JPS6385433A - Method and instrument for inspection by neutron radiography - Google Patents

Abstract

PURPOSE:To make non-destructive inspection of the internal damage of an object to be inspected by penetrating a hydrous material having contrast function into a part to be inspected to impregnate the material thereon, then expelling the impregnated material, projecting neutron thereto and detecting thermal neutron with a thermal neutron detector. CONSTITUTION:The hydrous material such as water is supplied into a metallic pipe 2 to penetrate and impregnate the hydrous material into the damaged part 8 of the section 8 to be inspected. The hydrous material is thereafter expelled from the inside surface of the metallic pipe 2. The fast neutron released isotropically from a neutron source 1 penetrates a thermal neutron absorber 4 and the thermal neutron detector 7 and is projected to the section 8 to be inspected of the metallic pipe 2. If the damaged section exists in the section 8, the thermal neutron is scattered by collision against the hydrous material and the thermal neutron detector opposed diametrally to the damaged part is decreased in the thermal neutron flux in said section than in the other section. The difference in the thermal neutron fluxes appears as a neutron radiography image on the detector 7. The presence or absence, size, shape, etc., in the damaged part of the metallic pipe 2 are thus non-destructively inspected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an inspection method and inspection apparatus using neutron radiography for destructively inspecting objects to be inspected such as metal pipes and metal containers.

(Prior technology) In conventional neutron radiography inspections, a research nuclear reactor is used as a neutron source, and the objects to be inspected, such as metal pipes and containers, are irradiated with powerful neutrons emitted from this reactor. . When a powerful neutron source such as a research reactor is used, the flow of neutrons emitted from the neutron source can be made into a highly parallel beam, and the object to be inspected is irradiated with this beam, and the scattered neutrons are An excellent neutron radiography image can be obtained, and by analyzing this neutron radiography image, it is possible to non-destructively inspect the presence or absence and shape of a damaged portion of an object to be inspected.

However, with conventional neutron radiography inspection equipment, in order to sample the inspected object (for example, the main steam pipe of a nuclear reactor), it is separated from the on-site equipment (for example, the reactor pressure vessel) and the separated inspected object is sampled. It is transported to the neutron beam extraction position, where it is irradiated with a powerful neutron beam from a research reactor for inspection.

For this reason, it has been difficult to inspect by neutron radiography when the object to be inspected cannot be separated or brought in.

On the other hand, the present applicant disclosed a control rod inspection device using neutron radiography in Japanese Patent Application Laid-open No. 81440/1983. This inspection device uses a neutron source of relatively weak radioactive isotopes for used control rods, which have high radioactivity.
Since the objective was to determine whether or not neutron absorbing material was present in the spent control rods, neutron radiography could be carried out and inspected relatively easily.

(Problem to be solved by the invention) Large-diameter piping such as main steam pipes, water tanks, etc. are installed in various plants such as nuclear power plants and thermal power plants. Attempting to non-destructively test the integrity of an object to be inspected using neutron radiography on-site involves various difficulties and problems. In particular, the health inspection of the inspected object does not use neutron radiography to determine the presence or absence of neutron absorbers like spent control rods, so the contrast of the neutron radiography image of the inspected object is significantly reduced. , M image quality is poor, and inspection accuracy is reduced, and it is also difficult to inspect the health of a relatively large object by neutron radiography using a neutron source of a weak radioactive isotope.

The present invention has been made in consideration of the above-mentioned circumstances, and actively utilizes the contrast function of a hydrogen-containing substance infiltrated into the inspection site of an inspection object such as metal piping or a container. The purpose of the present invention is to provide an inspection method and apparatus using neutron radiography that can easily and non-destructively inspect the health of the body on-site.

[Structure of the invention]

(Means for solving the problem) The inspection method using neutron radiography according to the first invention of the present invention involves bringing a hydrogen-containing substance into contact with the surface of an object to be inspected made of a metal material, thereby causing damage to the object to be inspected. After infiltrating the damaged area with a hydrogen-containing substance, the hydrogen-containing substance is removed from the surface of the object to be inspected, and then the object to be inspected is irradiated with neutrons, and neutrons are scattered by the hydrogen in the hydrogen-containing substance impregnated into the damaged area. neutrons are detected to inspect damaged parts of the object to be inspected.

In addition, the inspection device using neutron radiography according to the second invention of the present invention is such that a thermal neutron detector is arranged at the inspected part of the inspected object made of metal U material, and is placed at a predetermined distance from the inspected object. A neutron source that emits fast neutrons is disposed in the neutron source, and a neutron induction cavity that guides the fast neutrons is formed between the neutron source and the test site of the test object, and A thermal neutron detector detects thermal neutrons that are scattered and slowed down by a hydrogen-containing substance impregnated into the damaged part of the test object.

Furthermore, the inspection device using neutron radiography according to the third invention of the present invention arranges a thermal neutron detector at the inspected part of the inspected object formed of a metal material, and places the thermal neutron detector at a predetermined distance from the inspected object. A neutron source that emits fast neutrons is provided in the neutron source, and a neutron guide cavity that guides slow neutrons is formed between the neutron source and the inspected part of the object to be inspected, and the slow neutrons are introduced into the neutron guide cavity. In order to guide the neutrons, a moderator is provided to decelerate the fast neutrons, and the neutrons are emitted from the neutron source and decelerated to the inspected part of the inspected object.
A thermal neutron detector is used to detect thermal neutrons scattered by a hydrogen-containing substance impregnated into the damaged part of an object to be inspected.

(Function) The present invention involves bringing a hydrogen-containing substance such as water into contact with the surface of an object to be inspected, such as piping or a container made of metallic material, and applying a hydrogen-containing substance having a contrast function to a damaged area on the surface of the object to be inspected. infiltrate,
Make it adhere. Thereafter, hydrogen-containing substances are removed from the surface of the object to be inspected, and the region to be inspected of the object to be inspected is irradiated with neutrons emitted from a neutron source. In this case, the neutrons irradiated to the inspection site are fast neutrons from a neutron source or slow neutrons moderated by a moderator.

The neutrons irradiated onto the inspected area of the inspected object are slowed down by the hydrogen in the hydrogen-containing material impregnated in the damaged area and become thermal neutrons, and these thermalized neutrons are detected by a thermal neutron detector and detected. This is a non-destructive test to check the integrity of the inspected area.

In addition, when the inspected part of the inspected object is irradiated with slow neutrons (thermal neutrons and epithermal neutrons), 1,
- 10 - These slow neutrons are scattered by hydrogen in the hydrogen-containing substance impregnated in the damaged area. Scattered thermal neutrons are detected with a thermal neutron detector by taking advantage of the property that the thermal neutron flux is lower than when no hydrogen-containing substance is present, and the integrity of the inspected part of the inspected object is detected non-destructively. It's worth checking.

(Embodiment) Hereinafter, an embodiment of an inspection apparatus using neutron radiography according to the present invention will be described with reference to the accompanying drawings.

Figure 1 does not show the principle of an inspection device using neutron radiography of the present invention that irradiates fast neutrons.This inspection device uses weak portable neutrons II to inspect objects such as main steam pipes and process piping. The inside of the metal tube 2 is non-destructively inspected.

Neutron source 1 contains californium-252 (Cf-252
) is suitable, and the neutron source 1 is a portable point source type and is placed at a predetermined distance from the surface of the metal tube 2 as the object to be inspected. A neutron guiding cavity 3 that guides fast neutrons from a neutron source 1 toward a metal tube 2
is formed, and this neutron guiding cavity 3 is filled with cadmium (Cd
) or a thermal neutron absorber 4 such as boron carbide (B4C). This thermal neutron absorber 4 is formed in a sealed structure that covers the neutron source 1, and is preferably made of stainless steel (SUS), a
It is covered with a fast neutron shield 5 made of (Fe), lead (Pb), or the like.

Metal tube 2 of thermal neutron absorber 4 and fast neutron shield 5
The sides are curved according to the shape of the object to be inspected, and legs 6.6 are provided on both sides for fitting a neutron radiography inspection device into the metal tube 2.

Further, a thermal neutron detector 7 is provided on the metal tube 2 side of the thermal neutron absorber 4. The thermal neutron detector 7 is preferably a sheet of dysprosium (Dy), which is activated by irradiation with thermal neutrons to form a neutron radiographic latent image on the sheet.

Next, the operation of the inspection device using neutron radiography will be explained.

When non-destructively testing objects to be inspected such as metal pipes 2 or metal containers using this inspection device by neutron radiography, the objects to be inspected are injected with a hydrogen-containing substance such as water, or placed in a solution of a hydrogen-containing substance. After placing the object to be inspected and infiltrating it under pressure, the hydrogen-containing substances are removed. At this time, in order to effectively infiltrate and impregnate the damaged portion of the test object 2 with the hydrogen-containing substance, it is preferable to heat the test object, heat the hydrogen-containing substance, or apply pressure.

If a hydrogen-containing substance that has an affinity for water and has excellent permeability, such as alcohol, is soaked into the damaged area,
It is best to replace it later with less volatile water.

Therefore, when nondestructively inspecting the inside of the metal tube 2 by neutron radiography, a hydrogen-containing substance such as water is supplied into the metal tube 2 and the hydrogen-containing substance penetrates into the damaged part 8a of the inspected part 8. and impregnate.

After that, remove hydrogen-containing substances from the inner surface of the metal tube 2-12
= Do. At that time, if a damaged part 8a such as stress corrosion cracking (SCC) is present inside, the hydrogen-containing substance is impregnated into the damaged part 8a and functions as a contrast agent in the inspection by neutron radiography.

On the other hand, some of the fast neutrons emitted isotropically from the neutron source 1 are scattered and decelerated by environmental substances, and there is a possibility that some neutrons may be thermalized. 4 to absorb thermal neutrons.

In addition, the fast neutrons from the neutron source 1 are absorbed by the thermal neutron absorber 4.
, the inspected portion 8 of the metal tube 2 passes through the thermal neutron detector 7.
is irradiated. If a damaged part 8a exists in the inspected part 8 as shown in FIGS. 2 and 3, the fast neutrons irradiated to the metal tube 2 collide with the hydrogen of the hydrogen-containing substance impregnated in the damaged part 8a and decelerate. It becomes thermal neutrons and is scattered.

Among the fast neutrons irradiated to the damaged portion 8a of the inspection site 8, the neutrons that collide with hydrogen of the hydrogen-containing substance and are reflected in an almost opposite direction (180 degrees) are close to complete collisions and are most likely to become thermal neutrons. For this reason, when the thermal neutron detector 7 is placed in the flow of fast neutrons, the thermal neutrons that have been split approximately 180 degrees and scattered will flow into the thermal neutron detector 7, increasing the thermal neutron detection sensitivity. This thermal neutron is detected by a thermal neutron detector 7 made of a Dy sheet or the like.

At this time, a neutron radiography image is formed as a latent image on the Dy sheet of the thermal neutron detector 7, and the neutron radiography image can be confirmed by an indirect method using film exposure using β rays.

Note that neutron radiography images can be confirmed by a direct method using alpha rays. In this direct method, for example, alpha rays emitted when poron causes an (n, alpha) reaction with neutrons are utilized. By detecting the neutron radiography image, it is possible to non-destructively inspect the presence or absence of the damaged portion 8a of the inspected portion of the metal tube 2, the shape and size of the damaged portion, and the like.

Next, a second embodiment of an inspection apparatus using neutron radiography using fast neutron irradiation will be described with reference to FIG.

Since the neutron radiography inspection apparatus shown in FIG. 4 is not different in principle from the one shown in FIG. 1, the same parts are given the same reference numerals and the explanation will be omitted.

The neutron radiography inspection apparatus shown in FIG. 4 is basically different from the inspection apparatus shown in FIG. It is arranged at an angle to the pipe 2. The inspected portion 8 of the metal tube 2 is irradiated obliquely with high-speed neutrons.

Generally, the probability that fast neutrons are decelerated and thermalized by scattering is greatest when they are scattered at approximately 180 degrees, and in this sense, the inspection apparatus shown in FIG. 1 can improve detection accuracy. In forward scattering of neutrons, fast neutrons are not sufficiently decelerated and have a low probability of becoming thermal, so they are not suitable as a detection device, but in the case of side scattering, there is a high probability that they will be decelerated and become thermal neutrons. The detection device shown in FIG. 4 focuses on this point.

In fact, when examining the shape and size of the damaged portion 8a of the metal tube 2 in detail, it is recommended to use the detection device shown in FIG. 1 in combination.

The neutron radiography inspection device shown in FIG. A thermal neutron detector 7 is provided on the side corresponding to the region to be inspected 8 . This thermal neutron detector 7 is covered with a thermal neutron absorber 10 to prevent emission of background thermal neutrons.

Thermal neutron absorber 10 is connected to arm 1 via spring 11.
2, and this arm 12 is integrally held by the fast neutron shield 5.

The inspection apparatus using neutron radiography shown in FIG. 4 can also effectively and non-destructively inspect the damaged portion 8a such as SCC present in the inspected portion 8 of the metal tube 2.

FIG. 5 shows an inspection device using neutron radiography that utilizes slow neutron irradiation.

This inspection device uses slow neutrons to non-destructively inspect the inspected part of the inspected object, and it is installed in a 0f-252 or the like at a predetermined distance from the surface of the metal tube 2, which is the silkworm to be inspected. The child source 1 is placed.

This neutron source 1 is housed in a moderator 13 such as water, polyethylene, paraffin, etc., and the fast neutrons emitted from the neutron source 1 are slowed down by the moderator 13 and become slow neutrons. Slow neutrons include thermal neutrons and epithermal neutrons.

The slow neutrons that have been moderated by the moderator 13 enter the neutron guiding cavity 3.
The beam passes through the metal tube 2 and is irradiated onto the inspected portion 8 of the metal tube 2. At that time, the neutron guiding cavity 3 is defined by a thermal neutron absorber 4 such as cadmium (Cd), and this thermal neutron absorber 4 is covered with a neutron shield 15 formed of a hydrogen-containing material such as paraffin or polyethylene. . This hydrogen-containing substance may contain boron, which absorbs neutrons.

On the other hand, the slow neutrons irradiated to the inspected part of the metal tube (metal container, metal plate, etc.) 2 as the inspected object are scattered by the hydrogen-containing substance impregnated in the damaged part 8a of the inspected part 8. ,, These scattered thermal neutrons are detected by a thermal neutron detector 7. In this case, the thermal neutron detector 7 is arranged in close contact with the metal tube 2, and is provided diametrically opposite to the neutron source 1. A thermal neutron absorber 1 is installed outside the thermal neutron detector 7 to prevent leakage of background thermal neutrons.
0 is placed.

In addition, in order to efficiently guide low-speed neutrons emitted from the neutron source 1 and moderated by the moderator 13 to the neutron guiding cavity 3, the neutron guiding cavity 3 has a thermal neutron diffusion distance (approximately (about several cm) protrudes from the end of the thermal neutron absorber 4.

Thus, the fast neutrons emitted from the neutron source 1 become slow neutrons that are moderated by the moderator 13, and the test site 8 of the metal tube 2 is irradiated with these slow neutrons. Part 8 to be inspected
If there is a damaged area in the area, the neutrons collide with a hydrogen-containing substance such as water that has been pre-impregnated in the damaged area and are scattered, and the thermal neutron detector 7 facing the damaged area detects that the thermal neutron flux in that area is higher than that in other parts. descend. Therefore, a difference in thermal neutron flux occurs between the part corresponding to the damaged part and its surroundings, and this difference in thermal neutron flux is transmitted to the thermal neutron detector 7 in the neutron radiography image (
By monitoring this neutron radiography image, it is possible to non-destructively inspect the existence, size, shape, etc. of damaged parts of the metal tube 2.

FIG. 6 shows another modification of the inspection apparatus for neutron radiography using slow neutron irradiation.

This inspection apparatus is also similar in principle to the neutron radiography inspection apparatus shown in FIG. 5, so the same parts are denoted by the same reference numerals and the explanation thereof will be omitted.

The inspection apparatus shown in FIG. 6 has a neutron guiding cavity 3 installed obliquely, and irradiates the inspected region 8 of the inspected object 2A obliquely with decelerated slow neutrons emitted from the neutron source 1.

A thermal neutron detector 7 is provided in front of the radiation port 3a of the neutron guiding cavity 3, and the thermal neutron detector 7 detects the inspection target part 8.
Thermal neutrons scattered and reflected by the damaged portion 8a are made incident. In this case, since the thermal neutron absorber 4 is present on the opposite side of the object to be inspected from the thermal neutron detector 7, there is almost no incidence of thermal neutrons from outside the damaged area 8ag, and even a weak neutron source 1 can be efficiently inspected. can.

〔Effect of the invention〕

As described above, in the present invention, a hydrogen-containing substance having a contrast function is infiltrated into the inspected part of an object to be inspected, the damaged part is impregnated with this hydrogen-containing substance, and then the hydrogen-containing substance is removed. After that, neutrons from a neutron source are irradiated onto the part to be inspected, and the scattered thermal neutrons are detected by a thermal neutron detector.
Since the inspected part of the inspected object can be inspected using neutron radiography images, the presence or absence of internal damage, shape, and The size can be non-destructively tested, and the internal health of the object to be tested can be efficiently and effectively tested.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram showing an embodiment of the neutron radiography inspection device according to the present invention that utilizes fast neutron irradiation, and FIGS. 2 and 3 show the operation of the neutron radiography inspection device according to the present invention. The explanatory diagram, FIG. 4, is a diagram showing another embodiment of the neutron radiography inspection device according to the present invention, and FIG. 5 is a diagram showing the principle of the neutron radiography inspection device according to the present invention, which uses slow neutron irradiation. 6 are diagrams showing a modification of the neutron radiography inspection apparatus shown in FIG. 5. 1... Neutron source, 2... Metal tube (tested object), 2A
...Test object, 3. Neutron guiding cavity, 4. Thermal neutron absorber, 5. Fast neutron shield, 6. Legs, 7. Thermal neutron detector, 8. ... Part to be inspected, 8a
...Damaged part, 10...Thermal neutron absorber, 13...
Moderator, 15... thermal neutron shield.

Claims (1)

[Claims] 1. After bringing a hydrogen-containing substance into contact with the surface of an object to be inspected made of a metal material and permeating the damaged part of the object, the hydrogen-containing substance is removed from the surface of the object to be inspected. Excluding the hydrogen substance, then irradiating the object to be inspected with neutrons, detecting neutrons scattered by the hydrogen of the hydrogen-containing substance impregnated in the damaged area, and inspecting the damaged area of the object to be inspected. An inspection method using neutron radiography characterized by the following. 2. An inspection method using neutron radiography according to claim 1, wherein a hydrogen-containing substance is brought into pressure contact with the surface of an object to be inspected, and the hydrogen-containing substance is infiltrated into a damaged part of the object under pressure. 3. An inspection method using neutron radiography according to claim 1 or 2, which comprises heating the object and then bringing a hydrogen-containing substance into contact with the surface of the object. 4. After removing hydrogen-containing substances from the surface of the object to be inspected, the object to be inspected is irradiated with fast neutrons, and thermal neutrons that are scattered and moderated by the hydrogen-containing substances remaining on the damaged part of the surface of the object to be inspected are detected. An inspection method using neutron radiography according to claim 1. 5. A neutron radio according to claim 1, which decelerates fast neutrons emitted from a neutron source into a flow of slow neutrons, and irradiates this flow of neutrons to an object to be inspected from which hydrogen-containing substances have been removed. Inspection method using graphics. 6. A thermal neutron detector is placed at the part to be inspected of the object to be inspected made of a metal material, a neutron source that emits fast neutrons is placed at a predetermined distance from the object to be inspected, and the neutron source A neutron induction cavity for guiding fast neutrons is formed between the inspection target part of the inspection target body, and the inspection target part of the inspection target body is irradiated with fast neutrons from a neutron source, and the damaged part of the inspection target body is irradiated with fast neutrons. An inspection device using neutron radiography, characterized in that a thermal neutron detector detects thermal neutrons that have been scattered and moderated by a hydrogen-containing substance impregnated with a hydrogen-containing substance. 7. The neutron radiography inspection device according to claim 6, wherein the neutron guiding cavity is defined by a thermal neutron absorber. 8. The neutron radiography inspection device according to claim 7, wherein the thermal neutron absorber covers the neutron source and the neutron guiding cavity from the outside, and the thermal neutron absorber is covered with a fast neutron shield. 9. An inspection device using neutron radiography according to claim 6, wherein the object to be inspected is a metal tube, a metal container, or a metal plate. 10. The neutron radiography inspection device according to claim 6, wherein a thermal neutron absorber for preventing leakage of background thermal neutrons is disposed outside the thermal neutron detector. 11. A thermal neutron detector is placed at the part to be inspected of an object to be inspected made of a metal material, a neutron source that emits fast neutrons is placed at a predetermined distance from the object to be inspected, and the neutron source A neutron guiding cavity for guiding slow neutrons is formed between the inspection target part of the inspected object, and a moderator for moderating fast neutrons is provided in order to guide the slow neutrons to the neutron guiding cavity. The inspected part of the inspected object is irradiated with slowed slow neutrons emitted from a neutron source, and the thermal neutrons scattered by the hydrogen-containing material impregnated into the damaged part of the inspected object are detected by a thermal neutron detector. An inspection device using neutron radiography characterized by: 12. The neutron radiography inspection device according to claim 11, wherein the neutron source is housed in a moderator such as water, polyethylene, or paraffin. 13. The neutron radiography inspection device according to claim 11, wherein the neutron guiding cavity is defined by a thermal neutron absorber. 14. An inspection device using neutron radiography according to claim 11, wherein the neutron guiding cavity is formed within the moderator to protrude from the thermal neutron absorber toward the neutron source side by about the thermal neutron diffusion distance of the moderator. 15. An inspection device using neutron radiography according to claim 13, wherein the thermal neutron absorber is covered with a neutron shield. 16. The neutron radiography inspection device according to claim 11, wherein a thermal neutron absorber for preventing leakage of background thermal neutrons is disposed outside the thermal neutron detector.