Laboratory tests were performed to examine mixed nitric/hydrofluoric acid leach treatments for decontaminating dissolver residual solids (KECDVSR24H-2) produced during a 20- to 24-hr dissolution of a composite K East (KE) Basin canister sludge in 95?C 6 M nitric acid (HNO3). The starting dissolver residual solid for this testing, KECDVSR24H-2, contains radionuclides at concentrations which exceed the ERDF Waste Acceptance Criteria for TRU by about a factor of 70, for 239Pu by a factor of 200, and for 241Am by a factor of 50. The solids also exceed the ERDF criterion for 137Cs by a factor of 2 and uranium by a factor of 5. Therefore, the radionuclides of greatest interest in this leaching study are first 239Pu and 241Am (both components of TRU) and then uranium and 137Cs. Prior scoping tests examined four alternative leachants for residues created from nitric acid dissolution of composite KE floor and Weasel Pit area sludge (PNNL-12104). The leachant achieving the highest decontamination of the area composite residue, 6 M HNO3 / 0.3 M hydrofluoric acid (HF) at 90?C, was therefore used to leach the canister sludge residue (KECDVSR24H-2). The 137Cs concentrations in the solids decreased by a factor of 5 to less than half the ERDF criterion. Uranium concentrations in the solids decreased about a factor of 10 to less than half the ERDF criterion. The TRU concentrations decreased a factor of ~25 but remain approximately three times the ERDF criterion for direct disposal. The 239Pu concentrations also decreased ~25-fold but remain eight times the ERDF criterion in the residue. The 241Am concentrations decreased about a factor of 16 but exceed the EDRF criterion by a factor of 3.
Revised: June 1, 2001 |
Published: October 28, 1998