Patent Number: 
Section: claims

1. 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; anda double indexing path selector unit includinga 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, andinner 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. 2. The neutron flux mapping system according to claim 1, wherein the geared motor comprises an induction motor adapted to be controlled by an inverter. 3. The neutron flux mapping system according to claim 1, wherein:each driver further includes means for bring the helical gear into close contact with the detector cable; andthe means comprises at least one idle gear. 4. The neutron flux mapping system according to claim 3, wherein the at least one idle gear comprises:a first idle gear arranged to face the helical gear in a horizontal direction; anda second idle gear arranged to face the helical gear in a vertical direction. 5. The neutron flux mapping system according to claim 4, wherein the second idle gear is arranged toward the detector cable outlet in advance of a vertical center line of the helical gear by a predetermined angle. 6. The neutron flux mapping system according to claim 1, wherein each driver further includes an AC torque motor adapted to drive the storage reel. 7. The neutron flux mapping system according to claim 1, wherein each driver further includes an acoustic vibration sensor. 8. The neutron flux mapping system according to claim 1, wherein:the upper fixed plate is provided with stop plates; andthe control unit of the upper rotating plate is provided with limit switches, which selectively come into contact with the stop plates, respectively. 9. The neutron flux mapping system according to claim 8, wherein the stop plates are arranged to allow the upper rotating plate to rotate through a predetermined angle in a reciprocating manner. 10. The neutron flux mapping system according to claim 8, wherein:the control unit of the upper rotating plate is provided with a latch; andthe upper fixed plate of the selector unit body is provided with latch rods engagable with the latch. 11. The neutron flux mapping system according to claim 10, wherein the control unit further includes a plurality of limit switches adapted to detect a rotated position of the upper rotating plate in cooperation with the latch rods. 12. The neutron flux mapping system according to any one of claims 8 to 11, wherein the control unit further includes an acoustic vibration sensor. 13. The neutron flux mapping system according to any one of claims 1 to 8, wherein the driving unit and the control unit are mounted on an upper surface of the upper rotating plate. 14. The neutron flux mapping system according to claim 1, wherein:each inner path selector further includes 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 includes a plurality of path select switches arranged around the disc to correspond to the paths, respectively, each of the path select switches sensing alignment of a corresponding one of the paths with the path select tubing, thereby generating a sensing signal; andthe indexing mechanism is driven by a geared motor controlled by the sensing signal. 15. The neutron flux mapping system according to claim 14, wherein the plurality of path select switches are connected in the form of a matrix arrangement while being coupled to an input module included in a control system. 16. The neutron flux mapping system according to claim 15, wherein the control system controls the geared motor of the indexing mechanism, based on signals received from the path select switches. 17. The neutron flux mapping system according to claim 16, wherein:the indexing mechanism further includes a cam switch adapted to perform an ON/OFF operation every time the indexing mechanism rotates a predetermined unit angle; andthe control system checks, based on a signal generated in accordance with the ON/OFF operation of the cam switch, whether or not the indexing mechanism and the path select switches operate normally. 18. The neutron flux mapping system according to claim 17, wherein, when the index mechanism or one of the path select switches operates abnormally, the control system performs a control operation for treating, as being in a failure state, the inner path selector associated with abnormally-operating the index mechanism or path select switch, withdrawing the associated detector to a predetermined position when the detector has been inserted into the inner path selector, and preventing use of the inner path selector. 19. The neutron flux mapping system according to claim 1, wherein the double indexing path selector unit further includes tubing anti-twister means. 20. The neutron flux mapping system according to claim 19, wherein the tubing anti-twister means comprises:an anti-twister frame; anda rotating plate rotatably mounted in the anti-twister frame. 21. The neutron flux mapping system according to claim 20, wherein:the rotating plate is provided with a stop pin; andthe anti-twister frame is provided with stop plates engagable with the stop pin. 22. The neutron flux mapping system according to claim 21, wherein the stop plates are respectively mounted to diametrically-opposed ends of the anti-twister frame. 23. The neutron flux mapping system according to any one of claims 20 to 22, wherein the rotating plate is further provided with rotors. 24. The neutron flux mapping system according to claim 19, wherein the tubing ant-twister means further comprises withdraw limit switches each adapted to detect passage of the detector cable, associated therewith, through the double indexing path selector unit. 25. The neutron flux mapping system according to claim 24, wherein each of the withdraw limit switches is a non-contact type proximity reed switch. 26. The neutron flux mapping system according to claim 1, further comprising:detector storage guiders each arranged between an associated one of the drivers and the double indexing path selector unit; anda detector storage area adapted to store the detector guided by an associated one of the detector storage guiders.