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description | This application claims priority of U.S. Provisional Patent Application Ser. No. 61/360,736, filed Jul. 1, 2010 and U.S. Provisional Patent Application Ser. No. 61/360,744, filed Jul. 1, 2010, the disclosures of which are incorporated herein by reference in their entireties. This invention relates to ion implantation and, more particularly, to uniformity during ion implantation. Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity. Solar cells are one example of a device that uses silicon workpieces. Any reduced cost to the manufacture or production of high-performance solar cells or any efficiency improvement to high-performance solar cells would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability of this clean energy technology. There are many different solar cell architectures. Two common designs are the selective emitter (SE) and the interdigitated backside contact (IBC). A SE solar cell has high-dose stripes across the lightly doped surface impinged by sunlight. An IBC solar cell has alternating p-type and n-type stripes across the surface not impinged by sunlight. Both a SE and IBC solar cell may be implanted with ions to dope the various regions. “Glitches” may occur during the ion implantation process. A glitch is defined as a sudden degradation in the beam quality during an ion implantation operation, typically due to a variation in an operating voltage, which potentially renders the workpiece unusable. Such a glitch is typically caused by interactions between components along the beam path, which affect one or more operating voltages, and can be caused at various locations along the beam path. For example, ion implanters generally employ several electrodes along this beam path, which accelerate the beam, decelerate the beam, or suppress spurious streams of electrons that are generated during operation. Each of these electrodes is maintained at a predetermined voltage. Often, electrodes of different voltage are located near each other and therefore an arc may occur between electrodes. Generally, arcs occur across acceleration gaps, deceleration gaps, or suppression gaps, although arcs may occur elsewhere. Interaction between, for example, a source extraction voltage, source suppression voltage, and source beam current may cause a glitch. These glitches may be detected as a sharp change in the current from one of the power supplies. If the implantation is interrupted or affected by a glitch, the implanted solar cell or other workpiece may be negatively affected. For example, a solar cell may have a lower efficiency due to the lower implanted dose caused by a glitch. This may have a cost impact on the implanted workpieces. Thus, steps are usually taken to both minimize the occurrence of such glitches and to recover from the glitches if possible. FIG. 1 is a chart illustrating a glitch. The beam current is set to a predetermined value 10. The glitch 11 occurs during the period marked Δt outlined by the dotted lines 12, 13 where the beam current drops below the predetermined value 10. Minimizing the Δt period means that there is less negative impact on the workpiece being implanted. The glitch 11 may be sensed by measuring changes in voltage or current. An arc is typically sensed by either an abrupt voltage collapse, or an abrupt current surge. When a glitch is detected, one solution is to immediately reduce the ion beam current to zero, thus terminating the implantation at a defined location on the workpiece. This is referred to as “blanking the beam”. FIG. 2 is a chart illustrating blanking an ion beam. At time 100 when the glitch is first detected, the voltage is dropped to zero and then slowly built back up to the desired voltage level. At this time, implantation stops as well, and the position at this time is saved. In one instance, the voltage may be blanked for tens of milliseconds before voltage is recovered over the next hundred or more milliseconds. When the voltage recovers within 0.1-0.5% of the desired value, such as at time 101, implantation may continue from the location where it had stopped. Thus, once the glitch condition has been remedied, the implantation process ideally resumes at exactly the same location on the workpiece, with ideally the same beam characteristics as existed when the glitch was detected. The goal is to achieve a uniform doping profile, and this can be achieved by controlling the beam current or the workpiece scan speed (exposure time). However, blanking is time-consuming, which has a negative impact on throughput. Decreased throughput also results in higher costs. Repairing the dose loss caused by the glitch in such a manner may take over 30 seconds, which may be too time-consuming for the throughput demands of the solar cell industry. Ion beam stability and implant uniformity within the ion implanter are controlled by the speed of the voltage and current sources connected to the ion implanter. Therefore, there is a need in the art for an improved method of glitch recovery during the implantation of workpieces and, more particularly, solar cells. An ion implantation system and method are disclosed in which glitches in voltage are minimized by modifications to the power system of the implanter. These power supply modifications include faster response time, output filtering, improved glitch detection and removal of voltage blanking. By minimizing number of glitches and their duration, it is possible to produce solar cells with acceptable dose uniformity without having to pause the scan each time a voltage glitch is detected. For example, by shortening the duration of a voltage collapse to about 20-40 milliseconds, dose uniformity within about 3% can be maintained. The embodiments of this method are described herein in connection with an ion implanter. Beam-line ion implanters, plasma doping ion implanters, or flood ion implanters may be used. Any n-type and p-type dopants may be used, but the embodiments herein are not limited solely to dopants. Furthermore, embodiments of this process may be applied to many solar cell architectures or even other workpieces such as semiconductor wafers, flat panels, or light emitting diodes (LEDs). Thus, the invention is not limited to the specific embodiments described below. As noted above, glitches may cause non-uniformity of ion implantation. However, the extent of the non-uniformity is related to the duration of the glitch. FIGS. 3-4 are charts comparing dose versus workpiece y-position for glitches of various durations. FIG. 3 represents a 4 scan implant operating at 36 cm/sec scan rate. FIG. 4 represents a 4 scan implant at 18 cm/sec scan rate. In both charts, a uniform dose is desired. Glitches of various durations are modeled, where the glitch occurs as the ion beam was scanning across the wafer. A glitch of, for example, 50 ms may impact the dose of the workpiece by more than 5% in the region impacted by the glitch. In some embodiments, this degradation may be to an extent that, for example, a solar cell may have reduced efficiency. Smaller time periods may have negligible or acceptable effects on the workpiece. For example, a glitch of 10 ms may only reduce the dose in the affected region by about 1%. Similarly, a glitch of 20 ms may affect the impacted region by about 2-2.5%. Modeling indicates that glitch duration should be controlled within approximately 20-40 ms to maintain doping uniformity within approximately 2-3%. This level of uniformity may be sufficient for the production of solar cells. Thus, if glitches can be reduced to such durations, solar cell efficiency is not substantially impacted and throughput is not compromised. FIG. 5A is a first block diagram of a beam-line ion implanter 200. In one instance, this may be for doping a semiconductor wafer or solar cell. Those skilled in the art will recognize that the beam-line ion implanter 200 is only one of many examples of beam-line ion implanters that can produce ions. Thus, the embodiments disclosed herein are not limited solely to the beam-line ion implanter 200 of FIG. 5A. In general, the beam-line ion implanter 200 includes an ion source 280 to generate ions that form an ion beam 281. The ion source 280 may include an ion chamber 283. A gas is supplied to the ion chamber 283 where the gas is ionized. This gas may be or may include or contain, in some embodiments, hydrogen, helium, other rare gases, oxygen, nitrogen, arsenic, boron, phosphorus, aluminum, indium, antimony, carborane, alkanes, another large molecular compound, or other p-type or n-type dopants. The ions thus generated are extracted from the ion chamber 283 to form the ion beam 281. The ion beam 281 passes through a suppression electrode 284 and ground electrode 285 to the mass analyzer 286. The mass analyzer 286 includes a resolving magnet 282 and a masking electrode 288 having a resolving aperture 289. The resolving magnet 282 deflects ions in the ion beam 281 such that ions of a desired ion species pass through the resolving aperture 289. Undesired ion species do not pass through the resolving aperture 289, but are blocked by the masking electrode 288. Ions of the desired ion species pass through the resolving aperture 289 to the angle corrector magnet 294. The angle corrector magnet 294 deflects ions of the desired ion species and converts the ion beam from a diverging ion beam to ribbon ion beam 212, which has substantially parallel ion trajectories. The beam-line ion implanter 200 may further include acceleration or deceleration units in some embodiments. This particular embodiment has a deceleration unit 296. An end station 211 supports one or more workpieces, such as workpiece 138, in the path of ribbon ion beam 212 such that ions of the desired species are implanted into workpiece 138. The workpiece 138 may be, for example, a solar cell. The end station 211 may include a platen 295 to support one or more workpieces 138. The end station 211 also may include a scanner (not shown) for moving the workpiece 138 perpendicular to the long dimension of the ribbon ion beam 212 cross-section, thereby distributing ions over the entire surface of workpiece 138. Although the ribbon ion beam 212 is illustrated, other embodiments may provide a spot beam. It will be understood to those skilled in the art that the entire path traversed by the ion beam is evacuated during ion implantation. The beam-line ion implanter 200 may include additional components known to those skilled in the art and may incorporate hot or cold implantation of ions in some embodiments. The beam-line ion implanter 200 of FIG. 5A also includes two power supplies: a source suppression power supply 500 and an extraction power supply 501. In this embodiment, the suppression power supply 500 negatively biases the suppression electrode 284 relative to ground. In this embodiment, the resolving magnet 282, the unit surrounding the masking electrode 288, the angle corrector magnet 294, the deceleration unit 296 and the end station 211 are all connected to ground. The extraction power supply 501 is used to positively bias the ion source 280 relative to ground. There are three specific instances where the glitches may occur. First, the extraction electrode, which is positively biased, may arc to the suppression electrode 284, which is negatively biased. Second, the suppression electrode 284, which is negatively biased, may arc to a ground electrode 285. Lastly, a positively biased extraction electrode may arc to a ground electrode. A second block diagram of a beam-line ion implanter 400 is shown in FIG. 5B. This embodiment utilizes the same components described with respect to FIG. 5A, and therefore the description need not be repeated. However, by biasing the deceleration unit 296, the beam-line ion implanter 400 may operate in drift mode or process chamber deceleration (PCD) mode. The ion beam 281 and ribbon ion beam 212 are projected at a high speed until the deceleration unit 296 slows the ribbon ion beam 212 just prior to implantation into the workpiece 138. Drift or PCD mode allows the ion beam to maintain its desired characteristics with a minimum of, for example, beam “blow-up” due to space charge effects, while still implanting into the workpiece 138 at the desired energy. To implement this, the beam-line ion implanter 400 also includes four power supplies. The suppression power supply 500 negatively biases the suppression electrode 284 relative to the resolving magnet 282, the unit surrounding the masking electrode 288 and the angle corrector magnet 294, which are all at the same voltage. In this embodiment, the end station 211 is connected to ground. The extraction power supply 501 is used to positively bias the ion source 280 relative to ground. A deceleration suppression power supply 502 is used to negatively bias the deceleration unit 296 relative to the angle corrector magnet 294. A deceleration power supply 503 is used to negatively bias the resolving magnet 282, the unit surrounding the masking electrode 288 and the angle corrector magnet 294 relative to ground. In this embodiment, there are six specific instances where glitches may occur. First, as described above, the extraction electrodes may arc to the suppression electrode 284. Second, the suppression electrode 284 may arc to a ground electrode 285. Third, an extraction electrode may arc to a ground electrode 285. Fourth, an electrode in the deceleration unit 296 may arc to the deceleration suppression. Fifth, the deceleration suppression may arc to ground. Lastly, the source extraction electrode may arc to ground. The arcing corresponding to a glitch may be sensed by a voltage collapse to a value below the voltage threshold value or a current rise above the current threshold value. By improving arc detection of the voltage sources, it is possible to better control glitch duration. Faster arc detection and voltage recovery may be used to keep glitch durations below 20 ms. This allows, based on the data in FIGS. 3 and 4, a workpiece to be implanted to within 2-3% of the desired dose, which may be acceptable for workpieces such as solar cells. As described above, glitches of sufficiently short duration may not impact the efficiency of a solar cell and will not reduce the manufacturing throughput. Thus, it is desirable to reduce glitches is about 20-40 ms. Most currently available high voltage power supplies have slow arc detection and very slow recovery. In fact, in some embodiments, a power supply may take hundreds of milliseconds to return to its nominal value after a glitch. Regarding glitch detection, typically, a conventional power supply has a threshold of about 50%, meaning that it detects a fault when the voltage drops below 50% of the programmed value, or the current rises above 50% more than the adjusted value. Once this is detected, the power supply disables its output, a behavior also referred to as voltage blanking. After about 100 milliseconds, the voltage is ramped back to within 1-2% of the nominal value, and the power supply enables its output. In addition, most high voltage power supplies have slow control loop response, which is referred to as its time constant, due to the high output capacitance. For example, a high voltage power supply may have a 20 millisecond time constant. This lengthy time constant causes the output voltage to recover in about 100 milliseconds. This lengthy delay would cause an unacceptable drop of dose, rendering the solar cell unusable. Therefore, to keep the glitch recovery to within approximately 2% of the desired voltage in less than 20 ms, the power system of the ion implanter 200, 400 must be modified. First, the various power supplies are designed such that arc quenching or voltage blanking is eliminated. In other words, rather than disabling its output upon detection of a glitch, the redesigned power supplies attempt to overcome the glitch by increasing their current output, so as to attempt to maintain the nominal voltage. Thus, the redesigned power supplies exhibit the opposite behavior of conventional power supplies, which dramatically reduce their output current (typically to 0) upon detection of a glitch. Secondly, the threshold voltage for detection of an arc is increased, as compared to conventional power supplies. In some embodiments, a glitch is detected when the voltage drops between 20-40% of its adjusted value, or its current increases between 20-40% of its adjusted value. By using a tighter threshold, the corrective action initiated by the redesigned power supplies may commence sooner, saving time and thereby minimizing the voltage glitch. As described above, once the redesigned power supply detects that the voltage or current outside its tightened threshold, it begins to increase its current output to overcome the fault. Third, a resistance, such as 1 to 5 kΩ resistor is added in series with the output of each of the power supplies to filter arcs and limit the arc current. This resistance, in combination with the output capacitance of the power supplies serves as a filter that will help suppress arcs of short duration and absorb some energy from the arcs to minimize the damage caused. Fourth, the power supplies are modified to have faster recovery after an arc, such as less than 50 milliseconds. As described above, power supplies have a control loop, having a time constant, which is used to establish and maintain the output voltage. Due to the excessive output capacitance of high voltage power supplies, these time constants are typically long, such as longer than 20 ms. A time constant of 20 millisecond results in the output voltage recovering in 100 milliseconds or more. In the present disclosure, the power supply is redesigned to have a time constant of less than 10 ms, thereby reducing the recovery time. In some embodiments, the output capacitance of the high voltage power supply may be reduced to help reduce the time constant. In one embodiment, these features are all incorporated into the design of the power system of an ion implantation for use with solar cells. The extraction power supply 501 is redesigned to have faster recovery, such as a time constant of approximately 8 ms, and uses a tighter voltage threshold, such as 20-40%, for arc detection. In addition, voltage blanking is not used. An output resistance of 2 kΩ is used on the output of each power supply to further reduce the effects of arcs. In this embodiment, glitch recovery improves, as the ion beam may only be reduced for approximately 20-30 ms. In another embodiment, the extraction power supply 501 recovers in less than 50 ms to within approximately 0.1% of the desired voltage, which may be considered a full recovery in one instance. Similar changes may be made to the other power supplies. FIG. 6 is a chart illustrating an improved glitch recovery. At time 600 when the glitch is first detected, the voltage is dropped to a value above zero. Additionally, the voltage may recover back to the desired value faster than with the blanking illustrated in FIG. 2. A faster recovery means that the ion beam will not “disappear” or have a reduced dose for as long. This reduces non-uniformity of the implant dose. FIG. 7 shows a representative beam current based on the improved glitch control described herein. The duration of the beam current glitch 711, defined as the time between lines 712 and 713, is greatly reduced, compared to FIG. 1. These changes allow a high throughput method of manufacturing semiconductors, where exact dose uniformity is not a requirement, such as solar cells. In such an embodiment, a substrate is placed on the platen 295. Ions are then directed toward the substrate by energizing the various components of the ion implantation system. The use of the modified power supplies serves to minimize the duration of any glitches, thus helping to maintain the dose uniformity to within about 3%. A controller (not shown) monitors the beam current being directed at the substrate. As long as the dips in the beam current are within a certain limit, such as 2-5%, preferably 3%, the dose uniformity is acceptable, and the ion implantation is allowed to continue. Dips greater than this will cause an unacceptable change in dose, rendering the substrate ineffective as a solar cell. In this case, the scanning of the substrate is stopped, while the beam current is restored to its nominal level. In other embodiments, rather or in addition to monitoring beam current, the voltage of each power supply is monitored for glitches. Glitches of a sufficiently short duration, such as less than 40 milliseconds, are allowed and scanning is continued. However, glitches of greater duration require the scanning to stop until the beam current is restored. The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein. |
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048572616 | summary | TECHNICAL FIELD The invention relates to nuclear reactor vessels, and more particularly to a reactor vessel head area monitoring system. BACKGROUND OF THE INVENTION In a typical nuclear reactor power plant, a nuclear reactor vessel is used to generate heat for the production of steam and electricity. In one such design, the reactor vessel is a pressure vessel which encloses the core of nuclear fuel and coolant, typically borated water. As a means for generating data relating to the operating conditions within the pressure vessel, instrumentation devices are introduced to the nuclear core through ports or penetrations in the vessel. Some of these penetrations are provided for through the reactor vessel closure head. The closure head may also include penetrations for drive mechanisms of control rods, used to regulate the rate of nuclear reactions which take place within the core, and in turn control the power output of the plant. Although these ports are mechanically sealed to prevent the inadvertent leakage of coolant from the reactor vessel, the operating conditions of a nuclear reactor pressure vessel require additional safeguards. Typically, the pressure vessel maintains the coolant therein at an internal pressure of about 15 MPa (2250 psi) and a temperature of about 315.degree. C. (600.degree. F.). Because of such a large internal pressure, reactor coolant may leak from the mechanical joint of these penetrations, or when control rods are withdrawn. The coolant within the reactor vessel is slightly acidic and highly corrosive due to the presence of boric acid which is dissolved within the coolant. Boric acid is a neutron absorber used as a variable reactivity control over the long-term operation of the plant. Even though there are regulatory limits on the allowable amount of coolant which may be emitted from the reactor vessel, components on the exterior of, and in close proximity to, the reactor vessel head need to be periodically inspected to determine if coolant is being emitted. Since an operating nuclear reactor generates an irradiated environment, the inspection and/or maintenance of the reactor vessel head area is typically conducted at times when the reactor is shut down for normal inspection or maintenance procedures, such as refueling of the core. A usual telltale sign of the presence of a leak in this area is white boric acid crystal deposits on the reactor vessel head. Any of several methods for determining the presence of a possible leak source may be used, but verification of the existence of a leak, estimations of its size, and the identification of its location is best done visually. Generally, the control rod drive mechanisms and instrumentation ports are enclosed by a cooling shroud. This shroud provides protection for the drive mechanisms, as well as a means for directing the flow of air around the ports for natural circulation cooling of the ports and drive mechanisms. This can make it even more difficult to visually detect the presence of borated coolant in this area. DISCLOSURE OF THE INVENTION It is therefore an object of the present invention to provide a means for remotely monitoring the area around a reactor vessel closure head to detect the presence of borated coolant. It is another object of the present invention to provide a monitoring device which is remotely operable during reactor operation. The above objects are attained by the present invention, according to which, briefly stated, in a nuclear reactor pressure vessel having a removable closure head with a plurality of ports projecting therethrough, and an upwardly extending cooling shroud enclosing the ports, the shroud having a plurality of openings therein, a reactor vessel head area monitoring system comprises a series of video cameras attached to the shroud adjacent the openings. A wide angle, right angle lens is operably attached to each video camera such that it receives video images of the reactor vessel head area. A light source is attached to the shroud adjacent to the video camera to provide adequate lighting for the cameras in detecting the presence of boric acid crystals on the reactor vessel head. |
059995831 | abstract | The electromagnetic drive mechanism for the control rods of a nuclear reactor has a stationary gripper and coil, a movable gripper and coil, and a lifting armature and coil for moving the movable gripper to advance or retract the control rods in steps. A coil current driver responsive to a controller provides currents to the coils individually and in combinations. During the operations, coil current signals are sensed, sampled, digitized and processed to generate coil current data such as amplitude as a function of time. The measured coil current data is compared to nominal current data as well as historical current data, and the historical data is updated or appended to include the measured data. The comparison includes a check for correct timing relationships, such as the timing of the current notch occurring due to increased inductance upon pull-in of a gripper. Additionally, voltages or currents between the ac power source and the coils can be monitored for isolating a failure to particular circuit elements. |
claims | 1. An irradiation target harvesting system comprising:at least one storage container for receiving activated irradiation targets from an instrumentation tube system of a nuclear reactor;a discharge tube having an exit port configured to be coupled to the storage container; anda lock element provided in the discharge tube for blocking movement of the activated irradiation targets to the storage container;wherein the discharge tube comprises a first discharge tube section, a second discharge tube section and an apex formed at a conjunction of the first and second discharge tube sections,wherein the first and second discharge tube sections are directed downward from the apex,wherein the exit port is arranged at an end of the first discharge tube section,wherein the second discharge tube section is coupled to the instrumentation tube system, andwherein the discharge tube comprises a T-junction located between the lock element and the exit port, wherein the T-junction is configured for supplying and discharging pressurized gas into and out of the discharge tube. 2. The irradiation target harvesting system according to claim 1, wherein the exit port comprises a valve element for pressure-tight sealing the discharge tube. 3. The irradiation target harvesting system according to claim 1, wherein the first discharge tube section, the second discharge tube section and the apex have a shape of an inverse U. 4. The irradiation target harvesting system according to claim 1, wherein the lock element is at a first level, wherein the second discharge tube section has a base point opposite to the apex and the base point is at a second level, and wherein the first level is higher than the second level. 5. The irradiation target harvesting system according to claim 1, wherein the harvesting system comprises one or more magnets arranged at the first discharge tube section between the apex and the lock element. 6. The irradiation target harvesting system according to claim 5, wherein the one or more magnets are selected from a permanent magnet and a solenoid. 7. The irradiation target harvesting system according to claim 1, wherein the lock element comprises a magnetically or mechanically operated restriction element. 8. A radionuclide generation system comprising:an instrumentation tube system of a nuclear reactor including at least one instrumentation finger extending into a core of the nuclear reactor wherein the instrumentation tube system is configured to permit insertion and removal of irradiation targets into the instrumentation finger;a target drive system configured to insert the irradiation targets into the instrumentation finger in a predetermined linear order and to remove the irradiation targets from the instrumentation finger;a core monitoring system and an instrumentation and control unit linked to each other and configured to calculate an optimum axial irradiation position and time for the irradiation targets based on the actual state of the nuclear reactor as provided by the core monitoring system; anda target harvesting system according to claim 1. 9. The radionuclide generation system according to claim 8, wherein the target drive system is pneumatically operated. 10. The radionuclide generation system according to claim 8, wherein the target harvesting system comprises one or more magnets arranged at the first discharge tube section between the apex and the lock element and the lock element and the one or more magnets are remotely controlled by the instrumentation and control unit. 11. A method for harvesting activated irradiation targets from an instrumentation tube system of a nuclear reactor, wherein the method comprises the steps of:coupling the instrumentation tube system to a discharge tube having a first discharge tube section, a second discharge tube section and an apex formed at a conjunction of the first and second discharge tube sections, an exit port and a lock element between the apex and the exit port, wherein the first and second discharge tube sections are directed downward from the apex;passing the activated irradiation targets from the instrumentation tube system into the discharge tube and blocking movement of the activated irradiation targets out of the discharge tube by means of the lock element;separating a predefined quantity of the activated irradiated targets from another quantity of the activated irradiated targets in the discharge tube;coupling the exit port to a storage container and releasing the lock element to pass the predefined quantity of the activated irradiated targets under action of gravity into the storage container;wherein said separating step comprises passing the predefined quantity of the activated irradiation targets over the apex into the first discharge tube section and keeping the other quantity of activated irradiation targets in the second discharge tube section or the instrumentation tube system by means of the apex. 12. The method according to claim 11, further comprising a step wherein the other quantity of the activated irradiation targets separated from the predetermined quantity of activated irradiation targets is transferred from the second discharge tube section into a position in the instrumentation tube system prior to removing the storage container from the exit port. 13. The method according to claim 11, further comprising a step wherein irradiation targets and one or more dummy targets are inserted into the instrumentation tube system, wherein the dummy targets are made of an inert material that is not substantially activated under the conditions in the core of an operating nuclear reactor, and wherein the irradiation targets and the dummy targets have different magnetic properties. 14. The method according to claim 13, wherein the dummy targets inserted into the instrumentation tube system are ferromagnetic, and the irradiation targets inserted into the instrumentation tube system are non-magnetic or paramagnetic. 15. The method according to claim 14, further comprising a step wherein the dummy targets and/or the irradiation targets are exposed to a magnetic field when in the first discharge tube section. 16. The method according to claim 13, further comprising a step wherein the dummy targets and/or the irradiation targets are exposed to a magnetic field when in the first discharge tube section. 17. The method according to claim 13, wherein the irradiation targets are separated from the dummy targets by selectively removing one of the irradiation targets and the dummy targets from the discharge tube, the method further comprising the steps of exposing the irradiation targets or the dummy targets to a magnetic field, opening the lock element, and releasing one of the irradiation targets or the dummy targets from the discharge tube while keeping the other one of the irradiation targets or the dummy targets in the first discharge tube section by the action of the magnetic field. 18. The method according to claim 17, wherein the step of separating the irradiation targets from the dummy targets further comprises driving one of the dummy targets or the irradiation targets back into the instrumentation finger or a holding position in the instrumentation tube system while retaining the other one of the dummy targets or the irradiation targets in the first discharge tube section by means of the magnetic field. |
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claims | 1. A tokamak plasma vessel comprising:a toroidal plasma chamber;a plurality of poloidal field coils;an upper divertor assembly;a lower divertor assembly;wherein the plurality of poloidal field coils are configured to provide a poloidal magnetic field having a substantially symmetric plasma core and an upper and lower null, such that ions in a scrape off layer outside the plasma core are directed by the magnetic field past one of the upper and lower nulls to divertor surfaces of the respective upper and lower divertor assembly;wherein each of the upper and lower divertor assembly comprises:an inboard strike point divertor surface, located at the inboard strike point;an outboard strike point divertor surface, located at the outboard strike point;an inboard far divertor surface, located radially inwards of the inboard strike point divertor surface;an outboard far divertor surface, located radially outwards of the outboard strike point divertor surface; andat least one private divertor surface, located between the inboard and outboard strike point divertor surfaces;each far divertor surface and/or each private divertor surface comprises:a liquid metal inlet; anda liquid metal outlet located below the liquid metal inlet;configured such that in use liquid metal flows from the liquid metal inlet to the liquid metal outlet over at least the respective divertor surface. 2. A tokamak plasma vessel according to claim 1, wherein the poloidal field coils are configured to provide a symmetric magnetic field. 3. A tokamak plasma vessel according to claim 1, wherein the poloidal field coils are configured to provide a magnetic field which is asymmetric outside the plasma core so as to optimize interaction with the upward facing divertor surfaces. 4. A tokamak plasma vessel according to claim 1, and comprising a liquid metal supply means configured to supply liquid metal to each liquid metal inlet at a respective flow rate. 5. A tokamak plasma vessel according to claim 1, wherein each divertor surface over which the liquid metal flows is generally upward facing. 6. A tokamak plasma vessel according to claim 4, wherein the upper divertor assembly comprises at least one divertor surface over which liquid metal flows, wherein the divertor surface is generally downward facing, and wherein that divertor surface is at an angle such that, when the liquid metal supply means supplies liquid metal to the surface at the respective flow rate, the wetting of the liquid metal to the divertor surface prevents liquid metal from falling from the divertor surface. 7. A tokamak plasma vessel according to claim 6, wherein the divertor surfaces are arranged with reflective symmetry, such that the divertor surfaces of the upper divertor assembly are a reflection of the divertor surfaces of the lower divertor assembly in an equatorial plane of the tokamak plasma vessel. 8. A tokamak plasma vessel according to claim 6, wherein the generally downward facing divertor surface comprises channels. 9. A tokamak plasma vessel according to claim 1, wherein the liquid metal inlet of at least one of the divertor surfaces is located radially outwards of the respective liquid metal outlet. 10. A tokamak plasma vessel according to claim 1, wherein the liquid metal is lithium or tin. |
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claims | 1. A Betavoltaic cell comprising:a semiconductor substrate;p-n junctions formed of semiconductor; andelectrical contacts coupled to the p-n junctions, wherein the contacts are adapted to minimize beta radiation backscatter losses. 2. The Betavoltaic cell of claim 1 and further comprising a beta radiation source. 3. The Betavoltaic cell of claim 2 wherein the beta radiation source comprises Ni-63 or tritium (H-3) or both. 4. The Betavoltaic cell of claim 1 wherein the contacts occupy about 1% of an active device area of the p-n junctions. 5. The Betavoltaic cell of claim 2 wherein the radiation source comprises beta radiation producing particles and wherein a semiconductor surface area for accepting the radioactive particles is smaller than an overall device surface area. 6. The Betavoltaic cell of claim 1 wherein the surface of the semiconductor is passivated. 7. The Betavoltaic cell of claim 1 wherein the p-n junctions are formed from n doped semiconductor disposed underneath p doped semiconductor or a p doped semiconductor disposed underneath n doped semiconductor. 8. A Betavoltaic cell comprising:a semiconductor substrate;p-n junctions formed from semiconductor;cathode or anode contacts coupled to the p-n junctions wherein contact areas are adapted to minimize beta radiation backscatter losses;an anode or cathode contact formed on a back side of the substrate; anda beta radiation fuel. 9. The Betavoltaic cell of claim 8 wherein the contacts occupy about 1% of an active device area of the p-n junctions. 10. The Betavoltaic cell of claim 8 wherein the radiation fuel comprises beta radiation particles and wherein a semiconductor surface area for accepting the radioactive particles is smaller than an overall device surface area. 11. The Betavoltaic cell of claim 8, wherein the surface of the semiconductor is passivated. 12. The Betavoltaic cell of claim 8 wherein the beta radiation fuel comprises Ni-63, tritium (H-3) or both. 13. The Betavoltaic cell of claim 8 wherein the p-n junction is formed from n doped semiconductor disposed underneath p doped semiconductor or p doped semiconductor disposed underneath n doped semiconductor. 14. A Betavoltaic cell comprising:a semiconductor substrate;p-n junctions formed of semiconductor,a void proximal to the p-n junctions;cathode or anode contacts coupled to the p-n junctions, wherein the contacts have an area adapted to minimize beta radiation backscatter losses;an anode or cathode contact formed on a back side of the substrate; anda cap formed of semiconductor. 15. The Betavoltaic cell of claim 14 and further comprising a beta radiation source. 16. The Betavoltaic cell of claim 15 wherein the beta radiation source comprises Ni-63 or tritium (H-3) or both. 17. The Betavoltaic cell of claim 14 wherein the contacts occupy about 1% of an active device area of the p-n junctions. 18. The Betavoltaic cell of claim 14 wherein the radiation source comprises beta radiation producing particles and wherein a semiconductor surface area for accepting the radioactive particles is smaller than an overall device surface area. 19. The Betavoltaic cell of claim 14 wherein the surface of the semiconductor is passivated. 20. The Betavoltaic cell of claim 14 wherein the p-n junction is formed from n doped semiconductor disposed underneath p doped semiconductor or p doped semiconductor disposed underneath n doped semiconductor. 21. A Betavoltaic cell comprising:a semiconductor substrate having a passivated surface;p-n junctions formed of semiconductor supported by the semiconductor substrate, wherein an upper layer of the junctions comprise a passivated surface;a void proximal to the p-n junctions adapted to hold beta radiation particles;first contacts coupled to the p-n junctions, wherein the first contacts occupy less than about 1% of the area of the p-n junctions to minimize beta radiation backscatter losses;a second contact formed on a back side of the substrate; anda cap formed of semiconductor positioned to cover the void. 22. The Betavoltaic cell of claim 21 wherein the first contacts comprise an annealed metal. |
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abstract | A Z stage is placed on an XY stage in avoidance of an area to which a mark table is fixed. The mask M is placed on a holding mechanism provided on the Z stage. A middle value of the range adjustable by the focal adjustment mechanism is made coincident with the height of the mark table. The height of the mark table is measured and the heights of plural measurement points of the mask M are measured. The Z stage is moved in such a manner that the height of a middle value between highest and lowest values of the heights of these measurement points coincides with the height of the mark table. |
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claims | 1. An apparatus for generating, extracting and selecting ions used in a heavy ion cancer therapy facility comprising: an independent first (ECRIS 1 ) and an independent second electron cyclotron resonance ion source (ECRIS 2 ) for generating heavy and light ions respectively, a spectrometer magnet (SP 1 , SP 2 ) for selecting heavy ion species of one isotopic configuration positioned downstream of each ion source (ECRIS 1 , ECRIS 2 ); a magnetic quadrupole triplet (QT 1 , QT 2 ) positioned downstream of each analyzing slit (SP 1 , SP 2 ); an analyzing slit (ISL) located at an image focus of each spectrometer magnet (SP 1 , SP 2 ); beam diagnostic means (BD) located at each slit (SL, ISL) comprising at least profile grids and Faradays cups; a switching magnet (SM) for switching between high-LET ion species and low-LET ion species of said two independent first and second ion source; and a radio frequency quadrupole accelerator (RFQ) positioned downstream said switching magnet (SM) wherein a beam transformer (BTR) is positioned in between said analyzing slit (ISL) and said magnetic quadrupole triplet (QT 1 ; QT 2 ); said ion sources (ECRIS 1 , ECRIS 2 ) comprise exclusively permanent magnets and said RFQ has a 4-rod-like structure comprising alternating stems (ST) mounted on a common base plate (BP) within the RFQ, wherein said stems (ST) are acting as inductivity and mini-vane pair forming electrodes (EL) and are acting as capacitance for a xcex/2 resonance structure. 2. The apparatus according to claim 1 , wherein a solenoid (SOL) magnet is located at an exit of each ion source (ECRIS 1 , ECRIS 2 ). claim 1 3. The apparatus according to claim 1 wherein a magnetic quadrupole singlet (QS 1 , QS 2 ) is positioned downstream of each ion source (ECRIS 1 , ECRIS 2 ). claim 1 4. The apparatus according to claim 1 , wherein a focusing solenoid magnet (SOL) is positioned downstream of a chopper (CH) and upstream of said radio frequency quadrupole (RFQ) accelerator. claim 1 5. The apparatus according to claim 1 , wherein the low energy beam transport system (LEBT) comprises downstream of the switching magnet (SM) diagnostic means (F 01 , F 02 ) enclosing a Faraday cup and/or profile grids. claim 1 6. The apparatus according to claim 2 , wherein a magnetic quadrupole singlet (QS 1 , QS 2 ) is positioned downstream of each ion source (ECRIS 1 , ECRIS 2 ). claim 2 |
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description | Example embodiments described herein relate in general to nuclear reactors and in particular to providing passive cooling of a nuclear reactor containment. Nuclear reactors may be configured to be cooled via heat transfer to one or more coolant fluids circulated in or near the nuclear reactor. Such heat transfer may be referred to herein as heat rejection by the nuclear reactor. Various coolant fluids may be utilized to remove heat from the nuclear reactor. A coolant fluid may be a fluid that includes one or more various substances, including water, liquid metal, molten salt, a gaseous substance, some combination thereof, etc. In some nuclear plants, a nuclear reactor includes a containment system, also referred to herein as simply “containment,” for managing heat rejection by the nuclear reactor by facilitating circulation of a coolant fluid, such as water, to a point in the nuclear reactor where the coolant fluid absorbs heat rejected by the nuclear reactor, and the heated coolant fluid is then circulated to a heat return, or heat sink, where the heated coolant fluid may be cooled to release the absorbed heat. In some nuclear plants, the containment system may be impacted by heat rejection that exceeds the heat transfer capabilities of a power coolant loop that is used to induce work, for example to generate electricity. Accordingly, the containment system may utilize cooling to manage containment system temperature or prevent the containment system from exceeding its qualified temperature. In some nuclear plants, a nuclear reactor may experience excursions of temperature and/or pressure within a containment environment in which the nuclear reactor may be located. The temperature and/or pressure within the containment environment may be controlled to influence performance and/or integrity of the nuclear reactor. In some nuclear plants, such temperature and/or pressure control may be implemented through various control systems that manage pressure release and/or cooling of the containment environment. Such control systems may utilize computer-implemented functionality and/or operator-controlled functionality, which may thus consume electrical power, operator operations, some combination thereof, or the like. In addition, pressure control within the containment environment may involve releasing fluids from the containment environment. According to some example embodiments, a nuclear plant may include a nuclear reactor, a containment structure having one or more inner surfaces at least partially defining a containment environment in which the nuclear reactor is located, and a passive containment cooling system. The passive containment cooling system may include a coolant reservoir configured to hold a coolant fluid, a coolant channel coupled to the containment structure such that the coolant channel extends vertically from a coolant channel inlet at a bottom of the coolant channel to a coolant channel outlet at a top of the coolant channel, and a coolant supply conduit extending downwards from an inlet of the coolant supply conduit that is open to a lower region of the coolant reservoir. An outlet of the coolant supply conduit may be coupled to the coolant channel inlet, such that the coolant supply conduit is configured to direct a flow of coolant fluid downwards out of the lower region of the coolant reservoir and into the bottom of the coolant channel via the coolant channel inlet according to gravity, such that the coolant fluid rises through the coolant channel from the bottom of the coolant channel to the top of the coolant channel according to a change in coolant fluid buoyancy based on the coolant fluid absorbing heat rejected from the nuclear reactor in the containment environment. The passive containment cooling system may include a coolant return conduit having an inlet coupled to the coolant channel outlet at the top of the coolant channel. The coolant return conduit may extend upwards from the inlet of the coolant return conduit to an outlet of the coolant return conduit that is open to an upper region of the coolant reservoir that is above the lower region of the coolant reservoir, such that the coolant return conduit is configured to direct a flow of the coolant fluid to rise out of the top of the coolant channel via the coolant channel outlet and into the upper region of the coolant reservoir according to increased buoyancy of the coolant fluid at the top of the coolant channel over the buoyancy of the coolant fluid at the bottom of the coolant channel. The passive containment cooling system may include a first check valve assembly at a first vertical depth below a top surface of coolant fluid in the coolant reservoir, the first check valve assembly in fluid communication with the coolant reservoir and with the containment environment. The first check valve assembly may include one or more check valves coupled between a first check valve assembly inlet and a first check valve assembly outlet. The first check valve assembly inlet may be in fluid communication with the coolant reservoir. The one or more check valves may be configured to open in response to a pressure at an inlet of the one or more check valves being equal to or greater than a first threshold magnitude, the first threshold magnitude at least partially corresponding to a hydrostatic pressure of the coolant fluid at the check valve assembly outlet at the first vertical depth. The first check valve assembly may be configured to selectively enable one-way flow of a containment fluid, from the containment environment via the first check valve assembly inlet to the coolant reservoir via the first check valve assembly outlet, based on the one or more check valves opening in response to a pressure of the containment environment at the first check valve assembly inlet at the first vertical depth being equal to or greater than the first threshold magnitude. The first check valve assembly may extend through the containment structure and into the coolant channel at the first vertical depth, and the first check valve assembly may be open to the coolant channel, such that the first check valve assembly is in fluid communication with the coolant reservoir through the coolant channel. The first check valve assembly may be configured to selectively enable the one-way flow of the containment fluid, from the containment environment via the first check valve assembly inlet, to the coolant channel via the first check valve assembly outlet. The first threshold magnitude may be greater than a reference hydrostatic pressure of the coolant fluid in the coolant channel at the first vertical depth below the bottom of the coolant reservoir that results from the coolant reservoir being filled to a reference reservoir depth, such that the reference hydrostatic pressure of the coolant fluid in the coolant channel at the first vertical depth is equal to a hydrostatic pressure of the coolant fluid at a particular vertical depth that is a sum of the first vertical depth and the reference reservoir depth. The first check valve assembly may be configured to, subsequently to selectively enabling the one-way flow, inhibit the one-way flow of the containment fluid based on the one or more check valves closing in response to the pressure of the containment environment at the first check valve assembly inlet being less than the first threshold magnitude. The one or more check valves may include a series connection of a plurality of check valves between the first check valve assembly inlet and the first check valve assembly outlet. Each check valve of the plurality of check valves may be configured to open in response to a pressure at an inlet of the check valve being equal to or greater than the first threshold magnitude. The first check valve assembly may be configured to selectively enable the one-way flow based on all check valves of the series connection of the plurality of check valves opening. The one or more check valves may include a parallel connection of a plurality of sets of one or more check valves between the first check valve assembly inlet and one or more check valve assembly outlets. Each check valve of the plurality of sets of one or more check valves may be configured to open in response to a pressure at an inlet of the check valve being equal to or greater than the first threshold magnitude. The first check valve assembly may be configured to selectively enable the one-way flow based on any set of one or more check valves of the parallel connection of the plurality of sets of one or more check valves. The first check valve assembly may include a burst disc coupled in series with the one or more check valves. The burst disc may be configured to rupture in response to a pressure increase in the containment environment to a particular (or, alternatively, pre-determined) threshold (e.g., “set point”) pressure magnitude, thereby allowing the containment fluid pressure to reach the inlet of the first check valve assembly which allows containment fluid flow when the pressure at the inlet is equal to or greater than the first threshold magnitude. The nuclear plant may further include a second check valve assembly at a second vertical depth below the top surface of coolant fluid in the coolant reservoir. The second check valve assembly may be in fluid communication with the coolant reservoir and with the containment environment. The second vertical depth may be less than the first vertical depth. The second check valve assembly may be configured to selectively enable one-way flow of the containment fluid, from the containment environment to the coolant reservoir, based on one or more check valves of the second check valve assembly opening in response to a pressure of the containment environment at an inlet of the second check valve assembly being equal to or greater than a second threshold magnitude. The second threshold magnitude may at least partially correspond to a hydrostatic pressure of the coolant fluid at an outlet of the second check valve assembly at the second vertical depth. The nuclear plant may further include a fusible plug in fluid communication with the coolant reservoir and with the containment environment at a bottom vertical depth below the top surface of the coolant fluid in the coolant reservoir. The bottom vertical depth may be greater than the first vertical depth, such that a hydrostatic pressure of the coolant fluid at the bottom vertical depth is greater than the hydrostatic pressure of the coolant fluid at the first check valve assembly outlet at the first vertical depth. The fusible plug may be configured to at least partially melt in response to a temperature in the containment environment at an end of the fusible plug that is open to the containment environment being equal to or greater than a threshold temperature, such that the fusible plug exposes a flow conduit extending between the coolant reservoir into the containment environment to at least partially flood the containment environment with at least some of the coolant fluid. The first check valve assembly may be configured to, based on selectively enabling the one-way flow of the containment fluid in response to the pressure in the containment environment at the first check valve assembly inlet being equal to or greater than the first threshold magnitude, maintain a pressure in the containment environment at the bottom vertical depth at a magnitude that is less than the hydrostatic pressure of the coolant fluid at the bottom vertical depth, to enable flow of coolant fluid through the exposed flow conduit and into the containment environment in response to the fusible plug at least partially melting. The first check valve assembly and the fusible plug may be collectively configured to enable circulation of coolant fluid within the containment environment, from the coolant channel or other coolant routing pathway at the bottom vertical depth to the containment environment via the fusible plug and from the containment environment at the first vertical depth to the coolant channel or other coolant routing pathway via the first check valve assembly. According to some example embodiments, a method for operating a passive containment cooling system for a nuclear reactor may include directing a flow of coolant fluid downwards out of a lower region of a coolant reservoir via a coolant supply conduit according to gravity to a bottom of a coolant channel that extends vertically along a containment structure that at least partially defines a containment environment in which the nuclear reactor is located, and causing the coolant fluid to rise through the coolant channel from the bottom of the coolant channel toward an upper region of the coolant reservoir via a top of the coolant channel according to a change in coolant fluid buoyancy based on the coolant fluid absorbing heat rejected from the nuclear reactor in the containment environment via at least the containment structure. The method may include selectively enabling a one-way flow of a containment fluid, from the containment environment to the coolant reservoir via a first check valve assembly at a first vertical depth below a top surface of coolant fluid in the coolant reservoir, the first check valve assembly in fluid communication with the coolant reservoir and with the containment. The selectively enabling may be based on one or more check valves of the first check valve assembly opening in response to a pressure at an inlet of the one or more check valves being equal to or greater than a first threshold magnitude. The first threshold magnitude may at least partially correspond to a hydrostatic pressure of the coolant fluid at an outlet of the first check valve assembly at the first vertical depth. The first threshold magnitude may be greater than a reference hydrostatic pressure of the coolant fluid in the coolant channel at the first vertical depth below the top surface of the coolant fluid in the coolant reservoir that results from the coolant reservoir being filled to a reference reservoir depth, such that the reference hydrostatic pressure of the coolant fluid in the coolant channel at the first vertical depth is equal to a hydrostatic pressure of the coolant fluid at a particular vertical depth that is a sum of the first vertical depth and the reference reservoir depth. The method may further include inhibiting the one-way flow, subsequently to selectively enabling the one-way flow, based on the one or more check valves closing in response to the pressure of the containment environment at an inlet of the first check valve assembly being less than the first threshold magnitude. The one or more check valves may include a series connection of a plurality of check valves between an inlet of the first check valve assembly and the outlet of the first check valve assembly. Each check valve of the plurality of check valves may be configured to open in response to a pressure at an inlet of the check valve being equal to or greater than the first threshold magnitude. The selectively enabling may be based on all check valves of the series connection of the plurality of check valves opening. The one or more check valves may include a parallel connection of a plurality of sets of one or more check valves between an inlet of the first check valve assembly and one or more check valve assembly outlets. Each check valve of the plurality of sets of one or more check valves may be configured to open in response to a pressure at an inlet of the check valve being equal to or greater than the first threshold magnitude. The selectively enabling may be based on any set of one or more check valves of the parallel connection of the plurality of sets of one or more check valves. The selectively enabling may be based on a burst disc coupled in series with the one or more check valves, for example, between the inlet of the one or more check valves and an inlet of the first check valve assembly, rupturing in response to a pressure at the inlet of the first check valve assembly at the first vertical depth being equal to or greater than the first threshold magnitude. The method may further include directing at least a portion of the coolant fluid at a bottom vertical depth below the top surface of the coolant fluid in the coolant reservoir to flow into the containment environment via an exposed flow conduit between the coolant reservoir and the containment environment at the bottom vertical depth to at least partially flood the containment environment, based on a fusible plug in fluid communication with the coolant reservoir and with the containment environment, at the bottom vertical depth, at least partially melting to expose the flow conduit in response to a temperature in the containment environment at an end of the fusible plug that is open to the containment environment being equal to or greater than a threshold temperature. The first check valve assembly, based on selectively enabling the one-way flow, may maintain a pressure in the containment environment at the bottom vertical depth at a magnitude that is less than the hydrostatic pressure of the coolant fluid at the bottom vertical depth, to enable flow of coolant fluid through the exposed flow conduit and into the containment environment in response to the fusible plug at least partially melting. The first check valve assembly and the fusible plug may collectively enable circulation of coolant fluid within the containment environment, from the coolant channel or other coolant routing pathway at the bottom vertical depth to the containment environment via the fusible plug and from the containment environment at the first vertical depth to the coolant channel or other coolant routing pathway via the first check valve assembly. It should be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It should be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments. Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like) may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. Example embodiments may be described with reference to acts and symbolic representations of operations (e.g., in the form of flow charts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.) that may be implemented in conjunction with units and/or devices discussed in more detail below. Although discussed in a particular manner, a function or operation specified in a specific block may be performed differently from the flow specified in a flowchart, flow diagram, etc. For example, functions or operations illustrated as being performed serially in two consecutive blocks may actually be performed simultaneously, or in some cases be performed in reverse order. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, including those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Although described with reference to specific examples and drawings, modifications, additions and substitutions of example embodiments may be variously made according to the description by those of ordinary skill in the art. For example, the described techniques may be performed in an order different with that of the methods described, and/or components such as the described system, architecture, devices, circuit, and the like, may be connected or combined to be different from the above-described methods, or results may be appropriately achieved by other components or equivalents. It will be understood that a “nuclear reactor” as described herein may include any or all of the well-known components of a nuclear reactor, including a nuclear reactor core with or without nuclear fuel components, control rods, or the like. It will be understood that a nuclear reactor as described herein may include any type of nuclear reactor, including but not limited to a Boiling Water Reactor (BWR), a Pressurized Water Reactor (PWR), a liquid metal cooled reactor, a Molten Salt Reactor (MSR), or the like. As described herein, a nuclear reactor may include an Advanced Boiling Water Reactor (ABWR), an Economic Simplified Boiling Water Reactor (ESBWR), a BWRX-300 reactor, or the like. It will be understood that a “coolant fluid” as described herein may include any well-known coolant fluid that may be used in cooling any part of a nuclear plant and/or nuclear reactor, including water, a liquid metal (e.g., liquid sodium), a gas (e.g., helium), a molten salt, any combination thereof, or the like. It will be understood that a “fluid” as described herein may include a gas, a liquid, or any combination thereof. The present disclosure relates to a unique passive containment cooling system that utilizes one or more coolant channels coupled to a containment structure and extending vertically, from a coolant channel inlet at a bottom of the coolant channel to a coolant channel outlet at a top of the coolant channel, where the passive containment cooling system, also referred to herein as simply a “passive containment cooling system,” directs a coolant fluid to flow into the bottom of the coolant channel via the coolant channel inlet such that the coolant fluid rises vertically through the coolant channel, from the bottom of the coolant channel to a top of the coolant channel, according to a change in coolant fluid buoyancy based on the coolant fluid absorbing heat rejected from the nuclear reactor in the containment environment, where the coolant channel is coupled to the containment structure. The passive containment cooling system may supply the coolant fluid to the bottom of the coolant channel via the inlet thereof based on being directed to flow downwards (e.g., in the direction of gravitational acceleration) according to gravity from a coolant reservoir, via a coolant supply conduit extending downwards from an inlet of the coolant supply conduit that is open to a lower region of the coolant reservoir to an outlet of the coolant supply conduit that is coupled to the coolant channel inlet. Additionally, the passive containment cooling system may return the coolant fluid to an upper region of the coolant reservoir due to the increased buoyancy of the heated coolant fluid via a coolant return conduit having an inlet coupled to the coolant channel outlet at the top of the coolant channel and extending upwards from the inlet of the coolant return conduit to an outlet of the coolant return conduit that is open to the upper region of the coolant reservoir that is above the lower region of the coolant reservoir to which the inlet of the coolant supply conduit is open. As a result, the passive containment cooling system may drive circulation of coolant fluid upwards and out of the coolant channel and back into the coolant reservoir due to increased buoyancy due to absorbing heat rejected from the nuclear reactor, and the rising coolant fluid may be displaced in the bottom of the coolant channel by colder coolant fluid that flows downwards to the bottom of the coolant channel via a separate coolant supply conduit according to gravity, thereby enabling removal of heat from the containment environment. Because the colder coolant fluid is directed from a lower region of the coolant reservoir and the heated coolant fluid is directed into a higher, upper region of the coolant reservoir, the heated coolant fluid may remain above the colder coolant fluid in the coolant reservoir due to having increased buoyancy as a result of being heated by heat rejected from the nuclear reactor and thus being warmer than the cold coolant fluid, such that the coolant fluid that is directed to fall through the coolant supply conduit to the bottom of the coolant channel may be colder than the heated coolant fluid that is returned to the coolant reservoir via the coolant return conduit. Thus, it will be understood that the heated coolant fluid may be returned to the coolant reservoir via a coolant return conduit outlet that is open to the coolant reservoir at a greater height from a bottom of the coolant reservoir than the coolant supply conduit inlet. Accordingly, the circulation of coolant through the passive containment cooling system to remove heat rejected by the nuclear reactor to the coolant reservoir, where the coolant reservoir may function as an at least temporary heat sink, may be “passive” in that the circulation is not driven due to operation of a flow generator device, e.g., a pump, or based on intervention of an operator (e.g., including a human and/or processing circuitry, such as a processor executing a program of instructions stored on a memory, that generates an electrical control signal to control one or more devices), to induce or maintain a flow of coolant fluid. Accordingly, based on providing “passive” cooling of the nuclear reactor, the passive containment cooling system may enable improved operational efficiency of the nuclear plant based on reducing energy consumption to operate the nuclear plant and improved safety by not relying upon operator or control system intervention to control one or more devices to enable and/or control the cooling of the nuclear reactor. The coolant channel may be any type of conduit, including a pipe that is coupled (e.g., welded, bolted, secured through mechanical means, etc.) to a surface of a containment structure (e.g., an outer surface, an inner surface, an interior surface, any combination thereof, or the like), a channel defined within an interior of a structure that partially or entirely defines the containment structure (e.g., an integrated passive cooling containment structure), any combination thereof, or the like. The passive containment cooling system further may include one or more first check valve assemblies that enable passive control (e.g., control that is not controlled due to operator or control system intervention) of the pressure within the containment environment in which the nuclear reactor is located. The one or more first check valve assemblies are in fluid communication with both the containment environment and the coolant reservoir and may selectively enable one-way flow (also referred to herein as performing “venting”) of containment fluid out of the containment environment and to the coolant reservoir, via one or more channels and/or conduits to which the one or more first check valve assemblies are open and via which the one or more first check valve assemblies are in fluid communication with the coolant reservoir, based on whether the pressure in the containment environment at the inlets of the one or more first check valve assemblies reaches (e.g., is equal to or greater than) a threshold pressure magnitude that corresponds to a hydrostatic pressure of the coolant fluid the coolant reservoir at the outlets of the one or more first check valve assemblies, such that a pressure gradient from the containment environment to the one or more coolant channels or other pathway to the coolant reservoir through the one or more first check valve assemblies is ensured, thereby reducing or preventing the risk of backflow through the one or more first check valve assemblies from the one or more coolant channels or other pathway to the coolant reservoir into the containment environment. As a result, the one or more first check valve assemblies may selectively, based on actuation of one or more check valves included therein between a closed state and an open state, enable one-way flow of a containment fluid from the containment environment to the coolant reservoir to relieve the pressure in the containment environment. Such enabling of one-way flow of containment fluid to the coolant reservoir may be referred to as “venting” of the containment environment. The containment fluid may include one or more of a gas, liquid, solid material entrained in a gas and/or liquid, any combination thereof, or the like. In some example embodiments, the first check valve assembly may extend through the containment structure and into a coolant channel at a depth below the reservoir, such that the first check valve assembly is open to the coolant channel, is in fluid communication with the coolant reservoir through the coolant channel, and is configured to selectively enable the one-way flow from the containment environment to the coolant channel at the depth, but example embodiments are not limited thereto. The containment fluid may include radioactive material, and the one or more first check valve assemblies may, based on the selectively enabling of one-way flow out of the containment environment, selectively “vent” the containment fluid into the coolant reservoir and/or the flow of coolant fluid in one or more coolant channels or other pathway to the coolant reservoir, such that the containment fluid may be entrained in the upwards flow of the coolant fluid to the top of the one or more coolant channels or other pathway to the coolant reservoir and thus the containment fluid may be drawn into the coolant reservoir via the flow of the coolant fluid. As a result of being drawn into, and thus retained in, the coolant reservoir based on being vented into the coolant fluid in the one or more coolant channels or other pathway to the coolant reservoir, the containment fluid may be restricted, at least temporarily, from being released to an exterior of the nuclear plant. The coolant reservoir, in addition to functioning as a heat sink for heat removed from the containment environment via the coolant fluid, may function as a reservoir for radioactive materials included in the containment fluid. Additionally, containment fluid that includes a gas, such as water vapor (e.g., steam) may be condensed back into a liquid state by the coolant fluid in the coolant channel and/or reservoir, thereby mitigating pressure buildup in the nuclear plant containment and reducing or preventing the need to vent gases to an atmosphere external to the nuclear plant. The one or more check valve assemblies may include one or more check valves that are configured to actuate, between open and closed states, based on whether a pressure at an inlet of the one or more check valves reaches a threshold pressure. The one or more check valves may be configured to actuate open or closed (e.g., actuate to the open state or closed state) based on the pressure at the inlet and thus without any intervention by an operator (e.g., a human and/or processing circuitry) or control system to control the venting operation. Accordingly, the venting functionality provided by a check valve assembly may be understood to be “passive” at least by virtue of not operating based on operator or control system intervention. As a result, containment may be improved while also providing pressure release capability for the nuclear plant containment. It will be understood that the nuclear plant “containment” may encompass a structure that encompasses at least the containment environment, in which the nuclear reactor of the nuclear plant is located. It will be understood that “control system” intervention may refer to intervention by a control system that may include one or more instances of processing circuitry, for example a processor executing a program of instructions stored on a memory, where the intervention performed by the control system may include, without limitation, the control system generating an electrical signal, also referred to a control signal, that is communicated (e.g., transmitted) to a device to cause the device or another, separate device to perform an operation (e.g., actuate a valve, control a pump operation, etc.). The passive containment cooling system may further include one or more fusible plugs in fluid communication with the coolant reservoir and with the containment environment (e.g., based on the fusible plug(s) extending through the containment structure that at least partially defines the containment environment and into the coolant channel or other pathway) to the coolant reservoir at a depth that is below a lowest depth below the coolant reservoir at which the one or more check valve assemblies are located, such that a hydrostatic pressure of the coolant fluid in the coolant channel or other pathway to the coolant reservoir at the depth of the fusible plug in the coolant channel or other pathway to the coolant reservoir is greater than the greatest hydrostatic pressure of the coolant fluid in the coolant channel or other pathway to the coolant reservoir at the one or more check valve assembly outlet. The one or more fusible plugs, which may be any well-known fusible plug, may be configured (e.g., based on including a particular fusible alloy) to at least partially melt in response to a temperature in the containment environment at a portion of the fusible plug that is open to the containment environment at least meeting a threshold temperature (e.g., a melting temperature of the particular fusible alloy), such that the fusible plug at least partially melts to expose a flow conduit extending between the coolant reservoir and the containment environment via the fusible plug. As a result, at least some of the coolant fluid in the coolant channel or other pathway to the coolant reservoir may at least partially flood the containment environment, thereby providing temperature control in the containment environment and aid in limiting nuclear reactor temperature. Additionally, the one or more first check valve assemblies may be configured to selectively actuate to ensure that the pressure in the containment environment at the fusible plug is less than the hydrostatic pressure of coolant fluid in the coolant channel or other pathway to the coolant reservoir at the depth of the fusible plug, thereby ensuring a pressure gradient from the coolant channel or other pathway to the coolant reservoir into the containment environment when the temperature in the containment environment at the fusible plug reaches the threshold temperature, thereby reducing or preventing the risk that coolant fluid may not flow into the containment environment when the fusible plug at least partially melts. The flooding of the containment environment may provide cooling of the nuclear reactor and/or the containment environment and/or cooling of materials in the containment environment, including radioactive materials including, but not limited to fuel containing material (FCM), lava-like fuel containing material (LFCM), “corium” as the term is well-known to be understood in the nuclear power industry with regard to nuclear reactors, any combination thereof, or the like. The passive containment cooling system may be configured, based on the one or more first check valve assemblies being configured to actuate (and selectively enable the one-way flow out of the containment environment) at a particular threshold pressure magnitude and the fusible plug being configured to at least partially melt at a particular threshold temperature, to ensure that the fusible plug melts after the one or more first check valve assemblies have enabled the one-way flow, thereby enabling a flow path of fluid (e.g., coolant fluid) into the containment environment from the coolant channel or other pathway to the coolant reservoir via the flow conduit exposed by the at least partially melted fusible plug, upwards through the containment environment to the one or more first check valve assemblies, and back into the coolant channel from the containment environment via the one or more first check valve assemblies, Based on providing a capability to at least partially flood the containment environment via at least partially melted fusible plugs, such flooding capability may be considered to be “passive” in that the capability may be implemented without (e.g., independently of) operator or control system intervention. Accordingly, cooling performance of the nuclear reactor in response to pressure and/or temperature excursions, and the containment of radioactive materials and the prevention of release of said materials from the nuclear plant, may be improved. It will be understood that, as described herein, a “check valve” may be interchangeably referred to as a non-return valve, a reflux valve, a retention valve, a one-way valve, or the like and will be understood to refer to a valve that is configured to allow fluid (e.g., liquid and/or gas) to flow through the valve in only one direction (e.g., selectively enabling one-way flow) based on selectively actuating between a closed position in which the one-way flow is inhibited and an open position in which the one-way flow is enabled. Check valves as described herein may include any type of check valve that is well-known with regard to selectively enabling one-way fluid flow, including, without limitation, swing check valves, tilting disc check valves, clapper valves, stop-check valves, lift-check valves, in-line check valves, pneumatic non-return valves, any combination thereof, or the like. It will be understood that, as described herein, a “fusible plug” may include any type of fusible plug that is configured to at least partially melt in response to at least a portion of the fusible plug being exposed to a temperature that reaches (e.g., is equal to or greater than) a threshold temperature. For example, a fusible plug as described herein may include a body cylinder (at least partially comprising a body material) that includes a conduit extending throughout the length of the metal cylinder along its longitudinal axis, between opposite ends of the fusible plug, and where the conduit is filled with a particular material (also referred to as a “fusible alloy”) that is configured to melt at a melting temperature that is less than the melting temperature of the body material of the body cylinder, such that the particular body material may partially or entirely melt when a temperature at least one end of the body cylinder reaches the melting temperature, such that the particular fusible alloy material may at least partially flow out of the conduit to expose the conduit through the body cylinder and between the opposite ends of the fusible plug. Fusible plugs as described herein may include any well-known fusible plugs, including, without limitation, fusible plugs having a body material that includes brass, bronze, steel, and/or gun metal, fusible plugs having a fusible alloy that includes tin, any combination thereof, or the like. The passive containment cooling system may include multiple coolant channels that are coupled to the coolant reservoir via separate, respective coolant supply conduits and coolant return conduits, and the passive containment cooling system may include one or more separate first check valve assemblies extending into separate, respective coolant conduits or other pathways to the coolant reservoir. Additionally, multiple check valve assemblies may extend into a given coolant channel or other pathway to the coolant reservoir, at a same or different heights or depths within the given coolant channel or other pathway to the coolant reservoir, and one or multiple fusible plugs may extend into a given coolant channel or other pathway to the coolant reservoir, and a same or different heights or depths within the given coolant channel or other pathway to the coolant reservoir. FIG. 1 is a cross-sectional schematic side view of a nuclear plant that includes a passive containment cooling system that further includes a containment venting system and a containment flooding system, according to some example embodiments. FIGS. 2A-2C are expanded views of region A of FIG. 1, according to some example embodiments. FIG. 3 is an expanded view of region A of FIG. 1, according to some example embodiments. FIG. 5 is an expanded view of region B of FIG. 1, according to some example embodiments. FIG. 6 is a perspective view of a passive containment cooling system that includes one or more coolant channels integrated into the containment structure, according to some example embodiments. Referring to FIG. 1, the nuclear plant 1 includes a reactor building structure 110 on a foundation 2 (which may be the ground, bedrock, a structural foundation, any combination thereof, or the like), and a nuclear reactor 100 within the reactor building structure 110. The nuclear reactor 100 is within a containment environment 192 that is surrounded by, and is at least partially defined by, a containment structure 140 that provides pressure retention of the containment environment 192. An inner surface 140i of the containment structure 140 may at least partially define the containment environment 192. The containment structure 140 may be a solid structure, comprised of one or more pieces of material coupled together, and may include metal and/or concrete material pieces. In some example embodiments, the containment structure 140 may be a steel-concrete composite (SC) structure, as the term is well-known. As shown in FIG. 1, the nuclear plant 1 includes a passive containment cooling system 200 that is configured to provide passive cooling and containment of the containment environment 192, and the containment fluid 197 included therein, and of the nuclear reactor 100 included therein. The passive containment cooling system 200 includes a coolant reservoir 120, one or more coolant supply conduits 150, one or more coolant channels 160 coupled to the containment structure 140, and one or more coolant return conduits 170. As shown, the passive containment cooling system 200 may include one or more check valve assemblies 180, but example embodiments are not limited thereto. The passive containment cooling system 200 is configured to provide passive cooling of the containment environment 192 based on inducing and/or maintaining a flow or circulation of coolant fluid 122, 124, 125, 126 between the coolant reservoir 120 and the one or more coolant channels 160 to absorb heat 102 rejected by the nuclear reactor 100 and remove the heat to the coolant reservoir 120. As shown in FIG. 1, the passive containment cooling system 200 may include multiple coolant channels 160 that are coupled to separate portions of the containment structure 140 and which are coupled to the coolant reservoir 120 via separate, respective coolant supply conduits 150 and separate, respective coolant return conduits 170, and where separate, respective check valve assemblies 180 extend into separate, respective coolant channels 160, or one or more other pathways to the coolant reservoir 120, and, if needed, through the containment structure 140 thickness 141 to the separate, respective coolant channels 160 or the one or more other pathways to the coolant reservoir 120, and where separate, respective fusible plugs 190 extend into the separate, respective coolant channels 160 or one or more other pathways to the coolant reservoir 120 and, if needed, through the containment structure 140 thickness 141 to the separate, respective coolant channels 160 or the one or more other pathways to the coolant reservoir 120. The following description is directed to a single coolant channel 160 and the respective conduits 150, 170 and check valve assemblies 180, 380 and fusible plugs 190 extended thereinto, but it will be understood that said description may apply to all of the coolant channels 160, conduits 150, 170, check valve assemblies 180, 380 (second check valve assembly 380 is shown in FIG. 3), and fusible plugs 190 of the passive containment cooling system 200. As shown in FIG. 1, the coolant reservoir 120 is located vertically above the nuclear reactor 100, such that a top of the nuclear reactor 100 is located at a vertical height H1, and the bottom 120b of the coolant reservoir 120 is at a vertical height H2, where H2 is greater than H1. Accordingly, any fluid held in the coolant reservoir 120 may flow downwards (e.g., flow downwards or “fall” in the direction of gravitational acceleration “g”) from the coolant reservoir 120 to a height of any portion of the nuclear reactor 100. All heights H1 to H6 as described herein will be understood to be heights measured from a single, fixed reference height H0. As illustrated in FIG. 1, the heights H1 to H6 are shown to be heights from a top surface of the foundation 2 at a height H0, such that the top surface of the foundation 2 provides the reference height H0 via which the heights H1 to H6 of other elements in the nuclear plant 1 may be described and compared. But, it will be understood that, in some example embodiments, the top surface of the foundation 2 may have a variable height, and the heights H1 to H6 described herein may be understood to be heights from a single, constant reference height H0 that may be different from the height of the top surface of the foundation 2 (e.g., a height of global mean sea level (MSL), as the term is well-known). As shown in FIG. 1, the coolant reservoir 120 is configured to hold (e.g., be filled with) a coolant fluid 122, such that the top surface 122t of the coolant fluid 122 in the coolant reservoir 120 is at a depth D122 above the height (H2) of the bottom 120b of the coolant reservoir 120. Accordingly, it will be understood that the hydrostatic pressure of the coolant fluid 122 at the bottom 120b of the coolant reservoir 120 is equal to a pressure head of coolant fluid 122 having a height equal to depth D122. As shown in FIG. 1, and as described further below, the coolant reservoir 120 may be considered to have an upper region 121a and a lower region 121b that is below the upper region 121a (e.g., proximate to the bottom 120b and distal to the top surface 122t in relation to the upper region 121a). Additionally, the coolant fluid 122 held in the coolant reservoir 120 may include coolant fluid 123a, that is defined as the portion of the coolant fluid 122 that is within the upper region 121a, and lower coolant fluid 123b, that is defined as the portion of the coolant fluid 122 that is within the lower region 121b. As shown in FIG. 1, a coolant supply conduit 150 is coupled to the coolant reservoir 120, such that an inlet 152 of the coolant supply conduit 150 is open to the lower region 121b of the coolant reservoir 120 (e.g., opens directly into the lower region 121b of the coolant reservoir 120) and the coolant supply conduit 150 extends downwards (e.g., in the direction of gravitational acceleration “g”) from the inlet 152, downwards from the bottom 120b of the coolant reservoir 120, to an outlet 154. As shown, the inlet 152 may be at a vertical height H3, and the outlet 154 may be at a vertical height H4, where H3 is greater than H4, H4 is less than H1, and where H3 is equal to or greater than H2. Accordingly, it will be understood that, based on extending downwards from the bottom 120b of the coolant reservoir 120, the coolant supply conduit 150 may be configured to direct at least some of the coolant fluid 122 in the coolant reservoir 120 (e.g., coolant fluid 123b in the lower region 121b) to flow, as coolant fluid 124, downwards (e.g., at least partially in the direction of gravitational acceleration “g”) from the coolant reservoir 120 and into the coolant supply conduit 150 via inlet 152, and to flow at least partially downwards (e.g., “fall”) through the coolant supply conduit 150 to the outlet 154, according to gravity (e.g., gravitational acceleration). Accordingly, it will be understood that a flow of coolant fluid 124 through the coolant supply conduit 150 may be induced and/or maintained according to gravity, and thus may be induced and/or maintained without operation of any active flow generators (e.g., pumps) and without (e.g., independently of) operator or control system intervention and thus the flow may be considered to be “passive.” As shown in FIG. 1, the inlet 152 of the coolant supply conduit 150 may be elevated above the bottom 120b of the coolant reservoir 120 by a spacing height H152. In FIG. 1, H152 is shown to be a positive value, such that the height H3 of the inlet 152 is greater than the height H2 of the bottom 120b of the coolant reservoir 120. But, it will be understood that, in some example embodiments, the inlet 152 may be at the same height as the bottom 120b of the coolant reservoir 120 (e.g., H2 may equal H3), such that height H152 may be a null value. Additionally, while FIG. 1 illustrates the bottom 120b of the coolant reservoir 120 as being a flat, horizontal surface (e.g., being perpendicular to the direction of gravitational acceleration “g”), it will be understood that example embodiments are not limited thereto, and in some example embodiments the height H3 of the bottom 120b may be understood to be a lowest height of the bottom 120b of the coolant reservoir 120. For example, in some example embodiments, the bottom 120b may be angled (e.g., have a truncated conical shape) where the inlet 152 is at the height of the lowest portion of the bottom 120b (e.g., H3=H2), so that coolant fluid 123b in the lowest portion of the coolant reservoir 120 may be drawn downwards, into the inlet 152 according to gravity. Still referring to FIG. 1, the nuclear plant 1 includes one or more coolant channels 160 that are coupled to the containment structure 140, such that each coolant channel 160 extends vertically along the containment structure 140, from a coolant channel inlet 162 at a bottom of the coolant channel 160 to a coolant channel outlet 164 at a top of the coolant channel 160. In FIG. 1, the coolant channels 160 are illustrated as conduits (e.g., pipes) coupled to the outer surface 140o of the containment structure 140 (which may be implemented via any well-known methods of joining conduits to separate structures. It will be understood that the coolant channels 160, in some example embodiments, may be coupled to the inner surface 140i of the containment structure 140 instead of the outer surface 140o, for example to satisfy one or more physical constraints). But, it will be understood that example embodiments of coolant channels 160 are not limited thereto. For example, turning to FIG. 6, in some example embodiments, a containment structure 140 may include a concentric arrangement of an inner cylindrical shell 642 and an outer cylindrical shell 644, where the inner surface 642i of the inner cylindrical shell at least partially defines the containment environment 192, and where the outer surface 642o of the inner cylindrical shell 642 and the inner surface 644i of the outer cylindrical shell collectively define an annular gap space 648 in which one or more coolant channels 160 may be defined, e.g., by surfaces 642o and 644i alone or in combination with additional structural surfaces. For example, in FIG. 6, one or more column structures 646 extend vertically through the annular gap space 648, and further extend completely between surfaces 642o and 644i, to azimuthally partition the annular gap space 648 into multiple, isolated coolant channels 160, where a given coolant supply conduit 150 and coolant return conduit 170 may be coupled to a particular coolant channel 160. The coolant channels 160 shown in FIG. 6, being defined by the structures 642, 644, 646 that at least partially comprise the containment structure 140, extend through the interior of the containment structure 140 and may be understood to be integrated into the containment structure 140. As shown in FIG. 1, the inlet 162 of a coolant channel 160 may be coupled to an outlet 154 of the coolant supply conduit 150, such that the inlet 162 is at a same height as the height of the outlet 154 of the coolant supply conduit 150: height H4. As further shown, the height H5 of the outlet 164 of the coolant channel 160 at the top of the coolant channel 160 may be less than the height H2 of the bottom 120b of the coolant reservoir 120, but example embodiments are not limited thereto and in some example embodiments the coolant channel 160 may extend vertically up and above the height of the bottom 120b of the coolant reservoir 120, such that H5 may be greater than H2. In some example embodiments, the coolant return conduit 170 as described herein may be incorporated into an upper portion of the coolant channel 160 that extends above the height H1 of the nuclear reactor 100 to the height H6 of the outlet 174. As shown in FIG. 1, coolant fluid 124 that is directed to fall through the coolant supply conduit 150 to the outlet 154 according to gravity may be directed into the bottom of a coolant channel 160, at height H4 via the inlet 162 that is coupled to the outlet 154. As shown, the coolant channel 160 is coupled to the containment structure 140 and thus is configured to receive heat 102 rejected by the nuclear reactor 100 and through the containment environment 192 via at least a portion of the containment structure 140. The coolant fluid 124 that is in the coolant channel 160 may absorb at least some of the heat 102 and thus may become a heated coolant fluid 125. The heated coolant fluid 125 within the coolant channel 160 may have a change in buoyancy (e.g., change in density) based on absorbing said heat 102, such that the buoyancy of the heated coolant fluid 125 is increased (and density is reduced) in relation to the colder coolant fluid 124 that is being directed into the bottom of the coolant channel 160 via the coolant supply conduit 150. As a result, the heated coolant fluid 125 may rise (e.g., flow upwards, at least partially in a direction that is opposite the direction of gravitational acceleration “g”), from the bottom of the coolant channel 160 at height H4 to the top of the coolant channel 160 at height H5, based on having said increased buoyancy (e.g., reduced density), while the heated coolant fluid 125 is displaced at the bottom of the coolant channel 160 by the colder (and thus less buoyant and denser), newly-supplied coolant fluid 124 via the coolant supply conduit 150. It will be understood that the upwards flow (e.g., rising) of the heated coolant fluid 125 in the coolant channel 160 may be considered to be a “passive” driving of coolant fluid flow, as the flow, being induced by absorbing heat rejected from the nuclear reactor 100, is not being driven by an active flow generator (e.g., a pump), and is not being driven due to operator intervention to specifically control coolant fluid flow. It will be considered that any operator intervention and/or device operation in the nuclear plant 1 that adjust the heat rejection 102 by the nuclear reactor 100, which may indirectly affect coolant fluid 125 flow due to heat 102 absorption, is not considered herein to be operator intervention and/or device operation in the nuclear plant 1 to control coolant fluid flow. Still referring to FIG. 1, a coolant return conduit 170 is coupled, at an inlet 172, to the outlet 164 of a coolant channel 160 at the top of the coolant channel 160 (e.g., at height H5) and extends upwards to an outlet 174 that is at a greater height H6. As further shown in FIG. 1, the outlet 174 is open to the upper region 121a of the coolant reservoir 120. FIG. 1 illustrates the coolant return conduit 170 as extending upwards through the bottom 120b of the coolant reservoir 120 to a height H174 above the bottom 120b, such that the outlet 174 is upwards facing, similarly to the inlet 152 of the coolant supply conduit 150. But, it will be understood that example embodiments are not limited thereto. For example, the coolant return conduit 170 may extend upwards to height H6 and may turn and extend through a sidewall 120s of the coolant reservoir 120 so that the outlet 174 faces sideways (e.g., perpendicular to the direction of gravitational acceleration “g”). As shown, heated coolant fluid 125 that rises to the top of the coolant channel 160, at height H5, may be directed through outlet 164, and thus through the coupled inlet 172, such that the coolant return conduit 170 may be configured to direct a flow of the heated coolant fluid 125 to rise out of the top of the coolant channel 160 via the coolant channel outlet 164, as coolant fluid 126, and into the coolant reservoir 120 via conduit 170 and outlet 174, according to the increased buoyancy of the hotter coolant fluid 126 (due to having absorbed heat 102 as heated coolant fluid 125) at the top of the coolant channel 160 (e.g., at height H5) over a buoyancy of the colder coolant fluid 124 at the bottom of the coolant channel 160. In some example embodiments, the coolant supply conduit 150 and/or coolant return conduit 170 may be partially or completely insulated so as to mitigate heat loss by the coolant fluid 126 which might affect the upwards, buoyancy-driven flow of coolant fluid 126 and/or the downwards, gravity and/or density-driven flow of coolant fluid 124. Referring back to the coolant reservoir 120, the coolant reservoir 120 may be considered to be vertically divided into an upper region 121a and a lower region 121b, where the interface between the upper and lower regions 121a and 121b may be any height between the height H174 of the coolant return conduit outlet 174 from the bottom 120b of the coolant reservoir 120 (at height H2) and the height H152 of the coolant supply conduit inlet 152 from the bottom 120b of the coolant reservoir 120 (at height H2). In some example embodiments, the height H121 of the interface between the upper and lower regions 121a and 121b is a height H121 that is equally vertically distant from (e.g., halfway between) height H152 and height H174. In some example embodiments, the height H121 of the interface between the upper and lower regions 121a and 121b is the height H174 of the outlet 174 in the coolant reservoir 120, such that all portions of the coolant reservoir between height H2 and H6 are the lower region 121b, and all portions of the coolant reservoir 120 at or above height H6 are the upper region 121a. As shown in FIG. 1, the coolant supply conduit inlet 152 is open to the lower region 121b of the coolant reservoir 120, and the coolant return conduit outlet 174 is open to the upper region 121a of the coolant reservoir 120. It will be understood that, due to warmer coolant fluid 122 having increased buoyancy over colder coolant fluid 122, the coolant fluid 123a in the upper region 121a of the coolant reservoir 120 may be warmer, and have increased buoyancy, over the coolant fluid 123b in the lower region 121b of the coolant reservoir 120. It will be understood that warmer coolant fluid 126 may have an increased buoyancy (e.g., reduced density) over colder coolant fluid 122 in the coolant reservoir 120, including the coolant fluid 123b in the lower region 121b of the coolant reservoir 120. Accordingly, warmer coolant fluid 126 may occupy the upper region 121a, becoming part of the warmer, more buoyant coolant fluid 123a, while colder coolant fluid 122 may occupy the lower region 121b as coolant fluid 123b. Thus, as shown in FIG. 1, colder coolant fluid 122 occupying the lower region 121b of the coolant reservoir 120 (e.g., coolant fluid 123b) may be drawn into the coolant supply conduit 150, according to gravity and having less buoyancy (e.g., greater density) than the warmer coolant fluid 123a, via the inlet 152 that is open to (e.g., located within) the lower region 121b. Accordingly, the passive containment cooling system may supply colder, higher-density coolant fluid 123b to the coolant channel 160 as coolant fluid 124, while warmer coolant fluid 126 may be caused to rise above the colder coolant fluid 123b, as coolant fluid 123a, and thus be isolated from being inadvertently drawn into the coolant supply conduit 150 via inlet 152, based on the increased buoyancy (e.g., reduced density) of the coolant fluid 126 over the colder coolant fluid 123b in the lower region 121b. Furthermore, as shown in FIG. 1, the coolant return conduit outlet 174, being vertically higher in the coolant reservoir 120 than the inlet 152 by a vertical distance of dH152, is open to (e.g., located within) the upper region 121a, such that warmer, lower-density coolant fluid 126 is supplied directly into the upper region 121a to mix with, and become part of, coolant fluid 123a without mixing with the colder coolant fluid 123b in the lower region 121b. The coolant fluid 126 may remain in the upper region 121a as part of coolant fluid 123a, and thus remain isolated from inlet 152, due to having the increased buoyancy due to being warmer than coolant fluid 123b. Over time, at least some of the coolant fluid 123a may cool and may circulate into the lower region 121b to become coolant fluid 123b and thus to eventually be drawn back into the coolant supply conduit 150. As further shown in FIG. 1, the nuclear plant 1 may include a heat removal system (e.g., heat exchanger 128, which may be any well-known heat exchanger device) that is configured to remove the heat 102 introduced into coolant reservoir 120 by the coolant fluid 126, to thereby mitigate or prevent the risk of the coolant fluid 122 warming up, and thus potentially degrading the ability of the passive containment cooling system 200 to remove heat 102 from the containment environment 192. However, it will be understood that the coolant reservoir 120 may, at least temporarily, serve as a heat sink that may absorb and retain the heat 102 that is removed into the coolant reservoir via the coolant fluid 126, for at least a period of time, without the heat 102 being removed from the coolant reservoir 120 via operation of any heat exchanger 128. Accordingly, the passive containment cooling system 200 may enable a passively-driven (e.g., driven by gravity via coolant supply conduit 150 and via absorbed heat via coolant channel 160 and coolant return conduit 170) circulation of coolant fluid 122, 124, 125, 126 between the coolant reservoir 120 and the coolant channel 160 to remove heat 102 from the containment environment 192. It will be understood that absorbing heat 102 that is rejected by the nuclear reactor 100 via the containment environment 192 and at least a portion of the containment structure 140, as performed by the coolant fluid 125, amounts to removing heat from the containment environment 192. It will be understood that the flow rate of the coolant fluid 124, 125, 126 may be at least partially driven by the rate of heat rejection 102 by the nuclear reactor 100. Accordingly, the rate of heat removal from the containment environment 192 and into the coolant reservoir 120 by the coolant fluid may be proportional to the coolant flow rate through conduits 150, 170, and coolant channel 160, and such flow rate may be driven by and proportional to the rate of heat rejection 102 by the nuclear reactor 100. Such variation of flow and heat removal by the passive containment cooling system 200 may be partially or entirely driven by the rate of heat rejection 102 by the nuclear reactor 100 and may be performed without (e.g., independently of) any operator intervention in the nuclear plant 1, even without any such intervention with regard to operation of the nuclear reactor 100. Accordingly, the passive containment cooling system 200 may enable regulation of the temperature and/or pressure of the containment environment 192, at least temporarily, without (e.g., independently of) any operator or control system intervention. Still referring to FIG. 1, and referring further to FIGS. 2A-2C, the passive containment cooling system 200 may include a first check valve assembly 180 at a position that is a vertical depth DB180 below a bottom 120b of the coolant reservoir 120 and thus at a vertical depth DT180 below a top surface 122t of coolant fluid 122 in the coolant reservoir 120, where the first check valve assembly 180 is in fluid communication with both the coolant reservoir 120 and with the containment environment 192. As shown in FIG. 1, the first check valve assembly 180 may extend through the thickness 141 of the containment structure 140 (e.g., between surfaces 140i and 140o) and into the coolant channel 160, so as to be in fluid communication with the coolant reservoir 120 via the coolant channel 160, but example embodiments are not limited thereto and the outlet 180o of the first check valve assembly 180 may be open to another, separate conduit (also referred to interchangeably herein as a “pathway”) other than any coolant channel 160 at vertical depth DB180/DT180, where the other, separate conduit is in fluid communication with the coolant reservoir 120 and thus establishes fluid communication between the first check valve assembly 180 and the coolant reservoir 120. It will be understood that the vertical depth DT180 is equal to a sum of the vertical depth DB180 and the coolant reservoir depth D122 of coolant fluid 122, from the bottom 120b to the top surface 122t, in the coolant reservoir 120. The first check valve assembly 180 may include one or more check valves 182 coupled between a first check valve assembly inlet 180i, via an inlet conduit 181i, and a check valve assembly outlet 180o, via an outlet conduit 181o. As shown, the first check valve assembly inlet 180i is open to the containment environment 192, and the first check valve assembly outlet 180o is in fluid communication with the coolant reservoir 120 at vertical depth DB180/DT180 (e.g., is open to the coolant channel 160 or any other conduit to the coolant reservoir 120 at the vertical depth DB180/DT180). In some example embodiments, the one or more check valves 182 are configured to actuate to open (e.g., actuate from a closed state to an open state), thereby establishing a continuous flow conduit 187 (also referred to herein as a fluid conduit) between the inlet 180i and the outlet 180o and thus enabling a one-way flow 198 of some or all fluids located in the containment environment 192, such fluids being referred to herein as a containment fluid 197, to the coolant reservoir 120 in response to a magnitude of the pressure at the inlets 182i of the one or more check valves 182 being equal to or greater than a first threshold magnitude (e.g., PX1). Such configuration may be based on the one or more check valves 182 being structurally configured (e.g., based on including a spring-loaded actuator) to open in response to the pressure at the inlet 182i of the one or more check valves 182 being equal to or greater than the first threshold magnitude PX1) As shown in FIG. 1 and FIGS. 2A-2C, the one or more check valves 182 may have an inlet 182i that is coupled, via an inlet conduit 181i, to the inlet 180i that is open to the containment environment 192, such that the pressure at the inlet 182i of the one or more check valves 182 may be the same as (e.g., equal to) the pressure P192-1 of the containment environment at the inlet 180i of the first check valve assembly 180. Thus, the one or more check valves may be configured to open in response to the pressure P192-1 reaching (e.g., being equal to or greater than) the first threshold magnitude PX1. The first threshold magnitude PX1 may at least partially correspond to a hydrostatic pressure P180 of the coolant fluid 125 in the coolant channel 160 or other similar pathway to the coolant reservoir 120 at the first check valve assembly outlet 180o at the vertical depth DB180/DT180. It will be understood that the hydrostatic pressure P180 may be equal to a pressure head of the coolant fluid 122, 124, 125, and/or 126 having a height equal to the vertical depth DT180. In some example embodiments, the coolant reservoir 120 may be configured to be filled with coolant fluid 122 to a reservoir depth D122 such that the top surface 122t of the coolant fluid 122 in the coolant reservoir 120 is at a particular depth D122 above the bottom 120b of the coolant reservoir 120 throughout operation of the nuclear plant 1. In some example embodiments, the first reservoir depth D122 may vary based on the variation in amount of coolant fluid 122 in the coolant reservoir 120. In some example embodiments, a reference hydrostatic pressure P180 may be a hydrostatic pressure P180 that results from the coolant reservoir 120 being filled to a particular, reference depth D122, such that the reference hydrostatic pressure P180 may be equal to a pressure head of the coolant fluid 122, 124, 125, and/or 126 having a height equal to the vertical depth DT180 when the coolant reservoir 120 is filled with coolant fluid 122 to the particular reference depth D122. The one or more check valves 182 may be configured to actuate to the open state in response to the magnitude of the pressure at the one or more inlets 182i (and thus, for at least one of the check valves 182, the pressure P192-1 of the containment environment at the inlet 180i) reaching (e.g., being equal to or greater than) a first threshold magnitude PX1 that is at least greater than the reference hydrostatic pressure P180, such that, when the coolant reservoir 120 is filled to the particular reference depth D122, a pressure gradient is present across the one or more check valves 1182 when the magnitude of the pressure P192-1 reaches the first threshold magnitude PX1. It will be understood that, due to variation at any given time in the depth D122 to which the coolant reservoir 120 may be filled with coolant fluid 122, the first threshold magnitude PX1 may be set to be a magnitude that is at least a particular margin (e.g., 5% greater, 10% greater, 20% greater, a particular additional amount of pressure, any combination thereof, or the like) greater than the reference hydrostatic pressure P180 (e.g., the hydrostatic pressure P180 at the outlet 180o when the coolant reservoir 120 is filled to the particular reference depth D122), to improve the likelihood that the actual hydrostatic pressure P180 will be less than the first threshold magnitude PX1 at the inlets 182i of the one or more check valves 182 when the magnitude of the pressure P192-1 reaches the first threshold pressure PX1, thereby ensuring that a pressure gradient is present across the first check valve assembly 180 from the inlet 180i to the outlet 180o. It will be understood that, because the inlet 180i of the first check valve assembly 180 is at the same vertical depths DB180/DT180 as the rest of the first check valve assembly 180, the pressure P192-1 of the containment environment 192 at the inlet 180i may be understood to be a pressure P192-1 of the containment environment 192 at the vertical depth DB180/DT180. The one or more check valves 182 may be configured to selectively (e.g., reversibly) actuate based on whether a pressure at the inlet 182i of the one or more check valves 182 is equal to or greater than the first threshold magnitude PX1. Accordingly, the first check valve assembly 180 may be configured to selectively open a flow conduit 187 to selectively enable one-way flow 198 of a containment fluid 197, from the containment environment 192 to the coolant reservoir 120 via the first check valve assembly 180 and one or more coolant channels 160, or other pathway to the coolant reservoir 120, to which the outlet 180o is open, based on the one or more check valves 182 actuating to open (e.g., opening) in response to a pressure P192-1 of the containment environment 192 at the first check valve assembly inlet 180i at the vertical depth DB180/DT180 being equal to or greater than the first threshold magnitude PX1. The one-way direction of the one-way flow 198 may be ensured, thereby preventing backflow through the first check valve assembly 180 from the coolant channel 160 or other pathway into the containment environment 192, based on the first check valve assembly 180 defining the flow conduit 187 from inlet 180i to outlet 180o to extend through the one or more check valves 182, where the one or more check valves 182 are configured to enable one-way flow in the direction from inlet 180i to outlet 180o, and the one or more check valves 182 each being configured to open in response to the pressure at the inlet 182i of the check valve 182 at least reaching the first threshold pressure PX1 that is greater than a reference hydrostatic pressure P180 of the coolant fluid 125 at the outlet 180o at the vertical depth DB180/DT180 (e.g., a hydrostatic pressure of coolant fluid 125 that is equal to a pressure head of the coolant fluid at a height equal to depth DT180). In some example embodiments, the one or more check valves 182 may subsequently close, once pressure P192-1 drops below the first threshold magnitude PX1. Accordingly, the one-way flow of containment fluid 197 may be selectively enabled and inhibited to regulate the pressure within the containment environment. The selective enabling of one-way flow 198 of containment fluid 197 may be referred to herein as “venting” of the containment fluid 197, for example to regulate the pressure (e.g., P192-1) in the containment environment 192 and thus to mitigate or prevent the risk of overpressure of the containment structure 140. Operation (e.g., actuation) of the one or more check valves 182 of the first check valve assembly 180 may occur without (e.g., independently of) any operator intervention. Accordingly, the pressure relief, or “venting” functionality provided by the first check valve assembly 180 may be understood to be “passive.” In some example embodiments, where the outlet 180o of the first check valve assembly 180 is open to a coolant channel 160 at vertical depth DB180/DT180, the containment fluid 197, which may include radioactive material, solids, gasses, liquids, any combination thereof, or the like, may be entrained in the rising flow of the heated coolant fluid 125 through the coolant channel 160 and may be thus drawn into the coolant reservoir 120 with the coolant fluid 126. Similarly, where the outlet 180o is open to another pathway to the coolant reservoir 120, the containment fluid 197 may pass from the first check valve assembly 180 to the reservoir 120 via the other pathway. The coolant fluid 125, 126, 122 may quench some gases in the containment fluid 197 (e.g., steam) to thereby reduce the pressure in the coolant reservoir 120, and other parts of the containment fluid 197 may be retained in the coolant reservoir 120, at least temporarily, to reduce or prevent venting or escape of containment fluid 197 to the ambient environment external to the nuclear plant 1. Accordingly, the first check valve assembly 180 may enable improved passive containment of containment fluid while enabling passive regulation of pressure in the containment environment 192. While FIG. 1 illustrates one or more first check valve assemblies 180 extending into one or more coolant channels 160, it will be understood that example embodiments are not limited thereto. For example, one or more first check valve assemblies 180 of the passive containment cooling system 200 may, instead of extending into a coolant channel 160, be routed to the coolant reservoir 120 via one or more other, separate conduits, which may also be referred to as pathways, parallel pathways, or the like, into which the one or more first check valve assemblies 180 may extend. For example, a first check valve assembly 180 may extend, from the containment environment 192, into a separate conduit, also referred to as a separate pathway or parallel pathway (not shown in FIG. 1) that may extend to the coolant reservoir 120 independently of the one or more coolant channels 160. Accordingly, in some example embodiments, one or more first check valve assemblies 180 may be configured to enable “venting” of one or more one-way flows 198 of containment fluid 197 to the coolant reservoir 120 independently of (e.g., in parallel with) the one or more coolant channels 160, thereby enabling the coolant reservoir 120 to retain at least some of the material of the coolant fluid 197, independently of the one or more coolant channel 160. Referring now, generally, to FIGS. 2A-2C, the first check valve assembly 180 may include one or more various configurations of one or more check valves 182 shown therein, although example embodiments are not limited thereto. As shown in FIG. 2A, the first check valve assembly 180 may include a single check valve 182 having an inlet 182i that is that is coupled to the first check valve assembly inlet 180i via inlet conduit 181i, and thus inlet 182i is open to inlet 180i, and an outlet 182o that is coupled to the first check valve assembly outlet 180o via outlet conduit 181o, and thus outlet 182o is open to outlet 180o. Thus, in some example embodiments, a pressure P192-1 at the inlet 180i may be the pressure at the inlet 182i of the single check valve 182 of the first check valve assembly 180, and the check valve 182 may be configured to actuate from the closed state to the open state in response to the pressure at the inlet 182i reaching a first threshold magnitude PX1. Thus, the check valve 182 may actuate to open in response to the pressure P192-1 at the inlet 180i reaching the first threshold magnitude PX1, to thereby cause the first check valve assembly 180 to selectively establish an open flow conduit 187 between inlet 180i and outlet 180o via the check valve 182 and conduits 181i and 181o, and thus selectively enable the one-way flow 198 of containment fluid 197, based on the pressure P192-1 reaching the first threshold magnitude PX1. Referring to FIG. 2B, in some example embodiments, the one or more check valves 182 may include a series connection of a plurality of check valves 182-1 to 182-i (e.g., a series connection of “i” check valves, where “i” is a positive integer having a value equal to or greater than 2) between the first check valve assembly inlet 180i and the first check valve assembly outlet 180o. As shown in FIG. 2B, the outlets 182o of check valves 182-1 to 182-(i-1) may be coupled to the adjacent inlets 182i of adjacent check valves in the series connection via intermediate conduits 183-1 to 183-(i-1). Each check valve 182 of the plurality of check valves 182-1 to 182-i may be configured to actuate to open in response to a pressure at an inlet 182i of the each check valve 182 being equal to or greater than the first threshold magnitude PX1. Similarly to FIG. 2A, the inlet 182i of the first check valve 182-1 in the series connection may be coupled to, and open to, the inlet 180i via inlet conduit 181i, and the outlet 182o of the last check valve 181-i in the series connection may be coupled to, and open to, the outlet 180o via outlet conduit 181o. Accordingly, when the pressure P192-1 at inlet 180i, reaches the first threshold magnitude PX1, the first check valve 182-1 may actuate to open, as the pressure at the inlet 182i of the first check valve 182-1 may be the same as the pressure at inlet 180i, and then the next check valves 182-2 to 182-i in the series connection may actuate to open in succession in response to each preceding check valves 182 in the series connection opening and establishing fluid communication between the inlet 182i of the succeeding check valve 182 in the series connection with inlet 180i, until all check valves 182-1 to 182-i are opened and the flow conduit 187 between inlet 180i and outlet 180o via check valves 182-1 to 182-i is established. Thus, the first check valve assembly 180 may selectively enable the one-way flow 198 of containment fluid 197 based on all check valves 182 of the series connection of the plurality of check valves opening 182-1 to 182-i selectively actuating to open. Additionally, the one-way flow 198 may be inhibited in response to any of the check valves 182-1 to 182-i being closed. Thus, if the pressure P192-1 subsequently drops below the first threshold magnitude PX1 after initially reaching the first threshold magnitude PX1, the series connection of check valves 182-1 to 182-i may reduce the risk that the flow conduit 187 between inlet 180i and outlet 180o might remain open, as the closure of any one of the check valves 182-1 to 182-i would close the flow conduit 187 and inhibit the one-way flow 198. Thus, the series connection shown in FIG. 2B may reduce the risk of inadvertent backflow from the coolant channel 160 or other pathway to which the outlet 180o is open and into the containment environment 192 via the first check valve assembly 180, thereby improving reliability of the passive containment cooling system 200. Referring to FIG. 2C, in some example embodiments, the one or more check valves 182 may include a parallel connection of a plurality of check valves 182-1,1 to 182-i,j between inlet 180i and one or more outlets 180o-1 to 1800-j (e.g., a parallel connection of “j” sets of series connections of “i” check valves with at least inlet 180i, where “j” is a positive integer that is equal to or greater than 1 and “i” is a positive integer that is equal to or greater than 1). As shown in FIG. 2C, the inlets 182i of check valves 182-1,1 to 182-1,j may be coupled in parallel to the inlet 180i via inlet conduit 181i and separate, respective inlet branch conduits 281-1 to 281-j. As further shown, each separate branch (1 to j) of one or more (e.g., “i”) check valves 182 may be coupled in series between inlet 180i and a separate outlet 180o-1 to 180o j, similarly to the series connection of check valves 182-1 to 182-i as described with reference to FIG. 2B. But, example embodiments are not limited thereto, and in some example embodiments, two or more branches 1 to j of check valves 182 may be coupled in parallel between a single inlet 180i and a single outlet 180o, via one or more branch inlet conduits 281-1 to 281-j and one or more branch outlet conduits 282-1 to 282-j. Each check valve 182 of the plurality of check valves 182-1,1 to 182-i,j may be configured to open in response to a pressure at an inlet 182i of the each check valve 182 being equal to or greater than the first threshold magnitude PX1. Accordingly, when the pressure P192-1 at inlet 180i reaches the first threshold magnitude PX1, each of the check valves 182-1,1 to 182-i,j may open, as the pressure at the inlet 182i of each check valve 182-1,1 to 182-1,j may be the same as the pressure at inlet 180i and each series connection of one to i check valves in each parallel branch of check valves 182 may actuate in succession as described above with reference to FIG. 2B, thereby establishing multiple, parallel fluid conduits 187-1 to 187-j between inlet 180i and one or more outlets 180o-1 to 180-j. Thus, the first check valve assembly 180 may selectively enable the one-way flow 198 of containment fluid 197 based on any set of one or more check valves of the parallel connection of sets of one or more check valves 182-1,1 to 182-i,j actuating to open. Where “i” equals 1, such that the first check valve assembly 180 includes a parallel connection of check valves 182-1 to 182-j, the first check valve assembly 180 may selectively enable the one-way flow 198 of containment fluid 197 based on any check valve 182 of the parallel connection of check valves 182-1 to 182-j actuating to open Accordingly, in some example embodiments, the one-way flow 198 may be ensured, even if one or more of the check valves 182-1 to 182-j do not open, so long as at least one (e.g., any) of the check valves 182-1 to 182-j open. Still referring to FIGS. 2A-2C, in some example embodiments a check valve assembly includes a burst disc 186 coupled between the inlet 182i of the one or more check valves 182 and the inlet 180i of the first check valve assembly 180. For example, as shown in FIGS. 2A-2C, the burst disc 186 may be coupled in series with the one or more check valves 182 of the first check valve assembly 180. The burst disc 186, also known as a pressure safety disc, rupture disk, bursting disc, burst diaphragm, or the like, may be any well-known type of burst disc used to provide a non-reclosing pressure relief flow control (e.g., pressure relief) device. In some example embodiments, the burst disc 186 is configured to rupture in response to a pressure at the inlet side 186i of the burst disc 186 reaching the first threshold pressure PX1, or any other particular pressure threshold magnitude (e.g., a particular, or, alternatively, pre-determined “set point” threshold). Because the burst disc 186 may be between the inlet 182i of the first check valve 182 of the one or more check valves 182 as shown in FIGS. 2A to 2C, the inlet side 186i of the burst disc 186 is in open fluid communication with (e.g., open to) inlet 180i, such that the pressure P192-1 at inlet 180i is also the pressure at the inlet side 186i of the burst disc 186, and thus the burst disc 186 is configured to rupture if the pressure P192-1 reaches the first threshold magnitude PX1, or any other particular pressure threshold magnitude, to cause the pressure at the inlet 182i of one or more check valves 182 to reach the pressure P192-1 at inlet 180i, and thus the one or more check valves 182 may actuate to the open state to enable one-way flow 198 of the containment fluid 197 therethrough in response to the pressure P192-1 reaching the first threshold magnitude PX1. The burst disc 186 may provide an additional level of reliability to the first check valve assembly 180 based on preventing premature establishment of the flow conduit 187 through the first check valve assembly 180 if pressure P192-1 has not reached the first threshold magnitude PX1 at least once. Referring back to FIG. 1, while the passive containment cooling system 200 is shown as including one first check valve assembly 180 extending into each separate coolant channel 160 of the passive containment cooling system 200, it will be understood that, in some example embodiments, the passive containment cooling system 200 may include multiple first check valve assemblies 180 that each extend from the containment environment 192, through the thickness 141 of the containment structure 140, into the same coolant channel 160, at a same or different depths below the bottom 120b of the coolant reservoir 120 within the coolant channel 160. Referring now to FIG. 3, in some example embodiments, the passive containment cooling system 200 may include, in addition to the first check valve assembly 180, one or more additional, or second check valve assemblies 380 at a position that is a vertical depth DB380 below a bottom 120b of the coolant reservoir 120 and thus at a vertical depth DT380 below a top surface 122t of coolant fluid 122 in the coolant reservoir 120, where the one or more second check valve assemblies 380 is in fluid communication with both the coolant reservoir 120 and with the containment environment 192. As shown in FIG. 3, a second check valve assembly 380 may extend through the thickness 141 of the containment structure 240 and into the coolant channel 160 at a vertical depth DB380 below a bottom 120b of the coolant reservoir 120, and thus at a vertical depth DT380 below the top surface 122t of the coolant fluid 122 within the coolant reservoir 120, but example embodiments are not limited thereto and the outlet 380o of the second check valve assembly 380 may be open to another, separate conduit other than any coolant channel 160 at vertical depth DB380/DT380, where the other, separate conduit is in fluid communication with the coolant reservoir 120 and thus establishes fluid communication between the second check valve assembly 380 and the coolant reservoir 120. It will be understood that the vertical depth DT380 is equal to a sum of the vertical depth DB380 and the coolant reservoir depth D122 of coolant fluid 122, from the bottom 120b to the top surface 122t, in the coolant reservoir 120. As shown, the vertical depth DB380 may be less than the vertical depth DB180. For example, where the first and second check valve assemblies 180 and 380 both extend through the containment structure 140 to coolant channel 160 the one or more second check valve assemblies 380 may be located vertically higher in the coolant channel 160, and thus closer to the coolant reservoir 120, than the first check valve assembly 180. In some example embodiments, the second check valve assembly 380 includes an inlet conduit 381i that is open to the containment environment 192 via inlet 380i, and outlet conduit 381o that is in fluid communication with the coolant reservoir 120 at vertical depth DB380/DT380 (e.g., is open to the coolant channel 160 or any other conduit to the coolant reservoir 120 at depth DB380/DT380), and one or more check valves 382 coupled between the inlet conduit 381i and the outlet conduit 381o. It will be understood that the configuration of conduits and check valves 382 in the second check valve assembly 380 may be any of the configurations that the first check valve assembly 180 may have, including any of the configurations shown in any of FIGS. 2A-2C, such that the second check valve assembly 380 may include any series connection and/or parallel connection of check valves 382 that may be included in the first check valve assembly 180, and the configuration of check valves 382 in the second check valve assembly 380 may be the same as, or different than, the configuration of check valves 182 in the first check valve assembly 180. Similarly to the first check valve assembly 180, the second check valve assembly 380 is configured to selectively open a flow conduit 387, and thus selectively enable one-way flow 398 of the containment fluid 197, to the coolant reservoir from the containment environment 192, based on the one or more check valves 382 of the second check valve assembly 380 actuating to open in response to a pressure at the inlet(s) 382i of the one or more check valves 382, and thus the pressure P192-3 of the containment environment 192 at the second check valve assembly inlet 380i, and thus the pressure P192-3 in the containment environment 192 at vertical depth DB380/DT380 (where pressure P192-3 may be the same as or different than the pressure P192-1 at any given time) being equal to or greater than (e.g., reaching) a second threshold magnitude PX2. The second threshold magnitude PX2 may be different than the first threshold magnitude PX1. The second threshold magnitude PX2 may at least partially correspond to a hydrostatic pressure P380 of the coolant fluid 125 in the coolant channel 160 at the outlet 380o of the second check valve assembly. Restated, the second threshold magnitude PX2 may at least partially correspond to the hydrostatic pressure P380 of the coolant fluid 125 at depth DT380 below the top surface 122t of the coolant fluid 122 in the coolant reservoir 120, and thus may correspond to (e.g., equal to or be greater than by a particular proportional margin and/or margin magnitude) the pressure head of coolant fluid 122 at depth DT380 of coolant fluid. Similarly to the first threshold magnitude PX1, in some example embodiments the second threshold magnitude PX2 may correspond to (e.g., match or exceed by a particular margin proportion or magnitude) a reference hydrostatic pressure P380 at depth DT380 that results from the coolant reservoir 120 being filled with coolant fluid to the particular reference depth D122. It will be understood that the one or more check valves 382 of the second check valve assembly 380 may operate in the same manner described herein with reference to the one or more check valves 182 of the first check valve assembly 180 and thus may be configured to provide passive venting of the containment environment 192. Because the second check valve assembly 380 is spaced vertically above the first check valve assembly 180 in the passive containment cooling system 200 by a vertical spacing distance dH380, and because in some example embodiments pressures P192-3 and P192-1 may be the same magnitude at the same time (e.g., when the containment environment 192 is filled with gas at least between depths DB180/DT180 and DB380/DT380), the one or more check valves 382 of the second check valve assembly 380 may actuate to open and selectively enable one-way flow 398 from the containment environment 192 to the coolant channel 160 via the second check valve assembly 380 when pressure P192-3/P192-1 is equal to a second threshold magnitude PX2 that is greater than the hydrostatic pressure P380 at depth DT380 but is less than the hydrostatic pressure P180 at depth DT180. The one or more check valves 182 of the first check valve assembly 180 may subsequently actuate to open to selectively enable one-way flow 198 in response to pressure P192-3/P192-1 subsequently increasing from the second threshold magnitude PX2 to the first threshold magnitude PX1. It will be understood that the first and second check valve assemblies 180 and 380 may independently actuate to independently selectively enable or inhibit respective one-way flows 198 and 398 of containment fluid 197, and thus the “venting” of containment fluid 197 provided by the passive containment cooling system 200 may be provided at an incremental rate that is proportional to the pressure in the containment environment 192, as more flow conduits 387, 187 may be established by more check valve assemblies 380, 180 as the pressure within the containment environment 192 rises. The quantity of open flow conduits 187, 387 may be increased or reduced as the pressure within the containment environment 192 rises or falls, respectively, and such proportional and independent opening and closing of flow conduits may be implemented without (e.g., independently of) any operator intervention and thus may be understood to be a passive proportional venting capability provided by the passive containment cooling system 200. While FIG. 3 illustrates only a single second check valve assembly 380, it will be understood that the passive containment cooling system 200 may include any quantity of second check valve assemblies 380 that may be located at same or different vertical heights in the coolant channel 160 and may have separate, respective threshold pressures PX based on the respective depths of the respective second check valve assemblies below the bottom 120b of the coolant reservoir 120. It will be understood that in some example embodiments the passive containment cooling system 200 may not include any second check valve assemblies 380. While FIG. 3 illustrates a second check valve assembly 380 extending into a coolant channel 160, it will be understood that example embodiments are not limited thereto. For example, a second check valve assembly 380 of the passive containment cooling system 200 may, instead of extending into a coolant channel 160, be routed to the coolant reservoir 120 via one or more other, separate conduits, also referred to as separate pathways or parallel pathways, into which the one or more second check valve assemblies 380 may extend. For example, a second check valve assembly 380 may extend, from the containment environment 192, into a separate conduit, also referred to as a separate pathway or parallel pathway, (not shown in FIG. 1 or 3) that may extend to the coolant reservoir 120 independently of the one or more coolant channels 160. Accordingly, in some example embodiments, one or more second check valve assemblies 380 may be configured to enable “venting” of one or more one-way flows 398 of containment fluid 197 to the coolant reservoir 120 independently of the one or more coolant channels 160, thereby enabling the coolant reservoir 120 to retain at least some of the material of the coolant fluid 197, independently of the one or more coolant channel 160. In some example embodiments, a first check valve assembly 180 may extend into a coolant channel 160 while a second check valve assembly 380 extends into a separate conduit that extends to the coolant reservoir 120 independently of the coolant channel 160 into which the first check valve assembly 180 extends, or any other coolant channel 160. In some example embodiments, a second check valve assembly 380 may extend into a coolant channel 160 while a first check valve assembly 180 extends into a separate conduit that extends to the coolant reservoir 120 independently of the coolant channel 160 into which the second check valve assembly 380 extends, or any other coolant channel 160. It will be understood that, in some example embodiments, the first check valve assembly 180 may be absent from some or all of the coolant channels 160. In some example embodiments, the passive containment cooling system 200 may not include any first check valve assemblies 180. Still referring to FIG. 1, and further referring to FIG. 5, the passive containment cooling system 200 may include a fusible plug 190 at a bottom vertical depth DB190 below a bottom 120b of the coolant reservoir 120, and thus a depth DT190 below the top surface 122t of the coolant fluid 122 in the coolant reservoir 120, where the fusible plug 190 is in fluid communication with the coolant reservoir 120 and with the containment environment 192. For example, as shown in FIG. 5, the fusible plug 190 may extend, between opposite ends 190i, 190o, through the thickness 141 of the containment structure 140 and into the coolant channel 160 at a bottom vertical depth DB190 below a bottom 120b of the coolant reservoir 120, and thus a depth DT190 below the top surface 122t of the coolant fluid 122 in the coolant reservoir 120, but example embodiments are not limited thereto. For example, the end 190o of the fusible plug 190 may be open to another, separate conduit other than any coolant channel 160 at vertical depth DB190/DT190, where the other, separate conduit is in fluid communication with the coolant reservoir 120 and thus establishes fluid communication between the fusible plug 190 and the coolant reservoir 120. It will be understood that the vertical depth DT190 is equal to a sum of the vertical depth DB190 and the coolant reservoir depth D122 of coolant fluid 122, from the bottom 120b to the top surface 122t, in the coolant reservoir 120. The bottom vertical depth DB190/DT190 may be greater than the first vertical depth DB180/DT180 by a distance dH192, as shown in FIG. 1, such that a hydrostatic pressure P190 of the coolant fluid 124/125 in the coolant channel 160 at the bottom vertical depth DB190/DT190 (which may be a hydrostatic pressure P190 that corresponds to the pressure head of coolant fluid of depth DT190 of coolant fluid) is greater than the hydrostatic pressure P180 of the coolant fluid 125 in the coolant channel 160 at the first check valve assembly outlet 180o (e.g., hydrostatic pressure P180 that corresponds to the pressure head of depth DT180 of coolant fluid). In some example embodiments, the fusible plug 190 is configured to at least partially melt in response to a temperature T192 in the containment environment 192 at the fusible plug 190 (e.g., at the end 190i of the fusible plug 190 that is open to the containment environment 192) at least meeting a threshold temperature TX, such that the fusible plug 190 exposes a flow conduit 195 extending, between opposite ends 190o and 190i, between the coolant channel 160 or other pathway to the coolant reservoir 120 at the bottom vertical depth DB190/DT190 into the containment environment 192 to at least partially flood the containment environment 192 with at least some of the coolant fluid 124, 125. As shown in FIGS. 1 and 5, the fusible plug 190 may be positioned at the bottom of the coolant channel 160, e.g., at height H4, such that the coolant fluid 124 that passes over the end 190o of the fusible plug 190 that is open to the coolant channel 160, and thus would be the coolant fluid that would flood the containment environment 192 in response to the fusible plug 190 at least partially melting, would be the colder, coolant fluid 124 and would thus provide improved cooling within the containment environment 192. The fusible plug 190 may be any well-known type of fusible plug, including a fusible plug that includes a cylindrical body 191 (e.g., comprising brass, steel, etc.) extending through the thickness 141 of the containment structure 140 and having an inner surface 191i defining an inner cylindrical conduit 195 (also referred to herein as a flow conduit, a fluid conduit, or the like) that is filled with a fusible alloy 193 (e.g., tin) that is configured to melt in response to a temperature T192 at the end 190i of the fusible plug 190 reaching a threshold temperature TX (e.g., the melting point of the fusible alloy 193) such that the fusible alloy 193 may at least partially melt to open (e.g., expose) the cylindrical conduit 195 extending through the cylindrical body 191 and thus to establish a flow conduit through the fusible plug 190, via the exposed conduit 195, and thus to enable coolant fluid 124 to flow through the conduit 195 and into the containment environment 192. Once introduced into the containment environment 192, the flooding coolant fluid 124 may provide cooling of the containment environment 192 and/or nuclear reactor 100, containment, cooling, and control of radioactive materials in the containment environment (e.g., FCM, LFCM, corium, any combination thereof, o the like), reduce pressure in the containment environment 192 (e.g., via cooling and condensing steam in the containment environment 192), any combination thereof, or the like. In some example embodiments, the first check valve assembly 180 is configured to, based on the one or more check valves 182 selectively opening in response to the pressure P192-1 in the containment environment 192 at the first check valve assembly inlet 180i being equal to or greater than the first threshold magnitude PX1, maintain a pressure P192-2 in the containment environment 192 at the bottom vertical depth DB190/DT190 at a magnitude that is less than the hydrostatic pressure P190 of the coolant fluid 124 in the coolant channel 160 at the bottom vertical depth (e.g., DB190, and thus DT190), to enable flow of coolant fluid 124 through the exposed conduit 195 of the fusible plug 190 and into the containment environment 192 in response to the fusible plug 190 at least partially melting. For example, the first check valve assembly 180 may be vertically spaced apart from the fusible plug 190 by a vertical distance dH192, and the one or more check valves 182 may be configured to actuate to an open state in response to the pressure at the inlets 182i of the one or more check valves 182 reaching a threshold pressure PX1 that is less than the hydrostatic pressure P190 in the coolant channel 160 at the depth DB190/DT190 such that 1) the one or more check valves 182 open before the pressure P192-2 reaches the magnitude of the hydrostatic pressure P190, thereby ensuring that P192-2 does not reach the magnitude of hydrostatic pressure P190 and thus a pressure gradient from the coolant channel 160 to the containment environment 192 through the fusible plug 190 is ensured (thereby mitigating or preventing backflow out of the containment environment 192 through the fusible plug 190, and 2) a pressure gradient is present from depths DB190/DT190 to DB180/DT180 within the containment environment 192 when the fusible plug 190 at least partially melts (after the one or more check valves 182 have opened), so that a flow of fluid through the containment environment 192 proceeds from the fusible plug 190 to the first check valve assembly inlet 180i. It will be understood that, in some example embodiments, pressure P192-2 in the containment environment 192 at depth DB190/DT190 may be the same as, or different than, pressure P192-1 at the inlet 180i of the first check valve assembly 180. In some example embodiments, the first check valve assembly 180 is configured to selectively enable the one-way flow 198, based on the one or more check valves 182 actuating to open, in response to pressure P192-1 reaching a threshold magnitude PX1 that is lower than a pressure magnitude that corresponds to the temperature T192 at end 190i of the fusible plug 190 reaching the threshold temperature magnitude TX. For example, the fusible plug 190 may be configured to at least partially melt when temperature T192, at pressure P192-2, is a particular threshold temperature TX, and the temperature T192 may correspond to the magnitude of pressure P192-2, and the one or more check valves 182 may be configured to actuate to open in response to an inlet-side pressure (e.g., pressure at inlet 182i) being at a firs threshold magnitude PX1 that is less than the pressure that corresponds to temperature T192 being the threshold temperature TX. Accordingly, the first check valve assembly 180 may be configured to ensure that the one or more check valves 182 are open, and thus the flow conduit 187 is open and one-way flow 198 is enabled, when the temperature T192 reaches the threshold temperature TX and the fusible plug begins to at least partially melt, such that venting is ensured to be ongoing when the fusible plug 190 at least partially melts to expose conduit 195. Accordingly, the passive containment cooling system 200 may be configured to ensure that conduit 187 is open when conduit 195 is exposed, thereby establishing a conduit into the containment environment 192 via conduit 195 and out of the containment environment 192 via conduit 187. In some example embodiments, the first check valve assembly 180 and the fusible plug 190 are collectively configured to enable circulation of coolant fluid 124 within the containment environment 192, from the coolant channel 160 to the containment environment 192 via the exposed conduit 195 through the fusible plug 190 at the bottom vertical depth DB190/DT190 and from the containment environment 192 to the coolant channel 160 via the first check valve assembly 180 at the first vertical depth DB180/DT180. Accordingly, coolant fluid may circulate in and out of the containment environment 192 in an upwards flow direction that ensures that colder coolant fluid 124 enters the containment environment 192 via the melted fusible plug 190 flow conduit 195 and replaces heated coolant fluid within the containment environment 192, and the heated coolant fluid in the containment environment 192 is removed from the containment environment 192 via the first check valve assembly 180 to be returned to the coolant reservoir 120 to retain any entrained radioactive materials and thus to at least temporarily retain said materials within the nuclear plant 1, thereby improving containment. It will be understood that multiple fusible plugs 190 may extend through the thickness 141 of the containment structure 140, from the containment environment 192, to a same, common coolant channel 160, at a same or different depths from the bottom 120b of the coolant reservoir 120 within the coolant channel 160. While FIG. 1 illustrates one or more fusible plugs 190 extending into one or more coolant channels 160, it will be understood that example embodiments are not limited thereto. For example, one or more fusible plugs 190 of the passive containment cooling system 200 may, instead of extending into a coolant channel 160, be routed to the coolant reservoir 120 via one or more other, separate conduits, also referred to as separate pathways or parallel pathways, into which the fusible plug 190 may extend. For example, a fusible plug 190 may extend, from the containment environment 192, into a separate conduit, also referred to as a separate pathway or parallel pathway, (not shown in FIG. 1 or FIG. 5) that may extend to the coolant reservoir 120 independently of the one or more coolant channels 160. Accordingly, in some example embodiments, one or more fusible plugs 190 may be configured to enable at least partial flooding of the containment environment 192 via coolant fluid that is supplied to the fusible plug 190 via a pathway from the coolant reservoir 120 that is separate and independent of the one or more coolant channels 160 of the passive containment cooling system 200. It will be understood that, in some example embodiments, a fusible plug 190 may extend into a conduit, or pathway, to the coolant reservoir 120 that is independent of (e.g., coupled to the coolant reservoir 120 in parallel with) a conduit, pathway, or coolant channel 160 into which a first check valve assembly 180 and/or second check valve assembly 380 may extend. It will be understood that, in some example embodiments, the fusible plugs 190 may be absent from some or all of the coolant channels 160. In some example embodiments, the passive containment cooling system 200 may not include any fusible plugs 190. FIG. 4 is a flowchart that illustrates a method of operation of a passive containment cooling system, according to some example embodiments. The method shown in FIG. 4 may be performed with regard to any of the example embodiments of passive containment cooling system 200 as described herein, including any of the example embodiments shown in FIGS. 1, 2A-2C, 3, and 5-6. As shown in FIG. 4, the method may include cooling operations 401, check valve assembly operations 411, and fusible plug operations 421. Operations 401, 411, and 421 may be performed at least partially concurrently (e.g., simultaneously), sequentially, or the like. In some example embodiments, operation 411 may be performed independently of operations 401 and 421. In some example embodiments, operation 421 may be performed independently of operations 401 and 411. In some example embodiments, operations 411 and/or 421 may be omitted such that operation 401 is performed alone. In some example embodiments, operation 421 may be performed in response to the first check valve assembly 180 opening the flow conduit 187 and selectively enabling the one-way flow 198 in operation 411, as the passive containment cooling system 200 may be configured such that a fusible plug 190 of the passive containment cooling system 200 at least partially melts when the temperature T192 is at a magnitude corresponding to a pressure P192-1 at which the one or more check valves 182 of the first check valve assembly 180 are open. It will be understood that, in some example embodiments, operation 421 may be omitted, for example where the passive containment cooling system 200 does not include any fusible plugs 190. Referring first to operation 401, At S402, the method may include directing a coolant fluid 124 to flow downwards from a coolant reservoir 120 via a coolant supply conduit 150, according to gravity, to a coolant channel 160 coupled to the containment structure 140 that at least partially defines the containment environment 192 for a nuclear reactor 100, wherein the coolant channel 160 extends vertically along the containment structure 140, such that the coolant fluid 124 is directed into a bottom of the coolant channel 160 according to gravity. At S404, the coolant fluid 124 in the coolant channel 160 absorbs heat 102 rejected by the nuclear reactor 100 in the containment environment 192 via at least the containment structure 140. Such coolant fluid 124 that absorbs the heat 102 becomes a heated coolant fluid 125 and experiences a change in buoyancy (e.g., an increased buoyancy) and density (e.g., a decreased density) in relation to the buoyancy and density of the colder coolant fluid 124 that is supplied to the bottom of the coolant channel 160. At S406, the heated coolant fluid 125 rises (e.g., flows upwards) through the coolant channel 160 from the bottom of the coolant channel 160 toward the coolant reservoir 120 via a top of the coolant channel 160 according to the change in heated coolant fluid 125 buoyancy, in relation to coolant fluid 124 buoyancy, resulting from the coolant fluid 125 absorbing heat 102 at S404. The rising heated coolant fluid 125 may be displaced, at the bottom of the coolant channel 160, by fresh, colder coolant fluid 124 via the coolant supply conduit 150. At S408, the rising heated coolant fluid 125 reaches the top of the coolant channel 160 and continues to rise, through the coolant return conduit 170, as coolant fluid 126, according to the increased buoyancy and reduced density of the coolant fluid 126 over the coolant fluid 124 that is being supplied into the bottom of the coolant channel 160. The coolant fluid 126 rises upwards, through the coolant return conduit 170, and thus, at S410, flows into the upper region 121a of the coolant reservoir 120 via the outlet 174 of the coolant return conduit 170. The coolant fluid 126 may remain in the upper region 121a based on having increased buoyancy and reduced density over the colder coolant fluid 123b in the lower region 121b of the coolant reservoir 120. In some example embodiments, the coolant fluid 126 in the coolant reservoir 120 may cool over time and may sink down into the lower region 121b as coolant fluid 123b, to thus be directed back to the bottom of the coolant channel 160, thereby establishing a circulation of coolant fluid between the coolant reservoir 120 and the coolant channel 160. In some example embodiments, the heat removed from the containment environment 192 by the heated/return coolant fluid 125/126 may be retained in the coolant reservoir 120 for at least a period of time. At S412, in some example embodiments, the removed heat may be further removed from the coolant reservoir 120 via one or more various heat exchangers 128, thereby reducing or preventing the risk of heat removal degradation or overheating of the passive containment cooling system 200. Referring to operation 411, concurrently with or separately from any of S402 to S412 of operation 401, at S420 and S422, in response to the pressure at an inlet 182i of any check valves 182 of a first check valve assembly 180 reaching a corresponding threshold pressure PX at which the respective check valve 182 is configured to actuate to an open state (e.g., S420=YES), the check valve(s) 182 may open. For a check valve 182 having an inlet 182i that is open to an inlet 180i of the first check valve assembly 180, the pressure at the inlet 182i of said check valve 182 is the pressure P192-1 in the containment environment 192 at the inlet 180i, and thus the check valve 182 may actuate to the open state (e.g., “open”) in response to the pressure of the containment environment at the inlet 180i of the first check valve assembly 180 reaching the threshold pressure PX1 of the check valve 182. When all check valves 182 between an inlet 180i and an outlet 180o of a first check valve assembly 180 are open, a flow conduit 187 is opened and a one-way flow 198 from the containment environment 192 to the coolant channel 160 is selectively enabled, and thus, at S424, a containment fluid 197 may flow from the containment environment 192 to the coolant channel 160 via the one or more opened check valves 182 of the first check valve assembly 180. If, at S426, the pressure at the inlet 180i (e.g., pressure P192-1) does not drop below the first threshold magnitude PX1 (e.g., S426=NO), the flow conduit 187 remains open and the one-way flow 198 through the first check valve assembly 180 is maintained. If, at S426 and S428, the pressure P192-1 drops below the threshold pressure (e.g., S426=YES), the one or more check valves 182 of the first check valve assembly 180 may actuate to the closed state and thus the flow conduit 187 is closed and the one-way flow 198 is inhibited. The one-way flow 198 may be subsequently re-enabled if, at S420 and S422, the pressure P192-1 subsequently rises back to at least the threshold pressure PX1. It will be understood that the above operations S420-S428 of operation 411 may be performed in parallel with any of the operations S400 to S412 of operation 401. The above operations S420-S428 of operation 411 are described above with reference to the first check valve assembly 180, but it will be understood that, where the passive containment cooling system 200 includes one or more second check valve assemblies 380 in addition to the first check valve assembly 180, operations S420-S428 may be performed in parallel with regard to the one or more second check valve assemblies 380, in parallel with operations S420-S428 being performed with regard to the first check valve assembly 180. Concurrently with or separately from any of S402 to S412 and/or S420 to S428 (e.g., operation 401 and/or operation 411), at S430 and S432, one or more fusible plugs 190 at a bottom vertical depth DT190 in the coolant channel 160 may at least partially melt (e.g., based on the fusible alloy 193 extending through a conduit 195 defined by a cylindrical body 191 between an end 190i that is open to the containment environment 192 and an opposite end 190o that is open to the coolant channel 160), based on a temperature T192 at the containment environment-facing end 190i of the fusible plug 190 reaching a threshold temperature TX (e.g., S430=YES), where the threshold temperature TX may be a melting temperature of the fusible alloy 193 at the pressure P192-2 of the containment environment 192 at the end 190i. As a result of said at least partial melting at S432, at least some of the coolant fluid 124 in the coolant channel 160 at depth DT190 may, at S434 and as shown by line 422, flow through the conduit 195 exposed as a result of the melting at S432 into the containment environment 192 thereby at least partially flooding the containment environment 192. At S436, the coolant fluid 124 flooding the containment environment 192 may, if the containment environment 192 is filled with coolant fluid up to depth DT180, rise to depth DT180 based on absorbing heat from the containment environment 192, and the coolant fluid may, as shown by line 431, flow through the open flow conduit 187 through check valve assembly 180 at depth DT180, as part of the one-way flow 198, back into the coolant channel 160 at depth DT180 to be returned to the coolant reservoir 120 in S406 to S410. In some example embodiments, S420=YES and S426=NO whenever operation S430=YES, such that the flow conduit 187 may be open whenever the fusible plug 190 at least partially melts at S432. While a number of example embodiments have been disclosed herein, it should be understood that other variations may be possible. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. In addition, while processes have been disclosed herein, it should be understood that the described elements of the processes may be implemented in different orders, using different selections of elements, some combination thereof, etc. For example, some example embodiments of the disclosed processes may be implemented using fewer elements than that of the illustrated and described processes, and some example embodiments of the disclosed processes may be implemented using more elements than that of the illustrated and described processes. |
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047939656 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the pressure vessel of a pressurized water reactor system of an advanced design in which plural rod guides are cantilever-mounted at their lower ends and extend in parallel, vertical relationship to dispose the upper ends thereof adjacent a calandria assembly and, more particularly, to a simplified, flexible top end support for the cantilever-mounted rod guides of such a pressurized water reactor. 2. State of the Relevant Art Conventional pressurized water reactors employ a number of control rods which are mounted within the reactor vessel, generally in parallel axial relationship, for axial translational movement in telescoping relationship with the fuel rod assemblies. The control rods contain materials which absorb neutrons and thereby lower the neutron flux level within the core. Adjusting the positions of the control rods relatively to the respectively associated fuel rod assemblies thereby controls and regulates the reactivity and correspondingly the power output level of the reactor. Typically, the control rods, or rodlets, are arranged in clusters, and the rods of each cluster are mounted at their upper ends to a common, respectively associated spider. Each spider, in turn, is connected to a respectively associated adjustment mechanism for raising or lowering the associated rod cluster. In certain advanced designs of such pressurized water reactors, there are employed both control rod clusters (RCC) and water displacer rod clusters (WDRC), and also so-called gray rod clusters which, to the extent here relevant, are structurally identical to the RCC's and therefore both are referred to collectively hereinafter as RCC's. In an exemplary such reactor design, a total of over 2800 reactor control rods and water displacer rods are arranged in 185 clusters, each of the rod clusters having a respectively corresponding spider to which the rods of the cluster are individually mounted. Further, there are provided, at successively higher, axially aligned elevations within the reactor vessel, a lower barrel assembly, an inner barrel assembly and a calandria assembly, each of generally cylindrical configuration; a removable, upper closure dome seals the top of the vessel and is removable to gain access to the vessel interior. The lower barrel assembly has mounted therein, in parallel axial relationship, a plurality of fuel rod assemblies, comprising the reactor core. The fuel rod assemblies are supported at the lower and upper ends thereof, respectively, by corresponding lower and upper core plates. The inner barrel assembly comprises a cylindrical sidewall which is welded at its bottom edge to the upper core plate. Within the inner barrel assembly there are mounted a large number of rod guides disposed in closely spaced relationship, in an array extending substantially throughout the cross-sectional area of the inner barrel assembly. The rod guides are of first and second types, respectively housing therewithin the reactor-control rod clusters (RCC) and the water displacer rod clusters (WDRC); these clusters, as received in telescoping relationship within their respectively associated guides, generally are aligned with respectively associated fuel rod assemblies. One of the main objectives of the advanced design, pressurized water reactors to which the present invention is directed, is to achieve a significant improvement in the fuel utilization efficiency, resulting in lower overall fuel costs. Consistent with this objective, the water displacement rodlet clusters (WDRC's) function as a mechanical moderator and provide spectral shift control of the reactor. Typically, a fuel cycle is of approximately 18 months, following which the fuel must be replaced. When initiating a new fuel cycle, all of the WDRC's are fully inserted into association with the fuel rod assemblies, and thus into the reactor core. As the excess reactivity level of the fuel diminishes over the cycle, the WDRC's are progressively, in groups, withdrawn from the core so as to enable the reactor to maintain the same reactivity level, even though the reactivity level of the fuel rod assemblies is reducing due to dissipation over time. Conversely, the control rod clusters are moved, again in axial translation and thus telescoping relationship relatively to the respectively associated fuel rod assemblies, for control of the reactivity and correspondingly the power output level of the reactor on a continuing basis, for example in response to load demands, in a manner analogous to conventional reattor control operations. A reactor incorporating WDRC's is disclosed in U.S. patent application Ser. No. 217,503, filed Dec. 16, 1980 and entitled MECHANICAL-SPECTRAL SHIFT REACTOR and in further applications cited therein. A system and method for achieving the adjustment of both the RCC s and WDRC's are disclosed in the co-pending application of Altman et al., entitled "DISPLACER ROD DRIVE MECHANISM VENT SYSTEM." Each of the foregoing applications is assigned to the common assignee hereof and is incorporated herein by reference. A critical design criterion of such advanced design reactors is to minimize vibration of the reactor internals structures, as may be induced by the core outlet flow as it passes therethrough. A significant factor for achieving that criterion is to maintain the core outlet flow in an axial direction throughout the inner barrel assembly of the pressure vessel and thus in parallel axial relationship relative to the rod clusters and associated rod guides. The significance of maintaining the axial flow condition is to minimize the exposure of the rod clusters to cross-flow, a particularly important objective due both to the large number of rods and also to the type of material required for the WDRC's, which creates a significant wear potential. This is accomplished by increasing the vertical length, or height, of the vessel sufficiently such that the rods, even in the fully withdrawn (i.e., raised) positions within their inner barrel assembly, remain located below the vessel outlet nozzles, whereby the rods are subjected only to axial flow, and through the provision of a calandria assembly, which is disposed above the inner barrel assembly and thus above the level of the rods and which is disposed to withstand the cross-flow conditions. In general, the calandria assembly comprises a lower calandria plate and an upper calandria plate which are joined by a cylindrical side wall, and an annularly flanged cylinder which is joined at its loeer cylindrical end to the upper calandria plate and is mounted by its upper, annularly flanged end on an annular supporting ledge of the pressure vessel. The rod guides are cantilever-mounted at their lower ends to the upper core plate and at their upper ends to the lower calandria plate. Within the calandria assembly and extending between aligned apertures in the lower and upper calandria plates is mounted a plurality of calandria tubes, positioned in parallel axial relationship and respectively aligned with the rod guides. A number of flow holes are provided in the lower calandria plates, at positions displaced from the apertures associated with the calandria tubes through which the reactor core outlet flow passes as it exits from its upward passage through the inner barrel assembly. The calandria assembly receives the axial core outlet flow, and turns the flow from the axial direction through 90.degree. to a radially outward direction for passage through the radially oriented outlet nozzles of the vessel. The calandria thus withstands the cross-flow generated as the coolant turns from the axial to the radial directions, and provides for shielding the flow distribution in the upper internals ff the vessel. Advanced design pressurized water reactors of the type here considered incorporating such a calandria assembly are disclosed in the co-pending U.S. patent applications: Ser. No. 490,101 to James E. Kimbrell et al., for "NUCLEAR REACTOR"; U.S. patent application Ser. No. 490,059 to Luciano Veronesi for "CALANDRIA"; and U.S. patent application Ser. No. 490,099, "NUCLEAR REACTOR", all thereof concurrently filed on Apr. 29, 1983 and incorporated herein by reference. Maintenance of suhh reactors, for example, requires that the upper closure dome be removed to provide access to the calandria assembly which in turn is removed to afford access to the WDRC and RCC rod clusters for repair or replacement, and as well to the core for rearrangement or replacement of the fuel rod assemblies. To accomplish this, the calandria assembly typically is removable from the inner barrel assembly, withdrawing thereby the WDRC and RCC rods from within the corresponding rod guides. As before noted, the rod guides for each of the RCC and WDRC rod clusters are mounted rigidly at their bottom ends to the upper core plate, preferably by being bolted thereto, and extend in parallel axial relationshi to dispose the upper, free ends thereof adjacent the lower calandria plate. This cantilever-type mounting is necessitated to accommodate axial (i.e., vertical) movement of the free ends of the rod guides, which occurs due to thermal expansion and thus axial elongation of the rod guides, and fixed end motion caused by vibration and/or flexing of the upper core plate to which the bottom, fixed end of the rod guides are mounted. Because of these factors, it is not possible to rigidly and permanently secure the free ends of the rod guides to the lower calandria plate. Preferably, the design of the pressure vessel and particularly of the support structures which mount the free ends of the rod guides to the lower calandria plate permit both the assembly and removal of the calandria, relatively thereto, without special tools. Nevertheless, the mounting means for the free ends of the rod guides not only must constrain the same against lateral motion due to vibration, flow and thermal forces while accommodating the aforesaid axial movement of the free ends of the rod guides, but also must avoid wear of the reactor internals arising out of loads imposed on the guides and the previously discussed axial motion of the free ends of the guides. In some existing designs and as used with conventional reactors, split pins are employed at the free ends of the rod guides for restricting lateral motion while permitting a limited extent of axial motion. Such designs, however, present wear concerns for the reasons above-noted. In fact, due to the high loads and large axial motion of the free ends in the advanced design pressure vessels, the use of split pins for the free end supports is deemed not practical. There thus exists a substantial need for a top end support structure for the top, free ends of the rod guides in such advanced design reactors, which satisfies these complex structural and operational requirements but yet which is of simple design and employs a minimum number of parts, thereby to achieve cost economies both in the construction and also in the maintenance of such reactors. CROSS-REFERENCE TO RELATED APPLICATIONS The present invention is related to the top end support assembly disclosed in the co-pending application of Gillett et al. entitled "FLEXIBLE ROD GUIDE SUPPORT STRUCTURE FOR INNER BARREL ASSEMBLY OF PRESSURIZED WATER REACTOR", now U.S. Pat. No. 4,687,628 assigned to the common assignee hereof and incorporated herein by reference. As disclosed therein, respective, differently configured top support plates are mounted on the free ends of the RCC and the WDRC rod guides, respectively, and have mating, respective exterior and interior vertices to permit assemblage of same in an interdigitized array. Flexible linkages connect the top plates in a concatenated relationship, and serve to restrain relative, lateral movement while permitting relative axial movement therebetween. Stop pins are received in aligned bores of the contiguous interdigitated top plates and serve to limit the extent of load which can be applied to the linkages and thus the ultimate extent of relative movement between the concatenated top plates. The RCC top plates include openings, preferably of cylindrical configuration, which receive corresponding cylindrical extensions which are secured to and extend downwardly from the lower calandria plate, thereby establishing basic alignment of the concatenated and interleaved matrices of the plates. Leaf springs secured to the calandria bottom plate engage and exert a downward force on the top surfaces of the RCC top plates, thereby establishing a frictoonal force which further opposes lateral movement of the RCC top plates and correspondingly, through the concatenated and interleaved arrangement, any lateral movement of the WDRC top plates, as well, while permitting restrained axial displacement, or movement, of the individual RCC and WDRC rod guides. While the flexible support structure of the referenced Gillett et al. application satisfies many of the requrrements before noted, the structure is of complex design and requires the use of numerous elements, contributing to increased costs of construction and maintenance of the reactor. Because of the interdigitized and concatenated relationship of the WDRC and RCC top plates, removal of any individual WDRC rod guide requires removal of the four RCC rod guides, the top plates of which are received in mating and overlapping relationship about the corner vertices of the top plate of the WDRC rod guide which is to be removed; this, moreover, requires that not only the flexible linkage for the given WDRC top plate be removed, but also the flexible linkage associated with each of the surrounding, mating RCC top plates be removed. For the disclosed, preferred embodiment of the Gillett et al. application, this requires removal of nine flexible linkages, each of which is held in place by eight associated bolts, and thus removal of a total of 72 bolts. Further, each of the involeed WDRC and RCC rod guides must be released from its rigid mounting to the upper core plate, typically afforded likewise by bolts. The interleaved and interdigitated relationship of the WDRC and RCC top plates further requires that all the WDRC rod guides be installed prior to installation of the RCC rod guides. This imposes a necessary sequence of installation, which must be followed to achieve the desired assembly. Thus, there exists a need for a top end support for the cantilever-mounted WDRC and RCC rod guides of a pressurized water reactor, which affords the beneficial features of the Gillett et al. structure, but which employs a reduced number of parts including WDRC and RCC top plates of simplified configurations, and thus is of reduced cost, and which is free of the constraints of a prescribed sequence of assembly and disassembly and instead permits simplification thereof, thereby to reduce the time required for, and the costs of maintenance operations. SUMMARY OF THE INVENTION The present invention both satisfies the before-noted requirements of the top end supports for the rod guides and also achieves the aforestated objectives. Particularly, the simplified, flexible support structures for the top ends of the rod guides, in accordance with the present invention, comprise, as major components, interdigitized matrices of respective RCC and WDRC top plates for the corresponding RCC and WDRC rod guides, which are self-aligning during assembly without prescribing a given sequence of that assembly. Mating alignment surfaces are formed on the major arms of the RCC and WDRC top plates so as to permit a sliding, or telescoping, assemblage of same. The mating exterior and interior vertices of contiguous, respective WDRC and RCC top plates are machined to define corresponding keyway segments which are aligned when the contiguous WDRC and RCC top plates are mounted in position, and accommodate therein a key of generally rectangular configuration. One end of the key has a bore formed therein which is in alignment with a threaded bore in the RCC top plate. A flexible linkage of integral arms in a generally square configuration is received on each WDRC top plate. The respective linkage arms have central apertures in alignment with threaded bores centrally disposed in the corresponding major arms of the WDRC top plate and the linkage vertices have apertures in alignment with the bores in tee corresponding keys and the respective, aligned threaded bores in the contiguous RCC top plates. Bolts received through the central apertures of the linkage arms secure the linkage to the associated WDRC top plate and further bolts received through the apertures in the linkage vertices secure both the underlying key and the linkage to the contiguous, respective RCC top plates. In the assembled relationship, the flexible linkages laterally interlock the matrices of top plates in a two-dimensional, concatenated relationship in a plane perpendicular to the axes of the rod guides. Each WDRC top plate is linked rigidly in the lateral direction to the four respectively surrounding, contiguous, RCC top plates--and, in turn, each of the RCC top plates is laterally interlocked at its four interior vertices to the associated exterior vertices of four WDRC top plates which are interdigitized and contiguous therewith. The guides are thus essentially bound together laterally; however, the linkages are flexible in the out-of-plane direction and thus accommodate relative axial motion between adjacent guides. This compensates for local differences in the height of adjacent guides, arising out of manufacturing tolerances and/or due to differential axial expansion from thermal effects and/or bowing of the ood guides due to pressure differentials across the guides. Collectively, the leaf springs 140 function to resist movement of the rod guides in unison, or as a package, and the linkages serve to resist individual rod guide motion, relative to the stability afforded by the collective action of the leaf springs 140--correspondingly preventing wear of the rod guides and of each rod cluster, relative to its associated, individual rod guide. Generally cylindrical calandria extensions affixed to the lower calandria plate and projecting downwardly therefrom are received within corresponding apertures centrally disposed in the RCC top guides, and provide basic alignment of the matrix of the RCC top plates and, correspondingly, of the concatenated and interdigitized matrix of WDRC plates. Rod guide leaf springs are mounted on the lower calandria plate and extend downwardly therefrom, imposing an axial resilient load against the RCC top plates. The leaf springs generate sufficient lateral frictional force to offset fluctuating steady state loads imposed on the rod guides. Moreover, the calandria extensions provide overall lateral support during excessive load conditions, such as seismic and LOCA, wherein such loading exceeds the lateralffrictional force of the leaf springs. These and other advantages of the simplified, flexible rod guide support for the rod guides within the inner barrel assembly of a pressurized water reactor in accordance with the present invention will become more apparent from the following detailed description and drawings, wherein like reference numerals refer to like parts, throughout. |
description | This is a continuation of U.S. application Ser. No. 11/180,672, filed Jul. 14, 2005 now U.S. Pat. No. 7,329,889, which is a continuation of U.S. application Ser. No. 10/853,225, filed May 26, 2004, now U.S. Pat. No. 6,919,577, which is a continuation of U.S. application Ser. No. 10/012,454, filed Dec. 12, 2001, now U.S. Pat. No. 6,753,518, which is a continuation of U.S. application Ser. No. 09/642,014, filed Aug. 21, 2000, now U.S. Pat. No. 6,333,510, which is a continuation of U.S. application Ser. No. 09/132,220, filed Aug. 11, 1998, now U.S. Pat. No. 6,107,637, the subject matter of which is incorporated by reference herein. The present invention relates to an electron beam exposure or system inspection or measurement or processing apparatus having an observation function using charged particle beams such as electron beams or ion beams and its method and an optical height detection apparatus. Heretofore, a focus of an electron microscope has been adjusted by adjusting a control current of an objective lens while an electron beam image is observed. This process requires a lot of time, and also, a sample surface is scanned by electron beams many times. Accordingly, there is the possibility that a sample will be damaged. In order to solve the above-mentioned problem, in a prior-art technique (Japanese laid-open patent application No. 5-258703), there is known a method in which a control current of an optimum objective lens relative to a height of a sample surface in several samples are measured in advance before the inspection is started and focuses of respective points are adjusted by interpolating these data when samples are inspected. In this method, SEM images obtained by changing an objective lens control current at every measurement point are processed, and an objective lens control current by which an image of a highest sharpness is recorded. It takes a lot of time to measure an optimum control current before inspection. Moreover, there is the risk that a sample will be damaged due to the irradiation of electron beams for a long time. Further, there is the problem that a height of a sample surface will be changed depending upon a method of holding a wafer during the inspection. Moreover, as the prior-art technique of the apparatus for inspecting a height of a sample, there are known Japanese laid-open patent application No. 58-168906 and Japanese laid-open patent application No. 61-74338. According to the above-mentioned prior art, in the electron beam apparatus, the point in which a clear SEM image without image distortion is detected and a defect of a very small pattern formed on the inspected object like a semiconductor wafer such as ULSI or VLSI is inspected and a dimension of a very small pattern is measured with high accuracy and with high reliability has not been considered sufficiently. It is therefore an object of the present invention is to provide an electron beam exposure or system inspection or measurement apparatus and a method thereof in which the image distortion caused by the deflection and the aberration of the electron optical system can be reduced, the decrease of the resolution due to the de-focusing can be reduced so that the quality of the electron beam image (SEM image) can be improved and in which the inspection and the measurement of length based on the electron beam image (SEM image) can be executed with high accuracy and with high reliability. It is another object of the present invention is to provide an electron beam exposure or system inspection or measurement apparatus and a method thereof in which the height of the surface of the inspected object can be detected real time and the electron optical system can be controlled real time so that an electron beam image (SEM image) of high resolution without image distortion can be obtained by the continuous movement of the stage, an inspection efficiency and its stability can be improved and in which an inspection time can be reduced. It is a further object of the present invention to provide an electron beam exposure apparatus and a converging ion beam manufacturing apparatus in which very small patterns can be exposed and manufactured without image distortion and with a high resolution. In order to attain the above-mentioned objects, according to the present invention, there is provided an electron beam system inspection or measurement apparatus which is comprised of a detection apparatus including an electron optical system comprising an electron beam source, a deflection element for deflecting electron beams emitted from the electron beam source, and an objective lens for converging and irradiating electron beams deflected by the deflection element on an inspected object, an electron beam image detection optical system for detecting a secondary electron beam image generated from the inspected object by the electron beams deflected by the electron optical system and converged and irradiated, a projection optical system for projecting a luminous flux of a repetitive light pattern or lattice shape on the inspected object from the oblique upper direction of the inspected object and a detection optical system for detecting the position of an optical image by focusing the luminous flux of the repetitive light pattern which was reflected on the surface of the inspected object by the luminous flux of the repetitive light pattern projected by the projection optical system, an optical height detection apparatus arranged so as to optically detect a height of the surface in an area on the inspected object based on the change of the position of an optical image composed of a luminous flux of the repetitive light pattern detected by the detection optical system, a focus controller for focusing electron beams on the inspected object in a properly-focused state by controlling a current flowed to or a voltage applied to an objective lens of the electron optical system on the basis of the height of the surface on the inspected object detected by the optical height detection apparatus and an image processor for inspecting or measuring a pattern formed on the inspected object on the basis of the secondary electron beam image detected by the electron beam image detection optical system. In accordance with the present invention, there is provided an electron beam apparatus comprising a pattern writing apparatus including an electron optical system comprising an electron beam source, a deflection element for deflecting electron beams emitted from the electron beam source, and an objective lens for converging and irradiating electron beams deflected by deflection element on a processed object, a projection optical system for projecting a luminous flux a repetitive light pattern on the processed object from an oblique upper direction of the processed object and a detection optical system for detecting the position of an optical image by focusing the luminous flux of the repetitive light pattern which was reflected on a surface of the processed object by the luminous flux of the repetitive light pattern projected by the projection optical system, an optical height detection apparatus arranged so as to optically detect a height of the surface in an area on the processed object based on the change of the position of an optical image composed of the luminous flux of the repetitive light pattern detected by the detection optical system, and a focus controller for focusing electron beams on the processed object in a properly-focused state by controlling a current flowed to or a voltage applied to the objective lens of the electron optical system on the basis of the height of the surface on the inspected object detected by the optical height detection apparatus. Further, according to the another feature present invention, there is provided an electron beam system inspection or measurement apparatus which is comprised of a detection apparatus including an electron optical system comprising an electron beam source, a deflection element for deflecting electron beams emitted from the electron beam source, and an objective lens for converging and irradiating electron beams deflected by the deflection element on an inspected object, an electron beam image detection optical system for detecting a secondary electron beam image generated from the inspected object by the electron beams deflected by the electron optical system and converged and irradiated, an optical height detection apparatus for optically detecting a height of a surface in an area on the inspected object irradiated by electron beams deflected and converged by the electron optical system, a focus controller for focusing electron beams on the inspected object in a properly-focused state by controlling a current flowed to or a voltage applied to the objective lens of the electron optical system on the basis of the height of the surface on the inspected object detected by the optical height detection apparatus, a deflection controller for correcting an image distortion containing a magnification error of electron beams generated on the basis of the focus control by correcting a deflection amount of the electron optical system to the deflection element on the basis of the height of the surface on the inspected object detected by the optical height detection apparatus, and an image processor for inspecting or measuring a pattern formed on the inspected object on the basis of a secondary electron beam image detected by the electron beam detection optical system. In accordance with the present invention, there is provided an electron beam system inspection or measurement apparatus which is comprised of an electron optical system including an electron beam source, a deflection element for deflecting electron beams emitted from the electron beam source and an objective lens for converging and irradiating electron beams deflected by the deflection element on the inspected object, an electron beam image detection system for detecting a secondary electron beam image generated from the inspected object by the electron beams deflected and converged by the electron optical system, an optical height detection apparatus for optically detecting a height of a surface in an area on the inspected object irradiated by electron beams deflected and converged by the electron optical system, a focus controller for calculating a focus control current or a focus control voltage based on a correction parameter between a height of a surface on the inspected object and a focus control current or a focus control voltage from a height of a surface on the inspected object detected by the optical height detection apparatus and converging electron beams on the inspected object in a properly-focused state by supplying the calculated focus control current or focus control voltage to an objective lens of the electron optical system, and an image processor for inspecting or measuring a pattern formed on the inspected object on the basis of a secondary electron beam image detected by the electron beams image detection optical system. The present invention also provides that the electron beam system inspection or measurement apparatus further includes a deflection controller for correcting an image distortion containing a magnification error of an electron beam image generated on the basis of the focus control by correcting a deflection amount of the electron optical system to a deflection element on the basis of a height of a surface on the inspected object detected by the optical height detection apparatus. According to another feature of the present invention, there is provided an electron beam system inspection or measurement apparatus which is comprised of an electron optical system including an electron beam source, a deflection element for deflecting electron beams emitted from the electron beam source and an objective lens for converging and irradiating electron beams deflected by the deflection element on the inspected object, an electron beam image detection system for detecting a secondary electron beam image generated from the inspected object by the electron beams deflected and converged by the electron optical system, an optical height detection apparatus for optically detecting a height of a surface in a place in which a focus control delay is shifted in an area on the inspected object irradiated with electron beams by the electron optical system, a focus controller for calculating a focus control current or a focus control voltage based on a correction parameter between a height of a surface on the inspected object and a focus control current or a focus control voltage from a height of a surface on the inspected object detected by the optical height detection apparatus and converging electron beams on the inspected object in a properly-focused state by supplying the calculated focus control current or focus control voltage to an objective lens of the electron optical system, and an image processor for inspecting or measuring a pattern formed on the inspected object on the basis of a secondary electron beam image detected by the electron beam image detection optical system. According to the present invention, the electron beam system inspection or measurement apparatus further includes a deflection controller for correcting an image distortion containing a magnification error of an electron beam image generated on the focus control by correcting a deflection amount of the electron optical system to a deflection element on the basis of a height of a surface in a place in which a focus control delay is shifted on the inspected object detected by the optical height detection apparatus. Further, according to the present invention, there is provided an electron beam system inspection or measurement apparatus which is comprised of an electron optical system including an electron beam source, a deflection element for deflecting electron beams emitted from the electron beam source and an objective lens for converging and irradiating electron beams deflected by the deflection element on the inspected object, an electron beam image detection system for detecting a secondary electron beam image generated from the inspected object by the electron beams deflected and converged by the electron optical system, an optical height detection apparatus for optically detecting a height of a surface in a place in which a position displacement corrected amount is shifted in an area on the inspected object irradiated with electron beams by the electron optical system, a focus controller for calculating a focus control current or a focus control voltage based on a correction parameter between a height of a surface on the inspected object and a focus control current or a focus control voltage from a height of a surface in which a position displacement corrected amount is shifted in an area on the inspected object detected by the optical height detection apparatus and converging electron beams on the inspected object in a properly-focused state by supplying the calculated focus control current or focus control voltage to an objective lens of the electron optical system, and an image processor for inspecting or measuring a pattern formed on the inspected object on the basis of a secondary electron beam image detected by the electron beams image detection optical system. According to the present invention, the electron beam system inspection or measurement apparatus further includes deflection controller for correcting an image distortion containing a magnification error of an electron beam image generated on said focus control by correcting a deflection amount of said electron optical system to a deflection element on the basis of a height of a surface in a place in which a position displacement correction amount is shifted on the inspected object detected by the optical height detection apparatus. Further, according to the present invention, the optical height detection apparatus in the electron beam system inspection or measurement apparatus includes a projection optical system for projecting a luminous flux of linear or lattice shape or a repetitive light pattern on the inspected object from the oblique upper direction of the inspected object and a detection optical system for detecting a position of an optical image by focusing a luminous flux reflected on the surface of the inspected object by the luminous flux projected by the projection optical system, and in which a height of a surface of the inspected object is detected on the basis of the change of the position of an optical image detected by the detection optical system. Additionally, according to the present invention, the optical height detection apparatus in the electron beam system inspection or measurement apparatus includes a plurality of projection optical systems for projecting a luminous flux of linear or lattice shape or repetitive light pattern on the inspected object from the oblique upper direction of the inspected object and detection optical systems for detecting a position of an optical image by focusing a luminous flux reflected on the surface of the inspected object by the luminous flux projected by the projection optical systems disposed symmetrically with respect to an optical axis of the electron optical system, and in which position changes of optical images detected by the respective detection optical systems are synthesized and a height of a surface of the inspected object is detected on the basis of the position change of the synthesized optical image. Further, according to the present invention, white light is used as the luminous flux projected by the projection optical system in the optical height detection apparatus of the electron beam system inspection or measurement apparatus. Further, according to the present invention, S-polarized light is used as the luminous flux projected by the projection optical system in the optical height detection apparatus of the electron beam system inspection or measurement apparatus. According to the present invention, there is also provided an electron beam system inspection or measurement apparatus which is comprised of a detection apparatus including an electron optical system comprising an electron beam source, a deflection element for deflecting electron beams emitted from the electron beam source, and an objective lens for converging and irradiating electron beams deflected by the deflection element on an inspected object, an electron beam image detection optical system for detecting a secondary electron beam image generated from the inspected object by the electron beams deflected by the electron optical system and converged and irradiated, a projection optical system for projecting a luminous flux of lattice shape or a repetitive light pattern on the inspected object from the oblique upper direction of the inspected object and a detection optical system for detecting the position of an optical image by focusing the luminous flux of lattice shape or repetitive light pattern which was reflected on the surface of the inspected object by the luminous flux of lattice shape or repetitive light pattern projected by the projection optical system, an optical height detection apparatus arranged so as to optically detect a height of the surface in an area on the inspected object based on the change of the position of an optical image composed of a luminous flux of lattice shape or repetitive light pattern detected by the detection optical system, a focus controller for focusing electron beams on the inspected object in a properly-focused state by controlling a relative position of a height direction between a focus position obtained by the electron optical system and a table for holding the inspected object on the basis of the height of the surface on the inspected object detected by the optical height detection apparatus and an image processor for inspecting or measuring a pattern formed on the inspected object on the basis of the secondary electron beam image detected by the electron beam image detection optical system. According to other features of the present invention, there is provided an electron beam system inspection or measurement method which is comprised of the steps of moving an inspected object at least in a predetermined direction, optically detecting a height of a surface in an area on the inspected object irradiated with electron beams from an optical height detection apparatus on the basis of the change of the position of an optical image composed of a luminous flux of a repetitive light pattern or lattice shape, deflecting electron beams emitted from an electron beam source by a deflection element of an electron optical system and focusing the same on the inspected object by controlling a current flowed to or a voltage applied to an objective lens of the electron optical system based on the height of the surface on the detected inspected object in a properly-focused state, detecting a secondary electron beam image generated from the inspected object by irradiated electron beams deflected and focused in a properly-focused state by an electron beam image detection optical system, and inspecting or measuring a pattern formed on the inspected object based on the detected secondary electron beam image. Further, according to additional features the present invention, there is provided an electron beam system inspection or measurement method comprising the steps of moving an inspected object at least in a predetermined direction, optically detecting a height of a surface in an area on the inspected object irradiated with electron beams by an optical height detection apparatus, deflecting election beams emitted from an electron beams source by a deflection element of an electron optical system by controlling a current flowed to or a voltage applied to an objective lens of the electron optical system on the basis of the height of the surface on the detected inspected object such that the election beams are converged on the inspected object in a properly-focused state, correcting an image distortion containing a magnification error of an electron beam image generated based on the focus control by correcting a deflection amount to a deflection element of the electron optical system, detecting a secondary electron beam image generated from the inspected object by electron beams corrected, deflected, converged in a properly-focused state and irradiated by means of an electron beam detection optical system, and inspecting or measuring a pattern formed on the inspected object on the basis of the detected secondary electron beam image. According to the present invention, there is provided an electron beam system inspection or measurement method which is comprised of the steps of moving the inspected object at least in a predetermined direction, optically detecting a height of a surface in an area on an inspected object irradiated with electron beams from an optical height detection apparatus, calculating a focus control current or a focus control voltage on the basis of a correction parameter between the height of the surface on the inspected object and a focus control current or a focus control voltage, deflecting electron beams emitted from the electron beam source and focusing the same on the inspected object in a properly-focused state by supplying the calculated focus control current or focus control voltage to an objective lens of the electron optical system, detecting a secondary electron beam image generated from the inspected object by irradiated electron beams deflected and focused in a properly-focused state by an electron beam image detection optical system, and inspecting or measuring a pattern formed on the inspected object on the basis of the detected secondary electron beam image. Further, according to the present invention, the electron beam system inspection or measurement method further includes the step of correcting an image distortion containing a magnification error of an electron beam image generated on the basis of the focus control by correcting a deflection amount of a deflection element of the electron optical system on the basis of a height of a surface on the detected inspected object. Additionally, according to the present invention, there is provided an electron beam system inspection or measurement method which is comprised of the steps of moving an inspected object at least in a predetermined direction, optically detecting a height of a surface in an area on the inspected object irradiated with electron beams by an optical height detection apparatus, calculating a focus control current or a focus control voltage on basis of a correction parameter between the height of the surface on the inspected object and a focus control current or a focus control voltage from a height of a surface in a place in which a focus control delay on the detected inspected object is shifted, deflecting electron beams emitted from an electron beam source by a deflection element of an electron optical system and focusing the same on the inspected object in a properly-focused state by supplying the calculated focus control current or focus control voltage to an objective lens of the electron optical system, detecting a secondary electron beam image generated from the inspected object with irradiated electron beams deflected and focused in a properly-focused state by an electron beam image detection optical system, and inspecting or measuring a pattern formed on the inspected object on the basis of the detected secondary electron beam image. There is provided an electron beam system inspection or measurement method which is comprised of the steps of moving an inspected object at least in a predetermined direction, optically detecting a height of a surface in an area on the inspected object irradiated with electron beams by an optical height detection apparatus, calculating a focus control current or a focus control voltage on basis of a correction parameter between the height of the surface on the inspected object and a focus control current or a focus control voltage from a height of a surface in a place in which a position displacement corrected amount on the detected inspected object is shifted, deflecting electron beams emitted from an electron beam source by a deflection element of an electron optical system and focusing the same on the inspected object in a properly-focused state by supplying the calculated focus control current or focus control voltage to an objective lens of the electron optical system, detecting a secondary electron beam image generated from the inspected object with irradiated electron beams deflected and focused in a properly-focused state by an electron beam image detection optical system, and inspecting or measuring a pattern formed on the inspected object on the basis of the detected secondary electron beam image. In accordance with the present invention, there is also provided an electron beam system inspection or measurement method which is comprised of the steps of moving an inspected object at least in a predetermined direction, optically detecting a height of a surface in an area on the inspected object irradiated with electron beams from an optical height detection apparatus, deflecting electron beams emitted from an electron beam source by a deflection element of an electron optical system and focusing the same on the inspected object in a properly-focused state by controlling a relative position of a height direction between a focus position of an electron optical system and a table for holding the inspected object on the basis of a height of a surface on the detected inspected object, detecting a secondary electron beam image generated from the inspected object by irradiated electron beams deflected and focused in a properly-focused state by an electron beam image detection optical system, and inspecting or measuring a pattern formed on the inspected object on the basis of the detected secondary electron beam image. Further, according to the present invention, there is provided an optical height detection apparatus which is comprised of a plurality of projection optical systems for projecting a luminous flux of linear or lattice shape or repetitive light pattern on the inspected object from the oblique upper direction of the inspected object and detection optical systems for detecting a position of an optical image by focusing a luminous flux reflected on the surface of the inspected object by the luminous flux projected by the projection optical systems disposed symmetrically with respect to a predetermined optical axis, and in which position changes of optical images detected by the respective detection optical systems are synthesized and a height of a surface of the inspected object is detected on the basis of the position change of the synthesized optical image. Other features of the present invention include that in the optical height detection apparatus, a one-dimensional or two-dimensional image sensor is used as a detector for detecting the change of the position of the optical image. Further, as the detector for detecting the change of the position of the optical image, a mask having a transmission pattern similar to a projection pattern is vibrated and a photoelectric detector such as a photodiode is disposed behind the mask, whereby the change of the position is detected by a synchronizing-detection. Additionally, a shape formed by repeatedly arranging a plurality of rectangular patterns is used as a shape of luminous flux projected onto an object. Also, white light is used as a luminous flux projected onto an object. Further, a luminous flux is projected onto an object with an angle greater than 60 degrees and S-polarized light is used as a luminous flux projected onto an object. Further, the optical height detection apparatus includes two height detectors, and the two height detectors are disposed symmetrically with respect to a normal from a measured position on an object. Height detection values of the two height detectors are combined so that a height of the same observation position on the object can be constantly detected with high accuracy regardless of the change of the height of the object, the change of the inclination or the surface state of the object. Also, in the optical height detection apparatus, one or a plurality of height measurement patterns are selected from a plurality of pattern images and a height is measured by using these patterns, whereby a height measurement position on the object can be selected. Further, not only a height of an object but also an inclination thereof is detected by an image formed by arranging a plurality of rectangular patterns, and at least one of a height measurement position on the object and a detection error caused by the inclination of the object is corrected by using this information. Additionally, a height distribution on the cross-section of the object is detected by using an image formed by arranging a plurality of rectangular patterns. Further, the image in which a plurality of rectangular patterns are arranged is detected and processed by a two-dimensional image sensor or an arrangement in which a plurality of one-dimensional image sensors are disposed in parallel, whereby a height distribution of a two-dimensional surface of an object can be detected. According to the present invention, there is also provided an electron beam system automatic inspection apparatus which is comprised of an electron optical system for converging electrons emitted from an electron source on a focus, an observer for observing an arbitrary position at which an inspected object is brought by a stage for holding the inspected object and which can be moved within a plane through the electron optical system, a detector for continuously detecting a height of the inspected object in an observation area of the electron optical system by an optical method, and a positioner for constantly maintaining a relative position between a focus position of an electron beam image and the inspected object by using a result of height detection and wherein an automatic inspection can be executed by processing the resultant properly-focused electron beam image to detect a defect. Further, according to the present invention, there is provided an electron beam system automatic inspection method which is comprised of an electron optical system for converging electrons emitted from an electron source on a focus, an observer for observing an arbitrary position at which an inspected object is brought by a stage for holding the inspected object and which can be moved within a plane through the electron optical system, a detector for continuously detecting a height of the inspected object in an observation area of the electron optical system by an optical method, and a positioner for constantly maintaining a relative position between a focus position of an electron beam image and the inspected object by using a result of height detection and wherein an automatic inspection can be executed by processing the resultant properly-focused electron beam image to detect a defect. In accordance with the present invention, the electron beam system automatic inspection apparatus also includes two height detectors. The two height detectors are disposed symmetrical with respect to a normal from an observation position of an electron optical system on an object. Height detection values of the two height detectors are synthesized so that the height of the observation position of the electron optical system on the object can constantly be detected with high accuracy regardless of the change of the height of the object, the change of the inclination, or the surface state of the object. The electron beam system automatic inspection apparatus includes a positioner for constantly maintaining a relative position between the focus position of the electron beam image and the inspected object by using a result of height detection, and in which the automatic inspection can be executed by processing the resultant properly-focused electron beam to detect a defect. Further, according to the present invention, in the electron beam system automatic inspection apparatus, one or a plurality of slits used to measure a height are selected from a plurality of rectangular pattern images and a height is measured by using these slits to thereby select the height measurement position on the object. Thus, the stage scanning and a detection time delay of a height detector or a measurement position displacement caused by an adjustment error of an optical system can be corrected. Further, according to the present invention, in the electron beam system automatic inspection apparatus, not only a height of an object but also an inclination thereof is detected by an image formed by arranging a plurality of rectangular patterns, and at least one of a height measurement position on the object and a detection error caused by the inclination of the object is corrected by using this information. Further, according to the present invention, in the electron beam system automatic inspection apparatus, a height distribution on the cross-section of the object is detected by using an image formed by arranging a plurality of rectangular patterns, and electron beams are properly focused on an arbitrary area of the object by using this information. Further, according to the present invention, in the electron beam system automatic inspection apparatus, the image in which a plurality of rectangular patterns are arranged is detected and processed by a two-dimensional image sensor or an arrangement in which a plurality of one-dimensional image sensors are disposed in parallel, whereby a height distribution of a two-dimensional surface of an object can be detected, and electron beams are properly focused by using this information. Further, according to the present invention, the electron beam system automatic inspection apparatus has a function to control the focus position of the electron beams relative to the scanning of the stage at a sufficiently high speed by the arrangement of the electron optical system, an objective lens or an electrostatic lens or a condenser lens or a combination of one or a plurality of means of a deflection system. By using the inspected object surface height obtained from the optical height detection apparatus, an electron beam image can be obtained under the condition that the relative position between the surface of the inspected object and the focus position of the electron beam can be maintained constant. Further, according to the present invention, the electron beam system automatic inspection apparatus has a function to control the focus position of the electron beams relative to the scanning of the stage at a sufficiently high speed by the arrangement of the electron optical system, an objective lens or an electrostatic lens or a condenser lens or a combination of one or a plurality of means of a deflection system. By using the inspected object surface shape distribution obtained from the optical height detection apparatus, an electron beam image can be obtained under the condition that the relative position between the inspected object surface shape and the orbit of the focus position of the electron beam can be maintained constant. Further, according to the present invention, the electron beam system automatic inspection apparatus includes a Z stage which can finely adjust the height of the surface of the inspected object at a sufficiently high speed, and an electron beam image in which the relative position between the surface of the inspected object and the focus position of the electron beam can be maintained constant can be constantly obtained by using the inspected surface height obtained from the optical height detection apparatus. Further, the present invention utilizes a correction standard pattern made of a stable material which can be prevented from being affected with the irradiation of charged particle beams, the surface of which has a pattern that can be observed by a charged particle optical system and which has at least more than two stepped differences or inclinations of which height differences are clear. Further, the present invention is a height detection apparatus and a charged particle optical system correction method using the above-mentioned standard pattern fixed to a stage for holding an inspected object. Further, the present invention is an electron beam system automatic inspection apparatus capable of correcting a height detection apparatus and an electron optical system by using the above-mentioned standard pattern fixed to a stage for moving an inspected object. Furthermore, the present invention is an electron beam system automatic inspection apparatus including an electron optical system capable of changing a deflection amount of electron beams in real time in response to a fluctuation of a height of a sample surface and which has a function to correct a magnification based on a fluctuation of an inspected object surface as well as to adjust the focus of electron beams. Furthermore, the present invention is characterized by the application to apparatus (electron beam system length measuring apparatus, scanning electron microscope, electron beam exposing apparatus, converging ion beam manufacturing apparatus) using a charged particle optical system of the above-mentioned height detection apparatus. As described above, according to the above-mentioned arrangement, without being affected by the surface state of the inspected object, the image distortion caused by the deflection and the aberration of the electron optical system can be reduced and the decrease of the resolution due to the de-focusing can be reduced so that the quality of the electron beam image (SEM image) can be improved. Thus, the inspection and the measurement of length based on the electron beam image (SEM image) can be executed with high accuracy and with high reliability. Furthermore, according to the above-mentioned arrangement, since the height of the surface of the inspected object can be detected in real time and the electron optical system can be controlled in real time, an electron beam image (SEM image) of high resolution without image distortion can be obtained by the continuous movement of the stage, and the inspection can be executed. Hence, an inspection efficiency and its stability can be improved. In addition, an inspection time can be reduced. These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. An embodiment of an automatic inspection system for inspecting/measuring a micro-circuit pattern formed on a semiconductor wafer which is an inspected object according to the present invention will be described. A defect inspection of the micro-circuit pattern formed on the semiconductor wafer or the like is executed by comparing inspected patterns and good pattern and patterns of the same kind on the inspected wafer. Also in the case of an appearance inspection using an electron microscope image (SEM image), a defect inspection is executed by comparing pattern images. Furthermore, also in the case of the length measurement (SEM length measurement) executed by a scanning-type electron microscope which measures a line width or a hole diameter of a micro-circuit pattern used to set or monitor a manufacturing process condition of semiconductor devices, the length measurement can be automatically executed by the image processing. In the comparison inspection for detecting a defect by comparing electron beam images of a similar pattern or when a line width of a pattern is measured by processing an electron beam image, a quality of an obtained electron beam image exerts a serious influence upon the reliability of the inspected results. The quality of electron beam image is deteriorated by an image distortion caused by deflection and aberration of an electron optical system and is also deteriorated as resolution is lowered by a de-focusing. The deterioration of the image quality lowers a comparison and inspection efficiency and a length measurement efficiency. Referring now to the drawings, a height of a surface of an inspected object is not even and an inspection is executed over the whole range of heights under the same condition for a wafer as shown in FIG. 1(a), then as shown in FIGS. 1(b)-(d), electron beam images (SEM images) are changed in accordance with the inspection portions (area A, area B, area C). As a result, if an inspection is carried out by comparing an image (electron beam image of area A (height za) of a properly-focused point shown in FIG. 1(b), a de-focused image (electron beam image of area B (height zb) shown in FIG. 1(c), and a defocused image (electron beam image of area C (height zc) shown in FIG. 1(d), then a correct inspected result cannot be obtained. Moreover, in these images, the width of the pattern is changed, and an edge detected result of an image cannot be obtained stably so that the line width and the hole diameter of the pattern also cannot be measured stably. An electron beam apparatus according to an embodiment of the present invention will be described with reference to FIG. 2. An electron beam apparatus 100 composed of an electron beam column for irradiating electron beams on an inspected object (sample) 106 comprises an electron beam source 101 for emitting electron beams, a deflection element 102 for deflecting electron beams emitted from the electron beam source 101 in a two-dimensional fashion, and an objective lens 103 which is controlled so as to focus the electron beam on the sample 106. Specifically, the electron beam emitted from the electron beam source 101 is passed through the deflection element 102 and the objective lens 103 and focused on the sample 106. The sample 106 rests on an XY stage 105 and the position thereof is measured by a laser length measuring system 107. Further, in the case of an SEM apparatus, a secondary electron emitted from the sample 106 is detected by a secondary electron detector 104, and a detected secondary electron signal is converted by an A/D converter 122 into an SEM image. The SEM image thus converted is processed by an image processing unit 124. In the case of the length measuring SEM, for example, the image processing unit 124 measures a distance between patterns of a designated image. Also, in the case of an observation SEM (appearance inspection based on the SEM image), the image processing unit 124 executes a processing such as emphasis of the image or the like. The secondary electron includes a secondary electron with a higher energy level which is sometimes called a back-scattered electron. From the viewpoint of forming scanning electron images, it is not meaningful to discriminate between the back-scattered electron and the secondary electron. In accordance with the present invention, an electron beam image is prevented from being deteriorated in the above-mentioned electron beam apparatus (observation SEM apparatus, length measuring SEM apparatus). The quality of the electron beam image is deteriorated due to image distortion caused by deflection and aberration of the electron optical system, and a resolution is lowered by de-focusing. For preventing the image quality from being deteriorated, the present invention provides, as shown in FIG. 2, a height detection apparatus 200 composed of a height detection optical apparatus 200a and a height calculating unit 200b, a focus control apparatus 109, a deflection signal generating apparatus 108, and an entirety control apparatus 120. The height detection apparatus 200 composed of the height detection optical apparatus 200a and the height calculating unit 200b is arranged substantially similarly to a second embodiment which will be described later, and is installed about an optical axis 110 of an electron beam symmetrically with respect to the sample 106. An illumination optical system of each height detection optical apparatus 200a comprises a light source 201, a condenser lens 202, a mask 203 with a multi-slit pattern, a half mirror 205, and a projection/detection lens 220. A detection optical system of each height detection optical apparatus 200a comprises a projection/detection lens 220, a magnifying lens 264 for focusing an intermediate multi-slit image focused by the projection/detection lens 220 on a line image sensor 214 in an enlarged scale, a mirror 206, a cylindrical lens (cylindrical lens) 213, and a line image sensor 214. By the illumination optical system of the respective height detection optical apparatus which is installed symmetrically, a multi-slit shaped pattern is projected at the measurement position on the sample 106 for detecting an SEM image with the above-mentioned irradiation of electron beams. This regularly-reflected image is focused by the detection optical system of each height detection optical apparatus 200a and thereby detected as a multi-slit image. Specifically, since the height detection optical apparatus 200a projects and detects patterns of multi-slit shape from the left and right symmetrical directions and the height calculating unit 200b constantly obtains a height of a constant point 110 by averaging both detected values, it is necessary to locate a pair of height detection optical apparatus 200a in the left and right directions. Initially, a light beam emitted from the light source 201 is converged by the condenser lens 202 in such a manner that a light source image is focused at the pupil of the projection/detection lens. This light beam further illuminates the mask 203 on which the multi-slit shaped pattern is formed. Of the light beams, the light beam that was reflected on the half mirror 205 is projected by the projection/detection lens 220 onto the sample 106. The multi-slit pattern that was projected onto the sample is regularly reflected and passed through the projection/detection lens 220 of the opposite side. Then, the light beam passed through the half mirror 205 is focused in front of the magnifying lens 264. This intermediate image is focused on the line image sensor 214 by the magnifying lens 264. At that time, of the luminous flux, the portion that was passed through the half mirror 205 is focused on the line image sensor 214. In this embodiment, the cylindrical lens 213 is disposed ahead of the line image sensor 214 to compress the longitudinal direction of the slit and thereby the light beam is converged on the line image sensor 214. Assuming that m is a magnification of the detection optical system, then when the height of the sample is changed by z, a multi-slit image is shifted by 2mz·sin θ on the whole. By utilizing this fact, the height calculating unit 200b calculates a shift amount of the multi-slit image from a signal of a multi-slit image detected from the detection optical system of each height detection optical apparatus 200a, calculates a height of a sample from the calculated shift amount of the multi-slit image, and obtains a height on the electron beam optical axis 110 on the sample by averaging these calculated heights of the sample. Specifically, the height calculating means 200b calculates the height of the sample 106 from the shift amounts of the right and left multi-slit images. Here, an average value therebetween is calculated by using the height detected values obtained from the right and left detection system 200a, and is set to a height detection value at the final point 110. The position 110 at which the height is to be detected becomes an optical axis of the upper observation system. Incidentally, while the height detection optical apparatus 200a is arranged substantially similarly to a second embodiment as shown in FIG. 15 as described above, it is apparent that the optical system according to the first embodiment as shown in FIG. 10 or an optical system according to a third embodiment as shown in FIG. 16 or optical systems according to embodiments as shown in FIGS. 25, 26, 27, 30 may be used. The focus control apparatus 109 drives and controls an electromagnetic lens or an electrostatic lens on the basis of height data 190 obtained from the height calculating unit 200b to thereby focus an electron beam on the surface of the sample 106. A deflection signal generating apparatus 108 generates the deflection signal 141 to the deflection element 102. At that time, the deflection signal generating apparatus 108 corrects the deflection signal 141 on the basis of the height data obtained from the height calculating unit 200b in such a manner as to compensate for an image magnification fluctuation caused by the fluctuation of the height of the surface of the sample 106 and an image rotation caused by the control of the electromagnetic lens 103. Incidentally, if an electrostatic lens is used as the objective lens 103 instead of the electromagnetic lens, then the image rotation caused when the focus is controlled does not occur so that the image rotation need not be corrected by the height data 190. Further, if lens 103 is comprised of a combination of an electromagnetic lens and an electrostatic lens, the electromagnetic lens has a main converging action and the electrostatic lens adjusts the focus position, then the image rotation, of course, need not be corrected by the height data 190. Further, instead of directly controlling the focus position of the electromagnetic lens or the electrostatic lens 103 by the focus control apparatus 109 under the condition that the stage 105 is used as an XYZ stage, the height of the stage 105 may be controlled. The entirety control apparatus 120 controls the whole of the electron beam apparatus (SEM apparatus), displays a processed result processed by the image processing apparatus 124 on a display 143 or stores the same in a memory 142 together with coordinate data for the sample. Also, the entirety control apparatus 120 controls the height calculating unit 200b, the focus control apparatus 109 and the deflection signal generating apparatus 108 thereby to realize a high-speed auto focus control in the electron beam apparatus and an image magnification correction and an image rotation correction caused by this focus control. Furthermore, the entirety control apparatus 120 executes a correction of a height detected value, which will be described later. FIG. 3 shows a defect detection apparatus using an SEM image according to an embodiment of the present invention. Specifically, the appearance inspection apparatus using an SEM image comprises an electron beam source 101 for generating electron beams, a beam deflector 102 for forming an image by scanning beams, an objective lens 103 for focusing electron beams on an inspected object 106 formed of a wafer or the like, a grid 118 disposed between the objective lens 103 and an inspected object 106, a stage 105 for holding, scanning or positioning the inspected object 106, a secondary electron detector 104 for detecting secondary electrons generated from the inspected object 106, a height detection optical apparatus 200a, a focus position control apparatus 109 for adjusting a focus position of the objective lens 103, an electron beam source potential adjusting unit 121 for controlling a voltage of the electron beam source, a deflection control apparatus (deflection signal generating apparatus) 108 for realizing a beam scanning by controlling the beam deflector 102, a grid potential adjusting unit 127 for controlling a potential of the grid 118, a sample holder potential adjusting unit 125 for adjusting a potential of a sample holder, an A/D converter 122 for A/D-converting a signal from the secondary electron detector 104, an image processing circuit 124 for processing a digital image thus A/D-converted, an image memory 123 therefor, a stage control unit 126 for controlling the stage, an entirety control unit 120 for controlling the entirety, and a vacuum sample chamber (vacuum reservoir) 100. A height detection value 190 of the height detection sensor 200 is constantly fed back to the focus position control apparatus 109 and a deflection control apparatus (deflection signal generating apparatus) 108. When the inspected object 106 is inspected, the entirety control unit 120 continuously moves the stage 105 by issuing a command to the stage control apparatus 126. Concurrently therewith, the entirety control unit 120 issues a command to the deflection control apparatus (deflection signal generating apparatus) 108, and the deflection control apparatus 108 drives the beam deflector 102 to scan electron beams in the direction perpendicular thereto. Simultaneously, the deflection control apparatus 108 receives the height detection value 190 obtained from the height calculating unit 200b and corrects a deflection direction and a deflection width. The focus position control apparatus 109 drives the electromagnetic lens or electrostatic lens 103 in accordance with the height detection value 190 obtained from the calculating unit 200b, and corrects a properly-focused height of electron beam. At that time, the secondary electron detector 104 detects secondary electrons generated from the sample 106 and enters the detected secondary electron into the A/D converter 122 to thereby continuously obtain SEM images. When the appearance of the inspected object is inspected based on the SEM image, a two-dimensional SEM image should be obtained over a certain wide area. As a result, driving the beam deflector 102 to scan electron beams in the direction substantially perpendicular to the movement direction of the stage 105 while the stage 105 is being continuously moved, it is necessary to detect a two-dimensional secondary electron image signal by the secondary electron detector 104. Specifically, while the stage 105 is being continuously moved in the X direction, for example, the beam deflector 102 is moved to scan electron beams in the Y direction substantially perpendicular to the movement direction of the stage 105, and then the stage 105 is moved in a stepwise fashion in the Y direction. Thereafter, while the stage 105 is being continuously moved in the X direction, the beam deflector 102 is driven to scan electron beams in the Y direction substantially perpendicular to the movement direction of the stage 105, and a two-dimensional secondary electron image signal has to be detected by the secondary electron detector 104. The processes of (1) continuous movement of the stage, (2) beam scanning, (3) optical height detection, (4) focus control and/or deflection direction and width correction, and (5) secondary electron image acquisition should be executed simultaneously. In this way, the acquired SEM image is kept focused and distortion-corrected while the image is being acquired continuously and speedily. By this control, fast and high-sensitivity defect detection can be achieved. Then, the image processing circuit 124 compares corresponding images or repetitive patterns by comparing an electron beam image delayed by the image memory and an image directly inputted from the A/D converter 124, thereby resulting in the comparison inspection being realized. The entirety control unit 120 receives the inspected result at the same time it controls the image processing circuit 124, and then displays the inspected result on the display 143 or stores the same in the memory 142. Incidentally, in the embodiment shown in FIG. 3, while a focus is adjusted by controlling a control current flowing to the objective lens 103 having an excellent responsiveness, the present invention is not limited thereto, and the stage 105 may be elevated and lowered. However, if the focus is adjusted by elevating and lowering the stage 105, then responsiveness is deteriorated. Further, the appearance inspection apparatus using an SEM image will be described with reference to FIGS. 4 to 9. FIG. 4 shows the appearance inspection apparatus using an SEM image according to an embodiment of the present invention. In this embodiment, an electron beam 112 scans the inspected object 106 such as a wafer and electrons generated from the inspected object 106 are detected by the irradiation of electron beams. Then, an electronic beam image at the scanning portion is obtained on the basis of the change of intensity, and the pattern is inspected by using the electron beam image. As the inspected object 106, there is the semiconductor wafer 3 as shown in FIGS. 5(a)-5(c), for example. On this semiconductor wafer 3, there are arrayed a number of chips 3a which form the same product finally as shown in FIG. 5(a). An inside pattern layout of the chip 3a comprises a memory mat portion 3c in which memory cells are regularly arranged at the same pitch in a two-dimensional fashion and a peripheral circuit portion 3b as shown by an enlarged view in FIG. 5(b). When the present invention is applied to the inspection of the pattern of this semiconductor wafer 3, a detected image at a certain chip (e.g. chip 3d) is memorized in advance, and then compared with a detected image of another chip (e.g. 3e) (hereinafter referred to as “chip comparison”). Alternatively, a detected image at a certain memory cell (e.g. memory cell 3f) is memorized in advance, and then compared with a detected image of other cell (e.g. cell 3g) (hereinafter referred to as “cell comparison”) as shown in FIG. 5(c), thereby resulting in a defect being recognized. If the repetitive patterns (chips or cells of the semiconductor wafer, by way of example) of the inspected object 106 are equal to each other strictly and if equal detected images are obtained, then only defects cannot agree with each other when images are compared with each other. Thus, it is possible to recognize a defect. However, in actual practice, a disagreement between images exists in the normal portion. As a disagreement at the normal portion, there are a disagreement caused by the inspected object, and a disagreement caused by the image detection system. The disagreement caused by the inspected object is based on a subtle difference caused between the repetitive patterns by a wafer manufacturing process such as exposure, development or etching. This disagreement appears as a subtle difference of pattern shape and a difference of gradation value. The disagreement caused by the image detection system is based on a fluctuation of a quantity of illumination light, a vibration of stage, various electrical noises, and a disagreement between detection positions of two images or the like. These disagreements appear as a difference of gradation value of a partial image, a distortion of pattern, and a positional displacement of an image on the detected image. In the embodiment according to the present invention, a detection image (first two-dimensional image) in which gradation values of coordinates (x, y) aligned at the pixel unit are f1(x, y) and a compared image (second two-dimensional image) in which gradation values of coordinates (x, y) are g1(x, y) are compared with each other, a threshold value (allowance value) used when a defect is determined is set at every pixel considering the positional displacement of pattern and a difference between the gradation values, and a defect is determined on the basis of a threshold value (allowance value set at every pixel. A pattern inspection system according to the present invention comprises, as shown in FIGS. 4 and 7, a detection unit 115, an image output unit 140, an image processing unit 124 and an entirety control unit 120 for controlling the entire system. Incidentally, the present pattern inspection system includes an inspection chamber 100 whose inside is vacated and exhausted by vacuum and a reserve chamber (not shown) for inserting and ejecting the inspected object 106 into and from the inspection chamber 100. This reserve chamber can be vacated and exhausted by vacuum independently of the inspection chamber 100. Initially, the inspection unit 115 will be described with reference to FIGS. 4 and 7. Specifically, the inside of the inspection chamber 100 in the detection unit 115 generally comprises, as shown in FIG. 7, an electron optical system 116, an electron detection unit 117, a sample chamber 119, and an optical microscope unit 118. The electron optical system 116 comprises an electron gun 31 (101), an electron beam deriving electrode 11, a condenser lens 32, a blanking deflector 13, a scanning deflector 34 (102), an iris 14, an objective lens 33 (103), a reflecting plate 17, an ExB deflector 15, and a Faraday cup (not shown) for detecting a beam current. The reflecting plate 17 is shaped as a circular cone in order to achieve a secondary electron amplification effect. Of the electron detection unit 117, the electron detector 35 (104) for detecting electrons such as secondary electrons or reflection electrons is installed above the objective lens 33 (103), for example, within the inspection chamber 100. An output signal from the electron detector 35 is amplified by an amplifier 36 installed outside the inspection chamber 100. The sample chamber 119 comprises a sample holder 30, an X stage 31 and a Y stage 32 previously referred to as stage 105, a position monitoring length measuring device 107 and a height measuring apparatus 200 such as an inspected based plate height measuring device. Incidentally, there may be provided a rotary stage on the stage. The position monitoring length measuring device 107 monitors a position such as the stages 31, 32 (stage 105), and transfers a monitored result to the entirety control unit 120. The driving systems of the stages 31, 32 also are controlled by the entirety control unit 120. As a result, the entirety control unit 120 is able to precisely understand the area and the position irradiated with electron beams 112 on the basis of such data. The inspected base plate height measuring device is adapted to measure the height of the inspected object 106 resting on the stages 31, 32. Then, a focal length of the objective lens 33 (103) for converging the electron beam 112 is dynamically corrected on the basis of measured data measured by the inspected base plate height measuring device 200 so that electron beams can be irradiated under the condition that electron beams are constantly properly-focused on the inspected area. Incidentally, in FIG. 7, although the height measuring apparatus 200 is installed within the inspection chamber 100, the present invention is not limited thereto, and there may used a system in which the height measuring device is installed outside the inspection chamber 100 and light is projected into the inside of the inspection chamber 100 through a glass window or the like. The optical microscope unit 118 is located at the position near the electron optical system 116 within the room of the inspection chamber 100 and which position is distant to the extent that the optical microscope unit and the electron optical system cannot affect each other. A distance between the electron optical system 116 and the optical microscope unit 118 should naturally be a known value. Then, the X stage 31 or the Y stage 32 is reciprocally moved between the electron optical system 116 and the optical microscope unit 118. The optical microscope unit 118 comprises a light source 61, an optical lens 62, and a CCD camera 63. The optical microscope unit 118 detects the inspected object 106, e.g. an optical image of a circuit pattern formed on the semiconductor wafer 3, calculates a rotation displacement amount of circuit patterns based on the optical image thus detected, and transmits the rotation displacement amount thus calculated to the entirety control unit 120. Then, the entirety control unit 120 becomes able to correct this rotation displacement amount by rotating a rotating stage forming a part of stage 2 (105) which includes stages 31 and 32, for example. Also, the entirety control unit 120 sends this rotation displacement amount to a correction control circuit 120′, and the correction control circuit 120′ becomes able to correct the rotation displacement by correcting the scanning deflection position of electron beams caused by the scanning deflector 34, for example, on the basis of this rotation displacement amount. Moreover, the optical microscope unit 118 detects the inspected object 106, e.g. the optical image of the circuit pattern formed on the semiconductor wafer 3, observes this optical image, for example, displayed on the monitor 50, and sets the inspection area on the entirety control unit 120 by entering the coordinates of the inspection area into the entirety control unit 120 by using an input based on the optical image thus observed. Furthermore, the pitch between the chips on the circuit pattern formed on the semiconductor wafer 3, for example, or the repetitive pitch of the repetitive pattern such as the memory cell can be measured in advance and can be inputted to the entirety control unit 120. Incidentally, while the optical microscope unit 118 is located within the inspection chamber 100 in FIG. 7, the present invention is not limited thereto, and the optical microscope unit may be located outside the inspection chamber 100 to thereby detect the optical image of the semiconductor wafer 3 through a glass window or the like. As shown in FIGS. 4 and 7, the electron beam emitted from the electron gun 31 (101) travels through the condenser lens 32 and the objective lens 33 (103) and is converged to a beam diameter of about pixel size on the sample surface. In that case, a negative potential is applied to the sample by the ground electrode 38 (118) and the retarding electrode 37 and the electron beam between the objective lens 33 (103) and the inspected object (sample) 106 is decelerated, whereby a resolution can be improved in a low acceleration voltage area. When irradiated with electron beams, the inspected object (wafer 3) 106 generates electrons. The scanning deflector 34 (102) scans repeatedly electron beams in the X direction and electrons generated from the inspected object 106 in synchronism with the continuous movement of the inspected object (sample) 106 in the X direction by the stage 2 (105) are detected, thereby obtaining a two-dimensional electron beam image of the inspected object. The electrons generated from the inspected object are detected by the detector 35 (104), and amplified by the amplifier 36. In order to make the high-speed scanning possible, an electrostatic deflector of which deflection speed is high should preferably be used as the deflector 34 (102) for repeatedly scanning electron beams in the X direction. Moreover, a thermal electric field radiation type electron gun should preferably be used as the electron gun 31 (101) because it can reduce the irradiation time by increasing the electron beam current. Further, a semiconductor detector which can be driven at a high speed should preferably be used as the detector 35 (104). Next, the image output unit 140 will be described with reference to FIGS. 4, 7, and 8. Specifically, an electron detection signal detected by the electron detector 35 (104) in the electron detection unit 117 is amplified by the amplifier 36, and then converted by the A/D converter 39 (122) into digital image data (gradation image data). Then, the output from the A/D converter 39 (122) is transmitted by an optical converter (light-emitting element) 23, a transmission device (optical fiber cable) 24, and an electric converter (light-receiving device) 25. According to this arrangement, the transmission device 24 may have the same transmission speed as the clock frequency of the A/D converter 39 (122). The output from the A/D converter 39 is converted by the optical converter (light-emitting element) 23 into an optical digital signal, optically transmitted by the transmission device (optical fiber cable) 24 and then converted by the electric converter (light-receiver) 25 into digital image data (gradation image data). The reason that the output signal is converted into the optical signal and then transmitted is that, in order to supply electrons 52 from the reflection plate 17 into the semiconductor detector 35 (104), constituents (semiconductor detector 35, amplifier 36, A/D converter 39, and optical converter (light-emitting element) 23 from the semiconductor detector 35 to the optical converter 23 should be floated at a positive high potential by a high-voltage power supply source (not shown). More precisely, only the semiconductor detector 35 need be floated to the positive high potential. However, the amplifier 36 and the A/D converter 39 should preferably be located near the semiconductor detector in order to prevent noise from being mixed and a signal from being deteriorated. It is difficult to maintain only the semiconductor detector 35 at the positive high voltage, and hence all of the above-mentioned constituents should be held at the high voltage. Specifically, since the transmission device (optical fiber cable) 24 is made of a high insulating material, after the image signal which is held at the positive high potential level in the optical converter (light-emitting element) 23 is passed through the transmission device (optical fiber cable) 24, the electric converter (light-receiver) 25 outputs an image signal of earth level. The pre-processing circuit (image correcting circuit) 40 comprises, as shown in FIG. 8, a dark level correcting circuit 72, an electron beam source fluctuation correcting circuit 73, a shading correcting circuit 74 and the like. Digital image data (gradation image data) 71 obtained from the electric converter (light-receiving element) 25 is supplied to the pre-processing circuit (image correcting circuit) 40, in which it is image-corrected such as a dark level correction, an electron beam source fluctuation correction or a shading correction. In the dark level correction in the dark level correcting circuit 72, as shown in FIG. 9, a dark level is corrected on the basis of a detection signal 71 in a beam blanking period extracted based on a scanning line synchronizing signal 75 obtained from the entirety control unit 120. Specifically, the reference signal for correcting the dark level sets an average of a gradation value of a specific number of pixels in a particular position during the beam blanking period to the dark level, and updates the dark level at every scanning line. As described above, in the dark level correcting circuit 72, the detection signal detected during the beam blanking period is dark-level-corrected to the reference signal which is updated at every line. When the electron beam source fluctuation is corrected by the electron beam source fluctuation correcting circuit 73, as shown in FIG. 9, a detection signal 76 of which the dark level is corrected is normalized by a beam current 77 monitored by the Faraday cup (not shown) which detects the above-mentioned beam current at a correction cycle (e.g. line unit of 100 kHz). Since the fluctuation of the electron beam source is not rapid, it is possible to use a beam current that was detected one to several lines before. When a shading is corrected by the shading correcting circuit 74, as shown in FIG. 9, the fluctuation of the quantity of light caused in a detection signal 78 in which the electron beam source fluctuation was corrected at the beam scanning position 79 obtained from the entirety control unit 120 is corrected. Specifically, the shading correction executes the correction (normalization) at every pixel on the basis of reference brightness data 83 which is previously detected. The shading correction reference data 83 is previously detected, the detected image data is temporarily stored in an image memory, the image data thus stored is transmitted to a computer disposed within the entirety control unit 120 or a high-order computer connected to the entirety control unit 120 through a network, and processed by software in the computer disposed within the entirety control unit 120 or the high-order computer connected through the network to the entirety control unit 120, thereby resulting in the shading correction reference data being created. Moreover, the shading correction reference data 83 is calculated in advance and held by the high-order computer connected to the entirety control unit 120 through the network. When the inspection is started, the data is downloaded, and this downloaded data may be latched in a CPU in the shading correcting circuit 74. To cope with a full visual field width, the shading correcting circuit 74 includes two correction memories having pixel number (e.g. 1024 pixels) of an amplitude of an ordinary electron beam, and the memories are switched during a time (time from the end of one visual field inspection to the start of the next one visual field inspection) outside the inspection area. The correction data may have pixel number (e.g. 5000 pixels) of a maximum amplitude of an electron beam, and the CPU may rewritten such data in each correction memory till the end of the next one visual field inspection. As described above, after the dark level correction (dark level is corrected on the basis of the detection signal 71 during the beam blanking period), the electron beam current fluctuation correction (beam current intensity is monitored and a signal is normalized by a beam current) and the shading correction (fluctuation of quantity of light at the beam scanning position is corrected) are effected on the digital image data (gradation image data) 71 obtained from the electric converter (light-receiving element) 25, the filtering processing is effected on the corrected digital image data (gradation image data) 80 by a Gaussian filter, a mean value filter or an edge-emphasizing filter in the filtering processing circuit 81, thereby resulting a digital image signal 82 with an image quality being improved. If necessary, a distortion of an image is corrected. These pre-processings are executed in order to convert a detected image so as to become advantageous in the later defect judgment processing. Although the delay circuit 41 formed of a shift register or the like delays the digital image signal 82 (gradation image signal) with an improved image quality from the pre-processing circuit 40 by a constant time, if a delay time is obtained from the entirety control unit 120 and set to a time during which the stage 2 is moved by a chip pitch amount (d1 in FIG. 5(a)), then a delayed signal g0 and a signal f0 which is not delayed become image signals obtained at the same position of the adjacent chips, thereby resulting in the aforementioned chip comparison inspection being realized. Alternatively, if the delay time is obtained from the entirety control unit 120 and set to a time during which the stage 2 is moved by a pitch amount (d2 in FIG. 5(c)) of the memory cell, then the delayed signal g0 and the signal f0 which is not delayed become image signals obtained at the same position of the adjacent memory cells, thereby resulting in the aforementioned cell comparison inspection being realized. As described above, the delay circuit 41 is able to select an arbitrary delay time by controlling a read-out pixel position based on information obtained from the entirety control unit 120. As described above, compared digital image signals (gradation image signals) f0 and g0 are outputted from the image output unit 140. Hereinafter, f0 will be referred to as a detection image and g0 will be referred to as a comparison image. Incidentally, as shown in FIG. 7, the comparison image signal f0 may be stored in a first image memory unit 46 composed of a shift register and an image memory and the detection image signal f0 may be stored in a second image memory unit 47 composed of a shift register and an image memory. As described above, the first image memory unit 46 may comprise the delay circuit 41, and the second image memory unit 47 is not necessarily required. Moreover, an electron beam image latched within the pre-processing circuit 40 and the second image memory unit 47 or the like or the optical image detected by the optical microscope unit 118 may be displayed on the monitor and can be observed. The image processing unit 124 will be described with reference to FIG. 4. The pre-processing circuit 40 outputs a detection image f0(x, y) expressed by a gradation value (light and shade value) with respect to a certain inspection area on the inspected object 106, and the delay circuit 41 outputs a comparison image (standard image: reference image) g0(x, y) expressed by a gradation value (light and shade value) with respect to a certain area on the inspected object 106 which becomes a standard to be compared. The pixel unit position alignment unit 42 of image processing unit 124 displaces the position of comparison image, for example, in such a manner that the position displacement amount of the comparison image g0(x, y) relative to the above-mentioned detection image f0(x, y) falls in a range of from 0 to 1 pixel, in other words, the position at which a “matching degree” between f0(x, y) and g0(x, y) becomes maximum falls within a range of from 0 to 1 pixel. As a consequence, as shown in FIGS. 6(a) and 6(b), for example, the detection image f0(x, y) and the comparison image g0(x, y) are aligned with an alignment accuracy of less than one pixel. A square portion shown by dotted lines in FIG. 6 denotes a pixel. This pixel is a unit detected by the electron detector 35, sampled by the A/D converter 39 (122), and converted into a digital value (gradation value: light and shade value). That is, the pixel unit denotes a minimum unit detected by the electron detector 35. Incidentally, as the above-mentioned “matching degree”, there may be considered the following equation (expression 1):max|f0−g0|,ΣΣ|f0−g0|,ΣΣ(f0−g0)2 (expression 1) max|f0−g0| shows a maximum value of an absolute value of a difference between the detection image f0(x, y) and the comparison image g0(x, y). ΣΣ|f0−g0| shows a total of absolute value of a difference between the detection image f0(x, y) and the comparison image g0(x, y) within the image. ΣΣ(f0−g0) shows a value which results from squaring a difference between the detection image f0(x, y) and the comparison image g0(x, y) and integrating the squared result in the x direction and the y direction. Although the processed content is changed depending upon the adoption of any one of the above-mentioned (expression 1), the case that ΣΣ|f0−g0| is adopted will be described below. Mx assumes the displacement amount of the comparison image g0(x, y) in the x direction, and my assumes the displacement in the y direction (mx, my are integers). Then, e1(mx, my) and s1(mx, my) are defined by equations of (expression 2) and (expression 3), respectively:e1(mx,my)=ΣΣ|f0(x, y)−g0(x+mx, y+my) (expression 2)s1(mx,my)=e1(mx,my)+e1(mx+1,my)+e1(mx,my+1)+e1(mx+1,my+1) (expression 3) In the expression 2, ΣΣ shows a total within the image. Since what is required to calculate is a value obtained when mx assumes the displacement amount of the x direction in which s1(mx, my) becomes minimum and a value obtained when my assumes the displacement amount of the y direction, by changing mx and my as ±0, 1, 2, 3, 4, . . . n, in other words, by changing the comparison image g0(x, y) with a pixel pitch, there is calculated s1(mx, my) of each time. Then, a value mx0 of mx in which the calculated value becomes minimum and a value my0 of my in which the calculated value becomes minimum are calculated. Incidentally, the maximum displacement amount n of the comparison image should be increased as the positional accuracy is lowered in response to the positional accuracy of the detection unit 115. The pixel unit position alignment unit 42 outputs the detection image f0(x, y) at it is, and outputs the comparison image g0(x, y) with a displacement of (mx0, my0). That is, f1(x, y)=f0(x, y), g1(x, y)=g0(x+mx0, y+my0). A positional displacement detection unit (not shown) for detecting a positional displacement of less than a pixel divides the images f1(x, y), g(x, y) aligned at the pixel unit into small areas (e.g. partial images composed of 128* 256 pixels), and calculates positional displacement amounts (positional displacement amounts become real number of 0 to 1) of less than the pixel at every divided area (partial image). The reason that the images are divided into small areas is in order to cope with a distortion of an image, and hence should be set to a small area to the extent that a distortion can be neglected. As a measure for measuring a matching degree, there are the selection branches shown in the expression 1. An example is shown in which the third “sum of squares of difference” (ΣΣ(f0−g0)2) is adopted. Let it be assumed that an intermediate position between f1(x, y) and g1(x, y) is held at the positional displacement amount 0 and that, as shown in FIG. 6, f1 is displaced y−δx in the x direction, f1 is displaced by −δy in the by direction, g1 is displaced by +δx in the x direction, and that g1 is displaced by +δy in the y direction. That is, the displacement amounts of f1 and g1 are 2*δx in the x direction and 2*δy in the y direction. Since δx, δy are not integers, in order to displace f1 and g1 by δx, δy, it is necessary to define a value between the pixels. An image f2 in which f1 is displaced by +δx in the x direction and by +δy in the y direction and an image g2 in which g1 is displaced by −δx in the x direction and by −δy in the y direction are defined as the following equations of (expression 4) and (expression 5):f2(x, y)=f1(x+δx, y+δy)=f1(x, y)+δx(f1(x+1,y)−f1(x, y))+δy(f1(x, y+1)−f1(x, y)) (expression 4)g2(x, y)=g1(x−δx, y−δy)=g1(x, y)+δx(g1(x−1,y)−g1(x, y))+δy(g1(x, y−1)−g1(x, y)) (expression 5) The expression 4 and the expression 5 are what might be called linear interpolations. A matching degree e2(δx, δy) of f2 and g2 is represented by the following equation of (expression 6) if “sum of squares of difference” is adopted.e2(δx,δy)=ΣΣ(f2(x, y)−g2(x, y))2 (expression 6) ΣΣ denotes a total within small areas (partial images). The object of the positional displacement detection unit (not shown) for detecting a positional displacement of less than the pixel unit is to obtain a value δx0 of δx and a value δy0 of δy in which e2(δx, δy) takes the minimum value. To this end, an equation which results from partially differentiating the above-mentioned expression 6 by δx, δy is set to 0 and may be solved. The results are obtained as shown by the following equations of (expression 7) and (expression 8):δx={(ΣΣC0*Cy)*(ΣΣCx*Cy)ΣΣC0*Cx)*(ΣΣCy*Cy)}/{(ΣΣCx*Cx)*(ΣΣCy*Cy)−(ΣΣCx*Cy*(ΣΣCx*Cy)} (expression 7)δx={(ΣΣC0*Cx)*(ΣΣCx*Cy)ΣΣC0*Cy)*(ΣΣCx*Cx)}/{(ΣΣCx*Cx)*(ΣΣCy*Cy)−(ΣΣCx*Cy)*(ΣΣCx*Cy)} (expression 8) However, respective ones of C0, Cx, Cy establish relationships shown by the following equations of (expression 9), (expression 10) and (expression 11):C0=f1(x, y)−g1(x, y) (expression 9)Cx={f1(x+1,y)−f1(x, y)}−{g1(x−1,y)−g1(x, y) (expression 10)Cy={f1(x, y+1)−f1(x, y)}−{g1(x, y−1)−g1(x, y)} (expression 11) In order to obtain δx0, δy0, respectively, as shown by the (expression 7) and the (expression 8), it is necessary to obtain a variety of statistic amounts ΣΣCk*Ck (Ck=C0, Cx, Cy). The statistic amount calculating unit 44 calculates a variety of statistic amount ΣΣCk*Ck on the basis of the detection image f1(x, y) composed of the gradation value (light and shade value) aligned at the pixel unit obtained from the pixel unit position alignment unit 42 and the comparison image g1(x, y). The sub-CPU 45 obtains δx0, δy0 by calculating the (expression 7) and the (expression 8) by using the ΣΣCk*Ck which was calculated in the statistic amount calculating unit 44. The delay circuits 46, 47 formed of the shift register or the like are adapted to delay the image signals f1 and g1 by the time which is required by the less than pixel positional displacement unit (not shown) to calculate δx0, δy0. The difference image extracting circuit (difference extracting circuit: distance extracting unit) 49 is adapted to obtain a difference image (distance image) sub(x, y) between f1 and g1 having positional displacements 2*δx0, 2*δy0 from a calculation standpoint. This difference image (distance image) sub(x, y) is expressed by the equation of (expression 12) as follows:sub(x, y)=g1(x, y)−f1(x, y) (expression 12) The threshold value computing circuit (allowance range computing unit) 48 is adapted to calculate by using the image signals f1, g1 from the delay circuits 46, 47 and the positional displacement amounts δx0, δy0 of less than the pixel obtained from the less than pixel positional displacement detection unit (not shown) two threshold values (allowance values indicative of allowance ranges) thH(x, y) and thL(x, y) which are used by the defect deciding circuit (defect judgment unit) 50 to determine in response to the value of the difference image (distance image) sub(x, y) obtained from the difference image extracting circuit (difference extracting circuit: distance extracting unit) 49 whether or not the inspected object is the nominated defect. ThH(x, y) is the threshold value (allowance value indicative of allowance range) which determines the upper limit of the difference image (distance image) sub(x, y), and thL(x, y) is the threshold value (allowance value indicative of allowance range) which determines the lower limit of the difference image (distance image) sub(x, y). Contents of the computation in the threshold value computing circuit 48 are expressed by the equations of (expression 13) and (expression 14) as follows:thH(x, y)=A(x, y)+B(x, y)+C(x, y) (expression 13)thL(x, y)=A(x, y)−B(x, y)−C(x, y) (expression 14) However, A(x, y) is a term expressed by a relationship of the following equation of (expression 16) and which is used to correct the threshold values by using the less than pixel positional displacement amounts δx0, δy0 in response to the value of the difference image (distance image) sub(x, y) substantially. Also, B(x, y) is a term expressed by a relationship of the equation of the (expression 16) and which is used to allow a very small positional displacement of a pattern edge (very small difference of pattern shape, pattern distortion also returns to a very small positional displacement of pattern edge from a local standpoint) between the detection image f1 and the comparison image g1. Also, C(x, y) is a term expressed by a relationship of the equation of (expression 17) and which is used to allow a very small difference of gradation value (light and shade value) between the detection image f1 and the comparison image g1).A(x, y)={dx1(x, y)*δx0−dx2(x, y)*(−δx0)}+{dy1(x, y)*δy0−dy2(x, y)*(−δy0)}={dx1(x, y)+dx2(x, y)}*δx0+{dy1(x, y)+dy2(x, y)}*δy0 (expression 15)B(x, y)=|{dx1(x, y)*α−dx2(x, y)*(−α)}|+|{dy1(x, y)*β−dy2(x, y)*(−β)}|=|{dx1(x, y)+dx2(x, y)}*α|+|{dy1(x, y)+dy2(x, y)}*β| (expression 16)C(x, y)=((max1+max2)/2)*γ+ε (expression 17)where α, β are the real numbers ranging from 0 to 0.5, γ is the real number greater than 0, and ε is the integer greater than 0. dx1(x, y) is expressed by a relationship of the equation of (expression 18), and indicates a changed amount of a gradation value (light and shade value) with respect to the x direction+1 adjacent image in the detection image f1(x, y). dy2(x, y) is expressed by a relationship of the equation of (expression 19), and indicates a changed amount of a gradation value (light and shade value) with respect to the x direction−1 adjacent image in the comparison image g1(x, y). dy1(x, y) is expressed by a relationship of the equation of (expression 20), and indicates a changed amount of a gradation value (light and shade value) with respect to the y direction+1 adjacent image in the detection image f1(x, y). dy2(x, y) is expressed by a relationship of the equation of (expression 21), and indicates a changed amount of a gradation value (light and shade value) with respect to the y direction−1 adjacent image in the comparison image g1(x, y).dx1(x, y)=f1(x+1,y)−f1(x, y) (expression 18)dx2(x, y)=g1(x, y)−g1(x−1,y) (expression 19)dy1(x, y)=f1(x, y+1)−f1(x, y) (expression 20)dy2(x, y)=g1(x, y)−g1(x, y−1) (expression 21) max1 is expressed by a relationship of the equation of (expression 22), and indicates maximum gradation values (light and shade values) of x direction+1 adjacent image and y direction+1 adjacent image including itself in the detection image f1(x, y). max2 is expressed by a relationship of the equation of (expression 23), and indicates maximum gradation values (light and shade values) of x direction−1 adjacent image and y direction−adjacent image including itself in the comparison image g1(x, y).max1=max{f1(x, y),f1(x+1,y),f1(x, y+1),f(x+1, y+1)} (expression 22)max2=max{g1(x, y),g1(x−1,y),g1(x, y−1),g(x−1,y−1)} (expression 23) First, the first term A(x, y) in the equations of (expression 13) and (expression 14) for calculating the threshold values thH(x, y), thL(x, y) will be described. Specifically, the first term A(x, y) in the equations of (expression 13) and (expression 14) for calculating the threshold values thH(x, y) and thL(x, y) is the term used to correct the threshold values in response to the less than pixel positional displacement amounts δx0, δy0 which were calculated by the positional displacement detection unit 43. Since dx1 expressed by (expression 18), for example, is a local changing rate of a gradation value of f1 in the x direction, dx1(x, y)*δx0 expressed by (expression 15) can be regarded as a predicted value of the change of the gradation value (light and shade value) of f1 obtained when the position is shifted by δx0. Therefore, the first term {dx1(x, y)*δx0−dx2(x, y)*(−δx0)} can be regarded as a value which predict at every pixel a changing rate of a gradation value (light and shade value) of the difference image (distance image) of f1 and g1 obtained when the position of f1 is displaced by δx0 in the x direction and the position of g1 is displaced by −δx0 in the x direction. Similarly, the second term can be regarded as the value which predicts a changing rate with respect to the y direction. Specifically, {dx1(x, y)+dx2(x, y)}*δx0 is a value which can predict a changing rate of a gradation value (light and shade value of difference image (distance image) of f1 and g1 in the x direction by multiplying a local changing rate {dx1(x, y)+dx2(x, y)} of the difference image (distance image) between the detection image f1 and the comparison image g1 in the x direction with the positional displacement δx0. Also, {dy1(x, y)+dy2(x, y)}*δy0 is a value which predicts at every pixel a changing rate of a gradation value (light and shade value) of the difference image (distance image) of f1 and g1 by multiplying a local changing rate {dy1(x, y)+dy2(x, y) of the difference image (distance image) between the detection image f1 and the comparison image g1 in the y direction with the positional displacement δy0. As described above, the first term A)x, y) in the threshold values thH(x, y) and thL(x, y) is the term used to cancel the known positional displacements δx0, δy0. The second term B(x, y) in the equations of (expression 13) and (expression 14) for calculating the threshold values thH(x, y) and thL(x, y) will be described. Specifically, the second term B(x, y) in the equations of (expression 13) and (expression 14) for calculating the threshold values thH(x, y) and thL(x, y) is the term used to allow a very small positional displacement of pattern edge (very small difference of pattern shape and pattern distortion also are returned to very small positional displacements of pattern edge from a local standpoint). As will be clear from the comparison of the (expression 15) for calculating A(x, y) and the (expression 16) for calculating B(x, y), B(x, y) is an absolute value of a change prediction of a gradation value (light and shade value) of the difference image (distance image) brought about by the positional displacements α, β. If the positional displacement is canceled by A(x, y), then the addition of B(x, y) to A(x, y) means that the position aligned state is further displaced by α in the x direction and by β in the y direction considering a very small positional displacement of pattern edge caused by a very small difference based on the pattern shape and the pattern distortion. That is, +B(x, y) expressed by the equation of (expression 13) is to allow the positional displacement of +α in the x direction and the positional displacement of +β in the y direction as the very small positional displacements of the pattern edge caused by the very small differences based on the pattern shape and the pattern distortion. Further, the subtraction of B(x, y) from A(x, y) in the equation of (expression 14) means that the positional aligned state is positionally displaced by −α in the x direction and by −β in the y direction. −B(x, y) expressed by the equation of (expression 14) is adapted to allow the positional displacement of −α in the x direction and −β in the y direction. As shown by the equations of (expression 13) and (expression 14), if the threshold value includes the upper limit thH(x, y) and the lower limit thL(x, y), then it is possible to allow the positional displacements of ±α, ±β. Then, if the threshold value computing circuit 48 sets the values of the inputted parameters α, β to proper values, then it becomes possible to freely control the allowable positional displacement amounts (very small positional displacement amounts of pattern edge) caused by the very small difference based on the pattern shape and the pattern distortion. Next, the third term C(x, y) in the equations of (expression 13) and (expression 14) for calculating the threshold values thH(x, y) and thL(x, y) will be described. The third term C(x, y) in the equations of (expression 13) and (expression 14) for calculating the threshold values thH(x, y) and thL(x, y) is a term used to allow a very small difference of a gradation value (light and shade value) between the detection image f1 and the comparison image g1. As shown by the equation of (expression 13), the addition of C(x, y) means that the gradation value (light and shade value) of the comparison image g1 is larger than the gradation value (light and shade value) of the detection image f1 by C(x, y). As shown by the equation of (expression 14), the subtraction of C(x, y) means that the gradation value (light and shade value) of the comparison value g1 is smaller than the gradation value (light and shade value) of the detection image by C(x, y). While C(x, y) is a sum of a value which results from multiplying a representing value (max value) of a gradation value at the local area with the proportional constant γ and the constant as shown by the equation of (expression 17), the present invention is not limited to the above-mentioned function. If the manner in which the gradation value is fluctuated is already known, then it is possible to use a function which can cope with such manner. For example, if it is clear that a fluctuation width is proportional to a square root of a gradation value, then the equation of (expression 17) should be replaced with C(x, y)=(square root of (max1+max2))*y+ε. Thus, the threshold value computing circuit 48 becomes able to freely control a difference of allowable gradation value (light and shade value) by the inputted parameters γ, ε similarly to B(x, y). Specifically, the threshold value computing circuit (allowable range computing unit) 48 includes a computing circuit for computing {dx1(x, y)+dx2(x, y)} by the equations of (expression 18) and (expression 19) based on the detection image f1(x, y) composed of a gradation value (light and shade value) inputted from the delay circuit 46 and the comparison image g1(x, y) composed of a gradation value (light and shade value) inputted from the delay circuit 47, a computing circuit for computing {dy1(x, y)+dy2(x, y)} by the equations of (expression 20) and (expression 21) and a computing circuit for computing (max1+max2) by the equations of (expression 22) and (expression 23). Further, the threshold value computing circuit 48 includes a computing circuit for computing ({dx1(x, y)+dx2(x, y)}*δx0±|{dx1(x, y)+dx2(x, y)}|*α) which is a part of (expression 15) and a part of (expression 16) on the basis of {dx1(x, y)+dx2(x, y)} obtained from the computing circuit, δx0 obtained from the less than pixel displacement detection unit 43 and the inputted a parameter, a computing circuit for computing (dy1(x, y)+dy2(x, y))*δy0±|{dy1(x, y)+dy2(x, y)}|*β) which is a part of (expression 15) and a part of (expression 16) on the basis of {dy1(x, y)+dy2(x, y)} obtained from the computing circuit, δy0 obtained from the less than pixel displacement detection unit 43 and the inputted β parameter and a computing circuit for computing ((max1+max2)/2)*γ+ε) in accordance with the equation of (expression 17), for example, on the basis of (max1+max2) obtained from the computing circuit and the inputted γ, ε parameters. Further, the threshold value computing circuit 48 includes an adding circuit for positively adding ({dx1(x, y)+dx2(x, y)}*δx0+|{dx1(x, y)+dx2(x, y)}|*α), ({dy1(x, y)+dy2(x, y)}*δy0+|{dy1(x, y)+dy2(x, y)}|*β) obtained from the computing circuit and ((max1+max2)/2)*γ+ε) obtained from the computing circuit to output the threshold value thH(x, y) of the upper limit, a subtracting circuit for negatively computing (((max1+max2)/2)*γ+ε) obtained from the computing circuit and an adding circuit for positively computing ({dx1(x, y)+dx2(x, y)}*δx0−|{dx1(x, y)+dx2(x, y)|*α} obtained from the computing circuit, ({dy1(x, y)+dy2(x, y)}*δy0−|{dy1(x, y)+dy2(x, y)}|*β) obtained from the computing circuit and −((max1+max2)/2*γ+ε) obtained from the subtracting circuit to output the threshold value thL(x, y) of the lower limit. Incidentally, the threshold value computing circuit 48 may be realized by a CPU by software processing. Further, the parameters α, β, γ, ε inputted to the threshold value computing circuit 48 may be entered by an input means (e.g. keyboard, recording medium, network or the like) disposed in the entirety control unit 120. The defect deciding circuit (defect judgment unit) 50 decides by using the difference image (distance image) sub(x, y) obtained from the difference image extracting circuit (difference extracting circuit) 49, the threshold value of the lower limit (allowable value indicating the allowable range of lower limit) thL(x, y) obtained from the threshold value computing circuit 48 and the threshold value of the upper limit (allowable value indicating the allowable range of upper limit) thH(x, y) that the pixel at the position (x, y) is a non-defect nominated pixel of the following equation of (expression 24) is satisfied and that the pixel at the position (x, y) is a defect nominated pixel if it is not satisfied. The defect deciding circuit 50 outputs def(x, y) which takes a value of 0, for example, with respect to the non-defect nominated pixel and which takes a value greater than 1, for example, the defect-nominated pixel indicating a disagreement amount.thL(x, y)≦sub(x, y)≦thH(x, y) (expression 24) The feature extracting circuit 50a executes a noise elimination processing (e.g. contracts/expands def(x, y). When all of 3×3 pixels are not simultaneously the defect-nominated pixels, the center pixel is set to 0 (non-defect nominated pixel), for example, and eliminated by a contraction processing, and is returned to the original one by an expansion processing. After a noise-like output (e.g. all 3×3 pixels are not simultaneously the defect-nominated pixels) is deleted, there is executed a defect-nominated pixel merge processing in which nearby defect-nominated pixels are collected into one. Thereafter, barycentric coordinates and XY projection lengths (maximum lengths in the x direction and the y direction) are demonstrated at the above-mentioned unit. Incidentally, the feature extracting circuit 50a calculates a feature amount 88 such as a square root of (square of X projection length+square of Y projection length) or an area, and outputs the calculated result. As described above, the image processing unit 124 controlled by the entirety control unit 120 outputs the feature amount (e.g. barycentric coordinates, XY projection lengths, area, etc.) of the defect-nominated portion in response to coordinates on the inspected object (sample) 106 which is detected with the irradiation of electron beams by the electron detector 35 (104). The entirety control unit 120 converts position coordinates of the defect-nominated portion on the detected image into the coordinate system on the inspected object (sample) 106, deletes a pseudo-defect, and finally forms defect data composed of the position on the inspected object (sample) 106 and the feature amount calculated from the feature extracting circuit 50a of the image processing unit 124. According to the embodiment of the present invention, since the whole positional displacement of the small areas (partial images), the very small positional displacements of individual pattern edges and the very small differences of gradation values (light and shade values) are allowed, the normal portion can be prevented from being inadvertently recognized as the defect. Moreover, by setting the parameters α, β, γ, ε to proper values, it becomes possible to easily control the positional displacement and the allowance amount of the fluctuation of the gradation values. Further, according to the embodiment of the present invention, since an image which is position-aligned by the interpolation in a pseudo-fashion, an image can be prevented from being affected by a smoothing effect which is unavoidable in the interpolation. There is then the advantage that the present invention is advantageous in detecting a very small defect portion. In actual practice, according to the experiments done by the inventors of the present invention, having compared the result in which the defect is decided by calculating the threshold value allowing the positional displacement and the fluctuation of the gradation value similarly to this embodiment after an image which is position-aligned by the interpolation in a pseudo-fashion by using the result of the positional displacement detection of less than pixel and the result obtained by the defect judgment according to this embodiment, the defect detection efficiency can be improved by greater than 5% according to the embodiment of the present invention. The arrangement for preventing the electron beam image in the aforementioned electron beam apparatus (observation SEM apparatus, length-measuring SEM apparatus) from being deteriorated will be described further. Specifically, the quality of the electron beam image is deteriorated by the image distortion caused by the deflection and the aberration of the electron optical system and by the resolution lowered by the de-focusing. The arrangement for preventing the image quality from being deteriorated is comprised of the height detection apparatus 200 composed of the height detection optical apparatus 200a and the height calculating unit 200b, the focus control apparatus 109, the deflection signal generating apparatus 108, and the entirety control apparatus 120. FIGS. 10 and 11(a)-11(b) show the height detection optical apparatus 200a according to a first embodiment of the present invention. Specifically, the height detection optical apparatus 200a according to the present invention comprises an illumination optical system formed of a light source 201, a mask 203 in which the same pattern irradiated with light from the light source 201, e.g. the pattern composed of repetitive (repeated) rectangular patterns, a projection stop 211, a polarizing filter 240 for emitting S-polarized light and a projection lens 210 and which illuminates the multi-slit shaped pattern with the S-polarized light at an angle (θ=greater than 60 degrees) vertically inclined from the sample surface 106 by an angle θ and a detection optical system composed of a detection lens 215 for focusing regularly-reflected light from the sample surface 106 on the light-receiving surface of a line image sensor 214, a cylindrical lens 213 and a detection lens 216 for converging the longitudinal direction of the multi-slit shaped pattern on the light-receiving pixels of the line image sensor 214 and the line image sensor and which is used to detect a height of the sample surface 106 from the shift amount of the multi-slit image detected by the line image sensor 214. Light emitted from the light source 201 irradiates the mask 203 on which there is drawn the multi-slit shaped pattern which results from repeating the rectangular-shaped pattern, for example. As a result, the multi-slit-shaped pattern is projected by the projection lens 210 onto the height measuring position 217 on the sample surface 106. The multi-slit-shaped pattern drawn on the mask 203 is not limited to the slit-shaped pattern, and may be shaped as any shape such as an ellipse or a square so long as it is formed by the repetition of the same pattern. Generally, it can be a pattern that comprises a row of patterns with different shapes. Moreover, the spacing between the neighboring patterns can be different from each other. What is essential, as will be described later in detail using FIG. 11, is that by averaging the multiple height estimations computed from the movements of the multiple patterns, a more precise height estimation can be obtained. Therefore, hereinafter, the word “multi-slit-shaped pattern” or “luminous flux of repetitive light pattern” defines a pattern which comprises multiple arranged patterns with either different shapes or the same shape, whose spacing between the neighboring patterns are either different or the same. The multi-slit-shaped pattern projected onto the sample surface 106 is focused by the detection lens 215 on the line image sensor 214 such as a CCD. Assuming that m is the magnification of this detection optical system, then when the height of the sample surface 106 is changed by z, the multi-slit image is shifted by 2z·sin θ·m on the whole. By using this fact, it is possible to detect the height of the sample surface 106 from the shift amount of the multi-slit image obtained based on the signal received by the line image sensor 214. Reference numeral 110 denotes the optical axis of the upper observation system, i.e. the height detection position. Specifically, when the above-mentioned height detection apparatus is used as an auto focus height sensor, reference numeral 110 becomes the optical axis of the upper observation system. Incidentally, assuming that p is the pitch of the multi-slit-shaped pattern of the projected image of the projection lens 210, then the pitch of the pattern projected onto the sample surface 106 becomes p/cos θ, and the pitch of the pattern on the image sensor 214 becomes pm. Also, assuming that m′ is the magnification of the illumination projection system, then the pitch of the pattern on the mask 203 becomes p/m′. That is, the pitch of the multi-slit-shaped pattern formed on the mask 203 becomes p/m′. As shown in FIGS. 11(a), 11(b), when a height is detected on the sample 106 at its boundaries having different reflectances, an intensity distribution of a signal detected on the line image sensor 214 is affected by a reflectance distribution of a sample. However, if the multi-slit-shaped pattern is as thin as possible so long as a clear image can be maintained within a height detection range, then it is possible to suppress a detection error caused by a reflectance distribution on the surface of the object. Because, the detection error is caused as a center of gravity of a slit image is deviated due to a reflectance distribution of a sample, and an absolute value of this deviation increases in proportion to the width of the slit. In the embodiment as shown in FIG. 11(b), the third slit from left is affected by an influence of a fluctuation of a reflectance on the boundary of the sample, but the slit width is narrow so that the detection error is small. Furthermore, it is possible to reduce a detection error caused by the object and the detection fluctuation by averaging the height detected values of a plurality of slits. Although the detection error decreases as the slit width is reduced, this has a limitation. Thus, even when the slit width is reduced over a certain limit, no slit is clearly focused on the image sensor 214, and a contrast is lowered. This has the following relationship. Specifically, assuming that ±zmax is a target height detection range, then at that time, the multi-slit image on the image sensor 214 is de-focused by ±2zmax·cos θ. On the other hand, assuming that p is the cycle of the multi-slit-shaped pattern on the projection side and that NA is an NA (Numerical Aperture) of the detection lens 215, then this focal depth becomes ±a·0.61p/NA. That is, the condition that the slit cycle p satisfies (2max·cos θ)<(a·0.61p/NA) is the condition under which the multi-slit image can be constantly detected clearly. In the above, a is the constant determined by defining the focus depth such that its amplitude is lowered. When the focus depth is defined under the condition that the amplitude is lowered to ½, a is about 0.6. In the embodiment shown in FIG. 10, the projection stop 211 is placed at the front focus position of the projection lens 210, and the detection stop 216 is located at the rear focus position of the detection lens 215. It is for the purpose of eliminating fluctuations of magnifications caused when the sample 106 is elevated or lowered by placing the projection lens 210 and the detection lens 215 to the sample side tele-centric state. This embodiment shows the effect of making the shape and/or the spacing of the multi-slit-shaped pattern non-uniform. In order to enlarge the height detection range of the height detector 200 in this invention, using as many slits as possible is effective. By using many slits, a slit that is projected onto the sample 106 close to the optical axis of the upper observation system 110 is always found even if the height of the sample 106 changes greatly. However, in this case, when too many slits are used in the multi-slit-shaped pattern, the slits around the both ends can go outside the view area of the lens 210 or 215 or the image sensor 214, making it impossible to identify each slit, hence, making it impossible to estimate the movement (2mZ sin θ) of each slit. As illustrated in FIGS. 41(a) and 41(b), by making the center spacing of the multi-slit larger or by making the center slit wider, it becomes possible to identify each slit as long as the center spacing or the center slit is within the viewing area of the height detector 200. With this embodiment, the height detectable range becomes larger. Many variations of the multi-slit-shaped pattern can be easily analogized in which the shape of each slit and/or the spacing between the neighboring slits are made different in order to identify each slit. Also, in the embodiment shown in FIG. 10, the polarizing filter 240 is placed in front of the projection lens 210 to selectively project S-polarized light. This can achieve an effect for suppressing a positional shift caused by a multi-path reflection in a transparent film and an effect for suppressing a difference of reflectances between the areas. As shown in FIG. 12, when the surface of the sample is covered with a transparent film such as an insulating film for light, there occurs a phenomenon that projected light causes a multi-path reflection in the transparent film to thereby shift the position of projected light. Since S-polarized light is more easily shifted on the surface of the transparent film than P-polarized light, if the polarizing filter 240 is inserted, then S-polarized light becomes difficult to cause a multi-path reflection. On the other hand, FIG. 13 shows a graph graphing reflectances of resist and silicon which are examples of transparent films. Rs represents a reflectance of S-polarized light, Rp represents a reflectance of P-polarized light, and R represents a reflectance of randomly-polarized light. As described above, the S-polarized light has a smaller difference of reflectances between the materials. Further, a study of this graph reveals that the reflectance increases as the incident angle increases and that a difference between the materials decreases. Specifically, an error becomes difficult to occur at the pattern boundary. Therefore, the incident angle θ should preferably as large as possible. The incident angle should preferably become greater than 80° ideally, and it is preferable to use an incident angle of at least greater than 60°. Incidentally, the position of the polarizing filter 240 is not limited to the front of the projection lens 210, and may be interposed at any position between the light source 201 and the detector 214 with substantially similar effects being achieved. Although the light source 201 may be a laser light source or a light-emitting diode, it should preferably be a lamp of a wide zone such as a halogen lamp, a metal halide lamp or a mercury lamp. Alternatively, a laser or a light-emitting diode having a plurality of wavelengths may be used, and such a plurality of wavelengths may be mixed by a dichroic mirror. The reason for this is that single light tends to cause a multi-path interference within the transparent film to thereby shift projected light or a difference of reflectances due to a material or a pattern on the sample tends to increase so that a large error tends to occur. In the embodiment shown in FIG. 10, the cylindrical lens 213 is located in front of the line image sensor 214. The reason for this is that light is focused on the line image sensor 214 to increase a quantity of detected light and that an error is decreased by averaging reflected light from a wide area on the sample. However, the use of the cylindrical lens 213 is not an indispensable condition, and should be determined in response to the necessity. A height detection algorithm of the sample surface 106 according to an embodiment will be described next with reference to FIG. 14. Let it be assumed that n is the total number of slits, p is the pitch and y(x) is the detection waveform. Also, let it be assumed that ygo(i) (i=0, . . . , n−1) represents the position of the peak corresponding to each slit obtained when the height z=0 (relationship of ygo(i)=ygo(0)+p*i is satisfied). 1. Scan y(x) and calculate a position xmax of maximum value. 2. Calculate the substantial position of the peak i by searching left and right directions from xmax by each pitch P. 3. Assuming that xo represents the peak position of the left end, then the substantial position of the peak i becomes xo+p*i. The positions of the left and right troughs xo+p*i−p/2, xo+p*i+p/2. 4. Set ymin=max(y(xo+p*i−p/2), y(xo+p*i+p/2). That is, a larger one of left and right troughs is set to ymin. 5. Set k to a constant of about 0.3, and set yth=ymin+k*(y(xo+p*i)−ymin). That is, set amplitude (y(xo+p*i)−ymin)*k to a range value (threshold value) yth. 6. Calculate a center of gravity of y(x)−yth relative to a point at which y(x)>yth is satisfied between xo+p*i−p/2 and xo+p*i+p/2, and set the value thus calculated to yg(i). 7. Calculate weighted mean of yg(i)−ygo(i), and set the calculated weighted mean to image shift. 8. Calculate the height z by adding an offset to a value which results from multiplying the image shift with a detection gain (1/(2m·sin θ)). In this manner, there is realized the height detection which is difficult to be affected by the surface state of the sample 106. Incidentally, in this embodiment, the peak of the slit image is used but instead a trough between the slit images may be used. Specifically, a center of gravity of yth−y(x) is calculated with respect to a point of y(x)<yth and set to a center of gravity of each trough. Then, the shifted amount of the whole image is obtained by averaging the movement amount of these trough images. Thus, there can be achieved the following effects. Since the detection waveform is determined based on the product of the projection waveform and the reflectance of the sample surface, the bright portion of the slit image is largely affected by the fluctuation of the reflectance, and the shape of the detection waveform tends to change. On the other hand, the trough portion of the waveform is difficult to be affected by the reflectance of the sample surface. Therefore, by the height detection algorithm based on the measurement of the movement amount of the trough between the slit images, it is possible to reduce the detection error caused by the surface state of the object much more. The height detection optical apparatus 200a according to a second embodiment according to the present invention will be described next with reference to FIG. 15. In the first embodiment shown in FIG. 10, since the multi-slit-shaped pattern 203 is projected from the oblique upper direction, when the sample surface 106 is elevated and lowered, the position at which the pattern is projected on the sample, i.e. the sample measurement position 217 is shifted and displaced from the detection center 110. Assuming that Z is the height of the sample and θ is the projection angle, then this shift amount is represented by Z tan θ. At that time, if the sample surface 106 is inclined by ε, then there occurs a detection error. The magnitude of this detection error is Z·tan θ·tan ε. For example, when Z is 200 μm, θ is 70 degrees and tan ε is 0.005, the above-mentioned detection error becomes 2.7 μm. When this problem arises, the arrangement of the second embodiment shown in FIG. 15 can achieve the effects. Specifically, the pattern projection/detection are carried out from the left and right symmetrical directions, and the two detected values are averaged, whereby the height of the constant point 110 can be obtained. The second embodiment shown in FIG. 15 will hereinafter be described in detail. Since the arrangement is symmetrical, the same constituents are constantly located at the corresponding positions, and hence the other side of the constituents need not be described. It is to be appreciated that the projection and detection from the symmetrical direction are also the same. Light emitted from the light source 201 illuminates the mask 203 on which the multi-slit-shaped pattern is drawn. Of the light, light reflected by the half mirror 205 is projected by the projection/detection lens 220 onto the sample 106 at its position 217. The multi-slit-shaped pattern projected on the sample 106 is regularly reflected and focused on the line image sensor 214 by the projection/detection lens 220 disposed on the opposite side. At that time, a luminous flux that has passed through the half mirror 205 is focused on the line image sensor 214. Assuming that m is the magnification of the detection optical system, when the height of the sample is changed by z, the multi-slit image is shifted by 2mz·sin θ on the whole. By using this fact, the height of the sample 106 is calculated from the shifted amounts of the left and right multi-slit images. Then, an average value is calculated by using the height detection values of the left and right detection systems, and the average value thus calculated is obtained as a height detected value at the final point 110. When the above-mentioned height detection apparatus is used as the auto focus height sensor, the height detection position becomes the optical axis of the upper observation system. Incidentally, it is needless to say that the half mirror 205 may be replaced with a beam splitter of cube configuration as long as the beam splitter passes a part of light and reflects a part of light. Moreover, similarly to the first embodiment shown in FIG. 10, by using the cylindrical lens 213, the longitudinal direction of the slit may be contracted and focused on the line sensor 214. The height detection optical apparatus 200a according to a third embodiment of the present invention will be described next with reference to FIG. 16. Although this arrangement is able to constantly obtain the height of the constant point 110 similarly to FIG. 15, in FIG. 15, a quantity of light is reduced to ½ by the half mirror 205 so that, when light is passed through or reflected by the half mirror 205 twice, a quantity of light is reduced to ¼. Therefore, if a polarizing beam splitter 241 is inserted instead of the half mirror 205 and a quarter-wave plate is interposed between the polarizing beam splitter 241 and the sample 106 as shown in FIG. 16, then it becomes possible to suppress the reduction of the quantity of light to ½. Specifically, light emitted from the light source 201 illuminates the mask 203 having the multi-slit-shaped pattern formed thereon. Of the light, S-polarized component reflected by the polarizing beam splitter 241 is passed through the quarter-wave plate 242 and thereby converted into circularly-polarized light. This light is projected by the projection/detection lens 220 onto the sample 106 at its position 217. The multi-slit pattern projected onto the sample is regularly reflected, and then focused on the line image sensor 214 by the projection/detection lens 220 disposed on the opposite side. At that time, the circularly-polarized light is converted by the quarter-wave plate 242 into P-polarized light. This light is passed through the polarizing beam splitter 242 without being substantially lost, and then focused on the line image sensor 214, thereby making it possible to reduce the loss of the quantity of light. Moreover, if a laser for generating polarized light is used as the light source 201 to enable S-polarized light to pass the first polarizing beam splitter 241, then it becomes possible to substantially suppress the loss of the quantity of light. Assuming that m is the magnification of the detection optical system, then when the height of the sample is changed by z, the multi-slit image is shifted by 2mz·sin θ on the whole. By using this fact, the height of the sample 106 is calculated from the shift amounts of the left and right multi-slit images. An average value is calculated by using the two height detected values of the left and right detection systems, and the average value thus calculated is determined as a height detected value at the final point 110. When the height detection optical apparatus is used as the auto focus height sensor, the height detection position 110 becomes the optical axis of the upper observation system. It is needless to say that the longitudinal direction of the slit may be contracted by using the cylindrical lens 213 and focused on the line image sensor 214 similarly to the first embodiment shown in FIG. 10. Further, the manner in which an error caused by another cause can be canceled out by using the arrangement of the second or third embodiment shown in FIG. 15 or 16 will be described with reference to FIG. 18. FIG. 18 is a partly enlarged view of FIG. 10, in which reference numeral 210 denotes a projection lens and reference numeral 215 denotes a detection lens. If reference numeral 218 denotes a conjugation surface or focusing surface formed on the image sensor 214 by the detection lens 215, then the shift amount of projected light on this conjugation surface 218 is detected on the image sensor 214. When the height of the sample 106 is increased by z, the detection light reflection position 217 is shifted from the height detection position 110 by z·tan θ. Further, when the sample surface 106 is inclined by an angle εrad, the detection light reflected on the reflection position 217 is inclined by an extra angle of 2εrad due to a so-called optical lever effect. Then, the detection light position on the conjugation surface 218 is shifted by 2εz·cos(π−2θ)/cos θ. Since a height detection error results from multiplying this shifted amount with ½ sin θ, the detection error caused by the inclination of grad of the sample 106 is represented by −2εz/tan 2θ. For example, assuming that z is 200 μm, θ is 70 degrees and tan ε is 0.005, then the above-mentioned detection error becomes 2.4 μm. When this problem arises, the arrangement of the second or third embodiment shown in FIG. 15 or 16 can achieve the effects. Specifically, the error caused by the above-mentioned optical lever effect becomes the same magnitude and becomes opposite in sign when the projection or detection is carried out from the opposite direction as shown in FIG. 15 or 16. Therefore, when height detection values from the left and right image sensors are averaged, an error can be canceled out. Thus, it becomes possible to carry out the height detection which is free from the error caused by the inclination of the sample surface 106. Next, the manner in which the height of the sample surface 106 can be obtained accurately by the height calculating unit 200b even when the height z of the sample surface 106 is changed will be described with reference to FIGS. 19(a)-19(b). Although the optical system shown in FIG. 19(a) is identical to that shown in FIG. 10, if the height of the sample surface 106 is changed by z, then the detection position of the slit image is changed by z·tan θ. Since the pattern of the multi-slit shape is projected and the respective slits are reflected at different positions on the sample, the shift amount of each slit image reflects a height corresponding to each reflected position on the sample. Specifically, as shown in FIG. 19(b), there is obtained surface-shaped data of the sample 106. FIG. 19(b) shows a detection height of each slit with respect to the detection position corresponding to the height of the sample surface 106. A measurement point shown by a dotted line indicates measured data obtained when the sample 106 is located at the reference height. When the sample 106 is elevated by z, as shown by a solid line, the sample detection position corresponding to each slit is shifted to the left by z·tan θ. As is defined in the description of the embodiment shown in FIG. 10, assuming that p/cos θ is the pitch of the multi-slit-shaped pattern on the sample surface 106, then the slit corresponding to the visual field center 110 of the upper observation system is shifted to the right by z·tan θ/(p/cos θ)=z·sin θ/p. Therefore, the height calculating unit 200b can select a plurality of slits containing this slit at the center, average height detection values from these slits, determine the value thus averaged as a final height detection value, and can accurately obtain the height at the visual field center 110 of the upper observation system. In order for the height calculating unit 200b to calculate z·sin θ/p, it is necessary to know the height z. Since the z required may be an approximate value for selecting the slit, the height that was calculated previously or the detection height obtained before the detection position displacement is corrected may be used as the height z. Incidentally, the position equivalent to the visual field center 110 is shifted on the image sensor by zm·sin θ as the height of the sample 106 is changed by z. Further, when the appearance is inspected on the basis of the SEM image shown in FIGS. 3 and 4, the two-dimensional SEM images of a certain wide area should be latched. To this end, while the stage 105 is moved continuously, the beam deflector 102 should be driven to scan electron beams in the direction substantially perpendicular to the direction in which the stage 105 is moved, and the secondary electron detector 104 need detect the two-dimensional secondary electron image signal. Specifically, while the stage 105 is moved continuously in the X direction, for example, the beam deflector 102 should be driven to scan electron beams in the Y direction substantially perpendicular to the direction in which the stage 105 is moved, and then the stage 105 is moved stepwise in the Y direction. Thereafter, while the stage 105 is continuously moved in the X direction, the beam deflector 102 should be driven to scan electron beams in the Y direction substantially perpendicular to the direction in which the stage 105 is moved, and the secondary electron detector 104 should detect the two-dimensional secondary electron image signal. Also in this embodiment, the height detection apparatus 200 should constantly detect the height of the surface of the inspected object 106 from which the secondary electron image signal is detected and obtain the correct inspected result by executing the automatic focus control. However, due to an image accumulation time of the image sensor 214 in the height detection optical apparatus 200a, a calculation time in the height calculating unit 200b, the responsiveness of the focus position control apparatus 109 or the like, it is frequently observed that a focus control is delayed. Therefore, even when the focus control is delayed, light should be accurately focused on the surface of the inspected object 106 from which the secondary electron image signal is detected. In FIG. 20, let it be assumed that the stage 105 is continuously moved from right to left. In this case, taking the above-mentioned delay time into consideration, the height calculating unit 200b may calculate the height slightly shifted right from the visual field center 110 of the upper observation system, and the focus control apparatus 109 may control the focusing by controlling the focus control current or the focus control voltage to the objective lens 103. The shift amount of the necessary detection position becomes a product VT of the above-mentioned delay time T and the scanning speed (moving speed) V of the stage 105. Specifically, as shown in FIG. 20, the height calculating unit 200b can obtain the values corresponding to the heights by using signals from images of slit groups shifted to the right by VT/(p/cos θ) from the upper observation system visual field center 110 detected from the image sensor 214, average the values thus obtained, and can detect the height in which the delay time is corrected by determining the averaged value as the final height detection value. Incidentally, the measurement position shift amount VT on the sample corresponds to VTm·cos θ on the image sensor 214. As described above, even when the focus control is delayed, since the height calculating unit 200b can calculate the height of the surface of the inspected object 106 from which the secondary electron image signal is detected, the focus control apparatus 109 can accurately focus light on the surface of the inspected object 106 from which the secondary electron image signal is detected by controlling the focus control current or the focus control voltage to the objective lens 103. In this embodiment, the detection position displacement caused by the change of the height of the sample surface 106 shown in FIG. 19(b) and the time delay shown in FIG. 20 are both corrected. When the two-side projection shown in FIGS. 15 and 16 is used, the detection position displacement caused by the change of the height of the sample surface 106 is canceled out automatically so that only the time delay may be corrected. FIG. 21 shows an embodiment in which the time delay is corrected not by using the averaged value of the height detection values as shown in FIG. 20, but the final height detection value is calculated by applying a straight line to the surface shape of the detected sample surface 106. In this fashion, the height calculating unit 200b may apply a straight line to detected height data obtained from the position of each slit according to the method of least squares, for example, calculate the height of the position shifted by −zm·sin θ+VTm·cos θ on the image sensor (CCD) 214 by using the resultant straight line, and may determine the height thus obtained as the final detected height. As shown in FIGS. 5(a)-5(c), when the surface shape of the sample surface is partly uneven like the semiconductor memory comprising the memory cell portion 3c and the peripheral circuit portion 3b, it is possible to selectively detect only the height of the high portion of the surface shape of the sample surface by using a suitable method such as a Hough transform instead of the method of least squares. As described above, even when the focus control is delayed, since the height calculating unit 200b calculates the height in accordance with the surface shape of the inspected object 106 from which the secondary electron image signal is detected, the focus control apparatus 109 can precisely focus light on the surface shape of the inspected object 106 from which the secondary electron image signal is detected by controlling the focus control current or the focus control voltage to the objective lens 103. Also, as shown in FIGS. 5(a)-5(c), in the case of the semiconductor memory comprising the memory cell portion 3c and the peripheral circuit portion 3b which are different in height on the surfaces, it becomes possible to accurately focus light on the surface shape. In the embodiment shown in FIGS. 19, 20, 21, there is illustrated the detection time delay correction method obtained on the assumption that the scanning direction of the stage 2 and the projection-detection direction of multi-slit are substantially parallel to each other. A detection time delay correction method that can be used regardless of the scanning direction of stage and the projection-detection direction of multi-slit will be described next. Since the line image sensor 214 outputs image signals accumulated during a certain time T1, it can be considered that the line image sensor may obtain an average image of the period T1. Specifically, data obtained from the line image sensor 214 has a time delay of T1/2. Further, in order for the height calculating unit 200b formed of the computer, a constant time T2 is required. Thus, the height detection value indicates past information by a time of (T1/2)+2 in total. As shown in FIG. 22, assuming that detection values obtained at a constant interval are Z−m, Z−(m−1), . . . , Z−2, Z−1, Z0, then the height calculating unit 200b can estimate a present time Zc from these data. As shown in FIG. 22, for example, it is possible to obtain the present height Zc by extrapolating the latest detection value Z0 and a preceding detection value with straight lines as in the following equation of (expression 25):Zc=Z0+((Z0)−(Z−1))×((T1/2)+T2)/T1 (expression 25) Extrapolation straight lines may of course be applied to more than three points Z−m, Z−(m−1), . . . Z−2, Z−1, Z0 so as to reduce an error or a quadratic function, a cubic function or the like may be applied to these points. These extrapolation methods are mathematically well known, and when in use, the most suitable one may be selected in accordance with the magnitude of the change of the height detection value and the magnitude of the fluctuations. As another embodiment, the manner in which the height detection value is corrected and outputted will be described. When the height detection value changes stepwise at the interval T1, if the feedback is applied to electron beams by using such stepwise height detection values, then it is not preferable that the quality of electron beam image is changed rapidly at the interval T1. In this case, in addition to the extrapolation height detection value Zc, an extrapolation height detection value Zc′ which is delayed by a time T1 from a time a is calculated similarly. In the embodiment shown in FIG. 23, the extrapolation height detection values Zc and Zc′ are calculated by the following equation of (expression 26):Zc=(Z−1)+(((Z−1)−(Z−3))/(2T1))×2.5T1Zc′=(Z0)+(((Z0)−(Z−2))/(2T1))×2.5T1 (expression 26) On the basis of these Zc and Zc′, the height Z1 which is delayed by t from the time a can be calculated by interpolation as in the following equation of (expression 27):Z1=Zc+(Zc′−Zc)t/T1 (expression 27) As described above, the detection time delay caused by the CCD storage time and the height calculation time can be corrected. Thus, even when height of the inspected object 106 is change every moment, a height detection value with a small error can be obtained, and a feedback can be stably applied to the electron optical system which controls electron beams. Further, in the electron optical system shown in FIGS. 2, 3, 4 and 7, since the focus position thereof can be controlled at a high speed by a focus control current or a focus control voltage, the focusing can be made by an embodiment shown in FIG. 24. Specifically, while electron beams are scanned once, the focus control apparatus 109 dynamically changes the focus position by controlling the focus control current or the focus control voltage to the objective lens 103 such that the position thus changed may agree with the surface shape of the sample surface 106 detected by the height detection optical apparatus 200a and which is calculated by the height calculating unit 200b. Since the height calculating unit 200b is able to calculate the surface shape of the sample surface 106 from the image signal of the multi-slit-shaped pattern obtained from the image sensor 214 of the height detection optical apparatus 200a, while electron beams are scanned once, the focus control apparatus 109 can realize the properly-focused state by controlling the focus control current or the focus control voltage to the objective lens 103 in accordance with the surface shape of the sample surface 106 thus calculated. Thus, when an inspected object has a large stepped structure like a semiconductor memory, it becomes possible to accurately focus light on the inspected object constantly. FIG. 25 shows another embodiment of the two-side projection system shown in FIGS. 15 and 16. Specifically, in the embodiment shown in FIG. 25, two optical systems according to the embodiment shown in FIG. 10 are prepared and disposed side by side in which the detection directions are made opposite to each other. As shown in FIGS. 15 and 16, it is possible to realize a function equivalent to that of the arrangement which makes the left and right optical system common by using the half mirror 205. Specifically, also in the embodiment shown in FIG. 25, as the sample surface 106 is elevated and lowered, the detection apparatus 217 is moved right and left with the result that the position of the center of the detection apparatus 217 composed of the two optical systems can always be made constant. Therefore, it is possible to detect the height at the constant position 110 by averaging the height detection values obtained from these optical systems. Thus, it is possible to construct a height detector which can prevent a detection error from being caused when the detection position is displaced by the fluctuation of the height. However, since the patterns of multi-slit shape are projected at different positions, when the surface of the inspected object 106 has steps and undulations, detection light is not irradiated on the point 110 and a detection error occurs. Accordingly, the present invention is applicable when the surface of the inspected object has small steps and undulations. Furthermore, FIG. 26 shows another embodiment of the two-side projection system shown in FIGS. 15 and 16. Specifically, in the embodiment shown in FIG. 26, two optical system use an illumination and an image sensor. Light emitted from a light source 201 illuminates a mask pattern 203 of multi-slit shape. Light passed through a multi-slit 203 is traveled through a half mirror 205, converted by a lens 264 into parallel light, reflected by a mirror 206, and branched by a branching optical system (roof mirror) 266 into two multi-slit light beams. The multi-slit light beams thus branched are projected by a projection/detection lens 220 through a mirror 267 to thereby focus an image of a mask pattern 203 at the measurement position 217 on the sample 106. An incident angle obtained at that time is assumed as θ. A pair of multi-slit light beams reflected on the surface of the sample 106 are returned through the same light paths as those of projected light and reached to the half mirror 205. Specifically, a pair of multi-slit light beams reflected on the surface of the sample 106 are reflected on the respective mirrors 267, traveled through the respective projection/detection lenses 220, reflected on the respective mirrors 265, reflected on the branching optical system 266, reflected on the mirror 206, synthesized by the lens 264 and reached to the half mirror 205. Light reflected on the half mirror 205 is focused on the image sensor 214. On the sensor 214, light beams that were branched into two directions by the branching optical system 266 are synthesized one more time so that only one illumination system and one image sensor 214 are sufficient. Moreover, since the height calculating unit 200b may process only one waveform, a load may be decreased. Therefore, it is possible to inexpensively realize a height detection apparatus which can prevent a detection position from being displaced by the two-side projection system. As another embodiment, instead of an arrangement for controlling an angle of the mirror 206 electrically, if the mirror 206 is controlled in such a manner that the position at which the slit-shaped pattern image is focused on the image sensor 214 always becomes constant, then the irradiated position 217 of detection light on the sample can be maintained constant regardless of the height z of the sample 106. When the mirror is controlled as described above, the rotation angle of the mirror 206 and the height z are in proportion to each other so that the height z of the sample can be detected by detecting the rotation angle of the mirror 206. FIG. 27 shows an embodiment of another arrangement in which the detection position can be prevented from being displaced. Although the layout of the optical system is the same as that of the embodiment shown in FIG. 10, the whole of the detector can be elevated and lowered. If the height of the whole of the detector is controlled such that the position of the slit on the image sensor 214 always becomes constant, then the detection light irradiated position 217 can be maintained constant regardless of the height z of the sample 106. The height z of the whole of the detector presented at that time agrees with the height z of the sample 106. Another advantage of this arrangement will be described. In the embodiment shown in FIG. 10, if a magnification color aberration exists in the lens 215, the position of the multi-slit image on the image sensor 214 is displaced by the color of the sample surface 217. That is, an error occurs in the detection height. As a result, it is necessary to suppress the color aberration of the lens 215. On the other hand, in the arrangement shown in FIG. 27, the center of the multi-slit pattern is constantly located on the optical axis under control. Since the color aberration does not occur on the optical axis, the color aberration of the lens and the distortion of image do not cause the detection error. Therefore, it becomes possible to construct a height detector of a small detection error by an inexpensive lens. Further, since the detection multi-slit pattern is not de-focused as the height of the sample is changed, the size of each slit can be reduced to approximately the limit of resolution of lens. Furthermore, there is the advantage that a height detection error caused by the reflectance distribution of the sample can be reduced. A method of further decreasing a detection error by properly selecting the slit direction will be described next with reference to FIG. 28. When a semiconductor apparatus is inspected or observed as a sample, the semiconductor apparatus usually has a pattern such that an area such as a memory mat portion 3c is formed in each rectangular chip as shown in FIG. 28. Since it is customary that the memory mat portion has small patterns formed thereon, light tends to scatter/diffracted, thereby resulting in a low reflectance portion being formed. When the slit is irradiated on this boundary portion, a symmetry of a detection pattern obtained as a reflected light image is broken, and hence there occurs a detection error. On the other hand, when the longitudinal direction of the slit is irradiated on the pattern with an inclination angle φ relative to the pattern as shown in FIG. 28, a ratio of the portion in which the border line of the pattern crosses the slit relative to the length L of the slit is reduced so that an amount in which a symmetry of a detection pattern is fluctuated by a difference of reflectances at the boundary portion of the pattern can be decreased. That is, a detection error can be reduced. Thus, in addition to the error reduction achieved by the multi-slit, it is possible to achieve a further error reduction effect. In the embodiment shown in FIG. 28, the projection & detection direction and the longitudinal direction of the slit are perpendicular to each other, which is not always necessary. Specifically, the angle of the longitudinal direction of the slit projected on the sample 106 can be controlled by rotating the mask 203 on which there is formed the multi-slit like pattern. At that time, the cylindrical lens 213 and the line image sensor 214 also should be rotated in the direction opposing the sample 106 by the same angle as that of the mask 203. Assuming that η is this angle, then the direction of the slit projected on the sample 106 is rotated by arc tan(sin η/(cos η cos θ)) in the projection direction. While the method of correcting the detection position of the projection direction by the multi-slit and the method of canceling out the positional displacement by the two-side projection have been described so far with respect to the phenomenon in which the detection position is displaced by the height z of the sample surface 106, a method of reducing a displacement of a detection position in the longitudinal direction of the slit, i.e. in the direction perpendicular to the projection direction will be described. When the longitudinal direction of the slit is projected across areas having different reflectances on the sample as shown in FIG. 29(a), detection light is given an intensity distribution in the longitudinal direction of the slit. In this case, the height distribution of the sample is reflected on the height detection value with a weighting corresponding to the light quantity distribution of this detected light. Specifically, the height detection value considerably reflects information of the area having the high reflectance with the result that a height of a point displaced from the height measurement point 110 is unavoidably measured. The resultant detection error is reduced as the size L of the longitudinal direction of the slit is reduced. However, the detection light quantity is decreased and is easily affected by a local fluctuation of the reflectance on the surface of the sample. Therefore, the size of the slit cannot be reduced freely. Accordingly, as is seen in the embodiments shown in FIGS. 15, 16, 26, 27, in the arrangement in which detection light is projected from both sides, the projection positions are displaced in the longitudinal direction of the slit in such a manner that the projection positions of the right and left slits may not overlap as shown in FIG. 29(b). Then, in the case of this embodiment, only the multi-slit pattern of a direction 1 is projected across the two areas so that a height detection value based on a detection direction 2 does not cause an error. Thus, it is possible to reduce an error to ½ by averaging height detection values of the detection direction 1 and the detection direction 2. In the embodiment shown in FIG. 29(b), the length of the slit is reduced to L/2 such that the total width of the projection areas of the projection direction 1 and the projection direction 2 may become L. Consequently, as compared with FIG. 29(a), the detection position displacement of the longitudinal direction of the slit can be reduced to ¼ on the whole. An embodiment in which a two-dimensional distribution of the height of the sample 106 is obtained will be described next with reference to FIG. 30. Light emitted from the light source 201 illuminates the mask 203 with the pattern composed of rectangular repeated patterns, for example. This light is projected by the projection lens 210 at the position 217 on the sample 106. The multi-slit pattern projected onto the sample is focused by the detection lens 215 on the two-dimensional image sensor 214 such as a CCD. Assuming that m is the magnification of the detection system, then when the height of the sample is changed by z, the slit image is shifted by 2mz·sin θ. Since this shift amount reflects a height of a point at which the slit irradiates the sample, by using this shift amount, it becomes possible to detect the height distribution of the sample 106 in the irradiated range of the slit. In the embodiment shown in FIG. 30, the stop 211 is disposed at the front focus position of the projection lens 210, and the stop 216 is disposed at the rear focus position of the detection lens 215. The reason for this is that a magnification fluctuation caused when the sample 106 is elevated and lowered can be eliminated by disposing the lenses 210 and 215 in a sample-side tele-centric fashion. Consequently, the magnification fluctuation caused by the change of the height of the sample surface 106 can be suppressed, and a detection linearity can be improved. Moreover, as in the embodiment shown in FIG. 30, the polarizing filter 240 is disposed at the front of the projection lens 210 to selectively project S-polarized light. The reason for this is that, when a pattern formed on an insulating film or the like is inspected on the basis of the SEM image, the insulating film is a transparent film and therefore a multi-path reflection can be prevented in the transparent film, thereby making it possible to inspect the above-mentioned pattern while a difference of reflectances between the materials is suppressed. The polarizing filter 240 is not always disposed in front of the projection lens, and may be interposed between the light source 201 and the detector 214 with substantially similar effects being achieved. With respect to a multi-slit shift amount detection algorithm executed by the height calculating unit 200b, an embodiment different from FIG. 14 will be described next. FIG. 31 shows a method of detecting a phase change φ of a cyclic waveform. Assuming that p is a pitch of a multi-slit shaped pattern, then the phase change φ(rad) corresponds to a shift amount pφ/2π. This shift amount corresponds to a height change pφ/(2πm·sin θ) so that the height detection is concluded as the detection of the phase change of the cyclic waveform. The height detection in the height calculating unit 200b can be realized by a product sum calculation. Specifically, the detection waveform is assumed to be y(x). Then, a product sum of the detection waveform and a function g(x)=w(x)exp(i2πx/p), and a resultant phase may be obtained where i is the imaginary number unit, and w(x) is the correlation function of a proper real number. When this correlation function is a Gaussian function, w(x) is, in particular, called a Gavore filter, and w(x) may be any function as long as the function may be smoothly lost at the respective ends. While the complex function is employed in the above description, it will be expressed by a real number as follows. Having calculated the product sum of gr(x)=w(x)·cos(i2πx/p) and gi(x)=w(x)·sin(i2πx/p) with y(x), results are set to R and I, respectively. Then, the phase of y(x) is represented as φ=arc tan(I/R). However, since this phase is folded in a range of −π to π, phases may be coupled by searching the previous detection phases without a dropout or an approximate value of 2π-order of the phase is calculated by calculating the approximate position of the peak. Incidentally, while the weighting function w(x) and the width of the waveform y(x) are made substantially equal in this example, the portion which overlaps the weighting function w(x) is selected from the multi-slit image by reducing the width of the weighting function w(x) relative to the waveform y(x), and the shift amount of this portion can be calculated. Furthermore, by using a weighting function for selecting a right half portion from the multi-slit pattern existing range and a weighting function for selecting a left half portion from the multi-slit pattern existing range, the heights of the left half portion and the right half portion can be calculated with respect to the measurement position on the sample. Then, it is possible to obtain the height and the inclination of the sample by using such calculated results. Furthermore, while the above-mentioned algorithm constructs the filter matched with the pitch p of the well-known multi-slit shaped pattern and uses this filter to detect the phase, the present invention is not limited thereto, and an FFT (Fast Fourier Transform) is effected on y(x) and a phase corresponding to a peak of a spectrum is obtained, thereby making it possible to detect the phase of the waveform y(x). An embodiment of another slit shift amount measuring algorithm will be described next with reference to FIG. 32. In the embodiment shown in FIG. 14, the displacement of the slit image is measured by using the center of gravity. According to this method, such displacement is converted into a height on the basis of the position of the edge of the slit image. Initially, similarly to the embodiment shown in FIG. 14, the peak of each slit and the positions of troughs on the respective sides are calculated and a proper threshold value yth is calculated from the amplitude. Then, searching two points across this threshold value yth, resultant two points are set to (xi, yi) and (xi+1, yi+1). Then, x coordinates of a point at which the line connecting the above two points and threshold value cross each other are expressed by xi+(xi+1−xi) (yth−yi)/(yi+1−yi). This operation is effected on each of left and right inclined portions of the slit, the positions of the crossing points between the threshold values and this line are calculated, and then a middle point is determined as the position of the slit. Moreover, the peak position of the slit can be determined as the position of the slit. The interpolation is executed in order to calculate the peak position with an accuracy below pixel. There are various interpolation methods. When a quadratic function interpolation, for example, is carried out, if three points before and after the maximal value are set to (x1−Δx, y0), (x1, y1) and (x1+Δx, y2), then the peak position is expressed by x1+Δx (y2−y0)/{2(2·y2−y2−y0)}. While the above-mentioned methods have been described so far on the assumption that the position of the slit is calculated, the present invention is not limited thereto, and the position of the trough of the detection waveform is calculated and the shift of this position is detected, thereby making it possible to obtain the height of the sample. If so, the following effects can be achieved. The amount in which the waveform of the detection multi-slit pattern is fluctuated by the reflectance distribution on the surface of the sample increases much more when the reflectance boundary coincides with the peak portion of the multi-slit image as compared with the case in which the reflectance boundary coincides with the trough portion. The reason for this is that the detected light quantity distribution is determined based on a product of the light quantity distribution obtained when the reflectance of the sample is constant and the reflectance of the sample. Consequently, the bright portion tends to cause the change of the detected light quantity relative to the change of the same reflectance. Accordingly, if the position of the trough portion having the small fluctuation of the waveform is calculated, the position of the slit image can be detected and the height of the sample can be detected with a small error independently of the state of the reflectance of the sample. As the method of detecting the position of the trough portion, there may be used the algorithm for calculating a center of gravity relative to a code-inverted waveform −y(x) shown in FIG. 14 and the algorithm for calculating the point crossing the threshold value by the interpolation shown in FIG. 32. A method of detecting the position of the multi-slit image without the linear image sensor will be described next with reference to FIGS. 33(a)-33(b). As shown in FIG. 33(a), light emitted from a light source 201 illuminates a mask 203 on which the multi-slit shaped pattern is drawn. This multi-slit pattern is projected by a projection lens 210 at a position 217 on a sample 106. The multi-slit pattern projected onto the sample is focused by a detection lens 215 on a mask pattern 245. A quantity of light passed through this mask pattern 245 is detected by a photoelectric detector 246. The mask pattern 245 is the pattern having the same pitch as that of the mask 203, and is vibrated about h at a sin 2πft. In synchronism therewith, an output 248 of the photoelectric detector 246 is vibrated. If this is synchronizing-detected, then the direction of the positional displacement between the multi-slit image and the vibrating mask pattern 245 can be detected. If this detected positional displacement is fed back to the vibration center h of the pattern 245, then the position of the multi-slit image and the position of the vibrating mask pattern 245 can agree with each other constantly. Since the vibration center h of the pattern 245 obtained at that time is equal to 2mz·sin θ, the height of the sample can be obtained from this fact. FIG. 33(b) is a block diagram showing this fact. An oscillator 249 supplies a signal of sine wave of a sin 2πft. This sine wave signal is supplied to a multiplier 251, in which it is multiplied with a signal v(t) (248) from the photoelectric detector 246 and supplied through a low-pass filter 252. Since this signal indicates the positional displacement from the multi-slit image of the mask 246, this signal is inputted to a temporary delay loop composed of a subtracter 253 (subtracts h (=2mz·sin θ) obtained from a gain 255), an integrator 254, and the gain 255. This output becomes the vibration center h of the mask 245. The mask 245 is driven by a drive signal 247 which results from adding the signal a sin 2πft from the oscillator 249 to this signal. Thus, it is possible to maintain the multi-slit image and the vibration center position h of the mask pattern 245 coincident with each other. An embodiment concerning a method of correcting a focus control current or a focus control voltage and a focus position of charged particle optical system (objective lens 103) in the observation SEM apparatus and the length measuring SEM apparatus including the appearance inspection SEM apparatus shown in FIG. 2 or 3 or 4 or 7 will be described. When a relationship between the control current and the focus position is nonlinear, a nonlinear correction is required. A method of evaluating a linearity and determining a correction value will be described. A correction standard pattern 130 shown in FIG. 35 is fixed to a sample holder on the stage 2 which holds the inspected object 106 and located as shown in FIG. 34. The correction standard pattern 130 is made of a conductive material so as to prevent the correction standard pattern from being charged when electron beams 112, which are charged particle beams, are scanned. Upon correction, on the basis of the command from the entirety control unit 120, the stage control apparatus 126 is controlled in such a manner that this correction standard pattern 130 is moved about the upper observation system optical axis 110 in the observation area. The entirety control unit 120 uses this standard pattern 130 to obtain from the focus control apparatus 109 the focus control current or the focus control voltage under which the secondary electron image signal (SEM image signal) which is the charged particle beam image detected by the secondary electron detector 104 which is the charged particle detector becomes clearest at each point, and measures the same. At that time, the visibility of the secondary electron image (SEM image) which is the charged particle beam image is detected by the secondary electron detector 104. A digital SEM image signal converted by the A/D converter 39 (122) or the digital SEM image signal pre-processed by the pre-processing circuit 40 is inputted to the entirety control unit 120 and thereby displayed on the display 143 or stored in the image memory 47 and displayed on the display 50, thereby being visually confirmed or determined by the image processing for calculating a changing rate of an image at the edge portion of the SEM image inputted to the entirety control unit 120. Since the real height of the correction sample surface (correction standard pattern 130) is already known, if this height information is inputted by using an input (not shown), then the entirety control unit 120 is able to obtain a relationship between the real height of the sample surface and the optimum focus control current or focus control voltage by the above-mentioned measurement as shown in FIG. 36(a). Simultaneously, the height detection optical apparatus 200a and the height calculating unit 200b measure the height of the correction standard pattern 130, whereby the entirety control unit 120 obtains a correction curve indicative of a relationship between the real height of the sample surface and a measured height detection value measured by the height detection optical apparatus 200a and the height calculating unit 200b as shown in FIG. 36(b). A study of these two correction curves reveals that the entirety control unit 120 can detect, from the detection values obtained by the height detection optical apparatus 200a and the height calculating unit 200b, the optimum focus control current or focus control voltage under which a properly-focused charged particle beam image is picked up. Moreover, instead of obtaining separately two sets of correction curves of the height of the sample surface and the detection value obtained by the height detection optical apparatus 200a or the like and the real height of the sample surface and the focus control current or focus control voltage, the entirety control unit 120 may directly obtain a correction curve presented between the detection value obtained by the height detection optical apparatus 200a and the focus control current or focus control voltage as shown in FIG. 36(c). In this case, the real height of the correction standard pattern 130 need not be detected. Specifically, as shown in FIG. 38, the correction is made by using the correction standard pattern 130. In a step S30, a correction is started. In a step S31, the entirety control unit 120 issues a command to the stage control apparatus 126 in such a manner that the position n of the correction sample piece 130 is moved to the optical axis 110 of the electron optical system. Then, a step S32 and steps S33 to S38 are executed in parallel to each other. In the step S32, the entirety control unit 120 issues a height detection command to the height calculating unit 200b to thereby obtain non-corrected height detection data Zdn. At the same time, in the steps 33, the entirety control unit 120 issues a command to the focus control apparatus 109 so that the focus control signal of the electron optical system (objective lens 103) matches Ii. Next, in the step S34, the entirety control unit 120 issues a command to the deflection control apparatus 108 so that electron beams are scanned in a one-dimensional or two-dimensional fashion. In the next step S35, the entirety control unit 120 issues a command to the image processing unit 124 so that the SEM image thus obtained is processed to calculate a visibility Si of an image. In the next step S36, i=i+1 is set in the focus control signal Ii of the electron optical system (objective lens 103). Until i≦Nn is satisfied in the step S37, the steps S33 to S35 are repeated to thereby obtain the visibility Si of the image in each focus control signal Ii. If a NO is outputted in the inequality of i≦Nn in the step S37, then in the step S38, the entirety control unit 120 calculates the focus control signal In, in which the visibility Si of the image becomes maximum. In the next step S39, the entirety control unit 120 issues a command to the image processing unit 124 in such a manner that the image processing unit obtains an image distortion parameter composed of an image magnification correction, an image rotation correction or the like in each height Zn in the correction sample piece 130 and stores the image distortion correction parameter thus obtained in the memory 142. In the next step S40, the position n on the sample piece 130 is set to n=n+1. Then, until n≦Nn is satisfied in a step S41, the steps S31 to S39 are repeated to thereby obtain the focus control signal In under which the visibility of the image in the height Zdn of each sample piece becomes maximum and the image distortion correction parameter composed of the image magnification correction, the image rotation correction or the like. If a NO is outputted in the inequality of n≦Nn at the step S41, then in a step S42, the entirety control unit 120 obtains a correction curve shown in FIG. 36(c) from the focus control signal In under which a visibility of an image in the non-corrected height detection value Zdn and the height Zdn of each sample piece becomes maximum or if the real height Zn of each position n of the sample piece 130 is already known, the entirety control unit obtains correction curves shown in FIGS. 36(a), (b) from Zdn, Zn, In. Then, in a step S43, the entirety control unit 120 obtains a parameter (e.g. coefficient approximate to polynomial) of the above-mentioned correction curve, and stores the parameter thus obtained in the memory 142. Then, the processing is ended (S44). Incidentally, the correction standard pattern 130 shown in FIG. 35 has flat respective ends, and hence can correct a gain and an offset by effecting the correction in the above-mentioned two portions. While the correction standard pattern 130 has the correction curve of which the shape is stable, it is effective for executing a prompt correction when only a gain and an offset drift. When the shape of the correction curve is very stable and can be corrected by other methods, the gain and offset between the control currents to the optical system height detection optical apparatus 200a and the objective lens 103 may be corrected by the standard pattern having a one step difference as shown in FIG. 37(a). Moreover, when the shape of the correction curve is a simple shape that can be approximated by the quadratic function, there may be used the standard pattern having two step differences as shown in FIG. 37(b). Furthermore, when the charged particle beam apparatus such as the SEM apparatus has the Z stage, the Z stage is moved and detected in height not by the standard pattern shown in FIG. 37, but by an ordinary pattern having no step difference, and the image is evaluated, thereby making it possible to correct the control currents to the height detection optical apparatus 200a and the objective lens 103. In this case, although the focus can be adjusted by the Z stage, if a responsive speed of the stage is not sufficient relative to a speed at which the observation portion is changed, then the stage is placed in the fixed state, and the focus can be adjusted by the control current to the objective lens 103. The manner in which the correction is executed by using the correction parameter thus obtained and an appearance is inspected on the basis of the SEM image in the SEM apparatus shown in FIG. 2 or 3 will be described with reference to a flowchart shown in FIG. 39. Specifically, in a step S70, the processing is started. In the next step S71, the entirety control unit 120 reads out the correction parameter from the memory 142, loads a height detection apparatus correction parameter to the height calculating unit 200b, loads a height-focus control signal correction parameter to the focus control apparatus 109, and loads an image distortion correction parameter such as an image magnification correction to the deflection control apparatus 108. In the next step S72, the entirety control unit 120 issues a command to the stage control apparatus 126 so that the stage control apparatus moves the stage to a stage scanning start position. Then, steps S73, S74, S75, S76 are executed in parallel to each other. In the step S73, the entirety control unit 120 issues a command to the stage control apparatus 126 so that the stage control apparatus 126 drives the stage 2 with the inspected object 106 resting thereon at a constant speed. Simultaneously, in the step S74, the entirety control unit 120 issues a command to the height calculating unit 200b such that the height calculating unit 200b outputs correction detection height information 190 based on real time height detection and height detection apparatus correction parameters obtained from the height detection optical apparatus 200a to the focus control apparatus 109 and the deflection control apparatus 108. Further, at the same time, in the step S75, the entirety control apparatus 120 issues commands to the focus control apparatus 108 and the deflection control apparatus 109 such that the focus control apparatus 108 and the deflection control apparatus 109 continuously execute the focus control by using height-focus control signal correction parameters based on the scanning of electron beams and the corrected detection height and the deflection distortion correction by using the image distortion correction parameters such as image magnification correction based on the corrected detection height. Furthermore, at the same time, in the step S76, the entirety control unit 120 issues a command to the image processing unit 124 such that the appearance inspection is executed by obtaining SEM images continuously obtained from the image processing unit 124. In the next step S77, at the stage scanning end position, the entirety control unit 120 displays the inspected result received from the image processing unit 124 on the display 143 or stores the above inspected result in the memory 142. If it is determined at the next step S78 that the inspection is not ended, then a control goes back to the step S72. If it is determined at the step S78 that the inspection is ended, the processing is ended (step S79). While the SEM apparatus (electron beam apparatus) has been described so far in the above-mentioned embodiments, the present invention may be applied to other converging charged beam apparatus such a converging ion beam apparatus. In that case, the electron gun 101 may be replaced with an ion source. Then, in this case, while the secondary electron detector 104 is not always required, in order to monitor the state manufactured by the ion beams, a secondary electron detector or secondary ion detector may be disposed at the position of the secondary electron detector 104. Further, the present invention may also be applied to manufacturing apparatus of a wide sense which includes a pattern writing apparatus using electron beams. In this case, while the secondary electron detector 104 is not always required, because the main purpose is to utilize the electron beam for writing patterns on the sample 106, the secondary electron detector should preferably be used similarly in order to monitor the processing state or to align the position of the sample. It is apparent that optical apparatus such as ordinary optical microscope, optical appearance inspection apparatus and optical exposure apparatus may similarly construct an automatic focus mechanism by using the present height detection apparatus if they have a mechanism for controlling a focus position. In the case of apparatus in which a sample is not elevated and lowered in order to achieve the properly-focused state but a focus position of an optical system is changed, such apparatus can receive particularly remarkable effects of characteristics of highly-accurate height detection of wide range achieved by the present height detection apparatus. FIG. 40 is a diagram showing the embodiment of this case. Only points different from those of FIG. 2 will be described. Reference numeral 191 denotes a light source from which illumination light is irradiated on the sample 106 through a lens 196, a half mirror 195, and an objective lens 193. This image is traveled through the objective lens 193, reflected by the half mirror 195, and focused on an image detector 194 through a lens 197. At that time, the focus of the objective lens 193 should be properly focused on the surface of the sample 106. At that time, light can be properly-focused at a high speed if the apparatus includes the height detector 200. In this embodiment shown in this sheet of drawing, light is properly-focused by elevating and lowering the objective lens 193 but instead light may be properly-focused by elevating and lowering the stage 105. However, if the objective lens 193 is elevated and lowered, then effects of characteristics in which the present height detector 200 can execute the highly-accurate height detection in a wide range can be demonstrated more remarkably. Alternatively, the properly-focused state may of course be established by elevating and lowering the whole of optical system comprising 191, 193, 195, 196, 197, 194. Further, an optical system appearance inspection apparatus may be arranged by adding the image processing unit 124 or the like shown in FIGS. 2 and 3 to the arrangement shown in FIG. 40. Furthermore, a laser material processing machine may be arranged by using the arrangement of the embodiment shown in FIG. 40. According to the present invention, the image distortion caused by the deflection and the aberration of the electron optical system can be reduced, and the decrease of the resolution due to the de-focusing can be reduced so that the quality of the electron beam image (SEM image) can be improved. As a result, the inspection and the measurement of length based on the electron beam image (SEM image) can be executed with high accuracy and with high reliability. Additionally, according to the present invention, if the height information of the surface of the inspected object detected by the optical height detection apparatus and the correction parameters between the focus control current or the focus control voltage of the electron optical system and the image distortion such as the image magnification error are obtained in advance, then the most clear electron beam image (SEM image) can be obtained from the inspected object without image distortion, and the inspection and the measurement of length based on the electron beam image (SEM image) can be executed with high accuracy and with high reliability. Further, according to the present invention, in the electron beam system inspection apparatus, since the height of the surface of the inspected object can be detected real time and the electron optical system can be controlled real time, an electron beam image (SEM image) of high resolution without image distortion can be obtained by the continuous movement of the stage, and the inspection can be executed. Hence, an inspection efficiency and its stability can be improved. In addition, an inspection time can be reduced. In particular, the reduction of the inspection time is effective in increasing a diameter when the inspected object is the semiconductor wafer. Furthermore, according to the present invention, similar effects can be achieved also in observation manufacturing apparatus using converging charged particle beams. |
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claims | 1. A radiation protector treating method, for use with an electric melting furnace having electrodes, comprising the steps of: first, pulverizing a used radiation protector to obtain a pulverized radiation protector material and mixing the pulverized radiation protector material with boron powder and bismuth powder; then casting said pulverized radiation protector material mixed with said boron powder and bismuth powder into an electric melting furnace having electrodes and also casting a selected amount of silicon powder, lead oxide powder and carbon powder into the electric melting furnace; and then melting the material cast in said electric melting furnace to form a glassy melt; wherein said carbon powder amount is selected for adjusting electric current between electrodes so as to control the temperature of the glassy melt. |
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045335141 | claims | 1. A system for degassing a nuclear reactor comprising a nuclear reactor vessel containing a coolant with a concentration of gas therein, the coolant being in a hot temperature state during operation of the nuclear reactor, means for recirculating the coolant in the reactor vessel, means for extracting at least part of the coolant in the recirculating means, means for spraying the extracted coolant during shutdown when the coolant temperature is in at least a range between 130.degree. C. and 100.degree. C. into a space of the nuclear reactor vessel for separating the gas from the coolant, and means for extracting the gas in the space of the nuclear reactor vessel so as to degasify the nuclear reactor vessel for preventing stress corrosion cracking of the nuclear reactor vessel and associated equipment. 2. A system according to claim 1, wherein the nuclear reactor is a boiling water reactor and the space of the nuclear reactor vessel is at an upper portion of the vessel, the coolant contained in the vessel being provided below the space, and means for shutting down the reactor including control rods for being fully inserted into a core of the reactor for shutdown thereof. 3. A system according to claim 15, wherein the nuclear reactor further comprising residual heat removal means connected to the recirculating means, the residual heat removal means including piping containing coolant with a high concentration of gas therein, means for operating the residual heat removal means after completion of insertion of the control rods into the core of the reactor, and means for supplying the coolant in the piping of the residual heat removal means to the spraying means for spraying the coolant into the space of the nuclear reactor vessel for separating the gas from the coolant. 4. A method for degassing a nuclear reactor including a nuclear vessel containing a coolant with a concentration of gas therein, the coolant being in a hot temperature state during operation of the nuclear reactor, the method comprising, during shutdown of the nuclear reactor, the steps of extracting at least part of the coolant having the gas concentration therein from the nuclear reactor vessel, spraying the extracted coolant while in the hot temperature state of at least a range between 130.degree. C. and 100.degree. C. into a space of the nuclear reactor vessel for separating the gas from the coolant, and extracting the gas in the space of the nuclear reactor vessel so as to degasify the nuclear reactor vessel for preventing stress corrosion cracking of the nuclear reactor vessel and associated equipment. 5. A method according to claim 4, wherein the nuclear reactor includes a coolant recirculation system, and the step of extracting at least part of the coolant includes extracting at least a part of the coolant from the coolant recirculation system. 6. A method according to claim 4, wherein the nuclear reactor includes a residual heat removal system connected to the nuclear reactor vessel and containing coolant with a high concentration of gas in a piping of the residual heat removal system, the method further comprising during shutdown, the steps of subsequently operating the residual heat removal system, and the step of spraying including spraying the coolant contained in the piping of the residual heat removal system into the space of the nuclear reactor vessel for separating the gas from the coolant, and extracting the gas from the space. 7. A method according to claim 6, wherein the nuclear reactor generates steam within the nuclear reactor vessel and the steam is supplied to a load, the method further comprising during shutdown, the steps of discontinuing the supply of steam to the load and the step of spraying includes subsequently spraying the coolant in the hot temperature state into the space of the nuclear reactor vessel. 8. A method according to claim 6, wherein the gas contained in the coolant includes oxygen. 9. A method according to claim 6, wherein the nuclear reactor is a boiling water reactor and the space of the nuclear reactor vessel is at an upper portion of the vessel, the coolant contained in the vessel being provided below the space, the shutdown of the reactor including the steps of fully inserting control rods withdrawn from a core of the reactor during operation of the reactor into the core of the reactor for shutdown thereof. 10. A method for degassing a nuclear reactor including a nuclear reactor vessel containing a coolant having a concentration of gas, the vessel having a space in which vapors are generated during operation of the nuclear reactor for being supplied to a load, the method comprising, during start-up of the nuclear reactor, the steps of extracting gas from the space in the nuclear reactor vessel, extracting at least part of the coolant from the nuclear reactor vessel, spraying the extracted coolant having a temperature during start-up of at least in a range between 100.degree. C. and 175.degree. C. into the space of the nuclear reactor vessel for separating gas from the coolant while extracting gas from the space, discontinuing the spraying of the coolant into the space prior to vapors in the space being supplied to the load, and elevating an output of the nuclear reactor to a predetermined level. 11. A method according to claim 10, wherein the nuclear reactor includes a coolant recirculation system, and the step of extracting at least part of the coolant, includes extracting at least a part of the coolant from the coolant recirculation system during start-up of the nuclear reactor. 12. A method according to claim 11, wherein the gas contained in the coolant includes oxygen. 13. A method according to claim 11, wherein the nuclear reactor is a boiling water reactor and the space of the nuclear reactor vessel is at an upper portion of the vessel, the coolant contained in the vessel being provided below the space, the vapors within the space being steam generated during operation of the reactor, and the load including a turbine for driving a generator. 14. A system for degassing a nuclear reactor comprising a nuclear reactor vessel containing a coolant with a concentration of gas therein, the coolant being in a hot temperature state during operation of the nuclear reactor, means for recirculating the coolant in the reactor vessel, means for extracting at least part of the coolant in the recirculating means, means for spraying the extracted coolant during start-up when the coolant temperature is at least in a range between 100.degree. C. and 175.degree. C. into a space of the nuclear reactor vessel for separating the gas from the coolant, and means for extracting the gas in the space of the nuclear reactor vessel so as to degasify the nuclear reactor vessel for preventing stress corrosion cracking of the nuclear reactor vessel and associated equipment. 15. A system according to claim 14, wherein the nuclear reactor is a boiling water reactor and the space of the nuclear reactor vessel is at an upper portion of the vessel, the coolant contained in the vessel being provided below the space, and means for shutting down the reactor including control rods for being fully inserted into a core of the reactor for shutdown thereof. 16. A system according to claim 15, wherein the nuclear reactor further comprises residual heat removal means connected to the recirculating means, the residual heat removal means including piping contaning coolant with a high concentration of gas therein, means for operating the residual heat removal means after completion of insertion of the control rods into the core of the reactor, and means for supplying the coolant in the piping of the residual heat removal means to the spraying means for spraying the coolant into the space of the nuclear reactor vessel for separating the gas from the coolant. |
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summary | ||
052308588 | summary | This invention relates to boiling water nuclear reactors and more particularly to fuel bundles used in such reactors. A fuel bundle having an improved water rod is disclosed, this water rod having two discrete upper and lower compartments for containing water. BACKGROUND OF THE INVENTION Boiling water nuclear reactors contain discrete fuel bundles clustered together in the central portion of the reactor to form the steam generating core of the reactors. These fuel bundles have lower tie plates for supporting a group of upright fuel rods and admitting water moderator from the lower regions of the nuclear reactor. The bundles include an upper tie plate for maintaining the fuel rods upright and permitting water and generated steam to exit upwardly from the fuel bundle to the upper regions of the nuclear reactor. A channel surrounds both tie plates and the fuel rods extending therebetween to confine the flow path of the moderator between the tie plates and around the steam generating fuel rods. Additionally, fuel bundles contain fuel rod spacers distributed at vertical intervals from the bottom of the fuel bundle to the top of the fuel bundle. These spacers have the mechanical function maintaining the matrix of fuel rods in precise side-by-side relation. This prevents the otherwise flexible fuel rods from coming into abrading contact under the forces of the upward hydraulic flow as well as maintaining the fuel rods in their designed side-by-side relation for improved nuclear performance. Operation of the fuel bundles within the reactor can be described in terms of both thermal hydraulic performance and nuclear performance. In terms of thermal hydraulic performance, moderator in the liquid state enters the bottom of each fuel bundle through the lower tie plate, and flows upwardly within the channel and between the fuel rods. During this upward flow increasing amounts of vapor (steam) are generated. At first and in the lower portion of the fuel bundle, liquid flow predominates with an upwardly increasing array of vapor bubbles. Later and in the upper extremities of the bundle, vapor flow predominates with liquid forming an increasingly reduced fraction of the upward moderator flow. In order to maintain stable boiling within the fuel bundle, it is necessary that each of the fuel rods be coated with a film of liquid moderator (water) during the operation of the reactor. This film of water is particularly critical in the upper two phase (steam and water) region of a boiling water nuclear reactor. Further, the vapor fraction in the upwardly flowing moderator tends to increase to and towards the center of a fuel bundle. Therefore, it is the fuel rods in the central upper portion of the fuel bundle that are particularly critical when it comes to maintaining a film of water present over the surface of the fuel rods. It has been found that where this film is not present over the surface of a fuel rod, a phenomenon known as boiling transition can occur. Simply stated, in areas of boiling transition, the wall temperature of the fuel rods rapidly rises. Both the long term metallurgical life of the fuel rod cladding as well as the short term mechanical containment of the fuel rods is threatened by boiling transition. For this reason, it is well accepted in the nuclear industry that the absence of film coating the fuel rods in any portion of the fuel bundle of a boiling water nuclear is to be avoided during reactor operation. The fuel rod spacers distributed at the vertical intervals interior of the fuel bundles have a thermal hydraulic function. It has been found that these spacers cause augmentation of the necessary water film on the fuel rods immediately downstream of the moderator flow within the fuel bundle. In order to understand this phenomenon, some definition of terms and remarks about the complex and little understood phenomenon of boiling within a boiling water nuclear reactor should be made. First, and regarding the term "downstream of the spacer", the reader will understand that moderator flows from the bottom of the fuel bundle to the top of the fuel bundle. Therefore, the region that is downstream from the spacer is that volume of the fuel bundle immediately above the spacer. Further, it will be understood that it is likely that the region immediately upstream of a spacer (or immediately below the spacer) near the top of a fuel bundle is most likely to have a lack of liquid film coating the fuel rods. These regions of the fuel bundle will most likely be subject to boiling transition. Second, the problem of boiling relates at least to the interaction of four highly complex variables. These variables are film flow over the surface of the fuel rods, vaporization from the film on the fuel rods, entrainment of liquid film on the fuel rods within the upwardly flowing vapor, and finally deposition of liquid droplets from the upwardly flowing liquid droplets upon the fuel rods to help maintain the film. Simply stated, it has not been possible to accurately predict the interaction of these variables; design of boiling water nuclear reactor fuel bundles and spacers requires considerable testing of actual models in the form of full scale test assemblies. Finally, and because of the unpredictable interaction resulting in the boiling phenomena of boiling water nuclear reactor fuel bundles, it has been found that different designs of the spacers placed in the upper two phase region of the fuel bundle restore the necessary film coating to different degrees. Thus it will be understood in the following discussion, that the type and total number of spacers in a particular fuel bundle can vary. Regarding reactor nuclear performance, in a boiling water nuclear reactor, the density of the water is important. Simply stated, the nuclear reaction generates fast neutrons. The continuance of the nuclear reaction requires slow or thermalized neutrons. It is the function of the moderator to moderate the fast neutrons to the thermal state so that the reaction can continue. The sufficiency of this moderation is a function of the density of the moderator at any particular point within the interior of the reactor. As has already been mentioned, moderator density in the central upper region of the fuel bundle is low. To correct this condition, it is well known to insert so-called water rods in the interior of a boiling water nuclear reactor fuel bundle. These water rods are filled with liquid moderator to supply to the upper region of the fuel bundle the necessary moderator density for the efficient nuclear reaction. It is to be understood that conventional water rods, while having the nuclear efficiency of supplying water moderator to the upper central portion of the fuel bundle, have a thermal hydraulic deficiency. Specifically, and in order that the water rods remain full with liquid moderator, water is taken from the bottom of the fuel bundle and shunted directly through a heater rod to the top of the fuel bundle. The water bypasses the steam generating flow within the fuel bundle and to that extent is inefficient in its upward flow through the fuel bundle. It is the purpose of this invention to provide a fuel bundle with an improved water rod that both continues the water density in the upper two phase region of fuel bundles having water rods and yet improves the thermal hydraulic characteristics of the fuel bundle. SUMMARY OF THE INVENTION A fuel bundle having an improved water rod is disclosed, this water rod having two discrete upper and lower compartments for containing water. The bottom compartment flows moderator from the bottom of the fuel bundle through the water rod compartment to discharge points located through the water rod side walls between the upper most spacers; the top compartment opens upwardly and is naturally filled with liquid moderator settling out of the upwardly flowing moderator during reactor operation. There results the requisite presence of liquid moderator within the water rod for supplying the upper two phase region of the fuel rod with moderator density. At the same time, water flow through the lower compartment of the water rod from the bottom of the fuel bundle to the upper two phase region of the fuel bundle improves the thermal hydraulic performance. Specifically, water is discharged in the upper two phase region of the fuel bundle at the center of the fuel bundle where the density of the upwardly flowing moderator has the largest vapor fraction. This discharge preferably occurs between the first and second, or second and third spacers. As a result, liquid moderator is injected where it has the maximum beneficial effect on moderator density and the beneficial formation of a liquid film immediately upstream of the spacers. Improved thermal hydraulic performance of the fuel rods immediately adjacent to the water rods of the fuel bundle results. |
abstract | A damping area or “dash pot” on the upper ends of control rods absorb energy from dropped control rod assemblies without narrowing the diameter of guide tubes. As a result, coolant can freely flow through the guide tubes reducing boiling water issues. The dampening area reduces a separation distance between an outside surface of the control rod and an inside surface of the guide tubes decelerating the control rods when entering a top end of the guide tubes. In another example, the dampening area may be located on a drive shaft. The dampening area may have a larger diameter than an opening in a drive shaft support member that decelerates the drive shaft when dropped by a drive mechanism. |
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claims | 1. A method of generating a collimated electromagnetic emission, the method comprising:producing an excitation in a sample of multiple particles by vibrationally stimulating the sample thereby transitioning each particle of at least a quantity of the multiple particles from a lower first energy state to a higher second energy state,wherein the multiple particles of the sample are positioned on a planar support surface, andwherein the planar support surface comprises deformations that are quadratic or higher-order in transverse surface coordinates; andgenerating a collimated electromagnetic emission by de-excitation of at least a portion of the quantity of the multiple particles. 2. The method of claim 1, wherein vibrationally stimulating the sample comprises establishing phase coherence among at least some of the multiple particles of the sample. 3. The method of claim 1, wherein the collimated electromagnetic emission is generated by phased array emission. 4. The method of claim 3, wherein the planar support surface comprises a cathode. 5. The method of claim 4, wherein, as the electromagnetic emission is generated, the multiple particles comprise phase coherent emitting dipoles. 6. The method of claim 3, wherein the multiple particles of the sample are randomly positioned on the planar support surface. 7. The method of claim 3, wherein the collimated electromagnetic emission comprises a beam directed normal to the planar support surface. 8. The method of claim 7, wherein the multiple particles of the sample are positioned within an area on the planar support surface, and the beam has a cross-sectional area essentially equivalent to the area on the planar support surface. 9. The method of claim 7, wherein the planar support surface comprises aligned crystal planes. 10. The method of claim 9, wherein the crystal planes are aligned by rolling. 11. The method of claim 7, wherein the deformations are produced by at least one of ion bombardment and sputtering. 12. The method of claim 7, wherein the beam has a shape predetermined by a selected preparation of the deformations. 13. The method of claim 1, wherein:the collimated electromagnetic emission comprises a beam generated by phased array emissions from the multiple particles of the sample;the multiple particles of the sample are positioned on a support surface having a circular diameter; andthe support surface varies from a plane according to the time varying function:u(x,y)=c(t)x2+d(t)y2+f(t)xy in which:u is defined as a displacement from the plane;x is defined as a first position coordinate along a first axis in the plane;y is defined as a second position coordinate along a second axis in the plane perpendicular to the first axis;c(t) is a time varying first parameter;d(t) is a time varying second parameter; andd(t) is a time varying third parameter. 14. The method of claim 13, wherein the beam focuses as a spot smaller than the circular diameter at a distance Z from the support surface when:c(t)=0.80/2Z; d(t)=0.80/2Z; and f(t)=0. 15. The method of claim 13, wherein the beam focuses as a line segment having a length greater than the circular diameter at a distance Z from the support surface when:c(t)=−0.30/2Z; d(t)=0.90/2Z; and f(t)=0. 16. The method of claim 1, wherein vibrationally stimulating the sample comprises producing excitations via up-conversion of vibrational energy. 17. The method of claim 1, wherein the collimated electromagnetic emission comprises X-ray emission. 18. The method of claim 17, wherein the X-ray emission is generated by up-conversion of vibrational energy resulting in phase coherence. 19. An apparatus for generating a collimated electromagnetic emission, comprising:a support structure having a surface, wherein the surface comprises deformations that are quadratic or higher-order in transverse surface coordinates;a sample of multiple particles positioned on the surface;a device configured to vibrationally stimulate the sample thereby transitioning each particle of at least a quantity of the multiple particles from a lower first energy state to a higher second energy state such that a collimated electromagnetic emission is generated by de-excitation of at least a portion of the quantity of the multiple particles. 20. The apparatus of claim 19, wherein the surface of the support structure is planar. 21. The method of claim 20, wherein the collimated electromagnetic emission comprises a beam directed normal to the surface. 22. The method of claim 20, wherein the multiple particles of the sample are randomly positioned on the surface. 23. The method of claim 19, wherein the support structure comprises a cathode. 24. The method of claim 19, wherein the surface comprises aligned crystal planes. |
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claims | 1. A process comprising:inducing, with antiprotons, nuclear fission in a material, and thenmeasuring leakage of radioactive byproduct produced by the fission, and thenrepeating said inducing and then said measuring until producing, responsive to said inducing and then said measuring, a design for a nuclear fuel element. 2. The process of claim 1, further including: producing the nuclear fuel element according to the design. 3. A product produced by the process of claim 2, the product comprising the nuclear fuel element. 4. The process of claim 1, wherein said material includes depleted uranium. 5. The process of claim 1, wherein said design specifies a number of coating layers. 6. The process of claim 1, wherein said design specifies a thickness of each coating layer. 7. The process of claim 1, wherein said design specifies a composition of each coating layers. 8. A process of measuring fission daughter migration out of at least one nuclear rocket fuel element sample, the method comprising:exposing at least one sample of a nuclear rocket fuel element to antiprotons, and thenheating said at least one sample to nuclear rocket operational temperatures, and thenmeasuring the emission of fission daughters from said at least one sample. 9. The process of claim 8, wherein said at least one sample does not contain enriched uranium. 10. The process of claim 9, further including: producing, responsive to the measuring, a design for a nuclear fuel element. 11. The process of claim 10, further including: producing the nuclear fuel element according to the design. 12. A product produced by the process of claim 10, the product comprising the nuclear fuel element. 13. The process of claim 9, wherein said sample includes depleted uranium. 14. The process of claim 8, wherein said heating, exposing, and measuring take place concurrently. 15. A process comprising:inducing, with antiprotons, nuclear fission in a material to produce radioactive byproduct, and thenmeasuring leakage of the byproduct so as to produce a graphic representation of the leakage. 16. The process of claim 15, further including producing, responsive to the measuring, a design for a nuclear fuel element. 17. The process of any one of claims 1, 10, 16, wherein the producing a design for the nuclear fuel element comprises computer processing in producing the design for the nuclear fuel element. 18. Apparatus including:means for inducing, with antiprotons, nuclear fission in a material to produce radioactive byproduct; andmeans for producing a measurement of leakage of the byproduct so as to produce a graphic representation of the measured leakage. 19. The apparatus of claim 18, further including a design for a nuclear fuel element generated responsive to the measurement. 20. The apparatus of claim 18, further including a nuclear fuel element produced according to a design. |
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claims | 1. A system for regulating nuclear reactor core activity comprising:a naturally circulating nuclear reactor having a nuclear reactor cooling outlet,a nuclear reactor cooling inlet, anda nuclear core with a negative temperature reactivity coefficient;a steam generator having a saturated liquid space displaced above the nuclear reactor cooling outlet, anda steam space;a coolant loop where the coolant loop cycles coolant out through the nuclear reactor coolant outlet, where the coolant loop is in thermal communication with the saturated liquid space of the steam generator, and where the coolant loop cycles coolant in through the nuclear reactor coolant inlet;a steam piping system in fluid communication with the steam space of the steam generator;a three way valve having a valve shaft, in fluid communication at a three way valve inlet port with the steam piping system which leaves the steam generator;an expansion turbine directly fluidly connected to and in fluid communication with the three way valve only at a three way valve first outlet port;a condenser in fluid communication with the expansion turbine;a pump header in fluid communication with the condenser;a feedwater heater in fluid communication at a heater inlet port with the three way valve at a three way valve second outlet port and in fluid communication at a heater outlet port with the condenser;a feedwater pump having a pump inlet port in fluid communication with the pump header, anda pump discharge port;a feedwater header in fluid communication with the pump discharge port of the feedwater pump, in thermal communication with the feedwater heater, and in fluid communication with the saturated liquid space of the steam generator;an electric generator mechanically driven by the expansion turbine and electrically connected to an electrical grid; anda controller separate from and in data communication with both the valve shaft of the three way valve and the electric generator, where the controller is programmed torespond to an increase in power demand from the electric generator by directing movement of the valve shaft to concomitantly increase steam flow to the expansion turbine and decrease steam flow to the feedwater heater, andrespond to a decrease in power demand from the electric generator by directing movement of the valve shaft to concomitantly decrease steam flow to the expansion turbine and increase steam flow to the feedwater heater. 2. The electric generating system of claim 1 where the nuclear reactor includes fuel, and where the fuel is a nitride. 3. The electric generating system of claim 2 where the coolant includes lead. 4. The electric generating system of claim 3, where the coolant is a lead-bismuth eutectic. |
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043081010 | claims | 1. In combination with a substantially cylindrical nuclear reactor pressure vessel and a concrete support wall surrounding said pressure vessel, an attachment assembly for fixedly mounting said pressure vessel comprising: a support member having a first end portion attached to said pressure vessel and having a second, opposite end portion positioned proximate to a support surface of said support wall; a foot ring fixedly attached to said second end portion of said support member, with said foot ring overlapping and contacting a portion of said support surface of said support wall; a plurality of elongated prestressed tensile force transmitting members each including a first end portion fixedly positioned in a vertically lower end portion of said support wall and each elongated tensile force transmitting member further including a second, opposite end portion extending beyond said support surface of said support wall; a plurality of separate yoke assemblies positioned adjacent said support surface with each yoke assembly enclosing the second end portion of at least one of said elongated, prestressed tensile force transmitting members; attachment plate means mounted within each of said yoke assemblies for fixedly attaching said second end portion of said at least one tensile force transmitting member to said respective yoke assembly whereby said tensile force transmitting members draw said yoke assemblies toward said support surface; each yoke assembly having a radially outer force-transmitting surface contacting said support surface at a location radially outside said foot ring, and clamping means in force transmitting relationship with said elongated prestressed tensile force transmitting members and said foot ring for pressing said foot ring against said support surface. and a plurality of spaced block members are each fixedly attached to said bearing plates, with said blocking members each partially extending into one of the recesses formed in said foot ring to limit movement of said foot ring along the support surface in a direction radially away from said pressure vessel. with each bundle of prestressed rods spaced from one another and each bundle of prestressed rods partially enclosed by a separate yoke assembly. each of said apertures positioned to receive one of said prestressed rods extending therethrough. and a further quantity of said corrosion protecting compound is positioned within each of said thin walled tubular passageways. a plurality of elongated prestressed tensile force transmitting members each including a first end portion fixedly positioned in a vertically lower end portion of said support wall; a plurality of yokes each supported on said support surface, each yoke having a radially-outer surface in force transmitting connection with said support surface and a radially-inner surface in force transmitting connection with a portion of said foot ring, each yoke further having a mid-portion joining said radial outer and inner surfaces and mechanically connected to an upper end of at least one of said tensile force transmitting members; and, said fixing means further comprising blocking means fixed to the support wall and projecting from the portion of said support surface adjacent a radially outwardly facing surface of said foot ring for limiting moving of said foot ring along said support surface in a direction away from said nuclear reactor pressure vessel. 2. The combination according to claim 1, wherein said support member has a substantially truncated cone configuration and is formed of a sheet metal material. 3. The combination according to claim 1, wherein said foot ring is substantially cylindrical in cross-sectional configuration and includes a radial outward edge surface facing away from said pressure vessel. 4. The combination according to claim 3, wherein a plurality of separate metallic bearing plates are each embedded within the support surface of said support wall, with portions of each of the bearing plates contacting the overlapping portion of said foot ring to provide support therefor. 5. The combination according to claim 4, wherein said radial outward edge surface of said foot ring includes a plurality of recesses extending through portions thereof, with said recesses circumferentially spaced about the outward edge surface of said foot ring, 6. The combination according to claim 1, wherein a cooling conduit is fixedly mounted on the second end portion of said support member adjacent to said foot ring. 7. The combination according to claim 1, wherein said plurality of elongated tensile force transmitting members each comprises a prestressed steel rod. 8. The combination according to claim 7, wherein a plurality of said prestressed rods are grouped into a plurality of bundles with each bundle extending through a thin-walled substantially vertically extending tubular passageway formed through said support wall, 9. The combination according to claim 8, wherein said attachment plate means comprises a separate attachment plate fixedly mounted within each of said yoke assemblies, with each attachment plate having a plurality of apertures extending therethrough, and 10. The combination according to claim 8, wherein a hollow cap member surrounds an end portion of each yoke assembly and a corrosion protecting compound fills the space formed between said cap and said yoke assembly to protect the second end portions of said tensile transmitting members enclosed within said plurality of yoke assemblies, 11. The combination according to claim 1, wherein a side wall of said foot ring includes a surface portion curved away from a confronting portion of said support surface of said support wall to allow said foot ring to pivot relative to said support surface. 12. The combination according to claim 11, wherein said curved surface portion of said foot ring is positioned vertically beneath said force transmitting means. 13. In combination with a substantially cylindrically shaped nuclear reactor vessel, and a support wall surrounding said reactor vessel, an attachment assembly for positioning said nuclear reactor vessel within said support wall, said attachment assembly comprising a support surface on said support wall, a foot ring rigidly connected to the circumference of said reactor vessel and in contact with said support surface, and fixing means, said fixing means comprising: 14. An attachment assembly according to claim 13, wherein said blocking means comprises a plurality of separate blocking members extending from said support surface at predetermined locations adjacent said outwardly facing surface of said foot ring, with a plurality of said blocking members initially contacting said foot ring prior to operation of said nuclear reactor vessel. 15. The combination according to claim 13, wherein a plurality of elongated prestressed tensile force transmitting members are arranged in a plurality of channels each extending in a substantially vertical direction through said support wall. 16. The combination according to claim 15 wherein a corrosion protecting compound is introduced into each of said channels for protecting the elongated prestressed tensile force transmitting members extending through said channels, wherein said tensile force transmitting members and said compound fill said channels. 17. The combination according to claim 13, wherein said elongated prestressed tensile force transmitting members each comprises a prestressed steel rod. 18. The combination according to claim 13, wherein a swivelling caster is clamped between the radially inner surface of each yoke assembly and a portion of said foot ring for pressing said foot ring against said support surface while allowing thermal expansion of said foot ring. 19. The combination according to claim 1, wherein said clamping means comprises a plurality of separate swivelling casters, with each caster having a circular-cylindrical contact surface contacting both a radially inner surface of one of said yoke members and a portion of said foot ring. |
claims | 1. A nuclear reactor system including a nuclear reactor vessel,wherein the nuclear reactor vessel includes a first vessel serving as a region using fast neutrons, and a second vessel serving as a region using thermal neutrons in a nuclear reactor, energy of each thermal neutron being approximately 0.5 MeV or less, and the second vessel for the thermal neutrons is placed inside the first vessel for the fast neutrons or the first vessel for the fast neutrons is placed inside the second vessel for the thermal neutrons,the region using the fast neutrons includesa plurality of fuel assemblies, each fuel assembly being a bundle of 50 or more metal fuel rods, each metal fuel rod being obtained by inserting a metal fuel pin into a sheath made of stainless steel, the metal fuel pin having an alloy composition of zirconium (Zr) with uranium (U) and/or plutonium (Pu), anda liquid metal selected from metallic sodium (Na), Pb—Bi or Pb working as a primary coolant,a non-metallic material and radioactivity reducing assemblies are loaded in the region using the thermal neutrons, the non-metallic material being usable as a neutron moderator and as a secondary coolant, each radioactivity reducing assembly being obtained by putting a radioactive material into a sheath made of stainless steel or a Zr material, the radioactive material being obtained by processing minor actinide nuclides separated from spent fuel rods through reprocessing or radioactive nuclear fission products (FPs) separated and refined from the spent nuclear fuel, at least one selected from the group consisting of Se79, Sr90, Zr93, Tc99, Sn126, Cs135 and Cs137, being mixed and formed into a shape of a pellet or a pin, andthe nuclear reactor system is configuredto generate electricity by transferring thermal energy generated by the fast neutrons to a heat exchanger by use of the primary coolant, exchanging heat between the primary coolant and the secondary coolant in the heat exchanger, and thereafter supplying the thermal energy to a turbine system by use of the secondary coolant, andto simultaneously decrease a concentration of radionuclides by accelerating a rate of transmutation of radionuclides into stable nuclides by use of thermal neutrons generated by decelerating the fast neutrons. 2. The nuclear reactor system according to claim 1,wherein the nuclear reactor system uses metallic sodium (Na) as the primary coolant for the fuel assemblies, and carbon dioxide gas (CO2) as the secondary coolant for the radioactivity reducing assemblies, the carbon dioxide gas working as the coolant and as the moderator,the nuclear reactor system further includes a CO2 gas driven turbine, andwherein the nuclear reactor system enhances heat exchange efficiency by once supplying the CO2 gas, returning from the turbine system, to the radioactivity reducing second vessel, and thereafter supplying the CO2 gas to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 3. The nuclear reactor system according to claim 1,wherein the nuclear reactor system uses lead-bismuth (Pb—Bi) or Pb alone as the primary coolant for the fuel assemblies, and water (H2O) as the secondary coolant concurrently working as a moderator for the radioactivity reducing assemblies,the nuclear reactor system further includes a steam turbine, andwherein the nuclear reactor system enhances heat exchange efficiency by supplying H2O, returning from the turbine system, to the second vessel in which the radioactivity reducing assemblies are loaded, and thereafter supplying the H2O to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 4. The nuclear reactor system according to claim 1, wherein the nuclear reactor system uses supercritical carbon dioxide (CO2) gas as the secondary coolant. 5. The nuclear reactor system according to claim 1, wherein the reflector is arranged surrounding the plurality of fuel assemblies loaded in the first vessel, the reflector being deformable due to thermal expansion, the reflector having a structure which makes temperature and reflector efficiency inversely correlated to each other, the reflector being capable of automatically controlling nuclear fission reaction induced by fast neutrons. 6. The nuclear reactor system according to claim 5, whereina structure of the reflector uses carbon (C) or beryllium (Be) as a constituent material,the reflector is divided into four or more segments in a circumferential direction,a spring made of stainless steel with a large thermal expansion coefficient is attached to each reflector segment, andthe structure of the reflector is configured to decrease reflection efficiency depending on thermal expansion of the spring with a rise in temperature. 7. The nuclear reactor system according to claim 5, whereina structure of the reflector is divided into segments in a radial direction and in a height direction,each reflector segment is formed by filling graphite or carbon into a case made of stainless steel,each two reflector segments are connected by stainless steel, andthe structure of the reflector is configured to be capable of decreasing neutron reflection efficiency of the reflector depending on thermal expansion of the stainless steel. 8. The nuclear reactor system according to claim 1, whereina solenoid coil is arranged surrounding the radioactivity reducing assemblies which are loaded in the second vessel, the nuclear fission products (FPs) being mixed into each radioactivity reducing assembly, andthe nuclear reactor system is configured to accelerate a rate of β-decay of the radioactive nuclear fission products bygenerating a low-frequency electromagnetic field at a frequency of 50 kHz to 50 MHz, andconcurrently applying the thermal neutrons to the radioactivity reducing assemblies, the thermal neutrons being obtained by decelerating the fast neutrons which are generated in the first vessel outside the second vessel. 9. The nuclear reactor system according to claim 1, whereinsolenoid-shaped winding is arranged along a radial circumference of the second vessel,the radioactivity reducing assemblies into which the radioactive nuclear fission waste is mixed are loaded in the second vessel, andthe nuclear reactor system is configured to accelerate a rate of transmutation of FP elements into stable elements byapplying a low-frequency electromagnetic field at a frequency of 100 kHz to 10 MHz to the radioactivity reducing assemblies, andfurther bombarding an inside of the first vessel placed in the second vessel with thermal neutrons which are generated from a reactor core including the reflector. 10. The nuclear reactor system according to claim 1, whereinthe first vessel is formed in a shape of a cylinder with a diameter of 2 m or less,each fuel assembly to be contained in the nuclear reactor vessel includes 50 or more fuel rods, each of which is formed with a diameter of 5 to 15 mm and with a length of 2 m or less,six or more of the fuel assemblies are loaded in the first vessel, andthe reflector deformable due to thermal expansion is arranged surrounding the fuel assemblies in order to realize a load following control scheme. 11. The nuclear reactor system according to claim 1, whereinin the fuel assemblies, a fuel pin into which minor actinide elements are mixed is inserted into each fuel rod sheath, andthe nuclear reactor system is thereby configured to accelerate transmutation of radioactive minor actinide elements into stable elements by use of the fast neutrons. 12. The nuclear reactor system according to claim 1, whereina diameter of the nuclear reactor vessel is 2 m or greater,two or more of the first vessels serving as the fast neutron region and two or more of the second vessels serving as the thermal neutron region are set in the vessel,the metal fuel assemblies are loaded in each first vessel, and each first vessel is filled with the primary coolant of liquid metal,the radioactivity reducing assemblies containing minor actinides and/or radioactive nuclear fission products (FPs) separated and refined from the spent nuclear fuel, at least one selected from the group consisting of Se79, Sr90, Zr93, Tc99, Sn126, Cs135 and Cs137, being mixed and formed into a shape of a pellet or a pin, are loaded in each second vessel, andthe nuclear reactor system removes heat from the vessel and the radioactivity reducing assemblies containing the radioactive waste by making the secondary coolant flow in the vessel and the radioactivity reducing assemblies, and further uses the heat to generate electricity. 13. A method comprising: in a nuclear reactor system,forming a nuclear reactor vessel with a first vessel serving as a region using fast neutrons, and a second vessel serving as a region using thermal neutrons, energy of each thermal neutron being approximately 0.5 MeV or less;arranging a plurality of fuel assemblies and a liquid metal in the region using the fast neutrons, each fuel assembly being a bundle of 50 or more metal fuel rods, each metal fuel rod being obtained by inserting a metal fuel pin into a sheath made of stainless steel, the metal fuel pin having an alloy composition of zirconium (Zr) with uranium (U) and/or plutonium (Pu), the liquid metal working as a primary coolant;accelerating transmutation of radioactive minor actinide elements into stable elements by use of fast neutrons by inserting the metal fuel pin, into which minor actinide elements are mixed, into each fuel rod sheath in the fuel assemblies; andloading a non-metallic material and radioactivity reducing assemblies in the region using the thermal neutrons, the non-metallic material being usable as a neutron moderator and a secondary coolant, each radioactivity reducing assembly being obtained by putting a radioactive material into a sheath made of stainless steel or a Zr material, the radioactive material being obtained by processing minor actinide nuclides separated from spent fuel rods through reprocessing, or radionuclides as nuclear fission products, into a shape of a pellet or a pin, whereinthe methodgenerates electricity by transferring thermal energy generated by the fast neutrons to a heat exchanger by use of the primary coolant, exchanging heat between the primary coolant and the secondary coolant in the heat exchanger, and thereafter supplying the thermal energy to a turbine system by use of the secondary coolant, andsimultaneously decreases a concentration of radionuclides by accelerating a rate of transmutation of radionuclides into stable nuclides by use of thermal neutrons generated by decelerating the fast neutrons. 14. The method according to claim 13,wherein the method uses metallic sodium (Na) as the primary coolant for the fuel assemblies, and carbon dioxide (CO2) gas as the secondary coolant for the radioactivity reducing assemblies, the carbon dioxide gas working as the coolant and as the moderator,the method further uses a CO2 gas driven turbine, andwherein the method enhances heat exchange efficiency by once supplying the CO2 gas, returning from the turbine system, to the radioactivity reducing second vessel, and thereafter supplying the CO2 gas to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 15. The method according to claim 13,wherein the method uses lead-bismuth (Pb—Bi) or Pb alone as the primary coolant for the fuel assemblies, and water (H2O) as the secondary coolant concurrently working as a moderator for the reducing assemblies,the method further uses a steam turbine, andwherein the method enhances heat exchange efficiency by supplying H2O, returning from the turbine system, to the second vessel in which the radioactivity reducing assemblies are loaded, and thereafter supplying the H2O to the heat exchanger for transferring heat between the primary coolant and the secondary coolant. 16. The method according to claim 13, whereina solenoid coil is arranged surrounding the radioactivity reducing assemblies which are loaded in the second vessel, the nuclear fission products (FPs) being mixed into each radioactivity reducing assembly, andthe method accelerates a rate of β-decay of the radioactive nuclear fission products bygenerating a low-frequency electromagnetic field at a frequency of 50 kHz to 50 MHz, andconcurrently applying the thermal neutrons to the radioactivity reducing assemblies, the thermal neutrons being obtained by decelerating the fast neutrons which are generated in the first vessel outside the second vessel. 17. The method according to claim 13, whereinsolenoid-shaped winding is arranged along a radial circumference of the second vessel,the radioactivity reducing assemblies into which the radioactive nuclear fission waste is mixed are loaded in the second vessel, andthe method accelerates a rate of transmutation of FP elements into stable elements byapplying a low-frequency electromagnetic field at a frequency of 100 kHz to 10 MHz to the radioactivity reducing assemblies, andfurther bombarding an inside of the first vessel placed in the second vessel with thermal neutrons which are generated from a reactor core including the reflector. 18. The method according to claim 13, wherein the method performs load following control byforming the first vessel in a shape of a cylinder with a diameter of 2 m or less,using 50 or more fuel rods, each formed with a diameter of 5 to 15 mm and with a length of 2 m or less, in each fuel assembly to be contained in the nuclear reactor vessel,loading six or more of the fuel assemblies in the first vessel, andarranging the reflector, deformable due to thermal expansion, to surround the fuel assemblies. |
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062597590 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an incore piping section maintenance system according to the present invention will be described hereunder. FIG. 1 is a longitudinal sectional view showing a first embodiment of an incore piping section maintenance system according to the present invention, and FIG. 2 is a plain view showing the same. The incore piping section maintenance system is applied to an incore piping section of a light water reactor such as a boiling water reactor or the like, and performs a surface de-sensitization of metallographic structure of the incore piping section, a preventive maintenance of weld zones (welded or to be welded portion) or the like, and a preventive maintenance work. FIG. 1 and FIG. 2 each shows an example in which an incore piping section maintenance system according to the present invention is applied to an incore piping section 26 in a reactor pressure vessel 1 of a boiling water reactor. The reactor pressure vessel 1 has, as a whole, the same structure as the conventional reactor pressure vessel shown in FIG. 5 to FIG. 7, and therefore, like reference numerals are used to designate the identical components used in these figures, and the detailed explanation thereof is omitted herein. The incore piping section maintenance system 25 shown in FIG. 1 and FIG. 2 is installed and fixed to a maintenance target portion of the reactor pressure vessel 1 or in the vicinity thereof. The maintenance target portion includes an incore piping section 26, for example, an inner weld zone 27a of a core spray pipe 27 of a core spray system 15, or the like, and is a place suitable for preventive repair and preventive maintenance of the incore piping section 26 of the reactor pressure vessel 1. The incore piping section maintenance system 25 includes: a maintenance system main body 30 which is located at a maintenance target portion or in the vicinity of the target portion between the core shroud 4 and the inner wall of the reactor pressure vessel 1; a support means 31 which is located on the maintenance system main body 30 so as to reciprocate towards or apart from the maintenance target portion; a laser de-sensitization treatment means 32 which is rotatably supported around an axis of the support means 31 and carries out a laser beam irradiation with respect to the maintenance target portion; and an optical transmission means 33 which guides a laser beam oscillated from a laser generation device or equipment L, such as shown in FIG. 3, to the laser de-sensitization treatment means 32. Further, the incore piping section maintenance system 25 is supported on an overhead traveling crane (not shown) which is located above the reactor pressure vessel 1 and including a fuel exchanger or the like and is freely movable up and down by means of cable. A reference numeral 35 denotes a hang sling or hang hook of the incore piping section maintenance system 25. The maintenance system main body 30 is a main frame assembly which is constructed in a manner of integrally assembling a support plate 36 and a rectangular base frame 37 which functions as a traveling cradle. The support roller 38 supported on the support plate 36 is removably mounted from the outside to a shroud head bolt bracket 39 which projects from an outer peripheral wall of the core shroud 4 and functions as a support bracket. On the other hand, a pair of fixed cylinders 40 are located on a lower portion of the base frame 37 facing an inner peripheral wall of the reactor pressure vessel 1. The fixed cylinders 40 are arranged in parallel to each other and are provided with an actuating rod 42 which has a mounting head or mounting pad 41 so as to freely reciprocate. The actuating rod 42 constitutes a piston rod, and reciprocates between a non-actuation position retracting by an actuation of the fixed cylinder 40 and an actuation position projecting by the same. When the fixed cylinder 40 is situated on the actuation position, the mounting head 41 presses the inner peripheral wall of the reactor pressure vessel 1 so as to be frictionally held thereto. The maintenance system main body 30 constituting the main frame assembly are pressed against the shroud head bolt bracket 39 at its one side and is pressed against the inner peripheral wall of the reactor pressure vessel 1 at the other side, and thus, is stably fixed and supported. In the maintenance system main body 30, a screw shaft 44 is rotatably supported on the base frame 37. The screw shafts 44 are located in a state of mutually facing at opposite sides of the base frame 37 and are provided with a linear guide 45 which is freely reciprocated. The linear guide 45 is supported so as to be radially movable. Further, the screw shaft 44 is connected with a reversible driving motor 46 which is installed on the support plate 36 through a gear mechanism 47. When the driving motor 46 is driven, the linear guide 45 is reciprocated along the screw shaft 44. On the other hand, the screw shafts 44 located on the opposite sides of the base frame 37 may be driven so as to be synchronous with each other, or one of the screw shafts 44 may be replaced with a guide shaft for a slide guide. Moreover, the linear guide 45 is provided with a bridge-like guide shaft 48 which extends in a direction perpendicular to the screw shaft 44, and the fixed support means 31 is movably supported on the guide shaft 48. The support means 31 is moved while being supported to a frame or plate-like bridge guide member 50 of the linear guide 45 and is supported in a state of projecting downward from the linear guide 45. The guide shaft 48 for moving the support means 31 may be a screw shaft driven by a motor or an actuating rod driven by a cylinder. The support means 31 supported on the linear guide 45 is supported so as to be adjustable and movable in an XY direction on one plane formed by the maintenance system main body 30. Further, the support means 31 includes a cylindrical motor case 53 having a built-in revolving motor 52 as a support cylinder and has a support body (assembly) 54 which extends sideward from a lower end of the motor case 53 so as to be attached integrally therewith and is supported in form of a cantilever beam. The support body 54 of the support means 31 is provided with seal means 56 at its both sides. The seal means 56 is a ring or truss-like seal member 57 which is mounted at both sides of the support body 54 in a state of being arranged in parallel in a multi-stage, for example, two stages. Each seal member 57 has a hollow structure and is freely expandable and shrinkable by freely injecting or removing a compressive fluid, for example, a compressed air, into and from its interior. Moreover, the support body 54 of the fixed support means 31 is provided with a laser de-sensitization treatment means 32. The laser de-sensitization treatment means 32 is rotatably supported on the central portion of the support body 54 by means of bearing 59 while being connected to a revolving motor 52 through a gear mechanism 60. When the revolving motor 52 is driven, the laser de-sensitization treatment means 32 is rotatable around a shaft of the bearing 59. The laser de-sensitization treatment means 32 has a laser scanning optical system 61 and a laser irradiating section 62. The laser irradiating section 62 irradiates with a laser beam the incore piping section 26 which is the maintenance target portion so as to perform a surface de-sensitization of a metallographic structure of the incore piping section 26, a preventive repair of weld zones or the like and a preventive maintenance. In the laser de-sensitization treatment means 32, the laser scanning optical system 61 guides a laser beam incident upon a laser supply port 63 to the laser irradiating section, and therefore, a laser transmission path is formed by the laser scanning optical system 61 in the laser de-sensitization treatment means 32. The laser scanning optical system 61 is constructed in the combination with a condenser (converging) lens, a mirror or the like. A laser beam oscillated from the laser generation device or equipment is guided to the laser supply port 63 of the laser de-sensitization treatment means 32 via a flexible optical transmission means 33 such as an optical fiber cable or the like. The optical transmission means 33 is included in a transmission tube 65. The laser generation equipment may be located on an operation floor (not shown) above the reactor pressure vessel 1, or may be located on a fuel exchanger or the maintenance system main body 30. In the case of locating the laser generation equipment on the maintenance system main body 30, a waterproof treatment is required. On the other hand, in addition to the optical transmission means 33 for transmitting a laser beam, the transmission tube 65 includes power, as a driving source, and control signal cables, various flexible pipes for feeding and discharging an atmosphere (purge) gas filled in the laser de-sensitization treatment means or a pressurized fluid, for example, a pressurized air filled in the seal member 57, and further, sucking and recovering a bubble generated in the laser irradiating section 62. Meanwhile, the laser de-sensitization treatment means 32 is provided with an inspection monitoring camera means, not shown, and a lighting means, not shown, as a maintenance target portion (weld zone) detector at the laser irradiating section 62 or in the vicinity of the laser irradiating section. The lighting means is a underwater light, for example. The inspection monitoring camera is an underwater TV camera, for example, and the underwater TV camera is provided integrally with the underwater light. In the incore piping section maintenance system 25, it is possible to monitor a maintenance work by means of the inspection monitoring camera means from the outside of the reactor pressure vessel 1 and to perform the maintenance work in a water by remote control. Therefore, it is possible to smoothly perform a maintenance work in a state that a reactor well is filled with a water. Moreover, in order to confirm and specify a laser execution position, the laser de-sensitization treatment means 32 is provided with an ultrasonic testing equipment (UT equipment) UT as a weld zone detector, the UT equipment being located to a portion shown in FIG. 1, for example. The UT equipment detects the laser execution position and a degree of damage in the incore piping section 26. After the executing position of the incore piping section 26 is confirmed by the UT equipment, a laser de-sensitization treatment is carried out by the laser de-sensitization treatment means 32. Further, the laser de-sensitization treatment means 32 is provided with a ferrite indicator (FI) in place of the UT equipment or together with the UT equipment. The ferrite indicator FT distinguishes a difference in ferrite quantity between the weld zone and a base material of the incore piping section 26, and then, detects it, and thus, confirms the laser execution position, the ferrite indicator FT being located to a portion on the side or in the vicinity of the de-sensitization treatment means 32 as shown in FIG. 2, for example. After the laser execution position is confirmed, a laser beam is irradiated by the laser de-sensitization treatment means 32, and then, the incore piping section 26 is subjected to a laser de-sensitization treatment. Furthermore, a polishing means PL is incorporated in place of the laser de-sensitization treatment means 32 or together with the laser de-sensitization treatment means 32, the polishing means PL being located to a portion shown in FIG. 1, for example. The polishing means PL is located at an angular position of a predetermined angle, for example, 180.degree. to the laser irradiating section 62 of the laser de-sensitization treatment means 32, so as to freely reciprocate and carry out polishing with respect to a laser executed position. Next, an operation of the incore piping section maintenance system 25 will be described. The incore piping section maintenance system 25 is hung in the reactor pressure vessel 1 from a fuel exchanger (not shown) or the like by an operation of a worker, and then, is hoisted down above the downcomer portion 8 between the reactor pressure vessel 1 and the core shroud 4. In the upper portion of the downcomer portion 8, the incore piping section maintenance system 25 is placed on the shroud head bolt bracket 39 functioning as the support bracket, and then, an inner side of the maintenance system main body 30 is supported. On the other hand, an outer side thereof is pressed against the inner peripheral wall of the reactor pressure vessel by means of the fixed cylinder 40 and is frictionally supported. In this manner, the core pipe maintenance system 25 is stably fixed and supported on the incore piping section 26 which is a maintenance target portion or at the vicinity of the core pipe. The above-mentioned maintenance target portion is a weld zone between a pipe 66 and a header 67 of the core spray pipe 27, and the weld zone is a detection target portion of the incore piping section 26. The support means 31 of the core pipe maintenance system 25 is previously adjusted so as to be movable in an X-Y direction, so that the support means 31 faces the outside of the maintenance target portion in a state that the core pipe maintenance system 25 is fixed. Therefore, in a state that the incore piping section maintenance system 25 is fixed, when the driving motor 46 is driven, the support means 31 supported on the linear guide 45 is inserted into the pipe 66 of the core spray pipe 27 which is a maintenance target portion. When the support means 31 is inserted by a predetermined position in the pipe 66, a pressurized fluid, for example, a compressed air is supplied into the seal member paring with the seal means 56 so as to expand the seal member 57, and thus, watertight sealing is performed. The support means 31 is inserted into the pipe 66 and is sealed by the seal means 56, and thereafter, a coolant between seal members 57 is discharged with the use of a drain pipe of the transmission tube 65. Then, a purge gas in place of the coolant is supplied from a gas supply pipe, and is filled in the seal member, and thus, an atmospheric environment is formed. The coolant between seal members 57 is discharged, and the interior of the seal member is filled with a purge gas so as to be water-tightly separated from the outside, and thereafter, a maintenance work of the laser de-sensitization treatment portions is carried out by remote control. The laser de-sensitization treatment means 32 is rotatably supported on the fixed support means 31 via the bearing 59 and is provided with inspection monitoring camera means, an underwater light, an ultrasonic flaw detector and a ferrite indicator, which function or operate as the weld zone (maintenance target portion) detector in the laser de-sensitization treatment means 32. Thus, a position of the weld zone 27a, which is a maintenance target portion, is confirmed and detected. Thereafter, a laser beam is irradiated to the weld zone 27a within the core spray pipe 27 which is a maintenance target portion, from the laser irradiating section 62 of the laser de-sensitization treatment means 32, and a maintenance work of the incore piping section 26 is performed. The maintenance work by the laser de-sensitization treatment means 32 is performed by irradiating with a laser beam the weld zone 27a of the incore piping section 26 from the laser irradiating section 62. In this case, the laser irradiating section 62 is rotated along the inner periphery of the pipe 66 by a drive of the revolving motor 52, and then, a laser beam is irradiated over the entire periphery of weld zone of the incore piping section 26. The laser beam is irradiated over the entire periphery, and thereby, a surface de-sensitization of the incore piping section 26 is performed, and thus, a laser de-sensitization treatment for replacing a compressive stress of the weld zone 27a with a tensile stress is performed. By the laser de-sensitization treatment, a surface de-sensitization of the incore piping section 26 is performed, and thus, a preventive repair and preventive maintenance of the incore piping section 26 are performed. Therefore, it is possible to improve a normalization (soundness) and reliability of the incore piping section 26. In a preferred example, the laser de-sensitization treatment will be performed by using YAG laser generator generating a continuous laser beam (continuous wave CW) of the type of Nd-YAG laser (wavelength: 1.06 .mu.m) under an atmospheric environment. Next, the following is a description on an incore piping section maintenance system 70 of a second embodiment of the present invention. The incore piping section maintenance system 70 shown in FIG. 3 and FIG. 4 is an system for carrying out a laser de-sensitization treatment with respect to an outer peripheral surface of the incore piping section 26. The incore piping section maintenance system 70 is removably fixed on the incore piping section 26 which is a maintenance target portion or in the vicinity of the incore piping section 26. The incore piping section maintenance system 70 of a reactor is supported above the reactor pressure vessel 1 so as to be freely moved up and down by means of hang cable (not shown) extending from a fuel exchanger or the like. Further, the incore piping section maintenance system 70 of a reactor includes a maintenance system main body 71 which is inserted and supported in the pipe 66 of the core spray pipe 27 which is the incore piping section 26. The maintenance system main body 71 comprises a cylindrical body 72, and in the cylindrical body 72, a plurality of, for example, at least three main body supporting mechanisms 73 are radially housed therein so as to freely come in and out. The main body supporting mechanism 73 is constructed in combination with a link mechanism 74 such as a pantograph and a cylinder apparatus 75. When the cylinder apparatus 75 is activated, an inner guide 76, which is a guide member located at the distal end of the link mechanism 74, is projected outside the cylindrical body 72 so as to abut against an inner peripheral wall of the pipe 66, and thus, is fixed onto the inner peripheral wall of the pipe 66. The maintenance system main body 71 is provided with a revolving means 80 at its cylindrical end portion. In the revolving means 80, a revolving arm 82 is rotatably supported around its boss by means of revolving motor 81. The revolving arm 82 is freely rotatable around a shaft of the maintenance system main body 71 by a drive of the revolving motor 81. A free end portion of the revolving arm 82 is provided with a support means 84 such as a support beam which is slidable and swingable in a direction perpendicular to the arm. The support means 84 is slidably and swingably moved by means of a head driving unit 85, and thus, constitutes an axial direction moving means 86, which is axially movable with respect to the header 67. The support means 84 is provided with a laser desensitization treatment means 88, which is substantially the same as the laser de-sensitization treatment means shown in FIG. 1 and FIG. 2. The laser de-sensitization treatment means 88 irradiates with a laser beam from a laser irradiating section an outer peripheral wall of the core spray pipe 27 which is an incore piping section 26 and carries out a laser de-sensitization treatment with respect to the outer peripheral surface of pipe, and thus, a work for preventive maintenance and preventive repair is performed. A laser beam oscillated from the laser generation device or equipment is guide to the laser de-sensitization treatment means 88 via a flexible optical transmission means 33. The optical transmission means 33 is formed of an optical fiber cable or the like. Further, the optical transmission means 33 is included in the transmission tube 65 together with a cable for power and control signal of drive source. The incore piping section maintenance system 70 of a reactor is supported in its load with the use of an inner surface of the pipe 66 of the incore piping section 26 and is fixed on a maintenance target portion or in the vicinity thereof. More specifically, the maintenance system main body 71 of the incore piping section maintenance system 70 is fixed and supported on the inner peripheral surface of the pipe 66 by means of a plurality of, for example, three or more main body supporting mechanisms 73. The incore piping section maintenance system 70 is stably and securely supported in the pipe 66 by means of these three or more main body supporting mechanisms 73. The incore piping section maintenance system 70 is fixed in the pipe 66 of the incore piping section 26 by opening and closing an inner guide 76 which functions as a guide member of the link mechanism 74. The maintenance system main body 71 is fixed on a predetermined position in the pipe 66 of the incore piping section 26, and it is therefore possible to position and set the laser desensitization treatment means 88 on the outer peripheral surface of the pipe 66. After the incore piping section maintenance system 70 is fixed with the use of the pipe 66, the revolving motor 81 and the head driving unit 85 are operated. When the revolving motor 81 is driven, the laser de-sensitization treatment means 88 turns along an outer periphery of the pipe 66 so as to draw a circular orbit. Moreover, when the head drive unit 85 is operated, the support means 84 is moved in parallel with an axial direction of the pipe 66 and makes a swing motion as occasion demands. Thus, the laser de-sensitization treatment means 88 can effectively carry out a laser de-sensitization treatment with respect to the outer peripheral surface of the pipe 66 by a revolving (turning) motion by the revolving motor 81 and an axial movement by the head driving unit 85. As described above, the laser de-sensitization treatment means 88 carries out a predetermined laser irradiation with respect to the pipe outer peripheral surface of the incore piping section 26 of the reactor pressure vessel 1, and thereby, a surface de-sensitization of the pipe outer surface is performed, thus, making it possible to securely perform a work for preventive repair and preventive maintenance of the pipe outer surface for a short time, whereby the core spray pipe 27 can be normally restored, and it becomes possible to improve normalization and reliability of the incore piping section 26. It is to be noted that the present invention is not limited to the described embodiments and many other changes and modifications may be made without departing from the scopes of the appended claims. For example, the above embodiments of the present invention have made an explanation about the incore piping section maintenance system which is suitable for preventive maintenance and preventive repair of the incore piping section of the reactor pressure vessel. The incore piping section maintenance system may be applicable not only to a boiling water reactor, but also to a pressurized water reactor. Therefore, the incore piping section maintenance system may be applicable to an incore piping section of a reactor pressure vessel of the pressurized water reactor. It is to be noted that the present invention is not limited to the described embodiments and many other changes and modifications may be made without departing from the scopes of the appended claims. |
claims | 1. An apparatus for detecting a position of a control rod, the apparatus comprising:a control rod driving shaft having an outer circumferential surface on which position information is marked;a mirror configured to reflect the position information; anda detector configured to detect a position of the control rod driving shaft from the position information reflected by the mirror, when the control rod driving shaft moves vertically,wherein the mirror is disposed to surround the control rod driving shaft along the outer circumferential surface of the control rod driving shaft and is formed of quartz and has a ring shape,the position information is marked as a number or a bar code in order to determine an absolute position of the control rod driving shaft,the detector comprises:an optical system comprising a lens configured to receive an image of the position information reflected from the mirror;an optical fiber connected to the optical system and configured to transmit the image,the optical fiber comprises an inner fiber surrounded and protected by a high-temperature gel, an inner stainless tube, an aluminum tube, and an outer stainless tube, sequentially. 2. The apparatus of claim 1, wherein the detector comprises:a storage unit configured to store the image transmitted from the optical fiber; anda display unit configured to display the image stored in the storage unit to the outside of a nuclear reactor. 3. The apparatus of claim 1, wherein the mirror has a hollow truncated cone shape with a through-hole through which the control rod driving shaft passes. 4. The apparatus of claim 1, wherein a plurality of grooves for vertically moving the control rod driving shaft are formed in the outer circumferential surface of the control rod driving shaft, and the position information is formed between the grooves. 5. The apparatus of claim 2, further comprising an optical connector configured to transmit the image to the outside of the nuclear reactor. |
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abstract | An unirradiated nuclear fuel assembly transport canister that includes a clamshell type fuel assembly inner liner that has interior dimensions that closely conform to the outer envelope of the fuel assembly to be transported and exterior dimensions that conform to a generic overpack tubular container. The liner is inserted into the overpack tubular container which is in turn supported by a shock absorbing suspension system within a birdcage frame. |
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description | 1. Field of the Invention The present invention relates to an emergency core cooling system (ECCS) of a nuclear power plant particularly of a boiling water reactor (BWR). 2. Related Art The most recently known BWR is an advanced boiling water reactor (ABWR). The ECCS of the ABWR is divided into three sections. The safety of the ABWR of such type has been significantly improved compared with previously known ECCSs each including only two divided sections. The outline of the ECCS of a known ABWR having divided three sections will be described hereunder with reference to FIGS. 6 and 7. FIG. 6 is a schematic view of a front line of the ECCS of a known ABWR divided into three sections including first, second and third safety divisions. As illustrated in FIG. 6, each safety division of the ECCS includes a low-pressure flooding system (LPFL) 1, a residual heat removal system (RHR) 2, a reactor component cooling system (RCW) 3, not shown in FIG. 6, a reactor component sea water cooling system (RSW) 4, not shown in FIG. 6, and an emergency diesel generator (DG) 5. A high-pressure core flooding system (HPCF) 8 is provided for the first and second safety divisions, and a reactor core isolation cooling system (RCIC) 7 is provided for the third safety division. For convenience, the components of the ECCS illustrated in FIG. 6 are referred to as the ‘front line’ of the ECCS. Each of the areas sectioned by a physical separation wall is referred to a ‘safety division’. The safety divisions are designed based on safety so as to isolate one area from another during an incident, such as fire or flooding, that might occur inside a nuclear power plant and threaten the safety of the nuclear power plant. By isolating the safety divisions from each other, even if such an incident occurs in one safety division, the other safety divisions can be kept unaffected. FIG. 7 is a schematic view of a support line of the ECCS of a known ABWR illustrating a mechanism for cooling the heat generated in a nuclear reactor and a primary containment vessel. As illustrated in FIG. 7, each of the three systems includes the RCW 3 and RSW 4, respectively, and the same reference numerals indicate the same components in each of the three systems. Each system includes a RHR heat exchanger (RHR Hx) 12, RCW pumps 14, RSW pumps 15, an emergency heat-ventilating and air-conditioning system (HVAC) and emergency reactor auxiliary components 21, an IA and CRD pumps 22, containment vessel internal components (reactor internal pump (RIP) and drywell cooler (DWC)) 23, normal auxiliary components 24, and an RCW loop (circulation pipes) 25. In each system, the LPFL 1 and the RHR 2 share pumps to send water to the RHR Hx 12 by circulating the water in the reactor or in the suppression pool inside the primary containment vessel to cool the reactor and the primary containment vessel. The heat from the reactor and the primary containment vessel is transmitted to the RHR Hx 12 and is cooled at the RCW 3. Then, the heat transmitted to a RCW heat exchanger (RCW Hx) 13 is cooled by sea water. Since, as mentioned above, the ECCS for cooling the reactor and the primary containment vessel of the ABWR is divided into three sections, the possibilities of accidents due to failure of cooling occurring are significantly reduced compared with other known ABWRs. Hereinafter, for the sake of convenience, the RCW 3 and the RSW 4 are referred to as the ‘support line’ of the ECCS. However, the above-described reactor cooling system of the ABWR requires piping for each loop of the RCW 3 or, in other words, requires three sets of piping. The cost of the piping for each RCW 3 makes up the largest proportion of the entire cost of the ABWR. Thus, the cost of the above-described ABWR is no less than the cost for other previously known reactors. In order to solve the above-mentioned problems or inconveniences, a semi-four-section ECCS has been provided. This semi-four-section ECCS comprises a two-loop reactor cooling system, wherein the front line is divided into four safety divisions, as illustrated in FIG. 8 (for example, refer to Japanese Unexamined Patent Laid-open Publication No. 2000-275380). In this way, cost efficiency, operating rate, and safety are improved in comparison with a full-three-section ECCS for the known ABWR such as mentioned above. The front line of the semi-four-section emergency core cooling system (ECCS) is divided into four sections. However, these four systems provided for the four sections of the front line are more systems than necessary. In addition, four emergency power supplies are required for the four systems. As a result, the ECCS becomes expensive and large in size. Especially, in order to improve the safety of a next-generation BWR plant, a passive containment cooling system (PCCS) independent from the active ECCS is disposed so that the cooling ability and the reliability of the primary containment vessel are maintained even when the ECCS completely loses its functions. In this way, the next-generation BWR plant has achieved extremely advanced multiple-levels of protection. Moreover, recently an innovative reactor containment vessel having both a double containment function and an air cooling function has been introduced. By employing this containment vessel, the safety of the next-generation BWR plant has been enhanced significantly. Even after the water source of the PCCS is exhausted, the containment vessel can be naturally cooled by outside air. The containment vessel is compact and stores active components and heat exchangers in a compartment located in the lower part of the primary containment vessel. However, a known active ECCS comprises a large number of components, which makes it difficult to arrange all the components inside the compact containment vessel. Taking into consideration this problem, an object of the present invention is to satisfy a requirement for improving a design of the ABWR and the semi-four section ECCS and to provide an optimal ECCS for the next-generation BWR plant that is less costly and less space-consuming. The above and other objects can be achieved according to the present invention by providing an emergency core cooling system (ECCS) comprising a first safety division for an active emergency core cooling system, and a second safety division for an active emergency core cooling system, each of the first and second safety divisions including a high-pressure core cooling system and a low-pressure core cooling system, which is commonly used as a residual heat removal system. In a preferred embodiment of the above aspect, the emergency core cooling system may further comprise an emergency diesel generator provided for each of the first and second safety divisions, the emergency diesel generator operating as an emergency power supply equipment for supplying electricity to each of the first and second safety divisions. In a modification, the emergency core cooling system may further comprise an emergency diesel generator provided for the first safety division and an emergency gas turbine generator provided for the second safety division, the emergency diesel generator and emergency gas turbine generator operating as emergency power supply equipments for supplying electricity to the first and second safety divisions, respectively. In another modification, the emergency core cooling system may further comprise an emergency gas turbine generator provided for each of the first and second safety divisions, the emergency gas turbine generator operating as an emergency power supply equipment for supplying electricity to each of the first and second safety divisions. The emergency core cooling system may further comprise a third safety division including a passive cooling system. The passive cooling system may include a passive containment vessel cooling system and an isolation condenser. According to the present invention of the structures and characters mentioned above, a simple but highly reliable optimal hybrid safety system including a static safety system and an active ECCS may be provided for a next-generation nuclear reactor, preferably of BWR. More specifically, the numbers of active ECCSs and RHR heat exchangers can be significantly reduced with minimal effect on the design of the BWR. According to the present invention, an active ECCS may be disposed inside a containment vessel of a next-generation BWR having a reduced-size double containment vessel. The nature and further characteristic features may be made more clear from the following descriptions made with reference to the accompanying drawings. Preferred embodiments of the present invention will be described hereunder with reference to FIGS. 1 to 5, in which the same components as those illustrated in FIGS. 6 and 7 are indicated by the same reference numerals, and descriptions for components that have already been described with reference to FIGS. 6 and 7 are omitted herein. An active emergency core cooling system (ECCS) according to a first embodiment of the present invention will be first described with reference to FIGS. 1 and 2. FIG. 1 is a schematic view of the structure of the high-pressure core cooling systems, the low-pressure core cooling systems, the residual heat removal systems, and the emergency power supplies. FIG. 2 is schematic view illustrating the safety performance of the ECCS according to this embodiment. That is, as illustrated in FIG. 1, the active ECCS according to the first embodiment includes two (first and second) safety divisions. Each safety division includes a high-pressure core cooling system and a low-pressure core cooling system operated cooperatively with a residual heat removal system. The first and second safety divisions each include a high-pressure core flooding system (HPCF) 8 as a high-pressure core cooling system and a low-pressure flooding system (LPFL) 1 and a residual heat removal system (RHR) 2 as a low-pressure core cooling system. Furthermore, as an emergency power supply for each safety division, an emergency diesel generator (DG) 5 is provided. Instead of the DG 5, an emergency gas turbine generator (GTG) may be used. When using a GTG, since a GTG does not include a cooling water system, reliability of the emergency power supply may increase. The emergency power supply provided for each of the safety divisions may be a 100%-capacity power supply or, instead, may be two 50%-capacity power supplies. In other words, two small-sized emergency power supplies may be provided instead of one large-sized emergency power supply. It is hence to be noted that the HPCF 8 is an example of a high-pressure ECCS, and any other type of high-pressure ECCS may be used, and similarly, that the LPFL 1 is an example of a low-pressure ECCS, and any other type of low-pressure ECCS may be used. The difference between the first embodiment and a known ECCS is that the active ECCS according to the first embodiment includes only two safety divisions. In this way, only two sets of the LPFL 1 and the RHR 2 and two emergency power supplies are required. Furthermore, a reactor core isolation cooling system (RCIC) included in a known ECCS is omitted in the active ECCS according to the first embodiment. Accordingly, the active ECCS according to the first embodiment is more cost efficient and takes up less space compared with an active ECCS of the known ABWR such as shown in FIGS. 6 and 7. According to this embodiment, the total number of pumps is reduced to four, and the total number of heat exchangers for the residual heat removal system is reduced to two. A plant type emergency core cooling system known as a ‘BWR/4’ also has only two safety divisions. However, the large-diameter pipes of the external recirculation piping of the BWR/4 are subjected to a design-basis accident. Thus, the BWR/4 does not satisfy safety standards if it employs the system structure according to this embodiment. Therefore, to satisfy safety standards, the BWR/4 will must include a total of eight to ten pumps. According to this embodiment, the safety standards are satisfied by combining the ECCS with a BWR plant not including external recirculation piping (i.e., an ABWR plant or any post-ABWR plant). The ABWR uses internal recirculation piping and does not include external recirculation piping. Therefore, the possibility of a pipe rupture accident occurring in the large-diameter pipes of the external recirculation piping can be eliminated. Accordingly, the reactor core will not be exposed even in a loss-of-coolant accident. In this way, an ABWR having an extremely high safety level is provided. According to this embodiment, in the event of a design-basis accident, the reactor core is cooled only by the LPFL 1. Inherent safety is added to the ABWR by increasing the amount of water held inside the ABWR by increasing the length of the reactor pressure vessel by about two meters. In this way, the flooding of the reactor core can be maintained merely by the LPFL 1. FIG. 2 is a graph illustrating the analytical results of the change in water level inside the reactor during a design-basis loss-of-coolant accident. In FIG. 2, the vertical axis represents the water level inside a core shroud during a design-basis loss-of-coolant accident, and the horizontal axis represents time (seconds). As illustrated in FIG. 2, in the event of a loss-of-coolant accident, the water level of the reactor quickly becomes higher than the top of the effective fuel capacity of the reactor core. Accordingly, the core flooding is reliably ensured and maintained. A second embodiment of an ECCS according to the present invention will be described hereunder with reference to FIG. 3. Each of the safety divisions in an emergency core cooling system (ECCS) according to this embodiment includes an emergency gas turbine generator as an emergency power supply equipment for supplying electricity to the safety divisions. FIG. 3 illustrates the structure of a high-pressure core cooling systems, low-pressure core cooling systems, residual heat removal systems, and the emergency power supplies. As illustrated in FIG. 3, similar to the first embodiment, first and second safety divisions each include a low-pressure flooding system (LPFL) 1 and a residual heat removal system (RHR) 2 as a low-pressure core cooling system and a high-pressure core flooding system (HPCF) 8 as a high-pressure core cooling system. According to this embodiment, an emergency diesel generator (DG) 5 is disposed in the first safety division as the emergency power supply, and on the other hand, in the second safety division, a gas turbine generator (GTG) 6 is disposed as the emergency power supply. Structures of the ECCS, other than the above, according to this second embodiment are the same as the structures of the first embodiment. According to the second embodiment, the reliability of the ECCS can be enhanced by using various types of emergency power supply equipments. As a modification or alternation of this embodiment, a GTG may be provided in each safety division as an emergency power supply equipment for supplying electricity. By using the GTG for each safety division, the same advantages as those of the ECCS according to the first embodiment will be obtainable. Next, an ECCS third embodiment of the present invention will be described with reference to FIG. 4. According to this third embodiment, a passive cooling system is provided in a third safety division. The passive cooling system disposed inside the third safety division includes a passive containment cooling system and an isolation condenser. FIG. 4 illustrates a high-pressure core cooling system, a low-pressure core cooling system, a residual heat removal system, an emergency power supply equipment, and a passive cooling system provided for each safety division. That is, in this third embodiment, the third safety division includes an isolation condenser (IC) 16 and a passive containment cooling system (PCCS) 17 as a passive cooling system. As mentioned above, since the ECCS according to this third embodiment includes the IC 16, the ABWR plant can be maintained safely for a long time (e.g., about three days) even during a station black out, which is an incident having a significantly low incident rate in which both emergency power supplies for the first and second safety divisions and the external power supply fail simultaneously. The ECCS according to this embodiment has only two sets of residual heat removal systems (RHR) 2 and, thus, has a less reliable containment vessel cooling system compared with the known ABWR having three sets of RHRs 2. However, by providing the PCCS 17, the reliability of the ECCS according to this embodiment can be enhanced. FIG. 5 illustrates the structure of a reactor component cooling system (RCW) 3 and a reactor component sea water cooling system (RSW) 4 according to a fourth embodiment of the present invention. FIG. 5 illustrates two systems each including: an RHR heat exchanger 12; an RCW heat exchanger 13; RCW pumps 14; RSW pumps 15; an emergency heat-ventilating and air-conditioning system (HVAC) and emergency reactor auxiliary components 21; an IA and CRD pumps 22; containment vessel internal components (reactor internal pump (RIP) and drywell cooler (DWC)) 23; normal auxiliary components 24; and an RCW loop (circulation pipes) 25. According to the fourth embodiment, the piping arrangement of the RCW 3 constitutes two loops, each including two RCW pumps 14. Further, two loops of piping for the RSW 4 are provided for each loop of piping for the RCW 3, and in other words, a total of four loops of piping for the RSW 4 are provided. One of the RSW pumps 15 is disposed in each loop of piping for the RSW 4. An increased number of the RCW pumps 14 and the RSW pumps 15 may be arranged in each loop of piping for the RCW 3 and the RSW 4, respectively, as occasion demands. The piping of an RCW of a known ABWR comprises three loops, and each RCW pump for each RCW loop has a 50%-capacity (i.e., the entire system has an RCW pump capacity of 3×50%). In comparison, each of the RSW pumps 15 for each loop of piping for the RCW 3 according to this embodiment has a 100%-capacity (i.e., the entire system has an RCW pump capacity of 2×100%). In other words, according to the present invention, the RCW pump capacity of each loop has been increased from 50% to 100%. According to this embodiment, two RCW pumps 15 are disposed in each loop of piping for the RCW 3, so that the entire system has an RCW pump capacity of 4×50%, wherein the capacity of each of the RCW pumps 15 is 50%. On the other hand, in a known ABWR, the entire system has an RCW pump capacity of 6×25%, wherein the capacity of each RCW pump is 25%. Thus, all the active components of the ABWR according to this embodiment operate in accordance with the system structure based on a pump capacity of 4×50%. The required pump capacity of the ABWR according to this fourth embodiment of the structure described above is a 100%-capacity. In addition to satisfying this requirement, the ABWR has a safety allowance of 2×50%. Accordingly, the ABWR of this embodiment is capable of maintaining the excellent safety even in an event of an accident in which multiple failures of the active components of the ECCS occur or in which a single failure occurs while the systems are out of service. The results of a probabilistic safety assessment (PSA) for the ECCS of the ABWR according to this embodiment in operation can be significantly improved in comparison with the results of the ECCS of the known ABWR. Furthermore, the RCW 3 and the RSW 4 of the ECCS according to this embodiment are allowed to be out of service for maintenance while the ABWR plant is in operation. In other words, it becomes unnecessary to shutdown the plant to carry out the maintenance of the RCW 3 and the RSW 4. Accordingly, the entire cooling system of the nuclear reactor can be put to a stand-by state while the ABWR plant is shutdown. Thus, the result of the PSA, while the ABWR plant is shutdown, can be significantly improved. As described above, the reliability and safety of the entire system of the ECCS according to this embodiment can be significantly enhanced in comparison with the known ABWR by doubling the capacity per active component, such as a pump, in comparison with the capacity per active component of the known ABWR. As described above, although the capacity per active component of the ECCS is increased, the number of loops of piping for the RCW 3 can be reduced to two loops instead of three loops as in the known ABWR. In this way, cost for production can be significantly reduced and cost efficiency of the ABWR plant can be hence increased. Such cost reduction can be achieved because the pipes for the RCW 3 of the ECCS are extremely high quality and have an aseismatic design, and the production cost of these pipes makes up a large percentage of the production cost for the entire ABWR plant. Furthermore, according to this embodiment, on-line maintenance can be performed on the RSW 4 as a periodic maintenance program. Moreover, the time required for the periodic maintenance program can be shortened. For a periodic maintenance program of a known ABWR, the plant needs to be shutdown for about 45 days. For the ABWR according to this embodiment, it is possible to complete the periodic maintenance program in less than 30 days. In addition, both the safety and cost efficiency of the ABWR plant can be significantly enhanced. Still furthermore, in this embodiment, although the two RCW pumps 14 are provided for each loop of RCW 3, the number of RCW pumps 14 may be increased to four, six, eight, . . . , so as to enhance the reliability of the RCW system. Similarly, the number of loops of piping for the RSW 4 and the number of RSW pumps 15 may be also increased so as to enhance the reliability of the RSW system. It is to be noted that the present invention is not limited to the described embodiments and many other changes and modifications may be made without departing from the scopes of the appended claims. |
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claims | 1. A lithographic apparatus, comprising:a radiation source including a plurality of selectively addressable pn-junction elements, the radiation source generating patterned radiation through selective addressing of the plurality of selectively addressable pn-junction elements; anda projection system that projects the patterned radiation generated by the radiation source onto a target portion of a substrate. 2. The lithographic apparatus of claim 1, wherein each of the pn-junction elements is doped with impurities to increase emission of radiation at a desired frequency. 3. The lithographic apparatus of claim 1, wherein each of the pn-junction elements is covered by a layer of transparent oxide. 4. The lithographic apparatus of claim 1, further comprising:a voltage source that provides a potential difference of at least about 4V to reverse bias selectively addressed ones of the pn-junction elements. 5. The lithographic apparatus of claim 1, further comprising:a voltage source that provides a potential difference of about 5V to reverse bias selectively addresses ones of the pn-junction elements. 6. The lithographic apparatus of claim 1, further comprising:a filter that selects a desired range of wavelengths from the radiation emitted by selectively addresses ones of the pn-junction elements. 7. A lithographic method used to manufacture a device, comprising:selectively addressing an array of pn-junction elements to form a patterned beam of radiation; andprojecting the patterned beam of radiation onto a target portion of a substrate. 8. The method of claim 7, further comprising:doping the pn-junction elements with impurities to increase emission of radiation at a desired frequency. 9. The method of claim 7, further comprising:covering the pn-junction elements with layer of transparent oxide. 10. The method of claim 7, further comprising:providing a potential difference of at least about 4V to reverse bias the selectively addresses ones of the pn-junction elements. 11. The method of claim 7, further comprising:providing a potential difference of about 5V to reverse bias the selectively addresses ones of the pn-junction elements. 12. The method of claim 7, further comprising:filtering a desired range of wavelengths from the radiation emitted by the selectively addressed pn-junction elements. |
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042119286 | claims | 1. In radiographic apparatus for manipulating a quantity of radioactive material between a stored position and a use position including a capsule of said radioactive material, a storage unit with means defining a passage through it, for storing the capsule in the passage and shielding the surrounding environment from the stored radioactive material, and manipulating means connectible to said storage unit at a first end of said passage for moving said capsule between a stored position within the passage and a use position outside the second end of said passage, the improvement comprising: a shutter mounted on said storage unit for sliding movement transverse to the second end of said passage between first and second limits, said shutter in said first limit blocking said second end, said shutter having a hole through it which registers with said passage when the shutter is in said second limit, shutter-retaining means associated with said passage means adjacent said second end and resilient means cooperating with said retaining means and said storage unit for urging said retaining means to project an end-part toward said shutter, means in said shutter for receiving said end-part when said shutter is in said second limit and thereby retaining said hole in register with said passage, and means coupled to said capsule for pulling said retaining means away from said shutter against the action of said resilient means under control of said manipulating means for withdrawing said end-part from said receiving means and thereby permitting said shutter to move toward said first limit. 2. Apparatus according to claim 1 including operator means to move said shutter from said first limit to said second limit, said operator means including a tell-tale to indicate visually that said shutter is in one or the other of said limits. 3. Apparatus according to claim 1 wherein said hole is sized to permit said capsule to pass to a use position outside of said storage unit. 4. Apparatus according to claim 1 wherein said shutter retaining means is a tubular member fitted telescopically within said passage means, said resilient means cooperates with said tubular member and said passage means to project an end-part of said tubular member toward said shutter, and said receiving means is an annular recess surrounding said hole, said tubular member having an internal diameter substantially the same as the diameter of said hole. 5. Apparatus according to claim 4 wherein said tubular member has an external flange at said end-part and an internal flange at its other end, said resilient means comprises a coil spring surrounding said tubular member and exerting force on said external flange, and a plug within said tubular member is coupled to said capsule for cooperating with said internal flange for withdrawing said end-part from said annular recess. 6. Apparatus according to claim 1 including resilient means for urging said shutter toward said first limit. 7. Apparatus according to claim 1 including latch means for retaining said shutter in said first limit, and means to release said latch means to free said shutter to be moved toward said second limit. 8. Apparatus according to claim 7 wherein said release means comprises an element extending forward of said storage unit from said second end of said passage. 9. Apparatus according to claim 1 including a nipple fitted to said storage unit at said second end of said passage, for receiving a coupling element of guide tube means for said capsule, latch means for retaining said shutter in said first limit, and means operable by said coupling element upon attachment to said nipple to release said latch means to free said shutter to be moved to said second limit. 10. Apparatus according to claim 9 wherein said release means comprises an element extending forward of said storage unit from said second end of said passage into a position adjacent said nipple, for interaction with said coupling element. |
039490270 | description | FIG. 1 shows the compaction chamber 1 of an hydraulic press; the punches 2 and 3, which move in the direction shown by the arrows; and the UO.sub.2 pellet 4. FIG. 2 shows the pellet 4 after sintering, and the deformation of its lateral wall 5, which is incurved inwards. This pellet must be brought down to the prescribed dimensions by grinding it along the dotted lines 6 before it can be used. FIG. 3 represents the compaction chamber 11 of a mechanical press; the upper punch 12, mobile during the compression phase, shifts in the direction shown by the arrow; the lower punch 13, fixed during the compression; as well as the UO.sub.2 pellet 14. FIG. 4 shows the pellet 14 after sintering and its cone trunk form. Before using this pellet it will equally be necessary to bring it down to the prescribed dimensions by grinding it along the dotted lines 16. FIG. 5 represents the compression of a UO.sub.2 pellet according to the invention. It shows the compaction chamber 21, the upper punch 22, fixed during the compaction cycle, and the lower mobile punch 23 shifting in the direction of the arrow during the compaction phase. The compressed pellet is represented by reference number 24. As shown on FIG. 5, the upper part 28 of the walls of the compaction chamber 21 is slightly widened, so that the section near the upper punch 22 has a slightly larger surface than the section near the lower punch 23; the lower part 27 of the walls is cylindrical. The angle .alpha., as defined above, is equally shown on the figure. After compaction, the tablet 24 thus has slightly flared lateral walls. Since, owing to the particular friction conditions on compression, the green density of the part 30 of the pellet 24, situated near the upper punch 22 on compression, is smaller than the green density of the part 31 of the pellet, situated near the punch 23 on compression, the part 30 will shrink more than the part 31 of the pellet when sintered. Thus, after sintering, the pellet will have a substantially cylindrical form and does not need rectification. The angle .alpha., formed by the vertical axis of the mould and the intersection line between an axial plan and the inclined wall, will be determined for each fabrication batch separately, as a function of the interfering parameters, i.e. the nature of the powder, the diameter of the pellet, the compression density, the friction between the powder and the die wall, the internal friction between the grains, the state of the equipment surfaces, the kind of apparatus, the lubrification means etc. The invention will be hereinafter more fully described with the help of two different examples of pelletizing. EXAMPLE 1 Ceramic sinterable uranium oxide powder is compressed in an hydraulic press comprising a tungsten carbide-tipped die. The characteristics of the powder are the following: oxygen content : O/U = 2.08 PA1 apparent density : 2.1 PA1 average diameter of the grains : 1.6 .mu.m PA1 specific surface : 4 m.sup.2 /g. PA1 oxygen content : 2.07 PA1 apparent density : 2.1 PA1 average diameter of the grains : 0.6 .mu.m PA1 specific surface : 3 m.sup.2 /g Before the compression cycle, the equipment will be lubrified by means of a preliminary compression cycle with polystyrene balls containing 3 % zinc stearate. The diameter of the die is 12 mm and the conicity of the walls is defined by an angle .alpha. = 26'10", corresponding to a radius increase of 75 microns per cm height. After 10 seconds compression, the compressed UO.sub.2 pellet has a green density of 5.63 and a height of 11.9 mm. The pellet is then sintered for an hour, at 1650.degree.C in an argon atmosphere containing 5 % hydrogen. The density then reaches 10.47 or 95.5 % of the theoretical density. The height of the sintered pellet is 9.62 mm, and its diameter 9.83 mm. The shape of the pellet is then inspected with an apparatus having an accuracy of 2 microns. The difference in diameter found on the pellet is 12 microns. EXAMPLE 2 Uranium oxide powder is compressed in a rotative press with steel equipment, lubrified by means of a preliminary lubrification cycle with polystyrene balls containing 2 % zinc behenate. The characteristics of the powder are the following: The diameter of the mould is 15 mm and the conicity of the walls is defined by an angle .alpha. = 20'43", corresponding to a radius increase of 60 microns per cm height. The pellet, compressed to a density of 5.4, is sintered for 4 hours at 1650.degree.C in an argon atmosphere containing 5 % hydrogen. The obtained pellet then has a density of 10.36 or 94.5 % of the theoretical density. The diameter divergences of this pellet lie below 15 microns. After the same manufacturing cycle with classical double compression (as shown in FIG. 1) the obtained pellets have a "diabolo" form with diameter divergences of 70 microns. These examples clearly show the efficiency of the method according to the invention. The method according to the invention allows manufacture of pellets with diameter divergences lying within the prescribed diametrical tolerances. Thus, rectification of the pellets may be avoided and the fabrication cycle notably shortened. Avoiding rectification is particularly advantageous because no rectification scraps are formed and the recovery of said scraps is thus superfluous. Of course, this absence of rectification wastes is still more advantageous when the fuel pellets contain fissile material which should be very carefully handled. It is evident that the examples described above are not at all limitative and that the man skilled in the art will find numerous modifications or improvements without leaving the field of the invention. Compaction chambers with slightly inclined walls have already been proposed for facilitating the ejection of tablets. The very slight inclination proposed to this end could be defined by an angle of hardly 0.degree.3' and does not allow the advantages of the compression according to the invention to be obtained. This conicity, moreover, reduced the regularity form of the tablets, since the presses used had either two mobile punches or an upper mobile punch; the use of a lower mobile punch was as yet exceptional. |
abstract | An error detection device includes a control unit configured to identify two links that connects a relay communication device to two communication devices as a link pair, identify, from pluralities of inspection devices under the respective two links, a number of inspection devices corresponding to the number N of links where communication errors simultaneously occur (N is an integer of 1 or more) plus 1, determine (N+1) number of inspection flows between the (N+1) number of inspection device pairs, and generate inspection coverage information that includes the determined inspection flows. The error detection device includes a storage unit that stores the inspection coverage information, and a communication unit that sends the inspection coverage information to one device of the inspection device pairs. |
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041467965 | abstract | An apparatus for determining the depth of a radiation source within a body of material utilizing a radiation source holder moving the radiation source within the body. A plurality of switches have contacts that are fixed in relation to the movement of the radiation source within the material. Trigger means activates a particular switch at a preselected depth of the radiation source. Means for indicating the activation of a switch would thus produce a signal as a representative of the depth of the radiation source. |
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claims | 1. An in-situ repair method to seal a hollow, elongate member which extends into a reactor pressure vessel of a boiling water reactor and penetrates through a bottom head dome opening of a bottom head dome forming a lower end of the reactor pressure vessel, the reactor pressure vessel including a stub tube having a first end, a second end and a stub tube bore extending between the first and second ends that is aligned with the bottom head dome opening, the elongate member extending upward from the bottom head dome through the bottom head dome opening and through the stub tube bore, the elongate member secured to the stub tube adjacent the first, end with an upper stub tube attachment weld, the method comprising:cutting the elongate member at a given location below the second end of the stub tube to remove a section of the elongate member so as to form an upper portion which extends upward into the stub tube bore and reactor pressure vessel interior of the boiling water reactor, and a lower portion which extends downward through the bottom head dome opening to an undervessel area beneath the reactor pressure vessel, wherein an opening is provided at the given location between the upper and lower portions where the section was removed, andapplying a weld to attach the lower portion to the reactor pressure vessel so as to seal off potential leakage paths of reactor coolant between the upper portion and lower portion and through the bottom head dome sidewall to the undervessel area. 2. The method of claim 1, wherein attaching includes attaching the lower portion to a different location than the location where the elongate member was cut. 3. The method of claim 1, whereinthe lower portion includes an upper end, andapplying further includes:forming the weld on an interior surface of the reactor pressure vessel at the upper end, application of the weld forming a heat affected zone. 4. The method of claim 3, further comprising:applying a corrosion resistant material so as to substantially cover the heat affected zone. 5. The method of claim 4, wherein applying a corrosion resistant material further includes applying a corrosion resistant cladding alloyed with a noble metal so as to substantially cover the heat-affected zone. 6. The method of claim 4, wherein the applied corrosion resistant material is at a thickness in a range of at least about 0.3 to 0.6 mm. 7. The method of claim 6, wherein the applied corrosion resistant material is at a thickness in a range of 0.36 to 0.45 mm. 8. A control rod drive housing in a reactor pressure vessel of a nuclear reactor sealed in accordance with the method of claim 1. 9. A method for sealing an elongate hollow member in-situ within a reactor pressure vessel of a boiling water reactor, the reactor pressure vessel including a bottom head dome forming a lower end of the reactor pressure vessel, a stub tube, and the elongate hollow member, the bottom head dome having a bottom head dome opening, the stub tube having first and second ends with a bore there between that is aligned with the bottom head dome opening, the elongate member extending upward from an undervessel area through the bottom head dome opening and aligned stub tube bore, the elongate member secured to the stub tube adjacent the stub tube first end with an upper stub tube attachment weld, the method comprising:cutting out a section of the elongate member at a location below the upper stub tube weld to separate the elongate member into an upper portion which extends upward into the stub tube bore and reactor pressure vessel interior of the boiling water reactor, and a lower portion which extends downward through the bottom head dome opening to the undervessel area beneath the reactor pressure vessel;attaching the lower portion to a different location at the bottom head dome opening than where the elongate member was cut with a weld that is formed on an interior surface of the bottom head dome opening at an upper end of the lower portion, application of the weld forming a heat affected zone; andapplying a corrosion resistant material on the heat-affected zone. 10. The method of claim 9, wherein applying further includes applying a corrosion resistant cladding alloyed with a noble metal so as to substantially cover the heat-affected zone. 11. The method of claim 9, wherein the applied corrosion resistant material is at a thickness in a range of at least about 0.3 to 0.6 mm. 12. The method of claim 11, wherein the applied corrosion resistant material is at a thickness in a range of 0.36 to 0.45 mm. 13. A control rod drive housing in a reactor pressure vessel of a nuclear reactor sealed in accordance with the method of claim 9. |
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description | The following relates to the nuclear reactor arts, electrical power generation arts, nuclear safety arts, and related arts. Nuclear reactors employ a reactor core comprising a mass of fissile material, such as a material containing uranium oxide (UO2) that is enriched in the fissile 235U isotope. Primary coolant water, such as light water (H2O) or heavy water (D2O) or some mixture thereof, flows through the reactor core to extract heat for use in heating secondary coolant water to generate steam or for some other useful purpose. For electrical power generation, the steam is used to drive a generator turbine. In thermal nuclear reactors, the primary coolant water also serves as a neutron moderator that thermalizes neutrons, which enhances reactivity of the fissile material. Various reactivity control mechanisms, such as mechanically operated control rods, chemical treatment of the primary coolant with a soluble neutron poison, or so forth are employed to regulate the reactivity and resultant heat generation. In a pressurized water reactor (PWR), the primary coolant water is maintained in a superheated state in a sealed pressure vessel that also contains the reactor core. In the PWR, both pressure and temperature of the primary coolant water are controlled. To extract power from the PWR or other nuclear reactor, secondary coolant water is flowed in thermal communication with the primary coolant water. A steam generator device is suitably used for this thermal exchange. In the steam generator, heat (i.e., energy) is transferred from the reactor core to the secondary coolant water via the intermediary of the primary coolant water. This heat converts the secondary coolant water from liquid water to steam. The steam is typically flowed into a turbine or other power conversion apparatus that makes practical use of the steam power. Viewed another way, the steam generator also serves as a heat sink for the primary coolant. The steam generator may, in general, be located external to the pressure vessel, or internal to the pressure vessel. A PWR with an internal steam generator is sometimes referred to as an integral PWR, an illustrative example of which is shown in Thome et al., “Integral Helical Coil Pressurized Water Nuclear Reactor”, U.S. Pub. No. 2010/0316181 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. This publication discloses a steam generator employing helical steam generator tubing; however, other coil geometries including straight (e.g., vertical) steam generator tubes are also known. This publication also discloses an integral PWR in which the control rod drive mechanism (CRDM) is also internal to the pressure vessel; however, external CRDM designs are also known. Some illustrative examples of internal CRDM designs include: Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2010/0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety; and Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, Intl Pub. WO 2010/144563 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. During normal PWR operation, the primary coolant is subcooled and is at both elevated temperature and elevated pressure. For example, one contemplated integral PWR is designed to operate with the primary coolant at a temperature of greater than 300° C. and a pressure of about 2000 psia. These elevated conditions are maintained by emitted by the radioactive nuclear reactor core. In various abnormal event scenarios, this radioactivity can increase rapidly, potentially leading in turn to rapid and uncontrolled increase in primary coolant pressure and temperature. For example, in a “loss of heat sink event” the secondary coolant flow in the steam generator fails, leading to loss of heat sinking provided by the secondary coolant. In a scram failure, the control rod system is compromised such that the control rods may be unable to “scram”, that is, be released to fall into the reactor core, to provide rapid shutdown. While a scram failure may not cause immediate core heating, the loss of this safety system typically calls for immediate shutdown of the reactor. In a loss of coolant accident (LOCA), a rupture in the pressure vessel allows some of the primary coolant to be released under pressure from the pressure vessel. The released primary coolant generally expands as steam outside of the pressure vessel. A LOCA introduces numerous potential safety issues such as a possible release of radioactivity, emission of hot steam, and so forth. The loss of coolant as the reactor depressurizes can result in a condition where there is insufficient coolant left in the reactor vessel to cool the core. The resulting fuel damage releases fission products contained with the fuel. In view of such concerns, a PWR typically has an external containment structure to contain any release of primary coolant in a LOCA. The PWR also typically has an associated emergency core cooling system (ECCS) that is designed to respond to an abnormal condition by bringing about rapid cooling of the reactor core, suppressing any concomitant pressure increase, and recapturing any released primary coolant steam. The ECCS should operate in a failsafe manner. However, designing the ECCS to provide failsafe operation for a range of potential abnormal conditions such as loss of heat sinking, scram failure, or LOCA is difficult. Disclosed herein are improvements that provide various benefits that will become apparent to the skilled artisan upon reading the following. in one aspect of the disclosure, an apparatus comprises a pressurized water reactor (PWR) including a pressure vessel containing a nuclear reactor core and primary coolant water. The pressure vessel defines an internal pressurizer volume containing a steam bubble and having at least one steam pressure containment structure surrounds the PWR. An external heat sink is disposed outside of the containment structure. A condenser is disposed inside the containment structure and is operatively connected with the external heat sink. A valve assembly comprising one or more valves operatively connects the PWR with the condenser responsive to an abnormal operation signal such that the condenser condenses steam from the steam bubble while rejecting heat to the external heat sink and returns the condensed water to the PWR. In another aspect of the disclosure, a method comprises: operating a PWR disposed in a containment structure, the PWR including a pressure vessel containing a nuclear reactor core and primary coolant water and an internal pressure regulating steam bubble; and, responsive to an abnormal operation signal, performing an emergency core cooling process including operatively connecting a condenser disposed in the containment structure with the PWR to condense steam from the steam bubble while rejecting heat to an external heat sink disposed outside of the containment structure and to return the condensed water to the PWR. In some such methods, an inlet of the condenser is connected with the steam bubble during the operating, and the operative connecting responsive to an abnormal operation signal comprises connecting an outlet of the condenser with the PWR to return the condensed water to the PWR. In some such methods, after the operative connecting and responsive to pressure in the pressure vessel decreasing below a pressure threshold, the outlet of the condenser is connected with a sparger discharging into a water storage tank disposed inside the containment structure. In another aspect of the disclosure, a method comprises: operating a PWR disposed in a containment structure, the PWR including a pressure vessel containing a nuclear reactor core and primary coolant water and an internal pressure regulating steam bubble; and performing an emergency core cooling process including operatively connecting a quench tank containing water with dissolved neutron poison with the PWR such that the steam bubble pressurizes the quench tank to discharge water with dissolved neutron poison into the PWR. In some such methods, the dissolved neutron poison comprises a soluble boron compound. In some such methods, the operating comprises operating the PWR including said pressure vessel containing said nuclear reactor core and said primary coolant water wherein the primary coolant water does not contain a dissolved neutron poison. In another aspect of the disclosure, an apparatus comprises: a PWR including a pressure vessel containing a nuclear reactor core, primary coolant water, and a pressure regulating steam bubble; a quench tank containing water with dissolved neutron poison; a valved tank pressurizing path selectively connecting the steam bubble to the quench tank to pressurize the quench tank; and a valved soluble poison delivery path selectively connecting the quench tank to the PWR such that the quench tank under pressure from the steam bubble discharges water with dissolved neutron poison into the PWR. In another aspect of the disclosure, an apparatus comprises: a PWR including a pressure vessel containing a nuclear reactor core and primary coolant water, the pressure vessel defining an internal pressurizer volume containing a steam bubble and having at least one steam pressure control device; a containment structure surrounding the PWR; an external heat sink disposed outside of the containment structure; at least one condenser disposed inside the containment structure and operatively connected with the external heat sink; and a valve assembly comprising one or more valves, the valve assembly configured to (1) respond to a loss of heat sink event by operatively connecting the at least one condenser with the PWR to condense steam from the steam bubble and return the condensed water to the PWR and to (2) response to a loss of coolant accident (LOCA) by operatively connecting the at least one condenser with the PWR to condense steam from the steam bubble and return the condensed water to the PWR. With reference to FIG. 1, an illustrative nuclear reactor of the pressurized water reactor (PWR) type 10 includes a pressure vessel 12, which in the illustrative embodiment is a generally cylindrical vertically mounted vessel. Selected components of the PWR that are internal to the pressure vessel 12 are shown diagrammatically in phantom (that is, by dotted lines). A nuclear reactor core 14 is disposed in a lower portion of the pressure vessel 12. The reactor core 14 includes a mass of fissile material, such as a material containing uranium oxide (UO2) that is enriched in the fissile 235U isotope, in a suitable matrix material. In a typical configuration, the fissile material is arranged as “fuel rods” arranged in a core basket. The pressure vessel 12 contains primary coolant water (typically light water, that is, H2O, although heavy water, that is, D2O, is also contemplated) in a subcooled state. A control rod system 16 is mounted above the reactor core 14 and includes control rod drive mechanism (CRDM) units and control rod guide structures configured to precisely and controllably insert or withdraw control rods into or out of the reactor core 14. The illustrative control rod system 16 employs internal CRDM units that are disposed inside the pressure vessel 12. Some illustrative examples of suitable internal CRDM designs include: Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2010/0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety; and Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, Int'l Pub. WO2010/144563A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. In general, the control rods contain neutron absorbing material, and reactivity is increased by withdrawing the control rods or decreased by inserting the control rods. So-called “gray” control rods are continuously adjustable to provide incremental adjustments of the reactivity. So-called “shutdown” control rods are designed to be inserted as quickly as feasible into the reactor core to shut down the nuclear reaction in the event of an emergency. Various hybrid control rod designs are also known. For example, a gray rod may include a mechanism for releasing the control rod in an emergency so that it falls into the reactor core 12 thus implementing a shutdown rod functionality. The illustrative PWR 10 is an integral PWR, and includes an internal steam generator 18 disposed inside the pressure vessel 12. In the illustrative configuration, a cylindrical riser 20 is disposed coaxially inside the cylindrical pressure vessel 12. The riser 20 surrounds the control rods system 16 and extends upward, such that primary coolant water heated by the operating nuclear reactor core 14 rises upward through the cylindrical riser 20 toward the top of the pressure vessel, where it discharges, reverses flow direction and flows downward through an outer annulus defined between the cylindrical riser 20 and the cylindrical wall of the pressure vessel 12. This circulation may be natural circulation that is driven by reactor core heating and subsequent cooling of the primary coolant, or the circulation may be assisted or driven by primary coolant pumps (not shown). The illustrative steam generator 18 is an annular steam generator disposed in the outer annulus defined between the cylindrical riser 20 and the cylindrical wall of the pressure vessel 12. Vertically, the lower end of the illustrative steam generator 18 partially overlaps the control rod system 16, and the steam generator 18 extends upward to near the top of the cylindrical riser 20. The steam generator provides independent but proximate flow paths for downwardly flowing primary coolant and upwardly flowing secondary coolant. The secondary coolant enters at a feedwater inlet 22, flows upward through the steam generator 18 where it is heated by the proximate downwardly flowing primary coolant to be converted to steam, and the steam discharges at a steam outlet 24. FIG. 1 does not illustrate the detailed structure of the steam generator. Typically, the steam generator comprises steam generator tubes and a surrounding volume (or “shell”) containing the tubes, thus providing two proximate flow paths that are in fluid isolation from each other. In some embodiments, the primary coolant flows downward through the steam generator tubes (that is, “tube-side”) while the secondary coolant flows upward through the surrounding volume (that is, “shell-side”). In other embodiments, the primary coolant flows downward through the surrounding volume (shell-side) while the secondary coolant flows upward through the steam generator tubes (tube-side). In either configuration, the steam generator tubes can have various geometries, such as vertical straight tubes (sometimes referred to as a straight-tube once-through steam generator or “OTSG”), helical tubes encircling the cylindrical riser 20 (some embodiments of which are described, by way of illustrative example, in Thome et al., “Integral Helical Coil Pressurized Water Nuclear Reactor”, U.S. Pub. No. 2010/0316181 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety), or so forth. It will be noticed in FIG. 1 that the illustrative PWR 10 has the steam outlet 24 located at a low position, that is, near the bottom of the steam generator 18. However, the secondary coolant is converted to steam as the secondary coolant flows upwardly through the steam generator 18, such that the hottest steam is expected to be present near the top of the steam generator 18. The placement of the steam outlet 24 located at its illustrated low position reflects the presence of an annular steam jacket (not shown) disposed between the steam generator 18 and the cylindrical wall of the pressure vessel 12. This steam jacketing approach is optional, but has the benefit of providing a higher temperature outer surface for maintaining temperature stability. In an alternative embodiment, the steam jacket is omitted and the steam outlet is located at or near the top of the steam generator 18. The illustrative PWR 10 is an integral PWR including the steam generator 18 disposed inside the pressure vessel 12. In other embodiments, the PWR is not an integral PWR; rather the steam generator is located externally. In these embodiments, the feedwater inlet 22 and steam outlet 24 are suitably replaced by high pressure vessel penetrations flowing primary coolant water out of the pressure vessel, through the external steam generator, and back to the pressure vessel. Moreover, contemplated integral PWR designs may place the steam generator at various locations in the pressure vessel, such as partially surrounding the reactor core, or disposed inside cylindrical riser, or so forth. The pressure vessel 12 defines a sealed volume that, when the PWR is operational, contains primary coolant water in a subcooled state. Toward this end, the PWR includes an internal pressurizer volume 30 disposed at the top of the pressure vessel 12. The internal pressurizer volume 30 contains a steam bubble volume whose pressure controls the pressure of the primary coolant water in the pressure vessel 12. At least one steam pressure control device is provided to adjust or control the pressure of the steam bubble in the internal pressurizer volume 30. By way of illustrative example, the steam pressure control device or devices may include a heater 32 (e.g., one or more resistive heaters) that heats the steam to increase pressure, and/or a sparger 34 that injects cool water or steam into the steam bubble to reduce pressure. A baffle plate 36 separates the internal pressurizer volume 30 from the remainder of the sealed volume of the pressure vessel 10. By way of illustrative example, in some embodiments the primary coolant pressure in the sealed volume of the pressure vessel 12 is at a pressure of about 2000 psia and at a temperature of about 300° C. (cold leg just prior to flowing into the reactor core 14) to 320° C. (hot leg just after discharge from the reactor core 14). These are merely illustrative subcooled conditions, and a diverse range of other operating pressures and temperatures are also contemplated. With continuing reference to FIG. 1, the PWR 10 is disposed in a containment structure 40, which may by way of illustrative example comprise a concrete, steel, steel-reinforced concrete, or other structure. The containment structure 40 is intended to contain any release of primary coolant water from the PWR 10 in the event of a loss of coolant accident (LOCA). In some embodiments the containment structure 40 may be partially or wholly subterranean. In the illustrative embodiment, at least a flood well 42 portion of the containment structure is buried, and the lower portion of the PWR 10 including the nuclear reactor core 14 resides in this flood well 42. FIG. 1 also diagrammatically depicts an emergency core cooling system (ECCS) configured to remediate various abnormal operating conditions such as a loss of heat sinking event, or a scram failure. The ECCS includes a water storage tank 50 disposed inside the containment 40. The water storage tank 50 is also sometimes referred to as a refueling water storage tank (since it may optionally be utilized as a source of make-up primary coolant water during refueling of the PWR 10) or as a reactor water storage tank. The water storage tank 50 is also referred to herein by the acronym “RWST” 50. With reference to FIG. 1 and with further reference to FIG. 2, the ECCS a valve assembly comprising valves and piping for selectively interconnecting the RWST 50 and various components of the ECCS with each other and/or with the PWR 10. FIG. 1 shows a schematic diagram of the illustrative ECCS embodiment, with emphasis on its interconnection with the PWR 10. FIG. 2 shows a more detailed schematic diagram of the ECCS of FIG. 1 that depicts some additional features that may optionally be included. It is to be appreciated that both FIG. 1 and FIG. 2 show schematic diagrams of the ECCS for the purpose of illustrating preferred embodiments, and it is to be understood that further additional or substitute features may also or alternatively be included based on considerations of the specific design implementation, applicable government regulations, or so forth. In describing the illustrative ECCS embodiments, the following terminology is used herein. Terms such as “normally open” or “normally closed” refer to the normal condition or state of the valve or other element during normal operation of the PWR 10 for its intended purpose (for example, the intended purpose of generating electrical power in the case of a nuclear power plant). A term such as “abnormal operation signal” refers to a signal generated by a sensor or other device indicating that some metric or aspect of the PWR operation has deviated outside of the normal PWR operational space. By way of illustrative example, an abnormal operation signal may comprise a low reactor water level signal, or an abnormal operation signal may comprise a high reactor pressure signal. A low reactor water level signal may indicate a LOCA, while a high reactor pressure signal may indicate a LOCA or a loss of heat sinking event. Typically, abnormal operation signal (or a combination of such signals) will automatically trigger an audible, visual, or other alarm to notify reactor operation personnel of the deviation, and/or will trigger an automated response by the ECCS. In some cases and in some embodiments, reactor operation personnel may be able to override or cancel an automated ECCS response. In some cases and in some embodiments, the ECCS response to an abnormal operation signal or a combination of such signals may be initiated manually by reactor operation personnel. To enable automatic alarm triggering and/or automated ECCS response, ECCS control circuitry 54 is provided. In FIGS. 1 and 2 the ECCS control circuitry 54 is diagrammatically indicated; however, it is to be understood that the ECCS control circuitry 54 includes suitable electronics, analog and/or digital circuitry, digital processor or digital control integrated circuit (IC) chips, or so forth along with suitable sensor devices in order to detect abnormal conditions, generate corresponding abnormal operation signals, activate visual and/or auditory alarms, and perform ECCS operations such as opening valves, closing valves, or so forth in order to implement suitable emergency core cooling operations in response to a detected abnormal condition. Some sensors that may be employed include: a pressure sensor for detecting an abnormally high reactor pressure and generating the high reactor pressure signal; a water level sensor for detecting a low level of primary coolant water in the pressure vessel 12 and generating the low reactor water level signal; an in-core temperature sensor for detecting an abnormally high temperature of the nuclear reactor core 14, or so forth. Optionally, the ECCS control circuitry 54 may include processing capability in the form of a computer, microcontroller, or other digital processing device that is programmed or otherwise configured to process received abnormal operation signals and to generate suitable alarms and or cause the ECCS to perform a suitable automated response. In some embodiments, the ECCS control circuitry 54 is capable of making certain inferences in deciding a suitable response—for example, a combination of a low reactor water level signal and a low reactor pressure signal may be inferred to indicate a LOCA, whereas a high reactor pressure signal may be inferred to indicate a loss of heat sinking event. In embodiments in which an automated ECCS response is provided, the ECCS control circuitry 54 suitably includes actuation lines for causing valves to open or close. The actuation lines are typically wires or other electrical conductors, but other types of actuation such as pneumatic lines are also contemplated. Some types of abnormal events that are to be remediated by the ECCS entail an increase in pressure in the PWR 10. For example, a loss of heat sinking event (for example, caused by a loss of feedwater flow into the feedwater inlet 22 of the steam generator 18) will produce heating that in turn increases pressure inside the PWR 10. A LOCA will similarly typically lead to heating and pressure increase. An uncontrolled or excessive pressure increase in the PWR 10 is problematic since it can compromise the sealing integrity of the pressure vessel 12 and can lead to escape of primary coolant water in the form of high pressure steam. To control a pressure increase in the PWR 10, a condenser 60 is provided inside the containment structure 40. The condenser 60 is designed to operate at high pressure. The valve assembly includes a steam line 62 connecting the steam bubble in the internal pressurizer volume 30 of the PWR 10 with a condenser inlet 64 of the high pressure condenser 60. A steam vent vessel penetration 66 in the pressure vessel 12 is suitably provided for connecting the steam line 62 with the steam bubble in the internal pressurizer volume 30. The condenser 60 also has a condenser outlet 68 from which flows cooled steam, condensed water, or a cooled steam/water mixture. To provide failsafe operation, the condenser 60 is suitably a passive heat exchanger that rejects heat from the steam admitted at the condenser inlet 64 to an external heat sink 70 located outside of the containment structure 40. The condenser 60 is suitably of a “once-through” design having tubes surrounded by a shell (details not shown). In one suitable embodiment, steam from the internal pressurizer volume 30 of the PWR 10 flows on the tube-side and water from the external heat sink 70 flows on the shell-side; however, the reverse configuration is also contemplated in which the steam flows on the shell-side and water from the external heat sink 70 flows tube-side. In either case, liquid water from the external heat sink 70 flows via a first pipe 72 into the condenser 60 where heat from the steam transfers to the cooler water from the external heat sink 70 causing the latter to boil or vaporize. The resulting water from the external heat sink 70 (now in a steam phase or mixed steam/water phase) flows via a second pipe 74 back to the external heat sink 70. The flow of water/steam from the external heat sink 70 in the pipes 72, 74 is driven by gravity and density difference between the inflowing water and the outflowing steam or mixed steam/water. In the illustrative embodiment, the pipes 72, 74 have open ends at the external heat sink side that are in fluid communication with water in the external heat sink 70 so that water from the external heat sink 70 flows into the first pipe 72 and the water/steam mixture discharges out of the second pipe 74 into the external heat sink 70. However, in an alternative embodiment, the open ends of the pipes 72, 74 are replaced by a heat exchanger coupling disposed in the external heat sink 70 (not shown) forming closed recirculation path in which the steam/water mixture from the second pipe 74 condenses back into water (rejecting the heat into the external heat sink 70 as before) and the recondensed water flows back into the first pipe 72. The external heat sink 70 is suitably a body of water disposed outside the containment structure 40, such as a natural or artificial pond, lake, pool, or the like. Such an external heat sink 70 is also sometimes referred to as an “ultimate” heat sink. In some embodiments, the external heat sink 70 is located in a reactor services building or other structure or enclosure. The water volume of the external heat sink 70 should be sufficient to provide an extended period of operation of the high pressure condenser 60. For example, in some contemplated embodiments the external heat sink 70 is designed to have water volume sufficient for 72 hours continuous operation of the condenser 60. As diagrammatically indicated in FIG. 2, the external heat sink 70 may optionally include additional features such as a provision 76 for connection to other water sources (for example, to provide makeup water to the external heat sink 70 to further extend the period of operation of the condenser 60), and/or a vent 78 for releasing any steam that might be generated by the heat rejected from the condenser 60 into the ultimate heat sink 70. Note that if the external heat sink 70 is an open body of water or otherwise has sufficient exposed surface area, then the vent 78 is suitably omitted. The condenser 60 is connected by the steam pipe 62 with the steam vent vessel penetration 66 in the pressure vessel 12, which in some suitable embodiments is 3-inch (7.6 cm) penetration although otherwise-sized penetrations are also contemplated. As shown in FIG. 2, a high pressure vent 80 is also optionally connected with the steam pipe 62 to relieve any pressure exceeding the design limits of the condenser 66. An isolation valve V1 provides the ability to isolate the condenser 60 from the vessel penetration 66 during maintenance or repair. In some embodiments, the isolation valve V1 is normally open, and remains open during an ECCS response to an abnormal event. With the isolation valve V1 normally open, it follows that the condenser 66 is under high pressure during normal operation of the PWR. However, a valve V2 connected with the outlet 68 of the condenser 60 is normally closed. When an ECCS response calls for operation of the condenser 60, the valve V2 opens to allow flow from the steam bubble in the internal pressurizer volume 30 through the condenser 60 and to allow condensed water to flow through the opened valve V2 and into a reactor coolant inventory makeup line 82 that feeds into a vessel penetration 84 of the pressure vessel 12. This completes the flow circuit and allows the condensed water to flow back into the PWR. As shown in FIG. 1, in some embodiments a gas trap 86 is provided to trap gaseous nitrogen (N2) or gaseous oxygen (O2) that exits from the condenser outlet 68, in order to prevent these gases from entering into the pressure vessel 12. As shown in FIG. 2, check valves V3 may be provided on the reactor coolant inventory makeup line 82 (or, more generally, in series with the valve V2) to prevent backflow of primary coolant water from the pressure vessel 12 into the valve assembly. The various valves V2, V3 may also have redundancy as shown in FIG. 2, and the valve V2 as shown in FIG. 2 also includes a normally open isolation valve. As still further shown in FIG. 2 the reactor coolant inventory makeup line 82 and vessel penetration 84 may also serve as an inlet to the pressure vessel 12 for a reactor coolant inventory supply line 88, which may be used to provide makeup water during normal operation of the PWR. While the single vessel penetration 84 in conjunction with the valve assembly components V2, V3 provides the inlet for these multiple functions, alternatively two or more separate vessel penetrations may be provided, and/or multiple redundant vessel penetrations may be provided for a given function. The condenser 60 may be used in responding to various types of abnormal events, such as LOCA or loss of heat sinking events. In a suitable approach the ECCS control circuitry 54 opens the valve V2 to initiate operation of the condenser 60 responsive to a low reactor water level signal, a high reactor pressure signal, or the combination of both a low reactor water level signal and a high reactor pressure signal. The low reactor water level signal (either with or without a concomitant low reactor pressure signal) indicates a LOCA, while a high reactor pressure signal without a concomitant low reactor water level signal indicates an abnormal event other than a LOCA, such as a loss of heat sinking event. Thus, the same condenser 60 is used to respond to either a LOCA or a loss of heat sinking event. A loss of heat sink event or other abnormal event other than a LOCA is indicated by a high reactor pressure signal without a concomitant low reactor water level signal. In such a case, the principal concern is overpressurization of the pressure vessel 12. Toward this end, opening the valve V2 to initiate operation of the condenser 60 is expected to be a sufficient immediate response. In the case of a LOCA, however, there is a loss of primary coolant water from the pressure vessel 12, potentially causing exposure of the reactor core 14. Thus, a LOCA response entails opening the valve V2 to initiate operation of the condenser 60, and also expeditiously bringing about a state in which coolant can be added to the pressure vessel 12. To achieve the latter, it is desired to reduce the pressure in the pressure vessel 12 as quickly as possible, so that makeup water can be flowed into the pressure vessel 12 from the RWST 50. The condenser 60 operates efficiently when the steam entering at the inlet 64 is hot, which typically corresponds to steam under high pressure. For such hot steam, the temperature difference between the steam and the water flowing into the condenser 60 from the external heat sink 70 is large, leading to efficient rejection of heat to the external heat sink 70. However, as the pressure decreases (typically corresponding to cooler steam), efficiency of the condenser 60 decreases, and so the pressure reduction approximately exponential as a function of time with a long low-pressure “tail”. This slow late-stage depressurization is disadvantageous in responding to a LOCA because it delays achieving the state in which makeup water can be flowed into the pressure vessel 12 from the RWST 50. Accordingly, when responding to a LOCA the condenser 60 operates analogously to the response to a loss of heat sinking event or other non-LOCA event until the pressure in the pressure vessel 12 decreases to below a preselected pressure threshold. Once the pressure threshold is released, a low pressure vent valve V4 opens to connect the condenser outlet 68 with a sparger 90 discharging into the RWST 50. As shown in FIG. 2, the low pressure vent valve V4 may be a composite valve or sub-assembly including two redundant paths each comprising an air-operated valve (reopening) followed by a squib valve (non-reopening) arranged in series. The vent path including the low pressure vent valve V4 and the sparger 90 is sized to depressurize the reactor sufficiently to allow initiation of flow of makeup water from the RWST 50. In the illustrative configuration, the vent line including the low pressure vent valve V4 and sparger 90 is arranged in parallel with the condensate return path comprising the valves V2, V3, reactor coolant inventory makeup line 82, and vessel penetration 84—thus, the condenser 60 continues to operate while the sparger 90 accelerates depressurization. Once the reactor is sufficiently depressurized by action of the sparger 90, a valve V5 opens to allow water to flow from the RWST 50 into the reactor coolant inventory makeup line 82 and vessel penetration 84 in order to provide makeup water to compensate for primary coolant water lost in the LOCA. As shown in FIG. 2, the valve V5 may have redundancy, and may also include a normally open isolation valve. In a suitable embodiment, the valve V5 includes parallel squib valves that are actuated concurrently with the low pressure vent valve. V4 and the sparger 90. As further shown in FIG. 2, the valve V5 may be placed in series with a check valve V6 (which again, may include redundancy as shown in FIG. 2) in order to prevent backflow of primary coolant water from the pressure vessel 12 into the RWST 50. Flow of water from the RWST 50 to the pressure vessel 12 via the valves V5, V6, reactor coolant inventory makeup line 82, and vessel penetration 84 starts when the reactor pressure is less than the sum of the pressure in the containment structure 40 and the gravity head provided by the water level in the RWST 50. Toward this end, the RWST 50 is preferably located at an elevated position in the containment structure 40. In some LOCAs, the water capacity of the RWST 50 may be insufficient to ensure that the reactor core 14 remains immersed. For example, a LOCA initiated by a pipe break at a lower flange or low vertical position may result in a large quantity of the primary coolant water being drained from the reactor cavity. In such cases, an external water inlet 100 provides additional water through a valve V7. As seen in FIG. 2, this additional water inlet should feed into the reactor coolant makeup line 82 at a point upstream of the check valve V6. If the water inlet 100 is connected with a commercial water supply or other source of unfiltered water, then the water inlet 100 may include a screen or other filter to ensure that particulates do not enter the pressure vessel 12. (Similarly, a screen or filter 102 may be provided to clean water coming from the RWST 50 prior to flowing into the reactor coolant inventory makeup line 82.) As shown in FIG. 2, the valve V7 may have redundancy and also may include a normally open isolation valve. Although not illustrated in FIG. 2, the water supply feeding into the water inlet 100 may be the same as reactor coolant inventory supply line 88 that provides makeup water during normal operation of the PWR. With reference to FIG. 2, in some embodiments the available sparger 90 is also used as a vent for the second pipe 74 flowing steam or mixed water/steam back to the external heat sink 70. Toward this end, a connection 104 is diagrammatically shown in FIG. 2 to indicate a connection from the second pipe 74 to the sparger 90. A valve V8 is suitably configured to open if the pressure in the second pipe 74 exceeds a venting threshold pressure. The connection 104 and valve V8 should be located inside the containment structure 40. Some types of abnormal events that are to be remediated by the ECCS may not entail an increase in pressure in the PWR 10. For example, a scram failure entails a malfunction of the control rods system 16. In one type of scram failure, the control rods fail to insert adequately—this is sometimes also referred to as an anticipated transient without scram (ATWS). Scram failure may also be preemptively identified, for example by a CRDM diagnostic detecting an incipient problem. Typically, a scram failure does not generate an immediate problem such as a pressure rise or temperature rise; nonetheless, the scram failure would compromise the ability to respond to other types of failure (e.g., a LOCA or a loss of heat sinking event) and accordingly typically calls for immediate shutdown of the reactor. In some PWR systems, a secondary source of reactivity control is also provided in the form of a soluble poison injection system for delivering a controlled amount of dissolved soluble neutron poison into the primary coolant water. For example, the soluble neutron poison may comprise sodium pentaborate or another soluble boron compound. In such systems, the soluble poison injection system is used during normal PWR operation and under normal conditions the primary coolant water includes a controlled amount of dissolved boron compound or other dissolved neutron poison. In such PWR systems, the preexisting soluble poison injection system can also be used as part of the ECCS. In such a system, a scram failure response includes delivering a high concentration of soluble neutron poison into the primary coolant so as to quench core reactivity. However, there are disadvantages to employing soluble poison such as a boron compound during normal PWR operation. For example, dissolved boric acid is corrosive and can corrode some steel surfaces, potentially compromising the sealing integrity of the pressure vessel. In the illustrative system of FIGS. 1 and 2, the primary coolant water in the pressure vessel 12 does not contain dissolved neutron poison such as a boron compound during normal PWR operation. However, a tank 120 containing a solution of soluble neutron poison is provided for responding to a scram failure by delivering a high concentration of soluble neutron poison into the primary coolant water in the pressure vessel 12 so as to quench core reactivity. In the illustrative embodiment, the quench tank 120 is an emergency boron tank 120 containing a concentrated solution of sodium pentaborate or another soluble boron compound; however, the quench tank may in general contain a solution of another species of soluble poison. The emergency boron tank 120 is not used during normal operation of the PWR 10, and does not include a compressed gaseous nitrogen (N2) tank or other dedicated pressure source. Rather, the boron tank 120 is connected with the steam line 62 via a valve V10 to provide pressurization in the event of a scram failure. The steam line 62 is also connected with the high pressure condenser 60 via the normally open valve V1, and accordingly is already available for use in pressurizing the emergency boron tank 120 by adding the additional valve V10. The emergency boron tank 120 is also connected with the reactor coolant inventory makeup line 82 that feeds into a vessel penetration 84 of the pressure vessel 12 via a valve V11. The connection of the emergency boron tank 120 with the reactor coolant inventory makeup line 82 is upstream of the check valve V3 to prevent backflow of primary coolant water from the pressure vessel 12 into the boron tank 120. The valves V10, V11 may have redundancy and/or a normally open isolation valve, as shown in FIG. 2. The valves V10, V11 are normally closed (that is, are closed during normal operation of the PWR 10). In some embodiments the valves V10, V11 a composite valve or sub-assembly including a manual normally open isolation valve in series with two redundant (parallel) paths each comprising a squib valve (non-reclosing) arranged in series with a check valve to prevent backflow. When the ECCS control circuitry 54 detects a scram failure, the valves V10, V11 are opened manually or by an automatic control signal from the ECCS control circuitry 54. Since a scram failure is typically not accompanied by immediate deviation of PWR metrics or parameters from the normal operating space, the valves V10, V11 are suitably manually operated valves in some embodiments. Opening the valve V10 places the steam bubble in the internal pressurizer volume 30 into fluid communication with the emergency boron tank 120 to pressurize the emergency boron tank 120. The emergency boron tank 120 is suitably located above the RWST 50. The relative pressure head between the pressurized boron tank 120 and the primary coolant water pressure vessel 12 allows the boron solution to flow into the pressure vessel 12 through the reactor coolant inventory makeup line 82 and the vessel penetration 84. If the PWR 10 employs primary coolant pumps to drive circulation of the primary coolant water in the pressure vessel 12, these pumps should be shut down during the boron solution injection process. (Similarly, primary coolant pumps are typically shut down during ECCS response to a LOCA or other ECCS response entailing passive flow into the pressure vessel 12). In a suitable embodiment, the emergency boron tank 120 contains a solution of sodium pentaborate in water of sufficient concentration and volume to shut down the PWR 10 with the highest worth control rod withdrawn from the reactor core 14 and to maintain shutdown at cold conditions. The ECCS shown in FIGS. 1 and 2 is an illustrative example. It is to be understood that various levels of redundancy may be incorporated into the ECCS to failsafe operation. For example, in some embodiments, two redundant emergency boron tanks 120, each with its own valves V10, V11, is provided. Similarly, two high pressure condensers 60 may be provided, again each with its own separate associated valve set to maximize redundancy. Moreover, it is to be understood that various combinations of disclosed components or aspects may be employed in various embodiments. For example, the condenser 60 may be provided to respond to LOCA or loss of heat sinking events while omitting the emergency boron tank 120 and valves V10, V11 and providing a different response mechanism for scram failure. Conversely, the emergency boron tank 120 and valves V10, V11 may be provided for responding to scram failure, but in conjunction with different response mechanisms for responding to LOCA or loss of heat sinking events. Further, while the emergency boron tank 120 and valves V10, V11 is described in an illustrative embodiment in which soluble boron compound is not used in normal PWR operation, it is also contemplated to employ the emergency boron tank 120 and valves V10, V11 in conjunction with a PWR that uses boron for reactivity control during normal PWR operation. Other such combinations and variations are also contemplated. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. |
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description | The present application is a US National Phase of PCT Application No. PCT/IL2005/000871 filed on Aug. 11, 2005. The present application also claims the benefit under 35 USC 119(e) of U.S. Provisional Application No. 60/600,725 filed on Aug. 12, 2004 entitled “Medical Navigation System Based on Differential Sensor”; 60/619,792 filed on Oct. 19, 2004 entitled “Using a Catheter or Guidewire Tracking System to Provide Positional Feedback for an Automated Catheter or Guidewire Navigation System”, and 60/619,897 filed on Oct. 19, 2004 entitled “Using a Radioactive Source as the Tracked Element of a Tracking System ”, the disclosures of which are incorporated herein by reference. The present invention relates to location and tracking of a source of ionizing radiation, for example within a body of a subject. Existing techniques for intrabody tracking include direct video imaging using a laparoscope; fluoroscopy (performance of the procedure under continuous or periodic X-Ray imaging); electromagnetic tracking, optical tracking, computerized tomography (CT) tracking and ultrasonic image assisted tracking. Some of these techniques explicitly avoid ionizing radiation. Those techniques which employ ionizing radiation, such as fluoroscopy and CT, require sufficient amounts of ionizing radiation that radiation exposure for subjects and medical staff is a subject of concern. Some applications which require intrabody tracking, such as cardiac catheterization, require concurrently acquired images because the tissue through which the tracked medical device is being navigated moves frequently. Other applications which require intrabody tracking, such as intracranial procedures, are more amenable to the use of pre-acquired images because the relevant tissue is relatively static. An aspect of some embodiments of the present invention relates to using ionizing radiation from a source in order to detect its position, optionally in or near the body of a subject, without production of an image. Optionally, the source is integrally formed with or attached to a medical device. Medical devices include, but are not limited to, tools, implants, navigational instruments and ducts. In an exemplary embodiment of the invention, position of the source is determined by non-imaging data acquisition. For purposes of this specification and the accompanying claims, the phrase “non-imaging” indicates data acquired independent of an image acquisition process that includes the source and anatomical or other non-source features in a same image. Optionally, position is determined using a sensor which has angular sensitivity resulting in a detectable change in output resulting from radiation detection according to an effective angle of incidence of radiation from the source. Greater sensitivity in effective angle of incidence provides greater efficiency of the position determination in terms of speed and accuracy. Embodiments with an angular range of less than ±100 milliradians, optionally less than ±50 milliradians are disclosed. In an exemplary embodiment of the invention, greater sensitivity to effective angle of incidence can be achieved by moving a radiation detector and/or a shield. Optionally, the source of ionizing radiation has an activity in the range of 0.01 mCi to 0.5 mCi. Optionally, the source of ionizing radiation has an activity less than 0.1 mCi. Optionally, the source of ionizing radiation has an activity of about 0.05 mCi. In an exemplary embodiment of the invention, a radiation source which poses no significant health risk to a patient (i.e short term exposure) and/or medical personnel (i.e. long term exposure) may be employed. Optionally, the refresh rate for the location data insures that the locational information is temporally well correlated to the actual location of a tracked object (e.g. medical device). Recommended refresh rates vary according to the speed at which the tracked object moves and according to the environment in which the tracked object moves. In an exemplary embodiment of the invention, for tracking of medical devices through body parts which are more static, such as brain or digestive tract, lower refresh rates, for example 10 times/second may be adequate. In embodiments for tracking of medical devices through body parts which move frequently, such as the heart, higher refresh rates, for example 20 times/second may be desirable. Optionally, gating to an ECG output may be implemented so that positions from selected cardiac cycle phases are plotted. Optionally, the RMS error of a calculated position of the source of ionizing radiation is less than 10 mm, optionally less than 5 mm, optionally less than 2 mm, optionally less than 1 mm, optionally 0.5 to 0.8 mm or better. Variables which may influence the accuracy of determined position(s) include activity of the source in DPM, the accuracy and/or response time of radiation sensors employed for detection, and the speed of the implanted medical device. Improvement in one or more of these variables may compensate for one or more other variables. Optionally, reducing the speed of a tracked medical device may be employed to compensate for other variables. Optionally, location information is displayed in the context of anatomical imaging data. Optionally, relevant anatomical features are highlighted to facilitate navigation of the medical device by medical personnel. Optionally, determined positions may be displayed in the context of a separately acquired image. Optionally, two or more sources may be tracked concurrently. Optionally, multi-source tracking is used in determining orientation of an asymmetric medical device. Optionally, multi-source tracking is used in coordinating activity of two or more medical devices for a medical procedure. An aspect of some embodiments of the present invention relates to using a sensor with angular sensitivity to detect a direction towards a source of ionizing radiation. Optionally, two or three or more directions are determined, either concurrently or successively, so that a position may be determined by calculating an intersection of the directions. If three or more directions are employed, the location may be expressed as a three dimensional position. Optionally, a direction is used to determine a plane in which the source resides. Optionally, sensors for detection of radiation from the source achieve the desired angular sensitivity by rotation of at least a portion of the sensor about an axis through a rotation angle. For example, detectors or radiation shields may be rotated. Alternately or additionally, sensors may achieve the desired angular sensitivity by translational motion. An aspect of some embodiments of the present invention relates to a sensor with an angular sensitivity which causes changes in an output signal from at least one radiation detector in response to an effective angle of incidence between the detector and a source. A target value of the output signal is achieved at an angle indicating the direction towards the source. The direction is optionally used to determine a plane in which the source resides. Optionally the sensor may include more than one radiation detector, each radiation detector having a separate output signal. Optionally, one or more radiation shields may be employed to shield or shadow at least a portion of at least one of the radiation detectors from incident radiation. The degree of shielding changes as deviation from the angle indicating a direction towards the source occurs and the output signal varies according to the degree of shielding. Optionally, multiple radiation shields are employed in concert to form a collimator. The radiation shields may be either parallel to one another or skewed inwards. Optionally, the multiple radiation shield, whether parallel or skewed, may be rotated. Optionally, the deviation from target output is 1% of the output range per milliradian of angular displacement away from an angle indicating a direction towards the source. Optionally deviation in output indicates direction of deviation as well as magnitude of deviation. According to various embodiments of the invention, radiation detectors and/or radiation shields may be displaced to impart angular sensitivity. This displacement may be rotational and/or translational. An aspect of some embodiments of the present invention relates to a computerized system for locating a medical device, optionally within a body of a subject by using angular sensitivity of a sensor module to determine a direction. The sensor module measures incident radiation on one or more radiation detectors. Incident radiation produces an output signal which is translated to directional information by the system. An aspect of some embodiments of the invention relates to association of a source of ionizing radiation with a medical device to facilitate determination of a location of the device, optionally as the device is navigated within or near a subject's body during a medical procedure. Optionally, the source of ionizing radiation has an activity in the range of 0.01 mCi to 0.5 mCi. Optionally, the source of ionizing radiation has an activity less than 0.1 mCi. Optionally, the source of ionizing radiation has an activity of about 0.05 mCi. Association includes integrally forming the source and the device as a single unit. Association also includes attaching the source to the device. Optionally, the source is concentrated in an area having a largest dimension less than 10 mm, optionally less than 5 mm, optionally less than 2.5 mm, optionally less than 1 mm. An aspect of some embodiments of the invention relates to use of an ionizing radiation source with an activity of 0.1 mCi or less as a target for non imaging localization or tracking, optionally in a medical context. The source of ionizing radiation is selected to reduce a biological effect on the patient and/or medical personnel. This selection involves consideration of radiation strength, radiation type and/or amount of exposure time (e.g. time in the body for a patient undergoing a procedure). Alternatively or additionally, radiation sources which are constructed of biocompatible material and/or coated with biocompatible coatings may be employed. In an exemplary embodiment of the invention, a computerized system for tracking and locating a source of ionizing radiation is provided. The system comprising: (a) at least one non-imaging sensor module comprising at least one radiation detector, the at least one radiation detector capable of receiving ionizing radiation from the radiation source and producing an output signal; and (b) the CPU designed and configured to receive the output signal and translate the output signal to directional information. Optionally, the source of radiation is integrally formed with or attached to a medical device. Optionally, the at least one sensor module includes at least two sensor modules. Optionally, the at least two sensor modules includes at least three sensor modules. Optionally, the at least one of the at least one sensor module further comprises a locomotion device capable of imparting translational motion to the sensor module so that the sensor module is moved to a new location. Optionally, the locomotion device is operable by a translational motion signal from the CPU. Optionally, the system additionally comprises an imaging module, the imaging module capable of providing an image signal to the CPU, the CPU capable of translating the image signal to an image of a portion of the body of the subject. Optionally, the system further comprises a display device. Optionally, the display device is capable of displaying the image of the portion of the body of the subject with a determined position of the medical device superimposed on the image of the portion of the body of the subject. Optionally, the CPU receives at least two of the output signals and computes a position of the radiation source based on the output signals, Optionally, the CPU receives at least three of the output signals and computes a position of the radiation source based on the at least three output signals. Optionally, wherein the CPU computes the position repeatedly at intervals so that a position of the radiation source as a function of time may be plotted. Optionally, wherein the radiation source employs an isotope with a half life in the range of 6 to 18 months. Optionally, the system further comprises additionally comprising the radiation source capable of providing the radiation. Optionally, the directional information is produced when the source has an activity in the range of 0.01 mCi to 0.5 mCi. In an exemplary embodiment of the invention, a sensor for directionally locating an ionizing radiation source is provided. The sensor comprises: (a) at least one functional component; and (b) a displacement mechanism which imparts angular sensitivity to the sensor by moving the at least one functional component. Optionally, the at least one functional component comprising at least one radiation detector, the at least one radiation detector capable of receiving radiation from the radiation source and producing an output signal; wherein the displacement mechanism is capable of rotating the at least one radiation detector through a rotation angle so that the output signal varies with the rotation angle. Optionally, the at least one radiation detector comprises at least one first radiation detector and at least one second radiation detector and the output signal comprises at least one first output signal from the at least one first radiation detector and at least one second output signal from the at least one second radiation detector. Optionally, the sensor comprises at least one radiation shield installed at a fixed angle with respect to the at least one first radiation detector and the at least one second radiation detector so that a magnitude of the first output signal from the at least one first radiation detector and a magnitude of the second output signal from the second radiation detector vary with the rotation angle. Optionally, the sensor comprises: (a) at least one first radiation detector and at least one second radiation detector, each of the at least one first radiation detector and at least one second radiation detector capable of receiving radiation from the radiation source and producing at least one first output signal from the at least one first radiation detector and at least one second output signal from the at least one second radiation detector; (b) at least one radiation shield, the radiation shield rotatable about an axis of shield rotation through an angle of shield rotation, so that a magnitude of the first output signal from the at least one first radiation detector and a magnitude of the second output signal from the second radiation detector each vary with the angle of shield rotation. Optionally, the at least one radiation shield comprises: (i) a primary radiation shield located between the at least one first radiation detector and the at least one second radiation detector; (ii) at least one first additional radiation shield deployed to interfere with incident radiation directed towards the at least one first radiation detector; and (iii) at least one second additional radiation shield deployed to interfere with incident radiation directed towards the at least one second radiation detector. Optionally, wherein the at least one first additional radiation shield and the at least one second additional radiation shield are each inclined towards the primary radiation shield. Optionally, wherein the at least one first radiation detector and the at least one second radiation detector are organized in pairs, each pair having a first member and a second member and each radiation shield of the primary and additional radiation shields is located between one of the first member and one of the second member of one of the pairs so that the output signal varies with the rotation angle. Optionally, the sensor is additionally capable of revolving the at least a functional component about an axis of revolution through an angle of revolution. In an exemplary embodiment of the invention, a method of determining a location of a device is provided. The method comprises: (a) providing a device having a radiation source associated therewith; (b) determining a direction towards the radiation source; (c) further determining at least a second direction towards the radiation source; (d) locate the device by calculating an intersection of the first direction and the at least a second direction. Optionally, the further determining at least a second direction towards the radiation source includes determining at least a third direction towards the radiation source and additionally comprising: (e) calculating a point of intersection of the first direction, the second direction and the at least a third direction. In an exemplary embodiment of the invention, a method of manufacturing a trackable medical device is provided. The method comprises incorporating into or fixedly attaching a detectable amount of a radioactive isotope to the medical device. Optionally, the detectable amount is in the range of 0.01 mCi to 0.5 mCi. Optionally, the detectable amount is 0.1 mCi or less. Optionally, the detectable amount is 0.05 mCi or less. Optionally, the isotope is Iridium-192. An aspect of some embodiments of the invention relates to use of an ionizing radiation source with an activity of 0.1 mCi or less as a target for non imaging localization or tracking. According to one embodiment of the invention (FIGS. 2 and 4), a computerized system 40 locates and/or tracks a device. In the embodiment depicted in FIG. 4, the device is a medical device. Medical devices include, but are not limited to, tools, implants, navigational instruments and ducts. Tools include, but are not limited to, catheters, canulae, trocar, cutting implements, grasping implements and positioning implements. Implants include, but are not limited to, brachytherapy seeds, stents and sustained release medication packets. Navigational instruments include, but are not limited to, guidewires. Ducts include, but are not limited to, tubing (e.g. esophageal tubes and tracheal tubes). In exemplary embodiments of the invention, one or more moving tools are tracked. In an exemplary embodiment of the invention, position of the source is determined by non-imaging data acquisition. For purposes of this specification and the accompanying claims, the phrase “non-imaging” indicates data not acquired as part of an image acquisition process that includes the source and anatomical or other non-source features in a same image. Optionally, a sensor which is not suitable for and not connected to imaging circuitry is employed. Imaging relies upon information about many points, including at least one point of interest, and image analysis of the information determines characteristics of the point(s) of interest, for example position relative to an object. In an exemplary embodiment of the invention, position sensing provides information only about the source. This can improve detectability and/or accuracy. Optionally, the medical device is at least partially within a body of a subject 54 during at least part of the path upon which its location is determined. In FIG. 4, an exemplary embodiment in which system 40 is conFigured to track a device through the head of subject 54 during an intracranial medical procedure is depicted. This drawing is purely illustrative and should not be construed as a limitation of the scope of the invention. FIG. 2 shows an embodiment of system 40 including three sensor modules 20 which rely on angular detection acting in concert to determine a location of radioactive source 38. In the pictured embodiment, each of sensors 20 determines an angle of rotation 32 indicating a direction towards source 38. This angle of rotation 32 (FIG. 1) defines a plane in which source 38 resides and which crosses radiation detector 22. Angle of rotation 32 is provided as an output signal 34 which is relayed to computerized processing unit (CPU) 42. CPU 42 determines an intersection of the three directions (planes) which is expressed as a point. According to some embodiments of the invention, a source 38 located within the boundaries 24 of detection (FIG. 1) of sensor 20 may be accurately located by system 40 as radiation detector 22 of sensor module 20 is rotated through a series of rotation angles 32. A source 38 located outside of boundaries 24 will not be accurately located. For this reason, it is desirable, in some embodiments, that each of sensors 20 is deployed so that the predicted path of source 38 lies within boundaries 24. According to some embodiments of the invention, sensor 20 may move to keep source 38 within boundaries 24. The size and shape of boundaries 24 vary according to the configuration of sensor 20. Accuracy of determination of target rotation angle 32 contributes to accuracy of the location of source 38 as determined by system 40. Various modifications to sensor module 20 which can increase the sensitivity to small differences in rotation angle 32 are depicted as exemplary embodiments in FIGS. 3, 5, 6A and 6B and explained in greater detail hereinbelow. FIG. 4 provides a perspective view of an exemplary system 40 which employs angular detection and includes three sensor modules 20 dispersed upon the circumference of a circle 58. In the pictured embodiment, modules 20 feature radiation shields 36. In the pictured embodiment, each module 20 rotates about an axis tangent to circle 58. This rotation allows tracking of the medical device as explained in greater detail hereinbelow. According to various embodiments of the invention, rotational motion or translational motion may be employed to facilitate the desired angular detection. According to the embodiment depicted in FIG. 4, sensor modules 20 are situated below the head of subject 54 such that the vertical distance between the plane of sensor modules 20 and the region of interest within the head is approximately equal to the radius of circle 58. This arrangement assures that each of sensors 20 are deployed so that the predicted path of source 38 lies within boundaries 24. This arrangement may be repeatably and easily achieved by providing three of sensors 20 mounted on a board equipped with a raised headrest in the center of circle 58. This optionally permits a reclining chair or adjustable examination table to be easily positioned so that subject 54 is correctly placed relative to sensors 20 without an extensive measuring procedure. Positioning volume of system 40 is the set of spatial coordinates in which a location of source 38 may be determined. Positioning volume of system 40 has a size and/or shape dependent upon positions of sensor(s) 20, their design and/or their performance characteristics. Optionally, positioning volume of system 40 can be expressed as the intersection of boundaries of detection 24 of sensors 20. Optionally, two or more positioning volumes may be created, by using multiple sets of sensors 20. Optionally, these positioning volumes may overlap. The 3-dimensional position of the center of mass of a radiation source 38 is calculated by CPU 42 from the angle 32 measured by each of sensor modules 20, given the known location and rotation axis of each of modules 20. According to some embodiments of the invention, source 38 will be a piece of wire with a length of 1 to 10 mm. This range of lengths reflects currently available solid isotope sources 38 supplied as wires with useful diameters and capable of providing a sufficient number of DPM to allow efficient operation of system 40. System 40 determines the position of the middle of this piece of wire 38 and resolves the determined position to a single point, optionally indicating margins of error. Sensor module 20 includes at least one radiation detector 22. Radiation detector 22 is capable of receiving radiation from radiation source 38 attached to the medical device and producing an output signal 34. Radiation detector 22 may employ any technology which transforms incident radiation into a signal which can be relayed to CPU 42. If source 38 is a gamma radiation source, radiation detector 22 may be, for example, an ionization chamber, a Geiger-Mueller Counter, a scintillation detector, a semiconductor diode detector, a proportion counter or a micro channel plate based detector. Radiation detectors 22 of various types are commercially available from, for example, EVproducts (Saxonburg Pa., USA); Hammatsu Photonics (Hamamatsu City, Shizuoaka, Japan); Constellation Technology, (Largo, Fla., USA); Soltec Corporation (San Fernando Calif., USA); Thermo Electron Corporation, (Waltham Mass., USA): Bruker-biosciences (Billerica Mass., USA); Saint Gobain crystals (Newbury Ohio, USA) and Silicon Sensor GMBH (Germany). A suitable commercially available radiation detector 22 can be incorporated into the context of system 40 as part of sensor 20. Embodiments of the invention which rely upon a source 38 producing a small number of DPM and S types of detectors 22 which offer good sensitivity (i.e. high ratio between CPM and DPM) will improve the performance of sensor modules 20. As the distance between sensor 20 and source 38 increases, this consideration becomes more relevant. Embodiments of the invention which rely upon source 38 with a greater DPM output may permit use of less sensitive radiation detectors 22. Various types of sensor modules 20 are described in greater detail hereinbelow. System 40 further includes radiation source 38 capable of providing a sufficient amount of radiation for location and/or tracking at a rate which will not adversely affect a procedure being carried out by the medical device. For most medical procedures, 10 locations/second is sufficient to allow an operator of system 40 to comfortably navigate the medical device to a desired location. Based upon results from a computerized simulation described in greater detail hereinbelow, the amount of radiation to meet these criteria can be made low enough that it does not pose any significant risk to a patient undergoing a procedure of several hours duration with source 38 inside their body. Alternatively or additionally, the amount may be made low enough so that an operator of system 40 is not exposed to any significant risk from radiation exposure over time as explained hereinbelow. For example, using Iridium-192 increasing the activity of radiation source 38 from 0.01 mCi to 0.5 mCi improves accuracy only by a factor of 2 (FIG. 9B). However, activity levels below 0.1 mCi adversely affect response time (FIG. 9A). Activities greater than 0.1 mCi do not significantly improve response time. An activity of 0.05 mCi offers an acceptable trade-off between latency and accuracy as described in greater detail hereinbelow and provides a good compromise between performance and radiation dose. A 0.05 mCi source 38 meets permits system 40 to achieve adequate speed and accuracy with an amount of radiation produced so low that it may be safely handled without gloves. Radiation exposure for the patient from a 0.05 mCi source 38 is only eight times greater than average absorbed background radiation in the United States. For purposes of comparison to previously available alternatives, a 0.05 mCi source 38 exposes the patient to an Effective Dose Equivalent (EDE) of 0.0022 mSv/hr. A typical fluoroscopy guided procedure has an EDE of 1-35mSV per procedure and a typical Nuclear Medicine procedure has an EDE of 5 mSv. Thus, some embodiments of the invention may be employed to significantly reduce patient radiation exposure. Medical personnel are optionally exposed to even less radiation, with the level of exposure decreasing in proportion to the square of the intervening distance. For example, a doctor located one meter from a 0.05 mCi source 38 and performing procedures for 6 hours per day, 5 days a week, 52 weeks a year would accumulate a total annual EDE of 0.22 mSv. This is approximately 5% of the radiation exposure level at which exposure monitoring is generally implemented. This level of exposure corresponds to 1.4 e−4 mSV/hr which is orders of magnitude less than the 1-12 mSv/hr associated with a typical dose from fluoroscopic procedures. Iridium-192 has been used as an example because it is already approved for use in medical applications and is generally considered safe to introduce into the body of a subject. However this isotope is only an illustrative example of a suitable source 38, and should not be construed as a limitation of system 40. When choosing an isotope for use in the context of system 40, activity (DPM), type of radiation and/or half life may be considered. Activity has been discussed above. In addition, it is generally desired that disintegration events be detectable with reasonable efficiency at the relevant distance, for example 20-50 cm. Long half lives may be preferred because they make inventory control easier and reduce total costs in the long run by reducing waste. However, short half lives may reduce concerns over radioactive materials and/or may allow smaller sources to be used. According to some embodiments of the invention, source 38 is a source of positron emissions. According to these embodiments, sensors 20 determine a direction from which photons released as a result of positron/electron collisions originate. This difference optionally does not affect accuracy of a determined location to any significant degree because the distance traveled by a positron away from source 38 before it meets an electron is generally very small. Use of positrons in source 38 can effectively amplify total ionizing radiation emissions available for detection. Optionally, the use of multiple detector may allow the detection of pairs of positron annihilation events to be detected. Other examples of source types include gamma sources, alpha sources, electron sources and neutron sources. Regardless of the isotope, source 38 may be incorporated into a medical device (e.g. guidewire or catheter) which is to be tracked. Incorporation may be, for example, at or near the guidewire tip and/or at a different location in a catheter or in an implant. The source of ionizing radiation may be integrally formed with, or attached to, a portion of the guidewire or to a portion of the medical device. Attachment may be achieved, for example by gluing, welding or insertion of the source into a dedicated receptacle on the device. Attachment may also be achieved by supplying the source as an adhesive tag (e.g. a crack and peel sticker), paint or glue applicable to the medical device. Optionally, the source of ionizing radiation is supplied as a solid, for example a length of wire including a radioactive isotope. A short piece of wire containing the desired isotope may be affixed to the guidewire or medical device. This results in co-localization of the medical device and the source of radiation. Affixation may be accomplished, for example, by co-extruding the solid source with the guidewire during the manufacture of the guide wire. Alternately, or additionally, the source of ionizing radiation may be supplied as a radioactive paint which can be applied to the medical device and/or the guidewire. Regardless of the exact form in which the ionizing radiation source is supplied, or affixed to the guidewire or medical device, it should not leave any significant radioactive residue in the body of the subject after removal from the body at the end of a medical procedure. While source 38 is illustrated as a single item for clarity, two or more sources 38 may be tracked concurrently by system 40. System 40 may identify multiple sources 38 by a variety of means including, but not limited to, discrete position or path, frequency of radiation, energy of radiation or type of radiation. According to some embodiments of the invention, use of two or more resolvable sources 38 provides orientation information about the item being tracked. In other words, these embodiments permit determination of not only a 3-dimensional position defined by co-ordinates X, Y and Z, but also information about the orientation of the tracked object at the defined location. This feature is relevant in a medical context when a non-symmetrical tool is employed. System 40 may include a channel of communication 48 capable of conveying a data signal between the one or more sensor modules 20 and a computerized processing unit (CPU) 42. Channel of communication may be wired or wireless or a combination thereof. Wired channels of communication include, but are not limited to direct cable connection, telephone connection via public switched telephone network (PSTN), fiber optic connection and construction of system 40 as an integrated physical unit with no externally apparent wires. Wireless channels of communication include, but are not limited to infrared transmission, radio frequency transmission, cellular telephone transmission and satellite mediated communication. The exact nature of channel of communication 48 is not central to operation of system 40 so long as signal transmission permits the desired refresh rate. Channels of communication 48 may optionally permit system 40 to be operated in the context of telemedicine. Alternately, or additionally, channels of communication 48 may serve to increase the distance between source 38 and medical personnel as a means of reducing radiation exposure to the medical personnel to a desired degree. CPU 42 is designed and conFigured to receive output signal 34 via channel of communication 48 and translate output signal 34 to directional information concerning radiation source 38. This directional information may be expressed as, for example, a plane in which radiation source 38 resides. Output signal 34 includes at least rotation angle 32. Optionally, output signal 34 may also include a signal strength indicating component indicating receipt of a signal from source 38. Receipt of a signal from source 38 may be indicated as either a binary signal (yes/no) or a signal magnitude (e.g. counts per minute). According to various embodiments of the invention, output signal 34 may be either digital or analog. Translation of an analog signal to a digital signal may be performed either by sensor module 20 or CPU 42. In some cases, locating radiation source 38 in a single plane is sufficient. However, in most embodiments of the invention, it is desirable that CPU 42 receives two of output signals 34 and computes an intersection. If output signals 34 are expressed as planes, this produces a linear intersection 44 of two of the planes. This locates radiation source 38 upon the linear intersection 44. Optionally, results 44 of this calculation are displayed on a display device 43 as described in greater detail hereinbelow. In additional embodiments of the invention, CPU 42 receives at least three of output signals 34 and computes their intersection. If output signals 34 are expressed as planes and sensors 20 are positioned on the circumference of circle 58, this produces a point of intersection 44 of at least three planes, thereby locating radiation source 38 at the calculated point of intersection 44. Because system 40 is most often employed to track a medical instrument during a medical procedure, CPU 42 is often employed to compute the point of intersection repeatedly at predetermined intervals so that a position of radiation source 38 as a function of time may be plotted (see FIG. 10 a). The accuracy of each plotted position and of the plot as a whole may be influenced by the activity of source 38, the accuracy and response time of sensors 20 and the speed at which the implanted medical device is moving through subject 54. Because medical procedures generally favor precision over speed, an operator of system 40 may compensate for deficiencies in source 38, or accuracy or response time of sensors 20, by reducing the rate of travel of the medical device being employed for the procedure. FIG. 10B illustrates output of a simulated system 40 with tracking accuracy in the range of ±2 mm. CPU 42 may also optionally employ channel of communication 48 to send various signals to sensor module(s) 20 as detailed hereinbelow. Alternately, or additionally, CPU 42 may also optionally employ channel of communication 48 to send various signals to the medical device. According to various embodiments of the invention, system 40 may be employed in the context of procedures including, but not limited to, angioplasty (e.g. balloon angioplasty), deployment procedures (e.g. stent placement or implantation of radioactive seeds for brachytherapy), biopsy procedures, excision procedures and ablation procedures. While CPU 42 is depicted as a single physical unit, a greater number of physically distinct CPUs might actually be employed in some embodiments of the invention. For example, some functions, or portions of functions, ascribed to CPU 42 might be performed by processors installed in sensor modules 20. For purposes of this specification and the accompanying claims, a plurality of processors acting in concert to locate source 38 as described herein should be viewed collectively as CPU 42. According to some embodiments of the invention, system 40 concurrently employs three or more sensor modules 20 in order to concurrently receive three or more output signals 34 and compute three or more directions indicating signal source 38. If the directions are expressed as planes, the three or more planes intersect in a single point. However, system 40 includes alternate embodiments which employ two, or even one, sensor module 20 to localize source 38 to a single point. This may be achieved in several different ways as described hereinbelow. According to some embodiments of system 40 at least one of sensor module 20 is capable of rotating the at least one radiation detector 22 through a series of positions. Each position is defined by a rotation angle 32 so that receiving the radiation from source 38 upon detector 22 varies with rotation angle 32. This rotation may be accomplished in a variety of ways. For example, rotation mechanism 26 may be operated by feedback from 28 from radiation detector 22 according to a rule with amount of received radiation as a variable. Alternately, rotation mechanism 26 may be operated by a signal from CPU 42 according to a rule including amount of received radiation and/or time as variables. Alternately, rotation mechanism 26 may rotate radiation detector 22 according to a fixed schedule, with no regard to how much radiation impinges upon radiation detector 22 at any particular rotation angle 32. Rotation mechanism 26 may employ a wide variety of different mechanisms for achieving rotation angle 32. These mechanisms include, but are not limited to, mechanical mechanisms, hydraulic mechanisms, pneumatic mechanisms, electric mechanisms, electronic mechanisms and piezoelectric mechanisms. Optionally, an independent angle measuring element 30 may be employed to more accurately ascertain the actual rotation angle 32. Although angle measuring element 30 is depicted as a physically distinct component in FIGS. 1, 2 and 3, it could be physically integrated into rotation mechanism 26 without affecting performance of system 40 to any significant degree. Regardless of the exact operational details, the objective is to detect the rotation angle 32 at which sensor module 20 is pointing directly towards source 38. This angle will be referred to as the target rotation angle 32. According to some embodiments of system 40, radiation detector 22 (FIGS. 3, 5, 6A and 6B) includes at least one first radiation detector 22A and at least one second radiation detector 22B. These embodiments of system 40 rely upon comparison of output signals 34 from radiation detectors 22A and 22B for each rotation angle 32. A target angle of rotation 32 which produces output signals 34 from radiation detectors 22A and 22B with a known relationship indicates that radiation detectors 22A and 22B are both facing source 38 to the same degree. When radiation detectors 22A and 22B have identical receiving areas, the known relationship is equality. This target angle of rotation 32 is employed to determine a plane in which source 38 resides. In order to increase the sensitivity of system 40 to small differences between output signals 34 from radiation detectors 22A and 22B it is possible to introduce one or more radiation shields 36 at a fixed angle with respect to radiation detectors 22A and 22B. Radiation Shield 36 causes a magnitude of the component of output signal 34 from first radiation detector 22A and a magnitude of the component of output signal 34 from second radiation detector 22B to each vary with rotation angle 32 (see FIG. 3). Radiation shield 36 differentially shadows either radiation detectors 22A or 22B depending upon the relationship between angles of incidence 39 and 41. At some angle of rotation 32, neither radiation detector 22A nor 22B will be shadowed by radiation shield 36. This angle of rotation 32 is employed to determine a plane in which source 38 resides. This configuration insures that small variations from this target angle of rotation 32 cause relatively large differences in the output signals 34 from radiation detectors 22A and 22B because of the shadow effect. Therefore, use of radiation shield 36 in sensor module 20 increases the sensitivity of system 40. This increased sensitivity permits sensor module 20 to function effectively even with a low number of detectable radioactive counts. FIG. 6A illustrates an additional embodiment of sensor module 20 in which the radiation shield includes a primary radiation shield 36 located between first radiation detector 22A and second radiation detector 22B. The picture embodiment also includes a series of first additional radiation shields (36A1, 36A2, and 36A3) which divide first radiation detector 22A into a series of first radiation detectors and interfere with incident radiation directed towards first radiation detector 22A. The pictured embodiment also includes a series of second additional radiation shields (36B1, 36B2, and 36B3) which divide second radiation detector 22B into a series of second radiation detectors and interfere with incident radiation directed towards second radiation detector 22B. This configuration can insure that even smaller variations from target rotation angle 32 cause relatively large differences in the output signals 34 from radiation detectors 22A and 22B by increasing the shadow effect in proportion to the number of additional radiation shields (36A1, 36A2, 36A3, 36B1, 36B2, and 36B3 in the pictured embodiment). Therefore, use of additional radiation shields (e.g. 36A1, 36A2, 36A3, 36B1, 36B2, and 36B3) in sensor module 20 may serve to achieve an additional increase in sensitivity of system 40. Optionally, secondary radiation shields (36A1, 36A2, 36A3, 36B1, 36B2, and 36B3 in the pictured embodiment) are inclined towards primary radiation shield 36. The angle of secondary radiation shields 36A1, 36A2, 36A3, 36B1, 36B2, and 36B3 towards primary shield 36 can be changed, for example, using a motor to improve focus and/or define imaging volume. A similar effect may be achieved by holding radiation detectors 22A and 22B at a fixed angle and subjecting radiation shield(s) 36 (FIG. 6B) to angular displacement. Therefore, system 40 also includes embodiments in which radiation detector 22 includes at least one first radiation detector 22A and at least one second radiation detector 22B and output signal 34 includes discrete components from detectors 22A and 22B with at least one radiation shield 36 rotatable about an axis of shield rotation through an angle of shield rotation 32 so that a magnitude of discrete components of output signal 34 from detectors 22A and 22B each vary as a function of the angle of shield rotation 32. Referring now to FIG. 5, alternate embodiments of sensor module 20 of system 40 are conFigured so that radiation detector 22 includes a plurality of radiation detectors 22 and a plurality of protruding radiation shields 36 interspersed between the plurality of radiation detectors 22. According to these embodiments, plurality of radiation detectors 22 is organized in pairs, each pair having a first member 21 and a second member 23 and each protruding radiation shield 36 of the plurality of protruding radiation shields is located between first member 21 and second member 23 of the pair of radiation detectors 22. According to this embodiment, sensor module 20 is capable of rotating the radiation detectors 22 through a series of rotation angles 32 so that the receiving the radiation from radiation source 38 upon radiation detectors 22 varies with rotation angle 32. Each radiation detector produces an output signal 34. CPU 42 sums output signals 34 from all first members 21 to produce a first sum and all second members 23 to produce a second sum. Assuming that all of radiation detectors 22 are identical, when the sensor is aimed directly at the center of mass of source 38 (target rotation angle 32), the first sum and the second sum are equivalent. This embodiment insures that the total output for the entire module 20 increases rapidly with even a very slight change in rotation angle 32 in either direction. Alternately, or additionally, the sign of the total output for the entire module 20 indicates the direction of rotation required to reach the desired rotation angle 32 at which total output for the entire module 20. Thus, this configuration serves to increase both speed of operation and overall accuracy of system 40. This type of sensor module 20 may be operated (for example) by implementation of a first algorithm summing gamma ray impacts from source 38 for a period of time and allowing CPU 42 to decide, based on the sign of total output for the entire module 20, in which direction and to what degree to rotate radiation detectors 22 in an effort to reach a desired rotation angle 32. Alternately, CPU 42 may (for example) implement a second algorithm rotates radiation detectors 22 a very small amount in response to every detected count. Performance data presented herein is based upon a simulation of the second algorithm, but the first algorithm is believed to be equally useful. According to additional embodiments of system 40, a single sensor module 20 may be employed to determine two intersecting planes in which source 38 resides. This may be achieved, for example, by revolution of sensor module 20 or by moving sensor module 20 to a new location. According to some embodiments of the invention, sensor module 20 may be additionally capable of revolving radiation detector 22 about an axis of revolution 25 through an angle of revolution 29. Revolution is produced by a revolution mechanism 27 which may function in a variety of ways as described hereinabove for rotation mechanism 26. According to these embodiments of the invention angle of revolution 29 is included as a component of the orientation of sensor module 20 and is included in output signal 34. Revolution may be employed in the context of any or all of the sensor module 20 configurations described hereinabove and hereinbelow. Revolution may occur, for example, in response to a revolution signal 46 transmitted to sensor module 20 from CPU 42 via channel of communication 48. According to additional embodiments of the invention, sensor module 20 includes a locomotion device 31 capable of imparting translational motion 33 to module 20 so that the location of module 20 is changed. Locomotion may be initiated, for example, in response to a translational motion signal 46 transmitted to sensor module 20 from CPU 42 via channel of communication 48. According to various embodiments of the invention, locomotion may be used to either permit a single sensor module 20 to operate from multiple locations or to provide angular sensitivity to sensor module 20. In other words, translational motion may be used as a substitute for angular displacement, especially in embodiments which employ at least one radiation shied 36. In embodiments which employs translational motional, translation of a single sensor 20 in a first dimension permits acquisition of a first set of directional information. For example, in the embodiment of system 40 depicted in FIG. 4, successive vertical displacement of sensor 20A could be used to determine a first plane in which source 38 resides. Successive horizontal displacement of sensor 20B could be used to determine a second plane in which source 38 resides. Alternately, or additionally, a single sensor 20 may be subject to both vertical and horizontal displacement. Successive vertical and horizontal displacement permits a single sensor 20 to determine two non-parallel planes in which source 38 resides. Concurrent vertical and horizontal displacement along a single line permits a single sensor 20 to determine a single plane in which source 38 resides. Determination of intersection of 2 or 3 or more planes is as determined above. Optionally locomotion and revolution may be employed in the same embodiment of the invention. Optionally, system 40 further includes an imaging module 50 including an image capture device 56 capable of providing an image signal 52 to CPU 42. Imaging module 50 optionally includes an interface to facilitate communication with CPU 42. CPU 42 is capable of translating image signal 52 to an image of a portion of the body of subject 54. According to various embodiments of the invention, imaging module 50 may rely upon fluoroscopy, MRI, CT or 2D or multi-plane or 3D angiography. For intracranial procedures, imaging generally need not be conducted concurrently with the procedure. This is because the brain does not shift much within the skull. Images captured a day or more before a procedure, or a few hours before a procedure, or just prior to a procedure, may be employed. According to alternate embodiments of the invention, image data is acquired separately (i.e. outside of system 40) and provided to CPU 42 for alignment. Alignment methods and the algorithms for anatomical image display and tracking information overlay are reviewed in Jolesz (1997) Radiology. 204(3):601-12. The Jolesz article, together with references cited therein, provides enablement for a skilled artisan to accomplish concurrent display and alignment of image data and tracking data. The Jolesz reference, together with references cited therein, are fully incorporated herein by reference to the same extent as if each individual reference had been individually cited and incorporated by reference. In an exemplary embodiment of the invention, the location(s) determined by system 40 are registered with respect to the image. This may be accomplished, for example by registering system 40 and/or sensors 20 to image capture device 56. Regardless of which type of sensor module 20 is employed, system 40 may include a display device 43 in communication with CPU 42. Display device 43 may display the image of the portion of the body of the subject with a determined position of the medical device (corresponding to a position of source 38) superimposed on the image of the portion of the body of the subject. The superimposed determined position is optionally represented as a point on display screen 43. Optionally the point is surrounded by an indicator of a desired confidence interval determined by CPU 42. The confidence interval may be displayed, for example, as a circle, as two or more intersecting lines or as one or more pairs of brackets. Alternately, or additionally, display device 43 may display position coordinates of a determined position of the medical device (e.g., corresponding to a position of source 38 at a tip of guidewire). Display device 43 may be provided with a 3-dimensional angiography dataset from CT, MRI, or 3-D angiography, imaged either during the procedure or prior to the procedure. Appropriate software can be employed to extract a 3-D model of the vasculature from the angiography dataset, and display this model using standard modes of 3-D model visualization. A 3-dimensional graphical representation of the guidewire or catheter can be integrated into the 3-D model of the vasculature and updated with minimal temporal delay based on the position information provided by system 40 to indicate the position of the guidewire or catheter within the vasculature. The entire 3-D model including the vasculature and the catheter can be zoomed, rotated, and otherwise interactively manipulated by the user during performance of the procedure in order to provide the best possible visualization. Optionally, system 40 may further include one or more user input devices 45 (e.g. keyboard, mouse, touch screen, track pad, trackball, microphone, joystick or stylus). Input device 45 may be used to adjust an image as described hereinabove on display device 43 and/or to issue command signals to various components of system 40 such as rotation mechanism 26, revolution mechanism 27, locomotion device 31 or image capture device 56. The invention optionally includes a sensor 20 for determining a plane in which a radiation source resides as depicted in FIG. 3 and described hereinabove. Briefly, the sensor 20 includes at least one radiation detector 22, the at least one radiation detector capable of receiving radiation from radiation source 38 and producing an output signal 34. Sensor 20 is capable of rotating radiation detector 22 through a series of positions, each position defined by a rotation angle 32 so that the receiving the radiation from radiation source 38 upon radiation detector 22 varies with rotation angle 32. Rotation is optionally achieved as described hereinabove. A rotation angle 32 which produces a maximum output signal indicates the plane in which radiation source 38 resides. According to some embodiments of sensor 20, radiation detector 22 includes at least one first radiation detector 22A and at least one second radiation detector 22B and output signal 34 includes a first output signal from first radiation detector 22A and a second output signal from radiation detector 22B. According to some embodiments of sensor 20, at least one radiation shield 36 is further installed at a fixed angle with respect to detectors 22A and 22B. As a result, a magnitude of the first output signal 34 from the at least one first radiation detector and a magnitude of the second output signal 34 from radiation detector 22B each vary with rotation angle 32 as detailed hereinabove. A sensor 20 for determining a plane in which a radiation source resides and characterized by at least one radiation shield 36 rotatable about an axis of shield rotation through an angle of shield rotation 32 as described hereinabove in detail (FIG. 6B) is an additional embodiment of the invention Sensor 20 for determining a plane in which a radiation source resides as depicted in FIG. 5 and described hereinabove is an additional embodiment of the invention. According to alternate embodiments of the invention, a method 400 (FIG. 11) of determining a location of a medical device within a body of a subject is provided. Method 400 includes co-localizing 401 a radioactive signal source 38 with a medical device. Co-localization may be achieved, for example, by providing a device having a radiation source associated therewith or by associating a radiation source with a device. Method 400 further includes determining 402 a first plane in which the omni directional signal generator resides, further determining 403 a second plane in which the omni directional signal generator resides, calculating 404 a linear intersection of the first plane and the second plane as a means of determining a line upon which the medical device resides. Method 400 optionally includes further determining 405 at least one additional plane in source 38 resides. Method 400 optionally includes calculating 406 a point of intersection of the first plane, the second plane and the at least one additional plane as a means of determining a location of the medical device. Optionally, method 400 is successively iterated 408 so that a series of location are generated to track an implanted medical device in motion. Calculated locations may be displayed 410 in conjunction with anatomical imaging data if desired. The various aspects and features of system 40 and/or sensors 20 described in detail hereinabove may be employed to enable or enhance performance of method 400. System 40 and method 400 may employ various mathematical algorithms to compute the location of source 38. One example of an algorithm suited for use in the context of some embodiments of the invention calculates the position of source 38 from sensor output signal 34, sensor position, and sensor orientation (i.e. rotation angle 32) of three sensors as follows: 1) the plane defined by each sensor module 20 is calculated using an equation of the formAx+By+Cz=D 2) the coefficients A,B,C, and D are calculated as follows: a. Three non-collinear points are defined within sensor 20's internal reference frame. b. These three points are then shifted by the position of sensor 20 and rotated by the sensor orientation. This defines the plane in which source 38 would lie if output signal 34 was zero. c. These three points are then rotated about the axis of rotation angle 32 of sensor 20 by rotation angle 32 indicated by output signal 34. This defines the plane in which source 38 lies as measured by a particular sensor 20. d. Using the x,y,z coordinates of the three points, x1,y1,z1,x2,y2,z2,x3,y3,z3 in the following equations, A, B, C, and D are calculated as follows:A=y1(z2−z3)+y2(z3−z1)+y3(z1−z2) i.B=z1(x2−x3)+z2(x3−x1)+z3(x1−x2) ii.C=x1(y2−y3)+x2(y3−y1)+x3(y1−y2) iii.D=x1(y2*z3−y3*z2)+x2(y3*z1−y1*z3)+x3(y1*z2−y2*z1) iv.3) Calculation of A, B, C, and D for each of three sensors 20 produces a system of three equations in three unknowns: [ A 1 B 1 C 1 A 2 B 2 C 2 A 3 B 3 C 3 ] [ x y z ] = [ D 1 D 2 D 3 ] This system of equations can be solved to provide an exact solution for (x,y,z) (or part of the vector), the point of intersection of the three planes, which is the position of the source 38. Use of additional sensors 20 improves the accuracy by averaging the errors in the individual sensors, and may also provide a means of estimating the accuracy of the position measurement by indicating the extent to which the sensors agree with each other. When 4 or more sensors are used, the algorithm is as follows: Steps 1 and 2 above remain the same—the equation of the plane indicated by each sensor is calculated. Step 3 is modified as follows: 3) Once A, B, C, and D have been calculated for each of the sensors an over-determined system of more than three equations in three unknowns results: [ A 1 B 1 C 1 A 2 B 2 C 2 A 3 B 3 C 3 ⋮ ⋮ ⋮ ] [ x y z ] = [ D 1 D 2 D 3 ⋮ ] This over-determined system can be solved in a least square sense using methods familiar to those skilled in the art in order to obtain the best solution for (x,y,z), which is the most likely position of the tracked element. There is generally no exact solution due to the error in the sensor outputs, there may be no single point through which all of the planes pass. In order that the least square solution may be based on the error defined by the Euclidian distance between each plane and the solution for (x,y,z), it is necessary to scale all of the coefficients defining each plane by the lengths of their respective Normal vectors (the Normal vector is the vector defined by (A,B,C)). This is done by dividing A, B, C, and D by sqrt (A^2+B^2+C^2) before performing the least square solution. 4) The Euclidian distance between each of the planes and the calculated position can be used as a measure of the accuracy of the position measurement. Once the coefficients have been scaled by the length of the Normal vector, this distance can be calculated for each sensor as Ax+By+Cz−D. The mean value of the distances from each plane to the calculated position gives a measure of the extent to which all of the sensors agree on the position that was calculated. Overdetermined systems of equations may be solved using least square solution algorithms. Suitable least square algorithms are available as components of commercially available mathematics software packages. Optionally, other methods of solving equation sets as known in the art are used. Optionally, instead of a set of equations, other calculation methods are used, for example, neural networks, rule based methods and table look up methods in which the signals from the sensors are used to look-up or estimate a resulting position. In systems where the sensors move linearly, other solution methods may be used, for example, translating linear positions of the sensors into spatial coordinates of the source. In order to increase the accuracy and performance of system 40 and method 400, advance calibration may optionally be performed. The position and orientation of each of the sensor modules 20 can be calibrated instead of relying upon values based on the mechanical manufacturing of the system. The calibration procedure involves using system 40 to measure the 3-dimensional position of a source 38 at a number of known positions defined to a high degree of accuracy. Since the position of source 38 is known, the equations normally used to calculate the positions (described above) can now be used with the sensor positions and orientations as unknowns in order to solve for these values. Various minimization procedures are known in the art. The number of measurements needed to perform such a calibration may depends on the number of sensor modules 20 in system 40, since it is useful to make enough measurements to provide more equations than unknowns. This calibration procedure also defines the origin and frame of reference relative to which system 40 measures the position of the source, and can therefore provide alignment between the tracking system and another system to which it is permanently attached, such as a fluoroscopy system or other imaging system. In an exemplary embodiment of the invention, once a position of the source is known, the sensors can remain aimed at the source and not change their orientation. Optionally, if the source moves, determined for example, by a significant change in detected radiation (e.g., a drop of 30%, 50%, 70%, 90% or a greater or intermediate drop), the sensor is moved to scan a range of angles where the source is expected to be in. Optionally, the sensor generates a signal indicating on which side of the sensor the source is located, for example as described below. Optionally, the range of scanning depends on an expected angular velocity of the source, for example, based on the procedure, based on the history and/or based on a user threshold. If scanning within the range fails, the range is optionally increased. Optionally, if multiple target sources are provided (e.g., ones with different count rates and/or different energy of emission), the sensors jump between target angles. Optionally, a steady sweep between a range of angles encompassing the two (or more) sources is provided. Optionally, sweeping is provided by ultrasonic or sonic vibrations of the sensor or part thereof, for example, comprising a range of angles 1, 5, 10, 20, 50 or more times a second. Optionally, the amplitude of the vibration determines the range of angles. Optionally, the sensors or sensor portion is in resonance with one or more vibration frequencies. Optionally, scanning of the sensors, at least in a small range of angles, such as less than 10 or less than 5 or less than 1 degree, is provided even when the sensor is locked on a target source. The tracking accuracy of system 40 using Iridium-192 as source 38 as described hereinabove has been evaluated only by computer simulation. The simulation is a model of the random distribution of gamma photons emitted by a source 38 within a model head and absorbed by the photon-sensitive elements 22 in a compound differential sensor unit 20 of the type illustrated in FIG. 5. According to the simulation, radiation detector 22 of sensor module 20 rotates so that a new rotation angle 32 is defined every time a photon is absorbed by detector 22. If the photon is absorbed by a positive radiation detector 21 then radiation detector 22 of sensor module 20 rotates in the positive direction, and if it is absorbed by a negative sensor 23 then radiation detector 22 of sensor module 20 rotates in the negative direction. Total output signal 34 of sensor module 20 is its average orientation during the sample time. According to the simulation, performance is defined by two parameters, however other parameters may be used in a practical system: 1) The Root Mean Square (RMS) error when the target is stationary 2) The time to indicate a 9 mm change in calculated location after a 10 mm change in actual location of source 38.The following parameter values are fixed in the simulation: 1) Distance from the source to the sensor=25 cm (worst case distance) 2) Source distance for which sensor is geometrically optimized=25 cm 3) Width of photon-sensitive surface in each sub sensor=2 mm (18 in FIG. 5) 4) Sensor length=10 cm (14 in FIG. 5) 5) Height of dividing walls between sensors=5 cm (35 in FIG. 5) 6) Width of dividing walls at their base=4 nm (37 in FIG. 5) 7) Number of subsensors defined by walls in the compound sensor=7 (36 in FIG. 5) 8) Sensor sensitivity (fraction of incoming gamma rays which are detected)=0.3The simulation evaluated and optimized the following parameters with respect to influence on performance: 1) Rotation magnitude per absorbed photon (FIGS. 7a and 7b) 2) Sample time (FIGS. 8A and 8B) 3) Photons per second (source activity level) (FIGS. 9A and 9B) 4) Overall tracking accuracy (FIGS. 10a and 10b) The simulation determined that as rotation per photon impact increases, response time is improved (FIG. 7a). However, as rotation per photon impact increases, RMS position error also increases (FIG. 7b). There is clearly a trade-off between latency and accuracy. This parameter can be modified in real-time in order to optimize the trade-off using a motion detection algorithm as described hereinbelow. The simulation determined that sample time no significant impact on latency or accuracy (FIGS. 8A and 8B). This is because for small values of rotation per impact, the number of impacts per sample has minimal effect on accuracy and only determines the latency (the total amount of rotation per sample). However, if the number of impacts per sample is reduced as a result of a reduction in the sample time, then the reduction in sample time exactly compensates for the reduced response per sample leaving the latency unchanged. Radioactivity (number of photons emitted per second) has a very slight effect on accuracy, improving accuracy only by a factor of 2 as the activity increases from 0.01 mCi up to 0.5 mCi (FIG. 9B). It has a drastic effect on response time at low activity levels (FIG. 9A) where there simply are not enough photons to induce rapid rotation, however at activity levels above 0.1 mCi there is minimal improvement with increased activity level. Optimization of this trade-off between latency and accuracy (see below) is achieved with 0.05 mCi. This specific activity provides a good compromise between performance and radiation dose, providing a performance suitable for a typical medical application without imposing a safety risk to the patient or doctor. In order to optimize the tradeoff between accuracy and latency a motion detection algorithm was employed to increase the rotation per photon during motion of tracked source 38. This decreased latency time and increased accuracy. In the simulation, the percentage of photons hitting receiving elements 22 classed as positive 21 versus those classed as negative 23 was used as an indication of motion of tracked source 38. As the percentage moved farther away from 50% the rotation per photon was increased, reducing latency at the expense of accuracy during motion. In other words, system 40 begins by moving towards an estimated target rotation angle 32 in large steps. As estimated target rotation angle 32 is approached, the size of the steps is decreased. If target rotation angle 32 is passed, a small compensatory step in the opposite direction is employed. Results are summarized graphically in FIGS. 10a and 10b. Briefly, the RMS error of system 40 tracking a moving source 38 is 0.71 mm on average. Location of a stationary source 38 by system 40 produces an rms error of 0.62 mm. In summary, the simulation results indicate that with an activity of 0.05 mCi of 192Ir, compound differential sensors of the type illustrated in FIG. 5, and a motion detection algorithm which trades-off latency against accuracy, system 40 can achieve overall accuracy of approximately 1 mm RMS. Simulated sensitivity of sensor module 20 to changes in rotation angle 32 is illustrated in FIG. 12 which is a plot of output signal 34 as a function of rotation relative to target rotation angle 32 for a sensor of the type indicated in FIG. 5. The graph was produced using the formula:Total Output 34=A/(A+B) Where A is the sum of all right side sensors 21; and B is the sum of all left side sensors 23 and B The total range of output 34 (Y axis) from sensor 20 was arbitrarily defined as being in a range from 0 to 1. On the X axis, 0 indicates the angle of rotation 32 which indicates the direction of source 38. The total rotational range of sensor 20 was ±32 milliradians from this target rotation angle 32. Deviation of more than 32 milliradians away from target rotation angle 32 produced an output 34 of either 0 or 1, indicating the direction of rotation for a return to target rotation angle 32, but not the amount of rotation to reach target rotation angle 32. When output 34 is 0 or 1, the only conclusion that can be drawn about deviation from target rotation angle 32 is that it is greater than 32 milliradians in the indicated direction. The graph of FIG. 12 depicts output 34 for target rotation angle 32 as the middle of the dynamic range (0.5). Therefore, if output 34 is 0.6, a correctional rotation of 10 milliradians in the plus direction is indicated to achieve target rotation angle 32. An output 34 of 0.6 indicates a correctional rotation with the same magnitude (10 milliradians), but in the minus direction. Another way of depicting the same information would be to indicate a total dynamic range of +0.5 to −0.5 on the Y axis. This middle of the range could be zero, with one direction being positive and the other negative, or it can be any arbitrary number, with one direction being higher and the other lower. As illustrated in FIG. 12, at target angle 32 simulated sensitivity of sensor 20 to rotation is approximately 1% of the dynamic range per milliradian of rotation. This 1% sensitivity per milliradian is sufficient to provide the desired accuracy (1 mm rms), using a 5 cm×10 cm sensor module 20 with shields 36 having a height 35 of 5 cm interspersed between radiation detectors 22 and located 25 cm from source 38 with an activity of 0.05 mCi. Adjusting accuracy parameters, increasing the size of detectors 22, reducing the distance between sensor 20 and source 38 and increasing the activity of source 38 could each serve to reduce the level of directional sensitivity desired of sensor 20. Simulation results (not shown) using a sensor 20 of the type shown in FIG. 6A were similar to those described hereinabove. System 40 and/or sensors 20 rely upon execution of various commands and analysis and translation of various data inputs. Any of these commands, analyses or translations may be accomplished by software, hardware or firmware according to various alternative embodiments. In an exemplary embodiment of the invention, machine readable media contain instructions for transforming output signal 34 from one or more sensor modules 20 into position co-ordinates of source 38, optionally according to method 400. In an exemplary embodiment of the invention, CPU 42 executes instructions for transforming output signal 34 from one or more sensor modules 20 into position co-ordinates of source 38, optionally according to method 400. According to an exemplary embodiment of the invention a trackable medical device is manufactured by incorporating into or fixedly attaching a detectable amount of a radioactive isotope to the medical device. The radioactive isotope may or may not have a medical function according to various embodiments. Optionally, the radioactivity of the isotope has no medical function. Optionally, the radioactive isotope may be selected so that it can be used in the body without a protective coating without adverse reaction with tissue. In an exemplary embodiment of the invention, the detectable amount of isotope is in the range of 0.5 mCi to 0.001 mCi. Use of isotope source 38 with an activity in the lower portion of this range may depend on lower speeds of the device, sensitivity of detector(s) 22, distance from sensor 20. Optionally, at least 1, optionally at least 5, optionally at least 10, optionally at least 100 detectable counts per second are produced by the incorporated radioactive isotope. In the description and claims of the present application, each of the verbs “comprise”, “include” and “have” as well as any conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to necessarily limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments can be combined in all possible combinations including, but not limited to use of features described in the context of one embodiment in the context of any other embodiment. The scope of the invention is limited only by the following claims. |
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039792560 | claims | 1. In a nuclear reactor which includes first and second reactor safety channels coupled to the reactor, each of the first and second reactor safety channels being responsive to the same reactor parameter to develop first and second measurement signals respectively, with each of the first and second measurement signals having a magnitude which is a function of the reactor parameter being measured, a safety circuit for continuously monitoring the first and second reactor safety channels, comprising: first and second log amplifiers coupled to said first and second safety channels respectively, said first and second log amplifiers being responsive to said first and second measurement signals to develop first and second log measurement signals proportional to the log of said first and second measurement signals respectively, a summing circuit to which said log amplifiers are coupled developing a ratio signal being the subtraction of one of said log measurement signals from the other of said log measurement signals, an offset voltage circuit coupled to one of said first and second log amplifiers for applying a reference dc voltage thereto so that with the absolute values of said log measurements equal said ratio signal has a desired nonzero value, and a comparator circuit coupled to said summing circuit and responsive to said ratio signal to develop an alarm signal with the magnitude of said ratio signal being outside of a predetermined range of magnitudes. 2. The safety circuit of claim 1 wherein the absolute values of said predetermined range of magnitudes of said ratio signal are greater than zero and less than the magnitude which would exist with one of said log amplifiers being saturated. 3. The safety circuit of claim 2 further including control means coupled to said comparator means and responsive to said alarm signal to give a display thereof and to scram the reactor. |
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description | This application claims the benefit of DE 10 2011 083 206.8, filed on Sep. 22, 2011. This application also claims the benefit of DE 10 2012 211 816.0, filed on Jul. 6, 2012. The present embodiments relate to a device and a method to determine the position of a component that is moveable in a linear manner along an assigned axis according. In many technical applications, the position of moveable components is to be determined precisely. This may be achieved by integration over the movement trajectory of assigned drives (e.g., stepper motors or linear drives). For many applications such as, for example, in medical technology, measurement technology, optics or the like, the accuracy of such measurement methods is not sufficient. An example of the need for precise position determinations in medical technology may be found in the field of multi-leaf collimators. Multi-leaf collimators are used to shape the beam of an X-ray beam that may be generated by a linear accelerator in therapeutic radiation therapy. Such a collimator encompasses a plurality of leaves of a radio-opaque material (e.g., tungsten). The leaves are arranged in a moveable manner such that, by the positioning the leaves, the cross-sectional profile of the beam may be adjusted to match contours of the perimeter of an area of tissue located in the X-ray beam that is to be treated. This provides that the tissue to be treated (e.g., a tumor) receives the desired dose of radiation, while the surrounding tissue is exposed to as little radiation as possible. In modern methods of radiation therapy such as, for example, in dynamic arc irradiation, the position of the leaves is to be constantly adjusted since the beam moves in relation to the patient, and the contour of the perimeter of the tissue that is to be irradiated therefore changes as a function of an angular position of the beam to the patient. In intensity-modulated treatment, the aim of which is to distribute the radiation as regularly as possible in the zone to be irradiated and thus to make up for imbalances in the passage of radiation through the body, a constant adjustment of the position of the collimator leaves is provided. In order to provide a reliable operation of such a multi-leaf collimator, each position of the leaves is to be known precisely at all times. From the prior art, this may be achieved by installing a piezo transducer in direct contact with an edge of a respective leaf and generating surface waves in the leaf by using the piezo transducer. Such surface waves (e.g., edge waves) then run along the edge of the leaf and are reflected on a defined obstacle (e.g., on a corner of the leaf). The relative position of the leaf may be determined from a signal propagation time for the signal that has been transmitted or reflected. The disadvantage of the design of the prior art is that abrasion occurs between the moveable leaf and the piezo transducer. This may be reduced by providing targeted coatings on the piezo transducer using, for example, sputter coatings or adhesive wafers of hard material. However, there is still significant abrasion, restricting the life of the system and requiring costly inspections and maintenance. Comparable problems also occur when determining the position of other medical technology devices (e.g., in examination couches that are intended for use in investigations involving image-generating methods). The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a device and a method for determining a position of a component that is moveable in a linear manner along an assigned axis that allow a low-abrasion operation while providing reliable position determination are provided. To determine the position of a component that is moveable in a linear manner along at least one axis, a reference element extending in the direction of the axis is assigned to the component. The component may be brought into mechanical contact with the reference element. A piezo transducer is arranged on the reference element to generate and receive vibrations in the material used for the reference element. In contrast with the prior art, there is therefore no direct contact between the piezo transducer and the moveable component. For example, the piezo transducer is securely mounted and therefore does not have a contact surface that is in moveable contact with a further component. This completely avoids abrasion on the piezo transducer, such that there is no need for costly inspections and maintenance. In the device, the position of the component is determined by the generation of surface waves that are generated not in the leaf itself, but in the reference element. The surface waves emanating from the piezo transducer run along the reference element and are reflected at a point of contact between the reference element and the moveable component. The position of the component may be determined from the signal propagation time between the transmission of the signal and the signal being received and reflected. This allows a reliable position determination. The reference element may be configured as a panel arranged on a supporting frame. The panel-shaped design allows a good propagation of surface waves. In this design, it is useful if the moveable component is in mechanical contact with one edge of the reference element, on which the respective piezo transducer is arranged. Along the edge of such a panel-shaped reference element, a good wave propagation is possible. For example, along the edge, the waves are propagated as transverse waves while the waves run through the body of the reference element mainly in the form of longitudinal waves. The transverse waves may be reflected in a reliable manner and are therefore detected with a good signal-noise ratio. The mechanical contact between the moveable component and the reference element may be achieved using a sliding or rolling element. A mechanical contact of this kind allows a low-abrasion operation, such that long life is provided, and costly maintenance may essentially be avoided. In order to allow a reliable reflection of the signals generated by the piezo transducer, there may be a contact pressure of 5 to 10 N between the sliding or rolling element and the reference element. Advantageously, the reference element and the sliding or rolling element are magnetized. An option, for example, is the use of ferromagnetic (e.g., permanently magnetic) materials for the reference element and the sliding or rolling element. Through magnetization, the required contact pressure between the two elements may be generated without additional mechanical and hence abrasion-susceptible elements such as springs, for example, becoming necessary. A greater magnetic contact pressure between the sliding or rolling element and the reference element may be achieved if the sliding or rolling element is moveable in a groove of the reference element. In order to reduce the lateral contact between the sliding or rolling element and the groove and thus to avoid abrasion due to unnecessary friction, the groove may be conically shaped. As an alternative or addition thereto, side walls of the groove or side surfaces of the sliding or rolling element may be coated with a non-magnetic material such that, between the two elements, there are no magnetic forces that do not contribute to the desired contact pressure. This reduces the friction between the elements and thus reduces abrasion. In one embodiment, the device is configured to determine the position of a leaf in a leaf collimator for shaping a beam in an X-ray device. As a result of the small space the device uses, this may be suitable in order to allow precision in the adjustment of the leaves. In another embodiment, the device is configured to determine the position of an examination couch of a medical device. By using the device, the precision in the position adjustment (e.g., in examination couches in devices for image-generating methods) may be guaranteed. In one embodiment, a method for determining a position of a component that is moveable in a linear manner along at least one axis is provided. A piezo transducer that is attached to a reference element extending in the direction of the axis is used to generate a vibration signal in the reference element. This vibration signal (e.g., in the form of a surface wave or an edge wave) is reflected on a point of contact between the moveable component and the reference element. The vibration signal that is thus reflected is received again by the piezo transducer. A position of the point of contact on the reference element is determined from a time difference between transmission and reception. The position of the component in relation to the piezo transducer may thus be determined in a simple and reliable manner, and abrasion due to direct contact between the piezo transducer and the component may be avoided. In one embodiment, the vibration signal is generated on an edge of the reference element. The edge is in touching contact with the component. The edge offers an advantageous propagation path for the vibration signal. The vibration signal travels along the edge in the form of a transverse wave that may be reflected particularly well and may therefore be received with a good signal-noise ratio. The point of contact between the moveable component and the reference element may be generated by attaching a sliding or rolling element of the moveable component onto the edge of the reference element. This reduces the friction between the leaf and the reference element, such that abrasion is essentially avoided. To attach the sliding or rolling element (e.g., using magnetic forces), the sliding or rolling element and the reference element are magnetized. This dispenses with the need for mechanical elements to attach the two elements to each other such that abrasion is avoided. In one embodiment, a contact pressure of 5 to 10 N may be used in order to allow a good reflection of the vibration signal that has been received. The mode of operation of one embodiment of a device for the determination of a position of a component that is moveable in a linear manner along at least one axis is explained below with reference to the embodiment of a multi-leaf collimator. A multi-leaf collimator for therapeutic irradiation of tumors, for example, includes a plurality of leaves 10 that are moveable in a path of an X-ray beam. Through the movement of the leaves 10, which is provided by a mechanism that is not shown in the figure, a cross-sectional profile of the beam path may be shaped, and an adjustment may be made to match the contour of the perimeter of a tissue segment that is to be irradiated. In modern radio-therapeutic methods, the leaf position is adjusted dynamically in order, for example, to modulate the intensity of the radiation or, where there is a relative movement between the beam and the patient, to adjust a cross-sectional profile of the beam to match the perimeter contour that is a function of a respective angular position between the patient and the beam. In order to achieve a reliable irradiation level (e.g., to concentrate the maximum desired radiation intensity onto the tissue that is to be irradiated while the surrounding tissue is irradiated as little as possible and is therefore damaged as little as possible), the position of the leaf 10 is known precisely at all times. To achieve this, the multi-leaf collimator has a panel 12 that extends in a direction of the movement of the leaf 10 (e.g., in the direction of the arrow 14). A support 16, in which a rolling bearing 18 is arranged, is mounted on the leaf 10. The rolling bearing 18 runs along an edge 20 of the panel 12. To determine the position of the leaf 10, a piezo transducer 22 is arranged on the edge 20 of the panel 12. In order to measure the position of the leaf 10, a vibration is initiated by the piezo transducer 22 in the panel 12. This vibration is reflected as a transverse edge wave in a direction of the arrow 24 along the edge 20 and is reflected on the support point for the roller 18. The reflected wave travels back to the piezo transducer 22 and is received by the piezo transducer 22, travelling in an opposite direction to the original edge wave. From the propagation time of the original wave and of the reflected wave, the distance between the piezo transducer 22 and the support point for the roller 18 may be determined. The current position of the leaf 10 may be calculated from the determined distance between the piezo transducer 22 and the support point for the roller 18. In order to allow a reliable detection of the reflected wave (e.g., to achieve a high signal-noise ratio), the contact pressure of the roller 18 onto the edge 20 of the panel 12 may be around 5 to 10 N. In order to achieve such a contact pressure with a minimum mechanical outlay and minimum abrasion, the roller 18 and the panel 12 may be magnetized. For example, there is an option for using ferromagnetic (e.g., permanently magnetic) materials. The magnetization of the roller 18 may be arranged to be parallel to the axis 26 thereof. In order to achieve both a well-defined support point for the roller 18 and minimum abrasion between the roller 18 and the edge 20 during movement of the leaf 10, the roller 18 may run in a groove arranged in the edge 20. In order to achieve the aforementioned objectives, the roller 18 rests on the bottom of the groove and does not, however, touch side walls of the groove. A conical design of the groove may be used. In order to avoid unwanted forces between the roller 18 and the side walls of the groove, side surfaces of the roller 18 and the side walls of the groove are coated with non-magnetic materials, such that the force between the magnetized roller 18 and the magnetized panel 12 is advantageously directed onto the bottom of the groove. A multi-leaf collimator with low abrasion is created, since the piezo transducer, for example, is not in moveable contact with other components. This also leads to an improved transmission of vibrations, the result of which is a higher amplitude for the surface wave that travels along the edge 20. This again results in a more intensively reflected wave that, as a result of the improved transmission of vibrations to the piezo transducer 22, leads to a clear increase in the echo amplitude and hence to an improved signal-noise ratio. In addition, the use of magnetic rollers 18 on magnetic panels 12 leads to less force being exerted in the roller bearings and thus to reduced abrasion in the roller bearing, as a result of dispensing with the need for other mechanical power-generating systems such as springs, for example. The invention is of course not limited to the embodiment of a multi-leaf collimator that is described here by way of example. On the same basis, the position of any other components that are moveable in a linear manner may be determined. Examples of this are examination couches for medical devices, measurement equipment, optical instruments, machine tools or any other components. While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description. |
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description | This nonprovisional application claims priority under 35 U.S.C. §119(e) on U.S. Provisional Application No. 61/018,725 filed on Jan. 3, 2008 and under 35 U.S.C. §119(a) on U.S. Pat. No. 0,759,731 filed in France on Dec. 11, 2007, the entire contents of which are hereby incorporated by reference. The present invention relates in general to nuclear power stations comprising at least one high temperature reactor. More precisely, the invention relates, in accordance with a first aspect, to a nuclear power station of the type comprising: at least one high temperature reactor, comprising a core in which a plurality of fuel elements is arranged; a storage installation for fuel elements; means for transferring the fuel elements between the core and the storage installation. Each reactor must be shut down periodically in order to replace a portion of the fuel elements with new elements and reorganise the remaining elements. The spent fuel elements are transferred from the core to the storage installation associated with the reactor. They are then transferred from the storage installation to a centralised storage installation, which may be situated in the nuclear power station or at another site. Conversely, the new fuel elements are transferred from a storage unit situated on the nuclear power station site, to the dedicated storage installation of the reactor, then, when the fuel elements are replaced, into the reactor core. The transfer of fuel elements between the reactor and the storage installation dedicated to said reactor using a shielded transfer hood is known. The hood comprises a small barrel which may contain a plurality of fuel elements. It moves between the reactor and the storage installation by the main handling bridge of the nuclear power station. The transfer is performed by the sealed coupling of the hood to a removal aperture situated above the reactor core, then by transferring successively a plurality of fuel elements from the reactor core to the hood. Once the hood is full, the loading aperture of the hood is closed again, and the hood is moved to an unloading aperture situated in the upper biological protection slab of the storage installation. Next, the hood is coupled in a sealed manner to the aperture. The fuel elements are then unloaded from the hood. Once the unloading is finished, the hood is uncoupled, transported in the opposite direction to the reactor and coupled once more to the removal aperture in order to load other fuel elements. Transfers of new fuel elements are carried out with the hood, using a reverse procedure. The operations for removing spent fuel elements from the core to the storage installation, then loading new fuel from the storage installation to the core, are very lengthy. In fact, the hood must be moved many times between the core and the storage installation. The hood must be coupled each time, either above the core or above the storage installation. Moreover, all the transfers are performed in an inert atmosphere, which requires many inert gas-producing operations. In addition, the hood is very heavy. In order to minimise the risk of falls, the hood must be moved very slowly. In this context, the object of the invention is to propose a nuclear power station, in which the loading and unloading operations of the reactor core are faster. Accordingly, the invention relates to a nuclear power station of the above-mentioned type, characterised in that the transfer means comprise: a tunnel, of which a first portion is situated near the core and a second portion is situated in or near the storage installation; first transfer means suitable for transferring at least one fuel element between the core and the first stretch; second transfer means suitable for transferring at least one fuel element between the second portion and the storage installation; means for transferring at least one fuel element along the tunnel between the first and second portions. The nuclear power station may also have one or more of the following characteristics, considered individually or in all technically possible combinations: the first portion is situated above the core. the first transfer means comprise first connection means substantially sealed between the core and the first portion, the second transfer means comprise second connection means substantially sealed between the second portion and the storage installation, the tunnel forming a continuous sealed path with the first and second connection means for the fuel elements from the core to the storage installation. a first biological protection slab is situated above the reactor core, the tunnel being arranged at least in part beneath or in the first biological protection slab. the first biological protection slab comprises an aperture perpendicular to the core, the power station comprising a support stopper arranged removably in the aperture, the first portion of the tunnel being arranged in the support stopper. a second biological protection slab is situated above the storage installation, the second portion of the tunnel being situated at a lower elevation than that of the second biological protection slab. a first biological protection slab is situated above the reactor core, the tunnel being arranged at least in part above the first biological protection slab. the first biological protection slab comprises an aperture perpendicular to the core, the power station comprising a support stopper arranged removably in the aperture, the first portion of the tunnel being arranged above the support stopper. a second biological protection slab is situated above the storage installation, the second portion of the tunnel being situated above the second biological protection slab. the power station comprises: a plurality of high temperature reactors, each comprising a core in which a plurality of fuel elements is arranged; for each reactor, a dedicated fuel elements storage installation for said reactor; means for moving the tunnel between a plurality of service positions each corresponding to a reactor, the first portion of the tunnel being situated in each service position close to the core of the corresponding reactor and the second portion of the tunnel being situated in or near the storage installation dedicated to said reactor. The power station comprises: a plurality of high temperature reactors, each comprising a core in which a plurality of fuel elements is arranged; for each reactor, a fuel elements storage installation dedicated to said reactor; a plurality of connection tunnels connecting each two storage installations to each other, each connection tunnel comprising a first portion situated near one of the two corresponding storage installations and a second portion situated in or near the other of the two corresponding storage installations; for each connection tunnel, first transfer means suitable for transferring at least one fuel element between the corresponding storage installation and the first portion; for each connection tunnel, second transfer means suitable for transferring at least one fuel element between the second portion and the corresponding storage installation; for each connection tunnel, means for transferring at least one fuel element along the connection tunnel between the first and second portions. a biological protection slab is situated above each storage installation, the first and second portions of each connection tunnel being situated at elevations respectively lower than those of the biological protection slabs of the corresponding storage installations. the storage installations are arranged in a line, each connection tunnel connecting two adjacent storage installations along the line. According to a second aspect, the invention relates to a process for transferring fuel elements between a high temperature reactor and a fuel elements storage installation, in a nuclear power station having the above characteristics. According to the invention, the process comprises the following stages: transferring at least one fuel element between the reactor core and the first portion of the tunnel; transferring the or each fuel element along the tunnel between the first and second portions; transferring the or each fuel element between the second portion and the storage installation. According to a third aspect, the invention relates to a process for transferring fuel elements between two fuel element storage installations, in a nuclear power station having the above characteristics, the two storage installations being connected to each other by a connection tunnel comprising a first portion situated near one of the two storage installations and a second portion situated in or near the other of the two storage installations. According to the invention, the process comprises the following stages: transferring at least one fuel element between said one of two storage installations and the first portion; transferring the or each fuel element along the connection tunnel between the first and second portions; transferring the or each fuel element between the second portion and said other of the two storage installations. The nuclear power station shown schematically in FIG. 1 comprises four high pressure reactors 2. These four reactors are identical to each other. Each reactor 2 comprises a core 4, a principal heat exchanger 6, a primary conduit (not illustrated) for transferring the heat generated by the core 4 to the exchanger 6, an installation 8 for converting thermal energy into electricity and a secondary conduit (not illustrated) for transferring the heat from the exchanger 6 to the installation 8. The core 4 comprises a plurality of fuel elements 5 of hexagonal cross-portion. Each fuel element is about 900 mm high, and has a cross-portion that lies within a circle with a diameter of about 450 mm. These fuel elements are of a known type and will not be described in more detail here. The reactor operates at a temperature of between 750° C. and 1200° C., for example. The primary conduit contains a gas, generally a mixture of helium and nitrogen. This gas is circulated in the primary conduit by one or more compressors and passes through the core heating up in contact with the fuel elements. It is then taken to the principal exchanger 6, where it transfers its heat to the fluid circulating in the secondary conduit. It is then recompressed and recycled to the core 4. The secondary conduit too generally comprises a gas, for example helium or a gas mixture. This gas is circulated, heats up when passing through the exchanger 6, and is then taken to the conversion installation 8. This installation comprises for example one or more gas turbines, driving an alternator. The secondary gas drives the turbines, then is recompressed before being recirculated to the exchanger 6. The nuclear island of each reactor, in other words the core 4, the principal exchanger 6 and the primary conduit, is assembled in the same civil engineering structure 10 represented by a circle in FIG. 1. The nuclear islands of the four reactors of the power station are assembled in the same reactor building 12, the outline of which is represented by a dot-and-dash line in FIG. 1. Moreover, the power station comprises four nuclear fuel storage installations 14, 16, 18 and 20, each storage installation being associated with one of the nuclear reactors. The installations 14, 16 and 18 have the same capacity. They each have a storage capacity of at least one sixth of the total number of fuel elements arranged normally in the reactor core, this capacity being less than said total number. Preferably, each installation 14, 16, 18 has a capacity of about one third of said total number. The storage installation 20 has the largest capacity. It can receive all of the fuel elements for a core. The nuclear power station also comprises a new fuel element storage installation 22, waiting to be transferred into the core of one of the reactors 2. This installation is common to the four reactors. The power station also comprises a spent fuel element packing installation 24, for example in order to transport them outside the nuclear power station. The storage installations 14, 16, 18 and 20, the new fuel element storage installation 22, and the packing installation 24 are all arranged in the reactor building 12. The four reactors are arranged in a straight line. Similarly, the four storage installations 14, 16, 18 and 20, the packing installation 24 and the new fuel element storage installation 22 are also situated in a straight line, in that order. The storage installations 14, 16, 18 and 20 are each arranged near a reactor 2. Each nuclear island 10 is covered by a biological protection slab 26 (see for example FIGS. 3 and 5), which extends perpendicular to the reactor, to the principal exchanger 6 and to the primary conduit. The slabs 26 of the four reactors are of very thick concrete, and are situated substantially at the same elevation. The storage installations 14, 16, 18 and 20 are all of the same type. They are delimited laterally by concrete walls 28, and they are covered by a biological protection slab 29. The slabs 29 are of very thick concrete, and are all substantially at the same elevation. They are also at the same elevation as the protection slabs 26 of the different reactors. As shown in FIG. 4, each storage installation comprises a plurality of pits 30 in which a plurality of fuel elements 5 may be stacked. The installation also comprises a rolling bridge 31 provided with means for handling the fuel elements. The slabs 26 and 29 are joined up and form the floor of the principal hall of the nuclear power station. This hall covers the four reactors and the storage installations 14 to 20. It may be continuous or on the other hand be subdivided into four portions by internal dividing walls, each portion covering a reactor and the storage installation associated therewith. According to a first aspect of the invention, the nuclear power station comprises for each reactor 2, means 32 for transferring fuel elements between the core 4 of the reactor and the corresponding storage installation 14 to 20. In a first embodiment of the invention, illustrated in FIGS. 2 to 4, these means 32 comprise a movable tunnel 34, capable of serving each of the four reactors. The tunnel 34 is placed above the slabs 26 and 29 forming the floor of the principal hall of the reactor. The tunnel 34 is rectilinear. Its walls are shielded and are made up of steel and/or lead plates. When the fuel elements are to be transferred to or from a reactor, the tunnel 34 is placed in such a way that a first end portion 36 of the tunnel is situated above the reactor core, and a second end portion 38 opposite the first is situated above the corresponding storage installation. As shown in FIG. 3, the biological protection slab 26 comprises perpendicular to the reactor core 4, a circular aperture 40. During normal operation of the reactor, the aperture 40 is closed by a stopper. The stopper is solid, the control bars being arranged in crossing points situated beneath this stopper. When maintenance operations or operations to reload the reactor with fuel are required, a support stopper 42, visible in FIG. 3 for example, is placed in the aperture 40 in place of the stopper used for normal operation. The stopper 42 comprises at the centre thereof an opening 44 for the passage of a mechanism for lifting/lowering the fuel elements, and six openings 46 for the passage of the mechanism for handling the fuel elements. The openings 46 are arranged in a circle around the central opening 44 and are distributed regularly around it. It should be noted that some control bars are removed in order to use the crossing points thereof for the passage of the handling mechanism. As shown in FIG. 2, the first end portion 36 of the tunnel covers the opening 44, the tunnel passing between two of the openings 46. The end 36 of the tunnel is coupled in a sealed manner around the opening 44, for example by an inflatable joint not illustrated, and communicates with the opening 44. As shown in FIG. 3, the lifting/lowering mechanism 48 typically comprises a tube 49 extending from the opening 44 downwards and penetrating the reactor vessel 50 by an aperture 51 in the cover of the vessel. The mechanism 48 also comprises a boat 52 which can move vertically inside the tube 49. The mechanism 48 also comprises means 54 for moving the boat 52 between a high position in which the boat is situated inside the first end 36 of the tunnel, and a low position in which the boat is located inside the reactor vessel 50, immediately above the fuel elements. For example, the means 54 comprise a cable 56 from which the boat 52 is suspended, and means for winding and unwinding the cable 56 around a drum 57. The mechanism 58 for handling the fuel elements is illustrated in a simplified manner in FIG. 3 and in a detailed manner in FIG. 5. This mechanism typically comprises a tube 60 extending from an aperture 46 downwards and penetrating inside the vessel 50 by an aperture 62. The mechanism 58 also comprises a pantograph-type arm 64, known per se, provided with grasping means, suitable for seizing a fuel element 5 from the core. The arm 64 has a large enough degree of freedom to reach all the fuel elements situated in an angular segment of the core corresponding substantially to ⅙ of the circumference of said core. The arm 64 is in also suitable for transferring each block of this segment to the boat 52, in order to lift said block into the tunnel 34. The mechanism 58 can move from one opening 46 to another. When it is mounted in an opening 46, it allows ⅙ of the core to be loaded or unloaded. The six openings 46 thus allow access to all of the fuel elements in the core. The mechanism 58 is known and will not be described in more detail. The means 32 for transferring fuel elements also comprise means 66 for transferring the fuel elements along the tunnel between the first and second portions. The means 66 comprise for example a carriage 68 capable of moving in rails 69 along the tunnel, a lifting arm 70 mounted on the carriage 68, the arm being provided with means 72 for grasping fuel elements. The means 66 also comprise means for propelling the carriage 68 along the tunnel (not illustrated). The rails 69 are for example arranged in the upper portion of the tunnel 34. The carriage 68 rolls in the rails by means for example of 2 or 3 pairs of rollers. The means for moving the carriage along the tunnel comprise for example a drag chain. The arm 70 is mounted on the carriage 68 and has a degree of vertical freedom. Thus, the arm 70 is capable of seizing, by means of grasping means 72, a fuel element 5 arranged in the boat 52, and moving it upwards. The lower portion of the fuel element is then released from the boat, and the fuel element can then move freely along the tunnel. As shown in FIGS. 3 and 4, the transfer means 32 also comprise means 74 for transferring the fuel element 5 between the end 38 of the tunnel and the interior of the storage installation associated with the reactor. These means 74 comprise a hole 76 provided in the slab 29 and an elevator 78 arranged inside the storage installation. The hole 76 is arranged beneath the end 38 of the tunnel, immediately above the elevator 78, and communicates with the end 38. It is capable of being sealed by a shielded shutter 79. The elevator 78 comprises a support 80 and telescopic means 82 for moving the support 80 between a high position in which the support 80 is situated at the end 38 of the tunnel and a low position in which the support 80 is located on the loading face 84 of the pits 30. In the high position of the support 80, the arm 70 is suitable for laying down a fuel element on the support or seizing a fuel element arranged on the support 80. The loading face 84 corresponds substantially to the height of the pit 30. When the support 80 is in the low position, the bridge 31 is able to seize the fuel element arranged on the support 80 and move it to introduce it in one of the storage pits 30. As indicated above, the tunnel 34 is coupled in a sealed manner around the opening 44 on the one hand and around the aperture 76 on the other hand, for example by inflatable joints. It is therefore possible to maintain an inert atmosphere along the entire passage path of the fuel elements, in the core, in the tunnel 34 and inside the storage installation. In order to be able to move the tunnel 34 from one reactor to another, rails 86 are provided on the floor of the principal hall of the nuclear power station (FIGS. 1 and 2). The tunnel is mounted on carriages 88 that can move in the rails 86. The rails 86 extend parallel to the alignment of the reactors and the storage installations. A second embodiment in which the transfer tunnel between the core of each reactor and the corresponding storage installation is not movable but fixed, will now be described, with reference to FIG. 6. Only the points by which the second embodiment differs from the first will be detailed below. Like elements or elements performing the same functions will be designated by like reference numerals. In the second embodiment, each reactor comprises a dedicated tunnel 90, allowing fuel elements to be transferred between the reactor core and the corresponding storage installation. The tunnel 90 extends beneath the biological protection slabs 26 and 29. In this embodiment, the first end 36 of the tunnel is arranged in the thickness of the support stopper 42. However, the central portion 92 of the tunnel is fixed rigidly beneath the slab 26 and the slab 29. When the stopper 42 is in place in the aperture 40, the end 36 of the tunnel is placed in the extension of the central portion 92. The portion 36 is separated from the portion 92 by a narrow interstice 94. An inflatable joint 96 is provided to provide a seal between the portion 36 and the portion 92 in the region of the interstice 94. The means 48 for lifting and lowering the fuel elements 5 in the reactor core comprise in place of the boat 52 a grab 98 suspended from the cable 56. In addition, the tube 49 comprises at the lower end thereof a platform 100 on which the pantograph arms 64 are able to lay down or seize a fuel element. The platform 100 is placed vertical to the grab 98, in such a way that the grab is able either to lay down a fuel element 5 on the platform 100, or seize a fuel element which has been placed there by the pantograph arm 64. The means 66 for moving the fuel element along the tunnel from one end to the other comprise a carriage 102 moving along the tunnel in the rails 69, the carriage 102 being provided with a basket 104. The basket 104 defines inside it a housing that matches the shape of the fuel element to be transported. The tube 49 comprises a window 106 through which the basket can be introduced inside the tube 49. In addition, the tube 49 is extended above the support stopper 42 by an appendage 108 in which the grab 98 and the fuel element coupled thereto can be housed, as illustrated in FIG. 5. The carriage 102 has four rollers engaged in each rail, which allows it to cross the interstice 94 without loss of stability. The carriage 102 moves along the tunnel by a drag chain not illustrated. At the end 38 thereof, the tunnel penetrates directly into the storage installation through the side walls 28. In this installation, a fuel element can be removed from the basket 104 or laid down in the basket 104, either by the bridge 34 if the tunnel is arranged at an elevation such that it opens for example in the region of the loading face 84, or by dedicated handling means if the tunnel opens higher up. According to a second aspect of the invention independent of the first, illustrated in FIG. 1, the different storage installations are connected to each other by connection tunnels 110. Thus, the storage installations 14 and 16 are connected by a tunnel 110, the storage installations 16 and 18 are connected by another tunnel 110, the storage installations 18 and 20 are connected by a third tunnel 110, the storage installation 20 being connected to the new fuel storage installation 22 by a fourth tunnel 110 which passes through the packing installation 24. These tunnels are of the fixed type, and are therefore arranged typically beneath the biological protection slabs 29. The fuel elements circulate in these tunnels in carriages of the same type as carriage 102 propelled by drag chains. The tunnels 110 open directly into the stores 14, 16, 18, 20 and 22. The tunnels are placed at lower elevations than those of the slabs 29, preferably at elevations such that the fuel elements can be placed in the baskets of the carriages by the bridges 34 equipping the storage installations. The procedures for loading and unloading the reactor core according to a first embodiment of the invention will now be described. After shutting down the reactor, the stopper used in normal operation of the reactor is removed from the aperture 40, and the support stopper 42 is put in place. The tunnel 34 then moves along the rails 86 and is placed in such a way that the first end thereof is situated perpendicular to the opening 44 and the second end thereof perpendicular to the hole 76 of the corresponding storage installation. The tunnel 34 and the aperture 44 are then sealed, as are the tunnel 34 and the hole 76. If necessary, the equipment impeding access to the penetration apertures 51 and 62 into the core are dismantled. This equipment may be instrumentation means for the central aperture 51, and control bars for the apertures 62. Next, the means 48 for lifting and lowering the fuel elements and the means 58 for handling the fuel elements are placed on the stopper 42. The loading operation of some of the fuel elements of the core may then begin. Typically, half the fuel elements of the core are replaced with new fuel elements at each campaign. Such a replacement campaign is carried out every 1 to 2 years. Handling is carried out successively on each ⅙ of the core. One ⅙ of the reactor core is emptied into the associated storage installation. Elements at the end of their life are removed (one half) and elements that are not yet spent are retained. New elements are added to the elements that are not yet spent. One ⅙ of the core is then stacked according to the arrangement required (mixture of new elements and elements that are not yet spent). Once handling has been carried out on ⅙ of the core, the operation moves to another zone of the core. The handling means 58 are mounted on another aperture 46. The operation is repeated six times in total at each campaign, all the fuel elements in the core being emptied and half being put back in place. The other half is made up of new elements. To remove the fuel elements, the boat 52 is first lowered in the region of the core. During this time, the pantograph arm 64 seizes a fuel element to be removed. It lays it down in the boat 52 once said boat has reached its low position. The boat then rises to the high position. The arm 70 seizes the fuel element loaded in the boat 52 when said boat is in the high position. Next, the carriage 68 moves along the tunnel 34 to the end 38 thereof. Once the carriage has stopped, the elevator 78 searches for the fuel element 5 and lowers it inside the storage installation through the hole 76. When the elevator 78 has lowered the fuel element in the region of the loading face 84 of the pits, the bridge 31 takes hold of the fuel element again and inserts it in one of the pits. Next, the carriage goes back to the first end of the tunnel to search for another fuel element brought by the boat 52. It should be noted that the different handling means transferring the fuel elements from the core to the storage installation may work in parallel with each other. Thus, the carriage may perform its outward and return journeys along the tunnel while the elevator and the storage installation bridge transfer the fuel element into a pit. Similarly, the boat 52 may be lowered, receive a fuel element and lift it while the carriage 68 moves the previous fuel element from the first end 36 to the second end 38, the arm 70 lays it down on the elevator 78 and the carriage 68 returns to the first end. The pantograph arm may seize a new fuel element, position it in the boat 52 and go back to seize another fuel element while the carriage does an outward and return journey along the tunnel. These different tasks are therefore carried out at the same time, such that the time needed to remove one sixth of the fuel elements from the reactor core to the storage installation is shortened considerably compared with the state of the art using a hood. Once the transfer of the fuel elements is complete, the fuel elements at the end of their life are removed outside the nuclear power station or to the storage installation 20. New fuel elements are brought from the installation 22 to the storage installation associated with the reactor to be loaded. Next, the elements that are not yet spent and the new elements are loaded in the reactor core. Accordingly, a fuel element to be loaded is seized by the bridge and placed in the elevator support 80. The elevator raises the fuel element to the end 38 of the tunnel, where said fuel element is seized by the arm 70 mounted on the carriage. The carriage then moves the fuel element to the first end of the tunnel, while the elevator is lowered back down in the region of the loading face of the storage installation. The arm 70 lays down the fuel element in the boat 52. The carriage then returns to the second end to search for another fuel element. During this time, the boat 52 lowers the fuel element inside the reactor core. When the boat is in the low position, the pantograph arm seizes the fuel element and lays it down in the required place in the reactor core. In the same way as for the unloading, the different elements for handling the fuel elements work at the same time to load the reactor. The loading and unloading procedure for the second embodiment of the invention is substantially similar to the procedure described above with reference to the first embodiment. Only the operation of the lifting and lowering means of the fuel elements in the reactor core will be described below. To remove the spent fuel elements from the reactor core, the pantograph arm 64 first seizes a fuel element from the reactor core and places it on the tray 100 situated beneath the grab 98. The grab is lowered, seizes the fuel element placed on the tray 100 and lifts it to the protuberance 108. The carriage 102 then moves to engage the basket 104 inside the tube 49, which allows it to be placed beneath the fuel element held by the grab. The grab then lays down the fuel element inside the basket 104 and is uncoupled from said fuel element. The carriage then moves to the second end of the tunnel, and the fuel element is removed from the basket by the handling means provided for this purpose. As previously, here too the different handling means for the fuel elements work at the same time. The nuclear power station described above has many advantages. Because the transfer means between the core of each reactor and the corresponding storage installation comprise: a tunnel, of which a first portion is situated near the core and a second portion is situated in or near the storage installation; first transfer means suitable for transferring at least one fuel element between the core and the first stretch; second transfer means suitable for transferring at least one fuel element between the second portion and the storage installation; and means for transferring at least one fuel element along the tunnel between the first and second portions,the time required to remove the spent fuel elements from the core to the storage installation, or conversely to transfer the new fuel elements from the storage installation to the reactor core, is considerable reduced since the different means participating in the transfer of the fuel elements can work in parallel and operate at the same time. The tunnel, the connection means between this tunnel and the core on the one hand, and the connection means between the tunnel and the storage installation on the other hand, form a continuous path from the core to the storage installation. It is thus possible to transfer the fuel elements under an inert atmosphere from the core to the storage installation without breaking containment. Along this path, the tunnel and the connection means provide continuous biological protection to the operators. Moreover, the transfer of the fuel elements between the core and the storage installation is carried out without heavy and bulky objects, such as a hood, needing to be moved by a rolling bridge equipping the hall of the reactor. There is therefore no risk of the load falling during transfer. Moreover, this frees the reactor bridge, which can be used to carry out other tasks. The means employed to carry out the transfer are simple and inexpensive. The nuclear power station described above may have many variants. It may comprise only one high temperature reactor or any number of reactors. The tunnel may be rectilinear or not rectilinear. The same tunnel, in a given position, may serve a plurality of storage installations from the same reactor. In this case, the tunnel passes above a plurality of holes allowing fuel elements to be lowered into different storage installations. Conversely, the same tunnel may, in a given position, serve a single storage installation from a plurality of reactors. It is possible to envisage all sorts of transfer means between the reactor core and one end of the tunnel. These means may be a grab, a boat suspended from a cable, an elevator, or any other type of transfer means. Similarly, the transfer means between the storage installation and the tunnel may be of any type: grab, basket suspended from a cable, elevator, etc. These transfer means can be adapted equally well to a fixed tunnel arranged beneath the biological protection slabs or alternatively to a movable tunnel arranged beneath the biological protection slab. The means for transferring fuel elements along the tunnel may also be of any type. They may comprise a carriage provided with a grasping arm or a basket, or alternatively a cradle for receiving the fuel element. The fuel elements may be transferred upright or lying down, etc. The means for driving the carriage along the tunnel may also be of any type: drag chains, rack and pinion assembly, etc. In the case of a fixed tunnel arranged beneath the biological protection slabs, the end of the tunnel on the reactor side may be arranged not in the support stopper situated above the core, but beneath said support stopper. The nuclear power station may comprise all sorts of means for handling the fuel elements in the reactor vessel. These means may be a pantograph arm as described above, or for example a robotised arm having a plurality of degrees of freedom, or any other type of grasping means. The support stopper situated above the core may not comprise a single opening for removing the fuel elements and transferring them to the tunnel. The stopper may comprise a plurality of openings arranged at different places. Similarly, the storage installation may have different apertures allowing the fuel elements to be transferred between the interior of the storage installation and the tunnel. Each reactor may comprise a steam generator in place of the principal heat exchanger. Alternatively the primary fluid may drive directly a gas turbine coupled to an electric generator. The invention has been described for an embodiment in which the fuel elements are hexagonal, 900 mm high and with a cross-portion that lies within a circle of 450 mm diameter. It applies to fuel elements with all sorts of square, circular or other cross-portions. These elements may be of a greater or lesser height than 900 mm, the cross-portion thereof lying within a circle of any diameter, larger or smaller than 450 mm. In a variant, the connection tunnels between the storage installations may extend above the slab 29. It is then necessary to provide in the connection tunnels and stores handling means suitable for transferring the fuel elements between the ends of the tunnels and the stores. These means may be for example of the same type as the elevator 78 described in relation to the first embodiment of the invention. The storage installations are not necessarily arranged in line. They may for example be laid out in a star around the installation with the greatest capacity 20, the connection tunnels radiating from the installation 20. |
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047626615 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The upper end piece 10 shown in FIGS. 1 and 2 is intended for a fuel assembly for a light water reactor. This assembly may have a general known construction and thus will not be described in detail. In FIG. 1, in addition to end piece 10, only a few fuel elements 11 and guide tubes 13 have been shown some at least of which provide the mechanical integrity of the fuel assembly by connecting together the upper end piece 10 and a lower end piece similar to the lower end piece 10a of FIG. 3. Grids (not shown), spaced apart longitudinally along the guide tubes, hold the elements in place. In the embodiment shown in FIG. 1, guide tubes 13 are fixed to a structural member 14 forming the framework of the end piece 10. the structural member 14 comprises a base plate to which the guide tubes 13 are fixed. In the case illustrated in FIG. 1, guide tubes 13 are fixed by a sleeve and a threaded socket 15. They could be fixed by other methods, for example by welding. The structural member 14 also comprises vertical plates 18 which, with the base plate, define an inner space forming a caisson 19. The base plate is formed with openings (not shown) for the free circulation of water. Guide tubes 13 are provided for receiving control elements (not shown). The end piece shown in FIG. 1 is intended for an assembly whose guide tubes are adapted for allowing the passage of control elements which are either elements containing a neutron absorbing material, or elements modifying the moderation rate, by modifying the volume of moderator in the fuel assembly, so as to provide so called "spectral shift" mode operation. The control elements of each group are combined in a cluster by a mobile mount, which is generally called "spider". The two spiders 16 and 17 are disposed coaxially. Their lower parts are shown, in the position where they rest on the end piece, with a dash dot line. Spider 16 will generally support the absorbent element cluster and will be suspended from a handling tube surrounding a rod for handling the spider 17 which supports the elements controlling the moderation rate (elements containing fertile material). The absorbent cluster thus caps the fertile cluster. It may be moved by means of an uncouplable ratchet mechanism for releasing it in the core. The structural member 14, which may be manufactured by molding, contains all damping and hold-down means with which end piece 10 is equipped. The damping means comprise a bearing member 20, which may slide with respect to the structural member 14 in the direction of the axis of the guide tubes 13, which comprises means for guiding with respect to the structural member and which is urged by the resilient damping means integrated in the end piece towards the position shown in FIG. 1. This support member 20 is adapted for receiving the shock of the spider, or of one of the spiders (spider 16 in the case of FIG. 1) should the corresponding element cluster fall for example for stopping the reactor. The guide means comprise a hub 30 fixed in the center of the base plate and projecting upwardly. Orientation of hub 30 is fixed by the engagement of key 22, secured to the base plate, in a notch of the hub. The base plate also comprises a circular collar 23, coaxial with hub 30. The hub and the collar may be fixed by welding. The collar 23 defines a zone 24 for receiving the support zone of the resilient means. The guide means also comprise studs 26, four in number for example, each fixed close to a corner of the base plate, projecting upwardly. A single one of these studs 26 is shown. It comprises a top part of reduced diameter 27, separated from the low part by a shoulder 25. With the guide means which havejust been described and which are carried by the structural member 14 are associated complementary means fixed to the support member 20. This latter is in the form of a plate in which are formed wide water flow apertures or of an annular piece comprising radial fins in number equal to that of studs 26. In member 20 are formed holes 29 for receiving sleeve 31 aligned with the studs 26. The bore of each sleeve 31 has a diameter corresponding to that of the reduced diameter portion 27 of the corresponding stud. The external diameter of the sleeve corresponds to that of the lower part of stud 26. Each sleeve 31 is retained on the corresponding stud 26. For that, the sleeve has a groove 32 parallel to the axis in which is engaged a key 28 set in stud 27. For it to be possible to engage sleeve 31 while key is in position, groove 32 opens into a bayoned shaped groove 33 having an axial portion and a circumferential portion, emerging at the base of groove 32. To position sleeve 31, it is therefore sufficient to present groove 33 opposite key 28, to push it in then to rotate sleeve 31, by 90.degree. for example, so that the key is situated at the bottom of groove 32. Then the sleeve 21 may be fixed to the support member 20 for example by welding. To the support member 20 are fixed, for example by welding, a collar 34 identical to collar 23 and a hollow hub 36 cooperating with hub 30. The bore of hub 36 has a diameter such that hubs 36 and 30 have a sliding fit one on the other. In the top part of the bore grooves 38 are formed, two in number for example, extending substantially over two thirds of the height of the hub, defining shoulders 39. These shoulders form stops for a U shaped key 40 defining the rest position of the support member 20. Key 40 may be secured by welding when the support member 20 is forced into its lower most position, defined by the abutment of sleeves 31 on shoulders 25. The resilient damping means comprise a first spring 43 retained between the support member 20 and the structural member 14, whose endmost parts are surrounded by collars 23 and 34. Since the end piece shown in FIG. 1 is intended for an assembly which may receive, on the one hand, a cluster of absorbent elements and, on the other, a cluster of spectrum modification elements, the end piece also comprises a ring 41 mounted for sliding on hub 36 and a spring 42 coaxial with spring 43, but bearing on the structural member 14 and on ring 41. Spring 42 ends to hold ring 41 in abutment against member 20. In this latter are formed indentations for the passage of the lower part of spider 17, allowing this latter to come into abutment against ring 41 (as shown with a dash dot line) and to urge it downwardly. When the assembly is in position in a reactor and when the upper core plate 44 is in position, the thrust exerted by the upwardly flowing coolant is transmitted by the structural member 14 to springs 42 and 43 which in their turn bear on member 20. Should the cluster carried by spider 17 fall (cluster of elements for modifying the moderation rate in general), spider 17 comes into abutment against ring 41 and forces it down by overcoming the resilient force exerted by spring 42. This latter damps the shock by forming a resilient stop. Should the cluster carried by spider 16 fall, this latter strikes the support member 20 which is driven in while compressing springs 42, through ring 41 and 43. The springs act jointly as resilient end-of-travel stops. Similarly, the two springs come into play should there be a simultaneous fall of the two clusters, for example for shutting down the reactor. In the variant of the invention shown in FIG. 3 (where the parts corresponding to those of FIG. 1 are designated by the same reference number), end piece 10 forms a block which may be handled independently of the skeleton of the assembly. In the assembly properly speaking, the upper end of guide tubes 13 is fixed, by removable members such as sleeves or by welding, to a simple upper table 45 having large water passage openings (not shown). These openings correspond to those which are formed in the base plate of the structural member 14. Table 45 also has an external shape corresponding to that of the structural member 14. It is secured thereto by removable means (not shown) which may be formed by screws passing through the base plate of the structural member 14 and engaged in tapped holes in the table. The screws may be locked against rotation after mounting, for example by deformation of a thin cap which they comprise in a recess of corresponding shape in the base plate. So as to avoid any error of orientation during mounting, fool-proof means are provided on the structural member 14 and table 45. In the embodiment illustrated in FIG. 3, they comprise at least one stud 47 (key or split sleeve) intended to be engaged in a hole 46 of corresponding shape in table 45. In another embodiment, table 45 is secured to the structural member 14 only by studs 27 engaging in holes 46, judiciously spaced apart around the periphery of member 14 and table 45. With this arrangement, should there be a defect or failure of an element of end piece 10, only this latter need be replaced which only involves simple operations. Between the structural member 14 and the support member 20 of the end piece of FIG. 3 are compressed, in addition to springs 42 and 43, springs 48 each disposed about one of the studs 26. The action of springs 48 is added to that of springs 42 and 43 and increases the force exerted on the assembly by the upper core plate 44, which force opposes raising of the assembly through the action of the water which flows in the core. The end piece which has just been described will be adapted so as to be able to be gripped by handling grippers which will often lead to completing it with a peripheral groove or other means facilitating gripping thereof. |
abstract | A glassy cholesteric liquid crystalline composition comprising compounds with a volume-expanding core bound to one or more hybrid chiral-nematic (or Ch) pendant moieties and a method of producing oriented films of such compounds. The Ch pendant moieties are comprised of chiral spacer groups connected to the core via linker groups and nematic groups linked to the chiral spacer groups. Thin-films of the composition are morphologically stable for extended periods of time. Also, the thin-films are able to selectively interact with light from the visible to near-IR wavelength range. |
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abstract | An imaging system is provided having an EMI shield configured to shield one or more imaging components. The EMI shield includes a first material having a first plurality of conductive elements integrally formed within a first nonconductive material and also includes a generally nonconductive exterior. A method is provided for shielding EMI in an imaging system. The method includes providing an EMI shielding enclosure that includes a first material having a first plurality of conductive elements disposed in a first non-conductive material, and a second material having a second plurality of conductive elements disposed in a second non-conductive material, wherein the first plurality of conductive elements engages the second plurality of conductive elements to form a conduction path. Another method for shielding EMI in an imaging system is provided, that includes providing an EMI shielding enclosure having a first material that has a non-conductive surface and a second EMI shielding material disposed on the non-conductive surface of the first material. |
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041994051 | abstract | The invention relates to a graphite side reflector in block form for a gas-cooled high-temperature nuclear reactor. The blocks of the reflector extend radially continuously through the entire reflector wall thickness and recesses are provided in the inner end faces of at least the blocks disposed in the upper region of the reactor core. |
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claims | 1. A method of processing spent nuclear fuel into fast molten salt reactor fuel, the method comprising:providing fuel assemblies having spent fuel;removing the spent fuel from the fuel assemblies;granulating the removed spent fuel for process feed to a chlorination process;processing the granular spent fuel into chloride salt by ultimate reduction and chlorination, including reacting the granular spent fuel with anhydrous hydrogen chloride (AHCl);enriching the granular spent fuel salt;chlorinating the enriched granular spent fuel salt to yield molten chloride fuel salt;analyzing, adjusting, and certifying the molten chloride fuel salt for end use in a molten salt reactor;pumping the molten chloride fuel salt and cooling the molten chloride fuel salt; andmilling the solidified molten chloride fuel salt to predetermined specifications. 2. The method of claim 1, wherein the granulating step occurs in a semi-voided atmosphere using one or more of a ball mill, roller mill, or chopping mill. 3. The method of claim 1, wherein the granular spent fuel salt is enriched with one or more of uranium-235 (U235), plutonium-239 (Pu239), or mixed oxide (MOX). 4. The method of claim 1, wherein the chlorinating step occurs by reacting the enriched granular spent fuel salt with AHCl. 5. The method of claim 1, wherein the molten chloride fuel salt is pumped to stacked arrays of cooling trays or individual storage canisters. 6. The method of claim 1, wherein the molten chloride fuel salt is cooled to yield one or more of solid fuel salt bars, sticks, or canister solid forms. 7. The method of claim 1, wherein the milling step occurs via one or more of a ball mill, roller mill, or chopping mill. 8. The method of claim 1, wherein the fuel assemblies contain an array of fuel tubes aligned horizontally on a rod puller disassembly table. 9. The method of claim 1, wherein the fuel assemblies contain an array of fuel tubes and the spent fuel is removed by laser slitting of the fuel tubes, opening the tubes, and removing the spent fuel. 10. The method of claim 1, further comprising collecting dust and gases and recycling the dust and gasses. 11. The method of claim 1, wherein the enriching step occurs in an oxide reduction tank. 12. The method of claim 1, wherein the enriching step comprises low enriched uranium including high assay-low enriched uranium. 13. The method of claim 1, wherein the chlorinating step occurs by immersion in a molten chloride salt bath. 14. The method of claim 1, wherein spent fuel gases are collected by a fluidized bed and converted to chlorinated fuel salts. 15. The method of claim 5, wherein the pumping step comprises pumping the molten chloride fuel salt into stacked arrays of cooling trays, wherein the cooling trays are cooled by chilled water, and wherein the cooling trays are configured with multiple parallel and separate rows, each surrounded by cooling coils. 16. The method of claim 5, wherein the pumping step comprises pumping the molten chloride fuel salt into individual storage canisters, and wherein the individual storage canisters are inductively heated to liquid. 17. A method of processing spent nuclear fuel into fast molten salt reactor fuel, the method comprising:providing fuel assemblies having spent fuel containing uranium;removing the spent fuel from the fuel assemblies;granulating the removed spent fuel in a semi-voided atmosphere using a ball mill, roller mill, or chopping mill, for process feed to a chlorination process;processing the granular spent fuel into chloride salt by ultimate reduction and chlorination of the uranium by anhydrous hydrogen chloride (AHCl);enriching the granular spent fuel salt with uranium-235 (U235), plutonium-239 (Pu239), or mixed oxide (MOX);chlorinating the enriched granular spent fuel salt to yield molten chloride fuel salt using AHCl halide salt reduction;analyzing, adjusting, and certifying the molten chloride fuel salt for end use in a molten salt reactor;pumping the molten chloride fuel salt to stacked arrays of cooling trays or canisters and cooling the molten chloride fuel salt to yield solid fuel salt bars, sticks, or canister solid forms; andmilling the solidified molten chloride fuel salt to predetermined specifications for the fast molten salt reactor. 18. A method of processing spent nuclear fuel into fast molten salt reactor fuel, the method comprising:providing fuel assemblies having spent fuel;removing the spent fuel from the fuel assemblies;granulating the removed spent fuel for process feed to a chlorination process;processing the granular spent fuel into chloride salt by ultimate reduction and chlorination, including reacting the granular spent fuel with anhydrous hydrogen chloride (AHCl);enriching the granular spent fuel salt;chlorinating the enriched granular spent fuel salt to yield molten chloride fuel salt by reacting the enriched granular spent fuel salt with AHCl;analyzing, adjusting, and certifying the molten chloride fuel salt for end use in a molten salt reactor;pumping the molten chloride fuel salt and cooling the molten chloride fuel salt; andmilling the solidified molten chloride fuel salt to predetermined specifications. 19. The method of claim 18, wherein the fuel assemblies contain an array of fuel tubes and the spent fuel is removed by laser slitting of the fuel tubes, opening the tubes, and removing the spent fuel. 20. The method of claim 18, wherein the enriching step occurs in an oxide reduction tank. 21. The method of claim 18, wherein the chlorinating step occurs by immersion in a molten chloride salt bath. 22. The method of claim 18, wherein spent fuel gases are collected by a fluidized bed and converted to chlorinated fuel salts. |
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claims | 1. An out-of-core nuclear instrumentation device comprising:a detector signal-processing circuit that converts neutron flux leaking from a nuclear reactor vessel into a current value and performs a measurement processing on the neutron flux, the neutron flux being detected by a neutron detector disposed outside the nuclear reactor vessel,wherein the detector signal-processing circuit comprises:a current/voltage conversion part that converts the current value into a voltage value,a variable gain amplification part that amplifies the voltage value with a variable gain by a digital-to-analog (D/A) converter,a measurement range selection part that is provided in the current/voltage conversion part or the variable gain amplification part and selects a measurement range according to the current value,a temperature measurement unit that measures a temperature of the measurement range selection part,a temperature compensation part that outputs a gain compensation value to the D/A converter based on the temperature, anda selective adjustment control part that adjusts and controls a gain of the D/A converter with selective control of the measurement range and the gain compensation value. 2. The out-of-core nuclear instrumentation device according to claim 1,wherein the measurement range selection part comprises a current level response-use resistance circuit in which a plurality of serial bodies in which resistors and switches are connected in series are connected in parallel. 3. The out-of-core nuclear instrumentation device according to claim 1,wherein the measurement range selection part comprises a second D/A converter capable of selecting a gain according to the measurement range. 4. The out-of-core nuclear instrumentation device according to claim 3, further comprising:a constant temperature control part that performs constant temperature control in order to keep the variable gain amplification part at a constant temperature. 5. The out-of-core nuclear instrumentation device according to claim 1, further comprising:a fixed gain amplification part that is connected with the variable gain amplification part in series and amplifies an output of the variable gain amplification part with a fixed gain. 6. The out-of-core nuclear instrumentation device according to claim 2, further comprising:a fixed gain amplification part that is connected with the variable gain amplification part in series and amplifies an output of the variable gain amplification part with a fixed gain. 7. The out-of-core nuclear instrumentation device according to claim 3, further comprising:a fixed gain amplification part that is connected with the variable gain amplification part in series and amplifies an output of the variable gain amplification part with a fixed gain. 8. The out-of-core nuclear instrumentation device according to claim 4, further comprising:a fixed gain amplification part that is connected with the variable gain amplification part in series and amplifies an output of the variable gain amplification part with a fixed gain. |
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abstract | Two transducers to be rotated around a circumferential location on a cylindrical body for structural testing of the body are carried on a mounting and drive apparatus including a magnetic attachment which can be manually brought up to a pipe from one side only for fixed connection to the pipe on that side at a position axially spaced from a weld. A collar shaped support for the pair of transducers is formed of a row of separate segments which wrap around the pipe from the one side and is rotated around the axis of the pipe to carry the transducer around the circumferential weld. The segments carry rollers to roll on the surface and are held against the pipe by magnets. The transducers are carried on the support in fixed angular position to track their position but in a manner which allows slight axial or radial movement relative to the pipe. |
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abstract | An apparatus for controlling a neutron beam includes a plurality of columnar prisms 1 that are made of a material having a refractive index of less than 1 for a neutron beam, and are arranged so as to be multi-layered. The columnar prisms 1 each have an approximately right-triangle-shaped section, and are three-dimensionally multi-layered such that respective surfaces 1a, 1b, 1c of the columnar prisms are in parallel to one another. Stick-shaped members 5 are made of the above material, the stick-shaped members 5 are set in a plurality of grooves formed on a jig 6 that have the same shape, and upper surfaces of the grooves are flattened at the same time. |
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abstract | A method and system is provided for a nuclear reactor safety related application. The method includes executing two forms of a same application-specific logic, one of the two forms implemented as hardware logic, and the other of the two forms implemented as software instructions for execution by microprocessor-based controlling software. Each form of the application-specific logic is executed with a same set of inputs. The method compares a result produced from the execution of the hardware-implemented form to a result produced from the execution of the software-implemented form. When the compared results concur, the controlling software performs actions associated with the concurring results by executing microprocessor-based software. When the compared results fail to concur, the controlling software reports the failure of the compared results to concur to an operator by executing microprocessor-based software, and thereafter places the microprocessor-based software system into an inoperative (INOP) mode. |
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042382904 | abstract | In a nuclear reactor installation, a steam generator's live-steam line leading through the containment, is equipped with a fast-acting shut-off valve, to shut off the steam in the event of a line break. If the steam pressure rises in the generator, the valve acts as a safety valve and releases a small amount of steam, so that there is no danger of damage to the steam generator. The invention is of interest particularly for light-water reactors, e.g., pressurized-water reactors. |
abstract | To suppress a decrease of thickness due to corrosion of structural members and to achieve a removal of radionuclides with good efficiency in a nuclear power plant, oxidation decontamination is first conducted. An aqueous potassium permanganate solution is supplied from a circulation line to a reactor pressure vessel, which is a stainless steel structural member, and a reactor water cleanup system piping and a drain piping, which are carbon steel structural members. These structural members are oxidation-decontaminated by the action of potassium permanganate. Then the above-mentioned structural members are reduction-decontaminated by using an aqueous oxalic acid solution. The aqueous oxalic acid solution contains hydrazine. |
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051924935 | claims | 1. A system for improving the performance of nuclear power plant feedwater control systems and simplifying steam generator low water level reactor protection logic, comprising: means for redundantly measuring steam generator water level and generating a plurality of signals representative thereof; means for selecting a median steam generator water level signal from among said plurality of steam generator water level signals; and means for communicating said median steam generator water level signal to the feedwater control system. redundantly measuring steam generator water level and generating a plurality of signals representative thereof; selecting a median steam generator water level signal from among said plurality of steam generator water level signals; and communicating said median steam generator water level signal to the feedwater control system. 2. The system of claim 1 wherein said means for selecting said median steam generator water level signal includes a microprocessor responsive to said means for generating said plurality of steam generator water level signals. 3. The system of claim 2 wherein said means for communicating said median steam generator water level signal includes an output interface responsive to said microprocessor. 4. The system of claim 3 wherein said plurality of steam generator water level signals includes three signals designated as Signal A, Signal B and Signal C. 5. The system of claim 4 wherein said microprocessor is programmed first to select the high signal value as between Signal A and Signal B and store this value in said microprocessor memory as Signal D, second to select the high signal value as between Signal B and Signal C and store this value in said microprocessor memory as Signal E, third to select the high signal value as between Signal A and Signal C and store this value in said microprocessor memory as Signal F, fourth to select the low signal value as between Signal D and Signal E and store this value in said microprocessor memory as Signal G, and finally to select the low signal value as between Signal F and Signal G and store this value in said microprocessor memory as said median steam generator water level signal. 6. The system of claim 4 additionally comprising means for detecting the failure of said means for redundantly measuring steam generator water level. 7. The system of claim 6 wherein said means for detecting failure includes means for detecting whether any of said steam generator water level signals differs from the other steam generator water level signals by more than a predetermined difference value and communicating an alarm signal to the feedwater control system through said output interface. 8. The system of claim 7 wherein said means for detecting failure further includes means for detecting whether any of said steam generator water level signals is greater than a predetermined high limit signal value or whether any of said steam generator water level signals is less than a predetermined low limit signal value and communicating an alarm signal to the feedwater control system through said output interface. 9. The system of claim 8 wherein said means for detecting failure further includes means for detecting whether any two of said means for redundantly measuring steam generator water level has failed and communicating a signal to the feedwater control system through said output interface to change a feedwater control system status from automatic to manual. 10. A method for improving the performance of nuclear power plant feedwater control systems and simplifying steam generator low water level reactor protection logic, comprising the steps of: 11. The method of claim 10 wherein said step of selecting said median steam generator water level signal includes the steps of first selecting the high signal value as between Signal A and Signal B and storing this value as Signal D, second selecting the high signal value as between Signal B and Signal C and storing this value as Signal E, third selecting the high signal value as between Signal A and Signal C and storing this value as Signal F, fourth selecting the low signal value as between Signal D and Signal E and storing this value as Signal G, and finally selecting the low signal value as between Signal F and Signal G and storing this value as said median steam generator water level signal. 12. The method of claim 11 additionally comprising the step of detecting the failure of said measurement of said steam generator water level. |
abstract | Illustrative embodiments provide systems, applications, apparatuses, and methods related to nuclear fission deflagration wave reactor cooling. Illustrative embodiments and aspects include, without limitation, nuclear fission deflagration wave reactors, methods of transferring heat of a nuclear fission deflagration wave reactor, methods of transferring heat from a nuclear fission deflagration wave reactor, methods of transferring heat within a nuclear fission deflagration wave reactor, and the like. |
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040452824 | description | It should be noted in addition that, in this description, the expression "fuel assemblies" designates both the assemblies which contain fissile material and the assemblies which contain only fertile material. This figure shows diagrammatically and to a complete extent only two of the N measuring channels, namely those designated by the references A and B. Each of these N measuring channels is connected to one of the N monitored reactor core assemblies; in consequence, the complete association of the two computing circuits C and D together with all the N measuring channels will be explained in general principle without being completely illustrated. There are shown at 1, 2, 3 and 4 in the FIGURE four of the N temperature detectors constituted by thermocouples which each supply one of the N measuring channels such as A and B. Either of said measuring channels is identical in design with the channel A which comprises the following devices in series: an element for amplifying the measurement previously performed by the thermocouple 1, said element being constituted for example by two cascade-connected amplifiers 5 and 6 which have a suitable gain in order to detect small temperature variations; a summing amplifier 7 having three inputs to which are applied respectively in accordance with the essential feature of the invention, the signal which has been previously amplified for measuring the outlet temperature of the fuel assembly corresponding to the measuring channel A, the signal produced by the circuit C being such as to correspond to the opposite of the mean reactor core outlet temperature and the signal produced by the circuit D being such as to correspond to the fraction of the difference between the mean "hot" (T.sub.1) and "cold" (T.sub.2) core outlet temperatures so that the signal emitted by said summing amplifier 7 of channel A is initially of zero value; devices 8, 9 and 10 comprise respectively a threshold for pre-alarm, emergency shutdown and control rod drop constituted for example by open-loop amplifiers which can be actuated by positive or negative signals by means of a diode 7a and an amplifier 7b having a gain of 2 for rectifying the negative polarities, said diode and amplifier being connected in shunt on the output of said summing amplifier 7; regrouping OR-circuits 11, 12, 13 which trigger the standard safety actions such as pre-alarm, emergency shutdown or a control rod drop when the signals which may be delivered by each of said devices 8, 9 and 10 of each measuring channel which is similar to the channel A are applied respectively to said OR-circuits. The composition of the computing circuits C and D is directly dependent on the operations to be performed on the basis of two sets of temperatures measured on the one hand on a predetermined number of "hotter" core assemblies and on the other hand by a predetermined number of "colder" core assemblies. Thus the circuits C and D first have in common two operational amplifiers 14 and 15: the amplifier 14 for generating a signal corresponding to the mean "hot" (T.sub.1) core outlet temperature being placed at the output of a certain number of measuring amplifiers 6 selected from those which form part of measuring channels such as the channel A which are connected to "hot" core assemblies; the amplifier 15 for generating a signal corresponding to the mean "cold" (T.sub.2) core outlet temperature being placed at the output of a certain number of measuring amplifiers 6' selected from those which form part of measuring channels connected to "cold" core assemblies. The computing circuit C, the output of which feeds one of the three inputs of the summing amplifier 7 by means of a signal corresponding to the opposite value of the mean core outlet temperature is provided at the output of said amplifiers 14 and 15 with a summing amplifier 16 having a gain of 2:1 followed by an inverting amplifier 17. The circuit D, the output of which also feeds one of the three inputs of the summing amplifier 7 by means of a signal corresponding to the fraction of the difference between the mean "hot" and "cold" core outlet temperatures comprises a summing amplifier 19 followed by an assembly 20 placed at the output of the amplifier 14 for generating the mean "hot" temperature and at the output of an inverting amplifier 18 which is in turn placed at the output of the amplifier 15 for generating the mean "cold" temperature. By way of example, the assembly 20 aforesaid is constituted by a series of amplifiers having symmetrical outputs between which are connected N potentiometers for permitting initial adjustment of the fraction of the difference between the mean "hot" and "cold" core outlet temperatures in order to ensure that the signal initially emitted by the summing amplifier 7 is zero within each of the N measuring channels. In this example, the measuring amplifiers 5 and 6 have a gain in the vicinity of 235, the amplifiers having outputs which are symmetrical with the assembly 20 have a gain in the vicinity of 1.5, thus making it possible to obtain a satisfactory signal at the output of the summing amplifier 7. The core of a fast reactor contains about 85 fuel assemblies and it is sufficient to supply each of the operational amplifiers 14 and 15 with groups of 10 signals. It should finally be pointed out that the arrows such as the arrow 21 shown in the accompanying FIGURE represent diagrammatically a number of different signalling relays which make it possible, for example in the event of overstepping of emergency shutdown thresholds or of a control rod drop, to switch the output of the summing amplifier 7 to an external incident recorder. It is readily apparent that, at the time of monitoring of the nuclear reactor core, the different means shown diagrammatically in the FIGURE are conveniently arranged within suitable drawers fixed on a synoptic unit. This unit permits initial adjustment of the potentiometers of the assembly 20 as well as the adjustment on the one hand of the pre-alarm and emergency shutdown threshold values combined as a rule by means of a switch having preset voltages delivered by amplifiers in which the output values can be controlled and, on the other hand, the adjustment of the control-rod drop threshold values of the devices 10 which are smaller in number than the core assemblies but can be connected to either of the measuring channels. The synoptic unit aforesaid also serves to carry out the control operation proper by means of indicator lamps for signals delivered after the regrouping OR-circuits 11, 12, 13 and each pre-alarm device 8 when these latter are supplied. The aforesaid drawers which contain the means shown diagrammatically in the FIGURE are clearly connected to an assembly for collecting all the mesurements of the reactor core thermocouples, to the emergency bays for the transfer of orders for control rod drop and emergency shutdown, and also to the control-room console. |
055442048 | abstract | The reactivity of a neutron chain reaction in a nuclear reactor is automatically reduced upon failure of the coolant flow by a system in which nuclear-fuel particles are suspended against gravitational forces by forces of the coolant flow and are in the reactive zone when so suspended. Upon failure of the coolant flow, the particles settle into a space outside the reactive zone and thus do not contribute to the neutron chain reaction and reactivity is reduced. |
summary | ||
description | Field The present disclosure relates to a chimney structure including internal partitions having a common center, a reactor including the chimney structure, and/or a method of manufacturing the chimney structure. Description of Related Art In a reactor, for example an Economic Simplified Boiling Water Reactor (ESBWR), a chimney structure may be arranged between the reactor core outlet and the steam separator inlet to establish, enhance, and deliver natural circulation of a fluid (e.g., a steam and water mixture) in the reactor vessel. A chimney structure may have internal partitions to ensure the steam water mixture flows in the vertical direction and/or to establish better natural circulation flow inside the reactor. Many ESBWR reactors include a square-cell chimney structure having a round tube that surrounds a grid pattern of internal partitions. The internal partitions may define square cells and regions of small cross-section inside the round tube. For example, the square-cell chimney structure may be a round tube with square pegs as internal partitions inside the round tube. In a square-cell chimney structure, portions of the internal partitions near the periphery (i.e., adjacent to the round tube surrounding the internal partitions) can define regions of small cross-section. Portions of the internal partitions that are not adjacent to the periphery can define the square cells. The steam water mixture flowing through the regions of small cross-section may have a higher pressure drop across the chimney structure than the steam water mixture flowing through the square cells. Consequently, during the operation of the reactor, the steam-water mixture flowing through the regions of small cross-section may be susceptible to undesirable flow regime changes. Manufacturing the square-cell chimney structure may include numerous bending and welding steps to shape the internal partitions into a grid pattern and to join the internal partitions to the round tube. If the internal partitions have manufacturing defects, the numerous bends in the internal partitions may cause stress concentrations in the internal partitions. As a result, during the operation of a reactor including a square-cell chimney structure, the numerous welds and bends in the square-cell chimney structure have to be inspected frequently as part of periodic maintenance. The regions of small cross-section in the square-cell chimney structure may be more difficult to make and inspect during the operation of the reactor. Additionally, placing the square-cell chimney structure in a reactor may include forming complex connections between the internal partitions of the square-cell chimney structure and a bottom or a top support piece. During a refueling operation, it may be necessary to remove the internal partitions of the square-cell chimney structure. Disconnecting the connections between the internal partitions of the square-cell chimney structure and a bottom or a top support piece may extend the reactor downtime during a refueling operation. Accordingly, a chimney structure that reduces the regions of small cross-section defined by internal partitions, reduces the number of welds and bending steps in manufacturing the chimney structure, reduces the number of welds that are inspected during periodic maintenance, and/or has less pressure drop if a fluid (e.g., steam water mixture) flows through the chimney structure may be desired. Some example embodiments relate to a chimney structure including internal partitions having a common center. Some example embodiments also relate to a reactor including a chimney structure with internal partitions having a common center. Other example embodiments relate to a method of manufacturing a chimney structure including internal partitions having a common center. According to an example embodiment, a chimney structure includes a guide structure defining an opening; and a plurality of chimney partitions including 1 to N chimney partitions concentrically arranged and spaced apart from each other on the guide structure. The 1 to N chimney partitions each define a curved opening over the opening of the guide structure, and N may be an integer greater than 1. The 1 to N chimney partitions may each have a tubular shape, and the 1 to N chimney partitions may have different radii. Each one of the 1 to N chimney partitions may be spaced apart from an adjacent one of the 1 to N chimney partitions by a same distance. A value of the same distance may be configured to reduce the formation of Eddy currents if a steam mixture flows through the 1 to N chimney partitions. A value of the same distance may be about 16 inches. An upper surface of the guide structure may define M grooves spaced apart from each other, where M may be an integer greater than or equal to N. Parts of the 1 to N chimney partitions may be in the M grooves defined by the upper surface of the guide structure. The chimney structure may further include a top plate on the 1 to N chimney partitions. The top plate may define an opening over the curved openings of the 1 to N chimney partitions. The chimney structure may further include at least one rod secured to the guide structure. The chimney structure may further include a plurality of divider plates extending through the 1 to N chimney partitions. The divider plates and the 1 to N chimney partitions may define a plurality of curved opening sections, based on sectionally dividing the curved openings of the 1 to N chimney partitions. The chimney structure may further include a partition structure surrounding the 1 to N chimney partitions. An inner surface of the partition structure may define a round opening. The partition structure may include divider plates that divide the round opening into round opening sections. The 1 to N chimney partitions may each have a tubular shape, and the 1 to N chimney partitions may have different radii. The divider plates may be metal sheets. The divider plates may include notches corresponding to the 1 to N chimney partitions, and the 1 to N chimney partitions may be in the notches of the divider plates. The chimney structure may further include a plurality of slats between two adjacent chimney partitions among the 1 to N chimney partitions. The plurality of slats may be configured to divide a space between the two adjacent chimney partitions into smaller sections. The plurality of slats may be attached to the inside surface of the outer chimney partition among the two adjacent chimney partitions. The plurality of slats may be configured to be positioned toward the inner chimney partition among the two adjacent chimney partitions in order to divide the space between the two adjacent chimney partitions into smaller sections, and the plurality of slats may be configured to be positioned against the inner surface of the outer chimney partition among the two adjacent chimney partitions in order to avoid dividing the space between the two adjacent chimney partitions into smaller sections. The plurality of slats may be attached to the inner chimney partition among the two adjacent chimney partitions. The plurality of slats may be configured to be positioned toward the outer chimney partition among the two adjacent chimney partitions in order to divide the space between the two adjacent chimney partitions into smaller sections, and the plurality of slats may be configured to be positioned against the inner chimney partition among the two adjacent chimney partitions in order to avoid dividing the space between the two adjacent chimney partitions into smaller sections. The 1 to N chimney partitions may each have a tubular shape, and each one of the 1 to N chimney partitions may be spaced part from an adjacent one of the 1 to N chimney partitions by a distance that is about equal to an inner diameter of the 1st chimney partition among the 1 to N chimney partitions. The inner diameter of the 1st chimney partition may be about 16 inches. A diameter of the Nth chimney partition may be about 30 feet, and a height of the 1 to N chimney partitions may range from about 18 to 22 feet along the axial direction of the 1 to N chimney partitions. A value of N may be greater than or equal to 4 and less or equal to about 12. The 1 to N chimney may partitions include 2nd to (N−1)th chimney partitions between the 1st and the Nth chimney partitions in sequential order. The 1 to N chimney partitions may each have a tubular shape. The 1 to N chimney partitions may have different radii. A separation distance between the 1st chimney partition and the 2nd chimney partition may be different than a separation distance between two adjacent chimney partitions among the 2nd to (N−1)th chimney partitions. The 1 to N chimney partitions may include steel, and a thickness of the chimney partitions may range from about 0.25 inches to about 0.50 inches. In an example embodiment, a reactor may include a reactor wall, and the above-described chimney structure may be secured to the reactor wall. According to an example embodiment, a chimney structure may include a chimney housing defining an opening through an axial direction of the chimney housing; and a plurality of partitions including 1 to N partitions concentrically arranged in the opening of the chimney housing. The 1 to N partitions each define a curved opening along the axial direction of the chimney housing. The 1 to N partitions are spaced apart from each other and spaced apart from an inner surface of the chimney housing along the axial direction of the chimney housing. N may be an integer greater than 1. According to an example embodiment, a method of manufacturing a chimney structure includes concentrically arranging a plurality of chimney partitions on a guide structure. The guide structure defines an opening. The plurality of chimney partitions include 1 to N chimney partitions concentrically arranged and spaced apart from each other on the guide structure. The 1 to N chimney partitions each define a curved opening over the opening of the guide structure. N is an integer greater than 1. Example embodiments will now be described more fully with reference to the accompanying drawings, in which some example embodiments are shown. Example embodiments, may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example embodiments to those of ordinary skill in the art. In the drawings, like reference numerals in the drawings denote like elements, and thus their description may be omitted. It should be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It should be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments. Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like) may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, including those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. FIGS. 1A-1B are perspective views of a chimney structure according to an example embodiment. FIG. 2 is a plan view of the chimney structure illustrated in FIGS. 1A-1B. Referring to FIGS. 1A, 1B and 2, according to an example embodiment, a chimney structure 110 may include a plurality of chimney partitions 20-1 to 20-N having a common center. The chimney partitions 20-1 to 20-N may be positioned on a guide structure 39 with grooves G corresponding to the peripheries of the chimney partitions 20-1 to 20-N. Each one of the chimney partitions 20-1 to 20-N may define a curved opening that allows a fluid (e.g., a steam water mixture) to flow through the curved opening of the chimney partitions. The fluid may be a mixture that is 75 percent liquid water and 25 percent steam, but is not limited thereto. The guide structure 39 may also define a curved opening allowing fluid to flow through. When the chimney partitions 20-1 to 20-N are positioned in the grooves G of the guide structure 39, the curved openings of the chimney partitions 20-1 to 20-N may be arranged over the opening of the guide structure 39. An upper surface of the guide structure 39 may define M grooves G and the grooves G may be spaced apart from each other. The value for M may be an integer than that is greater than or equal to N, and N may be an integer that corresponds to the number of chimney partitions 20-1 to 20-N. Parts of the chimney partitions 20-1 to 20-N may be in the M grooves defined by the upper surface of the guide structure 39. The upper surface of the guide structure 39 may define groves G in a circular pattern, as described in more detail with reference to FIG. 3G. However, FIG. 3H illustrates another example of the guide structure 39 where only the inner and outer grooves G have circular patterns and the grooves G in between do not have a circular pattern. FIGS. 1A, 1B, and 2 illustrate an example where the chimney partitions 20-1 to 20-N each have a tubular shape with circular cross-sections and different radii (e.g., R1, R2, R3, RN). When the chimney partitions 20-1 to 20-N have a circular cross-section, the pressure drop of a steam water mixture flowing through the chimney partitions with 20-1 to 20-N with a circular cross-sectional area is theoretically less than a steam water mixture flowing through partitions having an equivalent cross-sectional area but a square cell cross-section. Equations (1) and (2) below represent the area of square (As) and the perimeter of a square (Ps) may be expressed as a function of the length of each side (x) of the square. Equations (3) and (4) below represent how the area of a circle (Ac) and the perimeter of a circle (Pc) may be expressed as a function of the radius (r) of the circle.As=x2 (1)Ps=4*x (2)Ac=π*r2 (3)Pc=2*π*r (4) Assuming the square cell and circular cell have equal cross-sectional areas, then the perimeter Ps of the square cell may be about 12% larger than a perimeter Pc of the circular cell. The hydraulic diameter of the chimney partitions 20-1 to 20-N with circular cross-sections may be about 13% larger than a square cell partition having the same cross-sectional area. As a result, assuming a square cell and a circular cell have the same cross-sectional area, the pressure drop of a steam mixture flowing through a chimney partition having a circular cross-section should be less than the pressure drop across a chimney partition having the same area with a square cell cross-sectional area. Because a chimney partition having a circular cross-section has a lower wetted surface than a chimney partition having a square cross-section with the same area, the pressure drop across the chimney partition having the circular cross-section theoretically should be lower than the pressure drop across the chimney partition having the square cross-section. Although FIGS. 1A, 1B, and 2 illustrate an example embodiment where the chimney partitions have circular cross-sections, example embodiments are not limited thereto. For example, the chimney partitions 20-1 to 20-N may alternatively have elliptical cross-sections and/or polygonal cross-sections having a common center. The chimney partitions 20-1 to 20-N may be formed of a metal and/or metal alloy. For example, the chimney partitions may be formed of steel such as SAE 304, or SAE 316 stainless steel. In some example embodiments, surfaces of the chimney partitions 20-1 to 20-N may be coated with at least one material capable of capturing nitrogen compounds containing N-16. The material capable of capturing nitrogen compounds containing N-16 may include at least one of a metallic compound having an acid center on a solid surface, a clay mineral (e.g., zeolite, sepiolite), hydroxyl apatite, carbon compounds such as activated carbon, metal carbides, and an ammonia decomposition catalyst supported by a metal (e.g., Pt, Ni, Ru, Mn). A thickness of the chimney partitions 20-1 to 20-N may be about 0.25 to about 0.50 inches thick, but example embodiments are not limited thereto. The chimney partitions 20-1 to 20-N may all have the same thicknesses. Alternatively, some or all of the chimney partitions 20-1 to 20-N may have thicknesses that are different from each other. In the chimney structure 110 illustrated in FIGS. 1A, 1B, and 2, each one of the chimney partitions 20-1 to 20-N may be spaced apart from an adjacent one of the chimney partitions 20-1 to 20-N by the same distance. When the chimney partitions 20-1 to 20-N are tubular in shape, each one of the chimney partitions 20-1 to 20-N may be spaced apart from an adjacent one of the chimney partitions 20-1 to 20-N by a distance that is about equal to an inner diameter of the first chimney partition 20-1 among the chimney partitions 20-1 to 20-N. A value of the spacing between the chimney partitions 20-1 to 20-N may be configured to reduce the formation of Eddy currents if a fluid (e.g., steam water) mixture flows through the chimney partitions 20-1 to 20-N and/or direct the circulation of the fluid through the chimney structure 110. If the spacing between the chimney partitions is too small, then flow instabilities such as Eddy currents may result when a fluid flows between through the spaces between adjacent chimney partitions 20-1 to 20-N. On the other hand, if the spacing between adjacent chimney partitions 20-1 to 20-N is too large, then the chimney structure 110 may be less effective at ensuring the fluid flows in the vertical direction when the chimney structure 110 is installed in an operating reactor. For example, if a steam water mixture flows through the chimney structure 110, the innermost chimney partition 20-1 may define an opening having an inner diameter of about 16 inches and the chimney partitions 20-2 to 20-N may be spaced apart from adjacent chimney partitions by about 16 inches. In other words, an inner surface of the chimney partition 20-2 may be spaced apart from an outer surface of the chimney partition 20-1 by about 16 inches, and inner surface of the chimney partition 20-3 may be spaced apart from an outer surface of the chimney partition 20-2 by about 16 inches. However, depending on the fluid intended to flow through the chimney structure 110 and/or depending on the application, the spacing between the chimney partitions 20-1 to 20-N may be a value that is different than 16 inches. Although the chimney partitions 20-1 to 20-N in the chimney structure 110 illustrated in FIGS. 1A, 1B, and 2 may be spaced apart from each other by the same distance, example embodiments are not limited thereto. In some example embodiments, at least some of the chimney partitions 20-1 to 20-N may be spaced apart from each other by different distances. For example, in some applications, the flow of the steam water mixture may be different through the central chimney partitions 20-1, 20-2 compared to the outer chimney partitions 20-3 to 20-N of the chimney structure 110. Accordingly, the inner chimney partitions 20-1 to 20-2 may be spaced apart from each other by a first distance, and the outer chimney partitions 20-3 to 20-N may be spaced apart from each other by a second distance that is different than the first distance. The second distance by less than or greater than the first distance. In one example embodiment, a height L of the chimney partitions may be about 20 feet plus or minus 2 feet along the axial direction of the chimney partitions, and an outer diameter of the outermost chimney partition 20-N may be about 30 feet. Even though FIGS. 1A, 1B, and 2 illustrate an example embodiment where the chimney structure 110 includes 5 chimney partitions 20-1 to 20-N, example embodiments are not limited thereto. For example, the number of chimney partitions 20-1 to 20-N may be an integer greater than or equal to 4 and less than or equal to 12 (or about 12). However, number of chimney partitions 20-1 to 20-N may vary depending on the application is not limited thereto. The outermost chimney partition 20-N of the chimney structure 110 may be a chimney housing that defines an opening through an axial direction of the chimney housing. A plurality of chimney partitions 20-1 to 20-4 may arranged to have a common center (e.g., concentrically arranged) within the outermost chimney partition 20-N as the chimney housing. The chimney partitions 20-1 to 20-4 may each define a curved opening along the axial direction of the chimney partition 20-N. The chimney partitions may be spaced part from each other and spaced apart from an inner surface of the chimney partition along the axial direction of the housing. FIGS. 3A to 3D illustrate a method of manufacturing a chimney structure including square cell partitions. Referring to FIG. 3A, a method of manufacturing a square-cell for use in a chimney structure including square cell partitions may include welding a T-shaped part 28-T to metal sheets 28. The reference character W in FIG. 3A illustrates the welds W. As shown in FIG. 3B, bent portions 28-B of the metal sheets 28 may be welded to the tube T surrounding the internal partitions of a chimney structure including square cell partitions. If there are metal defects D in the bent portions 28-B, then stress concentrations in the bent portions 28-B may result. During the operation of a reactor including a square-cell chimney structure, the numerous welds W and bends in the square-cell chimney structure have to be inspected as part of periodic maintenance. As shown in FIG. 3C, joining the square cell partitions to the top or bottom of a circular support piece may require complex connections. Lastly, as shown in FIG. 3D, there are numerous bends and welds in the regions of small cross section near the edge of the square-cell chimney structure that are difficult to make and inspect during the life of the component. According to an example embodiment, a method of manufacturing a chimney structure may include concentrically arranging a plurality of chimney partitions on a guide structure. The guide structure may define an opening. The plurality of chimney partitions may include 1 to N chimney partitions concentrically arranged and spaced part from each other on the guide structure. The 1 to N chimney partitions may each define a curved opening over the opening of the guide structure. The number of chimney partitions N may an integer greater than 1. The number of chimney partitions N may be an integer from 4 to 12 (or about 12), but is not limited thereto. In an example embodiment, a method may include concentrically arranging a plurality of chimney partitions that are tubular structures with circular cross-sections. The chimney partitions may be spaced apart from each other by the same distance. Alternatively, some or all of the chimney partitions may be spaced apart from each other by difference distances. Although the chimney partitions may be tubular structures with circular cross-sections, example embodiments are not limited thereto. The chimney partitions alternatively may have elliptical and/or polygonal (e.g., square, rectangular, octagonal) cross-sections. In such as a case, the chimney partitions may be arranged to have a common center. FIGS. 3E to 3F illustrate a method of manufacturing a chimney structure according to an example embodiment. Referring to FIG. 3E, fabricating round tube chimney partitions 36A to 36C may include bending and/or rolling flat metallic sheets (or sheets formed from a metal alloy) into tubular structures with one vertical weld W. The vertical welds W of the round tube chimney partitions 36A to 36C are in an orientation that may be optimal for inspection in future operation. Referring to FIG. 3F, the round tube chimney partitions 36A to 36C may be placed in the grooves G of a guide structure 39. The chimney partitions 36A to 36C may be held in place under compression between the guide structure 39 and a top plate (refer to reference character 40 in FIG. 4A) using at least one threaded rod 37 and nut 38 secured to the guide structure 39 and top plate. This simple assembly technique allows for ease of maintenance and inspections. Further, when a chimney structure according to an example embodiment is utilized in an ESBWR reactor, the simple assembly technique may allow for ease of future decommissioning. Instead of using a rod 37 and nut 38, the rod 37 may be clamped to the guide structure 39 and top plate. Even though FIGS. 3E to 3F illustrate an example where the chimney partitions are tubular in shape, example embodiments are not limited thereto and the shape of the chimney partitions 36A to 36C may alternatively have an elliptical and/or a polygonal cross-section. The chimney partitions 36A to 36C may be formed of steel such as SAE 304, or SAE 316 stainless steel. A thickness of the chimney partitions 36A to 36C may be in the range from 0.25 to 0.50 inches, but example embodiments are not limited thereto. A height of the chimney partitions 36A to 36C may be about 20 feet plus or minus 2 feet along the axial direction of the chimney partitions, and an outer diameter of the outermost chimney partition 36C may be about 30 feet, but example embodiments are not limited thereto. Even though FIGS. 3E to 3F illustrate an example embodiment where the chimney structure includes 3 chimney partitions 36A to 36C, example embodiments are not limited thereto. For example, the number of chimney partitions 36A to 36C may be an integer greater than or equal to 4 and less than or equal to 12. The number of chimney partitions 36A to 36C may be an integer greater than or equal to 4 and less than or equal to 12 (or about 12). However, number of chimney partitions 36A to 36C may vary depending on the application is not limited thereto. FIG. 3G is a plan view of a grooved plate in a chimney structure according to an example embodiment. Referring to FIG. 3G, according to an example embodiment, a guide structure 39 may have a round periphery. On the round periphery, threaded holes may be defined so at least one threaded rod 37 and corresponding nut 38 may be secured to the guide structure 39. An upper surface of the guide structure 39 may define grooves G corresponding to where the round tube chimney partitions 36A to 36C described previously may be concentrically arranged on the guide structure 39. An upper surface of the guide structure 39 may define M grooves G spaced apart from each other. Additionally, M may be an integer that is greater than or equal to the number of chimney partitions 36A to 36C. Parts of the chimney partitions 36A to 36C may be in the M grooves defined by the upper surface of the guide structure 39. FIG. 3G illustrates an example where the grooves G defined by the guide structure 39 are all circular in shape, but example embodiments are not limited thereto. For example, if the shape of the chimney partitions 36A to 36C concentrically arranged on the guide structure 39 have an elliptical and/or polygonal cross-section, then the shape of the grooves G defined by the guide structure 39 may be modified to have a corresponding elliptical and/or polygonal cross-section. Additionally, FIG. 3H is a plan view of a grooved plate in a chimney structure according to an example embodiment. In FIG. 3H, only the innermost groove G and the outermost groove G have a circular shape. The middle groove G of the guide structure 39 is not circular. The middle groove G of the guide structure 39 is defined in four locations by connecting portions 39C of the guide structure that connect an inner ring portion 39R of the guide structure to an edge of the guide structure 39. As a result, the openings O between the ring portion 39R of the guide structure 39 and the edge of the guide structure 39 may be larger compared to the openings in the guide structure shown in FIG. 3G. FIGS. 4A and 4B are a sectional view and a plan view of a chimney structure according to an example embodiment. Referring to FIGS. 4A and 4B, according to an example embodiment, a chimney structure 400 may include a guide structure 39 and a top plate 40. A number of chimney partitions 42-1 to 42-N may be held in place under compression between the guide structure 39 and the top plate 40. One or more threaded rod and nut 38 may be used to secure the guide structure 39 to the top plate 40. The top plate 40 may define an opening over openings defined by the chimney partitions 42-1 to 42-N. Parts of the chimney partitions may be inserted in grooves defined by an upper surface of the guide structure 39 and/or a lower surface of the top plate. In FIGS. 4A and 4B, reference number 42-1 illustrates an inner most one of the chimney partitions and reference number 42-N illustrates an outer most one of the chimney partitions. FIGS. 4A and 4B also illustrate two rings 42-2 and 42-3 corresponding to chimney partitions between the chimney partitions 42-1 and 42-N. In an ESBWR reactor the flow of the steam water mixture flow may be greater in the center of the reactor than edges of the reactor, due to differences in the heat generated in the reactor core. Accordingly, depending on the application, it may be practical to adjust the spacing between the chimney partitions 42-1 to 42-N so some of the chimney partitions are spaced apart from each other by different distances. A configuration where some chimney partitions 42-1 to 42-N are spaced apart from each other by greater distances compared to other chimney partitions 42-1 to 42-N can reduce manufacturing costs by lowering the number of chimney partitions 42-1 to 42-N in the chimney structure 400. For example, in FIGS. 4A and 4B, a separation distance between the chimney partitions 42-1 and 42-2 may be different than a separation distance between the chimney partitions 42-3 and 42-N. A separation distance between the chimney partitions 42-2 and 42-3 may be less than a separation distance between the chimney partition 42-3 and 42-N. The chimney partitions 42-1 to 42-N may be formed of a metal and/or metal alloy. For example, the chimney partitions may be formed of steel such as SAE 304, or SAE 316 stainless steel. In some example embodiments, surfaces of the chimney partitions 42-1 to 42-N may be coated with at least one material capable of capturing nitrogen compounds containing N-16. The material capable of capturing nitrogen compounds containing N-16 may include at least one of a metallic compound having an acid center on a solid surface, a clay mineral (e.g., zeolite, sepiolite), hydroxyl apatite, carbon compounds such as activated carbon, metal carbides, and an ammonia decomposition catalyst supported by a metal (e.g., Pt, Ni, Ru, Mn). A thickness of the chimney partitions 42-1 to 42-N may be about 0.25 to about 0.50 inches thick, but example embodiments are not limited thereto. The chimney partitions 42-1 to 42-N may all have the same thicknesses. Alternatively, some or all of the chimney partitions 42-1 to 42-N may have thicknesses that are different from each other. The chimney partitions 42-1 to 42-N may each have tubular shape with different radii and a common center. A separation distance between the innermost chimney partition 42-1 and an adjacent chimney partition 42-2 may be different than a separation distance between two adjacent chimney partitions among the chimney partitions 42-1 to 42-N. Although the chimney partitions 42-1 to 42-N are illustrated as having a tubular shape with a circular cross-section, example embodiments are not limited thereto. The chimney partitions 42-1 to 42-N may alternatively have an elliptical or polygonal cross-section. A height of the chimney partitions 42-1 to 42-N may be about 20 feet plus or minus 2 feet along the axial direction of the chimney partitions, and an outer diameter of the outermost chimney partition 20-N may be about 30 feet. Although FIGS. 4A and 4B illustrate a chimney structure including four chimney partitions 42-1 to 42-N having a common center, example embodiments are not limited thereto. The chimney partitions 42-1 to 42-N may include 2nd to (N−1)th concentrically arranged between the chimney partitions 42-1 and 42-N in sequential order. For example, the number of chimney partitions 42-1 to 42-N may be an integer greater than or equal to 4 and less than or equal to 12. The number of chimney partitions 42-1 to 42-N may be an integer greater than or equal to 4 and less than or equal to 12 (or about 12). However, number of chimney partitions 42-1 to 42-N may vary depending on the application is not limited thereto. Additionally, the chimney partitions 42-1 to 42-N may have a tubular shape with circular cross-sectional shapes and different radii. Alternatively, the chimney partitions 42-1 to 42-N may have elliptical or polygonal cross-sections instead of circular cross-sections. FIGS. 5A and 5B illustrate a chimney structure according to an example embodiment. Referring to FIGS. 5A and 5B, according to example embodiments, a chimney structure 500 may be the same as the chimney structure 110 described previously with regard to FIGS. 1A, 1B, and 2, except the chimney structure 500 may further include a partition structure 46 that includes a plurality of divider plates 47. The divider plates 47 of the partition structure 46 may define notches N that are spaced apart from each other. The number of notches N defined by the divider plates 47 may be equal to the number of chimney partitions 20-1 to 20-N in the chimney structure 500, and the number of notches N in the divider plates 47 may be spaced apart from each other at intervals equal to the spacing of the chimney partitions 20-1 to 20-N. The partition structure 46 may be placed on the chimney structure 500 so the notches N of the divider plates 47 fit over the chimney partitions 20-1 to 20-N. The divider plates 47 may extend through the chimney partitions 20-1 to 20-N. In other words, the chimney partitions 20-1 to 20-N may fit in the notches N of the divider plates 47. The divider plates 47 and the chimney partitions 20-1 to 20-N may define a plurality of curved opening sections, based on sectionally dividing the curved openings of the chimney partitions 20-1 to 20-N. The divider plates 47 may be metal sheets including notches that correspond to the chimney partitions 20-1 to 20-N. For example, the divider plates 47 may be made from SAE 304 or SAE 316 stainless steel. Although not illustrated, the partition structure may include a round housing surrounding the chimney partitions 20-1 to 20-N. An inner surface of the partition structure may define a round opening. The divider plates 47 of the partition structure 46 may divide the round opening into round opening sections. When the partition structure with a round housing is placed on the chimney structure 500, the divider plates 47 of the partition structure may sectionally divide the curved openings of the chimney partitions 20-1 to 20-N. Although FIGS. 5A and 5B illustrate an example where the partition structure 46 is constructed to fit over a chimney structure 500 including chimney partitions 20-1 to 20-N each having a tubular shape with circular cross-sections and different radii, one of ordinary skill in the art would understand various modifications in form may be made. For example, if the number of chimney partitions 20-1 to 20-N in the chimney structure is different than four, then the number of notches in the divider plates 47 may be adjusted to correspond to the number of chimney partitions 20-1 to 20-N. As another example, the partition structure 46 may be rotated 180 degrees and arranged so the chimney partitions 20-1 to 20-N are placed on the rotated partition structure 46. In other words, the divider plates 47 of the partition structure 46 may extend vertically from a bottom of the chimney partitions 20-1 to 20-N towards a top of the chimney partitions 20-1 to 20-N. Alternatively, if the chimney partitions 20-1 to 20-N have elliptical and/or polygonal cross-sections, then the notches N and orientation of the divider plates 47 may be adjusted to correspond to peripheries of chimney partitions having non-circular cross-sectional shapes. FIG. 5C illustrates a chimney structure according to an example embodiment. Referring to FIG. 5C, according to an example embodiment, a chimney structure 501 may be the same as the chimney structure 110 described previously with regard to FIGS. 1A, 1B, and 2, except the chimney structure 500 may further include a plurality of slats 52 between two adjacent chimney partitions among the chimney partitions 20-1 to 20-N. The plurality of slates 52 may be configured to divide a space between two adjacent chimney sections into smaller sections. The plurality of slats 52 may be attached to the inner chimney partition among the two adjacent chimney partitions. The plurality of slats 52 may be attached to the inner chimney partition using a hinge structure H. Because of the hinge structure H, the plurality of slats 52 may be configured to be positioned toward the outer chimney partition among the two adjacent chimney partitions in order to divide the space between the two adjacent chimney partitions into smaller sections, and the plurality of slats 52 may be configured to be positioned against the inner chimney partition among the two adjacent chimney partitions in order to avoid dividing the space between the two adjacent chimney partitions into smaller sections. For example, FIG. 5C illustrates an example where the plurality of slats 52 are attached to the outer surface of the chimney partition 20-3 with hinge structures H. The plurality of slats 52 may be adjusted open to extend towards the chimney partition 20-N. The plurality of slats may also be adjusted closed to be positioned against the outer surface of the chimney partition 20-3. When the chimney structure 501 is placed in an ESBWR reactor, positioning the plurality of slats 52 in a closed position may be beneficial during a refueling operation because it will be easier to move fuel rods through the chimney partitions 20-1 to 20-N when the plurality of slats 52 are in a closed position. When the plurality of slats 52 are in a closed position, the plurality of slats 52 do not divide the space between two adjacent chimney partitions into smaller sections. Alternatively, the plurality of slats 52 may be attached to the inside surface of the outer chimney partition among the two adjacent chimney partitions. The plurality of slats 52 may be attached to the insider surface of the outer chimney partition among two adjacent chimney partitions using a hinge structure H. Because of the hinge structure H, the plurality of slats may be configured to be positioned toward the inner chimney partition among the two adjacent chimney partitions in order to divide the space between the two adjacent chimney partitions into smaller sections, and the plurality of slats may be configured to be positioned against the inner surface of the outer chimney partition among the two adjacent chimney partitions in order to avoid dividing the space between the two adjacent chimney partitions into smaller sections. The plurality of slats 52 may be made from a metal and/or metal alloy. For example, the plurality of slats 52 may be made from SAE 304 or SAE 316 stainless steel. However, example embodiments are not limited thereto Even though FIG. 5C illustrates an example where the plurality of slats 52 are only between the chimney partitions 20-3 and 20-N, example embodiments are not limited thereto. The plurality of slats 52 may alternatively positioned between the chimney partitions 20-1 and 20-2 and/or between the chimney partitions 20-2 and 20-3. According to an example embodiment, a chimney structure may include a first plurality of slats between the chimney partitions 20-1 and 20-2, a second plurality of slats between the chimney partitions 20-2 and 20-3, and a third plurality of slats between the chimney partitions 20-3 and 20-N. Although FIG. 5C illustrates a chimney structure 501 including four chimney partitions 20-1 to 20-N having a common center, example embodiments are not limited thereto. The chimney partitions 20-1 to 20-N may include 2nd to (N−1)th concentrically arranged between the chimney partitions 20-1 to 20-N in sequential order. For example, the number of chimney partitions 20-1 to 20-N may be an integer greater than or equal to 4 and less than or equal to 12. However, number of chimney partitions 20-1 to 20-N may vary depending on the application is not limited thereto. FIG. 6 illustrates a chimney structure according to an example embodiment. Referring to FIG. 6, according to an example embodiment, a chimney structure 600 may include a plurality of chimney partitions 60-1 to 60-N having a common center. The chimney partitions may be positioned on a guide structure (not shown) with grooves corresponding to the peripheries of the chimney partitions 60-1 to 60-N. Each one of the chimney partitions 60-1 to 60-N may define an opening having a polygonal cross-section (e.g., a square, rectangle, octagon). The guide structure supporting the chimney structure 600 may also define an opening allowing fluid to flow through. When parts of the chimney partitions 60-1 to 60-N are positioned in the grooves of the guide structure, the openings of the chimney partitions 60-1 to 60-N may be arranged over the opening defined by the guide structure. FIG. 7 illustrates a reactor including a chimney structure according to an example embodiment. Referring to FIG. 7, according to an example embodiment, a reactor 700 includes a reactor core 112, a core inlet region 114, a chimney structure C secured to the reactor wall between reactor core 112 and a steam separator inlet region 116, and steam separators 118. The chimney structure C may be one of the above-described chimney structures according to example embodiments in FIGS. 1A, 1B, 2, 3E to 3H, 4A, 4B, 5A, 5B, and 6. Descriptions and/or features in each of the above-described chimney structures according to example embodiments should be considered as available in other chimney structures according to example embodiments. While a number of example embodiments have been disclosed herein, it should be understood that other variations may be possible. Such variations are not to be regarded as a departure from the spirit and scope of the present disclosure, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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058898328 | claims | 1. A control cluster for controlling a nuclear reactor, comprising: (a) a spider including: (b) a shock absorber having a socket slidable in said axial bore and spring means in said axial bore for urging said socket towards a position in which it projects downwardly from said spider and is in abutment against abutment means fast with said central portion; (c) a plurality of vertical control rods each having an upper plug formed with an upward extension traversing one of said through-hole and projecting upwardly out of the through-hole, wherein each said extension has at least two longitudinally spaced radially enlarged portions located within the through-hole, separated by at least one portion of reduced diameter, an upper one of said enlarged portions being slidably received in the respective through-hole for guiding the plug and being retained in abutment against shoulder means in the through hole by a nut in abutting contact with an upper surface of the respective finger and secured on a threaded upper end portion of the extension located entirely out of said through hole and a lower one of said enlarged portions having a diameter slighter than a diameter of said upper one for allowing a limited amount of lateral movement. 2. A control cluster according to claim 1, wherein said abutment means consists of an internal lower flange of said bore integral with said bottom part. 3. A control cluster according to claim 1, wherein said upper radially enlarged portion has a short cylindrical portion extending upwardly by a frustoconical abutment zone having an apex angle of about 110.degree. and downwardly by a frusto-conical zone merging with the portion of reduced diameter. 4. A control cluster according to claim 1, wherein said closing plug has at least one further axial portion of reduced diameter under the lower one of said radially enlarged portions. 5. A control cluster according to claim 1, further having a plurality of pins each engaged through a wall of a respective one of said fingers into a groove of a respective one of said plugs for preventing the plug from rotating, each of said pins which locks one of said fingers which is at an intermediate location on one said fin being in a direction oblique with respect to the respective fin. |
abstract | A mechanical device for supporting and attaching at least one ionizing radiation detection probe. For each detection probe it includes one probe-holder ending in a collimator-holder able to support a collimator intended to delimit a field of observation of the detection probe, and an attachment device intended to be attached to a glove port of a glove box, where the probe-holder, or each probe-holder, cooperates with the said attachment device. |
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claims | 1. A lithographic projection apparatus comprising: a radiation system constructed and arranged to supply a projection beam of radiation; a first object table for holding a mask; a second object table for holding a substrate; a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; and a gas structure constructed and arranged to supply a substantially laminar flow of flushing gas across at least a part of a path of said projection beam to displace ambient air therefrom, said flushing gas being substantially non-absorbent of said radiation, wherein said substantially laminar flow of flushing gas traverses a substantially non-obstructed region in said projection apparatus. 2. Apparatus according to claim 1 wherein said gas supply comprises a supply of flushing gas, a gas flow regulator and an evacuator constructed and arranged to remove flushing gas from said part of said beam path. claim 1 3. Apparatus according to claim 2 wherein said flow regulator comprises a flow restrictor. claim 2 4. Apparatus according to claim 2 wherein said flow regulator comprises a blowing unit. claim 2 5. Apparatus according to claim 1 , wherein said at least a part of the path includes a plurality of parts of said beam path substantially separated from each other. claim 1 6. Apparatus according to claim 1 , wherein said gas supply is arranged to provide separate laminar gas flows across a plurality of parts of said beam path, said parts of said beam path being substantially isolated from each other. claim 1 7. Apparatus according to claim 5 further comprising at least one partition comprised of a material substantially transparent to said radiation and positioned parallel to the direction of said laminar flow to isolate said part of said beam path. claim 5 8. The apparatus according to claim 7 , claim 7 wherein said partition closes a recess in said first object table in which said mask is mounted. 9. Apparatus according to claim 1 further comprising at least one cover member formed of a material substantially transparent to said radiation, said cover member being substantially planar and provided substantially parallel to the direction of said laminar flow to cover a non-planar surface of a component of said lithographic apparatus in a region of said part of said beam path. claim 1 10. Apparatus according to claim 9 wherein said cover member covers a non-planar surface of an element of one of said illumination system and said projection system. claim 9 11. Apparatus according to claim 7 wherein said material substantially transparent to said radiation is selected from the group comprising: CaF 2 , SiO 2 , MgF 2 and BaF 2 . claim 7 12. Apparatus according to claim 1 further comprising at least one flow control member provided in said part of said beam path. claim 1 13. Apparatus according to claim 1 wherein a speed of said laminar flow is greater than a maximum speed of movement of any moving parts in a region of said part of said beam path. claim 1 14. Apparatus according to claim 1 wherein a speed of said laminar flow is greater than a diffusion speed of air. claim 1 15. Apparatus according to claim 1 , wherein said flushing gas comprises one or more gases selected from the group comprising: N 2 , He, Ar, Kr, and Ne. claim 1 16. Apparatus according to claim 1 wherein said flushing gas in said part of said beam path has a contamination of air of less than 500 ppm. claim 1 17. Apparatus according to claim 1 wherein said flushing gas has an extinction coefficient, k, less than 0.005 per cm. claim 1 18. Apparatus according to claim 1 wherein said radiation of said projection beam has a wavelength less than 200 nm. claim 1 19. A method of manufacturing a device comprising: providing a substrate having a radiation-sensitive layer in a projection apparatus; irradiating portions of a mask bearing a pattern with a projection beam of radiation and imaging said irradiated portions of the mask onto target portions of said substrate; and providing flushing gas to flow in a substantially laminar flow across at least a part of a path of said projection beam to displace therefrom ambient air, said flushing gas being substantially non-absorbent of said radiation, and said laminar flow of flushing gas traversing a substantially non-obstructed region in said projection apparatus. 20. A device manufactured according to the method of claim 19 . claim 19 21. Apparatus according to claim 16 wherein said contamination of air is less than 100 ppm. claim 16 22. Apparatus according to claim 16 wherein said contamination of air is less than 10 ppm. claim 16 23. Apparatus according to claim 16 wherein said contamination of air is less than 1 ppm. claim 16 24. Apparatus according to claim 17 wherein said extinction coefficient is less than 0.001 per cm. claim 17 25. Apparatus according to claim 1 wherein said radiation of said projection beam has a wavelength selected from the group consisting of: between 152 nm and 162 nm and between 121 nm and 131 nm. claim 1 26. A lithographic projection apparatus comprising: a radiation system constructed and arranged to supply a projection beam of radiation; a first object table for holding a mask; a second object table for holding a substrate; a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; and a gas structure constructed and arranged to supply a substantially laminar flow of flushing gas, in a vicinity of said first object table and said second object table, across at least a part of a path of said projection beam to displace ambient air therefrom, said flushing gas being substantially non-absorbent of said radiation. 27. The apparatus according to claim 26 , wherein said gas structure comprises a gas flow regulator and an evacuator constructed and arranged to remove flushing gas from said part of said beam path. claim 26 28. The apparatus according to claim 26 , wherein said at least a part of the path includes a plurality of parts of said beam path substantially separated from each other. claim 26 29. The apparatus according to claim 26 , wherein said gas structure is arranged to provide separate laminar gas flows across a plurality of parts of said beam path, said parts of said beam path being substantially isolated from each other. claim 26 30. The apparatus according to claim 26 further comprising: claim 26 at least one cover member formed of a material substantially transparent to said radiation, said cover member being substantially planar and provided substantially parallel to the direction of said laminar flow to cover a non-planar surface of a component of said lithographic apparatus in a region of said part of said beam path. 31. The apparatus according to claim 26 , wherein a speed of said laminar flow is greater than a maximum speed of movement of any moving parts in a region of said part of said beam path. claim 26 32. The apparatus according to claim 26 , wherein a speed of said laminar flow is greater than a diffusion speed of air. claim 26 33. A lithographic projection apparatus comprising: a radiation system constructed and arranged to supply a projection beam of radiation; a first object table for holding a mask; a second object table for holding a substrate; a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; and a gas structure constructed and arranged to supply a substantially laminar flow of flushing gas, in a vicinity of said first object table, across at least a part of a path of said projection beam to displace ambient air therefrom, said flushing gas being substantially non-absorbent of said radiation. 34. The apparatus according to claim 33 , wherein said gas structure comprises a gas flow regulator and an evacuator constructed and arranged to remove flushing gas from said part of said beam path. claim 33 35. The apparatus according to claim 33 , wherein said at least a part of the path includes a plurality of parts of said beam path substantially separated from each other. claim 33 36. The apparatus according to claim 33 , wherein said gas structure is arranged to provide separate laminar gas flows across a plurality of parts of said beam path, said parts of said beam path being substantially isolated from each other. claim 33 37. The apparatus according to claim 33 further comprising: claim 33 at least one cover member formed of a material substantially transparent to said radiation, said cover member being substantially planar and provided substantially parallel to the direction of said laminar flow to cover a non-planar surface of a component of said lithographic apparatus in a region of said part of said beam path. 38. The apparatus according to claim 33 , wherein a speed of said laminar flow is greater than a maximum speed of movement of any moving parts in a region of said part of said beam path. claim 33 39. The apparatus according to claim 33 , wherein a speed of said laminar flow is greater than a diffusion speed of air. claim 33 40. A lithographic projection apparatus comprising: a radiation system constructed and arranged to supply a projection beam of radiation; a first object table for holding a mask; a second object table for holding a substrate; a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; and a gas structure mounted to an extremity of at least one of said radiation system and said projection system, said gas structure is constructed and arranged to supply a laminar flow of flushing gas across at least a portion of a path of said projection beam, said flushing gas being substantially non-absorbent of said radiation. 41. The apparatus according to claim 40 , wherein said gas structure comprises an evacuator constructed and arranged to remove flushing gas from said part of said beam path in a vicinity of said extremity of said at least one of said radiation system and said projection system. claim 40 42. The apparatus according to claim 41 , wherein the structure of flushing gas is provided through an outlet mounted to an extremity of said at least one of said radiation system and said projection system and said evacuator is provided with an inlet facing said outlet and mounted to an extremity of said at least one of said radiation system and said projection system. claim 41 43. The apparatus according to claim 42 , wherein at least one of said inlet and said outlet comprises vanes configured and arranged to control the flow of said flushing gas. claim 42 44. The apparatus according to claim 40 , wherein a speed of said laminar flow is greater than a maximum speed of movement of any moving parts in a region of said part of said beam path. claim 40 45. The apparatus according to claim 40 , wherein a speed of said laminar flow is greater than a diffusion speed of air. claim 40 46. The method according to claim 19 , wherein said flushing gas is provided in a vicinity of at least one of the mask and the substrate. claim 19 47. The method according to claim 19 , wherein said flushing gas flows across at least one substantially transparent cover member covering a non-planar surface of a component of the projection apparatus in a region of said part of said beam path, the cover member being substantially planar and substantially parallel to the direction of said laminar flow. claim 19 |
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summary | ||
description | The present invention relates to a disposal container and a storage system for high-level radioactive waste and, more specifically, to a disposal container for high-level radioactive waste using multiple barriers and a barrier system using thereof, the disposal container having the multiple barriers consisting of an inner wall made of carbon steel for excellent corrosion resistance and ease of manufacture, a middle wall made of Inconel, which is bonded to a lateral surface of the inner wall, and an outer wall made of copper, which is bonded to a lateral surface of the middle wall. High-level radioactive waste (hereinafter, “high-level waste”) refers to waste which contains high levels of radioactive materials, indicating waste solution resulting from the reprocessing of Spent Nuclear Fuel (SNF), or the SNF itself. In spite of utilization of SNF recycling technology such as pyroprocessing, etc., and management of the volume-reduced SNF in Generation-IV Reactor such as Sodium-cooled Fast Reactor, etc., the volume is small, however high-level waste is still generated. Thus, as long as human beings utilize nuclear power as an energy source, high-level waste is an inevitable consequence, and the importance of development of technology for safe disposal can not be overemphasized. Especially, high-level waste requires extremely special management due to high amount of long-lived radioactive nuclides (I-129, Cs-134, Sr-90, Pu-238, Am-241, Cm-244, etc.) and decay heat generated from such nuclides. Not only is it difficult to perform incineration or chemical treatment towards high-level waste, but radioactive materials are generated during few million years. Thus, it is extremely dangerous to store radioactive materials near residences of people. As long as industrial society of human beings becomes more advance, production of high-level waste is inevitable. Therefore, it is highly important to develop technologies for safely treating and disposing such waste, socially, nationally, and even worldwidely. Furthermore, it is extremely significant to develop such technologies for human beings' safe future. The only way to dispose of materials (radioactive materials, heavy metals, etc.), generated from high-level waste and dangerous to human beings, provided that there is no special disposal technology, is to dispose these materials deep beneath the surface, extremely kept away from human living environment. This is an eco-friendly way in which such materials coming from nature send back to nature, and harmful property against human beings becomes extinct automatically after a long period of time. The time period of isolating high-level waste from human environment requires tens of thousands of years, or several hundreds of thousands of years. From earlier, in 1956, the National Academy of Science (NAS) recommended searching several rock formation including bedded salt for deep geological disposal, wherein the deep geological disposal is appropriate for high-level waste treatment. Since the 1970s, USA, France, Canada, Japan, Swiss, Belgium, Sweden, Finland, etc., have accumulated technologies concerning deep geological disposal in accordance with each country's state. Accordingly, the technology development of deep geological disposal, as an eco-friendly waste disposal technology, has been well under way already in several major countries. As a deep geological disposal, currently being developed, there is a method for burying high-level waste in repositories at a depth of 500 to 1,000 metres below the ground's surface. Actually, in Finland, the world's largest nuclear power plants are under construction in Olkiluoto Island located in the northwest of Helsinki, a capital, along with deep geological repositories of high-level waste. And, in Sweden, a place to which underground repositories are installed has been determined in June, 2009. Since 2005, in France, a mine in 490 metres in length has been dug into underground in Bure in eastern France, and underground disposal research facilities of deep geological disposal which is 5 meters in diameter and 535 metres in total length has been installed, thereby focusing on a thorough investigation for complete disposal of high-level waste. In Korea, research on deep geological disposal technology of high-level waste, led by Korea Atomic Energy Research Institute, has been conducted since 1997. As a result, underground research tunnel (KURT) has been established in November, 2006, thereby developing a technological barrier system consisting of a disposal container, a buffer, and a back filler, preventing leakage of radioactive materials due to introduction of multiple barrier concepts, and performing a research on movement of underground water. The core technologies of such deep geological disposal of high-level waste are to develop a disposal container for sealing high-level waste, and to build deep geological repositories of the disposal container in which high-level waste is sealed and develop operations technologies. The factors affecting such technology developments are radioactive materials and decay heat generated from high-level waste, geological features of deep geological repositories of high-level waste, underground water which goes into repositories and its movement, shear deformation in supporting rock of deep geological repositories due to crustal movement like earthquake, etc. Actually, in order to endure disposal condition for a long disposal period (approximately 10,000 to 1,000,000 years) at a depth of 500 to 1,000 metres below the ground's surface in deep geological environment, the disposal container has to be designed to have sufficiently structural strength, easy production/delivery/treatment, and light weight for minimizing differential settlement by dead load of the disposal container upon disposal. For example, Korean Patent No. 10-1046515 discloses a module disposal container of high-level waste canister and buffer material, more particularly, the disposal container of high-level waste for storing and disposing high-level waste to deep underground rock, comprising: a canister, vacuum inside, for storing the high-level waste; a buffer material for storing the canister; and a shell, made of corrosion-resistant and high-intensity material, installed to the lateral surface of the buffer material, wherein the canister, the buffer material and the shell are integrated, and the buffer material and the shell are in polygonal-side shape; and a disposal system for storing and disposing high-level waste to the deep underground comprising: a disposal container which includes a canister for storing high-level waste, a first buffer material, in polygonal-side shape, for being integrated to the outside of the canister, and a shell, made of corrosion-resistant and high-intensity material, installed to the lateral surface of the first buffer material; a repository tunnel for being installed by digging rock formation and storing the disposal container in order to settle polygonal sides of the disposal container; a second buffer material, made of pure bentonite and installed between the disposal container and the repository tunnel; and a back filler for filling empty spaces between the second buffer material and the repository tunnel. Further, Korean Patent Publication No. 10-2010-0057238 discloses a module system of high-level waste canister and buffer material, more particularly, a disposal system of high-level waste for storing and disposing high-level waste to deep underground rock, a canister for storing high-level waste; a disposal container for storing the canister and a mixed buffer material; a disposal repository tunnel for being formed by digging rock formation and storing the disposal container; a second buffer material, made of pure bentonite and formed between the disposal container and the disposal repository tunnel; and a back filler for filling empty spaces between the second buffer material and the repository tunnel. However, such disposal container is mostly cylindrical and comprised of one-type metal material and the disposal container and fillers are filled inside of the titanium, square-shaped shell. Thus, the intensity of the disposal container is relatively weak. Furthermore, as for disposal container, it is important to make sure to maintain integrity no matter what kind of loads are applying in underground environment. The magnificent perspectives on selecting material of the disposal container are physicochemical factors, manufacturing convenience, and economical efficiency. The physicochemical factors are related to a lifespan of the disposal container and integrity. In standards in relation to the physicochemical factors, corrosion resistance is the most important, the mechanical strength, in normal, embrittlement sensitivity toward radiation, in normal, and quality dependency, important. Accordingly, corrosion resistance needs to be firstly secured on selecting materials of the disposal container. Also, lots of disposal container should keep the identical quality and thus, it is important to require the quality dependency of materials. Although it is necessary to secure mechanical strength of containers, actually, most of metals are superior in strength and thus, the importance is in normal. Next, embrittlement matter induced by radiation in microelement of metals needs to be kept below acceptable value (ppm). Further, materials of the disposal container should require superior processability and weldability and convenience in non-destructive inspection. However, there is a problem in which the disposal container, manufactured so far, has not been satisfied for the properties. (Patent document 001) Korean Patent Registration No. 10-1046515 (Patent document 002) Korean Patent Publication No. 10-2010-0057238 For solving above problems, the object of the present invention is to provide a disposal container for high-level radioactive waste using multiple barriers and a barrier system using thereof, the disposal container having the multiple barriers consisting of an inner wall made of carbon steel for excellent corrosion resistance and ease of manufacture, a middle wall made of Inconel, which is bonded to a lateral surface of the inner wall, and an outer wall made of copper, which is bonded to a lateral surface of the middle wall. Further, the another object of the present invention is to provide a disposal container for high-level radioactive waste using multiple barriers and a barrier system using thereof, attaching a heat sink to a lateral surface of the outer wall of the disposal container, arranging a radiation fin vertically between the heat sink and the outer wall, and installing a siphon pipe between the heat sink and the outer wall, thereby discharging heat, generated from the disposal container, outside for cooling. Further, the another object of the present invention is to provide a disposal container for high-level radioactive waste using multiple barriers and a barrier system using thereof, wherein a deposition hole is vertically formed at a repository tunnel in rock formation and the disposal container is installed inside the deposition hole, thereby being filled with Na-Bentonite as a filler. To accomplish above objects, the present invention comprises an inner wall, made of carbon steel, for being cylindrical in shape; a middle wall, made of Inconel, for being cylindrical in shape and bonded to an outer surface of the inner wall; and an outer wall, made of copper, for being bonded to a lateral surface of the middle wall. Hereinafter, the outer wall further installs a heat sink made of aluminum or copper and separated from a lateral surface for releasing heat which is generated inside and transferred to the outer wall, and a radiation fin made of materials same as the heat sink is combined between the heat sink and the outer wall. Hereinafter, the radiation fin is combined to the lateral surface of the heat sink. Hereinafter, a siphon pipe for storing refrigerants at a certain level is further installed between the heat sink and the outer wall, thereby making the inside in a vacuum state for releasing heat generated from the inside to the outer wall. A barrier system using the disposal container of high-level radioactive waste using multiple barriers comprises a disposal tunnel which is formed by digging rock formation; a deposition hole which is vertically or horizontally perforated, thereby storing the disposal container; and a buffer which is filled with the deposition hole and the disposal container. Hereinafter, the buffer is composed of Na-Bentonite. According to a disposal container for high-level radioactive waste using multiple barriers and a barrier system using thereof of the present invention, as constituted above, it provides a disposal container with multiple barriers consisting of an inner wall made of carbon steel, a middle wall made of Inconel, which is bonded to a lateral surface of the inner wall, and an outer wall made of copper, which is bonded to a lateral surface of the middle wall, thereby providing relatively superior corrosion resistance and manufacturing convenience. Further, according to the present invention, a heat sink is attached to a lateral surface of the outer wall of the disposal container; a radiation fin is arranged vertically between the heat sink and the outer wall; and a siphon pipe is installed between the heat sink and the outer wall, thereby discharging heat, generated from the disposal container, outside for cooling, thereby enabling to provide safe storage. Further, according to the present invention, a deposition hole is vertically formed at a repository tunnel in rock formation and the disposal container is installed inside the deposition hole, thereby being filled with Na-Bentonite as a filler, thereby satisfying property and economic feasibility. The configuration of a disposal container of high-level radioactive waste using multiple barriers of the present invention will be described in detail with the accompanying drawings. In the following description of the present invention, a detailed description of known incorporated functions and configurations will be omitted when to include them would make the subject matter of the present invention rather unclear. Also, the terms used in the following description are defined taking into consideration the functions provided in the present invention. The definitions of these terms should be determined based on the whole content of this specification, because they may be changed in accordance with the option of a user or operator or a usual practice. FIG. 1 illustrates a front sectional view showing the constitution of a disposal container of high-level radioactive waste using multiple barriers according to the present invention; FIG. 2 illustrates a front sectional view showing the constitution of a disposal container of high-level radioactive waste using multiple barriers according to other embodiments of the present invention; FIG. 3 illustrates a partial sectional perspective view of FIG. 2; FIG. 4 illustrates a front sectional view showing the constitution of a disposal container of high-level radioactive waste using multiple barriers according to another embodiments of the present invention; and FIG. 5 illustrates a partial sectional perspective view of FIG. 4. Referring to FIGS. 1 to 5, a disposal container of high-level radioactive waste using multiple barriers (10) according to the present invention consists of an inner wall (11), a middle wall (12) and an outer wall (13). First, the inner wall (11) made of carbon steel for excellent economic value and ease of manufacture is cylindrical in shape. Hereinafter, it is desirable that an upper side of the inner wall (11) is open for storing high-level radioactive waste inside, and a thickness may be adjustable optionally. Further, the middle wall (12) made of Inconel for excellent corrosion resistance is bonded to a lateral surface of the inner wall. Hereinafter, it is desirable that an upper side of the middle wall (12) is open for storing high-level radioactive waste inside equally to the inner wall (11), and a thickness may be adjustable optionally. Further, the outer wall (13) made of copper for excellent corrosion resistance is bonded to a lateral surface of the middle wall (12). Hereinafter, it is desirable that an upper side of the outer wall (13) is open for storing high-level radioactive waste inside equally to the inner wall (11), and a thickness may be adjustable optionally. Meanwhile, the upper sides of the inner wall (11), the middle wall (12), and the outer wall (13) are bonded to a cover (14), wherein a thickness of the cover (14) is the same with that of the upper sides of the inner wall (11), the middle wall (12), and the outer wall (13), by triplex-forming from a bottom in a series of carbon steel, Inconel, and copper. Continuously, as illustrated in FIGS. 2 and 3, the disposal container of high-level radioactive waste using multiple barriers (10) according to the present invention further installs a heat sink (15) made of aluminum or copper and separated from a lateral surface for releasing heat which is generated inside the inner wall (11) and transferred to the outer wall (13). Further, a radiation fin (16) made of materials same as the heat sink (15) is vertically combined between the heat sink (15) and the outer wall (13), and the radiation fin (16) is vertically combined even to the lateral surface of the heat sink (15), selectively. The strength between the heat sink (15) and the outer wall (13) may be further reinforced by installing such radiation fin (16). Further, if a thickness of the radiation fin (16) is thin in the center and gets thicker towards the outside, thin parts are broken under earthquake and shock is absorbed, thereby further enabling to improve seismic performance. Further, as illustrated in FIGS. 4 and 5, a siphon pipe (17) for storing refrigerants at a certain level may be further installed between the heat sink (15) and the outer wall (13), thereby making the inside in a vacuum state for releasing heat generated from the inside of the inner wall (11) and transferred to the outer wall (13). Hereinafter, in the siphon pipe (17), if heat generated from high-level radioactive waste is transferred through the inner wall (11), the middle wall (12), and the outer wall (13), the refrigerants vaporize into steam due to transferred heat and move up; the vaporized steam frozen by temperature of the heat sink (15) is converted to liquid refrigerants and moves down; vaporization and falling are repeated, thereby cooling the outer wall (13) and transferring cooling heat to the outer wall (13), the middle wall (12), and the inner wall (11). Hereinafter, the constitution of a barrier system using a disposal container of high-level radioactive waste using multiple barriers according to the present invention will be described in detail with the accompanying drawing. FIGS. 6 to 8 illustrate sectional views showing the constitution of a barrier system using the disposal container of high-level radioactive waste using multiple barriers according to the present invention. Referring to FIGS. 6 to 8, the barrier system using a disposal container of high-level radioactive waste using multiple barriers (1) according to the present invention consists of a disposal tunnel (A), a deposition hole (B), a disposal container (10), and a buffer (20). First, the disposal tunnel (A), as a general structure, is formed by digging rock formation. Further, the deposition hole (B) is vertically or horizontally perforated in the disposal tunnel (A), thereby storing the disposal tunnel (A). Further, as explained above, the disposal container (10) is composed of the inner wall (11), the middle wall (12) and the outer wall (13). Here, in the disposal container (10), the heat sink (15) is installed to the outer wall (13); and the radiation fin (16) may be further installed between the outer wall (13) and the heat sink (15), and the heat sink (15) outside, or the siphon pipe (17) may be installed between the heat sink (15) and the outer wall. Further, the buffer (20) is filled in the space between the deposition hole (B) and the disposal container (10). Here, it is desirable that Na-bentonite is used in the buffer (20), and the buffer (20) may be block-shaped. Meanwhile, if high-level waste repositories are constructed in deep crystalline rock, the buffer is compulsorily installed to prevent inflow of underground water through rock fracture, the disposal container corroded, and radioactive nuclide discharged. Along with the disposal container, the buffer is a key component of technological wall in high-level waste repositories. After digging deposition holes on the bottom of disposal cave and positioning the disposal container with wrapped waste, the buffer is installed by filling in the space between the disposal container and the rock wall of the deposition holes. The main functions of the buffer in the waste repositories are inflow suppression of underground water, control of discharge of radioactive nuclide, prevention of disposal container against external stress, and dispersion of decay heat, generated from waste, towards the outside, as well. For selecting a suitable material as a buffer in high-level waste repositories, several countries have conducted on many substances. As a survey result, it is revealed that clay-based material and cement-based material may be utilized as a buffer. However, the cement material increases pH of underground water more than 12.5, and it may be possible to accelerate erosion of disposal container in such pH condition. Thus, clay-based material is more preferred, as a buffer. The clay-based material has different physicochemical characteristics in accordance with constitutional minerals. As major minerals, there are Kaolinite, Illite, Montmorillonite, etc. Among them, Montmorillonite has higher swelling degrees than Kaolinite or Illite, thereby having much lower hydraulic conductivity under identical dry density. Also, since cation exchange capacity (CEC) and nuclide distribution coefficients are high due to large specific surface areas, it turns out to be superior as compared to other minerals even in radionuclide-retarding capacity. Thus, the more the clay-based material has Montmorillonite, the more it is known as being suitable as a buffer. Bentonite is a clay-based material, wherein it is primarily composed of Montmorillonite, thereby more preferring as buffer candidate than other clay in many countries currently planning on repository construction. In contact with water, Bentonite has swelling degrees, wherein interlayer of Montmorillonite is hydrated and volume is increased. After placing the disposal container in the deposition hole, the empty space between the disposal container and the deposition holes is filled with Bentonite buffers, thereby swelling in contact with water when underground water from surrounding rocks gets through the inside of the deposition holes and then, blocking underground water penetration. Since Bentonite has extremely high swelling degrees as compared to other clay, empty spaces may be filled up by means of swelling when there are empty spaces or cracks in the buffer while installing the buffer. Also, Bentonite has high absorption capacity towards most of cationic nuclides, thereby effectively enabling to prevent radioactive nuclides to be discharged to surrounding rocks in case that radioactive nuclides are discharged from waste. Besides, Bentonite is a stabilized natural material form by long-term conformational changes, thereby enabling to maintain long-term stabilization by keeping original states without characteristics changes during life time of high-level waste disposal plant. Bentonite may be classified into Na-Bentonite and Ca-Bentonite in accordance with types of exchangeable cation which exists in layers of Montmorillonite. Generally, Na-Bentonite has higher swelling than that of Ca-Bentonite and thus, it is known as more suitable buffer. It is desirable that Na-Bentonite is used in the present invention. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 1: barrier system10: disposal container11: inner wall12: middle wall13: outer wall14: cover15: heat sink16: radiation fin17: siphon pipe20: bufferA: disposal tunnelB: deposition hole |
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abstract | A fuel storage system for storing and drying nuclear fuel rods includes a vertically oriented capsule defining an internal cavity. A plurality of fuel rod storage tubes is disposed in the cavity. In one embodiment, each storage tube has a transverse cross section configured and dimensioned to hold no more than one fuel rod. Intact or damaged fuel rods may be stored in the storage tubes. After the fuel rods are loaded into the capsule, a lid is attached to a previously open top end of the capsule. In one embodiment, the lid may be sealed welded to the capsule for forming a gas tight enclosure. The interior of the capsule and multiple fuel rods contained therein may be dried together simultaneously via flow conduits formed in the lid that can be fluidly connected to a suitable drying process such as a forced gas dehydration system. |
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053612795 | summary | BACKGROUND OF THE INVENTION The present invention relates generally to the drive mechanism that positions control rods within the nuclear core of a boiling water reactor. More particularly, a control rod drive which is completely contained within the reactor pressure vessel is described. In boiling water reactors, the control rod drives are traditionally positioned outside and below the reactor pressure vessel. Since the control rods are each positioned within the pressure vessel, each drive must include a coupling that penetrates the pressure vessel. This design has several disadvantages. One of the most noticeable drawbacks is the requirement that the containment structure (as well as the reactor pressure vessel) must be very high in order to provide sufficient storage space for the control rods below the reactor fuel bundles. Another major drawback is the existence of a very large number of items that must penetrate the reactor walls (i.e. the connecting rods). SUMMARY OF THE INVENTION It is a general objective of the present invention to provide an internal control rod drive arrangement for a boiling water reactor that permits more compact pressure vessel designs and substantially reduces the number of vessel penetrations required to facilitate control of the control rod positioning. To achieve the foregoing and other objects and in accordance with the purpose of the present invention, a control rod drive system is disclosed for positioning the control rods relative to fuel rods positioned in a nuclear core of a boiling water reactor. In a first aspect of the invention the control rod drives each include a jack rod and a hydraulic jack. The jack rod is coupled to a control rod. It may be either integrally formed with the control rod or coupled via a connector. The hydraulic jack is positioned within the pressure vessel above the nuclear core. The jack is capable of lifting, lowering and holding the jack rod to position the control rod. In a preferred embodiment, the jack includes a hydraulically operated holding mechanism and a hydraulically operated lifting mechanism. The holding mechanism has holders arranged to selectively engage the jack rod to hold the jack rod in place. The lifting mechanism includes lifters arranged to selectively engage the jack rod and a lift cylinder arranged to lift or lower the jack rod when the holders are disengaged and the lifters are engaged. In a second preferred aspect of the invention a hydraulically operated hold control valve is also provided for each control rod drive. The use of hold control valves facilitates the use of an addressing system that dramatically reduces the number of hydraulic lines that are required to operate the system. The hold control valve is positioned within the jack and is moveable between an open position and a closed position. In the open position a communication path is formed between a first hydraulic line and a holding line. The holding mechanism includes a holding piston arranged to move the holders between engaged and disengaged positions. A A first side of the holding piston is influenced by the first hydraulic line and a second side of the piston is influence by the holding line. The lifting cylinder is influenced by a second hydraulic line. In a preferred embodiment, the hold control valve includes a plunger that is moveable between an open and a closed position and a biasing spring for biasing the plunger towards the closed position. Additionally, both the first and the second hydraulic lines are arranged to influence the plunger in a direction towards the open position. In a third aspect of the invention, an open grid is provided within the pressure vessel at a position above the nuclear core of the boiling water reactor. The grid includes a multiplicity of mounting surfaces with each mounting surface supporting one of the hydraulic jacks. The hydraulic lines required to control the jacks may be strung along the sides of the grid beams. In one preferred embodiment, each mounting surface includes an alignment foot that mates with an associated alignment recess in the associated control rod drive and a pair of spaced apart raised hydraulic ports that mate with associated port recesses in the associated control rod drive. The alignment foot and the raised hydraulic ports cooperate to align the control rod drive. In a separate preferred embodiment, the control rods are cruciform in shape and each mounting surface and each control rod drive has a cruciform opening therein through which the control rod may be withdrawn during maintenance operations. |
abstract | An apparatus and method for pressurizing SiC clad rods of a nuclear core component. A lower end of the rod is sealed with a lower end plug and an upper end of the rod is sealed between the cladding and an external piece of an upper end plug that has a through opening through which a separate internal piece of the upper end plug extends. The internal piece of the upper end plug is initially moveable within the through opening between an upper position that forms a gas tight seal and a lower position that forms a gaseous path through the through opening. The rod is placed in a pressure chamber pressurized to a desired pressure. When the pressure is reduced within the pressure chamber the internal pressure in the rod biases the internal piece of the upper end plug in the upper sealed position. |
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description | This application claims priority benefits of German Patent Application No. 10 2004 028 035.5 filed Jun. 9, 2004. The present invention relates to an apparatus for compensation of three-dimensional movements of a target volume on a patient couch during ion beam irradiation using, especially, a raster scanning apparatus. This apparatus comprises a position location and tracking system which detects the three-dimensional movements of the target volume longitudinally and transversely with respect to the ion beam. The apparatus further comprises a depth modulator, by means of which the depth of penetration of the ion beam can be re-adjusted. Furthermore, in a development, the apparatus is in operative connection with the raster scanning apparatus, which makes possible transverse deflection of the ion beam in fractions of milliseconds. An apparatus of such a kind is known from joint consideration of the publications DE 100 31 074 A1 and EP 99 107 127, in which the principle of a method for precision irradiation of moving target volumes using the ion raster scanning method is also presented. The method described requires dynamic correction of the transverse and longitudinal irradiation parameters in irradiation run time. The transverse correction is based on the raster scanning method and is described in the publication EP 99 107 127. Accordingly, using the raster scanning method, the settings in the transverse direction relative to the ion beam can be changed and thereby corrected from irradiation point to irradiation point. Because of the fact that an intensity control is also provided for the raster scanning method, this also makes it possible to modify the longitudinal irradiation parameters of a previously determined desired position. However, although the transverse modifications and corrections can be made in fractions of milliseconds, the longitudinal settings can be changed only in synchronicity with the cycle of the particle accelerator and, as a result, very slowly. The associated problem relating to the depth of penetration of the ion beam into tissue is illustrated in FIG. 1. FIG. 1 shows the consequences that changes in the consistency of the structure of healthy tissue covering the target volume in the upstream direction of the beam have on distribution of the dose in the case of photon irradiation (curves a and b) compared to ion irradiation (curves c and d), the depth of penetration w being plotted against the abscissa and the ion dose absorbed by the tissue being plotted against the ordinate. In the event of three-dimensional movement of the body of a patient on a patient couch, it is not only the location of the patient and, as a result, the location of the target volume transversely and longitudinally relative to the ion beam that changes, but also the composition, density, thickness and consistency of the healthy tissue arranged in the direction of the beam upstream of the target volume, which results, in the case of photon irradiation, in curve b (during or after movement) differing from curve a (before movement) in terms of dose distribution. In the case of ion irradiation, the consequences are much more serious, as comparison of curves c (before movement) and d (during or after movement) in FIG. 1 shows, because in the case of ion irradiation the dose distribution does not tail off exponentially along with the depth of penetration as it does in the case of photon irradiation but rather there is a dose escalation which can, because of the change in the covering tissue, be displaced, for example by the difference in depth of penetration Δw, in the event of movement, consequently missing the planned volume element of the target volume. The distribution of the dose administered by ion irradiation is therefore, in contrast to photons, extremely sensitive to changes in the longitudinal direction, for example in the event of changes in density, in the healthy tissue through which the beam passes. Such changes occur, for example in the course of organ movement due to breathing, on a shorter time scale than the accelerator cycle which governs the speed with which the conventional raster scanning method could react. This means that correction, including correction of depths of penetration, cannot exactly follow changes resulting from movement of the patient in a short time span from irradiation position to irradiation position using the conventional raster scanning method. Detection of the longitudinal displacement of the target volume, in the event of patient movement, solely by means of precision video cameras, as is known from the publication DE 100 31 074 A1, does not allow exact beam modification or correction, even if that modification could be carried out from beam position to beam position on the basis of the apparatus disclosed therein for the shift in the target volume. The intensity-modulated raster scanning method allows irradiation of deep-lying tumours with. extremely high geometric precision, albeit relatively slowly. However, the success of therapy is, in the case of beam therapy, dependent on the dose in the target volume, that dose generally being limited by the doses that are acceptable in the surrounding tissue. Compared to conventional photon irradiation, the geometric precision of the intensity-modulated raster scanning method makes it possible, in many cases, to obtain a dose escalation in the target volume, as shown in FIG. 1. In order to be able to utilise that precision, however, the relative location, in terms of position, of the target volume must, at all times during irradiation, coincide with the case assumed in an irradiation plan. The routinely used fixing of the target region does not provide sufficient accuracy in all cases, for example in the thoracic region. Any remaining change in length or displacement of the volume to be irradiated relative to the reference position for the irradiation plan results in incorrect positioning and, therefore, in an incorrect dose of ions. Accordingly, the number of ions actually administered per volume no longer agrees with the planned distribution, that is to say the homogeneity and geometry of dose distribution changes and the success of therapy is jeopardised as a result. This problem is illustrated by FIG. 2, which shows the relative dose homogeneity for a statically fixed target volume (curve e) and for a target volume of changed location (curve f), in dependence upon the depth of penetration w. Even in the case of a static or fixed target volume, the dose homogeneity decreases with increasing depth of penetration w because of scatter and absorption mechanisms of the ion beam in the tissue. However, when the target volume has a static, that is to say fixed, location, that decrease is not more than 10% (curve e, FIG. 2) of the dose introduced. In the event of movement of the target volume, however, considerable longitudinal changes in depth of penetration can occur, as already shown in FIG. 1, so that the relative dose homogeneity can, as shown in FIG. 2, deteriorate by up to 60% (curve f, FIG. 2) if compensation is not carried out. The problem of the invention is to provide an apparatus and a method for compensation of movements of a target volume during ion beam irradiation which overcome the problems described above and which improve the precision of irradiation of a target volume. The problem is solved by the subject-matter of the independent claims. Advantageous developments of the invention will be found in the dependent claims. In accordance with the invention, an apparatus and a method are provided for compensation of three-dimensional movements of a target volume on a patient couch during ion beam irradiation using a raster scanning apparatus. For the purpose, the compensation apparatus comprises a position location and tracking system, which detects the three-dimensional movements of the target volume longitudinally and transversely relative to the ion beam and which in the process is in operative connection with a movement measurement, control and read-out module SAMB. The compensation apparatus also comprises a depth modulator which is in operative connection with the movement measurement, control and read-out module SAMB for changing the depth of penetration w of the ion beam. In addition, the raster scanning apparatus, as part of the apparatus which deflects the ion beam transversely, is in operative connection with a location measurement, control and read-out module SAMO for changing excursion of the beam in a transverse direction. For the purpose, the movement measurement, control and read-out module SAMB comprises a microprocessor having a memory. The memory contains data of a model of a structure of the healthy tissue which covers the target volume in the upstream direction of the beam. The microprocessor additionally comprises computational components which break down the detected movements of the target volume vectorially into longitudinal and transverse components. The computational components also compare the longitudinal components against the stored model for correction of the depth of penetration of the ion beam. The data of a model in the memory are preferably derived from ultrasound sections or X-ray images of the healthy covering tissue over the target volume. Both X-ray investigations and also ultrasound investigations in the preliminaries to ion irradiation have the advantage that they are capable of exactly representing the healthy covering tissue over the target volume both in terms of its thickness and also in terms of its composition, its consistency and its density. As a result, the precision of compensation of longitudinal deviations can be carried out much more precisely than in the case of conventional apparatuses and methods. In addition, the validity of the model can be continuously ensured by further measurements using X-ray detection devices and/or ultrasound detection devices. In addition, this apparatus has the advantage that, on the basis of the detected change in the location and position of the current target volume at the moment of irradiation, it is possible to determine a three-dimensional correction vector for the radiological position of the volume element in question and, by compensating for the disruptive movement by means of appropriately directed displacement of the therapy beam, it is ensured that the number of ions optimised in the preliminaries to irradiation in accordance with an irradiation plan is delivered to the volume element in question. To compensate for movement of the target region during irradiation, the therapy beam is re-adjusted in all three spatial directions. Dividing the compensation into a transverse and a longitudinal component allows re-adjustment by means of the raster scanning apparatus and by means of a depth modulator. In the event that the target volume, because of its anatomical arrangement, does not move despite the fact that movements of the patient result in changes in the healthy tissue through which the beam passes, only longitudinal compensation is necessary; accordingly, the energy of the ion beam has to be modified in line with the movement so that in all cases the range of the ion beam is altered so that interaction with the target volume element is ensured. This is also the case when, for example, beam re-adjustment in the transverse direction in line with the movement of the target volume is carried out by a raster scanning apparatus in real time and it is consequently ensured during irradiation that the ion beam follows the moving target volume. In the concomitantly moved co-ordinate system, it again becomes necessary, in the event of movement of the tissue through which the beam passes relative to the target volume, to modify the depth of penetration of the ion beam in line with the particular tissue through which the beam is to pass. Even though the obtainable accuracy of distribution of the administered dose will be dependent on the quality of compensation, as is shown hereinafter in FIGS. 5 and 6, it is in principle possible to achieve high degrees of homogeneity that, by virtue of the subject-matter of the present invention, are comparable with the quality of static target volumes. Precision irradiation of moving target regions, or in the case of movement of the tissue through which the beam passes, is achieved by the very accurate compensation of movement, for which purpose the raster scanning apparatus and the depth modulator correct the beam positions during irradiation at a speed that is substantially greater than the movement of the target volume or of the tissue through which the beam passes. The corrected position is governed by the desired position in the uncorrected state and the actual displacement of the particular volume element of the target volume in the reference system of the irradiation plan. Fixed integration of movement compensation into the supervisory control system of the raster scanning apparatus makes possible a data exchange which ensures that the safety and reliability of the dose administered per unit volume of the target volume is improved despite three-dimensional movement. As a result, the subject-matter of the present invention allows the previously described raster scanning method to be extended to indications in target regions which are not capable of being fixed or not capable of being fixed adequately and/or to target regions in which the tissue through which the beam passes changes in terms of its energy-absorbing action as a result of movement. It makes it possible to irradiate tumours in the thorax and abdomen with a high degree of precision similar to that which is achievable in the case of fixed target regions. Existing alternatives having movement correction arrangements result either in less precision or in a significantly longer duration of irradiation. Those methods can disadvantageously reduce the prospects for successful therapy or the number of patients treated per unit time. Neither of those results occurs in the case of the described subject-matter of the invention. The apparatus according to the invention can, moreover, facilitate patient positioning because, in the event of slight errors in positioning, the beam position is automatically modified. In the case of the apparatus according to the invention, strict patient fixing is no longer imperative, as a result of which patient comfort is substantially increased. In a preferred embodiment of the invention, the raster scanning apparatus comprises two raster scanning magnets, which deflect an ion beam orthogonally in relation to a coupling-in direction into the raster scanning magnets, in an X and a Y direction, which are in turn perpendicular to one another, for scanning the area of the target volume slice-wise, the raster scanning magnets being controlled by fast-reacting power supply units. This has the advantage that transverse compensation of the transverse change in the target volume and its covering tissue due to movement can be carried out from irradiation position to irradiation position in fractions of milliseconds. The apparatus preferably comprises at least one accelerator, by means of which the energy of the ion beam can be adjusted so that the target volume can be irradiated slice-wise, staggered in terms of depth of penetration. With this there is associated the advantage that the entire target volume can be successively scanned slice-wise, the range of the ion beam being adjustable from slice to slice by changing the energy of the ion beam. For that purpose, the accelerator substantially consists of a linear accelerator and/or a synchrotron or cyclotron, in which protons and/or heavy ions of identical mass can be adjusted step-wise in terms of their energy. Because of the complexity of the control functions for the accelerator, modifying the energy of the ion beam to prespecified ranges within the irradiation space, especially within the target volume, is not possible with the required degree of precision in such a short time that the movements of a target volume or patient can be automatically followed. Rather, the cycles of the particle accelerator are matched to slice-wise scanning of the target volume. Therefore, in a further preferred embodiment of the invention, the depth modulator comprises two ion-braking plates of wedge-shaped cross-section which cover the entire irradiation zone of the ion beam and allow more rapid depth scanning modification in the case of a moving target volume than increasing the ion beam energy from energy level to energy level, so that compensation of the depth of penetration from irradiation point to irradiation point becomes possible by means of a depth modulator of such a kind. For the purpose, the wedge-shaped ion-braking plates of the depth modulator are preferably arranged on electromagnetically actuatable carriages. By means of those electromagnetically actuatable carriages, the position of the wedge-shaped ion-braking plates can be modified within fractions of milliseconds and accordingly the length of the braking path of the ions that is present in a region of overlap of the wedge-shaped braking plates can be varied by means of the ion-braking plates. For the purpose, the ion-braking plates overlap in the irradiation region of the ion beam and can accordingly modify the ions in terms of their range in line with spatial and temporal changes in the moving target volume. The ion-braking plates are preferably mounted on linear motors. Linear motors of such a kind have the advantage that continuous fine regulation of ion braking is possible for the purpose of modifying the scanning of the target volume in terms of depth. Furthermore, shifting the position of the wedge-shaped ion-braking plates with the aid of linear motors is not only extremely precise spatially but is also capable of matching a temporal displacement of the target volume in terms of depth at an extremely fast reaction speed so that continuous tracking and compensation of movements by means of depth compensation is possible. Alternatively, the modification of energy can also be effected by means of an electro-magnetic acceleration path in the accelerator or in the high-energy beam supply. In a further preferred embodiment of the invention, the position location and tracking system comprises at least two measurement sensors which detect the location, in terms of time and space, of markings on a target volume-containing region of the body of a patient from two spatial angles relative to an ion beam axis. Such markings can be applied using luminous inks that are tolerable to the skin, in the form of dots, lines or other geometric shapes, or in the form of luminous elements so that they are clearly registered and measured by the measurement sensors. In a further preferred embodiment of the invention, the measurement sensors are at least one precision video camera and/or X-ray detection means and/or ultrasound detection means, which co-operate with an image evaluation unit in the movement measurement, control and read-out module SAMB. This advantageously makes it possible for the movements of a region of the body in the vicinity of a target volume to be exactly measured and to be correlated with the temporal and spatial displacements in the location of the target volume and covering tissue, for example in the form of a stored look-up table. Irradiation of a tumour volume is in principle composed of image points set out in relation to one another in raster form in a planar arrangement in slice form, the ion beam being deflected by means of the raster scanning apparatus from irradiation point to irradiation point orthogonally to its beam axis in an X direction and a Y direction; the apparatus comprising, for the purpose of location detection, a multiwire proportional chamber as a location-sensitive detector, which is arranged in the beam direction upstream of the depth modulator and which forwards actual positions of the ion beam to a location measurement, control and read-out module for compensation of discrepancies between the actual transverse position and the desired transverse position based on an irradiation plan and on actual deviation of the target volume due to movement. Even if the energy of the ions in an ion beam can be kept constant by the accelerator in question, the number of ions per unit volume over time is still not constant. In order nevertheless to maintain an ion beam dose of equal magnitude at each volume point of the tumour tissue and accordingly to provide dose homogeneity, an ionisation chamber having a fast read-out is, in a preferred embodiment of the invention, arranged as a transmission counter in the beam path of the ion beam for the purpose of monitoring the intensity of the ion beam stream. A transmission counter of such a kind determines the dwell time of the ion beam at a volume point of the target volume to be irradiated, and a control and read-out module, SAMI, associated therewith delivers a signal to the read-out module to address the next volume point as soon as a prespecified beam dose has been reached. Accordingly, it is advantageously possible for a volume slice of the tumour volume over a planar extent to be scanned raster-wise from irradiation point to irradiation point. Preferably, the ionisation chamber is arranged between the deflecting device and the depth modulator, especially as the depth modulator, with its wedge-shaped ion-braking plates, controls ions solely in terms of their range without influencing the ion dose. A method for compensation of three-dimensional movements of a target volume on a patient couch during ion beam irradiation using a raster scanning apparatus comprises the following method steps. First, a healthy tissue structure covering the target volume in the upstream direction of the beam is detected in preliminary investigations and a digital model of the detected structure of the covering healthy tissue is produced. That model is stored in a memory of the movement control and read-out module SAMB, for example in the form of a look-up table. The target volume can then be positioned on a patient couch. During irradiation, three-dimensional movements of the target volume are detected in real time by means of a position location and tracking system. The movements are then divided vectorially into longitudinal and transverse components, and the transverse components of the movements are compensated by corrective control of raster scanning magnets of the raster scanning apparatus. The longitudinal components of the movements are finally compensated by comparison with the data of the stored model and comparison-based modification of the settings of a depth modulator. Accordingly, the invention advantageously makes available a method for three-dimensional compensation of target region movements in real time during ion irradiation, for example with protons or heavy ions. For the purpose, transverse excursion of the beam by the raster scanning system is combined with additional depth modulation. From the current measured deviation in the location and position of the particular volume element of the target volume from the reference position used in planning, especially taking into account the particular tissue through which the beam passes, a dynamic correction vector is determined and broken down into transverse and longitudinal components. The longitudinal component takes the particular tissue through which the beam passes into account in the calculation and determines the energy required to bring about the interaction of the ions in the particular volume element in the target volume. The transverse components are added as a dynamic offset to the desired position of the raster scanning system and the longitudinal component governs the setting of the depth modulator. By that means, the beam position is re-adjusted dynamically in all three spatial directions in line with the three-dimensional target region movement. As a result of complete integration into the supervisory irradiation control system of the ion beam therapy facility by means of a movement measurement, control and read-out module SAMB, the temporal sequence of irradiation is usually not affected. Direct communication between the individual electronics modules of the supervisory control system makes possible the availability of consistent, dynamic movement data in the entire system. For the purpose, preferably, in the preliminaries to irradiation, a digital model of the structure of tissue covering the target volume in the upstream direction of the beam is detected by means of X-ray and/or ultrasound investigations. Using such investigations in the preliminaries to irradiation, modifying the dose escalation in terms of depth during ion irradiation, in the case of movement, can be compensated very precisely in real time with re-adjustment of the depth modulator by means of the fact that longitudinal depth correction is carried out by means of the depth modulator from beam position to beam position. In a preferred example of carrying out the method, location measurement is registered and evaluated using a multiwire proportional chamber by way of a location measurement, control and read-out module SAMO. For the purpose of transverse compensation, information which is stored in the location measurement, control and read-out module SAMO of a supervisory control system and relates to the desired position of an irradiation plan is compared with the measured actual position of the beam position from the location-sensitive detector in real time taking into account the detected transverse movement component of the target volume, and transverse location compensation in the X and Y direction is carried out by means of the fast scanner magnet power supply units in co-operation with a control and read-out module SAMS for the raster scanning magnets of the raster scanning apparatus. In a preferred example of carrying out the method, a controlled, short-duration interruption in the event of the occurrence of unforeseen movement conditions outside the working range of compensation ensures flexible and yet safe use for any kind of movement. For that purpose, fast shut-down of the beam is initiated by the location measurement, control and read-out module SAMO of the location-sensitive detector in real time and/or by the movement, control and read-out module SAMB of the depth modulator, if the difference between a measured value and a desired value of the transverse beam position and/or of the longitudinal depth of penetration, respectively, exceeds a threshold value that can be set in the real-time software of the control and read-out modules SAMO and/or SAMB. In addition, besides correcting the desired position of the ion beam and controlling the depth modulator, the SAMB is responsible for monitoring faults in, or the failure of, the connected sub-systems for a position location and location tracking method and for depth modulation. The SAMB checks the resulting values for consistency and coherency and in the event of a fault initiates a corresponding interlock signal which interrupts irradiation. If the requisite correction parameters exceed the limits fixed in the course of preliminaries, the irradiation is interrupted for a short time until the values are again within the allowed range. FIG. 3 is a generalised representation of an arrangement and connection schema of the components of an apparatus according to a first embodiment of the invention. For the purpose, reference numeral 1 denotes a target volume and the broken line 20 denotes a three-dimensional movement of the target volume 1 on a patient couch 2. Reference numeral 3 denotes a raster scanning apparatus, which comprises a raster scanning magnet 7 for X excursion of an ion beam 5 consisting of protons or heavy ions and which comprises a further raster scanning magnet 8 for Y deflection of the ion beam 5. After the raster scanning apparatus 3, the ion beam 5 passes through a plurality of measurement chambers 23, of which ionisation chambers 14 and 15 serve to detect the dose of the ion beam 5, and multiwire proportional chambers 16 and 17 serve to measure the spatial positions of the ion beam 5 and, for the purpose, are arranged in the ion beam 5 in the beam direction upstream of a depth modulator 6. In addition, the ion beam 5 passes through an additional measurement chamber 21 for limit value monitoring, which is in direct operative connection with a supervisory control computer 19 of the irradiation room 18. In addition, the ion beam 5 also passes through a comb filter 22 before the depth modulator 6. The depth modulator 6 is arranged in front of the target volume 1 and comprises two wedge-shaped ion-braking plates 9 and 10, which, for depth modulation, can be moved relative to one another by means of linear motors 11 and 12 in order to carry out depth of penetration compensation taking into account the changes in the healthy tissue and the change in location of the target volume 1 in the event of movements of the patient on the patient couch 2. For the detection of movement, the irradiation room 18 has a position location and tracking system 4 which has, as measurement sensor, at least one precision video camera 13 and/or X-ray detection means and/or ultrasound detection means which is in operative connection with a control and read-out module SAMB for movement compensation. FIG. 3 accordingly shows an embodiment of an irradiation system according to the invention for an intensity-, location- and movement-modulated raster scanning method. The hardware overview of FIG. 3 constitutes a further development of the system of the subject-matter described in DE 100 31 074 A1 and EP 99 107 121, by means of which the precision irradiation of moving target regions is improved. The improvement in this irradiation system is achieved by the bringing together of the raster scanning system and the depth modulator and also by the processing of movement information measured in real time by the addition of a further electronics module SAMB to the supervisory control system and by using further communications interfaces and improved digital models. The invention accordingly makes possible improved dynamic three-dimensional re-adjustment of the therapy beam in real time with fine resolution and extremely high accuracy. FIG. 4 shows, in diagrammatic form, a block circuit diagram of the control and read-out modules SAM, together with connected external devices, of an apparatus according to FIG. 3. By means of FIG. 4 it is shown that the apparatus according to the invention and the method according to the invention are fully integrated into a supervisory irradiation control system, which is composed of a system control and sequence control and a supervisory control computer 19. In this exemplifying embodiment, the sequence control of the supervisory control system consists of a plurality of electronics modules, the control and read-out modules SAM having various functions, and the sequence control computer ASR. There is also a dedicated module SAMB exclusively for the compensation of target region movements. For safety-related reasons, a second, identical module can be used, which allows consistency checks on the data stream. The SAMB module is located in the data chain, which is shown in FIG. 4 by arrows, for example upstream of location measurement SAMO 1. The real time software on the SAMB reads movement information, at a fixed time interval, from the position and location tracking system 4 connected by way of an interface and, with the aid of a look-up table calculated in the course of preliminaries, determines the requisite compensation vector in the reference system of irradiation treatment. The frequency of movement measurement can be freely adapted to the particular position location and location tracking method and to the requisite measurement accuracy, for example 10 Hz to 100 Hz. If the length of the measurement interval exceeds the duration of location measurement in the supervisory control system, the determined compensation vector remains current until the next cycle of movement registration with the aid of the position location and location tracking system 4. In each measurement cycle of rapid location correction, for example in 150 μs, the SAMB ascertains the current transverse beam position from the stored desired data set and provides it with the transverse components of the current compensation vector. That new desired position is forwarded by way of an interface in the real time control by way of SAMO 1 to the control SAMS of the raster scanning magnets 7 and 8, which compares that value with the current measured actual position of SAMO 1 and, where appropriate, corrects the transverse beam position by way of a feedback control loop. The modified desired position and movement information are forwarded to all other modules of the supervisory control system for the purposes of logging and data consistency. Furthermore, from the desired longitudinal beam position and the determined longitudinal compensation component, SAMB calculates the settings of the depth modulator 6. Controlling the depth modulator 6 is carried out directly by way of an interface of the SAMB. FIG. 4 accordingly shows, by way of example, the data flow and the requisite interfaces. FIG. 5 shows, in diagrammatic form, by curves g to n, results of movement compensation with respect to relative dose homogeneity, DH, in dependence upon depth of penetration, w in mm, when movement compensation can be carried out with differing degrees of variance from σ=±0.0 mm (curve g) to σ=±3.0 mm (curve n). As a result of compensation using the apparatus according to the invention and the method according to the invention, a dose homogeneity is accordingly achieved which, despite a moving target volume, approximately reaches the dose homogeneity in the case of a target volume which is static, that is to say fixed on the patient couch. By way of comparison, these results are set against the relative dose homogeneity without compensation measures as shown in curve f and as also shown in FIG. 2. FIG. 6 shows, in diagrammatic form, results of movement compensation, to an enlarged scale, with respect to percentage deviation, ΔDH, of dose homogeneity in percent of dose homogeneity, DH, of a static target volume, in dependence upon depth of penetration, w in mm, when the movements can be detected and compensated with a variance of σ=±0.5 mm (curve i), σ=1.0 mm (curve k) and σ=1.5 mm (curve l). FIG. 7 illustrates the invention by way of the example of an apparatus 100 for modifying the depth of penetration W, shown in FIGS. 1, 8, 9 and 10, of an ion beam, in dependence upon a patient's movement, that is to say in dependence upon movement of regions of the body of the patient, for example the breathing movement of the chest. The apparatus 100 comprises a position location and tracking system 104 for monitoring movements of the patient, a depth modulator 106 for adjusting the depth of penetration of the ion beam into the patient and a movement measurement and control unit 108, which is in operative connection with the position location and tracking system 104 and the depth modulator 106. The movement measurement and control unit 108 comprises a microprocessor 110 having a memory, in which data of a model 112 have been stored. The model 112 describes the structure of healthy tissue which covers the target volume in the upstream direction of the beam and accordingly through which the ion beam must pass on irradiation. A model of such a kind is known, for example, from “A. Schweikard et al: Robotic motion compensation for respiratory movement during radiosurgery. Comput Aided Surg. 2000;5(4):263-77”. The movement measurement and control unit 108 receives information relating to the movement of the patient from the position location and tracking system 104. The unit, with the aid of the microprocessor, processes that information together with the model, in order to make available a control signal for the depth modulator 106. That control signal should control the depth modulator 106 in such a manner that the depth of penetration of the ion beam is always adjusted, irrespective of the movement of the patient, to the target volume element to be irradiated at the particular moment in the target volume (tumour) in the patient. (Hereinafter “target volume” and “target volume element” are sometimes used synonymously because the more precise meaning will emerge from the particular context.) For the purpose, especially the movement of the healthy tissue relative to the target volume element is required because different energy absorptions of the particle beam take place in the patient in dependence upon the healthy tissue that the beam passes through and accordingly the depth of penetration of the ion beam changes in dependence upon the tissue that the beam passes through in the event of movement of the healthy tissue relative to the target volume element. The change in range of the ion beam in dependence upon the tissue that the beam passes through can be calculated, for example, on-line during irradiation or determined with the aid of tables produced, for example, during therapy planning, which represent various tissue arrangements. In an expanded embodiment of the apparatus 100 for modifying the depth of penetration, additional means 114 for obtaining location information relating to the location of the ion beam relative to the patient may be provided. That location information can in turn be used together with the aid of the model and the information relating to the movement of the patient for the purpose of controlling a raster scanning apparatus 116. As a result, the ion beam can follow a movement of the target volume in a transverse direction to the ion beam, it simultaneously being possible, in dependence upon the movement of the healthy tissue relative to the target volume, for the depth of penetration to be modified. FIG. 8 shows an aspect, relevant to the invention, during beam therapy in a static situation, wherein neither the target volume 120, or tumour tissue 120, nor the covering tissue 122, or healthy tissue 122, through which the beam passes during therapy, move. Three irradiation points 124 (target volume elements) are shown in diagrammatic manner, which are in each case irradiated by the ion beams 126A, 126B and 126C. During therapy planning, the tissue 122 through which the beam passes is analysed. In order to reach the beam position 124 at a depth W, the ion beam energy is modified in line with the covering volume 122 through which the beam passes. In the process it is taken into account whether the beam passes through, for example, bone 128, as is the case for the ion beam 126B, or whether it does not (ion beams 126A and 126C). FIG. 9 then supplements the schema of FIG. 8 with patient movement; in this case, by way of example, the bones 128 correspond to the ribs of the chest and, during breathing, they move in the direction of the arrows A relative to the static target volume 120. In the case of non-moving tumour tissue 124A, for beam position 126C the composition of the particular covering volume 122 through which the beam passes changes in the course of breathing and in the course of irradiation: at timepoint T=T1 the beam does not pass through a rib 128 and at timepoint T=T2 the beam does pass through a rib 128. Accordingly, the beam energy must be modified in time-dependent manner in order to ensure that the ion beam 126C has the depth of penetration W on irradiation. For that purpose, the position location and tracking system monitors movements of the patient, in this case the movements of the chest, and transmits that information to the movement measurement and control unit, in which the model of the covering volume 122 through which the beam passes is compared and appropriate depth modulation of a depth modulator 130 is brought about. For example, the wedges 132 and 134 of the depth modulator 130 overlap to a greater extent at timepoint T2 than at timepoint T1. FIG. 10 then additionally takes into account the movement of the target volume 124B itself in direction B. Monitoring movements of the patient also allows, by means of the model, determination of the movement of the target volume. For example, in FIG. 10b, at timepoint T2, the tumour tissue 124B has moved downwards in the direction of arrows B and the healthy tissue 122 has moved upwards in the direction of arrows A. It is the function of a beam re-adjustment apparatus, for example of a raster scanning apparatus, to move the ion beam 126C, for example parallel to 126C, in a downwards direction so that the irradiation point 124 in question is always irradiated. In accordance with the invention it is now also possible, with the aid of the model, to take into account the changed conditions due to the relative movement of tumour tissue 124B and healthy tissue 122 when the beam passes through the healthy tissue 122 and in turn to control the depth modulator accordingly. The possibilities for carrying out correction of the depth of penetration in accordance with the invention are not limited to the known raster scanning method in the case of particle therapy as outlined at the beginning but can also be used in the case of intensity-modulated irradiation. In the process, in contrast to the raster scanning method, small regions of area are masked out, for example using multi-leaf collimators, and set against one another at varying intensities. 1 target volume 2 patient couch 3 raster scanning apparatus 4 position location and tracking system 5 ion beam 6 depth modulator 7 raster scanning magnet (X deflection) 8 raster scanning magnet (Y deflection) 9 wedge-shaped ion-braking plate 10 wedge-shaped ion-braking plate 11 linear motor 12 linear motor 13 precision video camera; X-ray detection means; ultrasound detection means 14 ionisation chamber 15 ionisation chamber 16 multiwire proportional chamber 17 multiwire proportional chamber 18 treatment room 19 supervisory control computer 20 broken line 21 additional measurement chamber 22 comb filter 23 measurement chambers 100 apparatus for modifying the depth of penetration 104 position location and tracking system 106 depth modulator 108 movement and control unit 110 microprocessor 112 model 120 target volume or tumour tissue 122 covering volume or healthy tissue through which the beam passes 124 irradiation point 124A beam position 126A ion beam 126B ion beam 126C ion beam 128 bone 130 depth modulator 132 wedge 134 wedge A direction of arrows B direction of arrows T time T1 timepoint T2 timepointdifference between measurement value and desired value Δw change in depth of penetration w depth of penetration SAMO1 location measurement, control and read-out module SAMO2 location measurement, control and read-out module SAMS control and read-out module of the raster scanning magnets SAMB movement measurement, control and read-out module |
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051436531 | claims | 1. A process for immobilizing, by a hydraulic binder, radioactive ion exchange resins which contain borates, said resins being in a suspension, comprising the steps of: (a) decanting said resins 100%; (b) placing the decanted resins in a vessel; (c) adding to said vessel an eluant solution having between 100 and 300 grams per liter of Ca(NO.sub.3).sub.2 with the proportion of eluant solution being from 1 to 2 liters per kilogram of said decanted resins; (d) adding to said vessel a hydraulic binder of low hydration heat to said resins and eluant solution, the relative weight of the water of the eluant solution to the binder (by weight) being such that ##EQU3## (e) mixing the contents of said vessel, the percent (by weight) of the said resins, hereinafter referred to as dry resins, to the contents of the vessel being between 3% and 10%. decanting the ion exchange resins 100%; placing the decanted ion exchange resins in a vessel with an eluant solution having one hundred to three hundred grams per liter of Ca(NO.sub.3).sub.2 in the ratio range of one to two liters per kg of decanted ion exchange resins; adding a low hydration heat hydraulic binder to said resins and eluant solution in said vessel so that the relative weight of the water of the eluant solution to the binder is ##EQU4## (a) providing a vessel adapted to enable the vessel and its contents to be weighed; (b) introducing the radioactive ion exchange resins into said vessel; (c) decanting the ion exchange resins 100%; (d) weighing said vessel and its contents to determine the weight of the decanted ion exchange resins; (e) introducing into the vessel an eluant solution having in the range of from 100 to 300 grams per liter of Ca(NO.sub.3).sub.2 in the ratio of 1 to 2 liters per kilogram of decanted ion exchange resins; (f) stirring the contents of said vessel; and (g) adding a low hydration heat hydraulic binder into said vessel so that the relative weight of the water of the eluant solution to the binder is given by ##EQU5## 2. Process as claimed in claim 1, wherein in order to increase the efficiency of the elution and to obtain a pH.gtoreq.9, lime is added to the eluant solution in the proportion of 200 grams of lime per kilogram of the 100% of said decanted resins. 3. Process as claimed in claim 1, wherein the hydraulic binder is a slag cement. 4. Process as claimed in claim 3, wherein the slag cement contains at least 80% of clinker by weight. 5. A process for immobilizing radioactive ion exchange resins, which contain borates in a quantity which can be present in an amount of up to the equivalent of 1000 g H.sub.3 BO.sub.3 /kg of dry ion exchange resins, said resins being in a suspension, comprising the steps of: 6. The process of claim 5 wherein said low hydration heat hydraulic binder is added in such a quantity that the percent by weight of ion exchange resins to the contents of the vessel, wherein said ion exchange resins are hereinafter referred to as dry resins, is between 3% and 10%. 7. The process of claim 5 wherein lime is added to the eluant solution in an amount sufficient to obtain a pH.gtoreq.9. 8. The process of claim 2 wherein the hydraulic binder is a slag cement. 9. The process of claim 1 wherein step (e) further includes maintaining the contents of said vessel at a pH.gtoreq.9. 10. The process of claim 1 wherein step (b) further includes weighting the resins in said vessel to determine the amount of eluant solution and binder to be introduced at steps (c) and (d). 11. The process of claim 1 wherein the contact between the eluant solution and the decanted resins in step (c) is maintained for a period of from one to three hours. 12. A process for immobilizing radioactive ion exchange resins which contain borates, said resins being in suspension, comprising the steps of: 13. The process of claim 12 wherein the contents of the vessel at step (e) are maintained in contact with one another for a period in the range of from one to three hours. |
summary | ||
summary | ||
claims | 1. An apparatus comprising:a pressurized water reactor (PWR) including:a vertically oriented cylindrical pressure vessel comprising upper and lower vessel sections that are secured together and having a cylinder axis of the cylindrical pressure vessel oriented vertically,a nuclear reactor core disposed in the lower vessel section, a hollow cylindrical central riser disposed concentrically with and inside the cylindrical pressure vessel wherein a downcomer annulus is defined between the hollow cylindrical central riser and the cylindrical pressure vessel, the downcomer annulus including (i) an upper portion with a relatively smaller inner diameter located in the upper vessel section, (ii) a lower portion with a relatively larger inner diameter located in the lower vessel section, and (iii) a transition region disposed between the upper portion and the lower portion, the inner diameter of the downcomer annulus transitioning in the transition region from the relatively smaller inner diameter of the upper portion to the relatively larger inner diameter of the lower portion, anda reactor coolant pump secured to the lower vessel section, the reactor coolant pump including (i) an impeller disposed above the nuclear reactor core and inside the pressure vessel in the transition region of the downcomer annulus to impel primary coolant downward through the downcomer annulus, (ii) a pump motor disposed outside of the pressure vessel, and (iii) a horizontally oriented drive shaft operatively connecting the pump motor with the impeller. 2. The apparatus of claim 1 wherein the upper vessel section has a larger diameter than the lower vessel section. 3. The apparatus of claim 1 wherein the lower vessel section includes an overhang at which the reactor coolant pump is secured with (I) the impeller disposed inside the pressure vessel in the downcomer annulus above the overhang and (II) the pump motor disposed outside the pressure vessel below the overhang. 4. The apparatus of claim 3 wherein the lower vessel section includes a flange by which the lower vessel section is secured with the upper vessel section, the flange having a larger diameter than the remainder of the lower vessel section so as to define the overhang at which the reactor coolant pump is secured. 5. The apparatus of claim 1 wherein the impeller is disposed inside the pressure vessel above an overhang of the pressure vessel and the pump motor is disposed outside of the pressure vessel below the overhang of the pressure vessel and the drive shaft operatively connects the pump motor below the overhang with the impeller above the overhang. 6. The apparatus of claim 1 wherein the downcomer annulus proximate to the impeller is shaped to define a pump casing that cooperates with the impeller to impel primary coolant downward through the downcomer annulus. 7. The apparatus of claim 1 wherein:the reactor coolant pump comprises a plurality of reactor coolant pumps including a corresponding plurality of impellers disposed in the downcomer annulus and spaced apart around the hollow cylindrical central riser, andthe downcomer annulus proximate to the plurality of impellers is shaped to define an annular pump casing that cooperates with the plurality of impellers to impel primary coolant downward through the downcomer annulus. 8. The apparatus of claim 1 wherein the reactor coolant pump further comprises a pump casing containing the impeller, the pump casing also disposed inside the pressure vessel in the downcomer annulus, the pump casing and the impeller cooperatively defining a centrifugal pump with the pump casing defining the volute chamber of the centrifugal pump. 9. The apparatus of claim 8 wherein the reactor coolant pump is secured to the lower vessel section. 10. The apparatus of claim 1 wherein the impeller is accessible by separating the upper and lower vessel sections. 11. An apparatus comprising:a pressurized water reactor (PWR) including:a vertically oriented cylindrical pressure vessel comprising upper and lower vessel sections that are secured together and having a cylinder axis of the cylindrical pressure vessel oriented vertically,a nuclear reactor core disposed in the lower vessel section,a hollow cylindrical central riser disposed concentrically with and inside the cylindrical pressure vessel wherein a downcomer annulus is defined between the hollow cylindrical central riser and the cylindrical pressure vessel, the downcomer annulus including (i) an upper portion with a relatively smaller inner diameter located in the upper vessel section, (ii) a lower portion with a relatively larger inner diameter located in the lower vessel section, and (iii) a transition region disposed between the upper portion and the lower portion, the inner diameter of the downcomer annulus transitioning in the transition region from the relatively smaller inner diameter of the upper portion to the relatively larger inner diameter of the lower portion,a reactor coolant pump including (i) an impeller disposed in the transition region of the downcomer annulus above the nuclear reactor core and in fluid communication with the downcomer annulus to impel primary coolant downward through the downcomer annulus, (ii) a pump motor disposed outside of the pressure vessel, and (iii) a horizontally oriented drive shaft operatively connecting the pump motor with the impeller, andan internal steam generator disposed in the downcomer annulus, the impeller of the reactor coolant pump being disposed below the internal steam generator. 12. The apparatus of claim 11 wherein the impeller is disposed inside the pressure vessel in the downcomer annulus below the internal steam generator to impel primary coolant discharged from the internal steam generator downward through the downcomer annulus. 13. The apparatus of claim 11, wherein the internal steam generator is disposed entirely in the upper vessel section with no portion of the steam generator being disposed in the lower vessel section. 14. An apparatus comprising:a pressurized water reactor (PWR) including:a vertically oriented cylindrical pressure vessel comprising upper and lower vessel sections,a hollow cylindrical central riser disposed concentrically with and inside the cylindrical pressure vessel wherein a downcomer annulus is defined between the hollow cylindrical central riser and the cylindrical pressure vessel, the downcomer annulus including (i) an upper portion with a relatively smaller inner diameter located in the upper vessel section, (ii) a lower portion with a relatively larger inner diameter located in the lower vessel section, and (iii) a transition region disposed between the upper portion and the lower portion, the inner diameter of the downcomer annulus transitioning in the transition region from the relatively smaller inner diameter of the upper portion to the relatively larger inner diameter of the lower portion,a nuclear reactor core disposed in the lower vessel section, anda plurality of reactor coolant pumps spaced apart around the hollow cylindrical central riser and secured to the lower vessel section wherein each reactor coolant pump includes (i) an impeller disposed inside the pressure vessel in the transition region of the downcomer annulus, (ii) a pump motor disposed outside of the pressure vessel, and (iii) a horizontally oriented drive shaft operatively connecting the pump motor with the impeller; anda steam generator disposed in the downcomer annulus;wherein the impellers are disposed below the steam generator and above the nuclear reactor core. 15. The apparatus of claim 14 wherein the downcomer annulus proximate to the plurality of impellers is shaped to define a common annular pump casing for the plurality of impellers that cooperates with the plurality of rotating impellers to impel primary coolant downward through the downcomer annulus. 16. The apparatus of claim 15 wherein the pressure vessel includes an overhang, the impellers of the reactor coolant pumps being disposed inside the pressure vessel above the overhang, the pump motors of the reactor coolant pumps being disposed outside of the pressure vessel below the overhang, and the drive shafts of the reactor coolant pumps being vertically oriented. 17. The apparatus of claim 14 wherein each reactor coolant pump further comprises a casing disposed inside the pressure vessel in the downcomer annulus and cooperating with the impeller to define a centrifugal pump with the pump casing defining the volute chamber of the centrifugal pump. |
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claims | 1. A grid module of a scattered-radiation grid comprising a number of grid modules disposed next to one another, each of the grid modules being equipped with a plurality of grid webs, wherein, on at least one edge side of at least one of the grid modules, a grid web running along the at least one edge side is designed to be broken through at least partly at a plurality of sections. 2. The grid module of claim 1, wherein the at least partly broken-through sections and non-broken-through sections are arranged alternately. 3. The grid module of claim 1, wherein on at least one edge side of at least one of the grid modules, at least two grid webs are present with the at least partly broken-through sections opposite one another and disposed on the edge side. 4. The grid module of claim 1, wherein the at least partly broken-through sections are disposed, viewed in the longitudinal direction of the webs, equidistant from one another. 5. The grid module of claim 1, wherein exclusively one of the at least partly broken-through sections is disposed at at least one longitudinal position of the at least one grid web. 6. The grid module of claim 1, wherein a number of the at least partly broken-through sections are disposed along the web height at a longitudinal position of the at least one grid web. 7. The grid module of claim 3, wherein the at least partly broken-through sections on at least two opposing grid webs are disposed and are embodied in relation to their size such that all the at least partly broken-through sections of one grid web lie opposite a breakthrough-free surface of the respective other edge-side grid web. 8. The grid module of claim 1, wherein, in relation to a height of the at least one edge-side grid web, the number of the at least partly broken-through sections is equal to the number of breakthrough-free surfaces. 9. The grid module of claim 1, wherein at at least one of a minimum and maximum height of the at least one edge-side grid web, an end-to-end non-broken-through area is embodied over the entire length of the grid web. 10. The grid module of claim 1, wherein grid webs adjacent to the grid webs disposed at the edge side also have lateral at least partly broken-through sections. 11. The grid module of claim 10, wherein at least one of the number and overall surface of the at least partly broken-through sections in the grid webs reduces from the grid webs of the edge area of the grid module to the center of the grid module. 12. The grid module of claim 1, wherein grid webs running exclusively parallel in one direction are provided. 13. The grid module of claim 1, wherein grid webs crossing each other at right angles are provided. 14. The grid module of claim 1, wherein at least one edge-side grid web is provided from outside with a plastic film. 15. A scattered-radiation grid for an x-ray detector of a CT system including a plurality of detector elements disposed in rows and columns over its surface, comprising:at least two grid modules arranged next to one another, each of the at least two grid modules possessing a number of grid webs disposed next to one another with irradiation zones between them, and at least one edge-side grid web of at least one of the grid modules being adjacent to at least one other web disposed running in parallel next to one another on the edge side of another of the grid modules in absence of an irradiation zone arranged between them, the grid webs adjoining each other and, without an intervening irradiation zone, each including a plurality of lateral breakthroughs, wherein the grid modules are embodied in accordance with claim 1. 16. A detector of a CT system with a modular-construction scattered-radiation grid, the scattered-radiation grid including the grid module of claim 1. 17. A CT system comprising a detector including a modular-construction scattered-radiation grid, the scattered-radiation grid including grid modules of claim 1. 18. The grid module of claim 2, wherein on at least one edge side of at least one of the grid modules, at least two grid webs are present with the at least partly broken-through sections opposite one another and disposed on the edge side. 19. The grid module of claim 2, wherein the at least partly broken-through sections are disposed, viewed in the longitudinal direction of the webs, equidistant from one another. 20. The grid module of claim 3, wherein the at least partly broken-through sections are disposed, viewed in the longitudinal direction of the webs, equidistant from one another. 21. The grid module of claim 20, wherein the at least partly broken-through sections and non-broken-through sections are arranged alternately. 22. The grid module of claim 20, wherein on at least one edge side of at least one of the grid modules, at least two grid webs are present with the at least partly broken-through sections opposite one another and disposed on the edge side. 23. The grid module of claim 20, wherein the at least partly broken-through sections are disposed, viewed in the longitudinal direction of the webs, equidistant from one another. 24. A scattered-radiation grid for an x-ray detector of a CT system including a plurality of detector elements disposed in rows and columns over its surface, comprising:at least two grid modules arranged next to one another, each of the at least two grid modules possessing a number of grid webs disposed next to one another with irradiation zones between them, and at least one edge-side grid web of at least one of the grid modules being adjacent to at least one other web disposed running in parallel next to one another on the edge side of another of the grid modules in absence of an irradiation zone arranged between them, the grid webs adjoining each other and, without an intervening irradiation zone, each including a plurality of lateral breakthroughs. 25. The scattered-radiation grid of claim 24, wherein the lateral breakthroughs of adjacent edge-side grid webs are disposed such that the breakthroughs of a grid web are each covered by the adjoining edge-side other grid web. 26. The scattered-radiation grid of claim 24, wherein the breakthroughs are dimensioned in relation to their number and distribution so that the increased scattered-radiation reduction as a result of the presence of the double grid webs in the edge area of the grid module is compensated for by the breakthroughs. 27. The scattered-radiation grid of claim 25, wherein the breakthroughs are dimensioned in relation to their number and distribution so that the increased scattered-radiation reduction as a result of the presence of the double grid webs in the edge area of the grid module is compensated for by the breakthroughs. 28. A detector of a CT system comprising the scattered-radiation grid of claim 24. 29. A CT system comprising a detector including the scattered-radiation grid of claim 24. |
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040000389 | abstract | Nuclear power station having a reactor buried in rock and machine groups formed with the use of turbines, compressors, generators or other apparatus, inclusive gas conduits; the individual machine groups and the gas conduits are arranged in rooms hollowed out in the rock for receiving and supporting these; to each group there leads at least one tunnel hollowed out in the rock; a safety chamber for a machine group concerned is situated adjacent the group and is secludable relatively to the atmosphere. |
052260658 | claims | 1. A device for disinfecting medical materials comprising: (a) a heat source to heat the medical materials to approximately 60.degree. C.; and (b) a source of gamma irradiation to expose the medical materials to a gamma irradiation dose of approximately 0.25 to 2.0 Mrads. (a) a source of radio-frequency waves for heating the medical materials to approximately 60.degree. C.; and (b) a source of gamma irradiation for exposing the medical materials to gamma radiation. (a) a heat source to heat the medical waste to a temperature of approximately 60.degree. C.; (b) a source of gamma irradiation capable of exposing the heated medical waste to gamma irradiation in the range of about 0.25 megarads to about 2.0 megarads; and (c) a shredding apparatus to shred the medical waste. (a) a heat source to heat the medical materials to approximately 60.degree. C.; and (b) a source of ionizing radiation capable of supplying a dose of approximately 0.25 to approximately 2.0 megarads to the medical materials. (a) a shredding apparatus to shred the medical waste; (b) a heat source to heat the shredded medical waste to a temperature of approximately 60.degree. C.; (c) a gamma radiation source to expose the heated medical waste to gamma irradiation. (a) a shredding apparatus to shred the medical waste; (b) a heat source to heat the shredded medical waste to a temperature of approximately 60.degree. C.; (c) an ionizing radiation source to expose the heated medical waste to an ionizing radiation dose of approximately 0.25 to 2.0 megarads. 2. A device for disinfecting medical materials, as recited in claim 1, further comprising a conveying apparatus to convey the medical materials to the heat source and the gamma source. 3. A device for disinfecting medical materials, as recited in claim 1, wherein the device comprises an entrance to receive the medical materials, wherein the heat source is located nearer the entrance than the gamma source, and wherein the conveying apparatus is between the entrance and the heat source and between the heat source and the gamma source. 4. A device for disinfecting medical materials, as recited in claim 1, wherein the gamma source comprises radioactive cobalt 60. 5. A device for disinfecting medical materials, as recited in claim 1, wherein the gamma source comprises radioactive cesium 137. 6. A device for disinfecting medical materials comprising: 7. A device for disinfecting medical materials, as recited in claim 6, further comprising a conveying apparatus to convey the medical materials to the radio-frequency source and the gamma source. 8. A device for disinfecting medical materials, as recited in claim 7, wherein the device comprises an entrance to receive the medical materials, wherein the radio-frequency source is located nearer the entrance than the gamma source, and wherein the conveying apparatus is between the entrance and the radio-frequency source and between the radio-frequency source and the gamma source. 9. A device for disinfecting medical materials, as recited in claim 6, wherein the gamma source comprises radioactive cobalt 60. 10. A device for disinfecting medical materials, as recited in claim 6, wherein the gamma source comprises radioactive cesium 137. 11. A device for disinfecting and processing medical waste comprising: 12. A device for disinfecting medical materials, as recited in claim 11, further comprising a conveying apparatus to convey the medical materials to the heat source, the gamma source, and the shredding apparatus. 13. A device for disinfecting and processing medical waste, as recited in claim 11, wherein the shredding apparatus comprises a particle forming apparatus for producing particles in a size range of approximately one quarter to one half inch. 14. A device for disinfecting and processing medical waste, as recited in claim 11, wherein the gamma source comprises radioactive cobalt 60. 15. A device for disinfecting and processing medical waste, as recited in claim 11, wherein the gamma source comprises radioactive cesium 137. 16. A device for disinfecting medical materials comprising: 17. A device for disinfecting medical materials, as recited in claim 16, wherein the heat source provides radio-frequency waves. 18. A device for disinfecting medical materials, as recited in claim 16, wherein the ionizing radiation source comprises a machine source of radiation. 19. A device for disinfecting medical materials, as recited in claim 18, wherein said machine source of radiation comprises an electron accelerator. 20. A device for disinfecting medical materials, as recited in claim 16, further comprising a conveying apparatus to convey the medical materials to the heat source and the ionizing radiation source. 21. A device for disinfecting medical materials, as recited in claim 16, wherein the device comprises an entrance to receive the medical materials, wherein the heat source is located nearer the entrance than the ionizing radiation source, and wherein the conveying apparatus is between the entrance and the heat source and between the heat source and the ionizing radiation source. 22. The device for disinfecting medical materials, as recited in claim 16, further comprising a shredding apparatus to shred the medical waste. 23. The device for disinfecting medical materials, as recited in claim 22, wherein the shredding apparatus comprises a particle forming apparatus to reduce the materials to particles in a size range of approximately one quarter to one half inch. 24. A device for disinfecting and processing medical waste comprising: 25. A device for disinfecting medical waste comprising: |
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claims | 1. An apparatus with which areas near surfaces in a water environment that are contaminated by radioisotopes are decontaminated by non-thermal laser peeling without suffering re-melting, re-diffusing and re-contaminating, the apparatus comprising:a piping structure with which a substance to be irradiated that has been deposited either on both the outer and inner surfaces of a nuclear reactor pressure vessel, and a nuclear reactor container tank, and the internal nuclear reactor structures and the like, all having been contaminated with radioisotopes, can be removed in the water environment, the piping structure being such that in order to secure a region in a water environment that is gas pressurized to discharge the water and filled with the gas so that it will not interfere with laser irradiation, it has a semi-hermetically closed, incomplete water seal that is half-open with a siphon provided downward, has a mechanical structure that withstands water pressure in a radial direction, and has an extendable bellows-like tube or any other extendable telescopic structure that enables the piping structure to be tilted over a wide range in an axial direction that is generally perpendicular to the surface to be irradiated with the laser. 2. The apparatus according to claim 1, further comprising a radiation detector or a light emission optical spectrometer to monitor the decontamination process in the neighborhood of either the area being removed by non-thermal laser peeling or the area where the radioisotopes separately recovered through an exhaust pipe are piled-up after the removal by non-thermal laser peeling. |
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043022901 | summary | BACKGROUND OF THE INVENTION This invention relates to structures of the type that are employable as a support for equipment, and, more particularly, to a head equipment support structure system that is designed to be cooperatively associated with a nuclear reactor vessel in a nuclear power generation system for purposes of accomplishing the support of equipment that is externally located in the head area of such a vessel. One of the main operating components of any nuclear power generation system is the nuclear reactor. Commonly, the latter is suitably supported within a pressure vessel. Furthermore, it is within this vessel that the nuclear reaction takes place from which there is generated the energy that is utilized to produce the power that is provided by the nuclear power generation system. In accord with established practice, the nuclear reactor vessel is in turn suitably housed within an appropriate form of containment structure, the latter commonly being made of concrete. For purposes of effectuating control over the operation of the nuclear reactor housed within the pressure vessel, there is a need to make use of various pieces of equipment. Some of these pieces are designed to be located internally of the vessel with means cooperatively associated therewith for effecting operation thereover from the exterior of the vessel, while others of these pieces are designed to be physically located externally of the vessel with means cooperable therewith extending into the vessel interior. In either case, however, all of the equipment is generally to be found located within the confines of the containment structure. Normally, in addition to such pieces of equipment, instrumentation is made use of for purposes of monitoring the activities taking place within the vessel. Thus, such instrumentation constitutes yet another form of means for which support must be provided in the immediate vicinity over the vessel. In summary, therefore, it should be readily apparent from the above that normally it is to be expected that there will be found a multiplicity of various pieces of equipment as well as various types of instrumentation extending outwardly from the vessel for which a need exists to provide support therefor. Insofar as regards this matter of providing support for the aforementioned equipment and/or instrumentation, there are a number of factors that must be borne in mind in arriving at a decision as to the nature of the support that should be utilized. More specifically, reference is had here to the fact that consideration must be given to much more than merely a selection of simply any given one of the many commonplace forms of support means that have been known to have been used heretofore by the prior art. For example, there is a need to consider the nature of the environment in which the subject equipment and/or instrumentation is being employed, and the potential for deleterious effects that such an environment may have on the ability of a given form of support means to provide the support deemed to be required therefrom. Moreover, it is of prime importance that consideration be given to the matter of safety. In addition, with regard to all of the above, there is the still further need to take cognizance of the fact that there exists various rules and regulations that have been promulgated by governmental agencies relating to this subject. Lastly, because of relatively recent incidents that have occurred involving nuclear power generation systems, other steps have been suggested for implementation looking towards the effectuation of additional improvements in the practices and procedures that it is recommended be followed in the course of constructing and operating each of the many components normally thought of being encompassed within a conventionally constructed nuclear power generation system. In order to effect the requisite degree of communication between the interior and the exterior of the nuclear reactor vessel for purposes of accomplishing the operation of the various pieces of equipment and instrumentation associated with the proper functioning of the nuclear reactor housed within and outside the reactor vessel, one of the means most frequently employed for this purpose is one form or another of cabling. The vast usage which is made of cabling in this regard creates the image of a virtual maze thereof within the confines of the containment structure directly over the reactor vessel. As such, there exists an obvious need to furnish some form of support therefor in order to provide effective separation therebetween for ease of ready identification thereof, etc. This need is further compounded by the fact that in many instances the use of redundant cabling is mandated by safety rules and/or regulations, or may be employed simply as a matter of prudent practice. Thus, there is a requirement for more than mere separation of such cabling. Namely, that cabling which may be viewed as constituting the primary set of cabling must be effectively isolated from the cabling which functions as a backup thereto such that the likelihood, that damage occasioned from the same source will be done concurrently to both the primary and the backup cabling, is very improbable. By way of further illustration of this point, sufficient separation and isolation of the backup cabling from the primary cabling should exist such that in the event that the latter is damaged, as for instance by fire, the probability that the backup cabling would suffer damage also from the same fire would be extremely remote. Apart from the functional requirements enumerated above which should be satisfied by any support structure that is selected for use in association with the reactor vessel of a nuclear power generation system, there are other attributes which such a support structure should possess. For example, means must be provided to enable access to be had periodically to the interior of the containment structure for purposes of effecting repairs and/or the carrying out of normal maintenance on the equipment housed therewithin. This encompasses the need to replace or repair the aforementioned cabling. Consequently, access must obviously be available thereto. In addition, such cabling should be provided with suitable connection means at the termination points thereof so as to enable the cabling to be readily disconnected for purposes of effecting the replacement thereof, etc. Moreover, besides the need to simply gain access to the interior of the containment structure, there also exists a need to periodically remove the head of the reactor vessel for purposes of exposing the interior thereof such as, for instance, to effectuate the performance of the refueling of the nuclear reactor. Accordingly, whatever form of support structure is selected for utilization within the containment structure for purposes of providing support for the pieces of equipment and/or instrumentation associated with the operation of the nuclear reactor must be suitably located or must embody the capability of being positioned so as to not impede the removal of the reactor vessel head. In this context, the support structure should be sufficiently movable to enable the removal of the head of the reactor vessel to be accomplished in an expeditious manner. A further complication in this regard, however, is the fact that a considerable amount of ductwork is to be found cooperatively associated with the reactor vessel, as well as a structure which is referred to by those skilled in this art as a missile shield. The existence of both this ductwork and the missile shield impose restrictions on the degree of accessibility that is afforded to the aforesaid support structure as well as function to limit the extent to which the subject support structure may be moved for purposes of effecting removal of the reactor vessel head. Essentially, the function of the ductwork that has been referred to above is to afford a means of funneling to the reactor vessel the cooling required in the course of the conduct of the operation of the nuclear reactor housed within the reactor vessel. The missile shield, on the other hand, referred to above commonly takes the form of a concrete member. The function thereof is to form a barrier in the event that an incident should occur whereby members confined within the containment structure are given impetus such that they take on the characteristics of missiles. Thus, the concrete missile shield is designed under such circumstances to absorb the kinetic energy possessed by such missile-like members such as to cause them to slow down, i.e., loose their potential to cause damage within the interior of the containment structure and/or to escape from the containment structure whereby they would pose a danger to personnel and equipment located externally of the containment structure. The need to periodically effect the refueling of the nuclear reactor housed within the reactor vessel has been alluded to hereinabove. With further regard thereto, it is important that this task be accomplished in a safe, yet timely fashion. Namely, it is important that the overall time required to perform the refueling operation be kept at a minimum inasmuch as during this period, the nuclear power generation system of which the nuclear reactor is a principal component is not producing power. Moreover, inasmuch as the nuclear reactor is housed within an environment which, if proper safeguards are not taken, can be hazardous to humans, it is important that the refueling operation be completed in a minimum of time. Accordingly, irrespective of what may occasion the need to shutdown the nuclear reactor, i.e., the need to refuel the latter, etc., it is important that the period during which a power outage occurs be kept to a minimum, both because of the effect that the power loss has on the customers of the power generation system as well as because of the desire to minimize the time during which the personnel working in the vicinity of the reactor are exposed to the potentially hazardous environment represented thereby. Thus, a further important consideration in selecting a support structure for use in cooperative association with the reactor vessel is that the structure which is selected for use should not have an adverse impact on the ability to effect a minimization of the time period during which the nuclear power generation system is in a non-power producting state. On the other hand, if further time-savings in this regard are achievable through the employment of a given support structure, this would enhance the desirability of making use of the latter. Yet another consideration that should be borne in mind in the course of determining the nature of the support structure that will be selected for use in effecting the separation and support of the pieces of equipment, instrumentation and cabling utilized in connection with the operation of the nuclear reactor housed within the reactor vessel is the ability thereof to be employed in retrofit situations. Namely, it would be desirable to have provided a form of support structure that is usable not only in new installations, but also is equally applicable for use in existing installations for purposes of effecting improvements over the support structures that are presently to be found employed therein. It is, therefore, an object of the present invention to provide a support structure system that is particularly suitable for use in cooperative relation with a reactor vessel in a nuclear power generation system for purposes of providing support for the head equipment associated therewith. It is another object of the present invention to provide such a head equipment support structure system that is operable in the manner of a cable support structure. It is still another object of the present invention to provide such a head equipment support structure system that, in addition, is operable in the manner of a missile shield. A further object of the present invention is to provide such a head equipment support structure system that is also operable in the manner of a ductwork support structure. A still further object of the present invention is to provide such a head equipment support structure system that is characterized in the ease with which it may be repositioned for purposes of effecting the removal of the head of the reactor vessel. Yet another object of the present invention is to provide such a head equipment support structure that is equally applicable for use in new installations as well as retrofit applications. Yet still another object of the present invention is to provide such a head equipment support structure system that renders it possible through the use thereof to attain measurable cost-savings and time-savings as compared to the costs and times associated with the use of prior art forms of support structure systems. SUMMARY OF THE INVENTION In accordance with the present invention there is provided a new and improved head equipment support structure system (HESS) that is particularly adapted to be cooperatively associated with the reactor vessel in a nuclear power generation system for purposes of functioning as a support for the head equipment that is operably connected therewith. The subject HESS is designed, when occupying the installed position thereof, to be physically located above and in spaced relation to the head of the reactor vessel. Moreover, when in this position the HESS is supported from structure which is located in surrounding relation to the reactor vessel. The HESS includes a multiplicity of spaced decks suitably interconnected so as to form an integral structure. In addition, the HESS includes a plurality of support columns extending substantially perpendicular to the multiple decks, and operable as support members for the HESS. The multiple decks are used for supporting and separating the electrical cabling that is to be found located in the head area of the vessel. This cabling is enclosed in flexible conduit and is routed from a position external of the reactor vessel through and onto the decks of the HESS, where the cabling is separated and support is provided thereto, for subsequent connection to other cabling located in supported relation on the surfaces of the walls that surround the reactor vessel. The decks of the HESS further function to afford missile protection, thus making of the HESS a missile shield, the latter being required to be emplaced over the head of the reactor vessel. In addition, the HESS has mounted thereto cooling ductwork employable for purposes of drawing air therethrough for effecting a cooling of equipment associated with the nuclear reactor housed within the reactor vessel. Lastly, the HESS is designed to be removable from the head of the reactor vessel as an integral structure. |
claims | 1. An extreme ultraviolet (EUV) light source comprising:a solid state laser configured to produce pulses of radiation, the pulses of radiation produced by the solid state laser comprising at least a first pulse of radiation;a second optical source configured to produce pulses of radiation, the pulses of radiation produced by the second optical source comprising at least a second pulse of radiation, the second pulse of radiation having a greater intensity than the first pulse of radiation;a vacuum chamber configured to receive a target material in an interior of the vacuum chamber, the target material comprising a material that emits EUV light when converted to plasma; andan optical element configured to direct the first pulse of radiation and the second pulse of radiation toward the interior of the vacuum chamber to, respectively, a first location in the interior of the vacuum chamber and a second, different location in the interior of the vacuum chamber, the first and second locations in the interior of the vacuum chamber being along a direction that is different from a direction of propagation of the first pulse of radiation and the second pulse of radiation in the interior of the vacuum chamber. 2. The EUV light source of claim 1, wherein the first pulse of radiation produced by the solid state laser has a first wavelength, and the second pulse of radiation produced by the second optical source has a second wavelength, the first and second wavelengths being different. 3. The EUV light source of claim 2, wherein the first pulse of radiation has a wavelength of 1.06 microns (μm), and the second pulse of radiation has a wavelength of 10.6 μm. 4. The EUV light source of claim 1, wherein the first pulse of radiation has a temporal duration of 5-20 picoseconds (ps). 5. The EUV light source of claim 1, wherein the first pulse of radiation has a temporal duration of 150 ps or less. 6. An extreme ultraviolet (EUV) light source comprising:a vacuum chamber configured to receive a target material in an interior of the vacuum chamber, the target material comprising a material that emits EUV light when converted to plasma;a solid state laser configured to produce pulses of radiation, the pulses of radiation produced by the solid state laser comprising at least a first pulse of radiation, the first pulse of radiation propagating on a first beam path to a first location in the interior of the vacuum chamber; anda second optical source configured to produce pulses of radiation, the pulses of radiation produced by the second optical source comprising at least a second pulse of radiation, the second pulse of radiation having a greater intensity than the first pulse of radiation, and the second pulse of radiation propagating on a second beam path to a second location in the interior of the vacuum chamber, the first and second locations in the interior of the vacuum chamber being different locations along a direction that is different from a direction of propagation of the first pulse of radiation and the second pulse of radiation in the interior of the vacuum chamber. 7. The EUV light source of claim 6, further comprising an optical element placed on the first beam path and the second beam path, the optical element positioned to receive the first pulse of radiation and the second pulse of radiation and to direct the first pulse of radiation to the first location and the second pulse of radiation to the second location. 8. The EUV light source of claim 7, wherein the optical element comprises a surface that is at least partially reflective. 9. The EUV light source of claim 7, wherein the optical element transmits one of the first pulse of radiation and the second pulse of radiation, and reflects the other of the first pulse of radiation and the second pulse of radiation. 10. The EUV light source of claim 7, wherein the wavelength of the first pulse of radiation is different from the wavelength of the second pulse, and the optical element comprises a dichroic mirror. 11. The EUV light source of claim 7, wherein the wavelength of the first pulse of radiation is different from the wavelength of the second pulse, and the optical element comprises a wedge-shaped optical element that directs the first pulse and the second pulse toward the interior of the vacuum chamber at different angles relative to the optical element. 12. The EUV light source of claim 6, further comprising a first optical element on the first beam path, wherein the first optical element directs the first pulse of radiation toward the first location in the interior of the vacuum chamber. 13. The EUV light source of claim 6, further comprising a first optical element on the first beam path, and a second optical element on the second beam path, wherein the first optical element directs the first pulse of radiation toward the first location in the interior of the vacuum chamber, and the second optical element directs the second pulse of radiation toward the second location in the interior of the vacuum chamber. 14. The EUV light source of claim 13, wherein the first optical element comprises one or more optical fibers. 15. The EUV light source of claim 6, wherein the first pulse of radiation has a wavelength of 1.06 microns (μm), and the second pulse of radiation has a wavelength of 10.6 μm. 16. The EUV light source of claim 6, wherein the first pulse of radiation has a temporal duration of 5-20 picoseconds (ps). 17. The EUV light source of claim 6, wherein the first pulse of radiation has a temporal duration of 150 ps or less. 18. The EUV light source of claim 6, wherein the target material comprises a target material droplet, and the EUV light source further comprises a target material delivery system coupled to the vacuum chamber, the target material delivery system configured to provide the target material droplet to the interior of the vacuum chamber. 19. The EUV light source of claim 18, wherein the target material delivery system releases the target material droplet onto a trajectory in the interior of the vacuum chamber, and the first and second locations are on the trajectory. 20. The EUV light source of claim 19, wherein the target material droplet comprises tin. 21. A photolithography system comprising:a lithography tool configured to process wafers; andan extreme ultraviolet (EUV) light source comprising:a vacuum chamber configured to receive a target material in an interior of the vacuum chamber, the target material comprising a material that emits EUV light when converted to plasma;an optical element in the interior of the vacuum chamber, the optical element positioned to direct EUV light to the lithography tool;a first optical source configured to produce pulses of radiation, the pulses of radiation produced by the first optical source comprising at least a first pulse of radiation, the first pulse of radiation propagating on a first beam path to a first location in the interior of the vacuum chamber; anda second optical source configured to produce pulses of radiation, the pulses of radiation produced by the second optical source comprising at least a second pulse of radiation, the second pulse of radiation having a greater intensity than the first pulse of radiation, and the second pulse of radiation propagating on a second beam path to a second location in the interior of the vacuum chamber, the first and second locations in the interior of the vacuum chamber being different locations along a direction that is different from a direction of propagation of the first pulse of radiation and the second pulse of radiation in the interior of the vacuum chamber. 22. The photolithography system of claim 21, wherein the first optical source comprises a solid state laser. 23. A method comprising:directing a first pulse of radiation toward a first location in a vacuum chamber of an extreme ultraviolet (EUV) source, the first location at least partially coinciding with a target material droplet comprising target material that emits EUV light when converted to plasma, and the first pulse of radiation comprising an intensity sufficient to transform the target material droplet into a geometric distribution of target material, the geometric distribution of target material occupying a larger volume than a volume occupied by the target material droplet; anddirecting second pulse of radiation toward a second location in the vacuum chamber, whereinthe second location is a different location than the first location,the second location at least partially coincides with the geometric distribution of target material,the second pulse of radiation has a greater intensity than the first pulse of radiation. 24. The method of claim 23, wherein the density of the geometric distribution increases along a direction of propagation of the second pulse of radiation. 25. The method of claim 23, wherein the first pulse of radiation propagates along a first beam path, and the second pulse of radiation propagates along a second beam path. 26. The method of claim 23, wherein the first pulse of radiation has a duration of 150 ps or less. |
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abstract | According to an embodiment, a nuclear fuel material recovery method of recovering a nuclear fuel material containing thorium metal by reprocessing an oxide of a nuclear fuel material containing thorium oxide in a spent fuel is provided. The method has: a first electrolytic reduction step of electrolytically reducing thorium oxide in a first molten salt of alkaline-earth metal halide; a first reduction product washing step of washing a reduction product; and a main electrolytic separation step of separating the reduction product. The first molten salt further contains alkali metal halide, and contains at least one out of a group consisting of calcium chloride, magnesium chloride, calcium fluoride and magnesium fluoride. The method may further has a second electrolytic reduction step of electrolytically reducing uranium oxide, plutonium oxide, and minor actinoid oxide in a second molten salt of alkali metal halide. |
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claims | 1. A method for detecting and analyzing anomalies in a machine during operation, including:receiving sensed signals from the machine indicative of vibration;receiving sensed signals from the machine indicative of non-vibration characteristics;receiving audio signals from a transducer positioned about components on the machine;correlating audio signals received from the transducer with sensed signals received from the machine indicative of vibration and non-vibration characteristics;cross-correlating all correlated signals;determining a location of an anomaly in the machine based on the cross-correlation; andtransmitting the determined location of the anomaly to a user at a desired location. 2. A method, as set forth in claim 1, wherein determining a location of an anomaly includes the step of determining a location of a vibration emanating from a component. 3. A method, as set forth in claim 1, wherein receiving audio signals from a transducer includes the step of receiving audio signals from a transducer as the transducer moves in relation to a component. 4. A method, as set forth in claim 1, wherein correlating audio signals received from the transducer with sensed signals received from the machine indicative of vibration and non-vibration characteristics includes the step of correlating audio signals with sensed signals to find a location of a strongest correlation between the audio and sensed signals. 5. A method, as set forth in claim 4, wherein cross-correlating all correlated signals includes the step of determining a location of a strongest cross-correlation, the determined location being indicative of a component being a source of the anomaly. 6. An apparatus for detecting and analyzing anomalies in a machine during operation, comprising:at least a first sensor configured to detect a parameter indicative of vibration;at least a second sensor configured to detect a non-vibration parameter;a transducer configured to receive audio signals related to components of the machine;a first model to correlate the received audio signals with the detected vibration and non-vibration parameters; anda second model to cross-correlate all correlated signals to determine a location of an anomaly in the machine based on the cross-correlation. 7. The apparatus of claim 6, wherein the second model is a neural network model. 8. The apparatus of claim 6, wherein the first model is an autoregression algorithm model. 9. The apparatus of claim 6, wherein the second model is a Fast Fourier Transform control model. 10. The apparatus of claim 6, wherein the non-vibration parameter includes temperature. 11. The apparatus of claim 6, wherein the non-vibration parameter includes humidity. |
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abstract | A method and a system. The system may include (a) evaluation units, (b) an object distribution system for receiving the objects and distributing the objects between the evaluation units, and (c) at least one controller. Each evaluation unit may include (i) a chamber housing that has an inner space, (ii) a chuck, (iii) a movement system that is configured to move the chuck, and (iv) a charged particle module that is configured to irradiate the object with a charged particle beam, and to detect particles emitted from the object. In each evaluation unit a length of the inner space is smaller than twice a length of the object, and a width of the inner space is smaller than twice a width of the object. |
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description | This application is a divisional of U.S. patent application Ser. No. 11/711,614 filed Feb. 28, 2007, now U.S. Pat. No. 7,773,717 the contents of which are incorporated by reference in its entirety. 1. Field of the Invention Example embodiment(s) are related in general to systems for aligning and handling fuel rods and water rods within a nuclear fuel bundle. 2. Description of the Related Art A reactor core of a nuclear reactor plant such as boiling water reactor (BWR) or pressurized water reactor (PWR) has several hundred individual fuel bundles of fuel rods (BWR) or groups of fuel rods (PWR). During a planned plant outage for the BWR, selected irradiated fuel bundles are removed from the reactor core at the nuclear power plant and placed in a spent fuel pool for inspection and possible reconstitution of the bundle and/or maintenance. For example, there may be leaking fuel bundle which necessitates removing the irradiated fuel bundle from the core, as it is desirable to service these bundles in the event of a broken fuel rod and/or damaged fuel spacer grid which may be causing the leak. Additionally, when the fuel bundle is removed from the core and placed in the spent fuel pool, it is desirable to manipulate the fuel bundle for inspection purposes in order to search for additional possible sources of damage or leaks, and/or to rotate the bundle for general maintenance and measurement. A typical fuel bundle for a BWR includes a plurality of fuel rods and centrally located water rods attached between an upper tie plate and a lower tie plate. For example, in FIG. 24A, there is shown a fuel bundle 15 for a BWR which includes a plurality of fuel rods 25 and one or more water rods (water rods obscured and which may or may not be centrally located within bundle 15), connected between an upper tie plate 30 and a lower tie plate 40. FIG. 24B shows the same fuel bundle 15 as it would look upon removal from the core and prior to removal of the channel 20 for inspection and maintenance. The bundle 15 includes a generally rectangular channel 20 which extends the length of fuel bundle 15 and surrounds the fuel rods, water rods and upper and lower tie plates 30, 40. The channel 20 is an extruded alloy which encases the bundle 15. The fuel bundle 15 is typically delivered into the spent fuel pool via a fuel handling bridge (not shown) which is permanent machinery in reactor plants. The fuel handling bridge attaches to the upper tie plate bail (handle) 35 of the fuel bundle 15 to move the fuel bundle 15 from the core to the spent fuel pool. Typically the fuel bundle 15 shown in FIG. 24B is centered over a fuel prep machine (FPM—not shown), and a carriage of the FPM is raised to receive the fuel bundle 15. As is well known in the art, the FPM is attached to a wall of the spent fuel pool in a nuclear power plant. Once the channeled fueled bundle 15 is place within the FPM, the channel 20 and upper tie plate 30 are removed to expose the fuel rods 25 and the fuel bundle 15 upper end for inspection and/or maintenance purposes. Of note, with continued power operations of the reactor core with the irradiated fuel bundle 15, the fuel bundle 15 can be subjected to bow or twist. Twist/bow is caused by the amount of time the fuel bundle 15 has been in-service. In other words, the more the bundle 15 is used in an operating reactor core (i.e., the greater the exposure of the bundle in megawatt-days per short time (MWD/st), the greater the twist/bow potential. Accordingly, if the bundle 15 in the FPM exhibits twist or bow, it becomes substantially more difficult to remove selected fuel rods 25 in order to service/inspect the fuel bundle 15. A fuel bundle exhibits twist and bow due to the growth of individual fuel rods over time and exposure within the core. In an example, a fuel bundle for a BWR is typically held together with a plurality of tie rods. The lower end plugs of the fuel rod screw into the lower tie plate 40, and the upper tie plate 30 slides in place over the fuel rods 25, water rods and tie rods. The upper end plug of the tie rods are threaded and receive nuts which secures the fuel bundle 15 together. As the fuel rods 25 grow due to irradiation, the fuel rods 25 have little room to expand as they are sandwiched between the upper tie plate (UTP) 30 and lower tie plate (LTP) 40. The fuel rods do not all grow exactly the same amount, resulting in an uneven growth; this causes portions of the fuel bundle 15 to lengthen more than other areas within the bundle 15, producing what's known as bow and twist. Most fuel bundle designs in BWRs (such as the fuel bundle 15) and PWRs include a plurality of fuel spacers 80, also referred to as spacer grids, which are axially spaced along the length of the fuel bundle 15. A typical fuel spacer 80 or spacer grid includes a plurality of cells or openings which accommodate the fuel rods and water rods there through. These fuel spacers 80 are generally not robust in construction, and can be damaged during routine in-service fuel inspections while removing and installing full and part-length fuel rods and water rods in the bundle within the spent fuel pool. The damage caused to the fuel spacers 80 could go unnoticed, and could cause additional damage to individual fuel rods 25 if a reconstituted fuel bundle (such as fuel bundle 15) is returned to power operations within the core. Accordingly, during removal and installation of the fuel rods 25 in a given irradiated fuel bundle 15 within the spent fuel pool, there is a substantial probability for fuel bundle component damage, either to the fuel rod itself, the spacers, the water rods or end plugs of fuel rods, which can occur during the in-service maintenance of the fuel rods within the spent fuel pool. Further, as the removed fuel bundle 15 within the spent fuel pool is completely submerged, most inspections are done remotely and maintenance or repair is done by operators standing well above the fuel bundle 15, while utilizing a remote camera system and length handling poles with implements at ends thereon. The handling poles are inserted down through the fuel bundle 15 to remove/install selected fuel rods. With the upper tie plate 30, the channel clip (not shown) and the channel 20 removed, workers typically utilize up to a 30-foot handling pole to perform maintenance, installation and/or removal of fuel rods 25. Particularly in the case of part-length filet rods, which in some case are substantially shorter than full-length fuel rods, only the skill and experience of the handler of the handling pole ensures that a part-length rod can be safely extracted (or installed) without causing damage to the fuel spacers 80 or adjacent fuel rods 25. This is true even with the use of remote cameras positioned down in the spent fuel pool for monitoring the maintenance procedure. Accordingly, conventional procedures for retrieving/installing a part-length fuel rod are time consuming if not impossible, cumbersome and must rely on the experience and skill of the operator manipulating the handling pole to avoid damaging a fuel spacer 80 or adjacent fuel rod 25. As fuel bundle designs are becoming even more complex, this inadvertent damage to the fuel spacers 80 and/or fuel rods 25 is even more likely without an adequate alignment and handling system. An example embodiment is directed to a system in a nuclear power plant for aligning a nuclear fuel bundle and handling selected fuel rods and/or water rods within the fuel bundle, where the fuel bundle resides in a spent fuel pool within the plant. The fuel bundle includes one or more water rods and a plurality of fuel rods including full-length fuel rods and part-length fuel rods extending vertically within the bundle through a plurality of axially spaced fuel spacers provided between a top end and bottom end of the fuel bundle, each fuel spacer including a plurality of individual cells accommodating corresponding fuel rods and water rods. The system includes a fuel prep machine (FPM) in the spent fuel pool for supporting the fuel bundle thereon, a bundle alignment assembly attached to the fuel prep machine for aligning fuel rods within the fuel bundle to remove any twist or bow within the fuel bundle, a rod grapple tool to extract selected part-length rods from the fuel bundle, and a fuel rod guide block slidable onto the top end of the fuel bundle for protecting an uppermost fuel spacer of the fuel bundle and aligning fuel rods within individual cells of all the fuel spacers in the fuel bundle. Another example embodiment is directed to a system of a reactor plant for removing bow and twist within a nuclear fuel bundle to permit inspection and replacement of one or more fuel rods or water rods within the fuel bundle, where the fuel bundle has been removed from a reactor core to a spent fuel pool within the plant. The system includes a fuel prep machine (FPM) in the spent fuel pool for supporting the fuel bundle thereon, and a bundle alignment system attached to the fuel prep machine for aligning fuel rods within the fuel bundle to remove any bow or twist within the fuel bundle. Another example embodiment is directed to a fuel rod alignment system for a fuel bundle residing in a spent fuel pool within the plant. The fuel bundle includes one or more water rods and a plurality of fuel rods including full-length rods and part-length rods extending vertically within the bundle through a plurality of axially spaced fuel spacers provided between a top end and a bottom end of the fuel bundle, each fuel spacer including a plurality of individual cells accommodating corresponding fuel rods and water rods. The system includes a fuel prep machine in the spent fuel pool for supporting the fuel bundle thereon, and a fuel rod guide block slidable onto the top end of the fuel bundle for protecting an uppermost fuel spacer of the fuel bundle and aligning fuel rods within individual cells of all the fuel spacers in the fuel bundle. Another example embodiment is directed to a system for removing a part-length fuel rod from a fuel bundle, where the fuel bundle resides in a spent fuel pool of a nuclear reactor plant. The system includes a fuel prep machine in the spent fuel pool for supporting the fuel bundle thereon, and a rod grapple tool having a first end handled by an operator above the fuel pool in the plant and a second end inserted at a top end of the fuel bundle on the fuel prep machine to retrieve the part-length fuel rod within the bundle. The second end has a protective, removable guide pin which prevents the rod grapple tool from damaging the fuel bundle as the rod grapple tool is inserted into the bundle. The system includes a guide pin retrieval tool for, when the rod grapple tool has been inserted into the fuel bundle so that the guide pin and gripper are in position over the part-length fuel rod to be extracted, removing the guide pin to permit the gripper of the rod grapple tool to be attached to an upper end plug of the part-length fuel rod to extract the part-length fuel rod from the bundle. As will be described in more detail below, an example embodiment is directed to a system for aligning and handling selected fuel rods within a fuel bundle of a nuclear reactor which facilitates the ability of handlers to remove and install fuel rods without damaging the fuel spacers or adjacent fuel rods. The example system may provide a straight-line path to facilitate the extraction of fuel rods including part-length fuel rods without merely relying on the skill of the handler to insure that the fuel rod is removed without damaging adjacent fuel rods or fuel spacers. The example system may thus enable the fuel rods, spacers or spacer grids, water rods and end plugs to be protected during maintenance and/or inspection procedures within the spent fuel pool. FIG. 1 is a side view of a system 1000 for aligning and handling selected fuel rods within a fuel bundle in accordance with an example embodiment. In FIG. 1, the fuel bundle 150 is supported by a fuel prep machine (FPM) 110. The FPM 110 is attached to a wall 105 of a spent fuel pool 103 within a nuclear reactor. The fuel bundle 150 is shown with its upper tie plate 30 and channel 20 removed, as this procedure is done once the fuel bundle 150 is lowered into the fuel prep machine 110. In this example, the fuel bundle 150 is for a BWR and has a 10×10 fuel rod matrix (10 rows by 10 columns of full-length and partial-length full rods), with a pair of centrally located circular water rods 170. However, fuel bundle 150 can have a configuration other than a 10×10 fuel rod matrix (9×9, 12×12, etc.), and a different number of water rods of different shapes and sizes, that may or may not be centrally located within the fuel bundle. System 1000 includes a bundle alignment assembly 200 attachable to the fuel prep machine 110. The bundle alignment assembly 200 is provided for aligning fuel rods and water rods within the fuel bundle 150 to remove any twist or bow within the fuel bundle 150 and to provide a straight-line path for fuel rod installation and/or removal. As will be seen in more detail below, the bundle alignment assembly 200 includes a series of alignment stations 210. Each alignment station 210 includes a plurality of rotatable pre-formed stainless steel blades and rigid stainless steel blades. In general, the bundle alignment assembly 200 is lowered into position onto the fuel prep machine 110 and held in place by mechanical means. The fuel bundle 150 is then placed into the fuel prep machine (FPM) 110 for inspection. When manually actuating the bundle alignment assembly 200 by means of a handling pole, the rotatable pre-formed stainless steel blades and the rigid stainless steel blades are rotated together into the fuel bundle 150, creating a protective grid above each fuel spacer 180 while also capturing each individual fuel rod in the forward half of the nuclear fuel bundle 150. One possible result of using the bundle alignment assembly 200 is to ensure that an in-service (i.e., irradiated) nuclear fuel bundle such as fuel bundle 150 has any twist and/or bow removed there from, a condition normally caused by the harsh environment within reactor vessels. The assembly 200 thus may provide a straight path for the removal and installation of individual fuel rods or water rods, while protecting the fuel spacers 180 from damage. System 1000 further includes fuel rod guide block 300 slidable onto the top end of the fuel bundle 150 for protecting an uppermost spacer from damage, shown as spacer 180A in FIG. 1. The fuel rod guide block 300 protects the uppermost spacer 180A of the fuel bundle 150 from damage while inserting fuel rods by physically protecting the upper side of the spacer 180A. The fuel rod guide block 300 also enables aligning of fuel rods within individual cells of all the fuel spacers 180 in the fuel bundle 150. Additionally, the fuel rod guide block 300 provides a lead-in to initially start a fuel rod into the fuel bundle 150 with desired proper alignment. Further, the rod guide block 300 provides an obvious visual indication as to where a fuel rod needs to be inserted into the fuel bundle 150. This can enable less experienced handlers to perform fuel rod removal and insert procedures without requiring the skill of and experience of the seasoned handler, since the fuel rod guide block 300 helps to properly align each of the fuel rods of the fuel bundle 150 in the vertical direction. As will be shown in further detail hereafter in FIG. 10, the fuel rod guide block 300 includes two horizontally-oriented, spaced (upper and lower) stainless steel plates separated by a plurality of vertically-arranged stainless steel tubes. Each of the plates has a plurality of openings which align with the locations of the fuel rods and water rods within the bundle 150. The fuel rod guide block 300 is held together by two vertically-oriented side plates attached by suitable fasteners to each of the upper and lower plate. A bail (handle) with restricted movement is attached to the fuel rod guide block 300 for the purpose of lowering it onto the fuel bundle 150 that is supported on the FPM 110, prior to in-service fuel inspections. Thus, the fuel rod guide block 300 is designed to slide onto the top of the nuclear fuel bundle 150 positioned in the FPM 110. As will be described in further detail below (FIGS. 11A and 11B), once installed, the fuel rod guide block 300 is limited to its downward travel into bundle 150 by creating a restricted fit between the water rods and tapered central openings in the upper plate of the fuel rod guide block 300 which are aligned with the water rods. The fuel rod guide block 300 comes to rest onto tapered sections of a water rod transition area. Although system 1000 is shown with both the bundle alignment assembly 200 and rod guide block 300 included, each can be used independently without the other for inspection and/or maintenance of an irradiated fuel bundle 150. In an example, fuel bundle 150 can be an irradiated fuel bundle that has been removed from the BWR core, a previously used bundle 150 that is stored within the spent fuel pool of the plant, a new fuel bundle 150 that has been stored within the spent fuel pool of the plant while awaiting placement within the reactor's core as a reload, a fuel bundle having been removed from an on-site new fuel storage fault for placement in the fuel pool, and/or a fuel bundle from a fixed or movable dry storage cask for placement into the fuel pool). In another example embodiment, the FPM 110 and only bundle alignment assembly 200 are used together for supporting a fuel bundle 150 and aligning the fuel rods and water rods of the bundle for inspection and/or rod replacement purposes. For any irradiated bundle 150 exhibiting twist and or bow, the FPM 110 and bundle alignment assembly 200 may thus constitute a system for removing the twist/bow within a fuel bundle to permit inspection and possible replacement of one or more fuel rods or water rods therein within the spent fuel pool of the plant. In this alternative embodiment, the rod guide block 300 may not necessarily be installed. In the event that an irradiated fuel bundle 150 exhibits no twist or bow, the bundle alignment assembly 200 does not need to be installed, only the rod guide block 300 is installed on the top of the bundle 150 above the uppermost spacer 180A. In this alternative embodiment, the rod guide block 300 with FPM 110 can represent a separate fuel bundle handling system, in which the FPM 110 supports fuel bundle 150 thereon and the rod guide block 300, when installed on the top end of the bundle 150, aligns each of the fuel rods 155 and water rods 170 of the fuel bundle 150 in the vertical direction. Referring again to FIG. 1, the system 1000 also includes a rod grapple tool 400. In particular, rod grapple tool 400 is utilized by a handler for the removal of fuel rods, such as certain tie rods and/or the shorter part-length fuel rods which are deeper within the fuel bundle 150. A different, pre-existing rod grapple tool may be used for the removal and/or reinsertion of standard full length fuel rods and certain tie rods, as the upper end plugs of the standard full length fuel rods and tie rods may be designed differently than that of the upper end plug of the part-length fuel rod. The rod grapple tool 400 is designed so as to mimic the dimensions of individual fuel rods. This allows the rod grapple tool 400 to safely pass through the fuel spacers 180 without causing component damage. As will be seen in more detail below (FIG. 15B, for example), the rod grapple tool 400 includes a gripper (also referred to as a rod grapple) at the end of the tool 400 that is inserted into the fuel bundle 150 for extracting a part-length fuel rod. For insertion of the rod grapple tool 400 into the bundle 150, the rod grapple tool 400 includes a removable guide pin (shown in more detail in FIGS. 15A and 15B). The guide pin is inserted into the gripper and is generally tapered to a rounded pin end. Since the gripper has a blunt end, the guide pin is provided to prevent damage to the fuel spacers 180 as the rod grapple tool 400 is inserted into the fuel bundle 150. Once the rod grapple tool 400 has been fitted with the guide pin, inserted into the fuel bundle 150 and positioned at a given axial location within the fuel bundle 150 above a part-length fuel rod to be extracted, a pin retrieval tool 500 is utilized to remove the guide pin from the end of the grapple tool 400. The pin retrieval tool 500 is shown in more detail hereafter and is attached at the end of a separate handling pole 502 for insertion down into the fuel pool to retrieve the guide pin from the rod grapple tool 400 end. Accordingly, the rod grapple tool 400 and pin retrieval tool 500 may comprise a separate system for removing a part-length rod from a fuel bundle, independent of the bundle alignment assembly 200 and rod guide block 300 of the system shown in FIG. 1. Further, the rod guide block 300, rod grapple tool 400 and guide pin retrieval tool may comprise a separate system for removing part-length rods for the fuel bundle 150, independent of the bundle alignment assembly 200. In general to remove a part-length rod from fuel bundle 150, the tapered, rounded guide pin is inserted in the end of the gripper so that only the tapered end of the guide pin extends from a lower housing of the rod grapple tool 400. The gripper is designed to be attached to an upper end plug of a part-length fuel rod for rod extraction. Once attached, the gripper is retracted into the lower housing so that the lower housing of tool mates with a shoulder of the end plug at the top of the part-length rod, providing a smooth continuous surface between the part-length rod and the attached rod grapple tool 400. The guide pin thus creates a lead-in for the rod grapple tool 400 to pass through each fuel spacer 180. Once the rod grapple tool 400 is in position above a selected part-length fuel rod, the guide pin is removed using the pin retrieval tool 500 so that the gripper of tool 400 can be inserted over the partial length rod's end plug and engaged for fuel rod extraction. As to be described in more detail below (FIGS. 17A and 17B), the pin retrieval tool 500 includes a tongue with a mating bore that receives a mating portion of the guide pin. The pin retrieval tool 500 is fixed to the end of the handling pole 502 to allow for remote handling of the guide pin within the fuel bundle 150. The pin retrieval tool 500 thus provides a positive means of capturing the guide pin 435 for repetitive use. FIGS. 2A through 2C illustrate an example fuel prep machine 110 used in system 1000 in accordance with an example embodiment. Many nuclear power plants employ fuel prep machines 110 in the spent fuel pool of the plant to support an irradiated fuel bundle 150, thus a detailed explanation is omitted for purposes of clarity. As shown in FIGS. 2A to 2C, the fuel prep machine (FPM) 110 generally includes a stanchion 114 extending from an FPM platform 115 down into the spent fuel pool of the plant. The FPM 110 includes a carriage 120 which slides up and down as needed on rails 116 formed on the stanchion 114. The carriage 120 includes an upper rotating fixture 122 and a lower rotating fixture 124 which permit rotational movement of the fuel bundle 150 therein. The FPM 110 is a permanent fixture in the spent fuel pool 103 and is mounted on one of the walls 105 of the spent fuel pool 103, as is known. The FPM platform 115 is the only portion of the FPM 110 that is above water and includes a safety handrail 117. A fuel bundle (such as bundle 150) is delivered to the FPM 110 via a fuel handling bridge (not shown, this is a permanent fixture in a reactor plant). Once in place over the carriage 120, the carriage 120 is raised to receive the fuel bundle 150. The fuel bundle 150 may be rotated in either direction up to 360 degrees as desired for inspection and/or maintenance purposes via upper and lower rotating fixtures 122, 124. FIG. 3A is a front view of the bundle alignment assembly 200 and FIG. 3B is a side view of assembly 200. FIG. 3C is an enlargement of detail A in FIG. 3B. Referring to FIGS. 3A and 3B, assembly 200 includes a plurality of axially-spaced alignment stations 210 mounted to a mounting frame 205 which is attached to the upper and lower rotating fixtures 122, 124 of the fuel prep carriage 120 on the FPM 110 as will be shown hereafter. The assembly 200 includes a bail 202 which enables it to be lowered onto and removed from the FPM 110. Each alignment station 210 includes a support plate 206 with a plurality of alignment blade bundles 220 mounted thereon. As best shown in FIG. 3C, the support plate 206 is mounted to a cross member 204 affixed to the mounting frame 205 and also to the mounting frame 205 by mechanical fastening means 214 (such as nut-screw-washer assemblies). Each alignment station 210 includes a plurality of alignment blade bundles 220 mounted thereon. In FIG. 3A, these are shown as blade bundles 220A, 220B and 220C. As will be seen in further detail below, the alignment blades of these bundles are rotated to align fuel rods and water rods in the front half of the fuel bundle 150 (due to clearance constraints of the FPM 110, half the bundle 150 is aligned at a time for inspection and/or rod removal/installation in that half), then the bundle 150 is rotated to inspect and/or service the other half of the same bundle. FIG. 4 is a partial side view of system 1000 in the vicinity of the lower rotating fixture 124 in order to show the connection of the bundle alignment assembly 200 to the fuel prep machine 110; FIGS. 5 and 6 are partial perspective views of the system 1000 to show the attachment of the upper mount block 208 to the upper rotating fixture 122. Referring to FIGS. 4-6, in order to mount the bundle alignment assembly 200, an upper mounting bracket 218 and a lower mounting 216 are installed on the upper and lower rotating fixtures 122 and 124. These will capture the mating surfaces of the bundle alignment assembly 200. As shown best in FIG. 4, a lower mounting bracket 216 is attached to the lower rotating fixture 124. The lower mounting bracket 216 is configured to receive an alignment pin 212 which is connected to the bottom of the mounting frame 205 of the bundle alignment assembly 200. The upper mounting bracket 218 is attached to the upper rotating fixture 122. Each upper mounting bracket 218 includes a feature which has a threaded cavity 217 therein. The brackets 218 are adapted to receive spring loaded pins 219 which screw therein to connect the upper mount blocks 208 at the upper end of the bundle alignment assembly 200 to the upper mounting brackets 218 of the upper rotating fixture 122. As best shown in FIG. 6, this secures the bundle alignment assembly 200 to the carriage 120 of the fuel prep machine 110, with the spring loaded pins 219 inserted into the threaded cavities 217 of the upper mounting brackets 218. Of note, FIG. 5 provides a clearer view of the internal arrangement of fuel rods, comprising full-length fuel rods 155 and part-length fuel rods 160, and water rods 170 within fuel bundle 150. For purposes of clarity, a number of full and part-length rods 155, 160 have been removed so that the water rods 170 and other part-length rods 160 can be seen. Also illustrated are the upper end plugs 165 on the part-length fuel rods 160. Further, the fuel spacer 180 with its individual cells may be seen in clearer detail. Accordingly, the bundle alignment assembly 200 is lowered into position via its bail 202 so that the lower alignment pins 212 are guided into the lower mounting brackets 216. The upper mounting blocks 208 are then positioned onto the upper mounting brackets 218 and the spring loaded pins 219 are engaged in the upper mounting brackets 218 to secure the bundle alignment assembly 200 into place. FIG. 7A is a perspective view of an alignment station 210 showing alignment blade bundles 220 in a neutral or disengaged position. Each alignment station 210 includes a plurality of blade bundles 220. As shown in FIG. 7A (as well as in FIG. 3A), three (3) alignment blade bundles 220A, 220B and 220C are mounted on a generally C-shaped support plate 206. Each blade bundle 220 includes a plurality of stainless steel blades 222. However, blades 222 can be formed of other metals, metal alloys or materials having high thermal resistance properties and/or high coefficients of thermal conductivity, such as inconel, high temperature polymers (plastics) and ceramics. Some of the individual blades 222 are shorter (shown as 222′) than others in a given blade bundle 220 so as to create a grid 230 around a portion of the fuel bundle 220 (in this example, half of bundle 150) when the blade bundles 220 are rotated into an engaged position. In FIG. 7A, the individual blade bundles 220 are shown in a neutral or disengaged position. They are movable into an engaged position by corresponding activation handles 226. FIG. 7B is a perspective view of the alignment station 210 showing the blade bundles 220 in an engaged position. As shown in FIG. 7B, the blade bundles 220A, 220B and 220C can be rotated into the fuel bundle 150 by actuating the activation handle 226. A hook used on the standard handling pole is used to actuate the activation handles 226 sequentially so as to first rotate the blade bundle 220B, then bundles 220A and 220C into the fuel bundle 150. FIG. 7C is a top view of the alignment station 210 with the blade bundles 220 in an engaged position to illustrate the grid 230 that is created for alignment of fuel rods 155/160 and water rods 170 within the fuel bundle 150. FIG. 7C also better illustrates the use of shorter blades 222′ to form grid 230. Alignment blade bundle 220B is rotatable in a first plane, and the other two blade bundles 220A and 220 C are rotated in a second plane above blade bundle 220B so as to form the grid 230 around groups of fuel rods 155, 160 and water rods 170. The top view of FIG. 7C shows how the grid 230 is created with an interior center space to provide an opening for the water rods 170. This grid 230 in the example of FIG. 7C thus aligns approximately half the fuel rods 155/160 in fuel bundle 150, which for an example 10×10 fuel matrix are forty-six (46) fuel rods and one (1) water rod. Half of the fuel rods 155/160 with one water rod 170 in bundle 150 are aligned at a time due to tolerance constraints of the FPM 110. The bundle 150 can simply be rotated within carriage 120 to permit rods 155/160/170 in the other half of the fuel bundle 150 to be aligned. Of note, the bundle 150 is straightened once the blade bundles 220A-C are inserted from one side. Selected fuel rods 155, 160 on the other side of the bundle 150 may still have bow or twist, but the overall bundle 150 profile will be straight in the axial direction. For each alignment station 210, the protective grid 230 formed by the alignment blade bundles 220 vertically aligns the fuel rods 155/160 and water rods 170 above each of the fuel spacers 180 in the bundle 150, as shown in FIG. 1 for example. Of course, alignment stations 210 can be located below the spacers 180 so that the grid 230 formed by blade bundles 220 vertically aligns the fuel rods 155/160 and water rods 170 below each of the fuel spacers 180. If desired, alignment stations 210 can be attached just above and below spacers 180 to form the grids 230 that align the fuel rods 155/160 and water rods 170 above and below each of the fuel spacers 180 in the bundle 150. In an alternative construction, the blade bundles 220 can be rotated horizontally to an engaged position such that individual blades 222 rotate independent of one another. In this embodiment, selected blades 222 may be removed from selected blade bundles 220 to align a particular portion of fuel rods 155/160 in the bundle 150. Different combinations of blades 222 in each of the blade bundles 220 of an alignment station 210 can thus be rotatable to align one or more of a half-section of the bundle 150, a quarter-section of the bundle 150 and an eighth section of the bundle 150, for example. It would be evident to one skilled in the art to include additional blades 222 with varying or different lengths to accommodate different fuel rod matrix configurations other than 10×10, such as fuel bundles having 9×9 fuel rod matrices or larger fuel bundles such as the developing 17×17 fuel rod groups for pressurized water reactors (PWRs). FIG. 8A is a perspective view of an alignment blade bundle 220 and FIG. 8B is an exploded view of FIG. 8A illustrating the constituent parts of the alignment blade bundle 220. Referring to FIGS. 8A and 8B, an alignment blade bundle 220 (each of the three alignment blade bundles have similar parts) includes a base plate 228 which has two side plates 232 connected thereto via a plurality of fasteners 234 such as the screws which are secured within threaded bores 235. The activation handle 226 is connected to one side of shaft 238 so as to be in rotational engagement with a shaft 238. The shaft 238 extends through a bearing/washer assembly shown generally at 239 and through a pair of pivot blocks 240. The blades 222 are attached to a blade holder 236 which is affixed to the top of the pivot blocks 240 via a series of fasteners 241 received in corresponding threaded bores 242 in the pivot blocks 240. Each blade bundle 220 also includes a fixed stainless steel blade 237 attached to blade holder 236. The purpose of fixed blade 237 is to provide a rigid point to begin fuel rod alignment. A limit stop 243 is provided beneath the blade holder 236 so as to limit rotational travel of the blades 222 to no more than 90 degrees from vertical. The blade bundle 220 is fixedly secured to the support plate 206 with a spring stop bolt 244 which compresses a spring 246 as it is tightened into a threaded bore 248 of the base plate 228. This allows a blade bundle 220 to be quickly removed from and/or reattached to support plate 206. An inspection tooling lug 250 is also attached to the base plate 228 via suitable fasteners 252 to permit an inspection tooling pole (not shown) to be attached thereon. FIG. 9 is a partial perspective view of the system 1000 illustrating the rod guide block 300 placed over the fuel bundle 150. Referring to FIG. 9, the fuel rod guide block 300 has a bail 302 which is attached to a standard handling pole 304 to be lowered down into the spent fuel pool and place just below the upper end plugs of the full length fuel rods 155 and the tops of the water rods 170 at the top end of bundle 150. As previously indicated, in the event that the irradiated fuel bundle 150 exhibits no twist or bow, only the rod guide block 300 need to be installed on top of the bundle 150 above the uppermost spacer 180A. The fuel rod guide block 300 when in place protects the uppermost spacer 180A from damage as fuel rods are inserted therein and also provides an aligned lead-in to initially start a replacement fuel rod (full-length fuel rod 155 or part-length rod 160) into the fuel bundle 150 with the desired proper alignment. Thus, the rod guide block 300 acts as both a shield (physically protecting spacer 180A) and a visual aid to show a handler where a fuel rod needs to be inserted into the fuel bundle 150 by providing a clear visual indication due to the structure and arrangement of an upper plate 305 of fuel rod guide block 300. Accordingly, less experienced handlers can perform fuel rod removal and insertion procedures without requiring the skill and experience of the seasoned handler, since the structure of the fuel rod guide block 300 helps to properly and perfectly align each of the fuel rods 155/160 of the fuel bundle 150 in the vertical direction. FIG. 10 is an exploded view of the fuel rod guide block 300 to illustrate constituent parts in more detail. As previously described, the fuel rod guide block 300 is lowered onto the fuel bundle 150 via a standard handling pole 304. In an example, this can be a handling pole with a ½″-13 threaded stud that located on the lowest end of the pole 304, that's used to lower the guide block 300 over the fuel bundle 150. The threaded stud is received in the threaded bore 303 in bail 302 of the fuel rod guide block 300. The fuel rod guide block 300 further includes an upper plate 305, a lower plate 306, and a plurality of stainless steel vertical tubes 308 dimensioned so as to be able to receive a replacement fuel rod 155, 160 or a rod grapple tool 400 there through. A pair of side plates 310 attach to the upper plate 305 and lower plate 306 so as to secure the tubes 308, upper plate 305 and lower plate 306 together. The side plates 310 include a plurality of holes 319 to facilitate decontamination and cleaning of tubes 308 within the guide block 300. As shown in FIG. 10, each of the upper plate 305 and the lower plate 306 have a plurality of threaded bores 313 which are configured to receive a plurality of fasteners 314 to attach the side plates 310 to the side surfaces of the upper and lower plates 305, 306. As the example fuel bundle 150 has a 10×10 fuel rod matrix, 92 tubes 308 are employed (a space is provided in the center for the water rods 170), and each of the top and bottom plates 305 and 306 have 92 fuel rod openings 316 for fuel rods 155/160 or grapple tool 400 passage. Openings 316 align with the tubes 308 as shown. The upper plate 305 and lower plate 306 also include a pair of central openings 318 that align with the water rods 170 in the fuel bundle 150. Accordingly, openings 316 and 318 mirror the locations of fuel rods 155/160 and water rods 170 in fuel bundle 150 and align with the tubes 308. Thus, as the fuel rod guide block 300 is positioned onto and/or over the fuel rods 155/160 and water rods 170 of the fuel bundle 150, the fuel rods 155/160 and water rods 170 are properly realigned, eliminating any bow and/or twist that might be present within the bundle 150 (such as in a case where the fuel rod guide block 300 is not used with bundle alignment assembly 200). A bail attachment plate 320 is provided on either side of the tubes 308, between its corresponding side plate 310 and the tubes 308. Each bail attachment plate includes a projection 322 which extends through an opening 324 in its corresponding side plate 310. Each projection 322 has a centrally threaded bore 326 which is to receive a fastener 328 which secures each arm 329 of the bail 302 to its corresponding bail attachment plate 320, i.e., the fasteners 328 are captured by the threaded bores 326 to secure the bail 302 to the bail attachment plates 320. A bail stop 330 is provided on each outside surface of each side plate 310, providing a restricted movement mechanism so as to prevent the bail 302 from traveling too far. As shown in FIG. 10, the bail stop 330 is secured to the side plate 310 and bail attachment plate 320 with a plurality of fasteners 332 which are captured in threaded bores 333 within the bail attachment plate 320. FIGS. 11A and 11B are partial cutaway views of the fuel rod guide block to illustrate the placement of the fuel rod guide block 300 over the fuel bundle 150 and on top of the uppermost space 180A. The fuel rod guide block 300 in FIGS. 11A and 11B is shown with an area where the tubes 308 have been removed to illustrate how the water rods 170 interact with the guide block 300. As the fuel rod guide block 300 is lowered by the handling pole 304, the fuel rods (full-length fuel rods 155 since this is the top of bundle 150) and water rods 170 extend through the apertures 316, 318 as the fuel rod guide block 300 is lowered down into the bundle 150. Downward travel of the fuel rod guide block 300 is terminated due to tapers 172 (neck-down features) of the water rods 170. The openings 318 in the upper plate 305 for the water rods are also tapered as best shown at 307 in FIG. 11B. Thus, when the tapered openings 318 meet the tapers 172 of the water rods 170, the fuel rod guide block 300 downward travel is halted. Accordingly the tapered surfaces 172, 307 prevent the fuel rod guide block 300 from traveling any further in the downward direction. FIG. 12 illustrates a partial perspective view of the system 1000 with the fuel rod guide block 300 in place on fuel bundle 150. Once the fuel rod guide block 300 is in position, the handling pole 304 is removed by rotating it counter clockwise to remove its stud from the threaded opening 303 in the bail 302. After the handling pole 304 is released from the fuel rod guide block 300, the handling pole 304 is used to tap the bail 302 either backwards or forwards. The handling pole 304 is then stored in its normal ready position hanging from the safety handrail 117 of the FPM platform 115, for example. FIG. 12 thus illustrates the system with the fuel rod guide block 300 in place. FIGS. 13-16B describe the rod grapple tool 400 in further detail; reference should be made to these figures for the following discussion. The rod grapple tool 400 is shown generally in FIG. 13 from the vantage point of the FPM platform 115 looking down into the spent fuel pool below towards the fuel bundle 150, which is secured within the carriage 120 attached to the FPM 110. As previously noted, the fuel bundle 150 includes a plurality of part-length rods 160. The part-length fuel rods 160 may be different heights, known as upper part-length rods and lower part-length fuel rods. The rod grapple tool 400 is used to retrieve (or install) either the upper part-length fuel rods or the lower part-length rods 160 from the fuel bundle 150. A handler grabs the rod grapple tool 400 by a handle 402 to lower the rod grapple tool 400 into the fuel bundle 150, such as through one of the tubes 308 in the fuel rod guide block 300. The rod grapple tool 400 includes a push-pull handle 404. In an optional variation, the push-pull handle 404 can include indicator markings (shown generally at 403) that indicates when the rod grapple tooling is in the fully extended position and/or when it is in the fully closed position, this part of the operation will be explained in further detail hereafter. FIGS. 14A through 14D illustrate constituent parts of the part-length rod grapple tool 400 in more detail. As shown in FIGS. 14A and 14B, the part-length rod grapple tool 400 includes a push-pull handle 404 which is connected to an activation rod 408 via a plurality of fasteners 409 that are received in holes 411 in the push-pull handle 404 to be captured by threaded bores 410 in the activation rod 408. A top end of activation rod 408 is inserted up through a threaded sleeve 405 on which a threaded acme nut 407 rides, into the push-pull handle 404, where it is secured to the push-pull handle by fasteners 409 such as screws. As shown in FIGS. 14A and 14B, the activation rod 408 is assembled with Delrin bushings 412, spiral retaining ring 414 and spaced retaining rings 416 which secure the Delrin bushings 412 along the activation rod 408. The Delrin bushings 412 keep the activation rod 408 centered in an upper housing 418. The upper housing 418 has the handle 402 at one end and a connector 422 at another end for attaching to a connector 424 of a lower housing 430 of the grapple rod tool 400. As the fasteners 409 are not strong enough to counter the potential rotational torque due to unscrewing the part-length rod 160 from its lower tie plate 40, a key stock 413 is provided in a slot 406 of activation rod 408 to absorb this torque. As will be seen in further detail, the lower housing 430 contains an extendable gripper rod 431 (see dotted line to denote within the interior of lower housing 430 in FIG. 14A) which has a gripper 432 attached at a distal end thereon. The gripper rod 431 is attachable to the activation rod 408 within the connectors 422, 424 of upper and lower housings 418, 430, and can be extended via push-pull handle 404 to extend the attached gripper 432 outside of the lower housing 430 so as to retrieve a part-length rod 160. Referring to FIGS. 14C and 14D, the activation rod 408 has a machined flat end connector 426 which mates with a corresponding machine flat end connector 428 of the gripper rod 431 within the connector 424 of the lower housing 430. The machine flats on end connectors 426 and 428 keep the activation rod 408 and gripper rod 431 from rotating so as to allow the gripper 432 at the end of the gripper rod 431 to be pulled. The upper and lower housings 418 and 430 are joined at flat facing surfaces 423 and 425 by the use of suitable mechanical fasteners 427. Prior to connecting these housings 418 and 430 together, the activation rod 408 is connected to the gripper rod 431 via the end connectors 426 and 428, as best shown in FIG. 14D. In particular, a threaded screw 429 is captured through aligned bores in both end connectors 426 and 428 of their respective rods 408, 431. The connection between activation rod 408 and gripper rod 431 allows the gripper 432 which is attached at the distal end of gripper rod to be extendable from the end of the lower housing 430, and hence retracted within lower housing 430. Accordingly, the rod grapple tool 400 has an extended position and a retractable or closed position. FIGS. 15A and 15B illustrate the extended position of the rod grapple tool 400. The extended position is only used when loading or removing the guide pin 435 from gripper 432, as well as locking the gripper 432 of rod grapple tool 400 onto a partial-length rod 160 so as to extract it from the fuel bundle 150. To extend gripper 432, while a handler holds the handle 402, the handler rotates the acme threaded nut 407 counter-clockwise until it comes into contact with the push-pull handle 404. This causes the gripper 432 at the end of gripper rod 431 to be extended out from the end of lower housing 430. As shown best in FIG. 15B, the protective guide pin 435 is inserted into the gripper 432. The guide pin 435 has a tapered, generally rounded end 437 and includes a mating portion 436 thereon to be captured by the guide pin retrieval tool 500 for removing the guide pin 435 from the gripper 432. Once the rod grapple tool 400 is returned to its retracted position, the protective guide pin 435 remains in place and abuts the edge of lower housing 430 so as to create a flush, smooth surface 450. The rod grapple tool 400 is then inserted down through the fuel bundle 150 and spacers 180 to a position above a part-length rod 160 to be extracted. FIGS. 16A and 16B illustrate the closed position of the rod grapple tool 400. Here the guide pin 435 is shown installed as having a flush surface 450 with the end of the lower housing 430, with the gripper rod 431 and its gripper 432 retracted therein. This is the position for insertion of the rod grapple tube 400 down through the fuel rod guide block 300 into the bundle 150. The blunt end 433 of the gripper 432 is thus not exposed. While holding the handle 402, the threaded nut 407 is rotated clockwise. This will draw the gripper 432 up into the lower housing 430 such that the guide pin 435 mates flush with the lower housing 430 at surface 450. FIGS. 17A-22 illustrate the structure and function of the guide pin retrieval tool 500 in further detail. Once the rod grapple tool 400 is in position within the bundle 150 between a spacer 180 and a part-length rod 160, which is to be extracted, the guide pin 435 needs to be removed from the rod grapple tool 400. This is accomplished with the pin retrieval tool 500. FIG. 17A is a perspective view of guide pin retrieval tool 500, and FIG. 17B is an enlarged view of detail A in FIG. 17A. The pin retrieval tool 500 is positioned between the top of the part-length rod to be extracted and the fuel spacer 180 above the part-length rod 160. The pin retrieval tool 500 is attached to a handling pole 502, only a portion of which is shown in FIG. 17A. The lower portion of the handling tool 502 may be bent as shown to account for limitations in the access of open space of fuel prep machine 110. The pin retrieval tool 500 is attached at the end of the handling pole 502 and includes a horizontal extension 504 to which is attached a tongue 506. As shown in the enlarged view of detail A in FIG. 17B, the tongue 506 includes a mating aperture 508 for capturing the mating portion 436 of the guide pin 435, as best shown in FIG. 20, 21 or 22. Accordingly, the tongue 506 is placed under the tapered end 437 of the guide pin 435 so that the mating aperture 508 engages with the mating portion 436 on guide pin 435. In an alternate example each of the mating aperture 508 and mating portion 436 can include threads thereon for engagement. The pin retrieval tool 500 also includes a pair of semicircular, serrated edges 510 and 512 which form a plurality of adjacent semicircular ridges that mate flush against the sides of adjacent full-length fuel rods 155 and/or part-length fuel rods 160 as the tongue 506 is inserted into the side of a fuel bundle 150. These serrated edges 510 and 512 help to maintain the pin retrieval tool 500 parallel with the side of the fuel bundle 150 being serviced. The serrated edges 510 and 512 thus help to maintain a proper alignment of the tongue 506 against the fuel bundle 150 so that the mating aperture 508 properly engages with the mating portion 436 on guide pin 435 and the tongue 506 without difficulty. FIG. 18 illustrates different tongue 506 length configurations. The tongue 506 can be reconfigured for varying lengths to reach part-length fuel rods 160 which may require tunneling several rows into the fuel bundle 150, in order to reach the interior part-length rod 160 to be extracted. Three different examples lengths of tongue 506A, 506B and 506C are shown in FIG. 18, for example. The pin retrieval tool 500 may be configured with tongue 506A for removing part-length rod 160 from the outside row of fuel rods 155/160, with tongue 506B for part-length rods that are a few rows into the bundle 150 interior, and with tongue 506C to reach part-length fuel rods 160 at the very center of the fuel bundle 150, around the water rods 170, if found to be located within this area of the fuel bundle 150. FIGS. 19-22 illustrate a process for removing the guide pin 435 from the rod grapple tool 400 within fuel bundle 150. Initially, the handling pole 502 lowers the pin retrieval tool 500 in the desired location within the bundle (FIG. 19), located just below the rod grapple tool 400 so that the tongue 506 is directly under the guide pin 435. The serrated edges 510 and 512 of the pin removal tool 500 abut flush to the sides of the fuel rods 155 and/or 160 of the fuel bundle 150 to ensure that the tongue 506 is properly oriented (level) so as to mate with the mating portion of the tongue's mating aperture 508 and mating portion 436 of the guide pin 435. The rod grapple tool 400 is then lowered as shown in FIG. 20 so that the guide pin 435 is received into the mating aperture 508 of tongue 506, and then manipulated to engage the mating portion 436 of the guide pin 435 with the mating aperture 508 of the pin removal tool 500 so as to capture the guide pin 435. FIG. 21 illustrates the guide pin 435 fully captured by the pin retrieval tool 500. As shown in FIG. 22, the handling pole 502 is then moved away from the fuel bundle 150 and stored suspended from FPM platform 115 with the guide pin 435 thereon. Of note, if the guide pin 435 is needed again, it is retrieved from the pin retrieval tool 500 underwater by the rod grapple tool 400. FIGS. 23A and 23B illustrate the procedure for attaching the gripper 432 of rod grapple tool 400 to an upper end plug 165 of a part-length rod 160. As previously described, the part-length rod grapple tool 400 must be placed in an extended position in order to remove the guide pin 435. This was shown previously in FIGS. 15A and 15B, in which the handler while holding the handle 402 rotates the threaded nut 407 counterclockwise until it comes into contact with the push-pull handle 404. This extends the gripper 432 with attached guide pin 435 from the end of the lower housing 430. Accordingly, once the guide pin 435 has been removed by the pin retrieval tool 500, the gripper 432 in its extended position is placed over the upper end plug 165 of the part-length rod 160. This attaches the part-length rod 160 to the rod grapple tool 400. As shown in FIG. 23A, the part-length rod upper end plug shoulder 167 can damage the spacer 180 when removing the part-length rod 160. However, and as previously described with reference to FIGS. 16A and 16B, rod grapple tool 400 is manipulated to its retracted position, which locks the part-length rod 160 and the rod grapple tool 400 together, making one long smooth tube for safe part-length rod 160 extraction. This flush connection is shown generally by surface 450 in FIG. 23B. Accordingly, potential damage due to exposed upper end plug shoulder 167 has been eliminated by the rod grapple tool 400. The part-length rod 160 can be removed without causing damage to any of the spacers 180. The example embodiments of the present invention being thus described, it will be obvious that the same may be varied in many ways. For example, the rod grapple tool 400 has been described a being designed for a part-length rod 160, with another grapple tool used for the full-length rods 155 and/or tie rods due to a different upper end plug configuration. A different version (shorter in length) of this rod grapple tool 400 may be used for the removal and/or the replacement of tie rods and full length fuel rods 155 within the fuel bundle 150 For example, the full-length rods and tie rods can be configured to have the same upper end plug design as that of the part-length rods 160; thus a rod grapple tool having the same gripper 432 could be used for attachment to the upper end plugs of the full length fuel rods 155 and tie rods for removal from the fuel bundle 150. Such variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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summary | ||
abstract | Illustrative methods are provided for annealing nuclear fission reactor materials, such as without limitation, a nuclear fission reactor core or fuel assembly or components thereof within the nuclear core. Annealing a metallic component of a nuclear fission reactor within the reactor core may include determining an annealing temperature for at least a portion of at least one metallic component of a nuclear fission fuel assembly of the reactor. The temperature of the core may be adjusted to affect the determined annealing temperature, which in some cases may be greater than the predetermined operating temperature range of the nuclear fission fuel assembly. The portion of the at least one metallic component of the nuclear fission fuel assembly is annealed within the core at the annealing temperature range. |
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description | This application claims priority to U.S. Patent Provisional Application 60/705,763, filed Aug. 5, 2005, which is incorporated by reference herein. The invention described and claimed herein was made in part utilizing funds supplied by the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. The government has certain rights in this invention. 1. Field of the Invention This invention relates generally to detection of special nuclear materials, and, more specifically, to a compact, low-cost gamma ray generator to aid in such detection. 2. Background Many non-intrusive active interrogation techniques utilize neutrons or gamma rays to detect special nuclear material (SNM) concealed in cargo. For active interrogation systems with neutron sources, neutron induced gamma rays are detected and, sometimes, transmitted neutrons are measured. Neutron induced gamma spectra of different materials are used as the fingerprints for them. Fast neutrons are often in use to obtain a deep penetration into large inspected objects and, thus, generate a very high background from surrounding materials. While this high background restricts the maximum screening speed of many neutron-based systems, neutrons also tend to activate the surrounding materials after an extensive long period of operation. On the other hand, gamma-based systems detect neutrons produced from photonuclear reactions or transmitted gamma rays. Because the neutron production cross sections of many special nuclear materials due to photofission are much higher than that of most common materials, the neutron background in gamma-based interrogation techniques is fairly low. Furthermore, the induced radioactivity of surrounding materials due to gamma rays of less than 16 MeV is rather small due to the high threshold energy of photonuclear reactions. However, most existing gamma-based interrogation systems use electron linacs and microtrons to generate the gamma beams; thus, the deployment of these systems is limited by their size, complexity and high cost of ownership. Thus there is a need for low-cost, portable gamma sources to use in active interrogation systems to detect SNM. In general, cylindrical gamma generators can be designed using a coaxial RF-driven plasma ion source, as has been done earlier in U.S. Pat. No. 6,907,097 for neutron generators and is included by reference herein. A plasma is produced by RF excitation in a plasma ion generator using an RF antenna. A cylindrical gamma-generating target is coaxial with, or concentrically arranged around, the ion generator and is separated therefrom by plasma and extraction electrodes which can contain many slots. The plasma generator emanates ions radially over 360°, and the cylindrical target is thus irradiated by ions over its entire inner surface area. The plasma generator and target can be made as long as desired. A co-axial gamma-tube design has several advantages that would carry over from the neutron tube system. The advantages include (i) high beam current, (ii) good cooling, (iii) simple design, (iv) compactness, and (v) spatially uniform photon flux. FIGS. 3 and 4 show different schematic views of a coaxial type gamma source that is very similar to the neutron tube design. For the (p,γ) target material, Table 1 lists four possible low-energy nuclear reactions that produce gamma-rays with energies greater than 6-MeV (the photofission threshold energy is approximately 5.5 MeV). Of these, the 163-keV 11B and 203-keV 27Al reactions may be the simplest to work with to create a gamma tube system through modification of co-axial neutron generator technology. Suitable target materials for these reactions include LaB6 or B4C (for p-B) and Al (for p-Al), which are easy to fabricate and also have good thermal, electrical, and mechanical properties. TABLE 1Four promising (p,γ) reactions for high energy gamma(6 to 18 MeV) productionCrossProtonGamma EnergySectionenergyTargetEγ (MeV)σ (mb)Ep (keV)Fabrication11B(p,γ)12C16.1, 11.7, 4.40.16160Easy27A1(p,γ)28Si11.5, 9.8, 1.8<0.03202.8Easy120~180632.219F(p,αγ)16O6.1, 6.92, 7.12160340Difficult7Li(p,γ)8Be12.24, 14.74,6441Moderate17.64 The p-B based system is particularly suitable for special nuclear material (SNM) detection. More than 90% of the excited 12C* produced from a 160 keV proton beam hitting on a B target decays directly to its ground state. Therefore, a p-B gamma generator can produce an intense 16.1 MeV gamma beam. Many SNMs have a much higher photoneutron production cross-section at 16.1 MeV gamma energy compared to other common materials. For example, the photoneutron production cross-sections of 235U at 16 MeV is ˜0.7 b as shown in FIG. 1, while the photoneutron production cross-section of 56Fe at the same energy is ˜0.01 b as shown in FIG. 2. The p-B based system can use a high current, low energy coaxial accelerator system because of its relatively small (p,γ) cross section. Lanthanum hexaboride (LaB6) is a rigid ceramic with good thermal shock resistance and good chemical and oxidation resistance. LaB6 also has high electron emissivity and good electrical conductivity. Similarly, boron carbide (B4C) is one of the hardest materials known, ranking third behind diamond and cubic boron nitride. B4C has very good chemical resistance, good nuclear properties (commonly used as a neutron absorber in reactors), and has low density (2.52 g/cm3). B4C can be formed as a coating on a suitable substrate by vapor phase reaction techniques, e.g., using boron halides or di-borane with methane or another chemical carbon source. The p-Al system reaction is also capable of detecting SNM and other contrabands because its branching ratios to different excited states are comparable to each other. Varying the proton beam energy can also change the energy level of 28Si* and, thus, the branching ratios. There are six resonances for the p-Al reaction between 500 to 680 keV. Gamma ray transmission spectroscopy can be used to detect elements besides SNM while neutron detectors can be used to monitor the presence of SNM. On the other hand, the system based on p-Al uses a modest-energy axial accelerator. Other possible materials to use as targets include LaB6, B4C, Al, LiF, Teflon™, and Mg. The main drawback with both the p-B and p-Al reactions is their low cross sections which necessitate operating the gamma tube at a high proton current to increase the source output. For example, in a boron-based interrogation system, a co-axial source producing an ampere of proton current at the 163-keV reaction resonance will only generate about 6×108 gammas/sec. The next boron resonance occurs at a higher energy (675 keV) and its cross section is even smaller (0.05 mb). Similarly, the resonant nuclear reaction for aluminum at a proton energy of 203-keV has a cross section of less than 0.03 mb. The other (p, γ) reactions in Table 1 have significantly larger reaction cross sections, but require scaling the gamma tube source voltage to higher energies. For the production of multiple discrete high-energy gammas, a beam of protons with energy greater than 340 keV are required. However, it is difficult to scale the coaxial tube design to these higher proton voltages. To achieve these higher energies, a simple axial accelerator concept can be used, as will be discussed later. FIG. 3 shows cross-section view of a gamma source geometry according to an embodiment of the invention. Gamma generator 10 has a cylindrical plasma ion source 12 at its center. There is a cylindrical gamma generating target 22 disposed around and spaced apart from the cylindrical plasma ion source 12. The principles of plasma ion sources are well known in the art. Conventional multicusp ion sources are illustrated by U.S. Pat. Nos. 4,793,961; 4,447,732; 5,198,677; 6,094,012, which are herein incorporated by reference. The ion source 12 includes an RF antenna (induction coil) 14 for producing an ion plasma 20 from hydrogen gas which is introduced from a hydrogen gas source 21 into the ion source 12. Antenna 14 is typically made of copper tubing which may be water cooled. For gamma generation, the plasma 20 is preferably a hydrogen ion plasma. The ion source 12 can also include a pair of spaced electrodes, plasma electrode 16 and extraction electrode 18, along its outer circumference. The electrodes 16, 18 control the passage of ions electrostatically from the plasma 20. The electrodes 16, 18 can contain many longitudinal slots 19 along their circumferences so that ions radiate out in a full 360° radial pattern. In an alternative embodiment (not shown), the electrodes 16, 18 can be grids. Coaxially or concentrically surrounding ion source 12 and spaced therefrom is the cylindrical target 22. The target 22 is the gamma generating element. Ions from the plasma source 12 pass through the slots 19 in the electrodes 16, 18 and impinge on the target 22, typically with energy of 120 keV to 150 keV. The target 22 may be made of any of the materials listed in Table 1, or others. In one embodiment, the target 22 is made of LaB6 or B4C. In another embodiment, the target 22 is made of aluminum. Gamma rays are produced in the target 22 as the result of ion induced (p,γ) reactions. Outer cylinder 24 defines the vacuum chamber in which the entire assembly 10 is enclosed. The extraction apertures in electrodes 16, 18 can be in the form of slots 19 whose length can be extended to any desired value. The hydrogen ion beam hits the target 22 in 360° and therefore the target area is very large. By making the gamma generator as long as practical in the axial or longitudinal direction, a high gamma flux can be obtained. For p-B gamma-based interrogation system, a long co-axial source that can produce ampere(s) of current is useful. FIG. 4 is a schematic cutaway drawing of a coaxial type gamma source 11, which is very similar to a coaxial neutron generator design. A cylindrical ion source is located at the center of the gamma generator. Hydrogen plasma is formed by RF induction discharge. An antenna 14 can be water-cooled copper tubing enclosed inside a quartz tube. It has been demonstrated that RF discharge plasma is capable of generating atomic hydrogen ion species higher than 90%. An extraction grid 17 controls the passage of ions electrostatically from the plasma. The ions are accelerated across a gap and impinge on a target 22 with full 160 keV energy. Permanent magnets 30 are in a regular arrangement around the plasma source and running longitudinally to form a magnetic cusp plasma ion source. The principles of magnetic cusp plasma ion sources are well known in the art, as cited above. To ensure reliable high voltage operation the gamma-ray generator 11 can also be vacuum pumped. With reasonable pumping, the pressure can drop to the 10−4 Torr range, which allows trouble free high voltage operation. The ion source can protected from the secondary electrons with a filter rod structure (not shown); this prevents high-energy electrons from accelerating back to the source and potentially over-heating it. The protection from the secondary electrons is especially important when generating gammas. Due to the fairly small cross-section of some of the nuclear reactions, the generator run at fairly high current, which can cause the ion beam power at the target to be on the order of 200 kW. Although the large surface area of the target helps to dissipate the thermal load, higher power operation of the gamma source may be more successful with appropriate target cooling systems, as have been used for neutron generators. FIG. 6 shows gamma ray spectra were collected from LiF, Teflon™, B4C, and Mg bombarded with a continuous beam of protons. Each spectrum was collected with a 5-inch NaI detector and normalized to I-μC of charge. The (p,γ) target to detector distance was set at 7 cm. Both boron carbide and magnesium have rather low gamma-ray yield which is consistent with the reported 11B cross section value given in Table 1. Magnesium was tested because it had been reported that a 6.19-MeV gamma-ray (in addition to 4.86-MeV and 0.82-MeV gammas) is produced corresponding to the 317-keV resonance of the 25Mg(p,γ)26 Al reaction. The spectra clearly show the 6.19-MeV gamma-ray and also gammas that arise from higher energy (4-MeV) branching channels that can occur for the 25Mg(p,γ)26 Al reaction. The LiF and Teflon™ spectra are dominated by the characteristic 6.13-MeV fluorine gamma-ray which was even observed for 250-keV protons from the accelerator (fluorine has a small resonant cross section of −0.2 mb at 224-keV proton energy). As indicated in Table 1, the resonant reaction for lithium occurs at 441-keV which accounts for the significant jump in the measured yield between the 350-keV and 450-keV spectra. The Li reaction is of interest because it produces 17.64-MeV (63% emission/reaction) and 14.74-MeV (37% emission/reaction) gamma-rays which coincide well with the peak of the photofission cross section. There also appears to be an unidentified, weak low-energy nuclear reaction in Teflon that produces 12-MeV gammas and may be due to a trace impurity in the material. As mentioned above, it is difficult to scale the coaxial tube design to proton voltages with energies greater than 340 keV, as are used for the larger cross section reaction shown in Table 1. To achieve these higher energies, a simple axial accelerator 40, as shown in FIG. 5, can be used. In this system, the protons are first produced in an rf-driven plasma source. The rf antenna is shown as 44. The protons are then extracted and accelerated to their full energy using a simple electrostatic accelerator column 45. The accelerated protons then impinge on a water-cooled, V-shaped target 42 (rather than a cylindrical target as in the coaxial design). The chamber 46 is vacuum pumped through a pumping port 48 to minimize the electrons produced by ionizing the gas in the beam path. A significant advantage of the source designs is its potential to scale to almost any length by stacking together individual base units. For example, the coaxial gamma tube can be taken to an order of magnitude higher power level by stacking ten of the 1-Amp systems together. In the base units, the lower vacuum plate is at ground potential and the upper one is at the target potential (e.g., ˜165 kV for the p-B reaction). These sources can be stacked on top of each other in a sequence, where two high voltage flanges are shared in one end of the two generators and, on the other end, the pumping chamber is shared with another generator. In this exemplary embodiment, the stack of ten generators can be operated with only five high voltage feeds, five vacuum pumps and five rf-systems. Another embodiment of the invention integrates gamma-ray and neutron generators to produce a new active interrogation source. Owing to its linear scalability, the dual source may be useful for many diverse applications ranging from very large fixed site interrogation systems to intermediate-size mobile or remote inspection systems to compact systems for assaying the internal contents of hazardous waste drum containers. While a simple, compact, and low-cost gamma source design is important for the wide deployment of these gamma-based interrogation systems, a sophisticated detection system and a contraband database are also desirable in order to make the best use of these systems. FIG. 7 shows a conceptual drawing of an exemplary embodiment for an integrated system design. A gamma source 50 is located in the ground as an easy way to shield inspection workers from the radiation. An array of detectors (one neutron detector is shown as 54) is positioned around a cargo container 58 to monitor neutrons and gammas coming out of the container 58 for signals that indicate the presence of SNM. Some of the detectors are sensitive to both gammas and neutrons, as fission also produces a significant amount of prompt gammas. It would be useful to have a database of induced gamma/neutron ratios for various combinations of materials and packaging. As discussed above for the p-Al based system, gammas of different discrete energies are produced by the gamma generator. Thus gamma detectors can be set on the top of the cargo container 58 for gamma transmission spectroscopy to identify other hazardous materials. This invention has been described herein in considerable detail to provide those skilled in the art with information relevant to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by different equipment, materials and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself. |
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H00004073 | abstract | Methods and associated apparati for use of collisions of high energy atoms and ions of He, Ne or Ar with themselves or with high energy neutrons to produce short wavelength radiation (.lambda..apprxeq.840-1300 .ANG.) that may be utilized to produce cathode-anode currents or photovoltaic currents. |
061342904 | abstract | In a transport container, at least one fuel assembly containing element including at least one fuel assembly is housed in a container having an inner surface portion to be fit to the at least one fuel assembly containing element. The inner surface portion has a predetermined shape substantially corresponding to a fit portion of the at least one fuel assembly containing element. The at least one fuel assembly containing element is pushed by a support against the inner surface portion of the container along a fixed support direction. Therefore, the fit portion of the at least one fuel assembly containing element is fit to the inner surface portion of the container so that the at least one fuel assembly containing element is fixedly supported to the container. |
042812526 | abstract | A coupling apparatus for separably connecting cable controls to the storage unit of a radiographic system, having a coupler component fixed to the storage unit and a separable component fitted to the control cable. The latter fits into an aperture in the fixed component, where it can be locked against removal. The fixed component locks the radioactive material leader for safe storage when the control cable is disconnected. Connection of the control cable permits the operator to release the lock on the leader. The act of releasing that lock establishes an interlock which prevents removal of the separable component from the fixed component. |
abstract | A method is described for producing nuclear fuel products, including the steps of receiving metallic or intermetallic uranium-based fuel particle cores, providing at least one physical vapour deposited coating layer surrounding the fuel particle core and embedding the nuclear fuel particles in a matrix so as to form a powder mixture of matrix material and coated fuel particles. The at least one physical vapour deposited coating layer may include inhibitors of inhibiting, stabilizing and/or reducing interaction between metallic and intermetallic uranium-based fuel particles cores and the matrix wherein the fuel particles typically may be embedded. The deposited coating layer may include neutron poisons. |
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048636819 | abstract | A solid or hollow replacement rod 40 for use in a pressurized water reactor (PWR) fuel assembly 10 inserts into cells of the spacer grids 18, 20 and 22 past mixing vanes 32, without damaging them, because of its asymmetric tip 42 formed by chamfer 54 and elongated curved surface 52 and its offset "x" formed by the bowed end section 44. |
047599111 | abstract | A gas cooled nuclear fuel element. A plurality of progressively sized rigid porous cylinders nested together in coaxial alignment are provided with varying quantities of nuclear fuel to enhance the power density while remaining within temperature limitations of the fuel and base material. |
description | The present invention relates to an electron beam device which is used for inspection and measurement. A scanning electron microscope (SEM) using an electron beam which is used to observe, inspect and measure a sample accelerates electrons emitted from an electron source and irradiates the electron so as to be converged on a surface of the sample using an electrostatic or electromagnetic lens. The electrons may be called as primary electrons. When the primary electron is incident, secondary electrons or reflection electrons may be generated from the sample. The secondary electrons or the reflection electrons are detected while scanning the electron beam so as to be deflected to obtain a minute pattern on the sample or a scanning image of composition distribution. Further, electrons which are absorbed onto the sample are detected to form an absorbed current image. As a desirable function of the scanning electron microscope, there is a function of performing scanning with a wide viewing field without causing the significant lowering of a resolution of the electron beam. As the miniaturization of a semiconductor is progressed, a two-dimensional high speed inspection of a resist pattern is required and scanning with a wide viewing field is required in order to expand an inspection area and lower a shrinkage. In order to achieve the above object, it is required to reduce a deflected chromatic aberration which is generated by the deflection of the electron beam. As an implementing method thereof, Patent Literature 1 and Patent Literature 2 suggest to use an electron optical element represented as E×B in which an electromagnetic deflector and an electrostatic deflector are combined. The E×B element is also used as a part of an energy filter of the electron beam or a deflecting element of the secondary electrons, which is disclosed in Patent Literature 3, Patent Literature 4, and Patent Literature 5 and Non-Patent Literature 1. Patent Literature 1: Japanese Patent No. 03932894 Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2001-15055 Patent Literature 3: Japanese Patent Application Laid-Open Publication No. 2001-23558 Patent Literature 4: Japanese Patent Application Laid-Open No. 2007-35386 Patent Literature 5: Japanese Patent Application Laid-Open Publication No. 2006-277996 Non-Patent Literature 1: Rev. Sci. Instrum., Vol. 64, No. 3, March 1993 p 659-p 666 However, in the related art, the following various problems occurring when the E×B element is used to correct the deflected chromatic aberration have not been considered. That is, (1) in correction of the deflected chromatic aberration, the deflection is significant in the electromagnetic deflection and the electrostatic deflection so that a voltage source having a high voltage and a current source having a high current are required, which may cause a response delay in deflection depending dynamic correction. (2) Geometric aberration (hereinafter, referred to as a parasitic aberration) which is caused by the increase of the deflection field is increased. (3) Due to a mechanical manufacturing and assembling error, deflection points of an electromagnetic deflector and an electrostatic deflector do not match to each other and a parasitic aberration similarly to (2) occurs. (4) An adjusting means of the E×B element which satisfies a requirement of high correction precision is not established. A first object of the present invention is to provide an electron beam device which is capable of suppressing the parasitic aberration caused by the response delay or deflection even when the deflected chromatic aberration is corrected and achieving the deflection with a wide viewing field at a high resolution. A second object of the present invention is to provide an electron beam device which is capable of suppressing the parasitic aberration caused by the manufacturing process and achieving the deflection with a wide viewing field at a high resolution. A third object of the present invention is to provide an electron beam device which is capable of easily adjusting an E×B element. A fourth object of the present invention is to provide an electron beam device which is capable of suppressing the parasitic aberration caused by deflection and the parasitic aberration caused by the manufacturing process. In order to achieve the first object, (1) an electromagnetic deflector is provided above a deflector which defines a position of an electron beam on a sample and an electrostatic deflector having a smaller inner diameter than the electromagnetic deflector, which is capable of applying an offset voltage, is provided so as to overlap the electromagnetic deflector. In order to achieve the second object, (2) any one of the electromagnetic deflector and the electrostatic deflector is configured to have a double stage structure. In order to achieve the third object, (3) the electromagnetic deflector and the electrostatic deflector are provided above a lens which is provided above an objective deflector which defines a position of the electron beam. In order to achieve the fourth object, (4) a means of automatically measuring a change in a position of the beam or a change in a deflected amount (scanning magnification) of a deflector which defines the position and the deflecting direction (rotation of the scanning area) when intensities of the deflectors are simultaneously and minutely changed or a voltage of an electron source is minutely changed or (5) the electrostatic deflector functions as both astigmatism corrector and a focal point corrector. According to the present invention, it is possible to correct the deflected chromatic aberration with a high sensitivity, reduce or correct the parasitic aberration, and achieve deflection with a wide viewing field while maintaining the high resolution. Hereinafter, embodiments will be described. A first embodiment will be described with reference to FIGS. 8, and 10 to 13. FIG. 10 is an overall schematic view of an electron beam device (scanning electron microscope) according to the embodiment. An electron beam 102 emitted from an electron gun 101 is focused on a sample by a first condenser lens 103, a second condenser lens 130, and an objective lens 108. Secondary electrons or reflection electrons 104 emitted from the sample are detected by a detector 105 which is disposed at the center. The electron beam on the sample is two-dimensionally scanned by an objective deflector 106 to obtain a two-dimensional image as a result. The two-dimensional image is displayed on a display device 119. In a scanning electron microscope according to the embodiment, an electromagnetic deflector 1023 and an electrostatic deflector 122 which suppress a deflected chromatic aberration are disposed above the objective deflector 106 which defines a position on the sample and the second condenser lens 130 so that height positions from the sample overlap in a concentric circle shape. Further, reference numeral 109 denotes a sample, reference numeral 110 denotes a holder (stage), reference numeral 111 denotes an electron gun controller, reference numeral 112 denotes a first condenser lens controller, reference numeral 114 denotes a scanning deflector controller, reference numeral 115 denotes an electromagnetic lens controller, reference numeral 116 denotes a sample voltage controller, reference numeral 117 denotes a storage device, reference numeral 118 denotes a control operating unit of the overall device, reference numeral 120 denotes an electromagnetic deflector controller, reference numeral 121 denotes an offset applied electrostatic deflector controller, and reference numeral 131 denotes a second condenser lens controller. Further, FIG. 11 illustrates one part of an electrooptic configuration in the scanning electron microscope in detail. As illustrated in FIG. 11, a deflected chromatic aberration correcting element 207 includes an electromagnetic deflector 1116 and an electrostatic deflector 206. A magnetic field of the electromagnetic deflector 1116 is orthogonalized to a magnetic field of the electrostatic deflector 206 so that the deflected chromatic aberration is generated while substantially maintaining a position of the electron beam. In the meantime, the objective deflector 210 defines a position of the electron beam on the sample and generates the deflected chromatic aberration along with the deflection. Therefore, each of the deflectors of the deflected chromatic aberration correcting element 207 is operated in association with the operation of the objective deflector 210 to compensate the deflected chromatic aberration. The electron beam on the sample is two dimensionally deflected so that each of the deflectors of the deflected chromatic aberration correcting element 207 is also two dimensionally deflected. However, in order to generate the deflected chromatic aberration, the deflection amount of each of the deflectors needs to be large. For this reason, a driving current of the electromagnetic deflector 1116 or a driving voltage of the electrostatic deflector 206 needs to be large. Further, in order to associate with the objective deflector 210, the driving thereof needs to be performed at a high speed with a high precision. Therefore, it is required to reduce the driving voltage or the driving current, that is, improve a deflection sensitivity. Further, when the deflection amount required for each of the deflectors is reduced, the geometric aberration (parasitic aberration) caused by the deflection is also reduced, so that double advantages may be achieved. In addition, reference numeral 201 denotes an electron source, reference numeral 202 denotes an earth electrode, reference numeral 208 denotes an electron trajectory only for electromagnetic deflection, reference numeral 209 denotes an electron trajectory only for electrostatic deflection, reference numeral 211 denotes a secondary electron or a reflection electron, reference numeral 212 denotes a detector, reference numeral 213 denotes an objective lens, reference numeral 214 denotes a condenser lens, and reference numeral 215 denotes a sample. FIG. 12 is a top view of a circumference of the deflector. In the configuration of the electrooptical system of the scanning electron microscope according to the embodiment, the electrostatic deflector 206 is disposed in the electromagnetic deflector 1116 and an offset of the voltage is applied to the electrostatic deflector 206 to reduce a speed of the electron beam. Further, the electrostatic deflector 206 is desirably disposed to form a concentric circle with the electromagnetic deflector 1116. An advantage of the above method is that the electromagnetic deflector 1116 is separated from the electrostatic deflector 206. By doing this, the electromagnetic deflector 1116 may be disposed outside the vacuum so that the deterioration of a degree of a vacuum due to degasification from an electromagnetic coil 1201 which is used for the electromagnetic deflector 1116 or charging-up due to a non-conductive ferrite 1202 may be avoided. Further, the electromagnetic deflector 1116 may be driven at a ground level potential. In the meantime, even though a mechanical error may occur in a relative deflection direction of both deflectors, the geometric aberration (parasitic aberration) due to the mechanical error may be corrected by octupolarizing the electrostatic deflector 206. The electrostatic deflector 206 is an octupolar deflector in which electrodes are disposed on a circumference and an offset voltage of the electrostatic deflector 206 and a potential of the electron beam match each other as much as possible by disposing the electrodes on the circumference. Further, the earth electrode 202 is inserted between the electrostatic deflector 206 and the electromagnetic deflector 1116. The earth electrode 202 stabilizes potential above and below the electrostatic deflector and serves as a vacuum partition to maintain a vacuum state of an electron beam passage. In addition, the electromagnetic deflector 1116 is configured to be a cosine winding type in order to reduce a multipolar field, which is a known technology. The cosine winding electromagnetic deflector 1116 has a different symmetric property of the geometric structure from the octupolar electrostatic deflector 206. The electromagnetic deflector 1116 of the embodiment adopts a cosine winding which generates only a dipole component and the electrostatic deflector 206 adopts an octupolar deflector which generates a multipolar component and corrects the geometric aberration (parasitic aberration). This is important to reduce the geometric aberration which is generated in accordance with the compensation of the deflected chromatic aberration. Further, as illustrated in FIG. 11, cylindrical electrodes (an upper control electrode 203 and a lower control electrode 204) which apply a voltage are disposed above and below the electrostatic deflector 206 and apply the same voltage as the offset voltage of the electrostatic deflector 206. In addition, needless to say, a deflected voltage and the offset voltage are applied to the electrostatic deflector. An effect of the electrode is to expand an area where the speed of the electron beam is reduced. A deflected electrical field of the electrostatic deflector 206 is leaked above and below the deflector. Therefore, in order to reduce the speed of the electron beam in the upper and lower areas as much as the offset voltage, more control electrodes need to be disposed above and below the deflector. A leak length of the deflected electric field depends on an inner diameter of the electrostatic deflector and a length of the electrode is set to be larger than the inner diameter to reliably achieve the speed reducing effect. This is also important to improve the precision that compensates a change of the trajectory of the electron beam by the electromagnetic deflector and a change of the trajectory of the electron beam by the electrostatic deflector. Accordingly, a voltage which is applied to the upper and lower control electrodes is desirably substantially equal to the offset voltage which is applied to the electrostatic deflector 206. Further, when the speed of the electron beam is decreased or increased, an electrostatic lens effect may occur. Therefore, in order to separate an electrostatic lens area from an electrostatic deflection area and reduce the geometric aberration (parasitic aberration), it is important to provide long control electrodes up and down. Similarly, a leakage of a magnetic field of the electromagnetic deflector 1116 needs to be considered and a total length of the electrostatic deflector 206, the upper control electrode 203, and the lower control electrode 204 needs to be longer than a total length of the electromagnetic deflectors 1116. FIG. 8 illustrates distribution of the electron beam in the electron microscope according to the embodiment. A sensitivity for correction of the deflected chromatic aberration largely depends on a distance between the deflected chromatic aberration correcting element (electrostatic deflector 122 and the electromagnetic deflector 1023) and a position of a crossover. In order to optimize a property of the objective lens 108, the location of a second crossover 802 is varied by an energy of the electron beam 102 which is used to observe the sample 109. Accordingly, in order to prevent a property of the deflected chromatic aberration correcting element from being significantly changed, additional deflected chromatic aberration correcting elements (an electrostatic deflector 122 and an electromagnetic deflector 1023) are disposed above the first crossover 801. In other words, the electromagnetic deflector 1023 and the electrostatic deflector 122 are disposed above a lens (the second condenser lens 130) which is disposed above the objective deflector 106 which defines a position of the electron beam. By increasing the sensitivity for correction of the deflected chromatic aberration, a voltage source having a high voltage and a current source having a high current are not necessary and a response delay at the time of deflection depending dynamic correction is improved. Next, an adjusting means of the electrooptic configuration of the scanning electron microscope according to the embodiment will be described with reference to FIG. 13. A beam position measuring mark 410 is disposed as a reference mark in order to measure a position of the electron beam on a sample 215. A predetermined intensity is applied to each of the deflectors by an electromagnetic deflector power source 1301 and an offset applied electrostatic deflector power source 402 to measure a change in the position of the electron beam when a minute amount of a voltage of an electron source 101 is changed by an electron source power source 407. By doing this, it is possible to evaluate a correcting capability in the deflected chromatic aberration correcting element (the electrostatic deflector 206 and the electromagnetic deflector 1116). Similarly, the correcting capability may be evaluated by measuring the change in the position of the electron beam when intensities of the electromagnetic deflector power source 1301 and the electrostatic deflector power source 402 are changed at a minute ratio. The same type of evaluation may be utilized in the deflected chromatic aberration property in the objective deflector 210 and the evaluation may be performed by measuring the change in the deflected amount (scanning magnification) and a deflection direction (rotation of the scanning area) of a deflector which defines a position. The deflection by the objective deflector 210 and an operation of the deflected chromatic aberration correcting element may be associated with each other from the above data. Further, reference numeral 213 denotes an objective lens, reference numeral 404 denotes an objective deflector power source, reference numeral 405 denotes an objective lens power source, and reference numeral 406 denotes a digital control system. In the embodiment, with respect to the electron source voltage of −3 kV, −2 kV is applied as an offset voltage. By operating the deflected aberration correcting elements (the electrostatic deflector 206 and the electromagnetic deflector 1116) in association with the objective deflector, a deterioration of the resolution of the obtained image may be reduced even when an image having a size of 80 μm square is scanned on the sample using the objective deflector. As a result, an image of a large area may be captured without moving the stage so that a throughput in multipoint size measurement is improved 80% or more. As described above, an electromagnetic deflector is provided above a deflector which defines a position of an electron beam on a sample and an electrostatic deflector having a smaller inner diameter than the electromagnetic deflector, which is capable of applying an offset voltage, is provided so as to overlap the electromagnetic deflector to provide the electron beam device which is capable of suppressing the parasitic aberration caused by the response delay or the deflection and implementing the deflection with a wide viewing field at a high resolution even when the deflected chromatic aberration is corrected. Further, the electromagnetic deflector and the electrostatic deflector are provided above the lens which is disposed above the objective deflector which defines the position of the electron beam to provide an electron beam device which is capable of easily adjusting the deflected chromatic aberration correcting element (E×B element). In addition, a means of automatically measuring a change in a position of the beam or a change in a deflected amount (scanning magnification) of a deflector which defines the position and the deflecting direction (rotation of the scanning area) when intensities of the deflectors (the electromagnetic deflector and the electrostatic deflector) are simultaneously and minutely changed or a voltage of an electron source is minutely changed is provided to provide an electron beam device which is capable of suppressing the parasitic aberration caused by deflection and the parasitic aberration caused by the manufacturing process. A second embodiment will be described with reference to FIGS. 1 to 4. Matters which are described in the first embodiment but are not described in this embodiment may be applied to this embodiment unless there are special circumstances. FIG. 1 is a schematic overall configuration view of an electron beam device (scanning electron microscope) according to this embodiment. This embodiment is different from the first embodiment in that an electromagnetic deflector 123 which forms a deflected chromatic aberration correcting element is configured to have a double stage structure. Further, same reference numerals as in FIG. 10 denote the same components. FIG. 2 is a cross-sectional view illustrating a main part for explaining an electrooptical configuration in the scanning electron microscope according to this embodiment. As illustrated in FIG. 2, a deflected chromatic aberration correcting element 207 includes two electromagnetic deflectors 216 and 217 and an electrostatic deflector 206. In addition, same reference numerals as in FIG. 11 denote the same components. With the double stage structure of the electromagnetic deflector (an upper stage electromagnetic deflector 216 and a lower stage electromagnetic deflector 217), a deflecting point may be adjusted. If the deflecting points of the electromagnetic deflector and the electrostatic deflector do not match, the electron trajectory is shifted from an axis inside the deflected chromatic aberration correcting element so that the geometric aberration (parasitic aberration) is increased. Even though the positions of the electromagnetic deflector and the electrostatic deflector match on the design, the processing or assembling error may occur so that the actual deflecting points do not match. Therefore, any one of the electromagnetic deflector and the electrostatic deflector may have a double stage structure. Both deflectors may have the double stage structure, which is not desirable in consideration of the complex structure or the increased cost. The deflector which has the double stage structure may be two dimensionally deflected and the intensity ratio and the deflection angle may be optimized in order to match the deflecting points. The optimization is performed in order to compensate the influence of the processing or assembling error so that the intensities and the deflection directions of the electromagnetic deflectors at upper and lower stages substantially match. FIG. 3 illustrates a top view of the deflected chromatic aberration correcting element. Also in this embodiment, an octopole deflector is used for the electrostatic deflection. Next, an adjusting means of the electrooptic configuration of the scanning electron microscope according to the embodiment will be described with reference to FIG. 4. A beam position measuring mark 410 is disposed as a reference mark in order to measure a position of the electron beam on a sample. A predetermined intensity is applied to each of the deflector by a upper stage electromagnetic deflector power source 401, a lower stage electromagnetic deflector power source 403, and the offset applied electrostatic deflector power source 402 to measure a change in the position of the electron beam when a minute amount of a voltage of an electron source is changed by the electron source power source 407. By doing this, it is possible to evaluate a correction capability in the deflected chromatic aberration correcting element. Similarly, the correcting capability may be evaluated by measuring the change in the position of the electron beam when intensities of the upper stage electromagnetic deflector power source 401, the lower stage electromagnetic deflector power source 403, and the electrostatic deflector power source 402 are changed at a minute ratio. The same type of evaluation may be utilized in the deflected chromatic aberration property in the objective deflector 210 and the evaluation may be performed by measuring the change in the deflected amount (scanning magnification) and a deflection direction (rotation of the scanning area) of a deflector which defines a position. The deflection by the objective deflector and an operation of the deflected chromatic aberration correcting element may be associated with each other from the above data. Further, in order to match the deflecting points in the electromagnetic deflection and the electrostatic deflection, in a state where the movement amounts of the deflections on the sample are compensated, the intensities of the electromagnetic deflection at the upper and lower stages and the deflection direction are adjusted so as to pass the center of the objective lens. In the embodiment, with respect to the electron source voltage of −3 kV, −2 kV is applied as an offset voltage. By operating the deflected aberration correcting elements in association with the objective deflector, a deterioration of the resolution of the obtained image may be reduced even when an image having a size of 80 μm square is scanned on the sample using the objective deflector. As a result, an image of a large area may be captured without moving the stage (holder) so that a throughput in multipoint measurement is improved 100% or more. As described above, the same effect as the first embodiment may be obtained in this embodiment. Further, the electromagnetic deflector has a double stage structure to provide an electron beam device which suppresses the parasitic aberration caused during the manufacturing process and achieves the deflection with a wide viewing field at a high resolution. A third embodiment will be described with reference to FIG. 5. Further, matters which are described in the first or second embodiment but are not described in this embodiment may be applied to this embodiment unless there are special circumstances. FIG. 5 is a schematic cross-sectional view illustrating a main part of an electrooptical configuration of an electron beam device (scanning electron microscope) according to this embodiment. Further, same reference numerals as FIG. 2 denote the same components. In addition, the entire configuration of the scanning electron microscope is substantially same as the first or second embodiment. The difference from the first and second embodiments is that in this embodiment, the electrostatic deflector is configured to have a double stage structure of an upper stage electrostatic deflector 502 and a lower stage electrostatic deflector 503 and the electromagnetic deflector 501 is configured to have a single stage structure. As an effect, the deflecting points may be matched similar to the second embodiment. In the embodiment, with respect to the electron source voltage of −3 kV, −2 kV is applied as an offset voltage. By operating the deflected aberration correcting elements in association with the objective deflector, a deterioration of the resolution of the obtained image may be reduced even when an image having a size of 80 μm square is scanned on the sample using the objective deflector. As a result, an image of a large area may be captured without moving the stage (holder) so that a throughput in multipoint measurement is improved 100% or more. As described above, the same effect as the first embodiment may be obtained in this embodiment. Further, the electrostatic deflector has a double stage structure to provide an electron beam device which suppresses the parasitic aberration caused during the manufacturing process and achieves the deflection with a wide viewing field at a high resolution. A fourth embodiment will be described with reference to FIG. 6. Further, matters which are described in any one of the first to third embodiments but are not described in this embodiment may be applied to this embodiment unless there are special circumstances. FIG. 6 is a schematic cross-sectional view illustrating a main part of an electrooptical configuration of an electron beam device (scanning electron microscope) according to this embodiment. Further, same reference numerals as in FIG. 2 denote the same components. In addition, the entire configuration of the scanning electron microscope is substantially same as the first or second embodiment. A characteristic (difference) of this embodiment is that a voltage applying electrode 602 is provided instead of the earth electrode. The object is to accelerate the electron beam in an area other than the deflected chromatic aberration correcting element 207, which may strengthen the electron beam trajectory from disturbance. The offset voltage which is applied to the electrostatic deflector 206 needs to be determined in consideration of a voltage which is applied to the voltage applying electrode and is also determined in consideration of both the correcting sensitivity and the electrostatic lens effect. In this embodiment, an electron source voltage is −2 kV and +2 kV is applied to the voltage applying electrode and −1 kV is applied to the electrostatic deflector. As compared with the first embodiment, even though the electrostatic lens effect is increased, the stability of the electron beam trajectory in an area other than the deflected chromatic aberration correcting elements is increased. As a result, in this embodiment, even though a size of 80 μm square is scanned on the sample using the objective deflector, the deflected chromatic aberration may be corrected and an image having a large area may be captured without moving the stage. Therefore, the throughput in the multiple point measurement is improved 80% or more and a reproducibility of length measurement is improved by 0.1 nm. As described above, the same effect as the second embodiment may be obtained in this embodiment. Further, the voltage applying electrode is provided between the electromagnetic deflector and the electrostatic deflector so as to accelerate the electron beam in an area other than the deflected chromatic aberration correcting elements and strengthen the electron beam trajectory from the disturbance. A fifth embodiment will be described with reference to FIG. 7. Further, matters which are described in any one of the first to fourth embodiments but are not described in this embodiment may be applied to this embodiment unless there are special circumstances. FIG. 7 is a schematic cross-sectional view illustrating a main part of an electrooptical configuration of an electron beam device (scanning electron microscope) according to this embodiment. Here, same reference numerals as in FIG. 2 denote the same components. Characteristics of this embodiment are in that the electrostatic deflector 701 functions as both a focal point corrector and an astigmatism corrector. Even though a coma aberration among geometric aberrations (parasitic aberrations) generated by the deflected chromatic aberration correcting element 207 is not corrected, an image plane curvature (focal point deviation) and an astigmatism may be corrected using an appropriate optical element. However, if the correction is performed, for example, in the objective lens 213, it is required to feedback an intensity and the deflection direction of the objective deflector 210, which causes control to become complicated. Therefore, the correction is desirably performed in the deflected chromatic aberration correcting element 207. As described above, a speed reduced electric field causes the electrostatic lens effect. Therefore, the focal point may be corrected by controlling the electrostatic lens effect. For example, the offset voltage is changed from −3 kV into −3.01 kV to change the focal point on the sample by 10 μm. This is because the focal point sensitivity is improved due to the presence of the offset voltage and if there is no offset voltage, an incomparable voltage is required to correct the same focal point. That is, it is understood that the reduction of the speed of the electron beam is effective for both correction of the deflected chromatic aberration and correction of the focal point. In this case, it is effective to perform the correction on a portion where the potential is significantly changed so that it is effective to change the offset voltage of the upper and lower stage control electrodes 703 and 704, that is, utilize as both the control electrode and the focal point corrector. Further, the electrostatic deflector is formed of octupolar electrodes, which is similar to the deflector as illustrated in FIG. 12. The voltages may be superimposed so as to generate an electric field having a quadrupolar symmetric property in these electrodes and the astigmatism caused by the quadrupolar field may be corrected. In addition, if the voltages are superimposed so as to generate an electric field having a hexapolar symmetric property in these electrodes, the coma aberration caused by the hexapolar field may be corrected. For example, examples of the voltage which is applied to eight electrodes are as follows. In the case of the deflection, in the clock wise direction, approximately, the voltages are 1:0.4:−0.4:−1:−1:−0.4:0.4:1, in the case of the correction of the astigmatism, the voltages are 1:0:−1:0:1:0:−1:0, and in the case of the correction of the coma aberration, the voltages are −1:1:−0.4:−0.4:1:−1:0.4:0.4. In the case of the correction of the coma aberration, the angle dependence of a high frequency is required for distribution of the voltages of the electrodes so that the polarities of the voltage of an electrode adjacent to an electrode to which a maximum voltage or a minimum voltage required for the correction is applied are inversed. A fact that the hexapolar field is created using an octupolar deflector is an important result in the view point of simplifying the structure of the deflector. As described above, an optical element of the embodiment is used to correct not only the deflected chromatic aberration, but also the geometric aberration (parasitic aberration) such as the image plane curvature or the astigmatism. A function of correcting the geometric aberration may correct not only the geometric aberration which is generated by the deflected chromatic aberration correcting element but also the image plane curvature or the astigmatism caused by the deflection which defines the position of the beam on the sample at a subsequent stage. This is very effective to implement the deflection with a wide viewing field at a high resolution, which is an object of the present invention. Another feature of this embodiment will be described with reference to FIG. 9. The configuration of the entire device of the embodiment is substantially same as that of the first or second embodiment, but one stage of a third condenser lens 901 is added. FIG. 9 is an electron trajectory view for explaining distribution of the electron beam in the scanning electron microscope according to the embodiment. Here, same reference numerals as in FIG. 8 denote the same components. As described above, a sensitivity of the deflected chromatic aberration correcting element (the electrostatic deflector 122 and the electromagnetic deflector 123) significantly depends on a distance from the first crossover 801. Therefore, in this embodiment, the condenser lens is configured to have triple stage structure to fix the distance from the first crossover 801. That is, the position of the crossover which depends on voltage of an electron beam which is applied to the sample or a divergence angle may be changed only by changing a position of a second crossover 802 and a position of a third crossover 902. In the embodiment, with respect to the electron source voltage of −3 kV, −2 kV is applied as an offset voltage. In addition to the image plane curvature, the astigmatism, and the coma aberration generated in the deflected chromatic aberration correcting element, three aberrations such as a deflected chromatic aberration, an image plane curvature, and an astigmatism which are generated by the deflection on the sample are corrected. As a result, even when an image having a size of 150 μm square is scanned on the sample using the objective deflector, the high resolution may be maintained in the obtained image and the image having a large area may be captured without moving the stage. By doing this, a throughput at the multipoint measurement is improved 120% or more. As described above, the same effect as the second embodiment may be obtained in this embodiment. Further, the electrostatic deflector serves as both a focal point corrector and an astigmatism corrector so that the focal point and the astigmatism are corrected in the deflected chromatic aberration correcting element. In addition, a distance between the deflected chromatic aberration correcting element and the crossover position is fixed to constantly maintain a sensitivity of the deflected chromatic aberration correcting element. Further, the present invention relates to a basic characteristic of the electron beam device. However, the present invention is not limited to the scanning electron microscope but may be widely applicable to the electron beam device such as measurement of a pattern size by the electron beams, detection of the defect or identification of the type of the detect, formation of the pattern, and observation with a wide viewing field. This embodiment will be described with reference to FIGS. 14 and 15. FIG. 14 adds the distribution of the electron beam to FIG. 10 and FIG. 15 illustrates the electrooptical system of the embodiment. In FIG. 10, the electron beam 102 emitted from the electron gun is focused by the first condenser lens 103 and the deflected chromatic aberration correcting element. In order to improve the sensitivity of the deflected chromatic aberration correcting element, it is required to apply electrons which are more than half of the voltage of the electron beam 102 as offset and the deflected chromatic aberration correcting element serves as an electrostatic lens. Therefore, in FIG. 10, the electron beam forms an image by the first condenser lens 103 and two lenses of the deflected chromatic aberration correcting element. This has an advantage in that the change of the position of an intermediate image formation 1 by the deflected chromatic aberration correcting element is adjusted by the first condenser lens 103 but the configuration of the device becomes complex. This is similar when the deflected chromatic aberration correcting element is disposed below the second condenser lens 130. In the meantime, in FIG. 15, the image is formed only by the deflected chromatic aberration correcting element. By adjusting the offset voltage, a sensitivity of correcting the deflected chromatic aberration is improved and a second intermediate image plane 1402 may be formed, which may simplify the electrooptical system. Further, the deflected chromatic aberration correcting element is combined with the first condenser lens 103 (in this case, a first intermediate image plane 1401 is formed between the first condenser lens and the deflected chromatic aberration correcting element) to independently adjust the sensitivity of correcting the deflected chromatic aberration and the position of the intermediate image plane. As described above, the deflected chromatic aberration correcting element also functions as an electrostatic lens to form an intermediate image, which simplifies the electrooptical system. Further, the present invention is not limited to the above embodiments but includes various modification embodiments. For example, the above-described embodiments have been described in detail in order to understand the present invention, but the present invention is not limited to an example which includes all described components. In addition, a part of the components of an embodiment may be replaced with a component of other embodiment and the component of an embodiment may be added to the component of the other embodiment. Furthermore, other component may be added to, deleted from, and replaced with a part of the components of each of the embodiments. As described above, the present invention has been described in detail, but main types of the present invention will be listed as follows. (1) An electron beam device which includes an electron source and a deflector which defines a position of an electron beam emitted from the electron source on a sample and obtains an image of the sample based on a secondary electronic signal which is generated from the sample by irradiating the electron beam whose position is defined by the deflector, or a signal of a reflection signal electron or an absorbed electron, further includes, a deflected chromatic aberration correcting element including an electromagnetic deflector which is disposed to be closer to the electron source than the deflector with respect to the sample and an electrostatic deflector which is separated from the electromagnetic deflector and has a smaller inner diameter than the electromagnetic deflector, is disposed inside such that a height position from the sample overlaps the electromagnetic deflector and applies an offset voltage. (2) In the electron beam device disclosed in (1), the electrostatic deflector of the deflected chromatic aberration correcting element also functions as a focal point corrector. (3) The electron beam device disclosed in (1), further includes upper and lower electrodes which are disposed above and below the electrostatic deflector of the deflected chromatic aberration correcting element and apply a voltage, and the upper and lower electrodes are used as a focal point corrector. (4) An electron beam device which includes an electron source and a deflector which defines a position of an electron beam emitted from the electron source on a sample and obtains an image of the sample based on a secondary electronic signal which is generated from the sample by irradiating the electron beam whose position is defined by the deflector, or a signal of a reflection signal electron or an absorbed electron, the electron beam device further includes, a deflected chromatic aberration correcting element including an electrostatic deflector which is disposed to be closer to the electron source than the deflector with respect to the sample and an electromagnetic deflector which has a larger inner diameter than the electrostatic deflector, and is disposed inside such that a height position from the sample overlaps the electrostatic deflector, and any one of the electrostatic deflector and the electromagnetic deflector of the deflected chromatic aberration correcting element is configured to have a double stage structure. (5) In the electron beam device disclosed in (4), the deflected chromatic aberration correcting element adjusts an intensity ratio and a deflection direction of a deflector which has a double stage structure so as to match a deflecting point when a deflector having a double stage structure among the electrostatic deflector and the electromagnetic deflector is interlocked and a deflecting point of the other deflector. (6) In the electron beam device disclosed in (1) or (4), the electrostatic deflector of the deflected chromatic aberration correcting element functions as a quadrupolar aberration corrector or a hexapolar aberration corrector. (7) The electron beam device disclosed in (1) or (4), further includes upper and lower electrodes which apply a voltage to upper and lower portions of the electrostatic deflector of the deflected chromatic aberration correcting element and are longer than the inner diameter of the electrostatic deflector. (8) The electron beam device disclosed in (1) or (4), further includes a grounded conductor or an electrode which applies a voltage between the electrostatic deflector and the electromagnetic deflector of the deflected chromatic aberration correcting element. (9) In the electron beam device disclosed in (1) or (4), wherein a total length of the electrostatic deflector and the upper and lower electrodes is larger than a total length of the electromagnetic deflector of the deflected chromatic aberration correcting element. (10) The electron beam device disclosed in (1) or (4), further includes a lens disposed between the deflector which defines a position of the electron beam on the sample and the deflected chromatic aberration correcting element. (11) An electron beam device which includes an electron source and a deflector which defines a position of an electron beam emitted from the electron source on a sample and obtains an image of the sample based on a secondary electronic signal which is generated from the sample by irradiating the electron beam whose position is defined by the deflector, or a signal of a reflection signal electron or an absorbed electron, the electron beam device further includes, a deflected chromatic aberration correcting element including an electromagnetic deflector which is disposed to be closer to the electron source than the deflector with respect to the sample and an electrostatic deflector which is separated from the electromagnetic deflector and has a smaller inner diameter than the electromagnetic deflector, is disposed inside such that a height position from the sample overlaps the electromagnetic deflector and applies an offset voltage, and a unit that automatically measures a change in the position of the electron beam, or changes in a deflected amount and the deflection direction of the deflectors or both of them when a voltage of the electron source or intensities of the electromagnetic deflector and the electrostatic deflector of the deflected chromatic aberration correcting element are simultaneously and minutely changed. 101 Electron gun (electron source) 102 Electron beam 103 First condenser lens 104 Secondary electron or reflection electron 105 Detector 106 Objective deflector 108 Objective lens 109 Sample 110 Holder (stage) 111 Electron gun controller 112 First condenser lens controller 114 Scanning deflector controller 115 Electromagnetic lens controller 116 Sample voltage controller 117 Storage device 118 Control operating unit of the overall device 119 Display device 120 Electromagnetic deflector controller 121 Offset applied electrostatic deflector controller 122 Electrostatic deflector 123 Electromagnetic deflector 130 Second condenser lens 131 Second condenser lens controller 201 Electron source 202 Earth electrode 203 Upper control electrode 204 Lower control electrode 206 Electrostatic deflector 207 Deflected chromatic aberration correcting element 208 Electron trajectory only for electromagnetic deflection 209 Electron trajectory only for electrostatic deflection 210 Objective deflector 211 Secondary electron 212 Detector 213 Objective lens 215 Sample 216 Upper stage electromagnetic deflector 217 Lower stage electromagnetic deflector 401 Upper stage electromagnetic deflector power source 402 Offset applied electrostatic deflector power source 403 Lower stage electromagnetic deflector power source 404 Objective deflector power source 405 Objective lens power source 406 Digital control system 407 Electron source power source 410 Beam position measuring mark 501 Electromagnetic deflector 502 Upper stage electrostatic deflector 503 Lower stage electrostatic deflector 602 Voltage applying electrode 701 Astigmatism corrector serving as electrostatic deflector and focal point corrector 703 Upper stage control electrode serving as focal point corrector 704 Lower stage control electrode serving as focal point corrector 801 First crossover 802 Second crossover 901 Third condenser lens 902 Third crossover 1023 Electromagnetic deflector 1116 Electromagnetic deflector 1201 Electromagnetic coil 1202 Ferrite 1301 Electromagnetic deflector power source 1401 First intermediate image plane 1402 Second intermediate image plane |
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