JP2001153991A - Peprocessing method for spent nuclear fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the processing speed, simplify the process and reduce the size of a reprocessing facility for reprocessing spent nuclear fuel. SOLUTION: As the reprocessing method by fluoride evaporation method for spent nuclear fuel, a fluorination device (a fluidized bed type reactor) 3 and a fluorination device (a flame type reactor) 4 are used. By a fluorination reaction in the fluorination device (fluidized bed type reactor) 3, uranium fluoride is obtained. By a fluorination reaction in the fluorination device (flame type reactor) 4, mixture of fluorides of uranium and plutonium is obtained. By using the flame reactor for fluorination reaction of spent fuel in this manner, since a continuous processing of spent nuclear fuel becomes possible, the processing amount of spent nuclear fuel can be increased. Since the fluoride of uranium and plutonium is recovered as a mixture, the refining process can be deleted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for reprocessing spent nuclear fuel generated in a nuclear power plant.

[0002]

2. Description of the Related Art Reprocessing of spent nuclear fuel includes:
There are a wet method using an aqueous solution and a dry method using no aqueous solution. The wet method is described in, for example, M. Benedict et al., Kiyose Ryohei, Nuclear Chemical Industry, Vol. IV, Chemical Engineering for Fuel Reprocessing and Radioactive Waste Management (Nikkan Kogyo Shimbun), p. The Purex method has been widely adopted. As the dry method, a high-temperature metallurgy method, a high-temperature chemical method, and a fluoride volatilization method, which are described in M. Benedict et al., Nuclear Chemical Industry, Vol. Among the high-temperature metallurgy methods, development of a molten salt electrolysis method is being advanced.

[0003] Regarding the fluoride volatilization method, the aforementioned M. Bene
dict et al., Nuclear Chemical Industry, Vol. IV, pages 16 et seq. FIG. 2 shows a configuration diagram of a conventional fluoride volatilization method. Spent nuclear fuel is oxidized in a pretreatment step to form uranium (U), plutonium (Pu), and fission product oxides. These oxides are pulverized and supplied to an alumina fluidized bed reactor, and a fluorination reaction is performed by supplying a gas containing a fluorinating agent. In the first stage fluorination step, F ₂ gas or a halogenated fluoride such as BrF ₅ or BrF ₃ is caused to act on U, Pu, and an oxide of a fission product.
U and some fission products volatilize as fluoride, but Pu remains in the fluorination apparatus as PuF ₄ . In this process, U and Pu are separated from each other. Pu becomes PuF ₆ by the reaction with F _{2 in} the second-stage fluorination step, and is volatilized.
The recovered U and Pu fluorides are separated and purified from the fission product fluorides by purification steps such as a distillation method, a partial condensation method, a solid adsorption method, a thermal decomposition method, and a selective reduction method.

In the above method, since the reaction rate of the fluorination reaction of Pu is slow, a single treatment requires several hours to several tens of hours. Therefore, improvement of the treatment speed is a development issue.
In addition, U and Pu are separated and recovered, and the purification is repeatedly performed in order to increase the purity. Therefore, there is a problem that the purification process is complicated.

[0005]

As a method for solving the problem of the conventional nuclear fuel reprocessing method using the fluoride volatilization method, that is, as a method for solving the complication of the refining process, the amount of Pu which is to be recovered is in a preferable amount. By including U, a method for simplifying the process can be considered. In this method, U and P
Since u is recovered as a mixture, the step of purifying Pu becomes unnecessary, and the process can be simplified. In order to realize this process, for example, the following steps can be considered. That is,
By using a fluidized bed reactor and by reacting with fluorine or a fluorine compound, U which is easily fluorinated is first recovered as fluoride, and then a stronger fluorinating agent or a high concentration fluorinating agent is used. Then, Pu, which is hard to be fluorinated, and the remaining U are recovered as a fluoride, and the ratio of U to Pu in the mixture of U and Pu is adjusted by adjusting the fluorination conditions. However, since this method uses a fluidized-bed reactor, an increase in equipment scale becomes a problem. Further, since the reaction rate in the fluorination reaction process is not improved, there is a problem of improving the processing speed.

[0006]

According to the present invention, a flame reactor is used for the fluorination reaction, and spent nuclear fuel is continuously supplied to the reactor for treatment. Here, the flame reactor is a device in which only the reaction section has a high temperature and the wall surface of the reactor has a lower temperature than the reaction section. The fluorination reaction rate of Pu in the flame reactor is faster than the fluorination reaction rate of Pu in the fluidized bed reactor, and the processing rate of spent nuclear fuel is improved by continuously processing spent nuclear fuel. can do. Further, since the flame reactor has a smaller and simpler structure than the fluidized bed reactor, it is possible to reduce the size of the reprocessing facility and reduce the equipment cost.

[0007] In the flame reactor as well, the above problem is solved if the fluoride of Pu generated by the fluorination reaction can be recovered as a mixture with the fluoride of U.

In the method for reprocessing spent nuclear fuel of the present invention,
First, after the spent nuclear fuel rods are uncoated, they are loaded into a fluidized bed reactor fluorinator, a fluorinating agent is supplied, and U is recovered as UF ₆ . After recovering an arbitrary amount of UF ₆ , U, Pu and fission products remaining in the fluidized bed reactor fluorinator are introduced into the flame reactor fluorinator together with the fluidized medium, and the fluorinating agent is supplied. And the resulting fluorides of U and Pu are collected as a mixture. In a fluidized bed reactor, the fluorination reaction of Pu, which has a slow reaction rate, is performed in a flame reactor, whereby the fluorination reaction rate of Pu can be improved. In addition, U and Pu generated by the fluorination reaction in the flame reactor
Does not require a Pu purification step.

In another reprocessing method of the present invention, after the spent nuclear fuel rods are uncovered, the nuclear fuel material is finely divided and introduced into a flame reactor fluorinator. Supply the fluorinating agent to the fluorinator,
By reacting with nuclear fuel material powder, U, Pu,
And a mixture of fission product fluorides is formed. The volatilized U, Pu, and the fission product fluoride are separated into a U fluoride and a mixture of U and Pu fluoride by a separation device. Since Pu is recovered as a mixture with U, the separation device used may be a simpler device than that used in the Pu purification step. In this method, since both the fluorination reaction of U and Pu is performed in a flame reactor, the equipment used for the fluorination reaction can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) The configuration of a reprocessing apparatus in which a method for reprocessing spent nuclear fuel according to an embodiment of the present invention will be described with reference to FIG.

After the spent nuclear fuel rods are uncovered, they are loaded into a fluidized bed reactor fluorination unit 3 and a fluorinating agent 1 is supplied to this unit. U which is most likely to be fluoride first becomes UF _{6 and} volatilizes. By selecting a fluorinating agent for fluorinating only U as the fluorinating agent 1, volatile UF ₆ can be recovered as high-purity UF ₆ . In this case, either know the production of UF ₆ for previously supplied amount of fluorinating agent 1, by measuring the amount of UF ₆ to generate, P
The amount of U to be mixed with u is left in the fluorination apparatus 3.
After collecting an arbitrary amount of UF ₆ , the fluidized bed reactor fluorination device 3
The remaining U, Pu, fission products, and the fluidized medium are supplied to the flame reactor fluorinator 4 together with the fluorinating agent 2, and the fluoride of U and Pu generated by the fluorination reaction is mixed in a low-purity mixture. To be collected. Non-volatile impurity nuclides such as fluorides, oxides, and metals are discharged from the lower portion of the fluorination apparatus 4 and are stably stored and disposed of by directly compacting, vitrifying, ceramic, and artificial rock.

The recovered UF ₆ is stored in a cylinder as it is or after being generated as needed. U collected
The mixture of the fluorides of Pu and Pu is converted from fluoride to oxide and reused as a mixed oxide fuel.

As described above, according to the present embodiment, the fluorination reaction of U is carried out by the fluidized bed reactor fluorinator, and the fluorination reaction of Pu is carried out by the flame fluoridation apparatus. Since the fluorination reaction of Pu, which requires a long reaction time, is completed quickly in the crystallization apparatus, the processing speed can be improved as compared with the method in which the fluorination reaction is performed using only the fluorination apparatus of the fluidized bed reactor. . In addition, since high-purity UF ₆ can be separated from the fluorinating device 3 and a mixture of U and Pu fluorides can be separated and recovered from the fluorinating device 4, a separating device is unnecessary, and the process can be simplified. This has the effect of making it possible.

(Embodiment 2) FIG. 3 shows a second embodiment of the present invention.
This will be described with reference to FIG.

After the spent nuclear fuel rods are uncoated, the nuclear fuel material is refined in a pretreatment step 5. The powder of the nuclear fuel material generated by the miniaturization is introduced into the fluorinator 4 of the flame reactor.
A fluorinating agent 2 such as fluorine gas is supplied to the fluorinating apparatus, and is reacted with the nuclear fuel material powder. At this time, it is desirable that the amount of the fluorinating agent supplied to the fluorinating device is larger than the amount of the supplied nuclear fuel material powder in an equal amount, and is introduced so as to surround the nuclear fuel material powder. UF ₆ and P generated by the reaction
uF ₆ and some impurity nuclide fluorides volatilize, and nonvolatile impurity nuclides such as fluoride, oxide, and metal are discharged from the lower part of the fluorination apparatus. By continuously supplying the nuclear fuel material powder to the fluorinator, continuous processing becomes possible.

The volatilized UF ₆ , PuF ₆ , and the fluoride of the impurity nuclide are separated by the separating device 6 into UF ₆ and a mixture of U and Pu fluoride. LiF and NaF are mixed and filled in the separation device 6 at an arbitrary ratio. LiF is used in an amount sufficient to adsorb the entire amount of PuF ₆ generated in the fluorination apparatus. Set the temperature inside the separation device to about 300 degrees,
A mixed gas of UF ₆ , PuF ₆ and a fluoride of an impurity nuclide generated by the fluorination apparatus is introduced. The whole amount of PuF ₆ and a part of UF ₆ , and most of fluorides of impurity nuclides are adsorbed on LiF or NaF. The gas that has passed through the separator is high-purity UF ₆ . After recovering UF ₆ , fluorine gas is flowed through the separation device, and the temperature inside the device is raised to about 450 ° C. By this operation, fluorides of U and Pu adsorbed on LiF or NaF are volatilized as UF ₆ and PuF ₆ . These are recovered as a low-purity mixture of U and Pu fluorides. By adjusting the amount of NaF to be charged into the separation device, the mixing ratio of U and Pu in the mixture of the fluorides of U and Pu can be adjusted.

A cold trap can be used as the separation device 6. In this case, the temperature in the separation device is set to, for example, about minus 50 degrees, and a mixed gas of UF ₆ , PuF ₆ and fluoride of impurity nuclide generated in the fluorination device is introduced. Then, the total amount of UF ₆ and PuF ₆ and a part of the fluoride of the impurity nuclide are solidified. After removal of the unsolidified gas, the separation device temperature is raised to a temperature slightly above the sublimation point of UF _6, to recover the UF ₆ some sublimated. The purity of the recovered UF ₆ is higher than before the solidification. The recovered UF ₆ is introduced into the next cold trap, and a sublimation operation is performed in the same manner.

By repeating these series of sublimation operations, UF ₆
Is purified and recovered as high-purity UF ₆ . The solid remaining in the separation device after the UF ₆ is recovered by performing the multistage sublimation operation contains UF ₆ , PuF _6, and fluoride of the impurity nuclide. After finishing the recovery of the high-purity UF ₆ , the temperature inside the separation device is raised to the sublimation point of PuF ₆ or more, and the solid remaining in the device is sublimated, and recovered as a low-purity mixture of U and Pu fluoride.

The recovered UF ₆ is stored in a cylinder as it is or after being generated as needed. When re-concentrate the U is still stored the more efficient of UF _6, if not reconcentrated better converted into oxides can be reduced storage space. The recovered mixture of U and Pu fluoride is converted from fluoride into oxide and reused as a mixed oxide fuel.

Finally, non-volatile fission products remain in the fluorination apparatus 4 as high-level waste. These can be stably stored and disposed by compression molding, vitrification, ceramic solidification, and artificial rock solidification as they are.

As described above, according to this embodiment, by using the flame reactor, the processing speed of spent nuclear fuel can be increased, and the throughput can be increased. The waste discharged from the reactor is only non-volatile impurity nuclides, and the amount of radioactive waste can be reduced. By adjusting the operating conditions of the separation device, the ratio of PuF ₆ in the mixture of the recovered U and Pu fluorides can be arbitrarily changed. UF ₆
To recover in high purity, reuse of U, for example, reconcentration,
And the management during storage of U and the like becomes extremely easy. Further, since U and Pu can be recovered as a mixture and directly as a raw material for fuel reprocessing, the cost for fuel reprocessing can be reduced, and nuclear non-proliferation can be increased because high-purity Pu is not treated alone. Since the apparatus and the processing facility can be simplified as compared with the conventional method, the economic efficiency can be improved.

(Embodiment 3) FIG. 4 shows a third embodiment of the present invention.
This will be described with reference to FIG.

After the spent nuclear fuel rods are uncoated, the nuclear fuel material is refined in a pretreatment step 5. The chemical form of the nuclear fuel material powder produced by the miniaturization is mainly oxide. The powder of the nuclear fuel material is solid fluoride (UF ₄ , Pu) by the pretreatment device 7.
It converted to F _4, etc.). UF _4, PuF ₄ of a solid-state fluoride, UF _6, PuF ₆ generation reaction rate of a flame reactor to be described later is faster than UF _6, PuF ₆ formation reaction rate of oxide nuclear fuel material. The nuclear fuel material converted into the solid fluoride is introduced into the flame reactor fluorinator 4. A fluorinating agent 2 such as fluorine is supplied to a fluorinating apparatus and reacted with the nuclear fuel material powder. The UF ₆ and PuF ₆ generated by the reaction and the fluorides of some impurity nuclides are volatilized, and the fluorides, oxides, and metals of the nonvolatile impurity nuclides are discharged from the lower part of the fluorination apparatus.

UF ₆ and PuF ₆ formed by the fluorination reaction
When the fluoride of some impurity nuclides, the UF _6, U and Pu
And a fluoride mixture. In the separation device 6, an arbitrary amount of a mixed gas of UF ₆ and PuF ₆ is first collected in the device, and the device is heated to about 250 degrees. At this time,
Although UF ₆ has no change in chemical form, PuF ₆ is thermally decomposed to solid PuF ₄ and separated from UF ₆ . Recover any amount of UF ₆ separated from PuF ₄ . Any amount of UF ₆
After recovering, Fluorine gas is introduced into the separation device to convert PuF ₄ to PuF ₆ and collect it as a mixture with the remaining UF ₆ .

The recovered UF ₆ is stored as it is or after it is generated as needed. U collected
The mixture of the fluorides of Pu and Pu is converted from fluoride to oxide and reused as a mixed oxide fuel.

As described above, according to the present embodiment, the rate of the fluorination reaction in the flame reactor is increased by converting the nuclear fuel material in the spent nuclear fuel from the oxide into a chemical form in which the reaction easily proceeds in advance. Therefore, the processing speed of spent nuclear fuel can be further improved. UF collected by separation device
By adjusting the amount of ₆ , U and P to be recovered later
It becomes possible to adjust the PuF ₆ content in the mixture of u fluoride. From a mixture of fluorides of U and Pu produced by fluorination reaction, high part of UF ₆ pure UF ₆
By recovering as, it is possible to high DF achieve UF _6.

[0027]

According to the present invention, when reprocessing spent nuclear fuel by the fluoride volatilization method, the use of a flame reactor for the fluorination reaction increases the fluoride production reaction rate. Since the processing speed per hour is increased and the spent nuclear fuel can be continuously processed, the throughput of the spent nuclear fuel can be increased. Further, the apparatus can be made smaller than a conventional fluidized bed reactor. By recovering uranium and plutonium as a mixture, the step of purifying plutonium becomes unnecessary, and the reprocessing step can be simplified. From the above, it is possible to reduce running costs and facility construction costs in the process of reprocessing spent nuclear fuel.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a spent nuclear fuel reprocessing apparatus used in a spent nuclear fuel reprocessing method according to a preferred embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional spent nuclear fuel reprocessing device using a fluoride volatilization method.

FIG. 3 is a configuration diagram of a spent nuclear fuel reprocessing device according to another embodiment of the present invention.

FIG. 4 is a configuration diagram of a spent nuclear fuel reprocessing device according to another embodiment of the present invention.

[Explanation of symbols]

3. Fluorination apparatus (fluidized bed reactor), 4. Fluorination apparatus (flame reactor), 6. Separation apparatus.

Claims (4)

[Claims] 1. A reprocessing method for recovering uranium and plutonium from spent nuclear fuel by forming fluorine of uranium and plutonium by causing fluorine or a fluorine compound to act on the spent nuclear fuel. A method for reprocessing spent nuclear fuel, characterized in that the process is simplified by including a preferred amount of uranium in the range of 1 to 40 times that of plutonium, thereby reducing the size of a reprocessing facility. 2. A reprocessing method for recovering uranium and plutonium from spent nuclear fuel by reacting the spent nuclear fuel with fluorine or a fluorine compound to form uranium and plutonium fluorides, comprising:
Spent nuclear fuel is loaded into a fluidized bed reactor and reacted with fluorine or a fluorine compound to convert uranium into fluoride, which is recovered from spent nuclear fuel. When the remaining uranium reaches a preferred value in the range of 1 to 40 times the plutonium remaining in the fluidized bed reactor, the spent nuclear fuel remaining in the fluidized bed reactor is transferred to the flame reactor. Introduce (3)
A method for treating a spent nuclear fuel, comprising reacting fluorine or a fluorine compound with the spent nuclear fuel in a flame reactor to recover a preferred amount of uranium containing uranium in a range of 1 to 40 times that of plutonium. Reprocessing method (the fluidized bed reactor referred to here is a reactor in which the wall of the reactor and the reactor have substantially the same temperature, and may be a rotary kiln or the like. In this system, only the reaction section has a high temperature, and the wall of the reactor has a lower temperature than the reaction section.) 3. A reprocessing method for recovering uranium and plutonium from spent nuclear fuel by forming fluorine of uranium and plutonium by reacting the spent nuclear fuel with fluorine or a fluorine compound. Is introduced into the flame reactor, and fluorine or a fluorine compound is allowed to act on the spent nuclear fuel to separate the volatile fluorides of uranium and plutonium into uranium and plutonium. Segregating to contain twice as much uranium as you like,
The method for reprocessing spent nuclear fuel according to claim 1 (here, the flame reactor is a device in which only the reaction section has a high temperature and the wall surface of the reactor has a lower temperature than the reaction section). 4. The reprocessing method according to claim 1, wherein the separation method in the reprocessing method is at least one method selected from a solid adsorption method, a multistage sublimation method, and a thermal decomposition method.