An alternative method for replacing the secondary neutron source between units of a large commercial pressurized water reactor

Abstract

The present invention belongs to the field of nuclear technology applications, and particularly relates to a method for replacing secondary neutron source units in large commercial pressurized water reactors. It includes the following steps: Step 1: Define the requirements for the core neutron source components of the target unit; Step 2: According to the requirements in Step 1, select the secondary neutron source components that do not return to the reactor of the same type of unit, and calculate and evaluate them respectively from the neutron source intensity and structure. The beneficial effects of the present invention are as follows: It realizes the core criticality supervision for the first cycle refueling startup of a newly built unit without primary neutron source components, or when one or two groups of secondary neutron source components in an in-service unit are unavailable, it realizes the core critical safety supervision during the conversion refueling process, ensures the normal startup of the unit, and has great economic benefits.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear technology applications, and particularly relates to a method for replacing secondary neutron source units in large commercial pressurized water reactors. Background Art

[0002] The secondary neutron source is a related component of the fuel assembly. Normally, there are two groups in the reactor core, which provide neutron source flux for the critical safety supervision of the reactor core during the startup process of the unit. When, due to external factors, a newly built unit cannot purchase the primary neutron source component, resulting in the inability to start the reactor normally, or when one or two secondary neutron source components in an in-service unit are accidentally damaged, resulting in the inability to reuse the secondary neutron source component, it will directly lead to the inability to perform critical safety supervision of the reactor core as required during the refueling process of the unit, greatly affecting the startup and overhaul progress of the unit and causing great economic losses. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for replacing secondary neutron source units in large commercial pressurized water reactors, which can enable a newly built unit to use the irradiated secondary neutron sources of other similar units to replace the neutron source components of the target unit in a timely manner when it is unable to purchase the primary neutron source or when the secondary neutron source of an in-service unit is accidentally damaged, so as to provide neutron source flux for the critical safety supervision of the reactor core during the startup process.

[0004] The technical solution of the present invention is as follows: A method for replacing secondary neutron source units in large commercial pressurized water reactors includes the following steps:

[0005] Step 1: Define the requirements for the neutron source components in the reactor core of the target unit;

[0006] Step 2: According to the requirements in Step 1, select the secondary neutron source components that do not return to the reactor in similar units, and calculate and evaluate them respectively from the neutron source intensity and structure.

[0007] The said Step 1 includes the neutron source intensity required by the technical specification of the power plant unit and the critical supervision requirements of the source range measurement channel during the refueling process.

[0008] The said Step 1 includes the requirement that "there should be counts in the shutdown state, and the count rate should reach at least 2 counts per second". For the target reactor, verify the requirements of the technical specification of the nuclear power plant where the reactor is located, and clarify that two neutron source components must be ensured simultaneously during the refueling process, and meet the requirement of 2 CPS per second for two columns of source range neutron detectors.

[0009] The said Step 2 includes the secondary neutron source intensity. After the secondary neutron source is unloaded from the reactor core, the source strength of the secondary neutron source will gradually weaken over time. Calculate through the calculation method of the secondary neutron source parameters of the reactor to obtain the source strength of the secondary neutron source component unloaded from the reactor core.

[0010] Step 2 includes obtaining the parameters after the irradiation of the secondary neutron source through the published energy spectrum data, calculating the nucleon density and decay photon parameters of each burnup zone of the reusable component by ORIGEN, establishing a full-core model of the full-load state after core refueling, and calculating the response of the off-core detectors caused by the photo-neutron source in the secondary source rod and the neutron source in the reusable component based on the established full-core model of the full-load state after core refueling. The result shows that after core refueling, the source range count rate meets the requirement of 2 cps.

[0011] Step 2 includes selecting a suitable shielding container according to the calculated energy spectrum and source term results of the neutron source assembly, which can realize the transfer of the secondary neutron source between units.

[0012] Step 2 includes inserting the corresponding fuel assemblies with the replacement neutron source in the target unit. During the core refueling process, monitor the two columns of source range neutron detection channels in the core, confirm that the count rate of the replaced secondary neutron source is greater than 2 CPS, meet the critical supervision requirements during core refueling, and complete the refueling.

[0013] The beneficial effects of the present invention are as follows: it realizes the core critical supervision during the first-cycle refueling startup of a newly built unit without a primary neutron source assembly, or realizes the core critical safety supervision during the conversion refueling process when one or two secondary neutron source assemblies in an in-service unit are unavailable, ensuring the normal startup of the unit and having great economic benefits. Description of the Drawings

[0014] Figure 1 It is a flow chart of a method for replacing secondary neutron sources between units of a large commercial pressurized water reactor. Detailed Embodiments

[0015] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0016] A method for replacing secondary neutron sources between units of a large commercial pressurized water reactor includes the following steps:

[0017] Step 1: Define the requirements for the core neutron source assembly of the target unit, including the neutron source intensity required by the technical specifications of the power plant unit and the critical supervision requirements of the source range measurement channels during the refueling process.

[0018] According to the requirements of the national standard "Nuclear Reactor Instrumentation Guidelines Part 1: General Principles" (GB127889.1-91), "There should be counts in the shutdown state, and the count rate should be at least 2 counts per second." Secondly, for the target reactor, verify the requirements of the technical specifications of the nuclear power plant where the reactor is located. For example, the technical specifications of Fangjiashan Nuclear Power Plant require that "the fuel loading and unloading operations can only be carried out when two columns of source range neutron detection channels are available, and the subcritical neutron flux must be continuously monitored by at least one column of source range measurement channels to be displayed on the main control panel."

[0019] According to the requirements described above in the national standards and the technical specifications of nuclear power plants, it is clear that during the refueling process, two neutron source assemblies must be ensured simultaneously, and the requirement of 2 CPS per second for two columns of source range neutron detectors must be met.

[0020] Step 2: According to the requirements in Step 1, select the secondary neutron source assemblies of the same type of unit that do not return to the reactor, and calculate and evaluate them respectively from the neutron source intensity and structure:

[0021] Secondary neutron source intensity: When the secondary neutron source is unloaded from the core, the source strength of the secondary neutron source will gradually weaken over time. By calculating through the "Calculation Method for Reactor Secondary Neutron Source Parameters", the source strength of the secondary neutron source assembly unloaded from the core is obtained. Taking the M310 unit as an example, the source strength of the secondary neutron source assembly out of the core calculated is shown in the following table:

[0022] Discharge time (days) Neutron source strength (n / s) γ activity (Bq) 0 3.22E+10 5.76E+10 180 3.94E+10 2.07E+10

[0023] Query the neutron energy spectrum of the secondary neutron source as shown in the following table:

[0024] Neutron energy (MeV) Fraction (%) 0.025 89.65 0.425 10.35

[0025] Query the γ-ray energy spectrum of the secondary neutron source

[0026] γ-ray energy (MeV) Yield (%) 0.602 97.80 1.690 47.57 0.722 10.76 0.645 7.42 2.090 5.49 1.368 2.624 0.713 2.276 0.968 1.882 1.045 1.833 1.325 1.580

[0027] Based on the above published energy spectrum data, the parameters of the secondary neutron source after irradiation are obtained. By calculating the nucleon density and decay photon parameters of each burnup zone of the reused assembly through ORIGEN, a full-core model of the full-load state after core refueling is established. Based on the full-core model of the full-load state after core refueling, the response calculation results of the photoneutron source in the secondary source rod and the neutron source in the reused assembly to the out-of-core detector are calculated. The results show that after core refueling, the source range count rate meets the requirement of 2 cps.

[0028] Discharge time of the secondary source (days) Fuel loading procedure Proximity source range count rate (CPS) 183 All fuel assemblies loaded 9 204 All fuel assemblies loaded 7

[0029] Evaluation of the structural availability of the secondary neutron source:

[0030] The secondary neutron source enters the core with the fuel assembly in the form of fixed related components in the reactor. For the fuel assemblies of the same unit type, their structural dimensions are the same, so the corresponding structure of the secondary neutron source is also the same. Therefore, there is no infeasibility in the mechanical structure, geometric structure, and in-core compatibility of the secondary neutron source replaced between units.

[0031] According to the calculated results of the neutron source assembly energy spectrum and source term, by selecting a suitable shielding container, the transfer of the secondary neutron source between units can be achieved.

[0032] Instead of inserting the corresponding fuel assemblies with the replacement neutron source in the target unit, during the core refueling process, monitor the two columns of source range neutron detection channels in the core to confirm that the count rate of the replaced secondary neutron source is greater than 2 CPS, meeting the critical monitoring requirements during core refueling, and complete the refueling.

[0033] Embodiment

[0034] A method for replacing between secondary neutron source units of a large commercial pressurized water reactor includes the following steps:

[0035] Step 1:

[0036] Clarify the required neutron source intensity and monitoring requirements for the core of the target unit. According to the requirements of the nuclear power plant technical specifications: "The fuel loading and unloading operations can only be carried out when the two columns of source range neutron detection channels are available, and the subcritical neutron flux must be continuously monitored by at least one column of source range measurement channels to be displayed on the main control." According to the national standard "Nuclear Reactor Instrumentation Guidelines Part 1: General Principles" (GB127889.1 - 91), it is required that "there should be counts in the shutdown state, and the count rate should reach at least 2 counts per second."

[0037] That is, according to the requirements, during the refueling process, two neutron source assemblies must be ensured simultaneously, and the requirement of 2 CPS per second for the two columns of source range neutron detectors should be met;

[0038] Step 2:

[0039] Calculate the intensity of the secondary neutron source of the replacement unit. The selected replacement secondary source assembly should be able to meet the above-mentioned critical monitoring count rate monitoring requirements during the core refueling process of the nuclear power unit. Therefore, calculate the source strength of the irradiated secondary neutron source assembly. Calculate the neutron source strength of the replacement neutron source through the equivalent full power days of the previous cycle of the replacement neutron source and the decay time during the out-of-core temporary storage period. According to the neutron source strength, calculate and evaluate whether the count rate value obtained by the source range neutron detector during the refueling process after it is installed in the fuel assembly of the target unit meets the requirements of critical monitoring for the core refueling of the target unit.

[0040] Step 3:

[0041] Evaluate the structural adaptability between the replacement neutron source assembly and the fuel assembly. The overall core-designed neutron source is regarded as a point source to achieve core critical monitoring. Therefore, the arrangement of the neutron source rods in the neutron source assembly does not affect core critical monitoring. The neutron source assemblies and fuel assemblies are matched between the same type of units. For example, for the 17*17 type fuel assembly, the corresponding neutron source assembly is inserted in the fuel assembly in the form of relevant components.

[0042] Step 4:

[0043] Transfer the secondary neutron source assembly to the target unit through a shielding container and insert it into the corresponding fuel assembly of the neutron source. The shielding container needs to have good neutron and gamma shielding effects. According to the neutron source intensity and energy spectrum, select an effective shielding container to achieve transfer between units and insertion into the fuel assembly;

[0044] Step 5:

[0045] During the refueling startup process, critical safety supervision of the refueling process is achieved through the core source range neutron detection channel.

Claims

1. A method for replacing between secondary neutron source units of a large commercial pressurized water reactor, characterized in that It includes the following steps: Step 1: Define the requirements for the neutron source assembly in the core of the target unit; The said Step 1 includes the neutron source intensity required by the technical specifications of the power plant unit and the critical supervision requirements of the source range measurement channel during refueling; The said Step 1 includes the requirement that "there should be counts in the shutdown state, and the count rate should reach at least 2 counts per second". For the target reactor, verify the requirements of the technical specifications of the nuclear power plant where the reactor is located, and clarify that two neutron source assemblies must be ensured simultaneously during refueling, and meet the requirement of 2 CPS for two columns of source range neutron detectors; Step 2: According to the requirements in Step 1, select the secondary neutron source assemblies of the same type of unit that do not return to the reactor, and calculate and evaluate them respectively from the aspects of neutron source intensity and structure; The said Step 2 includes the secondary neutron source intensity. After the secondary neutron source is unloaded from the core, the source strength of the secondary neutron source will gradually weaken over time. Calculate the source strength of the secondary neutron source assembly unloaded from the core through the calculation method of the secondary neutron source parameters of the reactor; The said Step 2 includes obtaining the parameters after irradiation of the secondary neutron source through the published energy spectrum data, calculating the nucleon density and decay photon parameters of each burnup zone of the reused assembly through ORIGEN, establishing a full-core model in the full-load state after core refueling, and based on the established full-core model in the full-load state after core refueling, calculating the response of the out-of-core detector caused by the photo-neutron source in the secondary source rod and the neutron source in the reused assembly. The calculation result shows that after core refueling, the source range count rate meets the requirement of 2 cps; The said Step 2 includes selecting a suitable shielding container according to the calculation results of the neutron source assembly energy spectrum and source term, and the transfer of the secondary neutron source between units can be realized; The said Step 2 includes inserting the corresponding fuel assembly with the substitute neutron source in the target unit. During the core refueling process, monitor the two columns of source range neutron detection channels in the core, confirm that the count rate of the substituted secondary neutron source is greater than 2 CPS, meet the critical supervision requirements during core refueling, and complete the refueling.

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