Method for determining annual emission load of airborne C-14 in pressurized water reactor nuclear power plant

Abstract

The invention discloses a pressurized water reactor nuclear power plant airborne C-14 annual discharge amount determination method, which comprises the following steps: S1, selecting a pressurized water reactor nuclear power plant which is of the same type and has been operated as a reference pressurized water reactor nuclear power plant, and taking C-14 operation discharge monitoring data of the reference pressurized water reactor nuclear power plant as a basis; and S2, calculating the C-14-year discharge amount of the pressurized water reactor nuclear power plant to be determined according to a formula. According to the method, on the basis of C-14 operation emission monitoring data of operated pressurized water reactor nuclear power plants of the same type, the airborne C-14 annual emission amount of the pressurized water reactor nuclear power plants is determined through factors such as reactor power, coolant density, energy utilization rate and radioactive effluent emission management plans; the method for determining the airborne C-14 concentrated emission amount according to the emission management factors of the reference nuclear power plant is clear in principle, simple in process and high in applicability, is suitable for analyzing the expected C-14 annual emission amount of the pressurized water reactor nuclear power plant and is also suitable for determining the conservative C-14 annual emission amount and the emission amount application value.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power technology, and in particular to a method for determining the annual emission of gas-borne C-14 in a pressurized water reactor nuclear power plant. Background Art

[0002] During the power operation of a pressurized water reactor nuclear power plant, when the primary coolant flows through the core area, the O-17 atoms and N-14 atoms contained in the coolant are irradiated by neutrons and produce C-14 through nuclear reactions O-17(n,α)C-14 and N-14(n,p)C-14 respectively. Most of the C-14 produced in the coolant is discharged to the environment in gaseous form, a small amount is discharged to the environment in the form of waste liquid, and the rest is confined in solid radioactive waste.

[0003] C-14 has a half-life of 5730 years and is an important radionuclide emitted into the environment during the normal operation of a pressurized water reactor nuclear power plant, accounting for more than 90% of the public dose rate generated by all emitted radionuclides. C-14 emitted into the environment during the operation of a pressurized water reactor nuclear power plant will participate in plant photosynthesis and enter the human food chain, ultimately affecting the environment and human life. Therefore, reasonably determining and controlling C-14 emissions is an important part of controlling the safe operation of a pressurized water reactor nuclear power plant.

[0004] During the period of stable power operation of a PWR nuclear power plant, the generation of C-14 in the core area coolant is stable and continuous. However, the amount of C-14 discharged from a PWR nuclear power plant to the external environment is not always in real-time correspondence with the amount of C-14 generated in the core coolant. After the C-14 generated in the coolant flows through the chemical volume control system and is treated by the waste treatment system, most of the C-14 is collected in the waste gas tank. In addition to a part of the stable continuous emission, the C-14 accumulated in the waste gas tank will be discharged into the environment through the chimney at regular intervals, which will cause a significant increase in the airborne C-14 emission of PWR nuclear power plants in a short period of time (especially the large-volume concentrated emission of waste gas during the reactor overhaul process). Therefore, the annual emission of airborne C-14 in the actual operation of PWR nuclear power plants is greatly affected by the specific waste gas management plan.

[0005] The traditional method for determining the annual C-14 emissions of a pressurized water reactor nuclear power plant first requires calculating the neutron injection rate in the neutron irradiation zone through the core design program or neutron transport program, and then calculating the annual C-14 production based on the O-17 content, N-14 content, coolant density, and coolant volume in the neutron irradiation zone. The annual airborne C-14 emissions of the pressurized water reactor nuclear power plant are then obtained based on the airborne distribution factor. This method is not only complicated, but also fails to identify the actual impact of nuclear power plant emission management on the annual airborne C-14 emissions. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an improved method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant.

[0007] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant, comprising the following steps:

[0008] S1. Select a PWR NPP of the same type and in operation as the reference PWR NPP, and use the C-14 operating emission monitoring data of the reference PWR NPP as the basis;

[0009] S2. Calculate the annual C-14 emissions of the pressurized water reactor nuclear power plant to be determined according to the following formula:

[0010]

[0011] Where A represents the annual emission of C-14 from the to-be-determined pressurized water reactor nuclear power plant, in GBq / a;

[0012] A0 represents the average value of historical data of annual C-14 emissions from reference PWR nuclear power plants, in GBq / a;

[0013] P represents the PWR power of the PWR nuclear power plant to be determined, in MWe;

[0014] P0 represents the power of the reference PWR nuclear power plant in MWe;

[0015] ρ represents the average coolant density of the PWR core of the PWR nuclear power plant to be determined, in kg / m 3 ;

[0016] ρ0 represents the average coolant density of the PWR core of the reference PWR nuclear power plant, in kg / m 3 ;

[0017] EA represents the energy utilization of the undetermined PWR nuclear power plant, a dimensionless number;

[0018] EA0 represents the energy utilization of the reference PWR nuclear power plant, a dimensionless number;

[0019] k is the emission management factor, which is an empirical coefficient related to the emission management and emission plan of pressurized water reactor nuclear power plants and is a dimensionless number.

[0020] In some embodiments, when k is less than 0, it indicates that the emissions of the pressurized water reactor nuclear power plant during the considered time period are lower than the reference emissions.

[0021] In some embodiments, k is taken to be 0 when determining the expected annual airborne C-14 emissions from a pressurized water reactor nuclear power plant in a best estimate case.

[0022] In some embodiments, when the number of million-kilowatt pressurized water reactors at the site exceeds four, k ranges from 0.25≤k≤0.65.

[0023] In some embodiments, in step S1, the reference PWR nuclear power plant is identical or similar to the PWR nuclear power plant to be determined in terms of core neutron spectrum, source of dissolved nitrogen in coolant, and waste treatment process.

[0024] In some embodiments, the core neutron energy spectrum of the reference pressurized water reactor nuclear power plant and the pressurized water reactor nuclear power plant to be determined is the same or similar, and the conditions that meet include: the same fuel core block type, the same or similar cladding material of the fuel rod, the same or similar arrangement of the fuel assemblies, the same or similar spacing between the fuel rods, the same or similar U-235 enrichment of the fuel rods, and the same or similar average linear power of the fuel rods.

[0025] In some embodiments, the source of dissolved nitrogen in the coolant of the reference pressurized water reactor nuclear power plant and the pressurized water reactor nuclear power plant to be determined is the same or similar, and the following conditions are met: the cover gas type of the volume control box is the same, the cover gas type of the boric acid supply box is the same, the alkalizing agent type of the coolant is the same, and the degassing treatment method of the feed water is the same.

[0026] The beneficial effects of the present invention are as follows: based on the C-14 operation emission monitoring data of the same type of operating pressurized water reactor nuclear power plants, the annual airborne C-14 emissions of the pressurized water reactor nuclear power plant are determined through factors such as reactor power, coolant density, energy utilization rate and radioactive effluent emission management plan; the principle is clear, the process is simple, and the applicability is strong. A method for determining the concentrated airborne C-14 emissions based on the emission management factors of the reference nuclear power plant is provided, which is not only suitable for analyzing the expected annual C-14 emissions of the pressurized water reactor nuclear power plant, but also suitable for determining conservative annual C-14 emissions and emission application values. DETAILED DESCRIPTION

[0027] A method for determining annual emissions of airborne C-14 from a pressurized water reactor nuclear power plant according to an embodiment of the present invention comprises the following steps:

[0028] S1. Select a pressurized water reactor nuclear power plant of the same type and in operation as the reference pressurized water reactor nuclear power plant, and use the C-14 operating emission monitoring data of the reference pressurized water reactor nuclear power plant as the basis.

[0029] Since C-14 in the coolant in the core area of ​​a PWR nuclear power plant is produced by neutron irradiation of O-17 atoms and N-14 atoms contained in the coolant, the amount of C-14 produced conforms to the basic law of neutron activation reaction, that is, the amount of C-14 produced in the coolant is proportional to the neutron injection rate in the neutron irradiation area, the target nuclear content (O-17 content in the coolant, N-14 content in the coolant), the coolant volume in the active area, and the reactor operation time. After determining the amount of C-14 produced by the PWR, combined with the C-14 emission history data of the reference PWR nuclear power plant and the difference between the PWR to be determined and the reference PWR, the range of the airborne C-14 emission of the PWR to be determined can be determined.

[0030] In some embodiments, before step S1, the process further includes identifying a source of C-14 in the coolant.

[0031] During the operation of the PWR coolant power, the O-17 atoms and N-14 atoms contained in the core coolant are irradiated by neutrons and produce C-14 through the nuclear reactions O-17(n,α)C-14 and N-14(n,p)C-14 respectively. The C-14 produced by other pathways is very small and can be ignored.

[0032] The O-17 content in the coolant can be determined based on the natural abundance of O-17. Since the microscopic cross section of the O-17 (n, α) C-14 nuclear reaction is very small, and the primary coolant is constantly replenished and renewed due to continuous up-filling and down-filling, it can be assumed that the O-17 content in the primary coolant is always maintained near its natural abundance (about 0.038%).

[0033] N-14 in the coolant comes from a variety of sources, such as nitrogen dissolved in the air during overhaul, introduced through added nitrogen-containing chemicals (such as hydrazine), and nitrogen blanketing above the tank in some pressurized water reactors that dissolves and is added to the coolant; in some pressurized water reactors, ammonia is added to the coolant to maintain the pH range.

[0034] For the PWR nuclear power plant selected for reference determination, factors such as the neutron injection rate in the core area and the dissolved nitrogen content in the coolant will affect the generation of C-14 in the primary loop, while the waste treatment process will affect the emission of C-14. Therefore, only the C-14 emission operation data of the operating PWR nuclear power plant with the same or similar reactor core design and waste treatment process are applicable to the reference of the PWR to be determined.

[0035] For a PWR NPP to be determined as a reference, it must be identical or similar to the PWR NPP to be determined in terms of core neutron spectrum, source of dissolved nitrogen in the coolant, and waste treatment process.

[0036] The conditions that the core neutron energy spectrum of the reference PWR nuclear power plant and the PWR nuclear power plant to be determined is the same or similar include:

[0037] The fuel pellet types (including UO2 fuel and MOX fuel) are the same;

[0038] The cladding materials of the fuel rods (including zirconium alloy, stainless steel, etc.) are the same or similar;

[0039] The layout of the fuel assemblies (hexagonal layout, square layout, etc.) is the same or similar;

[0040] The spacing between the fuel rods is the same or similar;

[0041] The U-235 enrichment of the fuel rods is the same or similar;

[0042] The average linear power of the core fuel rods is the same or similar.

[0043] As for the source of dissolved nitrogen in the coolant, the nitrogen-containing substances introduced by the dissolution of nitrogen in the air during overhaul and the addition of hydrazine during unit startup are very small. If the following conditions are met, it can be considered that the source of dissolved nitrogen in the coolant of the reference PWR nuclear power plant and the PWR nuclear power plant to be determined is the same or similar:

[0044] The type of cover gas (e.g. nitrogen, hydrogen) of the volume control box is the same;

[0045] The type of cover gas (e.g. nitrogen, hydrogen) of the boric acid supply tank is the same;

[0046] The type of alkalizing agent (e.g., ammonia, lithium hydroxide, potassium hydroxide, etc.) used in the coolant is the same; and

[0047] The degassing treatment method of the makeup water (e.g., degassing, not degassing) is the same.

[0048] For waste treatment processes, during the operation of a PWR, as the coolant flows through the chemical volume system and the radioactive waste treatment system, most of the C-14 will enter the waste gas tank through volatilization, purging, etc. and be discharged into the environment through the chimney. A small amount of C-14 will form radioactive waste liquid and be discharged into the environment after dilution, and the rest will be confined in solid waste. When the PWR to be determined and the reference PWR both treat the radioactive nuclide C-14 in the effluent or neither of them treats it, the ratio of the airborne C-14 release (the ratio of the airborne C-14 release to the C-14 generated in the coolant) of the two is the same or similar. In this case, the emission processes of the PWR to be determined and the reference PWR are similar.

[0049] S2. Calculate the annual C-14 emissions of the pressurized water reactor nuclear power plant to be determined according to formula (1):

[0050]

[0051] Where A represents the annual C-14 emission of the to-be-determined PWR NPP, in GBq / a; A0 represents the average value of the historical data of the annual C-14 emission of the reference PWR NPP, in GBq / a; P represents the PWR power of the to-be-determined PWR NPP, in MWe; P0 represents the power of the reference PWR NPP, in MWe; ρ represents the average coolant density of the PWR core of the to-be-determined PWR NPP, in kg / m 3 ; ρ0 represents the average coolant density of the PWR core of the reference PWR nuclear power plant, in kg / m 3 ; EA represents the energy utilization rate of the pressurized water reactor nuclear power plant to be determined, a dimensionless number; EA0 represents the energy utilization rate of the reference pressurized water reactor nuclear power plant, a dimensionless number.

[0052] Where k is the emission management factor, which is an empirical coefficient related to the emission management and emission plan of a pressurized water reactor nuclear power plant and is a dimensionless number. When k is less than 0, it means that the emissions of the nuclear power plant during the considered time period are lower than the reference emissions.

[0053] The smaller the absolute value |k| of the emission management factor k, the lower the flexibility of radioactive effluent emission management during the operation of the PWR nuclear power plant. The larger the absolute value |k|, the greater the range of variation of the annual emission during the operation of the PWR nuclear power plant. It is necessary to comprehensively consider the radioactive effluent management strategy of the PWR nuclear power plant, the emission control requirements of the nuclear power base and other factors to determine the emission management factor k.

[0054] In the best estimate case, when determining the expected annual airborne C-14 emissions from a PWR nuclear power plant, k can be taken as 0. When determining the conservative annual airborne C-14 emissions from a PWR nuclear power plant, k should be determined comprehensively based on factors such as the specific emission management plan and site capacity.

[0055] For the case where multiple million-kilowatt pressurized water reactors are planned for a site, the recommended k range for determining the conservative annual airborne C-14 emissions is 0.25≤k≤0.65. When the annual airborne C-14 emissions exceed 1.65 times the average annual emissions, the reasons for the excessively high airborne C-14 emissions should be analyzed.

[0056] The present invention is further described below with reference to an application example.

[0057] The airborne C-14 emissions of the Hualong One PWR were determined based on the operating experience of the Konvoi PWR:

[0058] Hualong One is a typical third-generation light water pressurized water reactor with a rated power of 1180MWe. During full-power operation, the coolant system pressure is 15.5MPa and the average coolant temperature is 307℃. During the power operation of the unit, the volume control box of the Hualong One pressurized water reactor is covered and purged with high-pressure nitrogen, the covering gas of the boric acid supply tank is hydrogen, and lithium hydroxide is used as the coolant alkalizer. The Konvoi pressurized water reactor is a second-generation pressurized water reactor developed in Germany with decades of good operating experience. The volume control box is covered and purged with high-pressure nitrogen, the covering gas of the boric acid supply tank is hydrogen, and lithium hydroxide is used as the coolant alkalizer. Therefore, the airborne C-14 emissions of the Hualong One pressurized water reactor can be determined based on the operating experience of the Konvoi pressurized water reactor, as follows:

[0059] Step 1: Identify the PWR to be determined and conduct a compatibility analysis with the reference PWR.

[0060] Table 1 lists the main factors affecting the production and emission treatment of C-14 in Hualong One PWR (pwr to be determined) and Konvoi PWR (reference PWR). According to the analysis, Hualong One PWR (pwr to be determined) and Konvoi PWR (reference PWR) are the same or similar in terms of C-14 production source, core neutron spectrum and waste treatment. Therefore, the annual C-14 emission data of Konvoi PWR has a good reference for Hualong One PWR.

[0061] Table 1 Comparison of the main features of Hualong One PWR and Konvoi PWR

[0062]

[0063] Step 2: Analysis of annual emissions of airborne C-14 from reference PWR operating data.

[0064] The annual emissions of airborne C-14 from a Konvoi type PWR from 2000 to 2014 were collected, collated and analyzed, and the results are shown in Table 2. From 2001 to 2014, the annual emissions of airborne C-14 from the Konvoi type PWR unit were in the range of 190GBq / a to 480GBq / a, and the corresponding energy utilization rate was in the range of 93% to 97%. The average annual emissions of airborne C-14 from the Konvoi type PWR unit was 308GBq / a, and the corresponding average energy utilization rate was 94%.

[0065] Table 2 Annual emissions of airborne C-14 from a Konvoi PWR from 2000 to 2014

[0066]

[0067] Step 3: Calculate the airborne C-14 emissions from the PWR to be identified.

[0068] The Konvoi type PWR (reference PWR) has an electrical power of 1406 MWe and an average coolant density of 0.709 kg / m 3 , the average annual emission of airborne C-14 from 2001 to 2014 was 308 GBq / a, corresponding to an average energy utilization rate of 94%. For the Hualong No. 1 PWR (to be determined), the unit's electrical power is 1180 MWe, and the average coolant density is 0.711 kg / m 3 , the corresponding average energy utilization is 90%.

[0069] According to the above formula (1) of the present invention, the expected annual gas-borne C-14 emission of the Hualong No. 1 pressurized water reactor (the pressurized water reactor unit to be determined) is 248 GBq / a, where the emission management factor k is 0, and the calculation process is as follows:

[0070]

[0071] When the emission management factor k is taken as 0.65, the conservative annual gas-borne C-14 emission of the Hualong One PWR (the PWR unit to be determined) is 428 GBq / a. The calculation process is as follows:

[0072]

[0073] Therefore, the expected annual airborne C-14 emissions of the Hualong One PWR (to be determined) are 248 GBq / a, and the conservative annual airborne C-14 emissions are 428 GBq / a. The latter can be used as the application value and management limit of the annual airborne C-14 emissions of the Hualong One.

[0074] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant, characterized in that: The following steps are involved: S1. Select a PWR NPP of the same type and in operation as the reference PWR NPP, and use the C-14 operating emission monitoring data of the reference PWR NPP as the basis; S2. Calculate the annual C-14 emissions of the pressurized water reactor nuclear power plant to be determined according to the following formula: Where A represents the annual emission of C-14 from the to-be-determined pressurized water reactor nuclear power plant, in GBq / a; A0 represents the average value of historical data of annual C-14 emissions from reference PWR nuclear power plants, in GBq / a; P represents the PWR power of the PWR nuclear power plant to be determined, in MWe; P0 represents the power of the reference PWR nuclear power plant in MWe; ρ represents the average coolant density of the PWR core of the PWR nuclear power plant to be determined, in kg / m 3 ; ρ0 represents the average coolant density of the PWR core of the reference PWR nuclear power plant, in kg / m 3 ; EA represents the energy utilization of the undetermined PWR nuclear power plant, a dimensionless number; EA0 represents the energy utilization of the reference PWR nuclear power plant, a dimensionless number; k is the emission management factor, which is an empirical coefficient related to the emission management and emission plan of pressurized water reactor nuclear power plants and is a dimensionless number.

2. The method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant according to claim 1, characterized in that: When k is less than 0, it means that the emissions of the PWR nuclear power plant during the considered time period are lower than the reference emissions.

3. The method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant according to claim 1, characterized in that: In the best estimate case, k is taken to be 0 when determining the expected annual airborne C-14 emissions from a PWR nuclear power plant.

4. The method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant according to claim 1, characterized in that: When the number of million-kilowatt pressurized water reactors at the site exceeds four, the range of k is 0.25≤k≤0.

65.

5. The method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant according to claim 1, characterized in that: In step S1, the reference pressurized water reactor nuclear power plant is identical or similar to the pressurized water reactor nuclear power plant to be determined in terms of core neutron spectrum, source of dissolved nitrogen in coolant, and waste treatment process.

6. The method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant according to claim 5, characterized in that: The conditions that the core neutron energy spectrum of the reference pressurized water reactor nuclear power plant and the pressurized water reactor nuclear power plant to be determined is the same or similar include: the type of fuel pellets is the same, the cladding material of the fuel rods is the same or similar, the arrangement of the fuel assemblies is the same or similar, the spacing between the fuel rods is the same or similar, the U-235 enrichment of the fuel rods is the same or similar, and the average linear power of the fuel rods is the same or similar.

7. The method for determining the annual emission of airborne C-14 in a pressurized water reactor nuclear power plant according to claim 5, characterized in that: The sources of dissolved nitrogen in the coolant of the reference pressurized water reactor nuclear power plant and the pressurized water reactor nuclear power plant to be determined are the same or similar and meet the following conditions: the covering gas type of the volume control box is the same, the covering gas type of the boric acid supply box is the same, the alkalizing agent type of the coolant is the same, and the degassing treatment method of the feed water is the same.

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