FR2611689A1 - Process for the separation of neptunium - Google Patents

Abstract

Process for the separation of neptunium using a reactant for extraction based on an acid phosphate such as diisodecyl hydrogen phosphate, di(2-ethylhexyl) hydrogen phosphate, and the like, characterised by the presence of hydrogen peroxide in the solution. As shown in the figure, the degree of extraction of NpO2<+> increases as a result of the presence of the nitrogen dioxide.

Description

NEPTUNIUM SEPARATION PROCESS
The present invention relates to a process for separating neptunium. More precisely, the
present invention relates to a separation process
neptunium by extraction using a reagent
extraction based on acid phosphate such as
Di-isodecyL phosphoric acid, Di-2-ethylhexyl acid
phosphoric, etc.

Neptunium is an element contained in relatively large quantities in spent nuclear fuels and whose recovery is sought
in a reprocessing process of fuels for the extraction of uranium and plutonium from
spent nuclear fuels, with the aim of
effective use of neptunium. Recently, the
neptunium is considered a very dangerous element
from the point of view of radio waste disposal
assets, and it was necessary to develop a
process for more efficient separation of neptunium
of a radioactive solution such as a solution of
spent fuel, a reprocessed waste solution
at high concentration, etc.

As a separation process, it is considered
than an extraction method using a solvent
organic is very satisfactory because it is capable
to continuously separate neptunium from a large
amount of radioactive solution. However, in the
case of the extraction of the prior art, neptunium
existing in the state of NpO2 as an ion
of valence V in solution was generally previously 2+
transformed into valence VI (ni02) or valence IV
(Np4 +) by using an oxidizing agent or a
reducing agent, then it was extracted with a solvent
organic.

This method has the drawback of posing the problem of preserving the state of oxidation and reduction in solution in order to improve the recovery by separation of neptunium, and requires a complicated operation since an oxidizing agent is used. or a reducing agent, which results in the production of a new waste solution containing these reagents.

To remedy these drawbacks, it is very desirable to use an organic solvent which is capable of directly extracting the neptunium in the state of valence V (ni02). As a method of separating neptunium satisfying this requirement, a method of extracting neptunium using
Di-isodecyl phosphoric acid was invented and has been the subject of a patent application (Journal of Japanese Patent Publication No. 30799/86). This process needs to be improved because the extraction rate decreases when the acid concentration increases, the latter being limited to about 2N.

An object of the present invention is to provide a process for the separation of neptunium in which the extraction rate has been improved by solving this problem.

Fig. 1 is a graph showing a result of Example.

After conducting extensive research for the purpose of achieving this goal, the present inventors have found that when separating neptunium in a valence state V <NpO2 +) using
Di-isodecyl phosphoric acid, addition of hydrogen peroxide increased the extraction rate.

When adding hydrogen peroxide, for the extraction of neptunium in the valence state V (NP02), in combination with another extraction reagent based on acid phosphate such as di-2ethylhexyl acid phosphoric acid, etc., the rate of extraction is increased and, while this extraction reagent could heretofore only be used in high concentration in acidic solution, it has become possible to use it for separating by extraction neptunium in the valence state V (NpO2).

By addition of hydrogen peroxide is meant the reduction of neptnium from valence V (NpO2 +) to valence IV (CNp4 +). However, this reduction reaction is hardly carried out in an acid solution of low concentration, for example of about 0.5 N, but only takes place in the presence of an extraction reagent based on acid phosphate.

The following non-limiting example is given by way of illustration of the invention.

After introducing nitric acid and a solution of neptunium 237 converted to valence V in a test tube fitted with a ground-glass stopper, a solution of hydrogen peroxide or water was introduced into it until a total volume of 2000 l was reached. 2 ml of an organic solvent consisting of 0.5 M di-isodecyl phosphoric acid + n-dodecane, or 0.5 M di-2-ethylhexyl phosphoric acid + ndodecane, were added thereto and the solution has been restless for a while.

After separation into an organic phase and an aqueous phase by centrifugation, 1 ml samples were taken from the two phases to carry out radioactivity measurements.

The 29 KeV y-rays emitted by neptunium 237 were detected using a Ge detector in order to obtain a neptunium distribution ratio.

A solution for converting neptunium into valency V used here, was prepared, after extracting the neptunium from a solution reduced to valence IV, by addition of hydroxylamine hydrochloride and ferrous sulfamic acid, with 0.5 M of a solution of thenoyltrifluoroacetone + xylene, reextraction with 10 M of nitric acid, then dilution with water to give a solution of nitric acid at 0.5 M, and heating on a hot bath in order to obtain a solution of 0.1 M nitric acid.

The result is illustrated in Figure 1. In this figure, the abscissas represent the stirring time in minutes and the ordinates the neptunium distribution ratio. In all cases, the extraction was an extraction of the valence V (NpO2 +) from the 0.5 M nitric acid solution, (A) and (C) represent the extraction obtained with the solution of '0.5 M di-isodecyl phosphoric acid + n-dodecane and (B) and (D) represent the extraction with 0.5 M di-2-ethylhexyl phosphoric acid + n-dodecane. , (A) and (B) contain hydrogen peroxide at a concentration of 0.4 M and (C) and (D) do not contain hydrogen peroxide.

As shown in the figure, whatever the extraction reagent, the NpO2 extraction rate increases due to the presence of hydrogen peroxide.

Claims (1)

CLAIM A process for the separation of neptunium using an acid phosphate extraction reagent such as di-isodecyl phosphoric acid, di-2-ethylhexyl phosphoric acid, etc., characterized by the presence of hydrogen peroxide in the solution.