An optimization method for the use of a black rod control rod assembly

Abstract

The present invention relates to the technical field of nuclear fuel management in nuclear power plants, and specifically discloses an optimization method for the use of black rod control rod assemblies, including the following steps: Step 1: Formulate a usage strategy for black rod control rod assemblies; Step 2: Establish an in-pile ledger for black rod control rod assemblies; Step 3: Formulate a replacement plan for related components during refueling overhaul. By using the method of the present invention, it is possible to avoid individual black rod control rod assemblies from being irradiated by excessive cumulative neutron fluence, and the probability of swelling of black rod control rod assemblies can be minimized.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear fuel management in nuclear power plants, and in particular relates to a method for optimizing the use of a black rod control rod assembly. Background Art

[0002] When the reactor is operating normally, the control rod assembly is exposed to high temperature, high pressure and high neutron flux. The silver-indium-cadmium absorber inside the black rod control rod cladding will gradually transform into silver-indium-cadmium-tin after being heated and absorbing neutrons, with a lower density and a larger thermal expansion coefficient, which will cause the absorber volume to increase and expand more easily at high temperatures. When its expansion volume exceeds the inner diameter of the outer cladding, it will inevitably lead to cladding swelling. The swelling rate of silver-indium-cadmium increases rapidly with the increase of neutron flux. In addition, silver-indium-cadmium is prone to creep deformation, and creep will also be accelerated by neutron irradiation.

[0003] The black rod control rod assembly can reach its design life under reasonable use, but there is no unified standard for the use strategy of the black rod control rod assembly. Different strategies will result in different performance and service life of the black rod control rod assembly. When the no-rod replacement strategy is adopted, various types of functional rods are used in a fixed manner. Since the lower end of the control rod will be in the core area when the temperature regulating rod group is in the reactor, it will be exposed to the highest neutron injection and the probability of swelling is the highest. Failure to replace the rods will inevitably shorten the service life of the temperature regulating rod group. When the rod replacement strategy is adopted, the black rod control rod assembly is arranged at different positions in the core in different cycles. However, the current rod replacement strategy is mainly based on the optimization of the replacement of related components. There is uncertainty in the probability of the black rod control rod assembly being used as a temperature regulating rod, resulting in a small number of black rod control rod assemblies being used as temperature regulating rods continuously, which will significantly shorten the service life of this small number of black rod control rod assemblies.

[0004] Therefore, there is an urgent need to provide a method to optimize the use strategy of the black rod control rod assembly to minimize the cumulative neutron flux irradiation received by a single set of black rod control rod assemblies. Summary of the invention

[0005] The object of the present invention is to provide a method for optimizing the use of a black rod control rod assembly, which can reasonably use the black rod control rod assembly, reduce the swelling probability during the service life of the black rod control rod assembly, and reduce the risk of sticking of the black rod control rod assembly.

[0006] The technical solution of the present invention is as follows:

[0007] A method for optimizing the use of black rod control rod assemblies is disclosed. The maximum number of cycles of the black rod control rod assemblies as temperature regulating rods is limited by the "average method". All black rod control rod assemblies in the reactor take turns to serve as temperature regulating rods to spread the cumulative neutron fluence irradiation received by the temperature regulating rods, thereby minimizing the cumulative neutron fluence irradiation received by a single group of black rod control rod assemblies.

[0008] The following steps are involved:

[0009] Step 1: Develop a strategy for using the black rod control rod assembly;

[0010] Limit the maximum number of cycles of cumulative use of the black rod control rod assembly;

[0011] Step 2: Establish a record of black rod control rod assemblies entering the pile;

[0012] After the first cycle of fuel loading of a new unit, a record of black rod control rod assemblies entering the reactor is established to track and count the information of all black rod control rod assemblies in the reactor and update them in a timely manner;

[0013] Step 3: Develop a replacement plan for components related to the refueling overhaul;

[0014] According to the records of black rod control rod assemblies entering the stack, a relevant assembly replacement plan is formulated under the restriction that the cumulative number of cycles of all black rod control rod assemblies as temperature regulating rods does not exceed the maximum number of cycles.

[0015] In step 1, the cumulative number of cycles used by the black rod control rod assembly is limited to not more than the maximum number of cycles N, where N is calculated by the following formula:

[0016]

[0017] Where:

[0018] N is the maximum number of cycles of the black rod control rod assembly as a temperature regulating rod;

[0019] t is the design life of the black rod control rod assembly, in years;

[0020] T is the average refueling cycle, in years;

[0021] N R is the number of temperature regulating rods in the pile;

[0022] N B is the number of black rod control rod assemblies in the pile.

[0023] The N cycles of the black rod control rod assembly as a temperature regulating rod within its design life can be continuous or intermittent, and there is no limit on the interval between two consecutive times of being a temperature regulating rod.

[0024] In step 2, the ledger is updated after each refueling overhaul, the core positions of all black rod control rod assemblies in the new cycle are supplemented, and the cumulative number of cycles and total reactor years of each set of black rod control rod assemblies as temperature regulating rods are updated.

[0025] In step 3, a replacement plan for related components is formulated according to the principle of minimizing the number of times the grippers of related components are replaced, minimizing the steps for replacing related components, and minimizing the distance of related component movement.

[0026] It also includes step 4: conducting an in-service inspection of black rod control rod assembly swelling;

[0027] Carry out in-service inspections within the design life of the black rod control rod assembly, add the inspection results to the black rod control rod assembly loading record, and formulate a subsequent cycle usage plan based on the inspection results.

[0028] In step 4, the in-service inspection focuses on the measured value of the rod diameter in the area 400 mm above the lower end plug weld.

[0029] In step 4, priority is given to checking the black rod control rod assembly whose cumulative cycle number as the temperature regulating rod reaches N and the black rod control rod assembly that is planned to serve as the temperature regulating rod in the subsequent cycles.

[0030] In step 4, the black rod control rod assembly that will subsequently serve as the temperature regulating rod is not allowed to swell, and the rod diameter cannot exceed the initial diameter of 9.7 mm; the black rod control rod assembly that will subsequently serve as the shutdown rod and power compensation rod is allowed to swell slightly, and the rod diameter cannot exceed 9.88 mm.

[0031] The remarkable effects of the present invention are:

[0032] (1) With the method of the present invention, compared with the strategy of not replacing rods, the temperature regulating rod is not prone to swelling, the risk of rod jamming is low, and the service life of the black rod control rod assembly fixed as the temperature regulating rod is extended.

[0033] (2) Compared with the common rod replacement strategy, the method of the present invention can prevent individual black rod control rod assemblies from being irradiated by excessive cumulative neutron flux, and can reduce the probability of swelling of the black rod control rod assembly to a minimum. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below with reference to specific embodiments.

[0035] Since the swelling of the black rod control rod assembly is closely related to the neutron fluence it receives, reducing the cumulative neutron fluence of the black rod control rod assembly can reduce the swelling probability of the black rod control rod assembly. When the cumulative neutron fluence received by the black rod control rod assembly is low enough, the volume increase of the silver-indium-cadmium absorber is not enough to contact and squeeze the control rod cladding, and the black rod control rod assembly will not swell.

[0036] A method for optimizing the use of black rod control rod assemblies is disclosed. The maximum number of cycles of the black rod control rod assemblies as temperature regulating rods is limited by an "average method". All black rod control rod assemblies in the reactor take turns to serve as temperature regulating rods, so as to spread the cumulative neutron fluence irradiation received by the temperature regulating rods as evenly as possible, thereby minimizing the cumulative neutron fluence irradiation received by a single group of black rod control rod assemblies.

[0037] The method comprises the following steps:

[0038] Step 1: Develop a strategy for using the black rod control rod assembly

[0039] In the reactor, each group of black rod control rod assemblies can be used as shutdown rods (S rod group), power compensation rods (G rod group) and temperature regulation rods (R rod group), and in different cycles they can be used as different types of functional rods and arranged at different positions in the core.

[0040] The black rod control rod assembly can be used as a shutdown rod and a power compensation rod throughout its design life, with no limit on the number of cycles it can accumulate. However, it cannot be used as a temperature regulating rod, with a limit on the number of cycles it can accumulate to no more than the maximum number of cycles N, which is calculated by the following formula:

[0041]

[0042] Where:

[0043] N is the maximum number of cycles of the black rod control rod assembly as a temperature regulating rod;

[0044] t is the design life of the black rod control rod assembly, in years;

[0045] T is the average refueling cycle, in years;

[0046] N R is the number of temperature regulating rods in the pile;

[0047] N B is the number of black rod control rod assemblies in the pile;

[0048] The N cycles of the black rod control rod assembly as a temperature regulating rod within the design life can be continuous or intermittent, and there is no limit on the interval between two consecutive times as a temperature regulating rod;

[0049] Step 2: Create a record of black rod control rod components entering the pile

[0050] After the first cycle of fuel loading of a new unit, a record of black rod control rod assemblies entering the reactor is established to track and count the information of all black rod control rod assemblies in the reactor, including control rod assembly identification numbers, refueling cycle numbers and corresponding core positions, in-service inspection results, etc.

[0051] After each refueling overhaul, the ledger is updated to add the core positions of all black rod control rod assemblies in the new cycle, and update the cumulative number of cycles and total reactor years of each group of black rod control rod assemblies as temperature regulating rods; if the in-service inspection of control rods is carried out during the refueling overhaul, the swelling inspection results of the inspected black rod control rod assemblies are supplemented;

[0052] Step 3: Develop a replacement plan for components related to the refueling overhaul

[0053] According to the black rod control rod assembly stacking ledger, under the condition that the cumulative number of cycles of all black rod control rod assemblies as temperature regulating rods does not exceed N, a replacement plan for related components is formulated according to the three principles of minimum number of replacement of related component grippers, minimum number of related component replacement steps, and shortest related component movement distance;

[0054] When the accumulated number of cycles of the black rod control rod assemblies in the reactor as temperature regulating rods reaches N, these black rod control rod assemblies will be adjusted to the core position of non-temperature regulating rods in the subsequent cycles;

[0055] Step 4: Conduct an in-service inspection of black rod control rod assembly swelling

[0056] Carry out 2-3 in-service inspections of the black rod control rod assembly within its design life, focusing on the measured rod diameter in the area 400mm above the lower plug weld;

[0057] Priority should be given to checking the black rod control rod assemblies whose cumulative cycle number as temperature regulating rods has reached N and the black rod control rod assemblies that are planned to be used as temperature regulating rods in subsequent cycles;

[0058] Based on the inspection results of the black rod control rod assembly, a subsequent cycle usage plan is formulated: the black rod control rod assembly that will subsequently serve as the temperature regulating rod is not allowed to swell, and the rod diameter cannot exceed the initial diameter of 9.7mm; the black rod control rod assembly that will subsequently serve as the shutdown rod and power compensation rod is allowed to have slight swelling, and the rod diameter cannot exceed 9.88mm.

[0059] Example

[0060] Taking the Fuqing Nuclear Power M310 / Hualong One unit as an example, t=15, N R =8,N B =49:

[0061] According to the design life of the reactor black rod control rod assembly, the average refueling cycle, the number of temperature regulating rods in the reactor, and the number of black rod control rod assemblies in the reactor, the maximum number of cycles that the black rod control rod assembly can be used as a temperature regulating rod is calculated by formula (1), where:

[0062] When annual material replacement T=1,

[0063] 18-month material change T = 1.5,

[0064] In the case of annual refueling, the number of cycles of replacing the black rod control rod assembly as the temperature regulating rod shall not exceed 3 times; in the case of 18-month refueling, the number of cycles of replacing the black rod control rod assembly as the temperature regulating rod shall not exceed 2 times.

[0065] After the method of the present invention was experimentally applied, no swelling was found during in-service inspections of two groups of black rod control rod assemblies of Fuqing Nuclear Power Unit 1 (three cycles totaling 3.5 reactor-years as temperature regulating rods) and six groups of black rod control rod assemblies (two cycles as temperature regulating rods, four groups for 2.5 reactor-years and two groups for 2 reactor-years).

[0066] The above shows and describes the basic principles, main features and advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention.

[0067] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An optimization method for the use of black rod control rod assemblies, characterized in that: It includes the following steps: Step 1: Formulate a usage strategy for black rod control rod assemblies; Limit the maximum number of cumulative cycles of black rod control rod assemblies; Step 2: Establish an in-pile ledger for black rod control rod assemblies; After the first cycle refueling of a new unit, establish an in-pile ledger for black rod control rod assemblies, track and statistically analyze all information of black rod control rod assemblies in the reactor and update it in a timely manner; Step 3: Formulate a replacement plan for related components during refueling outage; According to the in-pile ledger of black rod control rod assemblies, under the condition that the cumulative number of cycles of all black rod control rod assemblies as temperature regulating rods does not exceed the limit of the maximum number of cycles, formulate a replacement plan for related components; In Step 1, the number of cumulative cycles of black rod control rod assemblies is limited not to exceed the maximum number of cycles N, and N is calculated by the following formula: In the formula: N is the maximum number of cycles of black rod control rod assemblies as temperature regulating rods; t is the designed life of black rod control rod assemblies, in years; T is the average refueling cycle, in years; N R is the number of in-core temperature regulating rods; N B is the number of in-core black rod control rod assemblies.

2. An optimization method for the use of black rod control rod assemblies according to claim 1, characterized in that: The N cycles of black rod control rod assemblies as temperature regulating rods within the designed life are continuous or intermittent, and there is no limit to the interval time between two consecutive times as temperature regulating rods.

3. An optimization method for the use of black rod control rod assemblies according to claim 1, characterized in that: In Step 2, after each refueling outage, update the ledger, supplement the core positions of all black rod control rod assemblies in the new cycle, and update the cumulative number of cycles and total reactor years of each group of black rod control rod assemblies as temperature regulating rods.

4. An optimization method for the use of black rod control rod assemblies according to claim 1, characterized in that: In Step 3, formulate a replacement plan for related components according to the principles of the fewest number of grabs for replacing related component grippers, the fewest number of replacement steps for related components, and the shortest moving distance of related components.

5. An optimization method for the use of black rod control rod assemblies according to claim 1, characterized in that: It further includes Step 4: Conduct in-service inspection on the swelling of black rod control rod assemblies; Conduct in-service inspection within the designed life of black rod control rod assemblies, supplement the inspection results to the in-pile ledger of black rod control rod assemblies, and formulate a usage plan for subsequent cycles according to the inspection results.

6. An optimization method for the use of black rod control rod assemblies according to claim 5, characterized in that: In Step 4, the in-service inspection focuses on the measured value of the rod diameter in the area 400 mm above the weld of the lower end plug.

7. An optimization method for the use of black rod control rod assemblies according to claim 5, characterized in that: In Step 4, give priority to inspecting black rod control rod assemblies whose cumulative number of cycles as temperature regulating rods reaches N and black rod control rod assemblies planned to be used as temperature regulating rods in subsequent cycles.

8. An optimization method for the use of black rod control rod assemblies according to claim 5, characterized in that: In Step 4, subsequent black rod control rod assemblies used as temperature regulating rods are not allowed to have swelling, and the rod diameter cannot exceed the initial diameter of 9.7 mm; subsequent black rod control rod assemblies used as shutdown rods and power compensation rods are allowed to have slight swelling, and the rod diameter cannot exceed 9.88 mm.

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