Method for formulating zinc adding strategy of pressurized water reactor nuclear power unit in operation

Abstract

The invention relates to the technical field of nuclear power plant chemistry, in particular to a method for formulating a zinc adding strategy of a pressurized water reactor nuclear power unit in operation. The method comprises the following steps: determining a scale-caused axial power offset and scale-caused local corrosion risk assessment criterion; establishing a unit reactor core thermal hydraulic model according to the operating unit reactor core and fuel parameters; calculating each burnup step of the reactor core by using the unit reactor core thermal hydraulic model to obtain thermal hydraulic parameters of each channel of the reactor core; establishing a scale-caused axial power offset and scale-caused local corrosion risk assessment calculation model, and performing analysis and calibration; and determining a target zinc concentration and zinc adding starting and stopping time suitable for the nuclear power unit in operation by using a scale-caused axial power offset and scale-caused local corrosion risk assessment calculation model to form a complete zinc adding strategy. According to the invention, a relatively good zinc adding strategy of the nuclear power unit of the pressurized water reactor can be formed, and risks of axial power deviation caused by reactor core scale and local corrosion caused by fuel scale during zinc adding operation of the nuclear power unit are avoided.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power plant chemical technology, and in particular to a method for formulating a zinc addition strategy for an in-operation pressurized water reactor nuclear power unit. Background Art

[0002] Zinc dosing in the primary coolant circuit of pressurized water reactor (PWR) nuclear power plants has become an important means of mitigating primary stress corrosion cracking (PWSCC) and reducing radiation field levels and even collective doses. In domestic applications, some new units have implemented zinc dosing during hot testing, but there is currently no record of zinc dosing in operating nuclear power plants.

[0003] For operating nuclear power units that have been running for several cycles, an appropriate zinc addition strategy needs to be formulated before implementing zinc addition operation to reduce the risk of axial power deviation caused by core fouling and local corrosion caused by fuel fouling, so as to ensure that the operating nuclear power units can implement zinc addition operation smoothly and safely.

[0004] There is currently no precedent for zinc addition in the nuclear power units in operation in China that have been running for several cycles, and there are no public technical solutions on how to formulate zinc addition strategies for the nuclear power units in operation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for formulating a zinc addition strategy for an in-service pressurized water reactor nuclear power unit, which can form a better zinc addition strategy for the in-service pressurized water reactor nuclear power unit and ensure that the zinc addition operation of the in-service nuclear power unit will not cause the risk of axial power deviation caused by core fouling and local corrosion caused by fuel fouling.

[0006] The present invention provides a method for formulating a zinc addition strategy for an in-operation pressurized water reactor nuclear power unit, comprising the following steps: Step 1: Determine the risk assessment criteria for scale-induced axial power displacement and scale-induced localized corrosion; Step 2: Establish a thermal-hydraulic model of the reactor core based on the reactor core and fuel parameters of the operating reactor; Step 3: Use the unit core thermal-hydraulic model to calculate each core burnup step and obtain the thermal-hydraulic parameters of each core channel; Step 4: Establish a calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion; Step 5: Analyze and calibrate the calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion; Step 6: Use the calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion to determine the target zinc concentration, start and stop zinc addition time for the operating nuclear power units, and form a complete zinc addition strategy.

[0007] In a specific embodiment of the present invention, the step 1 is specifically as follows: Based on the experience of zinc-filled operation of pressurized water reactor nuclear power units, the off-core test and actual reactor operation data were combined to analyze the threshold value of the maximum boron deposition mass in the entire core that leads to scale-induced axial power offset and the threshold value of the maximum scale thickness on the fuel cladding that leads to scale-induced localized corrosion. In this way, the risk assessment criteria for scale-induced axial power offset and scale-induced localized corrosion were determined.

[0008] In one embodiment of the present invention, the evaluation of the scale-induced axial power offset is: Determine the critical value of axial offset caused by boron deposition based on the relationship between the number of core components and the axial power offset, where the critical value is when the maximum boron deposition mass in the core exceeds 0.862-0.136 kg; The risk assessment for scale-induced localized corrosion is as follows: Based on the relationship between the thickness of the fouling layer on the cladding surface and the local corrosion of the cladding, the critical value of the fouling thickness is determined, which is 50.8 μm.

[0009] In a specific embodiment of the present invention, step 3 specifically includes: Using the core design and operation data of the unit's specific cycle, with core design parameters, power distribution, physical model settings, unit thermal-hydraulic parameters, and water chemistry parameters as input parameters, the unit core thermal-hydraulic model is used to calculate each core burnup step, and the thermal-hydraulic parameters of each core channel are output as input to the calculation model for the risk assessment of scaling-induced axial power offset and scaling-induced localized corrosion.

[0010] In a specific embodiment of the present invention, the step 2 is specifically as follows: According to the core and fuel parameters of the unit, at least 1 / 4 core data is used for modeling, each fuel assembly is divided into four channels, and the symmetry of core loading is utilized to establish the unit core thermal-hydraulic model.

[0011] In a specific embodiment of the present invention, the core thermal hydraulic model adopts a water property table, a Levy cavitation relation, a single-phase convection relation, and a THOM subcooled boiling relation.

[0012] In a specific embodiment of the present invention, step 4 specifically includes: using the core loading plan of the operating nuclear power unit, the primary water chemical parameters, the steam generator data and the local thermal-hydraulic parameters of each channel as input parameters to establish a calculation model for the risk assessment of scale-induced axial power offset and scale-induced local corrosion.

[0013] In a specific embodiment of the present invention, step 5 specifically includes: using the core axial power excursion monitoring data of the unit for 2-3 fuel cycles before zinc addition, calibrating the scale-induced axial power excursion and scale-induced localized corrosion risk assessment calculation model; by fine-tuning the corrosion product release parameters before zinc addition, the maximum core boron mass and maximum scale thickness values ​​output by the calculation model are made consistent with the core boron mass and maximum scale thickness corresponding to the core axial power excursion monitoring data of the unit for 2-3 fuel cycles before zinc addition, so as to establish a representative corrosion product release benchmark in the cycle before zinc addition.

[0014] In a specific embodiment of the present invention, step 6 specifically includes: step 6-1: using the target zinc concentration, the time when zinc addition starts, and the time when zinc addition stops as variables, using a calculation model for risk assessment of scale-induced axial power deviation and scale-induced localized corrosion, respectively predicting the maximum boron deposition mass and maximum scale thickness of the core of the unit for at least three fuel cycles under different target zinc addition concentrations and zinc addition times; Step 6-2: Compare the predicted maximum boron deposition mass and maximum fouling thickness of the core for each fuel cycle with the risk assessment criteria described in step 1. If the predicted data for any subsequent cycle exceeds the threshold requirements in the risk assessment criteria, return to step 6-1, change the target zinc concentration, the start time of zinc addition, and the stop time of zinc addition, and re-use the scale-induced axial power offset and scale-induced local corrosion risk assessment calculation model to calculate the maximum boron deposition mass and maximum fouling thickness of the core; until the obtained maximum boron deposition mass and maximum fouling thickness of the core meet the threshold requirements in the risk assessment criteria, thereby obtaining a zinc addition strategy including the target zinc concentration and the timing of zinc addition.

[0015] In a specific embodiment of the present invention, during the calculation process of the scale-induced axial power offset and scale-induced local corrosion risk assessment calculation model, constraint parameters for the target zinc concentration and the timing of starting zinc addition can also be obtained, and the constraint parameters are used as influencing parameters for the timing of stopping zinc addition.

[0016] Compared with the prior art, the present invention's method for formulating a zinc dosing strategy for an operating pressurized water reactor nuclear power unit utilizes actual unit data, such as core design and power distribution, and establishes a core thermal-hydraulic model and a calculation model for evaluating the risks of scale-induced axial power shift and scale-induced localized corrosion based on proposed criteria for assessing and determining the risks of scale-induced axial power shift and scale-induced localized corrosion. Through analysis and calculation, a zinc dosing strategy applicable to zinc dosing operations in an operating nuclear power unit is formulated to ensure that zinc dosing operations do not cause the risks of scale-induced axial power shift and scale-induced localized corrosion in the unit. The present invention's method for formulating a zinc dosing strategy is applicable to operating pressurized water reactors, ensuring that zinc dosing operations in an operating nuclear power unit can be implemented smoothly and safely. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Flowchart showing the method for developing zinc dosing strategies for operating pressurized water reactor nuclear power units. DETAILED DESCRIPTION

[0018] In order to further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the present invention.

[0019] The embodiment of the present invention discloses a method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit, such as Figure 1 As shown, the following steps are included: Step 1: Determine the risk assessment criteria for scale-induced axial power displacement and scale-induced localized corrosion; Specifically, based on the zinc-adding operation experience of pressurized water reactor nuclear power units, the authors combined ex-core tests with actual reactor operation data to analyze the thresholds for the maximum boron deposition mass in the entire core that leads to scale-induced axial power shift and the thresholds for the maximum fuel cladding scale-induced localized corrosion. These criteria were then used to determine the risk assessment criteria for scale-induced axial power shift and scale-induced localized corrosion. For example, the evaluation of axial power deviation caused by scaling can be: Determine a critical value of axial offset caused by boron deposition based on the relationship between the number of core components and the axial power offset of the unit, where the critical value may be that the maximum boron deposition mass of the core exceeds 0.862-0.136 kg; For the risk assessment of scale-induced localized corrosion, it can be: Combined with the relationship between the thickness of the fouling layer on the cladding surface and the local corrosion of the cladding, the critical value of the fouling thickness is determined to be 50.8 μm. Step 2: Establish a thermal-hydraulic model of the reactor core based on the reactor core and fuel parameters of the operating reactor; Based on the reactor core and fuel parameters, the core thermal-hydraulic model was established using data from at least one-quarter of the reactor core. Each fuel assembly was divided into four channels, and the symmetry of the core loading was utilized to establish the core thermal-hydraulic model. The core thermal-hydraulic model incorporates a water property table, Levy cavitation relations, single-phase convection relations, and THOM subcooled boiling relations.

[0020] There can be multiple thermal hydraulic models of the reactor core, and the method for establishing the model is a conventional method; Step 3: Use the unit core thermal-hydraulic model to calculate each core burnup step and obtain the thermal-hydraulic parameters of each core channel; Using the core design and operation data of a specific cycle of the unit, with core design parameters, power distribution, physical model settings, unit thermal-hydraulic parameters, and water chemistry parameters as input parameters, the unit core thermal-hydraulic model is used to calculate each core burnup step, and the thermal-hydraulic parameters of each core channel are output; the thermal-hydraulic parameters of each core channel are used as input to a calculation model for assessing the risk of scale-induced axial power offset and scale-induced localized corrosion.

[0021] The core design parameters may include component wetted perimeter, hot perimeter, spacing parameters, grid position, grid drag coefficient, and power distribution; The thermal hydraulic parameters of the unit can be core thermal power, coolant flow / temperature / pressure; Water chemistry data can be boron / lithium concentrations, zinc injection strategies; The output parameters are local pressure, fluid temperature, mass flow rate, local heat flux, density, and mass evaporation rate of each channel in the core; Step 4: Establish a calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion; Specifically, a risk assessment calculation model for scale-induced axial power offset and scale-induced local corrosion is established using the core loading scheme of an operating nuclear power unit, primary circuit water chemical parameters, steam generator data, and local thermal-hydraulic parameters of each channel as input parameters.

[0022] The core loading scheme includes fuel assembly enrichment distribution, control rod layout, and burnup history; The primary water chemical parameters include boric acid concentration ( C B ), lithium concentration ( C Li ), target zinc concentration ( C Zn ); The local thermal-hydraulic parameters of each channel include pressure, fluid temperature, mass flow rate, local heat flux density, density, and mass evaporation rate; The proposed model for assessing the risk of scale-induced axial power shift and localized corrosion simulates the release and deposition of corrosion products. Based on the thermal-hydraulic parameters of each core channel obtained in step 3, it outputs predicted values ​​for the maximum core boron mass, core scale mass, and maximum scale thickness at the end of each cycle. The model also considers the impact of fuel cladding surface scale on the subcooled boiling rate. The predictions of core boron mass and maximum scale thickness for a given cycle are influenced by many variables: the core loading scheme, the localized subcooled boiling rate of specific rods, the boron concentration in the coolant system, the scale remaining in the core and coolant, and the corrosion product release rate of the steam generator. The model is analyzed and calibrated before calculations begin.

[0023] Step 5: Analyze and calibrate the calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion; Specifically include: The calculation model for risk assessment of scale-induced axial power excursion and scale-induced localized corrosion was calibrated using the core axial power excursion monitoring data from 2-3 fuel cycles before zinc addition. By fine-tuning the corrosion product release parameters before zinc addition, the maximum core boron mass and maximum scale thickness values ​​output by the calculation model were made consistent with the core boron mass and maximum scale thickness corresponding to the core axial power excursion monitoring data from 2-3 fuel cycles before zinc addition, thereby establishing a representative corrosion product release benchmark in the cycle before zinc addition.

[0024] The said fine adjustment refers to multiplying the corrosion product release rate by a coefficient of a 0-1 straight line; The said conformity refers to being close to but not exceeding the maximum boron mass corresponding to the axial power deviation of the actual operation of the unit.

[0025] Step 6: Determine the target zinc concentration, start and stop zinc addition times for the operating nuclear power units using the calculation model for the risk assessment of scale-induced axial power displacement and scale-induced localized corrosion; Specifically include: Step 6-1: Using the target zinc concentration, zinc dosing start time, and zinc dosing stop time as variables, and using the risk assessment calculation model for scale-induced axial power deviation and scale-induced localized corrosion, predict the maximum boron deposition mass and maximum scale thickness in the reactor core for at least three fuel cycles at different target zinc concentrations and zinc dosing times. Step 6-2: Compare the predicted maximum boron deposition mass and maximum fouling thickness for each fuel cycle with the risk assessment criteria described in Step 1. If the predicted data for any subsequent cycle exceeds the threshold requirements in the risk assessment criteria, return to Step 6-1, change the target zinc concentration, zinc addition start time, and zinc addition stop time, and recalculate the maximum boron deposition mass and maximum fouling thickness in the core using the scale-induced axial power offset and scale-induced localized corrosion risk assessment calculation model. This process continues until the obtained maximum boron deposition mass and maximum fouling thickness meet the threshold requirements in the risk assessment criteria, thereby determining the zinc addition strategy, including the target zinc concentration and zinc addition timing.

[0026] During the calculation process of the scale-induced axial power offset and scale-induced localized corrosion risk assessment model, control parameters for the target zinc concentration and the timing of zinc addition can be obtained. These control parameters can be used as parameters influencing the timing of zinc addition cessation. These control parameters include excessive silicon and nickel plasma concentrations in the primary coolant circuit of the nuclear power unit and unplanned shutdowns.

[0027] The method of the present invention has been verified by experiments. The Qinshan Nuclear Power Million M310 unit is the first nuclear power unit in operation that has been running for several cycles to implement zinc addition operation, and is currently running well.

[0028] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0029] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit, characterized in that: The following steps are involved: Step 1: Determine the risk assessment criteria for scale-induced axial power displacement and scale-induced localized corrosion; Step 2: Establish a thermal-hydraulic model of the reactor core based on the reactor core and fuel parameters of the operating reactor; Step 3: Use the unit core thermal-hydraulic model to calculate each core burnup step and obtain the thermal-hydraulic parameters of each core channel; Step 4: Establish a calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion; Step 5: Analyze and calibrate the calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion; Step 6: Use the calculation model for the risk assessment of scale-induced axial power deviation and scale-induced localized corrosion to determine the target zinc concentration, start and stop zinc addition time for the operating nuclear power units, and form a complete zinc addition strategy.

2. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 1, characterized in that: The step 1 is specifically as follows: Based on the experience of zinc-filled operation of pressurized water reactor nuclear power units, the off-core test and actual reactor operation data were combined to analyze the threshold value of the maximum boron deposition mass in the entire core that leads to scale-induced axial power offset and the threshold value of the maximum scale thickness on the fuel cladding that leads to scale-induced localized corrosion. In this way, the risk assessment criteria for scale-induced axial power offset and scale-induced localized corrosion were determined.

3. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 2, characterized in that: The evaluation of scale-induced axial power deviation is: Determine the critical value of axial offset caused by boron deposition based on the relationship between the number of core components and the axial power offset, where the critical value is when the maximum boron deposition mass in the core exceeds 0.862-0.136 kg; The risk assessment for scale-induced localized corrosion is as follows: Based on the relationship between the thickness of the fouling layer on the cladding surface and the local corrosion of the cladding, the critical value of the fouling thickness is determined, which is 50.8 μm.

4. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 1, characterized in that: The step 3 specifically includes: Using the core design and operation data of the unit's specific cycle, with core design parameters, power distribution, physical model settings, unit thermal-hydraulic parameters, and water chemistry parameters as input parameters, the unit core thermal-hydraulic model is used to calculate each core burnup step, and the thermal-hydraulic parameters of each core channel are output as input to the calculation model for the risk assessment of scaling-induced axial power offset and scaling-induced localized corrosion.

5. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 1, characterized in that: The step 2 is specifically as follows: According to the core and fuel parameters of the unit, at least 1 / 4 core data is used for modeling, each fuel assembly is divided into four channels, and the symmetry of core loading is utilized to establish the unit core thermal-hydraulic model.

6. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 5, characterized in that: The core thermal hydraulic model adopts a water property table, a Levy cavitation relation, a single-phase convection relation, and a THOM subcooled boiling relation.

7. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 1, characterized in that: The step 4 specifically includes: using the core loading plan of the operating nuclear power unit, the primary circuit water chemical parameters, the steam generator data and the local thermal hydraulic parameters of each channel as input parameters to establish a calculation model for the risk assessment of scale-induced axial power offset and scale-induced local corrosion.

8. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 1, characterized in that: The step 5 specifically includes: using the core axial power excursion monitoring data of the unit for 2-3 fuel cycles before zinc addition, calibrating the scale-induced axial power excursion and scale-induced localized corrosion risk assessment calculation model; by fine-tuning the corrosion product release parameters before zinc addition, the maximum core boron mass and maximum scale thickness values ​​output by the calculation model are made consistent with the core boron mass and maximum scale thickness corresponding to the core axial power excursion monitoring data of the unit for 2-3 fuel cycles before zinc addition, so as to establish a representative corrosion product release benchmark in the cycle before zinc addition.

9. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 1, characterized in that: The step 6 specifically includes: step 6-1: using the target zinc concentration, the zinc addition start time, and the zinc addition stop time as variables, and using a scale-induced axial power offset and scale-induced localized corrosion risk assessment calculation model to respectively predict the maximum boron deposition mass and maximum scale thickness of the core of the unit for at least three fuel cycles under different zinc addition target zinc concentrations and zinc addition times; Step 6-2: Compare the predicted maximum boron deposition mass and maximum fouling thickness of the core for each fuel cycle with the risk assessment criteria described in step 1. If the predicted data for any subsequent cycle exceeds the threshold requirements in the risk assessment criteria, return to step 6-1, change the target zinc concentration, the start time of zinc addition, and the stop time of zinc addition, and re-use the scale-induced axial power offset and scale-induced local corrosion risk assessment calculation model to calculate the maximum boron deposition mass and maximum fouling thickness of the core; until the obtained maximum boron deposition mass and maximum fouling thickness of the core meet the threshold requirements in the risk assessment criteria, thereby obtaining a zinc addition strategy including the target zinc concentration and the timing of zinc addition.

10. The method for formulating a zinc addition strategy for an operating pressurized water reactor nuclear power unit according to claim 9, characterized in that: During the calculation process of the scale-induced axial power deviation and scale-induced localized corrosion risk assessment calculation model, constraint parameters for the target zinc concentration and the timing of starting zinc addition can also be obtained, and the constraint parameters are used as influencing parameters for the timing of stopping zinc addition.

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