A method for measuring high neutron fluence rate based on reversible heat flow method

Abstract

The present invention discloses a method for measuring high neutron fluence rate based on reversible heat flow method, the method comprising: (S100) selecting boron crystal; (S200) obtaining n portions of calibration sample packages; (S300) respectively placing the calibration sample packages in a thermal neutron nuclear reactor with a constant neutron fluence rate for irradiation; (S400) scanning the corresponding reversible heat flow curve by modulated differential scanning calorimetry; (S500) fitting the neutron fluence of the calibration detector sample package and the reversible heat flow change; (S600) after irradiating the sample to be tested in the reactor with the neutron fluence rate to be tested, measuring the reversible heat flow change, calculating the neutron fluence received by the sample to be tested in the reactor to be tested, and calculating the fluence rate when the sample is irradiated by the reactor to be tested according to the irradiation time. The method of the present invention can obtain the neutron fluence rate according to the relationship between the irradiation fluence and the reversible heat flow change, and is particularly suitable for measuring the neutron fluence rate of a high fluence nuclear reactor.

Description

Technical Field

[0001] The invention relates to a method for measuring a high neutron fluence rate, and in particular to a method for measuring a high neutron fluence rate based on a reversible heat flow method. Background Art

[0002] Neutron fluence rate is an important parameter of nuclear reactors, which directly affects the fission reaction rate of nuclear reactors. Its detection has always been one of the key contents of reactor physics research at home and abroad. At present, neutron detection at home and abroad is achieved by detecting secondary charged particles generated by the interaction between neutrons and atomic nuclei. The main neutron fluence rate measurement methods used in the reactor are: micro-detector method, self-powered detector method, activated foil method, etc.

[0003] The most mature and commonly used method in the reactor is the activated foil method, but the activated foil method is limited by the decay constant of the detector sheet and quickly reaches saturation under high fluence conditions, so it cannot directly measure the fluence rate of the core of a high-fluence nuclear reactor. The usual practice is to measure the neutron fluence rate of a nuclear reactor at low fluence, and then infer it to the fluence rate at high fluence through calibration factors such as power. This method has the following problems:

[0004] (1) The correction factor at high fluence cannot be measured directly and can only be estimated using low fluence values, making it difficult to eliminate the error;

[0005] (2) Energy spectrum parameters such as neutron temperature and epithermal index can only be measured at low fluence. Therefore, the high neutron fluence rate measurement of the reactor is usually measured at a low power and then extrapolated to the high neutron fluence rate at high power.

[0006] (3) Under different injection conditions, various performance parameters of the reactor change, which also causes errors in the measurement.

[0007] Therefore, accurately measuring the neutron fluence rate in high-flux nuclear reactors has always been a global challenge facing reactor physics. Summary of the invention

[0008] The purpose of the present invention is to provide a method for measuring high neutron fluence rate based on the reversible heat flow method, which solves the problem that it is difficult to accurately measure the neutron fluence rate of a nuclear reactor. The neutron fluence rate can be obtained according to the relationship between the irradiation fluence and the reversible heat flow change, and is particularly suitable for measuring the neutron fluence rate of a high-fluence nuclear reactor.

[0009] In order to achieve the above object, the present invention provides a method for measuring high neutron fluence rate based on reversible heat flow method, the method comprising:

[0010] (S100) dividing the boron crystal into two parts, one part is used as a calibration detector sample, and the other part is used as a sample to be tested;

[0011] (S200) dividing the sample of the calibration detector into n portions, where n≥5, and wrapping them with polyethylene films to obtain n portions of calibration sample packages;

[0012] (S300) n portions of the calibration sample packages are placed in a thermal neutron nuclear reactor with a constant neutron injection rate for irradiation, and the irradiation time is t n , obtain n calibration sample packages with different irradiation doses;

[0013] (S400) scanning the corresponding reversible heat flow curves of n calibrated sample packages by modulated differential scanning calorimetry, under the following conditions: the protective gas is nitrogen, the modulation temperature is ±0.477°C / min, the modulation period is 60s, the scanning rate is 3°C / min, the temperature range is 35°C to 135°C, and the reversible heat flow change is integrated at 42°C to 125°C;

[0014] (S500) obtaining the reversible heat flow variation and the corresponding neutron fluence of each calibration detector sample package, fitting the neutron fluence and the reversible heat flow variation of the calibration detector sample package, and obtaining a fitting equation of y=ax+b, where y is the reversible heat flow variation, x is the neutron fluence, a is the fitting coefficient, and b is the fitting constant;

[0015] (S600) After the sample to be tested is irradiated for time t in the reactor with the neutron fluence rate to be tested, the modulated differential scanning calorimetry method of step (S400) is used to measure the reversible heat flow change, which is used as the y value in the fitting equation. The y value is substituted into the fitting equation to determine the neutron fluence x received by the sample to be tested in the reactor to be tested, and the fluence rate when the sample is irradiated by the reactor to be tested is calculated according to the irradiation time t.

[0016] Preferably, the detector is a neutron fluence rate detector.

[0017] Preferably, the boron crystals have a particle size of 10 to 20 μm and a purity of 99.9%.

[0018] Preferably, in the modulated differential scanning calorimetry, the mass of the crucible containing the sample is about 5 mg, and the mass of the sample is about 5 mg.

[0019] The method for measuring high neutron fluence rate based on the reversible heat flow method of the present invention solves the problem that it is difficult to accurately measure the neutron fluence rate of a nuclear reactor, and has the following advantages:

[0020] The method of the present invention effectively solves the world's difficult problem faced by reactor physics, that is, measuring the neutron fluence rate of a high-fluence nuclear reactor. The present invention needs to obtain the dependency between the irradiated fluence of the calibration detector sample and the change in reversible heat flow. The calibrated sample can be used as a detector. The sample has a small volume (soybean size), a light weight (0.1 g is sufficient), a wide applicable surface, can be directly placed in the detection position, can fully react in the nuclear reactor, and can read the neutron fluence rate data when the detector sample is completely separated from the nuclear reactor after irradiation. The method is particularly suitable for measuring the neutron fluence rate of a high-fluence nuclear reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a reversible heat flow curve diagram of Example 1 of the present invention.

[0022] Figure 2 It is a fitting diagram of neutron injection and reversible heat capacity change in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] A method for measuring the neutron fluence rate of a nuclear reactor based on a reversible heat flow method, comprising:

[0025] (S100) dividing boron crystals with a particle size of 10 to 20 μm and a purity of 99.9% into two parts, one part being used as a calibration detector sample and the remaining part being used as a sample to be tested;

[0026] (S200) dividing the calibration detector sample into n portions, n≥5, each portion being about 100 mg, and wrapping them with polyethylene films (the radioactivity generated by the polyethylene film after irradiation has a short period and will decay quickly to a safe range, with little impact on subsequent tests), to obtain n calibration sample packages;

[0027] (S300) The n calibrated sample packages of step S200 are placed in a thermal neutron nuclear reactor with a constant neutron injection rate and irradiated for t n hours, and obtain n sample packages with different irradiation doses;

[0028] (S400) scanning the corresponding reversible heat flow curves of n calibrated sample packages by modulated differential scanning calorimetry, the experimental conditions are: the sample crucible is about 5 mg, the sample mass is about 5 mg, the protective gas is nitrogen, the modulation temperature is ±0.477°C / min, the modulation cycle is 60s, the scanning rate is 3°C / min, the scanning temperature range is 35°C to 135°C, and the reversible heat flow change is integrated at 42°C to 125°C;

[0029] (S500) The reversible heat flow changes and corresponding neutron fluences of the sample packages of each calibration detector are tabulated in a table in the form of Table 1. In Table 1, sample packages 1, ..., sample packages n are boron-containing crystal samples irradiated in a nuclear reactor with a certain neutron fluence rate for t1, ..., t n Made after the time period; Φ1, ..., Φ n is the neutron flux of sample package 1, ..., sample package n; Q1, ..., Q n is the reversible heat flow change in the range of 42℃~125℃ after sample packages 1, ..., sample packages n are irradiated;

[0030] Table 1 shows the reversible heat flux change and corresponding neutron injection of the calibration detector sample package

[0031]

[0032] The irradiation dose of each sample package is Φ n is the horizontal axis, the reversible heat flow change Q n As the ordinate, make a straight line fit and get the linear equation: y = ax + b, which is the calibration equation of the detector;

[0033] (S600) After the sample to be tested is irradiated for time t in the reactor with the neutron fluence rate to be tested, the reversible heat flow change y is measured according to the method of step S400, and the y value is substituted into the linear equation of step S600 to calculate the fluence x received by the sample to be tested in the reactor to be tested. The fluence rate when the sample is irradiated by the reactor to be tested can be calculated according to the irradiation time t.

[0034] When using the method of the present invention to measure the injection rate in the test pile, it should be noted that the neutron energy spectrum of the test pile should be similar to the neutron energy spectrum of the calibration pile, and the experimental conditions, temperature range selection, packaging material selection, etc. are the same as those in the calibration pile experiment.

[0035] The CARR reactor of China Institute of Atomic Energy is a Chinese advanced research reactor (currently the highest neutron fluence rate in Asia), in which the neutron fluence rate cannot be directly measured. At present, its neutron fluence rate is determined by measuring the corresponding neutron fluence rate when the reactor is at low power, and then extrapolating it to the neutron fluence rate at the rated high power of the reactor according to the linear relationship between the reactor power and the neutron fluence rate, resulting in large measurement errors. The fitting equation obtained by the present invention is suitable for measuring neutrons in a high neutron fluence rate field, because there is no upper limit for measuring the reversible heat flow variation by a thermal analysis instrument, and there is no problem of exceeding the measuring instrument range when measuring the high neutron fluence rate with this instrument, and the more neutron irradiation injection the sample receives, the greater the reversible heat flow variation, and the smaller the relative measurement error, which is exactly what is needed for measuring the high neutron fluence rate.

[0036] The method for measuring the neutron fluence rate of a nuclear reactor based on the reversible heat flow method provided by the present invention is described in detail below through Examples 1-2.

[0037] Example 1

[0038] A method for measuring the neutron fluence rate of a nuclear reactor based on a reversible heat flow method, comprising:

[0039] (S100) dividing 1 g of boron crystals with a particle size of 10 to 20 μm and a purity of 99.9% into two parts, one part being used as a calibration detector sample and the remaining part being used as a sample to be tested;

[0040] (S200) dividing the calibration detector sample into 6 portions, each portion being about 80 mg, and wrapping each portion with polyethylene film to obtain 6 calibration sample packages;

[0041] (S300) One of the six calibrated sample packages in step S200 is not irradiated, and the remaining five are placed in a micro-neutron source nuclear reactor of the China Institute of Atomic Energy for irradiation. The reactor is a thermal neutron reactor and the neutron injection rate is constant at 8.5×10 11 n / cm 2 .s, the irradiation time of the five irradiated samples was 32h, 48h, 64h, 80h, and 96h, respectively, and the irradiation doses were 5.76×10 16 n / cm 2 ,8.64×10 16 n / cm 2 , 11.52×10 16 n / cm 2 , 14.40×10 16 n / cm 2 , 17.28×10 16 n / cm 2 The samples are numbered 2, 3, 4, 5, and 6, and the non-irradiated sample is numbered 1.

[0042] (S400) Boron crystal samples numbered 1, 2, 3, 4, 5, and 6 were subjected to modulated differential scanning calorimetry (MDSC) to measure their reversible heat flow changes using a Q2000 differential scanning calorimeter manufactured by TA Company of the United States. The experimental conditions were: the protective gas was nitrogen, the crucibles containing the samples were all around 5 mg, the sample mass was around 5 mg, the modulation temperature was ±0.477°C / min, the modulation period was 60s, the scanning rate was 3°C / min, the scanning temperature range was 35°C to 135°C, and the reversible heat flow changes were integrated in the range of 42°C to 125°C.

[0043] In order to reduce the influence of random factors such as the mass of the sample taken during annealing, the position difference of the sample on the sample holder in the instrument, the difference in the quality of the crucible, the difference in the quality of the sample, and the uniformity of the sample on the measurement results, each numbered sample is divided into more than 4 samples of different masses for measurement, and the upper and lower limits of the integration temperature are 42℃~125℃. In order to reduce the error of inaccurate integration limit value, multiple integrations are performed to take the average value, so that each numbered irradiated boron crystal sample has more than 4 measurement data. Taking sample 4 as an example, the parameters used and the 4 measurement data are listed in Table 2 (retain 5 significant figures).

[0044] Table 2 is the parameters and measurement data used to measure sample 4 in Example 1

[0045]

[0046] When processing data, negative values ​​are assumed to be endothermic and positive values ​​are assumed to be exothermic. One sample is scanned only once. Figure 1 The scanning curves and integral diagrams of 4 samples with different masses are given in .

[0047] (S500) The samples numbered 1, 2, 3, 4, 5, and 6 are measured according to the method for sample No. 4 and the results are listed in Table 2;

[0048] Table 2 shows the measurement results of the reversible heat flow variation of the six samples in Example 1.

[0049]

[0050] The measured reversible heat flow results in Table 2 were used to make a linear fit of the dependence between neutron irradiation injection and reversible heat flow change. The neutron irradiation injection was used as the horizontal axis and the unit was scale value × 10 16 n / cm 2 , the reversible heat flow change is the ordinate, the unit is J / g, and the fitting curve is as follows Figure 2 As shown, the fitting equation is: y = -0.0747x-3.4923;

[0051] (S600) The neutron injection rate of the test reactor CARR is measured. The neutron injection rate is measured at rated power using the above-mentioned reversible heat flow method. The specific method is as follows:

[0052] The same unirradiated boron crystal sample as that calibrated in the micro-pile was placed in the CARR stack 12 # At four different elevations of the vertical channel, the relevant measurement parameters of this position (these parameter values ​​are obtained by traditional measurement methods) are shown in Table 3:

[0053] Table 3 is the CARR stack 12 in Example 1 # Vertical channel related measurement parameters

[0054]

[0055]

[0056] The unirradiated sample was taken out after irradiation for 10833 seconds, and then the irradiated sample was annealed and its reversible heat flow change was measured by MDSC method. The same numbered sample was divided into several samples of different masses, and their reversible heat flow changes were scanned and measured respectively. Then the average of the measured values ​​was calculated to obtain the y value in the fitting equation. The measured reversible heat flow change was substituted into the fitting equation to obtain the neutron injection x value. The neutron injection rate of the CARR reactor irradiated sample was calculated from the irradiation time in Table 3, and the calculated neutron injection rate of the CARR reactor irradiated sample was compared with the reference value listed in Table 3 (the neutron injection rate measured at different low power of the reactor was extrapolated to the neutron injection rate at high power) to give the relative error value. Table 4 is the test results of 4 numbered samples after CARR reactor irradiation.

[0057] Table 4 is the test results of 4 numbered samples irradiated by CARR stack in Example 1

[0058]

[0059] From the test results, it can be seen that the measured neutron fluence rate is consistent with the reference value by about 3%, which proves that the reversible heat flow method can directly measure high neutron fluence rate.

[0060] Example 2

[0061] A method for measuring the neutron fluence rate of a nuclear reactor based on a reversible heat flow method, wherein the irradiated sample, the known reactor, and the reversible heat flow measurement conditions remain unchanged, that is, steps S100 to S500 are the same as those in Example 1, except that in step S600, the position of the test sample in the CARR stack is changed to measure the fluence rate at the position.

[0062] The same unirradiated boron crystal sample as that calibrated in the micro-pile was placed in the CARR stack 12 #The vertical channel sample was irradiated at a height of 136 cm in the channel for 3 h (3600 s × 3 = 10800 s). The reversible heat flux change measured by the MDSC method was -4.261 J / g. Substituting this value into the fitting equation, the neutron injection can be obtained as 1.0290E+17 n / cm 2 According to the irradiation time of 10800s, the neutron injection rate at the position of 136cm in the tunnel can be calculated to be 9.5282E+12n / cm 2 .s, where the parameter value is 9.4348E+12 / cm obtained by traditional measurement method 2 .s, the relative error between the two is +1%.

[0063] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for measuring high neutron fluence rate based on reversible heat flow method, characterized in that: The method includes: (S100) dividing the boron crystal into two parts, one part is used as a sample of the calibration detector, and the other part is used as a sample to be tested; (S200) dividing the sample of the calibration detector into n portions, where n≥5, and wrapping them with polyethylene films to obtain n portions of calibration sample packages; (S300) n portions of the calibration sample packages are placed in a thermal neutron nuclear reactor with a constant neutron injection rate for irradiation, and the irradiation time is t n , obtain n calibration sample packages with different irradiation doses; (S400) scanning the corresponding reversible heat flow curves of n calibrated sample packages by modulated differential scanning calorimetry, under the following conditions: the protective gas is nitrogen, the modulation temperature is ±0.477°C / min, the modulation period is 60s, the scanning rate is 3°C / min, the temperature range is 35°C to 135°C, and the reversible heat flow change is integrated at 42°C to 125°C; (S500) obtaining the reversible heat flow variation and the corresponding neutron fluence of each calibration detector sample package, fitting the neutron fluence and the reversible heat flow variation of the calibration detector sample package, and obtaining a fitting equation of y=ax+b, where y is the reversible heat flow variation, x is the neutron fluence, a is the fitting coefficient, and b is the fitting constant; (S600) After the sample to be tested is irradiated for time t in the reactor with the neutron fluence rate to be tested, the modulated differential scanning calorimetry method of step (S400) is used to measure the reversible heat flow change, which is used as the y value in the fitting equation. The y value is substituted into the fitting equation to determine the neutron fluence x received by the sample to be tested in the reactor to be tested, and the fluence rate when the sample is irradiated by the reactor to be tested is calculated according to the irradiation time t.

2. The method for measuring high neutron fluence rate based on reversible heat flow method according to claim 1, characterized in that: The detector is a neutron fluence rate detector.

3. The method for measuring high neutron fluence rate based on reversible heat flow method according to claim 1, characterized in that: The boron crystal has a particle size of 10 to 20 μm and a purity of 99.9%.

4. The method for measuring high neutron fluence rate based on reversible heat flow method according to claim 1, characterized in that: In the modulated differential scanning calorimetry, the mass of the crucible containing the sample is 5±1 mg, and the mass of the sample is 5 mg±1 mg.

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