Decontamination of sludgelike uranium-bearing wastes. Decontamination feasibility judgment using radon emanation coefficients and development of decontamination methods

It is difficult to decontaminate sludgelike uranium-bearing wastes by wet methods, such as employing nitric acid for selective uranium dissolution. This is because these uranium-bearing wastes have very small pores inside which uranium is deposited, and the decontamination liquid cannot get inside the pores and so cannot dissolve the uranium. The present study found that radon emanation coefficient measurements can be employed to judge if decontamination liquid can get inside the pores. In fact, the difficulty of decontamination was corroborated by these measurements. Accordingly, wet decontamination methods of selective uranium dissolution were abandoned. Instead two newly developed decontamination methods were considered: one employing C1F3 gas and the other employing adsorbent for uranium in a solution of completely dissolved sludgelike uranium-bearing wastes. These two methods were derived as a natural consequence of the difficulty in wet decontamination methods. In the former method, a high degree of decontamination below 3.3 ppm (0.3 Bq/g for 4.5% enriched uranium) was achieved by ClF3. In the latter, complete dissolution was achieved by the addition of NaOH and H2SO4 to the wastes. As a next research step, efforts to develop adequate adsorbents for uranium are desired. (author)