Electrochemical decontamination in easily processed electrolytes

Metallic surfaces can be reduced to very low levels of residual activity by electrochemical decontamination, thus reducing decommissioning and disposal costs. Two electrolyte systems have been developed which minimize the volume for disposal of secondary waste containing the bulk of the activity. Kraftanlagen, Heidelberg has developed a system for use in an immersion tank based on a KBr solution of acetylacetone. This leads to a continuous precipitation of the insoluble acetylacetonates of ferrous substrates together with such active species as 60Co. The bath performance can be maintained by continuous acetylacetone addition. From pilot scale trials, a solids waste volume of 1.1 dm3/m2 of surface decontaminated has been determined. Harwell has developed both immersion and in-situ processes based on nitric acid, as the spent electrolyte is compatible with existing UK waste treatment philosophy - potentially yielding an immobilized product volume of 0.6 dm3/m2 area treated. Nitric acid has the additional advantage of suppressing any hydrogen production. Both processes have been developed from laboratory to microprocessor controlled pilot scale units which have been demonstrated successfully for the treatment of genuine waste. The immersion tank process uses electroetching at low current densities for the treatment of extended areas, while the in-situ technique uses electropolishing in 6M HNO3 in an engineered head connected to a service trolley by an umbilical. This has also shown potential for incorporation in an integrated monitoring/decontamination system under robotic control. (abstract)