JP3319657B2 - How to convert transuranium oxalate into chloride - 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 for converting an oxalate of elemental transuranium to chloride, and more particularly to transuranium such as plutonium, americium and curium from high-level radioactive waste liquid generated from a fuel reprocessing plant. It relates to a method for converting elemental oxalate into chloride.

[0002]

2. Description of the Related Art As a method for recovering transuranic elements from high-level radioactive waste liquid in a nuclear fuel reprocessing facility, oxalic acid is added to high-level radioactive waste liquid to recover transuranium elements (referred to as oxalate precipitation method). , Molten salt (potassium chloride-
A method of electrolytically refining with a eutectic salt of lithium chloride) to separate and recover the transuranium element from other elements (referred to as an electrolytic refining method) has been studied.

In order to use the recovered transuranium oxalate for electrolysis in a molten chloride salt, the transuranium oxalate is converted to chloride (referred to as a chloride conversion method).
There is a need to.

[0004] Conventional chloride conversion methods for converting oxalate to chloride include adding 500 to 650 plutonium oxalate.
There is a method to obtain 99.9% pure plutonium chloride by reacting hydrogen chloride at a temperature of ° C (CSGarner et al, The pr
eparation of Plutonium Trichloride, LA-112, (194
Four)).

In addition, plutonium oxalate easily generates plutonium dioxide when heated at a temperature of 350 ° C. or more.
550 ℃), phosphorus pentoxide (reaction temperature 280 ℃), carbon tetrachloride (reaction temperature 280-720 ℃), thionyl chloride (reaction temperature 700-800 ℃), etc. (Toshio Nakai et al., Inorganic Chemistry Complete Book XVII-2
Plutonium, p 197-198).

[0006] From the above, as a general method of converting plutonium to chloride, a method of reacting a gaseous chlorinating agent at a high temperature in an atmosphere without moisture is generally used.

However, these chlorinating agents are generally corrosive, and the amount of corrosion tends to increase when the temperature is increased.
In addition, neptunium among the transuranium elements is recovered as an oxalate having a valence of IV, so that chlorination produces neptunium tetrachloride.

[0008] Chloride is generally known to have a high vapor pressure, whereas neptunium tetrachloride is 10 ^-4 atm at 400 ° C.
Experimental confirmation that uranium tetrachloride, which has a vapor pressure of 1 atm at 780 ° C and has the danger of volatilizing at high reaction temperatures and has the same vapor pressure curve as neptunium tetrachloride, volatizes about 28% at 741 ° C Have been. Since the volatilized neptunium needs to be recovered in the waste gas treatment process, if chloride conversion is performed at a high temperature, the facilities such as the waste gas treatment process may become enormous.

From the above, as a general method for converting transuranium element into chloride, gaseous chlorinating agent is not easily reacted at high temperature in a moisture-free atmosphere, but is easily converted to chloride at low temperature. You need a way to do it.

As a method for obtaining a transuranium element chloride at a low temperature, it has been reported that plutonium trichloride hexahydrate could be obtained by evaporating a plutonium hydrochloride solution to dryness (Toshio Nakai et al.). , Inorganic Chemistry XVII
-2 plutonium, p 197-198). However, when an oxalate of a transuranium element is dissolved in a hydrochloric acid solution and evaporated to dryness, oxalic acid is not decomposed and remains in the solution and only evaporated to dryness to obtain a chloride.

Generally, when a complex of a chelating reagent such as oxalic acid is compared with an anionic complex such as chloride ion,
Oxalic acid complexes tend to have higher stability constants. III
Stability constant of the oxalic acid complex of monovalent plutonium (log
k ₁ ) is 9.31 and the hydrochloric acid complex is −0.15, and oxalic acid forms a more stable complex (JJKatz, GTSeaborg and L.
R. Morss, The chemistry of the Actinide Elements. 2t
h.edition, volume 2.p799-811 (1986)).

Also, oxalic acid is a crystal having a melting point of 189 ° C., but it is known that it sublimates considerably around 100 ° C. (Dictionary of Chemical Encyclopedia). On the other hand, hydrochloric acid has a constant boiling point of 108 ° C, and tends to move into the gas phase more easily than oxalic acid (Chemical Encyclopedia).

For this reason, oxalic acid forms a complex salt with the rare earth element firmly during evaporation to dryness, and hydrochloric acid selectively moves into the gas phase. From the above, in order to obtain chloride by evaporation to dryness, it is necessary to decompose oxalate ions in the solution.

The transuranium element chloride obtained by decomposing oxalate ions and evaporating to dryness contains water of crystallization. Since coexistence of water affects electrolysis when electrolysis is performed using a molten salt, it is necessary to remove water contained in chlorides (hydrated salts) before and after the electrolytic refining step.

As a method of removing before the electrolytic refining step,
The temperature is gradually increased to 350K (77 ° C) in a nitrogen or argon atmosphere to form a monohydrate or dihydrate, and then the temperature is increased to 550K (277 ° C) in a dry hydrogen chloride gas atmosphere. Known method for obtaining anhydrous chloride salt (edited by “Molten Salt and Thermal Technology Research Group”, “Basic of molten salt and thermal technology” p2
72 (1993)).

[0016] As a method for removing after electrolytic refining step, OH in the molten salt ^- a method for removing water which is present as a dry hydrogen chloride gas and chlorine gas, the electrolyte in an inert electrode such as graphite It is known that the method of removing molten salt by
Basics of thermal technology, p265 (1993)) As a method for removing water in chlorides, anhydrous chlorides can be easily obtained by using existing technologies.

[0017]

According to the above-mentioned conventional method for converting a transuranium oxalate into a chloride, the temperature is 500 ° C.
Since the corrosive gas such as hydrogen chloride is brought into contact with the oxalate at the above high temperature, the corrosion of the structural material is accelerated when the ambient temperature increases. In addition, since the reaction temperature is high, a process for recovering volatile substances (transuranium tetrachloride) is required. Therefore, in the conventional technology, there is a problem that the problem of corrosion of the structural material caused by the high reaction temperature and the problem of the recovery of volatile substances must be solved.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to convert a transuranium oxalate such as neptunium, americium and curium from a high-level radioactive waste liquid generated from a fuel reprocessing facility in a nuclear fuel cycle. It is an object of the present invention to provide a method for converting a transuranium oxalate into a chloride which can easily convert to a chloride at a low temperature and solve the above problems.

[0019]

SUMMARY OF THE INVENTION The present invention provides oxalic acid from high-level radioactive liquid waste of a nuclear fuel reprocessing plant in which an alkali metal element, an alkaline earth metal element, a platinum group element, a rare earth element and a transuranium element are dissolved. The alkaline earth metal element, the rare earth element and the transuranium element are recovered as an oxalate, and the alkaline earth metal element, the rare earth element and the transuranium element oxalate are recovered as the alkaline earth metal element, the rare earth element and After converting to uranium element chloride,
Alkaline earth metal elements, rare earth elements and transuranium chlorides are dissolved in a molten salt of chloride and electrolytically purified using an insoluble cathode and an insoluble anode to deposit the transuranium elements on the cathode. In the method of converting the alkaline earth metal element, the rare earth element and the transuranium element oxalate into chloride during the process of separating and recovering by adding hydrochloric acid to the transuranium element oxalate, 100 ° C. After heating and dissolving to the following temperature, the oxalate ions in the hydrochloric acid solution are oxidized and decomposed into carbon dioxide and water, and then the hydrochloric acid solution from which the oxalate ions have been removed is heated to a temperature of 100 ° C or less. Water to evaporate water to remove hydrated chloride (hereinafter referred to as chloride
After the conversion to water chloride ), water of crystallization in the chloride is removed to obtain anhydrous chloride (hereinafter, referred to as chloride (anhydrous)) .

[0020]

[Effect] Add hydrochloric acid to transuranium oxalate 1
When heated to a temperature below 00 ° C., the transuranic element and oxalic acid dissolve in the hydrochloric acid solution. When an oxidizing agent such as hydrogen peroxide is added to the solution, oxalate ions are decomposed into water and carbon dioxide, and the carbon dioxide volatilizes and is removed from the hydrochloric acid solution.

When the solution obtained by decomposing oxalate ions is heated at a temperature of 100 ° C. or less to remove water, a chloride (hydrous salt) of a transuranium element can be obtained.
The water of crystallization can be removed to obtain the chloride (anhydrous) .

In the present invention, however, the reaction is carried out at a temperature of 100 ° C. or less, so that the corrosion of the structural material is prevented and the oxalic acid of the transuranium element is eliminated without volatilizing the tetrachloride of the transuranium element having a high vapor pressure. The salt can be converted to the transuranium chloride.

[0023]

【Example】

(First Embodiment) A first embodiment of the method for converting a transuranium oxalate into a chloride according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram for explaining a method for group separation of high-level waste liquid according to the present invention. The high-level waste liquid 1 contains fission products such as alkali metals, alkaline earth metals, platinum groups, rare earth elements, and transuranium elements such as plutonium generated during operation.

Oxalic acid 2 is added to the high-level waste liquid 1 to form oxalate (oxalate precipitation method 3), and the alkali metal element 5 and the platinum group element 6 are recovered in the filtrate 4, and the precipitate 7
Then, a rare earth element 8, a transuranium element 9, and an alkaline earth metal element 10 are recovered. The recovered precipitate 7 is converted to chloride 11,
The rare earth element 8 and the transuranium element 9 are separated by the electrolytic refining method 12.

FIG. 2 shows a method for converting a transuranium oxalate 13 to a chloride (anhydrous) 22 according to a first embodiment of the present invention. As a method for decomposing oxalic acid in hydrochloric acid solution, a method using hydrogen peroxide, a method for evaporating water in hydrochloric acid solution, a method using indirect heating, a method using chloride (hydrous salt) 18
As a method for removing water therein, a method of contacting with hydrogen chloride 20 in a stream of argon 19 was selected.

After adding hydrochloric acid 14 to the oxalate 13 of transuranium element and dissolving it, the mixture is heated 15 to 90 ° C., hydrogen peroxide 16 is added to decompose oxalic acid, and then evaporated to dryness 17 The chloride (hydrate salt) 18 is obtained. Then argon 19 and hydrogen chloride 20
And heated to about 280 ° C. to remove water of crystallization to obtain chloride (anhydrous) 22.

The principle of the chloride conversion method is described below. When oxalate 13 of transuranium element is added with hydrochloric acid 14, it dissolves in hydrochloric acid by the reaction of formula (1). _{Np (C 2 O 4) 2} · nH 2 O + 4HCl → Np 4+ + 4Cl - + 4H + + 2C 2 O 4 -2 + nH 2 O ··· (1) Am 2 (C 2 O 4) 3 · nH 2 O + 6HCl → 2Am ^{3+ + 6Cl - + 6H + +} 3C 2 O 4 -2 + nH 2 O ··· (1a)

Even if this solution is evaporated to dryness, oxalic acid remains and no chloride can be obtained. Therefore, by adding hydrogen peroxide 16 to the hydrochloric acid solution, oxalate ions can be decomposed into carbon dioxide and water by the reaction of equation (2) and removed from the hydrochloric acid solution. C ₂ O ₄ ^-2 + H ₂ O ₂ + 2H ⁺ → 2CO ₂ + 2H ₂ O (2)

When oxalic acid is removed and evaporated to dryness, the formulas (1) and (1a) are changed to the formulas (3) and (3a) to produce a transuranium element chloride.

Np (C ₂ O ₄ ) ₂ .nH ₂ O + 4HCl + 2H ₂ O ₂ → NpCl _4. (N + 4) H ₂ O + 4CO ₂ (3) Am ₂ (C ₂ O ₄ ) ₃ .nH ₂ O + 6 HCl + 3 H ₂ O ₂ → 2AmCl ₃ · (n + 6) H ₂ O + 6CO ₂ (3a)

Table 1 shows that a conventional technique of adding a hydrochloric acid solution to an oxalate of a transuranium element and directly heating it to evaporate water and decomposing oxalate ions in the hydrochloric acid solution by using hydrogen peroxide were used. The oxalic acid decomposition rate in the first embodiment of the present invention in which water is directly heated to evaporate water is compared and shown. The experiment was conducted using a rare earth oxalate similar in chemical properties to transuranium as a simulated substance of transuranium oxalate.

The decomposition rate of oxalic acid was evaluated based on the oxalic acid / rare earth element ratio in the materials obtained by the conventional technique and the first embodiment of the present invention. Rare earth elements are generally 3
Since oxalic acid generally exists as a divalent ion in a solution, the oxalic acid / rare earth element ratio in the rare earth oxalate given as an initial condition is 1.50.

[0033]

[Table 1]

In the present invention, lanthanum oxalate is added to 0.015 M
M hydrochloric acid (15 ml) is added and dissolved.
Table 1 shows the result of evaporating water by direct heating after a continuous addition at a rate of 0.5 ml / min.

In the prior art, the initial ratio of oxalic acid / rare earth element was 1.50 under the initial condition. In contrast,
According to the present invention, the oxalic acid / rare earth element ratio after decomposing oxalic acid with hydrogen peroxide was 0.074 or less, and it was confirmed that oxalic acid was decomposed and chloride was generated.

According to the equation (3a), 3M chloride ions are required to convert 1M of trivalent ions such as americium into chloride, and the molar ratio of chlorine / americium required to convert americium into chloride is required. Becomes 3.

Similarly, in order to convert 1M of tetravalent ions such as neptunium into chloride and recover it, 4M chloride ions are required, and the molar ratio of chlorine / neptunium required to convert neptunium into chloride is 4%. Becomes In the experiment
This means that 0.09 M chloride ions are added to 0.015 M lanthanum, and the chlorine / lanthanum molar ratio is 6. This would add twice the amount of the chemical equivalent.

According to the equation (2), 1 M of hydrogen peroxide is required to decompose 1 M of divalent oxalate ions, and the oxalic acid / hydrogen peroxide molar ratio required to decompose oxalic acid is required. Becomes 1. Lanthanum oxalate in experiment
Since the initial addition amount was 0.015M, the amount of oxalic acid in the solution was 0.0255M.

Since 150 ml of 30% hydrogen peroxide was added thereto, assuming a specific gravity of 1, this means that 1.38 M hydrogen peroxide was added, and the oxalic acid / hydrogen peroxide molar ratio was 61. This means that a substantial excess of 61 times the chemical equivalent is added.

When converting a trivalent transuranium element into a chloride, it is sufficient to add an amount equivalent to one time the chemical equivalent.
The molar ratio of chlorine / trivalent transuranium element is 3 to 6 in addition to 6,
The molar ratio of oxalic acid / hydrogen peroxide can be used in the range of 1 to 61 in addition to 61.

From the above, by adding hydrochloric acid to oxalic acid and dissolving it, by adding hydrogen peroxide, oxalate can be easily decomposed and chloride can be formed. Compared with the conversion method, volatile neptunium tetrachloride can be easily converted to chloride without transferring into the gas phase.

FIG. 3 shows that from the high level waste liquid 1 to the transuranium element 9
In the process up to recovering by electrorefining, steps including a conventional example (FIG. 3A) and an example of the present invention (FIG. 3B) are compared and shown.

That is, conventionally, as shown in FIG.
After conversion to oxide 25, addition of carbon 26 and heating 27 at 1014K (741 ° C.) in an atmosphere of argon 19, chlorine 28 is contacted to convert oxide 25 to chloride (no volatile elements) 29.

Partially volatile element 30 (neptunium tetrachloride 3
1. Since uranium tetrachloride 32) is volatilized, it is cooled 33, collected and mixed with the obtained chloride (with no volatile elements) 29, and then dissolved in a molten salt of potassium chloride-lithium chloride 34.

Then, after adding a reducing agent such as lithium 35 and extracting 37 into a cadmium 36 bath, electrolysis 38 is performed using the cadmium 36 bath as an anode, and a transuranium element 9 is recovered on the cathode, and an alkali metal It is separated from element 5, alkaline earth metal element 10, white metal element 6, and rare earth element 8.

On the other hand, in the embodiment of the present invention, FIG.
As shown in (b), oxalic acid 2 is added to high-level waste liquid 1 to form oxalate 13 (transuranium element 9, rare earth element 8, alkaline earth metal element 10), and alkali in filtrate 4 After being separated from the metal element 5 and the white metal element 6, hydrochloric acid 14 is added to the obtained oxalate 13 and dissolved by heating 15; hydrogen peroxide 16 is added to decompose oxalic acid; Dry
17 to obtain chloride (hydrate salt) 18.

The chloride (hydrous salt) 18 is dehydrated by adding argon 19 and hydrogen chloride 20 and heating 21 to about 300 ° C. 21 to obtain a chloride (anhydrous) 22. After dissolving this chloride (anhydrous) 22 in a molten salt of potassium chloride-lithium chloride 34, it is electrolyzed 38 using an insoluble anode and cathode, and the transuranium element 9 is recovered and the alkaline earth metal element 10, Separates from rare earth element 8.

Table 2 shows a conventional method for obtaining a chloride from an oxide using carbon and chlorine, and a processing method for an example of the present invention for obtaining a chloride from oxalate using hydrochloric acid and hydrogen peroxide. The equipment of each process and its capacity are shown.

The conventional example can be classified into the following six processes. A mixer that irradiates high-level wastewater with microwaves to add carbon to the denitrated oxide and mixes it, a chlorination reactor that reacts a mixture of carbon and oxide with chlorine at a temperature of 741 ° C,
A volatile matter recovery device that recovers volatile elements such as neptunium tetrachloride with a condenser, a chlorine gas recovery device that recovers unreacted chlorine gas, and chlorine gas that is located after the chlorine gas recovery device is not released to the environment. And a furnace for dissolving volatiles into recovered salts by mixing volatiles recovered from a waste gas treatment device and a volatiles recovery device with chlorides generated from a chlorination reactor.

In the conventional example, the equipment amount was calculated based on the processing amount of each process. Since the operation is performed three times a day, the chlorination reaction furnace, the volatile matter recovery device, and the furnace for dissolving the volatiles in the recovered salt have a processing capacity of 1/3 of the daily processing amount.

Further, only a mixer can be treated in an air atmosphere, and it is necessary to control the water and oxygen concentrations in the equipment below the chlorination furnace in the latter stage, and use a large amount of chlorine. It is necessary to design a corresponding device.

The embodiments of the present invention can be classified into the following four processes. Add oxalic acid to hydrochloric acid, dissolve it, decompose oxalic acid with hydrogen peroxide, evaporate to dryness to make chloride (hydrated), chlorination reactor, 277 ° C chloride (hydrated)
Dehydration with argon and dry hydrogen chloride gas to produce anhydrous chlorides, a hydrogen chloride gas recovery device to recover unreacted hydrogen chloride gas, and a chlorine gas recovery device located downstream of the hydrogen chloride gas recovery device There are four processes of waste gas treatment equipment for not discharging.

Per ton of spent fuel, 25.78 moles of transuranium elements (including uranium), 29.81 moles of alkaline earth elements, and 10
5.7 mol. Since 4 tons of uranium are reprocessed per day, the transuranium element is 103.12 mol, the alkaline earth metal and rare earth element is 542.04 mol, and the total is 645.16 mol.

In the present embodiment, it is necessary to add 15 ml of a 6N hydrochloric acid solution to dissolve 0.015 mol of rare earth element. Therefore, in the actual process, it is calculated to add 0.65 m ³ of hydrochloric acid. Since the reaction time was 5 hours, the operation was performed twice a day for a margin.

Therefore, the capacity that needs to be processed in one cycle is 0.325 m ³ . The chlorine reactor can be treated in an air atmosphere, but it is necessary to control the moisture and oxygen concentrations for the devices below the chlorination reactor in the latter stage, and to use hydrogen chloride, design the device corresponding to the use of hydrogen chloride. There is a need.

However, since hydrogen chloride gas is used for the purpose of dehydration, a smaller amount of chlorinating agent may be used as compared with the conventional example using chlorine for the purpose of chlorination. Therefore, the hydrogen chloride recovery device and the waste gas treatment device can be downsized as compared with the conventional example.

When comparing the conventional process and the main process amount of the present invention, the conventional process amount is 1.5 m ³ , whereas the embodiment of the present invention can be reduced to about half, that is, 0.8 m ³ . From this, if the construction cost is calculated simply by comparing the installed capacity, it can be expected that the cost of the main process will be reduced by about 50%.

Further, it is necessary to use an expensive material such as a corrosion-resistant material depending on the atmosphere to be used, so that the construction cost and the maintenance cost are different. In particular, in a process using a chlorinating agent, maintenance costs such as material replacement for corrosion and atmosphere management are required, so that the cost is expected to be high.

In particular, in the conventional example, in a chlorination furnace, a high concentration of chlorine is reacted at a temperature of 800 ° C., so that it is expected that the construction cost and the maintenance cost will be high. For this reason, the installed capacity is not simply proportional to the construction cost, but simply evaluating it can reduce the cost of the main process by about 50%.

[0060]

[Table 2]

(Second Embodiment) Next, a second embodiment according to the present invention will be described.
Will be described with reference to FIGS. 2 and 3 and Table 4. FIG. 2 shows a method for converting a transuranium oxalate into a chloride according to the present invention. As a method for decomposing oxalic acid in a hydrochloric acid solution, a method using hydrogen peroxide, a method for evaporating water in a hydrochloric acid solution, a method using indirect heating, and a method for removing water in chlorides (hydrous salts) include: The method of contacting with hydrogen chloride in an argon stream was selected.

After adding hydrochloric acid 14 to oxalate 13 and dissolving it, it is heated 15 to about 90 ° C., hydrogen peroxide 16 is added to decompose oxalic acid, and evaporated to dryness 17 to obtain chloride (hydrated salt). Get 18). After that, add argon 19 and hydrogen chloride 20 to 280 ℃
Heat to about 21 to remove water of crystallization and chloride (anhydrous) 22
Get.

The method of adding hydrogen peroxide is as follows: (1) Every 5 minutes
Table 3 shows the results obtained by adding two kinds of liquid at a time, namely, a method of adding 2.6 ml at a time and a method of (2) a method of continuously adding droplets of about 20 μl.

[0064]

[Table 3]

Hydrogen peroxide is unstable and is easily decomposed as shown in equation (4). (Chemical Dictionary) 2H ₂ O ₂ = 2H ₂ O + O ₂ +46.2 kcal (4) Therefore, when added at a stretch, unreacted hydrogen peroxide itself decomposes in the solution to efficiently decompose oxalic acid. I will not be. From the above results, as a method of adding hydrogen peroxide, oxalic acid can be decomposed more efficiently with the same amount of hydrogen peroxide when it is added continuously little by little than when it is added all at once.

Table 4 shows the results of decomposition of oxalic acid in hydrochloric acid using ozone in addition to hydrogen peroxide. Ozone was gradually blown in like the hydrogen peroxide to react with oxalic acid. As in the case of adding hydrogen peroxide, the decomposition rate of oxalic acid was 95% or more. Ozone has a strong oxidizing power.
(0 ° C, 1 atm) dissolves and gradually decomposes to oxygen at normal temperature. It is also effective to use ozone as a method for decomposing oxalic acid.

[0067]

[Table 4]

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. In the first embodiment, as shown in FIG.
Shows the steps of a method for converting oxalic acid into hydrochloric acid (anhydrous) 22 in which hydrogen peroxide 16 is used to decompose oxalic acid in the hydrochloric acid solution, and indirect heating is used to evaporate water in the hydrochloric acid solution As a method for removing water in the chloride (hydrate salt) 18 by using the method described above, a method of contacting with hydrogen chloride 20 in a stream of argon 19 has been described.

That is, in the first embodiment, as shown in FIG. 2, hydrochloric acid 14 was added to and dissolved in oxalate 13 of a transuranium element, heated to about 90 ° C. 15 and hydrogen peroxide 16 was added. After decomposing oxalic acid, it is evaporated to dryness 17 to obtain chloride (hydrated salt) 18. Thereafter, argon 19 and hydrogen chloride 20 were added, and the mixture was heated 21 to about 280 ° C. 21 to remove water of crystallization to obtain chloride (anhydrous) 22.

Here, in this embodiment, as a method for decomposing oxalate ions in hydrochloric acid, a method using electrolysis, a method using ultraviolet rays, or a method using γ rays is used instead of adding hydrogen peroxide.

In the electrolysis method, the Kolbe method is applied, and the carboxyl group of the carboxylic acid is converted to carbon dioxide by anodic oxidation to be released and decomposed. The reaction at the anode is shown in equation (5).

Anode: H ₂ C ₂ O ₄ = 2CO ₂ (g) + 2H ⁺ + 2e ⁻ −0.49 V vs. NHE (standard hydrogen electrode) (5)

In the method using ultraviolet rays, when water is irradiated with a wavelength of 184.9 nm as shown in the equation (6), radicals are generated, and the radicals act on oxalic acid and are decomposed. H ₂ O → OH + H (6) In the method using γ-rays, when γ-rays are irradiated, radicals are generated and oxalic acid is decomposed as in the case of irradiation with ultraviolet rays.

Table 5 shows the results of a decomposition experiment conducted by adding 50 ml of hydrochloric acid to 0.01 M of lanthanum oxalate (0.01 M of lanthanum, 0.015 M of oxalic acid) by the above four methods.

[0075]

[Table 5]

From the above results, the method of adding hydrogen peroxide according to the first embodiment can decompose oxalate ions in a hydrochloric acid solution in a short time, but requires the addition of a chemical. Also,
In the electrolysis, oxalate ions can be easily decomposed by repeatedly using the electrode, but the reaction time becomes longer as compared with the method of adding hydrogen peroxide.

When ultraviolet irradiation and γ-ray irradiation are performed, the reaction time is 3 hours, which is shorter than the method of adding hydrogen peroxide, but the decomposition rate is 90%. Although each has its advantages and disadvantages, it is possible to use a method of electrolysis, a method of ultraviolet rays, and a method of irradiating γ rays in addition to the method of adding hydrogen peroxide,
Further, these methods can be used in combination.

(Fourth Embodiment) In this embodiment, a method for removing water in the chloride (hydrate salt) 18 in FIG.
Evaporate and dry chloride (hydrated salt) 18 with nitrogen and argon
The temperature is gradually increased to 350 K (77 ° C.) in a stream of 19 to obtain chloride 40 of monohydrate or dihydrate, and then to 550 K (277 ° C.) in a dry hydrogen chloride 20 gas atmosphere. Thus, an anhydrous chloride salt 43 is obtained (see FIG. 4B). Also, there is a method of removing water present in the molten salt with dry hydrogen chloride gas or chlorine gas, or an electrolytic method using an inert electrode such as graphite.
(See FIG. 4C).

Therefore, when the obtained chloride (hydrate) 18 is electrolyzed 38 in a molten salt 41 of chloride 40, the water of crystallization of chloride (hydrate) 18 is removed as much as possible in a stream of argon 19. The water removal step is performed by applying a method of dissolving the chloride 40 in the molten salt 41 and removing it with dry hydrogen chloride gas or chlorine gas or a method of removing the same by electrolysis with an inert electrode such as graphite. Moisture can be removed without having to provide a new one.

FIG. 4 is a block diagram showing a method for removing water in chloride 18 after converting oxalate into chloride according to the present invention. FIG. 4 (a) shows a comparison between the first embodiment and this embodiment. (B) and (c) show the fourth embodiment, respectively.

In the first embodiment, as shown in FIG. 4 (a), argon 19 was added to chloride (hydrated salt) 18, heated to 77 ° C. 39, and chloride (monohydrate or dihydrate) was added. ) To 40, add hydrogen chloride 20 and heat to 300 ° C 21 to chloride (anhydrous)
Get 22. The obtained chloride (anhydrous) 22 is converted to potassium chloride-
After dissolving in a molten salt 41 such as lithium chloride, an anhydrous chloride (dissolved in the molten salt) 43 is obtained. Argon 19 and hydrogen chloride 20 were used at a purity of 99.999%, and were contacted at a flow rate of 1 l / min for 3 hours. The water in argon 19 and hydrogen chloride 20 was removed via a purifier and used repeatedly.

In the fourth embodiment, as shown in FIG. 4B, the chloride (hydrous salt) 18 was heated to 77 ° C. 39 while flowing argon 19, and the chloride (monohydrate or dihydrate) was heated. Salt) to 40.
Next, chloride 40 is dissolved 42 in a molten salt 41 such as potassium chloride-lithium chloride, and then hydrogen chloride 20 or chlorine
Inject 28 to obtain anhydrous chloride (dissolved in molten salt) 43.

Here, argon 19 having a purity of 99.999% was used and contacted at a flow rate of 1 l / min for 2 hours. Hydrogen chloride
20 or chlorine 28 having a purity of 99.999% is used.
Contact for 1 hour at a flow rate of 1 minute. Argon 19, hydrogen chloride 20
Alternatively, the water in chlorine 28 was removed through a purification device and used repeatedly.

FIG. 4C shows another example of the present embodiment.
As shown in, the chloride (hydrous salt) 18 is heated to 77 ° C while flowing argon 19 to the chloride 39 (monohydrate or dihydrate).
After adjusting to 40, molten salt such as potassium chloride-lithium chloride
After dissolving in 41, water is removed by electrolysis 38 to obtain anhydrous chloride (dissolved in molten salt) 43.

Argon 19 was used with a purity of 99.999%, and was contacted at a flow rate of 1 l / min for 2 hours. The water content of argon 19 was removed through a purifier and used repeatedly. electrolytic
38 was carried out for 1 hour while blowing argon having a purity of 99.999% at a flow rate of 1 l / min.

Further, the first embodiment and the fourth embodiment will be described with reference to FIG.
Table 6 shows the equipment and capacity of the process according to the example of the present invention. The daily oxalate treatment amount was determined by referring to the first embodiment.
103.12 moles of transuranium element per day, 542.04 moles in total for alkaline earth metals and rare earth elements 645.1 in total
Suppose you treat 6 moles.

The hydrochloric acid used was 0.65 m ³ , and the operation was 2 times a day.
Since it is a cycle, it is 0.325 m ^{3 in} one cycle.
0.4m ³ is required for chlorination reactor equipment. Further, the dewatering tank necessary for dehydration is required 0.4 m ³ as facilities for the 0.325 M ^3. Since the dehydration tank is used in a hydrogen chloride atmosphere at a temperature of 300 ° C., it is necessary to use a material having excellent heat resistance and corrosion resistance, which may increase costs.

Further, 1 mol of the obtained chloride was mixed with 1 liter of molten salt.
(About 5 wt% based on the molten salt)
645.16 l of molten salt are required. Therefore, the capacity of the electrolytic cell is 0.8 m ³ and the capacity of the equipment is 1 m ³ .

In the first embodiment, since a chlorine gas is generated at the anode without using a cadmium anode, it is desirable to use a material having excellent heat resistance and corrosion resistance. On the other hand, in the fourth embodiment, a chlorination reactor and a dehydration tank having a facility of 0.4 m ³ and a 1 m ³ electrolytic tank are required as in the first embodiment. Since argon gas is used at the following temperature, it is not necessary to use a material having excellent heat resistance and corrosion resistance.

In the method of blowing hydrogen chloride gas and chlorine gas with a molten salt, since chlorine gas is used, it is necessary to use a material having excellent heat resistance and corrosion resistance. In the method of removing by electrolysis, it is not necessary to blow chlorine, so that a facility for blowing chlorine gas becomes unnecessary, and as a result, the capacity of the facility is slightly reduced. There is no difference when comparing the total equipment capacity of the first embodiment and the fourth embodiment, but in the first embodiment, the dehydration tank uses hydrogen chloride gas at 300 ° C. Get higher.

[0091]

[Table 6]

(Fifth Embodiment) The fifth embodiment is different from the one shown in FIG.
In the first embodiment shown in FIG.
After adding hydrochloric acid 14 to 13 and heating 15, indirect heating is carried out in the process of evaporation to dryness 17 in which oxalate ions in the hydrochloric acid solution are decomposed and removed with hydrogen peroxide 16 and then water in the hydrochloric acid solution is removed. This is an example in which a direct heating method using microwaves is used instead of the method.

Table 7 shows that oxalic acid was dissolved in hydrochloric acid to decompose oxalate ions and then heated indirectly with a heater to evaporate the water, or directly heated by microwave irradiation. The evaporation times are shown in comparison.

According to the first embodiment, the hydrochloric acid used is 0.6
5 m ^3, the operation becomes 0.325 M ³ in one cycle for a day two cycles. Assuming that hydrochloric acid is water, the amount of heat required to evaporate 325 kg of water is 0.462 kcal / kg
℃ (100 ℃) and temperature difference before and after microwave heating 80 ℃
(= 100 ℃ -20 ℃), it becomes 1.2 × 10 ⁴ kcal.

On the other hand, in the case of microwave heating, if the microwave absorption efficiency is 0.5, the microwave oscillation output is 100 kW, and the conversion coefficient is 1.163 × 10 ⁻³ kWh / kcal, the heating time is 20 minutes. Therefore, it takes about 30 minutes to dehydrate 0.325 m ³ .

On the other hand, when heating indirectly, 100 kW
Even if the heater is used, the heating time is one hour. As is apparent from the above, as a method of evaporating water, a method of directly heating by microwaves other than the method of indirect heating is also effective.

[0097]

[Table 7]

[0098]

According to the present invention, the following effects can be obtained. (1) Ancillary equipment such as a chlorinating agent removal device can be miniaturized, and the process It can be greatly simplified. (2) Compared to the conventional method in which transuranium element is converted into oxide and then reacted with chlorinating agent at high temperature under moisture-free condition, volatile neptunium tetrachloride is not transferred into gas phase. In addition, there is no need for a waste gas facility for recovering volatile elements. (3) The equipment capacity can be reduced and the cost can be significantly reduced as compared with the conventional method in which a transuranium element is converted into an oxide and then reacted with a chlorinating agent at a high temperature in a moisture-free condition. (4) Compared with the conventional method in which transuranium element is converted into oxide and then reacted with chlorinating agent at high temperature under moisture-free conditions, it is easier to select corrosion-resistant materials and the amount used is smaller. , Which can greatly reduce the cost of the process.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a method for separating a group of high-level waste liquid for explaining one embodiment according to the present invention.

FIG. 2 is a block diagram illustrating a method for converting a transuranium oxalate into a chloride according to the present invention.

FIG. 3 (a) is a block diagram showing a conventional process up to recovery of transuranium element from high-level waste liquid by electrolytic purification, and FIG. 3 (b) shows a process including an embodiment of the present invention as in (a). FIG.

4 (a) to 4 (c) are block diagrams for removing water in chloride after converting oxalic acid to chloride in each of the examples according to the present invention.

[Explanation of symbols]

1: high level, 2: oxalic acid, 3: oxalate precipitation method,
4 ... filtrate, 5 ... alkali metal element, 6 ... white metal element, 7
... Precipitate, 8 ... rare earth element, 9 ... transuranium element, 10 ... alkaline earth metal element, 11 ... chloride conversion, 12 ... electrolytic purification method, 13 ... oxalate of transuranium element, 14 ... hydrochloric acid, 15 Heating (90 ° C), 16 hydrogen peroxide, 17 evaporation to dryness, 18 chloride (hydrated salt), 19 argon, 20 hydrogen chloride, 21 heating (300 ° C), 22 chloride ( Anhydrous), 23 ... microwave, 24
... Denitration, 25 ... Oxide, 26 ... Carbon, 27 ... Heating (741 ℃),
28 ... chlorine, 29 ... chloride (no volatile elements), 30 ... volatile elements, 31 ... neptunium tetrachloride, 32 ... uranium tetrachloride, 33 ... cooling, 34 ... potassium chloride-lithium chloride, 35 ...
Lithium, 36… Cadmium, 37… Extraction, 38… Electrolysis, 39…
Heating (77 ℃), 40 ... chloride (monohydrate or dihydrate), 41
... molten salt, 42 ... dissolved, 43 ... anhydrous chloride (dissolved in molten salt).

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-140293 (JP, A) JP-A-5-341099 (JP, A) JP-A-61-104299 (JP, A) JP-A-58- 199727 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G21C 19/44 C01G 56/00

Claims (4)

(57) [Claims] 1. An alkaline earth metal element using oxalic acid from a high level radioactive waste liquid of a nuclear fuel reprocessing facility in which an alkali metal element, an alkaline earth metal element, a platinum group element, a rare earth element and a transuranium element are dissolved. The rare earth element and the transuranium element were recovered as oxalate, and the alkaline earth metal element, the rare earth element and the transuranium element oxalate were converted into the alkaline earth metal element, the rare earth element and the transuranium element chloride. Thereafter, an alkaline earth metal element, a rare earth element and a transuranium element chloride are dissolved in a molten salt of chloride and electrolytically purified using an insoluble cathode and an insoluble anode, and the transuranium element is added to the cathode. In the method of converting the oxalate of the alkaline earth metal element, the rare earth element and the transuranium element into chloride during the process of separating and recovering by precipitation After adding hydrochloric acid to the transuranium oxalate and dissolving it by heating to a temperature of 100 ° C. or lower, oxidizing oxalate ions in the hydrochloric acid solution to decompose it into carbon dioxide and water, containing in hydrochloric acid solution of acid ions are removed by heating to a temperature of 100 ° C. or less was evaporating water
A method for converting an oxalate of a transuranium element into a chloride, comprising removing water of crystallization in the hydrated chloride after converting into a hydrated chloride and obtaining an anhydrous chloride. 2. A method for decomposing oxalate ions in the hydrochloric acid solution includes a method of continuously adding hydrogen peroxide or ozone little by little, a method of electrolysis, a method of irradiating ultraviolet rays, and a method of irradiating γ rays. how to oxalate salt of transuranic elements of claim 1 Symbol placement and selecting from one of the methods at least to the chloride. 3. Heating the hydrochloric acid solution to evaporate water
The method of converting the hydrate chloride, claim 1, wherein the selecting the at least one method of how to direct heating by irradiating method or microwave indirectly heated
A method for converting a transuranium oxalate into a chloride. 4. A removal of the crystal water in the hydrate salt chloride
The method anhydride chloride Ru obtained, a method of contacting the hydrogen chloride or chlorine in argon gas or nitrogen gas stream, was dissolved in a molten salt, a method for electrolytic or chlorine gas into the molten salt, hydrogen chloride gas 2. The method for converting uranium oxalate into chloride according to claim 1, wherein the method is selected from at least one of the following methods.