JPH09189790A - Method for diagnosing degradation of reactor structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for a degradation diagnosis test which is required to diagnose the degree of secular degradation of a weld and a base material in materials for a structure in a nuclear reactor. SOLUTION: A material supplied for a degradation diagnosis is prepared by cutting a positioning protrusion 2 on the inner face of a shroud and a fillet weld 4 around the protrusion 2 and taking them out from a nuclear reactor. A degradation diagnosis of materials for the weld is conducted by cutting out a minute specimen 7 from the fillet weld 4 of the supplied material and conducting a strength test. Moreover, a degradation diagnosis of base materials is conducted by cutting out a specimen for strength evaluation from the protrusion 2 and conducting a strength test.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor pressure vessel and a method for diagnosing aging deterioration of reactor internals, which deteriorate with age due to neutron irradiation and long-term thermal aging.

[0002]

2. Description of the Related Art For aging deterioration diagnosis of a reactor pressure vessel, for example, as shown in "Light Water Reactor Pressure Vessel Monitoring Test Handbook" published by the Japan Atomic Energy Society, the same materials as those used in the reactor are used. A method is used in which the monitoring test piece cut out from the above is placed in a capsule and installed in the reactor, and after operating for a predetermined period, the monitoring test piece is taken out and subjected to a Charpy test or a tensile test to check the strength. It was There is no particular method used for the materials or welding materials used in the reactor internals, but the same method as for the pressure vessel can be applied. But,
In the nuclear plants that have been operated so far, the materials of the reactor internals and welds have not been inserted into the capsule for monitoring test pieces, and this method can be applied to future plants, but the plant currently in operation Not applicable to.

[0003]

A material which has been operated for a certain period of time and which has been irradiated with neutrons to such an extent as to cause a change in the material quality of the structural material or has been aged at a high temperature has a material at the initial stage of operation. It may have deteriorated rather than strength, and it is necessary to diagnose the degree of this deterioration in order to maintain the healthy operating condition of the reactor. Deterioration diagnosis of the pressure vessel material may be performed using the monitoring test piece installed in the reactor, but there is no monitoring test piece for the material of the internal structure of the reactor and the material of the welded part. Inability to prepare materials.

It is an object of the present invention to provide a method for obtaining a test material for diagnosing deterioration of in-core structures and welded parts of structures.

Another object of the present invention is to provide a method for diagnosing deterioration of a weld having a small volume.

Another object of the present invention is to provide a method for diagnosing deterioration of a boundary portion between a base material portion and a welded portion.

[0007]

According to the present invention, the positioning projections on the inner surface of the shroud, which is one of the reactor internals, and the material of the fillet weld existing around the projections are
It is provided as a test material for deterioration diagnosis.

Further, according to the present invention, there is provided a method for applying a strength test method using a micro test piece to a deterioration diagnosis of a fillet weld portion existing around a positioning projection on an inner surface of a shroud.

Further, according to the present invention, there is provided a method of applying a strength test method using a micro test piece for diagnosing deterioration of a material at a boundary portion between a base material of a reactor internal structure and a welded portion. To be done.

According to the present invention, in a nuclear reactor which has been operated for a certain period of time, a set of materials for a positioning projection on the inner surface of a shroud which is one of the reactor internals and a fillet weld existing around the projection is provided. Is taken out of the reactor by an appropriate method during the periodic inspection of the reactor, and strength tests and physical properties are measured using this test material, observation of metallographic structure, segregation state of elements Of the welded part and the base material of the internal structure of the furnace can be diagnosed by observing the dislocation structure with an electron microscope.

Further, according to the present invention, a minute disc test piece or a minute tensile test piece is cut out from a fillet weld having a very small volume around the positioning projection on the inner surface of the shroud, and the strength test of the weld material is performed. By carrying out the method, it is possible to check the change in the strength of the material of the welded portion and diagnose the deterioration of the welded portion.

Further, according to the present invention, a minute disc test piece is cut out from the boundary between the positioning projection on the inner surface of the shroud and the fillet weld around the shroud so that the boundary exists at the center thereof. Then, the strength test of the small disc test piece can be performed to diagnose the deterioration of the boundary portion between the core material of the reactor internals and the weld material.

[0013]

1 and 2 are views showing a portion from which a test material for deterioration diagnosis is cut out. The shroud 1 is one of the nuclear reactor internal structures, and the fuel assembly enters the central part thereof. Since the reactor internals are immersed in the light water during the operation of the nuclear reactor, the neutrons emitted from the fuel assembly pass through the light water and irradiate the reactor internals including the shroud 1. Therefore, shroud 1 used for a long time
May change its material when exposed to neutron irradiation.
In addition, since light water has a high temperature of about 290 ° C. during the operation of the nuclear reactor, the material of the reactor internal structure including the shroud 1 may change due to thermal aging when operated for a long time. The shroud 1 is provided with four positioning projections 2 welded to the surface of the inner wall 3 of the shroud for use in positioning during plant construction. A fillet weld 4 is present around the positioning projection 2. The positioning protrusion 2 becomes unnecessary when the plant construction is completed. Therefore, after the plant construction is completed, the positioning projection 2 may be cut as shown in FIG. The positioning projection 2 can be cut together with the fillet weld 4 by, for example, a method using a cutter or a method using electric discharge machining. The cut positioning projections 2 and fillet welded portions 4 are taken out of the nuclear reactor and used as test materials for deterioration diagnosis.

FIG. 4 is a view showing a method of collecting a test piece for strength test from the fillet welded portion 4. The material of the welded portion of a nuclear reactor structure is usually stainless steel having a dual phase structure of ferrite and austenite. It is known that this type of material becomes brittle when subjected to thermal aging at high temperature for a long time. Embrittlement also progresses by neutron irradiation. On the other hand, the base material consisting only of an austenite structure hardly causes embrittlement due to thermal aging. Therefore, in terms of embrittlement, it is more important to inspect the material of the weld. Therefore, from the shroud 1 of the plant that has been operated for a long time, the fillet welded portion 4 together with the positioning protrusion 2 is provided.
It is important to cut into a sample material for deterioration diagnosis.
However, as shown in FIG. 4, the volume of the fillet weld is very small, and it is difficult to collect the strength test piece. In this case, a method of performing strength evaluation using a minute disc type test piece is applied. As a method for examining strength characteristics using a disk type test piece, for example, a small punch test method, a disk bend test method, a shear punch test method, and the like have been proposed. Yield strength, fracture strength, ductility-
It is possible to estimate mechanical properties such as brittle transition temperature (DBTT) and fracture toughness value. As shown in FIG. 4, one or more micro disk test pieces 6 are sampled from the fillet welded portion 4. Mechanical properties such as yield strength, fracture strength, ductility-brittleness transition temperature (DBTT), fracture toughness value, etc. by small punch test method, disk bend test method, and shear punch test method using the collected minute disk test piece 6. And the degree of deterioration is diagnosed.

FIG. 5 is a diagram showing another method of utilizing the fillet weld 4 in order to diagnose deterioration of the material of the weld. In this method, a minute tensile test piece 7 is cut out from the fillet welded portion 4 and a tensile test is performed to examine mechanical properties such as yield stress, breaking stress, breaking stretch and drawing, and to diagnose deterioration.

FIG. 6 is a diagram showing a method for diagnosing the deterioration of the boundary portion corresponding to the fusion point between the welded portion and the base metal portion. Deterioration may occur at the boundary, which is different from the case of welds alone or base metal alone, and it is necessary to examine the degree of deterioration by strength tests. However, when the boundary between the positioning projection 2 and the fillet weld 4 is used, the fillet weld 4
Because of the small volume, general strength test pieces cannot be collected. At this time, the micro disk test piece 8 for boundary test is sampled so that the weld boundary comes to the center of the test piece. As shown in FIG. 7, the boundary test micro disk test piece 8 has one side on the boundary test micro disk test piece base material side 9 and the other side on the boundary test micro disk test piece weld side 10 Has become. The indentation test of the center part of the test piece is performed by using the small disk test piece 8 for boundary part test and applying the small punch test method or the disk bend test method which is a test method of pressing the center part of the disk. At some stage in the process of increasing the load, the microdisk test piece for boundary test 8 was cracked from its center by a crack 11
Occurs. At this time, if the boundary is weak, the crack 11 propagates in the boundary. At this time, the degree of deterioration is diagnosed by examining the mechanical properties such as the crack initiation load, the fracture load, the fracture absorbed energy and the like.

FIG. 9 is a diagram showing a method of diagnosing deterioration of a base material. The positioning projection 2 made of the same kind of material as the core material of the furnace has a relatively large volume, and the fracture toughness test piece 12 having a general shape can be sampled. As shown in FIG. 9, a fracture toughness test piece 12 is sampled, a fracture toughness test is performed, and deterioration is diagnosed from the obtained fracture toughness value.

[0018]

According to the present invention, by utilizing the positioning projections on the inner surface of the shroud and the fillet welds existing around the positioning projections as test materials for deterioration diagnosis, the material of the reactor internal structure, It is possible to diagnose deterioration of the material of the welded portion.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a portion of a structure taken as a test material for deterioration diagnosis.

FIG. 2 is a perspective view showing in detail a portion taken as a test material for deterioration diagnosis.

FIG. 3 is a perspective view showing a state in which a portion serving as a test material for deterioration diagnosis is sampled.

FIG. 4 is an explanatory view showing a position where a disk-shaped test piece is sampled from a welded portion of a deterioration diagnosis test material.

FIG. 5 is an explanatory view showing a position where a tensile test piece is sampled from a welded portion of a test material for deterioration diagnosis.

FIG. 6 is an explanatory view showing a sampling position at which a disc-shaped test piece is sampled, targeting a boundary portion between a welded portion and a base material portion of a test material for deterioration diagnosis.

FIG. 7 is an explanatory diagram showing a state before a test of a disk-shaped test piece taken from a boundary portion between a welded portion and a base material portion of a test material for deterioration diagnosis.

FIG. 8 is an explanatory diagram showing a state after the test of the disk-shaped test piece taken from the boundary portion between the welded portion and the base metal portion of the deterioration diagnosis test material.

FIG. 9 is an explanatory view showing a sampling position for sampling a test piece for a fracture toughness test from a base material portion of a test material for deterioration diagnosis.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Shroud, 2 ... Positioning protrusion, 3 ... Shroud inner wall, 4 ... Fillet weld, 5 ... Protrusion cutting mark, 6 ... Micro disk test piece, 7 ... Micro tensile test piece, 8 ... Boundary test micro disk Test piece, 9 ... Micro disk test piece base material side for boundary test, 10 ... Micro disk test piece weld side for boundary test, 11 ... Crack, 12 ... Fracture toughness test piece.

Front Page Continuation (72) Inventor Shinobu Ogido 502 Jinritsucho, Tsuchiura-shi, Ibaraki Machinery Research Laboratory, Hiritsu Seisakusho Co., Ltd. (72) Inventor Shigeo Hattori 3-1-1 Sachimachi, Hitachi-shi, Ibaraki Stock Company Hitachi, Ltd., Hitachi Plant (72) Inventor, Takahiko Kato, 3-1-1, Saiwaicho, Hitachi City, Ibaraki Prefecture Hitachi Ltd., Hitachi Plant

Claims (6)

[Claims] 1. A method for diagnosing deterioration of a welded part, wherein a fillet weld existing around a positioning projection on an inner surface of a shroud which is an internal structure of a nuclear reactor is used as a material for diagnosing deterioration. 2. A brittleness, ductility, and toughness of the welded part are obtained by cutting one or more micro disks capable of punch-type strength test from the fillet welded part according to claim 1 and conducting a strength test of the micro disk. Deterioration diagnosis method for diagnosing fatigue strength and stress corrosion cracking resistance. 3. A microtensile test piece is cut out from the fillet welded portion of claim 1, and a tensile test is performed using this test piece to examine the yield strength, fracture strength, ductility, and fatigue strength of the welded portion. Deterioration diagnosis method for welds. 4. The fillet weld of the positioning projection of the shroud according to claim 1, so that the boundary between the weld and the base metal is located at the center of the micro disk for punch-type strength test. A deterioration diagnosis method for checking the strength of a weld boundary portion from the strength test of the minute disk. 5. The shroud positioning projection according to claim 1, wherein a notched prismatic or cylindrical test piece capable of performing a fracture toughness test from claim 2 and claim 3 or a portion other than a welded portion is used. Deterioration diagnosis method to cut out and perform strength diagnosis of the base material. 6. A hardness test, an observation of a metal structure, an observation of a dislocation structure, an ultrasonic test using a material for a positioning protrusion of the shroud and a fillet weld portion around the shroud according to claim 1.
A method of diagnosing the degree of material deterioration of the reactor internal structure by conducting material property evaluation tests such as electrochemical tests, EPR tests, pulse voltammetry tests, and magnetic property measurement tests.