JP3143854B2 - Nuclear fuel material recovery method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for recovering nuclear fuel material in a dry reprocessing apparatus. More specifically, the present invention relates to a method and an apparatus for continuously recovering useful metals such as uranium and plutonium from spent nuclear fuel.

[0002]

2. Description of the Related Art Conventionally, in the reprocessing of spent nuclear fuel, in order to separate and recover unburned fissile material and newly generated fissile material, a so-called wet process is performed. In the pretreatment step in the wet method, a “shear reach method” is generally performed. In this shearing reach method, spent nuclear fuel rods are cut into several centimeters in diameter along with their cladding tubes in the state of a fuel assembly by a shearing blade and put directly into a high-temperature concentrated nitric acid solution to leach and dissolve the nuclear fuel It is a way to make it. After dissolving in a nitric acid solution, uranium and plutonium are separated and recovered by a solvent extraction method called the so-called "Purex method" due to differences in solubility in organic solvents. On the other hand, in recent years, a reprocessing technique called a dry method utilizing the principle of electrolysis is being developed. In this dry method, spent nuclear fuel is converted into chloride, and the chloride is electrochemically purified in a molten salt bath in which the chloride is melted. Compared to the conventional wet method, this dry method does not use water, and therefore has the advantages of making the equipment compact and eliminating the generation of waste liquid.It has the advantage of low decontamination of uranium and plutonium from spent nuclear fuel. It is said that it has high resistance to nuclear proliferation because it can be separated.

[0003] For example, a method of chlorinating spent nuclear fuel and recovering it as a metal by a molten salt electrolysis method is performed by the Argonne Research Institute in the United States and the Russian Reactor Research Institute (RIAR). The molten salt electrolysis method at the Argonne Laboratory in the United States uses a metal container, reduces the spent nuclear fuel by metal,
Uranium is recovered from the reduced metal, and subsequently, nuclear fuel materials such as plutonium are further recovered by batch operation (Moriyasu Jobani, "FBR Metal Fuel Dry Reprocessing Technology", Nuclear Engineering Vol. 34, No. 4) No. 12 46-60
page). In addition, in the molten salt electrolysis method performed by the Russian Institute of Reactor Science (RIAR), spent nuclear fuel is chlorinated using a batch type crucible to produce an oxychloride compound, which is dissolved in the molten salt. Next, the uranium compound ions dissolved in the molten salt by electrolysis are collected on the electrode. A mixed gas of chlorine gas and oxygen is blown into the molten salt from which uranium has been recovered to precipitate and precipitate plutonium (Hiroaki Kamiyama, "High-Temperature Electrochemical Reprocessing Technology in Russia", Electrochemistry, Vol. 40, No. 31- 39).

[0004]

However, the molten salt electrolysis method at the Argonne Research Laboratory in the United States and the molten salt electrolysis method performed at the Russian Reactor Research Institute (RIAR) both assume batch processing. In order to use a continuous processing method, it is necessary to devise at least two processing apparatuses and alternately use these processing apparatuses. As described above, when the two processing devices are switched and used, there is a problem that operation control such as a switching operation is complicated. In addition, the equipment for handling nuclear fuel has limitations on the handling amount of nuclear fuel and the size and shape of the equipment such as the size, thickness, width, etc., in terms of the criticality safety management of nuclear fuel, and the processing capacity of batch type processing is limited. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an apparatus for recovering a nuclear fuel material which is compact in shape and does not cause a problem in criticality safety management. Another object of the present invention is to provide a method and an apparatus for recovering a nuclear fuel material for continuously recovering a useful metal element from spent nuclear fuel.

[0005]

The invention according to claim 1 is
As shown in FIG. 1, a recovery tank 11 having at least five reaction chambers 15a to 15e formed along a slanted bottom surface 11a and having a sealed shape in a flat plate shape having a thickness such that the stored nuclear fuel is not critical. , A chloride support salt, which is a reaction medium, is stored as a molten salt, and spent nuclear fuel oxide is supplied from the uppermost reaction chamber 15a, and the uppermost reaction chamber including the uppermost reaction chamber 15a In step 15a, the radioactive metal in the oxide is converted into chloride containing the metal oxychloride by reacting the radioactive metal in the oxide with the reactant contained in the chloride molten salt. The radioactive metal oxide (for example, mainly uranium dioxide) is deposited and collected on the electrode 21b by electrolysis, and the chlorine gas and the carbon monoxide gas are dissolved in the chloride in the reaction chamber 15c located next. A radioactive substance (eg, mainly plutonium dioxide) which is ionized in the molten salt in the reaction chamber 15d in which the oxide ions remaining in the molten salt are blown into the salt to metal ionize and then store the first molten metal 25a located next. In the molten salt 25a by using the first molten metal 25a as a cathode to precipitate and collect the molten metal in the first molten metal 25a, and store the second molten metal 25b located at the lowest position in the reaction chamber 15.
This is a method for recovering nuclear fuel by extracting a chloride remaining in the molten salt into the second molten metal 25b by mixing a reducing agent into the molten salt from step e. In the present specification, the “reactant contained in the molten chloride salt” refers to one or both of Cl ₂ and C as shown in the following formulas (1) to (4).

According to the second aspect of the present invention, an inclined bottom surface 11 is provided.
a recovery tank 11 formed in a flat plate-like shape having a thickness such that the stored nuclear fuel does not become critical and capable of storing a chloride-supporting salt as a reaction medium as a molten salt;
Reaction chambers 15a to 15e comprising at least 5 chambers inside
And a lower partition plate 12 provided upward on the bottom surface 11a of the recovery tank 11 so that molten salt flows from the upper reaction chamber to the lower reaction chamber, and a reaction chamber excluding the lowermost reaction chamber 15e. An upper partition plate 16 provided from above to below in 15a to 15d to prevent a short path of a molten salt from an upper reaction chamber to a lower reaction chamber; and a temperature not lower than the melting point of the chloride supporting salt and not higher than 900 ° C. To the reaction chambers 15a-1
A temperature control means 17 for controlling the temperature of each of the fuel cells 5e; a supply port 18 provided in the uppermost reaction chamber 15a for supplying a chloride supporting salt or a spent nuclear fuel oxide and a chloride supporting salt; A discharge port 14 provided in the reaction chamber 15e located therethrough for discharging a liquid molten salt, and a molten salt stored in the reaction chamber 15a provided in the upper reaction chamber 15a including the uppermost reaction chamber 15a are provided. Gas introducing means 19 for introducing chlorine gas into the reactor, and a reaction chamber 15b located below the reaction chamber 15a in which the first gas introducing means 19 is provided.
The first electrodes 21a and 21b for electrolyzing the molten salt stored in the reaction chamber 15b provided in the reaction chamber 15b, and the reaction chamber 15c located below the reaction chamber 15b provided with the first electrodes 21a and 21b
Gas introducing means 22 for introducing a gas containing chlorine gas and carbon gas into the molten salt stored in the reaction chamber 15c provided in the reaction chamber 15c; and a reaction chamber 15 provided with the second gas introducing means 22.
c provided in a reaction chamber 15d located below
d for electrolyzing the molten salt stored in d.
b and the reaction chamber 15 provided with the second electrodes 23a and 23b.
reaction chamber 15 located below d and including the lowest reaction chamber
e is a nuclear fuel material recovery apparatus provided with a reducing agent supply means 24 provided for supplying a reducing agent into a molten salt and a waste gas discharging means 26 for discharging waste gas from the reaction chambers 15a to 15e for each reaction chamber. .

The invention according to claim 3 is the invention according to claim 2, as shown in FIG. 1, wherein the second electrodes 23a, 23
This reaction chamber 1 is provided in a reaction chamber 15d in which a reaction chamber 3b is provided.
First metal supply port 2 for supplying first molten metal 25a to 5d
7 and a first metal outlet 2 provided in the reaction chamber 15d to discharge the first molten metal 25a stored in the reaction chamber 15d.
8 for recovering nuclear fuel material. As shown in FIG. 1, the invention according to claim 4 is the invention according to claim 2 or 3, wherein the reducing agent supply means 24 is provided in the reaction chamber 15e and is stored in the reaction chamber 15e. (2) Third gas introducing means 2 for introducing an inert gas into molten metal 25b
9 is a nuclear fuel material recovery device. The invention according to claim 5 is the invention according to any of claims 2 to 4, wherein the second molten metal 25b is provided in the reaction chamber 15e provided with the reducing agent supply means 24. This is a nuclear fuel material recovery device provided with a second metal supply port 31 to be provided and a second metal discharge port 32 provided in the reaction chamber 15e and discharging the second molten metal 25b stored in the reaction chamber 15e.

The spent nuclear fuel oxide (hereinafter referred to as “raw material”) of the present invention includes various oxides such as uranium, plutonium, and radioactive fission products such as cesium and strontium. Due to the composition ratio of the spent nuclear fuel, the metal oxide deposited on the cathode side 21b of the first electrodes 21a, 21b by molten salt electrolysis is mainly uranium dioxide. In addition, sodium chloride, potassium chloride, etc. may be used alone for the chloride support salt as a reaction medium,
Or these are used together. The combined use is preferable because the melting point of the supporting salt is lowered. Further, the addition of lithium chloride to these supporting salts is preferable because the melting point of the chloride supporting salt is further reduced. At least five reaction chambers are required, but may be six, seven, eight or more depending on the reactivity of each chamber. That is, the number of chambers is appropriately increased or decreased according to the amount of recovered nuclear fuel to be recovered per unit time, the required residence time (reaction time), and the like. The heating by the temperature control means 17 is performed by heating to a temperature not lower than the melting point of the chloride supporting salt and not higher than 900 ° C.
It is necessary to control the temperature of ~ 15f.

The first electrodes 21a and 21b are an anode and a cathode, respectively, and are provided in a pair in the reaction chamber. These first electrodes 21a and 21b may be any conductive material that does not melt at the above-mentioned heating temperature, and examples thereof include iron, tungsten, molybdenum, and graphite. Graphite is particularly preferred for the anode in terms of corrosion resistance. A chloride supporting salt is supplied from the supply port 18 of the apparatus at the time of start-up, and a mixture of the raw material and the chloride supporting salt is supplied during operation of the apparatus. This raw material has an average particle size of 50 to
It is preferable to grind in advance so as to have a range of about 500 μm. More preferably, it is about 50 to 200 μm. However, the average particle size of the raw material may be 500 μm or more if the reaction chamber is increased and the reaction time is lengthened.

(A) First Chlorination Step After the chloride supporting salt in the reaction chamber is converted into a molten salt, when the raw material is supplied from the supply port 18, the raw material is supplied to the first gas introduction means 19 in the uppermost reaction chamber 15 a. Is stirred in the molten salt by the gas introduced from the above and mixed with the molten salt. The introduced gas is A
In addition to being an inert gas such as r gas, the reaction can be performed more efficiently by including chlorine gas in the inert gas. The content of chlorine gas in the inert gas is 5 to 50.
% By volume is preferred. At this time, the metal oxide in the raw material is a reactant (C) contained in the molten chloride salt stored in the reaction chamber.
l ₂ , C) and is converted to chloride. The reaction of uranium dioxide in spent nuclear fuel oxide is shown in the following equations (1) and (2). The reaction of plutonium dioxide in the spent nuclear fuel oxide is shown in the following equations (3) and (4). UO ₂ + Cl ₂ → UO ₂ Cl ₂ (1) UO ₂ Cl ₂ + C + Cl ₂ → UCL ₄ + CO ₂ … (2) PuO ₂ + 2Cl ₂ → PuCl ₄ + O ₂ … (3) PuO ₂ + Cl ₂ → PuO ₂ Cl ₂ (4) From the above reaction, the oxygen in the raw material becomes carbon dioxide gas or oxygen, and is discharged as waste gas by the waste gas discharging means 26. The reactions of the above formulas (1) and (3) mainly occur in the upper reaction chamber. If the reaction is not completed with only one upper reaction chamber, the number of higher reaction chambers is increased to two or more.

(B) Electrolytic recovery step A chloride containing a radioactive metal oxychloride such as uranium or plutonium flows down to a lower reaction chamber in the electrolysis step in the form of a molten salt. In this reaction chamber, the electrolysis voltage is such that oxychloride compounds such as UO ₂ Cl ₂ and PuO ₂ Cl ₂ are electrolytically reduced, and chlorides such as UCl ₄ and PuCl ₄ flow unreacted into lower reaction chambers. To do it. That is, the electrode (cathode) 21b provided in this reaction chamber
Uranium dioxide and plutonium dioxide are electrochemically precipitated and recovered. These reactions are shown in the following formulas (5) and (6). UO ₂ Cl ₂ → UO ₂ + Cl ₂ ↑ (5) PuO ₂ Cl ₂ → PuO ₂ + Cl ₂ ↑ (6) The chlorine gas generated from the above reaction is discharged as waste gas by the waste gas discharging means 26. . In the first chlorination step, the reaction is carried out such that only uranium oxide becomes oxychloride (formula (1)). Therefore, in this electrolytic recovery step, only uranium is mainly recovered. Here, by configuring the electrode 13b to be replaceable, the electrolysis itself is continuously performed,
Radioactive metal oxides such as uranium dioxide and some plutonium dioxide can be recovered continuously. Radioactive metal oxides such as uranium dioxide and plutonium dioxide deposited on the electrode 21b are separated from the electrode by a mechanical method.

(C) Second Chlorination Step After the recovery of the radioactive metal oxide (mainly uranium dioxide), the molten salt flows down to the lower reaction chamber in the second chlorination step. This molten salt was not recovered in the electrolytic recovery step. It contains chlorides and metal oxides and chlorinates all non-chlorinated metal oxides in the lower reaction chamber.
That is, in this reaction chamber, the raw material is stirred in the molten salt by the chlorine gas and the carbon monoxide gas introduced from the second gas introduction means 19, and is converted into chloride. The content of chlorine gas in the inert gas is preferably 5 to 50% by volume, and the content of carbon monoxide gas in the inert gas is preferably 10 to 50% by volume. These reactions are represented by the following formulas (7), (8) and (9) on behalf of uranium and plutonium. UO ₂ Cl ₂ + Cl ₂ + 2CO → UCl ₄ + 2CO ₂ ↑ (7) UO ₂ +2 Cl ₂ + 2CO → UCl ₄ + 2CO ₂ … (8) PuO ₂ Cl ₂ + Cl ₂ + 2CO → PuCl ₄ + 2CO ₂ … ( 9) As represented by the above reaction, all the metal oxides remaining in the raw material are converted into chlorides, and the carbon dioxide gas generated during the reaction is converted into waste gas by the waste gas discharging means 26. Is discharged.

(D) Electrolytic reduction step After converting all the metal oxides remaining in the molten salt into chlorides, the molten salt flows down to the lower reaction chamber in the electrolytic reduction step. This molten salt mainly contains plutonium chloride (PuCl ₄ ), and in the lower reaction chamber, plutonium chloride is contained in the molten metal serving as a cathode, and the remaining uranium chloride is also provided by an electrode provided in the reaction chamber. Is electrochemically reduced and recovered by electrolysis of molten salt. These reactions are shown in the following formulas (10) and (11). UCl ₄ → U + 2Cl ₂ ↑ (10) PuCl ₄ → Pu + 2Cl ₂ ↑ (11) The chlorine gas generated from this reaction is discharged as waste gas by the waste gas discharging means 26.

(E) Reduction and extraction step After the electrolytic recovery of the metal oxide, the molten salt flows down to a lower reaction chamber in the reduction and extraction step. In the lower reaction chamber, metals not recovered in the electrolytic recovery step and the electrolytic reduction step are extracted. That is, the chloride remaining in the molten salt reacts with the reducing agent introduced from the reducing agent supply means 24 provided in the lowest reaction chamber and is extracted as the second molten metal. Examples of the reducing agent introduced from the reducing agent supply means 24 include alkali metals and alkaline earth metals, and lithium is particularly preferable. The following formula (12) represents the reduction reaction of metal M (valence n) with lithium. ^{Mn ++} nLi → M + nLi ⁺ (12) The reduced metal M is extracted into the second molten metal 25b,
The second molten metal 25b is sequentially supplied from the second metal inlet 31. The second molten metal 25b from which another unrecovered radioactive metal oxide is extracted is supplied from the second metal outlet 32 to the second metal outlet pipe 32a. Is discharged out of the recovery tank 11 through the
After all of the nuclear fuel material has been recovered, the molten salt
And is recycled again as chloride supporting salt.

Next, in general, the molten salt is not short-passed by the upper partition plate 16 and a sufficient reaction time is given by the lower partition plate 12 so that the molten salt is sequentially transferred from the uppermost reaction chamber to the lowermost reaction chamber. Flow. The rate and yield of the reaction in each recovery tank change depending on the temperature controlled by the temperature control means 17. In this case, the temperature of the molten salt is preferably in the range of 400 to 900 ° C. in the first salification step, and more preferably 600 to 800 ° C. in view of the stability of uranium oxychloride, the reaction rate, and the like. In the electrolytic recovery step, since the particle size of the precipitate tends to increase as the temperature increases, it is preferable to perform the molten salt at a temperature in the range of 500 to 800 ° C.
It is more preferable to carry out in the range of 0 to 800 ° C. The second salification step is preferably carried out at a temperature of the molten salt of 400 to 900 ° C.
It is more preferable to carry out in the range of 800 ° C.

In the electrolytic recovery step, the first electrodes 21a, 21b
The first and second gas introduction means 19, 22 are controlled by adjusting the voltage applied to the first and second gas supply means.
By adjusting the concentration, supply amount, and the like of the stirring gas introduced by the above, the processing capacity can be changed, and different types of precipitates can be collected. In the electrolytic reduction step and the reduction extraction step, continuous operation is enabled by configuring the molten metal to be able to be extracted outside the apparatus.

The invention according to claim 6 is the invention according to claims 2 to 5
The second electrodes 23a, 23
b is a nuclear fuel material recovery device in which the first molten metal 25a stored in the reaction chamber 15d provided with b is one of cadmium, magnesium, and zinc or an alloy thereof. The metal to be electrolytically reduced can be changed by changing the type of the molten metal 25a. The invention according to claim 7 is the invention according to claim 2 or 4, wherein the first, second and third gas introducing means 19, 22 and 29 are provided in the reaction chamber 15
a, 15c and 15e penetrate the tops of the reaction chamber 1
5a, 15c and 15e, gas introduction pipes 19b extending to the bottoms and having gas ejection portions 19a, 22a and 29a at the tips.
This is a nuclear fuel material recovery device comprising 22b and 29b.

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIGS. 1 and 2,
The recovery tank 11 of the spent nuclear fuel recovery device has an inclined bottom 1
It is composed of a collection tank main body 11b having a la and a lid 11c hermetically provided on the upper surface thereof. The recovery tank 11 can store a chloride supporting salt as a reaction medium as a molten salt, and is formed in a flat plate shape having a thickness such that the stored nuclear fuel does not become critical. In this embodiment, five reaction chambers 15a, 15b, 15c, and 15d are provided inside the recovery tank 11.
And four lower partitions 12 forming the collecting tank 1
1 are provided in the vertical direction at an interval on the bottom surface 11a.
These partition plates 12 have substantially the same height so that the molten salt, which is a chloride supporting salt, flows from the upper reaction chamber to the lower reaction chamber.

In each of the four reaction chambers 15a to 15d except for the lowermost reaction chamber 15e, four upper partition plates 16 are provided on the top surface of the recovery tank 11 at intervals from the top to the bottom. The lower ends of these partition plates 16 extend to a position lower than the upper end of the lower partition plate 12 to prevent a short path of the molten salt from the upper reaction chamber to the lower reaction chamber. As shown in FIG. 2, a heater 17a for increasing the temperature of each reaction chamber is provided for each of the reaction chambers 15a, 15b, 15c, 15d, and 15e on the outer surface of the recovery tank 11. The heater 17a is heated by the controller 17 to a temperature not lower than the melting point of the chloride-supporting salt and not higher than 900 ° C.
The temperature of a to 15e is controlled.

As shown in FIG. 1, a chute 18a for a raw material of a chloride supporting salt or spent nuclear fuel oxide is mounted above the uppermost reaction chamber 15a, and a supply port 18 is provided at the upper end of the chute. Can be A chloride supporting salt is supplied from the supply port 18 when the apparatus is started, and a mixture of spent nuclear fuel oxide and its reducing agent and a chloride supporting salt are supplied during operation of the apparatus. Examples of the reducing agent include carbon powder, that is, graphite powder. Reaction chamber 15e located at the bottom
Is provided with a discharge pipe 14a for discharging a liquid molten salt, and the discharge pipe 14a has a discharge port 14.

The uppermost reaction chamber 15a is provided with first gas introducing means 19 for introducing gas into the molten salt stored in the reaction chamber 15a and stirring the molten salt.
Ar gas containing chlorine gas is introduced from the first gas introduction means 19. In the reaction chamber 15b located next, a pair of first electrodes 21a and 21b are provided, each of which extends to the bottom through the lid 11c to electrolyze a molten salt to precipitate and recover uranium. The reaction chamber 15c
A second gas introducing means 22 for introducing a gas into the molten salt stored in the reaction chamber 15c and stirring the molten salt is provided. Ar gas containing chlorine gas and carbon gas is introduced from the second gas introduction means 22.

A reaction chamber 15d located below the reaction chamber 15c in which the second gas introducing means 22 is provided has a reaction chamber 1
A pair of second electrodes 23 for electrolyzing the molten salt stored in 5d
a and 23b are respectively provided to extend to the bottom through the lid 11c, and the lowermost reaction chamber 15e is provided with a valve 24a as a reducing agent supply means for supplying a reducing agent into the molten salt.
Is provided through the lid 11c. The metal is stored in the reaction chambers 15d and 15e in a state of being heated and melted by the heater 17a, respectively, and the molten salt is separated on the first and second molten metals 25a and 25b of the respective reaction chambers 15d and 15e. It is to be stored at. A portion of the second electrodes 23a and 23b corresponding to the molten salt of the cathode 23b is covered with an insulating material 23c, and a tip enters the first molten metal 25a, and the first molten metal 25a functions as a cathode. Is done.

All the reaction chambers 15a to 15e are provided with waste gas discharging means 26 for discharging waste gas generated in each reaction chamber for each reaction chamber, and the waste gas discharging means 26 is provided in each of the reaction chambers 15a to 15e. And a waste gas discharge pipe 26a connected to the top of each of the pipes. As shown in FIG.
A reaction chamber 15d provided with 3a and 23b is provided with a first metal supply port 27 for supplying a first molten metal 25a to the reaction chamber 15d, and a valve 27b is provided in the first metal supply port 27.
Is connected to the first metal supply pipe 27a provided with. Further, the reaction chamber 15d is provided with a first metal discharge port 28 for discharging the stored first molten metal 25a, and the first metal discharge port 28 has a first metal discharge pipe 28a having a valve 28b.
Is connected.

Returning to FIG. 1, a reaction chamber 15e provided with a supply pipe 24 as a reducing agent supply means is provided with the reaction chamber 15e.
A third gas introducing means 29 for introducing an inert gas into the molten metal stored in the reaction chamber 15e; a second metal supply port 31 for supplying a second molten metal 25b to the reaction chamber 15e;
A second metal outlet 32 for discharging the second molten metal 25b stored in the reaction chamber 15e is provided. The second metal supply port 31 is connected to a second metal supply pipe (not shown), and the second metal discharge port 32 is connected to a second metal discharge pipe 32a having a valve 32b. The first, second and third gas introducing means 19, 22 and 29 are provided in respective reaction chambers 15a, 1
The tips extend through the tops of 5c and 15e to the bottom of the respective reaction chambers, and are provided with gas introduction pipes 19b, 22b and 29b having gas ejection parts 19a, 22a and 29a at the tips. In this example, gas is pumped to the gas introduction pipes 19b, 22b and 29b by a compressor (not shown).

The operation of the thus configured device will be described. First, a predetermined amount of chloride supporting salt is supplied from the supply port 18 to the uppermost reaction chamber 15a. The controller 17 controls the heater 17a to heat and maintain the temperature of the reaction chamber 15a above the melting point of the chloride supporting salt. After this heating stores the chloride supporting salt as a molten salt in the reaction chamber 15a, the chloride supporting salt is further supplied to the reaction chamber 15a from the supply port 18. Molten salt is passed over the lower partition plate 12 to the next reaction chamber 15b.
When the heating is continued by further supplying the chloride supporting salt, all the reaction chambers 15a to 15e are eventually filled with the molten salt. Next, a mixture of the raw material which is the spent nuclear fuel oxide and its reducing agent and an additional chloride supporting salt are supplied from the supply port 18 to the reaction chamber 15a. The supplied raw material is the spout 1
The gas ejected from 9a is stirred and mixed into the molten salt in the uppermost reaction chamber 15a. The uranium and plutonium in the raw material react with chloride molten salt, chlorine gas in the introduced gas, graphite powder as a reducing agent, etc., as shown in the above-mentioned formulas (1) to (4), and uranium dioxide in the raw material In addition, plutonium dioxide becomes oxychloride or chloride of uranium or plutonium. The carbon dioxide gas and oxygen generated during the reaction are discharged to the outside as waste gas through a waste gas discharge pipe 26a.

The converted uranium and plutonium oxychlorides and chlorides pass through the lower partition plate 12 from the reaction chamber 15a as a molten salt and flow into the reaction chamber 15b without being short-passed by the upper partition plate 16. In the reaction chamber 15b, uranium oxychloride is mainly converted to uranium dioxide and deposited on the cathode 21b as shown in the above-mentioned formula (5). As shown in the formula (6), oxychloride of plutonium is also converted to plutonium dioxide and deposited on the cathode 21b, and in particular, the entire amount of uranium in the raw material is recovered. Chlorine gas generated during the reaction in the reaction chamber 15b is discharged to the outside as waste gas through a waste gas discharge pipe 26a.

After the recovery of uranium, the molten salt is supplied to the reaction chamber 15.
From b, it passes through the lower partition plate 12 and flows into the reaction chamber 15c without being short-passed by the upper partition plate 16. In the reaction chamber 15c, the chlorine gas and the carbon monoxide gas are blown into the chloride molten salt by the second gas supply means 22 to metalize oxide ions remaining in the molten salt. That is, oxides that have not yet been converted to chlorides are supplied to the reaction chamber 1
5c, the chlorine gas and the carbon monoxide gas introduced from the second gas introduction means 22 provided in the above formula (7).
As shown in (9), the whole is converted to chloride.
The carbon gas generated from this reaction is discharged as waste gas by the waste gas discharging means 26.

The molten salt after metal ionization is supplied to the reaction chamber 15.
From c, the flow passes through the lower partition plate 12 and into the reaction chamber 15d without being short-passed by the upper partition plate 16. The first molten metal 25a is stored in the reaction chamber 15d, and the molten salt is separated and stored on the first molten metal 25a. The first molten metal 25a is subjected to molten salt electrolysis of the molten salt as a cathode by the second electrode 23b, thereby forming the first molten metal 2a.
Precipitate and collect metal ions in 5a. That is, this reaction chamber 1
The metal ions in the molten salt react in the first molten metal 25a stored in the reaction chamber 15d by the pair of second electrodes 23a and 23b provided in 5d as shown in the above-described equations (10) and (11). Then, it is recovered in the first molten metal 25a. The chlorine gas generated from this reaction is discharged as waste gas by the waste gas discharging means 26. First molten metal 25a
Are sequentially supplied from the first metal inlet 27 through the first metal inlet tube 27a, and the first molten metal
5a is discharged from the first metal discharge port 28 to the outside of the recovery tank 11 via the first metal discharge pipe 28a.

The molten salt deposited and recovered in the first molten metal 25a flows from the reaction chamber 15d through the lower partition plate 12 to the lowermost reaction chamber 15e without being short-passed by the upper partition plate 16. Chloride which has not been precipitated by the molten salt electrolysis remains in the molten salt. The second molten metal 25b is stored in the reaction chamber 15e, and the molten salt is separated and stored on the second molten metal 25b. In this reaction chamber, by mixing a reducing agent into the molten salt, the chloride remaining in the molten salt is recovered by reduction extraction into the second molten metal 25b as shown in the above-mentioned formula (12). That is, the entire amount of chloride remaining in the molten salt is recovered in the second molten metal 25b by the reducing agent supplied from the supply pipe 24 which is a reducing agent supplying means provided in the reaction chamber. The gas generated by this reaction is discharged as waste gas by the waste gas discharging means 26. The second molten metal 25b is sequentially supplied from the second metal inlet 31 through a second metal inlet tube (not shown), and the second molten metal 25b on which the metal is deposited is sent from the second metal outlet 32 to the second metal outlet tube 32a. Is discharged out of the recovery tank 11 through the After the chloride is recovered, the molten salt is discharged from the outlet 14 and reused as a chloride supporting salt.

[0030]

Next, embodiments of the present invention will be described. In this example, the recovery tank is made of glass or metal and comprises five reaction chambers. The first reaction step corresponds to a first chlorination step, an electrolytic recovery step, a second chlorination step, an electrolytic reduction step, and a reduction extraction step, respectively. A pair of first electrodes for uranium recovery were provided in the second-stage reaction chamber in the electrolytic recovery step, and cadmium was used as the molten metal in the electrolytic reduction step and the reduction extraction step. The thickness A (FIG. 2) of the recovery tank is about 5 cm, the height B (FIG. 1) is about 40 cm, the length C (FIG. 1) is about 90 cm, and each reaction chamber stores 500 cc of molten salt. A partition plate was provided. First, 1 kg of a mixed salt (eutectic salt) of sodium chloride and potassium chloride was supplied to the upper reaction chamber and melted at 700 ° C. After melting, gradually replenish the same mixed salt,
A total of 6 kg of mixed salt was supplied to store molten salt in all five chambers. Next, Ar gas was spouted into the molten salt at a rate of about 0.7 liter / minute from the gas introduction pipes in the upper, middle, and lower chambers to stir the molten salt.

On the other hand, 500 g of uranium dioxide powder (average particle diameter 100 μm), strontium oxide powder 0.15 g (average particle diameter 20 μm), lanthanum oxide powder 1 g (average particle diameter 20 μm), cesium oxide powder 2
g (average particle diameter 20 μm) and cerium oxide 5 g (average particle diameter 20 μm) were prepared. Cerium oxide and lanthanum oxide were used instead of TRU elements. Then 12,000 g of a mixed salt (eutectic salt) of sodium chloride and potassium chloride
And the above-mentioned simulated nuclear fuel is intermittently transferred to the upper reaction chamber.
It was supplied from the supply port at a rate of 0 g / min. Simultaneously with this supply, Ar gas containing 10% by volume of chlorine gas is injected into the molten salt stored in the upper reaction chamber at a rate of about 3 liters / minute from a gas introduction pipe as the first gas insertion means. The salification reaction was performed in the upper reaction chamber. The supply of chlorine gas was stopped at an amount almost equal to the number of moles of uranium.

In the next reaction chamber, a constant current of 40 A was applied to the pair of first electrodes. The molten salt that had completed the salification reaction in the upper reaction chamber was electrolyzed in the middle reaction chamber, and produced a deposit on the cathode. In the next reaction chamber, 5 volume% of chlorine gas and 5 volume% of Ar gas containing carbon monoxide gas were reacted at a rate of about 0.5 liter / minute from a gas introduction pipe as a second gas introduction means. The salt was spouted into the molten salt stored in the chamber to perform a salification reaction. The supply amount of chlorine gas was supplied until the test was completed. In the next reaction chamber, a current of 1 A was applied to a pair of second electrodes using cadmium as a molten metal as a cathode. Cerium and lanthanum in the molten salt which had completed the salification reaction in the upper reaction chamber were electrolytically reduced and recovered in this reaction chamber. In the lowermost reaction chamber, Ar gas is ejected from a gas introduction pipe, which is the third gas introduction means, into the molten salt stored in the reaction chamber and stirred, and lithium as a reducing agent is supplied from the supply pipe to the molten salt. 5 g was supplied to the reaction chamber, and reduction extraction of other substances into the molten metal was performed.

The reaction yield of the chlorination reaction in the uppermost reaction chamber and the reaction yield of the chlorination reaction at the outlet of the lowermost reaction chamber were evaluated by measuring the amount of unreacted uranium oxide. Table 1 shows the salification reaction conditions. Next, the substance deposited on the cathode of the reaction chamber located in the second stage was measured by X-ray analysis, and as a result, most of uranium dioxide and a very small amount of cerium were deposited. Also, as a result of dissolving the substance precipitated in the first molten metal in the reaction chamber located at the fourth stage and measuring the substance by an atomic absorption method,
Lanthanum, cerium and uranium were deposited. Further, as a result of measuring the substance in the second molten salt in the lowermost reaction chamber by the atomic absorption method, most of cesium and strontium were detected.

[0034]

[Table 1]

[0035]

As described above, the present invention has the following many excellent effects. Since the supplied nuclear fuel moves sequentially from the upper reaction chamber to the lower reaction chamber and is recovered, each operation such as chlorination and electrolytic recovery can be performed by the same apparatus, and uranium can be continuously performed in a simple process. And plutonium can be recovered,
The stable processing and the improvement of the processing capability can be achieved. Since the recovery tank is in the form of a flat plate that does not become critical for the stored nuclear fuel, there is no problem in criticality safety management.

Even if the length C of the recovery tank (FIG. 1) is extended, the criticality safety is maintained unless the thickness A (FIG. 2) is changed. By increasing or decreasing the amount, it is possible to easily manufacture a continuous recovery apparatus that matches the residence time and processing capacity required for recovery, and it is also possible to improve the processing capacity by increasing the number of reaction chambers. Due to the upper partition plate, the molten salt does not short-pass. For this reason, a sufficient reaction time is given in each reaction chamber before it flows down to the lower reaction chamber. Since the temperature control means is provided in each reaction chamber, the optimum reaction conditions in each reaction chamber can be easily set by controlling the reaction temperature in each reaction chamber.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a spent nuclear fuel recovery device of the present invention.

FIG. 2 is a sectional view taken along the line DD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Recovery tank 11a Bottom surface 12 Lower partition plate 14 Outlet 15a-15e Reaction chamber 16 Upper partition plate 17 Controller (temperature control means) 17a Heater 18 Supply port 19 1st gas introduction means 19a, 22a, 29a Gas ejection part 19b, 22b , 29b gas introduction pipes 21a, 21b first electrode 22 second gas introduction means 23a, 23b second electrode 24 supply pipe (reducing agent supply means) 25a first molten metal 25b second molten metal 26 waste gas discharge pipe (waste gas) Discharge means) 27 1st metal supply port 28 1st metal discharge port 29 3rd gas introduction means 31 2nd metal supply port 32 2nd metal discharge port

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Sumio Yamagami, Naka-cho, Naka-machi, Naka-gun, Ibaraki Pref. 1002, 1414 Mitsubishi Materials Corporation Naka Energy Research Laboratory (56) References JP-A-6-265689 ( JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G21C 19/44

Claims (7)

(57) [Claims] 1. A flat plate having at least five reaction chambers (15a, 15b, 15c, 15d, 15e) along an inclined bottom surface (11a) and having a thickness such that the stored nuclear fuel is not critical. The chloride support salt as a reaction medium is stored as a molten salt in the recovery tank (11) formed as a result, and the spent nuclear fuel oxide is supplied from the reaction chamber (15a) located at the highest level, The oxychloride of the metal is reacted by sequentially reacting the radioactive metal in the oxide with the reactant contained in the chloride molten salt in the upper reaction chamber (15a) including the reaction chamber (15a). The radioactive metal oxide is deposited and collected on the electrode (21b) by subjecting the oxychloride to molten salt electrolysis in the reaction chamber (15b) located next, and the reaction chamber (15c) located next. Blow chlorine gas and carbon monoxide gas into the molten chloride salt and remain in the molten salt That oxide ions was metal ionization, then the first molten metal (25a) a reaction chamber for storing the position (15d)
The metal ionized radioactive material in the molten salt is subjected to molten salt electrolysis using the first molten metal (25a) as a cathode to precipitate and collect the radioactive material in the first molten metal (25a). Reaction chamber for storing metal (25b)
By mixing a reducing agent into the molten salt from (15e), chloride remaining in the molten salt can be removed from the second molten metal (25
b) A method for recovering nuclear fuel material, wherein the method comprises extracting and recovering the nuclear fuel material. 2. A recovery having a slanted bottom surface (11a) in which the stored nuclear fuel is sealed in a flat plate shape having a thickness that does not become critical and capable of storing a chloride-supporting salt as a reaction medium as a molten salt. A tank (11), and a reaction chamber comprising at least five chambers inside the recovery tank (11)
(15a, 15b, 15c, 15d, 15e) and the recovery tank (1) so that the molten salt flows from the upper reaction chamber to the lower reaction chamber.
The lower partition plate (1) provided upward on the bottom surface (11a) of (1)
2) and the reaction chambers (15a, 15b, 15c, 15) except for the lowermost reaction chamber (15e).
d) an upper partition plate (16) provided downward from above in the upper reaction chamber to prevent a short path of the molten salt from an upper reaction chamber to a lower reaction chamber; Temperature control means (17) for controlling the temperatures of the reaction chambers (15a, 15b, 15c, 15d, 15e) by heating to the following temperatures, and the chloride provided in the reaction chamber (15a) positioned at the highest level. A supply port (18) for supplying a material-supporting salt or spent nuclear fuel oxide and the chloride-supporting salt, and an outlet (14) provided in the lowermost reaction chamber (15e) for discharging a liquid molten salt A first gas introduction provided in the uppermost reaction chamber (15a) including the uppermost reaction chamber (15a) and introducing chlorine gas into the molten salt stored in the reaction chamber (15a). Means (19)
The reaction chamber (15b) provided in a reaction chamber (15b) located below the reaction chamber (15a) in which the first gas introduction means (19) is provided.
A first electrode (21a, 21b) for electrolyzing the molten salt stored in the first electrode (21a, 21b), and a reaction chamber (15c) located below the reaction chamber (15b) provided with the first electrode (21a, 21b). A second gas introduction unit (22) for introducing a gas containing chlorine gas and carbon gas into the molten salt stored in the reaction chamber (15c); and a reaction provided with the second gas introduction unit (22). The reaction chamber (15d) provided in the reaction chamber (15d) located below the chamber (15c)
A second electrode (23a, 23b) for electrolyzing the molten salt stored in the reaction chamber, and a lowermost reaction chamber located below the reaction chamber (15d) provided with the second electrode (23a, 23b). A reducing agent supply means (2) provided in the reaction chamber (15e) for supplying a reducing agent into the molten salt;
4) A nuclear fuel material recovery apparatus comprising: a waste gas discharging means (26) for discharging waste gas from the reaction chambers (15a, 15b, 15c, 15d, 15e) for each reaction chamber. 3. A reaction chamber provided with second electrodes (23a, 23b).
(15d) and the first molten metal (25a)
A first metal supply port (27) for supplying the first metal, and a first metal discharge port (28) provided in the reaction chamber (15d) and discharging the first molten metal (25a) stored in the reaction chamber (15d). The nuclear fuel material recovery device according to claim 2, comprising: 4. A reaction chamber provided with a reducing agent supply means (24).
A third gas introducing means for introducing an inert gas into the second molten metal (25b) provided in the reaction chamber (15e) and provided in the reaction chamber (15e)
The nuclear fuel material recovery device according to claim 2 or 3, further comprising (29). 5. A reaction chamber provided with a reducing agent supply means (24).
(15e) and a second molten metal (25b) in the reaction chamber (15e).
And a second metal outlet (32) provided in the reaction chamber (15e) for discharging the second molten metal (25b) stored in the reaction chamber (15e). The nuclear fuel material recovery device according to any one of claims 2 to 4, further comprising: 6. A reaction chamber provided with second electrodes (23a, 23b).
The nuclear fuel material recovery device according to any one of claims 2 to 5, wherein the first molten metal (25a) stored in (15d) is one of cadmium, magnesium, and zinc or an alloy thereof. 7. The first, second and third gas introducing means (19, 2).
2, 29) penetrates through the top of the reaction chamber (15a, 15c, 15e) and the tip extends to the bottom of the reaction chamber (15a, 15c, 15e), and the gas ejection part (19a, 22a, 29a) is provided at the tip. The nuclear fuel material recovery device according to claim 2 or 4, further comprising a gas introduction pipe (19b, 22b, 29b) having the same.