A long-short cycle modular small heap balancing cycle method
By employing partial low-leakage loading, three-batch refueling, and long-short cycle design, the fuel management problem of modular small reactor cores has been solved, achieving uniform utilization of fuel assemblies and good power distribution flattening, thereby improving the overall performance and safety of the reactor core.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-25
- Publication Date
- 2026-07-14
AI Technical Summary
Modular small reactor cores have problems such as fuel economy, power distribution flattening and maximum fuel rod burnup control, and existing technologies are difficult to achieve balanced cycle fuel management.
The design strategy employs partial low-leakage loading, three-batch refueling, and a long-short balanced cycle. By setting up a long-short cycle scheme for the fuel assemblies with three batches of refueling, combined with soluble boron to compensate for the core reactivity effect, the cross arrangement of fuel assemblies and the long-short-long-short balanced cycle are achieved.
It effectively reduced the maximum burnup of fuel rods, improved the overall performance of the reactor core, ensured safety and economy, and achieved uniform utilization of fuel assemblies and good flattening of power distribution.
Smart Images
Figure CN122393029A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of modular small reactor core technology, specifically relating to a method for balanced cycling of modular small reactors with long and short cycles. Background Technology
[0002] Modular small modular reactors (SMRs) have smaller core sizes, fewer assemblies, greater core leakage, and larger assembly burnup gradients. While using only a high-leakage loading configuration is beneficial for flattening the radial power distribution, it reduces fuel utilization. Conversely, using only a low-leakage loading configuration presents significant challenges in flattening the radial power distribution, which is detrimental to the core's thermal safety margin. Furthermore, modular SMR cores must minimize maximum fuel rod burnup while ensuring sufficient batch refueling burnup. These core characteristics and requirements present challenges to the balance cycle fuel management of modular SMR cores.
[0003] Current modular small reactor core balance cycle fuel management has problems such as fuel economy (characterized by average batch unloading burnup of components), power distribution flattening, and maximum fuel rod burnup control. Summary of the Invention
[0004] The purpose of this invention is to provide a modular small reactor core balancing cycle method with long and short cycles. Based on a partial low-leakage loading, three-batch refueling, and long and short balancing cycle design strategy, this method adopts a 24-month refueling cycle with long and short cycles, which has good power distribution flattening, an average batch unloading burnup of more than 40,000 MWd / tU, and a maximum fuel rod burnup of about 48,000 MWd / tU. This method can effectively support the design of a model small reactor core.
[0005] The technical solution of the present invention is as follows: A modular min-heap balancing loop method with long and short cycles, comprising: Step 1: The fuel enrichment level used in the core balance cycle is 4.4%~5.0%; Step 2: The core balancing cycle adopts a strategy of partial low-leakage loading, three-batch refueling, and long and short balancing cycles; Step 3: Set up a long-cycle plan for three batches of refueling fuel assemblies; Step 4: In the three batches of refueling fuel assemblies, 12 new fuel assemblies are arranged on the periphery of the reactor core, and 12 or 13 new fuel assemblies are arranged inside the reactor core. New fuel assemblies and old fuel assemblies are arranged alternately in each area of the reactor core. Step 5: The enrichment of the internal new fuel assembly is 4.45%, and the number of gadolinium-loaded fuel rods is 8 to 24; the enrichment of the external new fuel assembly is 4.95%, and the number of gadolinium-loaded fuel rods is 0 to 8.
[0006] In step 1, gadolinium-loaded fuel rods are used as flammable poison.
[0007] In step 1, the number of gadolinium-loaded fuel rods in a single fuel assembly can be selected as 0, 4, 8, 12, 16, 20, or 24.
[0008] In step 1, soluble boron is used to compensate for the slow reactivity of the reactor core.
[0009] In step 2, the partial low-leakage loading strategy places some new fuel assemblies in the inner core area and some new fuel assemblies in the outer core area; by adopting a three-batch refueling strategy, the fuel assemblies in the core are divided into new fuel assemblies, fuel assemblies that have undergone one cycle, and fuel assemblies that have undergone two cycles.
[0010] In the long-short balance cycle strategy described in step 2, the center fuel assembly of the long balance cycle uses one new fuel assembly, and the center fuel assembly of the short balance cycle continues to use the same fuel assembly. Then, the assembly is removed from the reactor and no longer used, thus achieving a long-short-long-short balance cycle. The long cycle length is 700 EFPD, and the short cycle length is 680 EFPD.
[0011] In step 3, for the long cycle of the balanced cycle: the first batch contains 25 fuel assemblies, the second batch contains 24 fuel assemblies, and the third batch contains 8 fuel assemblies. In step 3, for the short cycle of the balance cycle: the first batch contains 24 fuel assemblies, the second batch contains 25 fuel assemblies, and the third batch contains 8 fuel assemblies.
[0012] The beneficial effects of this invention are as follows: while ensuring the safety requirements and economy of modular small modular reactors, this invention effectively reduces the maximum burnup of fuel rods and supports the improvement of the overall performance of the reactor core. Attached Figure Description
[0013] Figure 1 Schematic diagram of core loading for a balanced long-cycle reactor; Figure 2 A schematic diagram of core loading for a balanced short-cycle reactor. Detailed Implementation
[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and figures. The illustrative embodiments and descriptions of this invention are only for explaining this invention and are not intended to limit this invention.
[0015] This invention provides a long-short cycle method for the core balance cycle fuel management of modular small modular reactors (SMRs). Based on a partial low-leakage loading, three-batch refueling, and a long-short cycle design strategy, this invention targets a modular SMR core with a thermal power of approximately 400 MW and an electrical power of approximately 100 MW, using 57 boxes of 17×17 commercial pressurized water reactor fuel assemblies. The active section height of the core is approximately 210 cm, and the average linear power density of the core is approximately 120 W / cm². The core balance cycle length is required to reach 24 months, with a corresponding plant availability >0.9. The core enthalpy rise factor is no greater than 1.60, and the hot spot factor is no greater than 2.60. The average batch burnup of the fuel assemblies is greater than 40,000 MWd / tU, and the maximum fuel rod burnout probability is low.
[0016] A modular min-heap balancing loop method with varying lengths of loops includes the following steps: Step 1: The fuel enrichment level used in the core balance cycle is 4.4%~5.0%; Gadolinium-loaded fuel rods are used as combustible poisons, and the number of gadolinium-loaded fuel rods in a single fuel assembly can be selected as 0, 4, 8, 12, 16, 20, 24, etc.; soluble boron is used to compensate for the slow reactivity effect of the reactor core.
[0017] Step 2: The core balancing cycle adopts a design strategy of partial low-leakage loading, three-batch refueling, and long and short balancing cycles.
[0018] The partial low-leakage loading strategy places some new fuel assemblies in the inner core region and some in the outer core region. Fuel assemblies placed in the inner core region have a relatively lower enrichment level and a relatively higher number of gadolinium-loaded fuel rods; fuel assemblies placed in the outer core region have a relatively higher enrichment level and a relatively lower number of gadolinium-loaded fuel rods.
[0019] By employing a three-batch refueling strategy, the fuel assemblies in the reactor core are divided into new fuel assemblies, fuel assemblies that have undergone one cycle, and fuel assemblies that have undergone two cycles.
[0020] Meanwhile, in order to minimize the maximum fuel rod burnup (which occurs in the center fuel assembly after three consecutive cycles), this invention proposes a long-short cycle strategy: the center fuel assembly in the long cycle of the balance cycle uses one new fuel assembly, the center fuel assembly in the short cycle of the balance cycle continues to use the same fuel assembly, and then the assembly is removed from the reactor and no longer used.
[0021] This achieves a balanced cycle of long-short-long-short.
[0022] The long cycle length is approximately 700 EFPD; the short cycle length is approximately 680 EFPD.
[0023] Step 3: Set up a three-batch refueling fuel assembly balance cycle scheme. For the long balance cycle: the first batch contains 25 fuel assemblies, the second batch contains 24 fuel assemblies, and the third batch contains 8 fuel assemblies; for the short balance cycle: the first batch contains 24 fuel assemblies, the second batch contains 25 fuel assemblies, and the third batch contains 8 fuel assemblies.
[0024] Step 4: Of the three batches of refueling fuel assemblies, 12 new fuel assemblies are arranged around the core, and 12 or 13 new fuel assemblies are arranged inside the core. The new fuel assemblies and old fuel assemblies are arranged alternately in each area of the core, thereby flattening the power distribution and minimizing neutron leakage.
[0025] Step 5: The new fuel assemblies inside the reactor core have a lower enrichment level and a higher number of gadolinium rods, while the new fuel assemblies outside the reactor core have a higher enrichment level and a lower number of gadolinium rods.
[0026] The internal new fuel assembly has an enrichment level of 4.45% and contains 8 to 24 gadolinium-loaded fuel rods; the external new fuel assembly has an enrichment level of 4.95% and contains 0 to 8 gadolinium-loaded fuel rods.
[0027] Example: A modular min-heap balancing loop method with varying lengths of loops includes: The reactor core has a thermal power of 385 MW and an active section height of 215 cm. The core consists of 57 17×17 commercial pressurized water reactor fuel assemblies. Each fuel assembly contains 264 fuel rods, 24 guide tubes, and 1 instrumentation tube. Gadolinium-loaded fuel rods are used as solid combustible poison, with a Gd₂O₃ mass percentage of 8%. The number of gadolinium rods varies, including 4, 8, 16, and 24. 235 U enrichment is 2.5%; gadolinium-free fuel rods 235 The enrichment of U is 4.45% and 4.95%; 20 control rods are arranged in the reactor; light water containing soluble boron is used as a coolant and moderator; stainless steel shrouds and water reflectors are arranged radially around the fuel assemblies, and water reflectors are arranged axially.
[0028] The core balancing cycle employs a long-short cycle strategy, using a three-batch loading and unloading method, with each batch corresponding to a different phase. Figure 1 and Figure 2 The serial number indicates that a new fuel assembly is loaded at this location, 2 indicates that a fuel assembly that has been burned through one cycle and is being reloaded, and 3 indicates that a fuel assembly that has been burned through two cycles and is being reloaded.
[0029] For the balanced long cycle, four new fuel assemblies with a gadolinium-free fuel rod enrichment of 4.45% are loaded at locations J05 / E01 / E09 / A05 (e.g., Figure 1(As shown); 8 fuel assemblies with an enrichment of 4.45% and containing 8 gadolinium-loaded fuel rods, loaded at positions H04 / H06 / F02 / F08 / D02 / D08 / B04 / B06 (as shown). Figure 1 (As shown); 4 fuel assemblies with an enrichment of 4.45% and containing 16 gadolinium-loaded fuel rods, loaded at locations G05 / E03 / E07 / C05 (as shown). Figure 1 (As shown); a fuel assembly with an enrichment of 4.45% and containing 24 gadolinium-loaded fuel rods, loaded at position E05 (as shown). Figure 1 (As shown); 8 fuel assemblies with an enrichment of 4.95% and containing 4 gadolinium-loaded fuel rods, loaded at positions H03 / H07 / G02 / G08 / C02 / C08 / B03 / B07 (as shown). Figure 1 (As shown); 25 fuel assemblies with lower enrichment or higher burnout were simultaneously unloaded. The core adopted a partially low-leakage loading mode, such as... Figure 1 As shown.
[0030] For the balanced short cycle, four new fuel assemblies with a gadolinium-free fuel rod enrichment of 4.45% are loaded at locations J05 / E01 / E09 / A05 (e.g., Figure 2 (As shown); 8 fuel assemblies with an enrichment of 4.45% and containing 8 gadolinium-loaded fuel rods, loaded at positions H04 / H06 / F02 / F08 / D02 / D08 / B04 / B06 (as shown). Figure 2 (As shown); 4 fuel assemblies with an enrichment of 4.45% and containing 16 gadolinium-loaded fuel rods, loaded at locations G05 / E03 / E07 / C05 (as shown). Figure 2 (As shown); 8 fuel assemblies with an enrichment of 4.95% and containing 4 gadolinium-loaded fuel rods, loaded at positions H03 / H07 / G02 / G08 / C02 / C08 / B03 / B07 (as shown). Figure 2 (As shown); 24 fuel assemblies with lower enrichment or higher burnup were simultaneously unloaded. The core adopted a partially low-leakage loading mode, such as... Figure 2 As shown.
[0031] The long-cycle refueling period of the balanced cycle is approximately 702 EFPD, and the short-cycle refueling period is approximately 680 EFPD, with an average cycle length of approximately 691 EFPD. Based on a 24-month refueling cycle requirement, the plant's availability is as high as 0.95. The average batch burnup of fuel assemblies in the balanced cycle is approximately 40,300 MWd / tU, and the maximum fuel rod burnup is approximately 48,000 MWd / tU. Under full-power steady-state operation, the maximum core enthalpy rise factor is less than 1.45, and the maximum three-dimensional power peak factor is less than 2.0. It can be seen that the small-reactor balanced cycle scheme with long and short cycles proposed in this invention, while meeting the 24-month refueling requirement, achieves good core power distribution flattening, while maintaining an average batch burnup greater than 40,000 MWd / tU and controlling the maximum fuel rod burnup to approximately 48,000 MWd / tU.
[0032] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A modular min-heap balancing loop method with long and short cycles, characterized in that, include: Step 1: The fuel enrichment level used in the core balance cycle is 4.4%~5.0%; Step 2: The core balancing cycle adopts a strategy of partial low-leakage loading, three-batch refueling, and long and short balancing cycles; Step 3: Set up a long-cycle plan for three batches of refueling fuel assemblies; Step 4: In the three batches of refueling fuel assemblies, 12 new fuel assemblies are arranged on the periphery of the reactor core, and 12 or 13 new fuel assemblies are arranged inside the reactor core. New fuel assemblies and old fuel assemblies are arranged alternately in each area of the reactor core. Step 5: The enrichment of the internal new fuel assembly is 4.45%, and the number of gadolinium-loaded fuel rods is 8 to 24; the enrichment of the external new fuel assembly is 4.95%, and the number of gadolinium-loaded fuel rods is 0 to 8.
2. The modular min-heap balancing loop method with long and short cycles as described in claim 1, characterized in that: In step 1, gadolinium-loaded fuel rods are used as flammable poison.
3. The modular min-heap balancing loop method with long and short cycles as described in claim 2, characterized in that: In step 1, the number of gadolinium-loaded fuel rods in a single fuel assembly can be selected as 0, 4, 8, 12, 16, 20, or 24.
4. The modular min-heap balancing loop method with long and short cycles as described in claim 3, characterized in that: In step 1, soluble boron is used to compensate for the slow reactivity of the reactor core.
5. The modular min-heap balancing loop method with long and short cycles as described in claim 1, characterized in that: In step 2, the partial low-leakage loading strategy places some new fuel assemblies in the inner core area and some new fuel assemblies in the outer core area; by adopting a three-batch refueling strategy, the fuel assemblies in the core are divided into new fuel assemblies, fuel assemblies that have undergone one cycle, and fuel assemblies that have undergone two cycles.
6. The modular min-heap balancing loop method with long and short cycles as described in claim 1, characterized in that: In the long-short balance cycle strategy described in step 2, the center fuel assembly of the long balance cycle uses one new fuel assembly, and the center fuel assembly of the short balance cycle continues to use the same fuel assembly. Then, the assembly is removed from the reactor and no longer used, thus achieving a long-short-long-short balance cycle. The long cycle length is 700 EFPD, and the short cycle length is 680 EFPD.
7. The modular min-heap balancing loop method with long and short cycles as described in claim 1, characterized in that: In step 3, for the long cycle of the balanced cycle: the first batch contains 25 fuel assemblies, the second batch contains 24 fuel assemblies, and the third batch contains 8 fuel assemblies.
8. The modular min-heap balancing loop method with long and short cycles as described in claim 1, characterized in that: In step 3, for the short cycle of the balance cycle: the first batch contains 24 fuel assemblies, the second batch contains 25 fuel assemblies, and the third batch contains 8 fuel assemblies.