Core design scheme and system of irradiation production of isotopes in pebble bed high temperature gas cooled reactor with side reflector

Abstract

The present application relates to nuclear reactor isotope irradiation production technical field, disclose a kind of pebble bed high temperature gas cooled reactor side reflector irradiation production isotope core design scheme and system, wherein, design scheme includes following steps: reduce the radius of active zone of core;Keep the relative position of side reflector thickness unchanged and irradiation channel and core boundary unchanged;Adjust the equivalent height of core;Adjusting mode includes: keep the equivalent height of core unchanged or increase the equivalent height of core;Adjust the loading scheme of core, fuel management strategy and safety analysis;Adjusting mode includes at least one of the following: increase the initial enrichment of fuel element;Adjust the discharge burnup target value;Adjust the cycle parameters of fuel ball in core;When the way of adjusting the equivalent height of core is to increase the equivalent height of core, increase the fuel enrichment and increase the fuel loading simultaneously;The present application can significantly improve the thermal neutron flux in the side reflector irradiation channel, thereby improving the isotope irradiation yield and economic benefit.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor isotope irradiation production technology, specifically relating to a core design scheme and system for isotope production by irradiation of the side reflector layer of a pebble bed type high-temperature gas-cooled reactor. It is particularly suitable for significantly improving the thermal neutron flux rate in the irradiation channels of the side reflector layer by adjusting the core geometry and fuel management strategy, while ensuring the inherent safety and operational stability of the reactor, thereby increasing the isotope irradiation output and economic benefits. Background Technology

[0002] The pebble bed high-temperature gas-cooled reactor (PBR) is a representative reactor type of fourth-generation advanced nuclear energy systems. It employs fully ceramic-coated spherical fuel elements, helium cooling, and a graphite moderation structure, possessing inherent safety. Its core active zone consists of approximately 420,000 randomly stacked spherical fuel elements, surrounded by a graphite side reflector. Within the graphite side reflector, in addition to control rod channels, absorber sphere channels, and cold helium channels, there are also neutron source channels and physical start-up device detector channels. These two types of channels can be used for the irradiation production of isotope targets.

[0003] In recent years, industry and academia have increasingly focused on the technological development of isotope irradiation production using the side reflector of high-temperature gas-cooled reactors. Graphite side reflectors possess advantages such as high thermal neutron flux and a limited proportion of fast neutrons with energies higher than 6.8 MeV, which are beneficial for producing high-purity isotopes. However, the HTR-PM reactor core layout uses a design with a diameter of 3.0 m (radius 1.5 m) and an equivalent height of 11.0 m, balancing the core fuel enrichment at 8.5%, with fuel elements passing through the core an average of 15 times. In this power generation-oriented design, the irradiation apertures are located within the side reflector. Because the leakage flux of neutrons from the core to the side reflector decreases rapidly with radial distance, the thermal neutron flux at the irradiation apertures is lower than that in the core center, significantly limiting the neutron economics of isotope production. Therefore, increasing isotope yield has not yet been considered an input requirement for core design.

[0004] Currently, there is a lack of core geometry optimization schemes specifically for isotope production through irradiation of the side reflector layer in pebble bed high-temperature gas-cooled reactors. Some research, such as Chinese patent application CN202510487600.3, discloses a method and system for neutron irradiation of the side reflector layer in a pebble bed high-temperature gas-cooled reactor. This method proposes setting specific isotope irradiation channels within the side reflector layer and optimizing the channel position, size iteratively, and the arrangement of specific components based on neutron energy spectrum conditions. However, it only focuses on the design of the irradiation channels themselves, rarely addressing the optimization of the overall core dimensions (especially radial dimensions and axial height). Furthermore, there is no complete technical solution in the existing technology regarding the quantitative effect of reducing the radial dimensions of the pebble bed high-temperature gas-cooled reactor core on increasing the neutron flux of the side reflector layer, or how to compensate for the reactivity loss caused by the reduction in radial dimensions by increasing fuel enrichment, increasing core height, or adjusting fuel management strategies.

[0005] Therefore, there is an urgent need for a core arrangement scheme that can significantly increase the thermal neutron flux level at the side reflector irradiation channels and maintain the reactor safety margin through reactivity compensation and fuel management, so as to fundamentally improve the output and economic benefits of isotope irradiation production and fill the technological gap in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing high-temperature gas-cooled reactors, such as low neutron flux levels and limited isotope yields in the side reflector irradiation channels. It provides a core design scheme and system for isotope production via side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor. Through design methods that optimize core radial dimensions, arrange channel positions, compensate reactivity, and flexibly adjust axial height, the thermal neutron flux rate at the irradiation channels is significantly improved without altering the inherent safety of the reactor. This creates superior neutron field conditions for efficient irradiation production of isotope targets, thereby maximizing isotope yield and economic benefits.

[0007] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a core design scheme for isotope production by irradiation of the side reflector layer of a pebble bed type high-temperature gas-cooled reactor, comprising the following steps: Reduce the radius of the active region in the reactor core; The core active region radius of the spherical bed high-temperature gas-cooled reactor has been reduced from the existing design of 1.5m to 1.2m–1.4m. This reduction in core radius increases the leakage fraction of neutrons from the core to the side reflector, improving the thermal neutron flux rate at the same radial distance within the side reflector by 20%–40%. Compared to existing core designs primarily focused on power generation, the reduced core radius results in a smaller fuel load, and the moderate reduction in core volume does not significantly decrease the reactor safety margin. Furthermore, by optimizing neutron leakage distribution, it provides a higher pore neutron flux rate level for isotope irradiation production.

[0008] Keep the thickness of the side reflector layer and the relative position of the irradiation channel to the core boundary unchanged; The thickness of the side reflector remains the same as the original design (typically 0.75 m). The radial positions of all relevant channels, especially the neutron source channels for isotope irradiation and the detector channels for the physics activation device, are moved towards the core while maintaining a constant distance from the core active zone boundary. The neutron reflection effect of the side reflector will cause a peak in the radial distribution of the thermal neutron flux rate at a certain location from the core boundary (see...). Figure 1 By keeping the relative distance between the pores and the core boundary constant, the peak neutron flux region can be effectively utilized, and there is no need to recalibrate the relative position of the pores and the core, which is beneficial to engineering implementation.

[0009] Based on the new core dimensions and geometry, design the cold / hot helium manifold structure; With the core radius reduced and the radial position of the channels within the reflector shifted inward, the structure and dimensions of the cold and hot helium headers in the ceramic reactor internals need to be adjusted accordingly. Computational fluid dynamics methods can be used to optimize the header structure design, ensuring coolant flow uniformity, structural strength, and channel position compatibility. Specific optimization designs can be implemented based on actual conditions.

[0010] Adjust the equivalent height of the reactor core; Two methods for adjusting the equivalent core height are provided, and one method can be selected and used according to the actual situation: 1) Keep the core equivalent height unchanged: Keep the original height of 11.0m unchanged, keep the axial height of the side reflector graphite / carbon brick unchanged, and keep the axial design of the control rod channel and absorber ball channel unchanged. This method is simple to implement and has little impact on the control rod drive mechanism. 2) Increase the equivalent core height: Increase the core height to 12.0m-14.0m, increase the number of axial layers of graphite / carbon bricks in the side reflector layer, and correspondingly lengthen the axial length of the control rod channels and absorber sphere channels. This method can effectively compensate for the reduced fuel loading due to the shrinkage of radial dimensions, increase the total fuel capacity of the core, and is suitable for long-life core design requirements.

[0011] Adjust the core loading scheme, fuel management strategy, and safety analysis; Due to the reduced core radial dimensions leading to a decrease in fuel element loading and an increase in neutron leakage, one or more of the following compensation measures are adopted to ensure that the reactor has sufficient residual reactivity to maintain normal operation and shutdown margin: 1) Increase the initial enrichment of fuel elements: Increase the fuel enrichment of the balanced reactor core from the original 8.5% to 9.0%–10.5%; 2) Adjust the target value of unloading fuel consumption: appropriately reduce the average unloading fuel consumption (from the original 90GWd / tU to 80GWd / tU~85GWd / tU), and increase the refueling frequency to maintain the core reactivity level; 3) Adjust the fuel ball circulation parameters in the reactor core: increase the average number of times the fuel ball passes through the reactor core or optimize the refueling rate and cycle of the MEDUL (multiple pass through the reactor core) fuel circulation mode to achieve a more uniform burnup distribution in the fuel elements; 4) When adjusting the core equivalent height by increasing the core equivalent height, both enrichment and fuel loading should be increased for dual compensation.

[0012] The above measures use dedicated physical programs for pebble bed high-temperature gas-cooled reactors, such as VSOP and HUAKUN, to perform fuel cycle iterative calculations, ensuring that the effective multiplication factor keff of the reactor core is always greater than 1.002 throughout the design life, and that the shutdown depth meets the safety design requirements.

[0013] Secondly, the present invention provides a core design system for isotope production by irradiation of the side reflector layer of a pebble bed type high-temperature gas-cooled reactor. This system is used to implement the aforementioned core design scheme for isotope production by irradiation of the side reflector layer of a pebble bed type high-temperature gas-cooled reactor.

[0014] This system includes: Core radial dimension module: used for design calculations to optimize core diameter reduction and determine the radius of the pebble bed active region; Side reflector and channel arrangement module: used to keep the side reflector thickness constant, keep the distance between the irradiation channel and the core boundary the same, and perform the geometric design of the side reflector and channel; Manifold Adjustment Module: Used for designing cold / hot helium manifold structures based on the new core dimensions and geometry.

[0015] Core equivalent height dimension module: used for design calculations to adjust the core equivalent height; Fuel Management Module: Used to formulate core loading schemes, fuel management strategies, and safety analysis. It supports the formulation of coupled fuel management strategies such as improving enrichment, adjusting unloading burnup, and optimizing cycle number.

[0016] The present invention has the following beneficial effects: 1. This invention proposes a principle for optimizing the radial dimensions of a pebble bed-type high-temperature gas-cooled reactor core, using the optimal irradiation conditions of the neutron source channels in the side reflector as an indicator. Unlike the design approach that focuses primarily on power core design, this invention elevates isotope irradiation production requirements to one of the inputs for the overall core design. By controlling the reduction of the core radius, the thermal neutron fluence at the same radial position within the side reflector can be increased by 20% to 40%. For example, reducing the radius from 1.5m to 1.3m increases the thermal neutron fluence at the neutron source channels by approximately 32%, and the isotope yield increases by approximately 30%, resulting in significant economic benefits.

[0017] 2. This invention proposes a collaborative design method that combines core radial dimension reduction, relative maintenance of pore position, and fuel management compensation. Traditional core design often considers physics in isolation. Thermal safety limits, and this invention systematically couples core geometry adjustment, pore neutron flux utilization and refueling strategy: radial reduction increases pore neutron flux, pores maintain relative position to ensure effective irradiation area, and reactive losses are compensated by a combination of increasing enrichment or reducing unloading burnup, thereby improving isotope irradiation conditions while ensuring core design safety.

[0018] 3. This invention proposes a channel positioning principle that maintains a constant distance between the irradiation channel and the core boundary. The radial position of the irradiation channel remains unchanged relative to the core boundary. Existing irradiation target geometry, irradiation equipment, and loading / unloading processes do not require significant modifications, resulting in low engineering implementation costs. The radial distribution of thermal neutron flux within the side reflector layer exhibits a characteristic of peaking and then decaying outwards from the core boundary. By resetting the irradiation channel at the same distance outside the new core boundary, the channel can be positioned near the peak thermal neutron flux region, eliminating the need for complex neutron field recalibration and significantly improving the convenience and repeatability of engineering implementation.

[0019] 4. This invention establishes a closed-loop design process encompassing core size optimization, channel repositioning, header adaptation and adjustment, fuel management compensation, and safety assessment feedback. Starting with core radius adjustment, through channel repositioning, header structure adaptation, and fuel strategy optimization, safety verification is finally achieved through physical-thermal coupling calculations. This design process can provide a reference for the future optimization design of high-temperature gas-cooled reactors driven by isotope irradiation requirements, and can be extended to thorium-based molten salt reactors and other fourth-generation reactor types for isotope irradiation production design.

[0020] 5. This invention provides two core height adjustment methods, allowing for the selection of different neutron flux levels and irradiation time combinations based on isotope type and production cycle requirements, thereby achieving customized production solutions.

[0021] 6. This invention, by reducing the radial dimensions of the reactor core and adjusting the position of the channels within the side reflector, does not involve structural changes to the main equipment such as the reactor pressure vessel, main helium blower, and steam generator. Since the active zone of the pebble bed type high-temperature gas-cooled reactor is composed of graphite internal components, the reduction in the radial dimensions of the core and the radial movement of the channels can be achieved by adjusting the design scheme of the graphite blocks and reprocessing them. The modification of the cold / hot helium manifold uses computational fluid dynamics-aided design, which falls within the scope of conventional design. A moderate increase in fuel enrichment has precedents in my country's nuclear fuel licensing practice, and existing nuclear fuel manufacturing production lines can support the mass production of fuel with enrichment levels of 9.0% to 17%. Overall, this scheme is entirely feasible in engineering. The main incremental costs are limited to the redesign and manufacturing of graphite components and the increase in fuel costs due to the increased fuel enrichment (approximately 5% to 10%), while the benefits from the increased isotope yield can be recovered within several irradiation cycles. Furthermore, this approach can also be applied collaboratively to the irradiation production design of existing research reactors, high-flux reactors, and new reactors such as thorium-based molten salt reactors, demonstrating broad application prospects. Attached Figure Description

[0022] Figure 1 A schematic diagram of the thermal neutron flux rate peak within the side reflector; Figure 2 This is a design roadmap for a core design scheme of a pebble bed type high-temperature gas-cooled reactor for isotope production by irradiation of the side reflector layer, as described in this invention. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0024] Example: Please refer to Figure 2 This embodiment provides a core design scheme for isotope production via side reflector irradiation in a pebble bed high-temperature gas-cooled reactor, using the neutron source channels in the side reflector of the pebble bed high-temperature gas-cooled reactor demonstration project (HTR-PM) for irradiation production. 131 I target and 238 The Pu target is used as a specific implementation example to illustrate the aforementioned solution of the present invention in detail.

[0025] Step 1: Reduce the radius of the active region in the reactor core; The active zone radius of the HTR-PM reactor core was reduced from 1.5m to 1.3m. Neutron physics-burnup coupling calculations performed using the VSOP program reduced the total number of fuel elements in the core from approximately 420,000 to approximately 320,000, a reduction of approximately 24%. The total core thermal power remained at the rated 250MW, thus increasing the average power density from approximately 1.6MW / m³ to approximately 2.2MW / m³. The maximum temperature of the fuel elements was re-verified using thermal-hydrodynamic calculation programs (such as THERMIX and RELAP5-3D) to ensure it did not exceed the normal operating safety limit of 1200°C.

[0026] Step 2: Keep the thickness of the side reflector layer and the relative position of the irradiation channel and the core boundary unchanged; The original side reflector thickness was 0.75 m (from the core active zone boundary to the metal internals). After reducing the core radius, the radial coordinate of the inner boundary of the side reflector shifted inward, but the position of the outer boundary remained unchanged; therefore, the absolute thickness of the side reflector remained constant. The isotope irradiation channel, originally located 0.20 m from the original core active zone boundary, has now been adjusted to 0.20 m from the new core boundary (absolute radius = 1.3 + 0.2 = 1.5 m, close to the original radial core boundary position). Experimental and simulation data show that this radial position is precisely near the peak region of the thermal neutron fluence within the side reflector, thus allowing full utilization of the maximum neutron fluence for isotope irradiation production.

[0027] Step 3: Design the cold / hot helium manifold structure based on the new core dimensions and geometry; The original cold helium header was located within the bottom reflector layer of the reactor core, while the hot helium header was located within the top reflector layer. Due to the reduced core radius, the radial flow channels within the original headers were excessively long from the center to the outer periphery, potentially leading to uneven radial flow distribution. Computational fluid dynamics methods were used to optimize the distribution of baffles and flow dividers within the headers, strictly ensuring that the flow distribution deviation in each circumferential and radial flow channel remained within 5% to meet thermal safety design requirements.

[0028] Step 4: Adjust the equivalent height of the reactor core; This embodiment adopts an adjustment method that maintains the equivalent core height unchanged: the equivalent core height remains constant at 11.0m. Due to the reduction in radial area, the total core volume decreases, but the core height remains at the original design value. The number of graphite blocks in the side reflector layer remains unchanged. The control rod stroke and the total length of the absorber sphere channels remain unchanged, requiring no modification to the drive mechanism parameters, thus demonstrating strong engineering adaptability.

[0029] Step 5: Adjust the core loading scheme, fuel management strategy, and conduct a safety analysis; Using the VSOP program for balanced reactor core neutron physics calculations: 1) Original baseline scheme (radius 1.5m, height 11.0m, enrichment 8.5%): balanced core k eff ≈1.005, with a shutdown depth of approximately 320 pcm; 2) Calculation results after changing only the core radius (1.3m) without adjusting the fuel parameters: Due to the approximately 24% reduction in fuel loading and the increase in neutron leakage, the equilibrium core k... eff It drops to about 0.998, indicating insufficient reactivity, and cannot maintain the critical level.

[0030] 3) Increase the fuel enrichment to 9.5%, keeping other parameters unchanged: recalculate the core balance k.eff The temperature was restored to approximately 1.008, and the shutdown depth reached 350 pcm, far exceeding the design lower limit requirement. At the same time, the highest temperature of the fuel element, calculated by THERMIX, was approximately 1085°C, which is below the 1200°C operating safety limit and meets the design safety requirements.

[0031] 4) Combining 6 Coupled calculations of LiAlO2 target irradiation (high absorption cross section): The neutron energy spectrum in the side reflector layer shifts slightly towards the hot zone due to the shrinkage of the core radius, further proving that the thermal neutron flux rate at the irradiation channel is crucial to the production and conversion efficiency of isotopes.

[0032] The overall performance comparison of the solutions is shown in Table 1 below: Table 1. Comparison of Overall Performance of the Solutions

[0033] Summary of Implementation Results: Through the scheme of this embodiment, the thermal neutron flux rate at the irradiation channel increased from 3.8 × 10⁻⁶. 12 n·cm -2 ·s -1 Upgraded to 5.0×10 12 n·cm -2 ·s -1 An increase of approximately 32%. 131 I output increased from 300 Ci to approximately 390 Ci. 238 Pu production increased by approximately 31.7%, and all safety parameters met design requirements. This indicates that the proposed solution effectively improves the production output and economic benefits of isotope irradiation while maintaining the inherent safety of the high-temperature gas-cooled reactor.

[0034] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A core design scheme for isotope production by irradiation of the side reflector layer of a pebble bed type high-temperature gas-cooled reactor, characterized in that: Includes the following steps: Reduce the radius of the active region in the reactor core; Keep the thickness of the side reflector layer and the relative position of the irradiation channel to the core boundary unchanged; Adjust the equivalent height of the reactor core; the adjustment methods include: keeping the equivalent height of the reactor core unchanged or increasing the equivalent height of the reactor core; Adjust the core loading scheme, fuel management strategy, and safety analysis; the adjustment methods include at least one of the following: increasing the initial enrichment of fuel elements; adjusting the unloading burnup target value; adjusting the circulation parameters of fuel balls in the core; when adjusting the core equivalent height by increasing the core equivalent height, simultaneously increasing the fuel enrichment and increasing the fuel loading.

2. The core design scheme for isotope production by side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that: The method of reducing the radius of the active core region includes reducing the radius of the active core region to 1.2m to 1.4m.

3. The core design scheme for isotope production by side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that: The methods for increasing the equivalent height of the reactor core include increasing the core height to 12.0m to 14.0m.

4. The core design scheme for isotope production by side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that: The method for adjusting the target value of unloading fuel includes increasing the fuel enrichment of the balanced reactor core to 9.0% to 10.5%.

5. The core design scheme for isotope production by side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that: The methods for adjusting the unloading fuel consumption target value include: reducing the average unloading fuel consumption and increasing the fuel replacement frequency.

6. The core design scheme for isotope production by side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that: The methods for adjusting the circulation parameters of the fuel balls within the reactor core include: increasing the average number of times the fuel balls pass through the reactor core or optimizing the refueling rate and cycle of the MEDUL fuel circulation mode.

7. The core design scheme for isotope production by side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that: The adjusted core loading scheme, fuel management strategy, and safety analysis are used to perform iterative fuel cycle calculations to ensure the effective core value-added factor k. eff It remains greater than 1.002 throughout its design life, and the shutdown depth meets the safety design requirements.

8. The core design scheme for isotope production by side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor according to claim 1, characterized in that: The design scheme also includes the design of a cold / hot helium manifold structure based on the new core dimensions and geometry.

9. A core design system for isotope production via side reflector irradiation in a pebble bed type high-temperature gas-cooled reactor, characterized in that: The system is used to implement the core design scheme as described in any one of claims 1 to 8; The system includes: Core radial dimension module: used for design calculations to optimize core diameter reduction and determine the radius of the pebble bed active region; Side reflector and channel arrangement module: used to keep the side reflector thickness constant, keep the distance between the irradiation channel and the core boundary the same, and perform the geometric design of the side reflector and channel; Core equivalent height dimension module: used for design calculations to adjust the core equivalent height; Fuel Management Module: Used to develop core loading plans, fuel management strategies, and safety analysis.

10. A core design system for isotope production by irradiation of the side reflector layer of a pebble bed type high-temperature gas-cooled reactor, characterized in that: The system also includes: Manifold Adjustment Module: Used for designing cold / hot helium manifold structures based on the new core dimensions and geometry.

Images