. FIG. 4 is a view showing regions on which the patterns are formed by vertically and horizontally transferring the substrate 107 as much as the beam transmission region of the beam blocking unit 112. When the initial beam transmission region is referred to as an “A” section, patterns can be formed on a “B” section and a “C” section in the same area as the “A” by horizontally transferring the substrate 107 through the substrate transfer device 108 and a pattern can be formed on a “D” section under the “A” section in the same area as the “A” section by vertically transferring the substrate 107. And, when the pattern is formed on the “D”, the same pattern can be formed on an “E” section and an “F” section by horizontally transferring the substrate 107. Herein, all the “A” to “F” sections correspond to the transmission unit I region of the beam blocking unit 112, wherein they have the same area and the fine patterns can be formed over the entire surface of the substrate 107 by vertically and horizontally transferring the substrate 107 as much as the transmission unit I region. At this time, the formed patterns are uniform by each of the sections in the substrate and therefore the continuity between sections is not maintained but there is hardly difference in terms of performance when practically being applied in comparison with patterns wholly maintaining the continuity because types and periods of the patterns are the same. That is, as shown in FIG. 2, because the intensity of the beams irradiated on the substrate through the transmission unit I is not the same as a specific value and it is reduced as getting away from a central axis, there is difference in the intensity of the beams between the central part and a peripheral part of the transmission unit I. Accordingly, because the pattern formed in the one section of the substrate is not entirely uniform in the central part and the peripheral part, the continuity between the sections is not maintained, but the types and periods of the patterns formed in each of the sections are the same and therefore there is hardly difference in the performance in comparison with the patterns wholly maintaining the continuity. As described above, in accordance with the present invention, it is possible to reduce a cost for constructing the system by remarkably reducing a cost for constructing the substrate transfer device in comparison with the conventional beam scanning method because the substrate is transferred after forming the pattern on the predetermined section and it is not required to maintain the continuity between the formed pattern sections. As described above, in accordance with the present invention, the apparatus for forming the nano pattern is capable of improving the uniformity of the patterns by enhancing the uniformity of the intensity of the beams contributing to forming the pattern by transmitting only the central part where the intensity of the expanded beam is the highest through the beam expansion unit and the beam blocking unit. Further, the present invention has an advantage of forming the uniform pattern over the entire surface of the substrate in a short time in comparison with the conventional beam scanning method by dividing the pattern forming region into the several small sections (that is, one section corresponds to the transmission unit region of the beam blocking unit) and sequentially forming the patterns on each of the sections by transferring the substrate as much as the each of the sections. As described above, in accordance with the present invention, to take only the advantages of the conventional beam expansion method and the beam scanning method, the patterns are sequentially formed by including the beam expansion unit and the beam blocking unit and transferring the substrate as much as the beam transmission region of the beam blocking unit and therefore only if the beam expansion unit, the beam blocking unit and the substrate transfer device for transferring the substrate are provided, any kinds of holographic lithography systems may be included. And, in accordance with the present invention to take only the advantages of the beam expansion method and the beam scanning method, the apparatus for forming the nano pattern and the method for forming the nano pattern using the same are capable of fabricating the fine patterns with the uniformity by each of the sections on the overall substrate at a low cost in a short time by including the beam expansion unit and the beam blocking unit to block only the beams of regions apart from the central part of the expanded beams through the beam expansion unit at the predetermined distance. As described above, although the preferable embodiment of the present invention has been shown and described, it will be appreciated by those skilled in the art that substitutions, modifications and changes may be made in this embodiment without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents. |
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claims | 1. An x-ray diffraction imaging (XDI) system comprising:a plurality of x-ray sources configured to generate x-rays directed toward an object;a primary collimator positioned a distance from said plurality of x-ray sources, wherein a plurality of nodes are defined within said primary collimator at a plurality of node distances from said plurality of x-ray sources, wherein each node of said plurality of nodes defines an x-ray intersection region; anda supermirror assembly comprising a plurality of mounting rails positioned adjacent said plurality of nodes. 2. The XDI system in accordance with claim 1, wherein said XDI system further comprises a plurality of detectors, wherein said plurality of x-ray sources, said primary collimator, and said plurality of detectors define a first axis extending therethrough, said plurality of x-ray sources define a second axis extending therethrough, the first axis perpendicular to the second axis, the first axis and the second axis define an x-ray fan plane, wherein each node distance of the plurality of node distances is defined by:X(N)=L/[1+(N*Pt)/Ps],where X(N) is the node distance, N is an integer, L is a length between said plurality of x-ray sources and said plurality of detectors along the first axis, Pt is a detector pitch between each detector of said plurality of detectors, and Ps is a source pitch between each x-ray source of said plurality of x-ray sources. 3. The XDI system in accordance with claim 2, wherein N includes a plurality of integers starting at 1, wherein said primary collimator defines a plurality of node arrays therein, wherein the number of said plurality of node arrays is equal to a value of the largest integer defined within N. 4. The XDI system in accordance with claim 2, wherein said plurality of node arrays are substantially parallel to each other and substantially parallel to the x-ray fan plane. 5. The XDI system in accordance with claim 2, wherein said plurality of mounting rails extend a length perpendicular to the x-ray fan plane. 6. The XDI system in accordance with claim 1, wherein said supermirror assembly further comprises at least one mirrored segment configured to be received by said plurality of mounting rails. 7. The XDI system in accordance with claim 6, wherein said at least one mirrored segment comprises a first edge and a second edge opposite said first edge. 8. The XDI system in accordance with claim 7, wherein said plurality of mounting rails comprises a first mounting rail configured to receive said first edge and a second mounting rail configured to receive said second edge. 9. The XDI system in accordance with claim 7, wherein said plurality of mounting rails are substantially trapezoidal. 10. The XDI system in accordance with claim 9, wherein each mounting rail of said plurality of mounting rails defines a first apex and a second apex opposite said first apex, at least one of said first apex and said second apex comprise at least one mounting groove defined therein, said at least one mounting groove configured to receive one of said first edge and said second edge. 11. The XDI system in accordance with claim 6, wherein said at least one mirrored segment comprises a plurality of mirrored segments, wherein at least a portion of said plurality of mirrored segments comprises a reflective surface that is substantially linear. 12. The XDI system in accordance with claim 1, wherein said XDI system is a multiple inverse fan beam (MIFB) XDI system. 13. A supermirror assembly for an x-ray diffraction imaging (XDI) system, the XDI system including a plurality of x-ray sources and a primary collimator positioned a distance from the plurality of x-ray sources, wherein a plurality of nodes are defined within the primary collimator at a plurality of node distances from the plurality of x-ray sources, wherein each node of the plurality of nodes defines an x-ray intersection region, said supermirror assembly comprising a plurality of mounting rails positioned adjacent the plurality of nodes. 14. The supermirror assembly in accordance with claim 13, wherein the XDI system further includes a plurality of detectors, wherein the plurality of x-ray sources, the primary collimator, and the plurality of detectors define a first axis extending therethrough, the plurality of x-ray sources define a second axis extending therethrough, the first axis perpendicular to the second axis, the first axis and the second axis define an x-ray fan plane, wherein said plurality of mounting rails extend a length perpendicular to the x-ray fan plane. 15. The supermirror assembly in accordance with claim 13 further comprising at least one mirrored segment configured to be received by said plurality of mounting rails. 16. The supermirror assembly in accordance with claim 15, wherein said at least one mirrored segment comprises a first edge and a second edge opposite said first edge. 17. The supermirror assembly in accordance with claim 16, wherein said plurality of mounting rails comprises a first mounting rail configured to receive said first edge and a second mounting rail configured to receive said second edge. 18. The supermirror assembly in accordance with claim 16, wherein said plurality of mounting rails are substantially trapezoidal. 19. The supermirror assembly in accordance with claim 18, wherein each mounting rail of said plurality of mounting rails defines a first apex and a second apex opposite said first apex, at least one of said first apex and said second apex comprise at least one mounting groove defined therein, said at least one mounting groove configured to receive one of said first edge and said second edge. 20. The supermirror assembly in accordance with claim 15, wherein said at least one mirrored segment comprises a plurality of mirrored segments, wherein at least a portion of said plurality of mirrored segments comprises a reflective surface that is substantially linear. |
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description | This is a Continuation of International Application PCT/EP2016/072246, which has an international filing date of Sep. 20, 2016, and which claims the priority of the German Patent Application No. 102015218763.2, filed Sep. 29, 2015. The disclosures of both applications are incorporated in their respective entireties into the present application by reference. The present invention relates to a reflective optical element, in particular for an operating wavelength in the DUV or VUV wavelength range, comprising a substrate, a dielectric layer system and a metallic coating between the substrate and the dielectric layer system, wherein the dielectric layer system comprises at least respectively one layer composed of a material having a lower refractive index n1 at the operating wavelength, one layer composed of a material having a higher refractive index n2 at the operating wavelength and one layer composed of a material having a refractive index n3 at the operating wavelength, where n1<n3<n2, wherein a layer having a medium refractive index n3 is arranged at at least one transition from a layer having a lower refractive index n1 to a layer having a higher refractive index n2 and/or from a layer having a higher refractive index n2 to a layer having a lower refractive index n1. Furthermore, the invention relates to an optical system, a lithography device and a microscopy device comprising such a reflective optical element. Inter alia, in microlithography using deep ultraviolet radiation (DUV radiation), or vacuum ultraviolet radiation (VUV radiation), in particular at wavelengths of between 150 nm and 300 nm, in optical systems dielectric mirrors are also used besides lens elements. In this case, an excimer laser that emits in said wavelength range often serves as a radiation source. Inter alia, excimer lasers that emit at 193 nm or at 248 nm are particularly widespread. U.S. Pat. No. 5,850,309 discloses a reflective optical element comprising a substrate, a dielectric layer system and a metallic coating between the substrate and the dielectric layer system. The metallic coating serves primarily for broadband reflection. The dielectric layer system serves to improve the properties of the reflective optical element. These include for example the reflectivity at the operating wavelength, the degree of polarization of the reflective radiation or else the resistance of the metallic coating to the DUV radiation and other environmental influences. The dielectric layer system described in U.S. Pat. No. 5,850,309 is constructed alternately from high and low refractive index materials. It can be divided into sub blocks, wherein different materials are used as low and respectively high refractive index layers in different sub blocks. As a result, in comparison with reflective optical elements comprising a metallic layer and without a dielectric layer system, increased reflectivities at the operating wavelength, i.e. the wavelength of the radiation source for which the respective reflective optical element is optimized, are achieved in conjunction with increased laser resistance. US 2011/0206859 A1 discloses a reflective optical element of the generic type in which an amorphous layer composed of silicon dioxide or doped silicon dioxide is provided between at least two periods of fluoridic high and low reflective index layers. It is one object of the present invention to develop the known reflective optical element further. This object is achieved, according to one formulation, with a reflective optical element, in particular for an operating wavelength in the DUV or VUV wavelength range, comprising a substrate, a dielectric layer system and a metallic coating between the substrate and the dielectric layer system, wherein the dielectric layer system comprises a layer composed of a material having a lower refractive index n1 at the operating wavelength, a layer composed of a material having a higher refractive index n2 at the operating wavelength and a layer composed of a material having a refractive index n3 at the operating wavelength, where n1<n3<n2, wherein a layer having the medium refractive index n3 is arranged at at least one transition from a layer having the lower refractive index n1 to a layer having the higher refractive index n2 and/or from a layer having the higher refractive index n2 to a layer having a lower refractive index n1, wherein the dielectric layer system comprises a four-layer sequence of (LMHM)m or (HMLM)m where L is the layer composed of a material having a lower refractive index n1 at the operating wavelength, H is the layer composed of a material having a higher refractive index n2 at the operating wavelength and M is the layer composed of a material having a refractive index n3 at the operating wavelength, and wherein n1<n3<n2, and m is the number of four-layer sequences in the dielectric layer system. It has been found that providing at least one layer composed of a material having a medium refractive index n3 at the operating wavelength allows the total number of individual layers of the dielectric layer system to be reduced compared with the previously known reflective optical element in conjunction with comparable properties. As a result, it is possible not only to reduce the production costs but also to lengthen the lifetime of the reflective optical element, since the probability of stresses or delamination occurring is reduced, which increases the mechanical stability. Furthermore, a higher broadband characteristic can be obtained. It should be pointed out that for the case where respectively more than one layer having a lower refractive index n1 and higher refractive index n2 is provided in the dielectric layer system, these layers are particularly preferably arranged alternately. Moreover, it should be pointed out that in the case of more than one layer composed of a material having a higher, lower or medium refractive index, these layers can be composed of respectively different materials, provided that the condition n1<n3<n2 is met for layers respectively arranged adjacently. In order to keep the production outlay lower, preferably only one material is ever used in each case. In the case of the reflective optical element proposed, in particular the optical properties of the metallic coating can be positively influenced in a targeted manner. Moreover, it is also possible to increase the stability of said reflective optical element with respect to environmental influences and radiation damage in conjunction with a reduced number of layers. Preferably, the layer of the dielectric layer system which is the furthest away from the substrate is a layer composed of a material having a medium refractive index n3, as a result of which the reflectivity of the reflective optical element at the operating wavelength can additionally be increased. Furthermore, as a result, the electric field of the standing wave that forms in the event of radiation reflection can be minimized, such that fewer secondary electrons that could adversely affect the lifetime of the reflective optical element are emitted. Preferably, the dielectric layer system comprises at least two layers composed of a material having a medium refractive index n3. Just two layers composed of a material having the medium refractive index n3 make it possible to achieve a sufficient influencing of the optical and other properties, for example the broadband characteristic, of the reflective optical element in conjunction with a significantly reduced number of layers. Given three, four, five or more layers composed of a material having a medium refractive index n3, it is possible to achieve a greater influencing of the optical and other properties of the reflective optical element in conjunction with a number of layers reduced to a somewhat lesser extent. Advantageously, the layer of the dielectric layer system which is second closest to the substrate is composed of a material having a medium refractive index n3, in particular if the dielectric layer system comprises at least two layers composed of a material having a medium refractive index n3, and/or the layer of the dielectric layer system which is the furthest away from the substrate is a layer composed of the material having a medium refractive index n3. The radiation resistance of the metallic coating and also the reflectivity can be increased as a result. Preferably, the substrate is composed of quartz, titanium-doped quartz glass, calcium fluoride or glass ceramic. Advantageously, the metallic coating comprises aluminum, an aluminum-silicon alloy, an aluminum-manganese alloy, an aluminum-silicon-manganese alloy, rhodium or a combination thereof. Such metallic layers can lead to a particularly broadband reflection or to a high reflection despite a broadband characteristic. Preferably, in the case of reflective optical elements for an operating wavelength in the range of between 240 nm and 300 nm the layer composed of a material having a lower refractive index n1 is composed of one or more materials of the group aluminum fluoride, cryolite, chiolite, lithium fluoride and magnesium fluoride, the layer composed of a material having a higher refractive index n2 is composed of one or more materials of the group yttrium oxide, hafnium oxide, scandium oxide, zirconium oxide, aluminum nitride and synthetic diamond, and the layer composed of a material having a medium refractive index n3 is composed of one or more materials of the group barium fluoride, gadolinium fluoride, lanthanum fluoride, neodymium fluoride, dysprosium fluoride, aluminum oxide, yttrium fluoride, ytterbium fluoride and silicon dioxide. In the case of reflective optical elements for an operating wavelength in the range of 150 nm to 240 nm, the layer composed of a material having a lower refractive index n1 is composed of one or more materials of the group aluminum fluoride, cryolite, chiolite, lithium fluoride and magnesium fluoride, the layer composed of a material having a higher refractive index n2 is composed of one or more materials of the group neodymium fluoride, gadolinium fluoride, dysprosium fluoride, lanthanum fluoride and aluminum oxide, and the layer composed of a material having the medium refractive index n3 is composed of one or more materials of the group magnesium fluoride, yttrium fluoride and silicon dioxide. The layer materials for the dielectric layer system are selected with regard, in particular, to increasing the reflectivity of the reflective optical element in such a way that the medium refractive index n3 differs from the higher refractive index n1 and from the lower refractive index n2 by at least 2%. In a further aspect, the object is achieved with an optical system for a lithography device or a microscopy device, and with a lithography device or a microscopy device for an operating wavelength in the DUV or VUV wavelength range comprising a reflective optical element as described. The microscopy devices can be wafer or mask inspection systems, for example. FIG. 1 shows a schematic basic diagram of a lithography device 1 for the DUV or VUV wavelength range. The lithography device 1 comprises, as essential components, in particular two optical systems 12, 14, an illumination system 12 and a projection system 14, which are both embodied as a catadioptric system in the present example. Carrying out the lithography necessitates a radiation source 10, particularly preferably an excimer laser, which emits for example at 308 nm, 248 nm, 193 nm or 157 nm and which can be an integral part of the lithography device 1. The radiation 11 emitted by the radiation source 10 is conditioned with the aid of the illumination system 12 such that a mask 13, also called reticle, can be illuminated therewith. To that end, the projection system 12 comprises at least one transmissive optical element and one reflective optical element. The lens element 120, which for example focuses the radiation 11, and the two mirrors 121, 122 are illustrated here in representative fashion. In a known manner, in the illumination system 12, a wide variety of transmissive, reflective and other optical elements can be combined with one another in an arbitrary, even more complex, manner. The mask 13 has a structure on its surface, said structure being transferred to an element 15 to be exposed, for example a wafer in the context of the production of semiconductor components, with the aid of the projection system 14. In modifications, the mask 13 can also be embodied as a reflective optical element. The projection system 14 also comprises at least one transmissive optical element and one reflective optical element. In the example illustrated here, two mirrors 140, 141 and two transmissive optical elements 142, 143 are illustrated in representative fashion, which serve for example in particular to reduce the structures on the mask 13 to the size desired for the exposure of the wafer 15. As in the case of the exposure system 12, in the case of the projection system 14 a wide variety of optical elements can be combined arbitrarily with one another in a known manner. FIG. 2 schematically shows the construction of a microscopy device 2 for the DUV or VUV wavelength range. In the present example, said microscopy device is embodied as a wafer inspection system and comprises an illumination system 16 and an imaging system 18, which are illustrated alongside one another for the sake of better clarity in the present example and are both embodied as a catadioptric system. Carrying out the wafer inspection necessitates a radiation source 163, particularly preferably an excimer laser, which emits for example at 308 nm, 248 nm, 193 nm or 157 nm and which can be an integral part of the microscopy device 2. The radiation 13 emitted by the radiation source 10 is conditioned with the aid of the illumination system 16 such that a wafer 17 can be illuminated therewith. To that end, the projection system 12 comprises at least one transmissive optical element and one reflective optical element. The lens element 160, which for example focuses the radiation 13, and the two mirrors 161, 162 are illustrated here in representative fashion. In a known manner, in the illumination system 16, a wide variety of transmissive, reflective and other optical elements can be combined with one another in an arbitrary, even more complex, manner. The radiation 13′ (shown displaced in a parallel fashion in FIG. 2) reflected at the surface of the wafer to be examined is guided through the imaging system 18 onto the detector 184 in such a way that structures on the surface of the wafer 17 are represented in an enlarged manner upon infringement on the detector, for example a spatially resolving surface detector, for instance on the basis of a CCD (charge-coupled device) sensor. The imaging system 18 also comprises at least one transmissive optical element and one reflective optical element. In the example illustrated here, two transmissive optical elements 180, 181, which serve for example in particular to magnify the structures on the wafer 17, and two mirrors 182, 183 are illustrated in representative fashion. As in the case of the illumination system 16, in the case of the imaging system 18 a wide variety of optical elements can be combined arbitrarily with one another in a known manner. Both the mirrors 121, 122, 140, 141 and the mask 13 from FIG. 1 and also the mirrors 161, 162, 182, 183 from FIG. 2 can be a reflective optical element, in particular for an operating wavelength in the range of 150 nm to 300 nm, comprising a substrate, a dielectric layer system and a metallic coating between the substrate and the dielectric layer system, wherein the dielectric layer system comprises a layer composed of a material having a lower refractive index n1 at the operating wavelength, a layer composed of a material having a higher refractive index n2 at the operating wavelength and a layer composed of a material having a refractive index n3 at the operating wavelength, where n1<n3<n2, wherein layers having a lower refractive index n1 and layers having a higher refractive index n2 are arranged alternately if more than respectively one thereof is provided, and a layer having a medium refractive index n3 is arranged at at least one transition from a layer having a lower refractive index n1 to a layer having a higher refractive index n2 and/or from a layer having a higher refractive index n2 to a layer having a lower refractive index n1. FIG. 3 schematically illustrates the construction of a reflective optical element 20 which is suitable for use in lithography using DUV or VUV radiation. A metallic coating 24 is arranged on a substrate 22. The substrate 22 can be composed of quartz, titanium-doped quartz glass, calcium fluoride or glass ceramic, for example. The metallic coating 24 comprises for example aluminum, an aluminum-silicon alloy, an aluminum-manganese alloy, an aluminum-silicon-manganese alloy, rhodium or a combination thereof, and serves primarily as a broadband mirror. In order firstly to protect the metallic coating 24 and secondly to influence the properties of the radiation reflected at the reflective optical element 20, a dielectric layer system 26 is provided on that side of the metallic coating 24 which faces away from the substrate 22, as a seal with respect to the vacuum. In one exemplary embodiment, illustrated schematically in FIG. 4, the dielectric layer system 26 comprises a four-layer sequence of (HMLM)m where L is the layer composed of a material having a lower refractive index n1 at the operating wavelength, H is the layer composed of a material having a higher refractive index n2 at the operating wavelength and M is the layer composed of a material having a refractive index n3 at the operating wavelength, wherein n1<n3<n2, and m is the integer number of four-layer sequences in the dielectric layer system. In the example illustrated here, m=1. The number m can be chosen arbitrarily in particular depending on the desired properties of the reflective optical element. Preferably, the layer 27 of the system 26 which is furthest away from the substrate 22 or the layer 25 of the system 26 which is second closest to the substrate 22 is a layer M having a medium refractive index n3. In the example illustrated in FIG. 4, both the second closest layer 25 and the layer 27 which is furthest away are composed of a material having a medium refractive index n3. The embodiment of a reflective optical element 20 proposed here, as illustrated by way of example in FIG. 4, thus comprises in its dielectric layer system two layers M having a medium refractive index n3 in addition to the known layers H and L having a higher and lower refractive index n1, n2, respectively. In a variant that is illustrated schematically in FIG. 5, the dielectric layer system 26 can also comprise a plurality of four-layer sequences 28 of (LMHM)m. In the example illustrated in FIG. 5, too, the layer 27 of the system 26 which is furthest away from the substrate 22 and the layer 25 of the system 26 which is second closest to the substrate 22 are a layer M having a medium refractive index n3. The dielectric layer system 26 comprises 2*m layers M. In further variants, at least one of the four-layer sequences 28 mentioned in connection with FIG. 4 or FIG. 5 can be arranged directly on the metallic coating 24 and/or as a block of the dielectric layer system 26 which provides sealing with respect to the vacuum or is furthest away from the substrate 22, and the remaining layers of the dielectric layer system can preferably be alternately arranged H and L and/or L and H layers. One or a plurality of four-layer sequences 28 can also be arranged at other positions within the dielectric layer sequence. The materials for the L and H layers can be always respectively one material or else, as described in U.S. Pat. No. 5,850,309, different materials in blocks. The material for the M layers is selected depending on the materials of the H and L layers respectively arranged in an adjoining fashion, with the proviso that n1<n3<n2 holds true at the operating wavelength for which the reflective optical element is optimized. In embodiments of a further reflective optical element, for example for a microscope device or for an optical system for a microscope device, instead of the four-layer sequences 28, three-layer sequences (HLM)m, (HML)m, (LMH)m or (LHM)m where m is the number of three-layer sequences 29 can also be arranged in the dielectric layer system 26, wherein it is likewise the case that n1<n3<n2. Said three-layer sequences are illustrated schematically in FIGS. 6 to 9. Moreover, both three-layer sequences 29 and four-layer sequences can be provided in a dielectric layer system 26. For the arrangement directly adjoining the metallic coating 24 on the side thereof facing away from the substrate 22, the three-layer sequences 29 (HML)m and (LMH)m illustrated in FIGS. 7 and 8 are preferred. For the arrangement furthest away from the substrate 22 or from the metallic coating 24, the three-layer sequences 29 (HLM)m and (LHM)m illustrated in FIGS. 6 and 9 are preferred. Preferably, in the case of reflective optical elements for an operating wavelength in the range of between 240 nm and 300 nm, the layer L, composed of a material having a lower refractive index n1 is composed of one or more materials of the group aluminum fluoride, cryolite, chiolite, lithium fluoride and magnesium fluoride, the layer H composed of a material having a higher refractive index n2 is composed of one or more materials of the group yttrium oxide, hafnium oxide, scandium oxide, zirconium oxide, aluminum nitride and synthetic diamond, and the layer M composed of a material having a medium refractive index n3 is composed of one or more materials of the group barium fluoride, gadolinium fluoride, lanthanum fluoride, neodymium fluoride, dysprosium fluoride, aluminum oxide, yttrium fluoride, ytterbium fluoride and silicon dioxide. In the case of reflective optical elements for an operating wavelength in the range of 150 nm to 240 nm, the layer L composed of a material having a lower refractive index n1 is composed of one or more materials of the group aluminum fluoride, cryolite, chiolite, lithium fluoride and magnesium fluoride, the layer H composed of a material having a higher refractive index n2 is composed of one or more materials of the group neodymium fluoride, gadolinium fluoride, dysprosium fluoride, lanthanum fluoride and aluminum oxide, and the layer M composed of a material having the medium refractive index n3 is composed of one or more materials of the group magnesium fluoride, yttrium fluoride and silicon dioxide. The layer materials for the dielectric layer system are selected with regard, in particular, to increasing the reflectivity of the reflective optical element in such a way that the medium refractive index n3 differs from the higher refractive index n1 and from the lower refractive index n2 by at least 2%. A reflective optical element composed of a quartz substrate having a metallic coating composed of aluminum comprises a dielectric layer system having five four-layer sequences of the type LMHM, that is to say 20 individual layers. It is designed for use with an excimer laser that emits at 193 nm. The reflectivity of this reflective optical element having a corresponding combination of high, medium and low refractive index materials previously mentioned as suitable for an operating wavelength in the range of 150 nm to 240 nm, given an angle of incidence of 10° with respect to the surface normal and unpolarized radiation, is above 95% for wavelengths of between 190 nm and 215 nm and then falls to values of between 95% and 90% to 250 nm. Between 250 nm and 300 nm, the reflectivity is still in the range of between approximately 88% and almost 90%. A reflective optical element having comparable reflectivity and comparable properties, but without medium refractive index layers, comprises a dielectric layer system having a significantly greater number of individual layers. Furthermore, a further reflective optical element composed of a quartz substrate having a metallic coating composed of aluminum was investigated, said further reflective optical element comprising a dielectric layer system having a first three-layer sequence of the type HML, an intermediate block of the type HLH and, providing sealing with respect to the vacuum, a second three-layer sequence of the type LHM, that is to say having a total of 9 individual layers. It is designed for use with an excimer laser that emits at 193 nm. The reflectivity of this further reflective optical element having a corresponding combination of high, medium and low refractive index materials previously mentioned as suitable for an operating wavelength in the range of 150 nm to 240 nm, given an angle of incidence of 20° with respect to the surface normal and unpolarized radiation, rises to a reflectivity of above 90% starting from a wavelength of approximately 186 nm and is above 95% for wavelengths of between approximately 196 nm and approximately 212 nm and then falls to values of between 95% and 90% up to approximately 275 nm. Up to 300 nm, the reflectivity decreases to approximately 82%. A reflective optical element having comparable reflectivity and comparable properties, but without medium refractive index layers, comprises a dielectric layer system having a significantly greater number of individual layers. A reflective optical element which is constructed in substantially just the same way, but in whose dielectric layer system the two layers composed of the medium refractive index material are omitted for comparison purposes, given likewise unpolarized radiation and given an angle of incidence of 20° with respect to the surface normal, has a significantly lower broadband characteristic and lower maximum reflectivity: The reflectivity rises to a reflectivity of above 90% starting from a wavelength of approximately 184 nm, and attains a maximum of approximately 94.8% at approximately 202 nm and falls below 90% again to give at approximately 230 nm. At approximately 244 nm, a local minimum of 87.2% is attained. In the wavelength range of approximately 268 nm to 300 nm, the reflectivity fluctuates in a range of approximately 90% to 91.2%. In variants comprising, instead of aluminum, a metallic coating composed of an aluminum-silicon alloy, an aluminum-manganese alloy, an aluminum-silicon-manganese alloy, rhodium or a combination thereof or with aluminum, comparable results were obtained. This also applies to variants which were optimized for excimer lasers that emit at other wavelengths, inter alia with materials suitable for an operating wavelength of between 240 nm and 300 nm. It should be pointed out that the reflective optical elements proposed here can have a reflectivity of above 90% even given a fixed wavelength of the incident radiation, but over an extended angle-of-incidence range of multiple 10°. |
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description | This invention relates to an illumination system for an electron beam lithography apparatus used for the manufacture of semiconductor integrated circuits. Electron beam exposure tools have been used for lithography in semiconductor processing for more than two decades. The first e-beam exposure tools were based on the flying spot concept of a highly focused beam, raster scanned over the object plane. The electron beam is modulated as it scans so that the beam itself generates the lithographic pattern. These tools have been widely used for high precision tasks, such as lithographic mask making, but the raster scan mode is found to be too slow to enable the high throughput required in semiconductor wafer processing. The electron source in this equipment is similar to that used in electron microscopes, i.e., a high brightness source focused to a small spot beam. More recently, a new electron beam exposure tool was developed based on the SCALPEL (SCattering with Angular Limitation Projection Electron-beam Lithography) technique. In this tool, a wide area electron beam is projected through a lithographic mask onto the object plane. Since relatively large areas of a semiconductor wafer (e.g., 1 mm2) can be exposed at a time, throughput is acceptable. The high resolution of this tool makes it attractive for ultra fine line lithography, i.e., sub-micron. The requirements for the electron beam source in SCALPEL exposure tools differ significantly from those of a conventional focused beam exposure tool, or a conventional TEM or SEM. While high resolution imaging is still a primary goal, this must be achieved at relatively high (10-100 μA) gun currents in order to realize economic wafer throughput. The axial brightness required is relatively low, e.g., 102 to 104 Acm−2sr−1, as compared with a value of 106 to 109 Acm−2sr−1 for a typical focused beam source. However, the beam flux over the larger area must be highly uniform to obtain the required lithographic dose latitude and CD control. A formidable hurdle in the development of SCALPEL tools was the development of an electron source that provides uniform electron flux over a relatively large area, has relatively low brightness, and high emittance, defined as D*α micron*milliradian, where D is beam diameter, and α is divergence angle. Conventional, state-of-the-art electron beam sources generate beams having an emittance in the 0.1-400 micron*milliradian range, while SCALPEL-like tools require emittance in the 1000 to 5000 micron*milliradian range. Further, conventional SCALPEL illumination system designs have been either Gaussian gun-based or grid-controlled gun-based. A common drawback of both types is that beam emittance depends on actual Wehnelt bias, which couples beam current control with inevitable emittance changes. From a system viewpoint, independent control of the beam current and beam emittance is much more beneficial. The present invention is directed to a charged particle illumination system component for an electron beam exposure tool and an electron beam exposure tool that provides independent emittance control by placing a lens array, which acts as an “emittance controller”, in the illumination system component. In one embodiment, a conductive mesh grid under negative bias is placed in the SCALPEL lithography tool kept at ground potential, forming a multitude of microlenses resembling an optical “fly's eye” lens. The mesh grid splits an incoming solid electron beam into a multitude of subbeams, such that the outgoing beam emittance is different from the incoming beam emittance, while beam total current remains unchanged. The mesh grid enables beam emittance control without affecting beam current. In another embodiment, the illumination system component is an electron gun. In yet another embodiment, the illumination system component is a liner tube, connectable to a conventional electron gun. The optical effect of the mesh grid may be described in geometrical terms: each opening in the mesh acts as a microlens, or lenslet, creating its own virtual source, or cross-over, having diameter d, on one side of the mesh grid. Each individual subbeam takes up geometrical space close to L, where L equals the mesh pitch. The beam emittance ratio after the mesh grid to the one created by the electron gun, equalsr=(L/d)2. In another embodiment of the present invention, the mesh grid includes multiple (for example, two, three, or more) meshes. In an odd numbered configuration (greater than one), the outward two meshes may have a curved shape; such a lens would enable beam emittance control and also reduce spherical aberration. In another embodiment of the present invention, the lens array is a continuous lens made of foil. Referring to FIG. 1, a conventional Wehnelt electron gun assembly is shown with base 11, cathode support arms 12, cathode filament 13, a Wehnelt electrode including Wehnelt horizontal support arms 15 and conventional Wehnelt aperture 16. The base 11 may be ceramic, the support members 12 may be tantalum, steel, or molybdenum. The filament 13 may be tungsten wire, the material forming the Wehnelt aperture 16 may be steel or tantalum, and the electron emitter 14 is, e.g., a tantalum disk. The effective area of the electron emitter is typically in the range of 0.1-5.0 mm2. The electron emitter 14 is preferably a disk with a diameter in the range of 0.05-3.0 mm. The anode is shown schematically at 17, including anode aperture 17a, the electron beam at 18, and a drift space at 19. For simplicity the beam control apparatus, which is conventional and well known in the art, is not shown. It will be appreciated by those skilled in the art that the dimensions in the figures are not necessarily to scale. An important feature of the electron source of SCALPEL exposure tools is relatively low electron beam brightness, as mentioned earlier. For most effective exposures, it is preferred that beam brightness be limited to a value less than 105 Acm−2sr−1. This is in contrast with conventional scanning electron beam exposure tools which are typically optimized for maximum brightness. See e.g., U.S. Pat. No. 4,588,928 issued May 13, 1986 to Liu et al. The present invention is shown in FIG. 2. A mesh grid 23 is disposed in the path of the electron emission 25 in the drift space 19. According to FIG. 2, the mesh grid 23 is placed in the electrostatic field-free drift space 19, insulated from the drift tube, or liner 20, and it is biased to a specified potential Um. The potential difference between the mesh grid 23 and the liner 20 creates microlenses out of each opening in the mesh grid 23. The electron beam 18 is split into individual subbeams (beamlets), and each beamlet is focused moving through its respective mesh cell, or microlens. The mesh grid 23 is separated from the liner 20 by an insulator 24. The mesh grid 23 and the insulator 24 may both be part of a mesh holder. One characteristic of the drift space 19 is that there is substantially no or no electric field present. The substantial absence of the electric field results in no acceleration or deceleration of electrons, hence the electrons are permitted to “drift”, possibly in the presence of a magnetic field. This in contrast to the vacuum gap 19a, which has a strong electric field. FIGS. 2(a) and 2(b) illustrate variations on FIG. 2. In particular, FIGS. 2(a) and 2(b) both show the mesh grid 23 within a liner 20 attached to an electron gun assembly 1. In FIG. 2(a), the liner 20 is attached to the electron gun assembly 1 via a liner flange 21 and an electron gun flange 16. In FIG. 2(b), the liner 20 is attached to the electron gun assembly 1 at weld 22. The liner 20 and electron gun assembly 1 could be attached by other techniques known to one of ordinary skill in the art, as long as the attachment is vacuum tight. Alternatively, the mesh grid 23 could be placed below the boundary between the liner flange 21 and the electron gun flange 16 or below the weld 22, within the electron gun assembly 1, as long as the mesh grid 23 remains within the drift space 19. One advantage of the embodiments illustrates in FIGS. 2(a) and 2(b) is that they permit the use of conventional non-optimal electron guns. A conventional electron gun produces a beam which is too narrow and too non-uniform. The arrangements in FIGS. 2(a) and 2(b) permit increased performance utilizing a conventional electron gun, since the mesh grid 23 contained within the liner 20 improves the beam emittance by making it wider and more uniform, which is more suitable for SCALPEL applications. The effect of the mesh grid 23 is more clearly illustrated in FIG. 2(c). The electron emission pattern from the Wehnelt gun of FIG. 1, is shown in FIG. 3. The relatively non-uniform, bell curve shaped output from the Wehnelt is evident. FIG. 4 illustrates the electron beam emittance through the mesh grid 23. The emittance on the left side of the mesh grid 23 is low, whereas after passing through the mesh grid 23, the emittance of the electron beam is much higher. The screen element that forms the mesh grid 23 can have a variety of configurations. The simplest is a conventional woven screen with square apertures. However, the screen may have triangular shaped apertures, hexagonal close packed apertures, or even circular apertures. It can be woven or non-woven. Techniques for forming suitable screens from a continuous layer may occur to those skilled in the art. For example, multiple openings in a continuous metal sheet or foil can be produced by technique such as laser drilling. Fine meshes can also be formed by electroforming techniques. The mesh grid 23 should be electrically conducting but the material of the mesh is otherwise relatively inconsequential. Tantalum, tungsten, molybdenum, titanium, or even steel are suitable materials, as are some alloys as would be known to one skilled in the art. The mesh grid 23 preferably has a transparency in the range of 40-90%, with transparency defined as the two dimensional void space divided by the overall mesh grid area. With reference to FIG. 4(a), the mesh grid has bars “b” of approximately 50 μm, and square cells with “C” approximately 200 μm. This mesh grid has a transparency of approximately 65%. Examples of mesh grid structures that were found suitable are represented by the examples in the following table. TABLE ICell dimension “C”, μmBar width “b”, μmGrid #120050Grid #28837Grid #35431 The cell dimension “C” is the width of the opening in a mesh with a square opening. For a rectangular mesh grid the dimension “C” is approximately the square root of the area of the opening. It is preferred that the openings be approximately symmetrical, i.e., square or round. The thickness t of the mesh grid is relatively immaterial except that the aspect ratio of the openings, C/t, is preferably greater than 1. A desirable relationship between the mesh grid parameters is given by:C:t>−1.5 In yet another embodiment, the lens array may include more than one mesh. In one embodiment, the lens array includes three meshes. The outer two meshes may be prepared having curved shape; such a lens would provide beam emittance control and decrease spherical aberration. In addition the outer two meshes may also be replaced with foils, such as an SiN foil, with a thickness of approximately 0.1 μm. Such a film would permit substantially no physical interaction (inelastic collisions), and therefore a transparency approaching 100%. Due to the large current being passed through the lens array (either mesh or continuous), the transparency is important. If a percentage of the beam impacts the structure of the mesh or continuous film, the high current is likely to melt the mesh or continuous film. FIG. 5 is more general representation of the optics of the present invention. 81 is the cathode of a standard high brightness electron gun, either a W hairpin, or a LaB6 crystal or a BaO gun as used in for example a CRT. 82 is the gun lens formed by the Wehnelt electrode and the extraction field. 83 is the gun cross-over with diameter dg. 84 is the electron beam emerging from the gun, with half aperture angle αg as they appear looking back from where the beam has been accelerated to 100 kV. The emittance of the gun is now E = π 2 4 d g 2 α g 2 After the beam has spread out to a diameter which is considerably larger than the diameter of the lenslets 85, the lens array 80 is positioned. Each lenslet 85 creates an image 86 of the gun cross-over with size di. Each subbeam 87 now has a half opening angle α. The emittance increase created by the lens array 80 can be derived. Liouvilles theorem states that the particle density in six dimensional phase space cannot be changed using conservative forces such as present in lenses. This implies that the emittance within each subbeam that goes through one lenslet is conserved and thus: N · π 2 4 d i 2 α i 2 = π 2 4 d g 2 α g 2 where N is the number of subbeams. The emittance of the beam appears to be N · π 2 4 L 2 α R 2 where L is the pitch of the lenslets 85 and thus V · π 2 4 L 2 is the total area of the lens array 80. The new emittance of the beam is termed the effective emittance. The emittance increase is Eeff/Egun=L2/di2. It is not necessary to create a real cross-over with the lenslet array. The calculation of the emittance increase then proceeds differently, but the principle still works. For a large emittance increase, it is beneficial to use a large pitch of the mesh grid 23. However, the newly formed beam should include a reasonably large number of subbeams so that the subbeams will overlap at essential positions in the system such as the mask. Example 1 illustrates typical values. A LaB6 gun of 0.2 mm diameter is used. The cross-over after the gun lens could be 60 μm, thus the emittance increase is a factor of eight using Grid #1 in Table 1. The lens array 80 may be the mesh grid 23 at potential V1, between liner 20 at potential V0as shown in FIG. 6, or include two grids 23 and 23′ at the potentials illustrated in FIG. 6(a ) or three grids 23, 23′, 23″ at the potentials illustrated in FIGS. 6(b) and 6(c), or any other configuration which contains a grid mesh with an electrostatic field perpendicular to the gridplane. The focal distance of the lenslets 85 in FIG. 5 is typically in the order of 4×Vacc/Efield, where Vacc is the acceleration potential of the electron beam and Efield the strength of the electrostatic field. In Example 1, the distance between the gun cross-over and the lens array could be typically 100 mm, calling for a focal length of about 50 mm to create demagnified images. Thus, at 100 kV acceleration, the field should be 10 kV/mm. In an alternative embodiment, if a specific configuration requires a strong field, the mesh grid 23 could be incorporated in the acceleration unit of the gun, between the cathode and the anode. This would have the additional advantage that the beam has not yet been accelerated to the full 100 kV at that point. In an alternative embodiment, the mesh grid 23 could also be incorporated in the electron gun in the Wehnelt-aperture 16 of FIG. 2. The mesh pitch must again be much smaller than the cathode diameter. This would lead to lenslet sizes in the order of μm's. The present invention has been confirmed by computer simulation with both Charged Particle Optics (CPO, Bowring Consultant, Ltd., and Manchester University) and SOURCE (by MEBS, Ltd.) models. In the SOURCE model, the mesh grid 23 is approximated by a series of circular slits. In both the CPO and SOURCE programs, a lens including two grounded cylinders with a biased mesh in the gap between those cylinders is simulated. FIG. 7 shows a detail of the SOURCE model, with fields. The lensfields are clearly visible in the openings in the mesh. Further, the modeling has been done with a three-dimensional simulation program CPO3d. FIG. 8 illustrates the potential distribution in the plane of the mesh. Again, the multi-lens effect in the mesh grid can be clearly seen. As indicated above the electron gun of the invention is most advantageously utilized as the electron source in a SCALPEL electron beam lithography machine. Fabrication of semiconductor devices on semiconductor wafers in current industry practice contemplates the exposure of polymer resist materials with fine line patterns of actinic radiation, in this case, electron beam radiation. This is achieved in conventional practice by directing the actinic radiation through a lithographic mask and onto a resist coated substrate. The mask may be positioned close to the substrate and the image of the mask projected onto the substrate for projection printing. SCALPEL lithography tools are characterized by high contrast patterns at very small linewidths, i.e., 0.1 μm or less. They produce high resolution images with wide process latitude, coupled with the high throughput of optical projection systems. The high throughput is made possible by using a flood beam of electrons to expose a relatively large area of the wafer. Electron beam optics, comprising standard magnetic field beam steering and focusing, are used to image the flood beam onto the lithographic mask, and thereafter, onto the substrate, i.e., the resist coated wafer. The lithographic mask is composed of regions of high electron scattering and regions of low electron scattering, which regions define the features desired in the mask pattern. Details of suitable mask structures can be found in U.S. Pat. Nos. 5,079,112 issued Jan. 7, 1992, and 5,258,246 issued Nov. 2, 1993, both to Berger et al. An important feature of the SCALPEL tool is the back focal plane filter that is placed between the lithographic mask and the substrate. The back focal plane filter functions by blocking the highly scattered electrons while passing the weakly scattered electrons, thus forming the image pattern on the substrate. The blocking filter thus absorbs the unwanted radiation in the image. This is in contrast to conventional lithography tools in which the unwanted radiation in the image is absorbed by the mask itself, contributing to heating and distortion of the mask, and to reduced mask lifetime. The principles on which SCALPEL lithography systems operate are illustrated in FIG. 9. Lithographic mask 52 is illuminated with a uniform flood beam 51 of 100 keV electrons produced by the electron gun of FIG. 2. The membrane mask 52 comprises regions 53 of high scattering material and regions 54 of low scattering material. The weakly scattered portions of the beam, i.e., rays 51a, are focused by magnetic lens 55 through the aperture 57 of the back focal plane blocking filter 56. The back focal plane filter 56 may be a silicon wafer or other material suitable for blocking electrons. The highly scattered portions of the electron beam, represented here by rays 51b and 51c, are blocked by the back focal plane filter 56. The electron beam image that passes the back focal plane blocking filter 56 is focused onto a resist coated substrate located at the optical plan represented by 59. Regions 60 replicate the features 54 of the lithographic mask 52, i.e., the regions to be exposed, and regions 61 replicate the features 53 of the lithographic mask, i.e., the regions that are not to be exposed. These regions are interchangeable, as is well known in the art, to produce either negative or positive resist patterns. A vital feature of the SCALPEL tool is the positioning of a blocking filter at or near the back focal plane of the electron beam image. Further details of SCALPEL systems can be found in U.S. Pat. Nos. 5,079,112 issued Jan. 7, 1992, and 5,258,246 issued Nov. 2, 1993, both to Berger et al. These patents are incorporated herein by reference for such details that may be found useful for the practice of the invention. It should be understood that the figures included with his description are schematic and not necessarily to scale. Device configurations, etc., are not intended to convey any limitation on the device structures described here. For the purpose of definition here, and in the appended claims, the term Wehnelt emitter is intended to define a solid metal body with an approximately flat emitting surface, said flat emitting surface being symmetrical, i.e., having the shape of a circle or regular polygon. Also for the purpose of definition, the term substrate is used herein to define the object plane of the electron beam exposure system whether or not there is a semiconductor workpiece present on the substrate. The term electron optics plane may be used to describe an x-y plane in space in the electron gun and the surface onto which the electron beam image is focused, i.e., the object plane where the semiconductor wafer is situated. As set forth above, in the present invention, an electron optical lens array is inserted into the illumination optics of the SCALPEL tool. The position of this lens array, or fly's eye lens, is such that each lenslet creates a beam cross-over with a smaller diameter d than the distance between the lenslets L, which increases the effective emittance of the beam by a factor (L/d)2. The electron optical lens array is a mesh grid with an electrostatic field perpendicular to the grid. One advantage over conventional systems is that the present invention allows the use of a standard high brightness electron gun. Another advantage is that the effective emittance can be varied without stopping a large part of the electron current on beam shaping apertures which is now the only way to change the emittance. Yet another advantage is that a homogeneous illumination of the mask may be obtained. Various additional modifications of this invention will occur to those skilled in the art. All deviations from the specific teachings of this specification that basically rely on the principles and their equivalents through which the art has been advanced are properly considered within the scope of the invention as described and claimed. |
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062529234 | claims | 1. A system for monitoring the integrity of contained spent nuclear fuel comprising: a sealed container; spent nuclear fuel in the container; at least one neutron and .gamma.-ray detector positioned to receive neutron flux and .gamma.-ray flux from the spent nuclear fuel; means for monitoring the integrity of the contained spent nuclear fuel based upon the detected neutron flux and .gamma.-ray flux; and at least one structural sensor for detecting the structural integrity of components within the container. 2. The system of claim 1, wherein the container is sealed by welding. 3. The system of claim 1, wherein the container is generally cylindrical. 4. The system of claim 1, wherein the spent nuclear fuel comprises at least one spent nuclear fuel assembly. 5. The system of claim 1, wherein the at least one neutron detector is positioned outside the container. 6. The system of claim 1, wherein the spent nuclear fuel comprises a plurality of spent nuclear fuel assemblies. 7. The system of claim 6, further comprising a neutron absorbing material inside the container between the spent nuclear fuel assemblies. 8. The system of claim 1, wherein the at least one neutron and .gamma.-ray detector is positioned inside the container and the system includes means for transmitting signals generated by the neutron and .gamma.-ray detector from inside the container to outside the container. 9. The system of claim 8, wherein the means for transmitting signals from inside the container to outside the container comprises an RLC circuit including the detector as a component providing a varying current and resistance and an external pick-up loop tuned to a resonant frequency of RCL circuit. 10. The system of claim 1, wherein the structural sensor comprises an interruptable circuit including a loop with an internal coil inside the container and an external coil outside the container for generating a reduced signal when the loop is interrupted. 11. The system of claim 1, wherein the at least one neutron detector comprises a semiconductor active region. 12. The system of claim 11, wherein the semiconductor active region comprises at least one material selected from the group consisting of SiC, Si, Ge, diamond, GaAs, GaP, PbO, PbBr.sub.2, PbI.sub.2, CdS, CdTe and CdZnTe. 13. The system of claim 11, wherein the semiconductor active region comprises SiC. 14. The system of claim 1, further comprising at least one temperature sensor positioned adjacent the container. 15. The system of claim 14, further comprising a plurality of the temperature sensors located outside the container. 16. The system of claim 15, wherein the spent nuclear fuel comprises at least one spent nuclear fuel assembly having an axial length and the plurality of temperature sensors extend in a substantially linear array along substantially the entire axial length of the spent nuclear fuel assembly. 17. The system of claim 1, further comprising a plurality of the neutron and .gamma.-ray detectors. 18. The system of claim 17, wherein the neutron detectors are positioned in a substantially linear array. 19. The system of claim 18, wherein the spent nuclear fuel comprises at least one spent nuclear fuel assembly having an axial length and the substantially linear array of neutron detectors extends along substantially the entire axial length of the spent nuclear fuel assembly. 20. The system of claim 19, wherein the spent nuclear fuel comprises a plurality of the spent nuclear fuel assemblies, a neutron absorbing material is disposed inside the container between the spent nuclear fuel assemblies along the axial length thereof, and the array of neutron detectors includes means for detecting a removal of the neutron absorbing material along at least a portion of the axial length of the spent nuclear fuel assemblies. |
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description | This invention relates to a method and system for the production or generation of heat by extracting the heat released when nuclei are fused together. There is a global need for an intensive source of energy which has security of supply, does not pollute and does not add to greenhouse gases. Such energy sources comprise hot gases and liquids which may be used in processes for providing useful outputs. These include industrial or domestic heat for direct heating of materials as in metal extraction or in chemical reactions or heating for buildings. These energy sources may also be transformed into kinetic energy through engines and the generation of electricity, which may be more convenient for some applications such as motors and vital for others such as lighting and electronic apparatus. Intensive sources of energy currently in use are derived from fossil fuels or nuclear power stations. Fossil fuels are not always found where they are needed, so that they require transportation in bulk around the globe. They produce energy by combustion which always makes greenhouse gases because it is a chemical reaction. Chemical reactions occur at the level of electrons in atoms. By contrast nuclear power depends on the re-arrangement of atomic nuclei with the release of heat. There are essentially two main types of reaction: fission of large unstable nuclei, and fusion of light nuclei. Nuclear fission depends on critical masses of dangerously radioactive fissionable material. As a result it is inherently suited only to the generation of electricity in massive installations. The chain reactions involved require elaborate, expensive control systems to prevent run-away reactions resulting in a meltdown. The entire installation is contaminated with radioactivity, some of which may last for generations and even millennia. There are no known ways of accelerating the process of radioactive decay. More satisfactory in principle than nuclear fission is nuclear fusion, in which nuclei of light elements such as hydrogen are caused to fuse to form larger stable nuclei such as those of helium. The fusion reaction releases vastly more energy than fission, the input materials are abundant and the products are potentially harmless. However, extremely high temperatures are necessary for fusion to occur, and it may even be necessary to use nuclear fission explosions to obtain enough heat to initiate the process of nuclear fusion. Even if conditions are reached which may be suitable for fusion, say in a plasma, the temperatures are so high that the reactor or torus may be badly damaged. To extract heat, it is necessary to keep the reactants from direct contact with the walls of the vessel by elaborate engineering. Nuclear fusion occurs naturally in the Sun and heat is produced predominantly by the conversion of hydrogen to helium, which gives a present composition of 74% hydrogen, 25% helium by mass and only the smallest traces of higher elements. Helium has a nucleus so stable that it is known as an alpha-particle. Heat is generated on the formation of the helium nucleus as the vibration of the new configuration of nucleons, which is another form of kinetic energy. Energy is also emitted in various forms as light, for example ultraviolet light, X-rays, visible light, infrared, microwaves and radio waves. Energy is transmitted to nearby atoms and nuclei, adding to their vibration, and increasing their temperature. The very small proportions of elements with higher atomic mass in the Sun shows that these elements are much more difficult to produce. They are thought to originate in supernova explosions which reach very much higher temperatures than the Sun, far too high to reach in an apparatus on Earth. The fusion of hydrogen nuclei to form helium nuclei is essentially the product of collision at high velocities, which is another way of describing temperature. High pressures in the Sun force particles close enough for any resulting vibration to be transmitted to the bulk of the gas, i.e., spreads the heat. The formation of a helium nucleus from protons is a slow process requiring multiple collisions and astronomical times, so that it is less likely that it could be reproduced economically. There is, however, the possibility of producing helium from the collision of two deuterium nuclei, which occurs naturally. This would be a faster process and yield a greater output of energy, because half the work of fusion is already done. However, the nature of the process is that only one collision is possible, because a hot helium nucleus would not be able to absorb any other nuclei to continue fusion. It would become a hot helium atom and lose its kinetic energy by warming up surrounding gases and the wall of the reactor. The other candidate, tritium, does not occur naturally, and the collision of two tritium nuclei would also be a single event, as would be the collision of, say, a deuterium nucleus with a tritium nucleus. Moreover, the stoichiometry of the reactions suggests the possibility of forming radioactive by-products. However, the introduction of a few tens of grammes of tritium into the plasma of a torus has been shown to produce a significant temperature rise. The invention is defined in the appended claims to which reference should now be made. Preferable features are defined in the dependent claims. In one embodiment, a process for the generation of heat by the fusion of light atomic nuclei is disclosed. The fusion of light nuclei according to embodiments of the invention takes place inside the product of collision, herein called the collision mass, of a heavy ion with a heavy particle, ion, plasma or atom at velocities which are comparable to, or a fraction of, the speed of light. Fusion temperatures are obtained by the collision in a collision zone of one or more heavy ions travelling at speeds which are substantial with respect to the speed of light, with target heavy ions or atoms. Embodiments of the present invention have the advantages that no radioactive material is produced, and the atomic species used in the process are readily available. Only small quantities of reaction materials are reacting in the process at any one time, and so there is no possibility of a runaway reaction. The problems of controlling large quantities of material at very high temperatures are avoided. The plant is not contaminated by radioactivity and toxic waste and so it can be decommissioned at the end of its life in substantially the same way as other industrial plant. There is no cost of very long term storage of radioactive waste and plants, such as arises from nuclear fission reactors. It is an advantage of the present invention that high temperatures are obtained and fusion occurs without the possibility of macroscopic damage to the apparatus. It is a further advantage of the process of this invention that it is fail-safe, because if the stream of heavy ions fails, the process stops. Embodiments of the invention use input materials which are readily available, does not produce harmful by-products, does not use or produce radioactive materials and does not add to greenhouse gases. Referring to FIGS. 1-3, and the flow chart of FIG. 4, a particle accelerator 101 or other accelerator is used to accelerate one or more first particle(s), preferably ion(s) or heavy ion(s) 17 to a first velocity with a high speed component which is preferably a speed comparable to the speed of light, step 41. This is performed under a partial vacuum. The accelerator 101, or a second accelerator, is also used to accelerate one or more second particle(s), preferably ion(s) or heavy ion(s) 23 to a second velocity with a high speed component which is preferably a speed comparable to the speed of light, step 45. Once again, this is performed under a partial vacuum. The trajectories of the two accelerate particles is arranged such that when the particles meet in a collision zone 11, the directions of the velocities of the first and second particle(s) are substantially opposite. Therefore the target second particle(s) 23 takes the form of one or more particle(s) 23 with a high speed and a direction opposite to that of the direction of the other first particle(s) 17. Preferably both particles have a speed which is comparable to the speed of light, to increase the impact of collision. The particle(s) 17 is then collided in the collision zone or colliding section (collider) of the apparatus with the second one or more second particles 23, 10 preferably a heavy particle 23 to form a coherent entity or collision mass, 15. The collision zone is located within a housing allowing the trajectories of the particles to be controlled by electromagnetic (EM) fields. These EM fields may comprise electric or magnetic fields or both, and are generated by EM control field generators 103. Furthermore, a partial vacuum is maintained within the housing so that particles can be accelerated and collided without interference from unwanted particles. The partial vacuum is maintained by vacuum pumps (not shown) known to those skilled in the art. The collider is the section of the apparatus in which the collision takes place. This is shown as the collision zone 11 in FIG. 1. This can be the part of the apparatus where the two accelerated particles collide. Where opposing particles collide, both particles comprise ions 17,23 so that they can be accelerated using a particle accelerator 101 along a line of collision 19 using techniques known to those skilled in the art, for example using electromagnetic fields, steps 41, 45. Both particles can be accelerated using a single accelerator and then fed into the collision zone at the appropriate time or, alternatively, two accelerators can be used so that each particle is accelerated by its own accelerator. Particle accelerators which may be used are those capable of accelerating particles to velocities preferably greater than a third of the speed of light. Suitable accelerators are linear accelerators and synchrotrons, in which electric and magnetic fields accelerate and control streams of ions. Successive stages of acceleration may be used, and one accelerator may provide the input for another. Such an arrangement may include a Van de Graaff electrostatic generator. Ions progressively lose more electrons as they pass through the stages of acceleration. The greater the mass of the ion, the lower the speed needed to produce a suitable collision mass, which requires less capital investment and running costs. When the accelerated particles are, for example, streams of ions or single ions, synchrotrons with intersecting storage rings and facilities for reversing flows can be used. Particles may pass through several stages of boosters before reaching storage rings, such as a linear accelerator, a booster synchrotron or an alternating gradient synchrotron individually or in series. Particles maybe injected from the storage rings as required for collision at points where the rings cross. This allows the particles to collide, and provides complete control over the entire process of heat generation. The energy of collision of two particles 17,23 depends on the momentum of the particles, which is proportional to their mass and velocity. It is their change of momentum on impact which smashes the structure of the ions. A range of particles may be used in the collision stage to produce optimum properties for engineering and physics. Examples of heavy atoms or ions which may be used as the first and second particles are copper, gold, platinum, silver, uranium, lead and iron. Rare earths (elements of the lanthanide series of the periodic table with atomic numbers from 57 to 71 inclusive) may also be used. The ions need to be easy to make and stable enough to accelerate to the desired velocities. Elements with an atomic number greater than argon (atomic number 18) may be suitable for the collision process. An important criterion is the nature of the collision product, which needs to be coherent enough to attract light ions by gravitational and electrostatic attraction and also needs to be not excessively dispersed. Such coherent entities have already been obtained with copper, gold and lead. However, it may not be necessary to cause the complete disintegration of the particles to subatomic or fundamental particles to form a collision mass which is capable of producing fusion of absorbed light atomic species. It is desirable to produce fusion at as low a temperature as possible in order to limit the power needed to accelerate the ions. The energy input for acceleration increases hyperbolically as the ion approaches the speed of light. Much of the energy input is wasted as electromagnetic emissions, which does not affect the particle's kinetic energy. Thus even a small reduction in velocity can save a considerable amount of power input, as long it forms a collision mass which is coherent and hot enough to cause the fusion of particles, preferably light nuclei which enter it. The most energy efficient process is, therefore, to use the heaviest available ion at the lowest possible speed to achieve a collision mass capable of fusing particles which are introduced into it. Accelerating a particle to a velocity of about a third of the speed of light consumes only a few percent of the power needed to accelerate to velocities close to the speed of light. Then if two particles are collided with opposing velocities, each at a speed of a third of the speed of light, the effective speed of one of the particles viewed from the reference frame of the other particle is approximately 0.6c, where c is the speed of light, using relativistic addition of velocities. This is enough to promote fusion of some light nuclei such as tritium when they are subsequently introduced (for example injected or fed) into the collision mass. These particles may be controlled by electric or magnetic fields or both so that they can be introduced into the collision mass. The collision mass does not have to destroy the light nuclei, but simply nudge them into a new configuration. Another advantage of a lower velocity is that it facilitates the orientation of trajectories, which is important for arranging collisions. The following description refers to the first and second particles being heavy ion(s). However, other particles maybe used as previously described. Each collision of one or more first and second heavy ion(s) produces a collision mass 15 with a high temperature, step 47. Collision masses are the loci for the fusion of further particles 13, preferably light nuclei. If the colliding particles are of equal mass and velocity, their momenta cancel out, and the entities formed by collision are comparatively stationary in the collision zone 11. If, however, one of the particles has a lower velocity or is stationary at the instant of collision, the momentum of the high velocity heavy ion is imparted to the whole collision mass 15. Further description of the nature of the collision mass is given in the attached appendix, to which reference should now be made. The residence i.e. the position of the collision mass (es) in the reaction chamber (housing) and lifetime of collision masses are controlled by choice of atomic number of the particles involved and the use of electromagnetic (EM) containment fields generated by an EM control field generator 103, step 48. These fields may comprise electric or magnetic fields or both, and allow for the location of the collision mass within a housing 105 of the apparatus to be controlled, as well as for stabilising the collision mass. The control field generator 103 shown in FIGS. 1 and 5 is in schematic only. Those skilled in the art will appreciate that the actual coils and plates necessary to provide the containment fields will be located inside the housing 105 needed to contain the particle (s) accelerated under a partial vacuum. Furthermore, containment fields may be located above and below the collision mass 15, and these are not shown in the Figures for clarity. The housing 105 containing the partial vacuum and containing the collision mass are known to those skilled in the art. It may comprise metal, for example stainless steel tubing, joined together for example using nuts and bolts or/and welding. The force of collision of the one or more first and second particles at velocities which are comparable to the speed of light is sufficient to reduce them to more fundamental particles for example quarks, which cluster together to form a coherent collision mass, as shown in FIGS. 1 and 2. The collision mass may also contain one or more protons or/and neutrons. The collision mass is maintained in the collision zone by the use of electric or magnetic fields or both generated by the EM control field generator 103. The collision mass has a surface of expelled electrons 25 which occupy a diffuse boundary 26 between the core 27 and the outside. At the surface are electrons 25 which have been displaced by the energy of the collision, because they are mobile. The core, 27, which contains by far the largest proportion of the mass, comprises substantially fundamental particles of which nuclei, protons and neutrons are composed, for example quarks. The positive charges in the core may be more evenly distributed. Therefore, the collision mass is a coherent entity with a mass which is approximately equal to the combined masses of the colliding heavy atomic species, but substantially devoid of atomic and nuclear structure as a result of the energy of the collision. The entity has an effective temperature which may briefly approach that of stellar bodies. However, collision is in part a random process, and so most first particle(s) 17 pass the second particle(s) 23 without colliding, and so is therefore preferable to use a stream of particles to form one or more collision masses. A stream (plurality) of first ions (rather than a single ion) 17 is preferably accelerated using the particle accelerator 101 and this stream is then preferably incident on a plurality (stream) of second particles, ions, or heavy ions 23 with a velocity which is substantially opposite in direction to that of the first stream of particles. The advantage of using streams of particles or ions is that there is a greater probability of collision of two particles. In one embodiment, the stream of particles or heavy ions comprises many millions of particles to achieve a sufficient number of collisions to generate useful heat. This represents a very small mass of material, because a kilogram contains many billions of heavy ions, which limits the possible extent of any damage to the surrounding apparatus. Further description of the quantities of reactants needed in order to produce heat according to embodiments of the invention is given in the attached appendix, to which reference should now be made. If streams of particles or heavy ions are collided with either an opposing stream of particles, heavy ions or a stationary particles or heavy atom, ion or particle, the collision masses form in the collision zone 11 as a cloud or “gas”. Collision masses remain separate from each other during the process because of electrostatic repulsion. The collision mass forms a cloud because collisions between particles from each stream of particles occur at slightly different locations which leads to a cloud of collision masses. The collision masses are distributed randomly in the cloud of collision masses situated in the collision zone, and each collision mass is of roughly nuclear dimensions and with extremely high temperatures for a short time. Particles which do not collide continue out of the reaction zone and play no further part except that, for the sake of economy, they may be recycled back into an earlier stage of the process. Nuclear fusion is defined in the Encyclopaedia of Applied Physics as the amalgamation of a projectile and a target nucleus to form another nucleus. According to this definition, the formation of a collision mass is not nuclear fusion, because a collision mass does not have a unique mass and is not the nucleus of a recognised element of the Periodic Table. As an unstable entity it degenerates into smaller entities, which may become recognised nuclei. The collision mass (es), formed by the collision of two heavy ions is heavy enough to form an entity with sufficient mass and charge to pull the raw materials for fusion into its interior by gravitational and electrostatic attraction. These materials are injected or introduced 13 into the collision zone, 11. This collision mass is a miniature sun or “fireball”. The charge of the collision mass allows it to be controlled and stabilised by electric and magnetic fields 48 so that it can act as an individual nuclear furnace for fusion reactions. It is held in the collision zone by these electric or/and magnetic fields long enough for one or more further particles, preferably light particles 13 (e.g. ions, atoms, molecules or plasma of low atomic number) to be injected or introduced (fed) into the collision (reaction) zone 11, step 43 where one or more of the further particles are drawn into 29 the collision mass by electrostatic and gravitational attraction. Appropriate particles 13 may also comprise protons, which undergo thermonuclear fusion to helium nuclei. This is analogous to the proton-proton reaction which generates the heat of stars, although other fusion reactions may be used. Light ions, atoms or molecules may be mixtures as required by the stoichiometry of the fusion reaction. Light ions, atoms and molecules are generally those with atomic numbers less than that of argon which has an atomic number of 18. Hydrogen, deuterium, tritium and lithium are particularly favourable for absorption by the collision mass and nuclear fusion. The most reactive and least likely to produce radioactivity is deuterium. Light ions, atoms or molecules may be fed separately or mixed in stoichiometric proportions as appropriate for nuclear fusion. Input energy may be saved by cracking molecules, e.g., thermally, before injecting them into the fusion stage, which may facilitate absorption into the collision mass. These particles 13 pass through the collision mass 15 or cloud of collision masses when these are at their hottest, step 43, and undergo tjsion with other particles which have entered the collision mass, for example light ions and release energy and heat. These particles 13 may also fuse with protons and neutrons originating from the heavy ions which have survived the collision and with the fundamental particles resulting from protons and neutrons destroyed in the collision. The process of producing heat by nuclear fusion may be terminated at this point (after heat extraction via for example heat exchangers described later), or alternatively, additional further particles, preferably light ions etc. maybe introduced or fed into the collision zone. A proportion 29 of the additional further particles are drawn into the collision mass on a random basis by electrostatic and gravitational attraction, together with fragments of heavy ions from other collisions, as shown in FIG. 3. Once the further particles have been drawn into the collision mass, they undergo fusion with the fundamental particles inside the collision mass and release heat. The zone of attraction of a collision mass is much greater than nuclear dimensions because of these electrostatic and gravitational forces. The release of further fusion energy further increases the temperature of the collision mass(es) 15. The heat of fusion in the form of the vibration of the nucleons of the resulting fused products, for example, a helium nucleus spreads to the rest of the collision mass in which it forms, and raises the temperature of the collision mass. This allows more particles, for example, light nuclei to be pulled into the collision mass to fuse and generate heat, if required. This succession of fusions ensures that the output of energy from the process is greater than the input. By this process, each heavy nucleus which takes part in a collision may give rise to the fusion of many light nuclei. Preferably in one embodiment, heat is generated by the fusion of light particles in many such collision masses forming a cloud or gas of collision masses. The cloud of collision masses are contained and stabilised by electric and magnetic fields. Even if one collision mass is formed or a cloud of collision masses is formed, the thermonuclear reaction is controlled by regulating the feed rate of further particles, preferably light particles 13. This may be continuous or intermittent. Methods of feeding the further, preferably light particles 13 are known to those skilled in the art and are not shown in the Figures, and comprise thermal evaporation and laser techniques, or a stream of plasma. Laser beams can be used as concentrated heat sources to cause evaporation when they are applied to bulk materials. If, however, a collision mass does not succeed in capturing light atomic species for fusion, it cools down, congeals into heavy ions again or mixtures of lighter ions, and becomes waste. There is, however, a limit on the thermonuclear reaction that it produces inert species such as helium which dilute the collision mass. After a succession of fusions inside a collision mass the quantity of inert species such as helium formed will dilute the reaction mixture inside the collision mass causing it to expand, reduce its temperature and so stop the fusion reaction so that no more fusion reactions can occur. This may be after a hundred or more fusions have taken place with the generation of proportionately large quantities of heat from a single collision of heavy ions. For that particular collision mass the process comes to and end, and it becomes effectively very hot gas. In this way it is possible to regulate fusion a few nuclei at a time. The temperature increase produced by each collision and subsequent fusion of particles or elements is temporary and, so in one embodiment, a continuous process for manufacturing heat requires new collision masses to be produced. Therefore, it is preferable to use a stream of heavy ions so that new collision masses can be created using the accelerator. The process can be terminated at any instant by stopping the flow of the stream of particles, for example, heavy ions into the collision zone. The position of collision masses and the fusion products is controlled by electric or/and magnetic fields generated by the EM control field generator. Preferably, in order to extract heat, the hot collision mass and fused particles may then evacuated using an extractor 79 for heat production. The extractor may simply comprise further electric or magnetic containment fields which progressively move the fusion reaction products along a housing 105 or tube which is surrounded by a heat exchange fluid so that heat can be extracted indirectly from the hot reaction products by extracting heat from the heated fluid surrounding the housing or tube using a heat exchanger. Alternatively a vacuum pump 79 can be used for heat extraction 21, step 56. The hot fusion reaction products can then be used directly as a source of heat or, alternatively, can be used indirectly to generate electricity via known methods. In one embodiment, the creation of collision masses is a continuous process by colliding streams of particles. The bulk temperature of the collision masses is controlled by the flow of the collision masses through the feed of the further particles, preferably light ions, which then subsequently undergo fusion, and therefore increase the temperature of the collision mass. The streamlined flows are determined by the geometry of the reactor. The more further particles, for example, light species, which are fed into the collision mass, the more fusion reactions that will occur and the more heat will be released, up until the collision mass is cooled by the production of the helium by-product. Heat is extracted from such a bulk process either directly as hot gases or indirectly by heat exchange as previously described. In this embodiment, the whole process is analogous to a chemical flow reactor, but with reactions at the nuclear instead of the electronic level. The same considerations of flow rates, residence times, heat transfer and separation techniques are applicable as in chemical engineering practice. The kinetics of the process depend on the probabilities of collision, numbers of ions, etc., just like the molecules of chemical reactions, because the streams are composed of billions of heavy and light ions. There is the possibility of back-mixing as well as plug flow and injection of plasmas of ions of the same or different species. Plug flow is where the reactants flow straight through the reactor and the reaction proceeds as the reactants travel through the reactor. Back mixing is where some of the reactants or resulting products are fed back into the input of the reactor. The stream of ions may also contain different constituent ions. Gases may be injected to improve the streamlining of flows, keep the high temperature plasma and gases from the walls of vessels, minimize losses and introduce chemical reactants to obtain specific effects. The process may preferably be continuous with electromagnetic control of flows, since the species are charged, but it may also be carried out as semi-continuous or batch reactions, which would produce heat in bursts. The other feature of the process according to embodiments of the invention is that, since it has to be carried out in high vacuum, there is an extraction system in the form of vacuum pumps at the output end of the apparatus. This also serves to suck out the reaction products in the form of hot gases, either for direct use or through heat exchange. FIG. 5 shows a schematic process for nuclear fusion according to a further embodiment in which fusion is achieved by colliding one or more first particle(s), preferably a heavy ion 17 from an accelerator with substantially stationary injected second particle(s), for example, heavy ions 31, atoms or plasma. Referring to FIG. 5, a particle accelerator 101 or other accelerator is used to accelerate one or more first particle(s) 17, preferably an ion or heavy ion 17 to a high speed, preferably a speed comparable to the speed of light. This is performed under a partial vacuum. The first particle 17 is then collided in the collision zone 11 or colliding section (collider) of the apparatus with one or more second particle(s), preferably a heavy particle or ion 31, to form a coherent entity or collision mass, 15. This target second particle 31 is stationary or at a relatively low speed in the collision zone 11 in which the collision takes place. Preferably the first particle (s) have a speed which is comparable to the speed of light, to increase the impact of the collision. The collider is the section of the apparatus in which the collision takes place. This is shown as the collision zone 11 in FIG. 5. This can be the part of the apparatus where the first accelerated particle(s) collide with the second substantially stationary particle(s). This produces a collision mass with enough heat to cause the fusion of the subsequently injected further particles, preferably light nuclei 13. A stationary cloud of second particles, preferably heavy ions or atoms 31, can be formed from heavy elements by known techniques of gasification by hot wire and laser techniques, which give atomised or substantially atomised particles. This requires less energy than a stream of heavy ions, and allows optimisation of the concentration of heavy atoms in the cloud or gas to increase the chances of suitable collisions. The heavy atomic species and plasma for collision are injected 31 into the collision zone, 11 for heavy atomic species. The stationary cloud of heavy ions may also take the form of a plasma prepared separately and introduced into the collision zone to facilitate the fusion reaction. Preferably the first particles 17 comprise a stream of accelerated particles and these are incident on a plurality of second particles 31 which are substantially stationary in the collision zone 11. This has the advantage of the increased probability of collision, which was explained with reference to previous embodiments. The position and lifetime of the collision mass can be controlled by electric or and magnetic fields generated by an electric or and magnetic (EM) control field generator 103 so the collision mass can be positioned in the housing 105 such that further particles can be introduced to undergo fusion in the collision mass. The remaining the steps for the production of heat according to this embodiment are the same as those in the previous embodiment, and so will not be described in further detail. As in previous embodiments, a heat extractor 79 may be used in order to extract the hot fusion reaction products and collision mass. As in previous embodiments, the hot extracted products may then be used directly for heat production or indirectly to produce electricity. Alternatively, the heat extractor may comprise a heat exchanger to extract heat from the housing 105 without the need to remove the reaction products from the housing 105. In all embodiments, it is preferable to use a stream of a (carrier) gas 61, such as hydrogen, helium or other species which is inert at the high temperatures produced by fusion, to sweep the hot plasma and gas of the collision mass out of the reaction zone to provide heat for industrial and other purposes. The heat can be converted into electricity or other energy using techniques known to those skilled in the art, for example turbines, and burners or heat exchangers. This is schematically shown in FIGS. 6 and 7. For clarity, in FIGS. 6 and 7, the EM control field generators are not shown. The carrier gas may be injected 61 so as to form streamlines 63 so as to act as barriers between the hot fusion products and the walls of the apparatus (housing) 105. The streamlines allows controlled mixing 65 of the carrier gas and the fusion products and collision mass(es) so that they are further away from the walls of the housing. The carrier gas reduces the temperature of the fusion products, particularly near the walls of the housing 105. The carrier gas helps to reduce the corrosion of the walls of the housing and also reduces the corrosion of any extraction equipment for extracting the hot collision mass and fusion products. The carrier gas may also be added tangentially to form a vortex into which hot fusion products are sucked and in which they are contained so as to prevent contact with the walls of the housing 105. The carrier gas 61 mixes 65 progressively with the hot gases of reaction in a streamlined flow 63 as it moves along the tube and reduces their temperature to a bulk temperature suitable for extraction by vacuum pumping apparatus 79. The carrier gas may be injected as streamlined flows immediately after the port through which light atomic species are injected for fusion, as shown in FIGS. 6 and 7. There may also be an advantage in using at least a proportion of hydrogen in the carrier gas, because hydrogen is the most efficient neutron moderator. Although no radioactive materials are required as inputs into the processes according to embodiments of the invention, there is a small possibility that some of the thermonuclear reactions may produce a few ancillary neutrons, though reactions would be preferred which avoid this. If any neutrons are produced, hydrogen from the collision product would reduce any potentially harmful effects. Hydrogen in the carrier gas would enhance this. There is a possible additional operation after that to inject electrons by electrodes to neutralize residual protons and assist the formation of hydrogen gas. After the extraction/vacuum pump, there are two possibilities as shown in FIGS. 6 and 7. In one embodiment, the hot output gases may be collected into a reservoir or used directly in other processes. If the carrier gas is hydrogen, this may be used to drive turbines and burnt as a fuel to complete the extraction of energy. Alternatively, in a further embodiment, the hot output gas may be pumped through a heat exchanger 111 to extract heat, and then recycled and injected back into the process as carrier gas, as shown in FIG. 7. It may be particularly advantageous to use helium as a carrier gas because it is less corrosive at high temperatures. An additional process would remove hydrogen from the recycled stream as the economics required. The processes of forming collision masses according to the embodiments by collision with stationary targets and collision of opposing streams are not mutually exclusive. It may be advantageous to use the collision of opposing streams in the presence of a cloud of atomic species or plasma injected into the collision area at the appropriate time. Light atomic species are introduced into the reaction zone in which collisions have occurred or are still occurring while the temperatures in the collision masses are high enough to cause fusion of the light nuclei. The reaction chamber is the section of the collider in which collision takes place with additional ports as necessary for injection of light ions, atoms or molecules and exhaustion of products. The reaction chamber is equipped with electric and magnetic fields for stabilisation of the collision products to keep them in position. The kinetics of heat production depend on the statistical probabilities of collision followed by absorption from streams of light ions. In the absence of direct observation, which is a feature of all bulk nuclear reactions, the simplest method of control is by measuring the temperature of the output. Similarly the number of collision masses formed from opposing streams will be a small proportion of the number of ions in each stream. To generalize, processes which depend on statistical probabilities are most easily controlled by feedback from output to input, in this case from temperature to rates of flow of ions, atoms and molecules. This is comparable with the situation in industrial and laboratory chemical processes, where analysis of outputs is used to follow the progress of reactions. The extraction of the hot ion and gas output stream from the fusion process is by the technique similar to that used to connect storage rings and divert flows in accelerators. Any residual heavy ions can be separated by the same sort of magnetic field techniques used in mass spectrometry. Hot plasmas and gases may be cooled to temperatures suitable for engineering purposes by diluting with gases, the flow of which may be directed to keep the high temperature stream from the walls. Storage systems may be used to smooth the flow of heat output. The hot gases can then be used as an input into other processes either directly or after heat exchange. They may be used to drive turbines or generate superheated steam which is used to drive turbines, as for the generation of electricity. Such electricity may be used to produce ambient temperature hydrogen for processes or distributed power generation, as in fuel cells. Hot gases may be used directly in the smelting of ores, or passed through heat exchangers to produce process heat for oil, chemicals and metallurgical processes. A whole complex of different processes may be fed from a thermonuclear heat generation plant. It may be particularly advantageous to dilute the plasma or gas from the storage vessel with hydrogen, because the output from the fusion reaction is likely to be largely hydrogen with a small proportion of helium. The entire output of hot gas may then be used directly in a burner to provide heat and dispose of waste product together with the production only of water, i.e., no greenhouse gases. Alternatively the inert gas nitrogen may be used as diluent, and simply vented to air after it has done its job. The total process of thermonuclear heat generation requires a substantial quantity of electricity to start up, and operate the accelerators and ancillary equipment, but once going it can produce more than enough electricity for its own purposes because of the fusion reaction. Ultimately the process becomes self-sustaining, while at the same time being self-regulating. In a further embodiment, the further particles to undergo fusion in the collision mass, for example, light atomic species may also be accelerated using a particle accelerator or other device to a high velocity in the same direction as the first particles 81. The further particles or light ions can be accelerated using the same accelerator used for accelerating the first ion or ions used to form the collision mass. A mixed high velocity stream of concurrent ions for collision and further ions such as light ions for fusion are accelerated 81 in the accelerator. Alternatively, a separate particle accelerator can be used. This embodiment is illustrated in FIG. 8. When, for example, the heavy ions collide with one or more second particle(s) 31, for example, another heavy atomic species, to form a collision mass, the light ion is then already present to be drawn into the collision mass for fusion. This embodiment has the advantage that precision timing is not needed in order to inject the further particles needed for fusion at the appropriate time. Preferably, both the first accelerated ion and the further particles or ions needed for fusion in the collision mass are stored in the same storage ring of the accelerator. This has the advantage that less capital investment is needed because fewer accelerators are required. Once a collision mass has been created, the steps for the production of heat according to this embodiment are the same as in previous embodiments, and so will not be described in further detail. This principle also works with a stream containing a mixture of light ions, for example a 50:50 mixture of hydrogen and deuterium. The hydrogen would generate protons which might not take part in fusion reactions and so would generate no heat, but would do no harm. They would probably each pick up an electron and emerge eventually as hydrogen gas. Such mixtures maybe readily formed by fractional electrolysis, distillation, diffusion or absorption or a succession of these processes much more cheaply than high purity deuterium. The output of processes according to embodiments of the invention is particularly suited to isolating deuterium from water as electricity by electrolysis and as heat by distillation. In a further embodiment, the process need not be continuous. It could be carried out in batches, but this is likely to be less economic. It is possible to keep heavy ions circulating in storage rings before injection into the collision zone. This may facilitate timing, but it is likely to be more costly than the production and use of heavy ions as a single operation. Since the ions are destroyed by the collision, it may be advantageous to use a different species in each stream for economic purposes. The schematic drawings show only the progress of successful collision masses through the system. Particles, for example heavy ions which do not collide, and atomic species which are sucked through by the extraction system can be readily separated for recycling into the process by use of their high velocity. Alternatively they may be recovered as raw material. A. The Nature of a Collision Mass The temperature of a collision mass depends on the momentum of the two colliding particles. At least one of the particles has to be an ion because charge is the only way of achieving high particle velocities in apparatus, though there may be additional mechanisms in stars, such as explosions. Momentum is the mass of a particle i.e. its atomic weight multiplied by its velocity. The acceleration of a particle meets increasing resistance as the speed of light is approached, because an increasing proportion of input energy is dissipated in the form of electromagnetic radiation as velocity increases. It is only the residual proportion of input energy which contributes to the mechanical momentum of the particle. Since it is this mechanical momentum which counts in the collision process, the lower the velocity at which suitable collisions can be achieved, the better. The corollary is to use ions which are as heavy as possible at the lowest velocity which achieves the desired properties in the collision product. The process of acceleration progressively strips off orbiting electrons from an ion, leaving a nucleus with a high positive charge, though there may remain some residual orbital electrons. The proposed model is that collision destroys any residual atomic structure and reduces the nucleons to fundamental particles form an entity, at least for a short time, rather than a scattering of fragments. This entity is the collision mass. It is this containment within a nuclear sized entity which produces the great concentration of heat manifesting itself as a very high temperature. In this sense the high temperature means very small particles moving at extremely high velocities. If protons are reduced to fundamental particles, there is no reason why neutrons should not also be reduced, and the likelihood is that they first decompose into protons and electrons, as they are known to do in a matter of minutes when liberated from nuclear structures. The protons formed by this decomposition would themselves be reduced to fundamental particles, but electrons produced by the decay of neutrons would survive as such because they are fundamental particles, and so irreducible. There are three different possible models of the resulting collision mass: a. the plum pudding model with electrons spread throughout a matrix, which must be positive b. the separation of charges with the electrons on the outside and c. the separation of charges with the electrons bunched together in the middle, surrounded by positive charges. Since the collision mass is an entity, its outside and interior are different, and so the mix of charges in the plum pudding model is most unlikely. Equally improbable is the bunching of electrons at the centre, because electrons are mobile, and most likely to congregate at the surface, as in the atom. Thus the most probable outcome is a positive core surrounded by mobile electrons. This is shown in FIG. 2 of the accompanying drawings. It shows the extreme model of a collision mass with at least some protons and neutrons completely destroyed, but it may not be necessary to reach that stage to make a collision mass which is hot enough to cause the fusion of absorbed light nuclei, such as those from deuterium. This is potentially a more economic process, but it has to be balanced against any decrease in the number of fusion reactions which can take place in the collision mass caused by its premature disintegration. Nor does the collision mass need to comprise two complete heavy ions, because a sufficiently large and hot enough entity may form from large fragments of heavy ions, subject to the same caveat. The nature of the collision mass affects the ease with which nuclei for fusion can enter the high temperature core. Deuterium as a positive ion may find it easier to be accommodated if electrons on the surface of the collision mass have time to re-position themselves to meet the incoming positive charge, and guide it in. In their absence the ion meets a very large positive charge from the core which repels. There is a case to be made that a neutral atom or an ion with a negative charge, which is quite possible, might be received more readily. At some stage the collision mass becomes so distended with the helium nuclei produced by fusion that it can no longer support a temperature high enough for fusion to continue, and it begins to cool and dissipate as very hot gases. It is most unlikely that the initial heavy nuclei which collided would reform, because atomic structures have been completely obliterated. Nor would neutrons be likely to reform. The most likely outcome is that each proton would attract an electron as it reformed to make a hydrogen atom, which would react with another to form hydrogen gas. There will not be enough electrons to go round, because the number of neutrons was about the same as the number of original protons in the colliding atomic species, and so almost twice as many protons would be formed as there would be electrons. The balance might continue as protons until they picked up an electron, or they could be fed with electrons exogenously as an added process e.g. from an electrode. Either way the heavy atomic species would be transformed back to molecular hydrogen. B. Quantities of Reactants A gram atom contains the order of 1023 (10 to the power) atoms. This would be the number of atoms in 1 g of hydrogen, 2 g of deuterium, 4 g of helium, 64 g of copper, 197 g of gold or 207 g of lead. The fusion of this number of nuclei represents a very large quantity of energy. (A hydrogen bomb is said to contain no more hydrogen than would fill a moderately small balloon, which is of the order of a gram atom.) The Joint European Torus (JET) experimental fusion reactor contains less than a gram of hydrogen. The liberation of fusion energy over a long period according to the invention would therefore require remarkably small quantities of material as in the following very rough approximations: Fusion of 2 g atom of deuterium at one fusion per collision mass needs 2 g atom of heavy ions to collide. If only one ion in a thousand collides, fusion of 2 g atom of deuterium at one fusion per collision mass requires 2 kg atom of heavy material to accelerate. At twenty fusions per collision mass, the fusion of 2 g atom of deuterium requires one twentieth of that, which is 100 g atoms of heavy material to accelerate. If only 0.1% of deuterium feed enters a collision mass and is fused, the process requires 2 kg atom of deuterium. On these assumptions, the release of the energy of fusion of 4 kg of deuterium requires 20 kg of lead. This would yield 4 g of helium and 20 g of hydrogen at a temperature approaching perhaps 10 million degrees. This could be diluted with hydrogen to 240 kg of hydrogen at 1000° K, or 5 million liters of hydrogen gas at Normal temperature and pressure (NIP). The quantities to be handled per second would be about a hundred thousandth of these numbers i.e. inputs of less than a tenth of a gram of deuterium and half a gram of lead, to produce outputs of 2.5 gs−1 (2.5 gram per second) of hydrogen at 1000° K, equivalent to 50 IS−1 (50 liters per second) of hydrogen at NTP. This provides an idea of the size of equipment required. At the output end it is not vast, because of the high temperature. |
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abstract | An EUV light source apparatus capable of easily detecting deterioration etc. of a window of an EUV light generating chamber. The EUV light source apparatus includes a driver laser, an EUV light generating chamber, a window which passes the laser beam into the EUV light generating chamber, an EUV light collector mirror, laser beam focusing optics which focuses a laser beam onto a trajectory of a target material, a temperature sensor which detects a temperature of the window, and a laser beam optics deterioration determination processing unit which determines deterioration of the window based on the temperature of the window detected by the temperature sensor when extreme ultra violet light is generated. |
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abstract | Disclosed is an X-ray topography apparatus including an X-ray source, a multilayer film mirror, a slit, a two-dimensional X-ray detector, and a sample moving device that sequentially moves the sample to a plurality of step positions. The X-ray source is a minute focal spot. The multilayer film mirror forms monochromatic, collimated, high-intensity X-rays. The direction in which the multilayer film mirror collimates the X-rays coincides with the width direction of the slit. The step size by which the sample is moved is smaller than the width of the slit. The combination of the size of the minute focal spot, the width of the slit, and the intensity of the X-rays that exit out of the multilayer film mirror allows the contrast of an X-ray image produced when the detector receives X-rays for a predetermined period of 1 minute or shorter to be high enough for observation of the X-ray image. |
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description | This application is the National Phase of International Application PCT/GB2014/051506 filed May 16, 2014, which designated the U.S. That International Application was published in English under PCT Article 21(2) on Nov. 20, 2014 as International Publication Number WO 2014/184574A1. PCT/GB2014/051506 claims priority to U.K. Application No. 1308851.3 filed May 16, 2013. Thus, the subject nonprovisional application also claims priority to U.K. Application No. 1308851.3 filed May 16, 2013. The disclosures of both applications are disclosure of that application is incorporated herein by reference. The present invention relates to x-ray detection apparatus and in particular to an apparatus that provides for the multi-spectral analysis of materials. An x-ray tube outputs radiation across a wide range of energy bands, the distribution of the energy being defined by the accelerating voltage applied to the tube. When x-rays impact a material, they are absorbed as they pass through. X-rays of different energies are absorbed differently which means that the initial x-ray intensity profile changes. Different materials cause a distinctive change in shape of the x-ray intensity spectra and thus if the spectra can be recorded with sufficient accuracy, it is possible to predict the material that the x-rays have passed through. While the mass absorption coefficient depends upon both the material type and also the energy of the incident photons, the mass absorption coefficient is independent of material thickness and density. Hence, faced with a resultant spectrum, and knowing the starting spectrum, it is possible to deduce the mass absorption coefficient values and hence the material type the x-rays have passed through. The detection of x-rays falls into two categories. The first is direct detection, where the energy of an x-ray photon impinging upon a particular material, such as CdTe or Ge is absorbed and converted into an electrical signal. The second is indirect detection in which an intermediate scintillator material first converts x-ray energy into visible light which is subsequently converted into an electrical signal by a detector. Direct detection has particular application in the identification of materials. X-ray detectors are typically operated in one of three modes: pulse mode, current mode and voltage mode. Current mode is used in cases where event rates are high and voltage mode is used for high energy detection. Pulse mode operation is widely preferred as it preserves amplitude, counting and timing information for individual pulses. Direct detection using pulse mode allows materials to be identified and is described in a number of published patent applications. For example: The international patent application published under number WO2008/142446 describes energy dispersive x-ray absorption spectroscopy in scanning transmission mode involving the calculation of the intensity ratios between successive frequency bands; The international patent application published under number WO2009/125211 describes an imaging apparatus and method; The international patent application published under number WO2009/130492 describes the determination of composition liquids; and The international patent application published under number WO2010/136790 describes a method for the identification of materials in a container. Whilst the techniques set out in the patent applications mentioned above are effective, the detectors themselves present limitations. Pulse mode detection provides counting and energy resolution information in the form of an x-ray spectrum. This x-ray spectrum, also referred to as a pulse height spectrum is typically produced by measuring the height of each pulse from the detector. A spectrum of the total number of detected counts per energy range (typically referred to as energy bins) is produced with the width of any given energy bin configured according to limitations such as detector resolution, electronics selection and input count rate. The pulse mode detection technique has been adopted in many materials identification applications because of the preservation of photon counting and energy information for individual pulses. A major issue limiting the materials sensitivity of energy dispersive detectors, the ability of the detector to detect different materials, is that these detectors have count rate limitations. Unlike current or voltage mode detectors where the time averaged current or voltage is measured, the electronics used in pulse mode detection must analyse the pulse from each x-ray interaction with the detector. As these pulses have a finite width in the time domain they begin to overlap as the count rate is increased. This phenomenon is known as pulse pile up and distorts the x-ray spectrum. In cases where samples exhibit large region to region variation in thickness or density it is possible that some detectors in an array (pixels) may see very high count rates while neighbouring pixels may see very low count rates. Pixels directed along the path of low density and/or thin sample path lengths may see rates which are in the extreme pulse pile up regime, leading to distortion of the energy spectrum. The obvious way of avoiding such pulse pile up problems is to reduce the input count rate by reducing the beam power or increasing the source to detector separation. The problem with a global reduction in x-ray flux is that highly absorbing regions fall into the measurement noise floor and become indistinguishable. Contributions to the measurement noise floor include spurious dark counts and Poisson noise, both of which become significant at low count rates. This makes global changes in x-ray flux undesirable and requires multiple shots to be taken in order to resolve each contrast level. This approach is time consuming and increases the absorbed x-ray dose. In materials identification applications users often require the shortest possible measurement time. Nowhere is this more important than in security scanning where, for example, high volumes of luggage must be scanned rapidly. This results in short integration times which in turn result in either higher Poisson errors or spectral distortion due to pulse pile up. These distortions in the energy spectrum limit the sensitivity of materials identification techniques, therefore limiting the materials which can be distinguished. Consequently, minimising spectral distortion is at the expense of counting errors and measurement time. Another way to avoid such pulse pile up is to reduce the width of the pulse produced in the detector electronics thereby minimising the probability of two pulses piling up. This leads to errors in the measurement of the pulse height (and therefore x-ray energy) known as ballistic deficit and the processing of such pulses requires faster analogue to digital sampling, lower noise amplifiers and low capacitance, fast rise time electronics. All of these features add to the cost and complexity of the detector electronics. According to a first aspect of the invention there is provided an x-ray imaging apparatus, the apparatus including an x-ray detector comprising a member configured to convert incident x-ray wavelength photons directly into an electronic signal, a position for a material under test, an x-ray source, and a structure configured to perturb an x-ray energy spectrum, each lying on a common axis, wherein the x-ray source is arranged to direct an x-ray energy spectrum along the common axis to impinge upon the member, the structure configured to perturb the x-ray energy spectrum, and a positioned material under test, wherein said structure lies between the x-ray source and the member and to one side of the position for material under test, the said structure intersecting the common axis, wherein the said structure comprises at least three adjacent regions, each region different to immediately adjacent regions and configured to perturb the x-ray energy spectrum differently. Advantageously, the regions lie laterally of one another, and preferably the structure comprises a plurality of regions lying laterally of one another, and preferably in two orthogonal directions. Advantageously, the plurality of regions is formed in an array, and the array may repeat itself in the structure. The structure may include a multiplicity of such arrays. For example, the plurality of regions may comprise a three by three array of nine regions. Preferably, the structure is planar or non-planar. The structure may be curved in at least one plane. Preferably, the difference between adjacent regions is the thickness of the material of the structure in adjacent regions. The structure may include a plurality of protrusions or depressions, the thickness of said protrusions or depressions changing in at least one direction thereof, each protrusion or depression providing at least three adjacent regions configured to perturb the x-ray energy spectrum. Preferably, the protrusions or depressions are pyramidal in shape. The structure may comprise a non-metallic layer having a multiplicity of depressions formed therein, each depression filled with metal. Preferably, the structure comprises a first non-metallic layer having a multiplicity of depressions formed therein and a second metallic layer including a corresponding number of protrusions each protrusion filling a corresponding depression. The second layer may cover the surface of the first layer in which the openings to the depressions are situated. Adjacent depressions or protrusions may be separated from one another by x-ray perturbing material and wherein the material separating adjacent depressions or protrusions may constitute one of the at least three regions. The non-metallic layer may be formed of silicon. The difference between adjacent regions may be the material from which the individual adjacent regions of the structure are formed. The adjacent regions may differ in thickness and in the material from which they are made. For example, the structure may comprise a substrate of even thickness, and the individual regions may be formed on a surface thereof by building up discrete layers of material on adjacent regions. The number of layers and/or the materials of those layers may differ. Techniques such as PVD, electro-deposition or laser ablation may be used to form the individual regions. In addition, the regional variation may be created by stacking layers of foils with cut-out regions one on top of each other so that the cut out regions stack in such a way to create a variety of thicknesses in a lateral sense. Another alternative would be to stack a series of wire meshes together in a similar fashion to the foils such that variations in material thicknesses are formed. Preferably, the individual wires of each wire mesh are rectangular in cross-section. This is similar to techniques used to form neutral density filters. Another alternative is to start with a certain thickness of material and cut out regions to create differing thicknesses. This could be done by laser micro-machining or ion-beam milling amongst the many techniques. Where the material property of the structure, such as thickness of the structure or a part of the structure changes continuously rather than by steps, taking any point on the structure, if its property (thickness) is different to the thickness of the structure at an adjacent point, then those two points may each be considered to be regions configured to perturb the x-ray energy spectrum differently. In some embodiments the x-ray detection apparatus includes or is associated with data recording means where visible wavelength photons are recorded. In some embodiments the x-ray detection apparatus includes or is associated with a database of recorded information characteristic of known substances. In some embodiments the x-ray detection apparatus includes or is associated with data processing software, and preferably, such data processing software is configured to perform processing steps to determine a material property of an object or substance. Where any of the aforementioned data recording means, database, data processor and date processing software are not embodied in the apparatus they may be embodied an another apparatus to which the x-ray detector apparatus of the invention is connected. According to a second aspect of the invention there is provided an x-ray detector suitable for use in an x-ray detection apparatus according to the first aspect of the invention and comprising a member configured to convert incident x-ray wavelength photons directly into an electronic signal and a structure for alignment with an x-ray energy spectrum source, the structure configured to perturb an x-ray energy spectrum, the said structure comprising at least three adjacent regions, each region different to immediately adjacent regions and configured to perturb the x-ray energy spectrum differently. Advantageously, the regions lie laterally of one another, and preferably the structure comprises a plurality of regions lying laterally of one another, and preferably in two orthogonal directions. According to a third aspect of the invention there is provided a structure configured to perturb an x-ray energy spectrum incident thereon, the structure comprising at least three adjacent regions, wherein each region is different to immediately adjacent regions, each adjacent region configured to perturb the x-ray energy spectrum differently. Advantageously, the regions lie laterally of one another, and preferably the structure comprises a plurality of regions lying laterally of one another, and preferably in two orthogonal directions. Advantageously, the plurality of regions is formed in an array, and the array may repeat itself in the structure. For example, the plurality of regions may comprise a three by three array of nine regions, and the structure may include a multiplicity of such arrays. Preferably, the structure is planar or non-planar. The structure may be curved in at least one plane. Preferably, the material difference between adjacent regions is the thickness of the material of the structure in adjacent regions. The structure may include a plurality of protrusions or depressions, the thickness of said protrusions or depressions changing in at least one direction thereof, each protrusion or depression providing at least three adjacent regions configured to perturb the x-ray energy spectrum. The protrusions or depressions may be pyramidal in shape. The structure may comprise a non-metallic layer having a multiplicity of depressions formed therein, each depression filled with metal. Advantageously, the structure comprises a first non-metallic layer having a multiplicity of depressions formed therein and a second metallic layer including a corresponding number of protrusions each protrusion filling a corresponding depression. Preferably, the second layer covers the surface of the first layer in which the openings to the depressions are situated. Adjacent depressions or protrusions may be separated from one another by x-ray perturbing material and wherein the material separating adjacent depressions or protrusions constitutes one of the at least three regions. Preferably, the non-metallic layer is formed of silicon. The depressions in the non-metallic layer are preferably formed by etching. The walls of pyramidal depressions preferably lie at 54.7 degrees to the surface of the non-metallic layer. The material difference between adjacent regions may be the material from which the individual adjacent regions of the structure are formed. The adjacent regions may differ in thickness and in the material from which they are made. For example, the structure may comprise a substrate of even thickness, and the individual regions may be formed on a surface thereof by building up discrete layers of material on adjacent regions. The number of layers and/or the materials of those layers may differ. Techniques such as PVD, electro-deposition, laser ablation or 3d-printing may be used to form the individual regions. In addition, the regional variation may be created by stacking layers of foils with cut-out regions one on top of each other so that the cut out regions stack in such a way to create a variety of thicknesses in a lateral sense. Another alternative would be to stack a series of wire meshes together in a similar fashion to the foils such that variations in material thicknesses are formed. Preferably, the individual wires of each wire mesh are rectangular in cross-section. This is similar to techniques used to form neutral density filters. Another alternative is to start with a certain thickness of material and cut out regions to create differing thicknesses. This could be done by laser micro-machining or ion-beam milling amongst the many techniques. It should be noted that the purpose of the structure is to perturb the x-ray/gamma ray energy spectrum, so that at least a proportion of the x-ray/gamma ray energy spectrum incident at each region of the structure is transmitted to the detector. According to a fourth aspect of the invention there is provided method of determining a material property of a substance comprising the steps of: a) positioning the substance in an x-ray detection apparatus according to the first aspect of the invention; b) causing the x-ray source to direct an x-ray energy spectrum along the common axis; c) analysing electronic signals emitted by the member configured to convert incident x-ray wavelength photons into electronic signals. Referring now to FIGS. 8 and 9, for the sake of clarity, the detector is shown in its most basic form and comprises an x-ray source 1, an object 2, a pixelated detector 3 and a structure 6. X-rays emitted from the x-ray source 1 pass through the object 2, the attenuated x-rays that have passed through the object 2 being detected by the detector 3, which converts incident x-rays directly into electronic signals. The x-ray source 1, object 2, pixelated detector 3 and structure 6 lie on a common axis A-A. The structure 6 may be a multi-absorption plate, a collimator or a combination of the two. The difference between FIGS. 8 and 9 lies in the position of the structure 6. The detector 3 may be Silicon diode detectors, Lithium drifted silicon detectors, High Purity Germaium detectors HPGe, Cd based detectors—CdTe, CdZnTe, CdMnTe and others, proportional counters, or Gas filled detectors. Referring now to FIGS. 1a and 1b, an object 2 having three regions of interest, ROI1, ROI2 and ROI3 is positioned between an x-ray source 1 and an array detector 3. The material of each region of interest has a different density. The purpose of FIGS. 1a and 1b is to illustrate the dynamic range limitations of detectors of the prior art when imaging such materials using a single x-ray beam source 1. FIG. 1b illustrates the signal related to each region of interest. ROI1 has the highest density and absorbs the most x-ray energy. In order for the detector 3 to be able to detect a signal, the x-ray flux from the source must be kept sufficiently high that the x-ray energy passing through ROI1 is distinguishable from the background noise. The problem that results is that where the material is least dense, in ROI3 so little x-ray energy is absorbed that the x-rays passing through ROI3 result in a count rate at the detector that exceeds the detector's maximum count rate. This causes pulse pile up and spectral distortion. The combination of materials ROI1, ROI2 and ROI3 is beyond the dynamic range of the detector 3. FIG. 2a illustrates an apparatus of the invention, which includes a multi-absorption plate 4. In the illustrated embodiment the multi absorption plate is mounted between the detector 3 and the object 2. However, the multi-absorption plate (MAP) 4 may be mounted between the x-ray source 1 and the object 2. The multi-absorption plate 4 illustrated in FIG. 2a includes a repeating pattern of elements 4a, 4b and 4c. In the illustrated example, the element 4a is an open aperture and hence does not absorb x-rays. The element 4b is comprised of a material which absorbs x-rays and is of a first thickness. The element 4c is comprised of the same material as 4b but twice the thickness. The element 4c could be a material or a combination of materials that absorb x-rays more readily than the material of element 4b. The source 1, object 2 and its regions of interest ROI1 to ROI3, and the detector 3 are identical to the embodiment of FIG. 1a. The difference between the two apparatus is the multi-absorption plate 4. The elements 4a to 4c of the MAP 4 cause three separate x-ray signals to be detected by the detector 3 for each region of interest. This is illustrated in FIG. 2b, which shows three signals related to each region of interest ROI1 to ROI3. For each region of interest all those x-rays passing through an element 4a are unaffected by the MAP and therefore the counts detected by the pixels of the detector aligned with elements 4a are the same as for the apparatus shown in FIGS. 1a and 1b. Looking at ROI1, for pixels of the detector 3 aligned with elements 4b, the x-ray count at the detector is lower. However, the count is still above the noise floor of the detector, i.e. within the detector's dynamic range. The element 4c of the MAP absorbs x-rays more readily than the element 4b resulting in fewer x-rays being counted by the pixels of the detector 3 aligned with elements 4c. The x-rays are absorbed by elements 4c to such an extent that the x-rays counted by the detector 3 are below the noise floor, i.e. outwith the dynamic range of the detector. Looking at ROI3, the least dense region of interest, for pixels of the detector 3 aligned with elements 4b, the x-ray count at the detector is lower. They are now below the maximum count rate of the detector 3 and hence within the detector's dynamic range. The element 4c of the MAP absorbs x-rays more readily than the element 4b resulting in fewer x-rays being counted by the pixels of the detector 3 aligned with elements 4c. The x-rays are absorbed by elements 4c more than elements 4b, so the count rate at the pixels of the detector 3 aligned with elements 4c is lower than for those aligned with elements 4b. As can be seen from FIG. 2b, for ROI2, the counts lie within the dynamic range of the detector for all the pixels of the detector 3, irrespective of which elements 4a to 4c they are aligned. One skilled in the art will appreciate that by introducing a multi-absorption plate, whilst one third of the signal associated with ROI1 has shifted out of the detector's dynamic range, i.e. below the noise floor, two thirds of the signal associated with ROI3 has been brought within the detector's dynamic range, whereas without the MAP the signal associated with ROI3 is outwith the detector's dynamic range. Those pixels where the counts lie outside the detector's dynamic range are unusable. Hence, the MAP leads to a slight reduction in image resolution. However, the whole sample can be imaged in a single acquisition, whereas in the apparatus of FIG. 1a, two acquisitions with the source at different flux settings would be required to obtain images for each region of interest falling within the dynamic range of the detector 3. FIG. 4 illustrates the change in counts and spectral shape for the multi-absorption plate 4. The elements 4a are apertures, the elements 4b and 4c being 1 mm and 2 mm thick copper respectively. The object in FIG. 4 was a 1 mm thick sheet of tin. FIG. 3 illustrates an alternative configuration where the multi-absorption plate 4 is replaced by a collimator 14. Instead of the elements 4a to 4c presenting different thicknesses of material as in the FIG. 2a embodiment, each element 14a to 14c of the collimator 14 is an aperture of different size. Each element 14a to 14c reduces the x-ray flux by a different amount. However, the energy distribution of the x-ray beam emanating from the source 1 is maintained, but the count rate is reduced more by the progressively smaller apertures of elements 14a to 14c. Referring now to FIGS. 6a and 6b, the apparatus illustrated in each figure is adapted to produce absorption edges. FIG. 6a illustrates a multi-absorption plate 20 similar to that shown in FIG. 2a, the difference being that whereas in FIG. 2a one of the elements 4a is an aperture, in FIG. 6a each element is comprised of a material through which the x-ray beam must pass. The MAP 20 comprises a repeating structure of four elements A to D each being materially different to the other. In such an arrangement, not only are the elements immediately adjacent one another different, but also those diagonally adjacent one another are different from one another. The material of each element A to D is selected to produce a different absorption edge. This may be achieved by each element A to D being comprised of a different material, by each element A to D being comprised of the same material but having a different thickness, or each element being comprised of a different material and each element having a different thickness. For example, element A may be comprised of gold, element B indium, element C lead and element D tin. FIG. 6b illustrates a different arrangement comprising a collimator 14 of the type shown in FIG. 3. In order to produce absorption edges a MAP 20 is placed between the object 2 and the collimator 14. Advantageously, the MAP 20 has a repeating pattern of elements A-D individual elements of which are aligned with individual collimators 14a, 14b, 14c. FIG. 6c illustrates an arrangement comprising a source 1, an object of interest 2, a detector 3, a collimator 14 and a MAP 20′. The MAP 20′ is a three by three array of regions A, B, C each having a different absorption edge and emitting a different fluorescence peak. The collimator in this figure is a three by three array of repeating regions of three by three collimators 14a to 14c. As can be seen in the figure, the first row of plate 30 the sequence of regions is A, B, C. In the row below it is B, C, A and in the row below that C, A, B. Hence, the region A of MAP 20′ overlies the nine collimators, the three collimators 14a to 14c shown in the Figure, the six collimators of the two rows below making up the 3×3 array of collimators. Region B of the MAP 20′ overlies the next 3×3 array of collimators and Region C the next 3×3 array of collimators. Each region A, B, C of the MAP 20′ has a different absorption edge and induces a different fluorescence peak. FIG. 6d illustrates an arrangement similar to that shown in FIG. 6c insofar as the arrangement comprises an x-ray source, a collimator 14, a MAP 20 and a detector 3. However, the configuration of the MAP 20 and the collimator 14 are different. The MAP 20 comprises four different types of material A to D, each having a different absorption edge and in which the individual regions of those materials is smaller than in the arrangement illustrated in FIG. 6c. The collimator 14′ of FIG. 6d comprises 4×4 array of a repeating pattern of groups of three collimators C1, C2 and C3. For any one group of collimators, each collimator is aligned with a different material of the MAP 20. This means that every count rate has each adsorption edge and fluorescence peak associated with it across a multitude of regions. FIG. 7 compares the x-ray spectrum recorded at the detector where the path between the x-ray source and the detector is open (the upper trace) and where a material having an absorption edge is placed between the x-ray source and the detector (the lower trace). It will be appreciated that each different region of the MAP 20 induces a different absorption edge and in this way a pattern of absorption edges and fluorescence peaks may be imposed on the x-ray spectrum incident on the plate. Hence, the x-ray spectrum incident on the detector is a multiplicity of different fluorescence peaks, each peak corresponding to an element of the MAP 20 on which the source x-ray spectrum was incident. The elements of the MAP must be of a suitable material in order to produce fluorescence peaks. Suitable materials include, but are not limited to: tungsten, gold, lead, tin and indium, which all have absorption edges and fluorescence peaks within the energy range of typical measurements of 30 to 80 keV. The energy of each of the multiplicity of spectra is of a suitable energy range to be useful for medical imaging, industrial imaging and the analysis of thin films and the like since the secondary x-rays of the fluorescence peaks are easily suitably interacting. The combination of the collimator 14 with the MAP having elements whose absorption edges are at wavelengths within the x-ray source emission spectrum is useful where the dynamic range of the detector 3 is likely to be exceeded. In each of the drawings the MAP 20 and collimator 14 are shown positioned between the object of interest and the detector. However, other configurations of the x-ray source, sample, MAP, collimator and detector are possible. For example the arrangement may be any of those listed below: Source/sample/MAP/detector; Source/MAP/sample/detector; Source/sample/collimator/detector; Source/collimator/sample/detector; Source/sample/collimator/MAP/detector; Source/sample/MAP/collimator/detector; Source/collimator/MAP/sample/detector; Source/MAP/collimator/sample/detector. The MAP may be manufactured in a multitude of different ways. The regions of the MAP may be: a) Different materials of different thickness; b) Different materials of the same thickness; c) The same material of different thickness. Where the MAP is to produce absorption edges and fluorescence peaks variants a and b are preferred. Variant c could be configured primarily to modify the spectral shape by hardening of the X-ray beam through attenuation. An absorption edge common to the whole MAP nevertheless be useful, for example to assist in calibration of the apparatus. FIGS. 10 to 15b illustrate different configurations of multi-absorption plate. FIGS. 10 and 11 illustrate an interference plate 26 (which may also be considered to be a multi-absorption plate, i.e. different regions of the plate have different x-ray absorption capabilities), of tungsten for example. Further, in addition to manufacturing the interference plate such that regions thereof have different thicknesses, it possible that the interference plate may have uniform thickness, with the material difference between adjacent regions being provided by forming the individual regions of the interference plate of different materials. The interference plate may comprise a substrate with the individual regions formed on or in the substrate. The individual regions may be formed in the base layer by etching or even machining the substrate. The interference plate may be formed by 3d-printing. The individual regions 26a-26d shown in FIGS. 10 and 11 may represent regions of different thickness or materials or combinations thereof. The individual regions may be formed on the substrate by deposition, for example by a technique well known in the art as “lift-off”. An advantage of such a technique is that the material deposited in the “lift-off” process may be the same as the material from which the substrate is formed. The material difference between adjacent regions is the thickness of each pixel. Further, the deposited material may be different to the substrate material, providing for the material difference between adjacent regions to be in material type and/or the material thickness. Further, in addition to manufacturing the interference plate such that regions thereof have different thicknesses, it possible that the interference plate may have uniform thickness, with the material difference between adjacent regions being provided by forming the individual regions of the interference plate of different materials. The interference plate may comprise a substrate with the individual regions formed on or in the substrate. The individual regions may be formed in the base layer by etching or even machining the substrate. The interference plate may be formed by 3d-printing. The individual regions may be formed on the substrate by deposition, for example by a technique well known in the art as “lift-off”. An advantage of such a technique is that the material deposited in the “lift-off” process may be the same as the material from which the substrate is formed. The material difference between adjacent regions is the thickness of each pixel. Further, the deposited material may be different to the substrate material, providing for the material difference between adjacent regions to be in material type and/or the material thickness. FIGS. 12a and 12b illustrate an alternative construction of interference plate 26. In this example the interference plate 26 is formed of four layers of material 26a to 26d, such as foil. The first layer is not perforated. The second layer 26b includes apertures 26b′ of a first width. The third layer 26c includes apertures 26c′ of a second width, and the fourth layer 26d includes apertures 26d′ of a third width. When stacked with the centres of the apertures 26b′ to 26d′ aligned the resulting structure has a cross-section 26′. When the layers 26a to 26d are stacked with the edges of the apertures aligned the resulting structure has a cross-section 26″. The structures 26′, 26″ each provide elongate regions of differing thickness. In FIG. 12b, two of the resulting interference plates 26 are stacked with the apertures aligned perpendicular to one another. The resulting interference plate provides an array of square regions, wherein adjacent regions are of differing thickness. FIG. 13 illustrates another alternative arrangement of interference plate 26 comprising three layers 26f to 26h of wire mesh, each of differing mesh size. When stacked one on top of the other, in some regions incident x-rays will impinge upon the wires of the first layer 26f, in other regions incident x-rays will impinge upon wires of the second layer 26g, and in other regions incident x-rays will impinge upon wires of the third layer 26h. Further, in other regions incident x-rays will impinge upon a combination of some of the wires of more than one of the layers 26f, 26g and 26h. Further, there will be regions where no wire is present and hence x-rays incident on these regions will pass through unperturbed. Preferably, the wires are rectangular in cross-section. In FIG. 14 the interference plate 30 comprises a block of material that represents a region of a multi-absorption plate and which varies in thickness along two axes across the plate. Hence, the thickness of the material changes continuously across the plate. Referring now to FIGS. 15a and 15b, there is shown a further alternative construction of interference plate 60 comprising a first layer 61 and a second layer 63. The first layer 61 is formed of a silicon wafer and having formed therein a multiplicity of depressions 62. In the illustrated example the depressions have a depth of 800 micron. The depressions are formed by etching. It is known that strong alkaline wet etchants such as potassium hydroxide or tetra methyl ammonium hydroxide will preferentially etch certain crystal planes of silicon compared to others due to a difference in the bond strength of silicon atoms in the different crystal planes. The {111} crystal planes are amongst the most resistant to the etchants and so the {100} and {110} planes will be etched at far greater rates than the {111} planes. The silicon wafer from which the first layer 61 is formed is a {100} oriented. A mask defining the array of depressions 62 is applied to a surface of the silicon wafer and an alkaline etchant applied. Where the alkaline etchant is in contact with the silicon it begins to etch down forming square based pyramidal shaped depressions 62. The sloping side-walls of the depressions 62 are the {111} planes of silicon and thus are angled at 54.7 degrees compared to the surface of the {100} silicon wafer. The etching process is allowed to proceed until the {111} side walls converge to form the apex of a pyramid shaped depression 62. The etchant used to create the depressions 62 was potassium hydroxide. The mask used to form the depressions 62 corresponds in shape to the plan view shown in FIG. 12a. In the illustrated example, the depressions are set out on a 1 mm×1 mm centre to centre grid. The distance between adjacent depressions 62 is approximately 50 microns. The number of depressions may be increased or decreased by increasing or decreasing the distance between the centres of the depressions. When the distance between depressions is changed the depth of the depression and hence the size of the base of the depression will change, the size of the base being a function of the depth of the depression and the wall angle of 54.7 degrees. For example, the depth of each depression may be reduced to 100 micron. FIGS. 15a and 15b illustrate a part of an interference plate. The interference plate might measure 26 cm×15 cm for example, and the depressions may be on a grid that is smaller than the 1 mm×1 mm centre to centre grid illustrated here. The second layer 63 is formed of metal such as nickel, copper or tin. It is this metal second layer 63 which perturbs the x-rays incident upon it, each pyramidal protrusion providing a substantially infinite number of regions of different thickness as the thickness of the metal changes along the slope of the walls of the pyramid. The first layer serves to assist in manufacture of the interference plate and post manufacture to support and protect the metal layer 63. As can be seen from FIGS. 16a and 16b, the second layer 63 includes pyramidal shaped protrusions 64 and a backing plate 65. The second layer 63 is formed by deposition molten metal on to the surface of the first layer 61, the molten metal filling the pyramidal depressions 62 and forming a thin backing plate 65 (in the order of a few microns) covering the surface of the first layer 61. The metal of the second layer 63 between adjacent pyramidal protrusions may be considered as a region of different thickness to an adjacent region, perturbing the x-ray energy spectrum differently to the metal of the adjacent pyramidal protrusions. Interference plates (also referred to as a multi-absorption plate) may be formed using three-dimensional printing techniques. FIG. 17 is a block diagram of a system according to an embodiment of the invention in which the detector 1 (which may be the detector of any of the previously described embodiments or other embodiments falling within the scope of the claims) provides an output to a data recording means 70. The data recording means is in communication with a data processor as is a database 71 in which data characteristic of known materials are recorded. The data recording means 70 and the database 71 are in communication with a data processor 72 which runs data processing software, the data processing software comparing information from the data recording means and the database to determine a material property of an object 3. A data output interface 73, such as but not limited to a VDU, is preferably included to which a determination of the data processing software may be outputted. In another embodiment of the system illustrated in FIG. 13, the detector 1 may output directly to the data processor 72, in which case the data recording means may be omitted, or the data recording means 70 may record data from the detector 1 via the data processor. Referring now to FIG. 16, there is shown a laboratory scale apparatus 100 according to the invention. The apparatus includes a cabinet 101 in which is mounted an x-ray source 102, a position for a material under test in the form of a sample stage 103 which is mounted on rails 104 so that the position of the stage may be adjusted. The apparatus 100 further includes an interference, or multi-absorption, plate 105 and an x-ray detector 106. The detector 106 forms part of an x-ray camera which includes a scintillator for converting the x-ray wavelength photons of the x-ray shadow image into visible wavelength photons. The camera captures an image which may then be analysed. The detector 106 may be the detector 1 of the embodiment illustrated in FIG. 17, and the elements 70 to 73 may form part of the apparatus 100 or may be embodied in components in communication with the apparatus 100. To determine a material property of a substance the substance is positioned on the sample stage 103 and the x-ray source 102 is caused to direct an x-ray energy spectrum through the so positioned sample, the plate 105 to impinge upon the detector 106. The x-ray spectrum is analysed according to the following steps: Step (i)—The detector 106 is pixelated: the intensity and energy of X-rays recorded by the detector for each pixel is compared with the recorded intensity and energy for its adjacent pixels and the differences are recorded; Step (ii)—The intensity and energy of X-rays recorded by the detector for each pixel is compared with the recorded intensity and energy for its adjacent pixels and the differences in intensity are recorded without a substance present in the apparatus; Step (iv)—The current differences between recorded intensities and energies between adjacent pixels as determined by the method steps (i) and (ii) are compared; Step (v)—Following the method steps (i) to (iv) for at least one known material and storing the differences in a database; and Step (vi)—Comparing the differences between recorded intensities for a substance under test with the differences between recorded intensities for known substances from the database. In this specification the term X-ray shall be considered also to be a reference to gamma rays. The fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Furthermore, features of one embodiment illustrated and/or described may be incorporated with features of one or more other embodiments where the possibility of such incorporation would be evident to one skilled in the art. |
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041750020 | abstract | A nuclear fuel pellet is made of a sintered, ceramic nuclear fuel mass and has a cylindrical configuration with a pair of opposite bottomed holes centrally provided one at each end. The bottomed holes are convergent toward their bottoms and each have a U-shaped cross-section. A ratio of the diameter of the opening to the depth of the bottom hole is smaller than unity. The nuclear fuel element is free from defects such as cracks, easy to manufacture and capable of reducing a PCMI (a pellet-clad casing mechanical interaction). |
abstract | A pig for transporting a container of biohazardous material, wherein the container comprises a bottle and a bottle closure. The pig includes a body comprising a compartment dimensioned to receive the container; a cap attachable to the body for closing the compartment thereby to shieldingly contain the biohazardous material in the container, the cap including: a collar sealingly engageable with the body and having an opening therethrough in communication with the compartment thereby to provide access to the bottle closure; a cap closure sealingly engageable within the opening of the collar to sealingly close the opening and cause the bottle closure to be gripped within the cap, wherein when the collar is disengaged from the body while the cap closure is engaged within the opening of the collar, the container remains gripped within the cap. A system for transporting and providing access to a biohazardous material includes the pig and an insert sealingly engageable within the opening of the collar while the cap closure is removed, the insert comprising an injection port extending fully therethrough in axial alignment with the compartment thereby to guide insertion of a syringe centrally through the container closure and into the container. A compression member for insertion into a pig for transporting a container of biohazardous materials is also provided. The compression member includes a flange; and spaced apart fingers supported by the flange and together forming a circle, the fingers each having a substantially vertical component extending upwards from the flange and a substantially horizontal component extending inwards from an end of the substantially vertical component distal from the flange, the spaced apart fingers resiliently compressible inwardly against the container by compressive engagement of a complementary annulus of the pig into which the compression member is dimensioned to be inserted. |
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054694809 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT The best solution to the above described problem is to maintain the flow rate of the pump at the normal level, so that the water head should be raised, while avoiding the rumbling of the pump. Thus the air introduction into the suction tube of the residual heat removing system can be prevented during the mid-loop operation. As described before, during the mid-loop operation, the residual decay heat has to be continuously removed, but after 5 days from the stopping of the atomic reactor, the residual decay heat is very low, to such an extent that the actually required flow rate is about 2000 GPM. Therefore, in order to meet the requirement, as shown in FIG. 3, a round-about pipe conduit 4 is installed between a suction pipe conduit 2 and discharge pipe conduit 3 of a residual heat removing pump 1, and a flow rate adjusting valve 5 is installed on the round-about pipe conduit 4. Thus, the flow rate which passes through the pump is maintained at the normal operation level, while the unnecessary flow corresponding to 2000 GPM is made to pass through the round-about pipe conduit 4. Therefore, even if the water head is low at the entrance of the residual heat removing system of a hot leg 6, the air introduction is prevented. For this purpose, the requirement is that a round-about pipe conduit of a proper size is additionally installed between the suction pipe entrance and the discharge pipe conduit of the residual heat removing pump, and a flow rate adjusting valve is installed on the round-about pipe conduit. Thus during the mid-loop operation, as the residual heat is gradually decreased, the round-about flow is gradually increased, so that the suction flow from the hot leg should be maintained at the proper level, thereby preventing the air introduction. Reference code 7 in the drawings indicates a reactor, 8 a cold leg, and 9 a heat exchanger. In the above described manner, the mid-loop operation can be speedily carried out, and therefore, the repair period can be shortened. If the analysis of B & W company is referred, a shortening of about 12 days can be realized. In the case of the nuclear power plant No. 2 of Gori of Korea, if the mid-loop operation is not carried out, the repair period is extended by about 20 days. If this is converted into the economic gain, it is equivalent to an improvement of the efficiency of 4 to 6%. The nuclear power plants on which the present invention can be applied are about 10 plants including the nuclear power plants No. 3 and 4 of Youngkwang, No. 3 and 4 of Ulchin, and No 5 and 6 of Youngkwang, and the 4 nuclear power plants designed by ABB-CE i.e., Palo Verde Unit 1, 2, 3 and 4. |
description | The present invention relates to a method for monitoring a beam position in a charged particle beam irradiation system, and controlling the beam position, and in particular, to a charged particle beam irradiation system suitable for application to a charged particle beam treatment apparatus for giving treatment to an affected part by irradiating the affected part with a beam of a charged particle such as a proton, a carbon ion, and so forth. There has been known a treatment method whereby an affected part of a patient of cancer, and so forth is irradiated with a charged particle beam (an ion beam) of a proton, a carbon ion, and so forth. A charged particle beam irradiation system (a particle beam emitting apparatus, or a charged particle beam emitting apparatus) for use in this treatment is provided with a charged particle beam generation unit, and a charged particle beam accelerated by the charged particle beam generation unit reaches an irradiation unit provided at a rotary gantry via a first transport system, and a second transport system provided at the rotary gantry, whereupon the charged particle beam emitted from the irradiation unit to irradiate the affected part of a patient. A double scatterer method (Non-patent Document 1, p. 2081, FIG. 35) whereby a beam is expanded by use of a scatterer to be subsequently cut out so as to match with the shape of an affected part, a wobbler method ((Non-patent Document 1, p. 2084, FIG. 41), and a scanning method ((Non-patent Document 1, pp. 2092 and 2093) for causing a fine beam to scan within an affected part have been known as a beam irradiation method of the irradiation unit. Attention has been focused on the scanning method among those beam irradiation methods because the scanning method has a feature that an effect on a normal cell is less, and equipment incorporating a nozzle is unnecessary. It is the feature of the scanning method that outputting of a charged particle beam is stopped in response to a dose to an irradiation subject, an irradiation position of the charged particle beam, called a spot, is changed by controlling energy, and a scanning electromagnet, and emission of the charged particle beam is resumed after completion of such a change, thereby irradiating the irradiation subject (the affected part) with the beam so as to match with the shape of the irradiation subject, while sequentially changing over the irradiation position. [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2008-175829 [Non-patent Document 1] REVIEW OF SCIENTIFIC INSTRUMENTS, Vol. 64, No. 8 (August, 1993), pp. 2074-2093 With the charged particle beam irradiation system, in order to effect irradiation so as to match with the shape of an affected part, a beam position monitor (hereinafter referred to as a spot position monitor) is installed at a position on the downstream side of a scanning electromagnet, and immediately before a patient as the irradiation subject. The spot position monitor is provided with a detector (hereinafter referred to as a channel) called as a multi-wire, representing a scheme whereby a quantity of an electric charge generated by passing of a charged particle beam is stored in a capacitor on a channel-by-channel basis to thereby read an induced voltage. As a signal detected by each of the channels is weak, an amplifier is installed on the downstream side of the channel, and the signal detected by the channel is sent out to a signal processor via the amplifier. The signal processor executes processing of a detection signal received, whereupon a beam monitor control unit finds a position passed by the charged particle beam, and a beam width of the charged particle beam on the basis of a processing signal. Both signal amplifiers, and the signal processors, corresponding to the number of the channels, are required of the spot position monitor. In order to find the position passed by the charged particle beam, and the beam width, it is necessary to execute signal amplification, and signal processing with respect to all the channels, so that there arises a problem that the further the number of the channels is increased, the longer it takes in order to detect the position of the charged particle beam, and the beam width. To cope with the problem described as above, Patent Document 1 has disclosed a method for measuring a charged particle beam, whereby a scope of the channels for use in computation is restricted on the basis of information on a position passed by the charged particle beam, and a beam width thereof, pre-designated in a bean-monitoring system provided with both signal amplifiers, and signal processors, corresponding to the number of the channels, before execution of the signal processing, thereby enhancing a processing speed. However, in the case of the method for measuring the charged particle beam, described as above, if a multitude of channels are required, the bean-monitoring system alone will become large in scale, and complex in configuration for the reasons of irradiation applied with a fine beam, and so forth, and therefore, a cost becomes high. It is therefore an object of the invention to provide a bean monitoring system, and a charged particle beam irradiation system, capable of monitoring a position passed by a charged particle beam, and a beam width thereof, in a simple configuration, and making a determination in short time during spot irradiation according to the scanning method. There is provided a beam monitor system wherein signals outputted from a plurality of wires are divided in a multi-wire type monitor for measuring a beam profile of a charged particle beam, an identical number of the wires are grouped, the signals of the respective groups are taken out one piece by one piece to be connected with each other, and the number of the pieces, corresponding to a number of the wires belonging to the one group, are put together to be connected to a signal processor storing connection information. According to the present embodiment, channels for use in working, out a position of the charged particle beam, and a beam width are restricted, so that it is possible to construct a monitor system simple in configuration as compared with a monitor system provided with a signal processor corresponding to all the channels. Embodiments of the invention are described hereinafter. A preferred embodiment of a particle beam irradiation system according to the invention is described hereinafter with reference to FIGS. 1 and 2. The particle beam irradiation system is a system for irradiating an affected part of a patient fixed on a treatment table (a bed) 10 inside a treatment room with a charged particle beam 12 (for example, a proton beam, a carbon beam, and so forth). The particle beam irradiation system according to the present embodiment is provided with a charged particle beam generation unit 1, a beam transport system 2, a scanning irradiation unit 3, and a control system 4. The beam transport system 2 connects the charged particle beam generation unit 1 to the scanning irradiation unit 3. The control system 4 is connected to a treatment planning unit 6, and an operation terminal 40, respectively. The operation terminal 40 is provided with an input device where an operator (a treatment worker) inputs data, and an instruction signal, and a display screen. The charged particle beam generation unit 1 includes an ion source (not shown), a front-stage accelerator 15, and a circular accelerator (synchrotron) 16. In the present embodiment, a synchrotron is described as an example of the circular accelerator 16; however, the circular accelerator 16 may be another accelerator such as a cyclotron, and so forth. The ion source is connected to a part of the charged particle beam generation unit 1, on the upstream side of the front-stage accelerator 15, and the circular accelerator 16 connected to a part of the charged particle beam generation unit 1, on the downstream side of the front-stage accelerator 15. The beam transport system 2 is connected to a part of the charged particle beam generation unit 1, on the downstream side thereof. The scanning irradiation unit 3 includes the treatment table 10 on which a patient 13 is placed, an irradiation nozzle (a nozzle device) 11, and a rotary gantry 14, as shown in FIG. 2. The treatment table 10 is disposed inside the treatment room to execute positioning of the patient 13 who is placed thereon. An upstream beam monitor 11a, a scanning electromagnet 11b, a dose-monitor 11c, and a downstream beam monitor 11d are sequentially disposed along a beam path, starting from the upstream side in the travelling direction of the charged particle beam in the irradiation nozzle 11. The upstream beam monitor 11a measures a position passed by a charged particle beam falling into the irradiation nozzle 11, and a beam width (beam diameter) of the charged particle beam. The scanning electromagnet 11b is provided with a first scanning electromagnet for causing a passing charged particle beam to make deflection-scanning in a first direction (for example, in an x-axis direction), and a second scanning electromagnet for causing the passing charged particle beam to make deflection-scanning in a second direction orthogonal to the first direction (for example, in a y-axis direction). Herein, the x-axis direction is one of directions in a plane vertical to the travelling direction of the charged particle beam falling on the irradiation nozzle 11, and the y-axis direction is a direction in the plane, vertical to the x-axis. The downstream beam monitor 11d is installed on the downstream beam side of the scanning electromagnet 11b to measure the position of the passing charged particle beam, and the beam width thereof. More specifically, the downstream beam monitor 11d is a monitor for measuring the position of the charged particle beam, scanned by the scanning electromagnet 11b, and the beam width. The dose-monitor 11c measures a radiation exposure dose of the passing charged particle beam. More specifically, the dose monitor 11c is a monitor for monitoring the radiation exposure dose of the passing charged particle beam that the patient is irradiated with. The rotary gantry 14 is rotatable around Isocentre (not shown). Rotation of the rotary gantry 14 enables an entrance angle of the charged particle beam that the patient 13 is irradiated with. The control system 4 is provided with a central control unit 5, an accelerator-transport-system controlling system 7, and an irradiation control system 8, as shown in FIG. 1. The central control unit 5 is connected to the treatment planning unit 6, the accelerator-transport-system controlling system 7, the irradiation control system 8, and the operation terminal 40, respectively. The accelerator-transport-system controlling system 7 is connected to the charged particle beam generation unit 1, and the beam transport system 2, respectively, thereby controlling constituent apparatuses thereof. The irradiation control system 8 is connected to the scanning irradiation unit 3, thereby controlling constituent apparatuses thereof. The irradiation control system 8 is described hereinafter with reference to FIG. 2. The irradiation control system 8 is provided with a patient apparatus control unit 8a, a monitor-monitoring control unit 8b, and a scanning-electromagnet power-supply control unit 8c. The patient apparatus control unit 8a is provided with a rotary gantry controller 8a1 for controlling constituent apparatuses of the rotary gantry 14, a treatment table controller 8a2 for controlling positioning by moving the treatment table 10, and a nozzle-apparatus controller 8a3 for controlling apparatuses disposed inside the nozzle 11. The rotary gantry controller 8a1 controls a rotation angle of the rotary gantry 14, thereby controlling the entrance angle of the charged particle beam that the patient 13 is irradiated with. The monitor-monitoring control unit 8b is provided with an upstream beam monitor-monitoring controller 8b1 for monitoring, and controlling the upstream beam monitor 11a, a downstream beam monitor-monitoring controller 8b2 for monitoring, and controlling the downstream beam monitor 11d, and a dose-monitoring controller 8b3 for monitoring, and controlling the dose monitor 11c. The upstream beam monitor-monitoring controller 8b1 has a function for measuring the position of the charged particle beam falling into the irradiation nozzle 11, and the beam width of the charged particle beam, and a function for determining whether or not the charged particle beam is abnormal (abnormality-determination processing). The downstream beam monitor-monitoring controller 8b2 has a function for measuring the position of the charged particle beam, scanned by the scanning electromagnet 11b, and the beam width, and a function for determining whether or not the charged particle beam is abnormal (abnormality-determination processing). More specifically, the functions are described as follows. The upstream beam monitor-monitoring controller 8b1 receives measurement data obtained by the upstream beam monitor 11a to execute processing, thereby finding the position passed by the charged particle beam, and the beam width of the charged particle beam. If a beam position obtained is outside a predetermined scope, or the beam Width obtained is outside a predetermined scope, the upstream beam monitor-monitoring controller 8b1 determines that the beam is abnormal, thereby outputting an abnormality signal to the central control unit 5. The central control unit 5 outputs a beam-stop command signal to the accelerator-transport system controlling system 7, thereby stopping the charged particle beam outgoing from the charged particle beam generation unit 1. In the present embodiment, a control is made such that the charged particle beam outgoing from the charged particle beam generation unit 1 is stopped. However, a control may be made such that the central control unit 5 controls the beam transport system 2, thereby stopping the charged particle beam falling on the irradiation nozzle 11. The downstream beam monitor-monitoring controller 8b2 receives measurement data obtained by the downstream beam monitor 11d to execute processing, thereby finding the position passed by the charged particle beam, and the beam width of the charged particle beam. If a beam position obtained is outside a predetermined scope, or the beam width obtained is outside a predetermined scope, the downstream beam monitor-monitoring controller 8b2 determines that the beam is abnormal, thereby outputting an abnormality signal to the central control unit 5. The central control unit 5 outputs a beam-stop command signal to the accelerator-transport system controlling system 7, thereby stopping the charged particle beam outgoing from the charged particle beam generation unit 1. In the present embodiment, a control is made such that the charged particle beam outgoing from the charged particle beam generation unit 1 is stopped. However, a control may be made such that the central control unit 5 controls the beam transport system 2, thereby stopping the charged particle beam falling on the irradiation nozzle 11. Herein, the beam position of the charged particle beam indicates a position of the center of gravity of the charged particle beam passing through, for example, a beam monitor (the upstream beam position monitor 11a or the downstream beam monitor 11d). Further, the beam width of the charged particle beam indicates a region of the charged particle beam having passed through the beam monitor, (the upstream beam monitor 11a or the downstream beam monitor 11d). There are the case of finding the beam width by working out an area of a region where the charged particle beam is detected by the beam monitor (the upstream beam monitor 11a or the downstream beam monitor 11d) disposed on the plane vertical to the travelling direction of the beam, and the case of finding the beam width by working out the area of a detection region of the charged particle, and a width of the detection region by use of the beam monitor described, and so on. The scanning-electromagnet power-supply control unit 8c controls a power supply (not shown) of the scanning electromagnet 11b, thereby controlling an excitation current energizing the scanning electromagnet 11b. When an excitation current value of the scanning electromagnet 11b is changed, a change occurs to an irradiation position of the charged particle beam toward the patient 13. Next, there is described a flow of treatment from a start of treatment applied to a patient up to treatment completion with reference to FIG. 4. In the present embodiment, there is described a spot-scanning irradiation method whereby an affected part of the patient 13 is divided into a plurality of strata (hereinafter referred to as layers) in the travelling direction of the beam (in the direction of a depth from a body surface of the patient 13, and each of the layers is separated into a plurality of small regions as spots before application of irradiation with the beam by way of example. The treatment-planning unit 6 stores treatment-plan information on patients, acquired beforehand. The treatment-plan information contains irradiation data (beam-energy information, beam irradiation-position information, target dose values of the charged particle beam, against the respective irradiation-positions, and so forth), and tolerance data (information on an allowable beam position, and an allowable beam width, in the upstream beam monitor 11a, information on an allowable beam position, and an allowable beam width, in the downstream beam monitor 11d, against the respective irradiation-positions, and so forth). In the present embodiment, the treatment-planning unit 6 has a configuration for finding the irradiation data, and the tolerance data, however, the configuration may be altered such that the treatment-planning unit 6 is to find the irradiation data, and the central control unit 5 is to find the tolerance data. In this case, the treatment-planning unit 6 transmits data necessary for finding the tolerance data to the central control unit 5, and the central control unit 5 works out the tolerance data on the basis of the data received. The target dose value as the irradiation data is decided for every spot position in the respective layers. Upon the patient 13 being fixed onto the treatment table (bed), a doctor inputs a preparation-start signal from the input device of the operation terminal 40. Upon the central control unit 5 having received the preparation-start signal, the central control unit 5 receives the treatment-plan information on a relevant patient from the treatment planning unit 6, thereby outputting bed-position information to the treatment table controller 8a2. The treatment table controller 8a2 moves the treatment table 10 such that the patient 13 is placed at a predetermined position on a line extended from a beam axis on the basis of the bed-position information, thereby completing positioning. Further, the central control unit 5 outputs gantry-angle information to the rotary gantry controller 8a1. The rotary gantry controller 8a1 rotates the rotary gantry 14 on the basis of the gantry-angle information to cause the rotary gantry 14 to be disposed at a predetermined angle. Further, the central control unit 5 transmits the target dose value of the charged particle beam, and tolerance data, for every irradiation-position, to the monitor-monitoring control unit 8b. The central control unit 5 works out an excitation current value necessary for exciting the scanning electromagnet 11b on the basis of the beam-energy information, and the irradiation-position information, contained in the irradiation data, to find an excitation current parameter, thereby transmitting the excitation current parameter to the scanning-electromagnet power-supply control unit 8c. Further, the central control unit 5 finds an operation parameter for an accelerated operation of the circular accelerator 16, and an operation parameter of the beam transport system 2, for transportation of the charged particle beam emitted from the circular accelerator 16 to the irradiation nozzle 11, on the basis of the treatment-plan information, thereby transmitting these operation parameters to the accelerator-transport-system controlling system 7. Upon completion of treatment preparation, the doctor inputs a treatment-start signal from the input device of the operation terminal 40. Upon the central control unit 5 receiving the treatment-start signal, the central control unit 5 transmits a command signal to the accelerator-transport-system controlling system 7. The accelerator-transport-system controlling system 7 sets an operation parameter corresponding to the layer to be initially irradiated (initial beam-energy information) to the circular accelerator 16, and the beam transport system 2, respectively. Upon the operation parameter being set to the circular accelerator 16, and the beam transport system 2, respectively, completing the treatment preparation (Step 30), the scanning-electromagnet power-supply control unit 8c excites the scanning electromagnet 11b on the basis of the excitation current parameter (Step 31). After the scanning electromagnet 11b is energized by an excitation current corresponding to the initial irradiation spot, the dose-monitoring controller 8b3 of the monitor-monitoring control unit 8b starts monitoring the radiation exposure dose of the beam on the basis of a target dose value against a relevant spot position (Step 32), thereby completing an irradiation preparation. Upon the central control unit 5 transmitting a beam-emission start command (Step 33), the accelerator-transport-system controlling system 7 activates the ion source, whereupon a charged particle (a proton or a heavy particle) is generated. The front-stage accelerator 15 accelerates the charged particle from the ion source, emitting the charged particle to the circular accelerator 16. The circular accelerator 16 further accelerates a charged particle beam. The charged particle beam that is revolving is accelerated up to a target energy to be emitted from the circular accelerator 16 to the beam transport system 2. The charged particle beam reaches the scanning irradiation unit 3 via the beam transport system 2. The charged particle beam travels along the beam axis inside the irradiation nozzle 11, passing through the upstream beam monitor 11a, the scanning electromagnet 11b, the dose monitor 11c, and the downstream beam monitor 11d in sequence. The charged particle beam emitted from the irradiation nozzle 11 is irradiated to an affected part of the patient 13. The dose-monitoring controller 8b3 receives measurement data obtained by the dose-monitor 11c to be processed, thereby finding a radiation exposure dose against a relevant irradiation spot. Irradiation with the charged particle beam is continued until a radiation exposure dose against the initial irradiation spot reaches the target dose value. Upon the dose-monitoring controller 8b3 determining that the radiation exposure dose has reached the target dose value, the dose-monitoring controller 8b3 outputs an irradiation-expiration signal to the central control unit 5 (Step 34). The central control unit 5 stops the emission of the charged particle beam (Step 35). First detection data detected by the upstream beam monitor 11a is fetched by the upstream beam monitor-monitoring controller 8b1, and second detection data detected by the downstream beam monitor 11d is fetched by the downstream beam monitor-monitoring controller 8b2, thereby finding an irradiation position of the charged particle beam, and a beam width (Step 36). If the position of the beam, and the beam width have no abnormality (if it is determined that the beam position is within the allowable beam position, and the beam width is within the allowable beam width) upon completion of the processing, there is made a determination on whether or not an irradiation spot upon irradiation-expiration is the final spot position in the layer. If it is determined that the irradiation spot is not the final irradiation spot position (If No), an operation reverts to Step 31, whereupon the scanning-electromagnet power-supply control unit 8c changes the excitation current value of the scanning electromagnet 11b so as to irradiate the next spot with the charged particle beam. Upon the scanning-electromagnet power-supply control unit 8c causing the scanning electromagnet 11b to be excited on the basis of the excitation current parameter (Step 31), the dose-monitoring controller 8b3 of the monitor-monitoring control unit 8b resumes monitoring of the beam dose on the basis of a target dose value against the next irradiation spot position (Step 32). Upon the central control unit 5 transmitting the beam-emission start signal, irradiation of the next irradiation spot position with the charged particle beam is started (Step 33). A control flow 37 from, scanning electromagnet setting (Step 31) up to a determination on whether or not the irradiation spot is the final irradiation spot position is repeatedly executed until it is determined that the irradiation spot upon the irradiation-expiration is the final spot position in the layer (until determined Yes). Upon completion of the irradiation to all the spots, the central control unit 5 determines whether or not the layer where the irradiation is completed is the final layer against the patient 13. If the layer is not the final layer (If No), the central control unit 5 transmits the command signal to the accelerator-transport-system controlling system 7. The accelerator-transport-system controlling system 7 sets an operation parameter corresponding to the layer to be next irradiated to the circular accelerator 16, and the beam transport system 2, respectively, thereby starting the preparation for the next operation (Step 30). This control flow 38 is repeated until the irradiation of all the layers is completed. Upon the completion of the irradiation of all the spots, and all the layers, treatment completion is reached (Step 39). Now, there is described hereinafter measurement on a beam position, and a beam width in a downstream beam monitor system according to the related art method. With the downstream beam monitor-monitoring controller according to the related art, in processing for measurement on the position of the charged particle beam, and the beam width, in FIG. 4, measurement data blocks corresponding to the number of all the channels in the downstream beam monitor are fetched, and subsequently, an offset portion of each of the channels is subtracted, thereby retrieving a peak channel. After completion of retrieval, data blocks corresponding to not more than N % (for example, 30%) of an output of the peak channel are excluded to thereby execute Gaussian-fit processing. Thereafter, the irradiation position of the charged particle beam and the beam width are worked out. Such a processing as described above has been similarly applied to the downstream beam monitor-monitoring controller according to the related art. With the method of the related art, data blocks on all the channels are fetched for processing although the number of the channels, actually necessary for working out the position of the beam, and the beam width, is only the channels corresponding to not less than N % of the output of the peak channel, so that it has been necessary to install the pulse counters in the monitor-signal processor, and the integrated-pulses fetching devices in the downstream beam monitor controller, corresponding to the number of the channels. For this reason, there has existed a problem that if a monitor system is made up of channels more than those in the past, a larger number of those devices, to the extent of an increase in the number, must be installed. A beam monitor system according to the present embodiment has been developed in order to solve the problem described as above. There is described hereinafter the beam monitor system according to the present embodiment. First, a configuration of the beam monitor system is described hereinafter. The beam monitor system according to the present embodiment is provided with a beam monitor, a monitor signal processor, and a beam-monitor control unit. Herein, a configuration example of a downstream beam monitor system, as the beam monitor system, is described with reference to FIG. 3. Further, an upstream beam monitor system is similar in configuration to the downstream beam monitor system, the configuration of the upstream beam monitor system differing only in respect of the number of channels of a beam monitor. The downstream beam monitor 11d is connected to the downstream beam monitor-monitoring controller 8b2 via a monitor signal processor 22. The downstream beam monitor 11d is a multi-wire ion-chamber type beam monitor. The downstream beam monitor 11d is provided with an X-electrode for detecting a position in an x-axis direction, passed by the charged particle beam, a Y-electrode for detecting a position in a y-axis direction, passed by the charged particle beam, high-voltage electrode (a voltage-application electrode, not shown) for applying a voltage, and a current-frequency converter (pulse generator) 23. In the present embodiment, a configuration whereby the X-electrode, and the Y-electrode are disposed in this order from the upstream side in the traveling direction of the charged particle beam is described by way of example, however, a configuration whereby the Y-electrode, and the X-electrode are disposed in this order may be adopted. Each of the X-electrode and the Y-electrode is charge-collection electrode made up of tungsten wires (wire electrodes) that are strung at equal intervals. The wire electrode as a constituent of the X-electrode as well as the Y-electrode is disposed on a beam track of the charged particle beam to thereby detect the charged particle beam. Application of a voltage to the high-voltage electrode causes an electric field to be generated between the X-electrode and the Y-electrode, thereby causing an electric field to be generated between the X-electrode and the high-voltage electrode. Upon the charged particle beam passing through an ion-chamber, an gas between the high-voltage electrode and the X-electrode as well as an gas between the high-voltage electrode and the Y-electrode undergoes ionization, whereupon an ion pair is generated, and the ion pair generated is moved to the X-electrode and the Y-electrode, respectively, by the agency of the electric field to be recovered by a wire (hereinafter, referred to as a channel). Accordingly, a beam shape 21 can be measured by measuring a quantity of an electric charge detected by each of the channels. Further, a position of the center of gravity of the beam, and a beam width can be worked out by processing respective quantities of the electric charges detected by the respective channels. The electric charge detected by each of the channels is inputted to the pulse generator 23. The pulse generator 23 converts the electric charge as received into a pulse signal, subsequently outputting the pulse signal (a detection signal) to the monitor signal processor 22. The monitor signal processor 22 is provided with a plurality of pulse counters, receiving the pulse signal as inputted to execute signal processing. More specifically, the pulse counter of the monitor signal processor 22 executes integration of pulse numbers on the basis of the pulse signal as inputted, outputting the pulse numbers as integrated to an integrated-pulses fetching device. The monitor signal processor 22 is provided with two units of the integrated-pulses fetching devices (a first integrated-pulses fetching device, and a second integrated-pulses fetching device). The first integrated-pulses fetching device is connected to the pulse counters linked to the X-electrode, collecting data blocks on the pulse numbers based on the signal detected by the X-electrode, thereby finding a beam position as well as a beam width of the charged particle beam, in the x-axis direction. The second integrated-pulses fetching device is connected to the pulse counters linked to the Y-electrode, collecting data blocks on the pulse numbers based on the signal detected by the Y-electrode, thereby finding a beam position as well as a beam width of the charged particle beam, in the y-axis direction. The first integrated-pulses fetching device, and the second integrated-pulses fetching device are each connected to a CPU inside the downstream beam monitor-monitoring controller 8b2. Respective data blocks (processing signals) of the beam position, and the beam width, as collected, and found by the first integrated-pulses fetching device, and the second integrated-pulses fetching device, respectively, are fetched by the CPU. The CPU works out a beam shape of the charged particle beam having passed through the wire electrode, and a position of the center of gravity as well as a beam width of the beam, on the basis of the processing signals. The beam shape of the charged particle beam indicates a beam shape in a plane (X-Y plane) vertical to the beam track of the charged particle beam. The downstream beam monitor-monitoring controller 8b2 can find a beam shape in the x-axis direction of the charged particle beam having passed through the X-electrode on the basis of the processing signal attributable to the detection signal from the X-electrode. Further, the downstream beam monitor-monitoring controller 8b2 can also find a beam shape in the y-axis direction of the charged particle beam having passed through the Y-electrode on the basis of the processing signal attributable to the detection signal from the Y-electrode. In the present embodiment, there is adopted a configuration whereby the downstream beam monitor-monitoring controller 8b2 finds the beam shape in the x-axis direction, and the beam shape in the y-axis direction, respectively, however, another configuration may be adopted whereby the first integrated-pulses fetching device finds the beam shape in the x-axis direction of the charged particle beam having passed through the X-electrode on the basis of the detection signal from the X-electrode, and the second integrated-pulses fetching device finds the beam shape in the y-axis direction of the charged particle beam having passed through the Y-electrode on the basis of the detection signal from the Y-electrode. In this case, the downstream beam monitor-monitoring controller 8b2 finds the beam shape in the X-Y plane on the basis of information on the beam shape in the x-axis direction, from the first integrated-pulses fetching device, and information on the beam shape in the y-axis direction, from the second integrated-pulses fetching device. Next, referring to FIG. 5, there is described hereinafter a method for measuring a beam position, and a beam width, using the downstream beam monitor system according to the present embodiment. The downstream beam monitor 11d according to the present embodiment is provided with an x-axis beam monitor 11d1 including the X-electrode, and the pulse generators 23, and a y-axis beam monitor 11d2 including the Y-electrode, and the pulse generators 23, as shown in FIG. 3. Since a configuration between the x-axis beam monitor 11d1 and the monitor signal processor 22 is identical to that between the y-axis beam monitor 11d2 and the monitor signal processor 22, the x-axis beam monitor 11d1 is described by way of example. The x-axis beam monitor 11d1 is comprised of, for example, 160 lengths of the wire electrodes (the X-electrode) that are strung at equal intervals, thereby having 160 channels. First, all the channels are divided into ten segments from Segment A to Segment J by 16 channels (ch), adjacent to each other. That is, the x-axis beam monitor 11d1 is made up of a plurality of the segments (10 segments in the case of the present embodiment), a plurality of the wire electrodes, adjacent to each other (16 channels of the wire electrodes, in the case of the present embodiment) being organized into one segment. Thus, the one segment is made up of the plural wire electrodes adjacent to each other. In the case where the wire electrodes of the x-axis beam monitor 11d1 are arranged in a physical row representing respective installation positions, and are sequentially indicated as channel 1, 2, 3, 4, . . . 160, respectively, by starting from an end of the row, Segment A includes the channels 1 to 16, Segment B the channels 17 to 32, Segment C the channels 33 to 48, Segment D the channels 49 to 64, . . . Segment I the channels 129 to 144, and Segment J the channels 145 to 160. Further, with the present embodiment, two segments adjacent to each other are organized into one group. More specifically, Segments A, B are organized into Group 1, Segments C, D Group 2, Segments E, F Group 3, Segments G, H Group 4, and Segments I, J Group 5. In this case, one group is made up such that a width of the plural wire electrodes making up the one group, from one end thereof to the other, is larger than the beam width of the charged particle beam scheduled to be emitted, and a beam distribution necessary for calculation of a beam position, and a beam width is to appear in Segment {(the number of the segments in one group)−1}. In FIG. 5, the respective channels (1ch to 32ch) of Segments A, B, belonging to Group 1, are connected to the respective pulse generators 23. The x-axis beam monitor 11d1 is provided with a number of the pulse generators (the current-frequency converters) 23, identical in number to the number of the wire electrodes belonging to the one group. In the case of the present embodiment, 32 units of the pulse generators 23 are provided on the downstream side of the wire electrodes in the x-axis beam monitor 11d1. The pulse generator 23 is connected to the monitor signal processor 22. The monitor signal processor 22 includes a number of the pulse counters, identical to the number of the pulse generators 23, and two units of the integrated-pulses fetching devices. More specifically, the monitor signal processor 22 includes a number of the pulse counters, identical in number to the sum (64 units in the case of the present embodiment) of the number (32 units in the case of the present embodiment) of the wire electrodes belonging to the one group of the x-axis beam monitor 11d1, and the number (32 units in the case of the present embodiment) of the wire electrodes belonging to the one group of the y-axis beam monitor 11d2. The monitor signal processor 22 is connected to a number of the wire electrodes belonging to the one group, respectively, via interconnections identical in number thereto, such that a detection signal outputted from one of the wire electrodes, selected from the respective groups of the x-axis beam monitor 11d1, is inputted from the same interconnection. If the pulse generators 23 and the monitor signal processor 22 are able to process all the signals (16 ch×2) of Group 1, as described above, this is sufficient. To describe a connection method according to the present embodiment, the wire electrodes of the respective channels belonging to one segment are connected to the monitor signal processor 22 via the same interconnection as that of the wire electrode of any one segment belonging to another group. For example, the respective wire electrodes of 33 ch to 48 ch of Segment C belonging Group 2 are connected to any one of the respective wire electrodes of 1 ch to 16 ch of Segment A belonging to Group 1. The respective wire electrodes of 65 ch to 80 ch of Segment E belonging Group 3 are connected to any one of the respective wire electrodes of 1 ch to 16 ch of Segment A belonging Group 1. The respective wire electrodes of Segment G belonging to Group 4 are connected to any one of the respective wire electrodes of 1 ch to 16 ch of Segment A belonging to Group 1. The respective wire electrodes of 129 ch to 144 ch of Segment I belonging to Group 5 are connected to any one of the respective wire electrodes of 1 ch to 16 ch of Segment A belonging to Group 1. In the same way as described above, the respective wire electrodes of Segment B belonging to Group 1 are connected to the respective wire electrodes of Segment D belonging to Group 2, the respective wire electrodes of Segment B belonging to Group 1 are connected to the respective wire electrodes of Segment F belonging to Group 3, the respective wire electrodes of Segment B belonging to Group 1 are connected to the respective wire electrodes of Segment H belonging to Group 4, and the respective wire electrodes of Segment B belonging Group 1 are connected to the respective wire electrodes of Segment J belonging to Group 5. Further, the respective channels from 33 ch to 48 ch of Segment C are connected to the respective channels from 1 ch to 16 ch of Segment A, and at this point in time, the respective channels of Segment C are connected thereto after permutation of respective connection destinations via a permutation connection P1. Further, the respective channels of Segment D in Group 2 are similarly connected to the respective channels of Segment B after permutation of respective connection destinations via the permutation connection P1. Segment E in Group 3 is connected to the respective channels of Segment A via a permutation connection P2 differing from the permutation connection P1, and the respective channels of Segment F as well are similarly connected to the respective channels of Segment B via the permutation connection P2. Segments G, H in Group 4 are connected to Segments A, B, respectively, via a permutation connection P3 differing from the permutation connections P1, P2, and Segments I, J in Group 5 are connected to Segments A, B, respectively, via a permutation connection P4 differing from the permutation connections P1, P2, and P3. Such connections are repeated until all the channels are connected to either Segment A, or Segment B, whereupon a configuration is completed. Thus, the wire electrode belonging to a segment is connected to the wire electrode belonging to a segment of another group via the permutation connection that differs on a group-by-group basis. An example of the permutation connection is described hereinafter. One segment is divided into a plurality of sections (for example, divided sections A1 to A4), as shown in FIG. 6, thereby executing permutation whereby the sections are interchanged on a section-by-section basis. For example, the permutation connection P1 is a permutation whereby the section C2 is interchanged with the section C1, P2 a replacement whereby the section E3 is interchanged with the section E2, P3 a permutation whereby the section G3 is interchanged with the section G1, and P4 a permutation whereby the section 14 is interchanged with the section I1. In the present embodiment, a permutation connection is executed according to the permutation example described as above. Next, there is described hereinafter an operation according to the present embodiment. Upon the monitor signal processor 22 receiving a detection signal from the wire electrode, the monitor signal processor 22 finds group information indicating which group's detection signal of the wire electrode a received detection signal is. Further, the monitor signal processor 22 arranges the detection signals in a different sequence on the basis of permutation connection information, thereby finding a beam shape of the charged particle beam having passed through the wire electrode. The monitor signal processor 22 transmits a processing signal containing both the group information, and beam-shape information, as found, to the CPU of the downstream beam monitor-monitoring controller 8b2. Further, a storage provided in the monitor signal processor 22 may store the detection signal received to subsequently process the detection signal stored, thereby transmitting the processing signal. The downstream beam monitor-monitoring controller 8b2 finds a beam width of the charged particle beam having passed through the wire electrode on the basis of the beam-shape information received. Further, the downstream beam monitor-monitoring controller 8b2 finds a beam position of the charged particle beam having passed through the wire electrode on the basis of both the beam-shape information, and the group information, as received. The downstream beam monitor-monitoring controller 8b2 causes both the beam position and the beam width, as found, to be displayed on the display screen provided in the operation terminal 40. A display unit displays the beam position as well as the beam width of the charged particle beam. Suppose the case where beam irradiation can be normally executed such as 50a at a normal time in FIG. 7, according to a target decided by the treatment-planning unit 6. Assuming that Segments I, J are actually irradiated with the beam, respective values detected at Segments I, J are replaced at the permutation connection P4 to be connected to Segments A, B, respectively, before being sent out to the pulse generators 23. At this point in time, an output appears like an output distribution (normal time) 51a, being unable to obtain a Gaussian distribution due to the effect of the permutation at P4. However, because where to be irradiated with the beam is pre-decided by the treatment planning unit 6, which of the permutation connections the actual irradiation beam has been applied can also be predicted on the basis of planned data. In the present embodiment, Segments I, J each are a planned target-position, so that the permutation by P4 can be predicted, and a Gaussian distribution like a reverse-permutation distribution 52a (normal time) can be obtained by execution of reverse-permutation. If, the Gaussian distribution is obtained, this will definitely indicate that the actual irradiation position is in agreement with the irradiation position according to the planned data, so that the beam position and the beam width can be accurately known. Furthermore, since the pulse generators 23 as well as the monitor signal processors 22, corresponding to the channels in one group only, are required, it is possible to realize a low-cost monitor system. Further, suppose the case (50b at an abnormal time) where an actual beam irradiation position differs from a target irradiation position based on a treatment plan, as shown by 50b in FIG. 7. Suppose, for example, the case where the actual beam irradiation positions have turned out Segments C, D whereas the target irradiation positions are Segments I, J. In such a case, values detected at Segments C, D, respectively, are replaced by P1 to be sent out to the pulse generators 23, respectively, whereupon an output distribution 51b (abnormal time) is obtained. However, because the target irradiation positions based on the treatment plan are Segments I, J, reverse-permutation of the output is executed via P4 at the monitor signal processors 22, and as a result, a reverse-permutation output distribution 52b (abnormal time) is obtained, so that the Gaussian distribution cannot be obtained. In this case, the downstream beam monitor-monitoring controller 8b2 outputs an error signal indicating a beam error to the central control unit 5. Upon the central control unit 5 receiving the error signal, the central control unit 5 outputs a beam-stop signal to the accelerator-transport-system controlling system 7, thereby stopping the charged particle beam outgoing from the circular accelerator 16. Further, the downstream beam monitor-monitoring controller 8b2 can identify an abnormal irradiation position of the charged particle beam by execution of irradiation position identification processing 60. If the reverse-permutation via P1, and the reverse-permutation via P2 are sequentially executed against an output distribution where an abnormal irradiation has occurred, thereby identifying a reverse-permutation whereby the Gaussian distribution is obtainable, it is possible to accurately determine to which channel an abnormal irradiation has been applied. In the case of the present embodiment, the Gaussian distribution is obtained by the reverse-permutation via P1, so that it becomes definitely clear that the abnormal irradiation has been applied to a specific channel in Group 2. Further, in the case where the beam width has undergone a change, there is run a simulation considering a permutation connection against an optional beam width in a scope, and the result of the simulation is compared with an actual irradiation distribution, whereupon the beam position, and the beam width can be identified. In this simulation, an operation from a sensor in a real-world beam monitor system up to before inputting to the pulse generator is simulated on a computer, an input is given such that a beam position, and a beam width each are changed at constant intervals from a given value to a given value on the assumption that the actual irradiation distribution at the time of an abnormal irradiation is a Gaussian distribution, respective results of computer outputs with respective permutation connections dependent on the beam positions, applied thereto, are compared with an actual irradiation distribution to find agreement therebetween, thereby finding a beam position as well as a beam width at the time of the abnormal irradiation. By so doing, with the monitor system according to the present embodiment, it becomes possible to more accurately administer a radiation exposure dose against a patient. With the particle beam irradiation system provided with the beam monitor system according to the present embodiment, the channels for use in working out the position of the charged particle beam, and the beam width are restricted, so that it is unnecessary to prepare both the amplifiers and the signal processors, corresponding in number to all the channels. A beam monitor system according to the related art is hereinafter compared with the beam monitor system according to the present embodiment. In the case of the beam monitor system according to the related art, if an x-axis beam monitor is made up of 160 lengths of wire electrodes, 160 units each of pulse generators, and pulse counters, disposed in the back-end stage thereof, are installed, the 160 units being identical in number to the number of the wire electrodes (the number of channels). If a y-axis beam monitor is made up of 160 lengths of wire electrodes, 160 units each of pulse generators, and pulse counters, disposed in the back-end stage thereof, are similarly installed. Accordingly, the monitor system according to the related art has 160 units of the pulse generators, and 160 units of the pulse counters. In contrast to the beam monitor system according to the related art, with the beam monitor system according to the present embodiment, even if the x-axis beam monitor is made up of 160 lengths of the wire electrodes, the beam position of the charged particle beam, and the beam width can be found by a configuration provided with 32 units of the pulse generators, and 32 units of the pulse counters, 32 units being sufficiently fewer than the number of the wire electrodes (the number of the channels). With the beam monitor system according to the present embodiment, the charge-collection electrode is made up of plural groups, each of the groups being made up of the plural wire electrodes adjacent to each other, and the signal processor is connected to all the wire electrodes via a number of interconnections, identical in number to the number of the wire electrodes belonging to the one group such that a detection signal outputted from one wire electrode selected from the respective groups is inputted from the same interconnection as described. Further, the signal processor has a configuration for finding the group information indicating which group's detection signal of the wire electrode a received detection signal is, thereby outputting the processing signal containing the group information to a beam monitor controller, whereupon the beam monitor controller finds the position of the charged particle beam having passed through the wire electrode, and the beam width on the basis of the processor. For this reason, a monitor system simple in configuration can be constructed. Further, with the present embodiment, the irradiation position can be accurately known by changing the wire connection method on a group-by-group basis, so that it is possible to realize a highly reliable monitor system. The particle beam irradiation system provided with the beam monitor system according to the present embodiment is effective on a method for irradiation by scanning with a fine charged particle beam, in particular. More specifically, in order to execute irradiation with high precision, a small width beam is required, and there is a tendency that the number of wires per unit length of a multi-wire type monitor for measuring a beam profile will increase, however, wires that are concurrently irradiated with the charged particle beam represent only a part of all the wires. The beam monitor system according to the present embodiment represents a method for executing signal-processing of a number of wire signals, corresponding to only a scope concurrently irradiated with the charged particle beam, the beam monitor system having a configuration whereby other wires are connected to a number of wires, corresponding to an irradiation scope, respectively, so that low-cost, and high-reliability can be realized. Further, with the particle beam irradiation system provided with the beam monitor system according to the present embodiment, the wire connection method is changed on the group-by-group basis, so that the irradiation position can be accurately known to thereby realize the highly reliable monitor system. There is described hereinafter a particle beam irradiation system according to another embodiment of the invention with reference to FIG. 8. With the particle beam irradiation system according to the first embodiment, the beam monitor system has the configuration whereby the two segments are organized into the one group, however, the particle beam irradiation system according to a second embodiment includes a beam monitor system whereby a plurality of segments are organized into one group. There is described hereinafter a configuration of the beam monitor system according to the present embodiment, differing from the case of the first embodiment. The beam monitor system according to the present embodiment represents the case of a beam monitor system where group numbers are N-groups, and the number of the channels in the segment is Lch. Assuming that a beam distribution necessary for calculation of a beam position, and a beam width is to appear in (M−1) segment, the number of the segments, necessary for make up one group, is M, so that it need be only sufficient to have the pulse generator 23, and the monitor signal processor 22, capable of processing all the signals (M×L ch) in the group. If the permutation connection, and the reverse-permutation at the monitor signal processor 22 are executed according to the same procedure as in the case of the first embodiment, this will enable the beam position, the beam width, and identification of the irradiation position at the time of erroneous irradiation to be accurately known in a way similar to the case of the first embodiment. Comparison of the present embodiment with the first embodiment is described by use of specific numerical values. If a beam distribution necessary for calculation of a beam position and a beam width corresponds to, for example, 96 ch, the number of the channels for one segment in the case of the first embodiment will be 96 ch, so that 192 ch is required to make up the one group, as shown by 70b. In the case of the present embodiment, if the number of channels for one segment is 32 ch, one group is made up of four segments, as shown by 70a, and 128 ch are required of the one group. In this case of the present embodiment, the number of the channels necessary to make up the one group can be reduced as compared with the case of the first embodiment, so that it is possible to construct a beam monitor system still lower in cost. With the particle beam irradiation system according to the present embodiment, the channels for use in working out the position of the charged particle beam, and the beam width are restricted, so that it is possible to construct a monitor system simple in configuration as compared with the monitor system made up of both the amplifiers and the signal processors, corresponding in number to all the channels. Further, with the present embodiment, the irradiation position can be accurately known by changing the wire connection method on the group-by-group basis, so that it is possible to realize a highly reliable monitor system. The particle beam irradiation system provided with the beam monitor system according to the present embodiment is effective on the method for irradiation by scanning with the use of a fine charged particle beam, in particular. More specifically, in order to execute irradiation with high precision, a small width beam is required, and there is a tendency that a multi-wire type monitor for measuring a beam profile will increase in the number of wires per unit length, however, wires that are concurrently irradiated with the charged particle beam represent only a part of all the wires. The particle beam irradiation system provided with the beam monitor system according to the present embodiment has a configuration whereby other wires are connected to a number of wires, corresponding to an irradiation scope, respectively, adopting a method for executing signal-processing of a number of signals, corresponding to only a scope concurrently irradiated with the charged particle beam, so that low-cost, and high-reliability can be realized. With the particle beam irradiation system provided with the beam monitor system according to the present embodiment, the wire connection method is changed on the group-by-group basis, so that the irradiation position can be accurately known to thereby realize the highly reliable monitor system. There is described hereinafter a particle beam irradiation system according to a third embodiment of the invention with reference to FIG. 9. In contrast to the first embodiment relating to the particle beam irradiation system provided with the beam monitor system for monitoring the beam position, and the beam width in execution of the spot-scanning irradiation method, the particle beam irradiation system according to the present embodiment is provided with a beam monitor system for monitoring a beam position, and a beam width in execution of a raster scanning irradiation method. The particle beam irradiation system according to the present embodiment is provided with the beam monitor system for monitoring the beam position, and the beam width in execution of the raster scanning irradiation method whereby an affected part of a patient 13 is divided into a plurality of layers in the travelling direction of the charged particle beam, thereby scanning with the charged particle beam while continuing irradiation of respective layers with the charged particle beam (the beam remaining ON). There is described hereinafter a configuration of the beam monitor system according to the present embodiment, differing from that of the first embodiment. Upon completion of treatment preparation, doctor inputs a treatment-start signal from the input device of the operation terminal 40. Upon the central control unit 5 receiving the treatment-start signal, the central control unit 5 transmits the command signal to the accelerator-transport-system controlling system 7. The accelerator-transport-system controlling system 7 sets an operation parameter corresponding to the layer to be initially irradiated (initial-irradiation beam-energy information) to the circular accelerator 16, and the beam transport system 2, respectively. Upon the operation parameter being set to the circular accelerator 16, and the beam transport system 2, respectively, thereby completing the treatment preparation (Step 30), the scanning-electromagnet power-supply control unit 8c excites the scanning electromagnet 11b on the basis of the excitation current parameter (Step 31a). After the scanning electromagnet 11b is excited by the excitation current corresponding to the initial irradiation spot, the dose-monitoring controller 8b3 of the monitor-monitoring control unit 8b starts monitoring of the radiation exposure dose of the beam on the basis of the target dose value against the relevant spot position (Step 32a), thereby completing the irradiation preparation. Upon the central control unit 5 transmitting the beam-emission start command (Step 33), the accelerator-transport-system controlling system 7 activates the ion source, whereupon the charged particle (the proton or the heavy particle) is generated. The front-stage accelerator 15 accelerates the charged particle from the ion source, emitting a charged particle beam to the circular accelerator 16. The circular accelerator 16 further accelerates the charged particle beam. The charged particle beam that is revolving is accelerated up to the target energy to be emitted from the circular accelerator 16 to the beam transport system 2. The charged particle beam reaches the scanning irradiation unit 3 via the beam transport system 2. Further, the charged particle beam travels along the beam axis inside the irradiation nozzle 11, passing through the upstream beam monitor 11a, the scanning electromagnet 11b, the dose monitor 11c, and the downstream beam monitor 11d in sequence. The charged particle beam emitted from the irradiation nozzle 11 is irradiated to the affected part of the patient 13. The dose-monitoring controller 8b3 receives the measurement data obtained by the dose-monitor 11c to be processed, thereby finding the radiation exposure dose against the relevant irradiation spot. Irradiation with the charged particle beam is continued until the radiation exposure dose against the initial irradiation spot reaches the target dose value. Upon the dose-monitoring controller 8b3 determining that the radiation exposure dose has reached the target dose value, the dose-monitoring controller 8b3 outputs the irradiation-expiration signal to the central control unit 5 (Step 34). The first detection data detected by the upstream beam monitor 11a is fetched by the upstream beam monitor-monitoring controller 8b1, and the second detection data detected by the downstream beam monitor 11d is fetched by the downstream beam monitor-monitoring controller 8b2, thereby finding the irradiation position of the charged particle beam, and the beam width (Step 35a). If the position of the beam, and the beam width has no abnormality (If it is determined that the beam position is within the allowable beam position, and the beam width is within the allowable beam width) upon completion of the processing, there is made a determination on whether or not the irradiation spot after irradiation-expiration is the final spot position in the layer. If it is determined that the irradiation spot is not the final irradiation spot position (If No), the scanning-electromagnet power-supply control unit 8c executes setting of a spot scanning-electromagnet on the basis of the excitation current parameter (Step 35b), the monitor-monitoring control unit 8b executes setting of a spot-dose target value (Step 35c). An operation reverts to Step 34, and a control flow 37a from the step (Step 34) for determination on the dose-expiration up to determination that an irradiation spot is the final spot position is repeatedly executed until it is determined that the irradiation spot upon the irradiation-expiration is the final spot position in the layer (until determined Yes). Upon completion of the irradiation of all the spots in the layer, the central control unit 5 determines whether or not the layer upon completion of irradiation is the final layer of the patient 13. If the layer is not the final layer (If No), the central control unit 5 transmits the command signal to the accelerator-transport-system controlling system 7. The accelerator-transport-system controlling system 7 sets an operation parameter corresponding to the layer to be next irradiated to the circular accelerator 16, and the beam transport system 2, respectively, thereby starting preparation for the next operation (Step 30). This control flow 38a is repeated until the irradiation of all the layers is completed. Upon the completion of the irradiation of all the spots, and all the layers, treatment completion is reached (Step 39). Thus, with the particle beam irradiation system according to the present embodiment, there is implemented the raster scanning irradiation method whereby the irradiation position is changed with the charged particle beam kept in an emitted state, thereby applying beam irradiation to the affected part. Further, the particle beam irradiation system according to the present embodiment can be applied to the particle beam irradiation system provided with the beam monitor system according to the second embodiment, for monitoring the beam position, and the beam width. With the particle beam irradiation system provided with the beam monitor system according to the present embodiment, the channels for use in working out the position of the charged particle beam, and the beam width are, restricted, so that it is unnecessary to prepare both the amplifiers and the signal processors, corresponding in number to all the channels. Therefore, a monitor system simple in configuration can be constructed. Further, with the present embodiment, the irradiation position can be accurately known by changing the wire connection method on the group-by-group basis, so that it is possible to realize a highly reliable monitor system. The particle beam irradiation system provided with the beam monitor system according to the present embodiment is effective on the method for irradiation by scanning with the fine charged particle beam, in particular. More specifically, in order to execute irradiation with high precision, the small width beam is required, and there is the tendency that the multi-wire type monitor for measuring the beam profile will increase in the number of wires per unit length, however, the wires that are concurrently irradiated with the charged particle beam represent only the part of all the wires. The beam monitor system according to the present embodiment represents the method for executing signal-processing of a number of wire signals, corresponding to only the scope concurrently irradiated with the charged particle beam, the beam monitor system having the configuration whereby other wires are connected to a number of wires, corresponding to the irradiation scope, respectively, so that low-cost, and high-reliability can be realized. Further, with the particle beam irradiation system provided with the beam monitor system according to the present embodiment, the wire connection method is changed on the group-by-group basis, so that the irradiation position can be accurately known, and a highly reliable monitor system can be realized. Now, it is to be pointed out that the invention be not limited to any of the details of description concerning the first, second, and third embodiments, respectively, and that various modifications may be made in the invention. For example, the first, second, and third embodiments each are described in detail for explanation with greater ease, however, the invention is not necessarily limited to any of the embodiments provided with all the configurations described. For example, in the embodiment, a signal processor is comprised of the current-frequency converters, and the digital signal processor including the pulse counters, however, the signal processor may be comprised of a circuit for integrating charges to be converted into a voltage to be outputted, and an analog monitor signal processor. Further, a monitor can include any suitable number of channels, segments, and groups, and permutation connections in a group may not be identical to each other. Further, as for permutation connection, one segment is divided into a plurality of segments, and subsequently, permutation is executed through interchange between the segments. However, the permutation is not limited thereto, and can be executed by any suitable method. |
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063209241 | summary | TECHNICAL FIELD The present invention relates to a spacer for nuclear fuel rods and particularly to a unique, substantially I-shaped spring and associated ferrule assembly for the fuel rod spacer. BACKGROUND In a nuclear reactor, for example a boiling water reactor, nuclear fuel rods are grouped together in an open-ended tubular flow channel, typically referred to as a fuel assembly or bundle. A plurality of fuel assemblies are positioned in the reactor core in a matrix and a coolant/moderator flows upwardly about the fuel rods for generating steam. In each assembly or bundle, fuel rods are supported between upper and lower tie plates in side-by-side parallel arrays. Spacers are employed at predetermined elevations along each fuel bundle to restrain the fuel rods from bowing or vibrating during reactor operation, and to protect the fuel rod assembly during possible loading events, such as handling and shipping. Typical spacers often include a plurality of ferrules arranged in side-by-side relation and secured by, for example, welding to one another to form the support matrix of the spacer. A single fuel rod passes through each generally cylindrically shaped ferrule. The ferrules include circumferentially spaced, axially extending interior protuberances (or hard stops) and spring assemblies seated in openings formed in opposite sides of the ferrule from the protuberances, for centering and biasing the fuel rods against the hard stops, thereby maintaining the fuel rods in fixed relation one to the other across the spacer. The spacer itself constitutes an obstacle to bundle performance in that its cross-section interferes with the flow of water/moderator through the bundle. An ideal spacer would have minimal impact on bundle performance (thermal hydraulics, critical power), while still restraining the rods in their intended positions and protecting them. Consequently, an optimum fuel bundle spacer should have as little cross-section as possible, use a minimum amount of material and simultaneously meet structural requirements for positioning and protecting the fuel rods. In developing new spacer spring designs for denser bundle matrices (for example, 8.times.8, 9.times.9, and 10.times.10), one challenge is to design the spring so that it will be sufficiently flexible to maintain historical preload limits as the space between the fuel rods becomes smaller (i.e., the spring deflection increases as the space decreases). Since it has been determined that the accelerated dead weight of the fuel rods at the. spacer locations damages the springs, a second challenge is to design the spring such that assembled fuel bundles can be shipped without the aid of plastic inserts to carry the weight of the rods as they travel on trucks. The damage mentioned above occurs because current spacer designs involve one spring being shared between two adjacent fuel rods, and this type of arrangement means that some fuel rods are sitting on the springs when the bundle is laid horizontally on the truck bed, causing the rod's own dead weight to be accelerated directly into the spring underneath it. Some prior spacer designs which include ferrules with one spring per two adjacent fuel rods are disclosed in commonly owned U.S. Pat. Nos. 5,173,252 and 5,078,961. In commonly owned application Ser. Nos. 08/380,591 filed Jan. 30, 1995 and 08/516,203 filed Aug. 17, 1995, spring designs are disclosed which are based on a one spring per fuel rod criteria, with the ability to ship without conventional plastic inserts. However, a disadvantage of these spring designs is that too much spring material protrudes into the subchannel regions between the ferrules, and their respective geometries are thought to be susceptible to self-vibration due to coolant water flow across the springs. DISCLOSURE OF THE INVENTION The spring design for ferrule spacers in accordance with this invention do not require plastic insert supports for the spacers during shipping. The individual springs and ferrules are simply aligned within the fixture (before welding), with the associated springs all oriented in a single chosen direction, such that the shipping loads, which occur during bundle shipment to customers, can be taken up by the hard stops on the ferrules and not by the springs themselves. In addition, the springs in accordance with this invention have the required flexibility but with minimal projection into the subchannels. More specifically, the spring is given generally the shape of an "I", so that only the lateral ends or ears of the spring protrude into the subchannel, with the majority of the spring geometry captured in a cutout formed in the ferrule. In the exemplary embodiment, the ferrule is substantially cylindrical, but with a pair of axially extending grooves or indents which provide a pair of hard stops on the interior of the ferrule when the fuel rod is inserted within the spacer. In the arcuate wail of the ferrule, opposite the pair of hard stops, there is a generally "I" shaped cutout or opening, also extending axially of the ferrule. Thus, the opening has a pair of relatively wider cutout portions connected by an axially extending narrower portion. The I-shaped spring in accordance with an exemplary embodiment of the invention also includes upper and lower wider portions, or flanges connected by a stem. Each flange is formed with a centrally located outward (away from the ferrule) projection, while the center portion of the narrower stem which connects the flanges is formed with an inward (toward the ferrule) projection. This inwardly directed projection is also provided with an inwardly extending dimple which is adapted to engage a fuel rod placed within the ferrule. The spring in accordance with the exemplary embodiment of the invention is also form ed with a pair of "T" shaped cutouts, one upright and one inverted, located on either side of the inward projection on the spring stem. When the spring is aligned within the "I" shaped opening of the ferrule, only the upper and lower flanges of the spring protrude from the ferrule and extend into the subchannel regions. The remaining portion of the spring including the entire stem portion is substantially located within the ferrule cut-out. This new design concept significantly reduces the amount of spring material that protrudes into the coolant flow, and the geometry is such that the spring is captured more securely within the ferrule cutout to thereby guard against spring movement due to flow-induced vibration. This is in sharp contrast to previous designs which have significant areas of the spring geometry within the subchannel flow, making the springs susceptible to movement from the force of the water impacting on the spring. Thus, in accordance with the exemplary embodiment of the invention, there is provided a sub-assembly for a spacer useful in a nuclear fuel bundle for maintaining a matrix of a plurality of nuclear fuel rods passing through the spacer in spaced-apart relation, comprising at least first and second ferrules lying adjacent one another for receiving respective nuclear fuel rods, each ferrule having fuel rod contacting points along one side of the ferrule for abutting a fuel rod within the ferrule and a substantially I-shaped opening along a side of the ferrule opposite the one side; a substantially I-shaped spring including a spring body lying in a plane and having opposite horizontal end portions connected by a vertical stem portion, a central portion of each horizontal end portions projecting away from the substantially I-shaped opening to one side of the plane and a center portion of the vertical stem projecting into the substantially I-shaped opening to an opposite side of the plane; the spring being disposed between said adjacent ferrules with the vertical stem seated in the opening of the first ferrule with the center portion of the stem adapted to bear against the fuel rod within the first ferrule and maintaining the fuel rod against the fuel rod contacting points of the first ferrule, the horizontal end portions lying substantially outside said I-shaped opening with the central portions of each end portion bearing directly against the second ferrule circumferentially between a pair of the fuel rod contacting points of the second ferrule. In another aspect, the present invention provides a spacer for maintaining a matrix of rods in spaced apart relation between upper and lower tie plates, the spacer assembly comprising a matrix of adjacent ferrules for receiving respective fuel rods: each ferrule having fuel rod contacting points along one side of the ferrule for abutting a fuel rod within the ferrule and a substantially I-shaped opening along a side of the ferrule opposite the one side; and a substantially I-shaped spring including a spring body lying in a plane and having opposite horizontal end portions connected by a vertical stem portion, a central portion of each of the horizontal end portions projecting away from the substantially I-shaped opening to one side of the plane and a center portion of the vertical stem projecting into the substantially I-shaped opening to an opposite side of the plane, the opening being disposed between the adjacent ferrules with the vertical stem seated in the opening of the first ferrule, with the center portion of the stem adapted to bear against the fuel rod within the first ferrule and maintaining the fuel rod against the fuel rod contacting points of the first ferrule, the horizontal end portions substantially outside the I-shaped opening with the central portions of each end portion bearing directly against the second ferrule circumferentially between a pair of the fuel rod contacting points of the second ferrule. The invention thus provides a spring and ferrule assembly where the spring has the required flexibility but with minimal projection into the subchannels between ferrules, and which provides the ability to ship fuel bundles without supports for the spacers. Other objects and advantages of the subject invention will become apparent from the detailed description which follows. |
054250633 | description | DETAILED DESCRIPTION OF THE INVENTION Proton beams may be generated by various types of accelerators. The proton beam energies useful for the process of the invention may range from about 5 MeV to about 40 MeV, preferably from about 10 MeV to about 30 MeV. The proton beam current may range from about 5 .mu.A to about 30 .mu.A, preferably from about 8 .mu.A to about 15 .mu.A. In the preferred embodiment of the present invention, proton irradiation may be performed using a 17.4 MeV proton beam generated by a proton accelerator (Japan Steel Works, Inc., Muroram-Shi, Hokkado, Japan; 17.4 MeV proton, 10 MeV deuteron cyclotron). The beam passes through the target cell window (0.001 inch thick titanium foil) relatively unimpeded and enters the target water with a beam energy of about 17.0 MeV and a beam current of about 12 .mu.A. Those persons having experience in the art will recognize that other proton source parameters may be chosen depending upon the desired application and the types and quantities at desired isotopes. The proton bombardment will generally last until sufficient isotopes are produced, commonly from about 10 minutes to about 30 minutes, also depending on the application involved and the quantities of isotopes required. Most preferably, the proton bombardment will last about 20 minutes at the preferred beam parameters described. Among other considerations, the high cost of [.sup.18 O]H.sub.2 O (currently $140/gram at greater than 97% enrichment level: Isotec, Inc., Miamisburg, Ohio), its heat transfer characteristics and the quantities of isotopes necessary for radiotracer synthesis together dictate that the target cell have a capacity of from about 2 mL to about 5 mL, most preferably about 2.5 mL. Generally, high temperatures are induced in the target water during bombardment due to the energy deposited by the beam. Measures to reduce cavitation, due to boiling, and evaporation may be employed, such as the use of a very high overpressure of a gas, e.g., helium. Preferably, a water recirculating cooling method may be employed to remove heat generated by the beam impact on the target. This cooling is facilitated by the excellent heat transfer capacity of a 1/2 inch thick silver target typically used to stop the proton beam after it travels through the water. The isotopes of interest, namely .sup.13 N and .sup.18 F, are preferably produced by proton irradiation of low-enriched [.sup.18 O]H.sub.2 O. The .sup.13 N isotope is preferably produced from a target containing non-enriched natural water by the .sup.16 O(p,.alpha.).sup.13 N nuclear reaction. This reaction can take place in low-enriched [.sup.18 O]H.sub.2 O, as is preferred in the present invention, because of the preponderance of [.sup.16 O]H.sub.2 O in the target. The .sup.18 F isotope is preferably produced via the .sup.18 O(p,n).sup.18 F nuclear reaction and the production of usable quantities requires substantial enrichment of the water target with [.sup.18 O]H.sub.2 O most preferably between about 20% and about 30% by weight. The relative proportion of [.sup.16 O]H.sub.2 O to [.sup.18 O]H.sub.2 O will be determined based on the relative quantities of .sup.13 N and .sup.18 F isotopes desired. Since the two isotopes are produced by two different proton induced nuclear reactions involving different oxygen isotopes, the proportion of .sup.13 N and .sup.18 F produced in the target water will depend upon the relative proportion of [.sup.16 O]H.sub.2 O and [.sup.18 O]H.sub.2 O in the target and the incident proton beam energy. For the present invention, the quantities of each isotope product must be sufficient to be usable for radiotracer synthesis. The relative quantities of each isotope may vary depending upon the desired application and the individual facility's proton beam characteristics, but one advantage of the process of the invention is that neither .sup.13 N nor .sup.18 F is produced in merely trace quantities. It is preferred, then, that the enrichment of the [.sup.18 O]H.sub.2 O be in the range of from about 10% to about 60%, more preferably in the range of from about 15% to about 40%. Most preferably, the [.sup.18 O]H.sub.2 O enrichment is in the range of from about 20% to about 30%. [.sup.18 O]H.sub.2 O is available in enrichment levels ranging from 20% to 99% from Isotec, Inc., Miamisburg, Ohio. It has been found that lower enrichment levels of [.sup.18 O]H.sub.2 O, e.g., below 60%, permits production usable quantities of .sup.18 F while simultaneously producing usable quantities of .sup.13 N. See Example 2 below. In particular, it has been found that the quantities of .sup.13 N and .sup.18 F produced with [.sup.18 O]H.sub.2 O enrichment in the most preferred range are well-suited for radiotracer synthesis for combined [.sup.13 N]NH.sub.3 and [.sup.18 F]FDG use for PET studies of myocardial function. When .sup.13 N atoms are produced during the irradiation process, a large fraction recoil and ionize. The atoms then pick up hydrogen from the water to form [.sup.13 N]NH.sub.4.sup.+. The water itself then oxidizes the [.sup.13 N]NH.sub.4.sup.+ to form either of two nitrogen oxides (NO.sub.x.sup.-), i.e., nitrite ([.sup.13 N]NO.sub.2.sup.-) and nitrate ([.sup.13 N]NO.sub.3.sup.-). [.sup.18 F]F.sup.-, on the other hand, generally does not form more complex ions when created in water. Once the .sup.13 N and .sup.18 F isotopic products have been collected on the anion exchange resin, the target water may be recovered for future re-use. This is especially preferred because of the high cost of the [.sup.18 O]H.sub.2 O used for enrichment. The present invention provides a method for removing the isotopes from the irradiated target water and further separating the isotopes. The isotope ions [.sup.18 F]F.sup.- and [.sup.13 N]NO.sub.x.sup.- are removed from the irradiated target water by passing the target water over an anion exchange resin. The ions selectively bind to the resin and the target water may be recovered for re-use. The isotopes are then separated from one another on the basis of the relative selectivities of each ion for the resin through the use of a sequential elution process. While not wishing to be bound by theory, it is generally accepted that anion exchange chromatography separates molecules on the basis of the charge carried by the anions being separated. Competing anions displace one another on the exchange resin on the basis of their relative selectivity for the resin or because a concentration differential in the eluant forces the equilibrium of the system in favor of their adsorption. Therefore, the separation of a mixture of anions can be effected by altering ionic strengths as well as pH. The anion exchange resin useful for the method of the present invention may be selected from the group of anion exchange resins having substantial affinity for F.sup.- and NO.sub.2.sup.- /NO.sub.3.sup.- anions, to allow differential elution. Generally, such anion exchange resins are classified as strong anion exchange resins. Preferred anion exchange resins are resins having quaternary ammonium functional groups characterizable by the formula: ##STR1## wherein X is a polymeric support resin and R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are independently selected from the group consisting of hydrogen, and alkyl groups having 1 to 4 carbons. Especially preferred anion exchange resins are those resins having functional groups characterizable by the formula EQU X--CH.sub.2 --N--(CH.sub.3).sub.3, wherein X is a polymeric resin support. Such an especially preferred resin is the AG 1 resin available in various forms from Bio-Rad Laboratories in Richmond, Calif. The AG 1 resin employs a copolymer of styrene and divinylbenzene as the support, with quaternary ammonium as the functional group. The degree of cross-linking in the polymeric support may be varied. Preferably, the AG 1 resins useful for the method of the invention may have between about 2% and about 10% cross-linking, most preferably about 8% cross-linking. It is preferred that the anion exchange resin be in the form of particles useful in column chromatographic applications, but membrane format resins have also been found to be useful. Resin particles of a variety of sizes are useful, preferably of a size within the range of 106 .mu.m diameter or less (140 mesh or higher). Smaller resin particles are preferred due to the small size at the column used in the preferred embodiment. It is most preferred that the ion exchange resin have a particle size in the range of 200-400 mesh, or from about 38 .mu.m to about 75 .mu.m in diameter, such as the AG 1-X8 resin available from Bio-Rad. The preferred anion exchange resins useful in the invention exhibit differential selectivities from various anions. The relative selectivity for the ions generated by the method of the invention is generally characterizable by the sequence: F.sup.- <NO.sub.2.sup.- <NO.sub.3.sup.-. The method of the invention takes advantage of this relative selectivity profile by eluting the [.sup.18 F]F.sup.- first, because of its lower affinity for the resin, and the [.sup.13 N]NO.sub.2.sup.- /NO.sub.3.sup.- later, because of their higher affinities. The anion exchange resin must generally have an anion electrostatically adsorbed to the resin prior to its use for separating other anions. To be effective, the anion electrostatically bound to the resin must have a relatively low affinity for the resin. More specifically, the original anion must have affinity for the resin similar to or lower than that of the anion sought to be extracted. Otherwise, the original anion will not be readily displaced, and the analyte anion will pass by the resin without binding. The F.sup.- anion exhibits very weak affinity for the preferred resins of the invention. As a result, the original anion bound to the resin must have a comparable or even lower affinity. The preferred original anions are OH.sup.- and CO.sub.3.sup.2-. The most preferred form of the resin is the carbonate form, where the original electrostatically adsorbed anion is CO.sub.3.sup.2-. The anionic radionuclides of the present invention have relatively different selectivities for the useful anion exchange resins described herein. F.sup.- anions generally have a much smaller selectivity than do NO.sub.2.sup.- or NO.sub.3.sup.- anions, i.e., on the order of 10-fold lower. Furthermore, the NO.sub.2.sup.- anion has an approximately three-fold lower selectivity than does the NO.sub.3.sup.- anion. Therefore, useful counterions for F.sup.- extraction may be selected from the group having selectivities between the selectivity of F.sup.- and the selectivity of NO.sub.2.sup.-. A counterion selected from the group having selectivities between the selectivities of NO.sub.2.sup.- and NO.sub.3.sup.- would cause the contamination of the F.sup.- fraction with NO.sub.2.sup.-, and, accordingly, anions in this range are less preferred. For the extraction of F.sup.-, therefore, preferred counterions include propionate, acetate, formate, HPO.sub.4.sup.-, IO.sub.3.sup.-, HCO.sub.3.sup.-, and CO.sub.3.sup.2-. The most preferred eluant counterion is a carbonate (CO.sub.3.sup.2-) solution. The carbonate anion in the eluant may preferably be derived from a potassium (K.sub.2 CO.sub.3) or cesium (Cs.sub.2 CO.sub.3) salt. However, those skilled in the art will perceive that other cations may be employed as long as they do not interfere with the purity of recovery of the anionic radionuclides, and interfere with subsequent syntheses involving these anionic radionuclides. For example, the ammonium cation (NH.sub.4.sup.+) is undesirable, as are other nitrogen-containing cations. The most preferred eluant for [.sup.18 F]F.sup.- elution is an aqueous solution of K.sub.2 CO.sub.3, having a concentration in the range of from about 0.001M to about 0.05M, preferably from about 0.005M to about. 0.02M, most preferably about 0.01M. The carbonate eluant is preferably slightly basic and must not be strongly basic since CO.sub.3.sup.2- will be degraded by strong base. The CO.sub.3.sup.2- eluant has a pH of from about 7.5 to about 9.0, preferably from about 7.7 to about 8.5. Most preferably, the CO.sub.3.sup.2- eluant has a pH of about 8.0. Those skilled in the art will recognize that a carbonate concentration of 0.01M is further preferable since the synthesis of [.sup.18 F]FDG employs reactants containing carbonate anion at or near this concentration. In the most preferred embodiment, approximately 1.5 mL of aqueous 0.01M K.sub.2 CO.sub.3 is required to elute the [.sup.18 F]F.sup.- from the resin. Using eluant having these characteristics will generally permit the recovery of about 99% of the bound [.sup.18 F]F.sup.- activity at about 99% radionuclidic purity. For the extraction of NO.sub.x.sup.-, a counterion having a selectivity near to or greater than that of NO.sub.2.sup.- is preferable. Such counterions include Cl.sup.-, BrO.sub.3.sup.-, HSO.sub.3.sup.-, CN.sup.-, Br.sup.-, ClO.sub.3.sup.-, HSO.sub.4.sup.-, and citrate. The most preferred eluant counterion is Cl.sup.-, present as a solution of hydrochloric acid (HCl). HCl is preferably employed at a concentration of about 1 acid equivalent per liter, i.e., 1N HCl. The cationic portion of the counterionic salt preferably contains no nitrogen, in order to avoid diluting the percentage of .sup.13 N in the eluate. Similar considerations apply to the selection of the counterion itself, i.e., NO.sub.2.sup.- and NO.sub.3.sup.- are less preferable as eluant counterions. In the most preferred embodiment approximately 1 mL of aqueous 1N HCl is required to elute the NO.sub.x.sup.- from the resin. Using HCl eluant having these characteristics will generally allow the recovery of about 94% of the [.sup.13 N]NO.sub.x.sup.- activity at about 99% radionuclidic purity. The eluants generally are solutions, most preferably, aqueous solutions. The eluant solutions may comprise a mineral or organic acid or its salt, an electrolyte mixture of acid and salt, a base, or an electrolyte mixture of base and salt soluble in water. The concentration of the eluant is such that precipitation does not occur in either the anion exchange resin or external liquid phase. Generally, the concentration is from about 0.001 moles/liter to about 10 moles/liter (M). Also, the pH of the eluant is selected such that precipitation does not occur. The separation column useful for the method of the invention may be of variable size. The diameter may range from about 1 mm to about 3 mm, preferably from about 2.5 mm to about about 3.5 mm. The length of the column may range from about 3 mm to about 10 mm, preferably from about 5 mm to about 8 mm. The separation column of the most preferred embodiment is approximately 2 mm in diameter and approximately 7 mm in length, therefore having a volume of approximately 0.022 mL. The volume of resin used for the separation of the isotope ions from the target water is therefore approximately 0.022 mL. Other dimensions of column and volumes of resin may be employed. The temperature during the elution process may vary widely, i.e., from about 0.degree. C. to about 100.degree. C. or the boiling point of the eluant. The thermal stability of the resin must be considered when selecting a temperature or range of temperatures for elution. It is preferred that the temperature be in the range of from about 20.degree. C. to about 50.degree. C. most preferably about ambient temperature Once the [.sup.13 N]NO.sub.x.sup.- has been eluted from the anion exchange resin, the eluate is acidic. The process of the invention used for converting NO.sub.x.sup.- to NH.sub.3, a form of .sup.13 N useful for numerous applications, including clinical PET imaging, requires a reduction the NO.sub.x.sup.- in alkaline solution. For this purpose, the NO.sub.x.sup.- eluate is basified by being transferred to a basifying reservoir holding an alkaline solution capable of providing sufficient excess OH.sup.- ions to raise the pH of the eluate to the range of about pH 9-10 without undesirably increasing the volume of the eluate. This process usually requires the use of a strong base at relatively high concentration. The preferred base is an NaOH solution. In the most preferred embodiment the base will be 2N NaOH, and approximately 1.5 mL will be held in the basifier for addition to the 1.5 mL bolus of eluate received from the elution of the NO.sub.x.sup.-. More generally, it is preferred that the base solution contain approximately double the available acid equivalents of OH.sup.- as compared to the acid equivalents present in the NO.sub.x.sup.- eluate. Furthermore, it is preferred that the base solution have a volume approximately equal to that of the NO.sub.x.sup.- eluate. It will be noted by those skilled in the art that nitrogen-containing bases, such as NH.sub.4 OH are less preferred because of their capacity to contaminate the [.sup.13 N]NH.sub.3 product with natural nitrogen [.sup.14 N]. After the pH of the NO.sub.x.sup.- eluate has been adjusted to pH 9-10, the NO.sub.x.sup.- in the eluate is preferably reduced by being transferred to a reaction vessel containing a strong reducing agent, preferably Devarda's alloy. Devarda's alloy is a commonly used strong reducing agent, that operates at alkaline pH, and contains variable amounts of copper, aluminum, and zinc. The Devarda's alloy most preferably contains approximately 50% copper, 45% aluminum, and 5% zinc, and is available from Aldrich Chemical Co. (Milwaukee, Wis.) The Devarda's alloy reduces NO.sub.x.sup.-, producing NH.sub.3 gas. The [.sup.13 N]NH.sub.3 gas is then transferred to the PET facility for use. While the target cell configuration useful for proton irradiation of low-enriched [.sup.18 O]H.sub.2 O in accordance with the present invention may be varied, the preferred embodiment is illustrated as 200 in FIG. 1. The target cell is shown in longitudinal section, i.e., a section in the vertical plane parallel to the path of a proton beam entering the cell. The preferred target cell is cylindrical, and therefore substantially circular in cross section, i.e., a section normal to the path of a beam entering the cell. The target cell is 2.5 cm in diameter with a thickness of 0.6 cm. Further details on the construction of the target cell may be found in "Impurities in the [.sup.18 O] Water Target and Their Effect on the Yield of an Aromatic Displacement Reaction with [.sup.18 F] Fluoride", D. J. Schlyer, M. L. Firouzbakht and A. P. Wolf, Int. J. Appl. Radiat. Inst. Part A (in press). The main target chamber 202 is fabricated from silver. The water cooling block 204, attached to the rear of the target chamber 202, is fabricated from aluminum. Standard HPLC couplings 206 are electron beam welded onto the back of the silver target chamber 202. This allows direct coupling of conduits, e.g., 236, 210, into the target cell ports, e.g., 208, 246. A stainless steel coiled loop conduit 210 (2 mL volume) serves as an expansion volume for the low-enriched [.sup.18 O]H.sub.2 O during loading. This is necessary because the target volume 212 is somewhat smaller when the front window 214 (0.001 inch thick titanium foil) is flat. Upon pressurization for irradiation, the water is displaced from the coil 210 into the cell 202 as the front window 214 deforms outwardly, as is shown. The target cell volume 212 when pressurized is approximately 2.5 mL. Low-enriched [.sup.18 O]H.sub.2 O target water 216 (labeled H.sub.2.sup.18 O) is contained in reservoir 218 and may be pushed through conduit 220 past valve 230 and valve 234 into target volume 212. Helium drive pressure is provided by helium supply 222 through conduit 224, and via valve 226 and conduit 228, to the target water reservoir 218. After irradiation, the target water is driven by helium pressure from target cell 202 via conduit 238, past valve 240, and through coil conduit 210. Target water passes from target volume 212, returning through conduit 236 and via valve 234 to valve 230. Valve 230 directs the irradiated target water through conduit 12 to the resin/recovery system, illustrated in greater detail as 10 in FIG. 2. Conductivity sensor 244 is present in target volume 212 providing feedback regarding whether the target cell 202 is filled and ready for irradiation. The entire loading and unloading process is preferably electrically remotely controlled, most preferably automated. This system has been used in carrying out the experiments described in Examples 1 and 2. Referring now to FIG. 2, an automated system for the quantitative recovery and separation of [.sup.18 F]F.sup.- and [.sup.13 N]NO.sub.2.sup.- /NO.sub.3.sup.- from irradiated low-enriched [.sup.18 O]H.sub.2 O is generally indicated as 10. A manual system similar to that represented in FIG. 2 has been used to carry out the experiments described in Examples 1 and 2. The system 10 includes a conduit 12 for transferring irradiated target water by helium drive pressure, through valve 14 and conduit 16, to a reservoir 18. From reservoir 18, the irradiated target water is passed through column 20, containing anion exchange resin 22, where the [.sup.18 F]F.sup.- and [.sup.13 N]NO.sub.2.sup.- /NO.sub.3.sup.- bind to the resin 22. The target water may then be recovered by passing through conduit 24 to valve 26 and conduit 28, to recovery reservoir 30 containing recovered target water 32. Pressure may be vented through pressure relief conduit 34, controlled by valve 36. K.sub.2 CO.sub.3 or other carbonate eluant 40 in reservoir 42 is then driven through conduit 44, past valve 46, and through conduit 48 until reaching valve 14. Helium drive pressure is generated from helium source 50, passed through conduit 52, controlled by valve 54, and through conduit 56. Valve 14 is operated to admit the carbonate eluant 40 through conduit 16 to reservoir 18. The carbonate eluant then passes to column 20 where the [.sup.18 F]F.sup.- is eluted from resin 22. Valve 26 is operated to pass the carbonate/[.sup.18 F]F.sup.- eluate from column 20 through conduit 24 to conduit 60. Valve 60 is operated to pass the [.sup.18 F]F.sup.- bolus through conduit 62. Valve 64 allows the bolus to pass through conduit 66 leading to hot lab 68. HCl eluant 70 in reservoir 72 is then passed through conduit 74 and admitted to conduit 48 by valve 46. Helium drive pressure is generated from helium source 50 through conduit 52 controlled by valve 54, through conduit 56. Valve 14 is operated to admit the HCl eluant through conduit 16 to reservoir 18 and to column 20 where the [.sup.13 N]NO.sub.2.sup.- /NO.sub.3.sup.- is eluted. Valve 26 admits the eluate through conduit 58, and valve 60 admits the eluate through conduit 70 to valve 72. Valve 72 is then operated to conduct the [.sup.13 N]NO.sub.2.sup.- /NO.sub.3.sup.- eluate through conduit 74 to basifying reservoir 76 containing NaOH 78. The basified .sup.13 N eluate is then returned to valve 72 by way of conduit 74, and conducted through conduit 84 to reducing reservoir 86 containing Devarda's alloy 88. Helium drive pressure is generated by helium source 94 to reverse flow from conduit 96 controlled by valve 98 through conduit 100. Once the .sup.13 N eluate is reduced to [.sup.13 N]NH.sub.3, it is passed through conduit 102 which would allow it to be transferred to the PET facility 104. EXAMPLE 1 Table 1 illustrates the effect of the nature and strength of the eluant used for extraction of [.sup.13 N]NO.sub.2.sup.- /NO.sub.3.sup.- and on the efficiency of recovery of the anions. The data were obtained using a manual system similar to that described above and illustrated in FIGS. 1 and 2. When the extraction reagent (eluant) is a carbonate anion (CO.sub.3.sup.2-), less than 1% of the [.sup.13 N]NO.sub.x.sup.- was found to be eluted from the anion exchange resin. Hydrochloric acid was found to be the most effective extraction reagent for [.sup.13 N]NO.sub.3.sup.- elution. The effectiveness of hydrochloric acid was also found to be a function of its concentration, with a higher concentration yielding greater recovery of [.sup.13 N]NO.sub.x.sup.-. TABLE 1 ______________________________________ Effect of the Nature and Strength of Extraction Reagent on Recovery Efficiency* Extraction % .sup.13 N Recovered Reagent Reagent Strength From AG1-X8 Resin ______________________________________ K.sub.2 CO.sub.3 0.01 M <1 Cs.sub.2 CO.sub.3 0.005 M <1 NaOH 1.0 N 5 NaOH 10.0 N 12 Sodium Citrate 0.1 M 7 Sodium Citrate 0.5 M 19 Sodium Citrate 0.045 M 24 Saline 0.9% 23 H.sub.2 SO.sub.4 1.0 N 43 HCl 0.1 N 16 HCl 0.5 N 53 HCl 1.0 N 82 HCl 2.5 N 89 ______________________________________ *All tests were carried out using 1 mL of the appropriate agent. EXAMPLE 2 A series of experiments was performed, using a manual system similar to that described above and illustrated in FIGS. 1 and 2, to determine the relationship between the level of enrichment of the target water by [.sup.18 O]H.sub.2 O and the production, distribution, and recovery of the radionuclides .sup.18 F and .sup.13 N. Data obtained from these experiments are described in Table 2. The percentage enrichment of target water was examined in the range of from about 20% to about 50%. The radionuclidic distribution was found to vary in relation to the percentage enrichment of the target water. At 20% [.sup.18 O]H.sub.2 O, the radionuclidic distribution after irradiation was 23% .sup.18 F to 77% .sup.13 N. At 50% [.sup.18 O]H.sub.2 O, however, the distribution had shifted to about 45% .sup.18 F to 55% .sup.13 N. At all enrichment levels studied, the percent recovery of the radionuclides was consistently very high, as was the percent radionuclidic purity of the extracted fractions. TABLE 2 ______________________________________ Results From Studies on .sup.18 F and .sup.13 N Separation Using AG1-X8 Anion Exchange Columns Recovered % Target Radionuclidic % Activity as % Purity in Enrich- .sup.18 F and Radionuclidic % Resin Extracted ment .sup.13 N (mCi Distribution Recovery.sup.a Fractions of H.sub.2.sup.18 O at EOB).sup.c .sup.18 F .sup.13 N .sup.18 F .sup.13 N .sup.18 F .sup.13 N ______________________________________ 50 195 45 55 >99 80 98.8 99.2 30 214 35 65 >99 81 99.4 98.4 20 163 23 77 >99 .sup. 94.sup.b 98.9 99.3 ______________________________________ .sup.a18 F was recovered from resin using 1.5 mL of 0.01 M K.sub.2 CO.sub.3. .sup.13 N was recovered from resin, after .sup.18 F extraction, using 1 mL of 1N HCl. .sup.b13 N was recovered from resin in this case using 1.5 mL of 1N HCl. .sup.c EOB is an abbreviation meaning "end of bombardment". Thus while we have described what are presently the preferred embodiments of the present invention, other and further changes and modifications could be made without departing from the scope of the invention, and it is intended by the inventors to claim all such changes and modifications. |
abstract | A process for dissolving nuclear fuel, in particular irradiated nuclear fuel, comprising immersion of the nuclear fuel in a nitric acid solution. This dissolution process further comprises mechanical milling of the nuclear fuel, this mechanical milling being performed in the nitric acid solution during the immersion. The disclosure also relates to the use of a mill equipped with mechanical milling structure to implement the dissolution process. |
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summary | ||
claims | 1. A method of producing a terminally sterile column assembly of a radionuclide generator, comprising:providing a column assembly of a radionuclide generator that includes:a column having a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide;an inlet port in fluid communication with the column; andan outlet port in fluid communication with the column, the outlet port includes a vent opening that provides fluid access to the column;positioning the column assembly in an orientation with the vent opening facing downwardly to prevent condensate from entering the vent opening from above;exposing the column assembly to steam for sterilization; andpositioning an outlet cover over the outlet port prior to exposing the column assembly to steam for sterilization, the outlet port including the vent opening. 2. The method of claim 1, wherein positioning the outlet cover over the outlet port includes positioning an outlet cover that includes a removable cap. 3. A method of producing a terminally sterile column assembly of a radionuclide generator, comprising:providing a column assembly of a radionuclide generator that includes:a column having a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide;an inlet port in fluid communication with the column; andan outlet port in fluid communication with the column, the outlet port includes a vent opening that provides fluid access to the column;positioning the column assembly in an orientation with the vent opening facing downwardly to prevent condensate from entering the vent opening from above;exposing the column assembly to steam for sterilization; andplugging the inlet port of the column assembly prior to exposing the column assembly to steam for sterilization. 4. A method of producing a terminally sterile column assembly of a radionuclide generator, comprising:providing a column assembly of a radionuclide generator that includes:a column having a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide;an inlet port in fluid communication with the column; andan outlet port in fluid communication with the column, the outlet port includes a vent opening that provides fluid access to the column;positioning the column assembly in an orientation with the vent opening facing downwardly to prevent condensate from entering the vent opening from above; andexposing the column assembly to steam for sterilization;wherein exposing the column assembly to steam includes exposing the column assembly to saturated steam under pressure. 5. A method of producing a terminally sterile column assembly of a radionuclide generator, comprising:providing a column assembly of a radionuclide generator that includes:a column having a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide;an inlet port in fluid communication with the column; andan outlet port in fluid communication with the column, the outlet port includes a vent opening that provides fluid access to the column;positioning the column assembly in an orientation with the vent opening facing downwardly to prevent condensate from entering the vent opening from above; andexposing the column assembly to steam for sterilization;wherein providing the column assembly comprises providing a plurality of column assemblies and wherein positioning the column assembly and exposing the column assembly comprise positioning the plurality of column assemblies and exposing the plurality of column assemblies, respectively. 6. The method of claim 5, wherein exposing the plurality of column assemblies to steam for a single sterilization cycle results in an amount of liquid remaining in the plurality of column assemblies that varies by 5% or less (relative standard deviation). 7. The method of claim 5, wherein exposing the plurality of column assemblies to steam for two sterilization cycles results in an amount of liquid remaining in the plurality of column assemblies that varies by 15% or less (relative standard deviation). 8. A column assembly of a radionuclide generator, comprising:a column and an outlet port, the column including a medium for retaining a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide, the outlet port in fluid communication with the column and covered with a vented outlet cover to provide a terminally sterilizable column assembly, the vented outlet cover having a vent opening that provides fluid access to the column and that prevents the ingress of gravity-driven liquid to produce a column assembly that consistently exhibits high yield,wherein the outlet port includes a needle structure and the vented outlet cover includes a pierceable membrane that receives the needle structure of the outlet port. 9. The column assembly of claim 8, wherein the outlet cover includes a body portion and a removable cap. 10. The column assembly of claim 9, wherein the vent opening is defined as an annular space between the removable cap and the body portion. 11. The column assembly of claim 10, further comprising:a bacteria retentive filter in the body portion. 12. A column assembly of a radionuclide generator, comprising:a column and an outlet port, the column including a medium for retaining a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide, the outlet port in fluid communication with the column and covered with a vented outlet cover to provide a terminally sterilizable column assembly, wherein means are provided to prevent the ingress of gravity-driven liquid to produce a column assembly that consistently exhibits high yield and that prevents migration of parent radionuclide away from the column,wherein the outlet port includes a needle structure and the vented outlet cover includes a pierceable membrane that receives the needle structure of the outlet port. 13. A column assembly of a radionuclide generator, comprising:a column and an outlet port, the column including a medium for retaining a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide, the outlet port in fluid communication with the column and covered with a vented outlet cover to provide a terminally sterilizable column assembly, wherein means are provided to prevent the ingress of gravity-driven liquid to produce a column assembly that consistently exhibits high yield and that prevents migration of parent radionuclide away from the column,wherein the means comprises a vent opening that provides fluid access to the column and that prevents the ingress of gravity-driven liquid. 14. The column assembly of claim 13, wherein the vent opening faces toward the column. 15. The column assembly of claim 13, wherein the outlet cover includes a body portion and a removable cap. 16. The column assembly of claim 13, wherein the vent opening is defined as an annular space between the removable cap and the body portion. 17. A column assembly of a radionuclide generator, comprising:a column and an outlet port, the column including a medium for retaining a long-lived parent radionuclide that produces a relatively short-lived daughter radionuclide, the outlet port in fluid communication with the column and covered with a vented outlet cover to provide a terminally sterilizable column assembly, the vented outlet cover having a vent opening that provides fluid access to the column and that prevents the ingress of gravity-driven liquid to produce a column assembly that prevents migration of parent radionuclide away from the column,wherein the outlet port includes a needle structure and the vented outlet cover includes a pierceable membrane that receives the needle structure of the outlet port. 18. The column assembly of claim 17, wherein the outlet cover includes a body portion and a removable cap. 19. The column assembly of claim 18, wherein the vent opening is defined as an annular space between the removable cap and the body portion. 20. The column assembly of claim 19, further comprising:a bacteria retentive filter in the body portion. |
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claims | 1. A method, in a data processing system, for converting a set of single-layer design rules into a set of split-layer design rules for double patterning lithography (DPL), the method comprising:identifying, by a processor in the data processing system, the set of single-layer design rules and minimum lithographic resolution pitch constraints for single exposure, wherein the set of single-layer design rules comprise a first plurality of minimum distances that are required by a set of first shapes in a single-layer design;modifying, by the processor, each of the first plurality of minimum distances in the set of single-layer design rules with regard to the minimum lithographic resolution pitch constraints for single exposure, thereby forming the set of split-layer design rules, wherein the set of split-layer design rules comprise at least a second plurality of minimum distances that are required by at least a set of second shapes and a set of third shapes in a split-layer design; andcoding, by the processor, the set of split-layer design rules into a design rule checker for use in designing a double patterning lithography design. 2. The method of claim 1, wherein the set of split-layer design rules comprise a set of intra-layer rules for each exposure layer in the set of split-layer design rules and a set of inter-layer rules for elements between each exposure layer in the set of split-layer design rules. 3. The method of claim 1, further comprising:generating, by the processor, a set of minimum overlap rules using a set of technology specific overlay specifications. 4. The method of claim 1, wherein generating the set of split-layer design rules includes multiplying a subset of the first plurality of minimum distances by a multiplier while another subset of the first plurality of minimum distances are reused, wherein the multiplier is determined based on the minimum lithographic resolution pitch constraints for the single exposure. 5. The method of claim 1, further comprising:identifying, by the processor, a two-layer design to be validated using the set of split-layer design rules;verifying, by the processor, for each shape in a plurality of shapes in the two-layer design, that each of the set of split-layer design rules required for the design have not been violated; andresponsive to the two-layer design failing to violate any of the set of split-layer design rules, generating, by the processor, a validated two-layer design. 6. The method of claim 5, further comprising:responsive to two-layer design violating at least one of the set of split-layer design rules, identifying, by the processor, at least one of the set of split-layer design rules that is violated; andindicating, by the processor, within the two-layer design, a location of where the at least one of the set of split-layer design rules is violated. 7. The method of claim 5, wherein verifying that each of the set of split-layer design rules required for the design-have not been violated comprises:examining, by the processor, each polygon in the two-layer design;measuring, by the processor, at least one layout parameter in the two-layer design for a set for layout features thereby forming a set of measurements; andcomparing, by the processor, the set of measurements to the set of split-layer design rules in order to identify violations of the set of split-layer design rules. 8. A computer program product comprising a non-transitory computer readable storage medium having a computer readable program stored therein, wherein the computer readable program, when executed on a computing device, causes the computing device to:identify a set of single-layer design rules and minimum lithographic resolution pitch constraints for single exposure, wherein the set of single-layer design rules comprise a first plurality of minimum distances that are required by a set of first shapes in a single-layer design;modify each of the first plurality of minimum distances in the set of single-layer design rules with regard to the minimum lithographic resolution pitch constraints for single exposure, thereby forming a set of split-layer design rules, wherein the set of split-layer design rules comprise at least a second plurality of minimum distances that are required by at least a set of second shapes and a set of third shapes in a split-layer design; andcode the set of split-layer design rules into a design rule checker for use in designing a double patterning lithography design. 9. The computer program product of claim 8, wherein the set of split-layer design rules comprise a set of intra-layer rules for each exposure layer in the set of split-layer design rules and a set of inter-layer rules for elements between each exposure layer in the set of split-layer design rules. 10. The computer program product of claim 8, wherein the computer readable program further causes the computing device to:generate a set of minimum overlap rules using a set of technology specific overlay specifications. 11. The computer program product of claim 8, wherein the computer readable program to generate the set of split-layer design rules further causes the computing device to multiply a subset of the first plurality of minimum distances by a multiplier while another subset of the first plurality of minimum distances are reused, wherein the multiplier is determined based on the minimum lithographic resolution pitch constraints for the single exposure. 12. The computer program product of claim 11, wherein the computer readable program further causes the computing device to:identify a two-layer design to be validated using the set of split-layer design rules;verify, for each shape in a plurality of shapes in the two-layer design, that each of the set of split-layer design rules required for the design have not been violated; andresponsive to the two-layer design failing to violate any of the set of split-layer design rules, generate a validated two-layer design. 13. The computer program product of claim 11, wherein the computer readable program further causes the computing device to:responsive to the two-layer design violating at least one of the set of split-layer design rules, identify at least one of the set of split-layer design rules that is violated; andindicate, within the two-layer design, a location of where the at least one of the set of split-layer design rules is violated. 14. The computer program product of claim 11, wherein the computer readable program to verify that each of the set of split-layer design rules required for the design have not been violated further causes the computing device to:examine each polygon in the two-layer design;measure at least one layout parameter in the two-layer design for a set for layout features thereby forming a set of measurements; andcompare the set of measurements to the set of split-layer design rules in order to identify violations of the set of split-layer design rules. 15. An apparatus, comprising:a processor; anda memory coupled to the processor, wherein the memory comprises instructions which, when executed by the processor, cause the processor to:identify a set of single-layer design rules and minimum lithographic resolution pitch constraints for single exposure, wherein the set of single-layer design rules comprise a first plurality of minimum distances that are required by a set of first shapes in a single-layer design;modify each of the first plurality of minimum distances in the set of single-layer design rules with regard to the minimum lithographic resolution pitch constraints for single exposure, thereby forming a set of split-layer design rules, wherein the set of split-layer design rules comprise at least a second plurality of minimum distances that are required by at least a set of second shapes and a set of third shapes in a split-layer design; andcode the set of split-layer design rules into a design rule checker for use in designing a double patterning lithography design. 16. The apparatus of claim 15, wherein the set of split-layer design rules comprise a set of intra-layer rules for each exposure layer in the set of split-layer design rules and a set of interlayer rules for elements between each exposure layer in the set of split-layer design rules. 17. The apparatus of claim 15, wherein the instructions further cause the processor to:generate a set of minimum overlap rules using a set of technology specific overlay specifications. 18. The apparatus of claim 15, wherein the instructions to generate the set of split layer design rules further cause the processor to multiply a subset of the first plurality of minimum distances by a multiplier while another subset of the first plurality of minimum distances are reused, wherein the multiplier is determined based on the minimum lithographic resolution pitch constraints for the single exposure. 19. The apparatus of claim 18, wherein the instructions further cause the processor to:identify a two-layer design to be validated using the set of split-layer design rules;verify, for each shape in a plurality of shapes in the two-layer design, that each of the set of split-layer design rules required for the design have not been violated; andresponsive to the two-layer design failing to violate any of the set of split-layer design rules, generate a validated two-layer design. 20. The apparatus of claim 18, wherein the instructions further cause the processor to:responsive to the two-layer design violating at least one of the set of split-layer design rules, identify at least one of the set of split-layer design rules that is violated; andindicate, within the two-layer design, a location of where the at least one of the set of split-layer design rules is violated. 21. The apparatus of claim 18, wherein the instructions to verify that each of the set of split-layer design rules required for the design have not been violated further cause the processor to:examine each polygon in the two-layer design;measure at least one layout parameter in the two-layer design for a set for layout features thereby forming a set of measurements; andcompare the set of measurements to the set of split-layer design rules in order to identify violations of the set of split-layer design rules. |
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description | A simplified drawing of a high energy ultraviolet light source is shown in FIG. 1. The major components are a plasma pinch unit 2, a high energy photon collector 4 and a hollow light pipe 6. The plasma pinch source comprises a coaxial electrode 8 powered by a low inductance pulse power circuit 10. The pulse power circuit in this preferred embodiment is a high voltage, energy efficient circuit capable of providing about 5 micro seconds pulses in the range of 1 kV to 2 kV to coaxial electrode 8 at a rate of 1,000 Hz. A small amount of working gas, such as a mixture of helium and lithium vapor, is present near the base of the electrode 8 as shown in FIG. 1. At each high voltage pulse, avalanche breakdown occurs between the inner and outer electrodes of coaxial electrode 8 either due to preionization or self breakdown. The avalanche process occurring in the buffer gas ionizes the gas and creates a conducting plasma between the electrodes at the base of the electrodes. Once a conducting plasma exists, current flows between the inner and outer electrodes. In this preferred embodiment, the inner electrode is at high positive voltage and outer electrode is at ground potential. Current will flow from the inner electrode to the outer electrode and thus electrons will flow toward the center and positive ions will flow away from the center. This current flow generates a magnetic field which acts upon the moving charge carriers accelerating them away from the base of the coaxial electrode 8. When the plasma reaches the end of the center electrode, the electrical and magnetic forces on the plasma, pinch the plasma to a xe2x80x9cfocusxe2x80x9d around a point 10 along the centerline of and a short distance from the end of the central electrode and the pressure and temperature of the plasma rise rapidly reaching extremely high temperatures, in come cases much higher than the temperature at the surface of the sun! The dimensions of the electrodes and the total electrical energy in the circuit are preferably optimized to produce the desired black body temperature in the plasma. For the production of radiation in the 13 nm range a black body temperature of about 100 eV is required. In general, for a particular coaxial configuration, temperature will increase with increasing voltage of the electrical pulse. The shape of the radiation spot is somewhat irregular in the axial direction and roughly gausian in the radial direction. The typical radial dimension of the source is 100-300 microns and its length is approximately 4 mm. In most prior art plasma pinch units described in the technical literature, the radiation spot emits radiation in all directions with a spectrum closely approximating a black body. The purpose of the lithium in the working gas is to narrow the spectrum of the radiation from the radiation spot. Doubly ionized lithium exhibits an electronic transition at 13.5 nm and serves as the radiation source atom in the buffer of helium. Doubly ionized lithium is an excellent choice for two reasons. The first is the low melting point and high vapor pressure of lithium. The lithium ejected from the radiation spot can be kept from plating out onto the chamber walls and collection optics by simply heating these surfaces above 180xc2x0 C. The vapor phase lithium can then be pumped from the chamber along with the helium buffer gas using standard turbo-molecular pumping technology. And the lithium can be easily separated from the helium merely by cooling the two gases. Coating materials are available for providing good reflection at 13.5 nm. FIG. 8 shows the lithium peak in relation to the published MoSi reflectivity. A third advantage of using lithium as the source atom is that non-ionized lithium has a low absorption cross section for 13.5 nm radiation. Furthermore, any ionized lithium ejected from the radiation spot can be easily swept away with a moderate electric field. The remaining non-ionized lithium is substantially transparent to 13.5 nm radiation. The currently most popular proposed source in the range of 13 nm makes use of a laser ablated frozen jet of xenon. Such a system must capture virtually all of the ejected xenon before the next pulse because the absorption cross section for xenon at 13 nm is large. The radiation produced at the radiation spot is emitted uniformly into a full 4xcfx80 steradians. Some type of collection optics is needed to capture this radiation and direct it toward the lithography tool. Previously proposed 13 nm light sources suggested collection optics based on the use of multi-layer dielectric coated mirrors. The use of multi-layer dielectric mirrors is used to achieve high collection efficiency over a large angular range. Any radiation source which produced debris would coat these dielectric mirrors and degrade their reflectivity, and thus reduce the collected output from the source. This preferred system will suffer from electrode erosion and thus would, over time, degrade any dielectric mirror placed in proximity to the radiation spot. Several materials are available with high reflectivity at small grazing incident angles for 13.5 nm UV light. Graphs for some of these are shown in FIG. 11. Good choices include molybdenum, rhodium and tungsten. The collector may be fabricated from these materials, but preferably they are applied as a coating on a substrate structural material such as nickel. This conic section can be prepared by electroplating nickel on a removable mandrel. To produce a collector capable of accepting a large cone angle, several conical sections can be nested inside each other. Each conical section may employ more than one reflection of the radiation to redirect its section of the radiation cone in the desired direction. Designing the collection for operation nearest to grazing incidence will produce a collector most tolerant to deposition of eroded electrode material. The grazing incidence reflectivity of mirrors such as this depends strongly on the mirror""s surface roughness. The dependence on surface roughness decreases as the incident angle approaches grazing incidence. We estimate that we can collect and direct the 13 nm radiation being emitted over a solid angle of least 25 degrees. Preferred collectors for directing radiation into light pipes are shown in FIGS. 1, 2 and 3. A preferred method for choosing the material for the external reflection collector is that the coating material on the collector be the same as the electrode material. Tungsten is a promising candidate since it has demonstrated performance as an electrode and the real part of its refractive index at 13 nm is 0.945. Using the same material for the electrode and the mirror coating minimizes the degradation of mirror reflectivity as the eroded electrode material plates out onto the collection mirrors. Silver is also an excellent choice for the electrodes and the coatings because it also has a low refractive index at 13 nm and has high thermal conductivity allowing higher repetition rate operation. In another preferred embodiment the collector-director is protected from surface contamination with vaporized electrode material by a debris collector which collects all of the tungsten vapor before it can reach the collector director 5. FIG. 9 shows a conical nested debris collector 5 for collecting debris resulting from the plasma pinch. Debris collector 5 is comprised of nested conical sections having surfaces aligned with light rays extending out from the center of the pinch site and directed toward the collector-director 4. The debris collected includes vaporized tungsten from the tungsten electrodes and vaporized lithium. The debris collector is attached to or is a part of radiation collector-director 4. Both collectors are comprised of nickel plated substrates. The radiation collector-director portion 4 is coated with molybdenum or rhodium for very high reflectivity. Preferably both collectors are heated to about 400xc2x0 C. which is substantially above the melting point of lithium and substantially below the melting point of tungsten. The vapors of both lithium and tungsten will collect on the surfaces of the debris collector 5 but lithium will vaporize off and to the extent the lithium collects on collector-director 4, it will soon thereafter also vaporize off. The tungsten once collected on debris collector 5 will remain there permanently. FIG. 7 shows the optical features of a collector designed by Applicants. The collector is comprised of five nested grazing incident parabolic reflectors, but only three of the five reflections are shown in the drawing. The two inner reflectors are not shown. In this design the collection angle is about 0.4 steradians. As discussed below the collector surface is coated and is heated to prevent deposition of lithium. This design produces a parallel beam. Other preferred designs such as that shown in FIGS. 1, 3 and 10 would focus the beam. The collector should be coated with a material possessing high glazing incidence reflectivity in the 13.5 nm wavelength range. Two such materials are palladium and ruthenium. It is important to keep deposition materials away from the illumination optics of the lithography tool. Therefore, a light pipe 6 is preferred to further assure this separation. The lightpipe 6 is a hollow lightpipe which also employs substantially total external reflection on its inside surfaces. The primary collection optic can be designed to reduce the cone angle of the collected radiation to match the acceptance angle of the hollow lightpipe. This concept is shown in FIG. 1. The dielectric mirrors of the lithography tool would then be very well protected from any electrode debris since a tungsten, silver or lithium atom would have to diffuse upstream against a flow of buffer gas down the hollow lightpipe as shown in FIG. 1. The preferred pulse power unit 10 is a solid state high frequency, high voltage pulse power unit utilizing a solid state trigger and a magnetic switch circuit such as the pulse power units described in U.S. Pat. No. 5,142,166. These units are extremely reliable and can operate continuously without substantial maintenance for many months and billions of pulses. The teachings of U.S. Pat. No. 5,142,166 are incorporated herein by reference. FIG. 4 shows a simplified electrical circuit providing pulse power. A preferred embodiment includes DC power supply 40 which is a command resonant charging supply of the type used in excimer lasers. C0 which is a bank of off the shelf capacitors having a combined capacitance of 65 xcexcF, a peaking capacitor C1 which is also a bank of off the shelf capacitors having a combined capacitance of 65 xcexcF. Saturable inductor 42 has a saturated drive inductance of about 1.5 nH. Trigger 44 is an IGBT. Diode 46 and inductor 48 creates an energy recovery circuit similar to that described in U.S. Pat. No. 5,729,562 permitting reflected electrical energy from one pulse to be stored on C0 prior to the next pulse. Thus, as shown in FIG. 1, in a first preferred embodiment, a working gas mixture of helium and lithium vapor is discharged into coaxial electrode 8. Electrical pulses from pulse power unit 10 create a dense plasma focus at 11 at sufficiently high temperatures and pressures to doubly ionize the lithium atoms in the working gas generating ultraviolet radiation at about 13.5 nm wavelength. This light is collected in total external reflection-collector 4 and directed into hollow light pipe 6 where the light is further directed to a lithography tool (not shown). Discharge chamber 1 is maintained at a vacuum of about 4 Torr with turbo suction pump 12. Some of the helium in the working gas is separated in helium separator 14 and used to purge the lightpipe as shown in FIG. 1 at 16. The pressure of helium in the light pipe is preferably matched to the pressure requirements of the lithography tool which typically is maintained at a low pressure or vacuum. The temperature of the working gas is maintained at the desired temperature with heat exchanger 20 and the gas is cleaned with electrostatic filter 22. The gas is discharged into the coaxial electrode space as shown in FIG. 1. A drawing of a prototype plasma pinch unit built and tested by Applicant and his fellow workers is shown in FIG. 5. Principal elements are C1 capacitor decks, C0 capacitor decks 1 GBT switches, saturable inductor 42, vacuum vessel 3, and coaxial electrode 8. FIG. 6 shows a typical pulse shape measured by Applicant with the unit shown in FIG. 5. Applicants have recorded C1 voltage, C1 current and intensity at 13.5 nm over an 8 microsecond period. The integrated energy in this typical pulse is about 0.8 J. The pulse width (at FWHM) is about 280 ns. The C1 voltage prior to breakdown is a little less than 1 KV. This prototype embodiment can be operated at a pulse rate up to 200 Hz. The measured average in-band 13.5 nm radiation at 200 Hz is 152 W in 4xcfx80 steradians. Energy stability at 1 sigma is about 6%. Applicants estimate that 3.2 percent of the energy can be directed into a useful 13.5 nm beam with the collector 4 shown in FIG. 1. A second preferred plasma pinch unit is shown in FIG. 2. This unit is similar to the plasma pinch device described in U.S. Pat. No. 4,042,848. This unit comprises two outer disk shaped electrodes 30 and 32 and an inner disk shaped electrode 36. The pinch is created from three directions as described in U.S. Pat. No. 4,042,848 and as indicated in FIG. 2. The pinch starts near the circumference of the electrodes and proceeds toward the center and the radiation spot is developed along the axis of symmetry and at the center of the inner electrode as shown in FIG. 2 at 34. Radiation can be collected and directed as described with respect to the FIG. 1 embodiment. However, it is possible to capture radiation in two directions coming out of both sides of the unit as shown in FIG. 2. Also, by locating a dielectric mirror at 38, a substantial percentage of the radiation initially reflected to the left could be reflected back through the radiation spot. This should stimulate radiation toward the right side. A third preferred embodiment can be described by reference to FIG. 3. This embodiment is similar to the first preferred embodiment. In this embodiment, however, the buffer gas is argon. Helium has the desirable property that it is relatively transparent to 13 nm radiation, but it has the undesired property that it has a small atomic mass. The low atomic mass forces us to operate the system at a background pressure of 2-4 Torr. An additional drawback of the small atomic mass of He is the length of electrode required to match the acceleration distance with the timing of the electrical drive circuit. Because He is light, the electrode must be longer than desired so that the He falls off the end of the electrode simultaneous with the peak of current flow through the drive circuit. A heavier atom such as Ar will have a lower transmission than He for a given pressure, but because of its higher mass can produce a stable pinch at a lower pressure. The lower operating pressure of Ar more than offsets the increased absorption properties of Ar. Additionally, the length of the electrode required is reduced due to the higher atomic mass. A shorter electrode is advantageous for two reasons. The first is a resulting reduction in circuit inductance when using a shorter electrode. A lower inductance makes the drive circuit more efficient and thus reduces the required electrical pump energy. The second advantage of a shorter electrode is a reduction in the thermal conduction path length from the tip of the electrode to the base. The majority of the thermal energy imparted to the electrode occurs at the tip and the conductive cooling of the electrode occurs mainly at the base (radiative cooling also occurs). A shorter electrode leads to a smaller temperature drop down its length from the hot tip to the cool base. Both the smaller pump energy per pulse and the improved cooling path allow the system to operate at a higher repetition rate. Increasing the repetition rate directly increases the average optical output power of the system. Scaling the output power by increasing repetition rate, as opposed to increasing the energy per pulse, is the most desired method for the average output power of lithography light sources. In this preferred embodiment the lithium is not injected into the chamber in gaseous form as in the first and second embodiments. Instead solid lithium is placed in a hole in the center of the central electrode as shown in FIG. 3. The heat from the electrode then brings the lithium up to its evaporation temperature. By adjusting the height of the lithium relative to the hot tip of the electrode one can control the partial pressure of lithium near the tip of the electrode. One preferred method of doing this is shown in FIG. 3. A mechanism is provided for adjusting the tip of the solid lithium rod relative to the tip of the electrode. Preferably the system is arranged vertically so that the open side of coaxial electrodes 8 is the top so that any melted lithium will merely puddle near the top of the center electrode. The beam will exit straight up in a vertical direction as indicated in FIG. 5. (An alternative approach is to heat the electrode to a temperature in excess of the lithium melting point so that the lithium is added as a liquid.) The hole down the center of the electrode provides another important advantage. Since the plasma pinch forms near the center of the tip of the central electrode, much of the energy is dissipated in this region. Electrode material near this point will be ablated and eventually end up of other surfaces inside the pressure vessel. Employing an electrode with a central hole greatly reduces the available erosion material. In addition, Applicant""s experiments have shown that the existence of lithium vapor in this region further reduces the erosion rate of electrode material. A bellows or other appropriate sealing method should be used to maintain a good seal where the electrode equipment enters the chamber. Replacement electrodes fully loaded with the solid lithium can be easily and cheaply manufactured and easily replaced in the chamber. The pinch produces a very large amount of viable light which needs to be separated from the EUV light. Also, a window is desirable to provide additional assurance that lithography optics are not contaminated with lithium or tungsten. The extreme ultraviolet beam produced by the present invention is highly absorbed in solid matter. Therefore providing a window for the beam is a challenge. Applicants preferred window solution is to utilize an extremely thin foil which will transmit EUV and reflect visible. Applicants preferred window is a foil (about 0.2 to 0.5 micron) of beryllium tilted at an incident angle of about 10xc2x0 C. with the axis of the incoming beam. With this arrangement, almost all of the visible light is reflected and about 50 to 80 percent of the EUV is transmitted. Such a thin window, of course, is not very strong. Therefore, Applicants use a very small diameter window and the beam is focused through the small window. Preferably the diameter of the thin beryllium window is about 1.0 mm. Heating of the little window must be considered, and for high repetition rates special cooling of the window will be needed. In some designs this element can be designed merely as a beam splitter which will simplify the design since there will be no pressure differential across the thin optical element. FIG. 10 shows a preferred embodiment in which radiation collector 4 is extended by collector extension 4A to focus the beam 9 through 0.5 micron thick 1 mm diameter beryllium window 7. Applicants experiments have shown that good results can be obtained without preionization but performance is improved with preionization. The prototype unit shown in FIG. 5 comprises DC driven spark gap preionizers to preionize the gas between the electrodes. Applicants will be able to greatly improve these energy stability values and improve other performance parameters with improved preionization techniques. Preionization is a well developed technique used by Applicants and others to improve performance in excimer lasers. Preferred preionization techniques include: 1) DC drive spark gap 2) RF driven spark gap 3) RF driven surface discharge 4) Corona discharge 5) Spiker circuit in combination with preionization These techniques are well described in scientific literature relating to excimer lasers and are well known. It is understood that the above described embodiments are illustrative of only a few of the many possible specific embodiments which can represent applications of the principals of the present invention. For example, instead of recirculating the working gas it may be preferable to merely trap the lithium and discharge the helium. Use of other electrodexe2x80x94coating combinations other than tungsten and silver are also possible. For example copper or platinum electrodes and coatings would be workable. Other techniques for generating the plasma pinch can be substituted for the specific embodiment described. Some of these other techniques are described in the patents referenced in the background section of this specification, and those descriptions are all incorporated by reference herein. Many methods of generating high frequency high voltage electrical pulses are available and can be utilized. An alternative would be to keep the lightpipe at room temperature and thus freeze out both the lithium and the tungsten as it attempts to travel down the length of the lightpipe. This freeze-out concept would further reduce the amount of debris which reached the optical components used in the lithography tool since the atoms would be permanently attached to the lightpipe walls upon impact. Deposition of electrode material onto the lithography tool optics can be prevented by designing the collector optic to re-image the radiation spot through a small orifice in the primary discharge chamber and use a differential pumping arrangement. Helium or argon can be supplied from the second chamber through the orifice into the first chamber. This scheme has been shown to be effective in preventing material deposition on the output windows of copper vapor lasers. Lithium hydride may be used in the place of lithium. The unit may also be operated as a static-fill system without the working gas flowing through the electrodes. Of course, a very wide range of repetition rates are possible from single pulses to about 5 pulses per second to several hundred or thousands of pulses per second. If desired, the adjustment mechanism for adjusting the position of the solid lithium could be modified so that the position of the tip of the central electrode is also adjustable to account for erosion of the tip. Many other electrode arrangements are possible other than the ones described above. For example, the outside electrode could be cone shaped rather than cylindrical as shown with the larger diameter toward the pinch. Also, performance in some embodiments could be improved by allowing the inside electrode to pertrude beyond the end of the outside electrode. This could be done with spark plugs or other preionizers well known in the art. Another preferred alternative is to utilize for the outer electrode an array of rods arranged to form a generally cylindrical or conical shape. This approach helps maintain a symmetrical pinch centered along the electrode axis because of the resulting inductive ballasting. Accordingly, the reader is requested to determine the scope of the invention by the appended claims and their legal equivalents; and not by the examples which have been given. |
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abstract | A spacer grid specifically designed for accident tolerant fuel utilizing fuel rods with SiC cladding for implementation in pressurized water reactors. The spacer grid has a generally square design that allows for ease of SiC fuel rod insertion during the fuel assembly fabrication process by providing a smooth contact geometry. The co-planar support allows the fuel rods to be rotated axially more freely at the grid location than a conventional six-point contact geometry used in existing fuel assembly designs. |
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abstract | A reflective resin sheet is bonded to one face of a supporting substrate transmitting a radiation ray and a resin sheet of the same material as that of the reflective resin sheet to the other face of the supporting substrate. A phosphor layer converting a radiation ray into visible light is formed additionally on the reflective resin sheet formed on one face of the supporting substrate. The phosphor layer is enclosed with an additional moisture-proof layer and the reflective resin sheet. It is possible to obtain a scintillator panel higher in sensitivity characteristics, stabilized in quality and more cost-effective by placing the reflective resin sheet between the supporting substrate and the phosphor layer. |
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abstract | Non-oxide debond coated reinforcing fibers that are resistant to oxidation at temperatures above about 1200xc2x0 C. are described. The debond coatings are non-hygroscopic, and exhibit debond performance equal to or better than the prior art such coatings. The coated fibers of the present invention comprise a non-oxide fiber with or without a thin conventionally applied pyrolytic carbon layer overcoated with a non-hygroscopic silicon and titanium containing single or multi-layer structure that imparts all of the properties demanded of a debond coating while additionally providing exceptional oxidation resistance protection. |
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