Fuel circulation method of pebble-bed high-temperature gas cooled reactor
By using an alternating preloaded fuel cycle method, the pebble bed high-temperature gas-cooled reactor forms a fuel density gradient transition during the fuel cycle, solving the problem of uneven axial power distribution and achieving improvements in safety and economy.
Patent Information
- Application Number
- CN202511506593.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-21
- Publication Date
- 2026-02-13
AI Technical Summary
In pebble bed high-temperature gas-cooled reactors, uneven axial power distribution occurs during fuel cycle, leading to increased hot spot temperature and the risk of material overheating, which limits reactor power output. Furthermore, existing technologies lack effective control measures.
The staggered preloaded fuel cycle method is adopted. By adding fuel elements with different enrichment and mixing ratios in the reactor vessel, a layered structure of alternating "pure fuel-high mixing ratio fuel" is formed, which gradually transitions to a fully loaded core, so as to achieve a uniform distribution of fuel density gradient and avoid neutron field distortion.
It effectively reduces the standard deviation of the core axial power distribution, lowers hot spot temperature, meets safety requirements, reduces the risk of material overheating, and improves fuel utilization efficiency and reactor economy.
Smart Images
Figure CN121528600A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the field of nuclear energy engineering technology, and in particular to a fuel cycle method for a pebble bed type high-temperature gas-cooled reactor. Background Technology
[0002] The pebble bed high-temperature gas-cooled reactor, as a type of nuclear power reactor, is characterized by its core, which is formed by the free stacking of spherical fuel elements. This structure gives the reactor the unique advantage of continuous refueling without stopping the reactor, significantly improving operational continuity. Its fuel cycle begins with initial core loading, successively going through the initial core construction and transition stages, and finally reaching a balanced core state.
[0003] During the transition phase, the reactor core contains fuel elements with diverse compositions, enrichment levels, mixing ratios, and burnup depths, resulting in an extremely complex neutron field distribution. At this stage, the power distribution within the core is significantly affected by changes in fuel density and neutron distribution caused by the fuel cycle, exhibiting a highly non-uniform axial power distribution. This non-uniform axial power distribution not only increases the hotspot temperature in localized areas of the core but also limits the reactor's power output. Summary of the Invention
[0004] To address the aforementioned technical problems, this disclosure provides a fuel cycle method for a pebble bed type high-temperature gas-cooled reactor.
[0005] This disclosure provides a fuel cycle method for a pebble bed type high-temperature gas-cooled reactor. The fuel cycle method for the pebble bed type high-temperature gas-cooled reactor includes the following steps.
[0006] Low-enrichment, high-mixture-ratio fuel elements are added to the reactor vessel, while all fuel elements already loaded in the initial core are unloaded from the reactor vessel to form a transition core.
[0007] Low-enrichment fuel elements and low-enrichment high-mixing-ratio fuel elements are added sequentially into the reactor vessel. At the same time, a portion of the fuel elements at the bottom of the transition core are unloaded each time they are added. This process is repeated a first set number of times to form a pre-loaded core.
[0008] Low-enrichment pure fuel elements are added to the top of the preloaded core, while the staggered fuel elements in the preloaded core are unloaded to form a fully loaded core.
[0009] Low-enrichment and high-enrichment mixed fuel elements are added to the top of the fully loaded core, while low-enrichment pure fuel elements at the bottom of the fully loaded core are unloaded. This process is repeated a second set number of times. In each cycle, the proportion of high-enrichment pure fuel elements gradually increases among the low-enrichment and high-enrichment mixed fuel elements added, thus forming a balanced core.
[0010] The technical solution provided in this disclosure has the following advantages compared with the prior art: By using a staggered preloading design, a gradient transition of fuel density is achieved. The preloaded core forms an alternating layered structure of "pure fuel - high-mixing-ratio fuel" along the axial direction. The top and bottom layers are low-enriched pure fuel, while the middle layers are arranged in a regular staggered manner. This effectively avoids neutron field distortion caused by direct large-area contact between pure fuel and mixed fuel. The standard deviation of the core axial power distribution is reduced, and the hot spot temperature is lowered. This fundamentally alleviates the power concentration problem, significantly reduces the risk of material overheating, and meets safety requirements such as fuel element power limits and shutdown margin.
[0011] Each stage of the fuel cycle process, including refueling and replacement operations, can be implemented using existing pebble bed high-temperature gas-cooled reactor refueling systems without requiring additional equipment or core structure modifications, thus lowering the technological threshold for implementation. Clearly quantified ranges are provided for fuel mixing ratios, enrichment, and loading amounts, facilitating standardized execution by engineers. Based on the non-stop refueling mode, parameters such as refueling rate and fuel ratio are clearly quantified, avoiding downtime losses caused by one-time refueling and mitigating operational deviations from manual control, further reducing operating costs. Combined with a dynamic balancing mode of "synchronous addition-discharge," unloading burnup is improved, reducing fuel waste.
[0012] In some embodiments, forming a preloaded core includes: adding low-enrichment pure fuel elements to the top of the transition core while unloading a portion of the fuel elements at the bottom of the transition core; and adding low-enrichment high-mixing-ratio fuel elements to the top of the transition core while unloading a portion of the fuel elements at the bottom of the transition core; repeating the above steps a first predetermined number of times, and finally adding low-enrichment pure fuel elements to the top of the transition core while unloading the remaining fuel elements at the bottom of the transition core.
[0013] In some embodiments, the loading amount of low-enrichment high-mixing-ratio fuel elements in forming the transition core is A; the loading amount of low-enrichment pure fuel elements added to the top of the transition core while a portion of the fuel elements at the bottom of the transition core are unloaded is 1 / B of A.
[0014] In some embodiments, the loading amount of low-enrichment high-mixing-ratio fuel elements in forming the transition core is A; when adding low-enrichment high-mixing-ratio fuel elements to the top of the transition core while unloading a portion of the fuel elements at the bottom of the transition core, the loading amount of low-enrichment high-mixing-ratio fuel elements added to the top of the transition core is 1 / B of A.
[0015] In some embodiments, the first set number is related to the value of B.
[0016] In some embodiments, forming a balanced core includes: unloading a portion of the low-enrichment pure fuel elements from the bottom of the fully loaded core and adding a mixture of low-enrichment and high-enrichment fuel elements to the top of the fully loaded core; and repeating this process a second predetermined number of times until the loading amount of the high-enrichment pure fuel elements is the same as the loading amount of the low-enrichment low-mixing fuel elements in the initial core.
[0017] In some embodiments, during the formation of the transition core, the loading amount of low-enrichment, high-mixing-ratio fuel elements is A; during the formation of the balanced core, after a second predetermined number of cycles, the loading amount of high-enrichment, pure fuel elements in the reactor vessel is A.
[0018] In some embodiments, during the formation of a balanced core, the highest burnup portion of the low-enrichment pure fuel elements discharged from the bottom of the fully loaded core is discharged as spent fuel, while the remaining portion is mixed with high-enrichment pure fuel elements and then added to the top of the fully loaded core.
[0019] In some embodiments, among the low-enrichment fuel elements discharged from the transition core, the 1 / n portion with the highest burnup among the low-enrichment pure fuel elements discharged from the bottom of the fully loaded core is discharged as spent fuel, and the remaining (n-1) / n portions are mixed with 1 / n portions of high-enrichment pure fuel elements and loaded onto the top of the fully loaded core.
[0020] In some embodiments, the value of n is related to the number of fuel cycles in a bed-type high-temperature gas-cooled reactor. Attached Figure Description
[0021] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.
[0022] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.
[0023] Figure 1 This is a schematic diagram of the stacking of spherical fuel elements in the core of a pebble bed type high-temperature gas-cooled reactor according to an embodiment of the present disclosure; Figure 2 This is a schematic diagram of an axially layered core structure of the pebble bed type high-temperature gas-cooled reactor described in the embodiments of this disclosure during the fuel cycle process. Detailed Implementation
[0024] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.
[0025] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.
[0026] The fuel cycle of a pebble bed high-temperature gas-cooled reactor begins with initial core loading, proceeding through initial core setup, transition, and finally reaching a balanced core. Among these processes, the transition core loading is the most complex, involving different power plateaus, varying refueling rates, and gradually increasing unloading burnup. Furthermore, the core loading transitions from an initial mixture of low-enriched fuel elements and graphite spheres to entirely low-enriched fuel elements; then to a mixture of low- and high-enriched fuel elements; and finally, entirely high-enriched pure fuel elements. The entire initial core setup and transition process takes 3-4 years.
[0027] During the transition phase, the reactor core contains fuel elements with varying compositions, enrichment levels, mixing ratios, and burnup depths, resulting in a complex neutron field distribution. Furthermore, in pebble bed high-temperature gas-cooled reactors, only control rods and absorber spheres are located in the graphite reflector layer near the active zone, lacking reactive compensation control devices like those used in pressurized water reactors for soluble poisons and combustible poisons to flatten axial power. Therefore, during the transition phase, the power distribution within the core is significantly affected by changes in fuel density and neutron distribution caused by the fuel cycle, resulting in a highly non-uniform axial power distribution. This non-uniform axial power distribution increases the hotspot temperature in localized areas of the core, limiting reactor power output and negatively impacting reactor safety and economics.
[0028] Based on this, this disclosure provides a fuel cycle method for a pebble bed type high-temperature gas-cooled reactor, which optimizes the fuel cycle method during the initial core loading and transition process of the pebble bed type high-temperature gas-cooled reactor to achieve flattened axial power and improve the operational safety and economy during the transition process.
[0029] In some embodiments, the fuel cycle method for a pebble bed high-temperature gas-cooled reactor includes at least the following steps S0 to S4.
[0030] S0. Initial core loading. The initial core is loaded entirely with low-enrichment, low-mixing-ratio fuel elements.
[0031] For example, in the initial core assembly, all fuel elements loaded in the reactor vessel are low-enrichment, low-mixing-ratio fuel elements.
[0032] For example, the loading of low-enrichment, low-mixing-ratio fuel elements in the initial core is A.
[0033] S1. Add low-enrichment, high-mixing-ratio fuel elements into the reactor vessel, while simultaneously unloading all the fuel elements already loaded in the initial core of the reactor vessel to form a transition core.
[0034] For example, in step S1, low-enrichment, high-mixing-ratio fuel elements are added into the reactor vessel, while low-enrichment, low-mixing-ratio fuel elements are removed from the reactor vessel to form a transition core.
[0035] For example, in step S1, the loading amount of low-enrichment, high-mixing-ratio fuel elements added to the reactor vessel is A. That is, the loading amount of high-enrichment, high-mixing-ratio fuel elements in the formed transition core is A.
[0036] S2. Low-enrichment fuel elements and low-enrichment high-mixing-ratio fuel elements are added sequentially into the reactor vessel. At the same time, a portion of the fuel elements at the bottom of the transition core are unloaded each time they are added. This process is repeated a first set number of times to form a pre-loaded core.
[0037] For example, step S2, which forms a preloaded core, includes steps S21 and S22.
[0038] S21. Add low-enrichment pure fuel elements to the top of the transition core, while unloading a portion of the fuel elements at the bottom of the transition core.
[0039] For example, a low-enrichment pure fuel element is added to the top of the transition core while a portion of the fuel elements at the bottom of the transition core are unloaded. The amount of low-enrichment high-mixing fuel element added to the top of the transition core is 1 / B of A.
[0040] For example, B is an odd number and B ≥ 3. For example, B is 3, 5, 7, 9, 11, 13, 15 or 17, and the value of B can also be larger. The specific value can be adapted according to actual needs, and this disclosure does not limit it.
[0041] S22. Add low-enrichment, high-mixing-ratio fuel elements to the top of the transition core, while simultaneously unloading a portion of the fuel elements at the bottom of the transition core.
[0042] For example, a low-enrichment, high-mixing-ratio fuel element is added to the top of the transition core while a portion of the fuel elements at the bottom of the transition core are unloaded. The loading of the low-enrichment, high-mixing-ratio fuel element added to the top of the transition core is 1 / B of A.
[0043] Steps S21 and S22 are executed repeatedly, with a first set number of cycles and a final cycle, adding low-enriched pure fuel elements to the top of the transition core while unloading the remaining fuel elements at the bottom of the transition core.
[0044] Specifically, in step S2, low-enrichment pure fuel elements are loaded into the transition core, while low-enrichment high-mixing-ratio fuel elements in the initial core are unloaded; and low-enrichment high-mixing-ratio fuel elements are loaded into the transition core, while the original low-enrichment high-mixing-ratio fuel elements at the bottom of the transition core are unloaded; the cycle is repeated a first set number of times, and for the last time, low-enrichment pure fuel elements are loaded into the transition core, while the remaining low-enrichment high-mixing-ratio fuel elements at the bottom of the transition core are unloaded.
[0045] For example, the first predetermined number of times is related to the value of B. That is, the specific number of times referred to by the first predetermined number of times is related to the value of B. For example, when B is an odd number, the first predetermined number of times = (B-1) / 2. For example, if B is 11, then the first predetermined number of times is 5.
[0046] For example, taking B as 11, in step S2, firstly, low-enrichment pure fuel elements are loaded, while simultaneously unloading the mixed fuel elements in the core, until the loading of low-enrichment pure fuel elements reaches A / 11; then, low-enrichment high-mixing-ratio fuel elements are loaded, while simultaneously unloading the original high-mixing-ratio fuel elements at the bottom of the core, until the loading reaches A / 11; the above two loading actions are repeated 5 times, and in the last cycle, low-enrichment pure fuel elements are loaded, while simultaneously unloading the remaining low-enrichment high-mixing-ratio fuel elements loaded in stage S1 at the bottom of the core.
[0047] It should be noted that the larger the value of B, the better the uniformity of power distribution, but the higher the operational complexity. Therefore, the value of B needs to be within a set range. For example, 3 ≤ B ≤ 20. For instance, B can be 3, 5, 7, 9, 11, 13, 15, 17, or 19.
[0048] S3. Add low-enrichment pure fuel elements to the top of the preloaded core, and simultaneously unload the staggered fuel elements in the preloaded core to form a fully loaded core.
[0049] For example, forming a balanced core includes: unloading a portion of the low-enrichment pure fuel elements from the bottom of the fully loaded core and adding a mixture of low-enrichment and high-enrichment fuel elements to the top of the fully loaded core; repeating this process a second predetermined number of times until the loading amount of the high-enrichment pure fuel elements is the same as the loading amount of the low-enrichment low-mixing-ratio fuel elements in the initial core.
[0050] Specifically, low-enrichment pure fuel elements are loaded into the preloaded core while the interleaved mixed fuel elements in the preloaded core are unloaded.
[0051] For example, in forming the transition core, the loading amount of low-enrichment, high-mixing-ratio fuel elements is A; in forming the balanced core, after a second predetermined number of cycles, the loading amount of high-enrichment, pure fuel elements in the reactor vessel is A.
[0052] Specifically, in the process of loading low-enrichment pure fuel elements into the transition core and simultaneously unloading the interleaved mixed fuel elements in the transition core, the loading amount of low-enrichment pure fuel elements is A.
[0053] S4. Add low-enrichment and high-enrichment mixed fuel elements to the top of the fully loaded core, while unloading the low-enrichment pure fuel elements at the bottom of the fully loaded core. Repeat this process a second set number of times. In each cycle, the proportion of high-enrichment pure fuel elements gradually increases among the low-enrichment and high-enrichment mixed fuel elements added, thus forming a balanced core.
[0054] For example, forming a balanced core includes: unloading a portion of the low-enrichment pure fuel elements from the bottom of the fully loaded core and adding a mixture of low-enrichment and high-enrichment fuel elements to the top of the fully loaded core; repeating the process a second predetermined number of times until the loading amount of the high-enrichment pure fuel elements is the same as the loading amount of the low-enrichment low-mixing fuel elements in the initial core.
[0055] Specifically, in the formation of a balanced reactor core, after the second predetermined number of cycles, the loading amount of highly enriched pure fuel elements in the reactor vessel is A.
[0056] In some embodiments, in step S4, when forming a balanced core, the portion of the low-enrichment pure fuel elements discharged from the bottom of the fully loaded core with the highest burnup is discharged as spent fuel, and the remaining portion is mixed with high-enrichment pure fuel elements and then added to the top of the fully loaded core.
[0057] For example, the low-enrichment fuel elements in the transition core are unloaded; wherein the portion of the low-enrichment fuel elements with the highest burnup is unloaded as spent fuel, and the remaining portion of the low-enrichment fuel elements is mixed with high-enrichment pure fuel elements and loaded into the transition core; the cycle is repeated a second set number of times until the loading amount of high-enrichment pure fuel elements is the same as the loading amount of low-enrichment low-mixing-ratio fuel elements in the initial core.
[0058] Specifically, of the low-enrichment pure fuel elements discharged from the bottom of the fully loaded core, the 1 / n portion with the highest burnup is discharged as spent fuel, and the remaining (n-1) / n portions are mixed with the 1 / n portion of high-enrichment pure fuel elements and then loaded onto the top of the fully loaded core.
[0059] For example, after a second set number of cycles, the loading of the high-enrichment fuel element is A.
[0060] For example, the value of n is related to the number of fuel cycles in a bed-type high-temperature gas-cooled reactor. That is, n is related to the number of fuel cycles selected when conducting reactor design. For example, in some high-temperature reactor designs, n is 1, 6, or 15, etc. The larger the n, the higher the unloading burnup, the more uniform the power distribution, and the better the economy. The specific value of n is adaptively selected according to actual needs, and this disclosure does not limit it. The value of n is not limited to the above and can also be other values.
[0061] In conjunction with the above, the fuel cycle method for the transition process of the pebble bed high-temperature gas-cooled reactor provided in this disclosure achieves a gradient transition of fuel density through an alternating preloading design: the reactor core forms an alternating layered structure of "pure fuel - high-mixing-ratio fuel" along the axial direction, with the uppermost and lowermost layers being low-enriched pure fuel, and the middle layers arranged in an alternating pattern, effectively avoiding neutron field distortion caused by direct large-area contact between pure fuel and mixed fuel, reducing the standard deviation of the axial power distribution of the reactor core, lowering the hot spot temperature, fundamentally alleviating the power concentration problem, significantly reducing the risk of material overheating, and simultaneously meeting safety requirements such as fuel element power limits and shutdown margin.
[0062] Each stage of refueling operations is compatible with existing pebble bed high-temperature gas-cooled reactor refueling systems that operate without reactor interruption, requiring no new equipment or core structure modifications, thus lowering the technical implementation threshold. Clearly quantified ranges are provided for fuel mixing ratios, enrichment, and loading amounts, facilitating standardized execution by engineers. Based on the non-stop refueling mode, parameters such as refueling rate and fuel ratio are clearly quantified, avoiding downtime losses caused by one-time refueling and mitigating operational deviations from manual control, further reducing operating costs. Combined with a dynamic balancing mode of "synchronous addition-discharge," unloading burnup is improved, reducing fuel waste.
[0063] In summary, the fuel cycle method for the transition process of a pebble bed high-temperature gas-cooled reactor provided in this disclosure can, on the basis of meeting safety requirements such as fuel element power limits, maximum fuel element temperature limits under normal operation / accident conditions, shutdown margin, and reactivity control margin, optimize the core axial loading strategy to make the axial fuel arrangement as uniform as possible during this stage, flatten the axial power distribution, reduce the core hot spot temperature, and at the same time improve fuel utilization efficiency, increase the reactor's maximum power, and enhance reactor economics.
[0064] In some embodiments, the total amount of fuel elements loaded in the reactor vessel is the same during both the addition and removal of fuel elements.
[0065] The term "same" here means that, after each of steps S1 to S4, the total amount of fuel elements loaded in the reactor vessel is the same. For example, if the total amount of fuel elements loaded in the reactor vessel after step S1 is A, then the total amount of fuel elements loaded in the reactor vessel after step S2 is also A.
[0066] In conjunction with the above, specifically, the pebble bed type high-temperature gas-cooled reactor fuel cycle method provided in this disclosure covers the stages from initial core loading (S0) to balanced core loading (S5), including four stages (S1-S4). These stages consist of: a transition stage from initial core loading to low-enrichment high-mixture fuel elements (S1); a transition stage from low-enrichment high-mixture to low-enrichment (excluding graphite spheres) fuel element preloading (S2); a transition stage from low-enrichment fuel element preloading to low-enrichment fuel element transition (S3); and a transition stage from low-enrichment to high-enrichment pure fuel element transition (S4). The mixed fuel elements consist of uranium-filled fuel element spheres and unfilled pure graphite spheres. During initial core loading, the core is fully loaded with low-mixture fuel elements.
[0067] Step S0 is the initial core assembly stage, in which the core is fully loaded with low-enrichment, low-mixing-ratio fuel elements, with a total loading quantity of A.
[0068] Step S1 is the transition stage from initial core loading to low-enrichment, high-mixing-ratio fuel elements. During this process, low-enrichment, high-mixing-ratio fuel elements are added to the initial core, while simultaneously unloading the low-mixing-ratio fuel elements already loaded in the initial core, until all the low-enrichment, low-mixing-ratio fuel elements loaded in the initial core are unloaded, and the high-mixing-ratio fuel element loading reaches A. At this point, the core is entirely composed of low-enrichment, high-mixing-ratio fuel elements.
[0069] Step S2 is the pre-loading transition stage from low-enrichment high-mixture fuel elements to low-enrichment fuel elements. First, low-enrichment pure fuel elements are loaded, while the mixed fuel elements in the core are unloaded, until the loading of low-enrichment pure fuel elements reaches A / 11; then, low-enrichment high-mixture fuel elements are loaded, while the original high-mixture fuel elements at the bottom of the core are unloaded, until the loading reaches A / 11; the above two loading actions are repeated five times, and the last time, low-enrichment pure fuel elements are loaded, while the remaining low-enrichment high-mixture fuel elements at the bottom of the core are unloaded.
[0070] Specifically, in step S2, the following actions are repeated in a loop: Add low-enrichment fuel elements to the transition core, with the amount being one-eleventh of the total loading A; Add low-enrichment, high-mixing-ratio fuel elements to the transition core, with the addition amount being one-eleventh of the total loading A; ... Add low-enrichment fuel elements to the reactor core, at a rate of one-eleventh of the total loading A; Add low-enrichment, high-mixing-ratio fuel elements to the reactor core, at a rate of one-eleventh of the total loading A; Add low-enrichment fuel elements to the reactor core, at a rate of one-eleventh of the total loading A.
[0071] During the aforementioned staggered loading process, the fuel elements already loaded in the reactor core are simultaneously unloaded until all the mixed fuel elements loaded in step S1 have been unloaded. At this point, the axial fuel loading of the reactor core is roughly divided into eleven layers, arranged in a staggered pattern of pure fuel elements, mixed fuel elements, ..., mixed fuel elements, and pure fuel elements, as shown below. Figure 2 As shown, this state, in which mixed fuel elements are still interleaved before the reactor core is fully loaded with pure low-enrichment fuel elements, is called low-enrichment fuel element preloading.
[0072] Step S3 is the transition phase from preloading low-enrichment fuel elements to full-load fuel elements. During this process, low-enrichment pure fuel elements (excluding graphite balls) are added to the core, while the mixed fuel elements already loaded in the core (staggered mixed fuel elements) are unloaded. This continues until all the low-enrichment, high-mixture fuel elements loaded in step S2 have been unloaded, and the low-enrichment fuel element loading reaches level A. At this point, the core is entirely composed of low-enrichment fuel elements, transitioning from low-enrichment preloading to full loading.
[0073] Step S4 is the transition stage from low-enrichment to high-enrichment pure fuel elements. During this process, the low-enrichment fuel elements loaded in stage S3 are first unloaded. The highest burnup 1 / n is treated as spent fuel and not returned to the core. The remaining (n-1) / n parts of the mixed 1 / n parts of high-enrichment pure fuel elements are returned to the core. This process is repeated, with the proportion of high-enrichment pure fuel elements gradually increasing until the high-enrichment element loading reaches A after the nth cycle. At this point, the core state is close to core equilibrium (S5).
[0074] Specifically, in step S4, fuel elements with low enrichment and high enrichment are added to the reactor core, and the proportion of high enrichment pure fuel elements gradually increases. At the same time, the fuel elements already loaded in the reactor core are unloaded until the low enrichment fuel elements loaded in step S3 are completely unloaded. At this point, the reactor core is composed entirely of high enrichment pure fuel elements, which is close to a balanced reactor core.
[0075] In summary, during the transition process of a pebble bed high-temperature gas-cooled reactor, by using low-enriched mixed fuel elements and pure fuel elements (excluding graphite spheres) in an alternating manner along the axial direction, a relatively uniform pre-loading state is introduced before the core is fully loaded with low-enriched fuel elements. This effectively reduces neutron field distortion and fuel density abrupt changes at the axial junction of mixed fuel elements and pure fuel elements, thereby flattening the axial power distribution, reducing core hot spots, and improving reactor safety.
[0076] During the fuel cycle in steps S1 and S2, the low-enrichment, high-mixing-ratio fuel elements have an increased number of cycles in the reactor core, longer operating time, and increased unloading burnup, which improves the reactor's economics.
[0077] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0078] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A fuel cycle method for a pebble bed type high-temperature gas-cooled reactor, characterized in that, include: Low-enrichment, high-mixing-ratio fuel elements are added to the reactor vessel, while all fuel elements already loaded in the initial core of the reactor vessel are unloaded to form a transition core. Low-enrichment fuel elements and low-enrichment high-mixing-ratio fuel elements are added sequentially into the reactor vessel. At the same time, a portion of the fuel elements at the bottom of the transition core are unloaded each time they are added. This process is repeated a first set number of times to form a preloaded core. The low-enrichment pure fuel element is added to the top of the preloaded core, while the staggered fuel elements in the preloaded core are unloaded to form a fully loaded core. Low-enrichment and high-enrichment mixed fuel elements are added to the top of the fully loaded core, while low-enrichment pure fuel elements are unloaded from the bottom of the fully loaded core. This process is repeated a second set number of times. In each cycle, the proportion of high-enrichment pure fuel elements gradually increases among the low-enrichment and high-enrichment mixed fuel elements added, thus forming a balanced core.
2. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that, The formation of the preloaded core includes: Add low-enrichment pure fuel elements to the top of the transition core while unloading a portion of the fuel elements at the bottom of the transition core; and add low-enrichment high-mixing-ratio fuel elements to the top of the transition core while unloading a portion of the fuel elements at the bottom of the transition core. The above steps are repeated a first set number of times, and on the last time, the low-enrichment pure fuel element is added to the top of the transition core, while the remaining fuel element at the bottom of the transition core is unloaded.
3. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 2, characterized in that, In the formation of the transition core, the loading amount of the low-enrichment, high-mixing-ratio fuel element is A; In the process of adding low-enrichment pure fuel elements to the top of the transition core while simultaneously unloading a portion of the fuel elements at the bottom of the transition core, the loading amount of the low-enrichment pure fuel elements added to the top of the transition core is 1 / B of A.
4. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 2, characterized in that, In the formation of the transition core, the loading amount of the low-enrichment, high-mixing-ratio fuel element is A; In the process of adding low-enrichment, high-mixing-ratio fuel elements to the top of the transition core while simultaneously unloading a portion of the fuel elements at the bottom of the transition core, the loading amount of the low-enrichment, high-mixing-ratio fuel elements added to the top of the transition core is 1 / B of A.
5. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 3 or 4, characterized in that, The first set number of times is related to the value of B.
6. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 1, wherein forming a balanced reactor core comprises: A portion of the low-enrichment pure fuel elements at the bottom of the fully loaded core are removed, and a mixture of low-enrichment and high-enrichment fuel elements is added to the top of the fully loaded core; this process is repeated a second set number of times until the loading amount of the high-enrichment pure fuel elements is the same as the loading amount of the low-enrichment low-mixing-ratio fuel elements in the initial loaded core.
7. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that, In the formation of the transition core, the loading amount of the low-enrichment, high-mixing-ratio fuel element is A; In the process of forming a balanced reactor core, after the second predetermined number of cycles, the loading amount of highly enriched pure fuel elements in the reactor vessel is A.
8. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that, In the formation of a balanced reactor core, the portion of the low-enrichment pure fuel elements discharged from the bottom of the fully loaded reactor core with the highest burnup is discharged as spent fuel, and the remaining portion is mixed with the high-enrichment pure fuel elements and then added to the top of the fully loaded reactor core.
9. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 8, characterized in that, Of the low-enrichment pure fuel elements discharged from the bottom of the fully loaded core, the 1 / n portion with the highest burnup is discharged as spent fuel, and the remaining (n-1) / n portions are mixed with 1 / n portions of high-enrichment pure fuel elements and then loaded onto the top of the fully loaded core.
10. The fuel cycle method for a pebble bed type high-temperature gas-cooled reactor according to claim 9, characterized in that, The value of n is related to the number of fuel cycles in the bed-type high-temperature gas-cooled reactor.