DE1592416A1 - Process for the reduction of plutonium - Google Patents

Description

Karlsruhe, the 6th Ιο. 1965 PTA 65/67 Ss / di

"Process for the reduction of plutonium"

The invention relates to a method for reducing plutonium, which is particularly useful in the processing of plutonium-containing nuclear fuels by extraction by means of organic solvents, advantageous for re-extraction taking place simultaneously with the reduction of plutonium can be applied.

For the reprocessing of separated nuclear fuel, in larger-scale aqueous processes are used in which an organic solvent, preferably tri-n-butyl phosphate (TBP) diluted with hydrocarbons, the valuable plutonium

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and uranium is extracted and separated from the spa products. The plutonium is separated from uranium from the organic solvent by reducing the plutonium (IV) to the easily re-extractable plutonium (III). The purpose reducing agents used have a significant disadvantage, iron (II) sulfamate Fe (NH ₂ SO _{3) 2 #} is mainly used for this purpose, has in addition to its good reduction properties the disadvantage of foreign ions - iron and sulfate - introduce into the plutonium-containing solution are not desired in the end product. It has therefore already been proposed to replace the iron (II) sulfamate with uranium (IV) solutions. In addition to certain advantages over iron (II) sulfamate, uranium (IV) solutions are easily oxidized by the air. B. Hydrazine stabilized and can contaminate the plutonium with uranium inadmissible.

It has now been found that plutonium by means of weakly acidic solution containing nitrite (reducing solution). If here the plutonium to be reduced is extracted in organic Solutions is present, then it is re-extracted at the same time by means of the reducing solution according to the invention. When using the Reducing agent according to the invention, in particular for the simultaneous re-extraction of plutonium from organic solutions, fall the above-described disadvantages of the previous reduction processes continue.

The acid concentration of the weakly acidic nitrite solution (Reducing solution) is preferably chosen to be less than 0.3 molar, in particular in the range between 0.3 and 0.3 molar. as Acid can be used, for example, nitric acid and an alkali nitrite, preferably sodium nitrite, as the nitrite, the Na ion added to the solution advantageously being used in the subsequent Processing steps does not interfere.

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The reduction process according to the invention is particularly advantageous when following the reduction in which the Plutonium is re-extracted with the reducing solution, again an oxidation of the trivalent plutonium to the tetravalent one should take place, for example for a new extraction. if the oxidation of plutonium in a known manner by means of a one to three molar nitric acid solution containing sodium nitrite is carried out, and beforehand a similar one for reduction Solution that is only less than 0.3 molar nitric acid, is used, then all that is needed is nitric acid added reducing solution containing re-extracted plutonium to become.

In the treatment of nuclear fuels by extraction in and re-extraction from organic solvents, the method according to the invention is useful Use the method very advantageously when plutonium and uranium coexist. Then you can either both nuclear fuels together with the one according to the invention Reduction solution can be re-extracted from the organic phase or separated from one another here.

For the joint re-extraction of the plutonium and uranium from the organic solvent, for example, the plutonium and uranium are first _{washed out with 0.2 η HNO 3} and 0.07 m NaNO ₃ solutions in countercurrent and the remaining uranium with approx. 0.02 η HNO ₃ .

To separate the plutonium from the uranium, the reduction of Pu (IV) to Pu (III) is carried out with a solution of _{0.1 - 0.2 m HNO 3} and 0.1 5 m NaNO ₂ , with the addition of NaNO ₃ as a salting-out agent for uranium.

Extractive removal of the uranium from the aqueous solution running out with fresh solvent prevents the uranium from going along with the plutonium in the aqueous phase .

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The process according to the invention is illustrated below with the aid of examples. The size and number information contained therein however, they mean a limitation of the invention, rather the procedure can also be carried out successfully in a modified form under the above guidelines:

Example 1 :

Aqueous solutions with tracer Pu (IV) or aqueous solution with 25 g of Pu (NO ₃ ). o, o7 η NaNO- and o, l or o, 2 η HNO- were added to the liter, an instant reduction to plutonium (III) took place. Without addition of NaNO. found with o, 2 η ENT. Disproportionation of the Pu (IV) nitrate solution to Pu (III) and Pu (VI) nitrate takes place.

Example 2 t

Tracer plutonium or 20% or 30% TBP solutions containing 25 g of Pu (IV) were treated with an aqueous solution of 0.07 η NaNO ₂ or 0.02 η HNO. stirred, the Pu (IV) was immediately reduced and the Pu (III) was washed out of the organic extractant quantitatively, corresponding to the distribution coefficient of the Pu (III) (approx. 99.7%). After adjusting the aqueous solution to 2 η HHO ₃ , the Pu (III) was oxidized to Pu (IV).

Example 3;

aqueous solutions with tracer plutonium or aqueous solution with 25 g Pu (IV) / 1 and ten times the amount of uranium, both in nitrate form, were mixed with o, o7 η NaNO ₂ and o, l - o, 2 η HNO ₃ , whereby the Pu (IV) was instantly reduced to Pu (III).

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Example 4 ι

Tracer plutonium or 25 g Pu (IV) / 1 and three to ten times the amount of uranium and ο, Ι η HNO-containing 30% TBP solution in n-dodecane was mixed with an aqueous solution of o, o7 η NaNO ₂ stirred, the plutonium immediately reduced to Pu (III) and the distribution coefficient of Pu (III) corresponding to (99-98%) was found in the aqueous solution.

Example 5:

Tracer plutonium or 25 g Pu (IV) / 1 and between three to ten times the amount of uranium in 3O% / o TBP-n dodecane solutions were with an aqueous solution of o, 2 η HNO-, ο, 5 m NaNO ₂ and 0.5 m NaNO ₃ - the NaNO, to increase the distribution coefficient of the uranium - stirred, the plutonium being reduced to Pu (III) and passing into the aqueous solution, while most of the uranium (according to the distribution coefficient) remained in the organic phase .

In this way, the plutonium can be separated from the uranium in countercurrent.

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Claims (6)

Karlsruhe, the 6th Io. 1965 PTA 65/67 Ss / di patent claims z 1. Process for the reduction of plutonium, in particular for the simultaneous re-extraction of plutonium from organic ones Solutions, characterized in that the plutonium means weakly acidic nitrite solution (reducing solution) is treated. 2. The method according to claim 1, characterized in that the acid concentration of the reducing solution is chosen to be less than 0.3 molar. 3. The method according to claim 1 or 2, characterized in that an alkali nitrite, preferably sodium nitrite, is used as the nitrite. 4. The method according to claim 1 or one of the following claims, characterized in that nitric acid is used as the acid. ^βΛ0 ORIGINAL ■ 009861/1625