A core loading method for a 24-month equilibrium cycle of the VVER reactor type

Abstract

The present invention relates to a core loading method for a VVER reactor type with a 24-month balanced cycle, belonging to the technical field of core fuel management design. The method replaces the same number of old fuel assemblies that have been used in the reactor for two cycles with 73-85 new fuel assemblies before the start of the Nth cycle; and replaces the same number of old fuel assemblies that have been used in the reactor for two cycles with 78-90 new fuel assemblies before the start of the N+1th cycle, ensuring that the total number of new and old fuel assemblies before and after loading and refueling is 163 groups unchanged. The method provided by the present invention can realize the shutdown and overhaul of the VVER reactor type every two years, which can significantly improve the availability and economic benefits of the power plant.

Description

Technical Field

[0001] The invention belongs to the technical field of core fuel management design, and particularly relates to a core loading method for a 24-month equilibrium cycle of a VVER reactor type. Background Art

[0002] At present, the core fuel management of domestic commercial VVER reactor types all adopts an 18-month refueling scheme. With the 18-month refueling scheme, a shutdown overhaul for refueling is required every one and a half years. However, with a 24-month refueling scheme, a shutdown overhaul for refueling is only needed every two years, and the average annual overhaul time will be reduced by 25%, which can significantly improve the availability and economic benefits of the power plant.

[0003] The design of the loading scheme for a 24-month equilibrium cycle is more difficult. Usually, new fuel assembly types need to be redesigned, including the enrichment of uranium fuel rods, the number of gadolinium-bearing fuel rods, and the enrichment of uranium in gadolinium-bearing fuel rods, to meet the requirements of cycle length and core parameters. Summary of the Invention

[0004] To solve the defects existing in the prior art, the purpose of the present invention is to provide a core loading method for a 24-month equilibrium cycle of a VVER reactor type. Through this method, refueling with a shutdown overhaul can be carried out every two years for the VVER reactor type, which can significantly improve the availability and economic benefits of the power plant.

[0005] To achieve the above object, a technical solution adopted by the present invention is:

[0006] A core loading method for a 24-month equilibrium cycle of a VVER reactor type. Before the start of the Nth cycle, 73 - 85 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor; before the start of the (N + 1)th cycle, 78 - 90 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor, ensuring that the total number of new and old fuel assemblies remains unchanged at 163 groups before and after loading and refueling, so as to meet the requirements of a 24-month refueling for the equilibrium cycle length.

[0007] The new fuel assemblies include three different 235 average U enrichments;

[0008] After the loading replacement, the new fuel assemblies and the burned old fuel assemblies are arranged alternately. The principle followed for the arrangement is: 235 The new fuel assemblies with a low average U enrichment are mainly arranged in the inner area of the core, 235 The new fuel assemblies with a high average U enrichment are mainly arranged in the outermost area and the second outermost area of the core.

[0009] Further, for the core loading method for a 24-month equilibrium cycle of the VVER reactor type as described above, 235For the new fuel assembly with the highest average U enrichment 235 The average U enrichment is 5.90 - 6.00%; 235 For the new fuel assembly with the second highest average U enrichment 235 The average U enrichment is 5.79 - 5.89%; 235 For the new fuel assembly with the highest average U enrichment 235 The average U enrichment is 5.32 - 5.42%.

[0010] Furthermore, for the core loading method of the VVER reactor type with a 24-month equilibrium cycle as described above, the 235 type of the new fuel assembly with the highest average U enrichment is H60Y9; the 235 type of the new fuel assembly with the second highest average U enrichment is H60Y7; the 235 type of the new fuel assembly with the lowest average U enrichment is H55Y3.

[0011] Furthermore, for the core loading method of the VVER reactor type with a 24-month equilibrium cycle as described above, each new fuel assembly of type H60Y9 includes 312 fuel rods, among which the number of uranium fuel rods is 300 - 306, and the number of uranium-gadolinium fuel rods is 6 - 12; the 235 U enrichment of the uranium fuel rods is 5.95 - 6.05%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 3.98 - 4.02%, and the Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 4 - 6%;

[0012] Each new fuel assembly of type H60Y7 includes 312 fuel rods, among which the number of uranium fuel rods is 282 - 288, and the number of uranium-gadolinium fuel rods is 24 - 30; the 235 U enrichment of the uranium fuel rods is 5.95 - 6.05%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 3.98 - 4.02%, and the Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 7 - 9%;

[0013] Each new fuel assembly of type H55Y3 includes 312 fuel rods, among which the number of uranium fuel rods is 279 - 285, and the number of uranium-gadolinium fuel rods is 27 - 33; the 235 U enrichment of the uranium fuel rods is 5.45 - 5.55%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 3.98 - 4.02%, and the Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 7 - 9%.

[0014] Furthermore, for the core loading method of the 24-month equilibrium cycle of the VVER reactor type as described above, before the start of the Nth cycle, the replaced 77 - 81 groups of new fuel assemblies are loaded, including 31 - 43 groups of H55Y3 type fuel assemblies, 18 - 30 groups of H60Y7 type fuel assemblies, and 12 - 24 groups of H60Y9 type fuel assemblies.

[0015] Furthermore, for the core loading method of the 24-month equilibrium cycle of the VVER reactor type as described above, before the start of the (N + 1)th cycle, the replaced 82 - 86 groups of new fuel assemblies are loaded, including 54 - 66 groups of H55Y3 type fuel assemblies and 18 - 30 groups of H60Y9 type fuel assemblies.

[0016] Furthermore, for the core loading method of the 24-month equilibrium cycle of the VVER reactor type as described above, before the start of the Nth cycle, 79 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor; before the start of the (N + 1)th cycle, 84 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor, ensuring that the total number of new and old fuel assemblies remains unchanged at 163 groups before and after the loading and refueling.

[0017] Furthermore, for the core loading method of the 24-month equilibrium cycle of the VVER reactor type as described above, each of the H60Y9 type new fuel assemblies includes 303 uranium fuel rods and 9 uranium-gadolinium fuel rods; the 235 U enrichment of the uranium fuel rods is 6.0%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 4.0%. The Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 5%;

[0018] Each of the H60Y7 type new fuel assemblies includes 285 uranium fuel rods and 27 uranium-gadolinium fuel rods; the 235 U enrichment of the uranium fuel rods is 6.0%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 4.0%. The Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 8%;

[0019] Each of the H55Y3 type new fuel assemblies includes 282 uranium fuel rods and 30 uranium-gadolinium fuel rods; the 235 U enrichment of the uranium fuel rods is 5.5%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 4.0%. The Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 8%.

[0020] Further, for the core loading method of the 24-month equilibrium cycle of the VVER reactor type as described above, before the start of the Nth cycle, the 79 new fuel assemblies to be loaded for replacement include 37 fuel assemblies of the H55Y3 type, 24 fuel assemblies of the H60Y7 type, and 18 fuel assemblies of the H60Y9 type. The 235 average U enrichment of the 79 new fuel assemblies is 5.64%.

[0021] Further, for the core loading method of the 24-month equilibrium cycle of the VVER reactor type as described above, before the start of the (N + 1)th cycle, the 84 new fuel assemblies to be loaded for replacement include 60 fuel assemblies of the H55Y3 type and 24 fuel assemblies of the H60Y9 type. The 235 average U enrichment of the 84 new fuel assemblies is 5.53%.

[0022] Adopting the core loading method of the 24-month equilibrium cycle of the VVER reactor type of the present invention has the following remarkable technical effects:

[0023] The present invention adopts a refueling scheme of 24 months, and it is only necessary to carry out a refueling during a shutdown major overhaul every two years. Compared with the 18-month refueling scheme, the average annual major overhaul time will be reduced by 25%, which can significantly improve the availability and economic benefits of the power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is an arrangement diagram of different fuel assemblies after loading 79 new fuel assemblies before the start of the Nth cycle in the core loading method of the 24-month equilibrium cycle of the VVER reactor type of the present invention for exemplary purposes;

[0025] Figure 2 FIG. is an arrangement diagram of different fuel assemblies after loading 84 new fuel assemblies before the start of the (N + 1)th cycle in the core loading method of the 24-month equilibrium cycle of the VVER reactor type of the present invention for exemplary purposes.

[0026] Figure 1 And Figure 2 Each fuel assembly in and is represented by a hexagon. The numbers in the top row of the hexagon represent the fuel assembly number (position); the number on the left in the middle row represents the cycle number of this fuel assembly, and the number on the right represents the position of this fuel assembly in the previous cycle; the numbers in the bottom row represent the type of this fuel assembly. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described below in conjunction with specific embodiments and the accompanying drawings of the specification.

[0028] The present invention provides a core loading method for a 24-month equilibrium cycle of a VVER reactor type, which is specifically described as follows:

[0029] When designing the core fuel management scheme, relevant design criteria need to be followed. The factors considered in the fuel management design criteria include the enthalpy rise factor, rod linear power density, moderator temperature coefficient, and maximum burnup of discharged fuel, etc. The design criteria are as follows:

[0030] (1) The power peak factor Kr of the fuel rod ≤ 1.60;

[0031] (2) The maximum linear power density Ql ≤ 448 W / cm (for UO 2 fuel rods) and Ql ≤ 360 W / cm (for U-Gd fuel rods);

[0032] (3) The moderator temperature coefficient is not positive;

[0033] (4) When inserting the most valuable control rod bundle, after the reactor is scrammed to the hot shutdown state, the return to critical temperature for core cooling is not greater than 120 °C;

[0034] (5) For the TVS-2M fuel assembly, the maximum design burnup limit does not exceed 60 MWd / kgU.

[0035] Based on the above design criteria, the core loading method provided by the present invention is as follows:

[0036] Before the start of the Nth cycle, replace the same number of used old fuel assemblies that have been used for two cycles in the reactor with 73 - 85 groups of new fuel assemblies; before the start of the (N + 1)th cycle, replace the same number of used old fuel assemblies that have been used for two cycles in the reactor with 78 - 90 groups of new fuel assemblies, ensuring that the total number of fuel assemblies before and after refueling is 163 groups, so that the equilibrium cycle length meets the requirement of refueling every 24 months.

[0037] The present invention adopts three types of fuel assemblies, having three different 235 average U enrichments, and the detailed information is shown in Table 1.

[0038] Table 1 Fuel Assembly Information

[0039]

[0040] Before the start of the Nth cycle, the 73 - 85 groups of new fuel assemblies for replacement loading include 31 - 43 groups of H55Y3 type fuel assemblies, 18 - 30 groups of H60Y7 type fuel assemblies, and 12 - 24 groups of H60Y9 type fuel assemblies.

[0041] Before the start of the (N + 1)th cycle, the 78 - 90 groups of new fuel assemblies for replacement loading include 54 - 66 groups of H55Y3 type fuel assemblies and 18 - 30 groups of H60Y9 type fuel assemblies.

[0042] The arrangement principle of new fuel assemblies during core loading is as follows: 235 New fuel assemblies with a low average U enrichment are mainly arranged in the inner area of the core. 235 New fuel assemblies with a high average U enrichment are mainly arranged in the outermost area and the second outermost area of the core.

[0043] Through the above design, the core loading method for the VVER reactor type with a 24-month equilibrium cycle provided by the present invention can meet the requirement of refueling during a shutdown overhaul only once every two years. Compared with the 18-month refueling scheme, the average annual overhaul time will be reduced by 25%, which can significantly improve the availability and economic benefits of the power plant.

[0044] Exemplarily, a core loading method for a VVER reactor type with a 24-month equilibrium cycle provided by the present invention is specifically as follows:

[0045] Before the start of the Nth cycle, 79 groups of new fuel assemblies are used to replace 79 groups of old fuel assemblies that have been used for two cycles in the reactor, so that the total number of fuel assemblies before and after refueling is 163 groups. Among them, the 79 groups of new fuel assemblies include 37 groups of H55Y3 type fuel assemblies, 24 groups of H60Y7 type fuel assemblies, and 18 groups of H60Y9 type fuel assemblies. The 235 average U enrichment of the new fuel assemblies is 5.64%.

[0046] Before the start of the (N + 1)th cycle, 84 groups of new fuel assemblies are used to replace 84 groups of old fuel assemblies that have been used for two cycles in the reactor, so that the total number of fuel assemblies before and after refueling is 163 groups. Among them, the 84 groups of new fuel assemblies include 60 groups of H55Y3 type fuel assemblies and 24 groups of H60Y9 type fuel assemblies. The 235 average U enrichment of the new fuel assemblies is 5.53%.

[0047] The detailed information of the three types of fuel assemblies is shown in Table 2.

[0048] Table 2 Exemplary fuel assembly information

[0049]

[0050]

[0051] Based on the above core loading method, the arrangements of different fuel assemblies after loading 79 groups of new fuel assemblies and after loading 84 groups of new fuel assemblies are respectively as Figure 1 and Figure 2 shown. The principle followed for the arrangement is: 235 New fuel assemblies with a low average U enrichment are mainly arranged in the inner area of the core. 235 New fuel assemblies with a high average U enrichment are mainly arranged in the outermost area and the second outermost area of the core.

[0052] Table 3 gives the calculation results of the main core parameters of the equilibrium cycle using the above exemplary core loading method.

[0053] Table 3 Core Calculation Results of Equilibrium Cycle

[0054]

[0055] It can be seen from the calculation results in Table 3 that the cycle length of the equilibrium cycle reaches about 680 days, which can meet the requirement of refueling every 24 months, and other core parameters all meet the limit requirements. This loading scheme is applicable to all nuclear power plant units of VVER reactor types.

[0056] In the core loading method for the 24-month equilibrium cycle of the VVER reactor type provided in the embodiments of the present invention, by increasing the average enrichment and quantity of the fuel assemblies, adopting a brand-new fuel assembly type, and at the same time, in order to avoid having spent fuel assemblies that are only used for one cycle and improve the utilization rate of the fuel, the method of alternating refueling with 73-85 groups and 78-90 groups is adopted, which is a partial low-leakage loading, so that the equilibrium cycle length reaches 24 months. When performing core refueling for the 24-month equilibrium cycle, 73-85 groups or 78-90 groups of new fuel are used to replace the same number of old fuel assemblies that have been used for two cycles, so that the total number of fuel assemblies after refueling is 163 groups, and each fuel assembly is used for two cycles in the core. Compared with the 18-month refueling scheme, the average annual overhaul time will be reduced by 25%, which can significantly improve the availability and economic benefits of the power plant.

[0057] The above embodiments are only illustrative examples of the present invention. The present invention can also be implemented in other specific ways or other specific forms without departing from the gist or essential features of the present invention. Therefore, the described embodiments should be regarded as illustrative rather than restrictive in any aspect. The scope of the present invention should be defined by the appended claims, and any equivalent changes to the intention and scope of the claims should also be included within the scope of the present invention.

Claims

1. A core loading method for a 24-month equilibrium cycle of a VVER reactor type, characterized in that: Before the start of the Nth cycle, 73 - 85 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor; before the start of the (N + 1)th cycle, 78 - 90 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor, ensuring that the total number of new and old fuel assemblies remains unchanged at 163 groups before and after loading and refueling, so that the equilibrium cycle length meets the requirement of refueling every 24 months; The described new fuel assembly includes three different 235 average U enrichments, 235 The new fuel assembly with the highest average U enrichment 235 has an average U enrichment of 5.90 - 6.00%; 235 The new fuel assembly with the second highest average U enrichment 235 has an average U enrichment of 5.79 - 5.89%; 235 The new fuel assembly with the lowest average U enrichment 235 has an average U enrichment of 5.32 - 5.42%; The newly loaded replaced fuel assemblies and the spent old fuel assemblies are arranged alternately, and the arrangement principle is as follows: 235 The new fuel assemblies with low average U enrichment are mainly arranged in the inner area of the reactor core, 235 The new fuel assemblies with high average U enrichment are mainly arranged in the outermost area and the second outermost area of the reactor core; The 235 new fuel assembly type with the highest average U enrichment is H60Y9; the 235 new fuel assembly type with the second highest average U enrichment is H60Y7; the 235 new fuel assembly type with the lowest average U enrichment is H55Y3; Each of the new fuel assemblies of the H60Y9 type includes 312 fuel rods, among which the number of uranium fuel rods is 300 - 306, and the number of uranium-gadolinium fuel rods is 6 - 12; the 235 U enrichment is 5.95 - 6.05%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 3.98 - 4.02%, and the Gd 2 O 3 mass percentage content is 4 - 6%; Each of the new fuel assemblies of the H60Y7 type includes 312 fuel rods, among which the number of uranium fuel rods is 282 - 288, and the number of uranium-gadolinium fuel rods is 24 - 30; the 235 U enrichment is 5.95 - 6.05%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 3.98 - 4.02%, and the Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 7 - 9%; Each of the new fuel assemblies of the H55Y3 type includes 312 fuel rods, among which the number of uranium fuel rods is 279 - 285, and the number of uranium-gadolinium fuel rods is 27 - 33; the 235 U enrichment is 5.45 - 5.55%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 3.98 - 4.02%, and the Gd of the uranium-gadolinium fuel rods 2 O 3 mass percentage content is 7 - 9%.

2. The core loading method for a 24-month equilibrium cycle of a VVER reactor type according to claim 1, characterized in that: Before the start of the Nth cycle, the 73 - 85 groups of new fuel assemblies for loading and replacement include 31 - 43 groups of H55Y3 type fuel assemblies, 18 - 30 groups of H60Y7 type fuel assemblies, and 12 - 24 groups of H60Y9 type fuel assemblies.

3. The core loading method for a 24-month equilibrium cycle of a VVER reactor type according to claim 1, characterized in that: Before the start of the (N + 1)th cycle, the 78 - 90 groups of new fuel assemblies for loading and replacement include 54 - 66 groups of H55Y3 type fuel assemblies and 18 - 30 groups of H60Y9 type fuel assemblies.

4. The core loading method for a 24-month equilibrium cycle of a VVER reactor type according to claim 1, characterized in that: Before the start of the Nth cycle, 79 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor; before the start of the (N + 1)th cycle, 84 groups of new fuel assemblies are used to replace the same number of old fuel assemblies that have been used for two cycles in the reactor, ensuring that the total number of new and old fuel assemblies remains unchanged at 163 groups before and after loading and refueling.

5. The core loading method for a 24-month equilibrium cycle of a VVER reactor type according to claim 1, characterized in that: Each of the new fuel assemblies of the H60Y9 type includes 303 uranium fuel rods and 9 uranium-gadolinium fuel rods; the 235 U enrichment of the uranium fuel rods is 6.0%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 4.0%. The Gd 2 O 3 mass percentage content of the uranium-gadolinium fuel rods is 5%; Each of the new fuel assemblies of the H60Y7 type includes 285 uranium fuel rods and 27 uranium-gadolinium fuel rods; the 235 U enrichment of the uranium fuel rods is 6.0%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 4.0%. The Gd 2 O 3 mass percentage content of the uranium-gadolinium fuel rods is 8%; Each of the new fuel assemblies of the H55Y3 type includes 282 uranium fuel rods and 30 uranium-gadolinium fuel rods; the 235 U enrichment of the uranium fuel rods is 5.5%, and the 235 U enrichment of the uranium-gadolinium fuel rods is 4.0%. The Gd 2 O 3 mass percentage content of the uranium-gadolinium fuel rods is 8%.

6. The core loading method for a 24-month equilibrium cycle of a VVER reactor type according to claim 4, characterized in that: Before the start of the Nth cycle, the 79 new fuel assemblies loaded for replacement include 37 fuel assemblies of the H55Y3 type, 24 fuel assemblies of the H60Y7 type, and 18 fuel assemblies of the H60Y9 type. The 235 average U enrichment of the 79 new fuel assemblies is 5.64%.

7. The core loading method for a 24-month equilibrium cycle of a VVER reactor type according to claim 4, characterized in that: Before the start of the (N + 1)-th cycle, the 84 new fuel assemblies loaded for replacement include 60 fuel assemblies of the H55Y3 type and 24 fuel assemblies of the H60Y9 type. The 235 average U enrichment of the 84 new fuel assemblies is 5.53%.

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