A fast reactor assembly with reactivity compensation function

Abstract

The application discloses a fast reactor assembly with reactivity compensation function, which comprises a metal outer sleeve, a reactivity compensation region in the metal outer sleeve and a fuel rod region outside the metal outer sleeve; the reactivity compensation region is provided with a moderator structure and a burnable poison structure; and the fuel rod region is provided with a plurality of fuel rod layers arranged in the radial direction of the metal outer sleeve from inside to outside. In the fast reactor assembly, the moderator structure and the burnable poison structure are combined to arrange, the neutron absorption capacity of the burnable poison material is ensured, the effective absorption of the residual reactivity is realized, the fast reactor assembly with the reactivity compensation function is used as a basic unit to build a small reactor core with the reactivity compensation function, the number of control rod assemblies is effectively reduced, the control rod assemblies in the reactor core are cancelled, the effective compensation of the reactivity is realized, and the safety of the reactor core is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear reactor design, and particularly relates to a fast reactor assembly with a reactivity compensation function. BACKGROUND

[0002] Metal cooled reactor refers to a fast neutron reactor system taking liquid metal (such as lead, lead bismuth, sodium, etc.) as a reactor core coolant. A long-life small metal cooled reactor (hereinafter referred to as "long-life small reactor") has a power of generally not more than 300 MWe, and can be stably operated for a long time (≥5 years) without fuel replacement or material pouring operation. The long-life small reactor is suitable for power supply, energy supply, and land mobile power supply in remote areas, isolated islands and offshore facilities, and has flexible application. Compared with water, the metal coolant has the advantages of high thermal conductivity, high boiling point, high density, etc., and through reasonable core design, the inherent safety of the core can be significantly improved. At the same time, the characteristics of long life and small size can reduce the cost of the reactor in the construction and operation process, and improve the economy. In summary, the long-life small reactor has good development potential.

[0003] A nuclear reactor generates energy through the chain fission reaction of fissile nuclides (such as 235 U) in the core. Stable operation of the nuclear reactor requires self-sustaining chain fission, that is, through control means to absorb the remaining reactivity, to maintain the core criticality, at which time the reactivity of the reactor is zero (ρ = 0). Common control means include control rods, burnable poisons, etc. Among them, the control rods absorb the remaining reactivity in the core by inserting into the core. Burnable poison control is to absorb the remaining reactivity by introducing nuclides with high neutron absorption cross section (such as 10 B, 157 Gd, etc.), which has mature application in pressurized water reactors. However, for fast reactors, the absorption cross section of traditional burnable poison nuclides is low under the fast neutron spectrum, and it is difficult to effectively absorb the reactivity, so the application is limited. Large metal cooled fast reactors have good breeding characteristics and relatively less neutron leakage, and the reactivity fluctuation in their life is small, and the core has sufficient space to arrange control rods, so the life reactivity compensation of the large metal cooled fast reactor is easy to achieve through control rods.

[0004] Compared with large metal-cooled fast reactor, the long-life small reactor is different in the life-time reactivity compensation. Firstly, the long-life requires a higher initial enrichment of the fuel in the reactor core, which results in a high residual reactivity at the beginning of the life and a large reactivity fluctuation (up to several thousand pcm) during the life. In order to effectively control the reactivity, the number of control rods needs to be increased and the value of a single control rod assembly needs to be improved. However, the small reactor is compact in space and cannot arrange a large number of control rod assemblies in the reactor core as in the large sodium-cooled fast reactor. With the limited number of control rods, the excessively high value of the control rods will cause serious power distortion in the reactor core and high safety risks: once a control rod is accidentally ejected, a large amount of reactivity will be introduced into the reactor core, which will cause a serious accident and even core meltdown. SUMMARY

[0005] In view of the foregoing problems in the prior art, the present application provides a fast reactor assembly with reactivity compensation function, which improves the neutron absorption capacity of the burnable poison in the fast reactor energy spectrum by joint arrangement of the burnable poison and the moderator, realizes effective absorption of the residual reactivity, reduces the number of control rods, especially cancels the control rod assembly in the reactor core, and achieves the purposes of effective reactivity compensation and improved safety of the reactor core.

[0006] The first aspect of the present application provides a fast reactor assembly with reactivity compensation function, which comprises a metal outer sleeve, a reactivity compensation region located in the metal outer sleeve, and a fuel rod region located outside the metal outer sleeve.

[0007] The reactivity compensation region is provided with a moderator structure and a burnable poison structure; the moderator structure comprises a moderator, and the burnable poison structure comprises a burnable poison.

[0008] The fuel rod region is provided with a plurality of layers of fuel rods arranged along the radial direction of the metal outer sleeve, and each layer of the fuel rods is formed by a plurality of fuel rods arranged at equal intervals along the circumference of the metal outer sleeve.

[0009] In an embodiment, the moderator is a metal hydride, and the burnable poison is boron carbide.

[0010] In an embodiment, the moderator is at least one of zirconium hydride, yttrium hydride and calcium hydride.

[0011] In an embodiment, the reactivity compensation region is sequentially provided with an inner cladding, the moderator structure, an air gap, the burnable poison structure and an outer cladding along the radial direction thereof, and the inner cavity of the inner cladding and the space between the outer cladding and the metal outer sleeve are both filled with a metal coolant.

[0012] In an embodiment, the metal outer sleeve has a hexagonal cross-sectional shape, and a plurality of fuel rods in each fuel rod layer are arranged in a hexagonal pattern at equal intervals outside the metal outer sleeve.

[0013] In an embodiment, in the axial direction, the fuel rod inner fuel height, the burnable poison structure burnable poison height, and the moderator structure moderator height are all the same.

[0014] The second aspect of the present application provides a small reactor core with a reactivity compensation function, comprising a core fuel assembly, which is the fast reactor assembly with a reactivity compensation function described above.

[0015] The third aspect of the present application provides a design method with a reactivity compensation function, comprising optimizing the compensation capacity of the fast reactor assembly.

[0016] In an embodiment, the burnable poison in the fast reactor assembly is boron carbide.

[0017] Optimizing the compensation capacity of the fast reactor assembly comprises the following steps: optimizing the B concentration in the boron carbide. 10

[0018] Optimizing the B concentration in the boron carbide comprises the following steps: at a certain neutron fluence level, calculating the maximum 10 B concentration under the condition as the optimized loading concentration; repeating the above calculation according to the position of the assembly and the different neutron fluence levels at different axial height positions in the assembly to obtain the B optimized loading concentration at different positions in the core. 10 The corresponding 10 B concentration as the optimized loading concentration; repeating the above calculation according to the position of the assembly and the different neutron fluence levels at different axial height positions in the assembly to obtain the B optimized loading concentration at different positions in the core. 10

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1. In the fast reactor assembly with a reactivity compensation function provided by the embodiment of the present application, the moderator structure and the burnable poison structure are jointly arranged in the reaction compensation region, the neutron absorption capacity of the burnable poison is improved by the moderation effect of the moderator, the reactivity control compensation capacity of the burnable poison is strengthened, and the effective absorption of the residual reactivity is realized.

[0021] 2. The small reactor core with a reactivity compensation function provided by the embodiment of the present application uses the fast reactor assembly with a reactivity compensation function as a fuel assembly, which can reduce the number of control rod assemblies, eliminate the control rod assemblies inside the core, realize effective compensation of reactivity, and at the same time improve the safety of the core.

[0022] ​​3、The fast reactor assembly with reactivity compensation function provided by the embodiment of the present application can be used for the combustible poison material (boron carbide) in the combustible poison structure 10 The concentration (abundance) of B can be adjusted. Based on the reactivity compensation fast reactor assembly, a small reactor core with reactivity compensation function is constructed. According to the neutron flux level of the position of the assembly in the core and the axial position in the assembly, the concentration of the partitioned combustible poison nuclide B in the assembly is matched and adjusted, so that the synchronous and uniform burnup of the core combustible poison can be ensured, and the residual penalty can be avoided. Finally, good compensation of reactivity is realized. 10 The concentration of B, so that the synchronous and uniform burnup of the core combustible poison can be ensured, and the residual penalty can be avoided. Finally, good compensation of reactivity is realized. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The structure diagram of the fast reactor assembly with reactivity compensation function provided by the present application is shown in the figure.

[0024] Figure 2 The structure diagram of the small reactor core with reactivity compensation function provided by the present application is shown in the figure.

[0025] Figure 3 The Figure 1 The calculation results of the compensation ability of different initial 10 B loading concentrations under given conditions.

[0026] Figure 4 The calculation results of the compensation ability of different initial Figure 1 The calculation results of the compensation ability of different initial eff The calculation results of the compensation ability of different initial 10 B loading concentrations (curve 2) and partitioned adjustment 10 B loading concentrations (curve 3).

[0027] In the figure: 1, fuel rod; 2, metal coolant; 3, inner cladding; 4, outer cladding; 5, air gap; 6, moderator structure; 7, combustible poison structure; 8, metal outer sleeve; 9, reflector assembly; 10, fast reactor assembly with reactivity compensation function. DETAILED DESCRIPTION

[0028] The present application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, a number of changes and improvements can be made. These all belong to the protection scope of the present application.

[0029] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0030] All the directionality indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative position relationship, motion condition, etc. between components in a certain specific posture (as shown in the drawings), and if the specific posture changes, the directionality indications will also change accordingly.

[0031] Embodiment 1

[0032] Referring to Figure 1 The embodiment provides a fast reactor assembly with a reactivity compensation function. The reactivity compensation fast reactor assembly comprises a reactivity compensation region, a metal outer sleeve 8, and a fuel rod region. The inner cavity of the metal outer sleeve 8 is the reactivity compensation region, and the fuel rod region is arranged outside the metal outer sleeve 8. The metal outer sleeve 8 is arranged as the reactivity compensation region. The reactivity compensation region is arranged with a moderator structure and a burnable poison structure. The moderator structure is made of a moderator 6, and the burnable poison structure is made of a burnable poison 7.

[0033] The fuel rod region comprises multiple layers of fuel rod layers arranged along the radial direction of the assembly. Each layer of the fuel rod layer is formed by multiple fuel rods 1 arranged at equal intervals along the circumference of the metal outer sleeve 8.

[0034] Referring to Figure 1 The reactivity compensation region is sequentially provided with an inner cladding 3, the moderator structure 6, an air gap 5, the burnable poison structure 7, and an outer cladding 4 from the inside to the outside along the radial direction thereof. The inner cavity of the inner cladding 3 and the space between the outer cladding 4 and the metal outer sleeve 8 are both filled with a metal coolant 2.

[0035] In an embodiment, the moderator structure can be an annular structure made of a moderator 6, and the burnable poison structure can be an annular structure made of a burnable poison 7.

[0036] In the reactivity compensation region, the burnable poison structure and the moderator structure are jointly arranged to improve the ability of the burnable poison to absorb neutrons through local moderation. The burnable poison material is boron carbide (B4C), and the moderator material is a metal hydride (such as zirconium hydride ZrHx, yttrium hydride YHx, calcium hydride CaHx, etc.). The B4C in the burnable poison material has a high thermal neutron absorption cross section and a low fast neutron absorption cross section. 10 The absorption cross section of the B nuclide to thermal neutrons is much larger than that to fast neutrons. The metal hydride moderator material plays a role in local neutron moderation and can increase the absorption of B to neutrons. 10 After the moderation of neutrons, the neutrons are mainly absorbed by B in the burnable poison B4C, thereby playing a role in absorbing the residual reactivity of the reactor core. 10

[0037] Referring to Figure 2 ​As shown, the combustible poison structure 7 is annularly loaded outside the outer layer, and the moderator structure 6 is annularly installed inside the combustible poison, and the volume of the moderator material can be adjusted by adjusting the inner diameter thereof.

[0038] The moderator material adopted by the present application is a metal hydride material (such as zirconium hydride ZrHx, yttrium hydride YHx, calcium hydride CaHx, etc.). This material has the characteristics of high hydrogen-containing density and large moderation ratio, and is suitable for generating good neutron moderation effect in a local area and enhancing the neutron absorption capacity of the combustible poison material. The combustible poison material adopted by the present application is boron carbide (B4C) material. The boron element in this compound contains multiple isotopes, among which 10 The B nuclides have a relatively high neutron absorption cross section, and the neutron absorption capacity thereof can be further optimized by optimizing the abundance of the B nuclides (referring to the percentage of the number of B nuclides in all B nuclides). 10 The B nuclides have a relatively high neutron absorption cross section, and the neutron absorption capacity thereof can be further optimized by optimizing the abundance of the B nuclides (referring to the percentage of the number of B nuclides in all B nuclides). 10 The B nuclides have a relatively high neutron absorption cross section, and the neutron absorption capacity thereof can be further optimized by optimizing the abundance of the B nuclides (referring to the percentage of the number of B nuclides in all B nuclides).

[0039] In this embodiment, the fuel rod 1 in the fuel assembly 2 is provided with a combustible poison structure 7 and a moderator structure 6. 235 The U enrichment degree is 11% to 19%. In order to reduce the influence of the moderator on the local power of the assembly, the inner layer fuel rod close to the metal outer sleeve is provided with a combustible poison structure 7 and a moderator structure 6. 235 The U enrichment degree is reduced to 5%.

[0040] Referring to Figure 3 As shown, the present embodiment also provides a small reactor core with a reactivity compensation function, and the internal four-ring assemblies are composed of the fast reactor assemblies 10 with the reactivity compensation function to form the core fuel assembly region.

[0041] In the fast reactor assembly 10 with the reactivity compensation function, the fuel rod inner fuel height, the combustible poison height in the combustible poison structure, and the moderator height in the moderator structure are all the same.

[0042] The fast reactor assemblies with the reactivity compensation function at different positions in the core and different axial positions in the assembly have different neutron fluence levels. The higher the neutron fluence level, the higher the requirement for the compensation capacity, and the absorption capacity can be improved by increasing the combustible poison loading (increasing the B abundance). 10 As shown in formula (1), where Σa represents 10 The B macroscopic absorption cross section can be used to measure the absorption capacity of the combustible poison, N p is the number of combustible poison nuclei, and σ a represents the microscopic absorption cross section.

[0043] ∑ a = N p σ a #(1)

[0044] However, too much10 The number of B cores will result in unused combustible poisons at the end of the core's lifespan, shortening the core's lifespan, i.e., residual penalty, which affects the reactor's economics.

[0045] on the other hand, 10 The degree of consumption of B during its lifetime is also related to the local neutron flux level, as shown in equation (2), where N p(t) / N p(0) Represents time t 10 The ratio of B nuclide quantity to lifetime quantity; σ a,eff F(t) represents the effective microscopic absorption cross section, and F(t) represents the neutron flux level.

[0046]

[0047] According to (1) and (2), for a given neutron flux level, a suitable... 10 A high B concentration ensures strong neutron absorption to enhance reactivity compensation and a relatively high consumption level to avoid residual penalty.

[0048] Furthermore, different optimal neutron flux levels can be determined accordingly. 10 B concentration. Adjust the compensatory zone for combustible toxic nucleotides accordingly. 10 The concentration of B enables effective neutron absorption of combustible poisons throughout the entire reactor core, as well as a synchronous and uniform consumption rate, avoiding residual penalties.

[0049] 10 The specific method for optimizing the B nuclide loading concentration is as follows: Based on the neutron flux level (2.61 × 10⁻⁶), 23 n / cm 2 For example, the open-source Monte Carlo program OpenMC is used to calculate different lifespans. 10 The compensation effect of combustible toxic substances at loading concentration B is as follows: Figure 3 As shown in the figure. The left vertical axis... The right-hand vertical axis represents the residual penalty level at the end of the lifespan of flammable toxins. This represents the difference in neutron absorption capacity between the beginning and end of a neutron lifetime. Under the premise of a relatively small residual penalty at the end of the lifetime, a larger difference indicates a stronger compensation capacity at the beginning of the lifetime. Figure 3 It can be seen that, with 10 As the loading concentration of B increases, ΔΣ first increases and then decreases, while the residual penalty remains constant. 10 The concentration of B increases rapidly afterward. Figure 4 The position of the middle arrow has the highest value of ΔΣ, but the residual penalty is relatively large at this point. To reduce the residual penalty at the end of life, choose The maximum ΔΣ corresponds to 10 The concentration of nuclide B is the optimal concentration.

[0050] Considering the non-uniformity of neutron fluence distribution in the core in the radial and axial directions, the optimization calculation can be repeated according to the neutron fluence level of each assembly in the radial direction of the core and the axial height of each assembly, and the optimal initial enrichment of each assembly is determined according to the neutron fluence level. 10 B loading concentration, as shown in Table 1.

[0051] Table 1 Optimal enrichment corresponding to different neutron fluences 10 B initial enrichment

[0052]

[0053] The core determined according to the above method 10 B initial enrichment loading scheme, the compensation effect calculated by the open source Monte Carlo neutron program OpenMC is as shown in Figure 4 . Figure 4 Curve 1 is the change of core reactivity during the lifetime without using compensation means, and the change value of the lifetime reactivity is about 6800 pcm; compared with the reactivity of the same core 10 B initial enrichment Figure 4 line 2), the compensation effect of the method of determining 10 B initial enrichment ​ line 3) is improved, and the residual penalty is significantly reduced, and the maximum reactivity fluctuation during the lifetime is about 570 pcm. This part of the reactivity can be compensated by fewer low-value control rods. It can be seen that the present application can effectively reduce the residual reactivity at the beginning of the lifetime by the compensation effect of the burnable poison, reduce the reactivity fluctuation during the lifetime, and finally realize the complete absorption of the residual reactivity of the core by a small number of control rod assemblies in the periphery.

[0054] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essential content of the present application. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A fast reactor assembly having a reactivity compensation function, characterized by comprising: The fast reactor assembly with the reactivity compensation function comprises a metal outer sleeve, a reactivity compensation region in the metal outer sleeve, and a fuel rod region outside the metal outer sleeve. The reactivity compensation region is provided with a moderator structure and a burnable poison structure; the moderator structure comprises a moderator, and the burnable poison structure comprises a burnable poison. The fuel rod region is provided with a plurality of fuel rod layers arranged in the radial direction of the metal outer sleeve; each fuel rod layer is formed by a plurality of fuel rods arranged in the circumferential direction of the metal outer sleeve. In the reactivity compensation region, an inner cladding, the moderator structure, an air gap, the burnable poison structure, and an outer cladding are sequentially arranged in the radial direction; the inner cavity of the inner cladding and the space between the outer cladding and the metal outer sleeve are filled with a metal coolant.

2. The fast reactor assembly having a reactivity compensation function according to claim 1, characterized by, The moderator is a metal hydride, and the burnable poison is boron carbide.

3. The fast reactor assembly having a reactivity compensation function according to claim 2, characterized by, The moderator is at least one of zirconium hydride, yttrium hydride, and calcium hydride.

4. The fast reactor assembly having a reactivity compensation function according to claim 1, characterized by, The metal outer sleeve has a hexagonal cross-sectional shape; the plurality of fuel rods in each fuel rod layer are arranged in a hexagonal pattern.

5. The fast reactor assembly having a reactivity compensation function according to claim 2, characterized by, In the axial direction, the fuel height of the fuel rods, the height of the burnable poison in the burnable poison structure, and the height of the moderator in the moderator structure are the same.

6. A small reactor core having a reactivity compensation function, characterized by comprising: The small reactor core comprises a core fuel assembly, and the core fuel assembly is the fast reactor assembly with the reactivity compensation function according to any one of claims 1-5.

7. A design method for a small-scale reactor core with reactive compensation function, characterized in that, The compensation capacity of the fast reactor assembly with the reactivity compensation function is optimized.

8. The method of designing a small reactor core with a reactivity compensation function according to claim 7, characterized by, The burnable poison in the fast reactor assembly is boron carbide. The optimization of the compensation capability of the fast reactor assembly with the reactivity compensation function includes the following steps: optimizing the B4C concentration 10 B concentration. For boron carbide 10 Optimizing the B concentration involves the following steps: at a neutron fluence level, calculating and determining... The largest under the conditions corresponding 10 B concentration is used as the optimized loading concentration; based on the location of the component in the core and the different neutron flux levels at different axial heights within the component, the above calculations are repeated to obtain the values ​​at different locations in the core. 10 B optimizes the loading concentration.

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