FR3076654A1 - Fast neutron reactor fuel element and fast neutron reactor core - Google Patents

Abstract

Fast neutron reactor fuel element and fast neutron reactor core Fast neutron reactor fuel element in which a liquid fuel containing a fissile material and a fertile material is charged, the fast neutron fuel element comprising a charging two-stage fuel material having a higher fuel region charged with a molten salt fuel and a lower fuel region charged with a liquid metal fuel. Figure for the abstract: Fig. 1 C

Description

Description

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Title of the invention: Fuel element of fast neutron reactor and core of fast neutron reactor

Technical Field The present invention relates to a fuel element for a fast neutron reactor and a core for a fast neutron reactor.

PRIOR ART Fast neutron reactors are configured so as to include a core in a reactor vessel, and the reactor vessel is filled with liquid sodium which acts as a refrigerant. This core is charged with a plurality of fuel assemblies, and each of the fuel assemblies consists of a plurality of fuel elements in which a fissile material such as plutonium (Pu) or a fertile material such as uranium ( U) depleted is enclosed in a sheath. Specifically, the fuel assembly is configured to include a plurality of fuel elements, a cladding tube that surrounds the plurality of fuel elements, an inlet nozzle that supports the lower end of these fuel elements, and a shield. against neutrons located below the fuel elements, and a refrigerant outlet flow portion located above the fuel elements.

A solid oxide or a solid metal alloy constitutes a common and proven chemical form of a nuclear combustible material included in a combustible element; however, there are examples of the use of a liquid fuel such as a liquid metal alloy or a molten salt. Incidentally, with respect to fuel elements loaded with solid oxide fuel, an example in which an oxide fuel in the form of pellets is enclosed in a cladding is described in Alan E. Waltar, and two other authors, "Fast Spectrum Reactors", translation supervised by: Naoyuki Takaki, ERC Publishing Co., Ltd.,

Nov. 2016, p. 583. In this example of the fuel element, a mixed U-Pu oxide is arranged to form a core fuel, and a cover fuel (depleted uranium oxide) including a fertile material is arranged above and below. of a core fuel region.

For example, JP 64 - 32189 A describes an example of a combustible element in which a liquid metal type fuel including a plutonium (Pu) -uranrum (U) -brsmuth (Bi) or similar alloy is enclosed in a sheath. In addition, JP 2014 - 10022 A describes an example of a combustible element in which a molten fluoride salt containing thorium (Th) and a fissile material, such as uranium 235 (235 U) or plutonium 239 (239Pu ), are enclosed in a sheath. However, in these fuel elements, no covering fuel is described. Summary of the invention [0005] When a fast neutron reactor is operated, a fissile material, such as 239 Pu, as the main component of a core fuel, is consumed by a fission reaction (consumption of combustible). In parallel, the core fuel of the fast neutron reactor contains a fertile material, such as 238L, and the fissile material, such as 239Pu, is newly produced by the capture of neutrons by the fertile material. Furthermore, when a cover fuel is disposed on the upper or lower part, or the upper and lower parts of the core fuel region, the fertile material, such as 238L, as the main component of the cover fuel, captures neutrons escaping from the core, producing fissile material, such as 239Pu.

Here, the covering fuel designates a fuel which contains almost no fissile material such as 239Pu and which, instead, contains a significant amount of the fertile material, such as 238L. Fertile material, such as 238L, is not directly converted into fuel from a fast neutron reactor, but is converted to fissile material, such as 239Pu, by a neutron capture reaction to capture neutrons. Thus, fissile material, such as 239Pu, is converted into the fuel of the fast neutron reactor.

[0007] The ratio of the production of fissile material to the consumption of fissile material in the fast neutron reactor is often called the conversion ratio or the generation ratio. Here, the conversion ratio for fissile Pu is defined in the following three ways: (1) Conversion ratio of core fuel = production of Pu of core fuel / consumption of Pu of core fuel; (2) Conversion ratio of cover fuel = production of Pu of cover fuel / consumption of Pu of cover fuel; and (3) Overall conversion ratio = core fuel conversion ratio + cover fuel conversion ratio.

Generally, in the fast neutron reactor, the conversion ratio of the core fuel is less than 1. However, the conversion ratio of the cover fuel is added so that it is possible to ensure that the overall conversion ratio is not less than 1 (that is to say, the fuel super-generation). In this case, as fuel consumption occurs, the total amount of Pu included in the cover fuel increases, while the amount of Pu remaining in the core fuel gradually decreases. Thus, the core fuel is replaced by fresh fuel after a certain consumption period (duration of the operating cycle). To improve the economic efficiency of the core fuel, it is necessary to have a long-lived fuel element allowing less frequent refueling.

In addition, to recycle the Pu produced from the covering fuel, it is necessary to carry out a series of recycling processes including the extraction of Pu, as spent fuel, from the reactor, the recovery of the Pu in a reprocessing installation set up outside the reactor, and its subsequent transformation into a core fuel.

In the fuel element described in Alan E. Waltar, and two other authors, "Fast Spectrum Reactors", translation supervised by: Naoyuki Takaki, ERC Pubbshing Co., Ltd., Nov. 2016, p. 583, the cover fuel is disposed on the upper and lower portions of the core fuel region. In this case, the overall conversion ratio slightly exceeds 1; however, since the core fuel conversion ratio is less than 1, it is necessary to reload the reactor frequently with fuel. In addition, there is a need for a recycling process to recover and recycle the 239Pu produced from the cover fuel.

The fuel elements described in JP 64 - 32189 A and JP 2014 - 10022 A do not have any covering fuel. Thus, in the same way as for the fuel element described in Alan E. Waltar, and two other authors, "Fast Spectrum Reactors", translation supervised by: Naoyuki Takaki, ERC Pubbshing Co., Ltd., Nov. 2016, p . 583, the conversion ratio of the core fuel is less than 1 and, therefore, it is necessary to frequently recharge the reactor with fuel.

The present invention relates to a fuel element of fast neutron reactor and a core of fast neutron reactor, which aim to lengthen the life of fuel elements loaded in the heart and to simplify the process for recycling spent fuel elements.

The fuel element of fast neutron reactor according to the present invention is a fuel element of fast neutron reactor into which is charged a liquid fuel containing a fissile material and a fertile material. The fast neutron reactor fuel element includes a two-stage fuel material loading region having an upper fuel region loaded with molten salt type fuel and a lower fuel region loaded with liquid metal type fuel .

The present invention relates to a fuel element of fast neutron reactor and a core of fast neutron reactor, which aim to extend the life of fuel elements loaded in the heart and to simplify the process for recycling spent fuel elements.

Brief description of the drawings [fig.l A] schematically illustrates the configuration of a fast neutron reactor core according to one of the embodiments of the present invention. FIG. 1A presents an example in which a schematic structure of a heart is illustrated in perspective.

[Fig.lB] schematically illustrates the configuration of a fast neutron reactor core according to one of the embodiments of the present invention. FIG. 1B illustrates an example of a structure in horizontal section of a fuel assembly constituting a core.

[Fig.lC] schematically illustrates the configuration of a fast neutron reactor core according to one of the embodiments of the present invention. Figure IC illustrates an example of a vertical sectional structure of a fuel element constituting a fuel assembly.

[Fig.2A] schematically illustrates a structure in vertical section of a fuel element and a core according to Example 1. Figure 2A illustrates an example of a structure in vertical section of a fuel element.

[Fig.2B] schematically illustrates a vertical sectional structure of a fuel element and a core according to Example 1. Figure 2B illustrates an example of a vertical sectional structure of an entire heart.

[Fig.3A] schematically illustrates a structure in vertical section of a fuel element and a core according to Example 2. Figure 3A illustrates an example of a structure in vertical section of a fuel element.

[Fig.3B] schematically illustrates a structure in vertical section of a fuel element and a heart according to Example 2. Figure 3B illustrates an example of a structure in vertical section of an entering heart.

[Fig.4A] schematically illustrates a structure in vertical section of a fuel covering element and a core according to Example 3. Figure 4A illustrates an example of a structure in vertical section of an element cover fuel used in a core.

[Fig.4B] schematically illustrates a structure in vertical section of a fuel covering element and a heart according to Example 3. Figure 4B illustrates an example of a structure in vertical section of a heart enter.

Detailed Description The embodiments of the present invention will be described in detail below with reference to the drawings. It should be noted that in the drawings, the common components are designated by the same reference numbers, and that duplicate descriptions are omitted.

Figures IA - IC schematically illustrate a configuration of a core 1 of fast neutron reactor according to one of the embodiments of the present invention. In Figures IA - IC, Figure IA shows an example in which a schematic structure of a core 1 is illustrated in perspective, Figure IB illustrates an example of a structure in horizontal section of a fuel assembly 2 constituting a core 1, and the figure illustrates an example of a vertical sectional structure of a fuel element 10 constituting the fuel assembly 2. It should be noted that in FIG. IA, only a few fuel assemblies 2 are drawn in the core 1; however, the core 1 is formed of a plurality, more specifically from several tens to several hundred fuel assemblies 2, all of which have a cylindrical shape.

In the present invention, the expression “fuel assembly 2” designates an assembly of the fuel elements 10 which can be fully manipulated during unloading and loading from and to the core 1. As illustrated in FIG. 1B, the assembly fuel 2 is formed of a plurality (several tens to several hundred) of the fuel elements 10 grouped in a cladding tube 4. In the cladding tube 4, an interval of predetermined size is provided between the fuel elements 10 adjacent to each other others, and a coolant 5 such as liquid sodium fills the gap.

The fuel element 10 may be what is called a fuel rod formed by the loading of a sheath 17 with the fissile material and the fertile material which serve as fuels. In particular, the interior of the cylindrical sheath 17 is not divided, but is divided into a gas plenum 14 and a fuel material loading region 11. In addition, the fuel material loading region 11 has a two-story structure with an upper fuel region 12 and a lower fuel region 13.

In this structure, a core fuel including a molten salt containing the fissile material, such as 239Pu, is charged in the upper fuel region 12, and a covering fuel including a liquid metal containing the fertile material, such as 238L, is loaded into the lower fuel region 13. Then, after loading these combustible materials and filling the gas plenum 14 with an inert gas, the upper end and the lower end of the sheath 17 are closed by an upper end plug 15 and a lower end plug 16.

In the following, several examples of the core fuel and the covering fuel loaded in the upper fuel region 12 and the lower fuel region 13 of the fuel element 10 are described.

Examples Example 1 FIGS. 2A and 2B schematically illustrate a structure in vertical section of a fuel element 10a and a core 1a according to Example 1, FIG. 2A illustrates an example of a structure in vertical section of the fuel element 10a, and FIG. 2B illustrates an example of an entire vertical sectional structure of the core 1a. It should be noted that the dotted line illustrated in Figure 2B indicates the central axis of the heart la. In Figure 2B, the concepts of a fuel assembly 2 and the fuel element 10a are eliminated and the illustrations are omitted.

In this example, a fuel of the molten salt type 12a including PuCl3, LC13, NaCl, MgCl2 or the like is charged as core fuel in the upper fuel region 12 of the fuel element 10a. In addition, a liquid metal fuel 13a including an L-Bi alloy or the like is charged as a cover fuel in the lower fuel region 13. It should be noted that the molten salt type fuel 12a of the core fuel must continue to be consumed as core fuel without being replaced for a predetermined period. Thus, the molten salt type fuel 12a in which the enrichment of fissile material, such as 239Pu, has been increased is used.

During the operation of the fast neutron reactor, in the upper fuel region 12 of the fuel element 10a, the 239Pu of the fissile material as the main component of the fuel of the molten salt type 12a is consumed by its own fission reaction (this is the fuel consumption). In addition, the molten salt fuel 12a contains 238L as a fertile material. Thus, fissile material, such as 239Pu, is newly generated by the neutron capture reaction in which 238U captures neutrons produced by the fission reaction of 239Pu. Thus, in the upper fuel region 12, 238U is transmuted to 239Pu as fuel.

In addition, in the lower fuel region 13 of the fuel element 10a, the 238U of the fertile material as the main component of the liquid metal type fuel 13a captures neutrons which escape from the fuel region upper 12, which transmutes fertile material into fissile material, such as 239Pu, through the neutron capture reaction. In other words, the fissile material, such as 239Pu, is produced in the lower fuel region 13 of the fuel element 10a.

Incidentally, at the border between the upper fuel region 12 and the lower fuel region 13, the molten salt type fuel 12a and the liquid metal type fuel 13a are brought into contact with each other at the molten state. In such a case, in the region in which the molten salt fuel 12a is in contact with the liquid metal fuel 13a, a chemical reaction shown in the following Formula (1) occurs between the 239Pudu metal transmuted from the 238U contained in the liquid metal type fuel 13a and 238U chloride contained in the molten salt type fuel 12a.

Pu (metal) + UC13 (chloride) -> PuCl3 (chloride) + U (metal) (1) Thus, the 239Pu of the metal contained in the fuel of the liquid metal type 13a becomes 239Pu in the chloride, and the 238U chloride in the molten salt fuel 12a becomes 238U in the metal. The chemical reaction occurs because plutonium (Pu) is more likely to bind to chlorine (Cl) than furanium (U).

The 239Pu chloride thus produced has a density lower than that of the liquid metal type fuel 13a. Conversely, the metal 238U has a higher density than that of the molten salt type fuel 12a. Thus, the chloride 239Pu diffuses into the molten salt type fuel 12a which is a core fuel, and the metal 238U diffuses into the liquid metal type fuel 13a which is a covering fuel.

Thus, at a boundary between the molten salt type fuel 12a and the liquid metal type fuel 13a, the chemical reaction represented in Formula (1) continues until the concentration of each of the substances involved in the chemical reaction reaches a predetermined equilibrium condition. Thus, as long as the chemical reaction of Formula (1) continues, the 239Pu as fuel is successively supplied from the liquid metal type fuel side 13a (cover fuel) to the molten salt type fuel side 12a (fuel of heart).

It follows, in this example, that the effective conversion ratio of the core fuel increases by an amount equivalent to the conversion ratio of the cover fuel in the following Formula (2): (Effective conversion ratio of the fuel of core) = (conversion ratio of core fuel) + (quantity equivalent to the conversion ratio of covering fuel) (2) [0039] Thus, in the core la according to this example, it is possible to extend the duration of life of the fuel element 10. As a result, it is possible to reduce the frequency of replacement of the fuel element 10 or of the fuel assembly 2 with new equivalents in the core 1a. Thus, in this example, the economic efficiency of the fuel in the fast neutron reactor can be greatly improved.

Incidentally, in the covering fuel (fuel of the liquid metal type 13a), it results from the chemical reaction of Formula (1) that 239Pu remains in a quantity at equilibrium with the core fuel (fuel of the salt type fade 12a). Then, the fission reaction of the remaining 239Pu and the fission reaction of the 238U contained in small amounts in the cover fuel occur.

Among the nuclides produced by fission, hereinafter called "PF nuclides (fission products)" produced by the fission reaction which takes place within these covering fuels, most PF nuclides, at l except the nuclides PF of the platinum family, have a lower density than that of the base material which is the fuel of the liquid metal type of the covering fuel. Thus, the PF nuclides float to the boundary between the cover fuel and the core fuel and cause a chemical reaction represented in the following Formula (3) with the molten salt of the core fuel, by which the nuclides in the form of PF salt diffuse into the fuel side of the heart.

PF nuclides float to the border between the cover fuel and the core fuel and cause a chemical reaction presented in the following Formula (3) with the molten salt of the core fuel, whereby the nuclides under the salt form of FP diffuse into the combustible side of the heart. PF (simple substance) + (3/2) MgCl3 (chloride) -> FPC13 (chloride) + (3/2) Mg (metal) (3) Thus, with the exception of PF nuclides of the family of platinum, the amount of PF nuclides remaining in the spent blanket fuel is almost zero. As a result, the process of recovering PF nuclides from the spent blanket fuel becomes almost unnecessary. More specifically, the FP separation process is almost useless in the reprocessing of spent cover fuel. Thus, the process for reprocessing the spent fuel element 10a is greatly simplified.

As described above, in the case of the fuel element 10a and the core 1a according to the present invention, the 239Pu as fuel is brought from the covering fuel side (fuel of liquid metal type 13a) to the core fuel side (molten salt type fuel 12a), so that it is possible to improve the effective conversion ratio of the core fuel. As a result, it is possible to reduce the frequency of replacement of the fuel element 10a and of the fuel assembly 2 in the core la, and that the effective duration of the operating cycle of the fast neutron reactor can be increased. .

Thus, the load factor of the fast neutron reactor comprising the core increases it, and the economic efficiency can be greatly improved. In addition, the process for reprocessing the spent fuel element 10a is greatly simplified, which also contributes to improving the economic efficiency of the fast neutron reactor comprising the core 1a.

It should be noted that the amount of 239Pu transferred from the covering fuel to the core fuel side can be adjusted by the conversion ratio of the covering fuel. In addition, the cover fuel conversion ratio can be adjusted by establishing and appropriately regulating the amount of neutrons escaping from the core fuel to the cover fuel, depending on the specifications and arrangements of the cover fuel. and core fuel.

Example 2 Figures 3A and 3B schematically illustrate a vertical sectional structure of a fuel element 10b and a core 1b according to Example 2, Figure 3A illustrates an example of a vertical sectional structure of l fuel element 10b, and FIG. 3B illustrates an example of an entire vertical sectional structure of the core lb. It should be noted that the dotted line illustrated in Figure 3B indicates the central axis of the heart lb. In Figure 3B, the concepts of a fuel assembly 2b and the fuel element 10b are eliminated and the illustrations are omitted.

As shown in Figs. 3A and 3B, the configuration of arrangement of the combustible materials in the fuel element 10b and the core 1b according to this example is almost identical to that of Example 1 (see FIGS. 2A and 2B). Only the differences between this example and Example 1 will be described below.

The difference with Example 1 lies in the fuels respectively loaded in the upper fuel region 12 and the lower fuel region 13. In this example, the upper fuel region 12 is loaded with a salt type fuel molten high enrichment 12b which contains a high concentration of fissile material as core fuel, and the lower fuel region 13 is charged with a liquid metal fuel 13b of low enrichment which contains a low concentration of material fissile as a cover fuel. In other words, the upper fuel region 12 is charged with molten salt fuel 12b of high enrichment which includes PuCl3, UC13, NaCl, MgCl2 or the like, and the lower fuel region 13 is charged with fuel type low enrichment liquid metal 13b which includes a Pu-U-Bi alloy or the like.

Here, the molten salt type fuel 12b of high enrichment loaded in the upper fuel region 12 can be substantially identical to the molten salt type fuel 12a loaded in the upper fuel region 12 of Example 1. In Furthermore, it is possible to affirm that the fuel of the liquid metal type 13b of low enrichment loaded in the lower fuel region 13 is almost identical to the fuel of the liquid metal type 13a loaded in the lower fuel region 13 of the example. 1, but that it differs from the liquid metal type fuel 13a in that it contains 239Pu as fissile material. However, fuel enrichment can be low.

In this example, similarly to Example 1, 239Pu is contained in the core fuel (the fuel of molten salt type 12b with high enrichment), and 238U is contained in the covering fuel (the fuel liquid metal type 13b with low enrichment). Thus, the facts that the 239 Pu fission reaction occurs in the core fuel and that 239Pu is produced by the 238U neutron capture reaction in the cover fuel are the same as in Example 1.

In addition, in the same way as in Example 1, the chemical reaction of Formula (1) takes place at the border between the core fuel and the covering fuel. For this reason, in the same way as in Example 1, the 239Pu converted into chloride by the chemical reaction is diffused in the molten salt fuel 12b of high enrichment in the core fuel, and the 238U converted into metal is diffused in the liquid metal fuel 13b of low enrichment in the cover fuel.

Thus, in this example, it is possible to obtain effects which are almost identical to those of Example 1. In other words, in this example also, the effective conversion ratio of the core fuel can be improved , and the replacement frequencies of the fuel element 10b and of the fuel assembly 2 in the core lb can be reduced. As a result, the lengthening of the operating cycle of the fast neutron reactor makes it possible to increase the load factor of the fast neutron reactor comprising the core 1b, and therefore to greatly improve the economic efficiency.

It should be noted that in this example, unlike Example 1, 239Pu is previously contained in the liquid metal fuel 13b of low enrichment in the cover fuel. Thus, the transfer of 239Pu from the liquid metal fuel type 13b of low enrichment to the molten salt fuel type 12b of high enrichment as core fuel starts at an early stage after the start of operation. In addition, the quantity transferred is greater than that of Example 1. Thus, in this example, it is possible to obtain an effective conversion ratio of the core fuel greater than that of Example 1.

In this example, in the reprocessing of the liquid metal fuel type 13b of low enrichment loaded in the lower fuel region 13, only a few types of PF nuclides such as PF nuclides of the platinum family can be eliminated, while the 239Pu is left in the liquid metal fuel 13b of low enrichment. In other words, to the extent that the liquid metal fuel 13b of low enrichment is refined rather than reprocessed, the recycling process is greatly simplified.

Example 3 FIGS. 4A and 4B schematically illustrate a structure in vertical section of a fuel covering element 10c and a core 1c according to Example 3, FIG. 4A illustrates an example of a structure in vertical section of the covering fuel element 10c, and FIG. 4B illustrates an example of an entire vertical sectional structure of the core le. It should be noted that the dotted line illustrated in Figure 4B indicates the central axis of the heart le. In Figure 4B, the concepts of a fuel assembly 2c and the fuel element 10c are eliminated and the illustrations are omitted.

As illustrated in FIG. 4B, the core 1a according to this example is separated into a central region 51, in which the fuel element 10a (see FIG. 2A) used in Example 1 is arranged, and an external peripheral region 52, in which is disposed the covering fuel element 10c illustrated in FIG. 4A. More specifically, in the core 1a according to this example, a plurality of covering fuel elements 10c is additionally disposed on the outer periphery part of the core 1a (see FIG. 2B) according to a first embodiment. It should be noted that, as described with reference to Figures IA - IC, the fuel covering elements 10c are arranged in the form of a unit of the fuel assembly 2 formed by the assembly of the plurality, and specifically of the tens to several several hundred covering fuel elements 10c.

The covering fuel element 10c is a covering fuel rod loaded with fertile material, but not loaded with fissile material. As illustrated in FIG. 4A, in the covering fuel element 10c, the molten salt type covering fuel 12c containing the fertile material is charged into the upper fuel region 12, and the liquid metal type covering fuel 13c containing the fertile material is loaded into the lower fuel region 13. In other words, the cover fuel of the molten salt type 12c including UC13, NaCl, MgCl2 or the like is loaded into the upper fuel region, and the cover fuel of liquid metal type 13c including a U-Bi alloy or the like is charged in the lower fuel region 13.

In the core illustrated in Figure 4B, the fissile material, such as 239Pu, is initially contained only in the molten salt type fuel 12a in the upper fuel region 12 of the fuel element 10a disposed in the region central 51. Thus, at the start of the exploitation of the core le, the fission reaction of the fissile material, such as 239Pu, is initiated in the upper fuel region 12 of the fuel element 10a in the central region 51.

At the same time, the liquid metal type fuel 13a of the fuel element 10a contains the fertile material, such as 238L. Fertile material, such as 238L, captures neutrons that escape from the upper fuel region 12 of the fuel element 10a, which transmutes the fertile material into fissile material, such as 239Pu. The fissile material, such as 239Pu, thus produced is consumed by fission. These reactions are identical to those described in the case of Example 1.

Similarly, the fertile material, such as 238L, is also contained in the covering fuel of the molten salt type 12c and the covering fuel of the liquid metal type 13c of the covering fuel element 10c. Fertile material, such as 238L, also captures neutrons that escape from the upper fuel region 12 of the fuel element 10a, which transmutes the fertile material into fissile material, such as 239Pu. The fissile material, such as 239Pu, thus produced is consumed by fission.

As illustrated in FIG. 4B, in the core according to this example, the liquid metal type fuel 13a containing the fissile material, such as 239Pu, is surrounded not only by the liquid metal type fuel 13a but also by the cover fuel of molten salt type 12c and cover fuel of liquid metal type 13c. Thus, the overall conversion ratio of the core fuel in the core le is obtained by adding not only a conversion ratio equivalent to the conversion ratio of the liquid metal fuel 13a, but also conversion ratios equivalent to the conversion ratios of the cover fuel of molten salt type 12c and cover fuel of liquid metal type 13c.

Thus, in this example, the effective conversion ratio can be greatly increased compared to that of Example 1, and the life of the fuel element 10a can also be lengthened. Therefore, it is possible to improve the economic efficiency of the fuel in the fast neutron reactor.

It should be noted that, in the case of the covering fuel element 10c also, a large number of nuclides produced by fission (PF nuclides) are produced by the fission reaction of the fissile material, such as 239Pu, in cover fuel of liquid metal type 13c. These PF nuclides have a density lower than that of the covering fuel of the liquid metal type 13c, with the exception of PF nuclides of the platinum family. Thus, the PF nuclides float to the border between the cover fuel of the molten salt type 12c and the cover fuel of the liquid metal type 13c.

PF nuclides which floated to the border between the cover fuel of the molten salt type 12c and the cover fuel of the liquid metal type 13c cause a chemical reaction similar to that of Formula (3) with the fuel cover type 12c molten salt to form FP salts. Thus, the PF salts diffuse in the covering fuel of the molten salt type 12c.

Thus, with the exception of PF nuclides of the platinum family, the quantity of PF nuclides remaining in the spent fuel of liquid metal type 13c used up is almost zero. As a result, the process of recovering PF nuclides from the spent cover fuel proves to be almost mutilated, which greatly simplifies the process of reprocessing the cover fuel of the liquid metal type 13c.

It should be noted that, in Example 3 described above, the fuel element 10a described in Example 1 is disposed in the central region 51 of the heart; however, the fuel element 10b described in Example 2 can be disposed there. In this case, as in Example 2, effects such as increasing the effective conversion ratio of the core fuel are expected.

In Example 3, it is assumed that the fissile material, such as 239Pu, is included neither in the covering fuel of the molten salt type 12c, nor in the covering fuel of the liquid metal type 13c previously charged in the covering fuel element 10c. However, a small amount of fissile material may be included.

It should be noted that the present invention is not limited to the embodiments and examples described above, and that the present invention includes various modified examples. For example, the embodiments and examples described above have been described in detail for the purpose of explaining the present invention so that it is simple to understand, and are not necessarily limited to all of the configurations described. In addition, it is possible to replace some of the configurations of certain embodiments and examples with configurations of other embodiments and examples. It is also possible to add the configuration of other embodiments and examples to the configuration of certain embodiments and examples. Furthermore, it is also possible to add configurations included in other embodiments and examples to some of the configurations of the embodiments and examples, to delete some of the configurations of the embodiments and examples, or to replace some of the configurations of the embodiments and examples by configurations included in other embodiments and examples.

Claims (1)

Claims [Claim 1] Fuel element (10) of a fast neutron reactor into which is loaded a liquid fuel containing a fissile material and a fertile material, the fuel element (10) of fast neutron reactor comprising a material loading region two stage fuel (11) having an upper fuel region (12) charged with molten salt type fuel and a lower fuel region (13) charged with liquid metal type fuel. [Claim 2] A fuel element (10) of a fast neutron reactor according to claim 1, wherein the upper fuel region (12) is loaded with a molten salt type fuel enriched with fissile material, and the lower fuel region (13) is loaded with a liquid metal fuel containing the fertile material. [Claim 3] A fuel element (10) of a fast neutron reactor according to claim 1, wherein the upper fuel region (12) is loaded with a molten salt type fuel enriched with fissile material, and the lower fuel region (13) is charged with a liquid metal type fuel having a lower enrichment than the molten salt type fuel charged in the upper fuel region (12). [Claim 4] A fuel element (10) of a fast neutron reactor according to claim 1, wherein the upper fuel region (12) is charged with a molten salt type fuel containing the fertile material, and the lower fuel region ( 13) is loaded with a liquid metal fuel containing the fertile material. [Claim 5] Core (1) of fast neutron reactor comprising a plurality of fuel assemblies (2), each of the fuel assemblies (2) being formed by assembling a plurality of fuel elements (10) of fast neutron reactor according to any one of claims 1 to 3, wherein the plurality of fuel assemblies (2) is arranged so as to have an overall cylindrical shape. [Claim 6] Core (1) of a fast neutron reactor, in which a plurality of fuel assemblies (2) is arranged to surround an outer peripheral portion of the core of a fast neutron reactor according to claim 5, each of the assemblies fuel (2) being formed by combining a plurality of fuel elements (10) of a fast neutron reactor according to claim 4.