Method for determining annual emissions of airborne c-14 from pressurized water reactor nuclear power plant

Abstract

Disclosed in the present invention is a method for determining annual emissions of airborne C-14 from a pressurized water reactor nuclear power plant. The method comprises: S1, selecting pressurized water reactor nuclear power plants of the same type which are already in operation as reference pressurized water reactor nuclear power plants, and using C-14 operation and emission monitoring data of the reference pressurized water reactor nuclear power plants as a basis; and S2, on the basis of a formula, calculating annual C-14 emissions from a pressurized water reactor nuclear power plant to be determined. On the basis of the C-14 operation and emission monitoring data of the pressurized water reactor nuclear power plants of the same type which are already in operation, the present invention determines annual emissions of airborne C-14 from pressurized water reactor nuclear power plants by taking into account factors such as reactor power, coolant density, energy utilization rate and radioactive effluent emission management plans; featuring clear principles, simple processes and high applicability, the provided method for determining centralized emissions of airborne C-14 on the basis of emission management factors of the reference nuclear power plants is suitable for analyzing expected annual C-14 emissions from pressurized water reactor nuclear power plants, and is also suitable for determining conservative annual C-14 emissions and emission application values.

Description

Method for determining annual airborne C-14 emissions from pressurized water reactor nuclear power plants Technical Field

[0001] This invention relates to the field of nuclear power technology, and in particular to a method for determining the annual C-14 emissions of pressurized water reactor nuclear power plants. Background Technology

[0002] During the operation of a pressurized water reactor nuclear power plant, when the primary coolant flows through the reactor core, the O-17 and N-14 atoms contained in the coolant are irradiated with neutrons and then 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 released into the environment in gaseous form, a small amount is released into the environment in liquid form, and the remainder is trapped in solid radioactive waste.

[0003] C-14, with a half-life of 5730 years, is a significant radionuclide emitted into the environment during the normal operation of pressurized water reactor (PWR) nuclear power plants, accounting for over 90% of the public dose rate from all emitted radionuclides. C-14 emitted into the environment during PWR operation participates in plant photosynthesis and enters the human food chain, ultimately impacting the environment and human lives. Therefore, rationally determining and controlling C-14 emissions is a crucial aspect of ensuring the safe operation of PWR nuclear power plants.

[0004] During stable power operation of a pressurized water reactor (PWR) nuclear power plant, the generation of C-14 in the coolant within the reactor core is stable and continuous. However, the amount of C-14 emitted into the environment by a PWR nuclear power plant does not always correspond in real-time to the amount of C-14 generated in the reactor core coolant. After the C-14 generated in the coolant flows through the chemical volume control system and is processed by the waste treatment system, most of the C-14 is collected in exhaust gas tanks. Besides a portion that is continuously and stably emitted, the C-14 accumulated in the exhaust gas tanks is periodically and centrally released into the environment through the chimney. This can cause a significant increase in the amount of airborne C-14 emitted by the PWR nuclear power plant in a short period (especially during reactor overhauls when large volumes of exhaust gas are released). Therefore, the annual airborne C-14 emissions during the actual operation of a PWR nuclear power plant are greatly affected by specific exhaust gas management plans.

[0005] Traditional methods for determining annual C-14 emissions from pressurized water reactor (PWR) nuclear power plants first require calculating the neutron flux rate in the neutron-irradiated area using core design or neutron transport programs. Then, based on the O-17 and N-14 content in the coolant, coolant density, and coolant volume in the neutron-irradiated area, the annual C-14 production is calculated. Finally, the annual airborne C-14 emissions are obtained based on the airborne allocation factor. This method is not only complex but also fails to identify the actual impact of nuclear power plant emission management on 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 C-14 emissions of pressurized water reactor nuclear power plants.

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

[0008] S1. Select a pressurized water reactor nuclear power plant of the same type that is already in operation as a reference pressurized water reactor nuclear power plant, and base it on the C-14 operation emission monitoring data of the reference pressurized water reactor nuclear power plant;

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

[0010]

[0011] In the formula, This indicates the C-14 emissions of pressurized water reactor nuclear power plants to be determined, in GBq / a.

[0012] This represents the average historical emissions data for C-14 years of pressurized water reactor nuclear power plants, in GBq / a.

[0013] This indicates the pressurized water reactor power of the pressurized water reactor nuclear power plant to be determined, in MWe.

[0014] This indicates the power output of a reference pressurized water reactor nuclear power plant, expressed in MWe.

[0015] This indicates the average coolant density of the pressurized water reactor core in the pressurized water reactor nuclear power plant to be determined, in kg / m³. 3 ;

[0016] This represents the average coolant density of the pressurized water reactor core in a reference pressurized water reactor nuclear power plant, expressed in kg / m³. 3 ;

[0017] This represents the energy utilization rate of a pressurized water reactor nuclear power plant to be determined; it is a dimensionless number.

[0018] This represents the energy utilization rate of a reference pressurized water reactor nuclear power plant; it is a dimensionless number.

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

[0020] In some embodiments, when A value less than 0 indicates that the emissions from 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 as 0 when determining the expected annual airborne C-14 emissions of a pressurized water reactor nuclear power plant under optimal estimation conditions.

[0022] In some embodiments, when the number of megawatt pressurized water reactors at the plant site exceeds four, the range of k is 0.25 ≤ k ≤ 0.65.

[0023] In some embodiments, in step S1, the reference pressurized water reactor nuclear power plant and the pressurized water reactor nuclear power plant to be determined are the same or similar in terms of core neutron energy spectrum, source of dissolved nitrogen in coolant, and waste treatment process.

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

[0025] In some embodiments, the conditions that 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 are the same or similar include: the cover gas type of the volume control tank is the same, the cover gas type of the boric acid supply tank is the same, the alkalizing agent type of the coolant is the same, and the degassing treatment method of the makeup water is the same.

[0026] The beneficial effects of this invention are as follows: Based on the C-14 operation emission monitoring data of similar operating pressurized water reactor nuclear power plants, the annual airborne C-14 emissions of pressurized water reactor nuclear power plants are determined by factors such as reactor power, coolant density, energy utilization rate, and radioactive effluent emission management plans. The principle is clear, the process is simple, and the applicability is strong. It provides a method for determining the concentrated airborne C-14 emissions based on the emission management factors of reference nuclear power plants. It is not only applicable to analyzing the expected annual C-14 emissions of pressurized water reactor nuclear power plants, but also applicable to determining conservative annual C-14 emissions and emission application values. Detailed Implementation

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

[0028] S1. Select a similar pressurized water reactor nuclear power plant that is already in operation as a reference pressurized water reactor nuclear power plant, based on the C-14 operation emission monitoring data of the reference pressurized water reactor nuclear power plant.

[0029] In pressurized water reactor (PWR) nuclear power plants, C-14 in the core coolant is produced by neutron irradiation of O-17 and N-14 atoms contained in the coolant. Therefore, the amount of C-14 produced conforms to the basic laws of neutron activation reactions, namely: the amount of C-14 produced in the coolant is directly proportional to the neutron flux rate in the neutron-irradiated area, the target nucleus content (O-17 content and N-14 content in the coolant), the coolant volume in the active area, and the reactor operating time. After determining the C-14 production amount of the PWR, by combining the historical C-14 emission data of the reference PWR nuclear power plant and the differences between the PWR to be determined and the reference PWR, the range of airborne C-14 emissions for the PWR to be determined can be determined.

[0030] In some embodiments, prior to step S1, the method further includes identifying the source of C-14 generation in the coolant.

[0031] During pressurized water reactor coolant power operation, O-17 and N-14 atoms in the coolant in the core region are irradiated with neutrons and then produce C-14 through nuclear reactions O-17(n,α)C-14 and N-14(n,p)C-14, respectively. Other pathways produce very little C-14, which 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 charging and discharging, it can be assumed that the O-17 content in the primary coolant remains near its natural abundance (approximately 0.038%).

[0033] N-14 in the coolant comes from various sources, such as nitrogen dissolved in the air during overhauls, nitrogen added by nitrogen-containing chemicals (such as hydrazine), nitrogen dissolved from the covering above the tank in some pressurized water reactors and added to the coolant; and ammonia added to the coolant in some pressurized water reactors to maintain the pH range.

[0034] For the selected pressurized water reactor (PWR) nuclear power plant as a reference, factors such as the neutron flux rate and dissolved nitrogen content in the core region affect the generation of C-14 in the primary circuit, while waste treatment processes affect C-14 emissions. Therefore, only C-14 emission operation data from existing PWR nuclear power plants with similar or identical reactor core designs and waste treatment processes are applicable as a reference for the PWR to be determined.

[0035] For a pressurized water reactor (PWR) plant to be selected as a reference, it must be identical or similar to the PWR plant to be selected in terms of core neutron energy spectrum, source of dissolved nitrogen in coolant, and waste treatment process.

[0036] Among them, the conditions that the core neutron energy spectra 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 include:

[0037] The fuel pellet types (including UO2 type fuel and MOX type 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 arrangement of fuel assemblies (hexagonal arrangement, square arrangement, etc.) is the same or similar;

[0040] The fuel rods are spaced at the same or similar intervals;

[0041] The fuel rods have similar or identical U-235 enrichment levels;

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

[0043] Regarding the source of dissolved nitrogen in the coolant, the amount of nitrogen-containing substances introduced due to nitrogen dissolution from the air during overhauls and the addition of hydrazine during unit startup is minimal. 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 can be considered the same or similar when the following conditions are met:

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

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

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

[0047] The degassing treatment method for makeup water (e.g., degassing or no degassing) is the same.

[0048] Regarding waste treatment processes, during pressurized water reactor (PWR) operation, as the coolant flows through the chemical volume system and radioactive waste treatment system, most C-14 enters the exhaust gas tank through volatilization and purging, and is emitted into the environment through the chimney. A small amount of C-14 forms radioactive liquid waste, which is diluted and then discharged into the environment. The remainder is trapped in solid waste. Only when both the PWR to be determined and the reference PWR treat the radionuclide C-14 in the effluent or do not treat it, will the proportion of airborne C-14 release (the proportion of airborne C-14 release to the amount of C-14 generated in the coolant) be the same or similar. In this case, the emission processes of the determined PWR and the reference PWR are similar.

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

[0050] (1)

[0051] In the formula, This indicates the C-14 emissions of pressurized water reactor nuclear power plants to be determined, in GBq / a. This represents the average historical emissions data for C-14 years of pressurized water reactor nuclear power plants, in GBq / a. This indicates the pressurized water reactor power of the pressurized water reactor nuclear power plant to be determined, in MWe. This indicates the power output of a reference pressurized water reactor nuclear power plant, expressed in MWe. This indicates the average coolant density of the pressurized water reactor core in the pressurized water reactor nuclear power plant to be determined, in kg / m³. 3 ; This represents the average coolant density of the pressurized water reactor core in a reference pressurized water reactor nuclear power plant, expressed in kg / m³. 3 ; This represents the energy utilization rate of a pressurized water reactor nuclear power plant to be determined; it is a dimensionless number. This represents the energy utilization rate of a reference pressurized water reactor nuclear power plant; it is a dimensionless number.

[0052] in, It is an emissions management factor, an empirical coefficient related to emissions management and emissions planning for pressurized water reactor nuclear power plants, and is a dimensionless number. A value less than 0 indicates that the nuclear power plant's emissions during the considered time period are lower than the reference emissions.

[0053] Emissions Management Factors The smaller the absolute value of |k|, the lower the flexibility in managing radioactive effluent emissions during the operation of a pressurized water reactor (PWR) nuclear power plant. The larger the absolute value of |k|, the greater the range of annual emissions variation during the operation of the PWR nuclear power plant. The emission management factor k needs to be determined comprehensively, taking into account factors such as the radioactive effluent management strategy of the PWR nuclear power plant and the emission control requirements of the nuclear power plant site.

[0054] Under optimal estimation conditions, k can be taken as 0 when determining the expected airborne C-14 emissions of a pressurized water reactor nuclear power plant. When determining the conservative airborne C-14 emissions of a pressurized water reactor nuclear power plant, k should be determined comprehensively based on factors such as the specific emissions management plan and site capacity.

[0055] When planning multiple 1,000 MW pressurized water reactors at a single plant site, the recommended range for determining the conservative annual airborne C-14 emissions is 0.25 ≤ k ≤ 0.65. If the annual airborne C-14 emissions exceed 1.65 times the average annual emissions, the reasons for the excessively high emissions should be analyzed.

[0056] The present invention will be further illustrated below with an application example.

[0057] Based on the operational experience of the Konvoi-type pressurized water reactor, the airborne C-14 emission of the Hualong One pressurized water reactor was determined as follows:

[0058] The Hualong One is a typical third-generation light water pressurized water reactor with a rated power of 1180 MWe. During full-power operation, the coolant system pressure is 15.5 MPa, and the average coolant temperature is 307°C. During full-power operation, the Hualong One pressurized water reactor uses high-pressure nitrogen for covering and purging the volume control tank, hydrogen for covering the boric acid supply tank, and lithium hydroxide as the coolant alkalizing agent. The Konvoi pressurized water reactor, a second-generation pressurized water reactor developed in Germany, has decades of successful operating experience. It also uses high-pressure nitrogen for covering and purging the volume control tank, hydrogen for covering the boric acid supply tank, and lithium hydroxide as the coolant alkalizing agent. 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 reference analysis between the pressurized water reactor to be determined and the reference pressurized water reactor.

[0060] Table 1 lists the main influencing factors on C-14 generation and emission treatment for the Hualong One pressurized water reactor (PWR) (to be determined) and the Konvoi-type PWR (reference PWR). Analysis shows that the Hualong One PWR (to be determined) and the Konvoi-type PWR (reference PWR) are similar or identical in terms of C-14 generation sources, core neutron energy spectrum, and waste treatment. Therefore, the annual C-14 emission data of the Konvoi-type PWR is a good reference for the Hualong One PWR.

[0061] Table 1. Comparison of main features between Hualong One pressurized water reactor and Konvoi-type pressurized water reactor

[0062]

[0063] Step 2: Analyze the annual emissions data of the pressurized water reactor based on the airborne C-14 emission data.

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

[0065] Table 2. Annual airborne C-14 emissions of a Konvoi-type pressurized water reactor from 2000 to 2014

[0066]

[0067] Step 3: Calculate the airborne C-14 emissions of the pressurized water reactor to be determined.

[0068] The Konvoi-type pressurized water reactor (reference pressurized water reactor) has an electric power of 1406 MWe and an average coolant density of 0.709 kg / m³. 3 The average annual airborne C-14 emissions from 2001 to 2014 were 308 GBq / a, corresponding to an average energy utilization rate of 94%. For the Hualong One pressurized water reactor (the pressurized water reactor unit to be determined), the unit's electrical power is 1180 MWe, and the average coolant density is 0.711 kg / m³. 3 The corresponding average energy utilization rate is 90%.

[0069] The expected annual airborne C-14 emissions of the Hualong One pressurized water reactor (the pressurized water reactor unit to be determined) can be obtained as 248 GBq / a using the formula (1) above in this invention, where the emission management factor k is taken as 0. The calculation process is as follows:

[0070]

[0071] When the emission management factor k is set to 0.65, the conservative annual airborne C-14 emission of the Hualong One pressurized water reactor (the pressurized water reactor unit to be determined) can be obtained as 428 GBq / a. The calculation process is as follows:

[0072]

[0073] Therefore, the expected annual airborne C-14 emissions of the Hualong One pressurized water reactor (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 for the annual airborne C-14 emissions of Hualong One.

[0074] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for determining the annual airborne C-14 emissions of a pressurized water reactor nuclear power plant, characterized in that, Includes the following steps: S1. Select a pressurized water reactor nuclear power plant of the same type that is already in operation as a reference pressurized water reactor nuclear power plant, and base it on the C-14 operation emission monitoring data of the reference pressurized water reactor nuclear power plant; S2. Calculate the C-14 emissions of the pressurized water reactor nuclear power plant to be determined using the following formula: In the formula, This indicates the C-14 emissions of pressurized water reactor nuclear power plants to be determined, in GBq / a. This represents the average historical emissions data for C-14 years of pressurized water reactor nuclear power plants, in GBq / a. This indicates the pressurized water reactor power of the pressurized water reactor nuclear power plant to be determined, in MWe. This indicates the power output of a reference pressurized water reactor nuclear power plant, expressed in MWe. This indicates the average coolant density of the pressurized water reactor core in the pressurized water reactor nuclear power plant to be determined, in kg / m³. 3 ; This represents the average coolant density of the pressurized water reactor core in a reference pressurized water reactor nuclear power plant, expressed in kg / m³. 3 ; This represents the energy utilization rate of a pressurized water reactor nuclear power plant to be determined; it is a dimensionless number. This represents the energy utilization rate of a reference pressurized water reactor nuclear power plant; it is a dimensionless number. It is an emission management factor, an empirical coefficient related to emission management and emission planning of pressurized water reactor nuclear power plants, and is a dimensionless number.

2. The method for determining the annual airborne C-14 emissions of a pressurized water reactor nuclear power plant according to claim 1, characterized in that, when A value less than 0 indicates that the emissions from the pressurized water reactor nuclear power plant during the considered time period are lower than the reference emissions.

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

4. The method for determining the annual airborne C-14 emissions of a pressurized water reactor nuclear power plant according to claim 1, characterized in that, When there are more than four 1,000 kW pressurized water reactors at the plant site, the range of k is 0.25 ≤ k ≤ 0.

65.

5. The method for determining the annual airborne C-14 emissions of 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 and the pressurized water reactor nuclear power plant to be determined are the same or similar in terms of core neutron energy spectrum, source of dissolved nitrogen in coolant and waste treatment process.

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

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

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