KR20100076487A - Fuel rod scanner using the pulsed neutron generator - Google Patents

Abstract

PURPOSE: A fuel rod inspection meter using a neutron generator is provided to reduce the weight of a fuel rod inspection meter by reducing the thickness of a shielding body. CONSTITUTION: A neutron generator is installed inside a shielding body(11). A gamma-ray detector(3) is arranged on the side facing the shielding body while leaving the fuel rod in the reaction site between a fuel rod(F) and a neutron which is emitted in the neutron generator. The neutron generator is composed of a pulse type neutron generator(20). The neutron generator is arranged at a fixed interval from the wall facing the fuel rod inside the shielding body in order to emit a thermal neutron transformed in neutron to the fuel rod.

Description

Fuel rod flaw detector using neutron generator {FUEL ROD SCANNER USING THE PULSED NEUTRON GENERATOR}

The present invention relates to a fuel rod flaw detector for inspecting nuclear fuel rods used in nuclear reactors, and more particularly, by using a neutron generator in place of ²⁵² CF as a neutron generator to reduce operating costs, extend life, manage and repair It relates to a fuel rod flaw detector using a neutron generator to facilitate the.

In general, nuclear fuel used in nuclear reactors sinters about 6 g of uranium oxide to form pellets, and 380 sintered pellets and springs are enclosed in a tube of hollow zircal alloy of about 4 m in length. After filling with helium gas, it is made of fuel rod sealed with end cap.

The fuel rods manufactured as described above have a skeletal body consisting of a support plate having a hole through which coolant passes, and a support grid for maintaining a gap between fuel rods in the middle and about 60 in a boiling water reactor and about 230 in a pressurized water reactor. The precision is mounted and fixed to form a nuclear fuel assembly (also called a fuel assembly) that forms a bundle of quadrilateral grids. The fuel assembly thus formed is integrally loaded and withdrawn from the reactor, whereby the nuclear fuel is loaded or the fuel is withdrawn from the reactor.

Fuel rods having the above-described configuration should be inspected in advance with defects such as integrity, concentration, and deviation of sintered bodies in fuel rods using flaw detectors to remove the defects and load them into the reactor to ensure stable nuclear fission in the reactor. do.

Examples of prior art flaw detectors for the inspection of such fuel rods include passive flaw detectors and active flaw detectors of NDA-TECH (USA).

The dual passive flaw detector detects fuel rod defects by detecting and analyzing the radiation emitted from the fuel rods. Neutral resources are not required, but the equipment is huge for accurate detection of the fuel rod defects. It is not used often.

In contrast, the active flaw detector detects defects in fuel rods by generating neutrons in the fuel cell, irradiating the fuel rods, and detecting and analyzing gamma rays emitted by uranium reacting with neutrons in the fuel rods. It can be installed and is most used because of the high accuracy of fuel rod detection.

1 is a cross-sectional view of the active flaw detector described above. As shown in FIG. 1, the prior art active flaw detector 1 includes a cylindrical shield 2 made of lead and one of the cylindrical shields 2. density measuring instrument is formed at a position where the fuel rods are transported on the side of measuring the length and density of the sintered body (3) and, ²⁵² CF crew (4), fuel rods (F) is drawn out to be located inside the shielding compartment provided with a ²⁵² CF Formed on the outer surface of the shielding box 2, and a gamma ray detector 5 having a photodetector and a BGO therein so as to detect gamma rays, and a fuel rod F being drawn into the shielding box 2; It comprises a fuel rod feeder (T) withdrawn from the shielding (2) the fuel rod after the inspection is completed.

The active flaw detector (1) using the ²⁵² CF source (4) of the prior art, which is constructed as described above, emits radiation for the safety of the worker because the ²⁵² CF continuously emits radiation including neutrons and gamma rays having high intensity. Since the complete shielding of the shielding should be performed, the size of the shielding body 2 becomes large, and thus, the total weight and volume of the flaw detector is increased, and thus mobility and installation efficiency are significantly reduced.

And in the case of active flaw detector (1) using a ²⁵² CF of the prior art ²⁵² CF continuously neutrons, because emits radiation, including gamma rays, such as repair, maintenance, when the operator from radiation, such as neutron and gamma radiation, such as performance testing In order to protect the system, a detection device such as a gamma ray detector must be configured outside the shielding box, thereby increasing the volume of the flaw detector, and the nuclear reaction of the fuel rod at the position where the detection device is separated from the position where the neutron reacts with the fuel rod. The detection of the signals reduces the amount of signals, making it difficult to measure the exact defects of the fuel rods, and this problem is compensated for by the software. Therefore, the prior art has a problem of generating a lot of additional costs, such as the development of software for the accurate measurement of the fuel rod defects.

In addition, since the half-life of ²⁵² CF is 2.65 years, it is necessary to replace the ²⁵² CF once every 2.65 years. Therefore, the replacement cost of expensive ²⁵² CF (as of October 2008: about 350 million won) is high. Have In the case of replacing ²⁵² CF, it is cumbersome to purchase in advance considering the manufacturing period of ²⁵² CF, and the replacement period is used for a long time (about 5 days) even when the purchase is completed. Since this becomes longer, there is a problem that the productivity of the fuel rod is significantly reduced.

In addition, the ²⁵² CF crew mentioned above was not supplied by the US FTC, but it was not possible to carry out a stable supply of crew, making it difficult to supply ²⁵² CF crew. Problems such as difficulty in purchasing occurred. Therefore, the development of an active flaw detector that does not use a ²⁵² CF source for fuel rod inspection is urgently needed.

Therefore, the present invention is to solve the problems of the prior art active fuel rod flaw detector, by using a neutron generator to replace the ²⁵² CF source used in the active flaw detector of the prior art, to reduce the replacement cost of ²⁵² CF, Reduce the weight of the shield to suit less neutrons and radiation, and place the gamma-ray detector at the position where the fuel rod reacts with the neutrons on the shield, reducing overall volume and weight to facilitate transport, installation and maintenance, and maintain neutrons during maintenance By stopping the operation of the generator and blocking the generation of radiation and neutrons at the source, it improves worker's work safety, and by allowing the gamma ray detector to be placed in the lower part of the neutron generator inside the shield, Inspection for defects such as deviations Is that of providing a fuel rod flaw detector with a neutron generator which allows to significantly improve the accuracy for that purpose.

Fuel rod flaw detector using the neutron generator of the present invention for achieving the above object, the neutron generator; A shielding box in which the neutron generator is built; And a gamma ray detector disposed on a surface facing the shield with the fuel rod interposed between the neutron generator and the fuel rod reacted by the neutron generator. Characterized in that it further comprises an additional equipment, such as density measuring instrument, fuel rod transporter to measure.

The neutron generator is composed of a deuterium-deuterium neutron generator, characterized in that configured to enable pulse control. Since the flaw detector according to the present invention applies the above-described neutron generator, the maintenance of the neutron generator is stopped during the maintenance work such as the repair and inspection of the gamma ray detector, and thus the operator can perform the safe maintenance work. Unlike the prior art, the gamma ray detector may be disposed adjacent to the shielding box with the fuel rod interposed therebetween, thereby improving the accuracy of the inspection of the fuel rod.

The shielding box is disposed inside the neutron generator, and formed of a sealed tube made of a lead wall filled with a moderator, wherein the wall surface of the fuel rod conveying side is formed of a deceleration shield plate for converting into a thermal neutron. .

In addition, the fuel rod flaw detector using the neutron generator of the present invention having the above-described configuration may be implemented as a multi-mode fuel rod flaw detector in which a fuel rod feeder, a density gauge, and a gamma ray detector are arranged in a plurality of rows to improve fuel rod inspection efficiency.

In the fuel rod flaw detector using the neutron generator of the present invention having the above-described configuration, the fuel rod length, the density distribution and the gap of the pellet are inspected by the density detector when the fuel rod is inspected.

When the fuel rods are transferred to the lower part of the shield, the neutron generator is driven to emit neutrons, and the neutrons emitted from the neutron generators are converted into thermal neutrons by the deceleration shield plate and then irradiated to the fuel rods.

The fuel rod irradiated with the thermal neutrons emits gamma rays when the fuel material in the fuel rods reacts with the thermal neutrons, and the emitted gamma rays are directly detected by a gamma ray detector facing the shielding rod with the fuel rods interposed therebetween. The structure of the crack, the mixing part, etc. of a pellet can be examined. In this case, as described above, the gamma ray detector is disposed at a position facing the shield with the fuel rods interposed therebetween, so that the gamma rays generated from the fuel rods can be detected without loss, so that accurate inspection of the fuel rods can be performed.

Fuel rod flaw detector using the neutron generator of the present invention having the above configuration,

First, to reduce the operating cost by reducing the replacement cost of ²⁵² CF,

Secondly, since it emits less neutrons and radioactivity than ²⁵² CF, it reduces the weight of the shield and reduces the weight of the fuel rod flaw detector to provide easy transportation and installation.

Third, by applying a neutron generator, if maintenance and performance tests are necessary, the neutron generator can be stopped to perform work, thereby greatly improving the ease of management and maintenance and worker safety.

Fourth, the gamma ray detector can be mounted at a position adjacent to the position where the neutron irradiated from the neutron generator reacts with the fuel rod, thereby remarkably improving the accuracy of inspection for defects such as integrity and detachment of the fuel rod sintered body. To provide.

Hereinafter, with reference to the accompanying drawings showing a preferred embodiment of the present invention will be described the present invention in more detail.

2 is a cross-sectional view of a fuel rod flaw detector (hereinafter referred to as a "detector") 10 using a neutron generator according to an embodiment of the present invention, Figure 3 shows a pulsed neutron generator 20 as an example of the neutron generator 4 is a diagram showing the arrangement of the gamma ray detector 3 and a gamma ray detection process in a flaw detector equipped with a ²⁵² CF source of the prior art, and FIG. 5 shows a method for analyzing the state of the fuel rod by the signal of the gamma ray detector. Drawing.

As shown in FIG. 2, the flaw detector 10 of the present invention includes a neutron generator 20, a shield box 11 in which the neutron generator 20 is embedded, and a fuel rod along the outer surface of the shield box 11. Fuel rod transporter (T) to transfer and the fuel rod (F) transported from the outside of the shield box 11 is located at a position opposite to the shield box (11) with the fuel rod (F) in between in the region where the neutron is irradiated It comprises a gamma ray detector (13). And as in the prior art, a density measuring device (3) for measuring the length, density, etc. of the fuel rod (F) using a Cs isotope or the like is provided in one area outside the shield box (11).

In the configuration of the flaw detector (1) of the present invention described above, the neutron generator 20, as shown in Figure 3, the feeder 22 for providing a small and medium number of moving force inside the vacuum case 21, and the neutron generation It may be composed of an ion source 23 for generating ions for the purpose, an acceleration stage 24 for accelerating the ions released from the ion source, and a neutron generation target 25 for the accelerated ions collide to generate neutrons . At this time, the neutron generator 20 of the present invention having the above-described configuration may be composed of a deuterium-deuterium neutron generator (DD neutron generator) or a deuterium-tritiated tank neutron generator (DT neutron generator), but the prior art ²⁵² CF and is preferably composed of a DD neutron generator by approximately 2 MeV considering the emission of neutrons 10 ^9, the release of about 10 neutrons per second than 2.5MeV ⁷ DT neutron generator which generates neutrons of approximately 14MeV per second, Pulse control is possible. In addition, the neutron generator 20 is disposed at a distance of about 5 cm or more from the deceleration shield plate 12 facing the fuel rod F to be transported so that the generated high-speed neutron is irradiated to the fuel rod after being converted into a thermal neutron. do. The neutron generator 20 arranged as described above is controlled to emit neutrons for a predetermined time during fuel rod inspection, for example, for 1 nsec by the pulse control, thereby preventing unnecessary nuclear reaction signals from being detected by the continuation of neutron radiation. In addition, the detection time of the delayed neutrons and the delayed gamma rays can be precisely controlled.

As described above, when the neutron generator 20 described above is applied to the fuel rod flaw detector, the replacement period of the neutron source is extended. That is, when the conventional ²⁵² CF source is applied, the half-life of the ²⁵² CF source is 2.6 years, so the ²⁵² CF source is purchased and replaced every 2.6 years. However, when applying a neutron generator, repair is performed once at about 5000 Hrs. As a result, it is easy to maintain and repair.

In addition, the price of the flaw detector using the ²⁵² CF source of the prior art is about 3 billion won (as of October 2008), but the flaw detector of the present invention takes about 1.6 billion won (as of October 2008), thereby reducing the installation cost. The ²⁵² CF source of the prior art required a high cost of about 350 million won (as of October 2008) to be replaced, but a cost of about 70 million won (as of October 2008) when the neutron generator was applied. Only) can reduce the operating cost of flaw detectors.

In addition, in the repair and replacement period of the prior art ²⁵² CF crew took about 5 days, when applying the neutron generator as in the present invention, the replacement and repair can be performed in one day by stopping the fuel rod production period To shorten the fuel rod productivity significantly.

Next, the shield 11 of the flaw detector 10 of the present invention described above is to block the radiation including gamma rays and neutrons emitted from the neutron generator, and the neutron generator 20 is located inside the neutron. Emitted from the generator It has a structure of lead material filled with a moderator 11a for decelerating fast neutrons.

In addition, since the neutron generator 20 of the flaw detector 10 of the present invention emits about 10 ⁷ neutrons and radiation of about 2.5 MeV per second, the wall of lead material constituting the shield 11 of the present invention uses ²⁵² CF. The shield 2 of the prior art active flaw detector (1, see FIG. 1) can be configured to have a thickness that is significantly less than the thickness for shielding the emission of 10 ⁹ neutrons of approximately 2 MeV per second at ²⁵² CF. And, this makes it possible to significantly reduce the weight of the flaw detector (10) to facilitate the transport and installation. In this case, the thickness of the shield 11 applied to the flaw detector 10 of the present invention is graphed according to the number of neutrons emitted from the neutron source and the energy of the neutron, and thus the detailed description thereof is easy. Omit.

In addition, the shield 11 has a moderator (in order to allow fast neutrons emitted from the neutron generator 2 to be converted into a reduced thermal neutron reacting with the fuel rod F). The deceleration shield plate 12 is configured to have a thickness to decelerate the neutrons at a suitable speed capable of reacting with the fuel rods as well as the fuel rods 11a). Is done. As a result, the neutron generated by the neutron generator 20 and the reactivity of uranium 235 (U235) in the fuel rod are remarkably improved.

The shield box 11 of the present invention having the above-described configuration is not limited to a cylindrical shape or the like, and may have various structures to block neutron sources and radiation emitted from the neutron generator 20. For example, the shield box 11 of FIG. 2 has a semicircular cylindrical upper wall as shown in FIG. 7, and a wall surface formed of a deceleration shield plate 12 facing the lower fuel rod F has a plate shape. It can be configured to have a sealed structure. At this time, the deceleration shield plate 12 has the appropriate thickness to be converted into a thermal neutron by delaying the speed of the high-speed neutron so that the high-speed neutron reacts with the uranium 235 (U235).

Next, the gamma ray detector 13 is located next to the position where the neutron generated by the neutron generator 20 is irradiated to the fuel rod F among the positions facing the deceleration shield plate 12 of the shield box 11. 2, it is shown that the fuel rod is located on the right side of the conveying direction. That is, when the fuel rod F moves from right to left, the gamma ray detector 13 has a neutron generated by the neutron generator 20 among the positions opposite to the deceleration shield plate 12 of the shield 11. It is located on the left, which is the next area of the position to be irradiated to F).

As described above, arranging the gamma ray detector 13 at a position directly facing the shield 11 with the fuel rod F interposed therebetween. First, the radiation generated by the neutron generator 20 is ²⁵² CF. This is to improve the detection efficiency of gamma rays because the intensity of the radiation and neutron source emitted from is small. Secondly, the neutron generator 20 is stopped during maintenance work such as repairing or inspecting the gamma ray detector 13. This prevents the worker from being exposed to radiation and neutrons, so that safe work can be performed.

That is, the gamma ray detector 13 of the present invention is arranged in a manner different from that of using the prior art ²⁵² CF, and the method of gamma ray detection is also applied to further improve the accuracy of the fuel rod inspection. FIG. 4 is a diagram showing the arrangement of the gamma ray detector 5 and the gamma ray detection process in a flaw detector equipped with a ²⁵² CF source of the prior art.

The gamma ray detection process by the gamma ray detector 13 of the present invention will be described with reference to FIGS. 2 and 4 as follows.

Referring first with reference to Figure 4. For comparison describes gamma-ray detecting process in the active flaw detector (1) using a ²⁵² CF crew of the prior art, in the case of active flaw detector (1) using a ²⁵² CF crew of the prior art, the radiation The gamma ray detector 5 is formed outside the shield 2 due to the exposure risk. Accordingly, the fuel rod F is irradiated for about 0.3 seconds by a neutron generated from the ²⁵² CF source 4 inside the shield box 2 and irradiated through a gap between the shield walls of the lead 4a. The nuclear reaction begins. After the nuclear reaction by the neutrons is performed in the fuel rods, gamma rays are detected after the portion of the fuel rods to which the neutrons are irradiated is transferred to the gamma ray detector 5 located outside the shield 2. Therefore, in the case of the active flaw detector 1 of the prior art having the configuration of FIG. 1, the fuel rods are detected by neutrons to detect the gamma rays delayed for 6 seconds after performing nuclear reactions, thereby determining the fuel rods' integrity, defects, and the like. Due to the many time delays, the accuracy of the test is lowered as well as it takes a lot of time.

However, in the case of the flaw detector 10 of the present invention using the neutron generator 20, since the driving of the neutron generator 20 can be stopped, the gamma ray detector 13 is shielded for repair. As shown in FIG. 2, the fuel rod F can be directly disposed at an adjacent position passing through the region where the neutron is irradiated to the fuel rod F at the bottom of the shield 11.

In this case, when the neutron generated from the neutron generator 20 located inside the shield 11 in the flaw detector 10 of the present invention is irradiated to the fuel rod F converted into a thermal neutron and starts to react, By the reaction of the fuel rod (F) immediately generated gamma rays and neutrons (prompted Gamma and Neutron) and delayed gamma rays and neutrons (delayed Gamma and Neutron) is generated. After 1 msec, only delayed gamma rays and neutrons and delayed heavy gamma rays are emitted. Therefore, the gamma ray detector 13 of the present invention detects the gamma rays emitted after 1 msec after the neutron is irradiated to the fuel rod F in the flaw detector 10 of the present invention to remove the unnecessary radiation components, thereby improving the accuracy of the fuel rod inspection. Configured to improve.

In the flaw detector 10 of the present invention, a method of detecting a gamma ray emitted after 1 msec after neutron is irradiated to the fuel rod F, for example, a fuel rod F to which the neutron is irradiated after the neutron is irradiated to the fuel rod Place the gamma ray detector 13 at a position where the region of is transported for 1 msec, or drive the gamma ray detector 13 to detect a delayed gamma ray and neutron after 1 msec after the neutron has been irradiated to the fuel rod F, thereby causing defects in the fuel rod. , A method of inspecting the integrity of breakage, etc. may be applied.

Referring to the operation of the flaw detector 10 of the present invention having the above-described configuration is as follows.

When inspecting the fuel rod (F) using the flaw detector 10 according to an embodiment of the present invention having the configuration of Figures 1 to 3, the operator shields using the fuel rod transporter (T) (11) At the bottom of the fuel rod (F) is to be transferred from left to right. At this time, the fuel rod F passes through the density measuring device 3 emitting the Cs isotope or the like, and the distribution, length, density, length of the spring, etc. of the pellets in the fuel rod F are examined.

5 is a view showing a state analysis method of the fuel rod by the signal of the gamma ray detector of the present invention. In FIG. 5, A is a line indicating the number of isotopes generated from the Cs isotope. Before the fuel rod F is introduced into the density meter, the number of photons emitted from the Cs isotope is saturated, and the fuel rod ( When F) is inserted, the movement of photons emitted from the Cs isotope by the fuel rods is interrupted and the number of photons detected is drastically reduced. When more than a certain number of photons are detected on the graph of the reduced number of photons, it can be seen that there is a gap between the pellets and the pellets. When the spring S at the end of the fuel rod F passes the density meter 3 during this inspection, the number of photons emitted from the Cs isotope detected again increases rapidly, and the length of this section is calculated and calculated. This makes it possible to check the length of the spring. At this time, when the number of photons is drastically reduced, the length of the photons is rapidly increased by the area of the spring S, and the length of the photons is calculated using the feed rate of the fuel rod F, and the pellet embedded in the fuel rod F. The length of the field.

In addition, when the fuel rod F passes through the density meter in the above-described process, since the number of photons detected by the density meter 3 again appears to be saturated, the number of photons starts to increase and decreases after being saturated. When the area is converted into the length by using the feed rate of the fuel rod F, etc., the length of the fuel rod F becomes to be the length of the fuel rod F.

Along with the inspection process of the densitometer 13 as described above, the fuel rod F transported through the density meter 13 enters the lower portion of the shield 11 and is generated in the neutron generator 20 and the moderator 11a. ) And the thermal neutron decelerated by the deceleration shield plate 12 will react. At this time, the neutron generator 20 is periodically repeated to emit the neutrons only for a predetermined time by the pulse control. As an example, the neutron generator 20 described above emits neutrons for about 1 nsec when the fuel rod F is positioned at the neutral yarn irradiation position under the shield 11. The released neutrons react with the fuel rod U235 to generate a variety of nuclear reaction products and emit gamma rays. As described above, when neutrons and gamma rays are emitted, the gamma ray detector 13 positioned at the lower portion of the fuel rod F is released from the fuel rod F after a predetermined time (about 1 msec) after the thermal neutron is irradiated to the fuel rod F. After detecting gamma rays and neutrons, the state information of the fuel rod F is output by the analysis operation. At this time, detecting a gamma ray emitted from the fuel rod F after a certain time after the thermal neutron is irradiated to the fuel rod (F), 1msec after the neutron is irradiated, unnecessary radiation emitted by the various nuclides initially This is because all of them disappear and only the gamma rays of delayed neutrons and delayed neutrons necessary for fuel rod inspection are emitted. The fuel rod inspection process is repeatedly performed to output information of the entire fuel rod. FIG. 5 is a diagram showing fuel rod information as a graph of gamma ray intensity emitted from the fuel rod as an example of the fuel rod information.

In FIG. 5, the line B represents the number of photons of the gamma ray. As shown in FIG. 5, gamma ray photons are not detected because there is no reaction by the thermal neutrons in the region of the fuel rod F made only of the zircaloy alloy tube. do. Subsequently, when a pellet containing a nuclear fuel material such as uranium 235 (U235) is transported in the fuel rod to react with neutrons, gamma rays are emitted according to the concentration of the nuclear fuel material such as uranium 235 included in the pellet.

In addition, in FIG. 5, the saturated region after increasing the number of photons of the initial gamma ray represents a pellet composed of a nuclear fuel material such as uranium 235 at 2%. The region (e) where the number of photons in the gamma rays increases more rapidly (s) and the region (f) that is saturated to emit the highest gamma photons shows an array of pellets composed of nuclear fuel materials such as uranium235 with an average concentration of approximately 4.5%. do. At this time, a small reduction region of gamma ray photons is generated, and cracking of pellets and mixing of pellets can be determined according to the size of the small reduction region of gamma ray photons. The crack part (c) where the cracking of the pellet occurred and the mixing part (a) in which other kinds of pellets are mixed can be confirmed as an area where the number of photons is reduced by about 10% compared to the saturation state, and according to the width of the reduced area. The crack part c and the mixing part a are identified.

The flaw detector 10 of the present invention having the configuration as described above has a density meter 3, a gamma ray detector 13, and a fuel rod transporter for inspecting the fuel rod F to improve the inspection efficiency of the fuel rod F. T) can be configured in multiples.

6 is a perspective view of a dual mode flaw detector 10 'in accordance with an embodiment of the multi-mode flaw detector of the present invention configured to perform simultaneous inspection of multiple fuel rods, wherein the dual mode flaw detector 10' has two Dual fuel rod feeders Ta and Tb are provided to simultaneously inspect the fuel rods Fa and Fb, and the fuel rods Fa and Fb are transferred to the neutron irradiation position of the shield at the front end of the shield 11. On the inlet side, a pair of density measuring instruments 3a and 3b for measuring the length, density and gap of each fuel rod Fa and Fb is provided, respectively, and shields the fuel rods Fa and Fb between them. And gamma ray detectors 13a and 13b for detecting gamma rays emitted in response to thermal neutrons in the respective fuel rods Fa and Fb at positions facing the deceleration shielding plate 12 of.

In this case, since the gamma ray detectors 13a and 13b are interfered by the gamma rays emitted from the adjacent fuel rods, the gamma ray detectors 13a and 13b are configured to remove the interference signal and to select and analyze only the gamma rays emitted from the fuel rod to be inspected. The same applies to the case where it is implemented to have three or more modes.

1 is a partial cross-sectional view of the active flaw detector described above;

2 is a cross-sectional view of a fuel rod flaw detector (hereinafter referred to as a "detector") 10 using a neutron generator according to an embodiment of the present invention,

3 is a view showing an example of a pulsed neutron generator 20,

4 is a view showing the arrangement of the gamma ray detector 3 and the detection of the gamma ray in a flaw detector equipped with a ²⁵² CF source of the prior art;

5 is a view showing a state analysis method of the fuel rod by the signal of the gamma ray detector,

FIG. 6 is a perspective view of a dual mode flaw detector among multi-mode flaw detectors capable of simultaneously inspecting a plurality of fuel rods. FIG.

* Explanation of the main symbols in the drawing *]

1: active flaw detector, 2, 11: shield, 3: density meter, 4: ²⁵² CF source

4a: lead 5, 13, 13a, 13b: gamma ray detector

12: deceleration shield

10: fuel rod flaw detector using a neutron generator

20: pulsed neutron generator (neutron generator)

11a: moderator F, Fa, Fb: fuel rod

T, Ta, Tb: fuel rod feeder c: crack

a: mixing part, P1: 2% pellet, P2: 4.5% pellet, S: spring

Claims (5)

A neutron generator; A shielding box in which the neutron generator is built; A fuel rod flaw detector using a neutron generator, comprising: a gamma ray detector disposed on a surface facing the shield with the fuel rod between the neutron generator and the fuel rod reacted from the neutron generator. The fuel rod flaw detector according to claim 1, wherein the neutron generator is a pulsed neutron generator. The fuel rod using the neutron generator according to claim 2, wherein the neutron generator is arranged to be spaced apart from the wall facing the fuel rod inside the shielding box so that the generated neutron is converted into a thermal neutron and irradiated to the fuel rod. Flaw detector. The method according to any one of claims 1 to 3, wherein the gamma ray detector is configured to detect a delayed gamma ray emitted from the fuel rod after a period of time after the radiation excluding the delayed gamma ray is extinguished after the thermal neutron is irradiated to the fuel rod Fuel rod flaw detector using a neutron generator, characterized in that. The fuel rod flaw detector according to claim 4, wherein the gamma ray detector is composed of a plurality of rows.

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