CN113593730B - A Non-Uniform MA Transmutation Rod Used in Fast Neutron Reactors - Google Patents

Abstract

The invention discloses a non-uniform MA transmutation rod used in a fast neutron reactor, which comprises: a fuel rod main body, the outside of which is provided with a MA nuclide coating or a mixed coating of MA nuclide and ⁶ LiD. The present invention arranges MA coating or the mixed coating of MA and ⁶ LiD on the outside of the fuel rod, due to the addition of ⁶ LiD, thermal neutrons can be converted into fast neutrons of 14MeV, and then the neutrons in the core can be improved. Therefore, the non-uniform MA transmutation rod for fast neutron reactors provided by the present invention deepens the burnup depth and improves the transmutation rate of MA nuclides.

Description

A Non-Uniform MA Transmutation Rod Used in Fast Neutron Reactors

technical field

The invention belongs to the technical field of nuclear reactor components, and more specifically, the invention relates to a non-uniform MA transmutation rod used in a fast neutron reactor.

Background technique

Nuclear energy is a new type of energy. Although nuclear energy facilitates our life, the accompanying radioactive nuclear waste seriously threatens the natural environment and human safety. Nuclear waste refers to useless materials that spontaneously produce α, β, and γ radiation and emit heat. The sources of nuclear waste are various, and there are roughly the following situations: (1) The processing and treatment of uranium ore before it is used as fuel and Nuclear industry front-end processing (2) Operation of various reactors (3) Decommissioning of nuclear equipment. Nuclear waste can be simply divided into two types: low-level radioactive waste and high-level radioactive waste.

High-level waste has extremely high radioactivity and is extremely harmful. The main components of high-level waste are actinides, of which a small amount of long-lived actinides such as ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, and ²⁴⁵ Cm Minor actinides are called minor actinides ^[8] . Because of their high radioactivity and long half-life, minor actinides cause serious harm to the environment, so they are the most difficult type of nuclear waste to deal with. Through ordinary geological deep Buried storage is likely to cause great safety hazards. Studies have shown that deep burial through glass or ceramic solidification can only ensure that nuclear waste will not leak for 100 years. Because minor actinide nuclides have a long decay cycle, the The handling of nuclides needs to consider other methods, and the minor actinides are also highly radioactive, and once leaked, it will be extremely harmful. There are already better treatment methods for low- and medium-level radioactive waste, and the disposal methods for high-level radioactive waste are still under development. The main characteristics of high-level radioactive waste are long duration of radioactivity and high toxicity of nuclides. The radioactive specific activity of high-level waste is greater than 3.7×10 ⁹ Bq/L. Among the minor actinide nuclides, Np-237 has a half-life of more than 100,000 years. Once these radionuclides enter the biosphere, they will be extremely harmful, and they cannot be degraded or eliminated by ordinary physical, chemical or biological methods. They can only rely on their own radioactive decay to slowly reduce their harm, and the substances produced by radioactive decay pass through the human body. When it is exposed, it will cause ionization, cause radiation damage, and increase the risk of cancer in the human body. It will take thousands, tens of thousands of years or even longer for high-level radioactive waste to become harmless. Therefore, once the high-level radioactive waste is not handled well and leaks, the impact on the environment will be serious and far-reaching.

Separation and transmutation technology is to separate the high-level radioactive waste and long-lived nuclide produced by the reactor to make targets, and have a nuclear reaction with neutrons in the reactor or neutron accelerator. The nuclear reaction may be a fission reaction, or it may be a neutron capture, conversion Short-lived nuclides or stable nuclides can reduce radioactive hazards.

Nuclear weapons were studied in the 1940s, and nuclear power was used to generate electricity ten years later. In the 1960s, a large amount of radioactive waste produced by nuclear reactions was accumulated. There is no reasonable disposal method for high-level radioactive waste. Therefore, scientists proposed many schemes such as deep burial geological disposal, Antarctic ice disposal, cosmic disposal, separation-transmutation, etc. In the 1870s, there was an upsurge of separation-transmutation of high-level radioactive waste. However, due to the defects of equipment and technology at that time, separation-transmutation was difficult to realize and the cost was high. The research on separation-transmutation technology showed a trough. From the 1980s to the present, separation-transmutation technology has regained attention for the following reasons:

(1) There are a large number of fissile nuclides and fissile nuclides in high-level radioactive waste. Separation-transmutation technology can make good use of this part of resources

(2) With the development of science and technology, the separation-transmutation technology has gradually become possible, such as extraction separation technology and ion exchange technology.

(3) At present, the only feasible way to dispose of radioactive waste is deep geological disposal, and the geological conditions required for deep geological disposal are very harsh, and some countries do not even have the conditions for deep geological disposal. A new method is urgently needed to dispose of high-level radioactive waste.

Separation technology can be divided into: extraction separation, high temperature separation, DIDPA process, wet method, dry method, oxide volatilization method.

Transmutation technology can be divided into: fast reactor transmutation, strong current proton accelerator transmutation, thermal reactor transmutation, light water reactor transmutation, fusion reactor transmutation, accelerator transmutation and other technologies.

The amount of MA loading directly affects the operation of the reactor, and also affects the transmutation rate. In MA, ²³⁷ Np and ²⁴¹ Am account for the vast majority, and the focus on dealing with the transmutation rate is to deal with the fuel consumption of ²³⁷ Np and ²⁴¹ Am. Nuclides in MA have a high probability of nuclear reactions with fast neutrons, and MA nuclides have a larger neutron fission cross section at higher neutron energies, and nuclides in MA can undergo capture fission reactions with neutrons to release energy. Moreover, MA nuclides can be converted into fissile nuclides by neutron radiation capture reaction, so MA can act as nuclear fission materials in sodium-cooled fast reactors to increase the backup reactivity of the reactor, so MA nuclides can be transmuted by sodium-cooled fast reactors Not only can MA nuclides be directly incinerated by using the characteristics of large fission cross section of MA nuclides at high neutron energy, but also can use MA nuclides to easily transform into fissile nuclides in sodium-cooled fast reactors to increase the backup of the reactor reactivity. But the addition of MA will affect the safety factor of the core.

The transmutation of MA nuclides in the fast reactor can be roughly divided into two types: uniform transmutation and non-uniform transmutation. Uniform transmutation generally does not change the size of the core, the size of the fuel rods, and the ratio of the pronuclides of the fuel. Adding MA uniformly into the fuel. For non-uniform transmutation, MA is generally made into transmutation rods instead of fuel rods and inserted into the core, or MA is made into coatings, and MA coatings are used to replace part of the nuclear fuel without changing the size of the fuel rods. Both ways have pros and cons. Compared with non-uniform transmutation, uniform transmutation rods are evenly distributed, and local power distortion will not occur. The disadvantage is that uniform transmutation changes the fuel composition of the core, causing uncertain safety hazards to the safety of the core. Non-uniform transmutation rods are easy to manufacture and do not require high manufacturing techniques. However, due to the limited arrangement of non-uniform transmutation rods, it is easy to cause sudden changes in local power and core melting. Therefore, it is necessary to improve the design and loading method of non-uniform transmutation rods.

Contents of the invention

An object of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages as will be described hereinafter.

In order to achieve these objects and other advantages according to the present invention, a non-uniform MA transmutation rod for a fast neutron reactor is provided, comprising:

The main body of the fuel rod is provided with MA nuclide coating or a mixed coating of MA nuclide and ⁶ LiD on the outside.

Preferably, wherein, the MA nuclide coating and the MA nuclide composition include ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, and the mass proportion of ²⁴¹ Am is 26.4% %, the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%.

Preferably, the radius of the non-uniform MA transmutation rod is 0.5 cm, and the thickness of the MA nuclide coating is 0.001-0.05 cm.

Preferably, wherein, the MA nuclide and ⁶ LiD mixed coating is prepared by uniformly mixing the MA nuclide and ⁶ LiD according to the mass ratio, and the mass ratio of the MA nuclide and ⁶ LiD is 7:3, 5: 5. One of 4:6 or 3:7.

Preferably, wherein, the loading amount of U and Pu isotopes in the fuel rod main body decreases with the increase of the loading amount of MA nuclide.

Preferably, wherein, the fuel rod body adopts MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein, ²³⁸ U, ²³⁵ U The ratio of 0.003:1, the ratio of ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025.

Preferably, wherein, the non-uniform MA transmutation rods are loaded in the inner area of the fuel assembly, the fuel assembly loaded with the non-uniform MA transmutation rods is provided with multiple layers in the core, and each layer of fuel assemblies has six sides in the middle layer of the core. Arranged in a shape, with intervals between adjacent two layers of fuel assemblies.

The present invention at least includes the following beneficial effects: the present invention is by setting the MA coating or the mixed coating of MA and ⁶ LiD on the outside of the fuel rod, due to the addition of ⁶ LiD, thermal neutrons can be converted into fast neutrons of 14MeV, and then It can increase the average energy of neutrons in the core, deepen the burnup depth of MA, and increase the transmutation rate of MA.

Other advantages, objectives and features of the present invention will partly be embodied through the following descriptions, and partly will be understood by those skilled in the art through the research and practice of the present invention.

Description of drawings

Fig. 1 is the structural schematic diagram of the non-uniform MA transmutation rod of embodiment 1;

Fig. 2 is the structural schematic diagram of the non-uniform MA transmutation rod of embodiment 2;

Figure 3 is a schematic diagram of the distribution of non-uniform MA transmutation rods in the fuel assembly;

Figure 4 is a schematic diagram of the distribution of fuel assemblies in the core;

Fig. 5 is a schematic diagram of the relationship between neutron flux changes in the core position;

Fig. 6 is the influence curve caused by the thickness of MA coating on the core reactivity _Keff ;

Fig. 7 is the change curve of the neutron flux of reactor with the addition of MA;

Figure 8 is the reaction chain of ⁶ LiD and thermal neutrons;

Figure 9 is a schematic diagram of the influence of ⁶ LiD on the reactor reactivity when the ratio of MA to ⁶ LiD is 7:3, 3:7 and 6:4

Fig. 10 is a schematic diagram of the change of neutron flux in the sodium-cooled fast reactor when the ratio of ⁶ LiD/MA is 7:3 and 3:7 respectively.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings, so that those skilled in the art can implement it with reference to the description.

It should be understood that terms such as "having", "comprising" and "including" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

It should be noted that in the description of the present invention, the orientation or positional relationship indicated by the term is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply No device or element must have a specific orientation, be constructed, and operate in a specific orientation and therefore should not be construed as limiting the invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and should not be understood as indicating or implying relative importance.

In the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "set with", "sleeved/connected", "connected", etc. should be understood in a broad sense, such as "connected", which can be Fixed connection, detachable connection, or integral connection, mechanical connection, electrical connection, direct connection, or indirect connection through an intermediary, or internal communication between two components. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

In addition, in the present invention, unless otherwise clearly specified and limited, a first feature may be "on" or "under" a second feature in that the first and second features are in direct contact, or that the first and second features pass through the middle. Media indirect contact. Moreover, "above", "above" and "above" the first feature on the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. "Below", "beneath" and "beneath" the first feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is less horizontally than the second feature.

Example 1

As shown in Figure 1: a kind of non-uniform MA transmutation rod for fast neutron reactor of the present embodiment, comprises fuel rod main body 1, and its exterior is provided with MA nuclide coating 2, and the nucleus of MA nuclide coating 2 The element composition includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm The proportion is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the non-uniform MA transmutation rod is 0.5 cm, the thickness of the MA nuclide coating 2 is 0.001 cm, and the mass of MA in each fuel rod is 2.0 g.

Example 2

A non-uniform MA transmutation rod used in a fast neutron reactor according to this embodiment includes a fuel rod main body, and an MA nuclide coating is provided on the outside thereof, and the nuclide composition of the MA nuclide coating includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am and ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the non-uniform MA transmutation rod is 0.5cm, the thickness of the MA nuclide coating is 0.002cm, and the mass of MA in each fuel rod is 3.9g.

Example 3

A non-uniform MA transmutation rod used in a fast neutron reactor according to this embodiment includes a fuel rod main body, and an MA nuclide coating is provided on the outside thereof, and the nuclide composition of the MA nuclide coating includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am and ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the non-uniform MA transmutation rod is 0.5cm, the thickness of the MA nuclide coating is 0.015cm, and the mass of MA in each fuel rod is 29g.

Example 4

A non-uniform MA transmutation rod used in a fast neutron reactor according to this embodiment includes a fuel rod main body, and an MA nuclide coating is provided on the outside thereof, and the nuclide composition of the MA nuclide coating includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am and ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the non-uniform MA transmutation rod is 0.5 cm, the thickness of the MA nuclide coating is 0.05 cm, and the mass of MA in each fuel rod is 93.1 g.

Example 5

A non-uniform MA transmutation rod for a fast neutron reactor according to this embodiment comprises a fuel rod main body, and a mixed coating of MA nuclide and ⁶ LiD is arranged on the outside, and the mass ratio of MA nuclide and ⁶ LiD is 3 : 7, the nuclide composition of MA nuclide includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, and the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the heterogeneous MA transmutation rod is 0.5 cm, and the thickness of the MA nuclide and ⁶ LiD mixed coating is 0.05 cm.

Example 6

A non-uniform MA transmutation rod used in a fast neutron reactor according to this embodiment comprises a fuel rod main body, and a mixed coating of MA nuclide and ⁶ LiD is arranged on the outside, and the mass ratio of MA nuclide and ⁶ LiD is 4 : 6, the nuclide composition of MA nuclide includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, and the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the heterogeneous MA transmutation rod is 0.5 cm, and the thickness of the MA nuclide and ⁶ LiD mixed coating is 0.05 cm.

Example 7

A non-uniform MA transmutation rod for a fast neutron reactor according to this embodiment comprises a fuel rod main body, and a mixed coating of MA nuclide and ⁶ LiD is provided on the outside, and the mass ratio of MA nuclide and ⁶ LiD is 5 : 5, the nuclide composition of MA nuclide includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, and the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the heterogeneous MA transmutation rod is 0.5 cm, and the thickness of the MA nuclide and ⁶ LiD mixed coating is 0.05 cm.

Example 8

A non-uniform MA transmutation rod for a fast neutron reactor according to this embodiment comprises a fuel rod main body, and a mixed coating of MA nuclide and ⁶ LiD is arranged on the outside, and the mass ratio of MA nuclide and ⁶ LiD is 7 : 3, the nuclide composition of MA nuclide includes ²³⁷ Np, ²⁴¹ Am, ²⁴³ Am, ²⁴⁴ Cm, wherein the mass proportion of ²³⁷ Np is 56.2%, the mass proportion of ²⁴¹ Am is 26.4%, and the mass proportion of ²⁴³ Am is 12%, and the mass proportion of ²⁴⁴ Cm is 5.4%. The fuel rod body uses MOX fuel, and the nuclide composition of MOX fuel includes ²³⁸ U, ²³⁵ U, ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu, wherein the ratio of ²³⁸ U and ²³⁵ U is 0.003:1, ²³⁸ The ratio of Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Pu and ²⁴² Pu is 0.025:1.5375:0.55:0.2975:0.1025. The radius of the heterogeneous MA transmutation rod is 0.5 cm, and the thickness of the MA nuclide and ⁶ LiD mixed coating is 0.05 cm.

The non-uniform MA transmutation rods of Examples 1 to 8 were respectively loaded into the inner layer of the MA transmutation assembly, and then the MA transmutation assembly loaded with the non-uniform MA transmutation rods was loaded into the core. Before carrying out the experiment, it is first necessary to determine the position of the MA transmutation rod in the core. Since the higher the neutron flux, the harder the neutron energy spectrum, the better the effect on the MA transmutation rate. The neutron The relationship between flux changes at the core position is shown in Fig. 5. According to Fig. 5, the neutron flux from the inside to the outside of the core decreases successively, and the average energy of neutrons in the center of the core is the highest, and the energy spectrum is the hardest, so the MA transmutation rods need to be arranged near the center, and the non-uniform MA The distribution of the transmutation rods 4 in the fuel assembly 5 is shown in FIG. 3 . The distribution of fuel assemblies 5 loaded with non-uniform MA transmutation rods 4 in the core 6 is shown in Fig. 4 .

The addition scheme of the MA nuclide coating that embodiment 1～embodiment 4 provides is: keep the radius of fuel rod main body constant, replace the thickness of MOX fuel rod main body with MA coating thickness, namely the MA nuclide coating The thickness and the radius of the fuel rod body are equal to the radius of the original fuel rod body, and the loading of U and Pu isotopes decreases with the increase of the MA loading, so the MA loading directly affects the operation of the reactor, and also affects the transmutation rate. will have an impact.

In the MA nuclide coating, ²³⁷ Np and ²⁴¹ Am account for the vast majority, and the key point in dealing with the transmutation rate is to deal with the burnup of ²³⁷ Np and ²⁴¹ Am. Nuclides in MA have a high probability of nuclear reactions with fast neutrons, and MA nuclides have a larger neutron fission cross section at higher neutron energies, and nuclides in MA can undergo capture fission reactions with neutrons to release energy. Moreover, MA nuclides can be converted into fissile nuclides by neutron radiation capture reaction, so MA can act as nuclear fission materials in sodium-cooled fast reactors to increase the backup reactivity of the reactor, so MA nuclides can be transmuted by sodium-cooled fast reactors Not only can MA nuclides be directly incinerated by using the characteristics of large fission cross section of MA nuclides at high neutron energy, but also can use MA nuclides to easily transform into fissile nuclides in sodium-cooled fast reactors to increase the backup of the reactor reactivity. But the addition of MA will affect the safety factor of the core.

Figure 6 shows the influence curve of the thickness of the MA coating on the reactivity K _eff of the core. It can be seen from the figure that the sodium-cooled fast neutron reactor operates independently for 300 days, and the initial reactivity is about 1.14. From 1.03 to 1.03, the reactivity gradually decreased with time. After adding MA coating to the core, when the thickness of the fuel rod MA coating is 0.001cm, the reactivity of the reactor after 300 days of operation is basically unchanged and slightly increased. When the coating thickness is 0.015cm, 0.05cm, 0.2cm , the initial reactivity is lower than that of the sodium-cooled fast reactor without MA, but the reactor reactivity gradually increases with the reactor running time. Table 1 shows the MA nuclide fission cross section, capture cross section, capture The comparison chart of fission ratio in thermal neutron reactors and fast neutron reactors. It can be seen from Table 1 that the capture fission ratio in fast reactors is small, and the probability of MA nuclides to undergo neutron capture fission reactions in fast reactors is higher, and the capture cross section The ratio to the fission cross section decreases with the increase of neutron energy. In fast reactors with high average neutron energy, MA nuclides can be used as additional fissile materials. MA nuclides absorb neutrons and are easily converted into volatile nuclides , so that the core has a higher backup reactivity, so adding MA to the core increases the reactivity of the core.

The change curve of the neutron flux of the reactor with the amount of MA added is shown in Fig. 7. It can be seen from Fig. 7 that, compared with no addition of MA, adding MA will lead to a lower neutron flux of the reactor, and the more MA content, The lower the neutron flux, the addition of MA nuclides consumes neutrons in the reactor, resulting in lower neutron flux.

But at the same time, the addition of MA will change the fuel temperature coefficient of the reactor and the cavitation coefficient of the reactor, resulting in a decrease in the safety factor of the reactor.

Table 1 Fission cross section (σ _f ), capture cross section (σ _c ) and capture fission ratio (α)

Table 2 MA nuclide coating thickness, transmutation rod radius, MA mass and MA nuclide coating weight list

It can be seen from Figure 7 that the greater the MA loading, the greater the impact on the core reactivity, and the lower the safety factor of the core. The research shows that with the increase of MA addition, the inherent safety of the sodium-cooled fast reactor core The Doppler effect becomes weaker, while K _eff decreases, and the positive feedback of the core increases due to the sodium cavitation effect, so the safety factor of the core should also be considered while considering the loading capacity.

Table 3 shows the value of nuclear reactor K _eff under different loads

Table 3 The value of nuclear reactor K _eff under different loads

MA coating thickness/cm Initial K _eff Burnup end K _{eff ΔKeff} 0.001 1.1414 1.1419 0.0005 0.002 1.1396 1.1423 0.0027 0.015 1.1244 1.1347 0.0103 0.05 1.1002 1.1250 0.0248

It can be seen from Table 3 that as the thickness of the MA coating increases, the value of ΔK _eff increases, and the influence on the reactivity of the core becomes more severe. Therefore, as the thickness of the MA coating increases, the The lower the safety factor.

Using RMC to calculate the transmutation rate of different MA coating thickness, the calculation method of transmutation rate is shown in the following formula:

Transmutation rate = initial nucleon density of each nuclide in MA/nucleon density of corresponding nuclides in MA at the end of burnup

The research results of transmutation rates of various minor actinides under different MA loadings are shown in Table 4. It can be seen from Table 4 that with the increase of MA coating thickness, the MA transmutation rate gradually decreases. This is because the increase in the thickness of the MA coating enhances its own shielding effect on neutrons, so that the inner layer of MA nuclides cannot react with neutrons, and the reaction between MA and neutrons is insufficient. At the same time, due to the limitation of neutron mean free path , so as the thickness increases, the transmutation efficiency of SFR for MA decreases. From the negative value of the transmutation rate of ²⁴⁴ Cm in Table 4, it can be seen that the sodium-cooled fast reactor has a poor transmutation effect on ²⁴⁴ Cm, which is because ²⁴³ Am is captured in the fast reactor and produces ²⁴⁴ Cm.

Table 4 Transmutation rates of various minor actinides under different MA loadings

Examples 5-8 are implementations of adding ⁶ LiD to the MA nuclide coating. ⁶ LiD can be used as a raw material for thermonuclear hydrogen bombs ^[10] , deuterium accounts for 0.015% of natural hydrogen, and a large amount of deuterium can be obtained in seawater, but tritium does not exist naturally. React via:

n+6Li→4He+T+4.9MeV (1)

Tritium can be obtained, and then through the reaction:

D+T→4He+n+17.6MeV (2)

T+6Li→Be+n+16.02MeV (3)

The neutrons generated by reactions (2) and (3) are both at about 14MeV, and the reaction chain is shown in Figure 8.

Therefore, ⁶ LiD can improve the conversion of thermal neutrons into 14 Mev fast neutrons. It is precisely because of this property of ⁶ LiD that ⁶ LiD is added to the core to increase the average energy of neutrons in the core and deepen the combustion of MA. consumption depth.

⁶ LiD is a substance that can convert slow neutrons into fast neutrons. Adding ⁶ LiD in the core will naturally affect the operation of the reactor. Taking the MA coating thickness of 0.05cm as an example, a preliminary study ⁶ What effect does the addition of LiD have on the reactivity of the reactor. Figure 9 shows the effect of ⁶ LiD on the reactor reactivity when the ratio of MA to ⁶ LiD is 7:3, 3:7 and 6:4.

The effects of different ⁶ LiD/MA loading ratios on the reactor reactivity are shown in Table 5

Table 5 Effects of different ⁶ LiD/MA loading ratios on reactor reactivity

It can be seen from Figure 9 that the addition of ⁶ LiD will have a negative impact on the reactivity of the reactor compared to the addition of MA only, and the higher the proportion of ⁶ LiD in the mixture, the deeper the negative impact on the reactivity, which is Because ⁶ LiD is mixed with MA as a substance that can convert slow neutrons into fast neutrons, when the proportion of ⁶ LiD increases, the proportion of MA in fuel rods will decrease relatively, and MA as a Additional fuel that increases the reserve reactivity, and a reduction in the MA share lead to a decrease in reactor reactivity, but the general trend of their reactivity increases with reactor operating time.

It can be seen from Table 5 that the addition of ⁶ LiD will affect the reactivity of the reactor core. The more the proportion of ⁶ LiD is added, the smaller the change of ΔK _eff is because the negative effect introduced by ⁶ LiD compensates for the positive effect of MA addition on the reactor reactivity. At the same time, it can be seen that the higher the ratio of ⁶ LiD/MA, the lower the initial K _eff . With the increase of the ratio of ⁶ LiD/MA, the reactor may reach subcriticality.

The thickness of MA and LiD mixed coating is 0.05cm ⁶ LiD/MA is 7:3:

Table 6 The disappearance rate of MA nuclides in the sodium-cooled fast reactor model for 300 days

The mixed thickness of MA and ⁶ LiD is 0.05cm, ⁶ LiD/MA is 3:7

Table 7 The disappearance rate of MA nuclides in the sodium-cooled fast reactor model for 300 days

Therefore, when the ratio of ⁶ LiD/MA is changed, the burnup depth of MA will be affected. In the design of non-uniform transmutation rods in sodium-cooled fast reactors, the ratio of ⁶ LiD mixed in MA should not be too high. The number of neutrons accounts for the vast majority, adding too much ⁶ LiD will affect the reactivity of the reactor, and at the same time reduce the proportion of each nuclide unit volume of MA, reducing the probability of nuclear reaction with neutrons per unit volume, resulting in The transmutation rate of MA decreases, the content of thermal neutrons in the fast reactor is less, and the conversion efficiency of ⁶ LiD is not high, so the reduction of the share of MA unit volume caused by the addition of ⁶ LiD to the MA coating has a greater impact on the reduction of the transmutation rate of MA than The effect of ⁶ LiD on the increase of MA transmutation rate ^. Figure 10 compares the change of neutron flux in the sodium-cooled fast reactor when the loading ratio of ⁶ LiD/MA is 7:3 and 3:7 respectively. Under different loading ratios, increasing the ratio of ⁶ LiD has little effect on the change of reactor neutron flux.

The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations to the present invention will be apparent to those skilled in the art.

Although the embodiment of the present invention has been disclosed as above, it is not limited to the use listed in the specification and implementation, it can be applied to various fields suitable for the present invention, and it can be easily understood by those skilled in the art Therefore, the invention is not limited to the specific details and examples shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims (5)

1. A non-uniform MA transmutation rod for a fast neutron reactor, comprising:

a fuel rod main body, the outside of which is provided with a MA nuclide coating or MA nuclide and ⁶ a mixed coating of LiD;

the MA nuclide coating and the MA nuclide composition comprise ²³⁷ Np、 ²⁴¹ Am、 ²⁴³ Am、 ²⁴⁴ Cm, where ²³⁷ The mass ratio of Np is 56.2%, ²⁴¹ am is 26.4% by mass, ²⁴³ am is 12% by mass, ²⁴⁴ the mass ratio of Cm is 5.4%;

the MA species ⁶ The LiD mixed coating is prepared from MA nuclide ⁶ The LiD is prepared by uniformly mixing according to the mass ratio, and MA nuclide ⁶ The mass ratio of LiD is one of 7:3, 5:5, 4:6 or 3:7.

2. The non-uniform MA transmutation rod for a fast neutron reactor according to claim 1, wherein the radius of the non-uniform MA transmutation rod is 0.5cm, and the thickness of the MA nuclide coating is 0.001-0.05 cm.

3. The non-uniform MA transmutation rod for a fast neutron reactor of claim 1, wherein the loading of U and Pu isotopes in the fuel rod body decreases with increasing MA nuclide loading.

4. The heterogeneous MA transmutation rod for a fast neutron reactor of claim 1, wherein the fuel rod body employs a MOX fuel, the nuclide composition of the MOX fuel comprising ²³⁸ U、 ²³⁵ U、 ²³⁸ Pu、 ²³⁹ Pu、 ²⁴⁰ Pu、 ²⁴¹ Pu and ²⁴² pu, wherein, ²³⁸ U、 ²³⁵ the ratio of U is 0.003:1, ²³⁸ Pu、 ²³⁹ Pu、 ²⁴⁰ Pu、 ²⁴¹ pu and ²⁴² pu is present in a ratio of 0.025:1.5375:0.55: 0.2975:0.1025.

5. The non-uniform MA transmutation rod for a fast neutron reactor according to claim 1, wherein the non-uniform MA transmutation rod is loaded in an inner region of a fuel assembly, the fuel assembly loaded with the non-uniform MA transmutation rod is provided with a plurality of layers in a reactor core, each layer of fuel assemblies are arranged in a hexagonal manner in the reactor core, and two adjacent layers of fuel assemblies are arranged at intervals.