JP4245487B2 - Material degradation diagnosis method for nuclear reactor structures - Google Patents

Description

  The present invention relates to a material deterioration diagnosis method for a nuclear reactor structure such as a light water cooled nuclear reactor.

FIG. 5 is a diagram schematically showing the structure of a boiling water reactor.
In FIG. 5, in-reactor structures such as a core shroud 3, a core support plate 4, an upper lattice plate 5, and a jet pump 6 are installed inside a reactor pressure vessel 2 containing a core 1.

Most of these in-furnace structures are made of stainless steel, and a diffuser 7 constituting a part of the jet pump 6, a shroud support plate 8 to which the diffuser 7 is connected, etc. use a nickel-based alloy.
Further, the reactor pressure vessel 2 is made of low alloy steel, and stainless steel or nickel base alloy is subjected to buttering welding (overlay welding) on the inner surface of the reactor pressure vessel 2.

By the way, since the reactor internal structure and the reactor pressure vessel 2 are subjected to irradiation of fast neutrons from the fuel for a long time during operation of the nuclear power plant, the stainless steel forming the reactor structure and the reactor pressure vessel 2 A nuclear reaction occurs in a constituent element such as a nickel-based alloy, and a gaseous component such as helium is slightly present in these materials. In the case of stainless steel or nickel-base alloy, the main nuclear reactions related to the production of helium are as shown in the following formulas (1) and (2).
¹⁰ B (n, ⁴ He) ⁷ Li (1)
⁵⁸ Ni (n, γ) ⁵⁹ Ni (n, ⁴ He) ⁵⁶ Fe (2)
That is, boron-10 ( ¹⁰ B in the formula) and nickel-58 ( ⁵⁸ Ni in the formula) contained in the material are main elements that are sources of transmutation helium. Boron-10 is a monoisotope of boron element contained in a trace amount as an impurity in stainless steel or nickel base alloy, and nickel-58 is a monoisotope of nickel which is a main constituent element of stainless steel or nickel base alloy. .

  As described in Non-Patent Document 1, it has become clear that gas components such as helium in the material described above cause cracks during welding. It is considered that the crack generation mechanism at the time of welding is caused by agglomeration at the crystal grain boundary near the molten metal to form bubbles by heating at the time of welding.

  Therefore, when repairing and welding reactor structures that have been irradiated with neutrons for the purpose of improving the safety and reliability of nuclear power plants, gas components such as helium in the material cause cracks by welding. It is necessary to examine whether or not there is a possibility, that is, whether or not welding is possible. For that purpose, it is extremely important to accurately grasp the amount of helium in the welding target portion.

  Conventionally, as a method for examining the amount of helium in a nuclear reactor structure that has been irradiated with neutrons, for example, the method described in Patent Documents 1 and 2, that is, the amount of helium contained in a microvolume sample collected from a welding object is gas. A method of measuring with a quantity measuring device is known.

Conventionally, as shown in FIG. 6, the amount of transmutation helium is analyzed from the chemical component 9, the neutron irradiation distribution 10, and the transmutation reaction cross-section 11 contained in the constituent material of the reactor structure by the transmutation helium amount analysis 12. A method of performing distribution prediction 13 and grasping the amount of helium in the repair welding target part is adopted.
Shohei Kawano, “Welding repair technology for reactor structural materials containing helium”, Journal of the Japan Welding Society, 2001, Vol. 70, No. 8, p.742 JP 7-244190 A (page 2) JP 10-111380 A (second page)

  In repairing a nuclear reactor structure, it is assumed that a portion where material deterioration such as stress corrosion cracking has occurred is welded over a wide range. Therefore, it is necessary to grasp all the helium amount in the repair welding target part, but the helium amount contained in the reactor structure varies depending on the location, and samples are taken from all the repair welding target parts to measure the helium amount. That is practically difficult. The reason why the amount of helium generated by transmutation varies depending on the location of the reactor structure is that the amount of neutron irradiation varies depending on the distance from the nuclear fuel.

  On the other hand, it is possible to quantitatively grasp the amount of helium in the target portion by the method of grasping the amount of helium in the portion to be repaired as shown in FIG. 6, but there are some problems as described below. I have it.

  That is, the first problem is that, among the chemical components 9 included in the constituent materials of the nuclear reactor structure, the amount of boron, which is an impurity element, is not measured at the manufacturing stage of the constituent materials and may not be accurately grasped. That is the point. Since the amount of boron differs depending on the production lot of the constituent material, it is necessary to accurately grasp the amount of boron in the material in order to accurately predict the amount of helium.

  The second problem is the accuracy of the neutron dose distribution 10. In order to derive the distribution of neutron dose received by the reactor structure, for example, a calculation program code that solves the two-dimensional multigroup transport equation by the discrete ordinate method is used. Since there is an error inherent in such analysis, it is necessary to accurately grasp the irradiation amount of the repair welding target site.

  The third problem is the accuracy of the transmutation helium amount analysis 11. In order to obtain the amount of transmutation helium, the transmutation reactions shown in the above formulas (1) and (2) are analyzed by the transmutation reaction equation, but it is necessary to correct the analytical error.

  Accordingly, an object of the present invention has been made in order to solve the above-described problems, and is a method for diagnosing material deterioration of a nuclear reactor structure capable of accurately predicting the distribution of transmutation helium contained in the nuclear reactor structure. Is to provide.

In order to achieve the above object, the invention of the method for diagnosing material deterioration of a nuclear reactor structure according to claim 1 includes a step of collecting a sample from a nuclear reactor structure that has been subjected to sexual irradiation, and boron from the collected sample. A step of analyzing the amount of -11, and an initial amount of boron consisting of the amount of boron-11 and the amount of boron-10 contained in the constituent material of the reactor structure before receiving neutron irradiation from the amount of boron-11 analyzed in the above step Using the estimation step, the boron-10 amount contained in the estimated initial boron amount , the chemical component containing nickel-58 contained in the constituent material of the reactor structure, and the neutron irradiation distribution And a step of predicting the distribution of transmutation helium contained in the reactor structure.

Further, the invention of the method for diagnosing material deterioration of a nuclear reactor structure according to claim 2 includes a step of collecting a sample from a nuclear reactor structure that has been irradiated with neutrons, and an amount of boron-11 and an amount of helium from the collected sample. Each of the steps of analyzing, and the step of estimating the initial amount of boron consisting of the amount of boron-11 and the amount of boron-10 contained in the constituent material of the reactor structure before receiving neutron irradiation from the amount of boron-11 analyzed in the above step The reactor structure using the boron-10 amount contained in the estimated initial boron amount , the chemical component containing nickel-58 contained in the constituent material of the reactor structure, and the neutron irradiation distribution a step of analyzing the transmutation helium weight distribution contained in the object, the helium amount of the above analysis, the transmutation helium weight distribution corrected by correcting the transmutation helium weight distribution said analysis And that step, characterized by a step of predicting a transmutation helium weight distribution contained in the reactor structure.

The invention of the method for diagnosing material deterioration of a nuclear reactor structure according to claim 3 includes a step of collecting a sample from the nuclear reactor structure that has been subjected to neutron irradiation, and a step of analyzing the amount of boron-11 from the collected sample. The step of analyzing the amount of helium and the step of estimating the amount of neutron irradiation, and the amount of boron-11 and boron contained in the constituent material of the reactor structure before receiving neutron irradiation from the amount of boron-11 analyzed in the step A step of estimating an initial boron amount consisting of -10 amounts, a step of correcting a neutron irradiation amount distribution from the estimated neutron irradiation amount , the boron-10 amount included in the estimated initial boron amount, and a reactor structure a step of analyzing the transmutation helium weight distribution contained in the reactor structure using neutron dose distributions chemical composition and correct containing nickel -58 included in the material of the The analysis helium amount, to a step of predicting obtaining a transmutation helium weight distribution corrected by correcting the transmutation helium weight distribution said analysis, the transmutation helium weight distribution contained in the reactor structure It is characterized by.

Further, the invention of the method for diagnosing material deterioration of a nuclear reactor structure according to claim 4 includes a step of collecting a sample from the nuclear reactor structure that has been irradiated with neutrons, and a step of analyzing the amount of boron-11 from the collected sample And a step of estimating the neutron irradiation amount, and an initial boron composed of the boron-11 amount and the boron-10 amount contained in the constituent material of the reactor structure before receiving the neutron irradiation from the boron-11 amount analyzed in the step A step of estimating the amount, a step of correcting the neutron irradiation distribution from the estimated amount of neutron irradiation, the amount of boron-10 included in the estimated initial boron amount, and nickel included in the constituent material of the reactor structure And a step of predicting the transmutation helium content distribution contained in the reactor structure using the chemical composition including -58 and the corrected neutron dose distribution.

  According to the present invention, the transmutation helium content distribution is analyzed from a sample collected from a reactor structure that has been irradiated with neutrons, and the transmutation helium content distribution is corrected based on the analyzed helium content. Since the transmutation helium content distribution can be accurately predicted, it is effective for extending the life of the nuclear reactor and for maintenance measures, and improving the reliability of the nuclear reactor.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, about the element which is common throughout each figure, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

Example 1
FIG. 1 is a process diagram showing a first embodiment of a diagnostic method for a nuclear reactor structure according to the present invention. In FIG. 1, first, a sample 15 is taken from the reactor structure 14 (step 1). Next, boron-11 quantity analysis 16 is performed on the collected sample 15 by a mass spectrometer or the like, thereby obtaining boron-11 quantity 17 by actual measurement (step 2).

The shape of the sample 14 to be collected is a solid having a size that is the minimum necessary for analysis and does not affect the function of the evaluation target. The dimensions of the sample satisfying this condition are a thickness of 0.1 mm to 20 mm and an area of 1 mm ^{2 to} 100 mm ² .

Since boron-11 undergoes almost no transmutation reaction even when irradiated with neutrons and does not decrease, the amount of initial boron contained in the constituent material of the reactor structure before receiving neutron irradiation from the measured amount of boron-11 17 18 is estimated (step 3).
Note that the initial boron amount 18 can be estimated by collecting the sample 15 from a portion made of the material of the same production lot as the reactor structure 14 that predicts the helium amount.

  From the estimated initial boron amount 18, the chemical component 9 included in the constituent material of the nuclear reactor structure such as nickel, the neutron irradiation distribution 10 and the transmutation reaction cross section 11 which have been examined in advance, the transmutation helium The quantity analysis 12 is performed, and the transmutation helium quantity distribution prediction 13 included in the nuclear reactor structure 14 is performed (step 4).

  As described above, according to this embodiment, it becomes possible to accurately grasp the amount of boron that has not been measured in the manufacturing stage of the constituent material, and accurately predict the amount of helium contained in the reactor structure. Can do.

(Example 2)
FIG. 2 is a process diagram showing Embodiment 2 of the method for diagnosing a reactor structure according to the present invention.
In FIG. 2, first, a sample 15 is collected from the nuclear reactor structure 14 (step 1). Next, a boron-11 quantity analysis 16 is performed on the collected sample 15 to obtain a boron-11 quantity 17 by actual measurement (step 2), and a helium quantity analysis 19 is performed to obtain a helium quantity 20 by actual measurement. (Step 5).

  Next, the initial boron amount 18 is estimated from the boron-11 amount 17 actually measured in the step 2 (step 3). From the estimated initial boron amount 18, the chemical component 9 included in the constituent material of the nuclear reactor structure such as nickel, the neutron irradiation distribution 10 and the transmutation reaction cross section 11, A conversion helium amount analysis 12 is performed to obtain a transmutation helium amount distribution 21 contained in the reactor structure (step 6).

  Furthermore, the transmutation contained in the nuclear reactor structure 14 is performed on the analyzed transmutation helium content distribution by performing transmutation helium content distribution correction 22 (step 7) with the helium amount 20 actually measured in step 5 described above. Helium amount distribution prediction 13 is performed.

  FIG. 3 is a diagram for explaining a method of correcting the transmutation helium amount distribution from the actually measured helium amount. FIG. 3A shows a cylindrical reactor structure 14 such as a core shroud having a circumferential angle of 0 ° to 90 °. A bird's-eye view when cut in a range of ° is schematically shown. 25 is a weld line, and 26-1 to 26-3 indicate sampling positions in the vicinity of the weld line 25.

  On the other hand, (b) shows the transmutation helium amount distribution 27 in the circumferential direction obtained by analysis of the vicinity of the circumferential weld line 25 on the inner surface of the cylindrical nuclear reactor structure 14. When the helium amounts of the three samples collected from the data collection positions 26-1 to 26-3 on the inner surface of the cylindrical nuclear reactor structure 14 are indicated by measured values 28-1 to 28-3, respectively, they are obtained by analysis. By fitting the circumferential transmutation helium amount distribution 27 to the measured values 28-1 to 28-3, a corrected transmutation helium amount distribution 29 can be obtained.

  As described above, according to this embodiment, it is possible to accurately grasp the amount of boron that has not been measured in the manufacturing stage of the constituent material, and to correct the analysis accuracy of transmutation helium. The amount of helium contained in the reactor structure can be accurately predicted.

(Example 3)
FIG. 4 is a process diagram showing Embodiment 3 of the nuclear reactor structure diagnosis method according to the present invention.
In the third embodiment, a step 8 of neutron irradiation estimation 23 for estimating the neutron irradiation dose from the specific gamma ray intensity of the collected sample 15 is added to the second embodiment shown in FIG. It has been corrected.

  That is, the neutron irradiation amount estimated from the specific gamma ray intensity in step 8 of the neutron irradiation estimation 23 is estimated, and the neutron irradiation distribution 10 is corrected (neutron irradiation distribution correction) 24 based on the estimated neutron irradiation amount. (Step 9), and further, by analyzing the amount of transmutation helium from the corrected neutron dose distribution 10, the chemical component 9 contained in the constituent material of the reactor structure, and the transmutation reaction cross section 11, the reactor A transmutation helium amount distribution 21 contained in the structure is obtained.

  Further, the transmutation helium amount distribution 21 analyzed in step 6 described in the second embodiment is corrected with the helium amount 20 actually measured in step 5 described in the second embodiment (transmutation helium amount distribution). By performing (correction) 22 (step 7), the transmutation helium amount distribution prediction 13 included in the nuclear reactor structure 14 is performed.

  As a method of estimating the neutron irradiation amount described above, the characteristic γ-ray intensity of cobalt-59 or the like generated by the nuclear transformation contained in the sample 15 can be measured, and the neutron irradiation amount can be analyzed from the measurement result.

  As described above, according to this embodiment, it is possible to accurately grasp the amount of boron that has not been measured in the manufacturing stage of the constituent material, and to correct the analysis accuracy of transmutation helium. In addition, the analysis accuracy of the neutron irradiation amount can be corrected, and the amount of helium contained in the reactor structure can be accurately predicted.

1 is a process diagram showing a first embodiment of a diagnostic method for a nuclear reactor structure according to the present invention. FIG. 5 is a process diagram showing a second embodiment of the nuclear reactor structure diagnostic method of the present invention. (A) And (b) is a schematic diagram and a characteristic diagram which show the example which correct | amends the transmutation helium quantity distribution with the helium quantity measured value in the diagnostic method of the nuclear reactor structure of this invention. FIG. 5 is a process diagram showing a third embodiment of the diagnostic method for a nuclear reactor structure according to the present invention. The longitudinal cross-sectional view which shows schematic structure of a boiling water reactor. FIG. 5 is a process diagram showing Example 1 of a conventional nuclear reactor structure diagnosis method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Reactor pressure vessel, 3 ... Core shroud, 4 ... Core support plate, 5 ... Upper lattice plate, 6 ... Jet pump, 7 ... Diffuser, 8 ... Shroud support plate, 9 ... Reactor structure Chemical components contained in the constituent materials, 10 ... Neutron irradiation distribution, 11 ... Transmutation reaction cross section, 12 ... Transmutation helium content analysis, 13 ... Transmutation helium content distribution prediction, 14 ... Reactor in-reactor equipment, 15 ... Sampling, 16 ... sample, 17 ... boron-11 quantity analysis, 18 ... boron-11 quantity, 19 ... initial boron quantity, 20 ... helium quantity analysis, 21 ... helium quantity, 22 ... transmutation helium quantity distribution, 23 ... nucleus Conversion helium amount distribution correction, 24 ... cylindrical reactor structure, 25 ... circumferential weld line, 26-1 to 26-3 ... sampling position, 27 ... circumferential helium amount distribution, 28 ... measured helium amount, 29 ... Correction Helium weight distribution, 30 ... neutron irradiation amount estimation, 31 ... neutron irradiation amount, 32 ... neutron dose distribution correction.

Claims (6)

Taking a sample from a reactor structure that has been subjected to neutron irradiation;
Analyzing the amount of boron-11 from the collected sample;
Estimating the initial boron content comprising the boron-11 content and the boron-10 content contained in the constituent material of the reactor structure before receiving neutron irradiation from the boron-11 content analyzed in the step;
Using the estimated amount of boron-10 included in the estimated initial boron amount , the chemical composition including nickel-58 included in the constituent material of the reactor structure, and the neutron dose distribution, And a process for predicting the distribution of the amount of transmutated helium contained therein. Taking a sample from a reactor structure that has been subjected to neutron irradiation;
Analyzing the amount of boron-11 and the amount of helium from the collected sample,
Estimating the initial boron content comprising the boron-11 content and the boron-10 content contained in the constituent material of the reactor structure before receiving neutron irradiation from the boron-11 content analyzed in the step;
Using the estimated amount of boron-10 included in the estimated initial boron amount , the chemical composition including nickel-58 included in the constituent material of the reactor structure, and the neutron dose distribution, Analyzing the transmutation helium content distribution included;
A helium amount described above analyzed, obtaining a transmutation helium weight distribution corrected by correcting the transmutation helium weight distribution said analysis,
And a method for predicting the distribution of transmutation helium contained in the nuclear reactor structure. Taking a sample from a reactor structure that has been subjected to neutron irradiation;
A step of analyzing the amount of boron-11 from the collected sample, a step of analyzing the amount of helium, and a step of estimating the neutron irradiation amount;
Estimating the initial boron amount composed of the boron-11 amount and the boron-10 amount contained in the constituent material of the reactor structure before receiving neutron irradiation from the boron-11 amount analyzed in the step;
Correcting the neutron dose distribution from the estimated neutron dose;
Nuclei contained in the reactor structure using the boron-10 amount contained in the estimated initial boron amount , the chemical composition containing nickel-58 contained in the constituent material of the reactor structure, and the corrected neutron dose distribution Analyzing the converted helium content distribution;
A helium amount described above analyzed, obtaining a transmutation helium weight distribution corrected by correcting the transmutation helium weight distribution said analysis,
And a method for predicting the distribution of transmutation helium contained in the nuclear reactor structure. Taking a sample from a reactor structure that has been subjected to neutron irradiation;
Analyzing the boron-11 amount from the collected sample and estimating the neutron irradiation amount;
Estimating the initial boron amount composed of the boron-11 amount and the boron-10 amount contained in the constituent material of the reactor structure before receiving neutron irradiation from the boron-11 amount analyzed in the step;
Correcting the neutron dose distribution from the estimated neutron dose;
Nuclei contained in the reactor structure using the boron-10 amount contained in the estimated initial boron amount , the chemical composition containing nickel-58 contained in the constituent material of the reactor structure, and the corrected neutron dose distribution A method for diagnosing material deterioration of a nuclear reactor structure, comprising a step of predicting a distribution of converted helium amount. 5. The method for diagnosing material deterioration of a nuclear reactor structure according to claim 3 or 4, wherein the method of estimating the neutron irradiation amount of the collected sample estimates the neutron irradiation amount from the specific gamma ray intensity of the sample. 5. The reactor structure according to claim 1, wherein the sample collected from the reactor structure has a thickness of 0.1 mm to 20 mm and an area of 1 mm ^{2 to} 100 mm ² . Material deterioration diagnosis method.

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