A fuel and method for increasing the neutron source strength in a nuclear reactor

Abstract

The application provides a fuel and a method for increasing the neutron source intensity of a nuclear reactor, wherein the abundance of O in the fuel is 1% to 50% 18 O is 1% to 50%, and alpha particles and the enriched 18 O can significantly enhance the initial neutron source intensity of a nuclear reactor core in a pressurized water nuclear power plant, and help to improve the start-up performance and reduce the dependence on external neutron sources. In the passive start-up mode without using an external neutron source, the application improves the isotope abundance of O in the fuel, and improves the (alpha, n) reaction neutron source in the nuclear reactor core in the pressurized water nuclear power plant. 18 O in the fuel, and improves the isotope abundance of O in the fuel, and improves the (alpha, n) reaction neutron source in the nuclear reactor core in the pressurized water nuclear power plant.

Description

Technical Field

[0001] This application relates to the field of passive reactor start-up technology, and more particularly to a fuel and method for increasing the neutron source intensity in a nuclear reactor. Background Technology

[0002] Currently, pressurized water reactor nuclear power plants commonly employ external neutron source startup during the fuel loading and startup phase. These primarily include primary neutron sources that spontaneously generate neutrons (such as californium-252) and secondary neutron sources that produce neutrons after activation by in-reactor irradiation (such as antimony-beryllium). However, external neutron source startup presents significant cost and safety risks: primary neutron sources ( 252 The production cost of Cf is extremely high, with a price of $100 million per gram; secondary neutron sources (Sb-Be) pose risks of pollution and maintenance. Therefore, research on passive reactor start-up technology has gradually emerged, which achieves passive start-up through three technical paths: optimizing the start-up process, improving detection efficiency, and increasing source intensity. Among these, increasing source intensity is the mainstream technical direction, and its neutron sources are mainly divided into three categories: spontaneous fission neutron sources, (α,n) reaction neutron sources, and delayed neutron sources.

[0003] However, in current pressurized water reactor nuclear power plant fuel loading and start-up phases, there are two main engineering applications: one is to introduce burnt-out fuel assemblies or spent fuel assemblies to increase the spontaneous fission neutron source term; the other is to use a secondary neutron source (Sb-Be) to enhance the source intensity. Among these, the method of increasing the spontaneous fission neutron source intensity by introducing burnt-out fuel assemblies or spent fuel assemblies has already been implemented in passive start-up methods without external neutron sources, while the proportion of neutrons produced by (α,n) reactions is relatively small. Summary of the Invention

[0004] To address the problems existing in the above-mentioned technologies, this application proposes a fuel and method for increasing the neutron source intensity in a nuclear reactor.

[0005] The first aspect of this application proposes a fuel for increasing the neutron source intensity in a nuclear reactor, wherein the fuel contains... 18 The abundance of O ranges from 1% to 50%.

[0006] In some embodiments of this application, the fuel contains 18 The abundance of O was 1%, 10%, 20%, 30%, 40%, or 50%.

[0007] In some embodiments of this application, the fuel is a fuel rod. 18 O is uniformly enriched in the fuel rods, so that the neutrons produced by the (α,n) reaction are uniformly distributed in the axial and radial directions of the reactor core.

[0008] In some embodiments of this application, the fuel rod is UO2 enriched to 3%.

[0009] In some embodiments of this application, 18 In the range of O abundance from 1% to 50%, the neutron yield of the (α,n) reaction in the nuclear reactor is related to... 18 The abundance of O showed a significant linear positive correlation.

[0010] In some embodiments of this application, the fuel contains an alpha emitter to provide a continuous source of alpha particles.

[0011] In some embodiments of this application, the α emitter is 238 U、 239 Pu or 241 At least one of Am.

[0012] The second aspect of this application proposes a method for increasing the neutron source intensity in a nuclear reactor, using the fuel described in any of the above embodiments as the nuclear reaction fuel for a pressurized water reactor nuclear power plant.

[0013] In some embodiments of this application, uranium-series or plutonium-series heavy nuclides undergo alpha decay in the nuclear reaction of the pressurized water reactor nuclear power plant to generate alpha particles, which then react with... 18 O reacts to produce neutrons.

[0014] In some embodiments of this application, the nuclear reaction equations are as follows: .

[0015] In summary, the fuel and method for increasing the neutron source intensity in a nuclear reactor proposed in this application have the following technical advantages compared to related technologies:

[0016] (1) High technical feasibility and wider adaptability: By improving 18 O abundance can directly increase the neutron source intensity during the reactor startup phase, significantly improve the startup neutron flux rate, and provide core support for critical ignition. The technical path is clear and easy to implement in engineering. Compared with the secondary neutron source (Sb-Be), which requires 2-3 months of in-reactor irradiation activation and cannot be used in the first cycle, this application does not require pre-activation and can be directly adapted to the reactor's full-cycle startup requirements.

[0017] (2) Excellent stability and significant economic benefits: The method adopted in this application 18 O is a stable isotope with no time decay in neutron production capacity, ensuring long-term stable start-up requirements; it avoids the source strength decay problem of burnup / spent fuel assembly and also solves the problem of secondary neutron source attenuation. 124 Sb (with a half-life of about 60 days) causes the source intensity to decay rapidly after the reactor is shut down, requiring repeated irradiation to reactivate it. At the same time, it does not require the design of dedicated source rods or the occupation of core grids like secondary neutron sources, and it also eliminates the special handling process of radioactive components during refueling, which greatly reduces operation and maintenance costs and the pressure of radioactive waste disposal.

[0018] (31) Uniform spatial distribution, safe and precise start-up: 18 O is uniformly enriched in the fuel rods, ensuring a uniform axial and radial distribution of neutrons generated by the (α,n) reaction within the reactor core. This avoids instrument response distortion caused by uneven neutron distribution in irradiated components and overcomes the drawback of secondary neutron sources being significantly affected by core flux distribution (e.g., insufficient source strength due to low flux rate at the bottom of the core). Furthermore, all fuel rods in the core are enriched with O. 18 O, with comprehensive neutron coverage and no blind spots, simplifies the determination of neutron counting sources, reduces the complexity of critical state analysis, and ensures a safe and controllable startup process.

[0019] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application, and do not constitute an undue limitation of this application.

[0021] Figure 1 An embodiment of this application is proposed 18 Figure showing the variation of neutron source intensity with burnup depth at natural abundance of O; Figure 2 Different embodiments proposed in this application 18 The effect of O abundance on neutron source intensity; Figure 3 Different embodiments proposed in this application 18 Comparison of neutron source strength at O ​​abundance; Figure 4 Different embodiments proposed in this application 18 The effect of O abundance on the (α,n) neutron source intensity is shown in the diagram. Figure 5 Different embodiments proposed in this application 18 Figure showing the effect of O abundance on the intensity of spontaneous fission neutron sources; Figure 6 An embodiment of this application proposes a (α,n) neutron source intensity and different 18 A graph showing the relationship between O abundance and O content. Detailed Implementation

[0022] Embodiments of this application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments are described below with reference to the accompanying drawings.

[0023] This application addresses the following related technologies: Currently, pressurized water reactor nuclear power plants commonly employ external neutron source startup during the fuel loading and startup phase. These primarily include primary neutron sources that spontaneously generate neutrons (such as californium-252) and secondary neutron sources that produce neutrons after in-reactor irradiation activation (such as antimony-beryllium). However, external neutron source startup presents significant cost and safety risks: primary neutron sources ( 252 The production cost of Cf is extremely high, with a price of $100 million per gram; secondary neutron sources (Sb-Be) pose risks of pollution and maintenance. Therefore, research on passive reactor start-up technology has gradually emerged, with the core approach being to achieve passive start-up through three technical paths: optimizing the start-up process, improving detection efficiency, and increasing source intensity. Among these, increasing source intensity is the mainstream technical direction, and its neutron sources are mainly divided into three categories: spontaneous fission neutron sources, (α,n) reaction neutron sources, and delayed neutron sources.

[0024] However, the current fuel loading and start-up phases of pressurized water reactor nuclear power plants fall into two categories in specific engineering applications: one is to introduce burnt-out fuel assemblies or spent fuel assemblies to increase the spontaneous fission neutron source term; the other is to use a secondary neutron source (Sb-Be) to enhance the source intensity. The burnt-out / spent fuel assembly scheme utilizes actinide nuclides with high spontaneous fission activity within the assembly (such as...). 240 Pu、 242 (Cm, etc.) to increase neutron flux during the start-up phase, but the following key problems exist: (1) Significant and uncontrollable source strength decay: The core defect is that the spontaneous fission nuclides in the components have short half-lives, and the source strength decays significantly over time; during long-term refueling and overhaul of the reactor, the source strength may decay to the lower limit of instrument detection, posing a safety risk to the next start-up. (2) Uneven spatial distribution leads to instrument response distortion: The neutron flux distribution of the irradiated components has inherent non-uniformity, with large gradients in the axial and radial directions, affecting the accuracy of instrument detection. (3) Detection blind zone exists and data analysis is complex: In the early stage of loading new fuel, a few irradiated components act as point sources, which are difficult to fully cover the entire core, forming a detection blind zone; during the subsequent start-up process, it is impossible to effectively distinguish whether the neutron count comes from external source breeding or the core's own critical chain reaction, increasing the difficulty of data analysis.

[0025] Although the secondary neutron source (Sb-Be) scheme is a commonly used source intensity enhancement method both domestically and internationally, it has prominent drawbacks, including: (1) limited startup and use: it requires 2-3 months of in-reactor irradiation for activation. 124 Sb cannot be used directly in the first loop; and 124 Sb has a half-life of only about 60 days, and the source intensity decays rapidly after reactor shutdown, requiring repeated irradiation for activation. (2) High radioactive risk: Activation produces a gamma-ray source. 124 Sb readily generates tritium during irradiation. 3H), increasing the pressure of radioactive waste treatment and discharge. (3) High operation and maintenance and design costs: Special design of neutron source rod assemblies is required, occupying core grid space; special treatment of radioactive assemblies is required during refueling, and the operation and maintenance process is complicated. Therefore, in the passive start-up mode without using external neutron sources, the method of increasing the spontaneous fission neutron source intensity by introducing burnup fuel assemblies or spent fuel assemblies has been realized, while the proportion of neutrons produced by (α,n) reaction is relatively small.

[0026] Therefore, this application proposes a fuel and method to increase the neutron source intensity in a nuclear reactor, by enhancing the neutron source intensity of the fuel. 18 The isotopic abundance of O increases the concentration of oxygen in the reactor. Reaction neutron source.

[0027] The following section, with reference to the accompanying drawings, provides a detailed description of a fuel and method for increasing the neutron source intensity in a nuclear reactor, as provided in this application.

[0028] The first aspect of this application proposes a fuel for increasing the neutron source intensity in a nuclear reactor, wherein the fuel contains... 18 The abundance of O ranges from 1% to 50%.

[0029] Among related technologies, methods to increase the spontaneous fission neutron source intensity by introducing burnt-out fuel assemblies or spent fuel assemblies in passive start-up methods without using an external neutron source have been achieved, but the proportion of neutrons produced by (α,n) reactions is relatively small. This application aims to increase the neutron intensity of the fuel by... 18 The isotopic abundance of O increases the (α,n) neutron source in the reactor. In pressurized water reactor nuclear power plants, heavy nuclides such as uranium and plutonium undergo α decay (e.g., α-decay). 238 U、 239 Pu、 241 The decay chain of nuclides such as Am produces alpha particles, which then react with... 18 The reaction that produces neutrons is represented by the following nuclear reaction equation: .

[0030] In the known natural world 18 The natural abundance of O is approximately 0.205%. If isotope separation techniques are used to... 18 The abundance of O2 was enriched to 1%-50%, which, considering technical feasibility and cost, is not excessively expensive. Alpha particles and enriched... 18 The O-reaction (α,n) can significantly enhance the initial neutron source intensity of the new reactor core, which helps improve startup performance and reduce dependence on external neutron sources.

[0031] For example, in some embodiments of this application, the fuel 18 The abundance of O is 1%, 10%, 20%, 30%, 40%, or 50%. The fuel is fuel rods. 18O is uniformly enriched in the fuel rods, ensuring a uniform distribution of neutrons produced by the (α,n) reaction along both the axial and radial directions of the reactor core. For example, to further increase the neutron yield of the (α,n) reaction in a pressurized water reactor nuclear power plant, α emitters can be incorporated into the new fuel, thereby providing a continuous source of α particles. The α emitter is... 238 U、 239 Pu or 241 At least one of Am, for example, in some embodiments of this application, the fuel rod is UO2 enriched at 3%.

[0032] In some embodiments of this application, 18 In the range of O abundance from 1% to 50%, the neutron yield of the (α,n) reaction in the nuclear reactor is related to... 18 The abundance of O showed a significant linear positive correlation.

[0033] The second aspect of this application proposes a method for increasing the neutron source intensity in a nuclear reactor, using the fuel in any of the above embodiments as the nuclear reaction fuel for a pressurized water reactor nuclear power plant.

[0034] In pressurized water reactor nuclear power plants, uranium-series or plutonium-series heavy nuclides undergo alpha decay during nuclear reactions, producing alpha particles. These alpha particles then interact with... 18 The reaction produces neutrons, and the nuclear reaction equation is as follows: .

[0035] The (α,n) reaction neutron source in the reactor is mainly composed of α particles and... 18 O reacts, and oxygen in nature... 18 The abundance of O is only 0.205%, therefore this application improves the abundance of O by increasing the abundance of O. 18 By examining the abundance of O and observing its impact on neutron source intensity, the research results can provide insights for reactor fuel rod design. 18 The optimal selection of O abundance provides data support and theoretical reference.

[0036] According to authoritative data released by the International Union of Pure and Applied Chemistry (IUPAC), the standard abundances of various stable isotopes of oxygen are as follows: 16 The abundance of O was 99.757%; 17 The abundance of O was 0.038%; 18 The abundance of O was 0.205%. In this embodiment, UO2 fuel rods with a 3% enrichment were used for the experiment. 18 The abundance of O was set as a multi-gradient variable, and the 0.205% natural abundance was set as the baseline group. Comparative calculations were performed to clarify the correlation between its abundance and the intensity of the in-reactor neutron source. Correspondingly... 18 The fuel rods with O abundance are shown in Table 1.

[0037] Table 1 Fuel rods corresponding to 18 O abundance

[0038] This embodiment uses the Reactor Monte Carlo Code (RMC) reactor physics analysis program, independently developed by the REAL Laboratory of the Department of Engineering Physics at Tsinghua University, to calculate burnup, and then uses SOURCES 4C (Version 4C of the SOURCES code system) to calculate neutron source strength. The specific calculation results are as follows: 18 The variation of neutron source intensity with burnup depth at natural abundance (0.205%), and the observation of the variation of neutron source intensity with fuel rod concentration in experimental groups 2-7 at the same burnup depth. 18 As the abundance of O increases, the total neutron source intensity in the nuclear reactor is calculated, and the results are as follows: Figures 1-2 Among them, when the fuel rods are in 18 When the O abundance reaches 10%, with increasing burnup depth, the neutron yield of the (α,n) reaction gradually surpasses that of spontaneous fission; and 18 With the further increase in O abundance, (α,n) reaction neutrons gradually became the dominant source of neutrons in the reactor.

[0039] Based on this, this application integrates the calculation results of fuel rods with different abundances into the same figure and conducts a systematic comparative analysis, such as... Figure 3 As shown, where by Figure 3 It can be seen that, under the same burn-out depth, as 18 As the O abundance increases, the total neutron source intensity in the nuclear reactor gradually increases.

[0040] Further analysis of the fuel rods 18 The abundance of O affects the reactor interior. The effects of the reaction on neutron yield and on the intensity of the spontaneous fission neutron source are shown in the following results. Figure 4 and Figure 5 ,from Figure 4 and Figure 5 The data analysis results show that the improvement 18 The abundance of O affects the reactor interior. The reaction has a significant moderating effect on neutron yield, but almost no effect on the spontaneous fission neutron production rate. Therefore, in fuel rods... 18 During the process of O abundance increasing in an equal gradient, The neutron yield of the reaction also showed a similar increasing trend, therefore the reactor's neutron yield... The neutron source strength of the reaction is related to that in the fuel rod. 18There is a clear linear correlation between the abundance of O. Under the same burnup depth, the (α,n) neutron source intensity in the nuclear reactor also increases with the abundance of O in the fuel rods. 18 O abundance increases linearly with increasing abundance, such as Figure 6 As shown, in 18 Within the O abundance range of 0.205%-50%, the neutron yield of (α,n) reactions is related to... 18 O enrichment showed a significant linear positive correlation. Therefore, all the above examples demonstrate that improving the enrichment of O in fuel rods... 18 The abundance of O can effectively increase the (α,n) reaction neutron source intensity in the new reactor core of a pressurized water reactor nuclear power plant.

[0041] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this application can be achieved, and this is not limited herein.

[0042] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A fuel for increasing the neutron source intensity in a nuclear reactor, characterized in that, The fuel 18 The abundance of O ranges from 1% to 50%.

2. The fuel according to claim 1, characterized in that, The fuel 18 The abundance of O was 1%, 10%, 20%, 30%, 40%, or 50%.

3. The fuel according to claim 1, characterized in that, The fuel is a fuel rod. 18 O is uniformly enriched in the fuel rods, so that the neutrons produced by the (α,n) reaction are uniformly distributed in the axial and radial directions of the reactor core.

4. The fuel according to any one of claims 1-3, characterized in that, The fuel rods are enriched with 3% UO2.

5. The fuel according to any one of claims 1-3, characterized in that, 18 In the range of O abundance from 1% to 50%, the neutron yield of the (α,n) reaction in the nuclear reactor is related to... 18 The abundance of O showed a significant linear positive correlation.

6. The fuel according to claim 1, characterized in that, The fuel contains an alpha emitter to provide a continuous source of alpha particles.

7. The fuel according to claim 6, characterized in that, The α emitter is 238 U、 239 Pu or 241 At least one of Am.

8. A method for increasing the neutron source intensity in a nuclear reactor, characterized in that, The fuel according to any one of claims 1-7 is used as the nuclear reaction fuel in a pressurized water reactor nuclear power plant.

9. The method according to claim 8, characterized in that, In the nuclear reaction of the pressurized water reactor nuclear power plant, uranium-series or plutonium-series heavy nuclides undergo alpha decay to generate alpha particles, which then react with... 18 O reacts to produce neutrons.

10. The method according to claim 9, characterized in that, The nuclear reaction equation is as follows: .

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