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description | The present application claims priority under The Paris Convention for the Protection of Industrial Property to Korean Application No. 10-2004-0001393 filed at the Korean Intellectual Property Office in DaeJeon Metropolitan City, Korea on Jan. 9, 2004, which application is hereby incorporated by reference. 1. Field of the Invention The present invention relates to a neutron flux mapping system for a nuclear reactor, and more particularly to a neutron flux mapping system for a nuclear reactor which has an improved architecture and an enhanced reliability while being efficient in terms of installation space and maintenance, and to which a substitution means is easily applicable when a failure of a part thereof occurs. 2. Description of the Related Art A nuclear reactor typically includes 30 to 60 thimbles, depending upon the capacity thereof. In order to produce a neutron flux map along each thimble, a neutron flux mapping system using movable detectors is used. Such a neutron flux mapping system includes detectors, detector cables, drivers adapted to insert or withdraw respective detectors into or out of a core of the nuclear reactor, and path selector units adapted to guide each detector into a particular one of the thimbles. In order to measure neutron flux in a nuclear reactor, four sets of drivers having dedicated detectors, and path selector units are typically used. In accordance with operation of the path selector units adapted to guide the detectors of respective detector/driver sets, the four detectors of respective detector/driver sets can be selectively inserted into associated ones of the thimbles, the number of which may be 30 to 60. Referring to FIGS. 1a and 1b, a conventional neutron flux mapping system is illustrated. The conventional neutron flux mapping system includes drivers 10, inlet detector guide tubings 11 each connected, at one end thereof, to an associated one of the drivers 10 while having a tubular shape to allow a detector to pass therethrough, and a path selector unit 30 connected to the other end of each inlet detector guide tubing 11. A detector cable, which carries a detector at a leading end thereof, is wound in each driver 10. In accordance with operation of each driver 10, the detector of the associated detector cable is inserted into the path selector unit 30 via the associated inlet detector guide tubing 11, and then is inserted into a selected one of the thimbles via the path selector 30. As shown in FIG. 1b, the conventional path selector system 30 has a double layered architecture having upper and lower layers, at which four upper path selectors 31 and four lower path selectors 32 are arranged, respectively. The path selector system 30 may also have a triple layered architecture. The layers of the path selector system 30 are connected by a plurality of detector guide tubings. That is, detector guide tubings extend from each of the upper path selectors 31, and are distributed to respective lower path selectors 32. In the above mentioned conventional neutron flux mapping system, each detector cable is inserted into a selected one of the thimbles via the associated upper and lower path selectors 31 and 32 in accordance with the associated driver 10, so as to achieve a remote neutron flux detection. However, the above mentioned conventional neutron flux mapping system is complex in architecture and occupies an excessive space because the path selector unit 30 has a double layered architecture. For this reason, there are a difficulty in managing the system, and thus, an increased possibility of failure. Furthermore, the interlayer distance of the path selector system 30, that is, the distance between the upper and lower path selectors 31 and 32, is short, thereby causing the detector guide tubings connecting the path selectors 31 and 32 to have a severe curvature. As a result, the detector cables reciprocating along the detector guide tubings may exhibit increased friction, thereby damaging the detectors, which are expensive. A failure may frequently occur in the drivers 10, which operate to insert or withdraw the detector cables. When a failure occurs in this system, a required repair should be carried out in the interior of a reactor containment vessel, that is, a highly radioactive region. In this case, there is a difficulty in performing tasks in that workers who perform tasks in the interior of the reactor containment vessel may be exposed to a large amount of radiation. In addition, in the conventional neutron flux mapping system, the lower path selectors 32 are connected to thimble isolation valves (that is, the thimbles), respectively, in a 1:1 manner For this reason, if even one of the lower path selectors 32 fails, the overall system cannot operate normally because it is impossible to measure neutron flux through the thimbles associated with the failed path selector. In this case, there is a reduction in power generation rate or the plant should be shut down. Meanwhile, each driver 10 should insert or withdraw the associated detector cable into or out of a desired thimble at a constant speed. However, the drivers 10 may frequently be rendered inoperable because of the structural problems, for example, the serious friction generated between the detector cables and the guide tubings, which is common in the conventional multiple layered path selector systems, cause the helical gear to exert excessive force which may result in wear or failure in the elements associated therewith. Furthermore, different stresses may be generated at each detector cable, depending on a variation in the insertion or withdrawal distance of the detector cable. For this reason, the expensive detector cable may frequently be damaged. Therefore, an object of the invention is to provide a neutron flux mapping system for a nuclear reactor, which has improvements in structures of drivers, path selectors, etc., thereby being effective in terms of installation space, while achieving a reduction in the failure rate thereof so that it is more safe and efficient in terms of maintenance and repair. Another object of the invention is to provide a neutron flux mapping system for a nuclear reactor, which is capable of, even when a failure occurs in a part of path selectors thereof, achieving measurement of neutron flux through all thimbles, using the remaining path selector(s). In accordance with the present invention, these objects are accomplished by providing a neutron flux mapping system for a nuclear reactor comprising: drivers each including a geared motor, a helical gear driven by the geared motor, and a storage reel adapted to supply, to the helical gear, a detector cable carrying a detector; and a double indexing path selector unit including a body including upper and lower fixed plates, and tie rods connecting the upper and lower fixed plates, a fixed shaft fixedly mounted at a central portion of the body, an outer path selector arranged to be rotatable about the fixed shaft, the outer path selector including an upper rotating plate arranged to be rotatable about the fixed shaft while carrying a drive unit for rotating the outer path selector about the fixed shaft, and a control unit for controlling the drive unit, and a lower rotating plate arranged to be symmetrical with the upper rotating plate, and connected to the upper rotating plate to rotate along with the upper rotating plate, and inner path selectors each including a hollow rotating shaft rotatably mounted between the upper and lower rotating plates of the outer path selector, a path select tubing connected, at an upper end thereof, to an upper end of the rotating shaft in the interior of the rotating shaft while extending downwardly and radially outwardly from the rotating shaft through a hole formed at the rotating shaft, and a disc mounted to a lower end of the rotating shaft, and provided with a plurality of circumferentially-arranged paths. The geared motor may comprise an induction motor adapted to be controlled by an inverter Each driver may further include means for bring the helical gear into close contact with the detector cable. The means may comprise at least one idle gear. Each driver may further include an AC torque motor adapted to drive the storage reel. The upper fixed plate may be provided with stop plates. The control unit of the upper rotating plate may be provided with limit switches, which selectively come into contact with the limit switches, respectively, to be switched to an ON state. The driving unit and control unit may be mounted on an upper surface of the upper rotating plate. Each inner path selector may further include an indexing mechanism adapted to rotate the rotating shaft such that the path select tubing is aligned with a selected one of the paths. The indexing mechanism may include a plurality of path select switches arranged around the disc to correspond to the paths, respectively. Each path select switch may sense alignment of a corresponding one of the paths with the path select tubing, thereby sensing the position of path select tubing. The indexing mechanism may be driven by a geared motor controlled by the position signal. The double indexing path selector unit may further include tubing anti-twister means. The neutron flux mapping system may further comprise detector storage guiders each arranged between an associated one of the drivers and the double indexing path selector unit, and a detector storage area adapted to store the detector guided by an associated one of the detector storage guiders. Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings. Referring to FIG. 2a, a neutron flux mapping system adapted to produce a map of neutron flux in a nuclear reactor installed in a nuclear power plant in accordance with the present invention is illustrated. As shown in FIG. 2a, the neutron flux mapping system mainly includes drivers 100, and a double indexing path selector unit 300. The neutron flux mapping system also includes tubings 110, 111, and 333 connected to one another, in this order, to extend to a region where inlets of thimble isolation valves 400 are arranged. Each driver 100 is provided with a detector cable carrying a detector (designated by reference numeral “201” in FIG. 3). The detector cable 201 may extend from the associated driver 100, pass through an inlet detector guide tubing 110, an upper detector guide tubing 111 arranged above the path selector unit 300, and a path select tubing 333, in this order, and then enter a selected one of the thimble isolation valves 400 through a lower detector guide tubing. The detector cable 201 inserted into the thimble isolation valve 400 then extends through the associated thimble in the reactor so as to measure neutron flux through the thimble. (Driver) As shown in FIG. 3, each driver 100, which is adapted to drive the detector cable 201 associated therewith, includes a geared motor 101, an inverter 102 adapted to control the rotating speed of the geared motor 101, a helical gear 103 connected to the geared motor 101 to be rotated in accordance with rotation of the geared motor 101, and idle gears 105 mounted to a cover 104 attached to a helical gear frame to bring the detector cable 201 into contact with the helical gear 103. The detector cable 201 has a spiral wire wound around the center of the detector cable along the circumference of the cable. The driver 100 also includes a storage reel 106 adapted to pull the detector cable 201 by a constant force, thereby winding the detector cable 201, an AC torque motor 107 adapted to drive the storage reel 106, and an acoustic vibration sensor 108 adapted to remotely monitor a drive state of the driver 100. The geared motor 101 has a structure in which a gear is attached to an induction motor. The rotating speed of the geared motor 101 is controlled in accordance with frequency and voltage controlled by the inverter 102. The helical gear 103 has a rotating shaft operatively connected to a rotating shaft of the geared motor 101 via a torque limiter 109. The helical gear 103 is formed with a trough (not shown) at a circumferential surface thereof, and with a spiral groove (not shown) at the trough. When the helical gear 103 rotates, the detector cable 201 is moved along the trough in a state of the spiral of the detector cable being engaged with the spiral groove, so that it is inserted into the core of the reactor through the path selector unit, which will be described hereinafter. Each idle gear 105 serves to depress the detector cable 201 against the helical gear 103 in order to maintain the detector cable 201 in a state of being seated on the helical gear 103 without being separated from the helical gear 103. In order to adjust the gap between helical gear and idle gear, each idle gear 105 is mounted to the cover 104, using several laminated shims each having a thin sheet structure (as seen in an enlarged view of FIG. 4). The idle gears 105 are arranged at upper and side surfaces of the cover 104 mounted to the helical gear frame, respectively. As shown in FIG. 4, the upper idle gear 105 is arranged toward an outlet of the driver 100 in advance of a vertical center line of the helical gear 103 by a certain angle θ. With this arrangement, the upper idle gear 105 offsets a force urging the detector cable 201 to rise from the helical gear 103, thereby increasing the contact area between the detector cable 201 and the helical gear 103. Accordingly, an enhancement in power transmission efficiency is obtained. The storage reel 106, which has a structure shown in FIGS. 3 and 5, is adapted to wind the detector cable 201 therearound, thereby storing the detector cable 201. The storage reel 106 pulls the detector cable 201 by a constant force in order to wind the detector cable 201 while preventing the detector cable 201 from being unwound. The AC torque motor 107, which controls rotation of the storage reel 106, is operatively connected with a rotating shaft of the storage reel 106 via a reduction gear. The AC torque motor 107 has characteristics of generating a small torque when the storage reel 106 exhibits a high rotating speed due to a small amount of the detector cable 201 wound therearound, while generating a large torque when the storage reel 106 exhibits a low rotating speed due to a large amount of the detector cable 201 wound therearound. By virtue of such characteristics of the AC torque motor 107, the detector cable 201 is wound around or unwound from the storage reel 106 in a state of being subjected to a constant tension. The acoustic vibration sensor 108 is mounted to a frame of the driver 100 to remotely monitor the drive state of the driver 100. The acoustic vibration sensor 108 is configured to detect mechanical vibrations, so that sound, which is propagated over air while having the form of noise, cannot be sensed by the acoustic vibration sensor 108. That is, the acoustic vibration sensor 108 senses only a vibration signal generated in the driver 100. For example, when the AC torque motor 107 fails, or when the torque limiter 109 is activated as an excessive force is applied to the detector cable 201, the acoustic vibration sensor 108 is activated. Thus, remote monitoring can be easily achieved. Double Indexing Path Selector Unit As shown in FIGS. 2a and 6, the double indexing path selector unit 300 according to the present invention includes a body 310 including upper and lower fixed plates 311 and 312 vertically connected by tie rods 313, an outer path selector 320 including upper and lower rotating plates 321 and 322 arranged inside the body 310 to be rotatable about a fixed shaft 315, and four inner path selectors 330 arranged around the fixed shaft 315 between the upper and lower rotating plates 321 and 322 of the outer path selector 320 while being circumferentially spaced apart from one another by an angle of 90°. The path selector unit 300 also includes a guide tubing anti-twister unit 340 adapted to prevent the inlet detector guide tubing 110 and upper detector guide tubing 111 from being twisted during rotation of the outer path selector 320, thereby preventing the tubings 110 and 111 from being damaged, and a withdraw limit switch assembly 350 adapted to sense passage of the detector cable 201 through the inlet detector guide tubing 110. As described above, the upper and lower fixed plates 311 and 312 are connected by the tie rods 313. The guide tubing anti-twister unit 340 is arranged above the upper fixed plate 311 while being supported by support rods 314. The lower fixed plate 312 is provided with passes P2 at positions corresponding to those of discs 339-1 included in the inner path selectors 330, respectively. The upper rotating plate 321 of the outer path selector 320 rotates about the fixed shaft 315 fixedly mounted in the body 310 (as seen in a plan view of FIG. 7). The lower rotating plate 322 (FIG. 6) is connected to the upper rotating plate 321 by a sleeve rotatably fitted around the fixed shaft 315, so that it is rotated along with the upper rotating plate 321. Where the upper and lower rotating plates 321 and 322 are unlimitedly rotated, a twisting phenomenon may occur at the inlet detector guide tubing 110 connected to the driver 100 and the upper detector guide tubing 111 extending from the inlet detector guide tubing 110. In order to avoid such a twisting phenomenon, the rotation of the outer path selector 320 is limited to a certain angle. This limitation is achieved by a latch 328 slidably mounted on a casing enclosing a control unit 325 fixed to the upper rotating plate 321, and two stop plates 318a and 318b mounted to the upper fixed plate 311 while being spaced apart from each other by an angle of 270°, as shown in FIG. 7. As shown in FIG. 7, a drive unit 324 is mounted on the upper rotating plate 321 of the outer path selector 320 to rotate the entire structure of the outer path selector 320 about the fixed shaft 315. The control unit 325 is also mounted on the upper rotating plate 321 of the outer path selector 320. The control unit 325 serves to maintain the rotated position of the outer path selector 320. The drive unit 324 includes a geared motor, and a drive belt 323 adapted to connect the geared motor to a pulley 316 fixed to the fixed shaft 315. The rotation of the outer path selector 320 is carried out in such a manner that, when the motor of the drive unit 324 rotates, the upper rotating plate 321 is rotated about the central axis of the outer path selector 320, that is, the fixed shaft 315, via the drive belt 323 because the fixed shaft 315 is maintained in a fixed state. Since the drive unit 324 and control unit 325 of the outer path selector 320 are mounted on the upper rotating plate 321, as described above, they allow the worker to have easy access thereto. Accordingly, it is possible to achieve an improvement in workability, thereby rapidly performing tasks, for example, a repair task, in a high radiation area. That is, there is a reduced amount of radioactive dust in the region where the drive unit 324 and control unit 325 of the outer path selector 320 are arranged, as compared to the region where the inner path selectors 330 are arranged. Also, the upper rotating plate 321 shields a considerable part of radioactive rays from rising upwardly from the region where the inner path selector 330 is arranged. Accordingly, when the worker accesses the drive unit 324 and control unit 325 to repair those units, there is an advantage in that danger to the worker caused by exposure to radioactive rays is relatively reduced. Since the drive unit 324 and control unit 325 are arranged on the upper surface of the upper rotating plate 321, there is also an advantage in that the worker can easily perform repair or replacement of those units. The latch 328 is operatively connected to a solenoid so that it is selectively engaged with one of latch rods 317a to 317d mounted on the upper fixed plate 311 to extend upwardly. In an activated state of the solenoid, the latch 328 is retracted, so that it is disengaged from the latch rod engaged therewith. In this state, the outer path selector 320 can be rotated when electric power is applied to the motor of the drive unit 324. Meanwhile, the lower rotating plate 322 is mounted at a lower end of the outer path selector 320 such that it is symmetrical with the upper rotating plate 321. The lower rotating plate 322 is rotated, integrally with the upper rotating plate 321, by virtue of the sleeve rotatably fitted around the fixed shaft 315. The lower rotating plate 322 is provided with circular openings H each adapted to receive a fitting portion of an associated one of the inner path selectors 330 (as seen in a lower part of FIG. 6). Now, operation of the double indexing path selector unit 300 having the above described configuration will be described. As shown in a concept diagram of FIG. 8a, the upper rotating plate 321 of the outer path selector 320 has a limited rotation range of 0° to 270° in accordance with a limiting function of the stop plates 318a and 318b. In this connection, the latch rods 317a to 317d are arranged at four quadrant positions on the upper fixed plate 311, that is, a 0° position (latch rod 317a), a 90° position (latch rod 317b), a 180° position (latch rod 317c) and a 270° position (latch rod 317d), respectively. The latch 328 of the control unit 325 may be engaged with a selected one of the latch rods 317a to 317d at a corresponding quadrant position. In accordance with the engagement of the latch 328 with a selected one of the latch rods 317a to 317d, the upper rotating plate 321 may be maintained in a fixed state at the corresponding engagement position, that is, the 0° position (latch rod 317a), 90° position (latch rod 317b), 180° position (latch rod 317c) or 270° position (latch rod 317d). In order to detect the position where the outer path selector 320 is maintained in a fixed state, limit switches 326a and 326b are arranged at upper and lower central positions on an outer casing wall of the control unit 325, respectively, as shown in FIG. 8a. Also, limit switches 327a and 327b are arranged at left and right casing walls of the control unit 325, respectively. The position detection may be carried out in such a manner that: the 0° position is detected as the left limit switch 327a is activated by the left stop plate 318a; the 270° position is detected as the right limit switch 327b is activated by the right stop plate 318b; the 90° position is detected as the lower limit switch 326b is activated by the latch rod 317c; and the 180° position is detected as both the upper and lower limit switches 326a and 326b are activated by the latch rod 317c (FIG. 8b). In particular, the detection of the 90° and 180° positions is achieved under the condition in which both the left and right limit switches 327a and 327b are in an inactive state. The latch rod 317c must have a vertical length longer than that of the remaining latch rods 317a, 317b, and 317d so that it can activate the upper limit switch 326a. On the other hand, an acoustic sound sensor (not shown) is provided at the control unit 325 to remotely monitor an operating state of the double indexing path selector unit 300. The acoustic sound sensor is configured to detect mechanical vibrations, similarly to the acoustic sound sensor 108 of each driver 100. Accordingly, the acoustic sound sensor of the control unit 325 senses a signal generated in the form of mechanical vibrations in the interior of the double indexing path selector unit 300. Sound, which is propagated over air, cannot be sensed by the acoustic vibration sensor. For example, when the drive unit 324 rotates idly due to failure thereof, this state is sensed by the acoustic vibration sensor of the control unit 325. As shown in FIGS. 2a, 6 and 9, and described above, there are four inner path selectors 330 arranged around the fixed shaft 315 between the upper and lower rotating plates 321 and 322 of the outer path selector 320 while being circumferentially spaced apart from one another by an angle of 90°. In the illustrated case, each inner path selector 330 is rotatably fitted, at the fitting portion thereof, in the associated opening H of the lower rotating plate 322. As described above, each inner path selector 330 includes one disc 339-1. The disc 339-1 is provided with a certain number of paths P1 determined in accordance with the number of the thimbles in the reactor. Practically, the number of the pathes P1 is determined to be larger than the number of the thimbles in the reactor, so as to provide a more or less number of spare pathes. The paths P1 are circumferentially spaced apart from one another by a desired angle. Thus, each inner path selector 330 serves to select one of the thimbles aligned with respective paths P1 thereof. The inner path selectors 330 perform a revolution about the fixed shaft 315 as the outer path selector 320 rotates. In order to select a desired thimble, each inner path selector 330 also includes one path select tubing 333. The path select tubing 333 is rotatable on the disc 339-1 thereof in accordance with operation of a geared motor 334 provided at the associated inner path selector 330. Each inner path selector 330 also includes an indexing mechanism 331 adapted to change the path of the path select tubing 333, through which one detector cable 210 extends, and a hollow rotating shaft 332. The path select tubing 333 is connected, at an upper end thereof, to an upper end of the hollow rotating shaft 332 in the interior of the hollow rotating shaft 332. The path select tubing 333 extends downwardly and radially outwardly from the hollow rotating shaft 332 through a hole formed at the hollow rotating shaft 332 such that it reaches the associated disc 339-1 at a lower end thereof. The lower end of the path select tubing 333 is arranged such that it is aligned with an optional one of the paths P1 provided at the associated disc 339-1. The hollow rotating shaft 332 is axially coupled to the upper and lower rotating plates 321 and 322 such that it is rotatable. The indexing mechanism 331 is rotated about the rotating shaft 332 in accordance with rotation of the rotating shaft 332 carried out by a unit angle corresponding to an angle defined between adjacent ones of the paths P1, every time a driving shaft connected to the geared motor 334 rotates one revolution. As described above, each disc 339-1 is arranged on the lower end of the associated inner path selector 330 while being fitted in the associated opening H of the lower rotating plate 322. Also, the paths P1 of the disc 339-1 are circumferentially arranged inside the periphery of the disc 339-1 while being spaced apart from one another by a certain angle. The paths P1 extend vertically throughout the disc 339-1 thereof. The lower end of the path select tubing 333 performs an intermittent rotation along the circumferentially-arranged paths P1 as it repeats angular rotation and stopping of the angular rotation in accordance with intermittent angular rotation of the indexing mechanism 331. Path select switches 338 are mounted on the upper surface of each disc 339-1 outside the paths P1 such that they are radially aligned with respective paths P1, in order to detect the position of the lower end of the associated path select tubing 333. Each path select switch 338 generates a signal to be used as a position control signal for the geared motor 334 adapted to drive the associated index mechanism 331. Where a number of path select switches 338 are used, respective circuits of the path select switches 338 may be connected in the form of a matrix arrangement, as shown in FIG. 10b. In this case, signals generated from the matrix circuit in accordance with a switching operation of each path select switches 338 may be sent to a control system (not shown) for controlling the associated geared motor 334. As shown in FIG. 9, each indexing mechanism 331 further includes a cam switch 335. The cam switch 335 performs an ON/OFF operation once when the indexing mechanism 331 rotates the unit angle. Based on a signal generated in accordance with such an ON/OFF operation of the cam switch 335, it is possible to check whether or not the associated inner path selector 330 has been rotated to a desired position. Thus, the cam switch 335 provides, along with the path select switches 338, a means for doubly checking a normal operation of the associated inner path selector 330. In response to signals from the path select switches 338 applied thereto, the control system checks whether or not the indexing mechanism 331 and path select switch 338 have operated normally in accordance with a truth table illustrated in FIG. 10c. This checking is achieved, based on the characteristics of the indexing mechanism 331, that is, the characteristics that the indexing mechanism 331 rotates the unit angle when the cam switch 335 performs an ON/OFF operation once. This operation will be described in more detail, in conjunction with the case in which the lower end of the path select tubing 333 is aligned with the path P1 of one disc 339-1 designated by a “Path No. 1” in accordance with a one-unit rotation of the path select tubing 333. In this case, the control system first receives a signal indicative of an once ON/OFF operation of the cam switch 335. Also, the path select switch 338, which corresponds to the path P1 of Path No. 1 while being designated by a “Switch No. 1”, is switched on. As a result, the control system receives a high-level signal (H) at an input terminal a thereof, as shown in the matrix circuit of FIG. 10b. At input terminals b, c and d thereof, the control system does not receive any high-level signal. In other words, the control system receives a low-level signal (L) at the input terminals b, c and d. Also, there is no high-level signal applied to an input terminal w of the control system, so that the input terminal w is maintained at a low-level state (L). On the other hand, the remaining input terminals x, y and z of the control system are maintained at a high-level state (H). These true values are indicated in the leftmost column of the truth table shown in FIG. 10c. Thus, the truth table of FIG. 10c shows true values arranged in association with all switches. Based on the above true values applied thereto, the control system identifies that the path select tubing 333 has been rotated to be aligned with the path P1 of Path No. 1. If the cam switch 335 or any one of the path select switches 338 operates abnormally, abnormal signals may then be generated. In this case, the control system treats the associated inner path selector 330 as being in a failure state. Where the associated detector 200 is in a state of being inserted in the path select tubing 333 of the inner path selector 330 in this case, the control system performs a control operation to withdraw the detector 200 to a position where withdraw limit switches 351 included in the withdraw limit switch assembly 350 are arranged above the double indexing path selector unit 300. Thereafter, the control system performs a control operation to prevent use of the failed inner path selector 330. On the other hand, in the conventional case shown in FIG. 1b, a detector cable, which passes a withdraw limit switch 35-1, may reach an associated lower path selector 32 along a selected one of various paths. For this reason, sensors are installed at all tubings 33-3 connected to a lower end of each lower path selector 32, respectively, in order to check whether or not the detector cable has passed through a correctly selected path. Furthermore, the installation of each sensor in the conventional case is achieved by drilling a hole through each tubing 33-3, and fitting the sensor in the hole such that it is protruded into the interior of the tubing 33-3. However, this installation method involves an increased sensor failure rate, in addition to high installation costs. That is, each sensor may frictionally contact the detector cable passing through the associated tubing 33-3, so that a serious friction problem may occur in that a failure may occur in the driving power transmission and detector cable. Furthermore, vibrations may be generated during the movement of the detector cable, so that the sensors may fail frequently. In the double indexing path selector unit 330 according to the present invention, however, the detector of each driver 100, which has passed through the associated withdraw limit switch 351, naturally passes through the associated inner path selector 330, as shown in FIG. 2b. Accordingly, there is an advantage in that it is only necessary to check whether or not the associated path select switch 338 has operated normally, in accordance with the method using the characteristics that the indexing mechanism 331 rotates the unit angle when the cam switch 335 performs an ON/OFF operation once, without an additional requirement to perform checking of the passage of the detector at the lower end of the associated inner path selector 330. The detailed arrangement and operations relating to the path select switches 338 associated with each inner path selector 330 will now be described with reference to FIG. 10a. A support bar 337 is attached, at one end thereof, to a lower end of the rotating shaft 332 included in each inner path selector 330 to support the path select tubing 333 of the inner path selector 330. A roller 336 is rotatably mounted to the other end of the support bar 337 such that it is spaced apart from a body of each path select switch 338 by a desired clearance to come into soft contact with a contact member of the path select switch 338. In order to secure a desired operational stability of the path select switches 338, the support bar 337 is adapted to rotate only in one direction, for example, a clockwise direction in the illustrated case. To this end, both the associated indexing mechanism 331 and geared motor 334 shown in FIG. 9 are also configured to be driven in one direction. Meanwhile, where an emergency situation occurs due to failure occurring at the detectors or drivers, the double indexing path selector unit can perform an emergency operation to cope with the emergency situation. That is, as shown in FIG. 7, the double indexing path selector unit performs an emergency operation by rotating the upper rotating plate 321 about the fixed shaft 315 to a certain angular position at intervals of 90° within a range of 270° to substitute the failed detector(s), driver(s) or inner path selector(s) with the normal detector, driver or inner path selector arranged adjacent thereto. This operation will be described in more detail with reference to FIG. 8a. Where all drivers 100, all detectors 200, and all inner path selectors 330 operate normally, the upper rotating plate 321 is maintained in a fixed state. In this state, the inlet detector guide tubings 110 and upper detector guide tubings 111 respectively connected thereto are normally connected to the associated path select tubings 333, respectively, as indicated by solid lines 333a in FIG. 8a (a-A, b-B, c-C, and d-D). However, where the driver 100, detector 200 or inner path selector 330 of a certain channel, for example, the channel A, has failed, the upper rotating plate 321 is rotated by an angle of +90° or −90° to shift the inlet detector guide tubing 110, upper detector guide tubing 111 and inner path selector 330, positioned at a channel B or D adjacent to the failed channel A, to the position of the channel A by 90° (to obtain channel connections a-B (or D), b-B, c-C, and d-D, as indicated by solid and phantom lines 333a and 333b in FIG. 8a). Accordingly, it is possible to achieve a substitutive measurement using the adjacent driver 100, detector 200 or inner path selector 330. In an extreme case in which the driver 100, detector 200, and inner path selector 330 of only one channel, for example, the channel A, operate normally, it is possible to achieve a normal measurement through all paths by sequentially rotating the outer path selector 320 at intervals of 90° up to an angular position of 180° in a forward direction, and up to an angular position of 90° in a backward direction (to obtain channel connections a-A, a-B, a-C, and a-D). Where the outer path selector 320 operates normally, it is possible to achieve a complete measurement through all paths associated with all channels, as long as the driver 100, inlet detector guide tubing 110, and inner path selector 330 associated with at least one of the channels A to D operate normally. Such a channel relation may be established, as described in the following Table 1: TABLE 1Channel Shift Path for Failure Recovery in Double Indexing PathSelector UnitFailed ChannelChannel Shift PathAccess Denied ChannelA−B or +DNoneB+A or −CNoneC+B or −DNoneD−A or +CNoneA, B++(CD)NoneB, C++(DA)NoneC, D++(AB)NoneD, A++(BC)NoneA, C+(DB) or −(BD)NoneB, D+(AC) or −(CA)NoneA, B, C+D, ++D, −DNoneB, C, D+A, ++B, −BNoneC, D, A+B, ++B, −BNoneD, A, C+C, ++C, −CNoneRemarks)“−” represents a counter-clockwise rotation of 90°, “+” represents a clockwise rotation of 90°, “−−” represents a counter-clockwise rotation of 180°, and “++” represents a clockwise rotation of 180°. Referring to the above Table 1, it can be seen that it is possible to check all thimbles (100%) as long as at least one of the four channels is in a normal state. Accordingly, although there may be several thimbles preventing insertion of the detector therein due to a poor state thereof, it is possible to satisfy a required operating condition in which it must be possible to perform tasks for at least 75% of thimbles, as prescribed in plant operating technical specifications. In accordance with the double indexing path selector unit 300 of the present invention, it is possible to measure all thimbles, using only the single-layered 12-path inner path selectors 330, which is illustrated in the embodiment of the present invention illustrated in FIG. 2b, as compared to the conventional path selectors having a double layered architecture including a 5-path layer and a 10-path layer. In accordance with the architecture of the present invention, it is possible to easily identify the position of each detector. Also, since the architecture of the present invention involves a gentle variation in the radius of curvature of tubings, it is possible to prevent damage to each detector cable or erroneous operation of the detector cable caused by an excessive radius of curvature of tubings involved in the conventional double layered architecture. Such curvature characteristics of the tubings according to the present invention may be concretely seen, referring to the following Tables 2 and 3 associated with equipment installed in Kori Nuclear Power Plant Unit #1 in Korea. TABLE 2Lengths and Angles of Tubings between Lower Layer Path Selector andIsolation Valves in Conventional Double Layered Path Selector SystemPath SelectorTubing Length (cm)Tubing Angle (degree)ChannelAverageMaximumAverageMaximumA170.19185.5325.48934.772B164.39204.4919.04141.819C168.34180.1823.66332.244D166.68196.7620.64439.236 TABLE 3Lengths and Angles of Tubings between Double Indexing Path Selectorand Isolation ValvesTubing Length (cm)Tubing Angle (degree)System ChannelAverageMaximumAverageMaximumA235.69265.2814.19722.665B250.90265.8611.91722.960C251.46265.2811.77322.665D250.82261.5110.80120.596 Referring to Tables 2 and 3, it can be seen that the double indexing path selector unit having a single layered architecture can have a tubing length increased by about 80 cm, as compared to those in the convention double layered path selector unit, and thus, can have a tubing angle reduced to 23° or below, as compared to a maximum angle of 42° in the double layered path selector unit. (Guide Tubing Anti-Twister Unit) As shown in FIG. 2, the inlet detector guide tubings 110 and upper detector guide tubings 111 may be twisted during rotation of the upper rotating plate 321 included in the outer path selector 320. Such a twist phenomenon generates torsion causing the tubings to rotate, and bending force causing the tubings to be shifted. Since the bending force is generated due to a moved distance of the tubings caused by an angular shift thereof, it may be absorbed as the tubings are elastically strained. In order to minimize the elastic strain inflicted on the tubings during the rotation of the outer path selector 320, the detector guide tubings are allocated closely at the guide tubing anti-twister unit 340. The height from the upper rotating plate 321 to the guide tubing anti-twister unit 340 is not less than a predetermined height so as to maintain strain of the tubings within an allowable elasticity range of the tubings. The torsion may be removed by a rotary bearing mechanism installed between a frame of the guide tubing anti-twister unit 340 and the tubings extending through the frame. This configuration will be described in detail with reference to FIGS. 11a and 11b. In order to prevent the inlet detector guide tubings 110 coupled to an upper end of the guide tubing anti-twister unit 340 and the upper detector guide tubings 111 coupled to a lower end of the guide tubing anti-twister unit 340 from being twisted, and thereby, being damaged, the guide tubing anti-twister unit 340 includes an anti-twister frame 344, a rotating plate 342 mounted to the anti-twister frame 344 such that it is rotatable with respect to the anti-twister frame 344, and adapted to carry respective lower ends of the inlet detector guide tubings 110 (via rotors 341a) and respective upper ends of the upper detector guide tubings 111 (via rotors 341b). The guide tubing anti-twister unit 340 also includes stop plates 345a and 345b respectively mounted to diametrically-opposed ends of the anti-twister frame 344 to limit a rotation range of the rotating plate 342 within a range of +90° to −90°, and a stop pin 346 provided on an upper surface of the rotating plate 342 at a peripheral portion of the rotating plate 342. Tie rod hangers 343 are provided at an outer peripheral surface of the anti-twister frame 344. The tie rods 314, which are coupled, at respective lower ends thereof, to the body 310 of the double indexing path selector unit 300, are connected to the tie rod hangers 343 at respective upper ends thereof, so that they are radially arranged. The rotation range of the rotating plate 342 is limited to 180°. Accordingly, when the outer path selector 320 rotates beyond the rotation range of the rotating plate 342 (that is, through an angle of more than 180°, but not more than 270°), the upper detector guide tubings 111 are strained within a range of 900 in a rotation direction of the outer path selector 320. At this time, the upper detector guide tubings 111 are prevented from being subjected to torsion caused by the rotation thereof, by virtue of the rotors 341b rotatably mounted to a lower portion of the guide tubing anti-twister unit 340 to receive respective upper ends of the upper detector guide tubings 111. Where the outer path selector 320 is driven to rotate 90° in a state in which the rotating plate 342 cannot rotate as the stop pin 346 is in contact with the stop plate 345a or 345b, longitudinal tension and rotational stress, that is, bending force and torsion, are exerted on the upper detector guide tubings 111 as the outer path selector 320 rotates. Such force is maximized at an intermediate position on a path, along which the outer path selector 320 rotates, (that is, a 45° position). As a result, the rotating plate 342 begins to rotate as the outer path selector 320 rotates beyond the intermediate position. Thus, the 90° rotation of the outer path selector 320 is completely carried out. In such a manner, the upper detector guide tubings 111 connected to both the outer path selector 320 and the rotating plate 342 are maintained in a stable state before the outer path selector 320 and the rotating plate 342 begin to rotate to a 90° position (that is, they are maintained at a 0° position), and after the outer path selector 320 and the rotating plate 342 complete the 90° rotation thereof (that is, they are maintained at the 90° position), as if a mechanical toggle switch operates. Experimentally, it could be seen that the rotational stress of the inlet detector guide tubings 110 caused by a ±90° twist thereof is only about 100 g·m, so that there is no damage to the tubings 110 caused by the twisting. Also, it could be seen that when the inlet detector guide tubings 110 are positioned at respective positions A, B, C and D arranged in this order in a clockwise direction while being spaced apart from one another by 90°, it is possible to prevent the inlet detector guide tubings 110 from interfering with one another in a +90°-twisted state by appropriately determining respective lengths of the tubings 110 such that the lengths of the tubings 110 arranged at the positions B and C are a certain length shorter than those of the tubings 110 arranged at the positions A and D. In accordance with the provision of the above described guide tubing anti-twister unit 340, when the outer path selector 320 rotates, this rotation is transmitted to the rotating plate 342 via the upper detector guide tubings 111 in the form of a relatively small rotating force, so that the rotating plate 342 is first rotated. When the rotating plate 342 is no longer rotated as the stop pin 346 comes into contact with the stop plate 345a or 345b, the upper detector guide tubings 111 are rotated about respective rotors 341b coupled to the lower portion of the rotating plate 342 in accordance with the rotating force of the upper rotating plate 321 not absorbed by the guide tubing anti-twister unit 340. FIG. 12 illustrates the coupling relation among the inner path selectors 330, the rotors 341a and 341b of the guide tubing anti-twister unit 340, and the upper detector guide tubings 111 in accordance with the rotation angle of the outer path selector 320. When the rotation angle of the upper rotating plate 321 of the outer path selector 320 corresponds to 0°, the rotors 341a and 341b of the guide tubing anti-twister unit 340, which are connected to respective inner path selectors 330, are maintained at initial positions thereof (that is, a 0° position), respectively, as shown in FIG. 12. When the upper rotating plate 321 rotates 90° in the clockwise direction, the guide tubing anti-twister unit 340 may also be rotated in the same direction to a 90° position thereof (as shown in the left one of the figures associated with the 90° position). Otherwise, the upper detector guide tubings 111 may be twisted through a certain angle in the clockwise direction under the condition in which the guide tubing anti-twister unit 340 is maintained at an initial state thereof (that is, a 0° position) (as shown in the right figure associated with the 90° position). When the upper rotating plate 321 rotates 180° in the clockwise direction, the guide tubing anti-twister unit 340 may be rotated in the same direction to a 180° position thereof (as shown in the left one of the associated figures). Otherwise, the upper detector guide tubings 111 may be twisted through a certain angle in the clockwise direction under the condition in which the guide tubing anti-twister unit 340 is maintained at a 90°-rotated state thereof (that is, the 90° position) (as shown in the associated right figure). On the other hand, when the upper rotating plate 321 rotates 270° in the clockwise direction, the guide tubing anti-twister unit 340 is maintained at the 180° position thereof after being rotated in the same direction to the 180° position, so that the upper detector guide tubings 111 are twisted through a certain angle in the clockwise direction in accordance with the remaining rotation angle of the upper rotating plate 321 not absorbed by the guide tubing anti-twister unit 340. The withdraw limit switches 351 are installed above the guide tubing anti-twister unit 340 (as seen in FIG. 6). Each withdraw limit switch 351 not only functions to prevent the associated detector 200 from being withdrawn beyond the installation position of the withdraw limit switch 351, but also functions as a reference point for measuring the position of the detector. In the illustrated case, four withdraw limit switches 351 are used to correspond to respective inlet detector guide tubings 110. In this case, each withdraw limit switch 351 is attached to an outer peripheral surface of the associated inlet detector guide tubing 110 in a state of being supported by a casing of the withdraw limit switch assembly 350 such that they do not interfere with one another As shown in FIG. 13, each withdraw limit switch 351 is activated by the associated detector 200 and detector cable, which have ferrous magnetic body. For each withdraw limit switch 351, a non-contact type self-contained proximity reed switch, which carries a magnet therein, is preferably used to eliminate the need to drill a hole through the associated inlet detector guide tubing 110 for identification of the position of the associate detector 200. In this case, accordingly, it is possible to prevent the detector cables 201 from being damaged due to friction, which may be generated in the conventional case in which a contact type switch is installed in a state of being protruded into the associated inlet detector guide tubing, so that it may come into frictional contact with the associated detector cable. Such a non-contact type proximity reed switch generally has an advantage in that it is strong agains radioactive rays because no semiconductor element is contained in the reed switch, as compared to non-contact type solid state proximity switches, which contain semiconductor elements. Meanwhile, a detector storage guider 360 is installed at each inlet detector guide tubing 110 to guide the associated detector to a detector storage area 370, in order to safely store the detector emitting a large amount of radioactive rays when the neutron flux mapping system is not in operation. As apparent from the above description, the present invention can provide a neutron flux mapping system for a nuclear reactor, which has improvements in structures of drivers, path selectors, etc., thereby being capable of reducing the installation space thereof, while achieving a reduction in the failure rate thereof, so that it is more safe and efficient in terms of maintenance and repair. The present invention can also provide a neutron flux mapping system for a nuclear reactor, which is cable of, even when a failure occurs in a part of path selectors thereof, achieving measurement of neutron flux through all thimbles, using the remaining path selectors. |
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abstract | A nuclear fission reactor, flow control assembly, methods therefor and a flow control assembly system. The flow control assembly is coupled to a nuclear fission module capable of producing a traveling burn wave at a location relative to the nuclear fission module. The flow control assembly controls flow of a fluid in response to the location relative to the nuclear fission module. The flow control assembly comprises a flow regulator subassembly configured to be operated according to an operating parameter associated with the nuclear fission module. In addition, the flow regulator subassembly is reconfigurable according to a predetermined input to the flow regulator subassembly. Moreover, the flow control assembly comprises a carriage subassembly coupled to the flow regulator subassembly for adjusting the flow regulator subassembly to vary fluid flow into the nuclear fission module. |
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summary | ||
description | This application is a continuation of U.S. application Ser. No. 11/187,633, filed Jul. 21, 2005, now abandoned which claims the benefit of U.S. Provisional Application No. 60/590,089, filed on Jul. 21, 2004. The entire teachings of the above application are incorporated herein by reference. In order to accelerate charged particles to high energies, many types of particle accelerators have been developed since the 1930s. One type of particle accelerator is a cyclotron. A cyclotron accelerates charged particles in an axial magnetic field by applying an alternating voltage to one or more “dees” in a vacuum chamber. The name “dee” is descriptive of the shape of the electrodes in early cyclotrons, although they may not resemble the letter D in some cyclotrons. The spiral path produced by the accelerating particles is normal to the magnetic field. As the particles spiral out, an accelerating electric field is applied at the gap between the dees. The radio frequency (RF) voltage creates an alternating electric field across the gap between the dees. The RF voltage, and thus the field, is synchronized to the orbital period of the charged particles in the magnetic field so that the particles are accelerated by the radio frequency waveform as they repeatedly cross the gap. The energy of the particles increases to an energy level far in excess of the peak voltage of the applied radio frequency (RF) voltage. As the charged particles accelerate, their masses grow due to relativistic effects. Consequently, the acceleration of the particles becomes non-uniform and the particles arrive at the gap asynchronously with the peaks of the applied voltage. Two types of cyclotrons presently employed, an isochronous cyclotron and a synchrocyclotron, overcome the challenge of increase in relativistic mass of the accelerated particles in different ways. The isochronous cyclotron uses a constant frequency of the voltage with a magnetic field that increases with radius to maintain proper acceleration. The synchrocyclotron uses a decreasing magnetic field with increasing radius and varies the frequency of the accelerating voltage to match the mass increase caused by the relativistic velocity of the charged particles. In a synchrocyclotron, discrete “bunches” of charged particles are accelerated to the final energy before the cycle is started again. In isochronous cyclotrons, the charged particles can be accelerated continuously, rather than in bunches, allowing higher beam power to be achieved. In a synchrocyclotron, capable of accelerating a proton, for example, to the energy of 250 MeV, the final velocity of protons is 0.61c, where c is the speed of light, and the increase in mass is 27% above rest mass. The frequency has to decrease by a corresponding amount, in addition to reducing the frequency to account for the radially decreasing magnetic field strength. The frequency's dependence on time will not be linear, and an optimum profile of the function that describes this dependence will depend on a large number of details. Accurate and reproducible control of the frequency over the range required by a desired final energy that compensates for both relativistic mass increase and the dependency of magnetic field on the distance from the center of the dee has historically been a challenge. Additionally, the amplitude of the accelerating voltage may need to be varied over the accelerating cycle to maintain focusing and increase beam stability. Furthermore, the dees and other hardware comprising a cyclotron define a resonant circuit, where the dees may be considered the electrodes of a capacitor. This resonant circuit is described by Q-factor, which contributes to the profile of voltage across the gap. A synchrocyclotron for accelerating charged particles, such as protons, can comprise a magnetic field generator and a resonant circuit that comprising electrodes, disposed between magnetic poles. A gap between the electrodes can be disposed across the magnetic field. An oscillating voltage input drives an oscillating electric field across the gap. The oscillating voltage input can be controlled to vary over the time of acceleration of the charged particles. Either or both the amplitude and the frequency of the oscillating voltage input can be varied. The oscillating voltage input can be generated by a programmable digital waveform generator. The resonant circuit can further include a variable reactive element in circuit with the voltage input and electrodes to vary the resonant frequency of the resonant circuit. The variable reactive element may be a variable capacitance element such as a rotating condenser or a vibrating reed. By varying the reactance of such a reactive element and adjusting the resonant frequency of the resonant circuit, the resonant conditions can be maintained over the operating frequency range of the synchrocyclotron. The synchrocyclotron can further include a voltage sensor for measuring the oscillating electric field across the gap. By measuring the oscillating electric field across the gap and comparing it to the oscillating voltage input, resonant conditions in the resonant circuit can be detected. The programmable waveform generator can be adjusting the voltage and frequency input to maintain the resonant conditions. The synchrocyclotron can further include an injection electrode, disposed between the magnetic poles, under a voltage controlled by the programmable digital waveform generator. The injection electrode is used for injecting charged particles into the synchrocyclotron. The synchrocyclotron can further including an extraction electrode, disposed between the magnetic poles, under a voltage controlled by the programmable digital waveform generator. The extraction electrode is used to extract a particle beam from the synchrocyclotron. The synchrocyclotron can further include a beam monitor for measuring particle beam properties. For example, the beam monitor can measure particle beam intensity, particle beam timing or spatial distribution of the particle beam. The programmable waveform generator can adjust at least one of the voltage input, the voltage on the injection electrode and the voltage on the extraction electrode to compensate for variations in the particle beam properties. This invention is intended to address the generation of the proper variable frequency and amplitude modulated signals for efficient injection into, acceleration by, and extraction of charged particles from an accelerator. This invention relates to the devices and methods for generating the complex, precisely timed accelerating voltages across the “dee” gap in a synchrocyclotron. This invention comprises an apparatus and a method for driving the voltage across the “dee” gap by generating a specific waveform, where the amplitude, frequency and phase is controlled in such a manner as to create the most effective particle acceleration given the physical configuration of the individual accelerator, the magnetic field profile, and other variables that may or may not be known a priori. A synchrocyclotron needs a decreasing magnetic field in order to maintain focusing of the particles beam, thereby modifying the desired shape of the frequency sweep. There are predictable finite propagation delays of the applied electrical signal to the effective point on the dee where the accelerating particle bunch experiences the electric field that leads to continuous acceleration. The amplifier used to amplify the radio frequency (RF) signal that drives the voltage across the dee gap may also have a phase shift that varies with frequency. Some of the effects may not be known a priori, and may be only observed after integration of the entire synchrocyclotron. In addition, the timing of the particle injection and extraction on a nanosecond time scale can increase the extraction efficiency of the accelerator, thus reducing stray radiation due to particles lost in the accelerating and extraction phases of operation. Referring to FIGS. 1A and 1B, a synchrocyclotron of the present invention comprises electrical coils 2a and 2b around two spaced apart metal magnetic poles 4a and 4b configured to generate a magnetic field. Magnetic poles 4a and 4b are defined by two opposing portions of yoke 6a and 6b (shown in cross-section). The space between poles 4a and 4b defines vacuum chamber 8 or a separate vacuum chamber can be installed between the poles 4a and 4b. The magnetic field strength is generally a function of distance from the center of vacuum chamber 8 and is determined largely by the choice of geometry of coils 2a and 2b and shape and material of magnetic poles 4a and 4b. The accelerating electrodes comprise “dee” 10 and “dee” 12, having gap 13 therebetween. Dee 10 is connected to an alternating voltage potential whose frequency is changed from high to low during the accelerating cycle in order to account for the increasing relativistic mass of a charged particle and radially decreasing magnetic field (measured from the center of vacuum chamber 8) produced by coils 2a and 2b and pole portions 4a and 4b. The characteristic profile of the alternating voltage in dees 10 and 12 is show in FIG. 2 and will be discussed in details below. Dee 10 is a half-cylinder structure, hollow inside. Dee 12, also referred to as the “dummy dee”, does not need to be a hollow cylindrical structure as it is grounded at the vacuum chamber walls 14. Dee 12 as shown in FIGS. 1A and 1B comprises a strip of metal, e.g. copper, having a slot shaped to match a substantially similar slot in dee 10. Dee 12 can be shaped to form a mirror image of surface 16 of dee 10. Ion source 18 that includes ion source electrode 20, located at the center of vacuum chamber 8, is provided for injecting charged particles. Extraction electrodes 22 are provided to direct the charge particles into extraction channel 24, thereby forming beam 26 of the charged particles. The ion source may also be mounted externally and inject the ions substantially axially into the acceleration region. Dees 10 and 12 and other pieces of hardware that comprise a cyclotron, define a tunable resonant circuit under an oscillating voltage input that creates an oscillating electric field across gap 13. This resonant circuit can be tuned to keep the Q-factor high during the frequency sweep by using a tuning means. As used herein, Q-factor is a measure of the “quality” of a resonant system in its response to frequencies close to the resonant frequency. Q-factor is defined asQ=1/R×√(L/C),where R is the active resistance of a resonant circuit, L is the inductance and C is the capacitance of this circuit. Tuning means can be either a variable inductance coil or a variable capacitance. A variable capacitance device can be a vibrating reed or a rotating condenser. In the example shown in FIGS. 1A and 1B, the tuning means is rotating condenser 28. Rotating condenser 28 comprises rotating blades 30 driven by a motor 31. During each quarter cycle of motor 31, as blades 30 mesh with blades 32, the capacitance of the resonant circuit that includes “dees” 10 and 12 and rotating condenser 28 increases and the resonant frequency decreases. The process reverses as the blades unmesh. Thus, resonant frequency is changed by changing the capacitance of the resonant circuit. This serves the purpose of reducing by a large factor the power required to generate the high voltage applied to the “dees” and necessary to accelerate the beam. The shape of blades 30 and 32 can be machined so as to create the required dependence of resonant frequency on time. The blade rotation can be synchronized with the RF frequency generation so that by varying the Q-factor of the RF cavity, the resonant frequency of the resonant circuit, defined by the cyclotron, is kept close to the frequency of the alternating voltage potential applied to “dees” 10 and 12. The rotation of the blades can be controlled by the digital waveform generator, described below with reference to FIG. 3 and FIG. 4, in a manner that maintains the resonant frequency of the resonant circuit close to the current frequency generated by the digital waveform generator. Alternatively, the digital waveform generator can be controlled by means of an angular position sensor (not shown) on the rotating condenser shaft 33 to control the clock frequency of the waveform generator to maintain the optimum resonant condition. This method can be employed if the profile of the meshing blades of the rotating condenser is precisely related to the angular position of the shaft. A sensor that detects the peak resonant condition (not shown) can also be employed to provide feedback to the clock of the digital waveform generator to maintain the highest match to the resonant frequency. The sensors for detecting resonant conditions can measure the oscillating voltage and current in the resonant circuit. In another example, the sensor can be a capacitance sensor. This method can accommodate small irregularities in the relationship between the profile of the meshing blades of the rotating condenser and the angular position of the shaft. A vacuum pumping system 40 maintains vacuum chamber 8 at a very low pressure so as not to scatter the accelerating beam. To achieve uniform acceleration in a synchrocyclotron, the frequency and the amplitude of the electric field across the “dee” gap needs to be varied to account for the relativistic mass increase and radial (measured as distance from the center of the spiral trajectory of the charged particles) variation of magnetic field as well as to maintain focus of the beam of particles. FIG. 2 is an illustration of an idealized waveform that may be required for accelerating charged particles in a synchrocyclotron. It shows only a few cycles of the waveform and does not necessarily represent the ideal frequency and amplitude modulation profiles. FIG. 2 illustrates the time varying amplitude and frequency properties of the waveform used in a given synchrocyclotron. The frequency changes from high to low as the relativistic mass of the particle increases while the particle speed approaches a significant fraction of the speed of light. The instant invention uses a set of high speed digital to analog converters (DAC) that can generate, from a high speed memory, the required signals on a nanosecond time scale. Referring to FIG. 1A, both a radio frequency (RF) signal that drives the voltage across dee gap 13 and signals that drive the voltage on injector electrode 20 and extractor electrode 22 can be generated from the memory by the DACs. The accelerator signal is a variable frequency and amplitude waveform. The injector and extractor signals can be either of at least three types: continuous; discrete signals, such as pulses, that may operate over one or more periods of the accelerator waveform in synchronism with the accelerator waveform; or discrete signals, such as pulses, that may operate at precisely timed instances during the accelerator waveform frequency sweep in synchronism with the accelerator waveform. (See below with reference to FIGS. 8A-C.) FIG. 3 depicts a block diagram of a synchrocyclotron of the present invention 300 that includes particle accelerator 302, waveform generator system 319 and amplifying system 330. FIG. 3 also shows an adaptive feedback system that includes optimizer 350. The optional variable condenser 28 and drive subsystem to motor 31 are not shown. Referring to FIG. 3, particle accelerator 302 is substantially similar to the one depicted in FIGS. 1A and 1B and includes “dummy dee” (grounded dee) 304, “dee” 306 and yoke 308, injection electrode 310, connected to ion source 312, and extraction electrodes 314. Beam monitor 316 monitors the intensity of beam 318. Synchrocyclotron 300 includes digital waveform generator 319. Digital waveform generator 319 comprises one or more digital-to-analog converters (DACs) 320 that convert digital representations of waveforms stored in memory 322 into analog signals. Controller 324 controls addressing of memory 322 to output the appropriate data and controls DACs 320 to which the data is applied at any point in time. Controller 324 also writes data to memory 322. Interface 326 provides a data link to an outside computer (not shown). Interface 326 can be a fiber optic interface. The clock signal that controls the timing of the “analog-to-digital” conversion process can be made available as an input to the digital waveform generator. This signal can be used in conjunction with a shaft position encoder (not shown) on the rotating condenser (see FIGS. 1A and 1B) or a resonant condition detector to fine-tune the frequency generated. FIG. 3 illustrates three DACs 320a, 320b and 320c. In this example, signals from DACs 320a and 320b are amplified by amplifiers 328a and 328b, respectively. The amplified signal from DAC 320a drives ion source 312 and/or injection electrode 310, while the amplified signal from DAC 320b drives extraction electrodes 314. The signal generated by DAC 320c is passed on to amplifying system 330, operated under the control of RF amplifier control system 332. In amplifying system 330, the signal from DAC 320c is applied by RF driver 334 to RF splitter 336, which sends the RF signal to be amplified by an RF power amplifier 338. In the example shown in FIG. 3, four power amplifiers, 338a, b, c and d, are used. Any number of amplifiers 338 can be used depending on the desired extent of amplification. The amplified signal, combined by RF combiner 340 and filtered by filter 342, exits amplifying system 330 though directional coupler 344, which ensures that RF waves do not reflect back into amplifying system 330. The power for operating amplifying system 330 is supplied by power supply 346. Upon exit from amplifying system 330, the signal from DAC 320c is passed on to particle accelerator 302 through matching network 348. Matching network 348 matches impedance of a load (particle accelerator 302) and a source (amplifying system 330). Matching network 348 includes a set of variable reactive elements. Synchrocyclotron 300 can further include optimizer 350. Using measurement of the intensity of beam 318 by beam monitor 316, optimizer 350, under the control of a programmable processor can adjust the waveforms produced by DACs 320a, b and c and their timing to optimize the operation of the synchrocyclotron 300 and achieve a optimum acceleration of the charged particles. The principles of operation of digital waveform generator 319 and adaptive feedback system 350 will now be discussed with reference to FIG. 4. The initial conditions for the waveforms can be calculated from physical principles that govern the motion of charged particles in magnetic field, from relativistic mechanics that describe the behavior of a charged particle mass as well as from the theoretical description of magnetic field as a function of radius in a vacuum chamber. These calculations are performed at step 402. The theoretical waveform of the voltage at the dee gap, RF(ω, t), where ω is the frequency of the electrical field across the dee gap and t is time, is computed based on the physical principles of a cyclotron, relativistic mechanics of a charged particle motion, and theoretical radial dependency of the magnetic field. Departures of practice from theory can be measured and the waveform can be corrected as the synchrocyclotron operates under these initial conditions. For example, as will be described below with reference to FIGS. 8A-C, the timing of the ion injector with respect to the accelerating waveform can be varied to maximize the capture of the injected particles into the accelerated bunch of particles. The timing of the accelerator waveform can be adjusted and optimized, as described below, on a cycle-by-cycle basis to correct for propagation delays present in the physical arrangement of the radio frequency wiring; asymmetry in the placement or manufacture of the dees can be corrected by placing the peak positive voltage closer in time to the subsequent peak negative voltage or vice versa, in effect creating an asymmetric sine wave. In general, waveform distortion due to characteristics of the hardware can be corrected by pre-distorting the theoretical waveform RF(ω, t) using a device-dependent transfer function A, thus resulting in the desired waveform appearing at the specific point on the acceleration electrode where the protons are in the acceleration cycle. Accordingly, and referring again to FIG. 4, at step 404, a transfer function A(ω, t) is computed based on experimentally measured response of the device to the input voltage. At step 405, a waveform that corresponds to an expression RF(ω, t)/A(ω,t) is computed and stored in memory 322. At step 406, digital waveform generator 319 generates RF/A waveform from memory. The driving signal RF(ω, t)/A(ω, t) is amplified at step 408, and the amplified signal is propagated through the entire device 300 at step 410 to generate a voltage across the dee gap at step 412. A more detailed description of a representative transfer function A(ω,t) will be given below with reference to FIGS. 6A-C. After the beam has reached the desired energy, a precisely timed voltage can be applied to an extraction electrode or device to create the desired beam trajectory in order to extract the beam from the accelerator, where it is measured by beam monitor at step 414a. RF voltage and frequency is measured by voltage sensors at step 414b. The information about beam intensity and RF frequency is relayed back to digital waveform generator 319, which can now adjust the shape of the signal RF(ω, t)/A(ω, t) at step 406. The entire process can be controlled at step 416 by optimizer 350. Optimizer 350 can execute a semi- or fully automatic algorithm designed to optimize the waveforms and the relative timing of the waveforms. Simulated annealing is an example of a class of optimization algorithms that may be employed. On-line diagnostic instruments can probe the beam at different stages of acceleration to provide feedback for the optimization algorithm. When the optimum conditions have been found, the memory holding the optimized waveforms can be fixed and backed up for continued stable operation for some period of time. This ability to adjust the exact waveform to the properties of the individual accelerator decreases the unit-to-unit variability in operation and can compensate for manufacturing tolerances and variation in the properties of the materials used in the construction of the cyclotron. The concept of the rotating condenser (such as condenser 28 shown in FIGS. 1A and 1B) can be integrated into this digital control scheme by measuring the voltage and current of the RF waveform in order to detect the peak of the resonant condition. The deviation from the resonant condition can be fed back to the digital waveform generator 319 (see FIG. 3) to adjust the frequency of the stored waveform to maintain the peak resonant condition throughout the accelerating cycle. The amplitude can still be accurately controlled while this method is employed. The structure of rotating condenser 28 (see FIGS. 1A and 1B) can optionally be integrated with a turbomolecular vacuum pump, such as vacuum pump 40 shown in FIGS. 1A and 1B, that provides vacuum pumping to the accelerator cavity. This integration would result in a highly integrated structure and cost savings. The motor and drive for the turbo pump can be provided with a feedback element such as a rotary encoder to provide fine control over the speed and angular position of rotating blades 30, and the control of the motor drive would be integrated with the waveform generator 319 control circuitry to insure proper synchronization of the accelerating waveform. As mentioned above, the timing of the waveform of the oscillating voltage input can be adjusted to correct for propagation delays that arise in the device. FIG. 5A illustrate an example of wave propagation errors due to the difference in distances R1 and R2 from the RF input point 504 to points 506 and 508, respectively, on the accelerating surface 502 of accelerating electrode 500. The difference in distances R1 and R2 results in signal propagation delay that affects the particles as they accelerate along a spiral path (not shown) centered at point 506. If the input waveform, represented by curve 510, does not take into account the extra propagation delay caused by the increasing distance, the particles can go out of synchronization with the accelerating waveform. The input waveform 510 at point 504 on the accelerating electrode 500 experiences a variable delay as the particles accelerate outward from the center at point 506. This delay results in input voltage having waveform 512 at point 506, but a differently timed waveform 514 at point 508. Waveform 514 shows a phase shift with respect to waveform 512 and this can affect the acceleration process. As the physical size of the accelerating structure (about 0.6 meters) is a significant fraction of the wavelength of the accelerating frequency (about 2 meters), a significant phase shift is experienced between different parts of the accelerating structure. In FIG. 5B, the input voltage having waveform 516 is pre-adjusted relative to the input voltage described by waveform 510 to have the same magnitude, but opposite sign of time delay. As a result, the phase lag caused by the different path lengths across the accelerating electrode 500 is corrected. The resulting waveforms 518 and 520 are now correctly aligned so as to increase the efficiency of the particle accelerating process. This example illustrates a simple case of propagation delay caused by one easily predictable geometric effect. There may be other waveform timing effects that are generated by the more complex geometry used in the actual accelerator, and these effects, if they can be predicted or measured can be compensated for by using the same principles illustrated in this example. As described above, the digital waveform generator produces an oscillating input voltage of the form RF(ω, t)/A(ω, t), where RF(ω, t) is a desired voltage across the dee gap and A(ω, t) is a transfer function. A representative device-specific transfer function A, is illustrated by curve 600 in FIG. 6A. Curve 600 shows Q-factor as a function of frequency. Curve 600 has two unwanted deviations from an ideal transfer function, namely troughs 602 and 604. These deviation can be caused by effects due to the physical length of components of the resonant circuit, unwanted self-resonant characteristics of the components or other effects. This transfer function can be measured and a compensating input voltage can be calculated and stored in the waveform generator's memory. A representation of this compensating function 610 is shown in FIG. 6B. When the compensated input voltage 610 is applied to device 300, the resulting voltage 620 is uniform with respect to the desired voltage profile calculated to give efficient acceleration. Another example of the type of effects that can be controlled with the programmable waveform generator is shown in FIG. 7. In some synchrocyclotrons, the electric field strength used for acceleration can be selected to be somewhat reduced as the particles accelerate outward along spiral path 705. This reduction in electric field strength is accomplished by applying accelerating voltage 700, that is kept relatively constant as shown in FIG. 7A, to accelerating electrode 702. Electrode 704 is usually at ground potential. The electric field strength in the gap is the applied voltage divided by the gap length. As shown in FIG. 7B, the distance between accelerating electrodes 702 and 704 is increasing with radius R. The resulting electric field strength as a function or radius R is shown as curve 706 in FIG. 7C. With the use of the programmable waveform generator, the amplitude of accelerating voltage 708 can be modulated in the desired fashion, as shown in FIG. 7D. This modulation allows to keep the distance between accelerating electrodes 710 and 712 to remain constant, as shown in FIG. 7E. As a result, the same resulting electric field strength as a function of radius 714, shown in FIG. 7F, is produced as shown in FIG. 7C. While this is a simple example of another type of control over synchrocyclotron system effects, the actual shape of the electrodes and profile of the accelerating voltage versus radius may not follow this simple example. As mentioned above, the programmable waveform generator can be used to control the ion injector (ion source) to achieve optimal acceleration of the charged particles by precisely timing particle injections. FIG. 8A shows the RF accelerating waveform generated by the programmable waveform generator. FIG. 8B shows a precisely timed cycle-by-cycle injector signal that can drive the ion source in a precise fashion to inject a small bunch of ions into the accelerator cavity at precisely controlled intervals in order to synchronize with the acceptance phase angle of the accelerating process. The signals are shown in approximately the correct alignment, as the bunches of particles are usually traveling through the accelerator at about a 30 degree lag angle compared to the RF electric field waveform for beam stability. The actual timing of the signals at some external point such as the output of the digital-to-analog converters, may not have this exact relationship as the propagation delays of the two signals is likely to be different. With the programmable waveform generator, the timing of the injection pulses can be continuously varied with respect to the RF waveform in order to optimize the coupling of the injected pulses into the accelerating process. This signal can be enabled or disabled to turn the beam on and off. The signal can also be modulated via pulse dropping techniques to maintain a required average beam current. This beam current regulation is accomplished by choosing a macroscopic time interval that contains some relatively large number of pulses, on the order of 1000, and changing the fraction of pulses that are enabled during this interval. FIG. 8C shows a longer injection control pulse that corresponds to a multiple number of RF cycles. This pulse is generated when a bunch of protons are to be accelerated. The periodic acceleration process captures only a limited number of particles that will be accelerated to the final energy and extracted. Controlling the timing of the ion injection can result in lower gas load and consequently better vacuum conditions which reduces vacuum pumping requirements and improves high voltage and beam loss properties during the acceleration cycle. This can be used where the precise timing of the injection shown in FIG. 8B is not required for acceptable coupling of the ion source to the RF waveform phase angle. This approach injects ions for a number of RF cycles which corresponds approximately to the number of “turns” which are accepted by the accelerating process in the synchrocyclotron. This signal is also enabled or disabled to turn the beam on and off or modulate the average beam current. While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. |
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abstract | An X-ray apparatus includes a collimator comprising a lamp and configured to adjusting an irradiation region of X-rays radiated from an X-ray source; an image acquirer configured to acquire an object image by imaging an object while the lamp is turned on; and a controller configured to acquire an object distance based on the object image and acquire a thickness of the object based on a detector distance and the object distance. The object distance is a distance between the X-ray source and the object, and the detector distance is a distance between the X-ray source and an X-ray detector. |
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claims | 1. A method of improving nuclear reactor performance, comprising:implementing a control rod operational plan for the nuclear reactor,the control rod operational plan including a degree of partial insertion for a control rod in the nuclear reactor before a scram of the nuclear reactor,the control rod operational plan simulated in the nuclear reactor, the simulating including a scram during at least a portion of an operating cycle of the nuclear reactor including an end of an operating cycle, andthe control rod operational plan decreasing an operating limit minimum core power ratio in the simulation for the scram during at least the portion of the operating cycle for the nuclear reactor including the end of cycle, compared to simulation results of the simulation of the nuclear reactor including a scram during at least a portion of an operating cycle of the nuclear reactor including an end of an operating cycle involving no insertion of the control rod in the nuclear reactor before a scram of the nuclear reactor. 2. The method of claim 1, wherein the control rod includes a control rod designated for a latest removal in the control rod operational plan. 3. A method of improving nuclear reactor performance, comprising:generating a control rod operational plan for the nuclear reactor, the generating includingselecting at least one control rod for consideration,selecting a degree of partial insertion for the selected control rod before a scram of the nuclear reactor,simulating the control rod operational plan, the simulating including a scram during at least a portion of an operating cycle of the nuclear reactor including an end of an operating cycle to generate a simulation result;determining whether the simulation result decreases an operating limit minimum core power ratio in the simulation, compared to simulation results of a simulation of the nuclear reactor involving no insertion of the selected control rod in the nuclear reactor before a scram of the nuclear reactor; andimplementing the generated control rod operational plan, if the determining step determines that the generated control rod operation plan decreases the operating limit minimum core power ratio compared to simulation results of the simulation of the nuclear reactor involving no insertion. 4. The method of claim 3, further comprising:repeating the steps of claim 3 with a different at least one control rod or degree of partial insertion, if the determining step determines that the generated simulation result does not decrease the operating limit minimum core power ratio compared to simulation results of the simulation of the nuclear reactor involving no insertion. |
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046817298 | abstract | A vessel for the storage and monitoring of nuclear fuel materials incorporates a device (12) within its interior for providing an externally detectable signal indicating whether any temperature rise has occurred. The device (12) comprises a magnet (32) attracted towards a boundary wall (11) of the vessel and maintained in that position by a temperature-sensitive element such as a thermal link (38). The magnet (32) is subjected to an oppositely directed force by a spring (30), which is effective to drive the magnet (32) away from the wall (11) in the event of a substantial temperature rise within the vessel thereby producing an externally detectable change in magnetic flux. |
054715148 | claims | 1. A fuel assembly for a light-water nuclear reactor comprising a bottom tie plate having through-holes therethrough, a top tie plate having through-holes therethrough, a plurality of vertical fuel rods extending between the bottom tie plate and the top tie plate, an inlet nozzle for directing coolant upwardly to said bottom tie plate so as to pass through said bottom tie plate, past said vertical fuel rods and through said top tie plate, said inlet nozzle defining a central vertical axis, and a debris catcher fixedly positioned within said inlet nozzle, said debris catcher comprising a support means for supporting at least one helical spring, said support means defining a channel which encircles said central vertical axis and extends in a first plane which is substantially perpendicular to said central vertical axis, and a helical spring fixedly positioned within said channel so as to extend in said first plane and trap debris in said coolant passing therethrough. 2. A fuel assembly according to claim 1, wherein said channel encircles said central vertical axis in the form of a spiral. 3. A fuel assembly according to claim 1, wherein said channel encircles said central vertical axis as an annulus. 4. A fuel assembly according to claim 3, wherein said support means defines a plurality of annular channels extending in said first plane. 5. A fuel assembly according to claim 4, including a plurality of helical springs respectively positioned in said plurality of annular channels. 6. A fuel assembly according to claim 1, wherein said support means defines a plurality of channels which encircle said central vertical axis and which extend in a plurality of parallel planes substantially perpendicular to said central vertical axis, and including a plurality of helical springs respectively positioned in said plurality of channels. 7. A fuel assembly according to claim 1, wherein said support means comprises two parallel plates which provide facing slots that define said channel. 8. A fuel assembly according to claim 1, wherein said support means comprises two spaced-apart, cruciform members that mount a plurality of rings therebetween that define said channel. |
059995831 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to analyzing over time the performance of a control rod drive mechanism of a nuclear reactor, and its associated control system, by digitizing, storing and analyzing current level signals developed during stepwise lifting and lowering of control rods using electromagnetically driven sequential gripping and moving devices. 2. Prior Art In a nuclear reactor for power generation, such as a pressurized water reactor, heat is generated by fission of a nuclear fuel such as enriched uranium, and transferred into a coolant flowing through a reactor core. The core contains elongated nuclear fuel rods mounted in proximity with one another on a fuel assembly structure through and over which the coolant flows. The fuel rods are spaced from one another in coextensive parallel arrays. Some of the neutrons and other atomic particles released during nuclear decay of fuel atoms in a given fuel rod pass through the spaces between fuel rods and impinge on the fissile material in an adjacent fuel rod, contributing to the nuclear reaction and to the heat generated by the core. Movable control rods are dispersed throughout the nuclear core to enable control of the overall rate of fission, by absorbing a portion of the neutrons passing between fuel rods, which otherwise would contribute to the fission reaction. The control rods generally comprise elongated rods of neutron absorbing material and fit into longitudinal openings or guide thimbles in the fuel assemblies running parallel to and between the fuel rods. Inserting a control rod further into the core causes more neutrons to be absorbed without contributing to fission in an adjacent fuel rod; and retracting the control rod reduces the extent of neutron absorption and increases the rate of the nuclear reaction and the power output of the core. The control rods are supported in cluster assemblies that are movable to advance or retract a group of control rods relative to the core. For this purpose, control rod drive mechanisms are provided, typically as part of an upper internals arrangement located within the nuclear reactor vessel above the nuclear core. The reactor vessel is typically pressurized to a high internal pressure, and the control rod drive mechanisms are housed in pressure housings that are tubular extensions of the reactor pressure vessel. One type of mechanism for positioning a control rod is a so-called magnetic jack, operable to move the control rod by an incremental distance into or out of the core in discrete steps. The control rod drive mechanism has three electromagnetic coils and armatures or plungers that are operated in a coordinated manner to raise and lower a drive rod shaft and a control rod cluster assembly coupled to the shaft. The three coils are mounted around and outside the pressure housing. Two of the three coils operate grippers that when powered by the coils engage with the drive rod shaft, one of the grippers being axially stationary and the other axially movable. The drive rod shaft has axially spaced circumferential grooves that are clasped by grip latches on the grippers, spaced circumferentially around the drive rod shaft. The third coil actuates a lift plunger coupled between the movable gripper and a fixed point. If control power to the control rod drive mechanism is lost, the two grippers both release and the control rods drop by gravity into their maximum nuclear flux damping position. So long as control power remains activated, at least one of the stationary gripper and the movable gripper holds the drive rod shaft at all times. The three coils are operated in a timed and coordinated manner alternately to hold and to move the drive shaft. The sequence of gripping actions and movements is different depending on whether the stepwise movement is a retraction or an advance. The stationary gripper and the movable gripper operate substantially alternately, although during the sequence of movements both grippers engage the drive shaft during a change from holding stationary to movement for advance or retraction. The stationary gripper can hold the drive shaft while the movable gripper is moved to a new position of engagement, for lowering (advancing) the drive shaft and the control rods. The movable gripper engages with the drive shaft when moving it up or down as controlled by the lift plunger. After the movable gripper engages the drive shaft, the stationary gripper is released and then the plunger is activated or deactivated to effect movement in one direction or the other. Typically, each jacking or stepping movement moves the drive rod shaft 5/8 inch (1.6 cm), and some 228 steps are taken at about 0.8 seconds per step, to move a control rod cluster over its full span of positions between the bottom and top of the fuel assembly. More particularly, for lifting (retracting) the control rods, the following steps are accomplished in sequence, beginning with the stationary gripper engaged in a drive rod groove and the movable gripper and plunger both being deactivated: 1. the movable gripper is energized and engages a drive rod groove; PA1 2. the stationary gripper is de-energized and disengages from the drive rod; PA1 3. the lift coil is energized and electromagnetically lifts the movable gripper and the drive rod an elevation equal to the span of the lift plunger; PA1 4. the stationary gripper is energized, re-engages and holds the drive rod (i.e., both grippers are engaged); PA1 5. the movable coil is de-energized and disengages the drive rod; PA1 6. the lift coil is de-energized, dropping the movable coil back to its start position, namely one step lower on the lifted drive rod. PA1 1. the lift coil is energized, moving the movable gripper one step up along the drive rod; PA1 2. the movable gripper coil is energized and the movable gripper grips the drive rod; PA1 3. the stationary coil is de-energized, releasing the drive rod; PA1 4. the lift coil is de-energized, dropping the movable coil and the drive rod by one step; PA1 5. the stationary coil is energized and the stationary gripper engages the drive rod, at a position one step higher than its previous position; and, PA1 6. the movable coil is de-energized and the movable gripper disengages from the drive rod. Similarly, for lowering (advancing) the control rods, the following steps are accomplished in sequence, again beginning with only the stationary gripper energized: A number of particular coil mechanisms and gripper mechanisms are possible. Examples of coil jacking mechanisms with a stationary gripper, a movable gripper and a lifting coil as described are disclosed, for example, in U.S. Pat. No. 5,307,384--King et al., U.S. Pat. No. 5,066,451--Tessaro and U.S. Pat. No. 5,009,834--Tessaro, all of which are hereby incorporated. Whatever mechanical arrangement is employed for the grippers and lifting coil/armature arrangement, a discrete time interval is needed to complete each sequential operation. In order to move the control rods quickly, reliably and efficiently, the respective grippers and coils must be operated accurately as to their timing. This requires that the coil energizing electric power signals to the respective coils be accurately timed. The power level of coil energization can be simply on and off, or preferably the coils can be energized at different levels during different operations in the sequence. For example, the lift coil signal can have an intermediate or "hold" current level for the lift coil, between the de-energized (zero) level and the full-on lifting level. At the intermediate level, the lift coil maintains the position of the movable coil. An intermediate current level may also provide sufficient power to move the movable gripper when it is disengaged from the control drive rod. An intermediate current level can be used with the stationary gripper coil for holding, as opposed to a higher level for positive initial gripping. The coil signals are switched between the levels in a coordinated manner by a logic controller. The logic controller generates timed signals to switch power regulation circuits on and off or between current levels. The timing relationships between and among current pulses applied to the stationary gripper coil, the movable gripper coil and the lift coil, are adjusted manually when setting up the control rod drive mechanism, and remain set. For example, an oscilloscope or chart recorder is set up to record the three coil currents. A timing signal at a known frequency can be provided and recorded together with the coil current signals as a reference. The actual determination of timing is done by reviewing the recorded signals and spacing the operations in time sufficiently to complete each step in the sequence before undertaking the next. The power regulation circuits attempt to maintain the required coil currents at the required times in the sequence of operations. However, the actual coil currents have current variations that reflect the status of the electromechanical operation. For example, the drive currents to the gripper coils typically show a brief reduction or notch in current when the associated gripper fully pulls in and the inductance of the gripper coil increases. The notch disappears as the power regulator responds to bring the current level to nominal. By noting the occurrence of the notch in the gripper coil current signal, the technician can determine the point in time at which the gripper engaged. The timing of the next operation, which depends on successful gripper engagement, is then set to occur at a slight delay after the gripper engagement time noted. Various circuit elements can be used in the control logic circuits to trigger the power regulator to generate the necessary control currents at preset times in the sequence. For example, cycles at a known frequency (such as the recorded timing reference signal) can be digitally counted, and a particular power regulation switching operation can be triggered by a signal gated from a cycle counter at a predetermined count. Alternatively, the timing can be set using other means such as adjusting the RC delays of monostable multivibrators that trigger one another in a cascade sequence. In any event, the timing is predetermined and set, giving some leeway or extra time to ensure completion of each operation before commencing the next, while nevertheless enabling the rods to be advanced or retracted relatively promptly through their span of movement. It would be advantageous to provide a more automated control mechanism that is responsive to operation of the device rather than preset timings based on the expectation that current levels will be reached and mechanical actions will occur at the needed times. It would also be advantageous if the control mechanism could include ongoing diagnostic and feedback capabilities, such that deviation from expected operation can be detected by comparison with historical or nominal operation and suitable corrective action taken. SUMMARY OF THE INVENTION It is an object of the invention to provide a method and apparatus for automatically analyzing the current levels and timing relationships of an operating control rod drive mechanism having coordinated electromagnetic gripping and moving coils, to ensure effective operation, and to diagnose electrical and mechanical faults. It is also an object of the invention to sample and digitize the coil current levels over time, and to automatically test for correct demanded current levels over time, and for the occurrence of current variations indicative of mechanical operations at the required times. It is another object to monitor for problems in the power regulations circuits, such as loss of power or excessive ripple. It is still another object to conduct such monitoring in an ongoing manner, and to store data respecting historical operations for comparison with present operations to identify differences, potential problems and trends. It is also an object to embody a control rod drive testing unit that can be integrated with the control rod drive logic, does not require separate instrumentation wiring to the coils, and can include a control rod drop tester. These and other objects are accomplished for an electromagnetic drive mechanism for the control rods of a nuclear reactor having 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. Additional objects and aspects of the invention will be apparent from the following nonlimiting description of exemplary practical embodiments. |
052992411 | claims | 1. In a transuranium element transmuting fast reactor core in which a fast reactor contains a plurality of fuel assemblies, said fuel assemblies comprising fuel pellets containing a minor actinide elements and a fissionable fuel, the amount of said minor actinide elements being controlled so as to prevent melting of said fuel pellets in said fuel assemblies, the improvement wherein the amount of .sup.242 Cm, .sup.244 Cm and .sup.241 Am in a said fuel assembly satisfy the equation EQU 1.2.times.10.sup.2 .times.M.sub.242 +2.8.times.M.sub.244 +1.1.times.10.sup.-1 .times.M.sub.241 <Q.sub.1 2. The reactor core of claim 1, wherein said fuel assembly contains an amount of minor actinide elements sufficient to maintain the excess reactivity of the reactor at substantially zero during operation of the reactor, wherein said excess reactivity is the amount of fissionable elements produced by neutron capture by said minor actinide elements which exceeds fissionable elements transmuted by fission of said fissionable fuel. 3. The reactor core of claim 1, wherein said fuel assemblies contain fissionable plutonium fuel and said core contains a core area having a central portion wherein the plutonium concentration in said core area is uniform and wherein the concentration of minor actinides decreases radially from said central portion of said core area. 4. The reactor core of claim 1, wherein said fuel assemblies contain fissionable plutonium fuel and said core contains a first core area having a first plutonium concentration and a second core area having a second plutonium concentration, wherein the plutonium concentration in said first core area is higher than the plutonium concentration in said second core area and wherein the concentration of minor actinide in said first core area is higher than the concentration of minor actinide in said second core area. |
abstract | In a canister horizontally installed and housed inside a concrete silo, at least two temperatures out of a temperature TB at a canister bottom portion to be one end portion in a lateral direction in a horizontally-installed attitude, a temperature TSB at a canister side surface lower portion located below a horizontal plane passing through a center of the canister, a temperature TT at a canister lid portion to be the other end portion in the lateral direction, and a temperature TST at a canister side surface upper portion located above the horizontal plane passing through the center of the canister are monitored, and occurrence of leakage of an inert gas inside the canister is detected when there is a change in a temperature difference between the at least two temperatures. |
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06294858& | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to microminiature thermionic converters having high energy-conversion efficiencies and variable operating temperatures, and to methods of manufacturing those converters using semiconductor integrated circuit fabrication and micromachine manufacturing techniques. The microminiature thermionic converters (MTCs) of the invention incorporate cathode to anode spacing of about 10 microns or less and use cathode and anode materials having work functions ranging from about 1 eV to about 3 eV. 2. Description of the Related Art Thermionic conversion has been studied since the late nineteenth century, but practical devices were not demonstrated until the mid-twentieth century. Thomas Edison first studied thermionic emission in 1883 but its use for conversion of heat to electricity was not proposed until 1915 by Schicter. Although analytical work on thermionic converters continued during the 1920's, experimental converters were not reported until 1941. The Russians, Gurtovy and Kovalenko, published data which demonstrated the use of a cesium vapor diode to convert heat into electrical energy. Practical thermionic conversion was demonstrated in 1957 by Herqvist in which efficiencies of 5-10% were reached with power densities of 3-10W/cm.sup.2. FIG. 1 illustrates the components and processes of a typical thermionic converter employing technology understood and applied prior to the present invention. A heat source 15 elevates the temperature of the emitter electrode 10 (typically, between 1400-2200 K). Electrons 50 are then thermally evaporated into the space, or interelectrode gap (IEG) 5, between the emitter electrode 10 and collector electrode 20. The electrodes are operated in a vacuum, near vacuum, or in low pressure vapor (less than several torr) 65 within a vacuum or rarefied vapor enclosure 60. The collector electrode 20 is cooled by a heat sink 25 and kept at a low temperature. The electrons 50 travel across the IEG 5 toward the collector electrode 20 and condense on the collector electrode 20. The electrons 50 then return to the emitter electrode 10 through the electrical leads 30, electrical terminals 35 and load 40 which connect the collector to the emitter. The figure shows an example configuration wherein the rarefied enclosure 60, itself, functions as a conduit of heat addition on one side and heat removal on the other. Alternatively, it is possible for the heat source and heat sink to be positioned inside enclosure 60 and function independently from it. Thermionic emission depends on emission of electrons from a hot surface. Valence electrons at room temperature within a metal are free to move within the atomic lattice but very few can escape from the metal surface. The electrons are prevented from escaping by the electrostatic image force between the electron and the metal surface. The heat from the emitting surface gives the electrons sufficient energy to overcome the electrostatic image force. The energy required to leave the metal surface is referred to as the material work function, .o slashed.. The rate at which electrons leave the metal surface is given by the Richardson-Dushman equation: EQU J=AT.sup.2 exp(-e.o slashed./kT), where A is a universal constant, T is the emitter temperature, k is the Boltzmann constant, and .o slashed. is the emitter work function. Large emission current densities are achieved by choosing an emitter with low work function and operating that emitter at as high a temperature as possible, with the following limitations. Very high temperature operation may cause any material to evaporate rapidly and limit emitter lifetime. Low work function materials can have relatively high evaporation rates and must be operated at lower temperatures. Materials with low evaporation rates usually have high work functions. Choosing the correct electrode material is a key component of designing functional thermionic converters. A general description of suitable materials is presented here in association with disclosing the principles of the converters of the present invention. Example materials suitable for the microminiature thermionic converters of the present invention and others (as well as methods for making them) are disclosed in a separate patent application Ser. No. 09/257,336 filed on the same day as the present application. That separate patent application is incorporated herein in its entirety. Once the electrons are successfully emitted, their continued travel to the collector must be ensured. Electrons that are emitted from the emitter produce a space charge in the IEG. For large currents, the buildup of charge will act to repel further emission of electrons and limit the efficiency of the converter. Two options have been considered to limit space charge effects in the IEG: thermionic converters with small interelectrode gap spacing (the close-spaced vacuum converter) and thermionic converters filled with ionized gas. Thermionic converters with gas in the IEG are designed to operate with ionized species of the gas. Cesium vapor is the gas most commonly used. Cesium has a dual role in thermionic converters: 1) space charge neutralization and 2) electrode work function modification. In the latter case, cesium atoms adsorb onto the emitter and collector surfaces. The adsorption of the atoms onto the electrode surfaces results in a decrease of the emitter and collector work functions, allowing greater electron emission from the hot emitter. Space charge neutralization occurs via two mechanisms: 1) surface ionization and 2) volumetric ionization. Surface ionization occurs when a cesium atom comes into contact with the emitter. Volumetric ionization occurs when an emitted electron inelastically collides with a Cs atom in the IEG. The work function and space charge reduction increase the converter power output. However, at the cesium pressures necessary to substantially affect the electrode work functions, an excessive amount of collisions (more than that needed for ionizations) occurs between the emitted electrons and cesium atoms, resulting in a loss of conversion efficiency. Therefore, the cesium vapor pressure must be controlled so that the work function reduction and space charge reduction effects outweigh the electron-cesium collision effect. An example of an operational thermionic converter is that found on the Russian TOPAZ-II space reactor. These converters operate at the emitter temperatures of 1700 K and collector temperatures of 600 K with cesium pressure in the IEG of just under one torr. Typical current densities achieved are<4 amps/cm.sup.2 at output voltages of approximately 0.5 V. These converters operate at an efficiency of approximately 6%. The control of cesium pressure in the IEG is critical to operating these thermionic converters at their optimum efficiency. A variety of thermionic converters are disclosed in the literature, including close-spaced converters. (See: Y. V. Nikolaev, et al., "Close-Spaced Thermionic Converters for Power Systems", Proceedings Thermionic Energy Conversion Specialists Conference (1993); G. O. Fitzpatrick, et al., "Demonstration of CloseSpaced Thermionic Converters", 28.sup.th Intersociety Energy Conversion Engineering Conference (1993); Kucherov, R. Ya., et al., "Closed Space Thermionic Converter with Isothermic Electrodes", 29.sup.th Intersociety Energy Conversion Engineering Conference (1994); and G. Oi. Fitzpatrick, et al., "Close-Spaced Thermionic Converters with Active Spacing Control and Heat-Pipe Isothermal Emitters", 31.sup.th Intersociety Energy Conversion Engineering Conference (1996).) Previously demonstrated thermionic converters, however, have not been able to achieve the current densities and conversion efficiencies predicted for the present invention. Others' efforts in the field of close-space converters demonstrate that expense and difficulty arise as a result of separately manufacturing and assembling at close tolerances the converter components such as the emitter, collector and spacers. additionally, the assembly process results in relatively large converters with spacing between the emitter and collector of up to several millimeters. A large gap spacing between the emitter and collector causes the energy conversion efficiency to drop dramatically, often necessitating Cs vapor systems even in converters otherwise designed to be "close-spaced." Such vapor systems are usually large and cumbersome, and precise control of Cs vapor pressures needed to maximize conversion efficiency (ensuring that space-charge reduction effects outweigh electron-Cs collision effect) is difficult. Miniature thermionic converters without ionized positive vapor in the IEG offer the simplest solution to thermionic energy conversion. The small IEG size itself reduces the density of electrons in the gap (and their resulting current limiting space charge). As alluded to above, the close-spaced converter has historically been difficult to manufacture for large-scale operation due to the close tolerances (several microns or even submicron interelectrode gap size) needed for efficient operation. As demonstrated below, however, large scale production and operation of these close-spaced converters is now possible using IC fabrication techniques according to the principles of the present invention. Spacings on the order of 0.25 microns can now be produced and maintained over relatively large emission areas. Also, the development of low work function electrodes eliminates the need for gas adsorption to lower the electrode work functions. The MTC has application both in government and in industry. MTCs could be retrofitted into almost any system requiring energy conversion from heat to electricity. MTCs are suitable for use in satellite and deep space missions where conventional thermionics alone and in conjunction with radioisotope thermal generators are currently used or planned. Increasing the efficiency of current fossil fuel plants and systems as well as introducing new technologies for increasing the efficiency an utility of renewable energy supplies such as solar would help to reduce U.S. dependency on fossil fuel consumption. Combustion heated MTCs could be used for high efficiency conversion of heat to electricity as stand alone units or as part of topping cycle or bottoming cycle cogeneration systems in larger central power plants. They are also suited to use in the new smaller gas fired combined-cycle plants that utilities are building to meet peak power demands. At lower power scales (typically less than 125 kWe), MTCs could prove to be more economical than conventional cogeneration systems using machinery with moving parts. Smaller mechanical systems have shown increased operating costs due to increased maintenance requirements. Very small MTC units (1-50 kWe) could be used with home heating systems (furnaces and water heaters) and small businesses to feed electricity back into the home/business or its community electric grid. MTCs could also be used with solar concentrators or central receiver power towers to generate electricity as stand alone units or in conjunction with other conversion technologies. These applications could by linked to an existing power grid or be deployed in any undeveloped region without a grid (eliminating the need in those areas for developing an expensive electric power grid). SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide a MTC which includes close-spaced electrodes with only a vacuum or near-vacuum within the IEG. It is another object of the invention to provide a MTC that does not require use of cesium vapor or other similar vapor in the IEG either to neutralize space charges or to enhance work function of the electrodes. It is another object of the invention to provide a method of manufacturing MTCs and MTC components monolithically using IC fabrication and micromachine manufacturing techniques. It is yet another object of the invention to provide MTCs having no moving parts, long maintenance intervals, no vibration as a consequence of their operation, and very quiet operation. These and other objects of the present invention are fulfilled by the claimed invention which utilizes integrated circuit (IC) fabrication methods and micromachine manufacturing (MM) techniques to provide a class of close-space thermionic converters demonstrating relatively large current densities and relatively high conversion efficiencies as compared with thermionic converters that are presently available. Advantages and novel features will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. |
052451950 | abstract | X-ray attenuation, particularly for protective garments is provided by a film of a thermoplastic elastomer containing from about 60 to about 90 weight percent of barium sulfate or other barium salt. Films having a thickness of about 1 mm provide attenuation equivalent to that of about 0.2 to 0.25 mm of lead foil. The film is pliant, durable, and resistant to cracking from normal flexure during use and wear. |
050230433 | description | DETAILED DESCRIPTION OF THE INVENTION An actively cooled device according to the invention includes at least one, generally a plurality of, e.g. strip or plate shaped elements of a heat resistant material which are each brazed directly to at least one coolant conduit (cooling pipe). Preferably, the cooling pipe has a circular cross section and is brazed to the element to be cooled over its entire exterior surface or over part of the circumference of the exterior surface. To realize the best possible contact between the coolant flowing through the cooling pipe and the interior wall of the cooling pipe to be cooled, the coolant may also be conducted in a helical manner by guide metal sheets in the cooling pipe. A plurality of cooling pipes may be brazed to one body or element. Nonmetallic materials, among them graphite, are preferred as heat resistant materials so that hereinafter reference will be made to graphite elements. However, other heat resistant materials may correspondingly be used. For use in fusion reactors, the material should have a low atomic number Z. Suitable materials, other than graphite, are, for example, carbides such as SiC, TiC, B.sub.4 C, also TiB.sub.2, sintered materials, ceramics, metal ceramic composite substances and certain metals, such as beryllium. In addition to the dissipation of heat, the metal cooling pipe preferably also serves as mechanical support for the element to be cooled, particularly to absorb the weight of the element to be cooled and other forces acting on the element. This has the great advantage that the mount is at the temperature of the coolant and not at the temperature of the element to be cooled. The element to be cooled is mechanically fastened to the cooling pipe over a large area by way of the brazed connection in the recess, that is without screws, springs or similar fastening elements. The cooling pipe should be thin walled, i.e. its wall thickness should at most be about 10% of the exterior diameter. However, the wall thickness must be sufficient to avoid noticeable deformations during operation. A durable and resistant brazed connection of graphite and metal is assured only if the metal has at least approximately the same coefficient of thermal expansion as graphite. This requirement is met, for example, by high melting point metals, such as molybdenum and some molybdenum alloys. Since these materials are relatively expensive and difficult to work with and to weld, only those parts of the coolant conduit which are brazed to a graphite element are made of these metals while the remainder of the coolant conduits is manufactured of conventional materials, such as austenitic high-grade steel. The connection between the cooling pipes of molybdenum or molybdenum alloy and the parts of the coolant conduit made of other materials may be effected by a conical or cylindrical brazed connection. Preferably, this connection includes a shrink fit in that the coolant pipe is made of austenitic high-grade steel or another suitable material and encloses the cooling pipe of molybdenum or a molybdenum alloy in a shrink fit so as to relieve the brazed connection of mechanical tensile stresses. In plasma physical devices, the heat shield may be exposed to quickly changing magnetic fields. In this case, the cooling elements may be given a finger-like shape so that no conductive loops exist through which electromagnetic forces are generated which would excessively mechanically stress the heat shield. With a finger-like configuration of the cooling element, the coolant is supplied through a second coaxial pipe in the actual cooling pipe, with the cooling power being increasable by helical conduction of the coolant. One embodiment of a heat shield element for a fusion reactor in which the above points are considered is shown in FIGS. 1a through 1c. The heat shield element shown in FIG. 1 is a diverter plate element for an experimental fusion reactor of the ASDEX Upgrade type. It includes a plate-like element 10 of highly pure graphite, with the element having a weakly trapezoidal shape when seen in a top view. Element 10 has a planar top surface 12 which, during operation, faces a heat source, e.g. a plasma discharge. The underside is provided with a groove 14 having a U-shaped cross section and a semicircular bottom portion. A cooling pipe 16 having a circular cross section is seated in groove 14 and is brazed, over approximately somewhat more than half its circumference, to the surface of groove 14 of graphite element 12 as indicated in FIG. 1a by reference numeral 18. Alternatively, the front end (on the left in FIG. 1a) of groove 14 may be expanded to provide room for a cap (not shown) which is brazed to the end of the cooling pipe. The wedge-shaped gaps between the planar wall portions of the recess having the U-shaped cross section and the cooling pipe are filled with brazing material to provide the largest area possible for the heat conductive connection between the cooling pipe and the graphite element. In the illustrated embodiment of the invention, cooling pipe 16 was made of molybdenum and had an exterior diameter of 24 mm and a wall thickness of 2 mm. A 3 [percent] titanium, 27 [percent] copper, 70 [percent] silver alloy served as brazing material. The brazed connection between the graphite and the cooling pipe may also be made by means of another known brazing material, see, for example, U.S. Pat. No. 3,673,038. Other suitable hard solders are, for example, copper-titanium alloys, pure titanium, zirconium and their alloys. Since the ductility of the brazing materials decreases with increasing melting temperature (in the above examples a maximum of about 1670.degree. C.) and the connection thus becomes brittle and subject to cracking more easily, generally a brazing material will be employed which has the lowest possible melting point (melting point about 400.degree. K. above the operating temperature). Cooling pipe 16 is closed at one end and connected, at the other end, with a coolant conduit pipe 20, which is made of austenitic high-grade stainless steel. The connection between cooling pipe 16 of molybdenum or a molybdenum alloy and conduit pipe 20 of high-grade steel or another conventional material is effected by a brazed connection 22, with the inner diameter of conduit pipe 20 preferably being dimensioned such that conduit pipe 20 is seated on cooling pipe 16 in a shrink fit and brazed connection 22 is thus mechanically relieved. Coolant is supplied through an interior pipe 24 made, e.g., of high-grade steel and extending from a coolant distributor 26 coaxially into cooling pipe 16, ending shortly before the inner face of cap 17 which is provided with an annular flow deflection groove. At the front end of coolant supply pipe 24, guide metal spirals 28 are arranged in the space between pipes 24 and 16 in such a manner that a helical twist is imparted to the coolant flow, as indicated by arrows, so that the heat transfer between the interior wall of cooling pipe 16 and the coolant is improved. Thus, the coolant flows through the interior 30 of inner pipe 24 to the front end of cooling pipe 16 and then through space 32 between the two pipes 16 and 24, back to a coolant collecting pipe 34. The strip or finger-like shape of the heat shield elements shown in FIG. 1 avoids large, closed conductive loops in which alternating magnetic fields could generate undesirable forces. FIG. 2 shows a somewhat simplified cross section of part of a heat shield made of the elements according to FIG. 1. Since, in the above-mentioned experimental reactor, the diverter plates are nonuniformly thermally stressed, the thickness of the graphite elements was selected to be approximately proportional to the thermal stress so that uniform heating of the graphite elements is assured during a longer (e.g. 10 seconds) plasma discharge. FIG. 3 shows a somewhat different embodiment of a heat shield of the type shown in FIG. 2. The elements of the heat shield according to FIG. 3 include graphite elements 310 having parallelogram-shaped cross sections, so that interstices 311 between the individual graphite heat shield elements extend obliquely to surface 312 of the graphite elements. The heat shield according to FIG. 3 is optically tight if the heat source is localized in such a manner that no heat radiation can pass through interstices 311. FIG. 4 is a cross-sectional view of a heat shield which is also optically tight with respect to a spatially expanded heat source. As can be seen, the heat shield elements contain plate-shaped graphite elements 410 whose facing side faces are provided with V-shaped grooves 413 or wedge-shaped complementary projections 415 which project thereinto so that interstices 411 are angled. FIGS. 5a and 5b are cross-sectional views of heat shield elements having bent, plate-shaped graphite elements 510a and 510b, respectively, which have a convex surface 512a and a concave surface 512b, respectively, facing the heat source. On its side facing away from the heat source, graphite element 510a is brazed to two cooling pipes 16 and 16a, while graphite element 510b is brazed to a plurality of cooling pipes 16, 16a, 16b, . . . . Graphite elements 510a and 510b have an essentially uniform thickness. FIG. 6 shows an embodiment of the element of a heat shield according to the invention which includes a graphite body 610 having an approximately arc-shaped cross section, with its convex face 612 facing the heat source. The opposite side 617 is planar and is provided with three grooves into which three cooling pipes 616, 616a, 616b are brazed. The center cooling pipe 616a has a larger diameter than the two outer cooling pipes 616, 616b. Of course, the use of a plurality of cooling pipes for one graphite body and/or the use of cooling pipes having different diameters is not limited to the exemplary graphite element configurations shown in the drawings. Thus, if each graphite element is brazed to only one cooling pipe, not all cooling pipes need have the same diameter. The cooling pipe or cooling pipes may of course also be completely surrounded by graphite. For example, cooling pipes 16 of FIGS. 2 to 4 may also be brazed to a further graphite element at their side shown free in these figures as is indicated in dashed lines, for example, in FIG. 3 for one heat shield element. The cooling pipes may also be brazed over their full surface area into a corresponding bore of the graphite element. In the heat shield shown in FIGS. 7 and 8, the coolant is introduced from a feeder line 34a at the one, upper end of cooling pipe 16 and exits at the lower end of the cooling pipes into a collecting pipe 26a. At its inlet end, spiral metal guide sheets 28a are provided in cooling pipe 16 so as to impart a helical twist to the flow of coolant, as explained in connection with metal guide sheets 28 in conjunction with FIG. 1a. Conduits 26a and 34a simultaneously serve as mechanical mounts for the heat shield elements. Otherwise, the heat shield elements correspond to those of FIG. 1 so that further explanations are unnecessary. FIG. 8 is a sectional view in a plane VIII--VIII of FIG. 7 and shows how a plurality of heat shield elements can be arranged in juxtaposition. The grooves, into which the cooling pipes are brazed, here likewise have a U-shaped cross section and are somewhat deeper than one-half the exterior diameter of the respectively brazed-in cooling pipe. Of course, elements having different shapes can also be employed here, for example those shown in FIGS. 3 and 4. The above-described embodiments can of course be modified in various ways without limiting the scope of the invention. In particular, statements of materials, dimensions and intended applications must not be interpreted to be limiting. For example, molybdenum alloys or also less expensive materials, such as Ni-Fe or Ni-Fe-Co alloys can also be employed for the cooling pipes instead of molybdenum, if, for example, magnetic characteristics play no part and operating temperatures are not too high. |
046845020 | description | DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particularly to FIG. 1, there is shown an elevational view of a nuclear reactor fuel assembly, represented in vertically foreshortened form and being generally designated by numeral 20. Basically, the fuel assembly 20 includes a lower end structure or bottom nozzle 22 for supporting the assembly on the lower core plate (not shown) in the core region of a reactor (not shown), and a number of longitudinally extending guide tubes or thimbles 24 which project upwardly from the bottom nozzle 22. The assembly 20 further includes a plurality of transverse grids 26 axially spaced along the guide thimbles 24 and an organized array of elongated fuel rods 28 transversely spaced and supported by the grids 26. Also, the assembly 20 has an instrumentation tube 30 located in the center thereof and an upper end structure or top nozzle 32 attached to the upper ends of the guide thimbles 24 in accordance with the present invention which will be fully described below. With such an arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conventionally handled without damaging the assembly parts. As mentioned above, the fuel rods 28 in the array thereof in the assembly 20 are held in spaced relationship with one another by the grids 26 spaced along the fuel assembly length. Each fuel rod 28 includes nuclear fuel pellets (not shown) and is closed at its opposite ends by upper and lower end plugs 34,36. The fuel pellets composed of fissile material are responsible for creating the reactive power of the reactor. A liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through the guide thimbles 24 and along the fuel rods 28 of the fuel assemmbly 20 in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods (not shown) are reciprocally movable in the guide thimbles 24 located at predetermined positions in the fuel assembly 20. Since the control rods are inserted into the guide thimbles 24 from the top of the fuel assembly 20, the placement of the components forming the top nozzle 32 and the arrangement of parts to be described below for connecting the top nozzle to the guide thimbles must accommodate the movement of the control rods into the guide thimbles from above the top nozzle. Components of the Top Nozzle Turning now to FIGS. 1 to 3, there is shown an exemplary embodiment of the top nozzle 32 which is mounted on the guide thimbles 24 of the fuel assembly 20. The top nozzle 32 basically includes an upper hold-down plate 38, a lower adapter plate 40, a plurality of tubular alignment sleeves 42 disposed between the upper and lower plates 38,40, and a plurality of leaf spring assemblies 44 extending in inclined fashion between the upper and lower plates 38,40 along the peripheries thereof. The upper hold-down plate 38 has a plurality of passageways 46 defined therethrough, while the lower adapter plate 40 has a plurality of openings 48, the passageways 46 and openings 48 being arranged in respective patterns which are matched to that of the guide thimbles 24 of the fuel assembly 20. More particularly, upper end portions 50 of the guide thimbles 24 extend upwardly through the openings 48 in the lower adapter plate 40 and above the upper surface 52 thereof. A plurality of lower retainers 54 are attached, such as by brazing, to the guide thimbles 24 below the lower adapter plate 40 for limiting downwaard slidable movement of the adapter plate relative to the guide thimbles and thereby supporting the adapter plate on the guide thimbles with the upper end portions 50 thereof extending above the adapter plate. Each lower retainer 54 on one guide thimble 24 has a series of scallops formed on its periphery which are aligned with those of the fuel rods 28 grouped about the respective one guide thimble so that the fuel rods may be removed and replaced during reconstitution of the fuel assembly 20. The upper hold-down plate 38 is composed of an array of hubs 58 and ligaments 60 which extend between and interconnect the hubs. Further, a plurality of upstanding bosses 62 are integrally connected with, and extend above, the respective hubs 5. Each boss 62 has one of the passageways 46 defined therein. Additionally, each boss 62 is of a cross-sectional size adapted to interfit within one of a plurality of holes (not shown) formed in the upper core plate (not shown) of the reactor core. The upper circumferential edge 64 of each boss 62 is chamfered for mating with a complementarily chambered edge on the upper core plate at the entrance of the holes defined therein. Edges having such shapes act as guiding surfaces which facilitate alignment and insertion of the respective bosses 62 into the corresponding holes in the upper core plate during installation of the fuel assembly 20 within the reactor core. Each of the alignment sleeves 42 extends between an aligned pair of the passageways 46 and openings 48 of the upper and lower plates 38,40. As depicted at the right side of FIG. 3, there are threaded features on each sleeve 42 and on the upper end portion 50 of each guide thimble 24 for attaching the sleeve and guide thimble together. Also, there is a reusable locking arrangement, generally designated as 66, integrally associated with both the sleeve 42 and the guide thimble upper end portion 50 for locking the attached sleeve and guide thimble together. The reusable locking arrangement 66 comprises the invention disclosed and claimed in the third patent application cross-referenced above and need not be described in detail herein for an understanding of the subject matter of the present invention which will be described below. With respect to the threaded features on the guide thimble 24 and sleeve 42, the upper end portion 50 of the guide thimble has an annular externally threaded section 68, whereas the alignment sleeve has a lower annular internally threaded section 70. The sleeve 42 is mounted through the passageway 46 of the upper hold-down plate boss 62 for slidable movement relative thereto and rotatable movement relative to the guide thimble upper end portion 50 for threading and unthreading its internally threaded section 70 onto and from the externally threaded section 68 of the guide thimble upper end portion in order to attach and detach the top nozzle 32 onto and from the guide thimble 24. The sleeve 42 is hollow so that, in addition to accommodating insertion of a control rod through it, a suitable tool (not shown) can be inserted into the sleeve for gripping it internally to rotate it in either direction for threading on and unthreading from the upper end portion 50 of the guide thimble 24. When threaded on the guide thimble upper end portion 50, the sleeve 42 cooperates with the lower retainer 54 to clamp the adapter plate 40 therebetween. Finally, the upper hold-down plate 38 and the lower adapter plate 40 each have a rectangular configuration with a plurality of corners (preferably four in number) 72 and 74 defined on respective peripheries thereof being opposite to and vertically aligned with one another. The leaf spring assemblies 44 are interposed between the upper hold-down plate 38 and the lower adapter plate 40 so as to yieldably support the movable upper plate above the stationary lower plate. The leaf spring assemblies 44 are arranged along the respective peripheries of the upper and lower plates 38,40 and engaged with the plates adjacent predetermined ones of the peripheral corners 72,74 thereon. The arrangement of the leaf spring assemblies 44 comprises the invention disclosed and claimed in the fourth patent application cross-referenced above and need not be described in detail herein for an understanding of the subject matter of the present invention which will be described below. While the use of leaf springs is illustrated herein, the present invention can just as readily be used in top nozzles employing coil springs. Alignment Sleeve Capture Arrangement Referring now to the left side of FIG. 3, there is shown in the top nozzle 32 of the fuel assembly 20 the capture arrangmeent of the present invention, being generally designated by the numeral 76, for retaining each of the alignment sleeves 42 in slidable engagement with the upper hold-down plate 38 of the top nozzle when it is detached from one of the guide thimbles 24. The capture arrangement basically includes an annular cavity 78, an annular shoulder 80, an annular retainer 82 and a bearing ring 84. A continuous internal cylindrical wall 86 defines a bore 88 through the hub 58 and partially through the boss 62 of the upper hold-down plate 38 below and in communication with the passageway 46 in the boss. The alignment sleeve 42 used to attach the top nozzle 32 to each of the guide thimbles extends through the bore 88 as well as the passageway 46. The bore 88 has an inside diameter larger than the inside diameter of the passageway 46 so as to form the annular cavity 78 surrounding an upper portion 90 of the alignment sleeve 42 which extends axially through the bore 88 and passageway 46. Also, the annular shoulder 80 of the capture arrangement 76 which forms a transition on the upper plate 38 between the larger inside diameter of the bore 88 and the smaller inside diameter of the passageway 46 surrounds the alignment sleeve upper portion 90 and defines an upper limit of the annular cavity 78. The annular retainer 82 is threadably attached to the upper hold-down plate 38 and spaced below the shoulder 80. Being in the shape of a collar, the retainer 82 surrounds the alignment sleeve upper portion 90 and has a neck portion 92 with a central hole 94 through which extends the alignment sleeve 42. The neck portion 92 defines a lower limit of the annular cavity 78. The retainer 82 also has a hollow body portion 96 with one end 98 being externally threaded for connection to an internally threaded lower end 100 of the continuous wall 86 of the upper plate 38 defining the bore 88. An opposite end 102 of the retainer body portion 98 is integrally connected with the neck portion 92, and the retainer body portion defines a lower portion of the annular cavity 78. It is readily apparent that the positions of the annular shoulder 80 and retainer 82 as the upper and lower limits of the annular cavity 78 can be reversed. For assembling the alignment sleeve capture arrangement 76 it is only necessary that one of them be made detachable from the upper hold-down plate 38. Lastly, as also seen in FIG. 4, the bearing ring 84 of the capture arrangement 76 encircles and is attached to the alignment sleeve upper portion 90. The bearing ring 84 has a central passage 104 and an internal groove 106 which opens into the passage and into which an annular section 108 of the alignment sleeve upper portion 90 is bulge fitted for rigidly connecting the ring to the alignment sleeve. The upper portion 90 of the alignment sleeve 42 has a reduced diametric size compared to a lower portion 110 thereof such that a radially extending ledge 112 is defined at the transition between the alignment sleeve portions 90,110 on which the bearing ring 84 is also seated. The ring 84 has an outside diameter less than the inside diameter of the annular cavity 78 and greater than respective inside diameters of the annular shoulder 80 and retainer neck portion 92 which define the upper and lower limits of the cavity. Therefore, on the one hand, the bearing ring 84 can slide, along with the alignment sleeve 42 relative to the upper hold-down plate 38, within the cavity 78 between the upper and lower limits thereof as the upper hold-down plate 38 moves along the alignment sleeve 42 when the sleeve is attached to the guide thimble upper end portion 50. On the other hand, the bearing ring 84 will retain the alignment sleeve 42 slidably attached to the hold-down plate 38 when the sleeve 42 is detached from the guide thimble upper end portion 50. To assembly the alignment sleeve capture arrangement 76, first and the lower adapter plate 40 of the top nozzle 32 with the leaf spring assemblies 44 installed thereon is lowered onto the guide thimbles 24 and the alignment sleeves 42 are threaded onto the upper end portions 50 of the guide thimbles. (This initial assembly is carried out in the shop, not at a work station or in the core.) Next, the retainers 82 are slid down over the installed alignment sleeves 42 and then the bearing rings 84 are inserted on the sleeves to their rest positions on the ledges 112 thereof. After the rings 84 are bulge fitted to the sleeves 42 by a suitable tool inserted into the sleeves, the retainers 82 can be threaded into the upper hold-down plate 38. As shown in FIG. 3, the leaf spring assemblies 44 are not compressed and the bearing ring 84 is engaged with the lower limit of the cavity 78, that being the retainer neck portion 92, However, when the upper core plate (not shown) is placed over the fuel assembly 20, it presses on the upper hold-down plate 38 and compresses or deflects the spring assemblies 44. The upper hold-down plate 38 thus slides downwardly relative to each alignment sleeve 42 and the retainer 80 and bearing ring 82 move away from one another, the ring becoming displaced toward the upper limit of the cavity 78. The top end 114 of the sleeve upper portion 90 extends upwardly through the passageway 46 and above the boss 62 on the upper hold-down plate 38. It will be readily understood that the configuration of the annular cavity 78 allows concurrent rotation and vertical axial movement of the alignment sleeve 42 for threading it on and from the guide thimble upper end portion 50 to respectively attach and detach the sleeve on and from the guide thimble. Such concurrent rotation and vertical movement is allowed all the while the ring 84 on the sleeve 42 remains captured within the cavity 78. To remove the top nozzle 32 for reconstituting the fuel assembly 20, first, pressure is applied on the upper hold-down plate 38. This can be done either by a suitable fixture (not shown) or just by inserting a threaded bolt (not shown) through the upper hold-down plate 38 and threading it into a complementarily threaded bore (not shown) in the lower adapter plate 40. The alignment sleeves 42 are then rotated to unthread them from the guide thimbles 24. When the fixture is used, the upper plate 38 is then removed separately with the alignment sleeves 42 being taken with them in view of their captured condition. Then, the lower adapter plate 40 can be lifted off the guide thimbles 24. However, if the threaded bolts are used, the upper and lower plate 38,40 can be lifted off as unitary subassembly with the sleeves 42 still being retained in the upper plate. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely an exemplary embodiment thereof. |
claims | 1. A multiple blade collimator device for collimating a beam of high-energy radiation emanating from a substantially point-like radiation source for irradiation of a treatment object and for stereotactic conformation radio therapy of tumors, the collimator device containing a plurality of opposing collimator blades from radiation-absorbing material which can be positioned into an optical path of the radiation to define arbitrary collimator shapes, the collimator device comprising: rear blade parts; front blade parts, each front blade part being linked to one associated rear blade part to form one collimator blade and in such a fashion that substantially no gap is generated in a volume of the radiation-absorbing material, each front blade part having a front edge; means for linearly displacing each of said rear blade parts towards and away from a central axis of the radiation beam; and means for adjusting each of said front blade parts in dependence on a position of a respective rear blade part to which said front blade part is linked such that said front edge is always parallel to the optical path of the radiation. 2. The collimator device of claim 1 , wherein at least one of said linear displacement means and said adjusting means comprise a forced mechanical coupling between all positions of said rear parts and of said respective front parts to align said front edges. claim 1 3. The collimator device of claim 2 , wherein said forced coupling between said linear displacing means for said rear parts of said collimator blades and the adjusting means for said front parts is effected via transmissions. claim 2 4. The collimator device of claim 3 , wherein said transmissions for said collimator blades are disposed alternately above, for one collimator blade, and below, for a neighboring collimator blade. claim 3 5. The collimator device of claim 3 , wherein said adjusting mean for said front parts is designed to align said front edges with respect to the radiation source in response to an individual adjustment of said respective collimator blade as well as in response to an adjustment of at least some of said collimator blades. claim 3 6. The collimator device of claim 5 , wherein said adjusting means comprise a link member. claim 5 7. The collimator of claim 6 , wherein said link member comprises a connecting link guide rigidly cooperating with a bearing of a driving toothed wheel and a link guide slider cooperating with said front part. claim 6 8. The collimator of claim 7 , further comprising a base frame and displaceable collimator block halves rigidly connected to the bearings of driving toothed wheels, wherein each block half accommodates one group of said collimator blades and wherein said connecting link guide is rigidly connected to said base frame. claim 7 9. The collimator of claim 7 , further comprising a cable control mounted to said slider, guided towards said front part, and mounted at one end above an imaginary axis of rotation and at an other end below an imaginary axis of rotation of said front part. claim 7 10. The collimator device of claim 7 , wherein said link member comprises a double-armed lever having a rear end to which said slider is mounted, wherein said lever is disposed with a rotation axle on said rear part and with a front end on a rear region of said front part. claim 7 11. The collimator device of claim 3 , wherein said rear part has a collimator toothed rack into which a driving toothed gear engages. claim 3 12. The collimator device of claim 11 , wherein said collimator toothed rack associated with said rear part is designed as gearing in a longitudinal edge of said rear part. claim 11 13. The collimator device of claim 12 , further comprising a collimator block in which said collimator blades are disposed, wherein in a region of said gearing in said longitudinal edge, an adjacent rear part is vertically displaced in said collimator block such that, above said gearing, a guiding element which is connected to a side of said collimator block engages in a guiding groove of said rear part. claim 12 14. The collimator device of claim 11 , wherein said adjusting means comprise a front edge toothed rack linked to said front part outside of an axis of rotation thereof into which a toothed wheel engages to effect an adjustment path for said front part which differs than an adjustment path of said rear part for aligning said front edge. claim 11 15. The collimator device of claim 14 , wherein said collimator toothed rack and said front edge toothed rack are disposed at a longitudinal edge of said rear part and have different subdivisions for obtaining different adjustment paths, wherein a toothed wheel engages both toothed racks with a subdivision difference lying within gearing tolerance limits. claim 14 16. The collimator device of claim 15 , wherein a subdivision of said front edge toothed rack, disposed below a collimator blade, is larger than a subdivision of said collimator toothed rack. claim 15 17. The collimator device of claim 15 , wherein a subdivision of said front edge toothed rack, disposed above said collimator blade, is smaller than a subdivision of said collimator toothed rack. claim 15 18. The collimator device of claim 15 , further comprising a collimator block in which said collimator blades are disposed and a base frame supporting said collimator block, wherein said toothed wheel is disposed in a displaceable collimator block and further comprising an additional toothed wheel engaging said collimator toothed rack and said front edge toothed rack and disposed on said base frame for displacing said collimator block relative to said base frame. claim 15 19. The collimator device of claim 14 , further comprising a base frame in which said toothed wheel is disposed. claim 14 20. The collimator device or claim 14 , further comprising a collimator block in which said collimator blades are disposed, wherein said toothed wheel is disposed in said collimator block to simultaneously serve as a driving toothed wheel. claim 14 21. The collimator device of claim 1 , wherein said front parts are substantially semi-circular bodies which are securely disposed in corresponding recesses at a front end of said rear parts, wherein said adjusting means generate a pivoting motion about an imaginary axis of rotation lying in a circular center of said semi-circular body. claim 1 22. The collimator of claim 21 , wherein a height of said rear part substantially corresponds to a diameter of said semi-circular body, wherein front ends of said rear parts are set back to allow all required inclined positions of said front edges of said front blade parts. claim 21 23. The collimator of claim 1 , wherein cross-sections of said front parts and said rear parts have an asymmetrical trapezoidal shape such that side surfaces thereof extend approximately parallel to the optical path, and further comprising limitations within which the front and rear blade parts are mounted, wherein said limitations have inner surfaces bordering outer collimator blades which extend at an inclined angle to abut these outer collimator blades without leaving gaps. claim 1 24. The collimator device of claim 23 , wherein said front parts have sufficient lateral play to permit adjustment, despite their trapezoidal shapes. claim 23 25. The collimator device of claim 1 , wherein said front edges can be displaced beyond a center line of a possible collimator opening. claim 1 26. The collimator device of claim 1 , wherein each collimator blade comprises an individual displacing means and an individual adjusting means each of which can be individually controlled. claim 1 27. The collimator device of claim 1 , further comprising a computer communicating with at least one of said displacing means and said adjusting means to adjust a contour and position of a collimator opening with respect to the radiation object in a respective direction of radiation, wherein said computer obtains adjustment data from a device for detecting a shape of the radiation object and further comprising a control means to examine a result of said contour adjustment. claim 1 28. The collimator device of claim 1 , further comprising a collimator block in which said collimator blades are disposed for positioning a collimator opening relative to the radiation object and the radiation source. claim 1 29. The collimator device of claim 28 , further comprising a gantry on which said collimator block is disposed, said gantry effecting relative motion between said collimator block and a patient such that the patient can be exposed to radiation from all sides, wherein a collimator opening is adjusted to the shape of the radiation object. claim 28 30. The collimator of claim 1 , wherein at least one longitudinal edge of said rear part has a guide. claim 1 31. The collimator of claim 30 , further comprising a collimator block in which said collimator blades are disposed, wherein said guide is a groove in said longitudinal edge in which a guiding element, cooperating with or integral with said collimator block, slides. claim 30 32. The collimator of claim 1 , wherein said displacing means function as compensating means for generating different radiation intensities via temporary insertion of collimator blades into a collimator opening during irradiation. claim 1 |
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claims | 1. A method for imaging an object of interest using penetrating radiation, comprising:(a) positioning a source of penetrating radiation and a radiation detector externally of the object of interest and with the object of interest positioned therebetween;(b) repeatedly measuring the penetrating radiation generated by the source of penetrating radiation and passing through the object of interest along each of at least one linear path extending from the source of penetrating radiation to the radiation detector and intersecting the object of interest, by: (i) exposing the object of interest to the penetrating radiation thereby allowing the radiation to pass through said object, and (ii) detecting the penetrating radiation which passes through the object of interest along each of the at least one linear path, thereby to generate a plurality of measurements for each of the at least one linear path;(c) processing the plurality of measurements for each of the at least one linear path to obtain at least one statistical parameter capable of describing a width of a temporal distribution of the plurality of measurements for each of the at least one linear path, and(d) reconstructing the image of the object of interest based on the at least one parameter describing the distribution of the plurality of measurements, thereby obtaining images of the object of interest. 2. The method of claim 1, characterized in that the penetrating radiation is detected with a detector and said measurements are obtained from signals generated by said detector. 3. The method of claim 1, characterized in that the at least one statistical parameter is capable of describing an error of the width of the temporal distribution of the plurality of measurements. 4. The method of claim 1, characterized in that the at least one statistical parameter is selected from a variance, a standard deviation, expected deviation, average absolute deviation or a moment of the distribution of the plurality of measurements obtained using the penetrating radiation. 5. The method of claim 1, characterized in that the method further includes obtaining at least one other statistical parameter capable of describing the center of the temporal distribution of the plurality of measurements for each direction of detection, and reconstructing another image of the object of interest based on the at least one other parameter. 6. The method of claim 5, characterized in that the at least one statistical parameter includes a statistical parameter capable of describing an error of the center of the temporal distribution of the plurality of measurements. 7. The method of claim 5, characterized in that the at least one other statistical parameter is selected from a mean, an average, an expected value, a median or a mode. 8. The method of claim 1, characterized in that the penetrating radiation is selected from electron beams, gamma radiation, infrared radiation, infrasound, ion beams, microwaves, radio waves, shock waves, sound, terahertz radiation, ultrasound, ultraviolet radiation, visible light, or x-rays. 9. The method of claim 1, characterized in that said plurality of measurements is selected from a plurality of intensity measurements, attenuation measurements and a field strength measurements. 10. An image processing method for determining relative movement of structures within an object of interest, comprising:(a) positioning a source of penetrating radiation and a radiation detector externally of the object of interest and with the object of interest positioned therebetween;(b) repeatedly measuring a penetrating radiation generated by the source of penetrating radiation and passing through the object of interest along each of at least one linear path extending from the source of penetrating radiation to the radiation detector and intersecting the object of interest, by: (i) passing the penetrating radiation through the object of interest, and (ii) detecting the penetrating radiation which passes through the object of interest along each of the at least one linear path, thereby to generate a plurality of measurements for each of the at least one linear path;(c) processing the plurality of measurements for each of the at least one linear path to obtain at least one parameter which describes a fluctuation of the plurality of measurements for each of the at least one linear path, and(d) reconstructing an image of the object of interest based on the at least one parameter, wherein said reconstructed image based on the fluctuation of the plurality of measurements provides information on the relative movement of structures within the object of interest. 11. The image processing method of claim 10, characterized in that the at least one statistical parameter which describes a fluctuation of the plurality of measurements is a statistical parameter capable of describing the width of the temporal distribution of the plurality of measurements for each direction of detection. 12. The image processing method of claim 10, characterized in that the at least one statistical parameter is selected from a variance, a standard deviation, expected deviation, average absolute deviation or a moment of the distribution of the plurality of measurements obtained using the penetrating radiation. 13. The image processing method of claim 10, characterized in that the penetrating radiation is detected with a detector and said measurements are obtained from signals generated by said detector. 14. The image processing method of claim 10, characterized in that the penetrating radiation is selected from electron beams, gamma radiation, infrared radiation, infrasound, ion beams, microwaves, radio waves, shock waves, sound, terahertz radiation, ultrasound, ultraviolet radiation, visible light, or x-rays. 15. A system for reconstructing an image of an object of interest comprising:(a) a source configured to emit penetrating radiation positioned externally of the object of interest;(b) a detector sensitive to said penetrating radiation positioned externally of the object of interest and opposite said source with respect to the object of interest, said detector configured to repeatedly measure the penetrating radiation generated by the source and passing through the object of interest along each of at least one linear path extending from the source of penetrating radiation to the radiation detector and intersecting the object of interest;(c) a processor having at least one algorithm that calculates at least one statistical parameter capable of describing a width of a temporal distribution of the plurality of measurements for each of the at least one linear path; and(d) an image reconstruction processor that reconstructs the image of the object of interest based on the at least one parameter describing the distribution of the plurality of measurements. 16. The system of claim 15, characterized in that said system further comprises means for holding the object of interest in a position relative to the source of penetrating radiation and the detector. 17. The system of claim 15, characterized in that said system further comprises rotational and translational means linked to the holding means for allowing collection of the substantially emitted penetrating radiation through the object of interest along a plurality of directions of detection. 18. The system of claim 15, characterized in that said system further includes a system controller means linked to said detector, said data processor means and said image reconstruction processor means for controlling the substantially emitted penetrating radiation, the production of measurements, and the processing and reconstruction of the measurements. 19. The system of claim 18 further comprising a computer linked to the system controller means. 20. The system of claim 19 characterized in that said computer includes input means for controlling the imaging system and means for storing the plurality of measurements. 21. The system of claim 15, characterized in that said penetrating radiation is selected from electron beams, gamma radiation, infrared radiation, infrasound, ion beams, microwaves, radio waves, shock waves, sound, terahertz radiation, ultrasound, ultraviolet radiation, visible light, or x-rays. 22. The system of claim 15, characterized in that said system is an environmental transmission electron microscope system, and wherein said penetrating radiation is electron beams. 23. The system of claim 15, characterized in that said system is an x-ray apparatus, and wherein the penetrating radiation is x-rays. 24. The system of claim 15, characterized in that the processor has another algorithm for calculating a statistical parameter capable of describing an error of the width of the temporal distribution of the plurality of measurements. 25. The system of claim 15, characterized in that the processor includes another algorithm for calculating a statistical parameter capable of describing a center of the temporal distribution of the plurality of measurements. 26. The system of claim 15, characterized in that the processor includes another algorithm for calculating a statistical parameter capable of describing an error of a center of the temporal distribution of the plurality of measurements. 27. The system of claim 15, characterized in that said measurements are obtained from signals generated by said detector. |
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052746860 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawings wherein like numerals represent like parts throughout the figures, a portion of a fuel assembly for which the present invention has application is generally designated by the numeral 10. Fuel assembly 10 is employed in a nuclear reactor and includes a plurality of fuel rods 20 which are mounted to a lower support grid 30. The fuel rods have a cladding tube 40 which contains fissionable fuel pellets 50. The cladding tube 40 is manufactured from a zirconium-alloy or other suitable alloy. The invention will be primarily described with reference to a zirconium-alloy cladding tube. In accordance with the invention, the cladding tubes have a coating 60 on at least a portion of the outside surface. The coating 60 is a thin film composed substantially of zirconium nitride. The film may have a thickness on the order of approximately 5 microns. The relative dimension of the coating 60 is exaggerated in FIG. 2. The thin film of zirconium nitride is wear resistant, and constitutes a barrier which resists corrosion of the tube substrate. Because of the relative thin film thickness, e.g., approximately 5 microns, the outer diameters of the coated cladding tubes or fuel rods do not significantly increase the coolant flow resistance through the fuel assembly 10. While the thin film of zirconium nitride may be applied to the zirconium-alloy cladding tube along substantially the entire length of the tube, the thin film is especially advantageous in the region 42 below the support grid where the tube is particularly susceptible to debris fretting due to the metallic particles and the high pressures and high temperatures of the surrounding water. In addition, the zirconium nitride coating may be applied in the region 44 of the cladding tube which engages the lower support grid 30 to enhance the corrosion and wear resistance of the tube. The zirconium nitride coating 60 is reactively deposited on the zirconium-alloy cladding tube 40 by means of an anodic ion plating process in apparatus 70 such as described, for example, in the following documents: H. Ehrich, "The Anodic Vacuum Arc. I. Basic Construction and Phenomenology", J. Vac. Sci Technol. A, 6, 134 (1988). H. Ehrich et al, "The Anodic Vacuum Arc. II. Experimental Study of Arc Plasma", J. Vac. Sci. Technol. A, 6, 2499 (1988). S. Meassick et al, "Anodic Vacuum Arc Deposition Processes", International Conference on Metallurgical Coatings and Thin Films, Apr. 22-26, 1991. S. Meassick et al "Investigation of the Properties of Type 303 Stainless Steel Thin Films Deposited with the Anodic Vacuum Arc", Mat. Res. Lett., 11, 66 (1992). A schematic representation of a prototype apparatus is shown in FIG. 3. The vacuum chamber 72 is pumped via a diffusion pump 74 to a base pressure of approximately 1.times.10.sup.-6 Torr. During operation of the anodic arc the pressure in the chamber rises to approximately 1.times.10.sup.-5 Torr. The cathode 76 consists of either a carbon, tungsten or zirconium rod 2.5 cm in diameter surrounded with a ceramic shield 78 so that there is no line of sight to the target fuel rod cladding tube 40. The anode 80 is constructed of a crucible into which the source material to be evaporated is placed. The crucible allows for the use of a substantial amount of material (on the order of 10 grams), and allows the direction of the metal vapor plasma to be tailored. Either tungsten or ceramic crucibles can be used. In the case of tungsten, part of the arc current is intercepted by the crucible, thereby indirectly heating the crucible. This indirect heating places limits on the current at which the arc can be run so that the material evaporated does not overheat and cause nucleate boiling. The crucible can also be constructed of a ceramic material (Al.sub.2 O.sub.3) in which case a separate tungsten electrode can be used to carry current to the anode material. This arrangement has the advantage that all of the current flows into the anode material, thereby heating its surface and greatly diminishing the chances of nucleate boiling. The anodic arc is powered by a low voltage dc power supply 82 (100 V, 100 A), operated in a current regulating mode, through a current limiting resistor 84. During anodic arc operation the arc voltage is approximately 17-20 V, and in conjunction with radiation at the most intense spectral line of the evaporated material is characteristic of proper arc operation. Ignition of the anodic arc occurs by physically contacting the anode 80 and cathode 76 together, thereby initiating a cathodic arc which transitions to the steady state anodic arc after approximately one second. After contact of the electrodes, one or more slowly moving cathode spots appear on the cathode 76, severely eroding it. In this phase the arc is sustained by cathodic material. The anode is heated due to ohmic heating and ion bombardment. Eventually, the anode 80 heats up sufficiently so that anode material is evaporated at which time the color of the arc changes to that of the most intense spectral line of the anode material and the cathode spots transform into many, rapidly moving spots that no longer erode the cathode. The anode to substrate distance is adjustable to approximately 45 cm. The substrate holder 86 is biasable positive or negative to approximately 300 V with a negative bias usually applied in order to accelerate ions into the target 40. The dc bias is applied via a low voltage (approximately 300) dc power supply 88. The rate of evaporation, and therefore deposition, are dependent on the arc current. Zirconium is the preferred anodic source material at 80, so that ZrN is reactively formed in chamber 72 with nitrogen supplied at 90 as backfill gas after evacuation. Titanium, to reactively form TiN, can also be used. Other anodic source materials that form nitrides in accordance with the invention, include hafnium (HfN), chromium (CrN), and tantalum (TaN). Materials can alternatively include TiAlVN, Cr, TiCN, TiC, CrC, ZrC, and NiTaB. In work performed by the investigations cited above, evaporation rates of approximately 0.04 g/min/Amp (3.2 g/min at 80 A) were achieved for type 303 stainless steel anodes while evaporation rates of 0.06 g/min/Amp were achieved for Aluminium. The maximum evaporation rate from the anode 80 is only limited by the current available from the dc power supply 82 (100 A). The coatings deposited with the anodic vacuum exhibited good adherence to the substrate. Cellophane tape tests were used for the initial analysis. Indentation tests were performed for a more objective measure of the adherence of the film. In these tests, the surface of the substrate was dented with a diamond tipped probe and the cracking, delamination or spalling of the coatings near the dent was visually observed. The coatings deposited with the anodic vacuum arc showed no delamination of spalling and only minimal cracking around the edge of the dent. Deposition rates of up to 6 .mu.m/min were achieved at a distance of approximately 20 cm from the anode with an arc current of 80 A. The deposition rate decreases as the square of the anode to target separation. It is evident that there is a material dependent threshold current for deposition. Above this threshold current, the deposition rate increases linearly with current. Below a threshold current the voltage-current characteristic is negative (negative resistance). This threshold current is again material dependent and occurs at approximately the same current as the threshold current for deposition. The threshold current for deposition is probably due to the fact that the anode must be heated sufficiently in order to allow evaporation to occur. Since radiation and conduction will be the primary cooling mechanisms of the anode before there is rapid evaporation, a larger heating current will be required for materials with a higher boiling temperature. Below this threshold voltage the arc is operating at least partially as a cathodic arc with cathode spots that cause erosion of the cathode. Above the threshold voltage, in addition to their rapid motion over the cathode, the cathode spots no longer cause erosion and the inclusion of cathode material in the coating. Thus, when operated in the anodic mode, the cathode spots are different in nature. The stoichiometry of the coatings showed that they were pure as far as could be determined with the EDS system. The deposited thin films were examined with a scanning electron microscope (SEM) in order to ascertain the surface roughness and defect densities of the films. There were no discernable surface feature down to the resolution limit of the instrument (.about.4 nm). In addition, the surface was found to be free of macroparticle inclusions. In order to evaluate the protective qualities of coatings deposited with the anodic vacuum arc, coatings of type 303 stainless steel, aluminium and nickel were deposited on iron substrates. The arc current for all samples used in the corrosion tests was 80 A. The corrosion inhibiting properties of these coatings against humid and marine environments was evaluated using salt spray fog testing according to standards ASTM B117 (10.about.) and MIL-STD 202F method 101D(11). Each sample was exposed to a salt spray environment at a temperature of 35.degree. C. a humidity of 85% and a spray solution consisting of 5% NaCl dissolved in water. Tests were conducted for up to 48 hours on the samples. The 0.75 .mu.m thick aluminium coating provided almost complete protection from corrosion. It is believed that the coating of ZrN will have similar effects on Zircalloy cladding corrosion. Coatings having a thickness in the range of about 3-7 microns should prove satisfactory. This is in stark contrast to coatings deposited with a cathodic arc which seem to require coating thicknesses on the order of 20 .mu.m in order to provide similar corrosion protection. While the 20 .mu.m thickness was from deposition rates substantially higher than used in commercial cathodic arc coaters, resulting in a large number of macroparticles that are large in size, the thickness of the protective coating must be greater than the macroparticle size for effective corrosion protection. The relatively poor protective properties of cathodic arc coating is due to the voids that are created by the inclusion of macroparticles in the coating for the cathodic arc, allowing the salt spray to penetrate to the substrate. The coatings produced with the anodic arc have no discernible surface texture and were amorphous in nature. An investigation of the protective properties of anodic arc coatings against salt spray indicates that even thin coatings can reliably protect a sample against corrosion. |
042723205 | description | DETAILED DESCRIPTION The high density target of this invention referred to hereinafter as a ball and shell target, is particularly advantageous for use with high power laser systems such as the above-referenced Shiva glass laser which provides sufficient energy for obtaining both high fuel densities and temperatures, not obtainable with other glass laser systems. A cryogenic DT shell with 20 TW of absorbed power can give a thermonuclear yield of several times the absorbed energy if the energy can be deposited into a Maxwellian distribution of electrons on a target with a 10-100 A surface finish. Using the laser pulses indicated in Table I, a shell of DT with an internal diameter (i.d.) of 250.mu. and 90.mu. thickness is impulsively accelerated to minimize the effects of Rayleigh-Taylor instability. TABLE I ______________________________________ TIME (SH) POWER (WATTS) PULSE ______________________________________ .0 6 .times. 10.sup.10 Constant .05 6 .times. 10.sup.10 Power .25 3 .times. 10.sup.11 Constant .27 3 .times. 10.sup.11 Power .3525 1.5 .times. 10.sup.12 Constant .3675 1.5 .times. 10.sup.12 Power .3875 5 .times. 10.sup.12 Linear Ramp .450 2 .times. 10.sup.13 Constant Power .470 2 .times. 10.sup.13 ______________________________________ Its calculated performance under various physical models is given in Table II. TABLE II ______________________________________ ENERGY ABSORBED NON-CLASSICALLY = 8.5 KJ INPUT ENERGY = 9.3 KJ .alpha. 3-T 1 2 2 4 4 ______________________________________ Inhibited Conduction NO NO NO YES NO YES Yield 23. KJ 8. KJ .53 KJ 3.28 J .131 KJ 1.55 J .rho..sup..GAMMA. MAX .91 .78 .20 .057 .046 .037 MAX AVG. FUEL .rho. 1280. 990. 135. 11.7 9.7 5.6 MAX AVG. FUEL TEMP 9.2 5.6 3.2 1.33 3.5 1.21 MAX FUEL VELOC- ITY .77 .76 .72 .38 .65 .38 (AT .rho.c) T.sub.e MAX 4.5 4.3 4.1 9.5 4.0 8.7 ______________________________________ If the energy is absorbed into a superthermal spectrum, the target performance is severely degraded, as shown. Recent experiments using the two beam Janus laser system are matched fairly well by a physical model that assumes an .alpha..about.4 and some inhibition of electron conduction, the last column in Table II. Alpha is the ratio of the effective temperature of the superthermal electrons to that of the main body electrons. Electron conduction inhibition in these calculations is based on a model for the onset of ion-acoustic turbulence, although such inhibition could come from magnetic fields as well. As shown at the top of Table II, with a pure DT target, less than 9% (8.5) of the absorbed energy was accounted for by inverse bremsstrahlung. The rest must be accounted for by non-classical processes which produce superthermal electrons. The inverse bremsstrahlung could be enhanced both by using a higher Z ablator and by frequency doubling. The combination of these two could lead to a considerable performance improvement. For the target compatible with the Shiva laser system, it is assumed that 10 TW of absorbed power is achievable and that only 1.mu. light will be available. The superthermal electrons result in a drop in the driving pressure one achieves. They also preheat the fuel which then is harder to compress. Within the constraints of this model, it is possible to pursue two lines of experiments, one which gives a larger yield but lower density than the bare DT shell, and the other which gives higher density but lower yield. DT gas-filled glass shells, generally similar in design to the exploding pusher targets imploded by the Janus laser system, give thermonuclear yields of about 1/2% of the absorbed laser energy. This is much better performance than targets previously used because the laser energy is better matched to the targets size and the density-radium (.rho.r) of the fuel is an order of magnitude higher. Mean fuel temperatures of greater than 10 keV are calculated. Such a target has the virtue of being able to tolerate large asymmetries in the absorbed energy and can be imploded without the necessity of producing a low density corona or atmosphere prior to the implosion. An embodiment of the target of this invention, referred to as a ball and shell target, shown in the drawing, is for 10 TW absorbed power and is capable of producing high densities. Referring now to the drawing, this target comprises a ball, generally indicated at 10, composed of a shell 11 of high-Z material, such as Au, which contains a quantity of gaseous DT fuel 12, shell 11 acting as a pusher and a preheat shield; surrounding ball 10 in spaced relation is an ablator-pusher shell 13 of lower-Z, lower density material, such as SiO.sub.2, defining a space containing a low-density material 14, such as CH (plastic foam), the CH serves to support the ball 10 within shell 13. By way of example, the Au pusher shell 11 has an inner radius of 0.0057 cm, an outer radius of 0.0068 cm (wall thickness of 0.0011 cm), a density of 19.3 gm/cm.sup.3, and a mass of 10.46 .mu.gm; the DT fuel has a density of 0.05 gm/cm.sup.3 and a mass of 0.0388 .mu.gm; the SiO.sub. 2 ablator-pusher shell 13 has an inner radius of 0.0400 cm, an outer radius of 0.0420 cm (wall thickness of 0.0020 cm), a density of 2.5 gm/cm.sup.3, and a mass of 105.6 .mu.gm; and the CH material 14 has a radial thickness of 0.0332 cm, a density of 0.02 gm/cm.sup.3, and a mass of 5.33 .mu.gm. It is not intended to limit the target to the specific materials and parameters exemplified above in that the pusher shell 11 could also be made of high-Z materials such as uranium (U), iron (Fe) and silver (Ag) or a mixture of selected high-Z materials, (Z of 26 and above), with an inner radius ranging from 0.005 cm to 0.01 cm and an outer radius of from 0.0055 cm to 0.012 cm. In addition the pusher could have an inner layer of lower-Z material such as SiO.sub.2 to act as a mandrel for fabrication purposes. The ablator-pusher shell 13 could be also composed Be, LiH, C, CH.sub.2, and B.sub.n H.sub.m (Z of 3 to 6) having an inner radius ranging from 0.03 cm to 0.05 cm, and an outer radius of from 0.04 cm to 0.0600 cm. The outer shell could also be a composite shell with an inner layer of higher-Z low density material such as TaCOH or SiO.sub.2. The low-density material 14 could also be composed of any low density gas or foam having a density of 10.sup.-4 to 10.sup.-1 gm/cm.sup.3. Also, the fuel 12 could vary in density from 0.01 to 0.21 gm/cm.sup.3 of DT or be composed of a solid hollow shell, or be composed of other gaseous or solid fuels such as LiD.sub..5 T.sub..5, D.sub.2, or B.sub.n D.sub.m T.sub.p. Should gaseous material be utilized as low density material 14, pusher shell 11 will be suspended within outer shell 13 by conventional support means, such as spiders, etc., well known in the art. Using the pulse shape of Table III, mean fuel densities of the above-exemplified target approach 150 g/cc with a yield of 4.times.10.sup.10 neutrons. TABLE III ______________________________________ TIME (SH) POWER (WATTS) PULSE ______________________________________ .0 10.sup.11 Constant .01 10.sup.11 Power .4 10.sup.13 Constant .42 10.sup.13 Power .43 5 .times. 10.sup.12 Linear .61 2 .times. 10.sup.13 Ramp ______________________________________ If, instead of supporting the ball 10 by the low density foam 14, as described above, it is levitated in density 10.sup.-4 g/cc gas atmosphere, the yield would be an order of magnitude higher. However, if a Maxwellian electron spectrum is generated, and a gas fill between ball 10 and shell 13 is used, then the target yields about 1/5 of breakeven. Illumination uniformity requirements are quite severe for the ball and shell target, illustrated in the drawing, in the absence of a preformed low density corona. LASNEX calculations indicate that the implosion pressures must be uniform to .+-.1% to achieve the densities indicated above. Since asymmetries of .+-.10-20% in laser intensity are expected--some corona may be necessary. This could be accomplished by surrounding the ablator shell with a 0.0001 cm thick, 0.0700 inner radius shell of SiO.sub.2 and filling the space with H.sub.2 having a density of 10.sup.-4 gm/cm.sup.3 and mass of 0.1 .mu.gm. A corona, or atmosphere, is a region of some thickness beyond the ablation surface that is penetrated supersonically by the energy deposited by the laser. This region allows electron conduction to smooth asymmetries in the absorbed energy before that energy is used to generate hydrodynamic motion of the target. To perform this function, the material in the corona must be raised to a high temperature. Theoretical calculations for a constant density corona, at a density just above the critical density for the laser being used, indicates that for a given thickness atmosphere, the required temperature is proportional to .lambda..sup.-1, where .lambda. is the laser wavelength. Similar estimates indicate that the energy required to heat the corona is proportional to .lambda..sup.-3 and that the shock generated by the prepulse used to heat the atmosphere is proportional to .lambda..sup.-7/3. It is this last effect which makes use of a high density atmosphere very difficult. Certain goals, such as the implosion of a DT shell to a density of 1000 g/cc, can only be achieved if the initial shock is limited to about one megabar. But heating a 300.mu. thick atmosphere, as exemplified above, at the critical density of 1.mu. light to the required temperature results in a 40 megabar shock. For such implosions, a 2.mu. laser will probably be required for the early part of the implosion. Because the illustrated target, modified as above to include an atmosphere, is not a low entropy implosion and because the low density foam between ablator shell 13 and ball 10 cushions the shock, it can survive the initial large shock generated by the explosion of the atmosphere forming layer about ablator shell 13. Initial 2-D calculations indicate one can probably tolerate .+-.10% asymmetries in absorbed power using an atmosphere generated in this fashion. The target illustrated in the drawing can also be modified in several other ways, which produces results intermediate those discussed above. For example, if a single thick glass shell is used, such as 13, the fuel will implode to higher density and low temperature than for the thin glass exploding pusher shell previously utilized. A similar effect is obtained by coating a high-Z material on the inside of the glass shell 13. Both of these get higher density than the exploding pusher glass shell but lower density than the atmosphere containing shell configuration described above. It has thus been shown that the present invention provides a high density laser-driven target that is compatible with high power laser systems such as the Shiva glass laser whereby both higher fuel densities and temperatures can be obtained. While particular embodiments of the invention have been illustrated and/or described, modifications will become apparent to those skilled in the art, and it is intended to cover in the appended claims all such modifications as come within the spirit and scope of the invention. |
044926685 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing and initially to FIGS. 1-3, there is illustrated a new and improved device or apparatus 20 and method for preventing the rotation of an elongated rod 22 about its longitudinal axis in a nuclear fuel assembly. The elongated rod 22 is disposed between spaced-apart plates of the nuclear fuel assembly, for example, an upper tie plate and a lower tie plate, and may be a spacer capture fuel rod, a spacer capture water moderator rod, a spacer capture rod other than a fuel rod or a water moderated rod, a fuel rod, a water moderator rod, or any other elongated rod in a nuclear fuel assembly. The rod 22 includes a thin wall cylindrical tube 24 that is normally terminated at its upper end by an upper end plug (not illustrated). The device 20 includes a lower end plug 26 that is welded to and terminates the lower end of the tube 24. The lower end plug 26 is of a two-piece construction consisting of a cylindrical body 28 that is welded to the lower end of the tube 24 and a stud portion or member 30 having a threaded lower end 32 for receipt of locking or retaining means, such as a locking or retaining nut or washer (not illustrated). The stud member 30 may be joined to the cylindrical body 28 by any convenient means, such as welding. The cylindrical body includes a pair of diametrically oppositely disposed, longitudinally extending, internal flat portions or flats 34 formed at the lowermost end of the cylindrical body 28. The outer surface of the flats 34 is tapered radially or chamfered to provide lead in surfaces 36 to facilitate the insertion of the rod 22 through the cells of the spacer grids during the assembly of the nuclear fuel assembly. In accordance with an important feature of the present invention, the flats 34 are configured to seat against and engage a pair of diametrically oppositely disposed, elongated external or out-of-cavity flat portions or flats 38 formed on the upper outer surface of a cylindrical boss or sleeve 40 of a lower tie plate of a nuclear fuel assembly positioned at the intersection of four, transversely disposed, elongated, web portions or members 42 of a lower tie plate of a nuclear fuel assembly. The circumferentially enclosed cylindrical boss or sleeve 40 also includes a circumferentially enclosed internal cavity 43 through which the lower portion of the stud member 30, including its threaded lower end 32, passes for subsequent retention therein by the receipt of suitable locking or retaining means. Thus, the rod 22 may be secured to the lower tie plate of the nuclear fuel assembly in such a manner as to prevent its rotation about its longitudinal axis by the receipt of the stud portion 30 within the cavity 43 of the sleeve 40 such that the flats 34 seat against and engage the flats 38 disposed outside of the cavity 43 of the sleeve 40. Subsequently, locking means, such as a retaining nut (not illustrated), is installed in engagement with the threaded lower end 32 of the stud portion 30 to retain the flats 34 seated against and in engagement with the flats 38, thereby to prevent the rotation of the rod 22 about its longitudinal axis. In accordance with an important feature of the present invention, an alternate embodiment of a device 20' (FIGS. 4-7) for preventing the rotation of an elongated rod 22 about its longitudinal axis includes a lower end plug 44 welded to the lower longitudinal end of the tube 24. Preferably, the lower end plug 44 is formed as a unitary member, although it could also be formed as a multiple-piece construction in the same manner as the lower end plug 26. The lower end plug 44 includes an upper cylindrical body portion 46 having four elongated grooves 48 formed therein that have longitudinal axes parallel to the longitudinal axes of the lower end plug 44 and of the rod 22. Preferably, the four grooves 48 are disposed 90.degree. apart about the periphery of the body portion 46 to form a spline. The lowermost portion of the portion 46 is tapered radially or chamfered to provide lead in surfaces 36 to facilitate the insertion of the rod 22 through the cells of the spacer grids during the assembly of the nuclear fuel assembly. The lower end plug 44 further includes a lower elongated stud portion 50 of a reduced diameter, as compared to the body portion 46, terminating in a threaded lower end 52. The grooves 48 are configured to receive and engage four, radially inwardly protruding, key members 54 disposed 90.degree. apart at the upper end of an anti-rotation sleeve 56. The inner bore 58 of the anti-rotation sleeve 56 is preferably configured to be slightly larger than the outer diameter of the cylindrical boss or sleeve 40 disposed at the intersection of the four, transversely disposed, elongated, web portions or members 42. A lower end 60 of the sleeve 56 includes four, longitudinally extending, elongated slots 62 disposed 90.degree. apart about the periphery of the sleeve 56 for the receipt of and the engagement by the web portions 42. Preferably, the sleeve 56 is secured to the lower tie plate of the fuel assembly by any convenient means, for example, by tack welding to the web portions 42. The rod 22 may thus be secured to the lower tie plate of the nuclear fuel assembly in such a manner as to prevent its rotation about its longitudinal axis by the receipt of the stud portion 50 within the internal cavity 43 of the sleeve 40 such that the grooves 48 receive and engage the key members 54. Subsequently, locking means, such as a retaining nut (not illustrated), is installed in engagement with the threaded lower end 52 of the stud portion 50 to retain the key members 54 within and in engagement with the grooves 48, thereby to prevent the rotation of the rod 22 about its longitudinal axis. In accordance with a further important feature of the present invention, a further alternative embodiment of a device 20" (FIGS. 8-10) for preventing the rotation of an elongated rod 22 about its longitudinal axis includes a lower end plug 64 welded to the lower longitudinal end of the tube 24 of the elongated rod 22. The lower end plug 64 is of a two piece construction including a main body portion 66 and a cylindrical locking sleeve 68. The main body portion 66 includes an upper section 70 with a radially outwardly extending annular shoulder portion 72, the upper surface of which is welded to the tube 24 and the lower surface of which is welded to the locking sleeve 68. The main body portion 66 further includes a lower elongated stud portion 74 terminating in a threaded lower end 76. The locking sleeve 68 has four elongated slots 78 formed therein that have longitudinal axes parallel to the longitudinal axes of the lower end plug 64 and of the rod 22. Preferably, the slots 78 are disposed 90.degree. apart about the periphery of the lower portion of the sleeve 68 and are configured in width, depth and spacing to receive and mate with the four, transversely disposed, elongated, web portions or members 42 of the lower tie plate of the nuclear fuel assembly. The slots 78 are formed by and between four downwardly extending projections or fingers 80 of the sleeve 68. The fingers 80 include lowermost end surfaces 82. The rod 22 may thus be secured to the lower tie plate of the nuclear fuel assembly in such a manner as to prevent its rotation about its longitudinal axis by the receipt of the stud portion 74 within the inner bore 43 of the sleeve 40 such that the slots 78 receive and engage the web members 42 such that the fingers 80 are disposed between the web members 42. Subsequently, locking means, such as a retaining nut (not illustrated), is installed in engagement with the threaded lower end 76 of the stud portion 74 to retain the web members 42 within and in engagement with the slots 78, thereby to prevent the rotation of the rod 22 about its longitudinal axis. Obviously, many modifications and variations of the present invention are possible in light of the above disclosure. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above. |
claims | 1. An apparatus comprising:a pressurized water reactor (PWR) including:a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum including a first section defining a first volume, a second section defining a second volume, a steam outlet and a feedwater inlet, the steam generator plenum being interposed between the upper plenum and the lower plenum and containing secondary coolant,wherein secondary coolant in the first section is kept separated from secondary coolant in the second section;a nuclear reactor core comprising fissile material disposed in the lower plenum;one or more risers arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum;a plurality of tubes passing through the steam generator plenum and arranged to convey primary coolant downward from the upper plenum to the lower plenum; anda steam separator operatively connected with the steam outlet and the feedwater inlet of the steam generator plenum to separate secondary coolant in a steam phase from secondary coolant in a water phase and return the secondary coolant in the water phase to the steam generator plenum by way of the feedwater inlet,wherein the steam separator is outside of the pressure vessel and elevated above the steam generator plenum so that natural circulation of the secondary coolant occurs in the steam generator plenum. 2. The apparatus of claim 1, wherein the one or more risers comprise:a hollow cylindrical central riser disposed within the pressure vessel;wherein the steam generator plenum comprises a steam generator annulus encircling the hollow cylindrical central riser. 3. The apparatus of claim 1, further comprising:an upper annular tube sheet connecting with upper ends of the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum and defining the boundary between the upper plenum and the steam generator plenum; anda lower annular tube sheet connecting with lower ends of the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum and defining the boundary between the lower plenum and the steam generator plenum. 4. The apparatus of claim 1, wherein the one or more risers comprise:a plurality of riser tubes passing through the steam generator plenum;wherein the riser tubes are inboard of and surrounded by the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum. 5. The apparatus of claim 4, wherein the steam generator plenum comprises a single connected volume through which passes both the riser tubes and the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum. 6. The apparatus of claim 4, wherein the steam generator plenum comprises a cylindrical volume through which passes both the riser tubes and the tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum. 7. The apparatus of claim 4, wherein the riser tubes have the same cross-section as the tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum. 8. The apparatus of claim 4, further comprising:an upper tube sheet connecting with upper ends of the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum and with upper ends of the riser tubes, wherein the upper tube sheet defines the boundary between the upper plenum and the steam generator plenum; anda lower tube sheet connecting with lower ends of the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum and with lower ends of the riser tubes, wherein the lower tube sheet defines the boundary between the lower plenum and the steam generator plenum. 9. The apparatus of claim 8 wherein at 25° C. the tension in the riser tubes is greater than the tension in the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum. 10. The apparatus of claim 1, wherein the steam generator plenum contains secondary coolant as a steam/water mixture. 11. The apparatus of claim 1, wherein there is no pump operatively disposed between the steam generator plenum and the steam separator, and the steam generator plenum and the steam separator are configured to circulate the secondary coolant by natural circulation. 12. The apparatus of claim 1, wherein an outer annular wall of the steam generator plenum comprises an inside wall of the pressure vessel. 13. The apparatus of claim 1, further comprising:a containment structure containing both the pressure vessel and the steam separator, the containment structure being configured to contain radioactive steam escaping from the pressure vessel. 14. An apparatus comprising:a pressurized water reactor (PWR) including:a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum including a first section defining a first volume, a second section defining a second volume, a steam outlet and a feedwater inlet, the steam generator plenum being interposed between the upper plenum and the lower plenum and containing secondary coolant,wherein secondary coolant in the first section is kept separated from secondary coolant in the second section;a nuclear reactor core comprising fissile material disposed in the lower plenum;one or more risers arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum;a plurality of tubes passing through the steam generator plenum and arranged to convey primary coolant downward from the upper plenum to the lower plenum; anda steam separator disposed outside of the pressure vessel and operatively connected with the steam generator plenum to separate secondary coolant in a steam phase from secondary coolant in a water phase and return the secondary coolant in the water phase to the steam generator plenum by way of the feedwater inlet,wherein there is no pump arranged to pump secondary coolant between the steam generator plenum and the steam separator,wherein the steam separator is arranged to allow natural circulation of the secondary coolant in the steam generator plenum. 15. An apparatus comprising:a pressurized water reactor (PWR) including:a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum including a first section defining a first volume, a second section defining a second volume, a steam outlet and a feedwater inlet, wherein the steam generator plenum is interposed between the upper plenum and the lower plenum and containing secondary coolant,wherein secondary coolant in the first section is kept separated from secondary coolant in the second section;a nuclear reactor core comprising fissile material disposed in the lower plenum;one or more risers arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum;a plurality of tubes passing through the steam generator plenum and arranged to convey primary coolant downward from the upper plenum to the lower plenum; anda steam separator disposed outside of the pressure vessel and operatively connected with the steam generator plenum to separate secondary coolant in the steam phase from secondary coolant in the water phase and return the secondary coolant in the water phase to the steam generator plenum by way of the feedwater inlet, wherein the steam separator is arranged to allow natural circulation of the secondary coolant in the steam generator plenum. 16. The apparatus of claim 15, wherein the steam generator plenum does not include or contain a shell-and-tube steam generator in which one of primary coolant and secondary coolant flows in one direction in tubes of the shell-and-tube steam generator and the other of primary coolant and secondary coolant flows in an opposite direction in the shell of the shell-and-tube steam generator. 17. An apparatus comprising:a pressurized water reactor (PWR) including:a pressure vessel divided into an upper plenum containing primary coolant, a lower plenum containing primary coolant, and a steam generator plenum including a first section defining a first volume, a second section defining a second volume, a steam outlet and a feedwater inlet, wherein the steam generator plenum is interposed between the upper plenum and the lower plenum and containing secondary coolant,wherein secondary coolant in the first section is kept separated from secondary coolant in the second section;a nuclear reactor core comprising fissile material disposed in the lower plenum;a plurality of riser tubes passing through an inboard cylindrical region of the steam generator plenum and arranged to convey primary coolant upward from the nuclear reactor core to the upper plenum;a plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum, wherein the plurality of tubes arranged to convey primary coolant downward from the upper plenum to the lower plenum pass through an outboard annular region of the steam generator plenum that surrounds the inboard cylindrical region of the steam generator plenum; anda steam separator disposed outside of the pressure vessel and operatively connected with the steam generator plenum to separate secondary coolant in a steam phase from secondary coolant in a water phase and return the secondary coolant in the water phase to the steam generator plenum by way of the feedwater inlet, andwherein the steam separator is elevated above the steam generator plenum so that natural circulation of the secondary coolant occurs in the steam generator plenum. |
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044217153 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Since the vertical baffle plates in pressurized water reactor cores are not welded together, gaps may exist between the plates that may allow jetting of the reactor coolant water through the gaps. In order to determine if such gaps exist after a period of reactor operation and in order to determine if corrective procedures are required, it is first necessary to measure the gaps between the plates. Once it is determined that the gap should be reduced, action can be taken to effect such a result. The invention described herein provides apparatus for remotely measuring gaps between plates in a nuclear reactor for determining if such gaps need to be reduced and provides apparatus for reducing the gap. Referring to FIG. 1, a pressurized water nuclear reactor is referred to generally as 20 and comprises a reactor vessel 22 having an inlet 24 and an outlet 26. A core plate 28 is suspended in the lower portion of reactor vessel 22 and serves to support fuel assemblies (not shown) when reactor 20 is operating. A generally cylindrical core barrel 30 is disposed in reactor vessel 22 for directing the flow of reactor coolant which may be water from inlet 24 down the annulus between reactor vessel 22 and core barrel 30 and into the lower end of reactor vessel 22. From the lower end of reactor vessel 22, the reactor coolant flows upwardly through holes in core plate 28, through the core area of the reactor, and out through outlet 26. In this manner, the reactor coolant passes in heat transfer relationship to the fuel assemblies which are normally disposed on core plate 28. Referring now to FIGS. 1-4, a plurality of vertical baffle plates 32 are disposed within core barrel 30 and on core plate 28 and define the outer perimeter of the reactor core in a conventional manner. While baffle plates 32 are connected together to form a rigid structure, they are not welded together along their lengths. Since baffle plates 32 are not welded or otherwise sealed along their lengths, gaps 34 may exist between adjoining baffle plates 32. However, when gaps 34 exceed approximately 0.0015 inches, it is generally advisable to reduce the width of the gap in order to prevent jetting of water therethrough as shown in FIG. 3. The jetting of water through gaps 34 can cause vibrations or lead to damage of the fuel assemblies in the core. One means of reducing gap 34 is by the use of peening apparatus 36 which can be used to hammer the edge of one of the baffle plates 32 so as to deform that baffle plate 32 near the end thereof as shown in FIG. 4. By slightly deforming the end of baffle plate 32 along its length, the adjoining baffle plates can be made to touch or otherwise reduce gap 34 therebetween. In this fashion, gap 34 can be reduced or eliminated thereby reducing or eliminating the jetting of water through gaps 34. However, before gaps 34 are attempted to be closed, it is first necessary to determine if a gap 34 exists between two selected baffle plates 32 and the size of the gap. Once the gap is determined to be of such a size that it would be advisable to close, then peening apparatus 36 may be employed to reduce the gap. Referring now to FIGS. 1 and 5, the baffle maintenance apparatus is referred to generally as 40 and comprises a vertical support member 42 with a bottom plate 44 attached thereto at its lower end and a top plate 46 attached thereto at its upper end. Vertical support member 42 may be a stainless steel metal member approximately 14 feet in length and capable of extending from core plate 28 to above the top of baffle plates 32 for supporting equipment to perform operations on baffle plates 32. A plurality of pins 48 are attached to the bottom of bottom plate 44 and are capable of being disposed in flow holes of core plate 28 for aligning and stabilizing vertical support member 42. In addition, an extension member 50 may be attached to top plate 46 for positioning baffle maintenance apparatus 40 on core plate 28. A plurality of vertical rods 52 may also be attached to top plate 46 and bottom plate 44 or attached to vertical support member 42 and are arranged parallel to vertical support member 42 for supporting and guiding carriage 54 along rods 52. Carriage 54 is slidably mounted on rods 52 and attached to drive means 56 for selectively moving carriage 54 along rods 52. Drive means 56 comprises a hydraulic motor 58 of approximately 2,000 in-lb torque that is mounted on vertical support member 42 and connected to chain drive mechanism 60 by means of gears 62. Chain drive mechanism 60 is also connected to carriage 54 for moving carriage 54 vertically along rods 52 under the influence of motor 58. In this manner, carriage 54 can be moved along the entire length of baffle plates 32 for performing maintenance operations thereon. Referring to FIGS. 5, 6 and 7, a gripper support assembly 64 is attached to top plate 46 and extends vertically substantially parallel to vertical support member 42 for supporting gripper mechanism 66. Gripper mechanism 66 comprises a mechanical latch 68 pivotally connected to hydraulic cylinder 70 which may be a 2-inch stroke Bimba hydraulic cylinder model number H-092-DUZ. When piston 72 of hydraulic cylinder 70 is moved upwardly latch 68 is caused to grip the top end of baffle plate 32 thereby providing an attachment for baffle maintenance apparatus 40 at the top of baffle plate 32. Similarly, when hydraulic cylinder 70 causes piston 72 to move downwardly, latch 68 is disengaged from baffle plate 32 as shown in phantom in FIG. 6. Gripper support assembly 64 also comprises a plurality of guide members 74 attached to gripper support assembly 64 and arranged to slide over the top of baffle plate 32 for guiding gripper mechanism 66 into proper alignment with baffle plate 32 and for providing additional stability for baffle maintenance apparatus 40. In general, two guide members 74 are provided with each gripper mechanism 66 and with each guide member 74 arranged at right angles to each other for contacting each of the two adjacent baffle plates 32. Thus, it can be seen that baffle maintenance apparatus 40 may be lowered onto core plate 28 with pins 48 disposed in core plate 28 and with gripper mechanism 66 capable of gripping the top of baffle plate 32 thereby positioning carriage 54 in proper relationship to baffle plates 32 for performing maintenance thereon. Referring now to FIGS. 8-11, carriage 54 comprises a mounting member 80 that is slidably disposed on rods 52 and a carriage plate 82 pivotally attached to mounting member 80 by means of pivot pin 84. The attachment of carriage plate 82 to mounting member 80 by means of pivot pin 84 allows carriage plate 82 to pivot in a horizontal plane as shown in phantom in FIG. 11. This pivoting of carriage plate 82 provides a means by which carriage plate 82 can be moved along rods 52 without interfering with baffle plates 32 but allowing carriage plate 82 to be pivoted into a position for performing operations on gaps 34 between baffle plates 32. As can be seen in the drawings, carriage plate 82 is provided with at least two attachment points for pivot pin 84 so that carriage plate 82 can be reversed to perform operations on the opposite baffle plate. A second hydraulic cylinder 86 which may be similar to hydraulic cylinder 70 is attached to carriage plate 82 and to mounting member 80 for selectively pivoting carriage plate 82 with respect to mounting member 80. Carriage plate 82 may have a wheel 88 rotatably disposed thereon for contacting a side of a baffle plate 32 while allowing carriage 54 to move vertically with respect to baffle plate 32. In this manner, carriage plate 82 can be pivoted into contact with baffle plate 32 by means of hydraulic cylinder 86 and can be moved vertically along rods 52 while wheel 88 is in contact with baffle plate 32. Still referring to FIGS. 8-11, a camera support 90 is mounted on mounting member 80 and provides a means to mount camera 92 and light source 94. Camera 92 which may be a Westinghouse Electric Corporation ETV 1250 and light source 94 which may be a 100-watt underwater light source are pivotably mounted on camera support 90 so that they can be manually directed toward the particular gap 34 on which operations are to be performed. Referring now to FIGS. 8 and 12, peening apparatus 36 comprises an hydraulic hammer 96 which may be a Model CH18 Stanley chipping hammer and is attached to table 98. A pressure-compensated pump (not shown) rated at approximately 18 GPM and 3000 psi and powered by a 20 HP motor is connected to and drives hydraulic hammer 96. Table 98 is slidably attached to bar 100 with bar 100 being fixedly attached to carriage plate 82 by means of posts 102. Table 98 is also attached to peening drive means 104. Peening drive means 104 comprises an hydraulic cylinder 106 which may be similar to hydraulic cylinder 70 and is mounted on drive rod 108. Drive rod 108 is slidably disposed through stop 110 which is attached to carriage plate 82. A coil spring 112 is disposed around drive rod 108 and between stop 110 and hydraulic cylinder 106 for damping the reciprocal movements of hydraulic cylinder 106. Drive rod 108 threaded on the end of hydraulic cylinder 106 for adjusting the compression of coil spring 112. A plurality of nipples 116 are mounted on hydraulic cylinder 106 and extend through slots 118 in carriage plate 82 for providing attachment of hydraulic lines to hydraulic cylinder 106. When hydraulic hammer 96 is activated, hammer chisel 120 reciprocates within hydraulic hammer 96 at a rate of approximately 2,000 times per minute. This causes hydraulic hammer 96 to vibrate at the same rate which causes table 98 to also vibrate. Since table 98 is attached to hydraulic cylinder 106 and to hydraulic hammer 96, the vibration of hydraulic hammer 96 is partially absorbed by coil spring 112. Thus the vibration caused by hydraulic hammer 96 can be dampened by coil spring 112. Hydraulic cylinder 106 also provides a means by which hydraulic hammer 96 may be moved toward or away from baffle plates 32. By activating hydraulic cylinder 106, piston 121 can be moved into or out of hydraulic cylinder 106 thereby sliding table 98 and hydraulic hammer 96 horizontally relative to baffle plates 32. Referring to FIG. 13, a plurality of hydraulic control valves 122, 124, 126 and 128 which may be Parker directional control valves model number D3W1-D-Y are mounted on an assembly and attached to vertical support member 42. Each control valve has a piston 130 with a wheel 132 on the end thereof for contacting actuator shaft 134. The movement of piston 130 into and out of the control valve opens or closes the valve thereby activating the equipment to which it is connected. Actuator shaft 134 is connected to drive cable 136 which is connected to a drive mechanism (not shown) that is located remote from the control valves. As actuator shaft 134 is moved relative to the control valves, each wheel 132 contacts actuator shaft 134, sequentially, thereby moving piston 130 and operating the corresponding control valve. In this manner, the control valves can be opened or closed in sequence from a remote location. Control valve 122 is connected hydraulically to hydraulic cylinder 70 for activating gripper mechanism 66. Control valve 124 is connected hydraulically to hydraulic cylinder 86 for selectively pivoting carriage plate 82 with respect to mounting member 80. Control valve 126 is connected hydraulically to hydraulic hammer 96 for activating or deactivating hydraulic hammer 96. And, control valve 128 is connected hydraulically to hydraulic cylinder 106 for moving table 98 and hydraulic hammer 96 toward or away from baffle plates 32. In the non-operating position, actuator shaft 134 does not contact any wheels 132 of the control valves. However, as actuator shaft 134 is moved upwardly, actuator shaft 134 sequentially activates control valves 122, 124, 126 and 128 in succeeding order. Likewise, as actuator shaft 134 is moved downwardly, the control valves are deactivated in reverse order. Referring now to FIGS. 8 and 14-23, a gauging mechanism 140 is attached to carriage plate 82. Gauging mechanism 140 is arranged on carriage 54 to be near baffle plates 32 for determining the width of gaps 34 between plates 32. Gauging mechanism 140 comprises a base 144 fixedly attached to plate 142 by means of screws 146 and a movable platform 148 slidably mounted on base 144. Platform 148 is formed in a "T" type configuration and has a plurality of holes 150 therein through which are disposed pins 152. Pins 152 are disposed through holes 150 and attached to base 144 in a manner to allow platform 148 to slide on pins 152 and laterally relative to base 144. Base 144 has a substantially cylindrical slot 154 therein that has a rectangular opening 156 along its top length. A cylindrical rod 158 is slidably disposed in slot 154 and has a post 160 attached thereto in a manner to extend through opening 156. Rod 158 is attached to a push-pull type cable (not shown) that leads to a location outside reactor vessel 22 so that rod 158 may be slid in slot 154 by pushing or pulling the cable. Platform 148 also has a diagonal groove 162 extending from one corner of platform 148 to the corner diagonally opposite therefrom. Post 160 extends into and is slidably disposed in groove 162 for sliding platform 148 on pins 152 and relative to base 144. When rod 158 is moved to a position as shown in FIG. 17, post 160 is located approximately midway along groove 162 and midway along slot 154. In such a position, platform 148 is centered on base 144 as shown in FIG. 18. When rod 158 is moved by the cable to a position as shown in FIG. 19, then post 160 is moved to an extreme end of slot 154 and groove 162 which causes platform 148 to slide on pins 152 into a configuration as shown in FIG. 20. Similarly, when rod 158 is pushed into a position as shown in FIG. 21, post 160 is moved to the other extreme end of slot 154 and groove 162 which causes platform 148 to be slid laterally on pins 152 and into a configuration as shown in FIG. 22. It can be seen that the movement of post 160 in groove 162 causes platform 148 to slide laterally with respect to base 144. In this manner the movement of rod 158 can result in the lateral movement of platform 148 relative to base 144. Referring now to FIGS. 14, 15, 16 and 23-30, gauging mechanism 140 also comprises a gauge 170 rotatably mounted on platform 148. Gauge 170 comprises a substantially cylindrical rod 172 slidably disposed in a substantially cylindrical slot 174 of platform 148. Slot 174 extends the entire length of platform 148 and has a rectangular opening 176 along its top length. Rod 172 has a post 178 attached thereto and extending through opening 176. Rod 172 is attached to a push-pull type cable that extends to a location remote from reactor vessel 22 for moving rod 172 through slot 174. Gauge 170 also comprises a short cylindrical member 180 and a circular member 182 rotatably mounted on platform 148. Post 178 extends through a bore in cylindrical member 180 and through circular member 182 and has a nut 184 attached to the top end thereof. Nut 184 prevents cylindrical member 180 and circular member 182 from being separated from post 178 but allows cylindrical member 180 and circular member 182 to rotate about post 178. Circular member 180 has a plurality of feeler gauges 186 attached thereto. Feeler gauges 186 may be thin metal strips ranging from 0.0015 inches to 1.050 inches in thickness for being disposed in gaps 34 to determine the width of the gaps between baffle plates 32. For example, circular member 180 may have four feeler gauges 186 disposed thereon at 90.degree. to each other. In addition, a like number of pins 188, 190, 192 and 194 are attached to the underside of circular member 180 and arranged at approximately 90.degree. to each other and equidistant between each feeler gauge 186 as shown in FIG. 14. A spring loaded stop 200 is mounted on platform 148 and comprises a dog 202 rotatably disposed on pin 204 with a spring 206 disposed therearound. Dog 202 is arranged to rotate in one direction and is spring-loaded to return to its original position but is prevented from rotating in the opposite direction by post 208. A set screw 210 is mounted on platform 148 and arranged to contact cylindrical member 180 for limiting the travel of cylindrical member 180. Referring now to FIGS. 27-30, in its initial position, gauge 170 is arranged to have a feeler gauge 186 substantially in alignment with opening 176 so as to be able to be inserted into a gap 34 between two baffle plates 32 as shown in FIG. 27. When rod 172 is pulled through slot 174 by cables, post 178 is moved through opening 176 and toward set screw 210 until a pin such as pin 190 contacts dog 202 as shown in FIG. 28. Since post 208 prevents dog 202 from rotating in a clockwise motion as viewed in FIG. 28, pin 190 is prevented from moving toward set screw 210. However, because circular member 182 is rotatably mounted on post 178, as post 178 is moved closer to set screw 210, circular member 182 rotates in a clockwise direction as shown in FIG. 29. It can be seen in FIG. 29 that pin 190 slides along stop 202 as circular member 182 rotates. As post 178 is moved even closer to set screw 210, circular member 182 continues to rotate and completes a 90.degree. rotation as circular member 182 contacts set screW 210 as shown in FIG. 30. At this point, rod 172 and post 178 may be pushed away from set screw 210 and into the original configuration of FIG. 27 except that circular member 182 will have been rotated 90.degree.. Since dog 202 can rotate about pin 204 in a counterclockwise direction, dog 202 can rotate and allow a pin such as pin 188 to pass by as shown in phantom in FIG. 30. In this manner, by moving rod 172 through slot 174, a plurality of feeler gauges 186 can be rotated and extended into a gap 34 between two adjacent baffle plates 32 in order to measure the width of the space between the two baffle plates. It should be noted that platform 148 can be arranged to mount gauge 170 on the side thereof rather than on the top so as to rotate feeler gauges 186 in a vertical plane rather than in a horizontal plane as illustrated in FIG. 31. OPERATION When it is desired to measure gap 34 between two adjacent baffle plates 32, nuclear reactor 20 is shut down and all of the fuel assemblies are removed in a conventional manner. With reactor vessel 22 still filled with reactor coolant, baffle maintenance apparatus 40 is lowered into reactor vessel 22 by means of extension member 50. As baffle maintenance apparatus 40 is lowered into reactor vessel 22, pins 48 are inserted into flow holes in core plate 28 and guide members 74 are slid over the top ends of baffle plates 32. In this position, vertical support member 42 is aligned substantially vertically relative to baffle plates 32. Next, actuator shaft 134's drive mechanism which is located remote from reactor vessel 22 is activated which causes actuator shaft 134 to move upwardly relative to control valves 122-128. As actuator shaft 134 contacts wheel 132 of control valve 122, piston 130 is depressed which opens control valve 122 and activates gripper mechanism 66. Activation of gripper mechanism 66 causes latch 68 to engage the top of baffle plate 32 as shown in FIG. 6. At this point baffle maintenance apparatus is firmly positioned in reactor vessel 22. As actuator shaft 134 continues to move upwardly, control valve 124 is similarly activated which causes hydraulic cylinder 86 to pivot carriage plate 82 into a position as shown in FIGS. 9, 10 or 11 depending on the particular gap 34 that is to be inspected. The pivoting of carriage plate 82 moves carriage plate 82, for example, from a position as shown in phantom in FIG. 11 to the position as shown in full in FIG. 11. It should be understood from a review of the drawings and particularly FIG. 10, that wheel 88 can be mounted on either side of carriage plate 82 and that carriage plate 82 can be mounted in a reverse manner on mounting member 80 for accessing the various corners of baffle plates 32. With carriage plate 82 in this configuration, gap 34 may be either inspected with gauging mechanism 140 or gap 34 may be closed by activating peening apparatus 36. Also, with carriage plate 82 in this configuration, camera 92 and light source 94 are directed toward the particular gap 34 to be inspected so that working personnel located remote from reactor vessel 22 may view the work area. Next, working personnel or automatic equipment may manipulate the cables connected to rod 172 for rotating a selected feeler gauge 186 (as previously described) into position for being inserted into the selected gap 34. Also, by moving rod 172, the selected feeler gauge 186 may be moved into a position as shown in FIG. 27 which will cause the feeler gauge to be inserted into the selected gap 34. In addition, cables may be manipulated to move rod 158 so as to laterally position the feeler gauge so that the feeler gauge may be inserted in gap 34. All of this may be performed in view of camera 92 so that the operating personnel may verify the movements. Similarly, additional feeler gauges 186 may be inserted into gap 34 so that operating personnel may determine the width of gap 34. If it is determined that gap 34 has a width greater than desired, actuator shaft 134 may again be moved so as to activate hydraulic hammer 96. With hydraulic hammer 96 vibrating, actuator shaft 134 may then activate control valve 128 for moving table 98 and hydraulic hammer 96 toward the baffle plate 32 for closing the gap 34 between the baffle plates. When hydraulic hammer 96 contacts baffle plate 32, a portion of the edge of the baffle plate is deformed which causes gap 34 to be reduced as shown in FIG. 4. In this fashion, each gap 34 may be inspected and if necessary, the gap may be reduced to eliminate or greatly reduce the jetting of water through the gap when the reactor is operating. In addition, drive means 56 may be employed in either the gauging or peening operation for moving carriage 54 including the gauging and peening apparatus along the length of each gap 34 so that the entire length of the gap may be inspected or reduced. Of course, baffle maintenance apparatus 40 may be deactivated and removed from reactor vessel 22 in the reverse manner to which it was inserted. Therefore, the invention provides apparatus for determining the size of a gap between two adjacent baffle plates in a nuclear reactor and for reducing those gaps that are determined to be too large. |
summary | ||
description | In all the figures of the drawing, sub-features and integral parts that correspond to one another bear the same reference symbol in each case. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown an ignition system 1 intended for the recombination of hydrogen in a gas mixture, specifically in the containment atmosphere of a safety vessel 2, excerpts of which are represented in FIG. 1, of a nuclear facility. For this purpose, the ignition system 1 contains a plurality of spark igniters 4 which are disposed inside the safety vessel 2 on an internal wall 3, and each of which is configured for on-demand production of ignition sparks for a controlled combustion of hydrogen released in the interior of the safety vessel 2. In order to be supplied with ignition energy, the spark igniters 4 are connected to a two-stage power supply system 6. The power supply system 6 contains a plurality of intermediate energy stores 8 connected to a central power supply unit 7. In the illustrative embodiment, low-voltage accumulators are provided as the intermediate energy stores 8. As an alternative, the intermediate energy stores 8 may also be configured as dry batteries. The intermediate energy stores 8 are suspended inside the safety vessel 2, from a further internal wall 9. A group of about 15 spark igniters 4 is connected to each of the intermediate energy stores 8. In other words, the spark igniters 4 are connected together in groups in order to supply them with energy, each group of spark igniters 4 being connected to the intermediate energy store 8 common to them. The grouped connection of the spark igniters 4 is symbolized in FIG. 1 by the bundled representation of power transmission lines 10. The power transmission lines 10 are in this case, in an embodiment suitable for high temperatures, configured as metal-clad cables with mineral insulation. On an input side, the intermediate energy stores 8 are connected to the central power supply units 7 via supply lines 12 fed through the safety vessel 2. Each of the intermediate energy stores 8 is configured for an autonomy time of about 24 hours and can be recharged via the central power supply unit 7. In the illustrative embodiment, a back-up diesel generation network is provided as the central power supply unit 7. As an alternative, it is also possible for a separate battery or a different power generator to be provided. However, each of the intermediate energy stores 8, which are respectively connected via the line 12 to the central power supply unit 7, contains an automatic switch 14 which is intended to trigger an ignition process and has a catalytically coated temperature sensor 16 and an integral pressure switch 18. The ignition system 1 is therefore equipped for redundant automatic ignition activation as a function of the pressure and/or the temperature in the interior of the safety vessel 2. In addition, each of the intermediate energy stores 8 is connected via a signal line 22 to a manual trigger system 24. The trigger system 24 may in this case for example form part of the control room of a nuclear power station on an input side, the trigger system 24 is connected via a signal line 26 to a hydrogen sensor 28. The power supply to the spark igniters 4 via the intermediate energy stores 8 respectively connected upstream of them may in this case alternatively be triggered via the automatic trigger 14 respectively integrated in the intermediate energy stores 8, or via the manual trigger system 24. Furthermore, each of the intermediate energy stores 8 is equipped with an integral cooling unit 29 in the form of a heat sink. The cooling unit 29 is in this case configured in such a way that a temperature of 100xc2x0 C. in the interior of the intermediate energy store 8 is not exceeded even in the case of an incident in which a large amount of heat is released. The intermediate energy stores 8 can therefore be operated reliably in a wide variety of incident scenarios, even in the embodiment as low-voltage accumulators. The spark igniter 4 of the ignition system 1 is schematically represented in FIG. 2. The spark igniter 4 is configured as a high-speed igniter with an operating frequency of about 100 Hz and as a low-energy igniter with an operating power of about 5 W, and for this purpose contains ignition electronics 30 whose essential components are a clock generator, a high-voltage transistor, a charging capacitor and an ignition transformer. The ignition electronics 30 are connected on the input side to the power supply line 10 which is connected to the intermediate energy store 8 allocated to the spark igniter 4. On an output side the ignition electronics 30 are connected to a spark gap 32 whose end 34 projects in a region of the interior of the safety vessel where an incident with increased release of hydrogen is to be expected. The spark igniter 4 contains a multi-layer housing 36 whose outer casing 38 consists of a material which is stable at high temperature, for example VA steel or titanium. An insulating casing 40 which, in the illustrative embodiment, is configured in a double-casing fashion as an air gap between the outer casing 38 and an inner casing 42, is disposed inside the outer casing 38. As an alternative, an insulant that is resistant to high temperatures and radiation and is disposed between the outer casing 38 and the inner casing 42 may also be provided for the insulating casing 40. Inside the housing 36, the ignition electronics 30 are disposed in an inner housing 44 configured as a radiation screen. An intermediate space 46 between the inner housing 44 and the inner casing 42 is filled in the manner of a water bath up to a level 48 with water W which serves as a heat sink integral to the spark igniter 4 The inner housing 44 is fastened to the housing 36 via a fastening element 50 made of an insulating material. At its end that faces the spark gap 32 and is closed off with a cover 52, the housing 36 is provided with a ceramic heat shield 54. The interior 46 communicates with the external space of the housing 36 via a discharge line 58 which can be closed off by a safety valve 56. The housing 36 is suspended via a fastening element 60 from the internal wall 3. The housing 36 suspended via the fastening element 60 from the internal wall 3 is in this case surrounded by a further insulating casing 62 disposed directly on the internal wall. In the event of an incident inside the safety vessel 2, the fact whether hydrogen has been released is ascertained by the hydrogen sensor 28 or by the temperature sensors 16 and/or the pressure switches 18 provided as sensors. If hydrogen has been released, then the spark igniters 4 are activated manually using the trigger unit 24 or automatically using the automatic triggers 14 integrated in the intermediate energy stores 8. An ignition spark which leads to controlled combustion or recombination of the hydrogen is in this case produced by the spark gap 32 of each spark igniter 4 at its end 34. By virtue of the spark igniter 4 configured as a high-speed igniter with an operating frequency of about 100 Hz, reliable ignition of the hydrogen is in this case ensured even in the case of comparatively fast gas displacement processes with flow speeds in excess of 10 m/s. In addition, by virtue of the high operating frequency of the spark igniters 4, particularly strong pre-ionization of the gas mixture is ensured, so that early ignition directly after the ignition group has been passed is ensured, even in the case of a slow-moving gas atmosphere. The levels of loading due to combustion which follow ignition are therefore particularly low. The ignition system 1 is configured for particularly high operating safety, even for a wide variety of incident situations. By virtue of the two-stage configuration of the power supply system 6 for the spark igniters 4, the ignition system 1 is suitable both for medium-term autonomous operation and for long-term continuous operation. In medium-term autonomous operation, the power supply for the spark igniters 4 takes place exclusively via the intermediate energy stores 8, which provide for an operating time of at least 24 hours without any extra supply. Reliable operation of the ignition system 1 is therefore ensured even if external devices fail. Reliable long-term operation of the ignition system 1 is in addition ensured by the central power supply unit 7. On account of their structure, the spark igniters 4 are configured for a high degree of operating safety even in the event of a wide variety of accident scenarios. The functional safety of the relevant ignition electronics 30 is in this case ensured even at high external temperatures due to the respective incident. This is contributed to, further to the insulating casing 40 provided in the housing 36 of each spark igniter 4, in particular by the integral heat sink in the form of the water W surrounding the internal housing 44 as well. This is because the water W vaporizes as a result of elevated temperature and thereby contributes through its heat of evaporation to cooling the ignition electronics 30. A particularly long working period is in this case ensured by the safety valve 56. This is because the rate at which the vaporized water W is discharged from the housing 36 can be adjusted using the safety valve 56. Even if the supply of water is limited, the integral heat sink is therefore available for a particularly long working period. |
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claims | 1. A laser-plasma extreme ultraviolet (EUV) radiation source comprising: a nozzle emitting a spray of target material into a plasma generation region; and collection optics positioned relative to the plasma generation region, said collection optics including at least one opening through which a laser beam propagates to impinge the target material and generate a plasma, said opening being positioned at a location asymmetrical relative to the collection optics so that the laser beam is directed off-axis relative to the collection optics and most of the strongest EUV radiation from the plasma reflected by the collection optics is not obscured by the nozzle. 2. The source according to claim 1 wherein the collection optics is dish-shaped. claim 1 3. The source according to claim 1 wherein the collection optics is a portion of a dish shape. claim 1 4. The source according to claim 1 wherein the collection optics includes two separate openings, each receiving a separate laser beam. claim 1 5. A laser-plasma extreme ultraviolet (EUV) radiation source comprising: a nozzle emitting a spray of target material into a plasma generation region; and collection optics positioned relative to the nozzle, said collection optics including at least one opening through which a laser beam propagates to impinge the target material and generate a plasma, said opening being positioned at a location asymmetrical relative to the collection optics so that the laser beam is directed off-axis relative to the collection optics and most of the strongest EUV radiation from the plasma reflected by the collection optics is not obscured by the nozzle but is disposed such that the angular distribution of the generated EUV radiation causes most of the strongest EUV radiation to be directed towards an edge of the collection optics. 6. A laser-plasma extreme ultraviolet (EUV) radiation source comprising: a nozzle emitting a spray of target material into a plasma generation region; and collection optics positioned relative to the plasma generation region, said collection optics including a single opening through which a single laser beam propagates to impinge the target material and generate a plasma, said opening being positioned at a location asymmetrical relative to the collection optics so that the laser beam is directed off-axis relative to the collection optics and most of the strongest EUV radiation from the plasma reflected by the collection optics is not obscured by the nozzle. 7. A laser-plasma extreme ultraviolet (EUV) radiation source for generating EUV radiation, said source comprising: target production hardware including a nozzle, said nozzle emitting a spray of target material into a plasma generation region; a laser beam source, said laser beam source generating a laser beam directed towards the plasma generation region; and collection optics positioned between the laser beam source and the target production hardware, said collection optics including at least one opening through which the laser beam propagates to impinge the target material and generate a plasma, said collection optics having a shape that is at least a portion of a dish, said plasma generation region being at a focal point of the collection optics and said target production hardware being proximate the focal point of the collection optics, said opening being positioned at a location asymmetrical relative to the shape of the collection optics so that the laser beam is directed off-axis relative to the collection optics and most of the strongest EUV radiation from the plasma reflected by the collection optics is not obscured by the target production hardware. 8. A laser-plasma extreme ultraviolet (EUV) radiation source for generating EUV radiation, said source comprising: target production hardware including a nozzle, said nozzle emitting a spray of target material into a plasma generation region; a laser beam source, said laser beam source generating a laser beam directed towards the plasma generation region; and collection optics positioned between the laser beam source and the target production hardware, said collection optics including at least one opening through which the laser beam propagates to impinge the target material and generate a plasma, said collection optics having a shape that is at least a portion of a dish, said plasma generation region being at a focal point of the collection optics and said target production hardware being proximate the focal point of the collection optics, said opening being positioned at a location asymmetrical relative to the shape of the collection optics so that the laser beam is directed off-axis relative to the collection optics and most of the strongest EUV radiation from the plasma reflected by the collection optics is not obscured by the target production hardware and wherein the collection optics is positioned relative to the nozzle such that the angular distribution of the generated EUV radiation causes most of the strongest EUV radiation to be directed towards an edge of the collection optics. 9. The source according to claim 8 wherein the collection optics is dish-shaped. claim 8 10. The source according to claim 8 wherein the collection optics includes two separate openings, each receiving a separate laser beam. claim 8 11. A method of generating extreme ultraviolet (EUV) radiation, said method comprising the steps of: providing target production hardware including a nozzle; emitting a spray of target material from the nozzle into a plasma generation region; directing at least one laser beam to the plasma generation region to heat the target material and generate the EUV radiation; and reflecting the generated EUV radiation from collection optics, said step of directing the laser beam including directing the laser beam through an opening in the collection optics so that the laser beam is off-axis relative to the collection optics and most of the strongest EUV radiation is not obscured by the target production hardware. 12. The method according to claim 11 wherein the step of directing the laser beam includes directing two separate laser beams through two separate holes in the collection optics, where both laser beams are off-axis relative to the collection optics. claim 11 13. A method of generating extreme ultraviolet (EUV) radiation, said method comprising the steps of: providing target production hardware including a nozzle; emitting a spray of target material from the nozzle into a plasma generation region; directing at least one laser beam to the plasma generation region to heat the target material and generate the EUV radiation; and reflecting the generated EUV radiation from collection optics, said step of directing the laser beam including directing the laser beam through an opening in the collection optics so that the laser beam is off-axis relative to the collection optics and most of the strongest EUV radiation is not obscured by the target production hardware and is reflected from an edge of the collection optics. |
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abstract | A method for treating a fluid waste, comprising adding one or more process additives to the fluid waste in an amount sufficient to change the wasteform chemistry is disclosed. The addition step may be chosen from adding a dispersant or a deflocculant an additive to decrease the reactive metal components, to bind fission products and decrease volatilization of toxic or radioactive elements or species during thermal treatment, or to target and react with the fine particle size component of the waste to decrease dusting and immobilize components in a durable phase. After mixing the fluid waste with the described additives the waste is eventually hot-isostatic pressing, to form a durable and stable waste form. |
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claims | 1. A method for preparing low level radioactive hazardous materials (LLHZ) for disposal which comprises: providing a softsided transportable container at a hazardous debris collection site, the softsided container including a bottom, side walls and a top defining an interior space; said softsided container having at least three layers of materials, an outer, middle and an inner layer, where the middle layer is a water impervious material, each layer having a closable opening located on the top of the container; providing a hardsided closed container containing LLHZ in the interior of said container, loading said hard sided container into the interior of the softsided container, and closing each of said closable tops of said inner, middle and outer layers. 2. A method for preparing LLHZ for disposal according to claim 1, wherein the hardsided container comprises a metal or plastic container. 3. A method for preparing LLHZ for disposal according to claim 1, further comprising transporting the softsided container containing said hardsided container to a landfill site and burying the softsided container containing said hardsided container at the landfill site. 4. A method for preparing LLHZ for disposal according to claim 1, wherein each of said layers is closable with a zipper. 5. A method for preparing LLHZ for disposal according to claim 4, where said zipper on said middle layer is a water tight zipper. 6. A method for preparing LLHZ for disposal according to claim 2, wherein the inner layer has a pocket in said sidewall and a rigid material is positioned in said pocket to thereby allow said softsided container to be self-supporting. 7. A method for preparing LLHZ for disposal according to claim 1 further comprising the steps of filling the void space in said interior of said softsided enclosure with a filler after the hardsided container is positioned in said interior. 8. A method for preparing LLHZ for disposal according to claim 1 wherein the void space in said interior of said softsided enclosure is not filled with a filler. 9. A method for preparing LLHZ for disposal according to claim 1 wherein said LLHZ contains objects with sharp edges. 10. A method for preparing LLHZ for disposal according to claim 1 wherein said hardsided container is a 55 gallon drum. 11. The method for preparing LLHZ for disposal according to claim 6 wherein said rigid material comprises cardboard material. 12. The method for preparing LLHZ for disposal according to claim 6 wherein each of said layers is closable with a zipper. 13. The method for preparing LLHZ for disposal according to claim 3 wherein said inner layer is constructed of non-woven polypropylene. 14. The method for preparing LLHZ for disposal according to claim 13 wherein said outer layer is constructed from woven or non-woven polypropylene. 15. The method for preparing LLHZ for disposal according to claim 2 wherein said middle layer is closable with a toothless zipper. 16. The method for preparing LLHZ for disposal according to claim 15 wherein said inner layer is closeable with a zipper. 17. A method for preparing LLHZ for disposal according to claim 2, wherein the softsided transportable container further comprises a rigid material positioned adjacent the inner layer. 18. The method of claim 1 wherein said hardsided closed container is sealed closed. 19. A method for preparing low level radioactive hazardous materials (LLHZ) for disposal which comprises: providing a softsided transportable container at a hazardous debris collection site, the softsided container including a bottom, side walls and a top defining an interior space; said softsided container having at least three layers of materials, an outer, middle and an inner layer, where the middle layer is a water impervious material, each layer having a closable opening located on the top of the container; providing a hardsided closable container, positioning LLHZ in the interior of said container, closing said hard sided container, loading said hard sided container into the interior of the softsided container, and closing each of said closable tops of said inner, middle and outer layers. 20. The method of claim 19 wherein said step of loading said hard sided container into the interior of the softsided container occurs before said step of positioning LLHZ in the interior of said hardsided container. |
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abstract | The invention relates to a charged particle lithography system comprising a beam generator for generating a plurality of charged particle beamlets, a beam stop array and a modulation device. The beam stop array has a surface for blocking beamlets from reaching a target surface and an aperture array in the surface for allowing beamlets to reach the target surface. The modulation device is arranged for modulating the beamlets by deflecting or not deflecting the beamlets so that the beamlets are blocked or not blocked by the beam stop array. A surface area of the modulation device comprises an elongated beam area comprising an array of apertures and associated modulators, and a power interface area for accommodating a power arrangement for powering elements within the modulation device. The power interface area is located alongside a long side of the elongated beam area and extending in a direction substantially parallel thereto. |
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description | This application is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. patent application Ser. No. 16/796,821, filed on Feb. 20, 2020, which in turn claims priority under 35 U.S.C. § 119 to: U.S. Provisional Patent Application Ser. No. 62/808,565, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,623, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,791, filed on Feb. 21, 2019; U.S. Provisional Patent Application Ser. No. 62/808,813, filed on Feb. 21, 2019; and U.S. Provisional Patent Application Ser. No. 62/833,106, filed on Apr. 12, 2019. The entire contents of each of the previous applications are incorporated by reference herein. This disclosure relates to hazardous material repository systems and methods. Hazardous material, such as radioactive waste, is often placed in long-term, permanent, or semi-permanent storage so as to prevent health issues among a population living near the stored waste. Such hazardous waste storage is often challenging, for example, in terms of storage location identification and surety of containment. For instance, the safe storage of nuclear waste (e.g., spent nuclear fuel, whether from commercial power reactors, test reactors, or even high-grade military waste) is considered to be one of the outstanding challenges of energy technology. Safe storage of the long-lived radioactive waste is a major impediment to the adoption of nuclear power in the United States and around the world. Conventional waste storage methods have emphasized the use of tunnels, and is exemplified by the design of the Yucca Mountain storage facility. Other techniques include boreholes, including vertical boreholes, drilled into crystalline basement rock. Other conventional techniques include forming a tunnel with boreholes emanating from the walls of the tunnel in shallow formations to allow human access. In an example implementation, a drillhole plug includes a frame or housing that includes a corrosion-resistant material and sized to fit within a milled portion of a directional drillhole that includes a hazardous waste repository; and a material that fills at least a portion of the frame or housing. The material exhibits creep such that the material fills one or more voids between the frame or housing and a subterranean formation adjacent the milled portion of the directional drillhole. In an aspect combinable with the example implementation, the milled portion is located at a vertical portion of the directional drillhole. In another aspect combinable with any of the previous aspects, the milled portion does not include casing and other portions of the directional drillhole include casing. In another aspect combinable with any of the previous aspects, the material includes a natural material. In another aspect combinable with any of the previous aspects, the natural material includes a rock material. In another aspect combinable with any of the previous aspects, the rock material includes at least one of shale, clay, or salt. In another aspect combinable with any of the previous aspects, the rock material is the same or substantially the same as the subterranean formation. In another aspect combinable with any of the previous aspects, the rock material is different than the subterranean formation. In another aspect combinable with any of the previous aspects, an outer diameter of the plug is greater than an outer diameter of the directional drillhole. In another aspect combinable with any of the previous aspects, the outer diameter of the plug is less than a diameter of the milled portion. In another example implementation, a method for sealing a drillhole includes milling a portion of a directional drillhole that includes a hazardous waste repository; inserting a drillhole plug into the milled portion; and sealing the directional drillhole with the material of the drillhole plug that fills one or more voids between the frame or housing and a subterranean formation adjacent the milled portion of the directional drillhole. The drillhole plug includes a frame or housing that includes a corrosion-resistant material and a material that fills at least a portion of the frame or housing. The material exhibits creep. In an aspect combinable with the example implementation, the milled portion is located at a vertical portion of the directional drillhole. In another aspect combinable with any of the previous aspects, the milled portion does not include casing and other portions of the directional drillhole include casing. In another aspect combinable with any of the previous aspects, the material includes a natural material. In another aspect combinable with any of the previous aspects, the natural material includes a rock material. In another aspect combinable with any of the previous aspects, the rock material includes at least one of shale, clay, or salt. In another aspect combinable with any of the previous aspects, the rock material is the same or substantially the same as the subterranean formation. In another aspect combinable with any of the previous aspects, the rock material is different than the subterranean formation. In another aspect combinable with any of the previous aspects, an outer diameter of the plug is greater than an outer diameter of the directional drillhole. In another aspect combinable with any of the previous aspects, the outer diameter of the plug is less than a diameter of the milled portion. Implementations of hazardous waste repository systems and methods according to the present disclosure may also include one or more of the following features. For example, a hazardous waste repository may be used to store hazardous waste material, such as spent nuclear fuel, isolated from human-consumable water sources. The hazardous waste repository may be suitable for storing the hazardous waste, such as radioactive or nuclear waste, for durations of time up to, for example, 1,000,000 years. Other features are described herein. The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims. FIG. 1 is a schematic illustration of an example implementation of a hazardous waste repository 100 (also referred to as a hazardous waste repository system), e.g., a subterranean location for the long-term (e.g., tens, hundreds, or thousands of years or more), but retrievable, safe and secure storage of hazardous material (e.g., radioactive material, such as nuclear waste which can be spent nuclear fuel (SNF) or high level waste, as two examples). For example, this figure illustrates the example hazardous waste repository 100 once one or more canisters 126 of hazardous material have been deployed in a subterranean formation 118. As illustrated, the hazardous waste repository 100 includes a drillhole 104 formed (e.g., drilled or otherwise) from a terranean surface 102 and through multiple subterranean layers 112, 114, 116, and 118. Although the terranean surface 102 is illustrated as a land surface, terranean surface 102 may be a sub-sea or other underwater surface, such as a lake or an ocean floor or other surface under a body of water. Thus, the present disclosure contemplates that the drillhole 104 may be formed under a body of water from a drilling location on or proximate the body of water. The illustrated drillhole 104 is a directional drillhole in this example of hazardous waste repository 100. For instance, the drillhole 104 includes a substantially vertical portion 106 coupled to a radiussed or curved portion 108, which in turn is coupled to a substantially horizontal portion 110. As used in the present disclosure, “substantially” in the context of a drillhole orientation, refers to drillholes that may not be exactly vertical (e.g., exactly perpendicular to the terranean surface 102) or exactly horizontal (e.g., exactly parallel to the terranean surface 102), or exactly inclined at a particular incline angle relative to the terranean surface 102. In other words, vertical drillholes often undulate offset from a true vertical direction, that they might be drilled at an angle that deviates from true vertical, and inclined drillholes often undulate offset from a true incline angle. Further, in some aspects, an inclined drillhole may not have or exhibit an exactly uniform incline (e.g., in degrees) over a length of the drillhole. Instead, the incline of the drillhole may vary over its length (e.g., by 1-5 degrees). As illustrated in this example, the three portions of the drillhole 104—the vertical portion 106, the radiussed portion 108, and the horizontal portion 110—form a continuous drillhole 104 that extends into the Earth. As used in the present disclosure, the drillhole 104 (and drillhole portions described) may also be called wellbores. Thus, as used in the present disclosure, drillhole and wellbore are largely synonymous and refer to bores formed through one or more subterranean formations that are not suitable for human-occupancy (i.e., are too small in diameter for a human to fit there within). The illustrated drillhole 104, in this example, has a surface casing 120 positioned and set around the drillhole 104 from the terranean surface 102 into a particular depth in the Earth. For example, the surface casing 120 may be a relatively large-diameter tubular member (or string of members) set (e.g., cemented) around the drillhole 104 in a shallow formation. As used herein, “tubular” may refer to a member that has a circular cross-section, elliptical cross-section, or other shaped cross-section. For example, in this implementation of the hazardous waste repository 100, the surface casing 120 extends from the terranean surface through a surface layer 112. The surface layer 112, in this example, is a geologic layer comprised of one or more layered rock formations. In some aspects, the surface layer 112 in this example may or may not include freshwater aquifers, salt water or brine sources, or other sources of mobile water (e.g., water that moves through a geologic formation). In some aspects, the surface casing 120 may isolate the drillhole 104 from such mobile water, and may also provide a hanging location for other casing strings to be installed in the drillhole 104. Further, although not shown, a conductor casing may be set above the surface casing 120 (e.g., between the surface casing 120 and the surface 102 and within the surface layer 112) to prevent drilling fluids from escaping into the surface layer 112. As illustrated, a production casing 122 is positioned and set within the drillhole 104 downhole of the surface casing 120. Although termed a “production” casing, in this example, the casing 122 may or may not have been subject to hydrocarbon production operations. Thus, the casing 122 refers to and includes any form of tubular member that is set (e.g., cemented) in the drillhole 104 downhole of the surface casing 120. In some examples of the hazardous waste repository 100, the production casing 122 may begin at an end of the radiussed portion 108 and extend throughout the horizontal portion 110. The casing 122 could also extend into the radiussed portion 108 and into the vertical portion 106. As shown, cement 130 is positioned (e.g., pumped) around the casings 120 and 122 in an annulus between the casings 120 and 122 and the drillhole 104. The cement 130, for example, may secure the casings 120 and 122 (and any other casings or liners of the drillhole 104) through the subterranean layers under the terranean surface 102. In some aspects, the cement 130 may be installed along the entire length of the casings (e.g., casings 120 and 122 and any other casings), or the cement 130 could be used along certain portions of the casings if adequate for a particular drillhole 104. The cement 130 can also provide an additional layer of confinement for the hazardous material in canisters 126. The drillhole 104 and associated casings 120 and 122 may be formed with various example dimensions and at various example depths (e.g., true vertical depth, or TVD). For instance, a conductor casing (not shown) may extend down to about 120 feet TVD, with a diameter of between about 28 in. and 60 in. The surface casing 120 may extend down to about 2500 feet TVD, with a diameter of between about 22 in. and 48 in. An intermediate casing (not shown) between the surface casing 120 and production casing 122 may extend down to about 8000 feet TVD, with a diameter of between about 16 in. and 36 in. The production casing 122 may extend inclinedly (e.g., to case the horizontal portion 110) with a diameter of between about 11 in. and 22 in. The foregoing dimensions are merely provided as examples and other dimensions (e.g., diameters, TVDs, lengths) are contemplated by the present disclosure. For example, diameters and TVDs may depend on the particular geological composition of one or more of the multiple subterranean layers (112, 114, 116, and 118), particular drilling techniques, as well as a size, shape, or design of a hazardous material canister 126 that contains hazardous material to be deposited in the hazardous waste repository 100. In some alternative examples, the production casing 122 (or other casing in the drillhole 104) could be circular in cross-section, elliptical in cross-section, or some other shape. As illustrated, the vertical portion 106 of the drillhole 104 extends through subterranean layers 112, 114, and 116, and, in this example, lands in a subterranean layer 118. As discussed above, the surface layer 112 may or may not include mobile water. In this example, a mobile water layer 114 is below the surface layer 112 (although surface layer 112 may also include one or more sources of mobile water or liquid). For instance, mobile water layer 114 may include one or more sources of mobile water, such as freshwater aquifers, salt water or brine, or other source of mobile water. In this example of hazardous waste repository 100, mobile water may be water that moves through a subterranean layer based on a pressure differential across all or a part of the subterranean layer. For example, the mobile water layer 114 may be a permeable geologic formation in which water freely moves (e.g., due to pressure differences or otherwise) within the layer 114. In some aspects, the mobile water layer 114 may be a primary source of human-consumable water in a particular geographic area. Examples of rock formations of which the mobile water layer 114 may be composed include porous sandstones and limestones, among other formations. Other illustrated layers, such as the impermeable layer 116 and the storage layer 118, may include immobile water. Immobile water, in some aspects, is water (e.g., fresh, salt, brine), that is not fit for human or animal consumption, or both. Immobile water, in some aspects, may be water that, by its motion through the layers 116 or 118 (or both), cannot reach the mobile water layer 114, terranean surface 102, or both, within 10,000 years or more (such as to 1,000,000 years). Below the mobile water layer 114, in this example implementation of hazardous waste repository 100, is an impermeable layer 116. The impermeable layer 116, in this example, may not allow mobile water to pass through. Thus, relative to the mobile water layer 114, the impermeable layer 116 may have low permeability, e.g., on the order of nanodarcy permeability. Additionally, in this example, the impermeable layer 116 may be a relatively non-ductile (i.e., brittle) geologic formation. One measure of non-ductility is brittleness, which is the ratio of compressive stress to tensile strength. In some examples, the brittleness of the impermeable layer 116 may be between about 20 MPa and 40 MPa. As shown in this example, the impermeable layer 116 is shallower (e.g., closer to the terranean surface 102) than the storage layer 118. In this example rock formations of which the impermeable layer 116 may be composed include, for example, certain kinds of sandstone, mudstone, clay, and slate that exhibit permeability and brittleness properties as described above. In alternative examples, the impermeable layer 116 may be deeper (e.g., further from the terranean surface 102) than the storage layer 118. In such alternative examples, the impermeable layer 116 may be composed of an igneous rock, such as granite. Below the impermeable layer 116 is the storage layer 118. The storage layer 118, in this example, may be chosen as the landing for the horizontal portion 110, which stores the hazardous material, for several reasons. Relative to the impermeable layer 116 or other layers, the storage layer 118 may be thick, e.g., between about 100 and 200 feet of total vertical thickness. Thickness of the storage layer 118 may allow for easier landing and directional drilling, thereby allowing the horizontal portion 110 to be readily emplaced within the storage layer 118 during constructions (e.g., drilling). If formed through an approximate horizontal center of the storage layer 118, the horizontal portion 110 may be surrounded by about 50 to 100 feet of the geologic formation that comprises the storage layer 118. Further, the storage layer 118 may also have only immobile water, e.g., due to a very low permeability of the layer 118 (e.g., on the order of milli- or nanodarcys). In addition, the storage layer 118 may have sufficient ductility, such that a brittleness of the rock formation that comprises the layer 118 is between about 3 MPa and 10 MPa. Examples of rock formations of which the storage layer 118 may be composed include shale, salt, and anhydrite (among others). Further, in some aspects, hazardous material may be stored below the storage layer, even in a permeable formation such as sandstone or limestone, if the storage layer is of sufficient geologic properties to isolate the permeable layer from the mobile water layer 114. In some aspects, the layer 118 may have properties suitable for a long-term confinement of nuclear waste, and for its isolation from a mobile water layer (e.g., aquifers) and a terranean surface. Such formations may be found relatively deep in the Earth, typically 3000 feet or greater, and placed in isolation below any fresh water aquifers. For instance, the appropriate formation may include geologic properties that enhance the long-term (e.g., thousands of years) isolation of material. Such properties, for instance, have been illustrated through the long term storage (e.g., tens of millions of years) of hydrocarbon fluids (e.g., gas, liquid, mixed phase fluid) without escape of substantial fractions of such fluids into surrounding layers (e.g., mobile water layer). For example, shale has been shown to hold natural gas for millions of years or more, giving it a proven capability for long-term storage of hazardous material. Example shale formations (e.g., Marcellus, Eagle Ford, Barnett, and otherwise) has stratification that contains many redundant sealing layers that have been effective in preventing movement of water, oil, and gas for millions of years, lacks mobile water, and can be expected (e.g., based on geological considerations) to seal hazardous material (e.g., fluids or solids) for thousands of years after deposit. In some aspects, the formation may form a leakage barrier, or barrier layer to fluid leakage that may be determined, at least in part, by the evidence of the storage capacity of the layer for hydrocarbons or other fluids (e.g., carbon dioxide) for hundreds of years, thousands of years, tens of thousands of years, hundreds of thousands of years, or even millions of years. Another particular quality of shale that may advantageously lend itself to hazardous material storage is its clay content, which, in some aspects, provides a measure of ductility greater than that found in other, impermeable rock formations. For example, shale may be stratified, made up of thinly alternating layers of clays (e.g., between about 20-30% clay by volume) and other minerals. Such a composition may make shale less brittle and, thus less susceptible to fracturing (e.g., naturally or otherwise) as compared to rock formations in the impermeable layer (e.g., dolomite or otherwise). For example, rock formations in the impermeable layer may have suitable permeability for the long term storage of hazardous material, but are too brittle and commonly are fractured. Thus, such formations may not have sufficient sealing qualities (as evidenced through their geologic properties) for the long term storage of hazardous material. In some aspects, the formation of the storage layer 118 and/or the impermeable layer 116 may form a leakage barrier, or barrier layer to fluid leakage that may be determined, at least in part, by the evidence of the storage capacity of the layer for hydrocarbons or other fluids (e.g., carbon dioxide) for hundreds of years, thousands of years, tens of thousands of years, hundreds of thousands of years, or even millions of years. For example, the barrier layer of the storage layer 118 and/or impermeable layer 116 may be defined by a time constant for leakage of the hazardous material more than 10,000 years (such as between about 10,000 years and 1,000,000 years) based on such evidence of hydrocarbon or other fluid storage. The present disclosure contemplates that there may be many other layers between or among the illustrated subterranean layers 112, 114, 116, and 118. For example, there may be repeating patterns (e.g., vertically), of one or more of the mobile water layer 114, impermeable layer 116, and storage layer 118. Further, in some instances, the storage layer 118 may be directly adjacent (e.g., vertically) the mobile water layer 114, i.e., without an intervening impermeable layer 116. In some examples, all or portions of the radiussed drillhole 108 and the horizontal drillhole 110 may be formed below the storage layer 118, such that the storage layer 118 (e.g., shale or other geologic formation with characteristics as described herein) is vertically positioned between the horizontal drillhole 110 and the mobile water layer 114. In this example, the horizontal portion 110 of the drillhole 104 includes a storage area in a distal part of the portion 110 into which hazardous material may be retrievably placed for long-term storage. For example, a work string (e.g., tubing, coiled tubing, wireline, or otherwise) or other downhole conveyance (e.g., tractor) may be moved into the cased drillhole 104 to place one or more (three shown but there may be more or less) hazardous material canisters 126 into long term, but in some aspects, retrievable, storage in the portion 110. Each canister 126 may enclose hazardous material (shown as material 145). Such hazardous material, in some examples, may be biological or chemical waste or other biological or chemical hazardous material. In some examples, the hazardous material may include nuclear material, such as SNF recovered from a nuclear reactor (e.g., commercial power or test reactor) or military nuclear material. Spent nuclear fuel, in the form of nuclear fuel pellets, may be taken from the reactor and not modified. Nuclear fuel pellet are solid, although they can contain and emit a variety of radioactive gases including tritium (13 year half-life), krypton-85 (10.8 year half-life), and carbon dioxide containing C-14 (5730 year half-life). Other hazardous material 145 may include, for example, radioactive liquid, such as radioactive water from a commercial power (or other) reactor. In some aspects, the storage layer 118 should be able to contain any radioactive output (e.g., gases) within the layer 118, even if such output escapes the canisters 126. For example, the storage layer 118 may be selected based on diffusion times of radioactive output through the layer 118. For example, a minimum diffusion time of radioactive output escaping the storage layer 118 may be set at, for example, fifty times a half-life for any particular component of the nuclear fuel pellets. Fifty half-lives as a minimum diffusion time would reduce an amount of radioactive output by a factor of 1×10−15. As another example, setting a minimum diffusion time to thirty half-lives would reduce an amount of radioactive output by a factor of one billion. For example, plutonium-239 is often considered a dangerous waste product in SNF because of its long half-life of 24,100 years. For this isotope, 50 half-lives would be 1.2 million years. Plutonium-239 has low solubility in water, is not volatile, and as a solid, its diffusion time is exceedingly small (e.g., many millions of years) through a matrix of the rock formation that comprises the illustrated storage layer 118 (e.g., shale or other formation). The storage layer 118, for example comprised of shale, may offer the capability to have such isolation times (e.g., millions of years) as shown by the geological history of containing gaseous hydrocarbons (e.g., methane and otherwise) for several million years. In contrast, in conventional nuclear material storage methods, there was a danger that some plutonium might dissolve in a layer that comprised mobile ground water upon confinement escape. In some aspects, the drillhole 104 may be formed for the primary purpose of long-term storage of hazardous materials. In alternative aspects, the drillhole 104 may have been previously formed for the primary purpose of hydrocarbon production (e.g., oil, gas). For example, storage layer 118 may be a hydrocarbon bearing formation from which hydrocarbons were produced into the drillhole 104 and to the terranean surface 102. In some aspects, the storage layer 118 may have been hydraulically fractured prior to hydrocarbon production. Further in some aspects, the production casing 122 may have been perforated prior to hydraulic fracturing. In such aspects, the production casing 122 may be patched (e.g., cemented) to repair any holes made from the perforating process prior to a deposit operation of hazardous material. In addition, any cracks or openings in the cement between the casing and the drillhole can also be filled at that time. As shown in this example, a drillhole seal 134a, such as a plug, packer, or other seal, is positioned in the vertical portion 106 of the directional drillhole 104. In some aspects, the drillhole seal 134a may prevent or help prevent hazardous waste stored in the canisters 126, or solids or fluids released by the hazardous waste in the canisters 126, from moving through the vertical portion 106 toward the terranean surface 102 from the horizontal portion 110. As further shown in this example implementation, the drillhole seal 134a is placed in the vertical drillhole portion 106, while the drillhole seal 134b is placed in the horizontal drillhole portion 110. Although two drillhole seals 134a and 134b are shown, more or fewer drillhole seals according to the present disclosure may be positioned in the hazardous waste repository 100. Further, in some aspects, both drillhole seals 134a and 134b (and others is applicable) may be positioned in the vertical drillhole portion 106. Alternatively, both drillhole seals 134a and 134b (and others is applicable) may be positioned in the horizontal drillhole portion 110. In some aspects, one or more drillhole seals (such as 134a or 134b) may be positioned in the transition drillhole portion 108. In some aspects, two or more drillhole seals (such as 134a and 134b) may be positioned in contact with each other in the directional drillhole 104. In some aspects, one or more of the previously described components of the repository 100 may combine to form an engineered barrier of the hazardous waste material repository 100. For example, in some aspects, the engineered barrier is comprised of one, some, or all of the following components: the storage layer 118, the casing 122, the canister 126, the seal 134, and the hazardous material 145, itself. In some aspects, one or more of the engineered barrier components may act (or be engineered to act) to: prevent or reduce corrosion in the drillhole 104, prevent or reduce escape of the hazardous material 145; reduce or prevent thermal degradation of one or more of the other components; and other safety measures to ensure that the hazardous material 145 does not reach the mobile water layer 114 (or surface layer 112, including the terranean surface 102). FIG. 2 is a schematic top view of an example implementation of a hazardous waste repository system 200 formed in one or more subterranean formations that include one or more faults (205 and 210). For example, the hazardous waste repository system 200 may include one or several hazardous waste repository 100. In this example, each hazardous waste repository 100 includes two horizontal drillhole portions 110 (e.g., in which hazardous waste, such as nuclear waste, is stored in hazardous waste canisters 126) that are each coupled to a single vertical drillhole portion 106. In other examples, there may be more or fewer hazardous waste repositories 100, and each hazardous waste repository 100 may have a 1:1 ratio of vertical drillhole portions 106 to horizontal drillhole portions 110. As shown in this example, one or more faults 205 and 210 are present. Each fault 205 and 210 may extend through a single subterranean formation (e.g., formation 114, or formation 116, or formation 118). Alternatively, in some cases, such faults 205 and 210 may extend through multiple subterranean formations (e.g., subterranean formations 116 and 118). In some aspects, the faults 205 or 210 may be present (e.g., naturally) in a particular subterranean formation (e.g., layer 118) in which the horizontal drillhole portion 110 that stores the hazardous waste is formed. Due to such naturally occurring faults 205 or 210, conventionally, underground disposal (e.g., in deep, human-unoccupiable directional drillholes) of nuclear waste (e.g., spent nuclear fuel or high level waste) cannot be done safely in regions in which faults occur due to likely seismic activity (e.g., earthquakes) associated with these faults 205 or 210. Since some nuclear waste is generated in regions that have large and frequent earthquakes (e.g., nuclear waste from commercial nuclear reactors in California, Taiwan, South Korea, and Japan to name a few), that assumption requires a distant location for disposal. Distant disposal can create legal issues (some countries are mandated to dispose within the country) and real or perceived risks from transportation. In some aspects, the shaking caused by a nearby earthquake is not the primary danger to the nuclear waste canisters 126 positioned in a hazardous waste repository of the deep directional drillhole 104 formed in the subterranean formation 118 (in this example). The reason is that such accelerations are typically less than 1 g (i.e., less than 980 gal, where a gal is the standard unit for acceleration, equal to 1 cm per second per second). Such accelerations present threats to surface structures, but the nuclear waste canisters 126, in some aspects, may be designed to endure much stronger accelerations. Rock at a depth of the subterranean formation 118, for example, when accessed by the directional drillhole 110, typically has a stress tensor measured by using standard geophysical techniques. Deep horizontal wellbores for hydraulic fracturing and extraction of oil and gas are typically drilled in the direction of maximum rock stress. For example, horizontal wellbores used to access regions of shale gas and/or shale oil extend in a direction of maximum horizontal stress in the rock layer through which such wellbores are formed. In the locations where an angle of the horizontal drillhole deviates from the direction of maximum horizontal stress, it does so because for that local rock, the direction of maximum stress changes. For example, in hydrocarbon recovery from shale, orientation along the direction of maximum horizontal stress is done because doing so is usually optimum for the process of hydraulic fracturing. In hydraulic fracturing, a series of perforations is made in the casing along its length in the horizontal section. High pressure water and sand is then pumped into the casing and out through the holes to fracture the rock. Under this pressure, the rock tends to fracture in the direction perpendicular to the drillhole. The desired outcome is a set of fracture planes that are perpendicular to the drillhole, so that when many holes are fractured, these fractures will be spread throughout a large volume of the target shale rock. If the fractures were parallel to the drillhole, then they would overlap, and a much smaller volume would be covered. For the underground disposal or storage of radioactive waste (e.g., SNF or high level waste), conventionally, orientation of any wellbore or human-occupiable underground repository was selected in an arbitrary direction without regard for, e.g., maximum horizontal stress of the rock layer or direction of faults therethrough. Arbitrary drillhole orientations of the horizontal drillhole portion 110 (e.g., relative to the vertical drillhole portion 106) may be acceptable, and in some cases useful, but they may also present a danger in a subterranean formation that is susceptible to seismic events, such as earthquakes. If a fault slips, that is, if the rock on one side of the fault moves with respect to the other side, and this fault crosses the hazardous waste repository section of the directional drillhole 104, then that slippage could break the continuity of the drillhole 104, could possible break one or more nuclear waste canisters 126 that is in horizontal drillhole portion 110, and at the same time create a path to the terranean surface 102 that would allow fluid, including gases and liquids, to reach the surface from the disposal section in an unacceptably short time. The hazardous waste repository system 200 shown in FIG. 2 is an example implementation of one or more hazardous waste repositories 100 formed in one or more subterranean formations in regions where earthquakes are frequent and/or likely to occur in the future. As described with respect to FIG. 1, the horizontal drillhole portions 110 may be formed in or under a subterranean formation (e.g., layer 118) that is or includes an impervious or impermeable seal to the transmission of fluid (e.g., liquid or gas) therethrough. For example, the formation may be shale, salt, clay, or other type of rock. As shown in this example, in the hazardous waste repository system 200, each of the horizontal drillhole portions 110 of the hazardous waste repositories 100 are oriented parallel to the particular fault 205 or 210 that extends through the same subterranean formation as the drillhole portions 110. For example, in some aspects, the horizontal (or nearly horizontal) drillholes 110 may achieve a greater safety against accidental rupture from earthquake faults 205 or 210 if such drillhole 110 are aligned perpendicular to the direction of maximum horizontal stress (that is, parallel to the faults 205 or 210). Thus, the hazardous waste repository system 200 includes horizontal drillhole portions 110 that are parallel to a direction in which a fracture caused by a seismic event is most likely to occur, either from extension of an existing fault 205 or 210 (which may or may not be known to geologists) or from the creation of a new fault during the earthquake or other seismic event. This orientation may significantly reduce the likelihood that an earthquake-induced fracture will cross the hazardous waste repository area of the deep directional drillhole 104. In an example operation, a particular subterranean formation (e.g., storage layer 118) may be determined as being suitable as a hazardous waste repository. For example, the particular subterranean formation may be suitable based on, e.g., one or more geologic parameters (e.g., permeability, ductility, brittleness), one or more test results on a liquid (e.g., brine) found in the subterranean formation, geographic location, or other criteria. The suitability of the particular subterranean formation as a hazardous waste repository may be, for example, its ability to sealingly store nuclear waste for a long period of time (e.g., tens of years, hundreds of years, thousands of years, tens of thousands of years). In a next step, a determination is made of whether one or more faults extend through the particular subterranean formation and, if so, where such fault (or faults) extend. For example, in some aspects, faults may be located (and known) from seismic records. In some aspects, faults may be identified from seismic reflection surveys (showing discontinuities in competent strata) or through geologic mapping. In some aspects, indirect methods, e.g., detection of methane leaks, might detect faults at a terranean surface, such as if the fault is hydraulically conducting. In some aspects, electromagnetic (EM) surveys may also diagnose fault locations. As further examples, faults may be known or determined since many faults occur in conjugate planes. For example, while the Hayward fault zone in California is a known fault, there are also faults at an acute (e.g., not quite 90 degrees) angle to the Hayward fault that can also create earthquakes. Thus, in some aspects, deep directional drillholes may be formed that are parallel to known (and the riskiest) faults while still intersecting other (less risky) faults. As another example, Taiwan is at an example of a collision margin (e.g., convergent margin where tectonic plates are moving toward each other). Thus, in this area, most of the faults are thrust and reverse with fault planes oriented in the collision direction. Relatedly, a stress tensor of the rock at depth can be determined using the geophysical techniques that are used in the oil and gas technology. However, even before drilling, it can be estimated by mapping of nearby faults. In a region that has a stress tensor that varies only slowly over location, the earthquake faults will be parallel, and thus mapping gives the desired direction. In a next step, a directional drillhole (e.g., a vertical portion, radius portion, and horizontal portion) may be formed and oriented parallel to the determined one or more faults without any intersection between the drillhole and the fault(s). The hazardous waste repository is then formed in, e.g., the horizontal portion of the directional drillhole and hazardous waste (e.g., radioactive waste) is emplaced therein. In some aspects, in an area that has nearby faults, an optimum location for a deep directional drillhole may be between two parallel faults and originated in the same direction as the faults. Thus, neither of these faults intersects the hazardous waste repository area of a deep directional drillhole, nor would such faults intersect the hazardous waste repository area if an earthquake lengthened the faults. In some aspects, the existence of these faults provides a relief for stress that could build in the rock; stress that, in the absence of these existing faults, might create a new fault. FIG. 3 is a schematic illustration of an example implementation of a drillhole seal 300 for a hazardous waste repository, such as hazardous waste repository 100 shown in FIG. 1. In some aspects, the drillhole seal 300 may be used as one or both of drillhole seals 134a or 134b in the repository 100. As shown in the example implementation of FIG. 1, for example, drillhole seal 134a is positioned in the vertical drillhole portion 106. In some aspects, when a drillhole (or wellbore), such as drillhole portion 106, is created, there is typically a “disturbed zone” that circumscribes the created drillhole, often extending into the rock layer a distance roughly equal to the radius of the drillhole. This disturbed zone provides a potential pathway for the waste (such as hazardous waste 145 if leaked from canisters 126) to be carried to the terranean surface 102 by, e.g., flowing water and brine. Another possible leakage path is in the space 302 (e.g., annulus 302) between a casing (e.g., the casing 120) and the rock formation (e.g., formations 112 through 118 and others) through which the drillhole 104 extends. For some drillholes, the annulus 302 is filled with cement. The capability to prevent leakage in this location is related, in some aspects, to the lifetime of the cement. The drillhole seal 300, as shown in FIG. 3, is placed in the vertical drillhole portion 106 of the deep directional drillhole 104 (e.g., a human-unoccupiable drillhole) that includes or is part of the hazardous waste repository 100. In some aspects, the seal 300 (also called a plug) may utilize a geologic formation property called “creep,” which may advantageously be utilized to seal the vertical drillhole portion 106 (in this example). Creep occurs, for example, in shale, in clay, in salt, and other rocks. Creep, generally, is a slow flow of the rock that tends to fill cracks and other discontinuities. In the example implementation shown in FIG. 3, the seal 300 includes one or more rock portions made of particular rocks (or a particular rock) that exhibits creep. As shown in FIG. 3 (and also with reference to components shown in FIG. 1), the drillhole seal 300 includes a frame or housing 304 that at least partially encloses a rock (or other natural) material 306. The rock material 306, in some aspects, is shale, or clay, or salt, or other rock material that exhibits creep. In some aspects, the frame or housing 304 is at least partially open to the annulus 302, the subterranean formation 116, or both. Thus, in some aspects, as the rock material 306 exhibits creep, the material 306 may move to fill in spaces between the frame 304 and, e.g., the formation 116 (e.g., fill in all or part of a disturbed zone around the vertical drillhole portion 106). In this example, a diameter, d, of the drillhole seal 300 is larger than a diameter, D, of the casing 120. Thus, in this example, a milled portion 308 of the casing 120 (and cement 130 and perhaps the formation 116) may be removed prior to installation of the drillhole seal 300 in the vertical drillhole portion 106. In such aspects, an expandable portion of the drillhole seal 300 (not shown), such as a packer-type device, may be expanded to adjust the drillhole seal 300 into the milled portion 308. In alternative aspects, the diameter, d, of the drillhole seal 300 may be less than the diameter, D, of the casing 120. In such aspects as well, an expandable portion of the drillhole seal 300 (not shown), such as a packer-type device, may be expanded to adjust the drillhole seal 300 to contact the casing 120. In alternative aspects, the diameter, d, of the drillhole seal 300 may be equal to or approximately equal to the diameter, D, of the casing 120. The example implementation of the drillhole seal 300 can be used at a rock layer that is similar in composition to the rock material 306 (e.g., shale, clay, salt, or other rock), but it can also be used at other layers (e.g., rock layers made of limestone or basalt) that are dissimilar to the rock material 306. In some aspects, the rock material 306 could be obtained from the drillhole 104 itself; if more material 306 is needed (e.g., for multiple drillhole seals 300), then such material 306 could be brought in from another location. In some aspects, salt can also be used for the rock material 306 in the seal 300. For example, salt has the property that local water can dissolve it, and that could help move it into the damaged zone (e.g., adjacent the milled portion 308) to help seal the damaged zone that circumscribes the drillhole portion 106. However, in some aspects, care must be taken to assure that any salt not be vulnerable to dissolution by deep brines. An indicator of safety against dissolution would be if those brines are already saturated with salt. In another example implementation, the rock material 306 may be comprised of multiple types of rock, at least one of which exhibiting the property of creep. Some of these types of rock material 306 may match the rock layer, e.g., in the subterranean formation 116, thus making the hole filled be similar at depth to the pre-existing rock. The rock material 306 of the seal 300 may not be identical to the subterranean formation 116, since the rock in the layer 116 will be solid, although perhaps cracked in the disturbed zone, but the rock material 306 in the seal 300 may consist of smaller pieces in order to be put in place. In some aspects, matching the rock type at depth may provide a more continuous seal that would otherwise be available with a conventional hydrocarbon operations seal (e.g., bridge plug, packer, or otherwise). In addition, in some aspects, the drillhole seal 300 may include other sealing materials, such as, for example, cement, bentonite, or other sealing material. Although described as positioned in the vertical drillhole portion 106, the drillhole seal 300 can be used with drillholes with any orientation (or formed for other purposes). A drillhole seal 300 in accordance with this disclosure could be used, for example, to seal conventional oil and gas wells. In an example operation, once the waste canisters have been emplaced in the directional drillhole 104, the milled portion 308 (e.g., of the casing 120 and cement 130 and possibly part of the layer 116) is optionally formed (e.g., with a reaming tool). For example, the portion of the casing 120 may be removed (e.g., milled out or otherwise cut away) to improve a secure seal between the seal 300 and the surrounding rock formation 116. In some aspects, a seal-to-casing seal may not be as secure. For example, without removing the portion of the casing 120, there is a possibility that a pathway will exist in the annulus 302 (or otherwise radially outside of the casing 120) that could convey water or brine, perhaps containing hazardous waste 145 to the terranean surface 102 or near surface (e.g., to a source of mobile water). In some aspects, only a portion of the casing 120 in the vertical drillhole 106 is removed, as it may not be necessary to remove all of the casing 120. For example, in some aspects, the intent is to seal the vertical drillhole 106 at several locations, and not necessarily at all depths. By removing the portion of the casing 120, a disc-shaped portion with an outer diameter greater than the diameter, D, of the casing 120 (and possibly the vertical drillhole portion 106) is formed at a particular depth in the vertical drillhole portion 106. In some aspects, the horizontal disposal repository drillhole sits underneath one or more layers of clay-rich shale, a rock that has appropriate creep properties. The vertical drillhole portion 106 may penetrate this layer. The shale (e.g., a “cap” layer) may also be self-healing and reduce fractures and other pathways that could allow gases and liquids to move quickly through the layer. Once the portion of the casing 120 is removed, drillhole seal 300 is inserted into the vertical portion 106 of the drillhole 104 to the depth at which the casing portion is removed. As the disc-shaped volume created by the removal of the casing 120 is filled by the drillhole seal 300, the pressure of rock at shallower depths presses against the rock layer 116 over a short period of time (days to years), thereby causing creep that “heals” (e.g., fills in) small cracks and discontinuities in the disc-shaped volume (e.g., the milled portion 308). As described, the downhole seal 300 may include the frame 304 or other structure (e.g., made of a corrosion resistant material) that holds or at least partially encloses the creep material 306. Such filling material 306 is not standard for sealing holes in the oil and gas industry since a quicker seal is typically desired. For that reason, cement is frequently a component. However, implementations of the drillhole seal 300 described here provides an engineered barrier for strong isolation and protection for thousands of years by taking advantage of the process of creep to provide a better long-term seal for a hazardous waste repository. The present disclosure also contemplates implementations of systems and methods to seal a portion (vertical portion 106, horizontal portion 110, or both) of the directional drillhole 104 that stores hazardous (e.g., nuclear) waste that include multiple drillhole seals 300 positioned in the directional drillhole 104. For example, once the waste canisters 126 have been emplaced in the directional drillhole 104, portions of the casing 120 at two or more depths are removed. In some aspects, each drillhole seal 300 includes rock material 306 that matches the natural geologic formation at the particular depth of each seal 300, and which, from the pressure of rock above, forms a good seal with that geologic formation. In some aspects, there may be a respective drillhole seal 300 positioned in the vertical portion 106 at each different geologic formation (e.g., subterranean formations 112, 114, 116, 118) between the terranean surface 102 and a formation in which a hazardous waste repository is located (e.g., subterranean formation 118). Alternatively, there may be a respective drillhole seal 300 positioned in the vertical portion 106 at less than all of the geologic formations between the terranean surface 102 and the formation 118 in which a hazardous waste repository is located. To install each drillhole seal 300, in this example, a portion of the casing 120 is removed as previously described. A particular drillhole seal 300 that includes a material 306 that has good creep properties and/or matches a geologic formation at a desired set-depth of the seal 300 is inserted into the vertical portion 106 of the drillhole 104 to the depth at which the casing portion is removed. As described, in this example, each seal 300 includes rock material 306 that matches the formation at a particular depth at which the seal 300 is to be set. To facilitate creep, the rock material 306 may be divided into small pieces prior to being formed into the seal 300. For example, if the space between pieces is less than 0.1 mm, then the creep time to fill the gaps is shorter than if there are gaps of several millimeters (or greater distances). In an example implementation of this method, the rock material 306 used to fill the annulus 302 at the depth would be rock that was obtained from that layer (e.g., subterranean formation 112, 114, 116, or 118) when the drillhole 104 was originally formed. Alternatively, the rock material 306 could be rock obtained from another drillhole, or it could be rock obtained from a location in which the same geologic formation comes closer to or reaches the terranean surface 102. Thus, the rock material 306 used to form the seal 300 may have as good of a match with the geologic formation as possible to assure that over time there will be little to no unconformity between the fill and the undrilled rock. In some aspects, there is not a seal 300 set to match every formation in the case of “layer cake” geology, i.e. geology that consists of many layers of different kinds of rock. In some aspects, there may be only one seal 300 that is set at a layer that will provide a seal against leakage. FIGS. 4A-4B are schematic illustrations of an example implementation of a nuclear waste dry cask 400 that encloses one or more nuclear waste canisters 420 for a hazardous waste repository according to the present disclosure. As shown, FIG. 4A shows a vertical cross-section of the nuclear waste dry cask 400 in which multiple nuclear waste canisters 420 are enclosed. FIG. 4B shows a radial cross-section taken from FIG. 4A. Generally, the nuclear waste dry cask 400 may enclose and store, for a transient amount of time, nuclear waste, such as SNF or high level waste. For instance, after spending several years in a cooling pool, nuclear waste in the form of SNF assemblies may be moved to “dry cask” storage. Currently, about one-third of the SNF inventory in the United States is in such storage, but that fraction is expected to grow rapidly. A conventional SNF assemblies is typically a rectangular solid in shape, between 8 to 12 inches wide (diagonal dimension of square cross section), and 14 feet long. In some aspects, thirty-six or more of the SNF assemblies are placed in a conventional canister (with a diameter of about 5 feet). The canister is filled with helium gas (to distribute heat generated by the assemblies), sealed, and placed inside a conventional concrete cask. A conventional cask may have walls that are typically 2 feet thick, which provide radiation (e.g., gamma ray) shielding for people in the vicinity of the cask. Air is circulated around the large canister (within the dry cask) to provide cooling. Conventional dry cask storage is designed (and licensed) for temporary storage. For permanent storage, the top concrete lid is removed, the canister weld broken, and the SNF assemblies lifted out and placed in disposal canisters. These steps must be done either under water or in a “hot cell” (e.g., a room certified for handing nuclear material) since the fuel assemblies can emit gases and other radioactive material. Example implementations of the nuclear waste dry cask 400 facilitates transfer of one or more nuclear waste canisters 420 (that may be circular, square, rectangular, or other shape in cross-section) that are stored in the nuclear waste dry cask 400 into permanent disposal (e.g., for hundreds if not thousands of years) in a deep, human-unoccupiable directional drillhole (such as drillhole 104 shown in the hazardous waste repository 100 in FIG. 1). In some aspects, nuclear waste 426, shown as an example in one of the canisters 426, is SNF in one or more SNF assembles that are formed from multiple SNF rods 428. As shown in FIGS. 4A-4B, nuclear waste 426 may represent a single SNF assembly with multiple rods 428 (however, other example implementations of the nuclear waste canister 426 may store multiple SNF assembles or even just a portion of a single SNF assembly). Other implementations of the nuclear waste dry cask 400 may store high level nuclear waste. In this example implementation, each nuclear waste canister 420 includes a housing 421 to which a lid 422 and bottom 424 are sealed (e.g., subsequent to emplacement of the nuclear waste 426). In some aspects, the example implementations include the loading of SNF assemblies 426 in individual nuclear waste canisters 420 (i.e., each SNF assembly 426 is loaded into a single canister 420 and each canister 420 is sized to enclose a single SNF assembly 426). In some aspects, the nuclear waste canister 420 may include radiation shielding (e.g., for gamma ray or X-ray radiation) around (or as part of) the circumferential housing 421 of the canister 420 (e.g., from and between lid 422 to bottom 424) but not at (or as part of) the lid 422 or bottom 424 of the canister 420. Multiple canisters 420 may then be loaded into the nuclear waste dry cask 400. Thus, in this example implementation of the nuclear waste dry cask 400, a single large canister that holds many (e.g., 36) SNF assemblies is not placed into the nuclear waste dry cask 400 but instead, multiple SNF canisters 420 are loaded into the nuclear waste dry cask 400. Once loaded, individual SNF canisters 420 can later be removed without the need for a hot cell or a cooling pool. The canisters 420 are sealed and prevent leakage of radioactive material (such as the SNF assemblies 426). As shown in FIG. 4A, the nuclear waste dry cask 400 includes a top 404 and a bottom 406 that connect with a housing 402 to define an inner volume 408 into which the nuclear waste canisters 420 may be emplaced. One or more cooling fluid flow paths 410 may be defined in the volume 408 through which a cooling medium (e.g., airflow, liquid coolant, or otherwise) is circulated to remove heat from the nuclear waste canisters 420. Further, one or both of the top 404 or bottom 406 may be moveable to expose the volume 408 to an environment external to the nuclear waste dry cask 400. In some aspects, one or both of the top 404 or bottom 406 is moveable without fully detaching the top 404 or bottom 406 from the housing 402, such as through a hinge between the top 404 or bottom 406 and the housing 402. Alternatively, one or both of the top 404 or bottom 406 may radially pivot (e.g., in an arc) about a pivot connection with the housing 402 to swing and expose the volume 408 to the environment. In this example implementation, each of the top 404, the bottom 406, and the housing 402 of the nuclear waste dry cask 400 includes or is comprised of radiation (e.g., gamma ray) shielding sufficient to protect, e.g., humans in an area near the cask 400, from such radiation. In some aspects, the top 404, bottom 406, and housing 402 include or are made of concrete of a sufficient thickness to provide such radiation shielding. Alternatively, the top 404, bottom 406, and housing 402 include or are made of another shielding material, such as tungsten, of a sufficient thickness to provide such radiation shielding. In some aspects, a thickness of tungsten (as a non-cementitious material example) sufficient for radiation shielding is less than, and perhaps orders of magnitude less than, a thickness of concrete sufficient for radiation shielding. As noted, in some aspects, each SNF canister 420 does not provide or excludes radiation shielding from the gamma rays except at the lid 422 and bottom 424. When the SNF canisters 420 are removed from the nuclear waste dry cask 400, the canisters 420, in some aspects, be inserted into a smaller concrete shield or lowered directly into a vertical entrance of the deep directional drillhole 104. For example, when inserting the nuclear waste canisters 420 stored in the nuclear waste dry cask 400 into the vertical entrance, the dry cask 400 may be placed above the vertical opening of the drillhole 104 (e.g., of the vertical portion 106). The bottom 406 of the dry cask 400 may be removed or moved (e.g., slid out to a side of the nuclear waste dry cask 400) to expose the inner volume 408 of the cask 400 in which the SNF canisters 420 are enclosed. The position of the dry cask 400 may be adjusted until a particular one of the SNF canisters 420 is in position above the vertical entrance of the disposal drillhole 104. The canister 420 is then lowered through the vertical entrance and ultimately to a hazardous waste repository in a horizontal drillhole portion 110 of the deep directional drillhole 104, e.g., for permanent storage. This process may be repeated, e.g., for each SNF canister 420 stored in the nuclear waste dry cask 400. In an alternative aspect, the top 404 of the nuclear waste cask 400 is removed (e.g., completely, slid away, or rotated away) to expose the inner volume 408, and the canisters 420 are raised into a smaller transfer cask. A transfer cask, in some aspects, may be a smaller version of the nuclear waste dry cask 400 and is designed to hold, typically, one SNF canister 420 (although it could hold two or more, but less than the nuclear waste dry cask 400). The transfer cask is much smaller than the nuclear waste dry cask 400 and may contain no particular cooling system since the SNF canister 420 may be in this transfer cask only for a short period of time (e.g., relative to the nuclear waste dry cask 400). The transfer cask is then moved to the disposal drillhole 104, and the SNF canister 420 lowered into the vertical opening as described. Thus, in some aspects, once the inner volume 408 is exposed, one or more SNF canisters 420 may be removed (e.g., lowered) from the volume 408 into a vertical entrance of a deep directional drillhole 104 (or alternatively into a transfer cask). In some aspects, no additional gamma ray shielding (besides that of the nuclear waste dry cask 400 and the individual SNF canisters 420, as described) is required or used to place the SNF canisters 420 into transfer casks or directly into the directional drillhole 104. Implementations of the nuclear waste dry cask 400 according to the present disclosure may, therefore, significantly simplify the process of transfer from dry cask temporary storage to permanent disposal in deep directional drillholes. FIGS. 5A-5B are schematic illustrations of an example implementation of a power generator system 500 for a hazardous waste repository in a directional drillhole. In some aspects (and with reference to certain components described and shown in FIG. 1), when hazardous waste, such as nuclear waste (e.g., SNF or high level waste or both), is disposed underground, such as in a human-unoccupiable deep directional drillhole (e.g., in drillhole 104), there may be instruments (as all or part of a hazardous waste repository monitoring system) placed near on in contact with one or more hazardous waste canisters (e.g., canisters 126) that store the hazardous waste (e.g., hazardous waste 145). In some aspects, the instruments (e.g., to measure radiation, temperature, pressure, and other environmental conditions in or surrounding the drillhole 104) may be able to communicate to the terranean surface 102. Such communication can facilitate “performance confirmation” of the hazardous waste repository 100, e.g., as possibly required by a regulatory agency. In some aspects, all or a part of a hazardous waste repository monitoring system (e.g., instruments, sensors, controllers, or otherwise) utilizes electrical power. Conventionally, such power could be supplied by a cable that extends within the directional drillhole 104 to the surface 102, but that cable then creates a pathway along which hazardous waste could escape (e.g., through a mobile liquid). A conventional alternative to wired power could be to include a battery at depth, but batteries have limited lifetimes. Example implementations of the power generator system 500 generates electrical power in the hazardous waste repository of a deep directional drillhole 104, e.g., to power one or more instruments that monitor hazardous waste stored in the repository. In some aspects, the hazardous waste is radioactive waste, such as SNF or high level waste. In some aspects, the power generator system 500 utilizes heat generated by the stored radioactive waste to generate electrical power. As shown in FIG. 5A (and with reference to certain components shown in FIG. 1), nuclear waste canisters 126 that enclose radioactive waste 145 (e.g., SNF assemblies) are emplaced in a hazardous waste repository in the directional drillhole 104. For example, in some aspects, a single nuclear waste canister 126 that stores nuclear waste in the directional drillhole 104 (and more specifically, the horizontal drillhole portion 110) produces heat energy at a rate of several hundred watts. As that energy is conducted away, e.g., through any filling within the drillhole portion 110, through casing 120 (if casing is used) and into the rock of the subterranean formation 118, the heat creates a temperature difference that can be exploited to obtain electric (or mechanical) power. In an example implementation, a nuclear waste canister 126 may enclose a single spent nuclear fuel assembly (represented as 145 in FIG. 5A). There may be several nuclear waste canisters 126 placed end-to-end within the hazardous waste repository of the directional drillhole portion 110. A temperature profile of such a configuration is shown in FIG. 5C, as a chart 550 of temperature at a radial distance from center of the canisters 126 along a cased drillhole axis (e.g., of the drillhole portion 110). In chart 550, the x-axis represents a distance (in meters) along the horizontal drillhole portion 110 in which the canisters 126 are emplaced. The y-axis represents a radial distance (in meters) from a centerline axis of the canisters 126. This configuration assumes a 100 W rate of power generation per canister 126 and a four foot spacing between canisters 126. In this example, the temperature difference between the end of the canisters 126 and the center of the four foot (cooler) gap between the canisters is about 20° C. This temperature difference, in some aspects, can be used to generate power by the power generator system 500. In the example implementation of power generator system 500, thermoelectric power is generated from heat that is output from the nuclear waste 145. For instance, the power generator system 500 may use or include a radioisotope thermal generators (RTG). As shown in FIG. 5A, the power generator system 500 is positioned in the directional drillhole 104 (e.g., in the horizontal drillhole portion 110) in an annular space between, e.g., the four foot gap between, adjacent nuclear waste canisters 126. The example power generator system 500 includes at least one flat sheet thermoelectric generator 506 positioned between heat transfer conductors 504 and heat transfer conductors 502. In this example, the heat transfer conductors 504 may be heat source conductors 504, as they are positioned closer to a heat source of the closest nuclear waste canister 126. The heat transfer conductors 502 may be heat sink conductors 502, as they are positioned further (relative to the conductors 504) from the heat source of the closest nuclear waste canister 126. An example implementation of the thermoelectric generator 506 is shown in FIG. 5B. As shown, the thermoelectric generator 506 includes plates 507 and 509 (e.g., ceramic plates) that provide thermal (e.g., conductive) contact with the respective heat sink conductors 502 and the heat source conductors 504. In some aspects, the plates 507 and 509 may be the conductors 502 and 504, respectively. Mounted between the plates 507 and 509 are n- and p-type semiconductor materials 511 that are in contact with the plates 507 and 509 through conductive members 513. Poles 514 are electrically connected to the thermoelectric generator 506 to provide current, I, based on operation of the generator 506. In some examples, the power generator system 500 may include or be placed in a container to hold the illustrated components. As shown, springs 508 are included to bias or urge the heat source conductors 504 and heat sink conductors 502 against the casing 120. However, the power generator system 500 could also be put inside a container that serves another purpose. For example, the power generator system 500 could be placed inside a device that measures temperature and pressure and the radioactivity of the environment, and which records such data or broadcasts the data to a distant recorder (e.g., on the terranean surface 102). In FIG. 5A, the flat sheet of the thermoelectric generator 506 is shown perpendicular to the illustration, but the generator 506 could be any orientation. As shown, a region to the right of the heat sink conductor 502 is empty. However, in some aspects, another set of thermoelectric conductors 506 can be placed in that region as well. For example, FIG. 5A shows the power generator system 500 filling the space 516 between two nuclear waste canisters 126 in the horizontal drillhole portion 110. In some aspects, however, depending on the desired amount of generated power, fewer thermoelectric generators 506 can be used, although longer heat conductors 502 and 504 might then be used to bring in heat from the hottest regions 518 of the drillhole portion 110. As further shown in FIG. 5A, radiation (e.g., gamma ray) shields 512 may be placed on ends of the nuclear waste canisters 126. A further radiation shield 510 may also be positioned near or in contact with the power generator system 500 to, e.g., reduce the exposure of the thermoelectric generators 506 to gamma rays from the nuclear waste 145. In some aspects, additional shielding could be added to the power generator system 500. In some aspects, radiation shielding is a tungsten shield, since tungsten is a gamma ray absorber and has good long-term anti-corrosion properties. Other gamma ray absorption materials may be used. In some aspects, the power generator system 500 is made of radiation resistant materials. Example implementations that use radiation resistant materials may not generate as much power (e.g., current) as a design that uses conventional materials. Such generators might use, for example, metals with different thermoelectric properties in contact with each other, rather than using semiconductors. In operation, the example implementation of the power generator system 500 has no moving parts other than the springs 508, which urge the heat transfer conductors 502 and 504 against the casing 120. During operation, only electrons move. The heat source conductor 504 conducts heat along a gap between the nuclear waste canisters 126 to a side of a thermoelectric generator 506. Another side of the thermoelectric generator 506 is in thermal contact (e.g., conductive) with a heat sink, e.g., a material in the drillhole portion 110 that is cooler than the canister 126, through the heat sink conductor 502. For example, the heat sink material may be fluid or other filler material within the drillhole portion 110, or the material may be an inner surface of the drillhole casing 120 (e.g., a carbon steel casing). Based on a temperature difference between the conductors 502 and 504 and across the thermoelectric generator 506, an electrical current is generated by the thermoelectric generator 506, which can be provided to one or more components or systems in the hazardous waste repository that require electrical power. In some aspects, the heat source conductor 504 may be attached to the nuclear waste canister 126 or other hot surface, such as the drillhole filler or casing 120 in a hot region near a canister 126. In some aspects, one or both of the heat source conductor 504 or heat sink conductor 502 may be a rod made of metal or some other conductive material such as glass. Alternatively, one or both of the heat source conductor 504 or heat sink conductor 502 may be a heat pipe or other heat transfer device such as a tube containing a gas such as helium. In some aspects, the power generator system 500 may provide other forms of power besides electrical power. For instance, based on the described temperature difference between the heat source and the heat sink, a differential pressure pump may be implemented based on a density difference at two ends of a tube caused by the temperature difference. If the tube were then closed in the middle, the density difference would become a pressure difference, and this pressure difference could be used to drive a generator or to send a signal directly to the surface using an acoustic wave. As another example, a power generator system may generate power directly from the gamma rays generated by the nuclear waste rather than from a temperature difference. FIG. 5D is a flowchart that illustrates an example process 580 that includes generating electric power with the power generator system 500 of FIG. 5A. Process 580 may begin at step 581, which includes placing one or more nuclear waste canisters and a power generator system (e.g., power generator system 500) in a hazardous waste repository of a directional drillhole. For example, one or more nuclear waste canisters that enclose radioactive, or nuclear, waste may be emplaced in the horizontal drillhole portion of the directional drillhole. In some aspects, all or a portion of the horizontal drillhole portion comprises a hazardous waste repository. The radioactive waste generates heat and radiation (e.g., gamma rays). In some aspects, the generated heat is transferred from the waste to the canister and, in some cases, an annulus of the drillhole portion. In an example embodiment, the emplaced power generator system is positioned in a space between adjacent nuclear waste canisters in the horizontal drillhole portion. Process 580 may continue at step 582, which includes urging heat transfer members of the power generator system into thermal contact with a heat source and a heat sink in the hazardous waste repository. For example, the power generator system may include a first heat transfer member that is urged (e.g., with springs or another biasing member) into thermal contact (e.g., conductive thermal contact, or convective thermal contact, or both) with a heat source. The heat source may be, for example, one or more nuclear waste canisters, a casing portion heated by one or more nuclear waste canisters, a drillhole backfill material heated by one or more nuclear waste canisters, or a combination thereof. The power generator system may include a second heat transfer member that is urged (e.g., with springs or another biasing member) into thermal contact (e.g., conductive thermal contact, or convective thermal contact, or both) with a heat sink. The heat sink may be, for example, a fluid in the drillhole, a casing portion unheated by one or more nuclear waste canisters, a drillhole backfill material unheated by one or more nuclear waste canisters, or a combination thereof. Process 580 may continue at step 583, which includes thermally contacting, with a heat transfer member, the heat source in the hazardous waste repository. For example, the first heat transfer member is placed into thermal contact (and in some aspects, physical contact) with the heat source so that a temperature of the first heat transfer member is adjusted to at or near a temperature of the heat source. Process 580 may continue at step 584, which includes thermally contacting, with another heat transfer member, the heat sink in the hazardous waste repository. For example, the second heat transfer member is placed into thermal contact (and in some aspects, physical contact) with the heat sink so that a temperature of the second heat transfer member is adjusted to at or near a temperature of the heat sink (which is less than the heat source). Process 580 may continue at step 585, which includes generating electric power with a thermoelectric generator thermally coupled to the heat transfer members based on a temperature difference between the heat source and the heat sink. For example, the thermoelectric generator is thermally coupled to the heat transfer members such that the temperature difference between the heat source and heat sink is translated across, e.g., semiconductor material of the thermoelectric generator. The semiconductor material generates an electric current based on the temperature difference. Process 580 may continue at step 586, which includes supplying the generated electric power to a portion of the hazardous waste repository. For example, in some aspects, the generated electrical power may be supplied to one or more components of a hazardous waste repository monitoring system, such as radiation sensors, temperature sensors, liquid sensors, or control systems (e.g., microprocessor based systems) communicably coupled to such sensors. In some aspects, such sensors or control systems (e.g., as described in U.S. patent application Ser. No. 16/430,005, incorporated by reference herein) may be located in the horizontal drillhole portion, another drillhole portion of the directional drillhole, or another directional or vertical drillhole formed in or adjacent the subterranean formation in which the hazardous waste repository is located. In some aspects, such sensors or control systems may be located at or near the terranean surface and electrical power is supplied from the power generator system toward the surface. While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. A first example implementation according to the present disclosure includes a nuclear waste dry cask that includes a housing that at least partially defines an inner volume sized to enclose a plurality of nuclear waste canisters. Each nuclear waste canister is sized to store a portion of nuclear waste. The housing includes radiation shielding. The cask further includes a lid sized to enclose a top opening of the inner volume and comprising radiation shielding; and a bottom sized to enclose a bottom opening of the inner volume and comprising radiation shielding. In an aspect combinable with the first example implementation, the portion of nuclear waste comprises a spent nuclear fuel (SNF) assembly. In another aspect combinable with any of the previous aspects of the first example implementation, each nuclear waste canister is sized to store a single SNF assembly. In another aspect combinable with any of the previous aspects of the first example implementation, the radiation shielding comprises a material that absorbs gamma rays or prevents gamma rays from passing therethrough. In another aspect combinable with any of the previous aspects of the first example implementation, the bottom is configured to move to expose the bottom opening of the inner volume. In another aspect combinable with any of the previous aspects of the first example implementation, the bottom is slideable to expose the bottom opening of the inner volume. In another aspect combinable with any of the previous aspects of the first example implementation, each SNF canister comprises radiation shielding only on a top surface and a bottom surface of the SNF canister. In another aspect combinable with any of the previous aspects of the first example implementation, the radiation shielding comprises concrete. In another aspect combinable with any of the previous aspects of the first example implementation, the lid is configured to move to expose the top opening of the inner volume. In another aspect combinable with any of the previous aspects of the first example implementation, the plurality of nuclear waste canisters comprise at least fifteen nuclear waste canisters. A second example implementation according to the present disclosure includes a method for storing nuclear waste that includes placing a plurality of nuclear waste canisters in a nuclear waste dry cask that comprises a housing that at least partially defines an inner volume sized to enclose the plurality of nuclear waste canisters. Each nuclear waste canister is sized to store a portion of nuclear waste. The housing includes radiation shielding. The method further includes enclosing a top opening of the inner volume with a lid that comprises radiation shielding; and enclosing a bottom opening of the inner volume with a bottom that comprises radiation shielding. In an aspect combinable with the second example implementation, the portion of nuclear waste comprises a spent nuclear fuel (SNF) assembly. In another aspect combinable with any of the previous aspects of the second example implementation, each nuclear waste canister is sized to store a single SNF assembly. In another aspect combinable with any of the previous aspects of the second example implementation, the radiation shielding comprises a material that absorbs gamma rays or prevents gamma rays from passing therethrough. Another aspect combinable with any of the previous aspects of the second example implementation further includes moving the nuclear waste dry cask over a vertical entrance of a directional drillhole. Another aspect combinable with any of the previous aspects of the second example implementation further includes moving the bottom to expose the bottom opening of the inner volume to the vertical entrance. In another aspect combinable with any of the previous aspects of the second example implementation, moving the bottom comprises sliding the bottom to expose the bottom opening of the inner volume to the vertical entrance. Another aspect combinable with any of the previous aspects of the second example implementation further includes moving at least one of the nuclear waste canisters out of the inner volume, through the bottom opening, and into the vertical entrance. Another aspect combinable with any of the previous aspects of the second example implementation further includes moving all of the nuclear waste canisters out of the inner volume, through the bottom opening, and into the vertical entrance. Another aspect combinable with any of the previous aspects of the second example implementation further includes moving at least one of the nuclear waste canisters into a hazardous waste repository of the directional drillhole. In another aspect combinable with any of the previous aspects of the second example implementation, each SNF canister comprises radiation shielding only on a top surface and a bottom surface of the SNF canister. In another aspect combinable with any of the previous aspects of the second example implementation, the radiation shielding comprises concrete. In another aspect combinable with any of the previous aspects of the second example implementation, the lid is configured to move to expose the top opening of the inner volume. In another aspect combinable with any of the previous aspects of the second example implementation, the plurality of nuclear waste canisters comprise at least fifteen nuclear waste canisters. A third example implementation includes a method for forming a directional drillhole for hazardous waste storage includes identifying a subterranean formation suitable to store hazardous waste; determining one or more faults that extend through the subterranean formation; forming a vertical drillhole from a terranean surface toward the subterranean formation; and forming a directional drillhole from the vertical drillhole that extends in or under the subterranean formation and parallel to at least one of the one or more faults. The directional drillhole includes a hazardous waste repository configured to store the hazardous waste. An aspect combinable with the third example implementation further includes forming the directional drillhole perpendicular to a direction of maximum horizontal stress of the subterranean formation. In another aspect combinable with any of the previous aspects of the third example implementation, the subterranean formation is located in an area of high risk of seismic activity. In another aspect combinable with any of the previous aspects of the third example implementation, the seismic activity includes earthquakes. In another aspect combinable with any of the previous aspects of the third example implementation, the hazardous waste includes radioactive or nuclear waste. In another aspect combinable with any of the previous aspects of the third example implementation, the nuclear waste includes spent nuclear fuel or high level waste. In another aspect combinable with any of the previous aspects of the third example implementation, the subterranean formation includes at least one of shale, clay, or salt. In another aspect combinable with any of the previous aspects of the third example implementation, the one or more faults includes at least two parallel faults. In another aspect combinable with any of the previous aspects of the third example implementation, forming the directional drillhole includes forming the directional drillhole between and parallel to the at least two parallel faults. In another aspect combinable with any of the previous aspects of the third example implementation, determining the one or more faults includes determining the one or more faults based on at least one of one or more seismic records; one or more seismic reflection surveys; a geologic mapping; or one or more electromagnetic (EM) surveys. In another aspect combinable with any of the previous aspects of the third example implementation, the directional drillhole does not cross the one or more faults. In a fourth example implementation, a hazardous waste repository system includes a directional drillhole that extends from an entry proximate a terranean surface to a subterranean formation that includes one or more faults that extend through the subterranean formation. The directional drillhole includes a substantially vertical portion coupled to the entry, a transition portion coupled to the substantially vertical portion, and a substantially horizontal portion that is coupled to the transition portion and is formed in or under the subterranean formation and parallel to at least one of the one or more faults. The system further includes a hazardous waste repository formed in the substantially horizontal portion of the directional drillhole; a storage container positioned in the hazardous waste repository, the storage container including an inner volume sized to enclose hazardous waste material; and a seal positioned in the directional drillhole that isolates the hazardous waste repository from the entry. In an aspect combinable with the fourth implementation, the directional drillhole extends perpendicular to a direction of maximum horizontal stress of the subterranean formation. In another aspect combinable with any of the previous aspects of the fourth example implementation, the subterranean formation is located in an area of high risk of seismic activity. In another aspect combinable with any of the previous aspects of the fourth example implementation, the seismic activity includes earthquakes. In another aspect combinable with any of the previous aspects of the fourth example implementation, the hazardous waste material includes radioactive or nuclear waste. In another aspect combinable with any of the previous aspects of the fourth example implementation, the nuclear waste includes spent nuclear fuel or high level waste. In another aspect combinable with any of the previous aspects of the fourth example implementation, the subterranean formation includes at least one of shale, clay, or salt. In another aspect combinable with any of the previous aspects of the fourth example implementation, the one or more faults includes at least two parallel faults. In another aspect combinable with any of the previous aspects of the fourth example implementation, the directional drillhole extends between and parallel to the at least two parallel faults. In another aspect combinable with any of the previous aspects of the fourth example implementation, the one or more faults are determined based on at least one of one or more seismic records; one or more seismic reflection surveys; a geologic mapping; or one or more electromagnetic (EM) surveys. In another aspect combinable with any of the previous aspects of the fourth example implementation, the directional drillhole does not cross the one or more faults. A fifth example implementation according to the present disclosure includes a power generator system that includes one or more heat transfer members configured to contact a heat source in a hazardous waste repository of a directional drillhole that stores nuclear waste in one or more nuclear waste canisters and a heat sink in the hazardous waste repository; and one or more thermoelectric generators thermally coupled to the one or more heat transfer members and configured to generate electric power based on a temperature difference between the heat source and the heat sink. In an aspect combinable with the fifth example implementation, the nuclear waste comprises spent nuclear fuel. In another aspect combinable with any of the previous aspects of the fifth example implementation, the heat source comprises at least one of the nuclear waste canisters or a casing disposed in the drillhole. In another aspect combinable with any of the previous aspects of the fifth example implementation, the heat sink comprises at least one of the casing disposed in the drillhole or a material that at least partially fills the drillhole. In another aspect combinable with any of the previous aspects of the fifth example implementation, the material comprises a liquid. Another aspect combinable with any of the previous aspects of the fifth example implementation further includes one or more biasing members configured to urge the one or more heat transfer members into thermal contact with the heat source and the heat sink. Another aspect combinable with any of the previous aspects of the fifth example implementation further includes at least one radiation shield. In another aspect combinable with any of the previous aspects of the fifth example implementation, the radiation shield comprises tungsten. In another aspect combinable with any of the previous aspects of the fifth example implementation, the one or more heat transfer members comprise a radiation resistant material. In another aspect combinable with any of the previous aspects of the fifth example implementation, the one or more thermoelectric generators comprise a radiation resistant material. A sixth example implementation according to the present disclosure includes a method for generating power in a hazardous waste repository of a directional drillhole that stores nuclear waste that includes contacting, with one or more heat transfer members of a power generator system, a heat source in the hazardous waste repository of the directional drillhole that stores nuclear waste in one or more nuclear waste canisters; contacting, with the one or more heat transfer members of the power generator system, a heat sink in the hazardous waste repository; and generating electric power with one or more thermoelectric generators thermally coupled to the one or more heat transfer members based on a temperature difference between the heat source and the heat sink. In an aspect combinable with the sixth example implementation, the nuclear waste comprises spent nuclear fuel. In another aspect combinable with any of the previous aspects of the sixth example implementation, the heat source comprises at least one of the nuclear waste canisters or a casing disposed in the drillhole. In another aspect combinable with any of the previous aspects of the sixth example implementation, the heat sink comprises at least one of the casing disposed in the drillhole or a material that at least partially fills the drillhole. In another aspect combinable with any of the previous aspects of the sixth example implementation, the material comprises a liquid. Another aspect combinable with any of the previous aspects of the sixth example implementation further includes urging, with one or more biasing members of the power generator system, the one or more heat transfer members into thermal contact with the heat source and the heat sink. Another aspect combinable with any of the previous aspects of the sixth example implementation further includes shielding gamma rays generated by the nuclear waste from the power generator system with at least one radiation shield. In another aspect combinable with any of the previous aspects of the sixth example implementation, the radiation shield comprises tungsten. In another aspect combinable with any of the previous aspects of the sixth example implementation, the one or more heat transfer members comprise a radiation resistant material. In another aspect combinable with any of the previous aspects of the sixth example implementation, the one or more thermoelectric generators comprise a radiation resistant material. A seventh example implementation according to the present disclosure includes a drillhole sealing system that includes a plurality of drillhole seals. Each drillhole seal includes a frame or housing comprising a corrosion-resistant material and sized to fit within a particular milled portion of a directional drillhole that comprises a hazardous waste repository; and a particular rock material that fills at least a portion of the frame or housing. The rock material is selected to match a geologic formation at a depth at which the particular drillhole seal is set and exhibits creep such that the material fills one or more voids between the frame or housing and the geologic formation at the depth and adjacent the particular milled portion of the directional drillhole. In an aspect combinable with the seventh example implementation, each particular milled portion is located at a vertical portion of the directional drillhole. In another aspect combinable with any of the previous aspects of the seventh example implementation, each particular milled portion does not include casing and other portions of the directional drillhole comprise casing. In another aspect combinable with any of the previous aspects of the seventh example implementation, the particular rock material comprises at least one of shale, clay, or salt. In another aspect combinable with any of the previous aspects of the seventh example implementation, an outer diameter of each drillhole seal is greater than an outer diameter of the directional drillhole. In another aspect combinable with any of the previous aspects of the seventh example implementation, the outer diameter of each drillhole seal is less than a diameter of the particular milled portion. In another aspect combinable with any of the previous aspects of the seventh example implementation, the particular rock material of one of the plurality of drillhole seals is different than the particular rock material of another of the plurality of drillhole seals. In another aspect combinable with any of the previous aspects of the seventh example implementation, a number of the plurality of drillhole seals matches a number of geologic formations between a terranean surface and subterranean formation in which the hazardous waste repository is formed. In another aspect combinable with any of the previous aspects of the seventh example implementation, the particular rock material of each of the plurality of drillhole seals matches a respective geologic formation adjacent the drillhole seal. In another aspect combinable with any of the previous aspects of the seventh example implementation, each frame or housing loosely contains the particular rock material. In another aspect combinable with any of the previous aspects of the seventh example implementation, the frame or housing comprises a wire or mesh enclosure. An eighth example implementation according to the present disclosure includes a method for sealing a drillhole that includes milling a first portion of a directional drillhole that comprises a hazardous waste repository and inserting a first drillhole plug into the first milled portion. The first drillhole plug includes a frame or housing that comprises a corrosion-resistant material and a first rock material that fills at least a portion of the frame or housing. The first rock material is selected to match a geologic formation at a depth at which the first drillhole plug is set and exhibits creep such that the first rock material fills one or more voids between the frame or housing and the geologic formation at the depth and adjacent the first milled portion of the directional drillhole. The method further includes milling a second portion of the directional drillhole and inserting a second drillhole plug into the second milled portion. The second drillhole plug includes a frame or housing that comprises the corrosion-resistant material and a second rock material that fills at least a portion of the frame or housing. The second rock material is selected to match a geologic formation at a depth at which the second drillhole plug is set and exhibits creep such that the second rock material fills one or more voids between the frame or housing and the geologic formation at the depth and adjacent the second milled portion of the directional drillhole. The method further includes sealing the directional drillhole with the first and second rock materials of the respective first and second drillhole plugs that fill one or more voids between the frames or housings and a subterranean formation adjacent the first and second milled portions of the directional drillhole. In an aspect combinable with the eighth example implementation, at least one of the first or second milled portions is located at a vertical portion of the directional drillhole. In another aspect combinable with any of the previous aspects of the eighth example implementation, each of the first and second milled portions does not include casing and other portions of the directional drillhole comprise casing. In another aspect combinable with any of the previous aspects of the eighth example implementation, at least one of the first or second rock materials comprises at least one of shale, clay, or salt. In another aspect combinable with any of the previous aspects of the eighth example implementation, an outer diameter of each of the first and second drillhole plugs is greater than an outer diameter of the directional drillhole. In another aspect combinable with any of the previous aspects of the eighth example implementation, the outer diameter of each of the first and second drillhole plugs is less than a diameter of the respective first and second milled portions. In another aspect combinable with any of the previous aspects of the eighth example implementation, the first rock material is different than the second rock material. In another aspect combinable with any of the previous aspects of the eighth example implementation, each frame or housing loosely contains the respective first or second rock material. In another aspect combinable with any of the previous aspects of the eighth example implementation, the frame or housing comprises a wire or mesh enclosure. In another aspect combinable with any of the previous aspects of the eighth example implementation, the second drillhole plug is uphole of and is in contact with the first drillhole plug. Another aspect combinable with any of the previous aspects of the eighth example implementation further includes milling a third portion of the directional drillhole; and inserting a third drillhole plug into the third milled portion. In another aspect combinable with any of the previous aspects of the eighth example implementation, the third drillhole plug includes a frame or housing that comprises a corrosion-resistant material and a third rock material that fills at least a portion of the frame or housing. In another aspect combinable with any of the previous aspects of the eighth example implementation, the third rock material selected to match a geologic formation at a depth at which the third drillhole plug is set. In another aspect combinable with any of the previous aspects of the eighth example implementation, the third rock material exhibits creep such that the third rock material fills one or more voids between the frame or housing and the geologic formation at the depth and adjacent the third milled portion of the directional drillhole. Another aspect combinable with any of the previous aspects of the eighth example implementation further includes further sealing the directional drillhole with the third rock material of the third drillhole plug that fill one or more voids between the frame or housing and the subterranean formation adjacent the third milled portion of the directional drillhole. A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, example operations, methods, or processes described herein may include more steps or fewer steps than those described. Further, the steps in such example operations, methods, or processes may be performed in different successions than that described or illustrated in the figures. Accordingly, other implementations are within the scope of the following claims. |
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abstract | A device for shielding at least a region of a creature from exposure to unwanted radiation during the use of an x-ray or other medical diagnostic machine or equipment includes one of a first portion sized and configured to shield an upper extremities region of the creature and a second portion sized and configured to shield a lower extremities region of the creature. The first and second portions are comprised of two opposite end regions constructed of a radiation absorbing material and connected by a middle region constructed of a non-radiation absorbing material. |
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051480328 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION FIG. 1 shows a part of a radiation therapy device 2 of common design, in which plates 4 and a control unit constructed in accordance with the principles of the invention are used. The radiation therapy device 2 comprises a gantry 6 which can be swiveled around a horizontal axis of rotation 8 in the course of a therapeutic treatment. The plates 4 are fastened to a projection of the gantry 6. To generate the high-powered radiation required for the therapy, a linear accelerator is located in the radiation therapy device 2. The axis of the radiation bundle emitted from the linear accelerator and the radiation therapy device 2 is designated by 10. Either electron radiation or photon radiation (X-ray radiation) can be used for the therapy. During the treatment, the radiation beam is trained on a zone 12 of a patient 13 which is to be treated and which lies in the isocenter of the gantry rotation. The rotational axis 8 of the gantry 6, the rotational axis 14 of a treatment table 16 and the beam axis 10 all intersect in the isocenter. The construction of such a radiation therapy device is described in detail in a publication "A Primer on Theory and Operation of Linear Accelerators in Radiation Therapy", U.S. Department of Health and Human Services, Rockville, MD, December 1981. FIG. 2 illustrates portions of the control unit and of the beam generation system in the radiation therapy device 2 according to FIG. 1. An electron beam 1 is generated in an electron accelerator 20. Accelerator 20 comprises an electron gun 21, a waveguide 22 and an evacuated envelope or guide magnet 23. A trigger system 3 generates injector trigger signals and supplies them to injector 5. Based on these injector trigger signals, injector 5 generates injector pulses which are fed to electron gun 21 in accelerator 20 for generating the electron beam 1. The electron beam 1 is accelerated and guided by waveguide 22. For this purpose, a HF source (not shown) is provided which supplies RF signals for the generation of an electromagnetic field supplied to waveguide 22. The electrons injected by injector 5 and emitted by electron gun 21 are accelerated by this electromagnetic field in waveguide 22 and exit at the end opposite to electron gun 21 as electron beam 1. Electron beam 1 then enters the guide magnet 23 which bends electron beam 1 by 270 degrees. Electron beam 1 then leaves guide magnet 23 through a window 7 along axis 10 and then encounters a first scattering foil 15, goes through a passage way 51 of a shield block 50 and encounters a second scattering foil 17. Next, it is sent through a measuring chamber 60, in which the dose is ascertained. If the scattering foils are replaced by a target, the radiation beam is a X-ray beam. Finally, aperture plate arrangement 4 is provided in the path of radiation beam 1, with which the irradiated field of the subject of investigation is determined. Aperture plate arrangement 4 comprises a pair of plates 41 and 42 which are moveable in a direction substantially perpendicular to axis 10 of radiation beam 1. An additional pair of aperture plates can be provided being moveable in a direction perpendicular to axis 10 and to the moving direction of plates 41 and 42. It is also possible that only one plate of said pair is moveable during radiation. Plates 41 and 42 are moved by a drive unit 43 which is indicated only with respect to plate 41 in FIG. 2. Drive unit 43 comprises an electric motor which is coupled to plate 41 and which is controlled by a motor controller 40. A position sensor 44 is also coupled to plate 41 for sensing its position. Motor controller 40 is coupled to a dose control unit which includes a dosimetry controller 61 for providing set values for the radiation beam dose rate in correlation with the position of plate 41 for achieving a given isodose curve. The dose rate of the radiation beam is measured by measuring chamber 60. In response to the deviation between the set values and the actual values, dosimetry controller 61 supplies signals to trigger system 3 which change the pulse repetition frequency so that the deviation between the set values and the actual values of the radiation beam dose rate is minimized. Thus, the dose control unit controls the dose rate of the radiation beam in correlation with the movement of plate 41 in order to achieve the given isodose curve. The ability to change the dose rate is generally known and it is particularly advantageous to use a digital dosimetry system. FIG. 3 shows a graph of dose rate and the accumulated dose for the radiation therapy device of FIGS. 1 and 2 with the moveable plate arrangement. During movement of the plate, the dose rate is changed in a way so that an accumulated dose is achieved which corresponds to a given rigid filter. The mathematical algorithm for a dynamic wedge filter is as follows: If one wants to generate a wedge-shaped isodose contour of an angle .alpha. at 10 cm depth, the dose profile at depth d can be expressed as: ##EQU1## wherein: D(d) is the dose at depth d; and .mu. is the attenuation coefficient of the beam. PA1 x is the jaw position; PA1 k is a scaling factor; PA1 D.sub.10 is the dose at the central axis 10 cm from the surface; PA1 .alpha. is the desired wedge angle; PA1 I.sub.1 is the machine's constant intensity during the idle time; PA1 t.sub.1 is the idle time; and PA1 D total is the total dose. Assume we have a moving jaw at constant speed v along a radiation field of length S.sub.0. Under the above conditions, it can be derived from equation (1) that the machine's intensity during the jaw movement should follow the function: ##EQU2## and the total dose is: ##EQU3## wherein: I is the machine's intensity; There has thus been shown and described a novel radiation therapy device which fulfills all the objects and advantages sought for. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings which disclose an embodiment thereof. For example, the variation of the radiation dose rate does not have to be done simultaneously with the movement of the plates. The radiation could be interrupted or intermittently kept constant during the movement of the plates. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow. |
abstract | A modular and transportable nuclear reactor system comprising a transportation module including a housing. A cask and a radiation shielding section are located in the housing with the shielding surrounding the cask. A high temperature sodium cooled reactor is located in the cask and the reactor is cooled by the natural circulation of in-vessel sodium. The reactor powers at least one thermal-to-electric conversion unit. |
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abstract | Disclosed is an electromagnetic wave interference (EMI)/radio frequency interference (RFI) shielding resin composite material including (A) a thermoplastic polymer resin, (B) a tetrapod whisker, and (C) a low melting point metal. |
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claims | 1. A method for machining a groove of poloidal segments of a vacuum chamber of a fusion reactor, comprising:collecting three-dimensional (3D) point cloud data of a surface of individual poloidal segments of the vacuum chamber of the nuclear fusion reactor;performing a reverse model reconstruction based on the three-dimensional point cloud data,to generate an actual 3D model of the vacuum chamber of the fusion reactor; andacquiring a sectional view of the vacuum chamber of the fusion reactor according to the actual 3D model; andextracting a cross-reconstruction region between two adjacent poloidal segments from the sectional view;calculating a target machining allowance of each of the poloidal segments according to the cross-reconstruction region and a preset segment boundary;generating a machining strategy for the groove of each of the poloidal segments according to the target machining allowance and a target groove size; andmachining the groove of each of the poloidal segments by using the machining strategy. 2. The method of claim 1,wherein the step of “calculating the target machining allowance of each of the poloidal segments according to the cross-reconstruction region and the preset segment boundary” is performed through steps of:calculating a total machining allowance based on an area of the cross-reconstruction region;if the preset segment boundary locates in the cross-reconstruction region,calculating an area ratio of two sub-regions divided by the preset segment boundary in the cross-reconstruction region; andcalculating the target machining allowance of each of the poloidal segments according to the area ratio and the total machining allowance; andif the preset segmenting boundary is outside the cross-reconstruction region,distributing the total machining allowance according to a preset distribution strategy to obtain the target machining allowance of each of the poloidal segments. 3. The method of claim 1,wherein the step of “generating the machining strategy for each of the poloidal segments according to the target machining allowance and the target groove size” is performed through steps of:calculating a difference between actual machining allowances of adjacent poloidal segments;if the difference is greater than a preset value,correcting the preset segment boundary according to the difference;wherein a corrected preset segment boundary is close to the poloidal segment with a larger actual machining allowance; andgenerating a groove machining parameter of each of the poloidal segments according to the corrected preset segment boundary and the target groove size;wherein a portion to be cut at an end face of one poloidal segment with the larger actual machining allowance is larger than the portion to be cut at the end face of the other poloidal segment with a smaller actual machining allowance. 4. The method of claim 1,wherein the step of “collecting the three-dimensional (3D) point cloud data of a surface of the individual poloidal segments of a vacuum chamber of the fusion reactor” is performed through steps of:taking a coordinate system of a laser tracker as a first 3D coordinate system; andcollecting a 3D point cloud data of the end face of each of the poloidal segments by using a measuring arm; andwherein the surface of the individual poloidal segments is composed of an end face and the side face;collecting the 3D point cloud data of the end face of each of the poloidal segments by using the measuring arm; andconverting the 3D point cloud data of the end face of each of the poloidal segments to the first 3D coordinate system according to a common reference point calibrated between the measuring arm and the laser tracker. 5. The method of claim 1,wherein the step of “performing the reverse model reconstruction,based on the three-dimensional point cloud data,to generating the actual 3D model of the vacuum chamber of the fusion reactor” is performed through steps of:establishing a second 3D coordinate system in a design software; andgenerating an ideal 3D model of the vacuum chamber of the fusion reactor in the design software;performing relationship matching between the 3D point cloud data of the surface of each of the poloidal segments and the ideal 3D model until a relationship matching result meets a target convergence accuracy to obtain an optimal fitting relationship between the 3D point cloud data of the surface of each of the poloidal segments and the ideal 3D model; andconverting the 3D point cloud data of the surface of each of the poloidal segments to the second 3D coordinate system according to the optimal fitting relationship; andperforming model reverse reconstruction on each of the poloidal segments under the second 3D coordinate system to generate the actual 3D model of the vacuum chamber of the fusion reactor. |
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052009866 | abstract | In an x-ray examination apparatus comprising. a frame (2) to which are connected an x-ray source (3) for emission of an x-ray beam and an x-ray detector (5) that is placed opposite the x-ray source, and PA0 filter means (31) that are placed between the x-ray source (3) and the x-ray detector (5) the filter means (31) comprising an x-ray absorbing filter body (33) and drive means for positioning the filter body in the x-ray beam, the drive means comprise two disk-shaped holding members between which the filter body is placed. The filter body is in a pivot-point pivotably fixed to one holding member and is provided with a pawl that engages a curved radial groove in the second holding member. By joint rotation of the holding members the filter body is translated in the x-ray beam whereas by rotation of one of the holding members only, the curved radial groove causes the filter body to rotate in the x-ray beam. |
053848128 | claims | 1. A cabling arrangement for a plurality of cables, each removably connectable at a first end to a head package on a reactor vessel located in a containment, the containment characterized by a wall having a near side surrounding the reactor vessel and defining a cavity, an operating deck outside the cavity, a sub-space below the deck and on a far side of the wall spaced from the near side, and an operating area above the deck, and each of the cables having a second end located in the sub-space, the arrangement comprising: a movable frame supporting the cables which extends through the frame; and positioning means for moving the frame with the cables between a first position outside the sub-space proximate the head package and a second position in the sub-space. a pivot arrangement near a first end of the frame distal from the reactor vessel and overhanging the sub-space for permitting the frame to pivot between the first position and a substantially vertically oriented intermediate position; and guide means for guiding the frame between the intermediate position and the second position. a movable cable carrier supporting a plurality of cables extending through the carrier, each of the cables connectable at a first end to a head package on the reactor vessel and each having a second end located in the sub-space, the carrier movable with the cables between a first position outside the sub-space spaced from and proximate the head package, oriented about horizontally and straddling a top of the wall, and a second position in the sub-space oriented about vertically proximate the far side of the wall, the carrier including: positioning means for moving the carrier between the first position and the second position, including: 2. The arrangement of claim 1, wherein the frame in the first position is oriented about horizontally and straddles a top of the wall, and in the second position is oriented about vertically proximate the far side of the wall. 3. The arrangement of claim 2, wherein the positioning means is characterized by: 4. The arrangement of claim 3, wherein the guide means comprises a track fixed in an about vertical orientation proximate the far side of the wall and engaging the frame for movement of the frame along the track between the intermediate position and the second position. 5. The arrangement of claim 4, wherein the guide means further comprises motive means for lifting the frame from the second position to the intermediate position. 6. The arrangement of claim 5, wherein the motive means is powered by a system selected from the group consisting of an electric motor system, a hydraulic system, and a pneumatic system. 7. The arrangement of claim 2, wherein the frame comprises a first end distal from the head package in the first position, and a connector plate at a second end opposite the first end and through which each of the cables pass in spaced relation. 8. The arrangement of claim 7, wherein the frame further comprises retraction means for retracting the first ends of at least some of the cables towards the connector plate when the first ends are disconnected from the head package. 9. The arrangement of claim 8, wherein the retraction means includes spring bias means for spring biasing each of the at least some of the cables such that a connector at the first end of each of the at least some of the cables is retracted toward the connector plate when each of the at least at some of the cables is disconnected from the head package. 10. The arrangement of claim 9, wherein the spring bias means comprises a plurality of elongated tension springs, each connected at a first end proximate the connector plate to a different one of the at least some of cables and each connected at a second end distal from the connector plate to a fixed member within the frame. 11. The arrangement of claim 2, wherein the frame further comprises support means for providing support to at least some of the plurality of cables between the first end of the frame and the second end of the frame when the frame is in the first position. 12. The arrangement of claim 11, wherein the frame further comprises separation means for preventing crossing of at least some of the cables between the first end of the frame and the second end of the frame. 13. The arrangement of claim 12, wherein the separation means includes at least one vertical member within the frame. 14. A cabling arrangement for a reactor vessel located in a containment characterized by a wall having a near side surrounding the reactor vessel and defining a cavity, an operating deck outside the cavity, a sub-space below the deck and on a far side of the wall spaced from the near side, and an operating area above the deck, the arrangement comprising: 15. The cabling arrangement of claim 14, wherein the support means includes a first fixed member extending between opposite sides of the carrier and the spacer means includes a second fixed member extending between an upper side and a lower side of the carrier. 16. The cabling arrangement of claim 14, wherein the retraction means includes a plurality of springs for biasing the first end of each of the cables towards the connector plate. 17. The cabling arrangement of claim 14, wherein the guide means includes motive means for raising the carrier between the second position and the intermediate position. 18. The cabling arrangement of claim 17, wherein the retraction means includes a plurality of springs for biasing the first end of each of the cables towards the connector plate. 19. The cabling arrangement of claim 18, wherein the support means includes a first fixed member extending between opposite sides of the carrier and the spacer means includes a second fixed member extending between an upper side and a lower side of the carrier. |
040574679 | description | DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 the primary cooling water enters from the bottom into the reactor core 1, which consists of numerous, vertical, parallel fuel assemblies, not shown, and flows from there to an annular steam generator housing 2 concentrically arranged above the reactor core 1, flows through the housing 2 from the bottom to the top and is pushed by pumps 3, which are driven by electric motors 4, into the previously referred to hollow ring 5 of box-shaped cross section, which has at its underside, and more specifically, at its outer rim, numerous openings 6, through which the primary cooling water flows downwardly into a ring canal or passage 7 and from there into a space 8 to the side and below the reactor. Should the primary circulating pumps 3 fail, a natural thermal circulation system is set up, in which the hot primary water flows upward in the reactor core as in normal operation. As the steam generators 9 remain in operation, the primary cooling water is cooled down here. First, natural circulation is produced through the standing mechanism of the pumps 3. When the water level drops, an internal natural thermal circulation system is set up between the hot reactor core 1 and the cold steam generator 9, which can be utilized for the emergency removal of the core decay heat. FIG. 2 shows how the hollow ring 5 is clamped between a step or internal flange 10a of the pressure vessel 10 and the inner periphery 11a of the closure head 11. This clamping point is made in a manner not shown in detail of a ferritic metal which is coated with a thin austenitic metal, so that no appreciable thermal expansion can occur with respect to the ferritic metal pressure vessel. The hollow ring 5 carries, depending on the number of pumps, for instance, four inlet sections 12 (see FIG. 3), through which the primary water cooled down in the steam generator 9 flows from the steam generator housing 2 into the running mechanisms of the pumps 3. In each pump housing 13, the primary water is deflected and pushed into the hollow ring 5, which communicates with the ring canal or passage 7 via openings 6 which are distributed over the circumference of the parts. This ring canal 7 is formed on the one hand by the inner wall of the pressure vessel 10 and, on the other hand, by the outer wall of the steam generator housing 2. This steam generator housing 2, in turn, is bounded at its inside wall by a separate, closed ring canal 14, into which the cold feed water pipes 15 are led downward. The steam generator housing 2 is supported at several vertically sliding surfaces 17 against the inside wall of the pressure vessel 10 and is terminated at its lower end by a conical bottom 16 which supports, on the other hand, the core barrel 18, containing the core 1, which has at its lower end an inlet cage 19 which is provided with numerous holes and is centered at the pressure vessel bottom 21 in a vertically slidable manner via a central post 20. The core barrel 18 rests with a projection on the conical bottom 16 of the steam generator housing 2 and is secured there by the support structure 22, which can be bolted to the hollow ring 5 at its upper side. This support structure 22 serves at the same time for guiding and mounting the control rod drives 23. As shown by FIG. 2, this support structure 22 has a top periphery provided with an external flange 22a in engagement with the hollow ring 5. The steam nozzle 24 as well as the feed water nozzle 27 are connected via a welded lip seal with the pressure vessel 10 and carry on the inside short pipe stubs 25 which are brought through the ring canal 7 and are likewise connected by a welded lip seal. The lip seals permit the pipe stubs to be slid outwardly and free from the internals. FIG. 3 shows in a cross section through the pressure vessel a view from below onto the hollow ring 5 with the pump inlets 12 as well as the openings 6. |
claims | 1. A neutron spectrometer monitor, comprising: a plurality of neutron detectors; said monitor is placed in proximity to a suspected concentration of neutron radiation; each of said plurality of detectors further comprising a detector means stacked on an absorbing layer, said absorbing layer, being composed of a first material that absorbs protons, and each of said absorbing layers is stacked on a hydrogenous substrate; said hydrogenous substrate being composed of a second material containing hydrogen atoms, said hydrogen atoms interacting with said suspected concentration of neutrons, said hydrogenous substrate converting said neutrons to recoil protons, each of said detector means detecting recoil protons passing through said absorbing layer; each of said absorber layers having a different thickness to absorb neutron energies from 1 to 250 MeV; said plurality of neutron detectors being housed in a chamber; each of said detector means being coupled to a means for data processing; said data processing means providing a count of recoil protons to a means for proton distribution; and said means for proton distribution determines a proton distribution pattern to construct a neutron spectrum pattern indicating the spectrum of neutrons from said suspected concentration. 2. The neutron spectrometer monitor, as recited in claim 1 , further comprising said first material that absorbs protons being tantalum. claim 1 3. The neutron spectrometer monitor, as recited in claim 2 , further comprising said plurality of neutron detectors having at least 12 of said detector means. claim 2 4. The neutron spectrometer monitor, as recited in claim 3 , further comprising said chamber serving as an outer shield. claim 3 5. The neutron spectrometer monitor, as recited in claim 4 , further comprising each of said detector means being a solid state detector. claim 4 6. The neutron spectrometer monitor, as recited in claim 5 , further comprising said plurality of neutron detectors having 12 of said detector means. claim 5 7. The neutron spectrometer monitor, as recited in claim 6 , wherein each of detector means is rectangular. claim 6 8. The neutron spectrometer monitor, as recited in claim 7 , further comprising each of said detector means being a depleted n/p diode. claim 7 9. The neutron spectrometer monitor, as recited in claim 8 , further comprising said chamber being rectangular. claim 8 10. The neutron spectrometer monitor, as recited in claim 2 , further comprising a floor of said chamber being composed of said second material. claim 2 11. The neutron spectrometer monitor, as recited in claim 10 , further comprising said chamber being composed of titanium. claim 10 12. The neutron spectrometer monitor, as recited in claim 10 , further comprising said second material being solid polyethylene. claim 10 |
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043436820 | summary | FIELD OF THE INVENTION The invention relates to a plant having a feed water heating means utilized for heating feed water introduced into nuclear units during plant start up and a method of operating the plant. BACKGROUND OF THE INVENTION Plants in use utilizing nuclear units for producing a steam supply utilize nuclear reactor coolant pump heat and decay heat from the nuclear fuel within the reactor to bring a nuclear steam supply system up to a maximum temperature before the reactor is made critical to generate nuclear heat. As the water temperature in the nuclear steam supply system increases, steam is generated which is then boiled off to maintain the nuclear steam supply system at desired pressure and temperature conditions. As steam is boiled off, feed water has to be added to the system to compensate for that lost in the boiled off steam. Feed water added to the system is cold and generally at a low temperature while the metal parts making up the nuclear steam supply system are at their maximum operating temperature. The resulting difference in temperature leads to large temperature gradients across the walls of the feed water piping in the system and of the inlet nozzles in the system with the result that the possibility of thermally induced cracks in the feed water piping walls and nozzles is increased. Further introduction of cold feed water into a hot nuclear steam supply system reduces the temperature of the water already in the system resulting in a decrease in volume of the water in the system. This decrease in volume of the water already in the system may lead to possible overfilling of the system as the newly heated feed water becomes heated and expands. It is therefore an object of our invention to provide for a plant incorporating an apparatus and a method of operating the same which will result in a reduction of temperature gradients in a nuclear steam supply system during start up of a plant incorporating such a system and at the same time to provide for a plant which will further minimize overfilling of the system with feed water during start up. GENERAL DESCRIPTION OF THE INVENTION Broadly our invention comprises a plant having feed water heating means for a nuclear steam supply unit where the feed water may be heated during start up procedures. The plant has a nuclear steam supply unit for changing water to steam, a turbine, and a main steam delivery line connecting the turbine with the nuclear steam supply unit. A condenser is connected to a discharge of the turbine and a feed water delivery line extends from the condenser to the nuclear steam supply unit. A feed water pump is included in the feed water delivery line and at least one high pressure heater is positioned in the feed water delivery line between the pump and the nuclear steam supply unit. A conventional high pressure heater steam delivery line extends from a steam extraction point on the turbine to the high pressure heater and a heater operation valve is included in this line. The heater is provided with a drain. In addition to the structure included above all of which is conventional, a start up steam line extending from the main steam delivery line to a high pressure heater is provided and includes therein a start up valve. Opening of the start up valve allows steam produced by the nuclear steam supply unit to pass into the high pressure heater in order that it may heat feed water entering into the nuclear steam supply unit prior to and during plant start up. The result is that temperature gradients in the feed water piping and inlet nozzles leading to the nuclear steam supply unit are reduced thus reducing thermal stress of these parts. The plant may include a plurality of high pressure heaters in the feed water line positioned between the feed water pump and the nuclear steam supply unit. In this event each high pressure heater is connected by a conventional high pressure heater steam delivery line having a heater operation valve therein which leads to an extraction point on the turbine. |
052251500 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of instrumentation for nuclear reactor vessels such as pressurized water reactors. In particular, the invention provides an integrated head structure having a shroud which encloses retractable instrumentation above the reactor vessel head or cover. The head structure provides a structural support for use when the head is removed as a unit from the reactor vessel, with integral shielding for elements which have been exposed to radiation. The head structure also provides a means for protecting the rod position indicators and control rod drive mechanisms from the heat of the reactor vessel, by providing a cooling air path. 2. Prior Art In a nuclear reactor such as a pressurized water reactor, a sealed reactor vessel houses a number of fuel rods in assemblies fixed in a vertical orientation between upper and lower core plates in the reactor vessel. Mechanisms are provided above the head of the reactor vessel for lowering control rods into spaces between the fuel rods by a required axial distance, for controlling the level of nuclear flux by absorbing a portion of the neutrons and gamma rays emitted by the fission process. Additionally, a plurality of instrumentation tubes are provided at spaces between the fuel rods in the fuel assemblies for sensing the conditions in the core, such as neutron or gamma flux levels, exit coolant temperature and the like. The control rod positioning apparatus and the instrumentation tubes for the sensors (or their connecting cables) extend through pressure penetrations in the head of the reactor vessel. When the reactor is to be serviced, the control rods are lowered into the assemblies which carry the fuel rods, and the instrumentation tubes are retracted from the fuel assemblies. The head of the reactor vessel is unbolted and lifted away using a polar crane provided in the containment structure for the reactor vessel, and the head with its depending structures is placed on a support structure or pedestal above a pool of water. The lowermost portions of the instrumentation tubes are the most heavily irradiated, and remain below the reactor head in the pool, or may be cut away and replaced. A reactor design having instrumentation tubes extending through the head of the reactor vessel is preferred over a design having the instrumentation entering the core from below. There are a number of known variations, including for example instrumentation tubes which are guided through a top entry around a curve to engage the fuel assemblies from below. Top entry avoids forming openings or seals in the bottom of the reactor vessel, and is safer in the event of an accident. The top entry design, however, results in a rather complex structure because the instrumentation tubes must interface with a plurality of control rod positioning devices and instrumentation tube connections over the head of the reactor vessel. It also may be necessary to protect these devices and connections from the heat of the reactor vessel to ensure proper operation. The instrumentation tubes and/or the electrical connections for the tubes are guided from one or more sealed entries through the head of the reactor vessel to instrumentation thimble tubes in a plurality of fuel assemblies in the core, by guides which are disposed below the head and form parts of the internal reactor structure. are shown in U.S. patents U.S. Pat. No. 3,827,935--Gruner et al; U.S. Pat. No. 3,853,702--Bevilacqua et al; U.S. Pat. No. 4,765,947--Babin et al; and U.S. Pat. No. 4,983,351--Tower et al. Normally, at least one sensor tube is provided for each fuel assembly in the reactor core. In the Westinghouse AP600 design which is the subject of the invention, a supply of cooling air is provided to the portions of the control rod drive mechanisms and instrumentation in the area above the head of the reactor vessel. The control rod drive mechanisms in reactors can be shrouded so as to confine cooling air to the area needing cooling. In known arrangements, the shroud is a lightweight enclosure. When the top of the reactor is removed and stored, thus exposing the irradiated lower portions of the instrumentation tubes, it is often necessary to erect temporary shielding around the head structure, and in particular the depending instrumentation tubes, to avoid exposing workers to undue levels of radiation. The cooling air shroud for the control rod drive mechanism in the AP600 design extends from the reactor vessel head to a seismic support plate. The cooling air shroud enables the control rod drive assembly to be raised from the reactor vessel together with the head of the reactor vessel. The support apparatus generally, and the seismic support in particular, ensure that the control rod drive mechanism remains vertically over the fuel assemblies such that the control rods are freely movable into the fuel assemblies to damp nuclear flux, and if necessary, to shut down the reactor in case of seismic disturbance or even missile attack. SUMMARY OF THE INVENTION It is an object of the invention to provide an integral shroud and radiation shield of sufficient strength and durability to enable the reactor head and the internal structures associated with the head to be handled safely as a self supporting structural unit. It is also an object of the invention to provide a shroud structure which is provided with shielding of increasing thickness proceeding downwardly, thereby providing the greatest extent of shielding at the most highly irradiated lower portions. It is a further object of the invention to simplify and facilitate reactor maintenance steps, by allowing the reactor head to be safely handled. It is another object of the invention to provide a self supporting integral head structure which eliminates the need for lift legs and seismic support tie rods, but does not interfere with the scarce space available for control rod guides and instrumentation tubes in the area over the reactor head. These and other objects are accomplished in a nuclear reactor such as a pressurized water reactor with a reactor vessel containing nuclear fuel interspersed with thimble tubes. The reactor has an integrated head package providing structural support, increasing shielding leading toward the head, and forming a temperature limited enclosure. A reactor head engages the reactor vessel. A control rod guide mechanism disposed over the head raises and lowers control rods in certain of the thimble tubes, traversing penetrations in the reactor head, and being coupled to the control rods. An instrumentation tube structure controls instrumentation tubes having sensors movable into certain of the thimble tubes for monitoring local conditions in the reactor fuel assemblies. A coupling for the sensors extends upwardly, also traversing the reactor head such that the sensors can be retracted. A shroud is attached over the reactor head and encloses the control rod guide mechanism and at least a portion of the instrumentation tubes when retracted. The shroud forms a structural element of sufficient strength to support the head, the control rod guide mechanism and the instrumentation tube structure, and includes radiation shielding material for limiting passage of radiation from retracted instrumentation tubes. More particularly, the shroud is thicker at the bottom adjacent the head, where the more irradiated lower ends of retracted sensors reside. The head, shroud and contents thus can be removed from the reactor as a unit and rested safely and securely on a horizontal surface. |
047566566 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is illustrated a nuclear reactor vessel 10 in which the present invention may be used. The vessel 10 typically includes a reactor core (not shown) and is filled with water to a level 11. A work platform 12 is rotatably supported at the upper end of the vessel 10 by bearings 13, and has an elongated rectangular slot 14 therein to provide access to the interior of the vessel 10. A jib crane 15 may be mounted on the work platform 12 and is provided with a hoist cable 16 suspended in vertical alignment with the slot 14. In the event that the reactor core becomes damaged in use, there may result an accumulation of debris 17 and a bed 18 of loose materials including gravel, partial fuel rods and pellets and the like at the bottom of the vessel 10. In order to restore the reactor vessel 10 to service, it is necessary to first remove this accumulated bed 18 of loose material and fused debris 17. For this purpose, various tools or end effectors such as saws, chisels, hydraulic grippers and the like must be lowered into the vessel 10 and operated for loosening and removing the accumulated material. For this purpose, there is provided a tooling system 20 including a control console 21, an end effector device or tool 25, which may be of any of the aforementioned types, provided with an adapter plate 26 for attachment to a handling tool 30, constructed in accordance with and embodying the features of the present invention. The handling tool 30 serves to provide support of the end effector 25 from the crane cable 16 and also serves to provide an interconnection between the end effector device 25 and the control console 21. While the control console 21 is diagrammatically illustrated immediately above the work platform 12, it will be appreciated that it could be disposed at any remote location and, if desired, suitable visual monitoring means (not shown) could be provided. Referring now also to FIGS. 2 through 7, the handling tool 30 comprises an elongated sectional structure including a plurality of interconnected, elongated structural sections or modules, each generally designated by the numeral 31, and which are substantially identical except for length. Preferably, the structural sections 31 are provided in 7-foot and 15-foot lengths, respectively designated 31A and 31B, and may be used in any combination to reach the desired working depth. In the illustrated embodiment, three of the sections 31A and one of the sections 31B are used to provide an overall length of 36 feet. While the handling tool 30 can be used to support the associated end effector device 25 at virtually any desired depth within the vessel 10, the location of the reactor core is such that, typically, the handling tool 30 will be utilized in lengths of 22, 29 or 36 feet. Since the structural sections 31 are all substantially identical except for length, only one will be described in detail. Each structural section 31 includes an elongated, circularly cylindrical, tubular body 32, integral at its upper and lower ends, respectively, with radially outwardly extending upper and lower annular flanges 33 and 34. The upper flange 33 is provided with two small guide pins 35 and one large guide pin 36, arranged in a generally triangular pattern and projecting vertically upwardly. The small guide pins 35 are respectively secured in holes 37 in the upper flange 33, while the large guide pin 36 is secured in a hole 38. Preferably, the large guide pin 36 has a length and a diameter which are greater than those of the small guide pins 35, thereby resulting in an asymmetrical arrangement of guide pins for a purpose to be more fully explained below. Also formed through the upper flange 33 are a pair of diametrically spaced-apart, internally threaded coupling bores 39. Carried by the lower flange 34 are two coupling bolt assemblies 40, respectively disposed in vertical alignment with two bores 41 (one shown in FIG. 4) formed through the lower flange 34 and each having a counterbore portion 42 at the upper end thereof. Each coupling bolt assembly 40 includes an elongated bolt 43 having a hex head 44 and provided intermediate its ends with a flange 45. The flange 45 has a short, radially outwardly extending, annular shoulder portion 46, integral at its outer end with a depending cylindrical portion 47 coaxial with and spaced from a surrounded portion of the bolt 43. A helical compression bias spring 48 is seated in the counterbore portion 42 of the bore 41 so as to encircle the lower end of the bolt 43 when it is inserted downwardly in the bore 41, the spring 48 being trapped vertically against the shoulder portion 46 of the flange 45 and being confined laterally between the bolt 43 and the cylindrical portion 47 of the flange 45. The bolt 43 has an externally threaded lower end 49. Each coupling bolt assembly 40 also includes a retaining bracket 50 which is generally hat-shaped, having a cylindrical side wall 51, integral at its upper end with a circular end wall 52 having a circular opening 53 formed centrally therethrough. Integral with the cylindrical side wall 51 at its lower end and extending laterally outwardly therefrom at diametrically opposed locations are a pair of attachment flanges 54 adapted to be fixedly secured, as by screws 55, to the upper surface of the lower flange 34. In use, the retaining bracket 50 is mounted with the opening 53 coaxial with the bore 41 for receiving the upper end of the bolt 43 therethrough. The opening 53 has a diameter less than the outer diameter of the flange 45 to prevent passage of the flange 45 therethrough. Thus, it will be appreciated that, in use, the bolt 43 is reciprocatively axially movable between a retracted position (not shown), wherein the flange 45 is disposed against the end wall 52 of the retaining bracket 50 and no part of the bolt 43 projects below the bottom surface of the lower flange 34, and coupling positions, wherein the lower end of the bolt 43 projects downwardly beneath the lower surface of the lower flange 34. The bias spring 48 resiliently urges the bolt 43 to its retracted position, and movement of the bolt 43 toward its coupling positions is limited by engagement of the flange 45 with the upper surface of the lower flange 34, as illustrated in FIG. 4. Also provided in the lower flange 34 are two small guide holes 57 (see FIG. 7) and one large guide hole 58 arranged for respectively simultaneously receiving therein the guide pins 35 and 36 of an adjacent structural section 31, as will be explained more fully below. Also formed in the tubular body 32 adjacent to the lower end thereof and spaced circumferentially therearound is a plurality of drain holes 59 for permitting the flow of water between the interior and the exterior of the tubular body 32. Each of the structural sections 31 also includes a pair of hydraulic control segments 60 disposed therein in side-by-side parallel relationship, each of the segments 60 comprising a section of hydraulic conduit. The control segments 60 are retained in place by upper and lower circular centering plates 61 and 62, having bores 63 (FIG. 5) therethrough for respectively receiving the adjacent ends of the control segments 60. The centering plates 61 and 62 are retained in place by a plurality of circumferentially spaced-apart screws 64 extending radially inwardly through complementary holes in the tubular body 32. Each of the control segments 60 is provided at its upper and lower ends, respectively, with male and female quick-connect/disconnect couplings 65 and 67 of known construction, being respectively provided with normally-closed valves 66 and 68. It is a significant aspect of the present invention that the structural sections 31 are adapted to be easily joined together and separated remotely in the irradiated underwater environment of the vessel 10. More particularly, in assembling together two of the sections 31, the lower section is supported by suitable means and the upper section is lowered over it to bring the coupling bolts 43 of the upper section 31 respectively into vertical alignment with the internally threaded coupling bores 39 in the lower section 31. In order to facilitate accurate alignment of the coupling bolt assemblies 40, the guide holes 57 and 58 of the upper structural section 31 are respectively lowered over the guide pins 35 and 36. The asymmetrical arrangement of the guide pins and guide holes, with one being larger than the other two, ensures proper orientation of the parts. Furthermore, the fact that the large pin 36 is longer than the small pins 35 permits the upper section 31 to engage the large pin 36 first and then pivot about that pin to the proper orientation for receiving the small pins 35. When the sections 31 have thus been properly oriented with respect to each other, the upper section 31 is lowered until its lower flange 34 rests upon the upper flange 33 of the lower section 31 in the coupling position illustrated in FIGS. 2 and 4. As the parts are moved to this configuration, the hydraulic control segments 60 of the two structural sections 31 will be disposed in vertical alignment with each other and the male quick-connect/disconnect couplings 65 of the lower section 31 will automatically engage the female quick-connect/disconnect couplings 67 of the upper section 31 in a known manner to provide a firm interconnection therebetween. This interconnection automatically effects opening of the valves 66 and 68, in a known manner, to permit the free flow of hydraulic fluid therethrough. A suitable torquing tool, such as a socket wrench, may then be lowered into the vessel 10 for engaging the hex heads 44 of the bolts 43 and torquing them into threaded engagement in the coupling bores 39 of the lower section 31, against the urging of the bias spring 48, this rotation of the bolts 43 being limited by engagement of the flange 45 with the upper surface of the lower flange 34, as explained above. It will be appreciated that the adapter plate 26 of the end effector device 25 is provided with guide pins 35 and 36 and internally threaded coupling bores 39 in the same manner as the upper flanges 33 of the structural sections 31. Thus, the lowermost one of the structural sections 31 can readily be connected to the end effector device 25 in exactly the same manner as was described above for the interconnection of two adjacent structural sections 31. It will be appreciated that the end effector device 25 is also provided with male hydraulic control fittings which are adapted to interconnect automatically with the female quick-connect/disconnect couplings 67 on the lowermost one of the structural sections 31, in the same manner was described above. Additional structural sections 31 are assembled in the same manner as described above until the handling tool 30 has the desired length. The support section 70 is similar to the structural sections 31, including a tubular body 71 (FIGS. 2 and 3) provided at its lower end with a radially outwardly extending annular attachment flange 72. Integral with the attachment flange 72 and extending upwardly therefrom is an elongated bail 73, the legs of which are spanned by a support rod 74 above the upper end of the tubular body 71. The attachment flange 72 is provided with a pair of small guide holes 77 and a large guide 78 which are substantially identical in shape and arrangement to the guide holes 57 and 58 described above in the lower flange 34 of the structural section 31. Also carried by the attachment flange 72 are two of the coupling bolt assemblies 40 described above. Two hydraulic couplings 85 and 86 have the lower ends thereof disposed within the tubular body 72 for alignment with the control segments 60 of an adjacent structural segment 31. The upper ends of the hydraulic couplings 85 and 86 project laterally outwardly in opposite directions through complementary openings in the tubular body 72, being supported by retainers 87, the hydraulic couplings 85 and 86 being adapted for connection to the associated control console 21. In use, the support section 70 is coupled to the upper flange 33 of the uppermost one of the structural sections 31, in the same manner as was described above for the interconnection of two adjacent structural sections 31. The bail 73 is supported by the crane cable 16. Thus, it will be appreciated that the interconnected structural sections 31 and the support section 70 cooperate to form the elongated handling tool 30 for support and operation of the associated end effector device 25, the interconnected hydraulic control segments 60 cooperating with the hydraulic couplings 85 and 86 to provide control lines 69 providing communication between the control console 21 and the end effector device 25 for hydraulic operation thereof. It is another important aspect of the present invention that end effector devices 25 can readily be interchanged on the handling tool 30, without completely removing the handling tool 30 from the reactor vessel 10. In this regard, a new end effector tool 25 is lowered into the vessel 10 and supported in any appropriate manner, either by the lowering device or on a suitable surface in the vessel 10. The bolts 43 in the lowermost one of the structural sections 31 are unscrewed from the end effector adapter plate 26, permitting the handling tool 30 to be pulled apart from the end effector device 25, whereupon it can then be coupled to the new end effector tool 25 in the same manner as was described above. It will be appreciated that, if necessary, any of the interconnected structural sections 31 could also be decoupled in the reactor vessel 10, in the same manner. In a constructional model of the invention, the tubular bodies 32 of the structural sections 31 are preferably formed of 3-inch diameter stainless steel pipe. In order to reduce radiation streaming up the assembled handling tool 30 and to reduce buoyancy effects, the tubular bodies 32 are filled with borated reactor vessel water during tool immersion, this water being drained through the drain holes 59 when the tool is removed. A hole (not shown) may be provided in the upper centering plate 61 of each of structural section 31 to permit insertion of a hose for flushing of the interior of the tubular body 32 prior to removing the handling tool 30 from the reactor vessel 10. Preferably, the hydraulic control segments 60 are rated at 4,000 psi working pressure, as are the quick-connect/disconnect couplings 65 and 67. Because of the design of these quick-connect/disconnect couplings 65 and 67, during each disconnection of an end effector device 25 for substituting a different device, approximately 0.32 cubic inches of hydraulic fluid will be released into the reactor vessel 10 and about 0.32 cubic inches of reactor vessel water will be introduced into the end effector handling tool hoses. But at these rates, only about 1.0 gallon of fluid will be exchanged between the reactor vessel and the handling tool hoses with every 725 connect/disconnect operations. It will be appreciated that suitable adapters may be provided for connection to the control console 21 to accommodate different pressure requirements for various end effector devices 25. The total dry weight of the assembled handling tool 30 is approximately 285 pounds, and it has a design load rating of 2,000 pounds in tension and is designed to withstand a lateral load of 135 pounds at the lower end when assembled to a 36 foot length. Preferably, the end effector device 25 has a maximum design pressure rating of 4,000 psi. While the present invention has been described for a hydraulic control application, it will be appreciated that the principles of the present invention could also be utilized for electrical or pneumatic control applications. In these cases the hydraulic control segments 60 would be replaced with suitable electrical or pneumatic control segments. From the foregoing, it can be seen that there has been provided an improved handling tool for the remote handling of an end effector device in an irradiated underwater environment, the tool being sectional for selectively varying the length thereof with the sections being connectable and disconnectable remotely underwater to provide support for the end effector device and also to provide a continuous control line between the end effector and the associated control console. |
046831045 | description | Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a worm gear, worm drive or leadscrew drive mechanism 1 acting as a support, which is the basic element of the equipment. As can be seen from the cross section at the end of the device, the leadscrew drive mechanism is formed of a hollow section, with a leadscrew or spindle 2 extending along its longitudinal axis. An electric motor 3 turns the leadscrew 2 causing a non-illustrated leadscrew nut to move a support plate 4 attached to the nut along a slot 5 machined into one of the lateral surfaces of the leadscrew drive. The slot is sealed by means of a sealing lip device 6 even when the support plate is moved, since a non-illustrated connecting element between the leadscrew nut and the support plate 4 is enclosed in the sealing lip device 6. The leadscrew drive is thus sealed on all sides and can therefore be used in a water environment. A combination of such conventional leadscrew drives results in a device according to the invention as illustrated in FIGS. 2 and 3. According to FIG. 2, four leadscrew drive mechanisms 1a are mounted vertically on a base plate 7. A cover plate 8 which extends parallel to the base plate 7, rests on the front ends of the leadscrew drives facing upward. Electric motors 3 are disposed on the upper surface of the cover plate, while the drive elements thereof, which are each connected with a respective leadscrew 2 of a leadscrew drive mechanism, pass through the cover plate. Flanges 9 of the electric motors 3 serve to fix the cover plate 8 relative to the leadscrew drives 1a which extend in vertical direction. For this purpose, bolts 10 are used which pass through the flange and engage the front ends of the respective leadscrew drive mechanisms 1a. Two rotary plates or turntables 11 are disposed on the base plate 7. Each of these plates serves for receiving a fuel element 12. The cover plate has openings 13 opposite the rotary plates 11 for accommodating rotary plates 11a fitted with centering devices 14 for the respective fuel element. An actuator 15 is assigned to each rotary plate 11, 11a which can rotate the rotary plate by means of a V-belt 16. The actuators 15 assigned to one fuel element are synchronized and the centering device 14 also serves as a driving device for the fuel element. Each transverse leadscrew drive mechanism 1b is attached to the support plates 4 of two vertical leadscrew drive mechanisms 1a, by means of mounting straps 17. The leadscrew drives 1b, disposed on opposite sides and at the same level, jointly support a further leadscrew drive mechanism 1c with their plates 4a. The support plate 4a of the mechanism 1c carries a tool carrier 18. The electric motors 3 assigned to the vertical leadscrew drives 1a are electrically synchronized, producing a uniform, precise movement of the leadscrew drives 1b in the direction of an arrow 19. The same applies to the electric motors assigned to the leadscrew drive mechanism 1b which are disposed transversely, so that the leadscrew drive mechanism 1c is also moved precisely and uniformly in the direction of an arrow 20. The leadscrew drive mechanism 1c serves to move the tool or accessory carrier mechanism 18 in the direction of an arrow 21. The inspection of a fuel element is performed as follows: Non-illustrated hoisting gear attached to lugs 22 sets the equipment down in a water-filled fuel element storage pit 23. The fuel element is loaded into the equipment and the inspection can start at once. While the inspection proceeds, a second fuel element is placed into the equipment. Simultaneous loading and inspection leads to a considerable time saving. The rotary plate drive mechanism assigned to a particular fuel element positions the fuel element in such a way that the tool carrier can travel into gaps between the fuel rods. The electric motors 3 can be remotely controlled by non-illustrated cables and by a non-illustrated control unit disposed outside the fuel element storage pit, in such a way that the tool carrier moves to the desired inspection position. As a rule, the tool carrier which can be fitted with various cleaning, inspection, or repair tools, can enter a fuel element at several levels along the longitudinal extent thereof. If the tool carrier enters into the gaps between the fuel rods from different sides, the fuel element is turned 90.degree. by means of the rotary table or plate. The leadscrew drive mechanism 1c to which the tool carrier 18 is attached, can only travel outside the space delimited by a vertical leadscrew drive mechanism 1a. The distance along which the tool carrier can travel along the direction of the arrow 20 by means of the transversely disposed leadscrew drive mechanism 1b, corresponds at least to the width of a fuel element. FIG. 3 shows a top-plan view of a device of basically identical construction to FIG. 2, with the cover plate removed. The device is constructed for one fuel element only, and the leadscrew drive mechanism supporting the tool carrier 18 travels inside the space delimited by the leadscrew drive mechanism 1a. In FIG. 3, fuel rods 24 and gaps 25 therebetween into which the tool carrier enters, are also shown. The foregoing is a description corresponding in substance to German application Pat. No. 34 19 765.6, dated May 26, 1984, the International priority of which is being claimed for the instant application, and which is hereby made part of this application. Any material discrepancies between the foregoing specification and the aforementioned corresponding German application are to be resolved in favor of the latter. |
052672794 | summary | FIELD OF THE INVENTION The present invention relates to a method and a structure for repairing an elongated metal hollow member which is welded to a reactor pressure vessel (RPV) in operation, and more particularly, to a repairing method and a structure therefor which are capable of preventing occurrence of any stress corrosion cracking in a weld of a metal hollow member during operation, which cracking allows a coolant to leak out of the RPV. BACKGROUND OF THE INVENTION Examples of this kind of hollow member include a housing for an incore monitor (ICM) which serves to monitor the neutron flux generating in the RPV, and a housing for a control-rod drive (CRD) which serves to drive the control rod. The hollow member, e.g. the ICM housing, extends through a wall of the RPV into the coolant while it is welded to the wall of the RPV through a cladding weld formed on an inner surface of the RPV wall. Such ICM housing is made of TYPE 304 stainless steel. In general, a welding residual stress exists in the weld as a result of the welding heat input. Under the presence of the welding residual stress, corrosion proceeds markedly at the weld of the ICM housing in the coolant, resulting in cracking. This phenomenon is referred to as the stress corrosion cracking. Upon the occurrence of the stress corrosion cracking in the weld of the ICM housing, there is the possibility that the coolant leaks out of the RPV. Once the stress corrosion cracking has occurred, repair may be conducted by a known method in which a shielding member is welded to the hollow member to surround the stress corrosion cracked portion as disclosed in JP-U-56-82696. On the contrary, as disclosed in JP-A-2-128195, an ICM housing lower half including a part thereof in which the stress corrosion cracking has occurred is cut and removed to replace it with a new ICM housing half welded to the remaining housing half. However, these repairing methods will make another new weld which presents a danger of stress corrosion cracking. SUMMARY OF THE INVENTION An object of the present invention is to provide a repairing method and a structure therefor which are capable of preventing occurrence of any stress corrosion cracking in a metal hollow member in an RPV. To this end, according to one aspect of the present invention, there is provided a method for repairing an elongated metal hollow member which is welded to a wall of a pressure vessel of a nuclear reactor and extends into a coolant within said pressure vessel, said method comprising the steps of removing said coolant out of said hollow member, cutting and removing a part of the hollow member, including a portion to be repaired, welding a new hollow member element with a remaining part of the hollow member into a new hollow member through a weld. An inner peripheral surface of a wall portion of the new hollow member including the weld is smoothed, and a metal sleeve is located on the inner peripheral surface of the wall portion in a coaxial relationship therewith. The metal sleeve is fitted onto the inner peripheral surface of the wall portion along an entire length of the metal sleeve, and the metal sleeve is heated throughout to provide a .delta. ferrite molten metal portion penetrating into both the wall portion and the metal sleeve. Further, according to another aspect of the present invention, there is provided a repairing structure of a part of an elongated metal hollow member, including a portion to be repaired, welded to a wall of a pressure vessel of a nuclear reactor, with the metal hollow member extending into a coolant within the pressure vessel. The structure comprises a molten metal portion at a portion of inner peripheral surface of a remaining part of the hollow member excluding the portion to be repaired and of a part of another hollow member, which members are welded together into a new hollow member through a weld. At the weld, the molten metal portion penetrates into both a wall portion of the new hollow member and of a metal sleeve, including .delta. ferrite, disposed on the inner peripheral surfaces. Other objects, functions and effects of the present invention will become more clear from the description of preferred embodiments to be described below in detail with reference to the accompanying drawings. |
044371888 | abstract | An X-ray emitting assembly comprising a flange for assembling a sheath assembly and a beam limiting device; the arrangement of said assembly, operationally associated with a radiation detector situated in a radiology equipment stand, enables in a simple way the operating axes of the sheath assembly and of the beam limiting device to be aligned along an axis z.sub.1 --z.sub.1. |
claims | 1. A particle beam irradiation apparatus that irradiates a target and limits unnecessary irradiation onto normal tissue without the use of a scatterer, bolus and collimator, said particle beam irradiation apparatus (i) being mounted in a rotating gantry for rotating an irradiation direction of a charged particle beam accelerated by an accelerator and (ii) comprising:a columnar-irradiation-field generation apparatus that generates a columnar irradiation field by enlarging the Bragg peak of the charged particle beam and includes (i) a plurality of absorbers, each absorber having a uniform thickness and reducing the energy of the charged particle beam in accordance with the thickness thereof through which the charged particle beam passes, (ii) a plurality of driving devices, each driving device configured to drive a respective absorber from the plurality of absorbers, and (iii) a change control apparatus for driving the driving devices;a scanning irradiation system positioned at a downstream side of the columnar-irradiation-field generation apparatus and that includes an X-direction scanning electromagnet that scans the charged particle beam in the X-direction and a Y-direction scanning electromagnet that scans the charged particle beam in the Y-direction; anda pair of position monitors that are positioned at a downstream side with respect to both the columnar-irradiation-field generation apparatus and the scanning irradiation system and that detect a passing position of the charged particle beam,wherein a uniform thickness of one absorber from the plurality of absorbers of the columnar-irradiation-field generation apparatus differs from the uniform thickness of another absorber from the plurality of absorbers,wherein the change control apparatus of the columnar-irradiation-field generation apparatus drives the driving devices so as to control the combined thickness of the plurality absorbers through which the charged particle beam passes, andwherein the columnar-irradiation-field generation apparatus generates the columnar irradiation field such that the enlarged Bragg peak is a Spread-Out-Bragg-Peak (SOBP) width, and the SOBP width has a depth in the direction of the charged particle beam that is larger than the cross-sectional dimension of the columnar irradiation field in an X-Y direction that is perpendicular to the charged particle beam. 2. The particle beam irradiation apparatus of claim 1, wherein each absorber from the plurality of absorbers is configured to be positioned along a beam axis of the charged particle beam such that each absorber from the plurality of absorbers is in alignment with the charged particle beam. 3. The particle beam irradiation apparatus of claim 1, wherein the change control apparatus is configured to drive the driving devices such that at least two absorbers from the plurality of absorbers are positioned along a beam axis of the charged particle beam such that the at least two absorbers from the plurality of absorbers are in alignment with the charged particle beam. 4. The particle beam irradiation apparatus of claim 1, wherein the columnar-irradiation-field generation apparatus further includes a depth-direction irradiation field enlargement apparatus for enlarging the Bragg peak of the charged particle beam, wherein said depth-direction irradiation field enlargement apparatus is positioned at a downstream side of the plurality of absorbers. 5. The particle beam irradiation apparatus of claim 4, wherein the depth-direction irradiation field enlargement apparatus includes:a ridge filter having a thickness distribution in which energy loss of the charged particle beam differs depending on the position thereon through which the charged particle beam passes;a pair of upstream deflection electromagnets that move the passing position, of the charged particle beam in the ridge filter;a pair of downstream deflection electromagnets that return the orbit of the charged particle beam toward a beam axis along which the charged particle beam has entered the depth-direction irradiation field enlargement apparatus; andan irradiation-field enlargement control apparatus that controls the pair of upstream deflection electromagnets and the pair of downstream deflection electromagnets in such a way that the charged particle beam passes through a predetermined thickness distribution of the ridge filter. 6. A particle beam irradiation apparatus that irradiates a target and limits unnecessary irradiation onto normal tissue without the use of a scatterer, bolus and collimator, said particle beam irradiation apparatus (i) being mounted in a rotating gantry for rotating an irradiation direction of a charged particle beam accelerated by an accelerator and (ii) comprising:a columnar-irradiation-field generation apparatus that generates a columnar irradiation field by enlarging the Bragg peak of the charged particle beam and includes (i) a plurality of absorbers, each absorber having a uniform thickness, (ii) a plurality of driving devices, each driving device configured to drive a respective absorber from the plurality of absorbers, and (iii) a depth-direction irradiation field enlargement apparatus positioned at a downstream side of the plurality of absorbers;a scanning irradiation system positioned at a downstream side of the columnar-irradiation-field generation apparatus and that includes an X-direction scanning electromagnet that scans the charged particle beam in the X-direction and a Y-direction scanning electromagnet that scans the charged particle beam in the Y-direction; anda pair of position monitors that are positioned at a downstream side with respect to both the columnar-irradiation-field generation apparatus and the scanning irradiation system and that detect a passing position of the charged particle beam,wherein a uniform thickness of one absorber from the plurality of absorbers of the columnar-irradiation-field generation apparatus differs from the uniform thickness of another absorber from the plurality of absorbers,wherein a change control apparatus drives the driving devices of the columnar-irradiation-field generation apparatus so as to control the combined thickness of the plurality absorbers through which the charged particle beam passes, andwherein the columnar-irradiation-field generation apparatus generates the columnar irradiation field such that the enlarged Bragg peak is a Spread-Out-Bragg-Peak (SOBP) width, and the SOBP width has a depth in the direction of the charged particle beam that is larger than the cross-sectional dimension of the columnar irradiation field in an X-Y direction that is perpendicular to the charged particle beam. 7. The particle beam irradiation apparatus of claim 1,wherein the columnar-irradiation-field generation apparatus is configured to generate (i) an outer columnar irradiation field having a first SOBP width, and (ii) an inner columnar irradiation field having a second SOBP width, which is different from the first SOBP width, andwherein the scanning irradiation system performs irradiation while scanning the outer columnar irradiation field generated by the columnar-irradiation-field generation apparatus in accordance with the distal form of the irradiation subject, and subsequently performs irradiation while scanning the inner columnar irradiation field inside the irradiation subject, relative to the outer columnar irradiation field. 8. The particle beam irradiation apparatus of claim 6,wherein the columnar-irradiation-field generation apparatus is configured to generate (i) an outer columnar irradiation field having a first SOBP width, and (ii) an inner columnar irradiation field having a second SOBP width, which is different from the first SOBP width, andwherein the scanning irradiation system performs irradiation while scanning the outer columnar irradiation field generated by the columnar-irradiation-field generation apparatus in accordance with the distal form of the irradiation subject, and subsequently performs irradiation while scanning the inner columnar irradiation field inside the irradiation subject, relative to the outer columnar irradiation field. |
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051679086 | claims | 1. Apparatus for removing hydrogen from an atmosphere having a mixture of gases, said apparatus including a housing and a catalyst system that catalyzes the oxidation of hydrogen in an exothermic reaction, said housing having at least one inlet opening and at least one outlet opening, said apparatus characterized by the improvement comprising A. first seal means sealing said openings gas tight, said first seal means opening as a function of a predetermined first response temperature, B. gas permeable filter system, substantially impermeable to aerosols and grease, said filter system being disposed in said housing in such a way that after opening of said first seal means, the gases or gas mixtures entering said inlet opening reach the catalyst system only after passing through said filter system, C. at least one additional opening provided in said housing, so arranged relative to said housing that said catalyst system, after opening of a second seal means, is exposed without interposition of said filter system, directly to the flow of said gases or gas mixtures, and D. said second seal means sealing said additional opening gas tight, said second seal means opening as a function of a predetermined second response temperature, said predetermined second response temperature being higher than said predetermined first response temperature. A. said housing being gas-tight except at said openings, said openings being arranged such that a gas flow of said atmosphere therein between said openings passes through said housing, B. first seal means having initially a sealing condition for sealing said openings gas-tight, and assuming a release condition for opening said inlet and said outlet openings in response to a predetermined first response temperature, C. said catalyst means being located in said housing exposed to the path of said gas flow between said inlet and said outlet openings, D. gas permeable filter means substantially impermeable to aerosols and grease, said filter means being disposed across the path of said flow of gases to said catalyst means from said inlet opening, and E. means for exposing said catalyst means selectively to atmospheric gas, without interposition of said filter means, said exposing means initially having a first condition in which gas flow traverses said filter means before contacting said catalyst means, said exposing means assuming a second condition in response to a predetermined second response temperature, and exposing, when in said second condition, said catalyst means to said gas flow without interposition of said filter means. A. said filter means is arranged to have different positions relative to catalyst when in said first and second conditions, B. said exposing means comprises a releasable element, said releasable element releasing said filter means from a position in said first condition, in response to said predetermined second response temperature, to a position in said second condition in which said gas flows to said catalyst means without interposition of said filter means. A. said catalyst means is arranged to have different positions relative to said filter means when in said first and second conditions, B. said exposing means comprises a disposing means, said disposing means disposing said catalyst means from a position in said first condition, in response to said predetermined second response temperature, to a position in said second condition in which said gas flows to said catalyst means without interposition of said filter means. 2. Apparatus according to claim 1, further characterized by said housing being divided into at least one filter chamber and one catalyst chamber, and by said inlet opening being provided in the vicinity of said filter chamber, and by said outlet opening and one additional opening being provided in the vicinity of said catalyst chamber, and by the position and area of said inlet opening and said outlet opening being selected so that after opening of said first seal means, as a result of natural convection, a flow is created through said inlet opening, said filter chamber containing said filter system, said catalyst chamber, and said outlet opening. 3. Apparatus according to claim 2, further characterized by the housing, made essentially parallelepipedic, having said filter chambers at its two ends, and between them, said catalyst chamber. 4. Apparatus according to claim 2, further characterized by the housing being subdivided by coarse-mesh nets into said filter chamber and said catalyst chamber. 5. Apparatus according to claim 2, further characterized by said housing being arranged for normally upright orientation and having a relatively upper wall portion and a relatively lower wall portion, said housing having said outlet opening in said upper wall portion and said inlet opening in said lower wall portion. 6. Apparatus according to claim 2, further characterized by said inlet opening, in said filter chamber, being covered by a relatively coarse filter means and the remainder of the filter chamber being filled with relatively fine, corrugated filter films. 7. Apparatus according to claim 6, further characterized by said relatively coarse filter means having a separation efficiency of about 80% for aerosols and grease particles, while said relatively fine filter films have a separation efficiency of 90 to 99%. 8. Apparatus according to claim 6, further characterized by said fine filter films being provided with holes, said holes of two adjacent filter films being arranged staggered with respect to one another. 9. Apparatus according to claim 1, further characterized by said first seal means comprising a cover plate, applied externally to the corresponding opening, said cover plate being soldered all the way around to housing by a solder that melts at said predetermined first response temperature, with tensioned springs being placed between said cover plate and housing wall, said springs pushing said cover plates away from said housing when said solder melts. 10. Apparatus according to claim 1, further characterized by an additional opening being provided in the bottom of said housing in the vicinity of said catalyst chamber. 11. Apparatus according to claim 10, further characterized by said second seal means comprising a plate applied externally to said additional opening and soldered all the way around with a second solder whose melting point determines said second response temperature, with tensioned springs being interposed between said plate and said housing, said springs forcing said plate away from said housing when said second solder melts. 12. Apparatus according to claim 10, further characterized by the second seal means having at least one flap pivotably articulated to said housing, said flap being soldered at least partially to said housing by means of a second solder whose melting point determines said second response temperature, and is openable by interposed tensioned springs when said second solder melts. 13. Apparatus according to claim 12, further characterized by the side of said flap which faces inward, prior to said second response temperature, being coated with said catalyst material. 14. Apparatus according to claim 1, further characterized by the housing having a frame of angle iron to which the panels forming the external housing walls are fastened in a gas-tight manner, preferably by soldering or welding. 15. Apparatus according to claim 14, further characterized by at least some of the panels forming said external housing walls being coated on their insides with catalyst material. 16. Apparatus according to claim 1, further characterized by said catalyst system comprising one or more catalyst elements which are fastened by flexible retaining means to said housing in such a fashion that after opening of said second seal, said catalyst elements drop out of said catalyst chamber to a distance which is determined by the length of said flexible retaining means. 17. Apparatus according to claim 1, further characterized by said housing being provided with means for generating and maintaining an inert gas atmosphere inside said housing at a pressure which is higher than that of the atmosphere surrounding said housing. 18. Apparatus for removing hydrogen from an atmosphere having a mixture of gases, said apparatus including a housing and a catalyst means that catalyzes the oxidation of hydrogen in an exothermic reaction, said housing having at least one inlet opening and at least one outlet opening, said apparatus characterized by the improvement comprising 19. Apparatus according to claim 18, further characterized in that 20. Apparatus according to claim 18, further characterized by said exposing means comprising at least one additional opening in said housing and a second seal means sealing said additional opening gas tight, said second seal means opening as a function of said predetermined second response temperature and opening said additional opening, wherein said additional opening is so arranged relative to said housing that said catalyst means, after opening of said additional opening, is exposed without interposition of said filter system, directly to the flow of said gases. 21. Apparatus according to claim 18, further characterized in that 22. Apparatus according to claim 21, further characterized by said catalyst means comprising one or more catalyst elements which are fastened by flexible retaining means to said housing in such a fashion that after being disposed by said disposing means, said catalyst elements drop out of said housing to a distance which is determined by the length of said flexible retaining means. 23. Apparatus according to claim 18, further characterized by said housing being provided with means for generating and maintaining an inert gas atmosphere inside said housing at a pressure which is higher than that of the atmosphere surrounding said housing. 24. Apparatus according to claim 18, further characterized by said housing having a vertically-extending body with vertically spaced openings, said vertically spaced openings arranged in said housing so as to create a chimney effect whereby a convection flow of gases created by the exothermic catalytic reaction is increased. 25. Apparatus according to claim 18, further characterized by said exposing means exposing said catalyst means in response to a temperature greater than a temperature at which said first seal means assume said release condition. 26. Apparatus according to claim 18, further characterized by said first seal means comprising a cover plate, applied externally to the corresponding opening, said cover plate being soldered all the way around to housing by a solder that melts at said predetermined first response temperature. 27. Apparatus according to claim 18, further characterized by said filter means having a separation efficiency of greater than about 80% for aerosols and grease particles. |
claims | 1. A charge generating device comprising:a substrate having a top surface and a bottom surface;a plurality of spaced-apart three-dimensional elements disposed on the top surface of the substrate;a plurality of cavities formed by the plurality of spaced-apart three-dimensional elements, the plurality of cavities being the area between the plurality of spaced-apart three-dimensional elements;a radioactive layer disposed on at least a portion of the plurality of spaced-apart three-dimensional elements and the top surface such that the plurality of cavities and the top surface are substantially coated by the radioactive layer, thereby forming a plurality of coated cavities;a first conducting layer disposed above the plurality of spaced-apart three-dimensional elements, wherein the first conducting layer is in electric contact with at least a portion of the plurality of spaced-apart three-dimensional elements;a second conducting layer disposed below the substrate, wherein the second conducting layer is in electric contact with the bottom surface of the substrate;a first scintillation layer disposed above the first conducting layer and in radiative contact with the first conducting layer; anda second scintillation layer disposed below the second conducting layer and in radiative contact with the second conducting layer. 2. The device of claim 1, wherein the plurality of spaced-apart three-dimensional elements are integrally formed with the substrate. 3. The device of claim 1, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise a wide band-gap semiconductor. 4. The device of claim 1, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise SiC, GaN, Ga2O3, diamond, GaAs, AlN, AlGaN, Al2O3, BN, AlAs, GaP, InP, B4C, or a combination thereof. 5. The device of claim 1, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise SiC, Ga2O3, diamond, GaN, or Al2O3. 6. The device of claim 1, wherein each of the plurality of spaced-apart three-dimensional elements has an average characteristic dimension of from 0.5 micrometers (μm) to 500 μm. 7. The device of claim 1, wherein each of the plurality of spaced-apart three-dimensional elements has an average height of from 1 μm to 500 μm. 8. The device of claim 1, wherein the plurality of spaced-apart three-dimensional elements form an array and each of the plurality of spaced-apart three-dimensional elements is separated from its neighboring three-dimensional elements by a distance of from 1 μm to 500 μm (edge to edge). 9. The device of claim 8, wherein the plurality of spaced-apart three-dimensional elements form a rectangular array, a hexagonal array, or a linear array. 10. The device of claim 1, wherein the radioactive layer emits alpha radiation, beta radiation, gamma radiation, or a combination thereof. 11. The device of claim 1, wherein the radioactive layer emits alpha radiation. 12. The device of claim 1, wherein the radioactive layer comprises 148Gd, 238Pu, 208Po, 210Po 243Cm, 244Cm, 241Am, 63Ni, 106Ru, 235U, 204Tl, 14C, 3H, 85Kr, 90Sr, 90Y, 147Pm, 109Gd, or a combination thereof. 13. The device of claim 1, wherein the radioactive layer comprises 241Am. 14. The device of claim 1, wherein the radioactive layer has a thickness of from 0.1 μm to 100 μm. 15. The device of claim 1, wherein the device further comprises: a scintillating material disposed within at least a portion of the plurality of coated cavities; a layer of a scintillating material disposed on the radioactive layer, such that the plurality of coated cavities are substantially coated by the layer of scintillating material; or a combination thereof. 16. The device of claim 15, wherein the scintillating material further performs as an energy degrader. 17. The device of claim 15, wherein the scintillating material comprises a ZnS-based phosphor, Tl:NaI, CsI, cerium-doped lutetium yttrium orthosilicate, bismuth germanate, plastic, CeF3, Eu:CaF2, PbWO4, CdWO4, Ce:Cs2LiYCl6, Ce:LaCl3, CeBr3, Ce:LaBr3, Pr:Lu3Al5O12, Ce:LuAlO3, Ce:Lu3Al5O12, Ce:Y2SiO5, cerium doped yttrium aluminum perovskite, cerium doped yttrium aluminum garnet, or a combination thereof. 18. The device of claim 1, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a metal. 19. The device of claim 1, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a metal selected from the group consisting of Al, Ti, Ni, Cu, Ga, Ag, Ir, Pt, Au, Cr, Mo, Pd, W, and combination thereof. 20. The device of claim 1, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a radioisotope. 21. The device of claim 1, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) 63Ni. 22. The device of claim 1, wherein the first scintillation layer is in physical contact with the first conducting layer. 23. The device of claim 1, wherein the second scintillation layer is in physical contact with the second conducting layer. 24. The device of claim 1, wherein the first scintillation layer, the second scintillation layer, or a combination thereof comprise(s) a scintillating material selected from the group consisting of a ZnS-based phosphor, Tl:NaI, CsI, cerium-doped lutetium yttrium orthosilicate, bismuth germanate, plastic, CeF3, Eu:CaF2, PbWO4, CdWO4, Ce:Cs2LiYCl6, Ce:LaCl3, CeBr3, Ce:LaBr3, Pr:Lu3Al5O12, Ce:LuAlO3, Ce:Lu3Al5O12, Ce:Y2SiO5, cerium doped yttrium aluminum perovskite, cerium doped yttrium aluminum garnet, and combinations thereof. 25. The device of claim 1, wherein the device further comprises a charge storage device electrically coupled to the first conducting layer and the second conducting layer. 26. A charge generating device comprising:a substrate having a top surface and a bottom surface;a plurality of spaced-apart three-dimensional elements disposed on the top surface of the substrate;a plurality of cavities formed by the plurality of spaced-apart three-dimensional elements, the plurality of cavities being the area between the plurality of spaced-apart three-dimensional elements;a radiation material disposed within at least a portion of the plurality of cavities, thereby forming a plurality of at least partially filled cavities;a first conducting layer disposed above the plurality of at least partially filled cavities and the plurality of spaced-apart three-dimensional elements, wherein the first conducting layer is in electric contact with the plurality of spaced-apart three-dimensional elements;a second conducting layer disposed below the substrate, wherein the second conducting layer is in electric contact with the bottom surface of the substrate;a first scintillation layer disposed above the first conducting layer and in radiative contact with the first conducting layer; anda second scintillation layer disposed below the second conducting layer and in radiative contact with the second conducting layer. 27. The device of claim 26, wherein the plurality of spaced-apart three-dimensional elements are integrally formed with the substrate. 28. The device of claim 26, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise a wide band-gap semiconductor. 29. The device of claim 26, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise SiC, GaN, Ga2O3, diamond, GaAs, AlN, AlGaN, Al2O3, BN, AlAs, GaP, InP, B4C, or a combination thereof. 30. The device of claim 26, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise SiC, Ga2O3, diamond, GaN, or Al2O3. 31. The device of claim 26, wherein each of the plurality of spaced-apart three-dimensional elements has an average characteristic dimension of from 0.5 μm to 500 μm. 32. The device of claim 26, wherein each of the plurality of spaced-apart three-dimensional elements has an average height of from 1 μm to 500 μm. 33. The device of claim 26, wherein the plurality of spaced-apart three-dimensional elements form an array and each of the plurality of spaced-apart three-dimensional elements is separated from its neighboring three-dimensional elements by a distance of from 1 μm to 500 μm (edge to edge). 34. The device of claim 33, wherein the plurality of spaced-apart three-dimensional elements form a rectangular array, a hexagonal array, or a linear array. 35. The device of claim 26, wherein the radioactive material emits alpha radiation, beta radiation, gamma radiation, or a combination thereof. 36. The device of claim 26, wherein the radioactive material emits alpha radiation. 37. The device of claim 26, wherein the radioactive material comprises 148Gd, 238Pu, 208Po, 210Po, 243Cm, 244Cm, 241Am, 63Ni, 106Ru, 235U, 204Tl, 14C, 3H, 85Kr, 90Sr, 90Y, 147Pm, 109Gd, or a combination thereof. 38. The device of claim 26, wherein the radioactive material comprises 241Am. 39. The device of claim 26, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a metal. 40. The device of claim 26, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a metal selected from the group consisting of Al, Ti, Ni, Cu, Ga, Ag, Ir, Pt, Au, Cr, Mo, Pd, W, and combination thereof. 41. The device of claim 26, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a radioisotope. 42. The device of claim 26, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) 63Ni. 43. The device of claim 26, wherein the first scintillation layer is in physical contact with the first conducting layer. 44. The device of claim 26, wherein the second scintillation layer is in physical contact with the second conducting layer. 45. The device of claim 26, wherein the first scintillation layer, the second scintillation layer, or a combination thereof comprise(s) a scintillating material selected from the group consisting of a ZnS-based phosphor, Tl:NaI, CsI, cerium-doped lutetium yttrium orthosilicate, bismuth germanate, plastic, CeF3, Eu:CaF2, PbWO4, CdWO4, Ce:Cs2LiYCl6, Ce:LaCl3, CeBr3, Ce:LaBr3, Pr:Lu3Al5O12, Ce:LuAlO3, Ce:Lu3Al5O12, Ce:Y2SiO5, cerium doped yttrium aluminum perovskite, cerium doped yttrium aluminum garnet, and combinations thereof. 46. The device of claim 26, wherein the device further comprises a charge storage device electrically coupled to the first conducting layer and the second conducting layer. 47. A charge generating device comprising:a substrate having a top surface and a bottom surface;a plurality of spaced-apart three-dimensional elements disposed on the top surface of the substrate;a plurality of cavities formed by the plurality of spaced-apart three-dimensional elements, the plurality of cavities being the area between the plurality of spaced-apart three-dimensional elements;a scintillating material disposed within at least a portion of the plurality of cavities, thereby forming a plurality of at least partially filled cavities;a first conducting layer disposed above the plurality of at least partially filled cavities and the plurality of spaced-apart three-dimensional elements, wherein the first conducting layer is in electric contact with the plurality of spaced-apart three-dimensional elements;a second conducting layer disposed below the substrate, wherein the second conducting layer is in electric contact with the bottom surface of the substrate;a first scintillation layer disposed above the first conducting layer and in radiative contact with the first conducting layer; anda second scintillation layer disposed below the second conducting layer and in radiative contact with the second conducting layer. 48. The device of claim 47, wherein the plurality of spaced-apart three-dimensional elements are integrally formed with the substrate. 49. The device of claim 47, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise a wide band-gap semiconductor. 50. The device of claim 47, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise SiC, GaN, Ga2O3, diamond, GaAs, AlN, AlGaN, Al2O3, BN, AlAs, GaP, InP, B4C, or a combination thereof. 51. The device of claim 47, wherein the substrate and the plurality of spaced-apart three-dimensional elements comprise SiC, Ga2O3, diamond, GaN, or Al2O3. 52. The device of claim 47, wherein each of the plurality of spaced-apart three-dimensional elements has an average characteristic dimension of from 0.5 μm to 500 μm. 53. The device of claim 47, wherein each of the plurality of spaced-apart three-dimensional elements has an average height of from 1 μm to 500 μm. 54. The device of claim 47, wherein the plurality of spaced-apart three-dimensional elements form an array and each of the plurality of spaced-apart three-dimensional elements is separated from its neighboring three-dimensional elements by a distance of from 1 μm to 500 μm (edge to edge). 55. The device of claim 54, wherein the plurality of spaced-apart three-dimensional elements form a rectangular array, a hexagonal array, or a linear array. 56. The device of claim 47, wherein the device further comprises a radioactive layer disposed on at least a portion of the plurality of spaced-apart three-dimensional elements and the top surface such that the plurality of cavities and the top surface are substantially coated by the radioactive layer, thereby forming a plurality of coated cavities such that the scintillating material is disposed within at least a portion of the plurality of coated cavities. 57. The device of claim 56, wherein the radioactive layer emits alpha radiation, beta radiation, gamma radiation, or a combination thereof. 58. The device of claim 56, wherein the radioactive layer emits alpha radiation. 59. The device of claim 56, wherein the radioactive layer comprises 148Gd, 238Pu, 208Po, 210Po, 243Cm, 244Cm, 241Am, 63Ni, 106Ru, 235U, 204Tl, 14C, 3H, 85Kr, 90Sr, 90Y, 147Pm, 109Gd, or a combination thereof. 60. The device of claim 56, wherein the radioactive layer comprises 241Am. 61. The device of claim 56, wherein the radioactive layer has a thickness of from 0.1 μm to 100 μm. 62. The device of claim 56, wherein the scintillating material is disposed as a layer on the radioactive layer, such that the plurality of coated cavities are coated by the layer of scintillating material. 63. The device of claim 47, wherein the scintillating material comprises a ZnS-based phosphor, Tl:NaI, CsI, cerium-doped lutetium yttrium orthosilicate, bismuth germanate, plastic, CeF3, Eu:CaF2, PbWO4, CdWO4, Ce:Cs2LiYCl6, Ce:LaCl3, CeBr3, Ce:LaBr3, Pr:Lu3Al5O12, Ce:LuAlO3, Ce:Lu3Al5O12, Ce:Y2SiO5, cerium doped yttrium aluminum perovskite, cerium doped yttrium aluminum garnet, or a combination thereof. 64. The device of claim 47, wherein the scintillating material further performs as an energy degrader. 65. The device of claim 47, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a metal. 66. The device of claim 47, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a metal selected from the group consisting of Al, Ti, Ni, Cu, Ga, Ag, Ir, Pt, Au, Cr, Mo, Pd, W, and combination thereof. 67. The device of claim 47, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) a radioisotope. 68. The device of claim 47, wherein the first conducting layer, the second conducting layer, or a combination thereof comprise(s) 63Ni. 69. The device of claim 47, wherein the first scintillation layer is in physical contact with the first conducting layer. 70. The device of claim 47, wherein the second scintillation layer is in physical contact with the second conducting layer. 71. The device of claim 47, wherein the first scintillation layer, the second scintillation layer, or a combination thereof comprise(s) a scintillating material selected from the group consisting of a ZnS-based phosphor, Tl:NaI, CsI, cerium-doped lutetium yttrium orthosilicate, bismuth germanate, plastic, CeF3, Eu:CaF2, PbWO4, CdWO4, Ce:Cs2LiYCl6, Ce:LaCl3, CeBr3, Ce:LaBr3, Pr:Lu3Al5O12, Ce:LuAlO3, Ce:Lu3Al5O12, Ce:Y2SiO5, cerium doped yttrium aluminum perovskite, cerium doped yttrium aluminum garnet, and combinations thereof. 72. The device of claim 47, wherein the device further comprises a charge storage device electrically coupled to the first conducting layer and the second conducting layer. 73. A method of making the device of claim 1, the method comprising:forming the plurality of spaced-apart three-dimensional elements on the top surface of the substrate; anddepositing the radioactive layer on at least a portion of the plurality of spaced-apart three-dimensional elements and the top surface such that the plurality of cavities and the top surface are substantially coated by the radioactive layer, thereby forming the plurality of coated cavities. 74. The method of claim 73, wherein the device further comprises a scintillating material disposed within at least a portion of the plurality of coated cavities, the method further comprises depositing the scintillating material within at least a portion of the plurality of coated cavities. 75. A method of making the device of claim 26, the method comprising:forming the plurality of spaced-apart three-dimensional elements on the top surface of the substrate; anddepositing the radioactive material within at least a portion of the plurality of cavities. 76. A method of making the device of claim 47, the method comprising:forming the plurality of spaced-apart three-dimensional elements on the top surface of the substrate; anddepositing the scintillating material within at least a portion of the plurality of cavities. |
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description | This application is based on French Patent Application No. 0451983 filed Aug. 9, 2004, the disclosure of which is hereby incorporated by reference thereto in its entirety, and the priority of which is hereby claimed under 35 U.S.C. §119. 1. Field of the Invention The invention relates to the field of managed communication networks and more particularly diagnostic devices for determining the cause of problems occurring within such networks. 2. Description of the Prior Art Problems occurring in managed communication networks can have many different causes. The main causes include, for example, power outages, broken connections, breakdowns or malfunctions of network equipments (or the components constituting them), and the integration of a new or old version of a network equipment (or a component constituting it) that is not entirely compatible with the remainder of the network. In the present context, the expression “network equipment” refers to a combination of hardware and software. A certain number of diagnostic devices (or tools) have been proposed for determining the causes of problems. Certain of these devices use techniques based on programming in object-oriented languages and/or rules-based languages, possibly managed by a rules engine. This applies in particular to the event correlation expert (ECXpert) device, devices from ILOG that use a programmable rules engine for diagnosis, Network Node Manager® version 6.4 devices, Network Node Manager Extended Topology® version 2.0 devices from Hewlett Packard, the Fault Detective for Data Communications (FDDC)® device from Agilent, and the TAC® device from CISCO. ALCATEL also offers a diagnostic device based on Bayesian probabilistic theory and used to define rules for refining hypotheses on the basis of concepts of additional evidence and background information, which lead to numbers each representing the probability that a hypothesis is true and used to construct Bayesian networks (also known as Bayesian diagrams) defining test operations associated with statistical or probabilistic weights. The main drawback of the above diagnostic devices is that they use static diagnostic models, i.e. models whose characteristics are fixed when they are designed and therefore cannot be adapted (or in the best case scenario only very partially adapted) to evolution of the resources of most networks, as much from the point of view of the hardware (or the versions thereof) as from the point of view of the software (or the versions thereof), or to evolution of the traffic in the network. This is a result of the fact that the diagnostic models are constructed from a knowledge base that is based on expert knowledge and that is rarely adapted to all the specific hardware and software and/or to all the combinations of hardware and/or software, and which additionally is at best representative of only what is known in the art at the time it was designed. U.S. Pat. No. 6,076,083 proposes a solution for adapting diagnostic models, but merely as a function of experience acquired in their use. This solution is therefore unable to take account of the evolution of the managed communication network, and is therefore inadequate. It is, of course, always possible to design new diagnostic models adapted to each evolution of the network, but this is particularly costly and necessitates a certain design time during which new causes of problems occurring within a network cannot be diagnosed correctly. The object of the invention is to improve on the situation of there being no prior art diagnostic device that is entirely satisfactory. To this end it proposes a diagnostic device for a communication network including network equipments coupled to a management system, said device including diagnostic means adapted to determine the cause of problems occurring in said network by means of one or more diagnostic models and processing means adapted to adapt said diagnostic model as a function of data provided by said management system that is representative of the composition of said network. The diagnostic device may have additional features and in particular, separately or in combination: said data is representative of modification of network equipment and said processing means include analysis means adapted to analyze the received data to determine actions to be undertaken to adapt said diagnostic model taking account of the network equipment modification or modifications that they represent and to generate instructions representative of said actions and adaptation means adapted to adapt a diagnostic model as a function of an instruction or instructions received from said analysis means, said processing means include a first memory coupled to said analysis means and adapted to store one or more reference diagnostic models and said analysis means are adapted to determine each adaptation action to be undertaken by comparing data received to one or more reference diagnostic models stored in said first memory, said analysis means are adapted to determine adaptation actions selected from a group including an action representative of a new model to be constructed, an action representative of a modification to be made to an existing diagnostic model, and an action representative of reconfiguration of an existing diagnostic model, the device further comprises a second memory coupled to said processing means and to said diagnostic means and adapted to store each diagnostic model transmitted by said processing means, said adaptation means are adapted, on receiving an instruction requiring the generation of a new diagnostic model because of specific network equipment modifications, to extract from said first memory a reference diagnostic model adapted to the composition of said network taking account of said specific modifications, in order to generate a new diagnostic model and then to store it in said second memory, said adaptation means are adapted, on receiving an instruction requiring the modification of an existing diagnostic model stored in said second memory because of specific network equipment modifications, to extract said existing diagnostic model from said second memory in order to modify it as a function of said specific modifications and then to store it when modified in said second memory, said adaptation means are adapted, on receiving an instruction requiring the reconfiguration of an existing diagnostic model stored in said second memory because of specific network equipment modifications, to extract said existing diagnostic model from said second memory in order to reconfigure it as a function of said specific modifications and then to store it when reconfigured in said second memory, said diagnostic means are adapted, on receiving a request for a selected diagnosis, to extract said selected diagnosis from said second memory and then to execute the extracted diagnostic model in order to deliver a diagnosis at an output, said data is transmitted by said management system in the form of notifications, at least some of said reference diagnostic models take the form of one or more Bayesian networks, at least some of said diagnostic models take the form of one or more Bayesian networks, The invention also provides a network management system or a service management system for a managed communication network, said system comprising one or more diagnostic devices of the kind defined hereinabove. Other features and advantages of the invention will become apparent on reading the following detailed description and examining the appended drawings. The appended drawings constitute part of the description of the invention as well as, if necessary, contributing to the definition of the invention. An object of the invention is to enable the cause of a problem that has occurred in a managed communication network to be determined by means of a diagnostic device including adaptive diagnostic models. The Invention applies to any type of managed networks including network equipments, and in particular Internet protocol (IP) networks. In the present context, the expression “network equipment” means a combination of hardware and software, for example core routers and edge routers. A diagnostic device DD of the invention is described first with reference to FIG. 1. In the embodiment shown, the diagnostic device DD is coupled to a management system MS of a managed communication network N. To this end it may take the form of a dedicated card or module adapted to be connected to the management system MS, where applicable via a connection interface. However, in the variant shown in FIG. 3, the diagnostic device DD forms part of the management system MS. In this case, the processing module MT of the diagnostic device DD is coupled to a management server SG of the management system MS. The management system MS to which the diagnostic device DD is coupled may be a network management system (NMS) or a service management system of the network N (when it is required to diagnose a service). It is considered hereinafter, by way of non-limiting example, that the management system MS to which the diagnostic device DD is coupled is a network management system (NMS). Moreover, the diagnosis may relate equally to the network level (network equipments and configuration) and to the management and service level (network equipments, configuration, quality of service (QoS) and service level agreements (SLA)). The diagnostic device DD firstly comprises a diagnostic module MD for determining causes of problems by means of one or more diagnostic models. Each time that it is requested to effect a diagnosis designated in a request, the diagnostic module MD activates (or uses or executes) the diagnostic model that corresponds to the designated diagnosis in order to deliver at an output a diagnosis, i.e. at least the cause or causes of a problem that has occurred within the network N. The diagnostic models are stored in a memory M2 of the diagnostic device DD, for example, taking the form of a database which the diagnostic module MD can access to select one of the models following reception of a diagnosis request, for example. The sending of a diagnosis request to the diagnostic device DD is generally requested by a network operator following reception by the network management system MS of one or more notifications from network equipments NE. The diagnosis request may be either generated by the management system MS or transmitted directly to the diagnostic device DD without passing through the management system MS. For example, these notifications are alarms that the network equipments NE transmit automatically to the network management system MS if they detect a problem (breakdown or malfunction) within themselves (i.e. at the level of one of their components, for example an input or output interface) or on one of their connections. Because these notifications do not always contain sufficient information, complementary information may be requested of the network equipments concerned by the network management system MS, generally at the request of the network operator. This complementary information can be management information and/or information on the functioning of certain network equipments NE, for example, which are generally stored in their management information base (MIB). This information can equally be measurements relating to network parameters, for example the bandwidth used on certain connections or by certain calls (traffic analysis) or the packet loss rates on certain connections or in certain calls, which in particular enable network operators to monitor and manage the quality of service (QoS) that is associated with each user client or service and is defined by a service level agreement (SLA). The invention relates to any type of diagnostic model, regardless of the network equipments NE concerned (whether pure components (hardware), pure software or combinations thereof. The diagnostic module MD is adapted as a function of the diagnostic model(s) that it uses. It is therefore designed to execute the scenario of a reference diagnostic model and uses a database, SNMP tools and the like, for example, and delivers to an output results constituting diagnoses. The diagnostic device DD of the invention also includes a processing module MT coupled to the network management system MS and responsible for adapting the diagnostic models, which are stored in the memory M2, for example, as a function of data representative of the composition of the network N supplied by the network management system MS. For the purpose of adapting the diagnostic models, the processing module MT includes an analysis module MA and an adaptation module MC that are coupled to each other, for example, as shown in FIG. 1. The analysis module MA is more specifically responsible for analyzing data that comes from the network management system MS in order to determine the actions that must be undertaken to adapt the diagnostic model stored in the memory M2, or one of these models, or to generate a new diagnostic model. Each action is determined as a function of information contained in the data received and in any complementary data requested. For example, the data is transmitted by the management system MS to the processing module MT in the form of notifications of modification of network equipment(s) NE (hardware and/or software). This transmission can be effected automatically, periodically, or each time that the management system MS receives information representative of a modification in the network N. Alternatively, it may be envisaged that the analysis module MA is configured to observe data in the management system MS representative of modifications in the network N. It may equally be envisaged that the analysis module MA be configured to request the management system MS to send it data representative of modification(s) in the network N since the preceding request, for example periodically. At least three types of action may be envisaged. A first type concerns generating a new diagnostic model to be constructed. A second type concerns modifying an existing diagnostic model. A third type concerns reconfiguring an existing diagnostic model. If the data received from the management system MS is insufficient for determining the action to be undertaken, the analysis module MA may request complementary information (complementary data) from the management system MS. The analysis module MA is also responsible for generating instructions representative of actions that it has determined following the reception of data and which are intended for the adaptation module MC. An instruction defines one or more actions to be undertaken and comprises information representative of modification(s) reported by the management system MS. For example, to determine each action to be undertaken, the analysis module MA can compare the data that it receives to one or more reference (or basic) diagnostic models that are stored in a memory M1 of the processing module MT. This memory M1 takes the form of a database, for example. The reference diagnostic models may be of different types. They can in particular take the form of rules and/or models or a Bayesian network (also known as a causal diagram). Any diagnostic model generation technique may be envisaged, and in particular the CodeBook technique, the neural network technique or the Petri network technique. A Bayesian network is a causality tree consisting of branches associated with complementary probabilities and comprising nodes designating basic (or elementary) tests to be effected and from which there may depart one or more sub-branches also associated with one or more probabilities and having nodes designating other basic (or elementary) tests to be effected and from which there may depart one or more sub-branches. In other words, a Bayesian network is a scenario for finding the root cause of a specific problem, for example the loss of packets in an IP VPN, by executing different tests according to the probabilities in question, so as to send back the cause of the problem and where applicable complementary information (for example the number of packets lost) if such information can be determined. Additional information on Bayesian networks and their use in diagnostic devices can be found in F. Jensen, “An introduction to Bayesian Networks”, UCL Press., 1996 (republished 2001). Each reference diagnostic model is adapted to determine at least one cause of an inventoried problem. For example, a reference diagnostic model may be dedicated to diagnosing packet loss in an IP router. Each reference diagnostic model may include tests and requests for active or passive measurements, requests for configuration verification, for verification of the consistency of the configuration of a service via the network, or to read parameters stored in management information bases (MIB) or available in certain network equipments such as routers and specific to an equipment. The reference diagnostic models may be generated by any means, and in particular from a knowledge base that is based on expert knowledge and comprises data (or information) coming from one or more sources, for example the design of the equipment (specifications, configurations, validation and the like, and problems and/or weaknesses encountered), the fabrication of the equipment (components used, technologies used and the like, and problems and/or weaknesses encountered), laboratory equipment tests (critical failures, reliability, bugs, compatibility, service lives and the like), and use under real life conditions (information coming in particular from user-clients, maintenance services and breakdown reports, for example statistical information relating to reliability and to failures of the equipments and components in time, the most frequent failures of equipments as a function of a specific use or a specific fabrication, equipment compatibility, service life and the like). A detailed example of obtaining information for generating diagnostic tests relating to quality of service (QoS) within an IP VPN is described in the paper by Gérard Delègue et al. “IP VPN Network Diagnosis: Technologies and Perspectives”, 3rd International Conference on Networking, March 2002. The adaptation module MC is responsible for adapting an existing diagnostic model or creating a new diagnostic model as a function of instructions received from the analysis module MA that are representative of one or more actions to be undertaken (generation, modification or reconfiguration). Each time that the adaptation module MC receives an instruction requiring the generation of a new diagnostic model accompanied by information representative of modification(s) reported by the management system MS, it extracts from the memory M1 one or more reference diagnostic models adapted to the constitution of the network N defined by the accompanying information. It then generates a new diagnostic model, for example by combining the extracted reference diagnostic models, where applicable after adapting (modifying and/or reconfiguring) at least one of them. It then stores this new diagnostic model in the memory M2 so that it can be used by the diagnostic module MD on demand. Moreover, each time that the adaptation module MC receives an instruction requiring the modification of an existing diagnostic model stored in the memory M2 accompanied by information representative of modification(s) reported by the management system MS, it extracts the existing diagnostic model from the memory M1 and then modifies it as a function of the reported modifications in the network N. Those modifications may necessitate the extraction of one or more reference diagnostic models from the memory M1 in order to integrate it into, or associate it with, the existing diagnostic model, where applicable after adaptation (modification and/or configuration). The adaptation module MC then stores the modified diagnostic model in the memory M2. For example, if the diagnostic model takes the form of one or more Bayesian networks, modifying it may consist in adding to the Bayesian network and/or eliminating therefrom one or more branches and/or sub-branches and/or one or more nodes each associated with at least one basic test and a selected probability. For example, if the modification of the network N relates to the replacement in a network equipment NE of a single-processor card by a multiprocessor card, the branch used to test the CPU is replaced with a multiple branch. FIGS. 2B and 2C show two examples of successive modifications made to a diagnostic model taking the form of a Bayesian network shown in FIG. 2A. To be more precise, in the example shown in FIG. 2A the Bayesian network is a scenario for determining the cause of packet loss (“LossPacket”) in an IP router of an Internet Protocol virtual private network (IP VPN). In this Bayesian network: “InterfaceInStatus” is a variable modeling the status of the input interfaces, “HighCPUUtilization” is a variable indicating whether the processing capacity (or CPU capacity) of a router is overloaded, and “IPForwardMIB” is a test variable for determining if an LSP has been set up or not. LossPacket first tests InterfaceInStatus (which is generally the most probable cause. Then, if the status of InterfaceInStatus is “OK”, it tests HighCPUUtilization (which is generally the second most probable cause). If the status of HighCPUUtilization is “NOK” (i.e. not OK), LossPacket sends HighCPUUtilization NOK plus the cause of the problem (for example “the capacity of a router is overloaded”) and the number of packets lost, if this can be determined. If the status of HighCPUUtilization is OK LossPacket tests IPForwardMIB. If the status of IPForwardMIB is NOK LossPacket sends IPForwardMIB NOK plus the cause of the problem (for example “an LSP has not been set up”) and the number of packets lost if this can be determined. If a new version of software has been installed in the network, a supplementary node must then be added to the FIG. 2A Bayesian network. To take account of this modification of the composition of the network, the adaptation module MC adds a branch including the node “QueueMib” to the FIG. 2A Bayesian network, which yields the modified Bayesian network shown in FIG. 2B. “QueueMIB” is a variable for verifying if the policy models (“policy-map”) are defined in an input interface and an output interface. If a new interface is installed in the network, a network portion must be added to the FIG. 2B Bayesian network. To take account of this modification of the composition of the network, the adaptation module MC adds two branches respectively including the node “InterfaceOperStatus” and the node “InterfaceAdminStatus” at the level of the InterfaceInStatus node of the FIG. 2B Bayesian network, which yields the modified Bayesian network shown in FIG. 2C. “InterfaceOperStatus” is a variable of the management information base (MIB) that indicates the current operational status of an interface. “InterfaceAdminStatus” is another variable of the management information base (MIB) that indicates the required status of an interface. If the model is produced using the elementary sequence diagram technique, the modification consists in updating a reference sequential scenario by adding simple tests to or eliminating them from existing sequences, for example. Each time that the adaptation module MC receives an instruction requiring the reconfiguration of an existing diagnostic model stored in the memory M2 accompanied by information representative of modification(s) reported by the management system MS, it extracts the existing diagnostic model from the memory M1 and then reconfigures it as a function of the reported modifications in the network N. The adaptation module MC then stores the reconfigured diagnostic model in the memory M2. For example, if the diagnostic model takes the form of one or more Bayesian networks, its reconfiguration may consist in updating one or more probabilities (or weightings). If the diagnostic model is not a Bayesian network, its reconfiguration may consist in modifying one or more administrative costs and/or one or more statistical or probabilistic weights, for example. The diagnostic device DD of the invention, and in particular its processing module MT and its diagnostic module MD, may be implemented in the form of electronic circuits, software (or data processing) modules or a combination of circuits and software. The invention is not limited to the embodiments of a diagnostic device and a network or service management system described hereinabove by way of example only, but encompasses all variants thereof that the person skilled in the art might envisage that fall within the scope of the following claims. |
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039882586 | description | These and further objects and advantages of the invention will be better understood from the following detailed description of several preferred embodiments and examples, which are not to be considered as limiting, in accordance with the invention. Reference is first made to a recent paper by A. H. Kibbey and H. W. Godbee entitled "A Critical Review of Solid Radioactive Waste Practices at Nuclear Power Plants," published March 1974 in ORNL-4924, which describes in great detail the sources and kinds of radwaste, the known methods using cementing materials and organic resins for matrix incorporation, the advantages of cements over organic resins, as well as illustrating in block form typical systems for treatment of radioactive wastes at boiling water and pressurized water reactor facilities. Thus there is no need to detail how the radioactive wastes are obtained for purposes of the present invention, except to note that it ultimately is formed into a slurry or liquid solution for mixing with a cementing material. The wastes can be allowed to accumulate for batch processing or may be processed continuously, both processes as such having been used with other cementing materials. In a typical batch process, dewatered wastes are collected in the waste mixing tanks. Concentrated liquid waste is mixed with the dewatered waste forming a slurry, and this slurry is pumped at a controlled rate to an in-line mixing pump. The dry cementing material is also added to the mixing pump. After suitable mixing, a cement-waste mixture is formed that is homogeneous. Details on suitable proportions will be later given, but in general the cement-waste mixture contains excess liquid above normal construction concrete proportions. It is preferred to add the alkali or alkaline earth metal silicate by injection as a solution subsequent to formation of the waste-cement mixture. This is conveniently done by adding the silicate to the waste-cement stream as it is fed into a suitable container where it is allowed to harden. A preferred container is a radiation shielding container such as a steel drum, though other materials, such as concrete, can also be used for the container. Cementing materials that can be used in the process of the invention include Portland cement (all types), natural cement (all types), masonry cement (all types), gypsum, gypsum cement or plaster, Plaster of Paris, lime (slaked or unslaked), and Puzzolans, all materials which harden by a combination of hydrolysis and hydration reactions upon the addition of water. The preferred cementing material is Type II Portland cement, as it is inexpensive and easily obtainable. While in general any alkali or alkaline earth silicate can be employed as the additive, sodium silicate is the preferred additive because of its low cost and ready availability. The proportions of the radwaste-cement-additive mixture can be varied over a rather wide range. In general, for solidifying 100 parts (by weight) of radwaste, it is preferred to use 20-100 parts (by weight) of the cementing material, and 5-50 parts (by weight) of the silicate additive. The silicate additive will preferably constitute 3-15% by weight of the final mixture. Since in the radwaste disposal process the emphasis is on increased liquid fixation in the solidified product allowing a maximum of waste to be incorporated into a minimum final volume, it is preferred to use relatively high proportions of the silicate additive, constituting at least 20% by weight of the combined cement-additive weight. What is optimum for certain wastes may not be optimum for other wastes, but simple experimentation with different waste samples will enable those skilled in this art to arrive at optimum proportions with little effort. The examples given below demonstrate suitable proportions that have been found to produce excellent results for different typical wastes from various nuclear power plants. The examples given in Table I below are for solidification of 100 parts (all by weight) of the waste described, employing a Type II Portland cement and sodium silicate obtained commercially as 41.degree. Be sodium silicate, which is a water solution of Na.sub.2 SiO.sub.3 having a density of 1.35-1.45 grams/cu. cm. (41.degree. is a hydrometer reading in Baume degrees): Table I ______________________________________ Waste 41.degree. Be 100 Parts Cement Na.sub.2 SiO.sub.3 ______________________________________ 1. Boric Acid Waste-up to 70 25 12% H.sub.3 BO.sub.3 adjusted to pH with NaOH 2. Waste Water-dissolved 50 10 solids approximately equal to raw water 3. Na.sub.2 SO.sub.4 Waste Solution-up to 50 10 25% Na.sub.2 SO.sub.4 with pH approximately 7 4. Water Slurry of Spent Ion 25 5 Exchange Bead Resins 5. Water Slurry of Spent Ion 25 10 Exchange Powder Resin ______________________________________ In the examples given in Table II below, the formulations are based on pounds per cubic foot of solid produced. The cement and additive used were the same as in Table I: Table II ______________________________________ Sodium Waste Waste Cement Silicate ______________________________________ 6. Waste evaporator 44.6 31.2 8.3 bottoms 7. Regenerant evaporator 56.6 25.5 5.9 bottoms 8. Filter cake 35 20.7 6.2 Included evaporator bottoms 9. Spent bead resins 43 23.1 5.8 Included evaporator 10.5 bottoms 10. Powdex/solka floc 32 18 9 Included evaporator 23 bottoms ______________________________________ As mentioned above, the equipment for carrying out the process of the invention is similar to that employed for other known processes using cement alone or resin as the binding agent. Waste mixing tanks and feed pumps are used to prepare the waste and feed the waste at a controlled rate to an in-line mixer. The wastes themselves normally include sufficient liquid to form a very fluid slurry. If not, additional liquid can be added as needed. The silicate itself is conveniently added as a liquid solution. It mixes readily with the very fluid slurry of cement and waste. Mixing can be carried out in the in-line mixer, but because the final waste-cement-silicate slurry gells quickly, it is preferred to add the silicate solution as the waste-cement slurry is introduced into a suitable disposable container, such as a steel drum, which provides additional radiation shielding as well as a convenient shipping container for the solidified mass. The silicate can be added at the container fillport, for example, through a concentric tube in the fillpipe, similar to the manner by which the catalyst is added to resin mixes. If the pH of the waste is acidic, it is preferred to neutralize or make same slightly basic by addition of a suitable base, such as NaOH. Formulated on the basis of volume flow, at a waste flow of 7.5 gpm, a typical cement-silicate flow is 45.4 pounds per minute of Portland cement and 1.0 gpm of sodium silicate flow. At these rates, a 50 cu. ft. container is filled in about 40 minutes. Gelling begins in about 2 minutes after filling of the container. Solidification to maximum hardness occurs in less than 7 days. The result is a free-standing solid with no surface liquids which is safe for handling, shipment, or long term storage at licensed buriel grounds. The principal benefits secured by the use of the silicate additive is to broaden the narrow liquid tolerence of the usual cements, and in particular increase the liquid absorption thereby improving shipping efficiency, increase container utilization by eliminating waste mounding as a result of the more fluid mix, and enable solidification of wastes such as concentrated borate solutions that could not be solidified heretofore with a cement binding agent. While we do not wish to be bound by the following explanation, we believe the above results are in part due to the added silicate increasing the number of hydration sites available to chemically bind water into the solid product thereby increasing the volume of liquid that can be incorporated into a solid with a given quantity of cementing material. Also, it is believed that the silicate additive catalyzes the cement hardening process by enhancing intermolecular bonding through hydrolysis reactions. While our invention has been described in connection with specific embodiments thereof, those skilled in the art will recognize that various modifications are possible within the principles enunciated herein and thus the present invention is not to be limited to the specific embodiments disclosed. |
claims | 1. A sampling device for use in optically analyzing a biological fluid comprising:(i) an aspirator for aspirating the fluid into the device;(ii) a thin measuring chamber having an upper and lower wall, the distance between said walls being in the range of 100-500 microns;(iii) a thick measuring chamber having an upper and lower wall, the distance between said walls being in the range of 0.5-3 cm; and(iv) means for excluding air from said measuring chambers; wherein the upper and lower walls of said thin and thick measuring chambers are transparent and the thin measuring chamber and the thick measuring chambers are in fluid communication. 2. A sampling device for use in optically analyzing semen, the sampling device comprising:(i) an aspirator for aspirating semen into the device;(ii) a thin measuring chamber having an upper and lower wall, the distance between said walls being in the range of 100-500 microns;(iii) a thick measuring chamber having an upper and lower wall, the distance between said walls being in the range of 0.5-3 cm; and(iv) means for excluding air from said measuring chambers; wherein the upper and lower walls of said thin and thick measuring chambers are transparent and the thin measuring chamber and the thick measuring chambers are in fluid communication. 3. A device according to claim 1 wherein the distance between said walls of said thin measuring chamber is in the range of 250-350 microns. 4. A device according to claim 1 wherein the distance between said walls of said thick measuring chamber is in the range of 0.8-1.2 cm. 5. A device according to claim 1 wherein said aspirator comprises a cylinder and a plunger. 6. A device according to claim 1 wherein said means for excluding air comprises a valve positioned in between said measuring chambers and said aspirator. 7. A device according to claim 1 further comprising an adapter for aligning the device in an optical instrument. 8. A device according to claim 1 which is disposable. |
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abstract | A waste form for and a method of rendering hazardous materials less dangerous is disclosed that includes fixing the hazardous material in nanopores of a nanoporous material, reacting the trapped hazardous material to render it less volatile/soluble, and vitrifying the nanoporous material containing the less volatile/soluble hazardous material. |
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050248057 | summary | FIELD OF THE INVENTION The present invention relates to a chemical method for decontaminating metal surfaces having an oxide coating containing radioactive substances, such as a pressurized water nuclear reactor system. BACKGROUND OF THE INVENTION The primary system surfaces of water-cooled nuclear reactors and equipment develop a corrosion product oxide ("rust") film during normal operation. The film incorporates radionuclides from the circulating coolant into its lattice, and becomes radioactive. This contributes to the out-of-core radiation fields, increases personnel radiation exposure, and hinders inspection and maintenance. Thus, effective decontamination has to substantially remove the oxide film, with minimal corrosion and metal substrate effects. Oxide removal depends upon the film's structure, which is a function of the coolant chemistry and the metal substrate. For boiling water nuclear reactors (BWR's), "oxidizing" conditions prevail (0.5-0.2 ppm O.sub.2), and the system alloys are 300 series stainless steels. These conditions result in a relatively thick, porous, hematite film, with iron as the predominant metal. Chromium is converted to chromates, and, hence, continually dissolves in the coolant. In contrast, pressurized water nuclear reactors (PWR's) operate with reducing water chemistry (<0.0005 ppm oxygen), and the primary system contains a large fraction of high nickel alloys. These conditions produce a denser, more coherent and tenacious oxide film, containing chromium in a nickel ferrite lattice. Thus, BWR films are easier to dissolve and remove than PWR films; the latter usually require an oxidation treatment for chromium removal before the film can be dissolved. For either case, iron represents the dominant metal species in solution after film removal. Commercially available decontamination solutions generally fall into three categories. These are the Citrox solutions, Can-Decon solutions and Low Oxidation State Metal Ion (LOMI) solutions such as are described in the processes discussed in "An Assessment of Chemical Processes for the Postaccident Decontamination of Reactor Coolant Systems" EPRI Report NP-2866 of February 1983. The first solution uses organic acid species only, such as the Citrox-like solutions, which contain organic acids that remove the oxide film by both dissolution and spallation mechanisms. Citric and oxalic acids are the usual components. These solutions are effective and ion exchange well, but produce particulates and have precipitated iron during plant applications. A second solution uses a chelant solution, such as the Can-Decon-like solutions which use chelants to avoid precipitation and reduce the particulate generation. However, the chelants usually depress the ion exchange parameters. A third solution is an LOMI solution which uses vanadium (II) in a picolinic/formic acid buffer. The vanadium (II) acts as a reductive dissolution agent on the oxide, and particulate generation is minimized. The principal drawbacks of these solutions are the inability to cation exchange the solution and the fact that vanadium can exist in multiple valence states. As the oxide film dissolves, ferric iron (III) accumulates in solution. Iron (III) can induce base metal corrosion, intergranular attack (IGA) and intergranular stress crack corrosion (IGSCC); it can also behave as an oxidizing-type inhibitor and limit corrosion. For Citrox-like solutions, above 25 to 30 parts per million (ppm) of iron results in increased corrosion with IGA and IGSCC tendencies. The chelants in Can-Decon solutions form strong complexes with iron (III). Therefore, three behavorial regimes can be observed: (a) at 0 to 25 ppm iron (III), free corrosion with increased IGA/IGSCC tendencies, (b) at 25 to 130 ppm iron (III), reduced corrosion and IGSCC tendencies, but IGA may still occur; and (c) above approximately 130 ppm iron (III), Citrox-like behavior with increased corrosion. The dissolved iron (III) also depresses the dissolution kinetics The LOMI process removes the iron in the reduced, divalent state, and iron corrosion effects are minimized. However, after four to eight hours, the vanadium exists as the quadravalent species, and the solution behaves like an iron-containing Citrox solution. Entire primary system decontamination is expected to result in dissolved iron concentrations of 100 to 200 ppm and last for about 20 to 96 hours. Thus, significant and deleterions iron (III)/metal effects upon corrosion, ion exchange and kinetics can be expected. SUMMARY OF THE INVENTION A method of decontaminating metal surfaces having an oxide coating containing radioactive substances, such as the primary system of a pressurized water nuclear reactor, uses an aqueous decontamination solution containing a weak chelating agent and a ferrous salt of an organic acid. The weak chelating agent is capable of forming multiligand complexes with the metals from which the oxide coating is formed, and is present in an amount of between 0.1 and 2.0 percent based on the weight of the solution. The ferrous salt is present in an amount to provide 50 to 500 parts per million iron based on the weight of the solution. The decontamination solution is passed over the metal surfaces to remove the oxide coating therefrom. The decontamination solution is regenerated by passing at least a portion thereof, after contact with the metal surfaces, through a cation exchange resin column or, preferably, through an electrolysis unit. |
abstract | An apparatus for measuring an image of a pattern to be formed on a semiconductor by scanning the pattern using a scanner, the apparatus including an EUV mask including the pattern, a zoneplate lens on a first side of the EUV mask and adapted to focus EUV light on a portion of the EUV mask at a same angle as an angle at which the scanner will be disposed with respect to a normal line of the EUV mask, and a detector arranged on another side of the EUV mask and adapted to sense energy of the EUV light from the EUV mask, wherein NAzoneplate=NAscanner/n and NAdetector=NAscanner/n*σ, where NAzoneplate denotes a NA of the zoneplate lens, NAdetector denotes a NA of the detector, and NAscanner denotes a NA of the scanner, σ denotes an off-axis degree of the scanner, and n denotes a reduction magnification of the scanner. |
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042740355 | claims | 1. A field emission electron gun comprising a cathode, a control electrode disposed in the vicinity of said cathode, and anode disposed along a beam path extending from said cathode for accelerating electrons emitted from said cathode, a variable D.C. voltage source connected between said cathode and said anode, switch means connected between said voltage source and said control electrode for changing-over the potential of said control electrode between ground potential and the potential of said cathode, and means for varying the position of said cathode relative to said control electrode said anode being fixed in position relative to one of said cathode and said control electrode at a position downstream of said control electrode along said beam path. 2. A field emission electron gun according to claim 1, wherein said means for varying comprises means for moving said cathode whereby the relative positions of said cathode and said control electrode are variable. 3. A field emission electron gun according to claim 1, wherein said means for varying comprises means for moving said control electrode whereby the relative positions of said cathode and said control electrode are variable. 4. A field emission electron gun according to claim 1, wherein said control electrode has a cylindrical shape, and said cathode is arranged in a central part of the cylindrical control electrode. 5. A field emission electron gun according to claim 1, 2, 3, or 4, wherein the D.C. voltage source comprises a single variable high-voltage source. 6. A field emission electron gun according to claim 1, further comprising a vacuum vessel containing said cathode, said control electrode and said anode, said D.C. voltage source, said switching means and said means for varying being arranged exteriorly of said vacuum vessel. 7. A field emission electron gun according to claim 1, wherein said means for varying includes a vertical moving means for supporting at least one of said cathode and said control electrode for enabling varying of the relative positions thereof. 8. A field emission electron gun according to claim 7, wherein the vertical moving means includes a bellows. 9. A field emission electron gun comprising a cathode, a control electrode disposed in the vicinity of said cathode, an anode disposed along a beam path extending from said cathode for accelerating a beam of electrons emitted from said cathode, a D.C. voltage source connected between said cathode and said anode, and switch means connected between said voltage source and said control electrode for changing-over the potential of said control electrode between ground potential and the potential of said cathode, said voltage source being variable between a low energy voltage level while said control electrode is connected to ground potential and a high energy voltage level when said control electrode is connected to the same potential as said cathode such that the energy of said beam of electrons can be changed from a low level to a high level without significant increase in the beam current. |
044420668 | claims | 1. A support floor for the core of a high temperature pebble bed nuclear reactor comprising: a plurality of support columns placed directly adjacent one another forming the reactor core floor; a bed of spherical fuel elements forming the reactor core; a cylindrical side reflector surrounding said columns and the reactor core; a thermal side shield arranged at a distance around said cylindrical side reflector to form an annular space; and means for retaining said support columns in their respective horizontal positions said means disposed in said annular space between the lower part of the side reflector and the thermal side shields to substantially prevent the formation of expansion gaps between said columns. 2. The support floor of claim 1, wherein said support columns have a hexagonal cross section. 3. The support floor of claim 2, wherein each of said support columns rests upon a circular column having a diameter smaller than the bottom surface of said support column and wherein said circular columns rest upon the layered floor of the nuclear reactor. 4. The support floor of claim 1, wherein the nuclear reactor is a high capacity reactor and said retaining means comprise a plurality of spring supports. 5. The support floor of claim 4, wherein said spring supports are arranged so that the gaps developing after an extended operating period of the nuclear reactor between the support columns remain under a predetermined maximum size. 6. The support floor of claim 1, wherein the nuclear reactor is a low capacity reactor and said retaining means comprise a plurality of supporting struts. 7. The support floor of claim 6, wherein the maximum possible differential radial thermal expansion of the support floor and said thermal side shield are arranged to define the clearance on said support struts. 8. The support floor of claim 1, wherein said retaining means comprise a plurality of spring supports as restoring elements, and wherein the restoring force of said spring supports is dimensioned so that the size of the gaps developing between said support columns remains smaller than the diameter of absorber balls added to the core of the reactor. 9. The support floor of claim 1, wherein said side reflector has a plurality of radial gaps. 10. The support floor of claim 3, further comprising a plurality of cooling gas bores arranged in said supporting columns. 11. The support floor of claim 10, wherein said cooling gas bores are in open communication with said core at one end and with a gas collecting space at the other end. 12. The support floor of claim 11, wherein said gas collecting space is defined by said circular columns the overlapping lower ends of said support columns and said reactor floor. |
052251497 | claims | 1. A method for detecting thermal hydraulic oscillation in a nuclear fission reactor core through which a reactor coolant passes while the fission reactions in the core generate neutrons and gamma radiation, comprising the steps of: positioning a first plurality of sensors, which are primarily responsive to neutron flux, at a respective plurality of first locations in the core; positioning a second plurality of sensors, which are primarily responsive to gamma radiation flux, at a respective plurality of second locations in the core; generating an output signal from each of said neutron sensors, commensurate with the neutron flux at each neutron sensor; generating an output signal from each of said gamma sensors, commensurate with the gamma radiation flux at each gamma sensor; comparing each neutron sensor output signal with a respective gamma sensor output signal and generating a comparison value signal for each of said comparisons; and in response to the comparison value signals generating output data indicative of core thermal hydraulic oscillations. generating intermediate output data indicative of the spatial distribution within the core, of said comparison values; monitoring the intermediate output data while coolant flows through the core; and in response to the monitored intermediate output data, generating said output data as final output data. the step of positioning includes supporting each neutron sensor in fixed spatial relationship to one gamma sensor, thereby defining a plurality of sensor pairs, and said step of comparing includes the step of comparing the neutron output signal with the gamma sensor output signal for each of said pairs. the step of comparing includes determining the difference of the signal amplitudes for each pair. said first plurality of sensors includes at least four neutrons flux sensors spaced apart axially in the core, and said second plurality of sensors includes at least four gamma flux sensor spaced apart axially in the core. sensing at each of a plurality of axially spaced apart zones within the core, changes in the local neutron flux and gamma flux; and from said sensed changes, generating output data indicative of incipient thermal hydraulic oscillations in the core. a plurality of a first type of sensor spatially distributed in the core, said first type of sensor having a first time dependent output signal, commensurate with the density of reactor coolant over a short range during the generation of power in the reactor core; a plurality of a second type of sensor spatially distributed in the core, said second type of sensor having a second time dependent output signal which, relative to the first type of sensor, is commensurate with the density of the coolant over a long range during power operation of the reactor core; means for associating each of said first type of sensors with one of said second type of sensors, to define a plurality of sensor pairs; means for generating a third output signal commensurate with a quantitative relationship between the first and second output signals from the sensors in each pair, thereby defining a plurality of paired time dependent measurement values; and means responsive to the paired measurement values, for generating output data indicative of thermal hydraulic oscillations in the core. 2. The method of claim 1, further including the steps of, 3. The method of claim 1, wherein 4. The method of claim 2, wherein the step of generating intermediate output data includes generating a comparison value in the form of a symbolic code indicative of whether the location of each neutron sensor is experiencing an increase or decrease in coolant voids. 5. The method of claim 3, wherein the step of positioning each sensor in each sensor pair at respective first and second locations, includes supporting the sensors in each pair no farther apart than about ten percent of the core axial dimension. 6. The method of claim 3, wherein the step of positioning each sensor in each sensor pair at respective first and second locations, includes the step of supporting the sensors no farther apart than about one inch. 7. The method of claim 3, wherein the step of positioning includes supporting each sensor in the sensor pair at respective first and second locations within a common housing. 8. The method of claim 3, wherein the neutron sensor output signal includes a time-dependent amplitude commensurate with the neutron flux and the gamma sensor output signal includes a time-dependent amplitude commensurate with the gamma flux and the step of comparing includes determining a time phase difference between the signal amplitudes for each pair. 9. The method of claim 3, wherein the neutron sensor output signal amplitude is commensurate with the neutron flux and the gamma sensor output signal is commensurate with the neutron flux, and 10. The method of claim 3 wherein, 11. The method of claim 8 wherein said plurality of sensor pairs include at least one pair in each of at least two axial zones in the core. 12. The method of claim 10 wherein each of said gamma sensors is located within a distance from one of said neutron sensors, equivalent to no more than about ten percent of the axial dimension of the core. 13. The method of claim 10, wherein each of said gamma sensors is located within about one inch from one of said neutron sensors. 14. A method for detecting thermal hydraulic oscillations parallel to the axis of the core of a boiling water nuclear reactor, comprising the steps of: 15. The method of claim 14, wherein the step of sensing includes supporting in each zone a gamma flux sensor in fixed spatial relation to a neutron flux sensor at substantially the same location in the zone. 16. The method of claim 15, wherein the step of sensing changes includes comparing the sensed neutron flux to the sensed gamma flux at each location and generating a comparison value signal commensurate with said comparison. 17. The method of claim 15, wherein the step of generating output data includes generating symbolically coded values for each location, commensurate with a quantitative relationship between the neutron and gamma fluxes as sensed at each location. 18. A system for monitoring thermal hydraulic oscillations in a boiling water nuclear reactor, comprising: 19. The system of claim 18, wherein the second type of sensor is responsive to gamma radiation intensity. 20. The system of claim 18, wherein the first type of sensor is responsive primarily to thermal neutron flux and the second type of sensor is responsive primarily to gamma radiation intensity. 21. The system of claim 20, including means for supporting the first and second sensors of a given pair within a common housing in the core. 22. The system of claim 21, wherein the housing is an in-core instrument tube passing through the full longitudinal dimension of the core, and wherein each tube contains a plurality of axially spaced neutron flux sensors, and at least one gamma flux sensor. |
abstract | An isotope production target rod for a power generating nuclear reactor is provided. The isotope production target rod can include at least one rod central body including an outer shell that defines an internal cavity and a plurality of irradiation targets within the internal cavity. The irradiation targets can be positioned in a spatial arrangement utilizing a low nuclear cross-section separating medium to maintain the spatial arrangement. |
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abstract | An EUV light source and method of operating same is disclosed which may comprise: an EUV plasma production chamber comprising a chamber wall comprising an exit opening for the passage of produced EUV light focused to a focus point; a first EUV exit sleeve comprising a terminal end comprising an opening facing the exit opening; a first exit sleeve chamber housing the first exit sleeve and having an EUV light exit opening; a gas supply mechanism supplying gas under a pressure higher than the pressure within the plasma production chamber to the first exit sleeve chamber. The first exit sleeve may be tapered toward the terminal end opening, and may, e.g., be conical in shape comprising a narrowed end at the terminal end. |
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051924943 | summary | The invention relates to an arrangement for protecting a cylindrical surface in a nuclear reactor containment against the effects of a core meltdown, the surface being located below the reactor vessel in a pool intended to be filled with water in order to granulate and cool molten core falling into it. In many types of reactors, if the core melts in a reactor accident and penetrates through the bottom of the reactor vessel, the molten core material will run down into a pool in the reactor containment. This is the case, for instance, in the type of reactor represented by the boiler reactors Oskarshamn 3(O3) and Forsmark 3(F3) in Sweden. In these reactors the central space below the reactor vessel is dry during normal operation, but in the event of an accident this space will be filled with water from a surrounding pool before the molten core penetrates the bottom of the reactor vessel. It is known from many industrial processes and from laboratory experiments that when a melt runs down into water it is fragmented into particles which solidify on their way through the water, thus forming a bed of particles at the bottom of the pool. The particles vary in size. Normally, approximately 98-99% of the bed mass will consist of particles having equivalent diameters between 1 and 12 mm. However, in certain cases steam explosions may occur and particles are then obtained which may be smaller than those obtained at normal fragmentation. The molten core material will form a particle bed of up to 25-30 m.sup.3 on the concrete floor of the reactor containment if the whole reactor core melts. Due to the high radioactivity of the core granulate enormous quantities of heat are generated in the bed, which must therefore be cooled if melting is to be avoided. Melting occurs at about 2000.degree. C. and a meltdown at this temperature would seriously damage the concrete and rapidly destroy the penetrations of steel or the like located in the floor and possibly also in the walls of the water pool. This would cause severe and unacceptable radioactive emission. The particle bed is cooled by water from the pool penetrating the bed from above. The water boils in the bed, forming steam which flows up through the bed and condenses in the water mass above the bed. If the bed containing small particles, is too high, or generates too much energy, the upwardly flowing steam will prevent the water from penetrating down through the bed. This phenomenon is known as dryout and means that the particle bed dries out and is heated to melting point which, as mentioned, results in concrete attack and destruction of penetrations. Reactor containment integrity is lost, with severe radioactive emission as a result. The object of the invention is to offer an arrangement by means of which the integrity of the reactor containment can be maintained in the event of an accident of the type mentioned. A specific object of the invention is to provide an arrangement which protects the penetrations, but the invention is also aimed at offering an arrangement which will protect the bottom and walls of the pool against attack from the bed. For this purpose the invention offers an arrangement for protecting a tubular surface (e.g. a penetration or the side wall of the pool) in a nuclear reactor containment against the effects of a core meltdown, the surface being located below the reactor vessel in a pool intended to be filled with water in order to granulate and cool molten core material falling into it. The arrangement is substantially characterised by a pipe or a tubular element located on the side of the tubular surface to be protected, thereby forming a gap between the surface and the pipe, the pipe having an inlet located below the surface of the water in the pool and above the highest level in the pool which granulate could be expected to reach, an outlet in the pipe communicating with the lower part of the pool, so that water is permitted to pass via the inlet, the gap and the outlet to the lower part of the granulate bed, and by screen devices preventing granulate from entering the gap. The tubular surface to be protected may thus be a penetration or a pipe through the bottom or side wall of the pool. Alternatively the tubular surface may constitute the side wall of the pool itself. According to a further development of the invention, the bottom of the pool may be lined with a perforated bottom wall to form a bottom gap between the bottom of the pool and the bottom wall, the perforations in the bottom wall then communicating with the gap below. The protective devices may comprise a screen over the inlet to the gap, said screen preventing granulate from falling directly into the gap. The protective device may even comprise a grating or the like covering the outlet from the gap or the pipe to the granulate bed to prevent granulate particles from entering and blocking the gap. Alternatively the protective device at the outlet may consist of slits in the pipe or of a labyrinth or the like. The invention is defined in the appended claims. It has been discovered that the dryout effect for particle beds can be increased by a factor of up to 3 if counter flow is avoided between steam and water through the particle bed. This can be achieved by placing vertical pipes in the pool, the pipes having an inlet located above the surface of the bed and below the surface of the water, and an outlet (e.g. in the form of axial slits in the lower end of the pipe) at the bottom of the pool. Water will thus run down through the pipe, permeate into the bed and form steam which will pass up through the particle bed without impeding the downward flow of water through the pipe. However, these simple pipes are not sufficient if the granulate bed is formed of layers with relatively small particles on top of a layer of relatively large particles; such bed structures cannot be entirely excluded since they may be formed by particles from small steam explosions settling on top of particles formed by normal hydrodynamic fragmentation. If the bed were to be cooled only by pipes extending down through the particle bed, the integrity of the penetrations of steel in the concrete floor of the pool might be endangered. However, this problem is solved according to the invention by arranging the pipes around the penetrations, thus preventing the penetrations from coming into direct contact with the core granulate and also ensuring that they are cooled by the water flowing down through the gap. Of course, an equivalent arrangement is possible for the side wall of the pool. In both cases the bottom of the pool can be protected by a bottom wall such as that described above. In the case of reactors with relatively small pool area, the granulate bed will be relatively deep and therefore difficult to cool. In such situations it is particularly suitable to allow the pipe to communicate with a bottom gap between the bottom of the pool and the bottom wall, as well as when the penetrations extend through the side wall of the pool, spaced from the bottom of the pool. |
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summary | ||
052951707 | abstract | A nuclear reactor has a passive system for adjusting the pH of post accident water in the containment vessel. A basic liquid is stored in the containment vessel at an elevation above the maximum post accident water level. When radiation levels in the containment vessel exceed a predetermined, normal level the basic liquid is gravitationally drained into sumps located in the containment vessel below the maximum post accident water level where it mixes with emergency core cooling system water, raising the pH of the water to about 7. |
041938437 | abstract | Defects in the fuel rods of nuclear fuel assemblies are ascertained and located by ultrasonic means. The fuel assemblies are subjected to ultrasonic waves. Differences in fuel rod resonance is indicative of defective rods. |
claims | 1. A system for creating a plurality of substantially uniform nano-scale features in a substantially parallel manner on a surface of a substrate comprising:a source operable to provide a directed flux of charged particles; andan array of micro-lenses positioned on the surface of the substrate, wherein each lens comprises an aperture such that the aperture defines a bottom that corresponds to a portion of the surface of the substrate; wherein the array is operable to receive the flux of charged particles, focus the flux of charged particles at selected focal points on the surface of the substrate corresponding to the bottoms of the apertures of the micro-lens array, andwherein the system is operable to displace the locations of the focal points on the surface of the substrate to allow for the formation of a plurality of substantially uniform nanometer sized features on the surface of the substrate in a substantially parallel manner. 2. The system of claim 1,wherein the system further comprises a voltage source operable to provide a selected voltage; andwherein the array of micro lenses further comprises an insulating layer and a conducting layer, such that providing the selected voltage between the conducting layer and the substrate is operable to said focus the flux of the charged particles at the selected focal points on the surface of the substrate. 3. The system of claim 2, wherein the source is operable to provide an ion beam. 4. The system of claim 3, wherein the source comprises a pulsed plasma source. 5. The system of claim 4, further comprising a gas source operable to provide a selected gas operable to etch the surface of the substrate in combination with the directed flux of charged ions. 6. The system of claim 5, wherein the array of micro-lenses further comprises a double lens structure. 7. The system of claim 1, wherein the source is operable to provide a directed electron beam. 8. A device comprising:a substrate, having a surface;a lens array positioned on the surface of the substrate, wherein the lens array comprises a plurality of lenses, wherein each lens comprises a hole such that a bottom of each hole is aligned with a portion of the surface of the substrate; anda plurality of nano-scale features on the surface, wherein each feature is positioned at the bottom of a hole, wherein the features are substantially identical in dimension, substantially identical in shape, and positioned in a substantially spatially uniform fashion with respect to each other. 9. The device of claim 8, wherein each of the features comprises a nanodot. 10. The device of claim 8, wherein each of the features comprises a nanowire. 11. The device of claim 8, wherein each of the features comprises a nanotube. 12. The device of claim 8, wherein each of the features is a nanodevice. 13. The device of claim 8, wherein each of the features is a nanocircuit. 14. The device of claim 8, further comprising circuitry positioned on a surface of the lens array, wherein the circuitry is operable to address and control one or more of the features. 15. The device of claim 8, wherein a smallest lateral dimension of the feature is less than 50 nm and at least approximately 1 nm. 16. The device of claim 8, wherein a smallest lateral dimension of the feature is less than 40 nm and at least approximately 1 nm. 17. The device of claim 8, wherein a smallest lateral dimension of the feature is less than 30 nm and at least approximately 1 nm. 18. The device of claim 8, wherein a smallest lateral dimension of the feature is less than 20 nm and at least approximately 1 nm. 19. The device of claim 8, wherein a smallest lateral dimension of the feature is less than 10 nm and at least approximately 1 nm. |
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description | This application claims priority to U.S. Provisional Patent Application No. 62/441,015, filed on Dec. 30, 2016 and entitled: CONTROL ROD DRIVE MECHANISM (CDRM) WITH REMOTE DISCONNECT MECHANISM, the contents of which are herein incorporated by reference in their entirety. This invention was made with Government support under Contract No. DE-NE0000633 awarded by the Department of Energy. The Government has certain rights in this invention. This disclosure generally relates to a control rod drive mechanism of a nuclear reactor with a feature to remotely disconnect the drive shaft from the control rod assembly. Nuclear reactors may have control rod drive mechanisms (CRDM) located on top of a reactor pressure vessel (RPV) within an upper containment vessel (CNV). The CRDM components inside the reactor pressure vessel may need to maneuver or release drive shafts by gravity during a rapid control rod insertion (SCRAM). The CRDM may be driven remotely by electromagnetic force across the pressure vessel boundary. The CRDM also may need to release the drive shafts from attached control rod assemblies (CRA). This allows upper and lower sections of the RPV to be separated for refueling. The CRA are released and left in the reactor core to avoid a possible reactivity excursion. A control rod drive mechanism includes a drive assembly located on top of a reactor pressure vessel. The drive assembly includes annular drive magnets extending around a top end of a drive shaft and annular drive coils on the outside of a pressure boundary. A latch assembly on the inside of the pressure boundary is coupled to annular drive magnets and engages with the drive shaft in response to actuation of the drive assembly. The drive coils also rotate the drive magnets and the engaged latch assembly to axially displace the drive shaft. Deactivating the drive coils disengages the latch assembly from the drive shaft, dropping a connected control rod assembly via gravity into a nuclear fuel assembly. The control rod drive mechanism also may include a disconnect assembly with a disconnect magnet, coupled to a top end of a disconnect rod that extends through the drive shaft. Annular disconnect coils on the outside of the pressure boundary extend around the disconnect magnet to hold the disconnect magnet and the disconnect rod in a raised position, in order to remotely disconnect the drive shaft from, or reconnect to, the control rod assembly. FIG. 1 illustrates a cross-sectional view of an example integral reactor module 5 comprising reactor pressure vessel 52. Reactor core 6 is shown located near a lower head 55 of the reactor pressure vessel 52. The reactor core 6 may be located in a shroud 22 which surrounds reactor core 6 about its sides. A riser section 24 is located above the reactor core 6 surrounded by steam generators 30. When primary coolant 28 is heated by reactor core 6 as a result of fission events, primary coolant 28 may be directed from shroud 22 up into an annulus 23 located above reactor core 6, and out of riser 24. This may result in additional primary coolant 28 being drawn into shroud 22 to be heated in turn by reactor core 6, which draws yet more primary coolant 28 into shroud 22. The primary coolant 28 that emerges from riser 24 may be cooled down by steam generators 30 and directed towards the outside of the reactor pressure vessel 52 and then returned to the bottom of the reactor pressure vessel 52 through natural circulation. Primary coolant 28 circulates past the reactor core 6 to become high-temperature coolant TH and then continues up through the riser section 24 where it is directed back down the annulus and cooled off by steam generators 30 to become low-temperature coolant TC. One or more control rod drive mechanisms (CRDM) 10 are operably coupled to a number of drive shafts 20 that may be configured to interface with a plurality of control rod assemblies 80 located above reactor core 6. A reactor pressure vessel baffle plate 45 may be configured to direct the primary coolant 28 towards a lower end 55 of the reactor pressure vessel 52. A surface of the reactor pressure vessel baffle plate 45 may come into direct contact with and deflect the primary coolant 28 that exits the riser section 24. In some examples, the reactor pressure vessel baffle plate 45 may be made of stainless steel or other materials. The lower end 55 of the reactor pressure vessel 52 may comprise a ellipsoidal, domed, concave, or hemispherical portion 55A, wherein the ellipsoidal portion 55A directs the primary coolant 28 towards the reactor core 6. The ellipsoidal portion 55A may increase flow rate and promote natural circulation of the primary coolant through the reactor core 6. Further optimization of the coolant flow 28 may be obtained by modifying a radius of curvature of the reactor pressure vessel baffle plate 45 to eliminate/minimize boundary layer separation and stagnation regions. The reactor pressure vessel baffle plate 45 is illustrated as being located between the top of the riser section 24 and a pressurizer region 40. The pressurizer region 40 is shown as comprising one or more heaters and a spray nozzle configured to control a pressure, or maintain a steam dome, within an upper end 56 or head of the reactor pressure vessel 52. Primary coolant 28 located below the reactor pressure vessel baffle plate 45 may comprise relatively sub-cooled coolant TSUB, whereas primary coolant 28 in the pressurizer region 40 in the upper end 56 of the reactor pressure vessel 52 may comprise substantially saturated coolant TSAT. A fluid level of primary coolant 28 is shown as being above the reactor pressure vessel baffle plate 45, and within the pressurizer region 40, such that the entire volume between the reactor pressure vessel baffle plate 45 and the lower end 55 of the reactor pressure vessel 52 may be full of primary coolant 28 during normal operation of reactor module 5. Shroud 22 may support one or more control rod guide tubes 94 that serve to guide control rod assemblies 80 that are inserted into, or removed from, reactor core 6. In some examples, drive shafts 20 may pass through reactor pressure vessel baffle plate 45 and through riser section 24 in order to control the position of control rod assemblies 80 relative to reactor core 6. Reactor pressure vessel 52 may comprise a flange by which lower head 55 may be removably attached to an upper reactor vessel body 60 of reactor pressure vessel 52. In some examples, when lower head 55 is separated from upper reactor vessel body 60, such as during a refueling operation, riser section 24, baffle plate 45, and other internals may be retained within upper reactor vessel body 60, whereas reactor core 6 may be retained within lower head 55. Additionally, upper reactor vessel body 60 may be housed within a containment vessel 70. Any air or other gases that reside in a containment region 74 located between containment vessel 70 and reactor pressure vessel 52 may be removed or voided prior to or during reactor startup. The gases that are voided or evacuated from the containment region 74 may comprise non-condensable gases and/or condensable gases. During an emergency operation, vapor and/or steam may be vented from reactor pressure vessel 52 into containment region 74, or only a negligible amount of non-condensable gas (such as hydrogen) may be vented or released into containment region 74. FIG. 2 illustrates an upper cross-sectional view of reactor module 5 and example control rod drive mechanism (CRDM) assemblies 10. Reactor module 5 may comprise an upper containment vessel 76 housing at least a portion of the CRDM 10. A plurality of drive shaft housings 77 may be located within upper containment vessel 76. A plurality of drive shafts 20 associated with CRDMs 10 may be located in a reactor pressure vessel 52 that is housed in main containment vessel 70. Drive shaft housings 77 may be configured to house at least a portion of drive shafts 20 during operation of reactor module 5. In some examples, essentially all of the CRDMs 10 may be housed within main containment vessel 70. Upper containment vessel 76 may be removably attached to main containment vessel 70. By removing upper containment vessel 76, the overall size and/or volume of reactor module 5 may be reduced, which may affect peak containment pressure and/or water levels. In addition to reducing the overall height of reactor module 5, the removal of upper containment vessel 76 from main containment vessel 70 may further reduce the weight and shipping height of reactor module 5. In some example reactor modules, several tons of weight may be removed for each foot that the overall height of reactor module 5 is decreased. Reactor pressure vessel 52 and/or main containment vessel 70 may comprise one or more steel vessels. Additionally, main containment vessel 70 may comprise one or more flanges by which a top head or a bottom head of main containment vessel 70 may be removed from the containment vessel body, such as during a refueling operation. During refueling, reactor module 5 may be relocated from an operating bay into a refueling bay, and a series of disassembly steps may be performed on the reactor module 5. The operating bay may be connected to the refueling bay by water, such that reactor module 5 is transported under water. Main containment vessel 70 may be disassembled, e.g., the top or bottom head may be separated from the containment vessel body, in order to gain access to CRDM 10 and/or to reactor pressure vessel 52. At this stage of refueling, reactor pressure vessel 52 may remain completely submerged in the surrounding water in the refueling bay. In some examples, an upper portion of CRDM 10, such as the plurality of drive shaft housings 77, may be located above water to facilitate access to CRDM 10 in a dry environment. In other examples, the entire CRDM 10 may be submerged in the pool of water in the refueling bay. CRDMs 10 may be mounted to an upper head of reactor pressure vessel 52 by nozzles 78. Nozzles 78 may be configured to support CRDMs 10 when main containment vessel 70 is partially or completely disassembled during the refueling operation. Additionally, CRDMs 10 may be configured to support and/or control the position of drive shafts 20 within reactor pressure vessel 52. Reactor pressure vessel 52 may comprise a substantially capsule-shaped vessel. In some examples, reactor pressure vessel 52 may be approximately 20 meters in height. Drive shafts 20 may extend from CRDMs 10, located at the upper head of reactor pressure vessel 52, into a lower head of reactor pressure vessel 52, so that they can be connected to control rod assemblies 80 that are inserted into reactor core 6 (FIG. 1). The distance from the upper head of reactor pressure vessel 52 to reactor core 6, while less than the overall height of reactor pressure vessel 52, may therefore result in the length of drive shafts 20 also being approximately 20 meters in length or, in some examples, somewhat less than the height of reactor pressure vessel 52. FIG. 3 is a perspective view of a control rod assembly 80 held partially above and partially inserted into a nuclear fuel assembly 90 in reactor core 6. As explained above, multiple drive shafts 20 extend down from rod drive mechanisms 10 to the top of reactor core 6. Control rod assembly 80 may include a cylindrical hub 82 that attaches to the bottom end of drive shaft 20. Arms 84 extend radially out from cylindrical hub 82 and attach at distal ends to top ends of control rods 86. Control rods 86 extend into a nuclear fuel assembly 90 that is alternatively referred to as a fuel bundle that forms part of reactor core 6. Nuclear fuel assembly 90 may include a top nozzle 92 that supports multiple guide tubes 94. Guide tubes 94 extend down from nozzle 92 and in-between nuclear fuel rods (not shown). Control rods 86 control the fission rate of the uranium and plutonium in the nuclear fuel rods. Control rods 86 are typically held by drive shaft 20 above nuclear fuel assembly 90 or held slightly inserted into nuclear fuel assembly 90. Reactor core 6 may overheat. A nuclear SCRAM operation is initiated where control CRDMs 10 in FIG. 1 release drive shafts 20 dropping control rods 86 down into guide tubes 94 and in-between the nuclear fuel rods. FIG. 4A shows a cross-sectional view of an example reactor pressure vessel 52. CRDMs 10 may be mounted to an upper head 96 of reactor pressure vessel 52 and configured to support a plurality of drive shafts 20 that extend through the length of an upper reactor vessel body 60 of reactor pressure vessel 52 towards reactor core 6 located in a lower head 98 of reactor pressure vessel 52. In some examples, lower head 98 may be removably attached to upper reactor vessel body 60 at a flange 100, such as by a plurality of bolts. In addition to housing a number of nuclear fuel rods, reactor core 6 may be configured to receive a plurality of control rod assemblies 80 that may be movably inserted between the fuel rods to control the power output of reactor core 6. When reactor core 6 is generating power, lower ends 102 of drive shafts 20 may be connected to control rod assemblies 80. Additionally, CRDMs 10 may be configured to control the location of control rod assemblies 80 within reactor core 6 by moving drive shafts 20 either up or down within reactor pressure vessel 52. Upper ends 104 of drive shafts 20 may be housed in CRDM pressure housing 77 located above upper head 96 of reactor pressure vessel 52, such as when control rod assemblies 80 are removed from reactor core 6. In some examples, CRDM pressure housing 77 may comprise a single pressure vessel configured to house upper ends 104 of drive shafts 20. In other examples, CRDM pressure housing 77 may comprise individual housings for each of the drive shafts 20. Lower ends 102 of drive shafts 20 are shown disconnected from control rod assemblies 80, such as may be associated with a refueling operation of reactor core 6. During an initial stage of the refueling operation, lower head 98 may remain attached to upper reactor vessel body 60 while drive shafts 20 are disconnected from control rod assemblies 80. Reactor pressure vessel 52 may remain completely sealed to the surrounding environment, which in some examples may comprise a pool of water that at least partially surrounds reactor pressure vessel 52, during the initial stage of the refueling operation. CRDMs 10 may comprise remote disconnect mechanisms by which drive shafts 20 may be disconnected from control rod assemblies 80 without opening or otherwise disassembling reactor pressure vessel 52. In some examples, reactor pressure vessel 52 may form a sealed region 106 that surrounds reactor core 6, control rod assemblies 80, and lower ends 102 of drive shafts 20. By remotely disconnecting drive shafts 20, control rod assemblies 80 may remain within reactor core 6 when drive shafts 20 are withdrawn, at least partially, into CRDM pressure housing 77. FIG. 4B illustrates the example reactor pressure vessel 52 of FIG. 4A partially disassembled. During the refueling operation, lower head 98 may be separated from upper reactor vessel body 60 of reactor pressure vessel 52. In some examples, lower head 98 may be held stationary in a refueling station while upper reactor vessel body 60 is lifted up by a crane and moved away from lower head 98 to facilitate access to reactor core 6. Drive shafts 20 are shown in a retracted or withdrawn position, such that lower ends 102 may be completely retained within upper reactor vessel body 60 and/or CRDM pressure housing 77. For example, CRDMs 10 may be configured to raise lower ends 102 of drive shafts 20 above a lower flange 108 used to mount upper reactor vessel 60 together with an upper flange 110 of lower head 98. Withdrawing lower ends 102 of drive shafts 20 into upper reactor vessel body 60 may provide additional clearance between lower flange 108 and upper flange 110 during the refueling operation and further may keep drive shafts 20 from contacting external objects or getting damaged during transport and/or storage of upper reactor vessel body 60. Additionally, upper ends 104 of drive shafts 20 may similarly be housed and/or protected by CRDM pressure housing 77 when drive shafts 20 are in the retracted or withdrawn position. As discussed above, control rod assemblies 80 may remain completely inserted in reactor core 6 during some or all of the refueling operation. In some examples, maintaining the insertion of control rod assemblies 80 within reactor core 6 may be dictated by nuclear regulatory and/or safety considerations. FIG. 5 is a side view and FIG. 6 is a plan view of a single-hinge type control rod drive mechanism 88 that includes a remote disconnect mechanism. Referring to FIGS. 5 and 6, a drive shaft housing 77 extends over the top end of drive shaft 20 and around the latch mechanism 138. Drive shaft housing 77 is alternatively referred to as an upper pressure boundary. As described above, drive shaft 20 enters reactor pressure vessel (RPV) 52 in FIG. 2 through a nozzle 78 connected on top to the bottom end of drive shaft housing 77. A bottom end of drive shaft 20 detachably connects to control rod assembly 80 as shown in more detail below. Control rod drive mechanism 88 includes a drive assembly 122 that raises and lowers drive shaft 20 and attached control rod assembly 80. Control rod drive mechanism 88 also includes a disconnect assembly 120 that disconnects drive shaft 20 from control rod assembly 80. Both drive assembly 122 and disconnect assembly 120 may be remotely activated and controlled from outside of the RPV 52 via electrical control signals. FIG. 7 is a side sectional view of control rod drive mechanism 88 and FIG. 8 is a more detailed sectional view of a single-hinge latch assembly 138 used in control rod drive mechanism 88. Referring to FIGS. 7 and 8, through-holes 158 are provided in drive shaft housing 77 and nozzle 78. Bolts (not shown) may be inserted into holes 158 to connect drive shaft housing 77 to nozzle 78 that extends up from the upper head of RPV 52 as shown above in FIG. 2. A disconnect rod 132 extends through the entire length of drive shaft 20 and a cylindrical disconnect magnet 134 is attached to a top end of disconnect rod 132. Disconnect magnet 134 extends up into drive shaft housing 77 and annular disconnect coils 136 extend around drive shaft housing 77 and disconnect magnet 134. When activated, disconnect coils 136 may hold disconnect magnet 134 in a raised position allowing disconnect rod 132 to retract vertically upwards within drive shaft 20. An upper end of drive shaft 20 includes a threaded outside surface 140. In one example, threads 140 may comprise ACME® type threads for linearly displacing drive shaft 20. Of course, any other type of threading or gearing also may be used. Drive shaft 20 extends from underneath disconnect magnet 134, through drive shaft housing 77 and nozzle 78, and into the upper head of RPV 52 (FIG. 1). Drive shaft 20 further extends through the length of RPV 52 and a bottom end includes a grapple 126 that connects to control rod assembly 80. Disconnect magnet 134 and disconnect coils 136 encompass the disconnect assembly 120. An annular arrangement of drive coils 128 may extend around the outside of drive shaft housing 77 and an annular arrangement of drive magnets 130 inside of drive shaft housing 77 may extend around drive shaft 20. Continuously activating drive coils 128 may raise drive magnets 130. Alternating activation of alternating drive coils 128 in FIG. 8 also may rotate drive magnets 130 around a center axis 156 of drive shaft 20. Drive coils 128, drive magnets 130 and latch assembly 138 form the drive assembly 122. A single-hinge latch assembly 138 is coupled on the bottom end to the drive shaft housing 77 and coupled on top to drive magnets 130. Latch assembly 138 includes an annular base 142 that includes a central opening that extends around drive shaft 20. A lip 143 extends out from an outside bottom end of base 142 and seats into a recess formed between the bottom end of drive shaft housing 77 and the top end of nozzle 78. Lip 143 functions as a hold-down holding base 142 down against the top surface of nozzle 78. An annular collar 148 is rotationally attached to base 142 and includes a step 144 that attaches on top of bearings 154 that extend around the top of base 142. Collar 146 also includes a center opening that receives and extends around drive shaft 20. Collar 146 is held vertically/elevationally down onto base 142 but rotates about central axis 156 of drive shaft 20 on top of bearings 154 and base 142. The outside end of a gripper 150 is pivotally attached to an upper end of collar 148 with a first pin 152A. The inside end of gripper 150 is pivotally attached to a bottom end of a latch 146 by a second pin 152B. A top end of latch 146 is attached to drive magnets 130. When drive magnets 130 are lowered a bottom end of latch 146 may sit on top of step 144 of collar 148. When activated, drive coils 128 lift drive magnets 130 vertically upwards also lifting latch 146. Lifting latch 146 causes the inside ends of grippers 150 to rotate upwards engaging with threads 140 on drive shaft 20. The outside ends of grippers 150 rotate about pins 152A which are held vertically in place by collar 148. After raising the inside ends of grippers 150, drive coils 128 may start rotating drive magnets 130 about central axis 156 of drive shaft 20. The bottom ends of drive magnets 130 start rotating raised latch 146 and attached gripper 150 around the outside circumference of drive shaft 20. Rotating gripper 150 also rotates collar 148 over the top of base 142 and around central axis 156 while remaining elevationally held down in place by base 142. The inside end of grippers 150 rotate within threads 140 moving drive shaft 20 axially and linearly upwards inside of drive shaft housing 77 and nozzle 78. Drive coils 128 may rotate drive magnets 130 in an opposite direction, also rotating attached grippers 150 within threads 140 in an opposite direction. Accordingly, grippers 150 axially and linearly move drive shaft 20 in an upward or downward direction as directed by an electrical control system. Deactivating drive coils 128 drops drive magnets 130 vertically downwards. Inside ends of grippers 150 also rotate downwards about pins 152B, disengaging from threads 140. Now released from grippers 150, drive shaft 20 is free to drop vertically downwards via gravity. FIG. 9 is a cross-sectional plan view of drive assembly 122. Annular drive coils 128 extend around the outside of drive shaft housing 77 and annular drive magnets 130 extend around the inside of drive shaft housing 77. Drive shaft 20 extends through a central opening formed in drive magnets 130 and disconnect rod 132 extends through a hole formed along the central axis of drive shaft 20. Threads 140 extend around the outside surface of drive shaft 20. When continuously activated, drive coils 128 generate an electromagnetic field that vertically lifts up drive magnets 130. When drive coils 128 are activated in an alternating pattern, the electromagnetic field also rotates drive magnets 130 around the central axis causing drive assembly 122 to operate effectively like an electrical motor. For example, the electrical control system may activate drive coils A during a first period and activate drive coils B during an alternating second period. The alternating activation of drive coils A and B cause drive magnets M to rotate about a vertical axis that extends through drive shaft 20. FIG. 10 is a cross-sectional plan view of single-hinge latch assembly 138. Disconnect rod 132 extends through the center of drive shaft 20. Threads 140 extend around the outside surface of drive shaft 20. Latch 146 has an annular cross-sectional shape and attaches to the inside end of gripper 150 via pin 152B. Collar 148 also includes an annular cross-sectional shape and attached to the outside end of gripper 150 via pin 152A. As explained above, latch 146 is attached to drive magnets 130 and can move vertically up and down. Drive shaft housing 77 also has an annular cross-sectional shape concentrically aligned with drive shaft 20. Also note that any number of grippers 150 may be located around drive shaft 20. For example, four grippers 150 may be located 90 degrees apart around drive shaft 20. FIGS. 11A-11E are side sectional views showing different operating positions of control rod drive mechanism 88. Referring to FIG. 11A, drive assembly 122 is shown in a lowered state. Drive coils 128 are deactivated and drive magnets 130 are in a lowered position, with the control rod assembly 80 fully inserted into reactor core 6 (FIG. 1). Lowered drive magnets 130 with attached latch 146 released grippers 150 from threads 140 of drive shaft 20. During a loss of electric power or forced SCRAM, drive coils 128 may deactivate, allowing gravity to drop drive shaft 20 downward, disconnected from latch assembly 138. Attached control rod assembly 80 accordingly drops into fuel assembly 90 neutralizing reactor core 6 (see FIGS. 1 and 3). Thus, CRDM 88 has the advantage of automatically scramming reactor core 6 whenever deactivated during a power failure. Disconnect assembly 120 is also shown in a lowered state. Disconnect coils 136 are deactivated and disconnect magnet 134 is in a lowered position sitting on top of drive shaft 20. In the lowered position, the bottom end of disconnect rod 132 extends in-between reciprocating arms 127A and 127B of grapple 126. Spread-apart grapple arms 127A and 127B press against and lock into grooves in cylindrical hub 82 of control rod assembly 80. FIG. 11B shows drive assembly 122 in a raised state. Drive coils 128 are activated and drive magnets 130 are in a raised position. Raised drive magnets 130 raise attached latch 146 moving inside ends of grippers 150 upward, interlocking with threads 140 of drive shaft 20. Locked grippers 150 can raise or lower drive shaft 20 based on the rotational direction of drive magnets 130. Disconnect assembly 120 is still shown in a lowered state where the bottom end of disconnect rod 132 remains inserted in-between grapple arms 127A and 127B. Spread-apart grapple arms 127A and 127B remain locked inside of cylindrical hub 82 locking the bottom end of drive shaft 20 to control rod assembly 80. FIG. 11C shows drive assembly 122 in a raised state. Drive coils 128 are activated and drive magnets 130 are raised, moving attached latch 146 upward engaging inside ends of grippers 150 with threads 140. Drive coils 128 also may start rotating drive magnets 130 causing grippers 150 to rotate around engaged threads 140 of drive shaft 20. Rotating grippers 150 force drive shaft 20 axially and linearly upwards into drive shaft housing 77 and lift connected control rod assembly 80 by a short distance that does not cause a reactivity insertion into the reactor core (within a so-called dead band). Raising drive shaft 20 also raises disconnect magnet 134, maintaining the bottom end of attached disconnect rod 132 in-between grapple arms 127A and 127B. In other words, raising drive shaft 20 and disconnect rod 132 together keeps the bottom end of drive shaft 20 attached to control rod drive mechanism 80, prior to the disconnection discussed below. FIG. 11D shows drive assembly 122 in a lowered state and disconnect assembly 120 in a raised state. Disconnect coils 136 are activated when drive shaft 20 and disconnect magnet 134 are in the raised position shown in FIG. 11C. Drive coils 128 then may rotate drive magnets 130 in an opposite direction lowering drive shaft 20 vertically downward. At the same time, disconnect coils 136 hold disconnect magnet 134 in a raised position. As grippers 150 continue to move drive shaft 20 linearly downward, the bottom end of disconnect rod 132 slides up and out from in-between grapple 126. Grapple arms 127A and 127B accordingly reciprocate inwards disconnecting from control rod assembly 80, which drops a short distance. Alternatively, drive coils 128 are deactivated dropping drive shaft 20 and disconnecting control rod assembly 80, with disconnect coils 136 holding disconnect magnet 134 in a raised position. FIG. 11E shows disconnect assembly 120 and drive assembly 122 both in a lowered state. Deactivating disconnect coils 136 releases disconnect magnet 134 causing the bottom end of disconnect rod 132 to slide in-between grapple arms 127A and 127B. Drive coils 128 then may deactivate disconnecting grippers 150 from drive shaft 20. Spread-apart grapple 126 then sits on the top of control rod assembly 80. Thus, drive coils 128 and disconnect coils 136 can be remotely activated and deactivated to linearly displace drive shaft 20 and also to disconnect drive shaft 20 from control rod assembly 80 during a reactor core refueling operation. Reconnecting the control rod assembly 80 after completion of refueling and re-assembly of reactor vessel 52 (FIGS. 4A and 4B) may be performed in reverse order of the steps shown in FIG. 11A to 11D. FIG. 12 is a side view of a dual-hinge type control rod drive mechanism 159. FIGS. 13A and 13B are side sectional views of control rod drive mechanism 159. FIG. 14 is a more detailed view of the dual-hinge latch assembly 160. Referring to FIGS. 12, 13A, 13B, and 14, drive assembly 122 and disconnect assembly 120 in control rod drive mechanism 159 include substantially the same drive and disconnect coils and magnets as described above. Drive shaft housing 77 and nozzle 78 are also all substantially the same as those described above. Disconnect rod 132, drive shaft 20, and threaded outside surface 140 are also similar to those described above. Similar to above, continuously activating drive coils 128 may raise and align drive magnets 130 with annular drive coils 128. Alternating activation of adjacent drive coils 128 also may rotate drive magnets 130 around a central axis 156 of drive shaft 20, to force linear motion of drive shaft 20 and attached control rod assembly 80. Dual-hinge latch assembly 160 is coupled at a bottom end to drive shaft housing 77 and coupled at a top end to drive magnets 130. Latch assembly 160 includes a similar base 142 at described above that includes a central opening that extends around drive shaft 20. A similar lip 143 extends out from an outside bottom end of base 142 and seats into a recess formed between the bottom end of drive shaft housing 77 and the top end of nozzle 78. Lip 143 functions as a hold-down holding base 142 down against a top surface of nozzle 78. Referring to FIG. 13A, drive assembly 122 is shown in a raised state. Activating drive coils 128 raises drive magnets 130 and attached latch 162. The lower ends of grippers 164 move upwards and inwards engaging with threads 140 of drive shaft 20. Locked grippers 164 can then raise or lower drive shaft 20 based on the rotational direction of drive magnets 130. Disconnect assembly 120 is shown in a lowered position where the bottom end of disconnect rod 132 is inserted in-between arms 127A and 127B of grapple 126. Spread-apart arms 127A and 127B lock inside of cylindrical hub 82 locking the bottom end of drive shaft 20 to control rod assembly 80. Referring to FIG. 13B, drive assembly 122 and disconnect assembly 120 are shown in lowered states. Deactivating drive coils 128 lowers drive magnets 130 and attached latch 162. The grippers 164 move downwards and outwards disengaging with threads 140 of drive shaft 20. Disconnect assembly 120 is still shown deactivated where the bottom end of disconnect rod 132 remains inserted in-between arms 127A and 127B of grapple 126. Spread-apart arms 127A and 127B remain locked inside of cylindrical hub 82 locking the bottom end of drive shaft 20 to control rod assembly 80. In FIG. 14 an annular collar 148 similar in design to FIG. 8 is attached, but rotationally de-coupled, to base 142 and includes a similar step 144 that attaches on top of bearings 154 that extend around the top of base 142. Collar 146 also includes a center opening that receives and extends around drive shaft 20. Collar 146 is held vertically/elevationally down onto base 142 but rotates about central axis 156 of drive shaft 20 on top of bearings 154 and base 142. The outside end of a hinge 168 is pivotally attached to a top end of collar 148 with a first pin 166A. The inside end of hinge 168 is pivotally attached to a lower end of a gripper 164 by a second pin 166B. The top end of a latch 162 is attached to drive magnet 130 and a bottom end of latch 162 is pivotally attached to a top end of gripper 164 by a third pin 166C. When activated, drive coils 128 lift drive magnets 130 vertically upwards also raising latch 162. Gripper 164 and the inside end of hinge 168 also move upwards, moving the bottom end of gripper 164 inwards engaging with threads 140 of drive shaft 20. After engaging the lower ends of grippers 164, drive coils 128 may start rotating drive magnets 130 about central axis 156 of drive shaft 20. The bottom ends of drive magnets 130 also start rotating raised latch 146 and engaged grippers 164 around drive shaft 20. Rotating grippers 164 also rotates collar 148 about central axis 156 while being held vertically down by base 142. The inside ends of grippers 164 rotate within engaged threads 140 moving drive shaft 20 linearly upwards inside of drive shaft housing 77 and nozzle 78. Drive coils 128 may rotate drive magnets 130 in an opposite direction, thus rotating grippers 164 within threads 140 in an opposite direction axially moving drive shaft 20 downward. Deactivating drive coils 128 drops drive magnets 130 and inside ends of grippers 164 downwards. Hinges 168 also rotate downwards and outwards disengaging the lower ends of grippers 164 from threads 140. Drive shaft 20 is now released from grippers 150 and is free to drop vertically downwards via gravity. FIG. 15 is a cross-sectional plan view of dual-hinge latch assembly 160. Disconnect rod 132 extends through a centerline of drive shaft 20. Threads 140 extend around the outside surface of drive shaft 20. Latch 162 has an annular cross-sectional shape and attaches at the bottom end to the top end of gripper 164. Collar 148 also includes an annular cross-sectional shape and attaches to the outside end of hinge 168 via pin 166A. As explained above, collar 146 is attached to drive magnets 130 and can move vertically up and down. Drive shaft housing 77 also has an annular cross-sectional shape concentrically aligned with drive shaft 20. FIGS. 16A-16G are simplified schematic diagrams showing different operations of the single-hinge type control rod drive mechanism 88 or double-hinge type control rod drive mechanism 159 described above, focusing on the primary elements to attain the CRDM functions described herein. For explanation purposes, the following abbreviations are used below. Drive coils 128=A Drive magnet 130=B Latch 146, 162=C Drive shaft 20=D Grippers 150, 164=E Disconnect coil 136=F Disconnect magnet 134=G Grapple 126=H Drive shaft housing 77=I Base 142=J Disconnect rod 132=K Control rod assembly 80=CRA Concentric electromagnetic coils A and F extend on the outside of drive shaft housing I, alternatively referred to as pressure boundary. Coils A and F on the outside interact to move cylindrical magnets B and G, respectively, inside pressure boundary I. Referring to FIG. 16A, drive coils A are initially de-energized. Latch C is fixed to annular drive magnets B and rests on base J inside drive shaft housing I. Referring to FIG. 16B, drive coils A are energized, lifting drive magnet B upwards until aligned with drive coils A. This lifts latch C and engages grippers E that pivot around pins that are vertically fixed with respect to the inside of pressure boundary I, yet allow for rotation of latch C. Grippers E fit into threaded grooves of drive shaft D. Referring to FIG. 16C, by operating drive coils A in a specific sequence, drive magnet B and latch C are set into rotary motion, while at the same time still maintaining a same elevation as drive coils A. This precludes disengagement of grippers E. The rotary motion of grippers E translates into linear drive shaft motion that raises drive rod D and the attached CRA. Referring back to FIG. 16A, upon a SCRAM signal or loss of electric power, drive coils A release drive magnet B causing grippers E to pivot down and outwards due to the drop of latch C. This provides a safety feature where a gravity-driven drop of drive shaft D drops attached CRA into the reactor core. FIGS. 16D-16G show how to remotely disconnect drive shaft D from the CRA prior to disassembly of reactor pressure vessel 52 in FIGS. 4A and 4B. Drive coils A are initially de-energized and latch C is resting on base J. This may be similar to the initial drive shaft engagement configuration shown in FIG. 16A. Referring to FIG. 16D, drive coils A are activated raising drive magnets B and latch C causing grippers E to engage with drive shaft D. As shown above in FIG. 11C, drive coils A then set drive magnet B and latch C into rotary motion, while at the same time maintaining a same elevation as drive coils A. Rotating grippers E move drive shaft D and disconnect magnet G linearly upwards into raised positions, lifting the attached CRA by a short distance that does not cause a reactivity insertion into the reactor core (within a so-called dead band). Referring to FIG. 16E, drive coils A are still energized holding drive magnet B, drive shaft D, disconnect magnet G, and disconnect rod K in raised positions. Disconnect coil F is energized holding disconnect magnet G and attached disconnect rod K vertically in place. Drive coils A then may rotate drive magnet B, latch C, and gripper E in an opposite direction linearly lowering drive shaft D. Grapple H on the bottom end of drive shaft D currently holds the CRA, and the bottom end of disconnect rod K starts moving up and out from the grapple arms. The arms of grapple H contract causing the CRA to drop by a short distance, until it rests again on top of the nuclear fuel assembly top nozzle 92 in FIG. 3. Referring to FIG. 16F, drive coils A remain energized and therefore hold drive magnet B in place. Disconnect coil F is then de-energized. This releases disconnect magnet G causing the bottom end of disconnect rod K to insert into and expand grapple H on the bottom of drive shaft D. Referring to FIG. 16G, drive coils A are de-energized releasing annular drive magnet B and latch C. Drive shaft D drops by a short distance until grapple H rests on top of the CRA cylindrical hub without being engaged. This allows the upper and lower sections of the reactor pressure vessel to be separated for refueling without removing the CRA. Re-connection of grapple H to the CRA is performed in reverse order. Drive coils A may move drive shaft D and disconnect magnet G vertically up into raised positions. Disconnect coils F may activate holding disconnect magnet G and disconnect rod K in the raised position. Drive coils A then may lower drive shaft D contracting and inserting grapple H into the CRA. Disconnect coils F then may be deactivated dropping disconnect magnet G and the bottom of disconnect rod K in-between grapple H. Grapple H expands locking into the CRA. Alternatively, grapple H is reengaged with the CRA by pulling up disconnect magnet G using the electromagnetic force of disconnect coil F. Disconnect magnet G is moved into the raised position without simultaneously energizing drive coil A. The weight of drive shaft D may be large enough so that only disconnect rod K moves upwards inside of drive shaft D. Grapple H contracts inserting into the CRA cylindrical hub. Disconnect coils F are then deactivated so the bottom of disconnect rod K drops back down into grapple H. Grapple H expands locking into the CRA. Having described and illustrated the principles of a preferred embodiment, it should be apparent that the embodiments may be modified in arrangement and detail without departing from such principles. Claim is made to all modifications and variation coming within the spirit and scope of the following claims. Some of the operations described above may be implemented in software and other operations may be implemented in hardware. One or more of the operations, processes, or methods described herein may be performed by an apparatus, device, or system similar to those as described herein and with reference to the illustrated figures. It will be apparent to one skilled in the art that the disclosed implementations may be practiced without some or all of the specific details provided. In other instances, certain process or methods have not been described in detail in order to avoid unnecessarily obscuring the disclosed implementations. Other implementations and applications also are possible, and as such, the following examples should not be taken as definitive or limiting either in scope or setting. References have been made to accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific implementations. Although these disclosed implementations are described in sufficient detail to enable one skilled in the art to practice the implementations, it is to be understood that these examples are not limiting, such that other implementations may be used and changes may be made to the disclosed implementations without departing from their spirit and scope. Although the examples provided herein have primarily described a pressurized water reactor and/or a light water reactor, it should be apparent to one skilled in the art that the examples may be applied to other types of power systems. For example, the examples or variations thereof may also be made operable with a boiling water reactor, sodium liquid metal reactor, gas cooled reactor, pebble-bed reactor, and/or other types of reactor designs. It should be noted that examples are not limited to any particular type of reactor cooling mechanism, nor to any particular type of fuel employed to produce heat within or associated with a nuclear reaction. Any rates and values described herein are provided by way of example only. Other rates and values may be determined through experimentation such as by construction of full scale or scaled models of a nuclear reactor system. Having described and illustrated the principles of a preferred embodiment, it should be apparent that the embodiments may be modified in arrangement and detail without departing from such principles. Claim is made to all modifications and variation coming within the spirit and scope of the following claims. |
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047568763 | abstract | Modular ultrafiltration device for the cooling liquid of a nuclear reactor, comprising a radiation absorbing containment (1), an ultrafilter (15) arranged in the containment (1), a heat exchanger (32) placed in the containment (1), and connection pieces intended for the various parts of the ultrafilter (15) and heat exchanger (32) and passing through the wall of the containment (1) in a leak-proof manner. A heat-insulating material (41) fills the inner volume of the containment (1). The modular device can easily be connected to an auxiliary circuit of the nuclear reactor. The ultrafiltration wall can be replaced without any difficulty. |
description | The invention relates to a fuel assembly for a boiling water reactor. A fuel assembly of this type comprises a bundle of fuel rods filled with nuclear fuel, which are held axially by a plurality of spacers. A water channel runs approximately centrally in the fuel-rod bundle, the lower end of the water channel carrying a stopper, through which a bore passes. The water channel is attached to the fuel assembly foot with the aid of said stopper. The fuel assembly foot itself, or at least part thereof, is formed by a frame part surrounding a sieve plate. In a fuel assembly known from EP 1 280 163 A1, the sieve plate includes a bore, into which a threaded sleeve is inserted from the underside of the sieve plate and soldered there. A soldering of this type requires an increased manufacturing outlay and is also problematic with respect to fatigue strength during use in a nuclear reactor. It is an object of the invention to provide a fuel assembly for a boiling water reactor, in which the fuel assembly foot is connected to the water channel in an alternative manner. This object is achieved by a fuel assembly with a skirt that is integrally formed on the underside of the stopper, which is arranged at the lower end of the water channel, and extends, in a rotationally-fixed manner, into an opening passing through the sieve plate. Furthermore, a bush is provided, having a first and a second longitudinal section, wherein the second longitudinal section projects from the underside of the sieve plate into the opening of the latter in a rotationally-fixed manner and wherein the outer side of a radial shoulder located between the two longitudinal sections bears against the underside of the sieve plate. Finally, the threaded bolt of a screw passes through the bush, which engages in a thread of the bore of the stopper. It is an advantage of the described connection that it completely dispenses with the complicated production of welded or soldered seams and therefore has a high fatigue strength, on the one hand, and low assembly outlay, on the other hand. The rotationally-fixed engagement of the skirt in the opening of the sieve plate rules out a change in the rotational position between water channel and fuel assembly foot. The rotational connection is preferably achieved in that the skirt has a polygonal contour and a region (which surrounds the skirt) of the screen-plate opening has a cross-sectional area complementary thereto. In a preferred embodiment, the mutually facing end faces of the second longitudinal section and of the skirt bear against one another, wherein the lengths of bush and skirt are such that there is a gap between the underside of the stopper and the upper side of the sieve plate. Thereby the prestress of the threaded bolt which is required for a fixed screw-connection is achieved by producing stress between the bush and the stopper. The sieve plate remains free from any introduction of force in the axial direction here. This is advantageous if the sieve plate is formed by elements flexible in said direction, for example by webs, which are arranged parallel to one another and have a curvature in the axial direction. When applying force in the axial direction, there is a risk that the webs will flex and the screw-connection will lose strength as a result. The proposed refinement, however, prevents this effectively. In order to prevent the screw from loosening by itself, the bush is arranged in the opening of the sieve plate in a rotationally-fixed manner and the screw is connected to the bush in a rotationally-fixed manner. In a preferred refinement, this is achieved in that the second longitudinal section of the bush has a polygonal contour and a region (which surrounds the bush) of the screen-plate opening has a cross-sectional area complementary thereto. The rotational lock between bush and screw is such that a circumferential region of the first longitudinal section of the bush interacts with the head of the bush in a torque-locking manner on account of a radially inwardly facing plastic deformation. The water channel is attached to the fuel assembly foot transversely with respect to the axial direction without play and in particular secure against tilting on account of the threaded bolt having a preferably thread-free longitudinal section, which extends away from the screw head and bears against the inner face of the bush by its outer circumferential face. The invention is now explained further by means of the exemplary embodiments illustrated in the attached drawings, wherein: FIG. 1 shows a fuel assembly of a boiling water reactor comprising a bundle of a multiplicity of fuel rods 1 filled with nuclear fuel. The fuel rods are attached laterally by a plurality of spacers 2 arranged in different axial positions. A water channel 4 extends in the axial direction 3 approximately centrally in the fuel-rod bundle. A fuel assembly top fitting 5 is arranged at the upper side of the fuel assembly and a fuel assembly foot 6 is arranged at the lower side. The fuel assembly foot 6 substantially comprises, as can be seen in FIG. 2, for example, a frame part 7 and a sieve plate 8. The sieve plate 8 is formed by a multiplicity of webs 9, which extend between two opposite walls 10, 12 of the frame part 7. The webs 9 are arranged, at a distance from one another, transversely with respect to their longitudinal direction. They are connected to one another in the same direction by struts 13 integrally formed thereon. An opening 14 passes through the sieve plate 8 at an eccentric position. The inner cross-sectional area of the opening 14 is in the shape of an octagon. To be more precise, the rims 15 (which define the opening 14) of the webs 9 bear against an imaginary cylinder of octagonal outline. For the purpose of attaching to the fuel assembly foot 6, a stopper 17, through which a threaded bore 16 passes, is arranged at the lower end of the water channel 4. A skirt 19 surrounding the threaded bore 16 projects in the axial direction from the underside 18 of the stopper 17, which underside faces the sieve plate 8 in the installed state. The outer circumferential face of the skirt 19 forms an octagonal cylinder casing and extends, in a rotationally-fixed manner, into the complementary opening 14 of the sieve plate 8. The stopper 17 itself has an approximately square contour. The edges 20 delimiting the underside 18 of the stopper 17 are beveled. A bush 22, which is subdivided into a first and a second longitudinal section 23, 24, is furthermore provided for the purpose of attaching the stopper 17 and the water channel 4. A radial shoulder 25 is arranged between the two longitudinal sections, as can best be seen in FIG. 6. The first longitudinal section 23 is annular and has a larger diameter than the second longitudinal section 24, which has an octagonal outline complementary to the opening 14. In the installed state (FIG. 3, 5, 6), said second longitudinal section 24 extends into the opening 14 in a rotationally-fixed manner. The bush 22 bears here against the underside 27 of the sieve plate 8, and the webs 9 forming it, by the outer side 26 of the radial shoulder 25. The length of the skirt 19 and of the second longitudinal section 24 of the bush 22 is in each case such that their sum is smaller than the thickness 28 (FIG. 5) of the sieve plate 8 or the height of the webs 9 forming it. Therefore there is an axial distance 32 between the mutually facing end faces 29, 30 of skirt 19 and bush 22. Furthermore, a screw 34 having a threaded bolt 35 and a head 36 is provided for attaching the water channel 4, wherein the threaded bolt 35 extends through the bush 22 and into the threaded bore 16 of the stopper 17. The threaded bolt 35 has a thread-free collar 33 extending axially away from the head 36. A recess 37 is located between the collar 33 and that section of the threaded bolt 35 which has a thread. The head 36 is supported on the inner side 38 of the radial shoulder 25. The bush 22 is thereby pressed against the underside 27 of the sieve plate 8 by the outer side 26 of the radial shoulder in the stressed state. The underside 18 of the stopper 17 here presses against the upper side 40 of the sieve plate. The fuel assembly foot 6, the bush 22 and the screw 34 are made of austenite. The water tank and the stopper 17 bounding it on the underside, on the other hand, are made of zircaloy. The first longitudinal section 23 of the bush 22 has a wall thickness which permits a radially inwardly directed deformation 41. As can be seen in FIGS. 3 and 4, two such deformations 41 have been realized at diametrically opposed locations of the first longitudinal section 23. The deformations 41 extend into two diametrically opposed notches 39 in the head 36. This fixes the screw 34 with respect to the bush 22 in terms of rotation. The latter, in turn, is fixed in terms of rotation in the opening 14. The screw 34 is thereby prevented from loosening by itself. The exemplary embodiment illustrated in FIG. 7-9 differs from that mentioned above merely in that the longitudinal section 24a of the bush 22 is longer, wherein the length of said section and the length of the skirt 19 are such that their sum is greater than the thickness 28 of the sieve plate 8. This forms a gap 42 between the upper side 40 of the sieve plate 8 and the underside 18 of the stopper 17. During stressing, the stopper 17 is therefore not supported on the upper side 40 of the sieve plate 8, but on the bush 22. This eliminates the risk that the webs 9 corrugated in the axial direction 3 will flex resiliently in this direction, which would lead to an undesired deformation of the webs in the axial direction under certain circumstances to produce the required prestress. 1 fuel rod 2 spacer 3 axial direction 4 water channel 5 fuel assembly 6 fuel assembly foot 7 frame part 8 sieve plate 9 web 10 wall 12 wall 13 strut 14 opening 15 edge 16 threaded bore 17 stopper 18 underside 19 skirt 20 edge 22 bush 23 first longitudinal section 24 second longitudinal section 25 radial shoulder 26 outer side 27 underside 28 thickness 29 end face 30 end face 32 axial distance 33 color 34 screw 35 threaded bolt 36 head 37 recess 38 inner side 39 notch 40 upper side 41 deformation 42 gap |
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description | A guide tube inspection camera fixture apparatus for inspecting internal surfaces of nuclear reactor control rod guide tubes is described below in more detail. The fixture supports an underwater camera used for the inspections. The camera is held in a fixed position which eliminates the need for a worker to hold the camera, and provides camera stability during the visual inspection process. The camera fixture provides for quality camera shots by negating the effects of water flow, water thermals, and hand held camera usage. Also, because there are no moving parts, foreign material exclusion is greatly reduced, and the number of crevices which trap contaminates is also reduced. The guide tube inspection camera fixture apparatus is manufactured from any suitable material, for example, aluminum, steel, stainless steel, and engineered plastic materials. Referring now to the figures, FIG. 1 is a sectional view, with parts cut away, of a boiling water nuclear reactor pressure vessel (RPV) 10. RPV 10 has a generally cylindrical shape and is closed at one end by a bottom head 12 and at its other end by a removable top head 14. A side wall 16 extends from bottom head 12 to top head 14. Side wall 16 includes a top flange 18. Top head 14 is attached to top flange 18. A cylindrically shaped core shroud 20 surrounds a reactor core 22. Shroud 20 is supported at one end by a shroud support 24 and includes a removable shroud head 26 at the other end. An annulus 28 is formed between shroud 20 and side wall 16. A pump deck 30, which has a ring shape, extends between shroud support 24 and RPV side wall 16. Pump deck 30 includes a plurality of circular openings 32, with each opening housing a jet pump 34. Jet pumps 34 are circumferentially distributed around core shroud 20. An inlet riser pipe 36 is coupled to two jet pumps 34 by a transition assembly 38. Each jet pump 34 includes an inlet mixer 40, and a diffuser 42. Inlet riser 36 and two connected jet pumps 34 form a jet pump assembly 44. Heat is generated within core 22, which includes fuel bundles 46 of fissionable material. Water circulated up through core 22 is at least partially converted to steam. Steam separators 48 separates steam from water, which is recirculated. Residual water is removed from the steam by steam dryers 50. The steam exits RPV 10 through a steam outlet 52 near vessel top head 14. The amount of heat generated in core 22 is regulated by inserting and withdrawing control rods 54 of neutron absorbing material, such as for example, hafnium. To the extent that control rod 54 is inserted into fuel bundle 46, it absorbs neutrons that would otherwise be available to promote the chain reaction which generates heat in core 22. Control rod guide tubes 56 extend vertically from control rod drives 58 to core support plate 60. Control rod guide tubes 56 restrict non-vertical motion of control rods 54 and also maintain the vertical motion of control rods 54 during insertion and withdrawal. Control rod drives 58 effect the insertion and withdrawal of control rods 54. Control rod drives 58 extend through bottom head 12. Fuel bundles 46 are aligned by a core plate 60 located at the base of core 22. A top guide 62 aligns fuel bundles 46 as they are lowered into core 22. Core plate 60 and top guide 62 are supported by core shroud 20. FIG. 2 is a perspective view of an inspection camera fixture apparatus 70 in accordance with an embodiment of the present invention. In an exemplary embodiment, inspection camera fixture apparatus 70 includes a base plate 72 and a unit-body tower 74 coupled to base plate 72. Specifically, a first end portion 76 of unit-body tower 74 is coupled to base plate 72 so that unit-body tower 74 is substantially perpendicular to base 72. Base plate 72 and unit-body tower 74 can be coupled together by any suitable method. In the exemplary embodiment, unit-body tower 74 is coupled to base plate 72 by welding. In another embodiment, unit-body tower 74 is coupled to base plate 72 by fasteners. In still another embodiment, first end 76 portion of unit-body tower 74 includes threads that engage a threaded bore in base plate 72. In the exemplary embodiment, unit-body tower 74 is welded to the center of base plate 72. However, in alternate embodiments, unit-body tower 74 is coupled to an area of base plate 72 other than the center. Base plate 72 is sized and shaped to be received in control rod guide tubes 56. In the exemplary embodiment, base plate 72 is circular. However, in alternate embodiments, base plate 72 has a shape that matches the shape of guide tube 56, for example a cruciform shape, a rectangular shape, a Y-shape, and any other suitable polygonal shape. Also, a plurality of openings 78 extend through base plate 72A support bracket 80 is coupled to a second end portion 82 of unit-body tower 74. Support bracket 80 extends from unit-body tower 74 so that support bracket 80 is substantially parallel to base plate 72. Support bracket 80 and unit-body tower 74 can be coupled together by any suitable method. In the exemplary embodiment, support bracket 80 is coupled to unit-body tower 74 by welding. In another embodiment, support bracket 80 is coupled to unit-body tower 74 by fasteners and/or clamping elements. In still another embodiment, second end portion 80 of unit-body tower 74 includes threads that engage a threaded bore in support bracket 80. An inspection camera 84 is coupled to support bracket 80. An input/output cable 86 is attached to inspection camera 84. Inspection camera 84 is positioned between support bracket 80 and base plate 72. A bore 88 extends through support bracket 80. Bore 88 is sized to receive inspection camera 84. Inspection camera 84 is secured to support bracket 80 by any suitable method. In one embodiment, set screws extend through support bracket 80 and engage camera 84 inside bore 88. In another embodiment, camera 84 has a threaded end portion and bore 88 includes threads sized to threadedly engage the threaded end portion of camera 84. A lifting device adapter 90 is attached to second end portion 80 of unit-body tower 74. Lifting device adapter 90 is configured to couple to a lifting device, for example handling poles, ropes, and remote operated tool manipulators. Inspection camera fixture apparatus 70 is used for a visual inspection of the inside surface of control rod guide tubes 56. During a shutdown of reactor 10, after control rods 54 are removed from control rod guide tubes 56, apparatus 70 is inserted into one control rod guide tube 56. Particularly, a handling pole (not shown) is connected to lifting device adapter 90 and a worker lowers apparatus 70 into position inside control rod guide tube 56. Inspection camera 84 is activated by a signal carried by input/output cable 86 to camera 84 and camera shots or photographs are taken of the inside surface of guide tube 56. Apparatus 70 can then be rotated to position camera 84 at a new cirumferential position within guide tube 56 before more camera shots are taken. Apparatus 70 can also be raised or lowered to position camera 84 at a new axial position within guide tube 56 before further camera shots are taken. When the inspection of the inner surface of guide tube 56 is complete, apparatus 70 is raised from guide tube 56 and inserted into the next guide tube 56 to be inspected. When the inspection of guide tubes 56 is complete apparatus is raised from reactor core 22 and disconnected from the handling pole. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. |
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048440493 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 schematically illustrates, in longitudinal cross-section, a water heater device, generally denoted as the numeral 10, having a generally cylindrical inner water tank 12 for containing water and a generally cylindrical outer shell 14 concentrically surrounding the inner water tank 12. The outer shell 14 is of a larger diameter than the water tank 12 and they cooperate to define an annular space 16 therebetween. As illustrated, the water heater device 10 is of the electrically heated type having, for example, an electrical resistance unit (not shown) projecting into the interior of the water tank 12 to heat the water therein. The bottom of the inner water tank 12 is formed with a concavity 18. The top end of the water heater device 12 is closed by a cap 20, which may be a separate component or may be unitary with the outer shell 14. The bottom end of the water heater device 10 is typically closed by a floor 22. With further reference to FIGS. 1, an insulating thermal collar 24 is located in the annular space 16. The collar 24 includes an enclosing envelope 26 filled with a thermal insulation material 28. The enclosing envelope 26 is fabricated of a fluid impermeable, pliable material such as, for example, polyethylene film, vinyl film, metalized polyester, metal foil, and the like. The thermal insulation material 28 can be a fibrous batt, such as interwoven fiberglass, or a loose, discrete, divided material, such as for example non-interengaged fiber glass, mineral wool, steel wool, cellulose, ceramic fiber, discrete particles or beads of plastic foam, and the like. It is contemplated, that in some applications, it may be necessary to cohesively hold the loose, discrete, divided insulation material together inside the envelope 26 to prevent the insulation material from shifting or settling within the enclosing envelope 26. In this event, a binder material is homogeneously dispersed throughout the mass of the insulation material 28 to cohesively hold the insulation material together, and possibly adhesively affix the insulation material to the wall of the envelope 26, to prevent the insulation material 28 from shifting or settling within the envelope 26. The binding material used is a function of the type of insulation material 28 and can be a thermosetting adhesive, thermoplastic adhesive, cold setting adhesive, ambient setting adhesive, or hot setting adhesive. For example, a suitable adhesive for use with fiber glass and mineral wood is phenolic or sodium silicate, and a suitable adhesive for cellulose is polyvinyl acetate. The collar 24 extends circumferentially around the inner water tank 12 in the annular space 16 proximate the bottom end of the water heater device 10. The collar 24 has a width greater than the radial width of the annular space 16 so that the collar 24 is radially compressed between the interior wall surface of the outer shell 14 and the exterior wall surface of the inner water tank 12 sufficiently to tightly seal the interface of the collar 24 and inner wall surface of the outer shell 14 and to tightly seal the interface of the collar 24 and exterior wall surface of the inner water tank 12. In addition, the collar 24 is in abutment with the water heater device floor 22. With reference to FIGS. 2, the enclosing envelope 26 of the collar 24 is in the form of an elongated generally cylindrical tube closed at both of its ends 27 and 29. The tubular collar 24 is circumferentially wrapped around the perimeter of the water tank 12 with the ends 27 and 29 thereof brought together into mutual abutment. The abutting ends 27 and 29 can be secured together by, for example, adhesive tape if necessary. With reference to FIG. 3, an alternative construction for the enclosing envelope 26 of the collar 24 is illustrated. Envelope 126 is in the form of an elongated generally cylindrical tube having one of its ends 127 closed and the other of its ends 129 open. The tubular collar 124, formed in part by envelope 126 is circumferentially wrapped around the perimeter of the water tank 12 and the closed end 127 is inserted into the open end 129. The ends 127 and 129 can be secured together by, for example, adhesive tape, if necessary. With reference to FIG. 4, a further alternative construction is illustrated. The enclosing envelope 226 of the collar 224 is in the form of an elongated generally cylindrical tube having both of its ends 227 and 229 open. The tubular collar 224 is circumferentially wrapped around the perimeter of the water tank 12 and one of the open ends 227 is inserted into the other of the open ends 229. The ends 227 and 229 can be secured together by, for example, adhesive tape, if necessary. With reference to FIG. 5, a still further alternative further construction is illustrated. The enclosing envelope 326 of the collar 324 is in the form of a closed toroid. The envelope 326 is filled with a suitable insulation material as previously described relative to collar 24. The toroid collar 324 is concentrically slid over the water tank 12. With reference once again to FIG. 1, the annular space 16 above the collar 24 is filled with an expanded foam thermal insulation material 30 such as urethane, polyethylene, polystyrene and the like, which functions as a thermal insulation surrounding the inner water tank 12. With reference to FIGS. 1, an insulating disc 32 is located at the bottom end of the inner water tank 12. The insulating disc 32 includes an enclosing envelope 34 filled with a thermal insulation material 36. The enclosing envelope 34 has a peripheral configuration matching that of the bottom end of the water heater 12 and a thickness preferably at least as great as the depth of the concavity 18. As shown, the envelope 34 has a generally circular perimeter to correspond to the perimeter of the bottom end of the inner water tank 12 so that the disc 34 overlays the bottom end of the tank. The enclosing envelope 34 is fabricated of a fluid impermeable, pliable material such as, for example, polyethylene film, vinyl film, metalized polyester, metal foil, and the like. The thermal insulation material 36 is either a fibrous batt such as interwoven fiberglass, or a loose, discrete, divided material such as, for example, non-interengaged fiber glass, steel wool, mineral wool, cellulose fibers, ceramic fibers, discrete particles or beads of plastic foam, and the like. It is contemplated that in some applications it may be necessary to cohesively hold the loose, discrete, divided insulation material together inside the envelope 34, and possibly adhesively affix the insulation material to the wall of the envelope 34, to prevent the insulation material from shifting or settling within the enclosing envelope 34. In this event, a binder material is homogeneously dispersed throughout the mass of insulation material 36 to cohesively hold the insulation material together and prevent the insulation material from shifting or settling within the envelope 34. The binder material used will be a function of the type of insulation material 36 and can be a thermosetting adhesive, thermoplastic adhesive, cold setting adhesive, ambient setting adhesive, or hot setting adhesive. For example, a suitable adhesive for use with fiber glass and mineral wool is phenolic or sodium silicate, and a suitable adhesive for cellulose is polyvinyl acetate. With reference to FIG. 7, an alternative construction for disc 32 is illustrated. Insulating disc 132 includes an enclosing envelope 134 having a peripheral configuration generally matching that of the bottom end of the water tank and a thickness preferably at least as great as the depth of the cavity 18. The envelope 134 includes a central inner circular pocket 138 concentrically surrounded by a perimeter outer pocket 140. The envelope 134 is fabricated of a fluid impermeable, pliable material such as, for example, polyethylene film, vinyl film, metalized polyester, metal foil and the like. The central circular pocket 138 is separated from the perimeter pocket 140 by a circular seal 142. The central circular pocket 138 is filled with a fibrous batt of insulation material, such as interwoven or interengaged fiberglass, and the perimeter pocket 140 is filled with a loose, discrete, divided insulation material such as, for example, non-interengaged fiber glass, mineral wool, steel wool, cellulose fibers, ceramic fibers, discrete particles of beads of plastic foam, and the like. However, it is contemplated that the central circular packet 138 be filled with the loose, discrete, divided insulation material and the perimeter pocket 140 be filled with the fibrous batt. It is contemplated that in some applications, it may be necessary to cohesively hold the loose, discrete, divided insulation together inside of the pocket. In this event, a binder material is homogeneously dispersed throughout the mass of insulation material within the pocket to cohesively hold the insulation material together, and possibly adhesively affix the insulation material to the wall of the pocket to prevent the insulation material from shifting or settling within the pocket. The binder material used will be a function of the type of insulation material used within the pocket and can be thermosetting adhesive, thermoplastic adhesive, cold setting adhesive, ambient setting adhesive, or hot setting adhesive. For example, a suitable adhesive for use with fiber glass and mineral wood is phenolic or sodium silicate, and a suitable adhesive for cellulose is polyvinyl acetate. With reference to FIGS. 8 and 9, there is illustrated, in schematic format, the results of various steps for manufacturing the water heater 10. The insulation collar 124 (or one of the alternative constructions) is circumferentially fitted around the perimeter of the inner water tank 12 proximate the bottom end thereof. The collar 124 can be secured to the wall of the water tank 12 by an adhesive, or tape. The insulating disc 32 (or the alternative construction) is disposed in overlaying relationship to the bottom end of the water tank 12, and can be secured in place by an adhesive or a tape. The outer shell 14 is coaxially moved over the inner water tank 12, the floor 22 is positioned over the bottom of the water tank 12 and the outer shell 14 assembly to close the bottom of the water heater device 10. An expandable foam insulation material 30 is injected into the annular space 16 between the inner water tank 12 and outer shell 14 above the collar 124 and allowed to expand in situ filling the annular space 16 above the collar 124. The collar 124 is radially compressed between the inner wall surface of the outer shell 14 and outer wall surface of the inner water tank 12 to form a seal at the interface of the collar 124 and outer shell 14 and a seal at the interface of the collar 124 and inner water tank 12, and functions as a stop or block to the expanding foam. The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom for modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention and scope of the appended claims. |
053655656 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the field of X-ray imaging equipment for producing a projection image on radiographic film or a reusable phosphor plate in combination with the moving tabletop of a computer tomography X-ray scanner. 2. Description of the Prior Art Analog radiography is a method by which projection X-ray images of the human body or other object are recorded on X-ray film or some other photosensitive surface. Analog radiology is known to provide excellent spatial resolution, but poor contrast resolution. Computerized radiography is a method by which projection X-ray images the human body or other objects are obtained by recording a latent image on a storage reusable phosphor plate which is then read under computer control by an interrogating light beam. The phosphor emits light of another wavelength which is proportional to the intensity of the X-ray. The emitted signal is digitized and displayed on a cathode ray tube monitor or laser printed on film or other media. Computerized radiography provides moderate spatial resolution and moderate contrast resolution which is improved over the contrast resolution realized by analog radiography. Computer tomography is a method by which the cross sectional images of a human body or other objects is obtained by rotating an X-ray tube and an opposing array of X-ray detectors about the human body or object. The collimated X-ray beam fans out laterally while it is narrowly collimated along its longitudinal axis. Computer tomography provides poor spatial resolution, but excellent contrast resolution. A very crude, low resolution projection image may also be obtained in a computer tomographic scanner by moving the object or human body through a collimated fanned beam and detector array. This is obtained by providing linearly moving the patient or object on a motorized tabletop on through a stationary collimated fan beam. Conventional slot analog radiography is also known. The procedure is to expose the patient with a collimated fan X-ray beam. Behind the patient is an X-ray barrier with a conforming slot defined through it. The collimated beam and its slotted barrier are moved in unison down the length of the patient as the patient stands between the two. Positioned behind the slotted X-ray barrier is a stationary film plate. The film plate is fixed relative to the patient and receives the projection X-ray image from the patient as the slotted barrier moves across it. The results are comparable to analog radiography, the only difference being that the patient is sequentially exposed to a collimated beam of X-rays as opposed to having an entire area simultaneously exposed to a shaped beam. The contrasting resolution obtainable by conventional slot radiography remains poor although the spatial resolution of the projection radiographs are good. Analog radiography and computerized radiography use traditional radiographic equipment whose fundamental technology has been substantially unchanged over the last 100 years. Computer tomography employs a radically different geometric design comprised of a gantry and motorized tabletop. In most if not all fully equipped radiology clinics and hospitals, one set of equipment is provided to produce high spatial resolution radiographs and another set of equipment to produce high contrast resolution axial radiographs. Hundreds of thousands of such units of each kind are used throughout the world. The cost of each of these units is substantial and currently both types of units are required to fully meet current standards of radiological practice. Therefore, what is needed is a single apparatus and methodology or some means by which existing radiographic equipment can be modified or used which would provide both the excellent spatial resolution of analog radiography while at the same time providing the high contrast resolution of computer tomography without the need to provide expensive duplicate sets of radiographic instrumentation. BRIEF SUMMARY OF THE INVENTION The invention is an apparatus for providing an analog radiograph of a patient. The apparatus comprises a fixed collimated X-ray source and an analog X-ray detecting assembly disposed immediately behind the patient for detecting projection X-ray images of the patient from the X-ray source. A mechanism is provided for moving the assembly in unison with the patient while the patient is being exposed to X-rays from the X-ray source. As a result, the analog radiograph is provided with high spatial resolution and contrast resolution. The collimated X-ray source is part of a computer tomography scanner. The mechanism for moving the assembly and patient in unison comprises a moveable tabletop upon which the patient is disposed and with respect to which the assembly is fixed. The moveable tabletop moves the assembly and patient past the fixed collimated X-ray source. The assembly comprises a rigid curved cassette carrier and a flexible film cassette disposed in the cassette carrier. The cassette carrier conforms the flexible film cassette to a predetermined curvature in order to minimize lateral magnification of the analog radiograph. The assembly further comprises a flexible X-ray grid. The flexible X-ray grid is disposed in the rigid cassette carrier and is conformed to the predetermined radius of curvature by the cassette carrier. The flexible X-ray grid may also be disposed in the flexible film cassette. In a retrofitted version of the invention the assembly is disposed on the mechanism for moving the patient. In an original-equipment-manufacturer (OEM) version the assembly is integrally combined in the mechanism for moving the patient. The invention can also be characterized as an improvement in a CT scanner having a moveable tabletop and a collimated X-ray source. The tabletop linearly moves the patient past the collimated X-ray source. The improvement comprises a curved analog X-ray detector for providing a record of a projection X-ray from the patient. An X-ray grid is disposed between the detector and the patient. The X-ray grid is fixed relative to the X-ray detector and patient so that the grid, detector and patient are moved in unison within the CT scanner by the moveable tabletop past the collimated X-ray source. As a result, an analog radiograph is produced with high spatial resolution and high contrast resolution. The invention is still further characterized as a method of providing a high spatial resolution and high contrast resolution analog projection radiograph comprising the steps of providing an X-ray grid and analog film X-ray detector at a relatively fixed position behind a patient. A collimated X-ray source is provided on a side of the patient opposing the X-ray grid and detector. The grid and detector simultaneously move in unison with the patient past the X-ray collimated source so that a high resolution analog radiograph is defined in the detector. The invention may be better visualized by turning to the following drawings wherein like elements are referenced by like numerals. |
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051397340 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Because the quantity of resin required for decontamination of an entire nuclear steam supply system is so large when utilizing the known chemical decontamination technologies, it has been determined that it is economically impractical to utilize the number of demineralizer vessels that would be needed to hold the entire quantity of necessary resin. Therefore, the methods of the present invention preferably utilize a limited number of vessels in conjunction with a means for replacing the resin beds as needed within those limited number of vessels during the decontamination operation while minimizing water usage, so as not to delay operation of the chemical decontamination system. In addition to resin replacement, it is sought to minimize personnel exposure from highly radioactive resin. Thus, the primary functional requirements to be met by a resin processing system will be to replace the spent resin as quickly as practical and to minimize the personnel exposure from the highly radioactive resin. Further, the apparatus used in conjunction with the methods of the present invention should be capable of storing all of the spent resin generated under either the CAN-DEREM or LOMI processes for decay and/or disposal off of the nuclear reactor critical path. Turning now in detail to the drawing, the FIGURE represents a schematic view of one embodiment of the apparatus utilized with the present invention. Other configurations are possible and do not affect the method and apparatus of the present invention. A fresh resin supply tank 10 is sized to hold all of the resin required for a particular chemical decontamination step. This, of course, will depend upon the number of resin beds being used within each decontamination step and the capacity of each such resin bed. In a typical example, a bank of demineralizers will contain three resin beds of approximately 165 cubic feet (4.67 cubic meters) each. Thus, the fresh resin supply tank would be sized to accommodate approximately 495 cubic feet (14 cubic meters) of resin. The time between decontamination steps is typically several hours, which allows for the bulk loading of fresh resin supply tank 10. In one preferred embodiment, fresh resin supply tank 10 is constructed with a cone shaped bottom to allow for gravity feed. The tank is arranged so that demineralized water from a demineralized water source 12 can be injected horizontally through piping 14 and valve 16 in a tee connection below the fresh resin supply tank 10. In such an arrangement, the resin will be educted from the fresh resin supply tank 10 and should be adequately mixed with the demineralized water for transport in a slurry fashion to a resin batching tank 18. This arrangement allows for the resin to be added to the fresh resin supply tank 10 in dry form. Thus, the volume requirements of the fresh resin supply tank 10 can be determined according to the volume of the dry resin and no additional allowance need be made for the addition of water. In a preferred embodiment, the fresh resin supply tank 10 will have a lid that can be manually opened to load the resin. Considering the large volume required for most of the processed steps, a pneumatic or other remote solids transport system may be appropriate to load the resin into the tank in a timely manner. (Typically, the resin beads are fragile and can be destroyed by use of a standard centrifugal pump with its accompanying shear action.) The resin slurry from the fresh resin supply tank 10 is delivered to the batching tank 18 by means of piping 20 and a fresh resin pump 22. Because of the concern for resin damage, an air-operated diaphragm pump is preferred for the fresh resin pump 22. Such a pump has the ability to run dry and economically. A process isolation valve 24 can also be provided. Normally, an operator can determine when a demineralizer is filled with resin by visual inspection through an open fill pipe. However, when used in conjunction with a nuclear reactor, this may not be practical since the equipment layout and the use in radioactive service would result in significant personnel exposure should such a visual inspection be undertaken. Thus, the resin batching tank 18 is provided as a way of calibrating the resin volume being added to a particular demineralizer bed. Therefore, the resin batching tank 18 is sized to hold one resin bed volume so that when the entire resin batching tank 18 contents are transported to a particular demineralizer 26, the resin bed tank 28 within the demineralizer 26 will be filled. (In actuality, the resin batching tank 18 is sized to hold one resin bed volume plus 50% more water in order to achieve a preferred resin to water ratio.) Using our previous example, the resin batching tank 18 volume would equal 1.5 times 165 cubic feet (4.67 cubic meters), or roughly 250 cubic feet (7.0 cubic meters). The demineralizer 26 is part of the clean-up sub-system of the nuclear reactor. One embodiment of such a clean-up sub-system is disclosed in incorporated-by-reference co-pending application Ser. No. 621,129 filed Nov. 26, 1990. The resin batching tank 18 is provided with two outlet nozzles, 30 and 32. Outlet nozzle 32 has a retention screen 34 to allow excess water to be drained or pumped out of resin batching tank 18. Outlet nozzle 30 is used for transferring the contents of the resin batching tank 18 to a particular demineralizer 26. Once again, it is preferred that the resin batching tank 18 have a cone-shaped bottom to facilitate complete resin removal. When a particular demineralizer 26 requires replacement of its resin, the full contents of resin batching tank 18 is transferred to that demineralizer 26 by means of piping 36 and resin feed pump 38. Resin feed pump 38 again is preferably an air-operated diaphragm pump. In addition, a process isolation valve 40 can be provided. In order that the resin processing system using a fresh resin supply tank 10 and a resin batching tank 18 can be properly utilized, a flexible hose 42 is attached to piping 36 so that the resin can be directed to the desired demineralizer 26. The flexible hose 42 can be attached and detached from a particular demineralizer 26 and, thereby, relocated to additional demineralizers 26 if so desired. It is, of course, also possible to construct an arrangement of pipes and valves such that the resin flow can be directed to the demineralizer 26 of choice. Other variations on this delivery system would be obvious to those of ordinary skill in the art. A typical demineralizer 26 includes a resin bed tank 28 to which process fluids 43 are fed via piping 44. The processed fluids 43, after passing through the resin bed tank 28, are removed through multiple screened outlets (for retaining resin) via piping 46 through valve 48 and return to the normal operating system through piping 50. In accordance with one embodiment of the present invention, a sluice water supply tank 52 is used to provide sluice water to the demineralizer 26 for removal of spent resin. The sluice water is pumped from the sluice water supply tank 52 by sluice water pump 54 to the demineralizer 26 through piping 56. Valve 48 on the process fluid outlet is closed and an alternate valve 58 is opened to allow the sluice water to flow into the resin bed tank 28 countercurrently to normal process fluid flow. In addition, a sluice water filter 60 can be provided in piping 56 to prevent resin fines from clogging the inside of the demineralizer screens during the fluffing and sluicing operations. Such a sluice water filter 60 can typically be a standard cartridge filter having a 25 micron or smaller filter rating. Finally, a process isolation valve 62 can be provided in piping 56. The spent resin is removed in slurry form from the resin bed tank 28 via piping 64 and now-open valve 66. The sluice water carrying the spent resin is directed to a spent resin storage tank 68. Excess water from this tank is drawn off through a screen 70, which acts to retain the resin, and is thereafter pumped back to the sluice water supply tank 52 for reuse on subsequent sluicing operations. In radioactive service, the sluice water must be treated as liquid rad waste prior to disposal. This treatment is costly in terms of manpower and radiation exposure. Therefore, reuse of the sluice water minimizes operating costs and offers a distinct advantage to the present invention over alternative techniques. The drawn-off excess water is returned to the sluice water supply tank 52 by use of piping 72 and sluice water recycle pump 74. The spent resin storage tank 68 is sized to be sufficient to hold all of the resin generated during a particular decontamination process step along with the additional water required for transport. The spent resin storage tank 68 will normally be large enough to hold all of the resin and accompanying water from the entire decontamination process. Removal of spent resin from the spent resin storage tank 68 between decontamination steps can be accomplished by means of a second outlet from the spent resin storage tank 68 that is unscreened. Use of valves 76 and 78 in conjunction with piping 80 allows for the spent resin to be transferred by use of the sluice water recycle pump 74. Closing valve 82 while opening valve 84 allows for the redirection of the spent resin to a disposal means 86. Such a disposal means 86 will typically include one or more high integrity containers. The method employed to provide sluice water to the demineralizer 26 and to remove spent resin from that demineralizer 26 and deliver it to the spent resin storage tank 68, can be employed with several demineralizers 26 in parallel. Thus, piping 56 can be split to be directed to such alternate demineralizers 26 via piping 88, 90, and 92. Each such demineralizer 26, would employ similar methods for removing spent resin, which would then be delivered to the spent resin storage tank 68 via piping 94, 96, and 98. In typical operation, a particular demineralizer 26 can be off-line for spent resin removal and rebatching while other demineralizers 26 are continuing in operation. In one preferred embodiment of the present invention, various bypasses and alternative flow patterns are provided to enhance the adaptability of the present system. Thus, for example, the demineralized water source 12 can also be directed to the sluice water supply tank 52 via piping 100 and valve 102, as well as directly to the demineralizer 26 via piping 104 and valve 106. Further, flow into and out of resin bed tank 28 can be better controlled by the addition of valves 108, 110, and 112, along with a bypass piping 114. Valve 112 and piping 114 can be used in conjunction with the sluice water to fluff the resin bed prior to resin regeneration. Sluice water can be directed from the sluice water supply tank 52 to the spent resin storage tank 68, bypassing the demineralizer 26, by use of piping 116 and valve 118. The spent resin storage tank 68 can also be utilized to collect material from the filtrate collection tank of the chemical clean-up sub-system described in the incorporated-by-reference co-pending application Ser. No. 07/621,129 filed Nov. 26, 1990 by means of connection 120. Sluice water can be supplied to a decontamination waste tank by means of connection 122 and valve 124. In operation, fresh resin supply tank 10 is bulk loaded during the time between decontamination steps, a period of usually several hours. Such bulk loading overcomes the problems of dealing with resin drums of modest size when large volumes are required in a short period. The resin batching tank 18 is filled from the fresh resin supply tank 10 and then the entire contents of resin batching tank 18 is transported to an individual demineralizer 26, completely filling the resin bed tank 28 with fresh resin. Once a particular demineralizer 26 has been in use and its resin is spent, sluice water is provided from sluice water supply tank 52 to the resin bed tank 28. The sluice water washes out the spent resin and delivers it in slurry form to the spent resin storage tank 68. Excess water is thereafter recycled to the sluice water supply tank 52. When the spent resin storage tank 68 is full, or at such other convenient time, the spent resin is removed and delivered to high integrity containers or other disposal means 86. Several advantages flow from use of the apparatus and method of the present invention. First, impact on critical path is minimized by use of the resin batching system. Personnel exposure to radioactivity is minimized while the resin bed tanks 28 are optimally filled with appropriate resin. In addition, the volume of sluice water required is minimized by recycling it for subsequent spent resin transfers. Having thus described the invention, it is to be understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification. It is to be limited only by the scope of the attached claims, including a full range of equivalents to which each claim thereof is entitled. |
abstract | The invention relates to a device for inspecting a fuel assembly in the pool of a nuclear plant, that comprises an image sensor with an observation field, and further comprising a boom with at least one removable fastener to the assembly, a reference graduation extending along an axis parallel to a longitudinal axis of the assembly, so that the image sensor can monitor within its field both the boom and the assembly. The device is designed so that the boom can be removably attached to the fuel assembly when the latter is suspended outside the pool by the hook of the machine for handling the fuel assemblies. The invention also relates to a corresponding method. |
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055685285 | abstract | A method for compensating a rod position indication system for non-linearity comprises the steps of applying an excitation current to a primary of a sensor for inducing a generally linear voltage that is representative of the position of a control rod on a secondary of the sensor. The excitation current includes a first frequency which is sufficient to provide the generally linear output for the sensor. The excitation current is then modified to include a second frequency which is sufficient for providing the generally linear output when the first frequency is insufficient to provide the generally linear output. |
claims | 1. A neutron shielding material containing epoxy resin as one of main component, comprising a hardened material which is prepared by mixing a base resin which contains a compound including two or more epoxy groups in the molecule as at least one component with a hardener for opening said epoxy rings and polymerizing thereof by heat setting said base resin at a temperature higher than room temperature. 2. A neutron shielding material containing epoxy resin as one of main component, comprising a hardened material which is prepared by mixing a base resin which contains a compound including two or more epoxy groups in the molecule as at least one component with a hardener for opening said epoxy rings and polymerizing thereof, wherein the setting temperature is approximately 40xc2x0 C. or higher. 3. A neutron shielding material according to claim 1 or 2 , wherein said base resin is a member selected from the group of bisphenol A epoxy compound, novolak epoxy compound, alicyclic glycidyl ether type epoxy compound, various glycidyl ester type epoxy compound, glycidyl amine type epoxy compound, and biphenol type epoxy compound or a mixture thereof, and said hardener is a member selected from the group of amine type hardener such as aromatic amine, alicyclic amine, and polyamide amine, acid anhydrate type hardener, and imidazole type hardening promoter or a mixture thereof. claim 1 2 4. A neutron shielding material according to claim 3 , wherein hardened material contains a fire retardant that said base resin contains. claim 3 5. A neutron shielding material according to claim 4 , wherein said fire retardant contains a member selected from the group consisting of metal hydroxide such as magnesium hydroxide, aluminum hydroxide, and calcium hydroxide, hydrates of said metal oxide, inorganic phosphoric compounds such as ammonium phosphate, organic phosphoric compounds such as phosphoric ester, and halogenated compounds such as hexabromo benzene and tetrabromobisphenol A. claim 4 6. A neutron shielding material according to claim 5 , wherein said hardened material contains a neutron absorbing material that is added to said base resin. claim 5 7. A neutron shielding material according to claim 6 , wherein said neutron absorbing material contains a member selected from the group consisting of boric compounds, cadmium compounds, gadolinium compounds, and samarium compounds. claim 6 8. A neutron shielding material according to claim 7 , wherein said hardened material contains a metal hydride or a hydrogen-absorbing alloy that is added to said base resin. claim 7 9. A neutron shielding material according to claim 3 , wherein said base resin and said hardener are so mixed that the equivalent ratio of the active hydrogen group in said amine type hardener to the epoxy group in said base resin may be 0.7 to 1.3 when the amine type hardener is used as said hardener or the equivalent ratio of the total of active hydrogen group and acid anhydride to the epoxy group in said base resin may be 0.7 to 1.3 when the amine type hardener is mixed up with the acid anhydride. claim 3 10. A neutron shielding material according to claim 5 , wherein said fire retardant, if it is a metal hydroxide or hydrate of said metal oxide, is added to said base resin at a ratio of 30% to 60% by weight of said base resin. claim 5 11. A neutron shielding material according to claim 7 , wherein said neutron absorbing material, if it is a boron carbide or boron nitride, is added to said base resin at a ratio of 0.1 to 10% by weight of said base resin. claim 7 12. A neutron shielding material according to claim 8 , wherein the components of the neutron shielding material are mixed up so that the viscosity of the liquid mixture of said base resin and said additives may not exceed 200 dPa.s immediately after addition thereof at 30xc2x0 C. to 100xc2x0 C. claim 8 13. A neutron shielding material according to claim 8 , wherein the components of the neutron shielding material are mixed up so that the viscosity of the liquid mixture of said base resin and said additives may not exceed 200 dPa.s at 30xc2x0 C. to 100xc2x0 C. for at least one hour. claim 8 14. A neutron shielding material according to claim 8 , wherein the components of the neutron shielding material are mixed up so that so that the hydrogen number density of the compound of said base resin and said additives may be 5xc3x9710 5 hydrogen atoms/cm 3 . claim 8 15. A neutron shielding material according to claim 5 , wherein said fire retardant is mixed so that the oxygen index of said hardened material after heating may exceed 20. claim 5 16. A neutron shielding material according to claim 5 , wherein the mean grain size of magnesium hydroxide is 0.5 to 5 xcexcm when magnesium hydroxide is used as said fire retardant. claim 5 17. A neutron shielding material according to claim 8 , comprising said hardened material which is obtained by reading said base resin with said additives at 30xc2x0 C. to 130xc2x0 C. as the first-order hardening and then reacting thereof at 130xc2x0 C. to 180xc2x0 C. as the second-order hardening. claim 8 18. A neutron shielding material according to claim 8 , comprising said hardened material which is obtained by reacting said base resin with said additives at room temperature as the first-order hardening and then reacting thereof at 60xc2x0 C. to 180xc2x0 C. as the second-order hardening. claim 8 19. A spent-fuel storage cask comprising an outer shell, an inner shell provided inside said outer shell, a basket provided inside said outer shell to store spent fuel assembly, and a neutron shielding material according to claim 1 which is placed between said inner and outer shells. claim 1 20. A spent-fuel storage cask comprising an outer shell, an inner shell provided inside said outer shell, a basket provided inside said outer shell to store spent fuel assembly, and a neutron shielding material according to claim 2 which is placed between said inner and outer shells. claim 2 |
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abstract | The present invention relates to calibration and normalization systems and methods for ensuring the quality of radiopharmaceuticals during the synthesis thereof, such as radiopharmaceuticals used in Positron Emission Tomography (PET) and Single-Photon Emission Computed Tomography (SPECT). |
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claims | 1. An electrostatic chuck, comprising:a first insulator on which a photomask is placed;an electrode supplied with a voltage and under the first insulator; anda second insulator under the electrode, whereinthe first insulator, the electrode and the second insulator have at least one vacant opening, the at least one vacant opening exposing a side of the photomask and providing an optical path that detects temperature from light incident on and reflected from the side of the photomask,the photomask is a reflective photomask including a conductive film, a quartz substrate on the conductive film, a reflection film on the quartz substrate and a circuit pattern on the reflection film, andthe conductive film includes at least one opening having a location corresponding to a location of the at least one vacant opening. 2. The electrostatic chuck as set forth in claim 1, further comprising:a temperature sensing unit disposed under the second insulator, detecting the temperature from a surface of the photomask. 3. The electrostatic chuck as set forth in claim 2, wherein the temperature sensing unit comprises:a multi-wavelength interferometer providing light incident on a backside of the photomask through the at least one vacant opening and measuring intensity of reflected light;a first evaluator calculating reflectance of the photomask from the measured intensity;a second evaluator determining a refractive index of the photomask from the reflectance; anda third evaluator obtaining the temperature of the surface of the photomask from the refractive index. 4. The electrostatic chuck as set forth in claim 1, wherein the multi-wavelength interferometer comprises:a light source emitting multi-wavelength light;a reference mirror;a beam splitter dividing the multi-wavelength light into first light incident on the reference mirror, and second light incident on the quartz substrate of the photomask through the at least one vacant opening; anda photodetector receiving first reflected light from the reference mirror and second reflected light from the reflection film of the photomask and detecting the intensity based on interference between the first reflected light and the second reflected light. 5. The electrostatic chuck as set forth in claim 4, wherein the first evaluator calculates the reflectance of the photomask in proportion to a square of a differential between a reference intensity value and a maximum intensity value obtained by the photodetector,wherein the second evaluator determines a relation of refractive indexes between the reflection film and the quartz substrate based on the reflectance, andwherein the third evaluator obtains the temperature by satisfying the relation. 6. The electrostatic chuck as set forth in claim 1, wherein the reflection film includes a stacked structure including at least one of silicon (Si), molybdenum (Mo), and beryllium (Be). 7. The electrostatic chuck as set forth in claim 3, wherein the multi-wavelength interferometer is a white-light interferometer. 8. The electrostatic chuck as set forth in claim 2, wherein the at least one vacant opening is shaped as one of a circle, an ellipse, and a polygon. 9. Exposure equipment comprising:an exposure light source emitting light with a wavelength;a lens condensing and directing the light to a photomask;the electrostatic chuck of claim 1 supporting the photomask; anda fixing unit supporting a wafer to be exposed by light reflected from the photomask. 10. The exposure equipment as set forth in claim 9, further comprising:a temperature sensing unit disposed under the second insulator, detecting temperature from a surface of the photomask. 11. The exposure equipment as set forth in claim 10, wherein the temperature sensing unit comprises:a multi-wavelength interferometer providing light incident on a backside of the photomask through the at least one vacant opening of the electrostatic chuck and measuring intensity of reflected light;a first evaluator calculating reflectance of the photomask from the measured intensity;a second evaluator determining a refractive index of the photomask from the reflectance; anda third evaluator obtaining the temperature of the surface of the photomask from the refractive index. 12. The exposure equipment as set forth in claim 11, wherein the multi-wavelength interferometer comprises:a light source emitting multi-wavelength light;a reference mirror;a beam splitter dividing the multi-wavelength light into first light incident on the reference mirror, and second light incident on the quartz substrate of the photomask through the at least one vacant opening; anda photodetector receiving first reflected light from the reference mirror and second reflected light from the reflection film of the photomask and detecting the intensity based on interference between the first reflected light and the second reflected light. 13. The exposure equipment as set forth in claim 12, wherein the first evaluator calculates the reflectance of the photomask in proportion to a square of a differential between a reference intensity value and a maximum intensity value obtained by the photodetector,wherein the second evaluator determines a relation of refractive indexes between the reflection film and the quartz substrate based on the reflectance, andwherein the third evaluator obtains the temperature by satisfying the relation. 14. The exposure equipment as set forth in claim 11, wherein the reflection film includes a stacked structure including at least one of silicon (Si), molybdenum (Mo), and beryllium (Be). 15. The exposure equipment as set forth in claim 11, wherein the multi-wavelength interferometer is a white-light interferometer. 16. The exposure equipment as set forth in claim 10, wherein the at least one vacant opening is shaped as one of a circle, an ellipse, and a polygon. 17. The exposure equipment as set forth in claim 9, wherein the light emitted from the light source is extreme ultraviolet and has a wavelength less than 13.4 nm. 18. A method of detecting temperature of a surface of a photomask, the method comprising:providing a reflective photomask on an electrostatic chuck having at least one vacant opening exposing a side of the substrate of the photomask, the photomask including a conductive film, a quartz substrate on the conductive film, a reflection film on the quartz substrate and a circuit pattern on the reflection film, the conductive film including at least one opening having a location corresponding to a location of the at least one vacant opening;irradiating multi-wavelength light from a light source on a reference mirror and on the reflection film and the quartz substrate of the photomask through the at least one vacant opening;detecting light intensity based on interference between first light reflected from the reference mirror and second light reflected from the reflection film;obtaining a maximum intensity value and a reference intensity value from the light intensity;calculating reflectance of the photomask based on the reference intensity value and the maximum intensity value;determining a relation of refractive indexes between the reflection film and the substrate based on the reflectance; andobtaining the temperature by satisfying the relation. 19. The method as set forth in claim 18, wherein calculating the reflectance calculates the reflectance of the photomask in proportion to a square of a differential between the reference intensity value and the maximum intensity value. 20. The method as set forth in claim 18, further comprising:irradiating multi-wavelength light from a multi-wavelength interferometer, the multi-wavelength interferometer being a white-light interferometer. 21. The electrostatic chuck as set forth in claim 1, wherein the conductive film includes chromium (Cr). |
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046577300 | abstract | The lower end of a nuclear reactor core barrel (16) is laterally stabilized within the reactor pressure vessel (10) by four auxiliary support structures (100) equiangularly disposed about the periphery of the reactor lower hemispherical shell (12). The core barrel lower support plate (18) has keys (122) secured thereto for disposition within recesses (114) defined within crossbeams (102) of the structures (100) through which horizontal radial and tangential forces, as well as severe vertical loads, are transmitted from the core barrel (16) to the reactor vessel (10). Shock absorbers (120) interconnect the keys (122) and the crossbeams (102), and divergent brackets (104) serve to radially space the crossbeam (102) from the shell wall (12) so as to define a vertical coolant flow channel (108) through each structure (100). The divergent brackets (104) serve to distribute radial loads from the core barrel (16) to the pressure vessel (10) as radial compression forces, and to convert tangential bending moments into circumferential shear and radial compression forces. Upper inclined portions (162) of the brackets (104) serve to vertically centralize the center of load (160) of horizontal tangential forces relative to the brackets' centers of gravity (152) so as to eliminate vertical bending moments, and inclined lower portions (139) of the brackets (104) serve to convert vertical bending loads into circumferential shear and radial compression forces. |
claims | 1. A nuclear reactor system comprising:a reactor vessel;a nuclear core including a plurality of nuclear fuel assemblies housed within the reactor vessel and configured to be immersed within a reactor coolant, the fuel assemblies structured to heat the reactor coolant;a primary coolant loop piping system configured to be in fluid communication with a heat utilization mechanism and the reactor vessel for conveying the reactor coolant between the reactor vessel and the heat utilization mechanism and back to the reactor vessel;an auxiliary piping system in fluid communication with the primary coolant loop piping system and being configured to add or extract reactor coolant to or from the primary coolant loop piping system;an acoustic transmitter acoustically coupled to a first location on an outer surface of either the primary coolant loop piping system or the auxiliary piping system and configured to transmit an acoustic pulse through the reactor coolant;an acoustic receiver acoustically coupled to a second location on an outer surface of the either of the primary coolant loop piping system or the auxiliary piping system that is substantially diametrically opposed to the first location, with the acoustic receiver configured to receive the acoustic pulse;a flow meter configured to measure a speed of the reactor coolant within the either of the primary coolant loop piping system or the auxiliary piping system and provide an output indicative thereof;a boron concentration meter configured to measure a boron concentration in the reactor coolant and provide an output indicative thereof; andan acoustic control system connected to the acoustic transmitter and the acoustic receiver, wherein the acoustic control system is configured to:receive a first output from the flow meter;receive a second output from the boron concentration meter; anddetermine a temperature of the reactor coolant based on:a time lag between a transmission of the acoustic pulse at the acoustic transmitter and a receipt of the acoustic pulse at the acoustic receiver;the output of the flow meter; andthe output of the boron concentration meter. 2. The nuclear reactor system of claim 1 including:a second acoustic transmitter acoustically coupled to a third location on the outer surface of the either of the primary coolant loop piping system or the auxiliary piping system and configured to transmit a second acoustic pulse through the reactor coolant;a second acoustic receiver acoustically coupled to a fourth location on the outer surface of the either of the primary coolant loop piping system or the auxiliary piping system that is substantially diametrically opposed to the third location, with the acoustic receiver configured to receive the second acoustic pulse; andwherein the acoustic control system is also connected to the second acoustic transmitter and the second acoustic receiver and is configured to determine a second time lag between a transmission of the second acoustic pulse at the second acoustic transmitter and the receipt of the second acoustic pulse at the second acoustic receiver and correlate the second time lag to a temperature of the reactor coolant. 3. The nuclear reactor system of claim 1 wherein the acoustic pulse is an ultrasonic pulse. 4. The nuclear reactor system of claim 1 wherein the either of the primary coolant loop piping system or the auxiliary piping system is a hot leg of the primary coolant loop piping system. 5. The nuclear reactor system of claim 1 wherein the either of the primary coolant loop piping system or the auxiliary piping system is a cold leg of the primary coolant loop piping system. 6. The nuclear reactor system of claim 1 wherein the acoustic transmitter and the acoustic receiver comprise solid state vacuum micro-electronic devices. 7. The nuclear reactor system of claim 1 further including a thermoelectric generator having a hot junction in thermal communication with a wall of the either of the primary coolant loop piping system or the auxiliary piping system, and wherein the acoustic transmitter and the acoustic receiver are powered by the thermoelectric generator. 8. The nuclear reactor system of claim 1 wherein the transmitted pulse of the acoustic transmitter and the output of the acoustic receiver are connected to a wireless transmitter and the transmitted acoustic pulse from the acoustic transmitter and the output of the acoustic receiver are wirelessly transmitted to the acoustic control system. 9. The nuclear reactor system of claim 8 wherein the wireless transmitter comprises solid state vacuum micro-electronic devices. 10. The nuclear reactor system of claim 1 wherein the transmitted acoustic pulse is a continuous stream of pulses. |
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summary | ||
048779695 | abstract | A flask for the transport of radioactive material comprises a hollow body containing a number of substantially identical members which cooperate to define a plurality of channels to receive radioactive waste containers. Each member is shaped to define substantially a half of an outer channel and a portion of a central channel. The members, conveniently aluminium bodies, are releasably secured to and in good thermal contact with the wall of the hollow body to provide for the conduction of heat generated within the waste containers. |
description | 1. Field of the Invention The present invention relates, in general, to direct vessel injection (DVI) nozzles for minimum emergency core cooling (ECC) water bypass and, more particularly, to a DVI nozzle which efficiently injects ECC into a reactor vessel of a pressurized light water reactor (PLWR) to cool a reactor core during a cold leg break (CLB) that may occur in a reactor coolant system of the PLWR, thus remarkably reducing the direct ECC bypass fraction to a broken cold leg and minimizing the amount of direct ECC bypass. 2. Description of the Related Art Generally, in a nuclear reactor to generate electric energy using a fission reaction, pressurized light water is used as a reactor coolant for carrying the thermal energy generated from the reaction of nuclear fuel. A pressurized light water reactor (PLWR), must be maintained core cooling state during a loss-of-coolant accident to remove the decay heat of core. In the event of coolant leakage from the reactor coolant system of a PLWR, the reactor core overheats, sometimes causing breakage of the PLWR. In an effort to protect the reactor core against coolant leakage from such a PLWR, emergency core coolant (ECC) is supplied from an outside ECC source to the reactor vessel. In the related art, the ECC is typically injected into the reactor vessel in one of two injection modes: a cold leg injection (CLI) mode and a direct vessel injection (DVI) mode. Korean Patent Registration No. 10-0319068 discloses a cylindrical reactor vessel 100 having a reactor core 101 therein to generate thermal energy through a fission reaction, as shown in FIG. 1 of the accompanying drawings. A core support 104 is placed in the reactor vessel 100 to support the reactor core 101 in the vessel 100, with a downcomer 105 defined between the reactor vessel 100 and the core support 104. A coolant is introduced into the vessel 100 through cold legs 102 and flows downwards through the downcomer 105 to reach a lower chamber 107 of the vessel 100, and flows to the reactor core 101 to absorb thermal energy from the reactor core 101 and is, thereafter, discharged to the outside of the vessel 100 through hot legs 103. In the above-mentioned conventional nuclear reactor, direct vessel injection (DVI) nozzles 106 are provided on the vessel 100 at positions adjacent to the cold legs 102 so that the DVI nozzles 106 inject ECC into the vessel 100 to supply ECC to the reactor core 101 in the event of a cold leg break (CLB). Furthermore, safe injection ducts 108 extend from positions around the DVI nozzles 106 to positions around the lower chamber 107 in an effort to prevent injected ECC from being swept into a broken cold leg 102 during a cold leg break (CLB). However, in the conventional reactor vessel 100 having the DVI nozzles 106 provided at positions adjacent to the cold legs 102, ECC to cool the reactor core 101 during a cold leg break (CLB) may be undesirably swept into a broken cold leg 102 to cause ECC loss. The results caused by the sweep-out of ECC into the broken cold leg 102 are illustrated in FIG. 2. FIG. 2 is a graph illustrating the results of MARS (RELAP5/Mod3 1D) code analysis executed by a computer when ECC provided to protect the reactor core 101 against a cold leg break (CLB) is injected into the vessel 100 in a conventional direct vessel injection (DVI) mode using the DVI nozzles 106 provided on the vessel 100 at positions horizontally offset from the cold legs 102 at 15° angles relative to the cold legs 102 in opposite directions. To calculate a core fuel cladding temperature, the reactor core 101 is divided into twenty vertically arranged volumes and the core fuel cladding temperature is calculated in individual volumes. The twenty volumes are respectively designated by the numbers, Node1, Node2, Node3, Node4, Node5, Node6, . . . Node20, sequentially in order from the bottom to the top of the reactor core 101 so that Node20 designates the top of the reactor core 101. when a cold leg break (CLB) occurs in the reactor coolant system of the vessel 100, some sections of the reactor core 101, namely Node10 to Node15, located within a region from the middle of the reactor core 101 to ⅔ of the way to the top of the core 101, may exceedingly overheat. Variations in the temperatures of four sections of the core 101, which are Node10, Node12, Node14 and Node15, during a cold leg break (CLB) are shown in the graph of FIG. 2. The graph of FIG. 2 shows that the core fuel cladding temperatures become stabilized when two hundred seconds pass after ECC is injected into the vessel 100 to protect the core 101 against the CLB. However, as the DVI nozzles 106 are provided at positions adjacent to the cold legs 102, the core fuel cladding temperatures rapidly increase after four hundred seconds pass after the injection of ECC into the vessel 100. This is so-called “core reheating” that cannot be allowed in the event of such a CLB of a reactor in which all the fuel rods are installed. The core reheating is caused by ECC which does not sufficiently cool the core 101 during the CLB. In other words, the core reheating is caused by an increase in the amount of direct ECC bypass fraction to a broken cold leg 102. Due to the increase in the amount of direct ECC bypass fraction to the broken cold leg 102, the amount of ECC flowing from the downcomer 105 to the reactor core 101 is reduced, while the amount of ECC swept into the broken cold leg 102 increases. When the sweep-out of ECC into the broken cold leg 102 continues, the temperature of the core 101 rapidly increases to cause reactor breakage. Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a direct vessel injection (DVI) nozzle which efficiently injects emergency core coolant (ECC), provided to protect a reactor core against a break in a reactor coolant system, such as a cold leg break (CLB) that may occur in a pressurized light water reactor (PLWR), thus remarkably reducing the direct ECC bypass fraction to a broken cold leg and minimizing the amount of direct ECC bypass. In order to achieve the above object, the present invention provides a DVI nozzle for minimum ECC bypass used in a PLWR having a reactor vessel with a reactor coolant system in which a coolant flows into the reactor vessel through a cold leg and passes through a reactor core prior to being discharged to the outside of the reactor vessel through a hot leg, and the DVI nozzle provided on the reactor vessel to directly inject ECC into the reactor vessel, which is placed on the reactor vessel at a position horizontally offset from a central axis of the hot leg at an angle of 10° to 30° and is involved within a region defined above the central axis of the hot leg in a vertical direction of the reactor vessel by a distance of 1.5 times the sum of diameters of the hot leg and the DVI nozzle. Preferably, the DVI nozzle for minimum ECC bypass is placed at a position horizontally offset from the central axis of the hot leg at an angle of 15° and is involved within a region defined between distances of 1 meter and 2 meters above the central axis of the hot leg in the vertical direction of the reactor vessel. Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. As shown in FIGS. 3 and 4, the reactor vessel 1 having direct vessel injection (DVI) nozzles 5 for minimum ECC bypass according to the present invention is used in a pressurized light water reactor (PLWR) and comprises cold legs 3, hot legs 4, DVI nozzles 5, a reactor core 6 and a core support 7. The reactor vessel 1 of the PLWR has a reactor coolant system in which a coolant flows into the reactor vessel 1 through the cold legs 3 and passes through the reactor core 6 prior to being discharged to the outside of the reactor vessel 1 through the hot legs 4. The DVI nozzles 5 are provided on the reactor vessel 1 to directly inject ECC into the vessel 1. In a detailed description, the DVI nozzles 5 are placed on the reactor vessel 1 at positions horizontally offset from the central axes of the hot legs 4 at 10° to 30° angles in opposite directions in a latitudinal sectional view of the reactor vessel 1. Furthermore, the DVI nozzles 5 are located within regions defined above the central axes of the hot legs 4 in vertical directions of the reactor vessel 1 by a distance of 1.5 times [1.5×(D+d)] the sum of a diameter D of each of the hot legs 4 and a diameter d of each of the DVI nozzles 5. Preferably, the hot legs 4 are placed on the reactor vessel 1 at two positions diametrically opposite to each other. The cold legs 3 are placed on the reactor vessel 1 at positions which are leveled with the positions of the hot legs 4 and are horizontally spaced apart from the central axes of the hot legs 4 at 60° angles in opposite directions. Thus, the reactor vessel 1 has two hot legs 4 and four cold legs 3. Preferably, four DVI nozzles 5 are placed on the reactor vessel 1 at positions horizontally offset from the central axes of the hot legs 4 at 15° angles in opposite directions and involved within regions defined between distances of 1 meter and 2 meters above the central axes of the hot legs 4 of the reactor vessel 1. The present invention will be described in more detail with reference to the accompanying drawings. FIGS. 3 and 4 illustrate an embodiment of the present invention. FIG. 3 shows the reactor vessel 1 having the DVI nozzles 5 for minimum ECC bypass according to the embodiment of the present invention. FIG. 4 is a latitudinal sectional view of the reactor vessel 1 of FIG. 3. In FIG. 3, the heights of the DVI nozzles 5 above the cold legs 3 and the hot legs 4 are illustrated. That is, the vertical positions of the DVI nozzles 5 on the reactor vessel 1 relative to the cold legs 3 and the hot legs 4 are shown in FIG. 3, while the horizontal positions of the DVI nozzles 5 on the reactor vessel 1 relative to the hot legs 4 are shown in FIG. 4. In a brief description, the DVI nozzles 5 of the present invention are far from the cold legs 3 and are close to the hot legs 4, unlike the conventional DVI nozzles. The cold legs 3 and the hot legs 4, through which the coolant flows, are provided on the reactor vessel 1 which has the reactor core 6 therein to generate thermal energy. A core support 7 is placed in the reactor vessel 1 to support the reactor core 6 in the reactor vessel 1, with a downcomer 2 defined between the reactor vessel 1 and the core support 7. The reactor coolant is introduced into the vessel 1 through the cold legs 3 and passes downwards through the downcomer 2 to reach a lower chamber 8 of the vessel 1, and flows to the core 6 to absorb thermal energy from the core 6. Thus, the coolant is heated while passing through the core 6 and, thereafter, flows to the hot legs 4 to be supplied to a steam generator (not shown) which generates steam. The steam is supplied to a turbine (not shown), thus rotating the turbine and generating electricity. In the reactor vessel 1 having a cylindrical shape, the cold legs 3 and the hot legs 4 are placed at positions higher than the core 6 so that the core 6 is always in contact with the coolant. Thus, the core 6 is prevented from quickly overheating during a cold leg break (CLB). In the reactor vessel 1 having the above-mentioned construction, the cold legs 3, the hot legs 4 and the DVI nozzles 5 to inject ECC into the vessel 1 are configured as follows. The hot legs 4 are placed on the cylindrical reactor vessel 1 at two positions diametrically opposite to each other. The cold legs 3 are placed on the reactor vessel 1 at positions leveled with the hot legs 4 and horizontally spaced apart from the central axes of the hot legs 4 at 60° relative angles in opposite directions. Thus, the reactor vessel 1 has two hot legs 4 and four cold legs 3. On the reactor vessel 1, the two hot legs 4 are horizontally spaced apart from each other at 180° angle. In the present invention, three or four hot legs may be provided on the reactor vessel 1. However, it is preferred to set the number of the hot legs 4 to two. The nuclear reactor having two hot legs is so-called “2-Loop reactor”, while the nuclear reactor having three hot legs is so-called “3-Loop reactor”. In the 3-Loop reactor, the three hot legs are horizontally spaced apart from each other at 120° angles, while three cold legs are provided on the reactor vessel so that the cold legs are horizontally spaced apart from the three hot legs at 60° angles. Thus, the 3-Loop reactor has three hot legs and three cold legs. In the preferred embodiment of the present invention, the DVI nozzles 5 are adapted to a 2-Loop PLWR. In the 2-Loop PLWR, the DVI nozzles 5 to inject ECC into the reactor vessel 1 to protect the reactor core 6 during a break of a cold leg 3 are placed on the reactor vessel 1 at positions horizontally offset from the central axes of the hot legs 4 at 10° to 30° relative angles, preferably, 15° angles, in opposite directions. The DVI nozzles 5 placed at the above-mentioned positions are horizontally offset from the central axes of the cold legs 3 at 30° to 50° relative angles, preferably, 45° angles. Thus, the DVI nozzles 5 are closer to the hot legs 4 than the cold legs 3, particularly, than the broken cold leg 3, so that the relative angle between the broken cold leg 3 and one DVI nozzle 5 closer to the broken cold leg 3 increases. As shown in FIG. 4, two hot legs 4a and 4b are placed on the reactor vessel 1 at two positions diametrically opposite to each other. Four cold legs 3a, 3b, 3c and 3d are placed on the reactor vessel 1 at positions horizontally spaced apart from the central axes of the hot legs 4a and 4b at 60° angles in opposite directions. Four DVI nozzles 5a, 5b, 5c and 5d are placed on the vessel 1 at positions horizontally offset from the cold legs 3a, 3b, 3c and 3d and the hot legs 4a and 4b. A cold leg break (CLB) and an injection of ECC into the reactor vessel 1 through the DVI nozzles 5 to protect the core 6 against the CLB will be described herein below while assuming that the first cold leg 3a is broken. When the first cold leg 3a is broken, the reactor coolant leaks from the reactor vessel 1 to the outside through the broken cold leg 3a, resulting in a rapid reduction in pressure of the reactor coolant system of the PLWR to 0.5 MPa or less. To supplement the coolant deficiency caused by the coolant leakage from the reactor vessel 1 in the event of the CLB, ECC is injected into the reactor vessel 1 through the four DVI nozzles 5a, 5b, 5c and 5d. In that case, a large part of ECC, which is injected into the vessel 1 through the first DVI nozzle 5a closer to the broken cold leg 3a, is swept into the broken cold leg 3a due to the suction force generated in the broken cold leg 3a and strongly acting on the first DVI nozzle 5a. In the related art, the sweep-out of ECC into the broken cold leg 102 during a cold leg break (CLB) is so-called “direct ECC bypass”, and the ratio of the amount of bypassed ECC to the amount of injected ECC is so-called “direct ECC bypass fraction”. The ECC, which is swept into the broken cold leg 3a, does not contribute to the cooling of the reactor core 6. However, the suction force generated in the broken cold leg 3a does not strongly act on the third DVI nozzle 5c closer to the third cold leg 3c which is placed opposite to the broken cold leg 3a. Thus, ECC, which is injected into the vessel 1 through the third DVI nozzle 5c, flows downwards from the upper portion 2a to the lower portion 2b of the downcomer 2 and passes through the lower chamber 8 of the reactor vessel 1 to contribute to the cooling of the reactor core 6. During the break of the first cold leg 3a, the total direct ECC bypass fraction in the reactor vessel 1 having the four DVI nozzles 5a, 5b, 5c and 5d is determined by the direct ECC bypass fraction of the DVI nozzle 5a which is located at a predetermined angle relative to the broken cold leg 3a. FIGS. 5a, 5b and 6 illustrate the angles and heights of the DVI nozzles relative to the hot legs on the reactor vessel according to the present invention. FIG. 5a is a latitudinal sectional view of the reactor vessel 1 to show the angles of the DVI nozzles 5a, 5b, 5c and 5d relative to the hot legs 4a and 4b. FIG. 5b is a 180° symmetry development view of the region HL×DD of the reactor vessel 1 of FIG. 5a on which two cold legs, one hot leg and two DVI nozzles are located. FIG. 6 is an enlarged sectional view of a part of the reactor vessel of FIG. 5a to show the angular intervals of the DVI nozzles 5a and 5d relative to the hot leg 4b. As shown in FIG. 5a, two DVI nozzles 5a and 5b are placed on the reactor vessel 1 at positions horizontally offset from the central axis of the hot leg 4b at 15° angles in opposite directions. As shown in FIG. 5b, two DVI nozzles 5a′ and 5b′ are located at a height L-1 defined above the central axis of the hot leg 4b in a vertical direction of the reactor vessel 1 by a distance of 2 times a diameter D of the hot leg 4b, preferably, by a distance of 1.5 times [1.5×(D+d)] the sum of the diameter D of the hot leg 4b and a diameter d of the DVI nozzle 5a′. FIG. 5b also shows that two DVI nozzles 5a and 5b are located at another height L-3 defined above the central axis of the hot leg 4b in a vertical direction of the reactor vessel 1 by a distance of the diameter D of the hot leg 4b. In the present invention, the height L-1 is preferably set to 2 meters, while the height L-3 is preferably set to 1 meter. In the first embodiment, the distance from the central axis of the hot leg 4b to the DVI nozzle 5a is determined, based on the regulations of ASME (American Society of Mechanical Engineers) stated “two nozzles must be located such that the axes of the two nozzles are spaced apart from each other by a distance of at least 1.5 times the sum of diameters of the two nozzles, otherwise a reinforcing material must be provided”. Thus, in the first embodiment, the height of the DVI nozzle 5a above the central axis of the hot leg 4b is determined by the distance of 1.5 times [1.5×(D+d)] the sum of the diameter D of the hot leg 4b and the diameter d of the DVI nozzle 5a. In the second embodiment, the height of the DVI nozzle 5a above the central axis of the hot leg 4b is determined, based on the regulations of KSPN (Korean Standard Nuclear Plant) and APR1400 (Advanced Pressurized reactor 1400) stated “in 2-Loop PLWR of 2800 MWt to 4000 MWt thermal power of core, the inner diameter of hot legs is set to 42 inches and the inner diameter of cold legs is set to 30 inches according to standard of pipe design”. Thus, in the second embodiment, the height of the DVI nozzle 5a above the central axis of the hot leg 4b is involved between 1 meter and 2 meters. The angles and heights of the DVI nozzles 5c and 5d relative to the hot leg 4a are determined in the same manner as that described for the determination of the angles and heights of the DVI nozzles 5a and 5b relative to the hot leg 4b. The DVI nozzles 5 are placed on the reactor vessel 1 at positions horizontally offset from the central axes of the hot legs 4a and 4b at 10° to 30° angles, preferably, 15° angles, in opposite directions. Furthermore, the DVI nozzles 5 may be located at the height L-3 in the same manner as that described for the DVI nozzles 5a, 5b, 5c and 5d or may be located at the height L-1 in the same manner as that described for the DVI nozzles 5a′, 5b′, 5c′ and 5d′. In the present invention, the height L-1 above the central axis of each of the hot legs 4a and 4b may be defined by a distance of 2 times (2×D) the diameter D of each of the hot legs 4a and 4b or a distance of 1.5 times [1.5×(D+d)] the sum of the diameter D of each of the hot legs 4a and 4b and the diameter d of each of the DVI nozzles 5, or may be set to 2 meters. The height L-3 may be defined by a distance of the diameter D of each of the hot legs 4a and 4b, or may be set to 1 meter. In the present invention, when the diameter D of the hot legs 4 is set to 42″ and the diameter d of the DVI nozzles 5 is set to 8.5″, the height L-1, which is defined by the distance of 1.5 times [1.5×(D+d)] the sum of the diameter D of each hot leg 4 and the diameter d of each DVI nozzle 5, is 1.92 meters. According to similarity tests, the direct ECC bypass fractions of the DVI nozzles 5a, 5b, 5c and 5d located at the height L-3 are lower than those of the DVI nozzles 5a′, 5b′, 5c′ and 5d′ located at the height L-1. However, the direct ECC bypass fractions of the DVI nozzles 5a′, 5b′, 5c′ and 5d′ located at the height L-1 are remarkably lower than those of conventional DVI nozzles placed closer to the cold legs so that the height L-1 of the DVI nozzles 5a′, 5b′, 5c′ and 5d′ above the hot leg 4b is preferably adopted. Thus, the DVI nozzles 5 of the present invention may be selectively located at the different heights L-1 and L-3 which have the same azimuthal angles and the same angles relative to the hot legs 4. FIGS. 7a to 8b show a reactor vessel of a ⅕-scale experimental facility, and results of similarity tests executed using the experimental facility in which airflow is adopted in similitude of steam flow according to the law of fluid similarity. FIG. 7a is a latitudinal sectional view of the reactor vessel of the ⅕-scale experimental facility for similarity tests according to the present invention. FIG. 7b is a ¼ symmetry development view of the region C-C of the reactor vessel of FIG. 7a, which shows the hot leg 4b, the broken cold leg 3a and the DVI nozzles 5. FIG. 8a is a graph comparatively showing the variations in the direct ECC bypass fractions according to different relative angles of the DVI nozzles located at the height L-1 of FIG. 7b during the similarity tests using the ⅕-scale experimental facility. FIG. 8b is a graph comparatively showing the variations in the direct ECC bypass fractions according to different relative angles of the DVI nozzles located at the height L-3 of FIG. 7b during the similarity tests using the ⅕-scale experimental facility. A further ⅕-scale experimental facility was used in the similarity test for a DVI nozzle N2′ located at the height L-1 to be horizontally offset from the broken cold leg 3a at a relative angle of 7°. A still further shows the ⅕-scale experimental facility was used in the similarity test for another DVI nozzle N4′ located at the height L-1 to be horizontally offset from the broken cold leg 3a at a relative angle of 52°. On the ⅕-scale experimental facility used in the similarity tests according to the present invention, the DVI nozzles N1 and N1′ are placed at positions horizontally offset from the broken cold leg 3a at a relative angle of −15° as shown in FIGS. 7a and 7b. The DVI nozzles N2 and N2′ are placed on the vessel of the experimental facility at positions horizontally offset from the broken cold leg 3a at a relative angle of 7°. The DVI nozzles N3 and N3′ are placed on the vessel of the experimental facility at positions horizontally offset from the broken cold leg 3a at a relative angle of 30°. Furthermore, the DVI nozzles N4 and N4′ are placed on the vessel of the experimental facility at positions horizontally offset from the broken cold leg 3a at a relative angle of 52°. The height L-1 of the DVI nozzles N1′, N2′, N3′ and N4′ above the central axis of the broken cold leg 3a (leveled with the central axis of the hot leg 4b) is set to 0.418 meter (scaled-up to 2.09 meters in a real reactor vessel 1). The height L-3 of the DVI nozzles N1, N2, N3 and N4 above the central axis of the broken cold leg 3a (leveled with the central axis of the hot leg 4b) is set to 0.2 meter (scaled-up to 1 meter in the real reactor vessel 1). The similarity tests using the ⅕-scale experimental facility of the present invention are executed while varying the heights and angles of the DVI nozzles 5 relative to the broken cold leg 3a and changing the flow velocity of air, injected into the cold legs 3, by 5 m/sec within a range from 5 m/sec to 20 m/sec. In that case, the similitude fluid air velocity in the cold legs 3 is about 18 m/sec. In the event of a break of the cold leg 3a of the reactor vessel 1 having the DVI nozzles 5a, 5b, 5c and 5d, the total direct ECC bypass fraction caused by the sweep-out of ECC into the broken cold leg 3a is determined by the direct ECC bypass fraction of the DVI nozzle 5a which is located closer to the broken cold leg 3a. Thus, in the similarity tests of the present invention, the sweep-out of fluid from the DVI nozzle 5a into the broken cold leg 3a is tested. In the event of a break of a cold leg 3a provided on the reactor vessel 1 of a PLWR which is configured such that the pressure in the vessel 1 must be maintained at a minimum level higher than a predetermined reference point, the reactor coolant leaks from the vessel 1 in the form of steam due to a reduction in the pressure of the vessel 1. Thus, in the similarity tests, air is injected into the vessel of the experimental facility through the cold legs 3. Furthermore, in the similarity tests, ECC in the liquid phase to cool the core 6 is injected into the vessel through the DVI nozzles at an injection speed 0.89 m/sec. The above-mentioned ECC injection speed 0.89 m/sec is scaled-down at a 1/SQRT(5) ratio of 2 m/sec which is the ECC injection speed in an ECCS (Emergency Core Cooling System) during an LBLOCA (Large Break Loss of Coolant Accident) reflood phase in a real power plant. That is, 2 m/sec×1/SQRT(5)=0.89 m/sec. Furthermore, the maximum flow air velocity of 20 m/sec through the cold legs 3 is scaled-down at a ratio of 44.7 m/sec which is the maximum steam velocity in a broken cold leg during the LBLOCA reflood phase in the real power plant. According to a transient analysis using a computer code, the steam velocity in the real power plant is about 40 m/sec. The results of the similarity tests executed using the ⅕-scale experimental facility of the present invention are shown in the graphs of FIGS. 8a and 8b. As shown in the graph of FIG. 8a showing the similarity test results for the DVI nozzles located at the height L-1, ECC injected into the vessel through the DVI nozzles N1′ and N2′ located at positions horizontally offset from the broken cold leg 3a at relative angles of −15° and 7° in the same manner as those of conventional reactors is swept into the broken cold leg 3a at direct ECC bypass fractions higher than 80% and 60% when the velocity of air in the cold legs is higher than 15 m/sec. However, the direct ECC bypass fractions of the DVI nozzles N3′ and N4′ located at positions of relative angles of 30° and 52° according to the present invention are remarkably reduced lower than 40%. Furthermore, as shown in the graph of FIG. 8b showing the similarity test results for the DVI nozzles located at the height L-3, the direct ECC bypass fractions of the DVI nozzles N1 and N2 located at positions of relative angles of −15° and 7° in the conventional manner are higher than 80% when the velocity of air in the cold legs is higher than 15 m/sec. Particularly, the direct ECC bypass fractions of the DVI nozzles N1 and N2 reach around 100% when the velocity of air in the cold legs is about 20 m/sec. However, the direct ECC bypass fractions of the DVI nozzles N3 and N4 located at positions of relative angles of 30° and 52° according to the present invention are remarkably reduced lower than 40%. The similitude fluid velocity in the broken cold leg during a cold leg break in a real power plant is about 18 m/sec. As apparent from the above description, the present invention provides a DVI nozzle for minimum ECC bypass. The DVI nozzle of the present invention efficiently injects ECC into a reactor vessel of a PLWR to cool the reactor core during a cold leg break (CLB) that may occur in the reactor coolant system of the PLWR. Thus, the DVI nozzle remarkably reduces the direct ECC bypass fraction to a broken cold leg and minimizes the amount of direct ECC bypass without requiring installation of additional elements, and thereby prevents safety accidents of reactor. Although a preferred embodiment of the present invention has been described 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. |
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041349415 | claims | 1. A process for reprocessing a spherically shaped fuel element for high temperature reactors consisting of a graphite matrix having enbedded separately therein coated fuel and fertile material particles, said fuel element having a solid spherical nucleus containing only fertile material particles encased by graphite, a zone including the same type of graphite containing only fuel material particles encased by said graphite and concentrically surrounding both said nucleus and said fuel material particle containing zone with a concentric pure graphite shell of the same type of graphite as that in both said fertile material containing nucleus and said fuel material particle containing zone comprising burning the graphite matrix in the Head-End stage of the reprocessing in two steps in which the first step comprises burning off the graphite of the shell and the fuel containing zone and the second step comprises burning off the graphite of the fertile material containing nucleus. 2. A process according to claim 1 wherein the fertile material is thorium oxide or thorium carbide and the fuel material is uranium oxide or uranium carbide. 3. A process according to claim 1 wherein in the fuel element the outer boundary of the fertile containing nucleus is contiguous with the inner boundary of the fuel containing zone. 4. A process according to claim 2 wherein the fuel containing zone has a lower crushing strength than the fertile material containing nucleus and the graphite shell. 5. A process according to claim 1 wherein the fuel containing zone has a lower crushing strength than the fertile material containing nucleus and the graphite shell. 6. A process according to claim 1 wherein there is present a thin pure graphite matric layer between the fertile material containing nucleus and the fuel containing zone. 7. A process according to claim 1 wherein the burning in both steps is in air at 1000-1200.degree. C. 8. The process of claim 7 wherein the shell and the fuel containing graphite zone are mechanically separated from the sphere by the application of pressure and then the resultant broken pieces of the fuel containing graphite zone and the shell have the graphite burned off separately from the fertile material containing nucleus. 9. The process of claim 8 wherein the fuel containing zone of the fuel element has a lower strength than the fertile material containing nucleus to facilitate said mechanical separation. 10. The process of claim 7 comprising burning off the graphite of the shell and the fuel containing zone is a first rotating furnace having an apertured wall therein, the apertures in said wall being smaller than the size of said fuel element sphere but larger than said nucleus, allowing the nuclei to fall through said apertures, retaining said fallen nuclei on a perforated surface, the performations of said surface being smaller than said nuclei but larger than the particles of fuel and allowing the fuel particles to pass through the perforations in said surface. 11. The process of claim 10 comprising conveying the fallen nuclei to a second rotating furnace, having an aperture wall, the apertures in the wall of said second furnace being smaller than said nuceli but larger than said fertile material particles, burning off the graphite of the fertile material containing nucleus and allowing the particles of fertile material to fall through said aperture wall of the second furnace. |
abstract | Prior to applying of ultraviolet rays to a surface of a wafer with a protective tape joined thereto that is placed and held on a holding table, an illumination sensor moves to a position below an ultraviolet irradiation unit having ultraviolet light emitting diodes arranged in one dimensional array to measure ultraviolet intensity in a position corresponding to a surface of the protective tape, and output voltage of each diode is controlled so as to maintain a uniform accumulated quantity of light in an area of the protective tape where ultraviolet rays are applied that is determined from the result of measurement and a turning velocity of the holding table. |
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044143397 | description | The following examples are given to illustrate the invention and should not be construed as limiting its scope. Unless otherwise indicated, all parts and percentages are by weight. EXAMPLE 1 A. Preparation of Aqueous Dispersion of Fe.sub.3 O.sub.4 (ELM Absorber) An aqueous dispersion of magnetic iron oxide (Fe.sub.3 O.sub.4) (ELM absorber) is prepared by mixing aqueous solutions of ferric and ferrous salts in amounts to maintain the Fe.sup.+3 /Fe.sup.+2 molar ratio at .about.2:1. Magnetic iron oxide is then precipitated at 0.degree.-10.degree. C. by rapid addition of 1 N NH.sub.4 OH and vigorous agitation until a pH of 9-10 is reached. Immediately thereafter, the dispersant is introduced with agitation to the aqueous medium containing the precipitated iron oxide and the mixture is heated at 90.degree. C. for one hour. During this period, hydrochloric acid is added until the pH of the mixture reaches 7.5. The particles of precipitated iron oxide are washed with deionized water and redispersed in deionized water containing .about.0.5 g of a potassium salt of a functionalized oligomer (Polywet KX-4 sold by Uniroyal Chemical) per gram of precipitated iron oxide, by using an ultrasonic probe. Magnetization of the dispersed iron oxide is measured by a Collpits oscillator circuit technique. B. Preparation of Magnetic Latex (Dielectric/ELM Absorber) To a 3-neck flask equipped with a stirrer, two addition funnels and a condenser is added a mixture of 507 g of the 28.5 percent solids dispersion of Fe.sub.3 O.sub.4 (200 gauss and average particle size of less than 0.08 micrometer) and 203 g of deionized water. The mixture is then heated under nitrogen atmosphere to 90.degree. C. while stirring the mixture. At this temperature of 90.degree. C., a monomer stream and an aqueous surfactant stream are separately introduced via the two addition funnels into the flask, each stream being introduced at the rate of .about.6 ml/min over a period of 65 minutes. The monomer stream consists of 64 g of styrene, 16 g of butyl acrylate and 3 g of t-butyl hydroperoxide. The aqueous stream consists of 110 g of deionized water, 2.9 g of the potassium salt of a functionalized oligomer ("Polywet KX-4") and 2 g of sodium formaldehyde hydrosulfite. The resulting reaction mixture is stirred and maintained under nitrogen at 90.degree. C. for an additional half hour. The resulting 25 percent solids latex is concentrated by distillation under vacuum to a 30.3 percent solids latex (dielectric/ELM absorber) having dispersed particles with a polymeric as well as magnetic characteristic. The particles of this latex have a narrow particle size distribution and an average particle diameter of 0.11 micrometer as determined by hydrodynamic chromatography. The latex remains stable in an applied magnetic field of 1800 gauss and exhibits properties common to magnetic colloids. For example, such magnetic colloids are magnetizable liquids that are instantly demagnetized upon removal of a magnetic field and levitate an object upon application of a magnetic field. Magnetization of the latex by a Collpits oscillator circuit technique, described by E. A. Peterson et al. in the Journal of Colloidal and Interfacial Science, 70, 3 (1977), is estimated to be 135 gauss. The particles of the latex are recovered by freeze drying the latex at -80.degree. C. under vacuum at 0.5 mm Hg. C. Preparation of ELM Composition (Dielectric/ELM Absorber/ELM Attenuator) One ELM composition (Sample No. 1) is prepared by dry blending 50.3 g of a dry powder of the aforementioned latex (55.4 percent dielectric/44.6 percent Fe.sub.3 O.sub.4) with 33.5 g of carbonyl iron (ELM attenuator) having an average portion size of 3-4 micrometers and sold by GAF Corporation under the trade name Super Fine Special. The blending is carried out on a Brabender mixing apparatus and the resultant blend is then compression molded into flat plates (0.8 cm thickness.times.2.6 cm diameter) at 2000 pounds of positive pressure and 230.degree. C. for 2 minutes. The sample is cooled to room temperature and the pressure on the sample is released. The resultant plate of the ELM composition is machined into two flat disks having a diameter of 2.54 cm and a thickness of 0.64 cm and 0.32 cm, respectively. A second ELM composition (Sample No. 2) is prepared following the foregoing procedure using 56.5 g of the dry powder of the latex and 18.8 g of the carbonyl iron. The sample is similarly blended, molded and fabricated into disks. For purposes of comparison, a third sample (Sample No. C) of dry particles of the latex is molded and fabricated into disks by the foregoing procedure. All of the foregoing samples are tested for ELM absorption and the results are reported in Table I. TABLE I __________________________________________________________________________ ELM Absorption (3) Sample Components, (1) % Density (2), Frequency Magnetic Attenuation No. Fe.sub.3 O.sub.4 Fe Polymer g/ml gHz Permeability Tangent M dB/cm __________________________________________________________________________ 1 26.8 40 33.2 2.57 0.3 2.662 0.173 0.262 1 2.244 0.393 1.658 2.4 1.382 0.586 4.548 5 1.198 0.246 3.899 8.5 1.330 0.154 4.540 2 33.5 25 41.5 2.16 0.3 2.210 0.177 0.224 1 1.741 0.391 1.329 2.4 1.230 0.533 3.606 5 0.991 0.190 2.610 8.5 1.139 0.102 2.810 C* 44.7 0 55.3 1.75 0.3 1.683 0.173 0.191 1 1.509 0.305 0.957 2.4 1.068 0.437 2.689 5 0.849 0.176 2.197 8.5 0.955 0.056 1.650 __________________________________________________________________________ *Not an example of the invention (1) Components of composition given in weight percent based on the weight of the composition. Polymer is a copolymer of styrene and butyl acrylate as described hereinbefore. (2) Density of the compositions on a dry weight basis. (3) The ELM absorption characteristics are measured by the procedures described in Dielectric Materials and Applications edited by Arthur R. Vo Hippel and published by the M.I.T. Press, Massachusetts Institute of Technology, Cambridge, Massachusetts, March, 1966. As evidenced by the data in Table I, the compositions of the present invention (Sample Nos. 1 and 2) exhibit significantly better attenuation at a given frequency than does the composition of Sample No. C. |
description | This application claims the benefit of Japanese Patent Application No. 2009-287082, filed Dec. 18, 2009, which is hereby incorporated by reference herein in its entirety. The present invention relates to an ion beam generator for performing high-precision and uniform microfabrication and planarization processing of a surface for microfabrication of a semiconductor substrate and a magnetic disk substrate, a substrate processing apparatus using the above generator, and a method of producing an electronic device by using the generator. A substrate processing apparatus provided with an ion beam generator is available as a technology for performing high-precision and uniform microfabrication and planarization processing of a surface for microfabrication of a semiconductor substrate and a magnetic disk substrate. Published Japanese Patent Application No. JP-A S60-127732 discloses a semiconductor processing apparatus that has an accelerating grid disposed obliquely relative to the surface of a semiconductor in order to perform high-precision surface processing. And, Published Japanese Patent Application No. JP-A 2008-117753 discloses an ion gun in which a lead-out electrode portion is disposed obliquely at both sides of a reference plane, and both sides of a substrate are planarized simultaneously. In an ion beam generator, a lead-out electrode generally has plural apertures through which ions are lead out, and an ion beam just lead out from the lead-out electrode is naturally in a nonuniform state having denseness and sparseness in correspondence with the presence, and not of the apertures. But, since the ion beam spreads gradually, peripherally, before reaching the substrate, the ion beam is irradiated uniformly to the substrate when a distance from the lead-out electrode to the substrate is long enough. The above-described prior art is an apparatus that causes the ion beam to enter obliquely to the substrate, but since the size of the entire apparatus is restricted, the distance from the lead-out electrode to the substrate cannot be assured sufficiently. In other words, there is a problem that the ion beam incident on the substrate cannot be made sufficiently uniform. Therefore, the number of apertures formed in the lead-out electrode is increased, and a pitch of apertures is narrowed, to make the ion beam uniform. This, however, is still insufficient. A subject of the present invention is to provide a uniform incident ion beam on the substrate in the ion beam generator, without increasing the size of the whole apparatus. In addition, the present invention has another subject to provide a substrate processing apparatus, which is provided with the above ion beam generator and is capable of performing uniform etching processing, and a production method of an electronic device including a uniform etching process using the above ion beam generator. A first aspect of the present invention is an ion beam generator that includes a discharge tank for generating plasma, a lead-out electrode having an annular grid portion provided with openings for leading out the ions generated in the discharge tank, while accelerating them, and a deflecting electrode for deflecting an annular ion beam, which is lead out of the lead-out electrode, in the annular center direction. A second aspect of the present invention is a substrate processing apparatus that includes a substrate holder for holding a substrate, and ion beam generators disposed to face both surfaces of the substrate held by the substrate holder, wherein the ion beam generators are those according to the present invention. A third aspect of the present invention is a method of producing an electronic device using the ion beam generator according to the present invention. The method includes generating plasma within the discharge tank, leading out an ion beam from the plasma within the discharge tank by applying a voltage to the lead-out electrode, deflecting the ion beam by applying a voltage to the deflecting electrode, and etching the surface of the substrate by the deflected ion beam. In the ion beam generator of the present invention, the ion beam lead out from the lead-out electrode is deflected by the deflecting electrode, so that the route of the ion beam from the lead-out electrode to the substrate can be provided sufficiently. Therefore, the substrate can be processed by a uniform ion beam without increasing the number of apertures in the lead-out electrode, narrowing the pitch of the apertures, or increasing the size of the apparatus. An electronic device can be produced with a good yield by performing uniform etching using the ion beam generator of the present invention. Embodiments of the present invention are described below with reference to the drawings, but the present invention is not limited to the embodiments. A substrate processing apparatus of the present invention is described below with reference to FIG. 1. FIG. 1 is a schematic view showing a structure of the apparatus of this embodiment viewed from above. As shown in FIG. 1, a substrate processing apparatus 100 is provided with a substrate (wafer) W, first and second ion beam generators 1a and 1b, which are arranged to face each other with the substrate W between them, a control unit 101, a counter 103, and a computer interface 105. The substrate W of this embodiment is, for example, a substrate for a magnetic recording medium, such as a hard disk, and generally has an opening at the center of a substantially disk-shaped substrate. The substrate W is held in a posture erected in a vertical direction by, for example, a substrate carrier (conveying apparatus) shown in FIG. 2A and FIG. 2B. The substrate processing apparatus of the present invention is used not only for both side processing of the substrate for a magnetic recording medium, such as a hard disk, but can also be used for one-side processing. As shown in FIG. 1, since it is difficult to provide a mechanism for rotating the substrate to an in-line conveying apparatus for both sides processing, because the space for the apparatus is limited, it is more effective to use the present invention. One configuration example of the substrate carrier is described below with reference to FIG. 2A and FIG. 2B. FIG. 2A and FIG. 2B are a front view and a side view schematically showing a structure of the carrier. As shown in FIG. 2A and FIG. 2B, the carrier is comprised of two substrate holders 20 and a slider member 10, which holds the substrate holders 20 in a vertical direction (vertically) and moves along a conveying path. Lightweight Al (A5052), or the like, is generally used for the slider member and the substrate holders. Each substrate holder 20 has, at its center, a circular opening 20a in which the substrate is inserted, and also, has a shape at its lower portion that the width decreases in two stages. Inconel L-shaped spring members 21, 22, and 23 are attached to three positions on the circumference of the opening 20a, and the spring member (movable spring member) 23 is configured to be pushed downward. The spring members 21, 22, and 23 are formed to have at their leading ends a V-shaped groove for holding an outer peripheral end face of the substrate and protrude into the opening 20a. The spring members 21, 22, and 23 are mounted rotationally, symmetrically. And, supporting nails of the two spring members 21 and 22 are arranged at positions symmetrical with respect to a vertical line running through the center of the opening of the substrate holder 20, and the supporting nail of the movable spring member 23 is arranged on the vertical line. By arranging in this way, a force is applied in a direction that the substrate W rotates, and the substrate W can be held more uniformly by the three supporting nails, even if the opening center of the substrate holder 20 and the center of the substrate W mounted are displaced slightly for some reason when the substrate W is mounted on the carrier. The displacement that is increased in the case of thermal expansion can be eliminated. The intermediate portion of the substrate holder 20 has its side end faces held by insulating members 11a and 11b, such as alumina, which are disposed within the slider member 10. And, the tip end portion makes a contact portion with a contact point for applying a substrate bias. The slider member 10 has a U-shaped cross-sectional shape with a recess portion 10b formed in a middle portion, as shown in FIG. 2B, and an upper thick portion 10a has slit grooves for holding the intermediate portion of the substrate holder 20 formed through the thick portion 10a to reach the recess portion 10b. The pair of insulating members 11a and 11b are disposed at both ends within the slit grooves, the insulating member 11a at the end side of the slider member 10 is fixed within the groove, and the insulating member 11b at the center of the slider member 10 is arranged to be movable horizontally. In addition, a leaf spring 12 is mounted to push the movable insulating member 11b toward the end side of the slider member 10. Thus, the substrate holder 20 is inserted in the grooves of the slider member 10, and a screw 13 is tightened to push the substrate holder 20 toward the exterior of the carrier so as to firmly fix it. Multiple magnets 14 are attached to the bottom of the slider member 10 with their magnetization directions alternately reversed, and the slider member 10 is moved by the interaction with a rotating magnet 40 that is arranged along a conveying path. Guide rollers 41 for preventing the slider from separating from the conveying path and rollers 42 for preventing the slider member 10 from falling are mounted to the conveying path, at prescribed intervals. Referring back to FIG. 1, the first ion beam generator 1a and the second ion beam generator 1b are disposed to face each other with the substrate W held therebetween, so as to face both sides of the substrate W. In other words, the first ion beam generator 1a and the second ion beam generator 1b each are arranged to irradiate the region therebetween with an ion beam, and the substrate carrier, which holds the substrate W having an opening, is disposed in the same region. According to the structure shown in FIG. 1, the ion beam irradiation surfaces of the first and second ion beam generators 1a and 1b and the to-be-processed surfaces of the substrate W are disposed substantially parallel to each other. The first ion beam generator 1a is provided with an electrode 5a, a discharge tank 2a for generating plasma, and a lead-out electrode 7a (electrodes 71a, 72a, and 73a from the substrate) as mechanisms for lead-out of ions from the plasma. The electrodes 71a, 72a, and 73a are connected with voltage sources 8a (81a, 82a, and 83a from the substrate) so as to be controllable independently. A neutralizer 9a is disposed close to the lead-out electrode 7a. The neutralizer 9a is configured such that the electrons can be irradiated to neutralize the ion beam irradiated by the ion beam generator 1a. The discharge tank is supplied with a processing gas, such as argon (Ar), by a gas introduction means, not shown. The discharge tank 2a is supplied with Ar by the gas introduction means, and RF (radio-frequency wave) power is applied from an RF source 84a to the electrode 5a to generate the plasma. Ions are lead out from the plasma by the lead-out electrode 7a to perform etching of the substrate W. Since the second ion beam generator 1b is also configured in the same manner as that of the above-described ion beam generator 1a, its description is omitted. The control unit 101 is electrically connected with the voltage source 8a of the ion beam generator 1a and a voltage source 8b of the ion beam generator 1b, and controls the voltage sources 8a and 8b. The counter 103 is connected with the control unit 101 and configured such that it can instruct the control unit 101 to start a cleaning treatment when it counts the number of substrates treated by the ion beam generators 1a and 1b, until it reaches a specified number (e.g., one thousand substrates). Especially, the control unit 101 has a program memory for storing programs (software) for performing overall control of an ion beam etching processing and a substrate conveying operation, and overall control of various added functions. The central processing unit (CPU) of a microcomputer reads sequentially required programs from the program memory and executes them. And, various types of storage media, such as a hard disk, an optical disk, a flash memory, etc., can be used for storage management of the programs. The computer interface 105 is connected with the control unit 101 and the counter 103, and is configured such that the apparatus user can input cleaning conditions (such as processing time). Referring to FIG. 3, FIG. 4A, and FIG. 4B, an ion beam generator 1 (1a and 1b) is described below in detail. FIG. 3 is a schematic sectional view showing a detailed structure of one embodiment of the ion beam generator according to the present invention. Since the first and second ion beam generators 1a and 1b have the same structure, the following description is made with the branch marks a and b omitted appropriately. As shown in FIG. 3, the ion beam generator 1 has a discharge tank 2 for confining the plasma. The pressure of the discharge tank 2 is generally kept in a range of about 1×10−4 Pa (1×10−5 mbar) to about 1×10−2 Pa (1×10−3 mbar). The discharge tank 2 is defined by a plasma confining container 3 and is provided with a multipole magnetic means 4, which traps the ions to be discharged within the discharge tank 2, resulting from the formation of plasma, around it. This magnetic means 4 is generally provided with multiple bar permanent magnets. Multiple relatively long bar magnets whose polarities are changed alternately may also be used to configure it so that an N and S cycle generates along only one axis. And, it may also have a checkerboard structure that shorter magnets are arranged such that the N and S cycle spreads on a plane formed by two mutually orthogonal axes. RF power is applied to the back wall of the plasma confining container 3 by RF coil means 5 and is supplied to the discharge tank 2 via a dielectric RF power coupling window 6 to generate plasma. As shown in FIG. 3, a lead-out electrode 7 is disposed at the front wall of the plasma confining container 3 to lead out ions from the plasma generated in the discharge tank 2 and to accelerate the ions that appear in an ion beam form from the plasma confining container 3. The ions lead out from a grid portion 74 of the lead-out electrode 7 are bent toward the to-be-processed substrate W by the electrical field formed by a deflecting electrode 30 to enter the substrate at an angle θ. The lead-out electrode 7 has a flat portion 75 that is disposed to face substantially parallel to the substrate W (irradiated surface) and the grid portion 74 that outputs the ions to the outside. The grid portion 74 has a structure that multiple micropores are formed to allow irradiation of the ion beam through them. The incident angle θ is desirably sixty degrees or more. The ion beam apparatus must be made large to enter the ion beam to the substrate at the above angle without using the deflecting electrode 30. Therefore, the ion beam generator of the invention can have a sufficient route for the ion beam from the lead-out electrode to the substrate by using the deflecting electrode to deflect the ion beam that is lead out from the lead-out electrode without making the apparatus large. As a result, the ion beam can be irradiated uniformly to the substrate. In this embodiment, the flat portion 75 does not have a grid portion, but may be configured to have a grid portion, such that the ion beam can also be irradiated from the flat portion 75. The deflecting electrode 30 comprises a first electrode tube 31 having a circular truncated cone shape, and a second electrode tube 32 having a circular truncated cone shape and a diameter smaller than that of the first electrode tube 31, and they are disposed to overlap mutually. The first electrode tube 31 has a circular truncated cone shape with its top and bottom opened. Similarly, the second electrode tube 32 also has a circular truncated cone shape with its top and bottom opened. These electrode tubes are set to have a different electrical potential to form an electrical field between them. The ion beam lead out from the lead-out electrode 7 enters between the first electrode tube 31 and the second electrode tube 32, and is deflected toward the substrate W by the electrical field formed between both the electrode tubes, to enter into the substrate W at the inclined angle θ. At this time, a region, where the ions enter at the angle θ, on the to-be-processed surface of the substrate W changes, depending on the range of the grid portion 74 of the lead-out electrode 7 and the position of the deflecting electrode 30, and the angle bent by the deflecting electrode 30. The range of the grid portion 74 can be made narrower as the position of the deflecting electrode 30 is closer to the to-be-processed surface, and the angle of bending the ions is larger. Since the size of the whole apparatus is restricted, the substrate W and the lead-out electrode 7 are arranged to have a distance of 300 mm or less. FIG. 4A and FIG. 4B are views illustrating a detailed structure of the deflecting electrode 30. FIG. 4A is a top view and FIG. 4B is a side view, showing that the first electrode tube 31 and the second electrode tube 32 form a circular ring-shape incident region 50 where the ion beam enters from the grid portion 74, and a circular ring-shape irradiation region 51 where the deflected ion beam is irradiated toward the substrate. Thus, the annular ion beam is deflected towards the center of the circular ring, while passing through the gap between the first electrode tube 31 and the second electrode tube 32. And, the disk-shaped substrate W can be uniformly processed by the irradiated ion beam. By entering the annular ion beam to the substrate, uniform substrate processing can be realized without rotating the substrate. FIG. 5A and FIG. 5B are top views illustrating the surface structure of the lead-out electrode 7. FIG. 5A is an example that the grid portion 74 having circular micropores is disposed in an annular region that is surrounded by two radius circles of the lead-out electrode 7. When the ion output width is narrow, a lead-out electrode, which is provided with multiple arc-shaped linear holes 76, can also be used, as shown in FIG. 5B. When the linear holes are formed, as shown in FIG. 5B, a fabrication time for production can be reduced and the production cost can be reduced substantially as a result. As the material for the lead-out electrode 7, it is common to use Mo in view of a rise in temperature due to heat from the plasma source, resistance to thermal expansion due to the rise in temperature, and securing of rigidity when the thickness is decreased, to secure the lead-out performance of the ion beam. Mo has very high hardness and must be fabricated for a long time. The grid itself must be exchanged periodically, because it is exposed to and worn by the irradiation of ions. By using the linear grid described in this embodiment, the operation time for processing can be reduced substantially, and the cost can be lowered. In this embodiment, the grid portion was formed into a circular ring shape, but it is not exclusively limited. For example, the grid portion may be formed into a substantially circular ring shape, or a ring shape of a substantially regular polygonal shape, such as a regular octagon shape. The action of the deflecting electrode 30 is described in detail with reference to FIG. 6A and FIG. 6B. As shown in FIG. 6A, the first electrode tube 31 and the second electrode tube 32, which have a circular truncated cone shape, are arranged to overlap mutually, and an electrical field 36, which is formed by applying a prescribed voltage between them by a DC power source 35, to deflect the ion beam by a prescribed angle. The first electrode tube 31 is applied with a positive electrical potential, and the second electrode tube 32 is applied with a negative electrical potential. A deflection angle can be changed arbitrarily by the electrical field. At this time, it is necessary to arrange such that the electrical field 36, which is generated by the two electrode plates 31 and 32, is formed in a localized style only in the vicinity between the electrodes. For example, the electrical potential of the second electrode tube 32 in FIG. 3 is made the same as the electrical potential of a lead-out electrode 71, so that the electrical field between the lead-out electrode 7 and the deflecting electrode 30 can be made small. According to the present invention, the first electrode tube 31 and the second electrode tube 32 may be a first electrode 33 and a second electrode 34, which have a ring shape, as shown in FIG. 6B. FIG. 7 shows a relationship between an ion beam width and an inclined angle of the ion beam, which is required when ions enter into the whole surface of a 65-mm diameter substrate. To maintain the parallelism of the ion beam, it is desirable that the ion beam width is the same before and after the ion beam is deflected, and the whole surface of the substrate W can be irradiated with the ion beam width in a cross section including the center of the substrate W. Considering the uniformity of the ion beam incident to the substrate W and geometrical displacement due to the mechanical tolerance of the substrate W, the deflecting electrode 30, and the grid portion 74, the width of the grid portion 74 is preferably determined to be not smaller than the value of the output beam width at the ion incident angle to the substrate W, as shown in FIG. 7. Meanwhile, the irradiation of excessive ions is not desirable in view of the use efficiency of the ion beam, and the width of the grid portion 74 also should be determined considering the uniformity of the beam. For example, when the ion beam enters the substrate W at an incident angle θ of eighty degrees, the width of the beam, which is output from the deflecting electrode 30, has preferably a region slightly larger than 12 mm. And, to realize the planarization by processing the substrate, it is preferable that the incident angle is sixty degrees or more. By appropriately adjusting the grid portion 74, the position of the deflecting electrode 30 from the to-be-processed surface and the ion beam bending angle, the whole surface of the substrate W can be uniformly irradiated with the ion beam at a prescribed angle θ, as shown in FIG. 3. FIG. 8 shows an embodiment that the deflecting electrode 30 is moved reciprocally. The ion beam generator according to this embodiment is provided with a drive mechanism (not shown) for moving the deflecting electrode 30 in an opposed direction relative to the lead-out electrode 7. The drive mechanism can adjust the position where the ion beam is incident upon the substrate W by moving the deflecting electrode 30 between the lead-out electrode 7 and the substrate W. As shown in FIG. 8, when the deflecting electrode 30 is arranged at a position A close to the lead-out electrode 7, the ion beam 37 enters one end of the substrate W. On the other hand, when the deflecting electrode 30 is arranged at a position B close to the substrate W, the ion beam 37 enters the other end of the substrate W. When the deflecting electrode 30 is arranged at a midpoint O between the point A and the point B, the ion beam mainly enters the center of the substrate W. When the grid portion 74 is made smaller than the width shown in FIG. 7, it occurs occasionally that the ion beam cannot be irradiated to the entire surface of the substrate W to be processed. In such a case, the ion beam can be made to sweep at a prescribed incident angle over the substrate by moving the deflecting electrode 30 between, for example, the to-be-processed substrate surface and the lead-out electrode surface opposed thereto. Thus, the ion beam can be irradiated to the entire surface of the substrate. When the ion beam is entered in a circular shape to sweep the to-be-processed circular substrate W at a prescribed angle, the incident region has a different area depending on the sweep positions on the to-be-processed substrate W, even if the ion emitting amount from the grid portion 74 is the same. In other words, since the area of the incident region is different between a case that a portion having a small radius on the substrate (position close to the center) is irradiated and a case that the ion beam enters a region having a large radius (position away from the center), the incident amount per unit area is different. As a result, the substrate is not etched uniformly. FIG. 9 is a view illustrating a moving velocity of the deflecting electrode 30 when the deflecting electrode 30 is reciprocally moved between the position A and the position B. It is controlled such that the moving velocity of the deflecting electrode 30 is relatively increased at the position O and relatively decreased at the positions A and B. Thus, the sweep velocity is modulated in conformity with the radius of an irradiation portion, so that the incident amount of ions to the to-be-processed substrate W can be made uniform. For example, the incident amount of ions upon the to-be-processed substrate W can be made uniform by modulating the sweep velocity to the operation of the deflecting electrode 30 so as to become inversely proportional to the radius of the corresponding to-be-processed substrate W. In the drawing, 91 indicates a range of irradiating the substrate. In the above embodiment, the flat portion 75 of the lead-out electrode 7 is a non-irradiated portion, which is not irradiated with the ion beam, but the present invention is not limited to the above, and the grid portion may be formed so that the ion beam can be irradiated. Thus, the to-be-processed substrate W can be irradiated with a vertical ion beam and an oblique ion beam at the same time. Referring to FIG. 1, the action of the substrate processing apparatus 100 of this embodiment is described below. One to-be-processed surface of the substrate W is processed by irradiating the ion beam from the first ion beam generator 1a to it. Similarly, the other to-be-processed surface of the substrate W is processed by irradiating the ion beam from the second ion beam generator 1b to it. In the substrate processing apparatus 100 of this embodiment, the first and second ion beam generators 1a and 1b each are configured to have the lead-out electrode 7, which has the grid portion 74 for emitting ions to the region outside of the contour of the to-be-processed substrate W. In addition, a deflecting electrode (not shown), which deflects the ion beam, which is lead out from the grid portion 74, toward the to-be-processed substrate W, is configured to be obliquely at a prescribed angle. Thus, the ions can enter obliquely the to-be-processed substrate W at the prescribed incident angle to perform the prescribed processing. The effect of processing the substrate by the ion beam generator of the present invention is described below. Examples of processing the substrate by entering the ion beam include fabrication of a film deposited on the substrate into a prescribed shape, fabrication of the whole surface, planarization processing upon the uneven surface formed on the substrate, etc. FIG. 10A to FIG. 10D show an example of microfabrication of a film deposited on the substrate into a prescribed shape by entering the ion beam. A photoresist 202 is formed in a prescribed shape by lithography on a to-be-processed film 201, which was deposited on the to-be-processed substrate W by a sputtering method or a CVD method. Using it as a mask, an ion beam 203 is irradiated from the ion beam generator to fabricate the to-be-processed film 201. For the use requiring the microfabrication, such as the fabrication of the semiconductor substrate, fabrication according to a designed pattern, namely, vertical processing more accurately conforming to the mask, is desired in order to secure the device performance. At this time, the ion beam generator accelerates the ions, which are generated by introducing a prescribed gas into the plasma source, by the lead-out electrode and irradiates the substrate with the ion beam to perform etching. FIG. 10A and FIG. 10B show fabrication shapes when the ion beam is entered from a vertical direction only, and FIG. 10C and FIG. 10D show that the ion beams are emitted obliquely by the apparatus of the present invention. At this time, when an inert gas, such as Ar or He is used, or when the to-be-processed material is a so-called hard-to-dry etch material and a volatile product is not formed by a chemical reaction between the to-be-processed material and the activated species generated by plasma, adhesive particles 204 are scattered from the processed surface of the substrate by sputtering. According to, for example, common sputtering theory, the particles are scattered in a certain distribution, which is proportional to a cosine of a discharge angle, so that they are partly scattered toward the side faces of the fabricated body to adhere thereto, to disturb the vertical progress of etching and to form a pattern side face deposited film 205. Because of the deposited film 205, the pattern side wall has a tapered shape, as shown in FIG. 10B. When etching is actually performed by such vertical incidence, a taper angle of about 75 degrees or more cannot be obtained. When the beam enters the tapered side wall at an ion incident angle of zero degrees with respect to the substrate, the ion incident angle to the side wall surface becomes very large. For example, according to FIG. 2 of a reference “R. E. Lee: J. Vac. Sci. Technol., 16, 164 (1979)”, when the taper angle is seventy-five degrees as described above, the etching velocity to a to-be-etched surface parallel to the substrate lowers extremely. It is to be understood that the taper angle is an angle formed between the side wall and the substrate surface, and the ion incident angle is an angle at which the incidence ion beam is inclined from a direction perpendicular to the incident surface. For example, it is zero degree when the ion beam enters vertically to the to-be-etched surface. On the other hand, when the ion beam generator 1 according to the present invention is used to irradiate an inclined ion beam 206 at an inclined angle of, for example, fifteen degrees, the ion beam has an incident angle of, for example, sixty degrees to the side face having a taper angle of seventy-five degrees and an incident angle of fifteen degrees to the to-be-etched surface. According to the above reference, the difference in etching velocity lowers considerably in comparison with the case that the ion beam is not inclined. As shown in FIG. 10D, the side wall of the to-be-processed film 201 is etched progressively, and a more vertical etched side surface can be obtained. FIG. 11A to FIG. 11F show fabrication examples of planarizing the uneven surface of the substrate by the ion beam generator of the present invention. As shown in FIG. 11A and FIG. 11D, a to-be-processed layer 208 is previously formed on the to-be-processed substrate W, and then, microfabrication processing is performed by etching processing, or the like, according to a lithographic method. The etching processing is performed by the incident ion beam shown in, for example, FIG. 10C and FIG. 10D. An embedded layer 209 is formed on the etched layer 208 by performing embedding film formation on it by, for example, a sputtering method. When the film formation is performed by sputtering, or the like, a level difference occurs between portions with and without a pattern on the surface of the embedded layer 209, as shown in FIG. 11A and FIG. 11D. It is because sputtering particles enter uniformly to the substrate surface, and volumes of the films formed on individual portions on the substrate are equal. In some semiconductor fabrication and magnetic disk fabrication, it is desired that such an uneven surface is planarized for assuring the device performance and convenience of the subsequent process. FIG. 11B and FIG. 11C show changes in surface shape when the ion beam 203 vertically enters the uneven surface. In this case, the surface parallel to the substrate W is fabricated uniformly, but since a taper portion has a very large incident angle of the ion beam, there is shown a shape that the progress of etching is suppressed. Since the ion beam has an effect of selectively etching the corners of protruded portions, the protruded portions are rounded, but a sufficient planarization effect cannot be obtained. Meanwhile, when the ion beam 206 enters substantially vertically to the stepped side wall surface, namely, in an inclined form with respect to the substrate surface, as shown in FIG. 11E and FIG. 11F, the stepped side wall can be etched at a very fast etching velocity in comparison with that on the surface parallel to the substrate. Thus, only the width of the protruded portions is narrowed gradually, to eliminate the protruded portions, finally, and the flat portion can be obtained. For example, when the side wall of the level difference has a taper of seventy-five degrees, the ion beam 206 enters at an angle of sixty degrees, and the ion beam is irradiated to the stepped surface at the incident angle of fifteen degrees. At this time, the incident angle of the ion beam to the surface parallel to the substrate W becomes sixty degrees, and the stepped surface is etched at a considerably fast etching velocity according to the above-described reference. Since the present invention can enter the uniform ion beam to the substrate, it is not necessary to rotate the substrate. According to the present invention, the provision of a substrate rotation mechanism is not preferable, because there is generated a portion where the entry of the ion beam is disturbed, because of its mechanism, or it is necessary to dispose sliding parts at the outer peripheral portion of the substrate, as shown in FIG. 5 of published Japanese Patent Application No. JP-A 2008-117753. Especially, the provision of the sliding parts at the outer peripheral portion of the substrate is not desirable, because it causes the unnecessary particles to adhere onto the substrate, and the yield is considerably disturbed. In addition, although it is not shown in the drawing, a very large mechanism is required to rotate the substrate without disturbing the ion beam and without providing the substrate portion with a sliding portion. Therefore, it is not suitable for the substrate processing apparatus, which is desired to be small, as in the present invention. As described above, according to the substrate processing apparatus 100 of this embodiment, the grid portions 74 for outputting the ion beams of the mutually opposed ion beam generators 1a and 1b are formed outside of the to-be-processed substrate W. And, the ion beam is deflected by the deflecting electrode 30 for deflecting it toward the to-be-processed substrate and irradiated to the to-be-processed substrate. Thus, a compact ion beam generator, capable of emitting a uniform inclined ion beam to perform etching processing with a higher pattern accuracy and planarization of the uneven surface with the generation of particles suppressed, can be configured. The ion beam generator of the present invention is preferably applied when the microfabrication or planarization is performed by etching the substrate surface in the production process of the electronic device, as described above. FIG. 12 is a view of a schematic structure of a production apparatus when the ion beam generator of the present invention is used for production of a magnetic recording medium. The production apparatus of this embodiment is an inline type production apparatus that has multiple evacuatable chambers 111 to 121 arranged in a connected form in an endless square form, as shown in FIG. 12. And, a conveying path for conveying the substrate to the adjacent vacuum chamber is formed within the individual chambers 111 to 121, and the substrate is processed in the individual vacuum chambers sequentially, while circulating through the production apparatus. And, the conveying direction of the substrate is changed in direction changing chambers 151 to 154, in which the conveying direction of the substrate, which is linearly conveyed between the chambers is turned by ninety degrees, and the substrate is sent to the next chamber. The substrate is introduced into the production apparatus by a load lock chamber 145, and after the processing is completed, the substrate is conveyed out of the production apparatus by an unload lock chamber 146. Plural chambers, such as the chambers 121, capable of performing the same processing may be disposed successively, to perform the same processing multiple times. Thus, a time taking processing can also be performed without extending the time taken. The apparatus of FIG. 12 has only the chambers 121 disposed in plural, but another chamber may also be disposed in plural. FIG. 13A is a schematic view of a laminated body that is processed by the production apparatus according to this embodiment. In this embodiment, the laminated body is formed on both sides of a substrate 301. But, for simplification of the drawing and description, the processing of the laminated body formed on one side of the substrate 301 is focused in FIG. 13A, and the laminated body formed on the other side and the processing on it are omitted. Therefore, the processing on the laminated body formed on one side of the substrate 301 is described referring to FIG. 13B to FIG. 13D and FIG. 14A to FIG. 14D, but the laminated body formed on the other side is also processed in the same manner. As shown in FIG. 13A, the laminated body is under processing into a DTM (Discrete Track Media) and comprises the substrate 301, a soft magnetic layer 302, a base layer 303, a recording magnetic layer 304, a mask 305, and a resist layer 306. The laminated body is introduced into the production apparatus shown in FIG. 12. As the substrate 301, for example, a glass substrate or an aluminum substrate having a diameter of 2.5 inch (65 mm) can be used. The soft magnetic layer 302, the base layer 303, the recording magnetic layer 304, the mask 305, and the resist layer 306 are formed on both of the opposite sides of the substrate 301, but the laminated body formed on one side of the substrate 301 is omitted for simplification of the drawing, and a description, as described above. The soft magnetic layer 302 is a layer that plays a part as a yoke of the recording magnetic layer 304 and contains a soft magnetic material, such as an Fe alloy or a Co alloy. The base layer 303 is a layer for a vertical orientation (laminated direction of the laminated body 300) of the easy axis of the recording magnetic layer 304, and contains a laminated body of Ru and Ta, or the like. The recording magnetic layer 304 is a layer that is magnetized in a vertical direction relative to the substrate 301 and contains a Co alloy, or the like. The mask 305 is used to form grooves in the recording magnetic layer 304, and a diamond like carbon (DLC), or the like, can be used. The resist layer 306 is a layer for transcribing a groove pattern on the recording magnetic layer 304. In this embodiment, the groove pattern is transcribed on the resist layer by a nanoimprint method, and the laminated body 300 in the above state is introduced into the production apparatus shown in FIG. 12. The groove pattern may also be transcribed by exposing and developing, without depending on the nanoimprint method. The production apparatus shown in FIG. 12 removes the grooves from the resist layer 306 by reactive ion etching in the first chamber 111, and then removes the mask 305, which is exposed in the grooves, in the second chamber 112, by the reactive ion etching. The cross section of the laminated body 300 at this time is shown in FIG. 13B. Subsequently, the recording magnetic layer 304 exposed in the grooves is removed by ion beam etching in the third chamber 113, and the recording magnetic layer 304 is formed as a concave-convex pattern having individual tracks separated in the radial direction as shown in FIG. 13C. At this time, for example, a pitch (groove width+track width) is 70 to 100 nm, the groove width is 20 to 50 nm, and the recording magnetic layer 304 has a thickness of 4 to 20 nm. The ion beam processing by the ion beam generator of the present invention can be performed in the third chamber 113, to effect etching processing at high pattern accuracy and excellent uniformity within the substrate. Thus, the process of forming the recording magnetic layer 304 in the concave-convex pattern is performed. Then, the mask 305 remaining on the surface of the recording magnetic layer 304 is removed by reactive ion etching in the fourth chamber 114 and the fifth chamber 115. As a result, the recording magnetic layer 304 has an exposed state, as shown in FIG. 13D. A process of filling an embedded layer 309 of a nonmagnetic material in the recessed portions of the recording magnetic layer 304 by forming as a film, and an etching process of removing the excessive portion of the embedded layer by etching are described below with reference to FIG. 14A to FIG. 14D. After the recording magnetic layer 304 of the laminated body 300 is exposed, as shown in FIG. 13D, the embedded layer 309 is formed on the surface of grooves 307, which are recessed portions of the recording magnetic layer 304 in the embedded layer forming chamber 117, as shown in FIG. 14A. The embedded layer forming chamber 117 functions as a second film forming chamber for forming and filling the embedded layer 309 of a nonmagnetic material on the recording magnetic layer 304. The embedded layer 309 is made of a nonmagnetic material that does not affect recording to and reading from the recording magnetic layer 304, and, for example, Cr, Ti, and their alloy (e.g., CrTi) can be used. The nonmagnetic material is adequate, even if it contains a ferromagnetic material, provided that the property as the ferromagnetic material, as a whole, is lost by containing another diamagnetic material or nonmagnetic material. The method of forming the embedded layer 309 is not particularly limited, but a bias voltage is applied to the laminated body 300 to perform RF-sputtering in this embodiment. Thus, the application of the bias voltage leads the sputtered particles into the grooves 307 and prevents the generation of voids. As the bias voltage, for example, a DC voltage, an AC voltage, or a DC pulse voltage can be applied. The pressure condition is not particularly limited, but an embedding property is good under a condition with a relatively high pressure of 3 to 10 Pa, for example. And, by performing RF-sputtering with a high ionization rate, protruded portions 308, on which an embedding material is easily laminated in comparison with the grooves 307, can be etched by the ionized discharge gas simultaneously when the film is formed. Therefore, a difference in thickness of the film laminated on the grooves 307 and the protruded portions 308 can be suppressed. The embedding material may be laminated on the grooves 307 as the recessed portions by collimated sputtering or low-pressure remote sputtering, but the distance between the substrate 301 and the target can be decreased, and the apparatus can be made compact by the method of this embodiment. Although it is not shown in the drawing, an etching stop layer may be formed before the embedded layer 309 is formed. For the etching stop layer, a material having an etching velocity lower than that of the embedded layer 309, under the condition of planarization described later for the embedded layer 309, as the upper layer, may be selected. Thus, there can be provided a function of suppressing damage to the recording magnetic layer 304 due to excessive progress of etching at the time of planarization. And, when a nonmagnetic metallic material is selected as the etching stop layer, the bias voltage at the time of forming the embedded layer 309 in the post-process can be functioned effectively, and the generation of voids can be suppressed effectively. FIG. 12 also shows the etching stop layer forming chamber 116. The surface after forming the embedded layer 309 is lower than the flat surface described above, although fine projections and recesses are mostly filled, as shown in FIG. 14A. When the embedded layer does not have a sufficient thickness on the fine projections and recesses, fine projections and recesses might be left. Then, in the first etching chamber 118, the embedded layer 309 is removed, as shown in FIG. 14B, but the embedded layer 309 is somewhat left on the recording magnetic layer 304. In this embodiment, the embedded layer 309 is removed by ion beam etching using an inert gas, such as an Ar gas as an ion source. At this time, the inclined ion beam is irradiated by the ion beam generator of the present invention to perform effective planarization of the level difference formed on the surface. The inclined angle of the ion beam may be single or a combination of multiple angles, or may also include vertical incidence, and the shape of the deflecting electrode 30 and the voltage applied to the deflecting electrode 30 can be selected depending on the level difference of the surface for optimization. The first etching chamber 118 is provided with the ion beam generators 1a and 1b of the present invention exemplified in FIG. 1. The first etching chamber 118 is a chamber for partly removing the embedded layer 309 by ion beam etching. For example, specific etching conditions include that a chamber pressure is 1.0×10−1 Pa or less, an electrode 73 has a voltage of +500V or more, an electrode 72 has a voltage of −500V to −2000V, and RF power for inductively coupled plasma (ICP) discharge is about 200 W. After the planarization, the ion beam etching is continued to remove completely the left embedded layer 309, as shown in FIG. 14C. FIG. 12 also shows the second etching chamber 119 for removing the above-described etching stop layer, not shown. The etching chamber 119 is comprised of a mechanism to apply bias, such as DC, RF or DC pulse to the carrier by ICP plasma using a reactive gas. As shown in FIG. 14D, a DLC layer 310 is then formed on the planarized surface. In this embodiment, the DLC layer 310 is formed in the protective film forming chamber 121 after adjusting to a temperature required for DLC formation in the heating chamber 120 or a cooling chamber. For example, the film forming conditions for a parallel plate CVD include that high frequency power is 2000 W, pulse-DC bias is −250V, a substrate temperature is 150 to 200 degrees C., a chamber pressure is about 3.0 Pa, gas is C2H4, and a flow rate is 250 sccm. ICP-CVD, or the like, may also be used. Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, when the mask 305 is carbon, there may be adopted a method of leaving the mask 305 instead of forming the etching stop layer. But, it has a possibility of causing the mask 305 to have an uneven thickness, because of two times of etching, such as etching for removal of the resist layer 306 and etching for removal of the excessive embedded layer 309. Therefore, it is preferable that the mask 305 is removed as in the above embodiment, and the etching stop layer is formed. And, the etching stop layer can also be formed on the bottoms and side walls of the grooves 307, and when a conductive material is used for the etching stop layer, it is preferable, because it becomes easy to apply a bias voltage, as described above. The DTM has been described above, but it is not exclusively limited. For example, the present invention can also be applied when the embedded layer 309 is formed on the concave-convex pattern of BPM having the recording magnetic layer 304 in a dotted form. The present invention is not limited to the exemplified substrate processing apparatus (magnetron sputtering apparatus), but can also be applied to a plasma processing apparatus, such as a dry etching apparatus, a plasma asher apparatus, a CVD apparatus, and a liquid crystal display production apparatus. The substrate processing apparatus of the present invention can also be configured by combining the characteristics described in the individual embodiments. As an electronic device that can use the ion beam generator of the present invention for its production, there are semiconductors, magnetic recording media, and the like. |
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048250872 | claims | 1. In combination with a system for irradiating a wafer-like target with an ion beam in a system end station comprising post-analysis electrode means for accelerating the ion beam to a given velocity incident upon a target located at a selected position downstream from the post-analysis electrode means, a flood gun inserted between the post-analysis electrode means and the target position for neutralizing positive charge build-up induced in the target by the ion beam, the flood gun comprising: a spiral wire grid anode having coil turns spaced a distance selected for admitting gas therethrough; a filament cathode extending lengthwise within the grid anode for receiving a bias voltage to stimulate the emission of electrons into the ion beam; means for introducing an inert gas through the grid anode for magnifying the flux of emitted electrons and lowering the peak electron energy to a value commensurate with the positive voltage level induced by the ion beam in the target; and means for supplying an adjustable bias voltage to the filament for amplifying the current of emitted electrons and for controlling the electron peak energy. 2. The combination of claim 1, wherein the inert gas is argon. 3. In combination with an ion implantation system for irradiating a target including a semiconductor wafer with an ion beam, an electron flood gun for neutralizing positive charge induced in the target by the ion beam, comprising: a cylindrical anode having openings therein for admitting gas therethrough; a filament cathode extending lengthwise within the anode for receiving a bias voltage to stimulate the emission of electrons into the ion beam; means for introducing an inert gas through the openings in the cylindrical anode for magnifying the flux of emitted electrons and lowering the peak electron energy to a value commensurate with the positive voltage level induced by the ion beam in the target; and means for supplying an adjustable bias voltage to the filament for amplifying the current of emitted electrons and for controlling the electron peak energy. 4. The combination of claim 3, further comprising means for generating a magnetic field at the target generally transverse to the ion beam for selectively inhibiting flow of flood electrons to the target. 5. The combination of claim 4, wherein the inert gas is argon. 6. In combination with the process of implanting ions into a semiconductor wafer using an incident ion beam, the method of neutralizing low magnitude voltage positive charge up of the water resulting from the ion implant process, comprising: providing an electron flood gun comprising an anode configured as a cylinder and having openings in the cylinder for admitting gas therethrough and a filament cathode extending lengthwise within the cylinder anode for directing electrons into the beam; bleeding inert gas through the cylinder anode into the flood gun for amplifying the electron current and lowering the average peak flood electron energy; and controlling the voltage applied to the electron gun filament to control the magnitude of the electron current and limit the average peak electron voltage to a value commensurate with the magnitude of the positive wafer charge. 7. The process of claim 6, further comprising the steps of setting the filament current to a value just sufficient to provide the requisite electron emission level and electron current, to provide an optimum combination of electron current magnitude, operating efficiency and filament lifetime. 8. The process of claim 7, further comprising the steps of preliminarily setting the filament current at an initial value which provides the requisite electron emission level and flood electron current; reducing the filament current decremently while adjusting the bias voltage applied thereto to maintain said electron current at a relatively constant value; monitoring the bias voltage while reducing the filament current to detect an initial increase in the bias voltage in response to a decremental increase in the filament current; returning the filament current to a selected previous value before the bias voltage increase-causing decrement; and operating the flood gun simultaneously while directing the ion beam onto the wafer and adjusting the bias voltage to maintain the filament current and flood gun electron current at said selected previous value. 9. The process of claim 8, wherein during said flood gun operation, the bias voltage is reduced to offset increases in the flood gun ambient pressure. 10. The process of claim 9, further comprising determining a pressure threshold value which provides a minimum acceptable beam current and, during operation of the flood gun, monitoring the ambient flood gun pressure and maintaining said pressure below said threshold value. 11. The process of claim 10, further comprising determining the percentage of emitted electrons which fall below a maximum acceptable average peak energy; mounting an electron collector adjacent the flood gun for providing a signal proportional to the electron current incident on said collector; determining the electron current I.sub.o when the collector is grounded; and monitoring the electron current I.sub.e with the collector biased negatively during operation of the flood gun and determining when the ratio I.sub.o /I.sub.e falls below a selected percentage; and responsively decreasing the pressure to provide the selected percentage. 12. The process of claim 6, further comprising periodically sampling the ion beams to determine the beam current; and terminating flood gun operation during said sampling. 13. The process of claim 6, further comprising monitoring the position of the wafer relative to the opposite edges of the ion beam; and disabling flood gun operation when the wafer position is outside said opposite edges of the beam. 14. In combination with the process of irradiating a target using an ion beam having an ion beam line axis, the method of neutralizing undesirable charge-up of the target resulting from the irradiation process, comprising: providing a flood gun adjacent the ion beam line axis having a filament surrounded by a grid anode for directing electrons into the beam; applying a current through the filament and a voltage between the filament and grid anode for generating charged particles directed into the ion beam; supplying inert gas at a selected pressure to the gun to amplify the current of charged particles and lower the average energy of the charged particles; controlling said energy and current levels by controlling the voltage between the filament and anode; applying an electric field along the direction of the beam line axis for directing flood electrons onto the target; adjusting the bias voltage to control the flood electron current emanating from said flood gun; and further comprising the step of applying a magnetic field transverse to the ion beam and across said target for inhibiting the flow of flood electrons to the target in the absence of an ion beam and for preventing secondary electrons emanating from the target from reaching the beam. |
claims | 1. For use in a nuclear fission reactor, a flow control assembly, comprising:a flow regulator subassembly, said flow regulator subassembly including:a first sleeve having a first hole, said first sleeve having a structure arranged to axially translate responsive to rotational engagement thereof;a second sleeve slidably inserted into said first sleeve such that relative rotation of said first sleeve with respect to said second sleeve is restricted, said second sleeve having a second hole, the first hole being progressively axially alignable with the second hole responsive to axial translation of said first sleeve; anda carriage subassembly having a structure arranged to rotatably engage said first sleeve. 2. For use in a nuclear fission reactor, a flow control assembly couplable to a selected one of a plurality of nuclear fission fuel assemblies arranged for disposal in the nuclear fission reactor, comprising:an adjustable flow regulator subassembly for modifying flow of a fluid stream flowing through the selected one of the plurality of nuclear fission fuel assemblies, said adjustable flow regulator subassembly including:an outer sleeve having a plurality of first holes, said outer sleeve having a structure arranged to axially translate responsive to rotational engagement thereof;an inner sleeve slidably inserted into said outer sleeve, said inner sleeve having a plurality of second holes, the first holes being progressively axially alignable with the second holes responsive to axial translation of said first sleeve; andan anti-rotation mechanism that engages said outer sleeve and said inner sleeve, the anti-rotation mechanism restricting relative rotation of said first sleeve with respect to said second sleeve and permitting axial translation of the first sleeve with respect to the second sleeve; anda carriage subassembly rotatably coupled to said outer sleeve. 3. The flow control assembly of claim 2,wherein said outer sleeve is generally cylindrical and rotatable; andwherein said inner sleeve is generally cylindrical. 4. The flow control assembly of claim 2, wherein said carriage subassembly is driven by a lead screw arrangement for rotatably engaging said outer sleeve. 5. The flow control assembly of claim 2 wherein said carriage subassembly is driven by a reversible motor arrangement for rotatably engaging said outer sleeve. 6. The flow control assembly of claim 5, wherein said carriage subassembly is at least partially controlled by a radio transmitter-receiver arrangement operating said reversible motor arrangement for rotatably engaging said outer sleeve. 7. The flow control assembly of claim 5, wherein said carriage subassembly is at least partially controlled by a fiber optic transmitter-receiver arrangement operating said reversible motor arrangement for rotatably engaging said outer sleeve. 8. A flow control assembly comprising:an outer sleeve defining therein a plurality of outer sleeve holes and having an outer sleeve engagement surface;an inner sleeve slidably insertable into the outer sleeve, the inner sleeve defining therein a plurality of inner sleeve holes that are progressively axially alignable with the plurality of outer sleeve holes;a carriage subassembly having a carriage subassembly engagement surface arranged to rotatably engage the outer sleeve engagement surface; andan anti-rotation mechanism that engages the outer sleeve and the inner sleeve, the anti-rotation mechanism restricting relative rotation of the outer sleeve with respect to the inner sleeve and permitting axial translation of the outer sleeve with respect to the inner sleeve. 9. The flow control assembly of claim 8, wherein:the outer sleeve engagement surface is threadedly defined in the outer sleeve; andthe carriage subassembly engagement surface is threadedly defined in the carriage subassembly. 10. The flow control assembly of claim 8, wherein the carriage subassembly includes a reversible motor arrangement. 11. The flow control assembly of claim 8, wherein the anti-rotation mechanism includes:a plurality of grooves defined in the outer sleeve; anda plurality of tabs defined in the inner sleeve, the plurality of grooves and the plurality of tabs being shaped to engage each other. 12. A flow control assembly comprising:an outer sleeve defining therein a plurality of outer sleeve holes and having an outer sleeve engagement surface;an inner sleeve slidably inserted into the outer sleeve, the inner sleeve defining therein a plurality of inner sleeve holes that are progressively axially alignable with the plurality of outer sleeve holes;a carriage subassembly rotatably coupled to the outer sleeve, the carriage subassembly having a carriage subassembly engagement surface arranged to rotatably engage the outer sleeve engagement surface; andan anti-rotation mechanism that engages the outer sleeve and the inner sleeve, the anti-rotation mechanism restricting relative rotation of the outer sleeve with respect to the inner sleeve and permitting axial translation of the outer sleeve with respect to the inner sleeve. 13. The flow control assembly of claim 12, wherein:the outer sleeve engagement surface is threadedly defined in the outer sleeve; andthe carriage subassembly engagement surface is threadedly defined in the carriage subassembly. 14. The flow control assembly of claim 12, wherein the carriage subassembly includes a reversible motor arrangement. 15. The flow control assembly of claim 12, wherein the anti-rotation mechanism includes:a plurality of grooves defined in the outer sleeve; anda plurality of tabs defined in the inner sleeve, the plurality of grooves and the plurality of tabs being shaped to engage each other. |
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abstract | A method for creating isotopes using laser beams, including the steps: 1) placing a target under plasma conditions, 2) bombarding the target under plasma conditions with particles generated using a bundle of laser beams, the bundle of laser beams being synchronized with the development of the plasma conditions, the fuel and the particles being selected in such a way that the interaction between the target under plasma conditions and the particles generates nuclear reactions, and 3) recovering the isotopes generated by the nuclear reactions. |
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description | The present disclosure relates to steel detection; more particularly, relates to using nuclear power plant water chemistry to simulate a detecting circuit of electrochemical corrosion potential (ECP) and alternative-current (AC) impedance for acquiring effect of preventing intergranular stress corrosion cracking (IGSCC) of boiling water reactor (BWR) by coating internal components with precious metal film through hydrogen water chemistry (HWC). A boiling water reactor may face IGSCC problem after a long time of operation. What may cause people to be more concerned are the damages happened on internal components of a reactor pressure vessel (RPV), like core shroud, upper plenum and lower plenum, which may cause serious problems to system safety. Cracking happened in reactor core shroud weld may have the following causes of IGSCC to the reactor pressure vessel: one is residual stress, one is sensitized material and the other is reactor core environment. Since internal components of the RPV can not be easily replaced, IGSCC can be somewhat prohibited by improving water environment in the reactor core. On running the BWR, the reactor core water will generate hydrogen peroxide and oxygen owing to radiolysis of reactor core fuel rods; and then hydrogen peroxide will generate oxygen and water. Thus, the reactor core water becomes highly oxidized. When the BWR is run under normal water chemistry, dissolved oxygen in the reactor core water is about 200 to 400 ppb, where, in a high-temperature pure water, dissolved oxygen is the main cause for corrosion of the internal components of the RPV. For solving the problem, hydrogen water chemistry (HWC) is used by adding hydrogen to feeding water for reacting hydrogen with oxygen or hydrogen peroxide into water to reduce dissolved oxygen in the reactor core water, where dissolved oxygen is kept below 10 ppb to prevent IGSCC. Although HWC can prevent IGSCC and save check and maintenance of the internal components and tubes in the reactor core, gas of N-16 generated may make radiation increase in nuclear power plant during operation and radiation of Co-60 in dry well may also increase after stopping operation. A metal coating technology has been introduced by GE Co., USA, for solving the problem concerning HWC. A tiny amount of soluble precious metal compound having a concentration of 20˜100 ppb is added into reactor core water. A residual heat removal system, (RHRS) uses temperature of the reactor itself to contact internal components of reactor pressure vessel (RPV) with cycling reactor core water for 24 hours. Thus, a precious metal film is coated on surfaces of the components. Through catalysis of the surfaces of the precious metal, like Pt, Rh, etc., to hydrogen, a utility ratio of hydrogen is improved. Furthermore, required amount of hydrogen to be filled is greatly reduced for HWC to protect the internal components of the RPV. Although HWC is used to improve water chemistry environment for preventing IGSCC of the internal components of the reactor core, radiation dose inside the reactor core has to be 4 to 5 times to that of a normal running BWR when hydrogen is filled to a concentration of 1˜2 ppm for reducing high oxidation of the reactor core water in the BWR. Moreover, main steam pipe and nuclear power plant may have too much radiation too. Hence, a detector is required to provide data for evaluating effect of preventing IGSCC of BWR by coating its internal components with precious metal film through HWC. The main purpose of the present disclosure is to acquire workability and effect of metal coating technology by simulating a detecting circuit of ECP and AC impedance through nuclear power plant water chemistry. The second purpose of the present disclosure is to simulate a BWR for acquiring effect of preventing IGSCC by coating internal components of the reactor core with precious metal film through HWC. To achieve the above purposes, the present disclosure is a nuclear power plant steel detecting device, comprising a gas mixing tube, a hydrogen filling barrel, an autoclave, an ECP analyzer and an electrochemical AC impedance analyzer, where the gas mixing tube comprises a plurality of gas cylinders and a plurality of fine-tuning control valves; where the gas mixing tube has a gas inlet tube between the gas mixing tube and the hydrogen filling barrel to provide gas to the hydrogen filling barrel through the gas inlet tube; where the plurality of gas cylinders comprising a hydrogen gas cylinder, an oxygen gas cylinder and a nitrogen gas cylinder; where each of the gas cylinders has one of the fine-tuning control valves at an end to control gas amount flown through and to be connected with the gas inlet tube through the corresponding one of the fine-tuning control valves; where the hydrogen filling barrel contains a hydrogen water solution; where the hydrogen filling barrel has an enclosed space contained inside; where the hydrogen filling barrel has a depressurizing valve group on a top end to be connected with the enclosed space; where the depressurizing valve group comprises a first depressurizing valve, a second depressurizing valve and a third depressurizing valve; where the first depressurizing valve, the second depressurizing valve and the third depressurizing valve are respectively connected with the gas inlet tube, a first air-releasing tube and a second air-releasing tube; where the hydrogen filling barrel has a water level monitor meter at a side; where the water level monitor meter has an upper valve and a lower valve; where the upper valve and the lower valve are separately connected with the enclosed space; where the hydrogen filling barrel has an outlet valve at an end to be connected with the enclosed space; where the outlet valve is connected with a gas-liquid inlet tube to drain the hydrogen water solution in the enclosed space through the outlet valve and to provide the hydrogen water solution to the autoclave through the gas-liquid inlet tube; where the autoclave simulates an environment of nuclear power plant water chemistry; where the autoclave is sealed by a top cover having an insulated joint; where the autoclave has a containing space within; where the containing space is able to be enclosed; where the containing space is connected with the gas-liquid inlet tube and the second air-releasing tube; where the autoclave has wires contained within to be spot-welded with the to-be-detected steel materials; where the wires penetrates through the insulated joint to reach out of the top cover of the autoclave and to be connected with the ECP analyzer and the electrochemical AC impedance analyzer; where reactants in the autoclave is cycled to be drained out to the hydrogen filling barrel through the second air-releasing tube; where the ECP analyzer has the to-be-detected steel materials as working electrodes to obtain ECPs of the to-be-detected steel materials; where the to-be-detected steel materials is made of stainless steel; where the ECPs of the to-be-detected steel materials is controlled to be not bigger than −0.23V on comparing to a voltage of a standard hydrogen electrode; where the to-be-detected steel materials comprises an uncoated steel, a Pd-coated steel, a Pt-coated steel and an Rh-coated steel; where the electrochemical AC impedance analyzer provides a plurality of AC signals having different frequencies to obtain characteristics of impedances of the to-be-detected steel materials to obtain coating conditions of the to-be-detected steel materials under the environment of nuclear power plant water chemistry to acquire safety of coated films of the to-be-detected steel materials; and where the nuclear power plant steel detecting device obtains a detecting circuit with the above comprised components to simulate a BWR to acquire effect of preventing IGSCC of the BWR with internal components coated with precious metal film under HWC. Accordingly, a novel nuclear power plant steel detecting device is obtained. The following description of the preferred embodiment is provided to understand the features and the structures of the present disclosure. Please refer to FIG. 1, which is a structural view showing a preferred embodiment according to the present disclosure. As shown in the FIGURE, the present disclosure is a nuclear power plant steel detecting device, where nuclear power plant water chemistry is used to build a detecting circuit of electrochemical corrosion potential (ECP) and alternative current (AC) impedance; and where the detecting device comprises a gas mixing tube 1, a hydrogen filling barrel 2, an autoclave 3, an ECP analyzer 4 and an electrochemical AC impedance analyzer 5. The gas mixing tube 1 has a plurality of gas cylinders 10 and a plurality of fine-tuning control valve 11; and has a gas inlet tube 12 between the gas mixing tube 1 and the hydrogen filling barrel 2. A switching valve 121 is set on the gas inlet tube 12 to control switching on and off of channel for providing gas to the hydrogen filling barrel 2 through the gas inlet tube 12. Therein, the plurality of gas cylinders 10 comprises a hydrogen gas cylinder 101, an oxygen gas cylinder 102 and a nitrogen gas cylinder 103. A fine-tuning control valve 11 is set at a front end of each of the gas cylinders 10 to be connected with the gas inlet tube 12 through the corresponding fine-tuning control valve 11. The hydrogen filling barrel 2 is used to form a hydrogen water solution. The barrel has a volume of 30 liters (L) and is made of SS316 stainless steel welded with an end plate to provide water source of the circuit and to be used as a buffer space for tolerating expansion and contraction of water in the circuit. The hydrogen filling barrel 2 has an enclosed space formed inside; and the hydrogen filling barrel 2 has a depressurizing valve group 21 at a top end to be connected with the enclosed space 20. The depressurizing valve group 21 comprises a first depressurizing valve 211, a second depressurizing valve 212 and a third depressurizing valve 213. The first, second and third depressurizing valves 211,212,213 are separately connected with the gas inlet tube 12, a first air-releasing tube 22 and a second air-releasing tube 23. A water level monitor meter 24 is set at a side of the hydrogen filling barrel 2, which has a upper valve 241 and a lower valve 242 separately connected with the enclosed space 20. At bottom of the hydrogen filling barrel 2, an outlet valve 25 is set to be connected with the enclosed space 20; and is connected with a gas-liquid inlet tube 26. The hydrogen water solution in the enclosed space 20 is drained out through the outlet valve 25 to be provided to the autoclave 3 through the gas-liquid inlet tube 26. The autoclave 3 simulates an environment of nuclear power plant water chemistry. The autoclave 3 has a furnace body 30 sealed by a top cover 31 having an insulated joint 311. Thus, a containing space 32, which is able to be sealed, is formed within the autoclave 3 and is connected with the gas-liquid inlet tube 26 and the second air-releasing tube 23. Inside the autoclave 3, there are wires 33 for spot-welding the to-be-detected steel materials 6. The wires 33 penetrate through the insulated joint 311 to reach out of the top cover 31 of the autoclave 3 to be connected with the ECP analyzer 4 and the electrochemical AC impedance analyzer 5. Therein, the autoclave 3 simulates the environment of nuclear power plant water chemistry at a pressure of 1050 Psi and a temperature of 288° C., whose inside water environment has a dissolved oxygen amount between 200 and 400 ppb, a dissolved hydrogen amount between 0.1 and 2 ppm, an electrical conductivity not bigger than 0.1 μS/cm and a pH value between 6.5 and 7.3. Reactants in the autoclave 3 are cycled and drained out to the hydrogen filling barrel 2 through the second air-releasing tube 23. The ECP analyzer 4 uses the to-be-detected steel materials 6 as working electrodes to detect ECP of the to-be-detected steel materials 6. Therein, the to-be-detected steel materials 6 is made of stainless steel, whose ECP is controlled to be not bigger than −0.23V on comparing to a voltage of a standard hydrogen electrode. The to-be-detected steel materials 6 comprise an uncoated steel, an oxidized-film coated steel, a Pd-coated steel, a Pt-coated steel and a Rh-coated steel. The electrochemical AC impedance analyzer 5 provides AC signals having different frequencies for detecting characteristics of impedances of the to-be-detected steel materials 6 to acquire coating conditions of the to-be-detected steel materials 6 under the environment of nuclear power plant water chemistry. Hence, safety conditions of the to-be-detected steel materials 6 coated with precious metal films are acknowledged. Thus, a novel nuclear power plant steel detecting device is obtained. The to-be-detected steel materials 6 is made of SS304, including uncoated steel, 304SS-perfilmed, 304-NMCA-800 ppbFe2O3, 304-NMCA-400 ppbFe2O3, 304-NMCA-200 ppbFe2O3, 304-NMCA-NoFe2O3 and six different steels coated with Pd, Pt and Rh. The to-be-detected steel materials 6 are spot-welded with 0.5 φmm wires 33 at rims. The wires 33 are made of stainless steel heated by a blowtorch for being tightly coated with shrinkable insulated tube. On using the present disclosure, a nuclear power plant using boiling water reactors (BWR) are simulated with a detecting circuit built with the above components. Under an environment of hydrogen water chemistry (HWC) for sensitize 304 steel and steels coated with different precious metals of Pd, Pt and Rh, hydrogen are blown into water to obtain different concentrations of dissolved oxygen and to record ECP values of the coated steels for acquiring effect of preventing intergranular stress corrosion cracking (IGSCC) of the BWR by coating internal components with the precious metal film. In a first stage, the gas mixing tube 1 and the hydrogen filling barrel 2 are used to adjust amount of dissolved oxygen in water and monitor water quality for simulating high-pressure high-temperature water environment in the reactor core of the BWR on coating oxidized films on the steels. At first, water is filled into the hydrogen filling barrel during a normal operation. Then, nitrogen is transferred to the hydrogen filling barrel 2 by the nitrogen gas cylinder 103 though the gas mixing tube 1 with fine-tuning and depressurizing for blowing out dissolved oxygen in water. Then, the gas cylinders 10 are used to add hydrogen, oxygen and nitrogen into water to reach a dissolved oxygen concentration, a dissolved oxygen concentration, an electrical conductivity and a pH value in water of the hydrogen filling barrel 2 for required water quality for HWC in the BWR. Therein, the high-pressure high-temperature water environment in the reactor core of the BWR comprises a dissolved oxygen amount between 200 and 400 ppb, a dissolved hydrogen amount between 0.1 and 2 ppm, a electrical conductivity not bigger than 0.1 μS/cm and a pH value between 6.5 and 7.3 for processing in the autoclave 3 for 720 hours at a temperature of 288° C., a volume of 2 litters and a pressure of 1050 Psi. In a second stage, under simulated water environments having different dissolved oxygen amounts while filling hydrogen to different concentrations, the working electrodes are assembled with different steel materials 6 coated with Pd, Pt and Rh (as the above mentioned six steels) to detect and record values of ECP and AC impedance of the uncoated steel, the oxidized-film coated steel, the Pd-coated steel, the Pt-coated steel and the Rh-coated steel under the same water environment. Therein, the ECP values are detected through a two-electrode method by the ECP analyzer 4. Because two reversible half-cell reactions are both happened on a surface of each of the to-be-detected steel materials 6 during redox, the ECP analyzer 4 detects potentials on the surface to obtain a mixed potential as a surface ECP value of each of the to-be-detected steel materials 6. The ECP analyzer 4 connects its positive electrode on each of the to-be-detected steel materials 6 as a working electrode and its negative electrode on a reference electrode (not shown in the FIGURE). Then, the high-impedance potential meter 40 (voltmeter) and the multi-channel scanner 41 (Keithley7001) are connected with the wires 33. An ECP value of each of the to-be-detected steel materials 6 is detected per minute and changes on potentials are digitally outputted to a data processor through RS232 to be recorded. In addition, for temperature and pressure safety of the detecting circuit, the present disclosure can further comprise a control device 7 connected with the autoclave 3, where the control device 7 comprises a temperature controller 70 and a pressure detector 71. Therein, the temperature controller 70 is used to prevent temperature of the detecting circuit from too high. When the temperature exceeds a first alarm setting of 300° C., a heating power supply is automatically switched off. When the temperature exceeds a second alarm setting of 310° C., the detecting circuit is automatically stopped running. The pressure detector 71 is used to prevent pressure in the detecting circuit from too high. When the pressure exceeds a third alarm setting of 1250 Psi, the detecting circuit is automatically stopped running and the third depressurizing valve 213 releases vapor for depressurizing. When the pressure exceeds a fourth alarm setting of 1300 Psi, the second and the third depressurizing valves 212,213 are both opened to release vapor. Moreover, for safety on filling hydrogen, the present disclosure can further comprises a hydrogen explosion-proof barrel 8 with the first air-releasing tube 22 connected with the hydrogen explosion-proof barrel 8 for detecting concentration of leaked hydrogen. When the concentration of leaked hydrogen exceeds a preset value, alarm is automatically turned on to prevent explosion. Therein, the hydrogen explosion-proof barrel 8 is filled with water to a ¾ water level and an end of the first air-releasing tube 22 is connected with a one-way outlet valve 221 to be inserted into water for safely releasing extra gas out of water surface through a seal principle while the barrel is kept sealed. Hence, for acquiring workability and effect of metal coating technology, the present disclosure simulates a detecting circuit of ECP and AC impedance built in a BWR to acquire effect of applying precious metal through HWC, where a corrosion environment for different to-be-detected steel materials, including an uncoated steel, an oxidized film steel, a Pd-coated steel, a Pt-coated steel and a Rh-coated steel, is used to simulate BWR water environment and changes of the water after added with hydrogen. An ECP analyzer is used to detect ECP values of the to-be-detected steel materials. Under the simulated BWR water environment, the ECP values of the to-be-detected steel materials each having a dissolved oxygen amount between 200 and 400 ppb are detected; changes on ECP values of the to-be-detected steel materials each having a hydrogen filling concentration between 0.1 and 2 ppm are detected; and changes on ECP values of the to-be-detected steel materials each being coated with precious metal film for reducing the hydrogen filling concentration are detected. The data obtained through detection thus provides important reference on whether to apply precious metal chemistry technology or not. To sum up, the present disclosure is a nuclear power plant steel detecting device, where nuclear power plant water chemistry is used to simulates a detecting circuit of ECP and AC impedance for acquiring effect of preventing IGSCC of BWR by coating internal components with precious metal film through HWC. The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the disclosure. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present disclosure. |
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abstract | The invention relates to a process for treating unwanted moderately saline waters for producing waters acceptable for treating soil, such as for irrigation. The treated water is also suitable for human and livestock consumption. The process includes passing moderately saline waters having 0.05% or more by weight and less than 1.00% by weight of the salts of Na, K, Ca, Mg, Fe, Cl, SO4, or CO3 or combinations thereof through an ion exchange resin. The ion exchange resin is pre-treated to be saturated with multivalent cations. Preferred multivalent cations include calcium (Ca2+) or magnesium (Mg2+) ions, or combinations thereof. After passing through the ion exchange resin, the effluent has decreased sodium cations and increased calcium and/or magnesium cations compared to the pre-treated moderately saline water. As the moderately saline waters passes through the ion exchange resin, the sodium content of the resin rises as the multivalent cation content lowers until the resin is unacceptable for further water treatment in accordance with the present invention. To regenerate the ion exchange resin, the resin is flushed with a brine solution having more than 1.00% by weight of the salts of Na, K, Ca, Mg, Fe, Cl, SO4, or CO3. Preferably, the brine is particularly high in calcium and/or magnesium content and low in sodium. The brine solution is flushed through the ion exchange resin until the ion exchange resin is sufficiently saturated with multivalent cations to again process moderately saline water having high sodium content. |
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claims | 1. A method for fault data correlation in a diagnostic system, comprising:receiving the fault data including a plurality of faults collected over a period of time;identifying a plurality of episodes within the fault data, wherein each episode includes a sequence of the faults;calculating a frequency of the episodes within the fault data;categorizing each of the episodes as an episode type, wherein the episode type is one of a well-known episode, an expected episode, and an unexpected episode;calculating a correlation confidence of the faults relative to the episodes as a function of the frequency of the episodes;outputting a report of the faults with the correlation confidence; andfiltering the report as a function of the episode type. 2. The method of claim 1 wherein the fault data includes a temporal data series comprising events with start times and end times, a set of allowed dwelling times, and a threshold frequency. 3. The method of claim 2 further comprising:finding all frequent principal episodes of a particular length in the temporal data series having dwelling times, as determined by the start and end times, within the allowed dwelling times;in successive passes through the temporal data series:incrementing the particular length to generate an increased length;combining frequent principal episodes to create combined episodes of the increased length;creating a set of candidate episodes from the combined episodes by removing combined episodes which have non-frequent sub-episodes;identifying one or more occurrences of a candidate episode in the temporal data series;incrementing a count for each identified occurrence;determining frequent principal episodes of the increased length; andsetting the particular length to the increased length; andproducing an output for frequent principal episodes;wherein a frequent principal episode is a principal episode whose count of occurrences results in a frequency meeting or exceeding the threshold frequency. 4. The method of claim 1 further comprising:identifying an initial fault in the sequence of faults in one of the episodes as a root cause; andreporting the root cause. 5. The method of claim 1 further comprising:calculating downtime as time duration between an initial fault and a final fault in the sequence of faults in one of the episodes; andreporting the downtime. 6. The method of claim 1 wherein the fault data is limited to a selected period of time. 7. A system for fault data correlation in a diagnostic system, the system comprising:a host system;a data storage device in communication with the host system, the data storage device holding fault data; anda temporal data mining (TDM) diagnostics tool executing on the host system, the TDM diagnostics tool including computer instructions for performing:receiving the fault data including a plurality of faults collected over a period of time;identifying a plurality of episodes within the fault data, wherein each episode includes a sequence of the faults;calculating a frequency of the episodes within the fault data;categorizing each of the episodes as an episode type, wherein the episode type is one of a well-known episode, an expected episode, and an unexpected episode;calculating a correlation confidence of the faults relative to the episodes as a function of the frequency of the episodes;outputting a report of the faults with the correlation confidence; andfiltering the report as a function of the episode type. 8. The system of claim 7 wherein the fault data includes a temporal data series comprising events with start times and end times, a set of allowed dwelling times, and a threshold frequency. 9. The system of claim 8 wherein the TDM diagnostics tool further performs:finding all frequent principal episodes of a particular length in the temporal data series having dwelling times, as determined by the start and end times, within the allowed dwelling times;in successive passes through the temporal data series:incrementing the particular length to generate an increased length;combining frequent principal episodes to create combined episodes of the increased length;creating a set of candidate episodes from the combined episodes by removing combined episodes which have non-frequent sub-episodes;identifying one or more occurrences of a candidate episode in the temporal data series;incrementing a count for each identified occurrence;determining frequent principal episodes of the increased length; andsetting the particular length to the increased length; andproducing an output for frequent principal episodes;wherein a frequent principal episode is a principal episode whose count of occurrences results in a frequency meeting or exceeding the threshold frequency. 10. The system of claim 7 wherein the TDM diagnostics tool further performs:identifying an initial fault in the sequence of faults in one of the episodes as a root cause; andreporting the root cause. 11. The system of claim 7 wherein the TDM diagnostics tool further performs:calculating downtime as time duration between an initial fault and a final fault in the sequence of faults in one of the episodes; andreporting the downtime. 12. The system of claim 7 wherein the fault data is limited to a selected period of time. 13. A computer program product for fault data correlation in a diagnostic system, the computer program product comprising:a storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for implementing a method, the method comprising:receiving the fault data including a plurality of faults collected over a period of time;identifying a plurality of episodes within the fault data, wherein each episode includes a sequence of the faults;calculating a frequency of the episodes within the fault data;categorizing each of the episodes as an episode type, wherein the episode type is one of a well-known episode, an expected episode, and an unexpected episode;calculating a correlation confidence of the faults relative to the episodes as a function of the frequency of the episodes;outputting a report of the faults with the correlation confidence; andfiltering the report as a function of the episode type. 14. The computer program product of claim 13 wherein the fault data includes a temporal data series comprising events with start times and end times, a set of allowed dwelling times, and a threshold frequency. 15. The computer program product of claim 14 further comprising:finding all frequent principal episodes of a particular length in the temporal data series having dwelling times, as determined by the start and end times, within the allowed dwelling times;in successive passes through the temporal data series:incrementing the particular length to generate an increased length;combining frequent principal episodes to create combined episodes of the increased length;creating a set of candidate episodes from the combined episodes by removing combined episodes which have non-frequent sub-episodes;identifying one or more occurrences of a candidate episode in the temporal data series;incrementing a count for each identified occurrence;determining frequent principal episodes of the increased length; andsetting the particular length to the increased length; andproducing an output for frequent principal episodes;wherein a frequent principal episode is a principal episode whose count of occurrences results in a frequency meeting or exceeding the threshold frequency. 16. The computer program product of claim 13 further comprising:identifying an initial fault in the sequence of faults in one of the episodes as a root cause; andreporting the root cause. 17. The computer program product of claim 13 further comprising:calculating downtime as time duration between an initial fault and a final fault in the sequence of faults in one of the episodes; andreporting the downtime. |
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summary | ||
abstract | An apparatus is disclosed for annealing only a portion of an elongated tubular workpiece. The apparatus includes an elongated tube dimensioned to receive the workpiece so that a first end of the workpiece together with the portion to be annealed is positioned within the tube while a second end of the workpiece extends outwardly from the tube. An induction coil is disposed coaxially around only a portion of the workpiece portion exteriorly of the tube while a source of pressurized nitrogen/hydrogen is fluidly connected to the interior of the tube. In an annealing operation, the tube is filled with hydrogen/nitrogen and the induction coil is energized thus heating only the portion of the workpiece for which annealing is desired. Simultaneously, hydrogen/nitrogen flows through the tube thus cooling the workpiece and maintaining an oxygen-free environment within the tube. |
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046559922 | summary | BACKGROUND OF THE INVENTION This invention relates to ultrasonic temperature measurement. The invention has arisen in consideration of the severe problems that arise in measuring temperature of coolant flowing in a fast-fission nuclear reactor cooled by liquid sodium. Monitoring of coolant temperature is not only vital for normal control purposes but it is also vital for safety purposes as temperature trends and transients can foreshadow the onset of incidents like blockage of coolant flow which might cause solid nuclear fuel to melt if corrective or preventative action is not taken. Various solutions to these problems have been considered such as reliance on flowmeter or thermocouple readings or by the acoustic detection of coolant boiling. However, with these known solutions uncertainties may arise especially where the normal flow is low, or there is cross-flow in which a normal flow could mask an abnormal flow. These uncertainties are increased when, as is often the case, the flow or temperature measuring device cannot be located precisely at the most sensitive localities (which are usually the discharge points of flow from defined channels into bulk zones) because of access or obstruction problems. Whilst, current practice does not itself involve any hazards, as the acceptable margin of safety can be suitably achieved, improved standard is continuously being sought. The present invention provides such an improved standard by the use of ultrasonics which may either replace or work in harness with known systems. The use of ultrasonic techniques to measure temperature is well known--see, for example, British Patent Specifications Nos. 2114299, 2002118, 1300159, 1202182, 1178529, 1178385 and 1035763. Patent No. 1300159, for instance, is specifically concerned with a device for ultrasonic measurement of the temperature of liquid metal coolant within a nuclear reactor. Such a device suffers from the drawback that it is invasive in the sense that the hardware is physically located at the position at which the temperature measurement is to be made and therefore interferes with the flow conditions prevailing at that position. FEATURES AND ASPECTS OF THE INVENTION According to the present invention there is provided a method of measuring temperature within a body of fluid in which ultrasound is transmitted through the fluid and the time taken for the ultrasound to traverse a known distance is translated into a corresponding temperature value, said method being characterised in that, to measure temperature at a selected zone or zones within said body of fluid, which zone or zones are demarcated by elements located at a known separation distance or distances within a containment structure for said body of fluid; (a) ultrasound is launched into the fluid medium at a location which is physically discontiguous with said zone(s) whereby the ultrasound propogates towards said zone(s) and undergoes reflection by said elements; and (b) the resulting ultrasound echoes are identified as being derived from a particular zone or zone(s) and the elapsed time therebetween is translated into a temperature value. The invention takes as its starting point the known fact that the sonic velocity is sodium (or other liquid for that matter) is a function of its temperature. The invention uses ultrasonic beams from an interrogating ultrasonic transducer or transducers which can be sighted on said elements (for example the opposite sides of a channel containing nuclear fuel swept by sodium coolant or reflectors specifically in the channel). By measurement of the time difference between echoes received back from the elements demarcating each zone, together with a knowledge of the distance apart of the elements, sonic velocity can be calculated and hence the means temperature between those points determined. It is also possible, because of the short time required to make a measurement, to monitor temporal fluctuations ("temperature noise" as it is sometimes called) which is a sensitive method of detecting local overheating. The beams from the interrogating transducers may be sighted to be penetrating or to be at a glancing incidence, the latter being very advantageous for measuring temperatures at an outlet from a channel. Where a number of zones lie on a common line which can be sighted along by a single interrogating transducer beam, it is possible for a number of temperature measurements to be taken and presented or recorded simultaneously. Interrogating transducers may be individual to each zone, or they may be arranged, e.g. on a sweep arm, so as to scan a multiplicity of zones. |
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