Methods for assessing the mitigation of annealing after ion irradiation of reactor pressure vessel steel

Abstract

This invention discloses a method for evaluating the degree of annealing mitigation after ion irradiation of reactor pressure vessel steel, comprising the following steps: obtaining characteristic nanohardness, dislocation loops, cluster number density, and average size before ion irradiation; irradiating a sheet sample with ion and simulating the damage area; obtaining characteristic nanohardness, dislocation loops, cluster number density, and average size after ion irradiation; performing vacuum thermal annealing on the ion-irradiated sheet sample; obtaining characteristic nanohardness, dislocation loops, cluster number density, and average size after vacuum thermal annealing; calculating the contribution of different types of defects to the yield strength increment of the sheet sample at different treatment stages; calculating the performance recovery degree of the sheet sample after vacuum thermal annealing based on defect recovery and nanohardness testing, respectively; evaluating the rationality of temperature selection in the annealing process after irradiation of reactor pressure vessel steel, and calculating the degree of annealing mitigation under this condition.

Description

Technical Field

[0001] This invention belongs to the field of service life extension technology evaluation for nuclear power materials, and specifically relates to an evaluation method for the degree of mitigation of thermal annealing after ion irradiation of RPV steel. Background Technology

[0002] The operational lifespan of a nuclear power plant largely depends on the lifespan of "non-replaceable equipment," such as the reactor pressure vessel (RPV), which is the only non-replaceable component within the reactor. During operation, the RPV is subjected to intense neutron irradiation, causing hardening / embrittlement effects on the material. Studies show that after neutron irradiation, RPV steel develops a series of microstructural defects, leading to changes in its mechanical properties (such as increased yield strength, decreased toughness, and increased brittleness). The embrittlement sources mainly include dislocation loops and solute atom clusters.

[0003] Irradiation embrittlement reduces the safety of RPV (Replacing Power Vehicle) service, and extending the service life of nuclear power plants is one of the most pressing issues in the global nuclear power engineering field. Extending the service life of "non-replaceable equipment" through life assessment, aging management, and technical maintenance is crucial. As a safety device in nuclear power plants subjected to long-term neutron irradiation, RPV aging is primarily caused by irradiation damage. To eliminate irradiation damage and extend RPV service life, thermal annealing has been proposed to mitigate irradiation defects, and related research has been included in nuclear power plant service life extension research projects in many countries.

[0004] High-temperature annealing can restore the toughness of RPV steel after irradiation and alleviate the irradiation embrittlement effect to some extent. In related irradiation studies, neutron irradiation experiments are radioactive, causing many inconveniences for material irradiation and annealing research. Ion irradiation is relatively inexpensive and efficient, and is currently widely used both domestically and internationally to simulate the damage effects induced by neutron irradiation. Because the correlation between irradiation embrittlement and irradiation defects in RPV steel is complex, there is currently a lack of evaluation methods for annealing mitigation of irradiation defects in RPV steel, making it difficult to assess the actual degree of annealing mitigation. Conventional research methods, through experimental characterization, can only qualitatively determine the annealing effect after irradiation, making it difficult to accurately and scientifically quantitatively assess the degree of annealing mitigation. Summary of the Invention

[0005] In view of this, in order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for evaluating the degree of mitigation of annealing after ion irradiation of reactor pressure vessel steel, and to provide technical evaluation guidance for extending the service life of RPV equipment in nuclear power plants.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for assessing the degree of mitigation of annealing after ion irradiation of reactor pressure vessel steel, comprising the following steps:

[0008] The reactor pressure vessel steel was prepared into sheet-like samples;

[0009] The characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of sheet-like samples before ion irradiation were obtained.

[0010] Ion irradiation was performed on sheet-like samples, and the damage area was simulated and calculated.

[0011] The characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of sheet-like samples after ion irradiation were obtained.

[0012] Vacuum thermal annealing was performed on sheet-like samples after ion irradiation.

[0013] The characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of sheet-like samples were obtained after vacuum thermal annealing.

[0014] The contribution of different types of defects (i.e. dislocation loops and solute atom clusters) to the yield strength increment of sheet samples under different treatment stages (i.e. before ion irradiation, after ion irradiation, and after vacuum thermal annealing) was calculated.

[0015] The performance recovery of sheet samples after vacuum thermal annealing was calculated based on defect recovery and nanohardness testing, respectively.

[0016] Based on two performance recovery parameters, the rationality of temperature selection in the post-irradiation annealing process of reactor pressure vessel steel is evaluated, and the degree of annealing mitigation R under these conditions (i.e., annealing temperature T and annealing time t in vacuum hot annealing) is calculated. pia .

[0017] According to some preferred embodiments of the present invention, the sheet sample is prepared by the following method: RPV steel material is processed into square sheet samples with a thickness of 0.5 to 1.5 mm and a side length between 10 and 15 mm by wire cutting; the surface of the sheet sample is polished with metallographic sandpaper of 400 to 2000#; and then polished to a mirror finish.

[0018] According to some preferred embodiments of the present invention, the sheet-like sample exhibits a characteristic nanohardness H before ion irradiation. unirr Obtained through the following method:

[0019] Nanohardness testing was performed on sheet-like samples. The Poisson's ratio (an intrinsic parameter of the material) of the reactor pressure vessel steel was set, the indentation depth was set to ≥2μm, and ≥10 indentation test points were used. For each indentation point, a set of curves relating nanohardness H to indentation depth h were obtained. The average curve of multiple curves was then plotted. The value of H on the average curve was analyzed. 2 By performing a linear fit with 1 / h and calculating the arithmetic square root of the intercept of the fitted line, the characteristic nanohardness H of the sheet-like sample before ion irradiation is obtained. unirr .

[0020] According to some preferred embodiments of the invention, the number density N of dislocation loops in the sheet-like sample before ion irradiation loop,unirr and average size D loop,unirr Obtained through the following method:

[0021] Dislocation loops in steel sheet samples from reactor pressure vessels were characterized using transmission electron microscopy (TEM). The characterization region was selected within 5 μm of the sample surface, and the number density N of dislocation loops within the field of view was statistically analyzed. loop,unirr and average size D loop,unirr .

[0022] According to some preferred embodiments of the invention, the number density N of the clusters in the sheet-like sample before ion irradiation cluster,unirr and average size D cluster,unirr Obtained through the following method:

[0023] Clusters in steel sheet samples from reactor pressure vessels were characterized using a three-dimensional atomic probe microanalysis method. The sample area was selected within 5 μm of the surface of the sheet sample, and the corresponding cluster number density N was statistically analyzed. cluster,unirr and average size D cluster,unirr .

[0024] According to some preferred embodiments of the invention, the ion irradiation is: irradiating a steel sheet sample of a reactor pressure vessel with a specific energy E of ≤300 keV and a specific damage amount of 0 to 10 dpa using protons.

[0025] According to some preferred embodiments of the present invention, the simulated damage region is calculated by irradiation damage distribution simulation using SRIM software, with the damage peak depth d peak ±100nm is considered the damage region, i.e., the depth range Ω of the damage peak region is d. peak -100nm to d peak +100nm.

[0026] According to some preferred embodiments of the present invention, the sheet-like sample exhibits a characteristic nanohardness H after ion irradiation. irr Obtained through the following method:

[0027] Nanohardness tests were performed on sheet-like samples after ion irradiation. The Poisson's ratio for reactor pressure vessel steel was set, the indentation depth was set to ≥2 μm, and ≥10 indentation test points were used. For each indentation point, a set of curves relating nanohardness H to indentation depth h was obtained. The average curve of multiple curves was then plotted. The H value of the average curve was analyzed. 2 A linear fit is performed with 1 / h, and the h of the linear fit region is 0.1×(d). peak -100) to 0.2×(d) peak +100), calculate the arithmetic square root of the intercept of the fitted straight line, which yields the characteristic nanohardness H of the irradiated area. irr ;

[0028] According to some preferred embodiments of the invention, the number density D of dislocation loops in the sheet-like sample after ion irradiation loop,irr and average size D loop,irr Obtained through the following method:

[0029] Dislocation loops in ion-irradiated sheet-like samples were characterized using transmission electron microscopy. The depth range of Ω within the characterization region, including the damage peak region, was determined, and the number density D of dislocation loops within the field of view was statistically analyzed. loop,irr and average size D loop,irr .

[0030] According to some preferred embodiments of the invention, the number density N of the clusters in the sheet-like sample after ion irradiation cluster,irr and average size D cluster,irr Obtained through the following method:

[0031] Clusters in sheet-like samples after ion irradiation were characterized using a three-dimensional atomic probe microanalysis. The characterization region included the depth range Ω of the damage peak region, and the corresponding cluster number density N was statistically analyzed. cluster,irr and average size D cluster,irr .

[0032] According to some preferred embodiments of the present invention, the vacuum thermal annealing treatment is as follows: the sheet-like sample after ion irradiation is subjected to vacuum thermal annealing treatment, and the vacuum degree is better than (but not higher than, the lower the vacuum degree value, the better the vacuum degree) 5 × 10 - 4 The temperature is set at Pa and maintained for at least 30 minutes, with a heating rate of 10 ± 5 °C / min. The target temperature is set to T, and the holding time is t. After the holding time, the furnace is cooled to room temperature. The vacuum degree during the heating, holding, and cooling processes is better than 5 × 10⁻⁶. -4 Pa.

[0033] According to some preferred embodiments of the present invention, the sheet-like sample exhibits a characteristic nanohardness H after vacuum thermal annealing. pia Obtained through the following method:

[0034] Nanohardness tests were performed on sheet-like samples after ion irradiation. The Poisson's ratio for reactor pressure vessel steel was set, the indentation depth was set to ≥2 μm, and ≥10 indentation test points were used. For each indentation point, a set of curves relating nanohardness H to indentation depth h was obtained. The average curve of multiple curves was then plotted. The H value of the average curve was analyzed. 2 By performing a linear fit with 1 / h and calculating the arithmetic square root of the intercept of the fitted line, the characteristic nanohardness H of the annealed original irradiated region can be obtained. pia ;

[0035] The fitted region h is 0.1×(d peak -100) to 0.2×(d) peak +100).

[0036] According to some preferred embodiments of the invention, the number density N of dislocation loops in the sheet-like sample after vacuum thermal annealing is... loop,pia and average size D loop,pia Obtained through the following method:

[0037] Dislocation loops in sheet-like samples after vacuum thermal annealing were characterized using transmission electron microscopy. The depth range of Ω within the characterization region, including the damage peak region, was determined, and the number density N of dislocation loops within the field of view was statistically analyzed. loop,pia and average size D loop,pia .

[0038] According to some preferred embodiments of the invention, the number density N of the clusters in the sheet-like sample after vacuum thermal annealing is... cluster,pia and average size D cluster,pia Obtained through the following method:

[0039] Clusters in sheet-like samples after vacuum thermal annealing were characterized using a three-dimensional atomic probe microanalysis. The characterization region needed to include the depth range Ω of the damage peak region, and the corresponding cluster number density N was statistically analyzed. cluster,pia and average size D cluster,pia .

[0040] According to some preferred embodiments of the present invention, the contribution of different types of defects to the yield strength increment of a sheet-like sample at different treatment stages is calculated, including calculating the yield strength increment Δσ caused by irradiation defects based on the characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of the sheet-like sample before and after ion irradiation. defect,irr :

[0041] Δσ loop,irr =5.19×10 -10 ·[(N loop,irr ·D loop,irr ) 0.5 -(N loop,unirr ·D loop,unirr) 0.5 ]

[0042] Δσ cluster,irr =1.73×10 -10 ·[(N cluster,irr ·D cluster,irr ) 0.5 -(N cluster,unirr ·D cluster,unirr ) 0.5 ]

[0043] Δσ defect,irr =[(Δσ loop,irr ) 2 +(Δσ cluster,irr ) 2 ] 0.5

[0044] In the formula, Δσ loop,irr Δσ represents the yield strength increment caused by dislocation loops after ion irradiation. cluster,irr Δσ represents the yield strength increment caused by solute clusters after ion irradiation. defect,irr This represents the total increase in yield strength caused by ion irradiation defects, including dislocation loops and solute clusters. Coefficients such as 5.19 and 1.73, used in the formula, represent the degree of influence of different defects on the increase in yield strength.

[0045] According to some preferred embodiments of the invention, the contribution of different types of defects to the yield strength increment of a sheet sample at different processing stages is calculated, including calculating the yield strength increment Δσ caused by residual irradiation defects based on the characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of the sheet sample before ion irradiation and after vacuum thermal annealing. defect,pia :

[0046] Δσ loop,pia =5.19×10 -10 ·[(N loop,pia ·D loop,pia ) 0.5 -(N loop,unirr ·D loop,unirr ) 0.5 ]

[0047] Δσ cluster,pia =1.73×10 -10 ·[(N cluster,pia ·D clustet,pia ) 0.5 -(N cluster,unirr ·D cluster,unirr ) 0.5 ]

[0048] Δσ defect,pia =[(Δσ loop,pia) 2 +(Δσ cluster,pia ) 2 ] 0.5

[0049] In the formula, Δσ loop,pia Δσ represents the yield strength increment caused by dislocation loops after vacuum heat annealing. cluster,pia Δσ represents the yield strength increment caused by solute clusters after vacuum heat annealing. defect,pia This represents the total increase in yield strength caused by irradiation defects after vacuum heat annealing, including dislocation loops and solute clusters. Coefficients such as 5.19 and 1.73, used in the formula, represent the degree of influence of different defects on the increase in yield strength.

[0050] According to some preferred embodiments of the present invention, the degree of performance recovery R based on defect recovery after vacuum thermal annealing of sheet-like samples is calculated. defect Perform the following formula:

[0051]

[0052] Performance recovery degree R based on defect recovery defect This represents the degree to which the "recovery of defects" affects the irradiation embrittlement of materials.

[0053] According to some preferred embodiments of the present invention, the degree of performance recovery R of sheet-like samples after vacuum thermal annealing is calculated based on nanohardness testing. hardnesstest Perform the following formula:

[0054]

[0055] Performance recovery degree R based on nanohardness test hardnesstest This represents the degree of recovery in "hardness".

[0056] According to some preferred embodiments of the present invention, the rationality of temperature selection in vacuum thermal annealing of sheet-like samples after ion irradiation is evaluated based on two performance recovery parameters:

[0057] If R defect >R hardnesstest The evaluation indicates that the temperature in the vacuum heat annealing process under these conditions is too high.

[0058] If R defect =R hardnesstest The appropriateness of the temperature in the vacuum heat annealing process under these conditions was evaluated.

[0059] If R defect <R hardnesstest The evaluation indicates that the temperature in the vacuum heat annealing process under these conditions is too low.

[0060] According to some preferred embodiments of the invention, the degree of annealing relief R pia Perform the following formula:

[0061]

[0062] Due to the adoption of the above technical solutions, the advantages of this invention compared to the prior art are as follows: The evaluation method for the degree of mitigation of annealing after ion irradiation of reactor pressure vessel steel of this invention overcomes the shortcomings of traditional experimental studies that can only qualitatively evaluate the mitigation effect of irradiation annealing. It can more accurately, scientifically and rationally quantitatively evaluate the degree of mitigation of annealing after irradiation of RPV steel, and reasonably guide the optimization of annealing process, providing a scientific and reasonable evaluation method for the development of nuclear power RPV life extension annealing engineering technology. Detailed Implementation

[0063] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0064] This invention provides a method for evaluating the degree of mitigation of annealing after ion irradiation in RPV steel. By quantitatively calculating the degree of mitigation after irradiation by considering the contribution of different defects to material properties, the method effectively evaluates the annealing effect of RPV steel and provides reasonable guidance for optimizing the annealing process. This provides a technical method reference for the theory and engineering application of annealing extension of nuclear power RPV. The method for evaluating the degree of mitigation of annealing after ion irradiation in reactor pressure vessel steel in this application includes the following steps:

[0065] 1) RPV steel material is processed into sheet samples of a certain size by wire cutting, and the surface is ground and polished;

[0066] 2) Characterize the sample’s characteristic nanohardness, number density and average size of dislocation loops and clusters before ion irradiation;

[0067] 3) Ion irradiation with specific energy and damage amount was carried out on RPV steel samples, and the damage area was calculated by SRIM simulation;

[0068] 4) The characteristic nanohardness, number density and average size of dislocation loops and clusters of the sample were characterized again after ion irradiation.

[0069] 5) Vacuum heat annealing treatment was carried out on irradiated RPV steel samples under specific conditions such as vacuum degree, heating rate, temperature, and holding time.

[0070] 6) After heat annealing, the characteristic nanohardness, number density and average size of dislocation loops and clusters of the samples were characterized again.

[0071] 7) Calculate the contribution of different types of defects to the yield strength increment under different treatment stages of RPV steel;

[0072] 8) Calculate the performance recovery degree of RPV steel after irradiation annealing based on defect recovery and nano-hardness test, respectively;

[0073] 9) Based on the two performance recovery parameters obtained in step 8, evaluate the rationality of the temperature selection in the post-irradiation annealing process of RPV steel, and finally calculate the annealing mitigation degree R under this condition. pia .

[0074] Specifically, this embodiment includes the following steps:

[0075] Step 1: Prepare sheet-like samples

[0076] RPV steel material is processed into square sheet samples with a thickness of 1mm and a side length between 10 and 15mm by wire cutting. The surface of the sample is polished with metallographic sandpaper of 400 to 2000# and then polished to a mirror finish to obtain sheet samples of RPV steel.

[0077] Step 2: Characterization before ion irradiation

[0078] Obtaining the characteristic nanohardness H of sheet-like samples before ion irradiation unirr Dislocation loop number density N before ion irradiation loop,unirr and average size D loop,unirr Number density N of clusters before ion irradiation cluster,unirr and average size D cluster,unirr Data. Details are as follows:

[0079] 2.1) Characteristic Nanohardness Characterization

[0080] Nanoindentation technology was used to test the nanohardness of sheet-like samples. A continuous stiffness mode was selected, the Poisson's ratio of the RPV material was set, the indentation depth was set to ≥2μm, and ≥10 indentation test points were used. For each indentation point, a set of curves relating nanohardness H to indentation depth h was obtained. The average curve of multiple curves was then plotted. The value of H on the average curve was analyzed. 2 By performing a linear fit with 1 / h and calculating the arithmetic square root of the intercept of the fitted line, the characteristic nanohardness H of the unirradiated sample is obtained. unirr .

[0081] 2.2) Characterization of dislocation loops

[0082] Dislocation loops in RPV steel sheet samples were characterized using transmission electron microscopy (TEM). For samples before ion irradiation, the sample region within 5 μm of the surface was selected. The number density N of dislocation loops within the field of view was statistically analyzed using TEM. loop,unirr and average size D loop,unirr .

[0083] 2.3) Characterization of solute clusters

[0084] RPV steel sample clusters were characterized using a three-dimensional atomic probe microanalysis (3D Atomic Probe). For samples before ion irradiation, the sample region selected was within 5 μm of the surface. The number density N of the corresponding clusters was statistically analyzed using 3D Atomic Probe technology. cluster,unirr and average size N cluster,unirr .

[0085] Step 3: Ion Irradiation

[0086] Ion irradiation was performed on sheet-like samples, and the damaged area was simulated and calculated. Specifically:

[0087] RPV steel samples were subjected to proton irradiation at a specific energy E (E≤300keV) and a specific damage amount (0~10dPa). The irradiation damage distribution was then simulated using SRIM, with the damage peak depth d... peak The area within 100 nm to the left and right is considered the damage region, i.e., the depth range Ω of the damage peak region is d. peak -100 to d peak +100nm.

[0088] Step 4: Characterization after ion irradiation

[0089] Obtaining the characteristic nanohardness H of sheet-like samples after ion irradiation irr Dislocation loop number density N after irradiation loop,irr and average size D loop,irr Number density N of irradiated clusters cluster,irr and average size D cluster,irr Specifically:

[0090] 4.1) Characteristic Nanohardness Characterization

[0091] Referring to step 2a of the nanoindentation test, when calculating the characteristic nanohardness for the irradiated sample using linear fitting of the average nanohardness curve, the h of the fitting region is 0.1 × (d peak -100) to 0.2×(d) peak +100), calculate the arithmetic square root of the intercept of the fitted straight line, which yields the characteristic nanohardness H of the irradiated area. irr .

[0092] 4.2) Characterization of dislocation loops

[0093] Dislocation loops in RPV steel samples were characterized using transmission electron microscopy (TEM). For ion-irradiated samples, the characterization region needed to encompass a depth range of Ω. The number density N of dislocation loops within the field of view was statistically analyzed using TEM. loop,irr and average size D loop,irr .

[0094] 4.3) Characterization of solute clusters

[0095] RPV steel sample clusters were characterized using a three-dimensional atomic probe microanalysis (3D ATM). For ion-irradiated samples, the characterization region needed to encompass a depth range of Ω. The number density N of the corresponding clusters was statistically analyzed using 3D ATM technology. cluster,irr and average size D cluster,irr .

[0096] Step 5: Vacuum heat annealing and mitigation treatment

[0097] The ion-irradiated samples were subjected to vacuum annealing, requiring a vacuum level better than 5 × 10⁻⁶. -4 Pa, and maintain for at least 30 minutes, with a heating rate of 10±5℃ / min, setting the target temperature as T, and the holding time as t. After the holding time, cool with the furnace to room temperature. The vacuum level must be better than 5×10 during the heating, holding, and cooling processes. -4 Pa.

[0098] Step 6: Characterization after heat annealing and mitigation treatment

[0099] The three characterization steps were repeated sequentially to obtain the characteristic nanohardness H of the sheet-like sample after ion irradiation and vacuum thermal annealing. pia The number density N of dislocation loops after annealing loop,pia and average size D loop,pia Number density N of clusters after annealing cluster,pia and average size D cluster,pia Specifically:

[0100] 6.1) Nanohardness characterization

[0101] For nanoindentation testing, referring to step 2a, when calculating the characteristic nanohardness by linearly fitting the average nanohardness curve of the irradiated and annealed sample, the h of the fitting region is 0.1 × (d peak -100) to 0.2×(d) peak +100), calculate the arithmetic square root of the intercept of the fitted straight line, which yields the characteristic nanohardness H of the original irradiated region after annealing. pia .

[0102] 6.2) Characterization of dislocation loops

[0103] Dislocation loops in RPV steel samples were characterized using transmission electron microscopy (TEM). For samples annealed after ion irradiation, the characterization region needed to encompass a depth range of Ω. The number density N of dislocation loops was statistically analyzed using TEM. loop,pia and average size D loop,pia .

[0104] 6.3) Characterization of solute clusters

[0105] RPV steel sample clusters were characterized using a three-dimensional atomic probe microanalysis (3D Atomic Probe). For samples annealed after ion irradiation, the characterization region needed to encompass a depth range of Ω. The number density N of the corresponding clusters was statistically analyzed using 3D Atomic Probe technology. cluster,pia and average size D cluster,pia .

[0106] Step 7: Calculate the contribution of defects to the yield strength increment of RPV steel at different treatment stages, in MPa:

[0107] 7.1) Based on steps two and four, calculate the yield strength increment Δσ caused by irradiation defects after ion irradiation according to the following formula. defect,irr :

[0108] Δσ loop,irr =5.19×10 -10 ·[(N loop,irr ·D loop,irr ) 0.5 -(N loop,unirr ·D loop,unirr ) 0.5 ]

[0109] Δσ cluster,irr =1.73×10 -10 ·[(N cluster,irr ·D cluster,irr ) 0.5 -(N cluster,unirr ·D cluster,unirr ) 0.5 ]

[0110] Δσ defect,irr =[(Δσ loop,irr ) 2 +(Δσ cluster,irr ) 2 ] 0.5

[0111] In the formula, Δσ loop,irr Δσ represents the yield strength increment caused by dislocation loops after ion irradiation. cluster,irr Δσ represents the yield strength increment caused by solute clusters after ion irradiation. defect,irr This represents the total yield strength increment caused by ion irradiation defects, including dislocation loops and solute clusters.

[0112] 7.2) Based on steps two and six, calculate the yield strength increment Δσ caused by residual irradiation defects after annealing according to the following formula. defect,pia :

[0113] Δσ loop,pia =5.19×10 -10 ·[(N loop,pia ·D loop,pia ) 0.5 -(N loop,unirr ·D loop,unirr ) 0.5 ]

[0114] Δσ cluster,pia =1.73×10 -10 ·[(N cluster,pia ·D cluster,pia ) 0.5 -(N cluster,unirr ·D cluster,unirr ) 0.5 ]

[0115] Δσ defect,pia =[(Δσ loop,pia ) 2 +(Δσ cluster,pia ) 2 ] 0.5

[0116] In the formula, Δσ loop,pia Δσ represents the yield strength increment caused by dislocation loops after vacuum heat annealing. cluster,pia Δσ represents the yield strength increment caused by solute clusters after vacuum heat annealing. defect,pia This represents the total yield strength increment caused by irradiation defects after vacuum heat annealing, including dislocation loops and solute clusters.

[0117] Step 8: Calculate the performance recovery degree of RPV steel after irradiation annealing based on defect recovery and nano-hardness test, respectively.

[0118] 8.1) Calculate the degree of performance recovery R of RPV steel after irradiation annealing due to defect recovery using the following formula. defect :

[0119]

[0120] 8.2) Calculate the performance recovery degree R of RPV steel after irradiation annealing based on nanohardness testing using the following formula. hardnesstest :

[0121]

[0122] Step 9: Based on the two performance recovery parameters obtained in Step 8, evaluate the rationality of the temperature selection in the post-irradiation annealing process of RPV steel:

[0123] If R defect >R hardnesstest The evaluation indicates that the annealing temperature is too high under these conditions.

[0124] If R defect =R hardnesstest The annealing temperature under these conditions is deemed appropriate.

[0125] If R defect <R hardnesstest The evaluation indicates that the annealing temperature is too low under these conditions.

[0126] Simultaneously, the degree of annealing mitigation R under this condition is calculated according to the following formula. pia :

[0127]

[0128] Implementation Cases

[0129] In this embodiment, domestically produced RPV steel (A508-3 steel) was subjected to 240keV proton irradiation with a damage amount of 1.6 dpa, followed by annealing at 500℃ for 1 hour. The degree of mitigation of annealing after irradiation was calculated and evaluated. The specific steps are as follows:

[0130] 1) Preparation of sheet samples

[0131] Domestic RPV steel material was processed into square sheet samples of 15mm×15mm×1mm by wire cutting. The surface of the sample was polished with metallographic sandpaper of 400#, 800#, 1200# and 2000# in sequence. After polishing, it was polished to a mirror finish to obtain sheet samples of RPV steel.

[0132] 2) Characterization before ion irradiation

[0133] The characteristic nanohardness H before irradiation was obtained respectively. unirr Dislocation loop number density N before irradiation loop,unirr and average size D loop,unirr Number density N of clusters before irradiation cluster,unirr and average size D cluster,unirr data:

[0134] 2.1) Characteristic nanohardness characterization: The characteristic nanohardness H of the unirradiated sample was calculated by nanoindentation testing. unirr =2.35 GPa.

[0135] 2.2) Characterization of dislocation loops: The number density N of dislocation loops was statistically obtained by transmission electron microscopy. loop,unirr=0, average size D loop,unirr =0.

[0136] 2.3) Solute cluster characterization: The number density N of clusters was statistically obtained through three-dimensional atomic probe characterization. cluster,unirr =0, average size D cluster,unirr =0.

[0137] 3) Ion irradiation

[0138] RPV steel samples were subjected to proton irradiation with energy E = 240 keV and a damage dose of 1.6 dpa. The irradiation damage distribution was simulated and calculated using SRIM software, and the irradiation damage distribution curve was obtained. The damage peak was located at depth d. peak The depth range of the damage peak region Ω is 900 nm to 1000 nm, with a wavelength of 1000 nm.

[0139] 4) Characterization after ion irradiation

[0140] Repeat the three characterization steps in step 2 sequentially to obtain the characteristic nanohardness H after irradiation. irr Dislocation loop number density N after irradiation loop,irr and average size D loop,irr Number density N of irradiated clusters cluster,irr and average size D cluster,irr Specifically:

[0141] 4.1) Nanoscale hardness characterization: The hardness of H was characterized by nanoindentation testing and fitting of the region h from 90 nm to 220 nm. 2 Using 1 / h, the characteristic nanohardness H of the irradiated region after proton irradiation is calculated. irr = 4.13 GPa.

[0142] 4.2) Characterization of dislocation loops: The number density N of dislocation loops within the damaged region Ω after proton irradiation was statistically obtained by transmission electron microscopy. loop,irr =2×10 22 m -3 Average size D loop,irr =3.2nm.

[0143] 4.3) Solute cluster characterization: The number density N of corresponding clusters in the damaged region Ω after proton irradiation was statistically obtained by three-dimensional atomic probe characterization. cluster,irr =14.6×10 23 m -3 Average size D cluster,irr =1.33nm.

[0144] 5) Vacuum heat annealing relief treatment

[0145] Annealing was performed using a tubular vacuum annealing furnace. The sheet-like sample was placed in a crucible of appropriate size, then placed in the middle section of the tubular annealing furnace tube. The vacuum pump was turned on, and the vacuum level was increased to 5 × 10⁻⁶. -4 After Pa, hold for 30 min, then set the heating rate to 10℃ / min, the temperature to T=500℃, and the holding time to t=1h to begin heat treatment. After the holding time, cool with the furnace to room temperature. During the annealing process, maintain the vacuum level at 8×10⁻⁶. -5 Pa.

[0146] 6) Characterization after heat annealing and mitigation treatment

[0147] The characterization process in step 4 was repeated sequentially to obtain the characteristic nanohardness H after annealing. pia The number density N of dislocation loops after annealing loop,pia and average size D loop,pia Number density N of clusters after annealing cluster,pia and average size D cluster,pia Specifically:

[0148] 6.1) Nanoscale hardness characterization: The hardness of H was characterized by nanoindentation testing and fitting of the region h from 90 nm to 220 nm. 2 Using 1 / h, the characteristic nanohardness H of the irradiated region after proton irradiation is calculated. pia =2.86 GPa.

[0149] 6.2) Characterization of dislocation loops: The number density N of dislocation loops within the original damaged region Ω after irradiation annealing was statistically obtained by transmission electron microscopy. loop,pia =0, average size D loop,pia =0.

[0150] 6.3) Characterization of solute clusters: The number density N of corresponding clusters in the original damaged region Ω after irradiation annealing was statistically obtained by three-dimensional atomic probe characterization. cluster,pia =1.15×10 23 m -3 Average size D cluster,pia =1.05nm.

[0151] 7) Calculate the contribution of defects to the yield strength increment of RPV steel under different treatment stages.

[0152] 7.1) Based on steps 2 and 4, calculate the yield strength increment Δσ caused by irradiation defects after ion irradiation according to the following formula. defect,irr :

[0153] Δσ loop,irr =5.19×10 -10 ·[(N loop,irr ·D loop,irr ) 0.5-(N loop,unirr ·D loop,unirr ) 0.5 =131MPa

[0154] Δσ cluster,irr =1.73×10 -10 ·[(N cluster,irr ·D cluster,irr ) 0.5 -(N cluster,unirr ·D cluster,unirr ) 0.5 =241MPa

[0155] Δσ defect,irr =[(Δσ loop,irr ) 2 +(Δσ cluster,irr ) 2 ] 0.5 =274MPa

[0156] In the formula, Δσ loop,irr Δσ represents the yield strength increment caused by dislocation loops after ion irradiation. cluster,irr Δσ represents the yield strength increment caused by solute clusters after ion irradiation. defect,irr This represents the total yield strength increment caused by ion irradiation defects, including dislocation loops and solute clusters.

[0157] 7.2) Based on steps 2 and 6, calculate the yield strength increment Δσ caused by residual irradiation defects after annealing according to the following formula. defect,pia :

[0158] Δσ loop,pia =5.19×10 -10 ·[(N loop,pia ·D loop,pia ) 0.5 -(N loop,unirr ·D loop,unirr ) 0.5 ] = 0

[0159] Δσ cluster,pia =1.73×10 -10 ·[(N cluster,pia ·D cluster,pia ) 0.5 -(N cluster,unirr ·D cluster,unirr ) 0.5 =60MPa

[0160] Δσ defect,pia =[(Δσ loop,pia ) 2 +(Δσ cluster,pia ) 2 ] 0.5=60MPa

[0161] In the formula, Δσ loop,pia Δσ represents the yield strength increment caused by dislocation loops after vacuum heat annealing. cluster,pia Δσ represents the yield strength increment caused by solute clusters after vacuum heat annealing. defect,pia This represents the total yield strength increment caused by irradiation defects after vacuum heat annealing, including dislocation loops and solute clusters.

[0162] 8) Calculate the performance recovery of RPV steel after irradiation annealing based on defect recovery and nano-hardness testing, respectively.

[0163] 8.1) Calculate the degree of performance recovery R of RPV steel after irradiation annealing due to defect recovery according to the following formula. defect :

[0164]

[0165] 8.2) Calculate the performance recovery degree R of RPV steel after irradiation annealing based on nanohardness testing according to the following formula. hardnesstest :

[0166]

[0167] 9) Based on the calculation results in step 8, since R defect >R hardnesstest The evaluation indicates that the annealing temperature under these conditions is too high. The annealing temperature can be optimized, and the same method can be applied again for evaluation to obtain the best possible annealing mitigation value (the higher the mitigation, the better). This will allow for the selection of the optimal annealing process parameters.

[0168] Simultaneously, the degree of annealing mitigation R under this condition is calculated according to the following formula. pia :

[0169]

[0170] For domestically produced RPV steel irradiated with 240keV protons to 1.6dPa, vacuum annealing at 500℃ for 1h resulted in an annealing mitigation rate of 74.5%.

[0171] Because RPV steel is irradiated during service, the resulting irradiation defects can cause RPV steel hardening, which is a safety hazard for RPV equipment. Excessive hardening can lead to embrittlement and potentially brittle fracture, causing the container to rupture. Irradiation-induced hardening can be mitigated by annealing, reducing the degree of irradiation hardening. In this application, the degree of annealing mitigation represents the extent to which irradiation hardening in the RPV steel material is restored after annealing; a higher value is better.

[0172] The present invention relates to a method for calculating the degree of mitigation of nuclear power water reactor pressure vessel (RPV) steel based on thermal annealing for ion irradiation damage, comprising the following steps: 1) machining RPV steel material into sheet samples of a certain size by wire cutting, and grinding and polishing the surface; 2) characterizing the characteristic nanohardness, number density and average size of dislocation loops and clusters of the sample before ion irradiation; 3) subjecting the RPV steel sample to ion irradiation with specific energy and damage amount, and calculating the damage area through SRIM simulation; 4) characterizing the characteristic nanohardness, number density and average size of dislocation loops and clusters of the sample again after ion irradiation; 5) performing thermal annealing under a specific vacuum... Vacuum hot annealing was carried out on irradiated RPV steel samples under conditions including temperature, heating rate, temperature, and holding time; 6) After hot annealing, the characteristic nanohardness, number density, and average size of dislocation loops and clusters of the samples were characterized again; 7) The contribution of different types of defects to the yield strength increment of RPV steel at different treatment stages was calculated; 8) The performance recovery degree of RPV steel after irradiation annealing was calculated based on defect recovery and nanohardness test, respectively; 9) Based on the two performance recovery degree parameters obtained in step 8, the rationality of temperature selection in the annealing process of RPV steel after irradiation was evaluated, and finally the annealing mitigation degree R under this condition was calculated. pia This method overcomes the shortcomings of traditional experimental studies, which can only qualitatively assess the mitigation effect of irradiation annealing. It can more accurately and scientifically quantitatively assess the degree of mitigation of annealing after RPV steel irradiation, and reasonably guide the optimization of annealing process. It provides a scientific and reasonable evaluation method for the development of nuclear power RPV life extension annealing engineering technology.

[0173] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for evaluating the degree of mitigation of annealing after ion irradiation of reactor pressure vessel steel, characterized in that, Includes the following steps: The reactor pressure vessel steel was prepared into sheet-like samples; The characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of sheet-like samples before ion irradiation were obtained. Ion irradiation was performed on sheet-like samples, and the damage area was simulated and calculated. The characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of sheet-like samples after ion irradiation were obtained. Vacuum thermal annealing was performed on sheet-like samples after ion irradiation. The characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of sheet-like samples were obtained after vacuum thermal annealing. Calculate the contribution of different types of defects to the yield strength increment of sheet-like samples at different processing stages; The performance recovery of sheet samples after vacuum thermal annealing was calculated based on defect recovery and nanohardness testing, respectively. Based on two performance recovery parameters, the rationality of temperature selection in the post-irradiation annealing process of reactor pressure vessel steel is evaluated, and the degree of annealing mitigation under these conditions is calculated. ; The degree of annealing relief Perform the following formula: ； in, The performance recovery degree based on defect recovery after vacuum thermal annealing of sheet samples is calculated according to the following formula: ； In the formula, This represents the increase in yield strength caused by irradiation defects; This represents the increase in yield strength caused by residual irradiation defects; The performance recovery of sheet-like samples after vacuum heat annealing, based on nanohardness testing, is calculated using the following formula: ； In the formula, The characteristic nanohardness of sheet-like samples before ion irradiation. The characteristic nanohardness of sheet-like samples after ion irradiation; The characteristic nanohardness of sheet-like samples after vacuum thermal annealing; The contribution of different types of defects to the yield strength increment of sheet-like samples at different treatment stages was calculated. This included calculating the yield strength increment caused by irradiation defects based on the characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of the sheet-like samples before and after ion irradiation. : ； ； ； In the formula, This represents the increase in yield strength caused by dislocation loops after ion irradiation. This represents the increase in yield strength caused by solute clusters after ion irradiation. This represents the total yield strength increment caused by ion irradiation defects, including dislocation loops and solute clusters. The number density of dislocation loops in the sheet-like sample after ion irradiation. The average size of the dislocation loops in the sheet-like sample after ion irradiation. The number density of dislocation loops in the sheet-like sample before ion irradiation. The average size of the dislocation loops in the sheet-like sample before ion irradiation. The number density of clusters in the sheet-like sample after ion irradiation. The average size of the clusters in the sheet-like sample after ion irradiation. The number density of clusters in the sheet-like sample before ion irradiation. The average size of the clusters in the sheet-like sample before ion irradiation; The contribution of different types of defects to the yield strength increment of sheet-like samples at different processing stages was calculated. This included calculating the yield strength increment caused by residual irradiation defects based on the characteristic nanohardness, number density and average size of dislocation loops, and number density and average size of clusters of the sheet-like samples before ion irradiation and after vacuum thermal annealing. : ； ； ； In the formula, This represents the increase in yield strength caused by dislocation loops after vacuum heat annealing. The yield strength increment caused by solute clusters after vacuum heat annealing. This represents the total yield strength increment caused by irradiation defects after vacuum heat annealing, including dislocation loops and solute clusters. The number density of dislocation loops in the sheet-like sample after vacuum thermal annealing. The average size of the dislocation loops in the sheet-like sample after vacuum heat annealing is given. The number density of dislocation loops within 5 μm of the surface of the sheet-like sample in the field of view of a transmission electron microscope. The average size of dislocation loops within 5 μm of the surface of the sheet-like sample in the field of view of a transmission electron microscope. The number density of clusters in the sheet-like sample after vacuum heat annealing. The average size of the clusters in the sheet-like sample after vacuum heat annealing is given. The number density of clusters in the sheet-like sample before ion irradiation. The average size of the clusters in the sheet-like sample before ion irradiation.

2. The evaluation method according to claim 1, characterized in that, The sheet-like sample is prepared by the following method: the steel material of the reactor pressure vessel is cut and processed into sheet-like samples with a thickness of 0.5-1.5 mm and a side length of 10-15 mm. The surface of the sheet-like sample is then ground and polished to a mirror finish.

3. The evaluation method according to claim 1 or 2, characterized in that, The characteristic nanohardness of the sheet-like sample before ion irradiation Obtained through the following method: Nanohardness tests were performed on sheet-like samples. The Poisson's ratio for reactor pressure vessel steel was set, the indentation depth was set to ≥2μm, and ≥10 indentation test points were used. A set of nanohardness values ​​was obtained for each indentation point. H and indentation depth h The relationship curve is plotted, and the average curve of multiple curves is calculated. The average curve is then analyzed. H 2 and 1 / h By performing linear fitting and calculating the arithmetic square root of the intercept of the fitted line, the characteristic nanohardness of the sheet-like sample before ion irradiation is obtained. .

4. The evaluation method according to claim 1 or 2, characterized in that, The number density of dislocation loops in the sheet-like sample before ion irradiation and average size Obtained through the following method: Dislocation loops in steel sheet samples from reactor pressure vessels were characterized using transmission electron microscopy (TEM). The characterization region was selected within 5 μm of the sample surface, and the number density of dislocation loops within the field of view was statistically analyzed. and average size .

5. The evaluation method according to claim 1 or 2, characterized in that, The number density of clusters in the sheet-like sample before ion irradiation and average size Obtained through the following method: Clusters in steel sheet samples from reactor pressure vessels were characterized using a three-dimensional atomic probe microanalysis method. The sample area was selected within 5 μm of the surface of the sheet sample, and the number density of the corresponding clusters was statistically analyzed. and average size .

6. The evaluation method according to claim 1, characterized in that, The ion irradiation was performed on a steel sheet sample from the reactor pressure vessel. E Energy ≤300keV E Proton irradiation with a damage level of 0-10 dpa.

7. The evaluation method according to claim 6, characterized in that, The simulated damage area was calculated using SRIM software to simulate the distribution of irradiation damage, with the damage peak depth as the basis. ±100nm is considered the damage region, i.e., the depth range Ω of the damage peak region is... d peak -100nm to d peak +100nm.

8. The evaluation method according to claim 7, characterized in that, The characteristic nanohardness of the sheet-like sample after ion irradiation Obtained through the following method: Nanoscale hardness testing was performed on sheet-like samples after ion irradiation. The Poisson's ratio for reactor pressure vessel steel was set, the indentation depth was set to ≥2μm, and ≥10 indentation test points were used. A set of nanoscale hardness values ​​was obtained for each indentation point. H and indentation depth h The relationship curve is plotted, and the average curve of multiple curves is calculated. The average curve is then analyzed. H 2 and 1 / h By performing a linear fit and calculating the arithmetic square root of the intercept of the fitted line, the characteristic nanohardness of the irradiated area can be obtained. ; Fitted region h 0.1×( d peak -100) to 0.2×( d peak +100).

9. The evaluation method according to claim 1 or 7, characterized in that, The number density of dislocation loops in the sheet-like sample after ion irradiation and average size Obtained through the following method: Dislocation loops in ion-irradiated sheet-like samples were characterized using transmission electron microscopy (TEM). The Ω depth range of the characterization region, including the damage peak region, was determined, and the number density of dislocation loops within the field of view was statistically analyzed. and average size .

10. The evaluation method according to claim 1 or 7, characterized in that, The number density of clusters in the sheet-like sample after ion irradiation and average size Obtained through the following method: Clusters in sheet-like samples after ion irradiation were characterized using a three-dimensional atomic probe microanalysis. The characterization region included the Ω depth range of the damage peak region, and the corresponding cluster number density was statistically analyzed. and average size .

11. The evaluation method according to claim 7, characterized in that, The vacuum thermal annealing process involves subjecting the sheet-like sample after ion irradiation to vacuum thermal annealing, with a vacuum level better than 5 × 10⁻⁶. -4 Pa, and maintain for at least 30 minutes, with a heating rate of 10 ± 5 °C / min, and set the target temperature to [value missing]. T The heat preservation time is t After the holding time is completed, the furnace is cooled to room temperature. The vacuum degree during the heating, holding, and cooling processes is better than 5×10⁻⁶. -4 Pa.

12. The evaluation method according to claim 11, characterized in that, The sheet-like sample exhibits characteristic nanohardness after vacuum heat annealing. Obtained through the following method: Nanoscale hardness testing was performed on sheet-like samples after ion irradiation. The Poisson's ratio for reactor pressure vessel steel was set, the indentation depth was set to ≥2μm, and ≥10 indentation test points were used. A set of nanoscale hardness values ​​was obtained for each indentation point. H and indentation depth h The relationship curve is plotted, and the average curve of multiple curves is calculated. The average curve is then analyzed. H 2 and 1 / h Perform linear fitting and calculate the arithmetic square root of the intercept of the fitted line to obtain the characteristic nanohardness of the original irradiated area after annealing. ; Fitted region h 0.1×( d peak -100) to 0.2×( d peak +100).

13. The evaluation method according to claim 1 or 11, characterized in that, The number density of dislocation loops in the sheet-like sample after vacuum thermal annealing. and average size Obtained through the following method: Dislocation loops in sheet-like samples after vacuum thermal annealing were characterized using transmission electron microscopy (TEM). The Ω depth range of the characterization region, including the damage peak region, was determined, and the number density of dislocation loops within the field of view was statistically analyzed. and average size .

14. The evaluation method according to claim 1 or 11, characterized in that, The number density of clusters in the sheet-like sample after vacuum heat annealing and average size Obtained through the following method: Clusters in sheet-like samples after vacuum thermal annealing were characterized using a three-dimensional atomic probe microanalysis. The characterization region needed to include the Ω depth range of the damage peak region, and the corresponding cluster number density was statistically analyzed. and average size .

15. The evaluation method according to claim 1, characterized in that, The rationality of temperature selection in vacuum thermal annealing of sheet-like samples after ion irradiation is evaluated based on two performance recovery parameters: like The evaluation indicates that the temperature in the vacuum heat annealing process under these conditions is too high. like The appropriateness of the temperature in the vacuum heat annealing process under these conditions was evaluated. like The evaluation indicates that the temperature in the vacuum heat annealing process under these conditions is too low.

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