Nuclear fuel assembly

Abstract: A nuclear fuel assembly comprises an upper tie plate, a lower tie plate; and a plurality of fuel rods having opposite ends thereof held by said upper tie plate and said lower tie plate, the upper tie plate having a first nuclear fuel identification code (74B) and a second nuclear fuel identification code (74A) represented in a different manner from than that of the first nuclear fuel identification code, marked adjacently to each other, wherein the codes are suitable to be detected by different sensors, respectively.

Description: BACKGROUND OF THE INVENTION The present invention relates to a nuclear fuel assembly of the kind referred to in the preamble portion of claim 1. Such a fuel assembly is known from US-A-4 636 846. More particularly, the present invention relates to a nuclear fuel assembly which is adapted to be identified in a fuel storage pool. In the past, the identification of a nuclear fuel identification number of a fuel assembly loaded into a fuel storage pool has been effected by an operator by watching on a television monitor a video image taken by a marine TV camera. This is reported in Nuclear Technology, Vol. 72, March 1986, pp. 321 - 327. In the prior art method in which the video image of the TV camera is monitored through the TV monitor, there are some cases where it is not possible to identify the fuel identification number marked on the fuel assembly if clad (soft clad primarily consisting of Fe 2 O 3 ) is deposited on the fuel assembly. In US-A-4 636 846 an identification code of a nuclear fuel element according to the preamble of the independent claim is disclosed. Relying on optical principles, it suffers from the same disadvantages as the method described above. A solution to the above problem is disclosed in JP-A-57-53688, particularly Fig. 4 thereof. Eddy current sensors are inserted into recesses formed on a top surface of a handle of the fuel assembly to detect the fuel identification number. In the eddy current sensor disclosed in JP-A-57-53688, a detection accuracy of the sensor is lowered when a groove narrower than a diameter of the eddy current sensor or a hole having a narrower diameter than the diameter of the eddy current sensor is to be detected. Characters of 8 mm square size are engraved in a handle of a fuel assembly. A width of those curved characters is as narrow as approximately 1.6 mm. Accordingly, the detection accuracy of the nuclear fuel identification number by the eddy current sensor is low. Since the diameter of the eddy current sensor is usually approximately 5 - 10 mm, the reduction of the detection accuracy is inevitable. In the ultrasonic wave sensor disclosed in JP-A-60-207095, a signal processing time for detecting the nuclear fuel identification number is long and it is difficult to apply the sensor to a number of fuel assemblies in a fuel storage pool, which require a short response time. This is also true in a case where an eddy current sensor having a long signal processing time is used. JP-A-57-110994 is similar to JP-A-60-207095. SUMMARY OF THE INVENTION It is the object of the present invention to provide a nuclear fuel assembly bearing identification codes which are adapted to be identified by independent optical and ultrasonic nuclear fuel identification code readers in a short time and by redundancy with a high accuracy, also if the code is covered with a soft clad. The above object is achieved according to the present invention with a fuel assembly as claimed in claim 1. The dependent claims relate to features of preferred embodiments. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a nuclear fuel identification code reader; Fig. 2 shows an enlarged view of a portion II in Fig. 1; Fig. 3 shows a detailed block diagram of a nuclear fuel handling control unit, a nuclear fuel identification code monitor and a nuclear fuel identification code processing unit of Fig. 1; Fig. 4 shows a perspective view of a fuel assembly of Fig. 1; Fig. 5 shows a plan view of a handle of Fig. 4; Fig. 6 shows a VI-VI sectional view of Fig. 5; Fig. 7 illustrates a standard digital pattern of a nuclear fuel identification code of Fig. 5; Fig. 8 shows a reflected wave received by an ultrasonic wave probe 9 of Fig. 2. DESCRIPTION OF THE PREFERRED EMBODIMENTS A nuclear fuel identification code reader is now explained with reference to Figs. 1, 2 and 3. The nuclear fuel identification code reader comprises a sensor handling unit 1, an ITV camera 5, an ultrasonic wave probe 9, an ultrasonic wave probe scanner 10, a nuclear fuel handling control unit 22, a nuclear fuel identification code monitor 28 and a nuclear fuel identification code processing unit 43. The sensor handling unit 1 utilizes a portion of a nuclear fuel handling unit 51. The nuclear fuel handling unit 51 is used to move a used fuel assembly 66 in a fuel storage pool 63. The used fuel assembly 66 is taken out of a core of a nuclear reactor and loaded and stored in a fuel rack 65 arranged in the fuel storage pool 63. The fuel storage pool 63 is filled with water 64. The fuel rack 65 is arranged under a water level of the water 64. The nuclear fuel handling unit 51 is constructed to cross the fuel storage pool 63. The nuclear fuel handling unit 51 includes a movable truck 52, a laterally movable truck 53, a grapple 54, a clamp 55 and a hoist 56. The movable truck 52 is driven by a drive motor 58 on a pair of rails 57 arranged on both sides of the fuel storage pool 63. The laterally movable truck 53 has the grapple 54, the clamp 55 and the hoist 56 and is driven by a drive motor 60 on a pair of rails 59 arranged on the movable truck 52. The grapple 54 is raised and fallen by the hoist 56 and a drive motor 62. The grapple 54 is rotated by a drive motor 61 to allow adjustment of an angle of the clamp 55 in a horizontal plane. The drive motor 61 is mounted on the laterally movable truck 53. The grapple 54 is constructed by several linked expandable pipes. The lamp 55 is mounted at the bottom end of the grapple 54. A direction of movement of the movable truck 52 is represented by X, a direction of movement of the laterally movable truck 53 is Y, the elevation of the grapple 54 is represented by Z 1 and the rotation is represented by  1 . Position signals representing the displacements X, Y, Z 1 and  1 are detected by synchronous signal generators (not shown) mounted on the respective drive shafts of the fuel handling unit 51. The sensor handling unit 1 has a hoist 2, a drive motor 3 and a grapple 4. The hoist 2, the drive motor 3 and the grapple 4 are mounted on the movable truck 53. A drive motor (not shown) which corresponds to the drive motor 61 and serves to rotate the grapple 4 is mounted on the laterally movable truck 53. The grapple 4 is also constructed by several linked expnadable pipes. The grapple 4 is moved up and down by the hoist 2 and the drive motor 3. The elevation of the grapple 4 is represented by Z 2 and the rotation is represented by  2 . Position signals representing the displacements Z 2 and  2 are detected by synchronous signal generators (not shown) mounted on the respective drive shafts of the sensor handling unit 1. A mount table 6 is arranged at the bottom end of the grapple 4. The ITV camera 5 is mounted on the mount table 6. Four downwardly extending frames 7 are fixed to the mount table 6 by screws. An illumination device 8 is arranged at the bottom ends of the frames 7. The ultrasonic wave probe scanner 10 is mounted on the mounted table 6 by an arm 11. A detailed structure of the ultrasonic wave probe scanner 10 is explained below. A drive motor 13 is mounted at a top of a bottom-opened box 12. An upwardly extending rotary screw 14 linked to a rotation shaft of the drive motor 13 meshes with a nut (not shown) mounted on a support member 16 which is mounted on the arm 11. A pair of guide members 15A and 15B which hold the rotary screw 14 therebetween are mounted on the drive motor 13. The guide members 15A and 15B extend through the support member 16 so that they are vertically movable. Another drive motor 17 is mounted on a side of the box 12 which faces the ITV camera 5. A rotary screw 18 horizontally arranged in the box 12 has one end thereof linked to a rotation shaft of the drive motor 17 and the other end thereof supported by a bearing (not shown) mounted on the side of the box 12. A probe holding table 19 engages with the rotary screw 18. Two ultrasonic wave probes 9 are mounted on the probe holding table 19. They are arranged to traverse the rotary screw 18. A pair of fixing guides 21 is arranged in the box 12. An encoder 20 measures the displacement of the ultrasonic wave probe 9 along the axis of the rotating screw 18. The ITV camera 5 and the ultrasonic wave probe 9 constitute a nuclear fuel identification code detection means. The nuclear fuel handling control unit 22 comprises input/output means 23A and 23B, a nuclear fuel handling unit control means 24, a nuclear fuel monitor unit control means 25, a memory 26 and a console panel 27. The input/output means 23A supplies control signals to the drive motors 58, 60, 61 and 62 and receives the position signals representing the displacements X, Y, Z 1 and  1 from the corresponding synchronous signal generators (not shown). The input/output means 23B supplies control signals to the drive motors 3, 58 and 60 and the drive motor (not shown) which drives the grapple 4, and receives the position signals representing the displacements X, Y, Z 2 and  2 from the corresponding synchronous signal generators (not shown). The input/ output means 23A inputs and outputs the signals related to the nuclear fuel handling unit control means 24, and the input/output means 23B inputs and outputs the signals related to the nuclear fuel monitor unit control means 25. The nuclear fuel handling unit control means 24 and the nuclear fuel monitor control means 25 are included in a computer 48. The nuclear fuel identification code monitor 28 has a video signal digitizer 29 and a signal processing microprocessor 30. The microprocessor 30 has a memory 33, an image processing means 31 and a nuclear fuel number identification/discrimination means 32. The video signal digitizer 29 is a kind of A/D converter which converts a video signal (analog signal) sent from the ITV camera 5 to a digital signal. The video signal digitizer 29. The image signal processing means 31 and the fuel number identification/discrimination means 32 are coupled to the input/output means 23B. The nuclear fuel identification code monitor 28 thus constructed identifies the nuclear fuel identification code based on the video signal derived from the ITV camera 5. The nuclear fuel identification code monitor 34 comprises a pulse generation means 35, a signal receive means 36, a probe scanner control means 38 which is constructed by a microprocessor, and a signal processing microprocessor 39. The microprocessor 39 has an ultrasonic wave signal processing means 40, a nuclear fuel number identification means 41, and a memory 42. The pulse generation means 35 is connected to the ultrasonic wave probe 9 and the probe scanner control means 38. The signal receive means 36 is connected to the ultrasonic wave probe 9 and the ultrasonic wave signal processing means 40. The ultrasonic wave signal processing means 40 is coupled to the encoder 20. The probe scanner control means 38 is connected to the drive motors 13 and 17, the encoder 20 and a limit switch 37, and further to the input/output means 23B. The nuclear fuel identification code monitor 34 thus constructed identifies the nuclear fuel identification code based on the reflected wave of the ultrasonic wave derived from the ultrasonic wave probe 9. The nuclear fuel identification code processing unit 43 comprises a fuel number processing means 44 and a memory 45. A numeral 46 denotes a display and a numeral 47 denotes a printer. The display 46 may be mounted on the console panel 27. A structure of the fuel assembly 66 loaded in the fuel rack 65 is explained with reference to Fig. 4. The fuel assembly 66 loaded in the fuel rack 65 is an assembly of used fuel which is taken out of a center of a boiled-water type nuclear reactor. The fuel assembly 66 comprises an upper tie plate 67, a lower tie plate 69, a plurality of fuel rods 70 and a plurality of fuel spacers 71. The top and bottom ends of the fuel rods 70 are held by the upper tie plate 67 and the lower tie plate 69. The fuel spacers 71 are arranged axially of the fuel assembly 66 to keep a predetermined spacing between the fuel rods 70. A channel box 68 mounted on the upper tie plate 67 surrounds a bundle of fuel rods 70 supported by the fuel spacers 71. The upper tie plate 67 has a handle 72 arranged at the top thereof. A nuclear fuel identification number 74 is marked on the top 73 of the handle 72. As shown in Figs. 5 and 6, the nuclear fuel identification number 74 includes a nuclear fuel identification number 74A coded by recesses 75 having circular cross-sections, and a nuclear fuel identification number 74B which is a combination of alphanumeric characters. Those two types of nuclear fuel identification numbers are marked in parallel on the top 73 of the handle 72. The nuclear fuel identification number 74B can be recognized by a human when he/she looks it but the nuclear fuel identification number 74A cannot be recognized by the human by just looking it. Both of the nuclear fuel identification numbers 74A and 74B are marked by engraving on the top 73 of the handle 72. The nuclear fuel identification number 74A is a combination of the recesses 75 which corresponds to the nuclear fuel identification number 74B. The cross-section of the recess 75 need not necessary be circular but it may be trianglar, square or rectangular, or even oval. In the nuclear fuel identification number 74A, each area sectioned by broken lines 76 corresponds to one character. In Fig. 5, the nuclear fuel identification number 74A represents "2FABC". Each coded symbol of the nuclear fuel identification number 74A is represented by the combination of up to six recesses 75 (two lines of three recesses). Each symbol of the nuclear fuel identification number 74A is a digital signal represented by the presence or absence of the recess 75. Fig. 7 shows a correspondence between the digitized symbols representing the nuclear fuel identification number 74A and the alphanumeric characters (0 - 9, A - Z). In Fig. 7, the black dot represents the presence of the recess 75 and a white dot represents the absence of the recess 75. It is possible to digitize 36 alphanumeric characters by arranging six recesses 75 (two lines of three recesses) as shown in Fig. 7. A plurality of digital symbols shown in Fig. 7 may be arranged on the top 73 in combination with the characters of the nuclear fuel identification number 74B. Assuming that a diameter of the recess 75 is approximately 1 mm and a spacing W 1 between the recesses 75 in one digital symbol is at least approximately 1 mm, the presence or absence of the recess 75 can be detected by the ultrasonic wave. Since a spacing W 2 between lines of recesses 75 is approximately 3 mm, the nuclear fuel identification number 74A and the nuclear fuel identification number 74B can be marked in parallel on the top 73 having a width of approximately 12 mm. A recess 76 which is used as a reference to read the nuclear fuel identification number 74A is formed on the top 73 of the handle 72. The recess 76 is orthogonal to the side of the handle 72 and it is positioned on the left of the first digital symbol of the nuclear fuel identification number 74A. Without the recess 76, the nuclear fuel identification code monitor 34 cannot specify the nuclear fuel identification number 74A detected by the ultrasonic wave. In the example shown in Fig. 5, the nuclear fuel identification number 74A may be read as either "2FABC" or "CBAF2". If it is determined that the nuclear fuel identification number 74A is to be read from the end adjacent to the recess 76, the number 74 is read as "2FABC". A width W 3 of the recess 76 is either wider or narrower than a width W 4 (diameter) of the recess 75 so that the nuclear fuel identification code monitor 34 can easily discriminate the recess 75 of the digital symbol and the recess 76 of the read reference. The recess 76 need not be linear but it may be circular, triangular or square in cross-section so long as it is positioned on the left of the lines of recesses 75. The fuel assembly 66 having the nuclear fuel identification numbers 74A and 74B marked in parallel on the top 73 of the handle 72 is loaded into the center of the boiled-water type nuclear reactor after the used fuel assembly 66 has been removed from the center of the reactor. The operation of the nuclear fuel identification code reader of the present invention is now explained. An operator specifies, through the console panel 27, the operation of the nuclear fuel handling or the operation of the detector for the nuclear fuel identification code. The specified operation signal is supplied to the computer 48. If the former operation is specified, the nuclear fuel handling unit control means 24 is activated, and if the latter operation is specified, the nuclear fuel monitor control means 25 is activated. It is now assumed that the specified operation is the operation of nuclear fuel handling. Before the function of the nuclear fuel handling unit control means 24 is explained, the operation of the nuclear fuel handling unit 51 in the nuclear fuel handling operation is briefly explained. A plurality of used free assemblies 66 are carried to a predetermined postion in the fuel storage pool 63 from the top thereof while they are loaded in a container. Then, the movable truck 52 and the laterally movable truck 53 are driven to move the clamp 55 above the container. As the grapple 54 descends, the clamp 55 is lowered to the position of the handle 72 of the fuel assembly 66 in the container. After the clamp 55 has held the handle 72, the grapple 54 is raised. When the bottom end of the fuel assembly 66 reaches a level which is a predetermined distance above the top end of the fuel rack 65, the elevation of the grapple 54 is stopped. The movable truck 52 and the laterally movable truck 53 are again driven to move the fuel assembly 16 to a level which is a predetermined distance (specified by the operator through the console panel 27) above the fuel rack 65. When it reaches that level, the grapple 54 is lowered to load the fuel assembly 66 to a predetermined position in the fuel rack 65. The above movement is referred as a movement 1 ○. When the fuel assembly is taken out of the fuel storage pool 63 for fuel processing, the opposite movement (movement 2 ○) is carried out. Namely, the fuel assembly 66 taken out of the fuel rack 65 is loaded into the container. The clamp 55 may be moved, while it does not clamp the fuel assembly 66, from the position of the fuel rack 65 to other position (movement 3 ○), from the position of the fuel rack 65 to the position of the container (movement 4 ○), or from the position of the container to the position of the fuel rack 65 (movement 5 ○). The memory 26 stores data relating to the loading status of the fuel assembly 66 at the respective positions (X-Y ID coordinate) of the fuel rack 65. The memory 26 stores "0" for the position at which the fuel assembly 66 is not loaded, and "1" for the position at which the fuel assembly 66 is loaded. The ID coordinate is not represented by absolute distances on X and Y axises but it is represented by the code applied to the fuel assembly load position. The position signals representing the displacements X, Y, Z 1 and  1 measured by the synchronous signal generators are converted to the digital signals by the input/output means 23A and they are supplied to the nuclear fuel handling unit control means 24 of the computer 48. A limit switch (not shown) mounted on the nuclear fuel handling unit 51 detects when the grapple 55 reaches a grapple upper limit level A and a mount level B of the fuel assembly (in the fuel rack 65 and the container). The detection signal is supplied to the computer 48. The nuclear fuel handling unit control means 24 uses those signals to control and monitor the position of the nuclear fuel handling unit 51. When the used fuel assembly 66 is to be moved in the fuel storage pool 63, the operator specifies N target positions (X-Y ID coordinate) necessary for the fuel handling unit 51 to move the fuel assembly 66, through the console panel 27. The P ℓ or P which is shown in JP-B-58-21238, column 6, lines 8-10 is also specified through the console panel 27. The nuclear fuel handling unit control means 24 discriminates in the manner described and shown in JP-B-58-21238, column 7, line 26 to column 8, line 11 and Figs. 3 and 4. That is, the load status of the fuel assembly 66 at the target position, the correctness of the data (P ℓ or P) specified by the operator and the open/close status of the clamp 55 are checked, and if the check result is normal, the control signal for the corresponding movement (one of the movements 1 ○ - 5 ○) is supplied to the nuclear fuel handling unit 51 to control the corresponding movement. If the check result is not normal, the nuclear fuel handling unit control means 24 inhibits the start of the nuclear fuel handling unit 51. When the fuel assembly 66 is moved by the nuclear fuel handling unit 51, the data on the load status of the fuel assembly 66 at the respective positions of the fuel rack 65, which is stored in the memory 26, is updated as the movement proceeds. When the operator specifies the operation of the detector for the nuclear fuel identification code, the nuclear fuel monitor unit control means 25 moves the sensor handling unit 1. One of the pair of ultrasonic wave probes 9 mounted on the probe support table 19 moves on an extended line of an arrow R 1 (Fig. 5) and the other moves on an extended line of an arrow R 2 which is parallel to the arrow R 1 . In the present embodiment, the pair of ultrasonic wave probes 9 can substantially simultaneously detect the two lines of recesses 75 of the nuclear fuel identification number 74A. When the ultrasonic wave probe 9 reaches the end point of scan, it is detected by the encoder 20. The detection signal (position signal of the ultrasonic wave probe 9) of the encoder 20 is supplied to the probe scanner control means 38. When the ultrasonic wave probe 9 reaches the end point of scan, the probe scanner control means 38 stops the drive motor 17 and produces an end of ultrasonic wave scan signal E 1 (step 80E). After the step 80F, it drives the drive motor 13 to elevate the ultrasonic wave probe 9 to a predetermined position (step 80G). Then the detection of the nuclear fuel identification number 74A by the ultrasonic wave probe 9 is terminated. As described above, the ultrasonic wave probe 9 irradiates the ultrasonic wave to the top 73 of the handle 72 and receives the reflected ultrasonic wave from the top 73. A relationship between a horizontal position of the ultrasonic wave probe 9 driven by the drive motor 17 and the reflected ultrasonic wave is shown in Fig. 8. The reflected wave in Fig. 8 is detected by the ultrasonic probe 9 which is moved on the extended line of the arrow R 1 . The ultrasonic wave generated by the ultrasonic wave probe 9 is mostly reflected by the area of the top 73 which has no recess 75, and the reflected ultrasonic wave is received by the ultrasonic wave probe. However, since the bottom of the recess 75 is arcuate as shown in Fig. 6, the ultrasonic wave is scattered in the area of recess 75 and little reflected wave reaches the ultrasonic wave probe 9. Accordingly, the amplitude of the reflected wave is zero in the area of recess 75. Clad may deposit on the top 73 of the handle 72 of the fuel assembly 66 which fuel assembly is loaded in the center of the nuclear reactor and a portion of the recesses 75 may be covered by the clad. Even if the recesses 75 on the top 73 of the handle 72 of the fuel assembly 66 loaded in the fuel rack 65 are covered by clad, it is possible to detect the recesses 75 by the ultrasonic wave. This is due to the fact that there is no substantial difference between acoustic impedances of water and water-containing clad (primary constituent is ferric oxide). The reflected wave signal detected by the ultrasonic wave probe 9 is supplied to the signal receive means 36. In the reflected wave signal of Fig. 8, a zero reflected wave output area having a width W 3 corresponds to the recess 76 which is the read reference recess. Other zero reflected wave output areas correspond to the recesses 75. As a method for detecting the digitized recesses 65 of the nuclear fuel identification number 74A, one of the following methods may be adopted: 1) two-dimensionally scanning one ultrasonic wave probe, 2) linearly scanning a plurality of parallelly arranged ultrasonic wave probes, and 3) two-dimensionally scanning the ultrasonic wave beam by electronically switching ultrasonic wave probes by using an array sensor having a plurality of ultrasonic wave probes arranged two-dimensionally to cover the entire area of the nuclear fuel identification number 74A. The present embodiment adopts the method 2).

Claims: A fuel assembly (66) comprising an upper tie plate (67) having as a first nuclear fuel identification code an optically readable character code (74B), a lower tie plate (69) and a plurality of fuel rod (70) having opposite ends thereof held by said upper tie plate and said lower tie plate, characterized in that the upper tie plate (67) has further as a second nuclear fuel identification code (74A) ultrasonically detectable recesses, (75) marked adjacently to the optically readable characters (74B). A fuel assembly according to claim 1, characterized in that the upper tie plate (67) includes a handle (72) having the first nuclear fuel identification code expressed by characters (74B) and the second nuclear fuel identification code (74A) of the corresponding content expressed by a plurality of separate recesses (75). A fuel assembly according to claim 2, characterized in that on top of the handle (72) an additional recess (76) is formed, having a width different from the width of the recesses constituting the second nuclear fuel identification code (74A) and serving as a read reference for the second nuclear fuel identification code.

Inventors: MAKI HIDEO, OMOTE TATSUYUKI, SENOH MAKOTO, TAKAHASHI FUMINOBU, TSUCHITA KENJI, YOSHIDA TOMIHARU, MAKI, HIDEO, OMOTE, TATSUYUKI, SENOH, MAKOTO, TAKAHASHI, FUMINOBU, TSUCHITA, KENJI, YOSHIDA, TOMIHARU
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1989
Main classification: G21C17
IPC codes: G21C17