JPH0694888A - Reprocessing method for spent nitrided fuel - Google Patents

Abstract

PURPOSE:To provide a reprocessing method suitable for nitrided fuel. CONSTITUTION:After used nitrided nuclear fuel is processed by heating so as to allow fusion products of a low boiling point to be separated, when the aforesaid used nuclear fuel is dissolved into fusion zinc containing uranium, nitride other than uranium nitride and plutonium nitride is reduced by uranium so as to be formed into simple substance. The metallic simple substance thus refined is dissolved into fusion zinc. In this case, since uranium nitride and plutonium nitride do not be dissolved into fusion zinc, precipitations are filtered so as to be recovered, and when zinc is removed out of precipitations, uranium nitride and plutonium nitride can thereby be recovered out of used nitrided nuclear fuel.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a reprocessing method for separating reusable materials from spent nitride fuel.

[0002]

2. Description of the Related Art A nuclear reactor is a device that uses a fissile material such as uranium or plutonium to safely and continuously perform a controlled fission reaction to obtain energy. There are several types of nuclear reactors, and among them, fast breeder reactors are called "dream reactors" because more nuclear fuel (plutonium) is produced in the reactor than burned nuclear fuel. Research and development is underway with the aim of commercialization. Since this fast breeder reactor uses high-speed neutrons for nuclear fission, various measures such as using metallic sodium as a coolant have been made in order to prevent the energy of neutrons from being lowered.

By the way, in any nuclear reactor, the reactivity decreases due to the wear of the fissile material in the fuel, and the criticality is no longer reached at a certain time.
After a certain period of time, the fuel will have to be replaced. However, not all the spent fuel taken out of the nuclear reactor is useless, but it includes plutonium newly generated in the nuclear reactor and the rest of uranium 235 that has not yet been fissioned. Further, the spent fuel contains a large amount of uranium 238 as a parent substance (which is a raw material for plutonium).
In view of the uranium resource reserves, therefore, in Japan, useful substances that can be used as nuclear fuel again are recovered without discarding all used nuclear fuel. Reprocessing is carried out in order to recover useful substances (nuclear fuel) from such spent nuclear fuel. In the process of this reprocessing, fission products are removed to become radioactive waste and separated. The fuel becomes a new fuel body again through processes such as conversion, concentration and processing. Such a series of cycles is called a nuclear fuel cycle, and in order to establish a nuclear fuel cycle, it is necessary to first establish a fuel reprocessing method.

The most frequently used method for recovering uranium and plutonium from spent nuclear fuel is the Purex method. In the Purex method, spent nuclear fuel taken out from a fuel rod is dissolved in nitric acid, and plutonium and uranium are extracted and separated and recovered from this aqueous solution by a mixed solution of tributyl phosphate (TBP) and dodecane. And since the oxide fuel is suitable for the Purex method,
A nuclear fuel cycle has been established when uranium oxide is used as a fuel.

[0005]

By the way, in order to use the nuclear fission energy as an energy resource that can be used for a long period of time, the above-mentioned fast breeder reactor is indispensable. Considering from the viewpoint that a fast breeder reactor undergoes nuclear fission in a state where the energy of neutrons in the reactor is not lowered, nitride fuel is used in the fast breeder reactor because the energy of neutrons is not lower than that of oxide fuel. It is more suitable as an available fuel than an oxide fuel.

However, when the Purex method is used to reprocess the nitride fuel, when the nitride fuel is dissolved in nitric acid, the uranium nitride is entirely uranium nitrate (U).
A nitric acid aqueous solution of O ₂ (NO ₃ ) ₂ ) is obtained, and what is obtained by thermal decomposition of the nitrate extracted from this is an oxide of uranium or plutonium. Therefore, in order to obtain a nitride fuel suitable as a fuel for a fast breeder reactor again, such an oxide of uranium or plutonium must be converted into a nitride again. However, this requires a lot of cost and processing, and conversely reduces the advantages of nitride nuclear fuel.

The present invention has been made in view of the above problems, and an object thereof is to provide a reprocessing method suitable for a spent nitride fuel in order to establish a suitable nitride nuclear fuel cycle. Especially.

[0008]

In order to solve the above problems, in the processing method according to the present invention, spent nitride fuel is decoated and then treated in a molten metal bath in which a reducing agent is dissolved. , Reducing the nitride of FP (fission product) and dissolving it in the molten metal bath to separate it from the nitride fuel, and reuse the separated nitride fuel in the form of nitride as nuclear fuel. Is characterized by. The reducing agent used is preferably uranium metal, and the molten metal used is preferably zinc.

That is, the treatment method according to the present invention is a method of treating spent nitride fuel in a nuclear reactor to separate reusable substances, and includes a step of performing leaching treatment with molten zinc. Specifically, a heat treatment step of removing the substance having a low boiling point from the spent nitride fuel by subjecting the spent nitride fuel to heat treatment, and uranium to the heat treated spent nitride fuel. And a reduction step of reducing the nitride of a specific fission product contained in the spent nitride fuel, and an leaching step of leaching the spent nitride fuel that has undergone the reduction step with molten zinc. And are included.

[0010]

[Function] The spent nitride fuel contains a substance (FP) produced by nuclear fission as an impurity. In the present invention, by heating the nitride fuel after decladding, Those with a low boiling point are removed. At this stage, most of the non-metal elements constituting the impurities and the low-boiling metal elements are removed.

Here, due to fission, two or more FPs (fission products) are produced from the raw material UN (uranium nitride). Here, if fission products generated from one UN are designated as FP (1) and FP (2), one UN is one N
Since it has only (nitrogen), one of the FP elements becomes a nitride and the other FP element becomes a simple substance as shown in the following formula.

UN → FP (1) N + FP (2) or FP (1) + FP (2) N In this case, whether FP (1) is a nitride or FP (2) is a nitride Depends on the stability of FP (1) N and FP (2) N.

Therefore, among those treated in the molten zinc bath after the heat treatment, there are FP element simple substance and FP element nitride.

Among these, the metal element among the simple substance of FP element forms a molten alloy with molten zinc. On the other hand, since uranium metal is mixed in molten zinc, it is more unstable than UN.
Elemental nitrides are reduced to elemental metals by uranium metal before forming molten alloys with molten zinc. Here, since the nitride fuel is deposited in the molten zinc bath, it is separated from the FP element (impurity) dissolved in the molten zinc bath by the filtration method. Therefore, at this stage, most of the metal elements constituting the impurities will be removed.

Most of the non-metal elements and metal elements constituting impurities are removed from the spent nitride fuel that has passed through these steps, and therefore, it can be used as U nitride, Pu nitride, and nuclear fuel. Finally, a mixture of other MA (minor actinide) nitrides will be obtained. Since this mixture can be used as it is as a nuclear fuel after the zinc is removed, it is possible to establish a nuclear fuel cycle of a nitride fuel by adopting the method of the present invention.

The zinc used can be reused by separating and recovering it by distillation. Also,
The FP element separated from zinc by distillation is treated as a solidified body with a high volume reduction using zinc that remains in a small amount as a matrix.

Incidentally, it was separated from zinc by distillation.
From the FP element, it is possible to vaporize and collect Sr, which is a highly exothermic nuclide by heating, and to collect the platinum group element by a known metallurgical method.

[0018]

Example A characteristic of the treatment method according to the present example is that spent nitride fuel, after decladding, is treated with a molten zinc bath in which uranium metal is dissolved, and nitridation of FP (fission product) element The substance is reduced and dissolved in the molten zinc bath to be separated from the nitride fuel, and the separated nitride fuel is reused as a nuclear fuel in the form of nitride.
The reducing agent used is preferably uranium metal, and the molten metal used is preferably zinc.

In short, this embodiment is characterized in that the actinide element and the FP element are separated by utilizing the difference in thermodynamic properties between them, and the principle is as follows. . (1) Utilizing the difference in stability of nitrides.

(2) Utilizing the difference in the boiling points of the simple substances.

(3) Utilizing the reduction reaction of nitride to a simple substance by uranium metal.

(4) Utilizing leaching from uranium nitride by forming a molten alloy with elemental Zn. The following is a description of each item.

(1) Utilizing the difference in stability of nitrides.

When a nitride fuel is used in a nuclear reactor and undergoes nuclear fission, it produces two or more FPs (fission products). Here, the number of nitrogen atoms contained in the nitride fuel UN is one for each uranium atom.

When the fission products generated from one UN are designated as FP (1) and FP (2), one UN is 1
Since it has only N (nitrogen) pieces, one of the FP elements becomes a nitride and the other FP element becomes a simple substance, as shown in the following formula.

UN → FP (1) N + FP (2) or FP (1) + FP (2) N In this case, whether FP (1) is a nitride or FP (2) is a nitride Depends on the stability of FP (1) N and FP (2) N.

Therefore, among those treated in the molten zinc bath after the heat treatment, there are FP element simple substance and FP element nitride.

Here, the temperatures of 1300K and 2000 are shown in FIG.
Standard nitride formation free energies and stability of each element at K are shown. And from this FIG. 2, ThN, Z
rN is the most stable, followed by UN, PuN, rare earth nitrides, alkaline earth metal nitrides, alkali metal nitrides, Z
It can be seen that the transition metal nitrides other than r are stable in order. The nitrides of B, Al, Si, Tl, and Hf are relatively stable, but do not form as FP (fission products). In addition, it is considered that the nitrides which are not described are in the above order, estimated from the values of the nitrides of the elements belonging to the same family. There are no nitrides of the platinum group elements Ru, Rh and Pd.

Here, as a result of uranium fission, many FPs
(Fission products) are produced, but the main elements are atomic numbers from Kr to rare earth elements (Kr, Rb, Sr, Y, Zr, N).
b, Mo, Ru, Rh, Pd, Ag, Cd, In, S
n, Sb, Te, I, Xe, Cs, Ba, rare earth element)
Is.

The number of atoms of FP generated by fission of uranium is as follows: rare earth element + alkaline earth metal element + Zr
And the total number of other elements are almost the same. Therefore, in the FP (fission product) generated in the nuclear reactor, the rare earth element, the alkaline earth element and Zr are obtained as the nitride, and the other elements are obtained as the simple substance.

This will be specifically described as follows. That is, in the spent nitride fuel, Sr, Y, Zr,
Nb, Ba and rare earth elements will be obtained in the form of nitride, while Kr, Rb, Y, Mo, Tc, Ru, R
h, Pd, Ag, Cd, In, Sn, Sb, Te, I,
Elements such as Xe and Cs can be obtained in a single form.

(2) Utilizing the difference in boiling points of simple substances.

Some FP elements have a relatively low boiling point in a simple substance state. Therefore, by selecting an appropriate treatment temperature, the FP element having a relatively low boiling point can be vaporized and separated. Note that FIG. 3 shows the boiling points of elemental elements.

As shown in FIG. 3, the FP element having a relatively low boiling point and its boiling point are Kr;
b: 668 ° C., Sr: 1380 ° C., Cd; 765 ° C., S
b: 1570 ° C, Te: 990 ° C, I: 184 ° C, X
e: -108 degreeC, Cs: 678 degreeC, Ba: 1640 degreeC. Therefore, these FP elements can be vaporized and separated by bringing the system to an appropriate temperature (S10 in FIG. 1).
3).

(3) Nitride to be a simple substance by uranium metal
Utilizes reduction reaction.

In the elements M (1) and M (2), the nitride of M (2) is
Nitride of M (1) M (1) N when more stable than M (1) nitride
And M (2) simple substance are mixed, M (1) N is reduced to the simple substance M (1) as shown in the following formula, while the simple substance M (2) becomes the nitride M (2) N.

M (1) N + M (2) → M (1) + M (2) N Here, referring to FIG. 2 showing the stability of nitrides of each element, it is included in the spent nitride fuel. Among the things that
Rare earth nitrides, alkaline earth nitrides, alkali metal nitrides and transition metal nitrides will be reduced to a simple substance by the uranium metal in the molten zinc bath. As a result, actinide elements whose nitrides are more stable than uranium (all of which can be used as nuclear fuel) and other elements (rare earth nitrides, alkaline earth metal nitrides, alkali metal nitrides and transition metals) Metal nitrides; all of which cannot be nuclear fuels) can be separated.

(4) Utilization of leaching from uranium nitride by forming a molten alloy with elemental Zn. Many elements form molten alloys with zinc. FP element is 10 in zinc
A molten alloy is formed at a temperature of 00 ° C or lower and a boiling point of zinc or lower at a concentration of about 5%. Therefore, by dipping the spent nitride fuel in a molten zinc bath, the uranium metal-reduced rare earth element, alkaline earth metal element, alkali metal nitride and transition metal nitride element, and the spent nitride fuel are used. Among them, originally Mo, Tc, Ru, Rh, P
d, Ag, In, Sn (Kr, Rb, Cd, Sb, T
The elements e, I, Xe and Cs, which have already been vaporized and separated in the previous stage, can be leached and separated and recovered as a molten zinc alloy.

A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a process of a reprocessing step according to the preferred embodiment of the present invention. Regarding the process of this embodiment, a reprocessing process and an FP processing process, which are main processes, will be described.

1) Reprocessing Step The nitride fuel is housed in a metal cylinder having a diameter of about 0.5 cm-2 cm and both ends are sealed by welding (this is called a fuel pin). The operation of cutting the end of the fuel cell and separating the fuel and cladding tube is called decladding. Spent nitride fuel is, for example, nitride FBR (Fast Breeder Reactor)
From the above, it is carried into the nitride reprocessing plant. In this embodiment as well, the used nitride fuel carried in is first decoated and taken out from the fuel pin (S101). The decoated fuel is crushed by a crusher into granules (S102).
The finer the particle size is, the more convenient it is for separation, but it is preferable to prevent the powder from scattering during the separation process. By the way, decoating and crushing may be carried out in separate steps, but it should be carried out in a single step by the tube expansion decoating method (a process of expanding a cladding tube with a roller and simultaneously crushing nuclear fuel), which has been reported recently. Is also possible.

The granules are then subjected to heating (S103) and contact / reduction / leaching treatment (S104) as shown in FIG. Through this whole process, actinide is separated from FP in the form of nitride.

Here, FIG. 2 is a periodic table listing the free energy of formation of a nitride of a predetermined element, FIG. 3 is a periodic table listing the physical property values of a predetermined element, and FIG. 4 is described therein. It is a classification of elements based on their properties. In addition,
In FIG. 4, elements having a high boiling point and stable nitride are group A, elements having a low boiling point and stable nitride are group B, elements having a high boiling point and unstable nitride are shown in FIG. Group C, elements having a low boiling point and unstable nitride are classified as group D.

First, in the heating step S103, the D group elements of FIG. 4 are vaporized and separated, and the elements of the A, B, and C groups remain in the particles as they are. The heating temperature is alkali metal R
The boiling point of b and Cs is about 700 ° C. (Rb: 68
8 ° C, Cs: 678 ° C), approx. 1 for rapid vaporization separation
About 000 ° C is desirable.

In the next contact / reduction / leaching process S104,
The granules are treated with molten zinc containing uranium metal. Here, zinc is selected because it has a low melting point and a low boiling point and is easy to handle (by the way, the melting point of zinc is 41
At 9 ° C, the boiling point is 907 ° C). The reason why the metal used in the leaching step S104 must have a low melting point is that an element having a high melting point requires a high processing temperature equal to or higher than the melting point and is difficult to put into practical use as a device material. Further, the boiling point must be low because elements having a high boiling point require a high temperature in the distillation for recovery, which makes it difficult to recover and reuse them after the treatment in this step. From these viewpoints, the elements that can be used in the leaching process S104 are Zn,
Alkali metal elements, alkaline earth elements, Cd, Sm, E
u, Tl, or a non-metal element. However, alkali metal elements, alkaline earth elements, Sm and Eu have strong reactivity with air and are difficult to handle. Also, Cd and T
l is a toxic substance and is a problem. Non-metallic elements are not preferable because they may form a compound with the FP element. Therefore, considering these points, it can be concluded that zinc is the most suitable.

In this contact / reduction / leaching process S104,
The elements of the A and B groups are reduced by uranium in the molten zinc to become a simple substance (Zr remains as a nitride). Then, these are dissolved, leached, and separated in zinc together with the element of the C group which is originally a simple substance. That is, the elemental or elemental metal element forms a molten alloy with molten zinc and dissolves in the molten zinc. And, since nitride does not dissolve in molten zinc, by filtering this, U nitride, Pu nitride, and other MA (minor actinide) nitrides that can be used as a nuclear fuel can be treated with other FP elements (impurities). ) Will be separated from. In fact, since the density of zinc is about 7, the difference between the specific gravity of the spent nitride fuel and the specific gravity of the molten zinc causes the spent nitride fuel to be deposited in the molten zinc bath and the FP element to be leached. Become.

In this way, the FP element is leached by molten zinc, but the leaching of the impurity FP element is because the nitride of the impurity FP element is more unstable than uranium nitride. This is because the nitride of the impurity FP element is easily reduced by the uranium metal (the following formula).

U + FPN → UN + FP Since ZrN is more stable than UN, Zr will precipitate as a nitride in the molten zinc bath. The reason why uranium is used as a reducing agent is that all FPs except Zr are used.
This is because the elemental nitride can be reduced to a simple substance, and at the same time,
This is because there is no problem when reprocessing the fuel even if it remains in the granules to be treated, and there is no problem if it remains in the molten zinc used for leaching and mixes with high-level waste (mixed in the regenerated fuel). However, it goes without saying that there is no problem).
The amount of U used in this step is an amount corresponding to FP existing in the spent nitride fuel. Since the amount of FP existing in the spent nitride fuel is almost equal to the sum of U and Pu burned in the reactor, the amount of U required for reduction is equal to the sum of burned U and Pu. is there. However,
It is possible to use excess U to accelerate the reaction. However, since excess U mixes with FP to increase the amount of waste, it is appropriate that the amount of U eventually used is up to 10 times that of burned U and Pu.

Here, the specific gravity of the spent nitride fuel is about 10, and when this is pulverized into granules, the bulk specific gravity becomes about 3. Therefore, the volume of the granules per ton of the spent nitride fuel is 300 liters. Therefore, S104
The volume of the molten zinc bath used in is approximately 1 per ton of spent nitride fuel because it is necessary to sufficiently soak the spent nitride fuel.
000 liters are needed. At this time, since the density of zinc is about 7, the difference in specific gravity between the spent nitride fuel and the molten zinc causes the spent nitride fuel to be deposited in the molten zinc bath and the FP element to be leached. .

After the leaching treatment in S104, the U.Pu nitride containing Zr nitride is separated from zinc by the filtration method, but the zinc containing leaching (FP) remains in the U.Pu nitride. . Here, this remaining amount is 1 /
If it corresponds to 100, the leaching treatment has a decontamination factor of 10
It is 0. That is, the amount of FP in the U and Pu nitrides after the leaching process is 1/100 of the original amount. Here, if it is desired to further remove FP, it is desirable to perform the leaching process again.

The U and Pu nitrides after the leaching treatment are
Contains all actinide elements. That is, U, N
p, Pu, Am, Cm and their daughter nuclide Th are contained in the U and Pu nitrides after the leaching treatment (S10).
5). This is because Np, Pu, Am and Cm nitrides are U
This is because it has the same stability as N and is not reduced by uranium metal.

The zinc remaining in the U and Pu nitrides is vaporized and recovered by heating (S106). Then, when zinc is separated by distillation, U, Np, Pu, Am, Cm are later added.
And a mixture of Th nitrides is obtained (S107),
Since they can be used as nuclear fuels themselves, they will be processed into nitride fuels and used again (S108).

By the way, in recent years, in order to reduce the burden of high-level waste disposal, the movement to separate Np, Am, and Cm, which are ultralong half-life nuclides, from high-level waste has been activated, but Not successful enough. That is,
The main one of the methods called this group separation is PUREX.
After separating U and Pu in the process, Np, Am, Cm
The high-level waste liquid containing N is subjected to the extraction operation again to obtain Np, A
This is a method for separating m and Cm, and various extraction solvents have been tried at present, but the separation with other FP elements is difficult and has not been sufficiently successful.

However, in the method of this embodiment, all the actinide elements can be separated from other FP elements at once in the reprocessing step due to the special thermodynamic properties of the actinide nitride (except Zr), It is possible to solve the major problems of high-level waste disposal and group separation. This process is extremely simple, and the devices for the reprocessing process and group separation process are simple and few, and the reprocessing facility will be rationalized.

That is, in the present embodiment, as in the conventional method, once the FP element and MA are separated and then this MA is mixed with U and Pu again, no step is performed, that is, from the spent nitride fuel to PUREX. Without the troublesome process of reconverting U oxides recovered by the method to nitride fuels,
Easily recovered U, Pu, Np, Am,
A mixture of Cm nitrides is obtained (S107). Then, this mixture can be simply reprocessed as a new nitride fuel immediately after starting from the fuel manufacturing / processing step (S10).
8), this advantage is great.

The separated zinc containing the elements of the A, B and C groups is subjected to a distillation treatment, and the zinc is recovered and reused as a leaching solvent (S106). On the other hand, the FP element remaining by distillation is treated as a solidified body with high volume reduction, but in the Examples, this solidified body with high volume reduction is a solidified body with a small amount of zinc left as a matrix. (S107).

However, in the present example, the FP element recovered as a solidified body having a high volume reduction contains a platinum group element useful as a catalyst, Sr useful as a heat source, Cs useful as a radiation source, and the like. ing. Therefore, these useful substances need to be separated from others in a suitable manner. In this example, the FP element after being separated from the actinide element is treated by the following method.

2) FP treatment step The remaining elements of the A, B and C groups are treated as a metal block. This is the most compact high level waste. In some cases, all of the zinc may be left unremoved, either as a zinc alloy or in the form covered with zinc to form high level waste. Zinc is stable to water as seen in zinc-iron plates and is effective as a high-level waste matrix. Storage of high-level waste of metal lumps
It is extremely easy to handle at the time of disposal. This is because the volume and weight per spent fuel is small, and since it is a metal, it has high thermal conductivity and is easy to cool. Therefore, by treating as a metal lump like this method, the waste treatment facility / equipment can be extremely simplified and rationalized.

Further, from the metal lump, Sr, which is a highly exothermic element,
Has a low boiling point of 1380 ° C. and can be vaporized and recovered. Among the rare earth elements, Sm is 1790 ° C. and Eu is 1600.
It has a relatively low boiling point of ℃ and can be vaporized and recovered. In addition,
The low-boiling Cs, Sr, etc. have been vaporized and separated in advance in S103, but by being heated again in this step, even those that could not be separated in S103 can be separated and recovered. These separated elements can be recovered in parallel with other treatments.

In addition, the metal mass contains extremely expensive platinum group elements, which can be recovered by the pyrometallurgical or hydrometallurgical methods used in the known non-ferrous metallurgical industry. The simplest method is to feed this metal mass into the copper metal mass of coarse scouring in the initial process of a copper scouring plant. Thus, the product is processed and refined according to the existing process. By the way, naturally, some of the constituent elements of the metal ingot have a radioisotope, and therefore cannot be added to the process of the existing factory. However, it is clear that the platinum group element in the metal ingot can be purified and recovered by applying the technology of the existing factory process. By the way, Ru and Tc whose higher-order oxides are volatile can be separated and recovered by treating with oxygen and ozone and converting into vaporizable oxides (Ru04 and Tc207).

In this way, the useful elements in the metal mass are easily recovered by the method of the present invention, and the residual high-level waste is advantageous in that the volume and weight are further reduced. That is,
In this example, FP is obtained as a metallic solid mainly composed of a transition metal. This is a solid to which a glass component is not added like a vitrified body. Therefore, a solidified body having a higher degree of volume reduction than the conventional solidified body can be obtained. Further, since it does not contain the highly exothermic nuclides Cs and Sr, the calorific value is small. High volume reduction,
The solidified body with low heat generation is easy to handle during processing, storage and disposal. In addition, each facility / device is significantly smaller than that of the conventional solidified body.

[0062]

The useful effects of the method for reprocessing spent nitride fuel according to the present invention will be summarized as follows.

The spent nitride fuel uranium nitride is
After reprocessing, it is recovered in the form of nitrides, significantly streamlining the process of remanufacturing the recovered nitride fuel.

The reprocessing process is simplified.

The reprocessing facility and equipment are compact.

Np, Am, and Cm, which are problematic nuclides in the disposal of high-level waste, can be recovered simultaneously with U and Pu.

The high-level waste can be made into a very compact form, and the high-level waste treatment, storage and disposal can be remarkably rationalized.

Useful metals can be easily recovered. That is, Cs, which is useful as a gamma radiation source, and Sr, which is useful as a heat source, can be easily recovered from the spent nitride fuel, and the precious platinum group element can be easily recovered as an alloy.

[Brief description of drawings]

FIG. 1 is a diagram showing a process of a reprocessing step according to a preferred embodiment of the present invention.

FIG. 2 is a periodic table listing free energies of formation of nitrides of predetermined elements.

FIG. 3 is a periodic table listing physical property values of predetermined elements.

FIG. 4 is a diagram in which predetermined elements are classified based on their properties for use in the description of the present embodiment.

[Procedure amendment]

[Submission date] March 19, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

FIG. 2 is a diagram showing the free energy of formation of a nitride of a predetermined element based on the periodic table .

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

FIG. 3 is a diagram showing physical property values of predetermined elements based on the periodic table .

Claims (3)

[Claims] 1. A spent nitride fuel is decoated and then treated in a molten metal bath in which a reducing agent is dissolved to reduce the nitride of the fission product element and to dissolve it in the molten metal bath to form a nitride. A method of separating from fuel and reusing the separated nitride fuel in the form of nitride as nuclear fuel. 2. A method for treating spent nitride fuel to separate reusable substances, the method comprising the step of leaching with molten zinc. 3. A method for treating spent nitride fuel to separate reusable substances, wherein the spent nitride fuel is heat treated to reduce the amount of spent nitride fuel from the spent nitride fuel. A heat treatment step to remove substances at the boiling point, and uranium is added to the heat treated spent nitride fuel,
A reduction step of reducing the nitride of a specific fission product contained in the spent nitride fuel, and an leaching step of leaching the spent nitride fuel that has undergone the reduction step with molten zinc. The processing method characterized by.