JP2020201169A - Fuel assemblies and core of fast reactor - Google Patents

Abstract

To provide a fuel assembly of a fast reactor capable of further reducing frequency of replacement of the fuel assembly loaded in a core.SOLUTION: A fuel assembly loaded in a core of a fast reactor has a plurality of fuel elements 2. The fuel element 2 includes: a liquid metal fuel region 7 in which liquid metal fuel 10 containing fuel parent material is present therein; a molten salt fuel region 6 that is disposed above the liquid metal fuel region 7 and in which molten salt fuel 9 containing fissile material and the fuel parent material is present; and a spent fuel region 11D that is located above the molten salt fuel region 6 and in which spent fuel 11 containing the fuel parent material is present. The liquid metal fuel region 7 comes into contact with the molten salt fuel region 6 and the molten salt fuel region 6 comes into contact with the spent fuel region 11D. The fuel parent material supplied from the molten salt fuel region 6 to the liquid metal fuel region 7, and from the spent fuel region 11D via the molten salt fuel region 6 to the liquid metal fuel region 7 is converted into fissile material in the liquid metal fuel region 7, and the converted fissile material is supplied to the molten salt fuel region 6.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fuel assembly of a fast reactor and a core of a fast reactor.

In a fast reactor, a core is arranged in a reactor vessel, and the reactor vessel is filled with a liquid metal as a coolant, for example, liquid sodium or the like. The core is loaded with multiple fuel assemblies having multiple fuel elements in which fissile materials such as fissile plutonium (eg, ²³⁹ Pu) and fuel parent materials such as depleted uranium (U) are encapsulated in cladding. Will be done. Specifically, the fuel assembly has a plurality of fuel elements, a trumpet pipe and an entrance nozzle. The entrance nozzle supports the lower ends of multiple fuel elements. A wire spacer attached to the fuel element is wound around the outer surface of each fuel element, and the wire spacers hold the fuel elements at a predetermined interval between the fuel elements. The trumpet tube surrounds a bundle of fuel elements supported by an entrance nozzle. The lower end of the trumpet tube is attached to the entrance nozzle. At the upper end of the trumpet pipe, a coolant outflow portion located above the fuel element is formed.

Solid oxide fuel and solid metal alloy fuel are generally used as the nuclear fuel material contained in the fuel element, and have abundant achievements. Japanese Patent Laying-Open No. 2018-71997 uses a mixed oxide fuel (MOX fuel) in which uranium and plutonium, which are solid oxide fuels, are mixed as a core fuel, and uranium, which is another solid oxide fuel, and minor actinide are mixed. The core of a fast reactor using the other mixed oxide fuel (MAOx fuel) as the internal blanket fuel is described.

However, there are also examples of using liquid fuels such as liquid metal alloys and molten salts as nuclear fuel materials. For example, in Japanese Patent Application Laid-Open No. 64-32189, a liquid metal fuel such as a plutonium (Pu) -uranium (U) -bismus (Bi) alloy is sealed in a cladding tube, and a molten salt region containing no nuclear fuel material is defined. Fuel elements placed in cladding above the liquid metal fuel region are disclosed. Further, Japanese Patent Application Laid-Open No. 2014-10022 describes a fuel element in which a molten fluoride salt containing thorium (Th) and a fissile material (uranium 235 ( ²³⁵ U), plutonium 239 ( ²³⁹ Pu), etc.) is sealed in a cladding tube. Is disclosed. However, these fuel elements described in JP-A-64-32189 and JP-A-2014-10022 do not have blanket fuel.

JP-A-2018-71997 Japanese Unexamined Patent Publication No. 64-32189 Japanese Unexamined Patent Publication No. 2014-10022

By operating a fast reactor, fissile materials ( ²³⁹ Pu, etc.), which are the main components of the core fuel, are consumed by the fission reaction (combustion of nuclear fuel). On the other hand, in the core fuel existing in the core fuel region in the core of a fast reactor, fuel parent material ( ²³⁸ U, etc.) also exists in addition to fissile material, and by capturing neutrons of the fuel parent material contained in the core fuel. Fissile material ( ²³⁹ Pu, etc.) is newly generated. When the blanket region is arranged above and below the core fuel region or around the core fuel region, the fuel parent material ( ²³⁸ U, etc.), which is the main component of the blanket fuel in the blanket region, is the core fuel region. Fissile material ( ²³⁹ Pu, etc.) is produced by capturing the neutrons leaking from the reactor.

Here, the blanket fuel is a nuclear fuel that contains almost no fissile material such as ²³⁹ Pu and instead contains a large amount of fuel parent material such as ²³⁸ U. The fuel parent material ( ²³⁸ U, etc.) does not contribute to fission in the core of the fast reactor as it is, but it changes to a fissile material ( ²³⁹ Pu, etc.) by the neutron capture reaction that captures neutrons, so that the fast reactor Contributes to fission in the core.

The ratio of the amount of fissile material produced to the amount of consumption in a fast reactor is often referred to as the conversion ratio or growth ratio. Here, the conversion ratio for fissile Pu, which is a fissile material, is defined in the following three ways.

(1) Core fuel conversion ratio
Core fuel Pu production / Core fuel Pu consumption (2) Blanket fuel conversion ratio
Blanket fuel Pu production / Core fuel Pu consumption (3) Core conversion ratio
Total of core fuel conversion ratio and blanket fuel conversion ratio Generally, in a fast reactor, the core fuel conversion ratio <1, but by adding the blanket fuel conversion ratio, a conversion ratio ≥ 1 is achieved for the entire core. That (ie, fuel proliferation) is possible. In this case, as the combustion of the nuclear fuel progresses, the amount of Pu in the entire core including the blanket fuel increases, but the amount of Pu contained in the core fuel gradually decreases. Therefore, the fuel assembly loaded in the core of the fast reactor is replaced with a new fuel assembly having a burnup of 0 GWd / t after a predetermined combustion period (operation cycle length) has elapsed. In order to improve the fuel economy of the core, a long-life fuel assembly that requires less frequent replacement of the fuel assembly is required.

Further, in order to reuse the Pu generated by the blanket fuel, the fuel assembly containing the core fuel and the blanket fuel, which is taken out as the spent fuel assembly from the core of the fast reactor after the elapse of a predetermined combustion period, is reprocessed. A series of recycling treatments such as transporting to a processing facility, recovering Pu from the nuclear fuel in the spent fuel assembly at the reprocessing facility, and processing the recovered nuclear fuel into core fuel are required.

Each fuel element described in JP-A-64-32189 and JP-A-2014-10022 does not have a blanket fuel. For this reason, in the core of a fast reactor loaded with each fuel assembly containing each fuel element, the conversion ratio of the core fuel is less than 1, and it is necessary to frequently change the fuel.

For this reason, the inventors have worked on the development of a long-life fuel assembly that can further reduce the frequency of refueling.

An object of the present invention is to provide a fuel assembly of a fast reactor and a core of a fast reactor capable of further reducing the replacement frequency of the fuel assembly loaded in the core.

The features of the present invention that achieve the above-mentioned object are
Has multiple fuel elements
The fuel element is located above the first fuel region and the first fuel region where the liquid metal fuel containing the fuel parent material is present, and the second fuel region where the molten salt fuel containing the nuclear fissionable material and the fuel parent material is present. , And a third fuel region located above the second fuel region and in which the nuclear fuel material, including the fuel parent material, is present.
The upper end of the first fuel region is in contact with the lower end of the second fuel region, and the upper end of the second fuel region is in contact with the lower end of the third fuel region.

During operation of the high-speed furnace, in the fuel element, the fuel parent material in the second fuel region is arranged below the second fuel region from the second fuel region and comes into contact with the second fuel region. In the first fuel region, the fuel parent material supplied from the second fuel region is converted into a fissionable material, and this nuclear fissure material produced by the conversion in the first fuel region is converted from the first fuel region to the first fuel region. The fuel parent material supplied to the two fuel regions and further contained in the nuclear fuel material in the third fuel region is supplied to the first fuel region via the second fuel region and converted into a fissionable material in the first fuel region. Since this fissionable material is also supplied from the first fuel region to the second fuel region, the life of the fuel assembly having the fuel element is further extended, and the fuel assembly loaded in the core of the fast reactor is replaced accordingly. The frequency is further reduced.

The purpose mentioned above is
Has multiple fuel elements
The fuel element is arranged above the nuclear fuel material filling region, which is mixed and filled with liquid metal fuel containing the fuel parent material and the molten salt fuel containing the nuclear fission material and the fuel parent material, and the nuclear fuel material filling region. It has a nuclear fuel material area where nuclear fuel material including fuel parent material exists,
The upper end of the nuclear fuel material filling region can also be achieved by contacting the lower end of the nuclear fuel material region.

The fuels of the liquid metal fuel containing the fuel parent material and the molten salt fuel containing the nuclear fission material and the fuel parent material, which are mixed and filled in the nuclear fuel material filling region in the fuel element when the operation of the high speed reactor is started, are respectively. Within the molten fuel element, there is a first fuel region in which the molten liquid metal fuel resides, and a molten molten salt fuel that is located above the first fuel region and is in contact with the first fuel region. A second fuel region is formed. As a result, the fuel parent material in the second fuel region is supplied from the second fuel region to the first fuel region arranged below the second fuel region, and in the first fuel region, from the second fuel region. The supplied fuel parent material is converted into a nuclear fissure material, and this nuclear fissure material produced by the conversion in the first fuel region is supplied from the first fuel region to the second fuel region, and further, the nuclear fuel in the nuclear fuel material region. The fuel parent material contained in the substance is supplied to the first fuel region via the second fuel region and converted into a fissionable substance in the first fuel region, and this nuclear fissure material is also supplied from the first fuel region to the second fuel region. Therefore, the life of the fuel assembly having the fuel element is further extended, and the replacement frequency of the fuel assembly loaded in the core of the fast reactor is further reduced accordingly.

The preferred configuration of the nuclear fuel material replenishment method in the fuel assembly is described below.

(A) It has a plurality of fuel elements, and the fuel elements are arranged above the first fuel region and the first fuel region in which the liquid metal fuel containing the fuel parent material is present, and the fissionable substance and the fuel parent material are contained. It has a second fuel region in which the molten salt fuel containing the fuel is present, and a third fuel region in which the nuclear fuel material including the fuel parent material is present, which is located above the second fuel region, and the upper end of the first fuel region is the second. A method of replenishing nuclear fuel material in a fuel assembly of a fast reactor, which is in contact with the lower end of the fuel region and the upper end of the second fuel region is in contact with the lower end of the third fuel region.
When the nuclear fuel material in the third region disappears, the fuel assembly loaded in the core of the fast reactor is taken out of the reactor vessel and taken out.
Remove the upper end plug that is blocking the upper end of the cladding of the fuel element contained in the removed fuel assembly.
After that, the nuclear fuel material including the fuel parent material is replenished from the upper end of the cladding tube into the cladding tube to form a third fuel region located above the second fuel region.
A method of replenishing nuclear fuel material in a fuel assembly of a fast reactor in which the upper end of a cladding tube is closed by an upper end plug.

According to the present invention, the frequency of replacement of the fuel assembly loaded in the core can be further reduced.

It is a vertical sectional view of the fuel element used for the fuel assembly of the fast reactor of Example 1 which is a preferable example of this invention. It is a cross-sectional view of the fuel assembly having a plurality of fuel elements shown in FIG. It is a perspective view of the core of the fast reactor loaded with a plurality of fuel assemblies shown in FIG. It is a vertical cross-sectional view of the core of the fast reactor shown in FIG. 3 on the central axis. It is explanatory drawing which shows the replenishment method of the nuclear fuel material in the fuel assembly shown in FIG. 2, (a) is the state of the fuel element contained in the fuel assembly before the start of a fast reactor, (b) is the fuel element. In the state where the spent fuel existing above the molten salt fuel region is exhausted, (c) is a state in which the upper end plug of the fuel element is removed and the spent fuel is replenished in the cladding tube from the upper end of the cladding tube. (D) is an explanatory view showing a state in which the upper end of the cladding tube is closed with an upper end plug after the replenishment of the spent fuel into the cladding tube is completed. It is a vertical cross-sectional view of the fuel element contained in the fuel assembly of the fast reactor with a burnup of 0 GWd / t of Example 2, which is another preferable embodiment of the present invention. It is a vertical cross-sectional view of the fuel element included in the fuel assembly of the fast reactor of Japanese Patent Application No. 2017-238372 which is the prior application of the present invention. It is a vertical cross-sectional view of the fuel element contained in the fuel assembly of the fast reactor of Example 3, which is another preferable Example of this invention. FIG. 8 is a vertical cross-sectional view of the core of a fast reactor loaded with a fuel assembly having a plurality of fuel elements shown in FIG. 8 on the central axis. It is a vertical cross-sectional view of the blanket fuel element contained in the blanket fuel assembly loaded in the blanket region surrounding the core fuel region in the core of the fast reactor of Example 4, which is another preferred embodiment of the present invention. It is a vertical cross-sectional view of the core of the fast reactor of Example 4 shown in FIG. 10 on the central axis. It is a vertical cross-sectional view of the fuel element contained in the fuel assembly of the fast reactor of Example 5, which is another preferable Example of this invention. It is a vertical cross-sectional view of the core of a fast reactor loaded with a fuel assembly having a plurality of fuel elements shown in FIG. 1 on the central axis.

A long-lived fuel assembly that reduces the frequency of refueling is proposed by Japanese Patent Application No. 2017-238372. An outline of this fuel assembly will be described below with reference to FIG.

The fuel assembly having a burnup of 0 GWd / t proposed by Japanese Patent Application No. 2017-238372 supports the lower ends of the plurality of fuel elements 2D shown in FIG. 7 by the entrance nozzle, and the plurality of fuel elements supported by the entrance nozzle. It is configured by surrounding 2D with a trumpet tube, which is a tubular structure. The lower end of the trumpet tube is attached to the entrance nozzle. A plurality of such fuel assemblies are loaded into the core of a columnar fast reactor to form the core of a columnar fast reactor.

The fuel element 2D has a liquid metal fuel region 7 and a molten salt fuel region from the lower end to the upper end in a cladding tube 3 whose upper end is closed by the upper end plug 4 and whose lower end is closed by the lower end plug 5. 6 is placed. The molten salt fuel region 6 is located above the liquid metal fuel region 7. In the cladding tube 3, a gas plenum 13 is formed above the molten salt fuel region 6. Molten salt fuel 9, such as PuCl ₃ , UCl ₃ , NaCl and MgCl ₂ , contains fissile material (eg, ²³⁹ Pu, etc.) and fuel parent material (eg, ²³⁸ U) at a burnup of 0 GWd / t. The molten salt fuel region 6 is filled. The liquid metal fuel 10, for example, a U-Bi alloy is filled in the liquid metal fuel region 7. The liquid metal fuel 10 is a blanket fuel. The liquid metal fuel 10 does not contain fissile material and contains a fuel parent material (for example, ²³⁸ U) at a burnup of 0 GWd / t.

During the operation of the fast reactor, in the molten salt fuel region 6 of the fuel element 2D, the fissile material ²³⁹ Pu, which is the main component of the molten salt fuel 9, is consumed by its own fission reaction (that is, combustion of nuclear fuel). To. Furthermore, due to the neutron capture reaction in which ²³⁸ U, which is the fuel parent substance contained in the molten salt fuel 9, captures the neutrons generated in the fission reaction of ²³⁹ Pu, fissile materials ( ²³⁹ Pu, etc.) are newly added in the molten salt fuel region 6. Is generated in.

Further, in the liquid metal fuel region 7 of the fuel element 2D, ²³⁸ U, which is the main component of the liquid metal fuel 10, captures neutrons leaking from the molten salt fuel region 6, and the neutron capture reaction causes fissionability. It is nuclear-converted into a substance ( ²³⁹ Pu, etc.). That is, a fissile material ( ²³⁹ Pu or the like) is produced in the liquid metal fuel region 7 of the fuel element 2D.

By the way, at the boundary between the molten salt fuel region 6 and the liquid metal fuel region 7, the molten salt fuel 9 and the liquid metal fuel 10 are in contact with each other in a molten state, so that in the region where the molten salt fuel 9 and the liquid metal fuel 10 are in contact with each other. , by a chemical reaction shown in equation (2) below, ²³⁸ U is ²³⁸ U next metal chloride contained in the molten salt fuel 9, ²³⁹ Pu of metal contained in the liquid metal fuel 10, chloride ²³⁹ Pu It becomes.

The chloride ²³⁹ Pu produced as described above has a lower specific gravity than the liquid metal fuel 10, and conversely, the metal ²³⁸ U has a higher specific gravity than the molten salt fuel 9. Therefore, ²³⁹ Pu of chloride diffuses into the molten salt fuel 9 which is the core fuel existing in the molten salt fuel region 6, and ²³⁸ U of the metal is the liquid metal which is the blanket fuel existing in the liquid metal fuel region 7. It diffuses into the fuel 10.

The chemical reaction of the formula (2) that occurs at the boundary between the molten salt fuel 9 and the liquid metal fuel 10 continues until the concentration of each substance involved in this chemical reaction reaches a predetermined equilibrium condition. Therefore, as long as the chemical reaction of the formula (2) continues, the fuel parent substance ²³⁸ U will be the liquid metal fuel (blanket fuel) 10 from the molten salt fuel region 6 in which the molten salt fuel (core fuel) 9 is present. The existing liquid metal fuel region 7 is continuously supplied, and conversely, the fissile material ²³⁹ Pu is continuously supplied from the liquid metal fuel region 7 to the molten salt fuel region 6.

As a result, in this embodiment, the effective conversion ratio of the core is increased by the conversion ratio of the blanket fuel 10 as shown in the following formula (1).

(Effective conversion ratio of core)
= (Conversion ratio of core fuel) + (Conversion ratio of blanket fuel)… (1)
The fuel assembly loaded into the core of the fast reactor comprises a plurality of fuel elements 2D having a liquid metal fuel region 7 and a molten salt fuel region 6 located above the liquid metal fuel region 7 and in contact with the liquid metal fuel region 7. , ²³⁹ Pu, which is a fissionable substance, is burned in the molten salt fuel region 6 in each fuel element 2D, but the supply of ²³⁸ U from the molten salt fuel region 6 to the liquid metal fuel region 7 and the liquid metal fuel region 7 Since ²³⁹ Pu, which is a nuclear fissionable substance, is continuously supplied to the molten salt fuel region 6, the nuclear fisible material such as ²³⁹ Pu in the molten salt fuel region 6 can be burned for a long period of time. Therefore, the replacement frequency of the fuel assembly having a plurality of fuel elements 2D proposed by Japanese Patent Application No. 2017-238372 can be reduced. As a result, the economic efficiency of fuel in the core of a fast reactor loaded with a fuel assembly having a plurality of fuel elements 2D can be greatly improved.

The inventors further conducted various studies in order to realize a fuel assembly capable of further reducing the replacement frequency as compared with the fuel assembly having a plurality of fuel elements 2D proposed by Japanese Patent Application No. 2017-238372. .. As a result of this study, the inventors placed a molten salt fuel region in contact with the liquid metal fuel region above the liquid metal fuel region, and brought the nuclear fuel material containing the fuel parent material into contact with the molten salt fuel region. It has been found that by arranging it above the molten salt fuel region, the replacement frequency can be further reduced as compared with the fuel assembly having a plurality of fuel elements 2D proposed by Japanese Patent Application No. 2017-238372.

Any of spent fuel, depleted uranium, and natural uranium is used as the nuclear fuel material containing the fuel parent material, which is placed above the molten salt fuel region in contact with the molten salt fuel region.

Examples of the present invention reflecting the above-mentioned examination results will be described below.

The fuel assembly of the fast reactor of Example 1, which is a preferred embodiment of the present invention, will be described with reference to FIGS. 1 and 2.

In the fuel assembly 24 of the present embodiment, a bundle of a plurality of fuel elements 2 around which a wire spacer (not shown) is wound on an outer surface is placed in a trumpet pipe 14 which is a tubular structure having a regular hexagonal cross section. It is arranged. The plurality of fuel elements 2 are arranged in an equilateral triangle lattice in the trumpet pipe 14. The lower end of each fuel element 2 is supported by an entrance nozzle (not shown). The lower end of the trumpet tube 14 is attached to the entrance nozzle. The wound wire spacers form a gap of a predetermined width between adjacent fuel elements 2. This gap is a coolant passage through which liquid metal, which is a coolant, flows.

The fuel element 2 has a molten salt fuel region (second fuel region) 6 and a liquid metal fuel region (second fuel region), similar to the fuel element 2D of the fuel assembly proposed by Japanese Patent Application No. 2017-238372 shown in FIG. 1 Fuel region) 7 is arranged in a cladding tube 3 sealed by an upper end plug 4 and a lower end plug 5. The molten salt fuel region 6 is in contact with the upper end of the liquid metal fuel region 7 and is arranged above the liquid metal fuel region 7. The molten salt fuel 9 filled in the molten salt fuel region 6 is, for example, PuCl ₃ , UCl ₃ , NaCl and MgCl ₂ , and is a core fuel. The molten salt fuel 9 contains a fissile material (eg, ²³⁹ Pu, ²⁴¹ Pu, etc.) and a fuel parent material (eg, ²³⁸ U) in the fuel assembly 24 having a burnup of 0 GWd / t. The liquid metal fuel 10 filled in the liquid metal fuel region 7 is, for example, a U-Bi alloy and a blanket fuel. The liquid metal fuel 10 does not contain fissile material but contains a fuel parent material (for example, ²³⁸ U) in the fuel assembly 24 having a burnup of 0 GWd / t.

The molten salt fuel 9 and the liquid metal fuel 10 are in contact with each other at the boundary positions between the molten salt fuel region 6 and the liquid metal fuel region 7.

The melting point of the molten salt fuels 9, PuCl ₃ , UCl ₃ , NaCl and MgCl ₂ , is 837 ° C. For example, by lowering the respective concentrations of PuCl ₃ and UCl ₃ by setting the molar ratio of NaCl and MgCl ₂ in the range of 5: 5 to ₂ : 1, the melting points of PuCl ₃ , UCl ₃ , NaCl and MgCl ₂ are set to 500 ° C. It can also be: PuCl _{3, UCl 3,} by adjusting the respective amounts of NaCl and MgCl _2, can be PuCl _3, UCl _3, preferably the melting point of the melting point of NaCl and MgCl _2. Further, the melting point of the U-Bi alloy, which is the liquid metal fuel 10, is in the range of 880 ° C. to 1200 ° C., and the melting point of the U-Bi alloy is set to the desired melting point in the range of 880 ° C. to 1200 ° C. by changing the ratio of Bi. can do.

In the fuel element 2, unlike the fuel element 2D, a support member (for example, a wire net) 12 having a large number of through holes is arranged at the upper end position of the molten salt fuel region 6 and attached to the inner surface of the cladding tube 3. Further, in the cladding tube 3, the spent fuel region (nuclear fuel material region) (third fuel region) 11D including the spent fuel 11 which is the nuclear fuel material containing the fuel parent material (for example, ²³⁸ U) is supported by the cladding tube 3. It is formed on top of 12. Since the specific gravity of the spent fuel 11 is larger than the specific gravity of the molten salt fuel 9 and the liquid metal fuel 10, the support member 12 is the spent fuel 11 in the cladding tube 3 from the upper side to the lower side of the molten salt fuel region 6. Supports the spent fuel 11 so that it does not fall. The gas plenum 13 is formed in the cladding 3 above the spent fuel region 11D. The gas plenum 13 is filled with an inert gas.

Instead of the spent fuel 11, natural uranium or depleted uranium, which is a nuclear fuel material containing a fuel parent substance, may be used. When natural uranium or depleted uranium is used, the natural uranium or depleted uranium is also filled on the support member 12 provided in the cladding tube 3.

In the fuel assembly 24 having a burnup of 0 GWd / t, the liquid metal fuel region 7 in the cladding 3 of the fuel element 2 is filled with a large number of pellet-shaped solid liquid metal fuels 10 and melted in the cladding 3. The salt fuel region 6 is filled with a large number of pellet-shaped solid molten salt fuels 9, and the spent fuel region 11D in the cladding 3 is filled with a large number of pellet-shaped solid spent fuels 11. There is. The spent fuel 11 is an oxide fuel in a spent fuel assembly taken out from the cores of light water reactors such as boiling water reactors and pressurized water reactors, and other fast reactors.

The liquid metal fuel 10, the molten salt fuel region 6, and the spent fuel region 11D in the fuel element 2 are the nuclear fuel material filling region 8. The axial length of the nuclear fuel material filling region 8 is called the effective fuel length. The effective fuel length of the fuel assembly 24 is the same as the effective fuel length of the fuel element 2. In all the fuel assemblies 24 loaded in the core 1, the positions of the boundary between the liquid metal fuel region 7 and the molten salt fuel region 6 in each fuel element 2 from the lower end of the effective fuel length are the same. There is.

The core 1 arranged in the reactor vessel (not shown) of a fast reactor has a plurality of fuel assemblies 24 including a plurality of fuel elements 2 as shown in FIG. The alternate long and short dash line shown in FIG. 4 indicates the central axis of the core 1. FIG. 4 shows a vertical cross section of the core 1 about the central axis. The core 1 loaded with a plurality of fuel assemblies 24 including the plurality of fuel elements 2 forms a liquid metal fuel layer 7B, a molten salt fuel layer 6B, and a nuclear fuel material layer 11A from the lower end to the upper end in the axial direction. ing. The liquid metal fuel layer 7B is arranged with a liquid metal fuel region 7 in each fuel element 2 included in each fuel assembly 24 loaded in the core 1, and the liquid metal fuel layer 7B is a fuel element thereof. It is formed by the liquid metal fuel region 7 in 2. The molten salt fuel layer 6B is arranged with a molten salt fuel region 6 in each fuel element 2 included in each fuel assembly 24 loaded in the core 1, and the molten salt fuel layer 6B is composed of these fuel elements. It is formed by the molten salt fuel region 6 in 2. The nuclear fuel material layer 11A is filled with spent fuel 11 which is a fuel material containing a fuel parent material in each fuel element 2 contained in each fuel assembly 24 loaded in the core 1 (a spent fuel region ( The nuclear fuel material region) 11D is arranged, and the nuclear fuel material layer 11A is formed by the spent fuel region 11D in these fuel elements 2.

A part of the fuel assembly 24 in the core 1 is a fuel assembly having a burnup of 0 GWd / t. The operation of the fast reactor is started. Liquid metal (for example, liquid sodium), which is a coolant existing in the reactor vessel, is supplied into the trumpet pipe from the entrance nozzle in the fuel assembly 24, and is formed in the coolant passage formed between the fuel elements 2. Is released to the outside of the fuel assembly 24.

During the operation of the fast reactor, in each fuel element 2 of the fuel assembly 24, in the molten salt fuel region 6, the fissile material ²³⁹ Pu, which is the main component of the molten salt fuel 9, fissiones due to the capture of neutrons. Generates heat. The generated heat is transferred to the liquid metal, which is a coolant that rises in the coolant passage formed between the fuel elements 2. This liquid metal cools the fuel element 2. The liquid metal (coolant) whose temperature has risen due to the generated heat is discharged into the reactor vessel from the upper end of the fuel assembly 24. As the fission progresses, ²³⁹ Pu and the like of the fissile material contained in the molten salt fuel 9 are consumed. Further, the neutron capture reaction to capture ^{neutrons 238} U contained in the molten salt fuel 9 occurs in fission reaction ²³⁹ Pu, in molten salt fuel area 6 fissile material ⁽²³⁹ Pu, etc.) are newly generated.

When the operation of the high-speed furnace is started, fission of a fissile material such as ²³⁹ Pu occurs in each fuel element 2, and the temperature in the fuel element 2 becomes higher than the melting point of the molten salt fuel 9 and the liquid metal fuel 10. , The molten salt fuel 9 and the liquid metal fuel 10 are each in a molten state. Therefore, at the boundary between the molten salt fuel region 6 and the liquid metal fuel region 7, the molten molten salt fuel 9 and the molten liquid metal fuel 10 come into contact with each other. Since the specific gravity of the molten molten salt fuel 9 is smaller than the specific gravity of the molten liquid metal fuel 10, the molten molten salt fuel 9 is located above the molten liquid metal fuel 10 in the cladding tube 3.

Further, in the liquid metal fuel region 7 of the fuel element 2, ²³⁸ U, which is the main component of the liquid metal fuel 10, captures neutrons leaking from the molten salt fuel region 6, and the neutron capture reaction causes fissionability. It is nuclear-converted into a substance ( ²³⁹ Pu, etc.). That is, fissile material ( ²³⁹ Pu, etc.) is newly generated also in the liquid metal fuel region 7 of the fuel element 2.

In the vicinity of the boundary between the molten salt fuel region 6 and the liquid metal fuel region 7 where the molten salt fuel 9 and the liquid metal fuel 10 are in contact with each other in a molten state, the molten salt fuel 9 is produced by the chemical reaction represented by the following formula (2). ²³⁸ U is ²³⁸ U next metal chloride contained, ²³⁹ Pu of metal contained in the liquid metal fuel 10 becomes ²³⁹ Pu chloride.

Pu (metal) + UCl ₃ (chloride) → PuCl ₃ (chloride) + U (metal)… (2)
The chemical reaction represented by the formula (2) occurs because Pu is more likely to bind to chlorine (Cl) in U and Pu.

Since ²³⁹ Pu of chloride has a lower specific gravity than liquid metal fuel 10 and ²³⁸ U of metal has a higher specific gravity than molten salt fuel 9, ²³⁹ Pu of chloride diffuses into the molten salt fuel region 6 and the metal. ²³⁸ U diffuses into the liquid metal fuel region 7. As long as the chemical reaction of formula (2) continues, ²³⁸ U of metal is continuously supplied to the liquid metal fuel region 7, and ²³⁹ Pu of chloride is continuously supplied to the molten salt fuel region 6.

By the way, in the liquid metal fuel region 7, as a result of the chemical reaction of the formula (2), an amount of ²³⁹ Pu that is in equilibrium with the molten salt fuel 9 remains. Then, a fission reaction of ²³⁹ Pu remaining in the liquid metal fuel region 7 and a fission reaction of ²³⁸ U and the like contained in the liquid metal fuel 10 in the liquid metal fuel region 7 to a small extent also occur.

Of the fission-producing nuclides (hereinafter referred to as FP (Fission Products) nuclides) generated by the fission reaction in the liquid metal fuel region 7 of each fuel element 2, most of the FP nuclides except the platinum group FP nuclides are liquid. The specific gravity is smaller than that of the liquid metal fuel 10 in the metal fuel region 7. Therefore, the generated FP nuclei rise to the boundary between the molten salt fuel region 6 and the liquid metal fuel region 7, and further, the molten salt of the molten salt fuel 9 in the molten salt fuel region 6 that comes into contact with the liquid metal fuel 10. It causes a chemical reaction represented by the following formula (3) with MgCl ₃ (chloride), which is a component, and diffuses into the molten salt fuel region 6 in the form of an FP salt.

FP (elemental substance) + (3/2) MgCl ₃ (chloride)
→ FPCl ₃ (chloride) + (3/2) Mg (metal)… (3)
That is, in the used liquid metal fuel 10, almost no FP nuclide remains except for the platinum group FP nuclide. Therefore, the process of recovering the FP nuclide from the used liquid metal fuel 10 is almost unnecessary, that is, the process of separating the FP nuclide is almost unnecessary in the reprocessing of the used liquid metal fuel 10. Therefore, the reprocessing process of the used fuel assembly 24 is greatly simplified.

In the fuel assembly 24 of this embodiment, in each fuel element 2, there is a spent fuel region 11D including the spent fuel 11, which is a nuclear fuel material region, above the molten salt fuel region 6. The operation of the spent fuel 11 in the spent fuel region 11D will be described below.

During the operation of the fast reactor, the molten molten salt fuel 9 is in contact with the spent fuel 11 on the support member 12 through a large number of through holes in the support member 12. When the uranium concentration in the molten salt fuel region 6 of the fuel element 2 decreases due to a nuclear reaction during the operation of the fast reactor, the spent fuel 11 dissolves into the molten molten salt fuel 9 in contact with the fuel element 2. Therefore, the uranium concentration in the molten salt fuel region 6 is kept uniform.

The fuel parent substance ²³⁸ U (metal) contained in the spent fuel 11 dissolved in the molten molten salt fuel 9 diffuses into the molten salt fuel region 6 in which the molten salt fuel 9 exists. A part of ²³⁸ U (metal) diffused in the molten salt fuel region 6 captures neutrons in the molten salt fuel region 6 and is converted into a fissile material ²³⁹ Pu. This ²³⁹ Pu becomes ²³⁹ Pu of chloride in the molten salt fuel region 6.

Moreover, the rest, liquid metal fuel 10 to melt the molten salt fuel region 6 remain ²³⁸ U (metal) most occupy ²³⁸ U of ²³⁸ U diffused into the molten salt fuel region 6 (metal) (metal) Descends to the liquid metal fuel region 7 where The ²³⁸ U (metal) descending to the liquid metal fuel region 7 captures the neutrons leaking from the molten salt fuel region 6 in the liquid metal fuel region 7 and is converted into ²³⁹ Pu. In the vicinity of the boundary between the molten salt fuel region 6 and the liquid metal fuel region 7, the spent fuel 11 on the support member 12 diffuses into the molten salt fuel region 6 and is liquid by the chemical reaction represented by the above formula (2). The ²³⁹ Pu converted from the above-mentioned ²³⁸ U (metal) that has descended to the metal fuel region 7 also becomes ²³⁹ Pu of chloride in the liquid metal fuel region 7. Since ²³⁹ Pu of chloride produced in the liquid metal fuel region 7 has a lower specific gravity than that of the liquid metal fuel 10, it diffuses into the molten salt fuel region 6. Furthermore, due to its chemical reaction, ²³⁸ U of chloride contained in the molten salt fuel 9 ²³⁸ U next to the metal, the ²³⁸ U diffuses into the liquid metal fuel region 7. As described above, in the liquid metal fuel region 7, ²³⁹ Pu converted from ²³⁸ U (metal), which is the fuel parent material contained in the spent fuel 11, is supplied to the molten salt fuel region 6.

In the fuel assembly 24 having a burnup of 0 GWd / t, the spent fuel 11 on the support member 12 contains fissile Pu ( ²³⁹ Pu, etc.) and minor actinides (hereinafter referred to as MA) in addition to the fuel parent material. .. MA includes ²³⁷ Np, ²⁴¹ Am, ^{242 M} Am, ²⁴³ Am, ²⁴³ Cm, ²⁴⁴ Cm, ²⁴⁵ Cm, ²⁴⁶ Cm and the like. The fissile Pu and MA contained in the spent fuel 11 dissolved in the molten molten salt fuel 9 diffuse into the molten salt fuel region 6. The fissile Pu diffused into the molten salt fuel region 6 captures neutrons and undergoes fission in the molten salt fuel region 6. This fission also consumes the fissile Pu contained in the spent fuel 11. The MA diffused into the molten salt fuel region 6 also captures neutrons and undergoes fission. Due to this nuclear fission, the MA contained in the spent fuel 11 is also consumed in the molten salt fuel region 6, and eventually disappears. MA generated by fission of fissile material ( ²³⁹ Pu, etc.) in the molten salt fuel region 6 also captures neutrons, undergoes fission, and disappears.

A part of ²³⁸ U existing in the spent fuel region 11D filled with the spent fuel 11 in the fuel element 2 captures neutrons leaking from the molten salt fuel region 6 and is converted into ²³⁹ Pu. ²³⁹ Pu generated by this conversion is also contained in the spent fuel 11 dissolved in the molten molten salt fuel 9. The ²³⁹ Pu produced in the spent fuel region 11D also captures neutrons in the molten salt fuel region 6 and undergoes fission.

This embodiment has a liquid metal fuel region 7 in which the liquid metal fuel 10 exists and a molten salt fuel region 6 in contact with the liquid metal fuel region 7 arranged above the region 7 and in which the molten salt fuel 9 exists. In the fuel assembly containing a plurality of fuel elements 2 and loaded in the core 1 of the fast reactor, the molten salt fuel region 6 in each fuel element 2 burns ²³⁹ Pu, which is a nuclear fission material, but the molten salt fuel. The supply of the fuel parent material (for example, ²³⁸ U) from the region 6 to the liquid metal fuel region 7 and the supply of the nuclear ^fissure material ²³⁹ Pu from the liquid metal fuel region 7 to the molten salt fuel region 6 continue. Therefore, a nuclear fissionable substance such as ²³⁹ Pu in the molten salt fuel region 6 can be burned for a long period of time. Therefore, the fuel assembly 24 of the present embodiment loaded in the core 1 of the fast reactor has a replacement frequency similar to that of the fuel assembly having a plurality of fuel elements 2D proposed by Japanese Patent Application No. 2017-238372. It can be reduced.

In the fuel assembly 24 of the present embodiment, the liquid metal fuel 10 in the liquid metal fuel region 7, that is, the fuel parent material in the liquid metal fuel region 7 during the operation of the fast reactor without reprocessing the blanket fuel. The fissile material (eg, ²³⁹ Pu) converted from (eg, ²³⁸ U) can be continuously supplied to the molten salt fuel region 6, and the fissile material is fissioned in the molten salt fuel region 6. Is sustained for a long time.

In this embodiment, a spent fuel region 11D in which the spent fuel 11 exists above the molten salt fuel region 6 is formed in the fuel element 2, and as described above, the spent fuel region 11D and the molten salt are formed. In each of the fuel region 6 and the liquid metal fuel region 7, the fuel parent material (for example, ²³⁸ U) contained in the spent fuel 11 captures neutrons and is converted into fissile material (for example, ²³⁹ Pu). Each fissionable material (eg, ²³⁹ Pu) converted from the fuel parent material (eg, ²³⁸ U) contained in the spent fuel 11 in the spent fuel region 11D and the liquid metal fuel region 7 is a molten salt fuel. In the molten salt fuel region 6 together with the fissile material (eg, ²³⁹ Pu) supplied to the region 6 and converted from the fuel parent material (eg, ²³⁸ U) contained in the spent fuel 11 in the molten salt fuel region 6. Contribute to nuclear fission in.

As described above, in the fuel assembly 24 of the present embodiment, since the spent fuel region 11D in which the spent fuel 11 exists is formed in the fuel element 2, the fuel proposed by Japanese Patent Application No. 2017-238372 Compared to the fuel assembly having element 2D, the fuel assembly 24 is substantially as large as the amount of fuel parent material (eg, ²³⁸ U) contained in the spent fuel 11 as a fissile material (eg, ²³⁹ Pu). ) Can be increased. Therefore, the fuel assembly 24 of the present embodiment has a longer life than the fuel assembly having the fuel element 2D proposed by Japanese Patent Application No. 2017-238372, and therefore has a longer life than the fuel assembly having the fuel element 2D. The replacement frequency is also reduced. This embodiment can extend the length of the effective operating cycle of the fast reactor. The economic efficiency of fuel in the core 1 of the fast reactor loaded with the fuel assembly 24 can be further improved.

According to this embodiment, since the spent fuel 11 is filled in each fuel element 2 included in the fuel assembly 24, the reprocessing of the spent fuel 11 is performed during the operation of the fast reactor. Can be carried out within.

In the fuel assembly 24 of this embodiment, the life of the fuel assembly 24 can be further extended by replenishing the nuclear fuel material, that is, the spent fuel in each fuel element 2. The method of replenishing the nuclear fuel material in the fuel assembly 24 will be specifically described with reference to FIG. In FIG. 5, (a) shows the state of the fuel element 2 contained in the fuel assembly 24 having a combustion degree of 0 GWd / t before the start of the fast reactor, and (b) shows the molten salt fuel region in the fuel element 2. The state in which the spent fuel 11 existing above 6 has disappeared is shown, and in (c), the upper end plug 4 of the fuel element 2 is removed and the spent fuel 11 is replenished in the cladding 3 from the upper end of the cladding 3. The state is shown, and (d) shows the state in which the upper end of the cladding tube 3 is closed with the upper end plug 4 after the replenishment of the spent fuel 11 into the cladding tube 3 is completed.

In the fuel element 2 included in the fuel assembly 24 having a burnup of 0 GWd / t before the start of the fast reactor shown in FIG. 5 (a), a large number of pellet-shaped solid liquid metal fuels 10 are placed in the liquid metal fuel region 7. A large number of pellet-shaped solid molten salt fuels 9 are filled in the molten salt fuel region 6, and a large number of pellet-shaped solid spent fuels 11 are filled in the spent fuel region 11D. It does not have the molten salt fuel 9 and the liquid metal fuel 10.

When the operation of the high-speed furnace is started and the temperature of the nuclear fuel material in the fuel element 2 becomes higher than the melting point of the molten salt fuel 9 and the liquid metal fuel 10, the molten salt fuel 9 and the liquid metal fuel 10 are charged in the fuel element 2. Melt. Even if the molten salt fuel 9 and the liquid metal fuel 10 are melted, the arrangement of the molten salt fuel region 6 and the liquid metal fuel region 7 in the fuel element 2 is maintained as shown in FIG. 5A. When the operating time of the high-speed furnace elapses, the spent fuel 11 filled in the fuel element 2 of the fuel assembly 24 is eluted into the molten salt fuel 9 in the molten salt fuel region 6, and the spent fuel is used. 11 disappears (see FIG. 5B).

When the spent fuel 11 in the fuel element 2 is exhausted, the operation of the fast reactor is stopped. The fuel assembly 24, which is loaded in the core 1 of the fast reactor and the spent fuel 11 in the fuel element 2 is extinguished, is taken out of the reactor vessel of the fast reactor. The fuel assembly 24 taken out of the reactor vessel is transported to a replenishment area where replenishment of nuclear fuel material (for example, spent fuel 11) is carried out.

In this replenishment area, a dismantling step of the fuel assembly 24 is carried out. In this step, the trumpet pipe of the fuel assembly 24 is removed from the entrance nozzle, and the lower end plug 5 of each fuel element 2 is removed from the entrance nozzle. The wire spacer wound around the outer surface of the cladding tube 3 of the fuel element 2 is removed. The upper end plug 4 is removed from the upper end of the cladding tube 3. After removing the upper end plug 4, an opening is formed at the upper end of the cladding tube 3 (see FIG. 5C).

After the dismantling step of the fuel assembly 24 is completed, the replenishment step of the spent fuel 11 into the cladding tube 3 is carried out. That is, a large number of pellet-shaped solid spent fuels 11 are filled into the cladding tube 3 from the opening formed at the upper end of the cladding tube 3. A predetermined number of pellets of the filled spent fuel 11 are placed on a support member (eg, wire mesh) 12 located above the molten salt fuel region 6. The upper end plug 4 is attached to the upper end of the cladding tube 3 and the cladding tube 3 is sealed (see FIG. 5D).

After that, a reassembly step of the fuel assembly 24 is carried out in the replenishment area. That is, one end of the wire spacer is attached to the lower end plug 5, the wire spacer is wound around the outer surface of the cladding tube 3 in which the wire spacer is sealed, and the other end of the wire spacer is attached to the upper end plug 4. The lower end plug 5 of each fuel element 2 is attached to the entrance nozzle, and the bundle of the fuel element 2 is inserted into the trumpet pipe. The lower end of the trumpet tube surrounding the bundle of fuel elements 2 is attached to the entrance nozzle.

The disassembling step of the fuel assembly 24, the replenishing step of the spent fuel 11, and the reassembling step of the fuel assembly 24 are performed by remote control in a sealed area in the refueling area.

When natural uranium or depleted uranium, which is a nuclear fuel material containing a fuel parent substance, is used instead of the spent fuel 11, the cladding tube is used in the above-mentioned replenishment step of the spent fuel 11 (replenishment step of the nuclear fuel material). From the opening formed at the upper end of 3, a large number of pellet-shaped solid natural uranium or depleted uranium is filled into the cladding 3.

The reassembled fuel assembly 24 is reloaded into the core 1 of the fast reactor. The fast reactor is then restarted. After the restart, the molten salt fuel 9 and the liquid metal fuel 10 in each fuel element 2 contained in the reloaded fuel assembly 24 are melted. The operation of the fast reactor in which the fuel assembly 24 is loaded in the core 1 is continued until the replenished spent fuel 11 in the fuel element 2 is exhausted. The life of the fuel assembly 24 having the fuel element 2 replenished with the spent fuel 11 is further extended, and the replacement frequency of the fuel assembly 24 is further reduced.

The fuel assembly of the fast reactor of Example 2, which is another preferred embodiment of the present invention, will be described with reference to FIG.

The fuel assembly of Example 2 has a plurality of fuel elements 2A shown in FIG. In the fuel element 2A, the particulate (or powdery) molten salt fuel 9 and the liquid metal fuel 10 are mixed and filled below the support member (for example, wire mesh) 12. The spent fuel 11 is filled above the support member 12 in the cladding 3 of the fuel element 2A. In the fuel element 2A, the region below the support member 12 filled with the mixed particulate (or powdery) molten salt fuel 9 and the liquid metal fuel 10 is referred to as a nuclear fuel material filling region. The nuclear fuel material area is in contact with the spent fuel 11.
The mixing ratio of the particulate (or powdery) molten salt fuel 9 and the particulate (or powdery) liquid metal fuel 10 in the mixed cladding 3 is the fuel element 2 of the fuel assembly 24 of Example 1. It is the same as the ratio of the molten salt fuel 9 in the molten salt fuel region 6 and the liquid metal fuel 10 in the liquid metal fuel region 7 in the above.

In a fuel assembly having a burnup of 0 GWd / t having a fuel element 2A, the particulate (or powdery) molten salt fuel 9 and the particulate (or powdery) liquid metal fuel 10 in the fuel element 2A are melted. Absent. After the fuel assembly is loaded into the core of the fast reactor, the operation of the fast reactor is started. When the temperature of the fuel element 2A rises above the melting points of the molten salt fuel 9 and the liquid metal fuel 10 due to the nuclear fission of the nuclear fissionable substance (239Pu, etc.) contained in the molten salt fuel 9 in the fuel element 2A, the fuel element 2A melts. The salt fuel 9 and the liquid metal fuel 10 are melted, and the melted molten salt fuel 9 and the melted liquid metal fuel 10 are separated below the support member 12. As a result, similarly to the fuel element 2 of the fuel assembly 24 of the first embodiment, the molten salt fuel region 6 in which the molten salt fuel 9 exists and the liquid metal fuel region 7 in which the liquid metal fuel 10 exists in the fuel element 2A. Is formed, and the molten salt fuel region 6 comes into contact with the liquid metal fuel region 7 and is formed above the liquid metal fuel region 7.

The fuel assembly of the present embodiment having the fuel element 2A can obtain each effect obtained in the first embodiment.

The fuel assembly of the fast reactor of Example 2, which is another preferred embodiment of the present invention, will be described with reference to FIGS. 8 and 9.

The fuel assembly of this embodiment has a plurality of fuel elements 2B shown in FIG. The fuel element 2B is different from the fuel element 2 used in the first embodiment only in the molten salt fuel region in which the molten salt fuel is present and the liquid metal fuel region in which the liquid metal fuel is present, and the other configurations are the fuel elements. Same as 2. That is, the fuel element 2B has a molten salt fuel region 6A in which the molten salt fuel 9A is present and a liquid metal fuel region 7A in which the liquid metal fuel 10A is present. In a fuel assembly having a burnup of 0 GWd / t having a fuel element 2B, a molten salt fuel 9A containing a highly enriched fissile Pu (eg, ²³⁹ Pu) is present in the molten salt fuel region 6A, and is a liquid metal fuel. In region 7A is a liquid metal fuel 10A containing a low enrichment fissile Pu (eg, ²³⁹ Pu). The enrichment of the fissile Pu of the liquid metal fuel 10A is smaller than the enrichment of the fissile Pu of the molten salt fuel 9A. The molten salt fuel 9A containing a highly enriched fissile Pu specifically contains PuCl ₃ , UCl ₃ , NaCl, and MgCl ₂ . The liquid metal fuel 10A containing a low-rich fissile Pu specifically contains a Pu-U-Bi alloy. The major difference between the fuel element 2B of the present embodiment and the fuel element 2 of the first embodiment is that the liquid metal fuel region of the fuel element 2B contains fissile Pu (for example, ²³⁹ Pu).

The molten salt fuel region 6A of the fuel element 2B is filled with a large number of pellet-shaped solid liquid metal fuels 10, and the molten salt fuel region 6 in the cladding 3 is filled with a large number of pellet-shaped solid molten salt fuels. 9 is filled, and the spent fuel region 11D in the cladding tube 3 is filled with a large number of pellet-shaped solid spent fuel 11.

The degree of enrichment of fissile Pu in the molten salt fuel 9A may be the same as the degree of enrichment of fissile Pu in the molten salt fuel 9 in the fuel element 2 contained in the fuel assembly 24 of Example 1.

The core 1A of a fast reactor loaded with a plurality of fuel assemblies having the fuel element 2B of this embodiment will be described with reference to FIG. A core 1A loaded with a plurality of fuel assemblies including a plurality of fuel elements 2B forms a liquid metal fuel layer 7C, a molten salt fuel layer 6C, and a nuclear fuel material layer 11A from the lower end to the upper end in the axial direction. There is. The liquid metal fuel layer 7C is arranged with a liquid metal fuel region 7A in each fuel element 2B included in each fuel assembly loaded in the core 1A, and the liquid metal fuel layer 7C is composed of these fuel elements 2B. It is formed by the liquid metal fuel region 7A inside. In the molten salt fuel layer 6C, a molten salt fuel region 6A in each fuel element 2B included in each fuel assembly loaded in the core 1A is arranged, and the molten salt fuel layer 6C is composed of these fuel elements 2B. It is formed by the molten salt fuel region 6A inside. The nuclear fuel material layer 11A is the same as the nuclear fuel material layer 11A of the core 1.

Also in the fuel assembly of this embodiment, a fission reaction of ²³⁹ Pu occurs in the molten salt fuel region 6A in the fuel element 2B as in the fuel element 2 in the fuel assembly 24 of the first embodiment, and the liquid metal fuel region 7A At ²³⁸ U, a neutron capture reaction produces ²³⁹ Pu.

Further, in the vicinity of the boundary between the molten salt fuel region 6A and the liquid metal fuel region 7A, a chemical reaction represented by the formula (2) occurs as in Example 1. Therefore, due to this chemical reaction, ²³⁹ Pu, which became chloride, diffused from the liquid metal fuel region 7A into the molten salt fuel region 6A even in the fuel element 2B, and ²³⁸ U, which became metal, became the molten salt fuel region. It diffuses from 6A into the liquid metal fuel region 7A.

The spent fuel 11 filled on the support member 12 in the fuel element 2B also operates in the same manner as the spent fuel 11 in the fuel element 2 in the fuel assembly 24 of the first embodiment.

In this example, each effect produced in Example 1 can be obtained. Further, in this embodiment, in the fuel element 2B of the fuel assembly having a burnup of 0 GWd / t, the liquid metal fuel 10A in the liquid metal fuel region 7A contains a low-enrichment fissile Pu. The supply of ²³⁹ Pu from the fuel region 7A to the molten salt fuel region 6A is started early after the start of operation of the fast reactor. Moreover, the amount of ²³⁹ Pu supplied is larger than that in Example 1. Therefore, the effective conversion ratio of the core in this embodiment is larger than that in Example 1.

Further, in this embodiment, in the retreatment of the liquid metal fuel 10A containing the fission Pu having a low enrichment degree existing in the liquid metal fuel region 7A, the platinum group FP nuclides while leaving ²³⁹ Pu in the liquid metal fuel 10A. It is only necessary to remove a small number of FP nuclides such as. That is, since the liquid metal fuel 10A may be refined instead of being reprocessed, the recycling process is greatly simplified.

The core of the fast reactor of Example 4, which is another preferred embodiment of the present invention, will be described with reference to FIGS. 10 and 11.

As shown in FIG. 11, the core 1B, which is the core of the fast reactor of this embodiment, has a central region 21 and an annular outer peripheral region 22 surrounding the central region 21. The outer peripheral region 22 is a blanket region. The central region 21 is loaded with the plurality of fuel assemblies 24 used in the first embodiment, and the outer peripheral region 22 is a plurality of blanket fuel assemblies having the plurality of blanket fuel elements 16 shown in FIG. 10 (FIG. 10). (Not shown) is loaded.

In the blanket fuel assembly, a bundle of a plurality of blanket fuel elements 16 around which a wire spacer (not shown) is wound around an outer surface is arranged in a trumpet pipe 14 as shown in FIG. The plurality of blanket fuel elements 16 are arranged in an equilateral triangle lattice in the trumpet pipe 14. The lower end of each blanket fuel element 16 is supported by an entrance nozzle (not shown). The lower end of the trumpet tube 14 is attached to the entrance nozzle. The wound wire spacer forms a coolant passage through which the liquid metal, which is a coolant, flows, which is a gap having a predetermined width between the adjacent fuel elements 2.

In the blanket fuel element 16, the molten salt blanket fuel region 17 and the liquid metal blanket fuel 20 in which the molten salt blanket fuel 19 is present are contained in a cladding tube 3 in which the upper and lower ends are sealed by the upper end plug 4 and the lower end plug 5. The existing liquid metal blanket fuel region 18 is formed. The molten salt blanket fuel region 17 is located above the liquid metal blanket fuel region 18 and is in contact with the upper end of the liquid metal blanket fuel region 18. The molten salt blanket fuel 19 is a molten salt blanket fuel containing UCl ₃ , NaCl and MgCl ₂ . The liquid metal blanket fuel 20 is a liquid metal blanket fuel containing a U-Bi alloy.

Specifically, in the blanket fuel element 16, the molten salt blanket fuel region 17 in the cladding tube 3 is filled with a large number of pellet-shaped solid molten salt blanket fuels 19, and the liquid metal blanket fuel in the cladding tube 3 is filled. Region 18 is filled with a large number of pelletized solid liquid metal blanket fuels 20.

In the blanket fuel element 16, the molten salt blanket fuel region 17 and the liquid metal blanket fuel region 18 are the nuclear fuel material filling regions 8A. The axial length of the nuclear fuel material filling region 8A is called the effective fuel length. The effective fuel length of the blanket fuel assembly having the blanket fuel element 16 is the same as the effective fuel length of the blanket fuel element 16. In all blanket fuel assemblies loaded in the core 1B, the positions of the boundaries between the molten salt blanket fuel region 17 and the liquid metal blanket fuel region 18 in each blanket fuel element 16 from the lower end of the effective fuel length are the same. It has become.

In a 0 GWd / t burnup blanket fuel assembly having the blanket fuel element 16, the molten salt blanket fuel 19 filled in the molten salt blanket fuel region 17 and the liquid metal blanket fuel 20 filled in the liquid metal blanket fuel region 18 are , Both are solid. At a burnup of 0 GWd / t, the molten salt blanket fuel 19 and the liquid metal blanket fuel 20 contain a fuel parent material ( ²³⁸ U, etc.) but no fissile material ( ²³⁹ Pu, etc.).

When the operation of the fast reactor having the core 1B is started, first, a fission reaction of a fissile material ( ²³⁹ Pu or the like) occurs in the molten salt fuel region 6 of the fuel element 2 existing in the central region 21. When the temperature in the fuel element 2 of the fuel assembly 24 becomes higher than the melting points of the molten salt fuel 9 and the liquid metal fuel 10, each of the molten salt fuel 9 and the liquid metal fuel 10 is in a molten state. Further, when the temperature in the blanket fuel element 16 becomes higher than the melting points of the molten salt blanket fuel 19 and the liquid metal blanket fuel 20, each of the molten salt blanket fuel 19 and the liquid metal blanket fuel 20 is also in a molten state.

At the boundary between the molten salt blanket fuel region 17 and the liquid metal blanket fuel region 18, the molten molten salt blanket fuel 19 and the molten liquid metal blanket fuel 20 come into contact with each other. Since the specific gravity of the molten molten salt blanket fuel 19 is smaller than the specific gravity of the molten liquid metal blanket fuel 20, the molten molten salt blanket fuel 19 is located above the molten liquid metal blanket fuel 20 in the cladding tube 3. It will be.

In each fuel assembly 24 loaded in the central region 21, as described in Example 1, the supply of ²³⁸ U of metal from the molten salt fuel region 6 to the liquid metal fuel region 7 and the liquid of ²³⁹ Pu of chloride Supply is performed from the metal fuel region 7 to the molten salt fuel region 6, and further, ²³⁸ U contained in the spent fuel 11 in the spent fuel region 11D, the spent fuel region 11D, the molten salt fuel region 6 and the liquid Conversion to ²³⁹ Pu takes place in the metal fuel region 7.

Within each blanket fuel element 16 of the blanket fuel assembly, the fuel parent material ( ²³⁸ U, etc.) existing in each of the molten salt blanket fuel region 17 and the liquid metal blanket fuel region 18 is also the molten salt fuel region of the fuel element 2. The neutrons leaking from 6 are captured and converted into fissile material ( ²³⁹ Pu, etc.). The fissile material thus produced (such as ²³⁹ Pu) is burned by fission in the molten salt blanket fuel region 17 and the liquid metal blanket fuel region 18.

In this example, each effect produced in Example 1 can be obtained. Further, in this embodiment, since the core 1B surrounds the central region 21 with the outer peripheral region 22, the conversion ratio of the entire core 1B is the conversion ratio of the core fuel (molten salt fuel 9) in the central region 21 and the central region. It is the sum of the conversion ratios of the blanket fuel (liquid metal fuel 10) in 21 and the conversion ratios of the molten salt blanket fuel 19 and the liquid metal blanket fuel 20 in the outer peripheral region 22.

Therefore, in this embodiment, the effective conversion ratio of the core can be greatly increased as compared with the first embodiment, and further, the life of the fuel assembly 24 having the fuel element 2 can be extended. , The fuel economy of fast reactors can be improved.

Also in the blanket fuel element 16, many fission-producing nuclides (FP nuclides) are produced by the fission reaction of the fissile material ( ²³⁹ Pu, etc.) in the liquid metal blanket fuel 20. These FP nuclides, except for the platinum group FP nuclides, are smaller than the specific gravity of the liquid metal blanket fuel 20. Therefore, the FP nuclides excluding the platinum group FP nuclides rise to the boundary between the molten salt blanket fuel region 17 and the liquid metal blanket fuel region 18. The FP nuclei that have risen to the boundary between the molten salt blanket fuel region 17 and the liquid metal blanket fuel region 18 cause a chemical reaction represented by the formula (3) between the molten salt blanket fuel 19 and become an FP salt. The generated FP salt diffuses into the molten salt blanket fuel region 17.

Therefore, in the used liquid metal blanket fuel 20, almost no FP nuclide remains except for the platinum group FP nuclide. Therefore, the process of recovering the FP nuclide from the used liquid metal blanket fuel 20 is almost unnecessary, and the reprocessing process of the used liquid metal blanket fuel 20 is greatly simplified.

In the central region 21 of the core 1B of the present embodiment, instead of the fuel assembly 24 of the first embodiment, the fuel assembly having the fuel element 2A of the second embodiment and the fuel assembly having the fuel element 2B of the third embodiment are provided. , And any of the fuel assemblies having the fuel element 2C of Example 5 described below may be loaded.

The fuel assembly of the fast reactor of Example 5, which is another preferred embodiment of the present invention, will be described with reference to FIGS. 12 and 13.

The fuel assembly of Example 5 has a plurality of fuel elements 2C shown in FIG. The fuel element 2C has a configuration in which an adsorbent 23 for adsorbing FP nuclides is added to the fuel element 2 used for the fuel assembly 24 of the first embodiment. The adsorbent 23 is installed on the inner surface of the cladding tube 3 of the fuel element 2C and is arranged above the spent fuel region 11D. Specifically, the adsorbent 23 is arranged in the gas plenum 13. Other configurations of the fuel element 2C are the same as those of the fuel element 2.

As shown in FIG. 13, the core 1C of the fast reactor loaded with the fuel assembly having the plurality of fuel elements 2C has the adsorbent layer 23A in the core 1 of the fast reactor loaded with the fuel assembly 24 of the first embodiment. It has an added configuration. In the adsorbent layer 23A of the core 1C, the adsorbent 23 in the fuel element 2C used for the fuel assembly 24 is arranged.

When the operation of the fast furnace in which the fuel assembly having the plurality of fuel elements 2C is loaded in the core is started, the metal of the metal generated in the fuel element 2 of the fuel assembly 24 in the first embodiment in the fuel element 2C. ²³⁸ U of molten salt fuel region 6 is supplied to the liquid metal fuel region 7, ²³⁹ Pu of chloride is supplied from the liquid metal fuel region 7 to the molten salt fuel region 6, and further, within the spent fuel region 11D. The ²³⁸ U contained in the spent fuel 11 of the above is converted to ²³⁹ Pu in the spent fuel region 11D, the molten salt fuel region 6 and the liquid metal fuel region 7.

FP nuclides such as Cs produced by the fission reaction of ²³⁹ Pu reach the gas plenum 13 from the molten salt fuel region 6. FP nuclides such as Cs in the gas plenum 13 are adsorbed and removed by the adsorbent 23.

The adsorbent 23 provided in the fuel element 2C in this embodiment is applied to the fuel element 2A used for the fuel assembly of the second embodiment and the fuel element 2B used for the fuel assembly of the third embodiment, respectively. You may.

In this example, each effect produced in Example 1 can be obtained. Further, in this embodiment, since the adsorbent 23 is arranged above the spent fuel region 11D in the fuel element 2C, the adsorbent 23 adsorbs FP nuclides such as Cs generated in the fission reaction of ²³⁹ Pu. Since it can be removed, the pressure increase in the cladding tube 3 can be suppressed.

1,1A, 1B, 1C ... core, 2,2A, 2B, 2C ... fuel element, 3 ... cladding tube, 6,6A ... molten salt fuel region, 6B, 6C ... molten salt fuel layer, 7,7A ... liquid metal Fuel region, 7B, 7C ... Liquid metal fuel layer, 8,8A ... Nuclear fuel material filling region, 9,9A ... Molten salt fuel, 10,10A ... Liquid metal fuel, 11 ... Spent fuel, 11A ... Nuclear fuel material layer, 11D ... spent fuel region (nuclear fuel material region), 12 ... support member, 13 ... gas plenum, 16 ... blanket fuel element, 17 ... molten salt blanket fuel region, 18 ... liquid metal blanket fuel region, 19 ... molten salt blanket fuel, 20 ... Liquid metal blanket fuel, 21 ... Central region, 22 ... Outer region, 23 ... Adsorbent, 24 ... Fuel aggregate.

Claims (10)

Has multiple fuel elements
The fuel element is arranged above the first fuel region and the first fuel region in which the liquid metal fuel containing the fuel parent material is present, and the second fuel in which the molten salt fuel containing the nuclear fissure material and the fuel parent material is present. It has a region and a third fuel region that is located above the second fuel region and in which the nuclear fuel material, including the fuel parent material, is present.
A fast reactor fuel characterized in that the upper end of the first fuel region is in contact with the lower end of the second fuel region and the upper end of the second fuel region is in contact with the lower end of the third fuel region. Aggregation. The fuel assembly of a fast reactor according to claim 1, wherein the nuclear fuel material existing in the third fuel region exists on a support member having a plurality of through holes provided in the fuel element. The fuel assembly of a fast reactor according to claim 1 or 2, wherein the adsorbent is arranged in the fuel element above the third fuel region. The liquid metal fuel contains a fissile material in addition to the fuel parent material,
The fast reactor according to any one of claims 1 to 3, wherein the degree of enrichment of the fissile material contained in the liquid metal fuel is smaller than the degree of enrichment of the fissile material contained in the molten salt fuel. Fuel assembly. The fuel assembly of a fast reactor according to any one of claims 1 to 4, wherein the nuclear fuel material existing in the third fuel region is any one of spent fuel, natural uranium and depleted uranium. Has multiple fuel elements
The fuel element is arranged above the nuclear fuel material filling region and the nuclear fuel material filling region, which are mixed and filled with a liquid metal fuel containing a fuel parent material and a molten salt fuel containing a nuclear fission material and a fuel parent material. It has a nuclear fuel material area where nuclear fuel material including fuel parent material exists,
A fuel assembly of a fast reactor, characterized in that the upper end of the nuclear fuel material filling region is in contact with the lower end of the nuclear fuel material region. The fuel assembly of a fast reactor according to claim 6, wherein the nuclear fuel material existing in the nuclear fuel material region exists on a support member having a plurality of through holes provided in the fuel element. The fuel assembly of a fast reactor according to claim 6 or 7, wherein the adsorbent is located in the fuel element above the nuclear fuel material region. A core of a fast reactor, characterized in that the plurality of fuel assemblies according to any one of claims 1 to 8 are loaded. A central region where the plurality of fuel aggregates are arranged, a fourth fuel region where a liquid metal blanket fuel containing a fuel parent material is present, and a melt which is arranged above the fourth fuel region and contains a fuel parent material. A plurality of blanket fuel assemblies having a plurality of blanket fuel elements including a fifth fuel region in which the salt blanket fuel is present are arranged and have an outer peripheral region surrounding the central region.
The core of a fast reactor according to claim 9, wherein the upper end of the fourth region is in contact with the lower end of the fifth fuel region.

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