Sodium-cooled fast reactor core damage evaluation method based on gas cavity radioactivity

Abstract

The application discloses a sodium-cooled fast reactor core damage evaluation method based on a covering gas cavity radioactivity, which comprises monitoring and evaluating related parameter values; judging a core state according to the monitored covering gas cavity radioactivity; and qualitatively and quantitatively judging a sodium-cooled fast reactor core damage type by combining a fuel cladding gas tightness damage fraction and a fuel cladding damage fraction with corresponding instrument monitored parameter values, wherein only the covering gas cavity radioactivity monitoring value is involved in the calculation process, and the calculation result is compared with other monitoring values, so that the sodium-cooled fast reactor core damage judgment accuracy of the application is ensured, and protection guidance measures under unexpected accident conditions can be effectively provided.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear and radiation emergency, and in particular relates to a sodium-cooled fast reactor core damage assessment method based on the radioactivity of a covering gas cavity. Background Art

[0002] Emergency response feedback has formally confirmed that the results of accident source term estimation and dose prediction models are unusable in early accident response countermeasures. Furthermore, source term estimation and dose dispersion simulation results are inaccurate. Therefore, it is extremely important to guide protective actions based on the results of fuel damage assessment. In sodium-cooled fast reactors, core damage can directly reflect fuel damage. 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 the radioactivity of the covering gas cavity, which can guide protective actions under accident conditions.

[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 the radioactivity of a covered air cavity, comprising the following steps:

[0005] (1) Monitor and evaluate relevant parameter values; relevant parameters include the covered air cavity radioactivity (MVRM);

[0006] (2) determining the core state based on the radioactivity of the covered air cavity;

[0007] (3) Assessment of the proportion of fuel cladding airtightness damage;

[0008] (4) Assessment of the proportion of fuel cladding damage;

[0009] (5) Based on the above evaluation of the fuel cladding airtightness damage share and the fuel cladding damage share, the core damage type and damage share are obtained.

[0010] Furthermore, in step (1), the relevant parameters also include the main container liquid level (MVL), the main container covering gas pressure (MVP), the primary circuit hot end temperature (RTD), the source range rate monitoring reading (SRM), and the main container wall temperature (WVT).

[0011] Furthermore, the cover gas cavity radioactivity (MVRM) includes four groups, namely MVRM1, MVRM2, MVRM3 and MVRM4; the MVRM1 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 0.1% of the cladding airtightness is damaged; MVRM2 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 1% of the fuel cladding is damaged; MVRM3 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 100% of the cladding airtightness is damaged; MVRM4 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 100% of the fuel cladding is damaged.

[0012] Furthermore, the set value (MVL) of the main container liquid level includes the main container alarm liquid level MVL1 and the main container liquid level (MVL2) corresponding to the fuel upper conversion area.

[0013] Furthermore, the set value of the main container covering gas pressure is the main container overpressure protection system liquid seal device action pressure (MVP1).

[0014] Furthermore, the set value of the primary circuit hot end temperature (RTD) is that the core may be exposed (RTD1).

[0015] Furthermore, in the step (2), the relevant parameters are continuously monitored when the radioactivity MVRM1 of the covering air cavity is less than 0.1% and the cladding airtightness is damaged and the fission products are released into the radioactivity MVRM1 corresponding to the covering air cavity.

[0016] Furthermore, in step (2), when the radioactivity MVRM2 of the covering air cavity is less than 1% and the cladding airtightness is damaged and the fission products are released into the radioactivity MVRM2 corresponding to the covering air cavity, the fuel cladding airtightness damage ratio is evaluated.

[0017] Furthermore, in the step (2), when the radioactivity MVRM2 of the covering air cavity is ≥1% and the fuel cladding is damaged and released to the radioactivity MVRM2 corresponding to the covering air cavity, the fuel cladding damage share is evaluated.

[0018] Furthermore, in step (3), the fuel cladding airtightness damage fraction is evaluated by formula (1),

[0019]

[0020] Furthermore, in step (4), the fuel cladding damage fraction is calculated using formula (2):

[0021]

[0022] Furthermore, in step (5), the core damage types include no damage, fuel cladding airtightness damage, and fuel cladding damage.

[0023] The beneficial effect brought about by the technical solution of the present invention is a sodium-cooled fast reactor core damage evaluation method based on the radioactive activity of the covering gas cavity. By calculating the fuel cladding airtightness damage fraction and the fuel cladding damage fraction and combining them with the corresponding instrument monitoring parameter values, the sodium-cooled fast reactor core damage type is qualitatively and quantitatively judged. In the calculation process, only the covering gas cavity radioactive activity monitoring value is involved, and the calculation result is compared with the corresponding other monitoring values, thereby ensuring the accuracy of the judgment of the sodium-cooled fast reactor core damage of the present invention and effectively providing protective guidance measures for accident conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0026] The embodiment of the present invention is based on the characteristics of the nuclear island monitoring equipment of the 600MW demonstration fast reactor project and is aimed at the situation where the core of the sodium-cooled fast reactor reactor is damaged in a nuclear emergency.

[0027] Refer to the attached Figure 1 A core damage assessment method for a sodium-cooled fast reactor based on the radioactivity of a covering gas cavity comprises the following steps:

[0028] (1) Evaluate and monitor relevant parameter values; relevant parameters include the covered air cavity radioactivity (MVRM);

[0029] (2) determining the core state based on the radioactivity of the covered air cavity;

[0030] (3) Assessment of the proportion of fuel cladding airtightness damage;

[0031] (4) Assessment of the proportion of fuel cladding damage;

[0032] (5) Based on the above evaluation of the fuel cladding airtightness damage share and the fuel cladding damage share, the core damage type and damage share are obtained.

[0033] Preferably, in step (1), the relevant parameters also include the main container liquid level (MVL), the main container covering gas pressure (MVP), the primary circuit hot end temperature (RTD), the source range rate monitoring reading (SRM), and the main container wall temperature (WVT).

[0034] Preferably, the cover gas cavity radioactivity (MVRM) includes four groups, namely MVRM1, MVRM2, MVRM3 and MVRM4; the MVRM1 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 0.1% of the cladding airtightness is damaged; MVRM2 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 1% of the fuel cladding is damaged; MVRM3 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 100% of the cladding airtightness is damaged; MVRM4 represents the radioactivity corresponding to the release of fission products into the cover gas cavity when 100% of the fuel cladding is damaged.

[0035] Preferably, the set values ​​of the main container liquid level (MVL) include the main container alarm level (MVL1) and the main container liquid level (MVL2) corresponding to the fuel upper conversion zone. If the MVL is lower than MVL1, it indicates that the fuel cladding may be damaged; if the MVL is lower than MVL2, it indicates that the fissile area of ​​the core is exposed and the fuel temperature is rising.

[0036] Preferably, the set value of the main vessel covering gas pressure (MVP) is the main vessel overpressure protection system liquid seal device action pressure (MVP1). The MVP cannot determine the core damage state and is used to correct the covering gas radioactivity and assist in determining the covering gas cavity radioactivity MVRM.

[0037] Preferably, the set value of the primary circuit hot end temperature is possible core exposure (RTD1). RTD can only determine the core damage state, but cannot determine the core damage state quantitatively. When possible core exposure (RTD1) occurs, the fuel temperature rises.

[0038] Preferably, the set value of the main container wall temperature (WVT) is the main container wall temperature WVT1 when the main container structural integrity is challenged, indicating that the fuel cladding is seriously damaged.

[0039] Preferably, in step (2), the relevant parameters are continuously monitored when the radioactivity MVRM of the covering air cavity is less than 0.1% and the cladding airtightness is damaged and the fission products are released to the radioactivity MVRM1 corresponding to the covering air cavity.

[0040] Preferably, in step (2), when the radioactivity MVRM of the covering air cavity is less than 1% and the cladding airtightness is damaged, and the fission products are released to the radioactivity MVRM2 corresponding to the covering air cavity, the fuel cladding airtightness damage proportion is evaluated.

[0041] Preferably, in step (2), when the radioactivity of the covering air cavity MVRM≥1% and the radioactivity released by the fuel cladding reaches MVRM2 corresponding to the covering air cavity, the fuel cladding damage share is evaluated.

[0042] Preferably, in the step (3), the evaluation of the airtightness breakage fraction of the fuel cladding is calculated by using the formula (1).

[0043]

[0044] Under accident conditions, there is a considerable amount of sodium vapor in the cover gas cavity, and the

[0050] ,

[0049] ,

[0054] ,

[0053] ,

[0052] ,

[0051] , , , , , , Na and 24 Na will affect the radioactivity of the gas. By MVRM3 - MVRM1, the 22 Na and 24 Na and the influence of normal conditions on radioactivity are offset.

[0045] 1) When MVP < MVP1, after the release of radioactive substances, some radioactive substances will diffuse with the cover gas into the compensation container. Therefore, it is necessary to consider the dilution of radioactive substances in the cover gas cavity by the compensation container;

[0046] Radioactivity of the cover gas cavity (t) = MVRM(t + 10 min) × λ1

[0047] 2) When MVP ≥ MVP1, after the main container overpressure protection system acts, in addition to considering the dilution problem of the compensation container, since some radioactive substances are discharged into the containment tank with the cover gas of the main container through the liquid seal; it is necessary to correct the radioactivity of the cover gas of the main container;

[0048] Radioactivity of the cover gas cavity (t) = MVRM(t + 10 min) × λ2

[0049] Among them, λ1 is a correction factor, λ2 is a correction factor, and the specific value is the ratio of the gas volume entering the containment tank to the total cover gas volume.

[0050] Since the detection of the cover gas detector has a 10 - minute delay, the data it reflects is the radioactivity 10 minutes ago.

[0051] Compare the results of the airtightness breakage fraction of the fuel cladding calculated above with the results of relevant parameters to further determine whether an accident condition has occurred; when the results of the airtightness breakage fraction of the fuel cladding correspond to the results of the main container liquid level (MVL), the main container cover gas pressure (MVP), the primary loop hot - end temperature (RTD), the source range count rate monitoring reading (SRM), and the main container wall temperature (WVT), it is determined that the airtightness of the fuel cladding is broken; the determination criteria for the relevant parameters are:

[0052] (1) MVL2 < main container liquid level ≤ MVL1;

[0053] (2) Primary loop hot - end temperature > RTD1;

[0054] (3) Source range count rate monitoring reading > SRM1;

[0055] (4) Main container wall temperature < WVT1;

[0056] Preferably, in the step (4), the evaluation of the fuel cladding breakage fraction is calculated by using the formula (2).

[0057]

[0058] Under accident conditions, there is a considerable amount of sodium vapor in the cover gas cavity, in which 22 Na and 24 Na will affect the radioactivity of the gas, in which 22 Na and 24 Na will affect the radioactivity of the gas. The influence of 22 Na and 24 Na as well as the influence of normal condition radiation is offset by (MVRM4 - MVRM2). ​​​​​​​​​​​​​​​​​​​​​​Based on the above calculation results and parameter monitoring data, the core damage types of the sodium-cooled fast reactor are obtained: no damage, fuel cladding airtightness damage, and fuel cladding damage. The calculated fractions quantify the corresponding damage. Among them, no core damage corresponds to 0.1% fuel cladding airtightness damage, fuel cladding airtightness damage corresponds to the release of fission products in the fuel rod gap, and fuel cladding damage corresponds to the release of fission products in the fuel block. 100% damage means 100% core melt.

[0067] 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 evaluating core damage in a sodium-cooled fast reactor based on the radioactivity of the covering gas cavity, characterized by: It includes the following steps: (1) Evaluate and monitor relevant parameter values; the relevant parameters include the covered gas cavity radioactivity (MVRM); the covered gas cavity radioactivity (MVRM) includes four groups, namely MVRM1, MVRM2, MVRM3 and MVRM4; MVRM1 represents the radioactivity corresponding to the release of 0.1% of the fission products with damaged cladding airtightness into the covered gas cavity; MVRM2 represents the radioactivity corresponding to the release of 1% of the damaged fuel cladding into the covered gas cavity; MVRM3 represents the radioactivity corresponding to the release of 100% of the fission products with damaged cladding airtightness into the covered gas cavity; MVRM4 represents the radioactivity corresponding to the release of 100% of the damaged fuel cladding into the covered gas cavity; (2) Judge the core state according to the covered gas cavity radioactivity; (3) Evaluation of the damaged share of the fuel cladding airtightness; the evaluation of the damaged share of the fuel cladding airtightness is calculated by the following formula, 1) When MVP < MVP1, the covered gas cavity radioactivity (t) = MVRM(t + 10 min) × λ1 2) When MVP ≥ MVP1, the covered gas cavity radioactivity (t) = MVRM(t + 10 min) × λ2, where λ1 is a correction factor, λ2 is a correction factor, and the specific value is the ratio of the gas volume entering the containment tank to the total covered gas volume; (4) Evaluation of the damaged share of the fuel cladding; the evaluation of the damaged share of the fuel cladding is calculated by the following formula, 1) When MVP < MVP1, the covered gas cavity radioactivity (t) = MVRM(t + 10 min) × λ1 2) When MVP ≥ MVP1, the covered gas cavity radioactivity (t) = MVRM(t + 10 min) × λ2, where λ1 is a correction factor, λ2 is a correction factor, and the specific value is the ratio of the gas volume entering the containment tank to the total covered gas volume; (5) Obtain the core damage type and damage share according to the above evaluation of the damaged share of the fuel cladding airtightness and the evaluation of the damaged share of the fuel cladding.

2. The method for evaluating core damage of a sodium-cooled fast reactor based on the radioactivity of the covering gas cavity according to claim 1 is characterized by: In step (1), the relevant parameters further include the main vessel liquid level (MVL), the main vessel covered gas pressure (MVP), the hot leg temperature of the primary circuit (RTD), the source range count rate monitoring reading (SRM), and the main vessel wall temperature (WVT).

3. The method for evaluating core damage of a sodium-cooled fast reactor based on the radioactivity of the covering gas cavity according to claim 2, wherein: The set values of the main vessel liquid level (MVL) include the main vessel alarm liquid level (MVL1) and the main vessel liquid level (MVL2) corresponding to the fuel up-conversion zone.

4. The method for evaluating core damage of a sodium-cooled fast reactor based on the radioactivity of the cover gas cavity according to claim 2, wherein: The set value of the main vessel covered gas pressure (MVP) is the action pressure (MVP1) of the liquid seal of the main vessel overpressure protection system.

5. The method for evaluating core damage of a sodium-cooled fast reactor based on the radioactivity of the covering gas cavity according to claim 1 is characterized by: In step (2), when the covered gas cavity radioactivity MVRM < the radioactivity MVRM1 corresponding to the release of 0.1% of the fission products with damaged cladding airtightness into the covered gas cavity, continue to monitor the relevant parameters.

6. The method for evaluating core damage of a sodium-cooled fast reactor based on the radioactivity of the covering gas cavity according to claim 1 is characterized by: In step (2), when the covered gas cavity radioactivity MVRM < the radioactivity MVRM2 corresponding to the release of 1% of the fission products with damaged cladding airtightness into the covered gas cavity, evaluate the damaged share of the fuel cladding airtightness.

7. The method for evaluating core damage of a sodium-cooled fast reactor based on the radioactivity of the covering gas cavity according to claim 1 is characterized by: In the step (2), when the radioactivity of the covering air cavity MVRM≥1% and the radioactivity released from the fuel cladding reaches MVRM2 corresponding to the covering air cavity, the fuel cladding damage share is evaluated.

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