Process for separating metals

Abstract

An electrorefining apparatus is capable of operating in continuous mode, and includes a criticality control mechanism, preferably a geometric criticality control mechanism, for example, to control the dimensions of the apparatus. Electrochemical cells include a large surface area per unit volume, preferably in the form of thin, flat plates. Cells include a crusting liquid cathodes, a cast cathode, a fluidised cell or pulsed bed, a moving belt cathode, a consolidating cathode, or a liquid anode and a plate cathode. A continuous process for the isolation of metals, typically uranium, from spent nuclear fuels includes electrochemically treating the spent nuclear fuels in the apparatus.

Description

FIELD OF THE INVENTION [0001] This invention relates to processes for the separation of metals from compositions containing metals. The invention includes processes for the treatment of spent nuclear fuel forming part of a process for reprocessing, conditioning and / or partitioning nuclear fuels. Reference will be made hereinafter mainly to nuclear fuels but it should be understood that the invention is not restricted to any particular type of material and has application outside the nuclear industry. The processes involve the purification of a substance which is liquid at its operating temperature and at this temperature is comprised wholly or largely of ionic species. Such substances generally fall within one of two main classes, ionic liquids and molten salts. Ionic liquids typically have a relatively low melting point and usually contain an organic cation, whereas molten salts are generally totally inorganic and most commonly have a melting point of at least several hundred degre...

AI Technical Summary

Benefits of technology

[0050] The process of the present invention is analogous to the ANL process, wherein a metallic fuel feed is electrorefined and a uranium metal product is collected on a cathode. However, the process of the present invention shows significant advantages over this prior art method in that it is a continuous process, and is well suited to scale up as a consequence of the criticality safe nature of the apparatus of the invention. The present process also allows for the use of ionic liquids, as well as molten salts, in its operation.

Problems solved by technology

This limits the recovery, purification and electroplating of metals on to surfaces from aqueous solution to those metals whose electrode reduction potentials are more positive than the cathodic limit of the aqueous solution.

However, after a period of use the molten salt becomes loaded with fission products which not only begin to affect the quality of the product, but also result in too much heat generation within the salt.

The ANL process is, unfortunately, a batch process, since the uranium is collected in a receptacle at the bottom of the apparatus, requiring that the process is interrupted in order that the receptacle may be withdrawn and the product recovered.

In addition, the operation of the process is mechanically intense, involving the use of rotating anodes which are designed to scrape the product off the cathodes; difficulties are encountered on occasions due to the seizure of this mechanism.

A disadvantage of the lithium reduction process for producing a metallic feed from an oxide is the production of Li2O by-product.

However, these processes for the clean up of the ionic liquid are disadvantageous from an economic point of view.

However, when this method is applied to a composition which comprises a metal or metal compound comprising a uranium or a transuranic element, problems of criticality may arise, since ionic liquids serve as moderators in such systems.

In such circumstances, the difficulties may be obviated by placing a limit on the allowable dimensions of the electrochemical cell.

The application of a suitable potential difference between the anode and the cathode results in electrochemical oxidation of the metal at the anode, causing it to enter into the liquid electrolyte medium.

However, the process shows significant advantages over the earlier method in that it is free from the moving components, such as rotating anodes, which often cause problems with the ANL process.

Nevertheless, although the system of WO-A-02 / 066712 also shows benefits over the ANL process in providing for semi-continuous operation, it is still essentially limited in applicability to batch electrorefiners.

Additionally, it suffers from the disadvantage of limited size, and the geometry of the system can cause difficulty in achieving a uniform potential field.

Consequently, the system is not well suited to scale-up.

Thus mixtures of uranium and plutonium oxides, together with the oxides of other actinide metals, may additionally be contaminated with oxides of other, chemically active, metals such as, for example, those associated with zircalloy cladding.

One approach to criticality safety is asymmetric control, one dimension of the system is restricted, so that a critical mass of fissile material cannot be obtained.

However, the known prior art does not provide a single example of metal electrorefiner or oxide electrolyser that displays such geometric safety and is capable of providing an industrial scale throughput.

However, no further attention is paid to this matter, and no other options are considered.

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