A method for improving discharge burnup in a transition phase of a pebble bed high temperature reactor

Abstract

The present application relates to a kind of ball bed type high temperature reactor transition stage discharge burnup promotion method, belong to nuclear reactor technical field, including in the fuel transition circulation of ball bed type high temperature reactor body, the transition circulation includes sequentially carried out graphite ball replacement stage and fuel ball replacement stage, wherein the graphite ball replacement stage is the stage that graphite ball of initial loading of reactor core is gradually replaced by low enrichment fuel ball, the fuel ball replacement stage is the stage that low enrichment fuel ball in reactor core is gradually replaced by high enrichment fuel ball;In the graphite ball replacement stage, high enrichment fuel ball is added to reactor core, to replace at least part of originally should be added low enrichment fuel ball, to reduce the number of daily new fuel ball in the graphite ball replacement stage and the discharge number of graphite ball, prolong the duration of the graphite ball replacement stage.The present application improves the utilization rate of fuel, accelerates high temperature reactor engineering process.

Description

Technical Field

[0001] This invention relates to a method for improving fuel burnup during the transition phase of a pebble bed type high-temperature reactor, belonging to the field of nuclear reactor technology. Background Technology

[0002] Pebble bed high-temperature gas-cooled reactors have attracted widespread attention in the nuclear power field due to their inherent safety, power generation efficiency, and promising prospects for process thermal applications. In this type of reactor, the core is composed of a large number of fuel spheres and graphite spheres mixed and stacked. Through online loading and unloading without stopping the reactor, the fuel elements are continuously circulated, thereby maintaining the core criticality and flattening the power distribution.

[0003] During the fuel transition cycle, the ratio of fuel pellets to graphite pellets in the reactor core needs to be adjusted multiple times before gradually transitioning to a balanced cycle. Taking a typical pebble bed high-temperature reactor as an example, the transition process usually includes the following steps: a first transition stage in which the ratio of fuel pellets to graphite pellets gradually increases; a second transition stage in which the ratio continues to increase until the entire core consists of low-enriched fuel pellets; and a third transition stage in which low-enriched fuel pellets are gradually replaced by high-enriched fuel pellets, finally entering a balanced cycle stage where all fuel pellets are high-enriched.

[0004] During the aforementioned transition process, the third transition phase begins with the removal of low-enriched fuel balls from the reactor core. Prior to the third transition phase, only graphite balls, not fuel balls, are removed from the core. The core initially contains a large number of graphite balls, and to gradually replace them with fuel balls, new fuel balls must be continuously added to the core while an equal number of graphite balls are removed. Under rated power operating conditions, to compensate for reactivity and maintain power levels, a certain number of new fuel balls must be added to the core daily, and correspondingly, the same number of graphite balls must be removed daily. Since the required fuel ball to graphite ball replacement ratio differs in each phase, the duration of the first two transition phases is determined by the total number of core balls and the daily circulation number of balls. In the existing scheme, the combined duration of the first two transition phases is relatively short, resulting in insufficient equivalent irradiation time for the low-enrichment fuel balls discharged in the early stage of the third transition phase within the reactor core. This leads to limited burnup accumulation, which in turn results in significantly lower burnup of the low-enrichment fuel balls discharged in the early stage of the third transition phase, far below the burnup level at the end of the phase. In other words, the fuel balls discharged in the early stage of the third transition phase are discharged before they have been fully burned up within the reactor core, causing a significant decrease in fuel utilization efficiency. Therefore, improvements are urgently needed. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention designs a method for improving fuel consumption during the transition phase of a pebble bed type high-temperature reactor, which improves fuel utilization and accelerates the engineering process of high-temperature reactors.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for improving burnup during the transition phase of a pebble bed high-temperature reactor includes a graphite ball replacement phase and a fuel ball replacement phase, wherein the graphite ball replacement phase is a phase in which the graphite balls initially loaded in the reactor core are gradually replaced by low-enrichment fuel balls, and the fuel ball replacement phase is a phase in which the low-enrichment fuel balls in the reactor core are gradually replaced by high-enrichment fuel balls. During the graphite ball replacement phase, high-enrichment fuel balls are added to the reactor core to replace at least part of the low-enrichment fuel balls that would otherwise have been added, thereby reducing the number of new fuel balls added and the number of graphite balls removed each day during the graphite ball replacement phase, and extending the duration of the graphite ball replacement phase.

[0007] Furthermore, the graphite sphere replacement stage includes a first replacement sub-stage and a second replacement sub-stage; The first replacement sub-stage includes: the initial ratio of fuel balls to graphite balls in the reactor core is a first ratio; by adding low-enriched fuel balls to the reactor core and replacing the low-enriched fuel balls with high-enriched fuel balls at a set replacement ratio, and removing the graphite balls, the ratio of fuel balls to graphite balls in the reactor core is increased to a second ratio. The second replacement sub-stage includes, starting from the second ratio, continuing to add low-enrichment fuel balls to the core and replacing the low-enrichment fuel balls with high-enrichment fuel balls at a set replacement ratio of 2, and discharging graphite balls until all graphite balls are discharged.

[0008] Furthermore, the replacement ratio is determined based on the core power level and reactivity requirements, ensuring that the reactivity provided by the high-enrichment fuel balls added per unit time is not lower than the reactivity provided by the low-enrichment fuel balls that should be added per unit time in the original scheme.

[0009] Furthermore, the enrichment degree of the high-enrichment fuel ball is 1.5 to 2.5 times that of the low-enrichment fuel ball.

[0010] Furthermore, the enrichment degree of the high-enrichment fuel sphere is 8.5%; and the enrichment degree of the low-enrichment fuel sphere is 4.2%.

[0011] Furthermore, in the first substitution sub-stage, the first ratio is 7:8 and the second ratio is 10:5.

[0012] Furthermore, it also includes type identification of each ball element discharged from the reactor core, and assigning graphite balls to the unloading storage device and fuel balls to the recirculation channel.

[0013] Furthermore, the type identification is achieved through a fuel consumption measurement and positioning distributor, which simultaneously measures the fuel consumption value of the ball element.

[0014] Furthermore, it also includes storing pellets in pellet tanks via a pellet separation device during the fuel transition cycle of the pebble bed high-temperature reactor body.

[0015] Furthermore, counting point one and counting point two are sequentially set on the return circulation channel.

[0016] Compared with the prior art, the present invention has the following features and beneficial effects: This invention reduces the daily addition of new fuel balls and the amount of graphite balls discharged by replacing some low-enriched fuel balls with high-enriched fuel balls during the graphite ball replacement stage, while maintaining the same core power level. This extends the duration of the graphite ball replacement stage and the corresponding equivalent irradiation time, significantly improving unloading burnup and thus increasing the utilization rate of unloaded fuel balls. Since high-enriched fuel is used during the graphite ball replacement stage, it enters the core more than 300 days earlier, reducing the time for the high-temperature reactor to reach core equilibrium and accelerating the high-temperature reactor engineering process. The total time for the entire core to reach high-enriched fuel ball equilibrium cycle is shortened, accelerating the transition cycle process of the high-temperature reactor. Detailed Implementation

[0017] The present invention will now be described in more detail with reference to the embodiments.

[0018] A method for improving burnup during the transition phase of a pebble bed high-temperature reactor includes a graphite ball replacement phase and a fuel ball replacement phase, which are performed sequentially during the fuel transition cycle of the pebble bed high-temperature reactor. The graphite ball replacement phase is the phase in which the graphite balls initially loaded in the reactor core are gradually replaced by low-enrichment fuel balls, and the fuel ball replacement phase is the phase in which the low-enrichment fuel balls in the reactor core are gradually replaced by high-enrichment fuel balls.

[0019] In the graphite ball replacement phase, high-enrichment fuel balls are added to the reactor core to replace at least part of the low-enrichment fuel balls that should have been added, thereby reducing the number of new fuel balls added and the number of graphite balls discharged each day during the graphite ball replacement phase, and extending the duration of the graphite ball replacement phase.

[0020] As described above, in a pebble bed reactor, the total number of fuel pellets in the core remains constant during the fuel transition cycle. During the graphite pellet replacement phase, the core initially contains a large number of graphite pellets, which need to be gradually replaced with low-enriched fuel pellets. In this phase, for every new fuel pellet added to the core, one graphite pellet must be removed to maintain a constant core pellet count. Therefore, the duration of the graphite pellet replacement phase depends on the daily rate of new fuel pellet addition; a faster addition rate results in a shorter time required for all graphite pellets to be replaced, while a slower addition rate results in a longer time.

[0021] In this embodiment, high-enrichment fuel balls are added to the reactor core to replace at least part of the low-enrichment fuel balls that would otherwise be added. Since the enrichment of high-enrichment fuel balls is higher than that of low-enrichment fuel balls, that is, the reactivity provided by a single high-enrichment fuel ball is greater than that of a single low-enrichment fuel ball, the daily reactivity compensation required to maintain the core criticality state remains constant under the premise that the core power level remains unchanged. After replacing part of the low-enrichment fuel balls with high-enrichment fuel balls, the total number of new fuel balls required to be added each day can be reduced accordingly.

[0022] The reduction in the number of new fuel pellets added daily means a corresponding reduction in the number of graphite pellets discharged from the reactor core each day. With a fixed total graphite pellet load in the reactor core, the reduction in the number of graphite pellets discharged per unit time extends the time required for all graphite pellets to be replaced, thereby extending the duration of the graphite pellet replacement phase.

[0023] With the extended duration of the graphite ball replacement phase, the low-enrichment fuel balls that were originally unloaded at the beginning of the fuel ball replacement phase have an equivalent irradiation time inside the reactor core due to the extended duration of the entire graphite ball replacement phase. The longer the fuel balls operate in the reactor core, the more significant the increase in fuel burnup during unloading. Therefore, the unloading burnup of the low-enrichment fuel balls unloaded at the beginning of the fuel ball replacement phase is significantly improved, thus increasing fuel utilization. The early addition of high-enrichment fuel greatly reduces the time for the high-temperature reactor to reach core equilibrium, thereby accelerating the high-temperature reactor engineering process.

[0024] Furthermore, the graphite sphere replacement stage includes a first replacement sub-stage and a second replacement sub-stage; The first replacement sub-stage includes: the initial ratio of fuel balls to graphite balls in the reactor core is a first ratio; by adding low-enriched fuel balls to the reactor core and replacing the low-enriched fuel balls with high-enriched fuel balls at a set replacement ratio, and removing the graphite balls, the ratio of fuel balls to graphite balls in the reactor core is increased to a second ratio. The second replacement sub-stage includes, starting from the second ratio, continuing to add low-enrichment fuel balls to the core and replacing the low-enrichment fuel balls with high-enrichment fuel balls at a set replacement ratio of 2, and removing graphite balls until all graphite balls are removed.

[0025] As can be seen from the above description, in the first replacement stage, because high-enrichment fuel balls are used to replace low-enrichment fuel balls, the total number of new fuel balls added in each cycle group is less than the number of low-enrichment fuel balls that should be added in the corresponding stage of the original scheme, and the graphite ball discharge rate is reduced accordingly.

[0026] In the second replacement stage, high-enrichment fuel balls are also used to replace low-enrichment fuel balls. The replacement ratio 2 can be the same as the replacement ratio 1, or it can vary depending on the core energy requirements.

[0027] Overall, in the two sub-stages mentioned above, since the number of new fuel balls added each day is less than in the original plan, the number of graphite balls discharged from the core each day is reduced accordingly. Under the condition that the total graphite ball loading in the core is constant, the calendar time required for all graphite balls to be replaced is extended, thereby extending the duration of the graphite ball replacement stage.

[0028] Meanwhile, since the high-enrichment fuel balls are introduced into the core in the first replacement stage, the cumulative proportion of high-enrichment fuel balls in the core increases earlier, shortening the overall time required for the entire core to transition to a balanced cycle of high-enrichment fuel balls.

[0029] Furthermore, the replacement ratio is determined based on the core power level and reactivity requirements, ensuring that the reactivity provided by the high-enrichment fuel pellets added per unit time is no less than that provided by the low-enrichment fuel pellets that should have been added per unit time in the original scheme.

[0030] As described above, the fission energy required for the reactor core to operate varies depending on its power level. Higher power levels require more energy to maintain operation per unit time, while lower power levels require less. Furthermore, the burnup state of the reactor core changes continuously at different stages of the fuel transition cycle, and the total amount of fissile nuclides remaining in the core gradually decreases. To maintain a constant power output, newly added fuel pellets are needed to replenish the fission energy consumed by burnup. The current power level and reactivity requirements of the reactor core jointly determine the total fission energy required to be replenished per unit time.

[0031] Therefore, the replacement ratio must meet the requirement that the total fission energy provided by the combination of high-enrichment fuel balls and low-enrichment fuel balls added per unit time is not less than the total fission energy provided by the low-enrichment fuel balls added per unit time in the original scheme (i.e., the original transition scheme without the use of high-enrichment fuel balls as substitutes).

[0032] If the replacement ratio is too low, the total fission energy of the new fuel pellets added per unit time will not meet the energy requirements for the core to maintain the current power level, and the core power will decrease, making it impossible to maintain the rated operating state. If the replacement ratio is too high, the total fission energy of the new fuel pellets added per unit time will exceed the energy requirements for the core to maintain the current power level, and the core power will increase, exceeding the rated operating range, which may lead to the risk of over-power operation.

[0033] Therefore, the replacement ratio needs to be precisely determined based on the current power level and reactivity requirements of the reactor core, so that the total fission energy provided by the new fuel pellets added per unit time (including high-enrichment fuel pellets and the remaining low-enrichment fuel pellets) matches the total fission energy required for the reactor core to maintain its current power level. Under this matching condition, the total number of new fuel pellets added daily is effectively reduced, and correspondingly, the number of graphite pellets discharged from the reactor core daily decreases. Given a fixed total graphite pellet load in the reactor core, the calendar time required for all graphite pellets to be replaced is extended, thus extending the duration of the graphite pellet replacement phase.

[0034] Furthermore, the enrichment of high-enrichment fuel spheres is 1.5 to 2.5 times that of low-enrichment fuel spheres. Within this enrichment ratio range, the fission energy provided by a single high-enrichment fuel sphere is significantly higher than that of a single low-enrichment fuel sphere. This allows for the replacement of the fission energy provided by a larger number of low-enrichment fuel spheres with fewer high-enrichment fuel spheres, thereby effectively reducing the number of new fuel spheres added daily.

[0035] Specifically, the enrichment of the high-enrichment fuel spheres is 8.5%, while the enrichment of the low-enrichment fuel spheres is 4.2%.

[0036] Specifically, in the first substitution phase, the first ratio is 7:8 and the second ratio is 10:5.

[0037] Furthermore, it also includes type identification of each ball element discharged from the reactor core, and assigning graphite balls to the unloading storage device and fuel balls to the recirculation channel.

[0038] Type identification is achieved through a fuel consumption measurement and positioning distributor, which simultaneously measures the fuel consumption value of the ball element.

[0039] Furthermore, it also includes storing broken pellets in a pellet tank through a pellet separation device during the fuel transition cycle of the pebble bed type high-temperature reactor core. This prevents broken pellets from entering subsequent burnup measurement and positioning distributors, pneumatic conveying transmitters, and other equipment, causing equipment blockage or damage. At the same time, it prevents broken pellets from accumulating in the outer loop of the reactor core, which would affect the normal operation of the loading and unloading system.

[0040] Furthermore, counting point one and counting point two are sequentially set on the return circulation channel.

[0041] Among them, counting point one is two out of three, that is, three independent counting detectors are used to count the passing fuel balls, and only when any two or more of the three detectors detect the passing of the ball element at the same time is a valid count confirmed.

[0042] Counting point two is a two-out-of-one approach, which means that two independent counting detectors are used to count the passing fuel balls, and a valid count is confirmed when either of the two detectors detects the passing of the ball element.

[0043] By setting up counting points one and two, the reliability of counting the returned fuel balls was significantly improved.

[0044] The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor, as described in the present invention, is illustrated below with reference to specific application scenarios: Example 1 This embodiment is a comparative embodiment. It should be noted that the enrichment degree of the high enrichment fuel ball is 8.5%, which is written as high enrichment fuel ball (8.5%), and the enrichment degree of the low enrichment fuel ball is 4.2%, which is written as low enrichment fuel ball (4.2%).

[0045] In this embodiment, after the high-temperature reactor completes the initial loading, the ratio of low-enrichment fuel balls (4.2%) to graphite balls in the reactor core is 7:8, with a total of 420,000 balls. The reactor core is in rated power state (250MWt), and the reactor is loaded and unloaded without stopping.

[0046] During the fuel transition cycle, the proportion of graphite spheres in the reactor core fuel goes through three stages: the first transition stage, the second transition stage, and the third transition stage. For ease of description, the first transition stage is defined as A, the second transition stage as B, and the third transition stage as C, and finally, the equilibrium stage D is reached.

[0047] A: Low-enrichment fuel spheres (4.2%): Graphite spheres = 7:8 → Low-enrichment fuel spheres (4.2%): Graphite spheres = 10:5.

[0048] During this process, 3 parts of low-enrichment fuel balls (4.2%) are added, 3 parts of graphite balls are discharged, and 7 parts of low-enrichment fuel balls (4.2%) and 5 parts of graphite balls are circulated until the ratio of low-enrichment fuel balls (4.2%) to graphite balls is 10:5.

[0049] B: Low-enrichment fuel pellets (4.2%): Graphite pellets = 10:5 → Low-enrichment fuel pellets (4.2%) throughout the core.

[0050] During this process, 5 parts of low-enrichment fuel balls (4.2%) are added, 5 parts of graphite balls are removed, and 10 parts of low-enrichment fuel balls (4.2%) are recycled until the entire core is composed of low-enrichment fuel balls (4.2%).

[0051] C: Low-enriched fuel pellets throughout the core (4.2%) → High-enriched fuel pellets throughout the core (8.5%).

[0052] During this process, one part of high-enrichment fuel ball (8.5%) is added, one part of low-enrichment fuel ball (4.2%) is removed, and the remaining 14 parts of low-enrichment fuel balls (4.2%) are recycled until all of them are high-enrichment fuel balls (8.5%).

[0053] D: Balanced cycle, add 1 part of high enrichment fuel ball (8.5%), remove 1 part of high enrichment fuel ball (8.5%), and recycle the remaining 14 parts of high enrichment fuel balls (8.5%).

[0054] In Phase C, low-enrichment fuel pellets (4.2%) begin to be unloaded from the reactor core. By the end of Phase C, all low-enrichment fuel pellets (4.2%) have been unloaded. At the beginning of Phase C, the unloading burnup of low-enrichment fuel pellets (4.2%) is about 20 GWD / tU. At the end of Phase C, the unloading burnup of low-enrichment fuel pellets (4.2%) is about 55 GWD / tU.

[0055] It is evident that at the beginning of stage C, the fuel consumption of the low-enrichment fuel balls (4.2%) was less than half that at the end of stage C, meaning that the fuel balls were not fully utilized at the beginning of stage C.

[0056] In actual operation, after the initial core loading is completed, according to the actual operating data, in Phase A, when the reactor is stable at 200MW (hot helium temperature 570℃, main steam temperature about 520℃), the number of fuel cycle balls per day is about 5000, and the number of new low enrichment fuel balls (4.2%) added to the core per day is 5000 × (3 / 15) = 1000 (balls / day). Therefore, the operating time of Phase A is 420,000 / (5000 / day) = 84 days.

[0057] In Phase B, at the same power level, assuming the same number of new low-enrichment fuel balls (4.2%) added to the core each day (1000 balls), the average number of fuel balls circulated per day in Phase B is 1000 ÷ (5 / 15) = 3000 (balls / day), and the duration of Phase B is 420,000 / (3000 / day) = 140 days.

[0058] The total time for Phase A and Phase B was 84 days + 140 days = 224 days.

[0059] In this embodiment, the equivalent irradiation time of the low-enrichment fuel balls unloaded in the early stage of C is about 336 days in the reactor core [224 days + 112 days (equivalent operating time of initial loading)].

[0060] Example 2 In this embodiment, under 200MW operating conditions, based on theoretical calculations or operational data, the number of new low-enrichment fuel balls (4.2%) added daily is 1000. According to the principle of energy conservation (i.e., the reactivity is the same before and after), if the low-enrichment fuel balls (4.2%) are replaced with high-enrichment fuel balls (8.5%), then the number of fuel balls to be added daily is approximately 500 high-enrichment fuel balls (8.5%).

[0061] The graphite balls in the initial charge [low enrichment fuel balls (4.2%): graphite balls = 7:8] are replaced at a ratio of 2 / 15. That is, for every 15 balls in the cycle, 2 high enrichment fuel balls (8.5%) are added and 2 graphite balls are removed (this is the same in both stages A and B, i.e., the first ratio and the second ratio are the same). The number of cycles per day is 500 / (2 / 15) = 3750. The core cycle time is 420,000 / 3750 = 112 days. Each cycle (112 days) can replace 2 graphite balls. To replace all 8 graphite balls, it is necessary to cycle 8 ÷ 2 / cycle = 4 times. Each cycle takes 112 days. The time to replace all 8 / 15 of the graphite balls in the initial charge with high enrichment fuel balls (8.5%) in 4 cycles is 112 × 4 = 448 days.

[0062] Compared to 224 days in Example 1, this adds 448 days - 224 days = 224 days, which not only reduces the number of fuel balls added each day, but also extends the time for all graphite balls to be unloaded.

[0063] Meanwhile, in this embodiment, the initial unloading fuel consumption of the low enrichment fuel balls (4.2%) in stage C is approximately 33 GMD / tU, which is a significant improvement compared to 20 GMD / tU in Example 1.

[0064] Meanwhile, in this embodiment, the equivalent irradiation time of the low-enrichment fuel balls unloaded in the early stage of C within the reactor core is approximately 560 days [448 days + 112 days (equivalent operating time of initial loading)], which is significantly longer than the 336 days in Embodiment 1.

[0065] The working principle of this invention is as follows: In a pebble bed high-temperature reactor, the total number of fuel pellets in the core remains constant during the fuel transition cycle. During the graphite pellet replacement phase, the core initially contains a large number of graphite pellets, which need to be gradually replaced with low-enriched fuel pellets. In this phase, for every new fuel pellet added to the core, one graphite pellet is correspondingly removed to maintain a constant number of pellets in the core. Therefore, the duration of the graphite pellet replacement phase depends on the daily rate of addition of new fuel pellets; the faster the addition rate, the shorter the time required for all graphite pellets to be replaced, and the slower the addition rate, the longer the time required.

[0066] By adding high-enriched fuel balls to the reactor core to replace at least part of the low-enriched fuel balls that would otherwise be added, the reactivity provided by a single high-enriched fuel ball is greater than that of a single low-enriched fuel ball. Therefore, under the premise of constant core power level, the daily reactivity compensation required to maintain the core criticality state remains constant. After replacing part of the low-enriched fuel balls with high-enriched fuel balls, the total number of new fuel balls required to be added each day can be reduced accordingly.

[0067] The reduction in the number of new fuel pellets added daily means a corresponding reduction in the number of graphite pellets discharged from the reactor core each day. With a fixed total graphite pellet load in the reactor core, the reduction in the number of graphite pellets discharged per unit time extends the time required for all graphite pellets to be replaced, thereby extending the duration of the graphite pellet replacement phase.

[0068] With the extended duration of the graphite ball replacement phase, the low-enrichment fuel balls that were originally unloaded at the beginning of the fuel ball replacement phase have an equivalent irradiation time inside the reactor core due to the extended duration of the entire graphite ball replacement phase. The longer the fuel balls operate in the reactor core, the more significant the increase in fuel burnup during unloading. Therefore, the unloading burnup of the low-enrichment fuel balls unloaded at the beginning of the fuel ball replacement phase is significantly improved, thus increasing fuel utilization. The early addition of high-enrichment fuel greatly reduces the time for the high-temperature reactor to reach core equilibrium, thereby accelerating the high-temperature reactor engineering process.

[0069] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0070] Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor, characterized in that: During the fuel transition cycle of the pebble bed high-temperature reactor core, the transition cycle includes a graphite ball replacement stage and a fuel ball replacement stage performed sequentially. The graphite ball replacement stage is the stage in which the graphite balls initially loaded in the core are gradually replaced by low-enrichment fuel balls, and the fuel ball replacement stage is the stage in which the low-enrichment fuel balls in the core are gradually replaced by high-enrichment fuel balls. During the graphite ball replacement phase, high-enrichment fuel balls are added to the reactor core to replace at least part of the low-enrichment fuel balls that would otherwise have been added, thereby reducing the number of new fuel balls added and the number of graphite balls removed each day during the graphite ball replacement phase, and extending the duration of the graphite ball replacement phase.

2. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 1, characterized in that: The graphite sphere replacement stage includes a first replacement sub-stage and a second replacement sub-stage; The first replacement sub-stage includes: the initial ratio of fuel balls to graphite balls in the reactor core is a first ratio; by adding low-enriched fuel balls to the reactor core and replacing the low-enriched fuel balls with high-enriched fuel balls at a set replacement ratio, and removing the graphite balls, the ratio of fuel balls to graphite balls in the reactor core is increased to a second ratio. The second replacement sub-stage includes, starting from the second ratio, continuing to add low-enrichment fuel balls to the core and replacing the low-enrichment fuel balls with high-enrichment fuel balls at a set replacement ratio of 2, and discharging graphite balls until all graphite balls are discharged.

3. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 2, characterized in that: The replacement ratio is determined based on the core power level and reactivity requirements, ensuring that the reactivity provided by the high-enrichment fuel pellets added per unit time is no less than that provided by the low-enrichment fuel pellets that should have been added per unit time in the original scheme.

4. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 1, characterized in that: The enrichment level of the high-enrichment fuel sphere is 1.5 to 2.5 times that of the low-enrichment fuel sphere.

5. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 4, characterized in that: The high-enrichment fuel pellets have an enrichment of 8.5%; the low-enrichment fuel pellets have an enrichment of 4.2%.

6. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 2, characterized in that: In the first substitution sub-stage, the first ratio is 7:8 and the second ratio is 10:

5.

7. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 1, characterized in that: It also includes type identification of each ball element discharged from the core, and assigning graphite balls to the discharge storage device and fuel balls to the return circulation channel.

8. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 7, characterized in that: The type identification is achieved through a fuel consumption measurement and positioning distributor, which simultaneously measures the fuel consumption value of the ball element.

9. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 1, characterized in that: It also includes storing pellets in pellet tanks through a pellet separation device during the fuel transition cycle of the pebble bed high-temperature reactor body.

10. The method for improving fuel consumption during the transition stage of a pebble bed type high-temperature reactor according to claim 1, characterized in that: The return circulation channel is equipped with counting point one and counting point two in sequence.