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DEVELOPMENT AND OPTIMIZATION OF AN EASY-TO-PROCESS ELECTROLYTE FOR ELECTROCHEMICAL DECONTAMINATION OF STAINLESS STEEL

Objective

This work aims at optimizing an acetyl-acetone base electrolyte so that it can be used for electrochemical decontamination of stainless steels. Kraftanlagen Heidelberg developed the electrolyte under the preceding EC programme from 1984 to 1988 (contract No. FI1D0004, report EUR 12383).

With regard to waste management and disposal, the obtained electrolyte came up to all expectations. An advantage of the organic electrolyte as compared to the phosphoric/sulphuric acid electrolyte is its long radiological service life (the activity settles out continuously). It is easy to convert the crystalline by-product (sediment) by high-pressure compaction into a form that is suitable for disposal. As only small residues of acetyl-acetonates are dissolved in the electrolyte, it is possible to reduce considerably the electrolyte volume by evaporation.

In tests with radioactive samples of carbon steel, the obtained results concerning removal effects, duration of treatment, surface quality, and decontamination factors, were satisfactory or good. However, pitting was observed in the tests with samples of stainless steel. As a consequence, the surface was not uniformly removed. Parts of the original surface were visible for a long time. This resulted in poor decontamination factors or long treatment times, respectively. In addition, larger volumes of secondary wastes were produced than with a uniformly removed surface. It is therefore necessary to optimize this electrolyte, if it is to be used for the treatment of stainless steel.
This work aims at optimising an acetylacetone base electrolyte so that it can be used for electrochemical decontamination of stainless steels. In cyclovoltametric, potentiostatic and galvanostatic analyses, it was possible to verify the assumptions as to the anodic dissolution mechanism of potassium bromide and potassium chloride. The dissolution mechanism when using the potassium fluoride electrolyte and glycol electrolytes still remains to be investigated and clarified. The replacement of potassium bromide by potassium fluoride as conductive salt showed positive results. Satisfactory removal rates along with a good anode current yield could be achieved. The aqueous electrolyte along with potassium fluoride as conductive salt demonstrated that the scattering behaviour depends on the viscosity and on the rated current density. When using glycol as solvent along with potassium bromide as conductive salt, no pitting was noted on the electrode. The decontamination tests with the aqueous electrolyte using potassium fluoride as conductive salt and also the tests with organic glycol electrolytes along with potassium bromide as conductive salt showed good results.
WORK PROGRAMME

1.Quantitative investigations concerning the dissolution mechanism
2.Optimization of the aqueous electrolyte through replacing the potassium bromide by other conductive salts.
3.Investigations into scattering and its effect on abrasion, surface quality and decontamination factor
4.Development of a water-free electrolyte.
5.Decontamination tests with contaminated samples.
6.Processing of spent electrolyte.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Kraftanlagen AG
Address
Im Breitspiel 7
69126 Heidelberg
Germany