A core damage assessment method for sodium-cooled fast reactors based on radionuclide sampling

Abstract

The present invention discloses a sodium-cooled fast reactor core damage assessment method based on radioactive nuclide sampling. The method comprises the following steps: calculating the release amount of nuclides at the sampling moment of the sodium-cooled fast reactor and the decay of the parent nucleus at the sampling moment, taking the activity of the third-generation decay daughters, obtaining the release share of the nuclides at the sampling moment of the sodium-cooled fast reactor under accident conditions, comparing the calculated nuclide release share with the nuclide release share during an actual accident, and obtaining a determined sodium-cooled fast reactor core damage type. The core damage type includes three types: no core damage, fuel cladding airtightness damage, and fuel cladding damage. The determined core type is used to quickly guide safety protection and rescue measures in emergency situations.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear and radiation emergency response, and in particular relates to a sodium-cooled fast reactor core damage assessment method based on radionuclide sampling. Background Art

[0002] Due to the increase in fuel power density and burnup, the performance of fuel and cladding in sodium-cooled fast reactors has always been of great concern. Fuel damage detection plays a crucial role in fast reactor safety. Under normal reactor operation, extensive fuel element seal failure or significant fuel element cladding failure is unacceptable. If fuel element seal failure exceeds the permissible limit, the primary coolant and cover gas circuit may become severely contaminated with fission products, potentially allowing nuclear fuel to leak into the primary circuit. In sodium-cooled fast reactors, core damage best reflects the extent of fuel damage, making its determination crucial. This determination provides effective data support for protection during accident conditions. Summary of the Invention

[0003] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a sodium-cooled fast reactor core damage assessment method based on radionuclide sampling, which can qualitatively determine the damage state of the core and quantitatively evaluate the damage degree of the core.

[0004] To achieve the above-mentioned object, the present invention adopts the following technical solution: a method for evaluating core damage of a sodium-cooled fast reactor based on radionuclide sampling, comprising the following steps:

[0005] (1) Sampling of nuclides;

[0006] (2) Estimation of the release activity of the nuclides at the time of sampling;

[0007] (3) Estimation of the source term of the nuclides at the time of reactor sampling;

[0008] (4) Estimation of the release fraction of nuclides at the time of sampling;

[0009] (5) Compare the estimated release fraction of the above-mentioned specific nuclides with the cladding airtightness damage and fuel cladding damage to determine the type of core damage.

[0010] Furthermore, in step (2), the release activity of the nuclide is calculated by formula (1),

[0011]

[0012] Among them, A i Indicates the release amount of the i-th nuclide at the sampling time, Bq; A c % represents the specific activity of the i-th nuclide in the primary sodium loop at the sampling time, Bq / g; M crepresents the mass of sodium remaining in the primary circuit at the time of sampling, t; represents the specific activity of the i-th nuclide in the main container cover gas cavity, the top protective cover and the containment hall at the sampling time, Bq / cm 3 ; V j Represent the free volumes of the main container covering the gas cavity, the top protective cover and the containment hall, m 3 .

[0013] However, the influence of gas pressure and temperature needs to be considered in gas sampling, so the specific activity of a certain nuclide sample is corrected by formula (2):

[0014]

[0015] in, Represents the specific activity of the i-th nuclide in the sample, Bq / cm 3 ;P v,j represents the gas pressure in the sampling cavity (main container covering gas cavity, top protective cover and containment hall), Pa; P s,j Indicates the gas pressure of the nuclide sample, Pa; T v,j represents the temperature in the sampling cavity (main container covering gas cavity, top protective cover and containment hall), ℃; T s,j Indicates the temperature of the nuclide sample, °C.

[0016] Furthermore, in step (3), the source term of the nuclide is estimated by the activity of the third generation daughter during the nuclide decay process; the radioactive nuclide decays from the parent nucleus, and the activity change during the decay process is as follows:

[0017]

[0018] Among them, A p (t): activity of the parent nucleus changing with time, Bq; A p (0): Initial activity of the parent nucleus, Bq; λ p : decay constant of the parent nucleus

[0019] The first generation of progeny is calculated from the amount of mother nucleus generated:

[0020]

[0021] Among them, A d1 (t): Activity of the first generation of progeny changing with time, Bq; f d1 : first generation daughter branching ratio; λ d1 : decay constant of the first generation daughter nucleus;

[0022] Assuming that there are no first-generation and second-generation progeny, the activity of the second-generation progeny is calculated as:

[0023]

[0024] Among them, A d2 (t): Activity of the second generation progeny changing with time, Bq; f d2 : second generation daughter branching ratio; λ d2 : decay constant of the second generation daughter nucleus;

[0025] Assuming that the third generation progeny has no initial activity and there are no second generation progeny, the calculation formula for the third generation progeny is:

[0026]

[0027] Among them: A d3 (t): Activity of the third generation progeny changing with time, Bq; f d3 : branching ratio of the third generation daughter; λ d3 : Decay constant of the third generation daughter nucleus.

[0028] The initial activity A of the parent nucleus is calculated by the core inventory during the decay process. p (0), the core inventory is calculated by formula (7),

[0029]

[0030] Where, I is the actual core inventory, Bq; I D is the core inventory under balanced refueling conditions, Bq; Bu is the actual fuel consumption, MWd / t; Bu D To balance the fuel consumption under refueling conditions, MWd / t.

[0031] Furthermore, in step (4), the release fraction F of the nuclide is calculated by formula (8),

[0032]

[0033] Among them, A d3 (t) is the activity of the third generation progeny changing with time, A i is the release amount of the i-th nuclide at the sampling moment.

[0034] Furthermore, in step (5), the release fraction of each of the above nuclides is compared with the release fraction of the nuclides under the condition of 100% cladding airtightness damage and 100% fuel cladding damage to determine the damage type of the core; the damage types of the core are divided into three categories: no damage to the core represents 0.1% fuel cladding airtightness damage, fuel cladding airtightness damage represents the release of fission products in the gap between the fuel rods), and fuel cladding damage represents the release of fission products in the fuel blocks; among which, 100% damage to the fuel cladding means 100% melting of the core.

[0035] The beneficial effect brought about by the technical solution of the present invention is a sodium-cooled fast reactor core damage assessment method based on radioactive nuclide sampling, which calculates the release amount of nuclides at the sampling moment and the decay of the parent nucleus at the sampling moment, takes the activity of the third-generation decay daughters to obtain the release share of nuclides at the sampling moment of the sodium-cooled fast reactor under accident conditions, compares the calculated nuclide release share with the nuclide release share during the actual accident, and obtains a determined sodium-cooled fast reactor core damage type for quickly guiding emergency safety protection and rescue measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flow chart of a method according to an embodiment of the present invention;

[0037] Figure 2 Schematic diagram of radionuclide decay according to an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0039] Refer to the attached Figure 1 A method for evaluating core damage of a sodium-cooled fast reactor based on radionuclide sampling comprises the following steps:

[0040] (1) Sampling of radionuclides from sodium-cooled fast reactors;

[0041] (2) Estimation of the release activity of nuclides at the time of sampling in a sodium-cooled fast reactor;

[0042] (3) Estimation of the source term of nuclides at the time of sampling for sodium-cooled fast reactors;

[0043] (4) Estimation of the release fraction of nuclides at the time of sampling in sodium-cooled fast reactors;

[0044] (5) Compare the estimated release fractions of the above-mentioned specific nuclides with the cladding airtightness damage and fuel cladding damage to determine the core damage type of the sodium-cooled fast reactor.

[0045] The method of the present invention is based on the characteristics of fission products and their release pathways in a 600MW demonstration sodium-cooled fast reactor project, and is designed to address the scenario of a damaged sodium-cooled fast reactor core during a nuclear emergency. After a sodium-cooled fast reactor core is damaged, radioactive fission products are primarily concentrated in the primary coolant and the main containment gas. If the main containment gas cavity leaks, some radioactive fission products are present in the reactor top shield, the containment hall, and the exhaust chimney.

[0046] Preferably, in step (2), the release activity of the nuclide is calculated by formula (1),

[0047]

[0048] Among them, A i Indicates the release amount of the i-th nuclide at the sampling time, Bq; A c % represents the specific activity of the i-th nuclide in the primary sodium loop at the sampling time, Bq / g; M c represents the mass of sodium remaining in the primary circuit at the time of sampling, t; represents the specific activity of the i-th nuclide in the main container cover gas cavity, the top protective cover and the containment hall at the sampling time, Bq / cm 3 ; V j Represent the free volumes of the main container covering the gas cavity, the top protective cover and the containment hall, m 3 .

[0049] The sampling gas needs to consider the influence of gas pressure and temperature, so the specific activity of a certain nuclide sample is corrected by formula (2):

[0050]

[0051] in, Represents the specific activity of the i-th nuclide in the sample, Bq / cm 3 ;P v,j represents the gas pressure in the sampling cavity (main container covering gas cavity, top protective cover and containment hall), Pa; P s,j Indicates the gas pressure of the nuclide sample, Pa; T v,j represents the temperature in the sampling cavity (main container covering gas cavity, top protective cover and containment hall), ℃; T s,j Indicates the temperature of the nuclide sample, °C.

[0052] Preferably, refer to the attached Figure 2 In step (3), the source term of the nuclide is estimated by the activity of the third generation daughter during the nuclide decay process; the radioactive nuclide decay process is caused by the decay of the parent nucleus, and the activity change during the decay process is as follows:

[0053]

[0054] Among them, A p (t) is the activity of the parent nucleus changing with time, Bq; A p (0) is the initial activity of the parent nucleus, Bq; λ p is the decay constant of the parent nucleus

[0055] The first generation of progeny is calculated from the amount of mother nucleus generated:

[0056]

[0057] Among them, A d1(t) is the activity of the first generation progeny changing with time, Bq; f d1 is the first generation daughter branching ratio; λ d1 is the decay constant of the first generation daughter nuclei;

[0058] Assuming that there are no first-generation and second-generation progeny, the activity of the second-generation progeny is calculated as:

[0059]

[0060] Among them, A d2 (t) is the activity of the second generation progeny changing with time, Bq; f d2 is the second generation daughter branching ratio; λ d2 is the decay constant of the second generation daughter nucleus;

[0061] Assuming that the third generation progeny has no initial activity and there are no second generation progeny, the calculation formula for the third generation progeny is:

[0062]

[0063] Among them: A d3 (t) is the activity of the third generation progeny changing with time, Bq; f d3 is the branching ratio of the third generation daughter; d3 is the decay constant of the third generation daughter nuclei.

[0064] The initial activity A of the parent nucleus is calculated by the core inventory during the decay process. p (0), the core inventory is calculated by formula (7),

[0065]

[0066] Where, I is the actual core inventory, Bq; I D is the core inventory under balanced refueling conditions, Bq; Bu is the actual fuel consumption, MWd / t; Bu D To balance the fuel consumption under refueling conditions, MWd / t.

[0067] Preferably, in step (4), the release fraction F of the nuclide is calculated by formula (8),

[0068]

[0069] Among them, A d3 (t) is the activity of the third generation progeny changing with time, A i is the release amount of the i-th nuclide at the sampling moment.

[0070] Preferably, in step (5), the release fraction of each of the above nuclides is compared with the release fraction of the nuclides under the condition of 100% cladding airtightness damage and 100% fuel cladding damage to determine the damage type of the core; the damage types of the core are divided into three categories: no damage to the core represents 0.1% fuel cladding airtightness damage, fuel cladding airtightness damage represents the release of fission products in the fuel rod gap, and fuel cladding damage represents the release of fission products in the fuel block; wherein, 100% damage to the fuel cladding means 100% melting of the core.

[0071] According to the operating experience of Russian fast reactors BOR-60 and BN-600, when the cladding airtightness is 100% damaged, the proportion of fission products released into the primary circuit is 134 Cs and 137 Cs is 20%, 131 I is 5%, others are 0.1%, and other nuclides mainly refer to 89 Sr. 90 Sr. 140 Ba, 140 La, 95 Zr and 95 Nb et al.

[0072] According to the "Preliminary Safety Analysis Report on the 600MW Demonstration Fast Reactor Project (CFR600)", when the fuel cladding is 100% damaged, the release proportion of fissile nuclides into the primary circuit is shown in the following table.

[0073] Table 1 Release proportion of fissile nuclides into the primary circuit

[0074]

[0075] In practical applications, radionuclides can be detected preferentially based on the above release ratios. 87 Kr, 133 Xe, 131 I. 132 I. 134 Cs, 137 Cs, 140 Ba, 90 If the corresponding nuclide is detected, it indicates that the core is damaged, enabling a qualitative judgment of the core damage. By calculating the release fraction of the corresponding nuclide at the time of sampling and comparing it with the two 100% release fractions mentioned above, the cladding airtightness damage fraction and the fuel cladding damage fraction can be determined, thereby quantitatively determining the damage extent of the sodium-cooled fast reactor core.

[0076] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for assessing core damage in a sodium-cooled fast reactor based on radionuclide sampling, characterized by: The following steps are involved: (1) Sampling of radionuclides from sodium-cooled fast reactors; (2) Estimation of the release activity of nuclides at the time of sampling in a sodium-cooled fast reactor; (3) Estimation of the source term of nuclides at the time of sampling for sodium-cooled fast reactors; (4) Estimation of the release fraction of nuclides at the time of sampling in sodium-cooled fast reactors; (5) Compare the above-mentioned release fraction estimation results of specific nuclides with the cladding airtightness damage and fuel cladding damage to determine the core damage type of the sodium-cooled fast reactor; In step (2), the release activity of the nuclide is calculated using formula (1), Among them, A i Indicates the release amount of the i-th nuclide at the sampling time, Bq; A c % represents the specific activity of the i-th nuclide in the primary sodium loop at the sampling time, Bq / g; M c represents the mass of sodium remaining in the primary circuit at the time of sampling, t; represents the specific activity of the i-th nuclide in the main container cover gas cavity, the top protective cover and the containment hall at the sampling time, Bq / cm 3 ; V j Represent the free volumes of the main container covering the gas cavity, the top protective cover and the containment hall, m 3 ; In step (3), the source term of the nuclide is estimated by expressing the activity of the third generation daughters in the nuclide decay process, and is calculated by formula (6): Among them: A d3 (t) is the activity of the third generation progeny changing with time, Bq; A p (0) is the initial activity of the parent nucleus, Bq; λ p is the decay constant of the parent nucleus; f d1 is the first generation daughter branching ratio; λ d1 is the decay constant of the first generation daughter nucleus; f d2 is the second generation daughter branching ratio; λ d2 is the decay constant of the second generation daughter nucleus; f d3 is the branching ratio of the third generation daughter; d3 is the decay constant of the third generation daughter nucleus; The initial activity A of the parent nucleus is calculated by the core inventory during the decay process. p (0), the core inventory is calculated by formula (7), Where, I is the actual core inventory, Bq; I D is the core inventory under balanced refueling conditions, Bq; Bu is the actual fuel consumption, MWd / t; Bu D The corresponding fuel consumption under balanced refueling conditions, MWd / t; In step (4), the release fraction F of the nuclide is calculated by formula (8): Among them, A d3 (t) is the activity of the third generation progeny changing with time, A i is the release amount of the i-th nuclide at the sampling moment.

2. The method for evaluating core damage of a sodium-cooled fast reactor based on radionuclide sampling according to claim 1, wherein: The specific activity of the i-th nuclide in the main container covering gas cavity, the top protective cover and the containment hall at the sampling time is Corrected by formula (2), in, Represents the specific activity of the i-th nuclide in the sample, Bq / cm 3 ;P v,j represents the gas pressure in the sampling chamber, the main container covering the gas cavity, the top protective cover and the containment hall, Pa; P s,j Indicates the gas pressure of the nuclide sample, Pa; T v,j represents the temperature in the sampling chamber, the main container covering the gas cavity, the top protective cover and the containment hall, ℃; T s,j Indicates the temperature of the nuclide sample, °C.

3. The method for assessing core damage of a sodium-cooled fast reactor based on radionuclide sampling according to claim 1, wherein: In step (5), the release ratio of each of the above nuclides is compared with the release ratio of nuclides under the condition of 100% damage of cladding airtightness and 100% damage of fuel cladding to determine the damage type of the core.

4. The method for evaluating core damage of a sodium-cooled fast reactor based on radionuclide sampling according to claim 1, wherein: There are three types of core damage: no core damage represents 0.1% fuel cladding airtightness damage, fuel cladding airtightness damage represents the release of fission products between fuel rods, and fuel cladding damage represents the release of fission products in fuel blocks; among them, 100% fuel cladding damage means 100% core melting.

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