Radioactive Waste Minimization by Electrolytic Extraction and Destruction in a Purex-Truex Actinide Separation System

Electrolytic extraction of noble metals from nitric acid media was investigated. The largest deposition yield was obtained for Pd, supported by its large rate constants. Rate constants of RuNO³⁺ and ReO₄^- were, however, smaller than that of Pd²⁺; their yield can be improved under high cathode current supply in lower nitric acid concentration. Rather high apparent activation energy was observed for the deposition of RuNO³⁺. Peculiar masking or synergistic effects in their electrodeposition behaviors might be due to mutual interaction of RuNO³⁺, Pd²⁺ with ReO₄^- in nitric acid solution. Sufficiently different redissolution potentials for deposited metals indicate their fractional recovery by anode processing.

Mediatory electrochemical oxidation (MEO) was investigated for the mineralization of waste OD[iB]CMPO (hereafter CMPO) by burning its bulky hydrocarbon moiety under the existence of various kinds of metal ions. Only Ag^2+/+ offered high-current efficiency up to 75%, fairly exceeding that by direct electrooxidation. Redox coupling characterized by a simple electron transfer, M^m+ + ne^- <=> M^(m-n)+ provided high E⁰, will act exactly as an active mediator. As for the destruction paths for CMPO by MEO, cleavage between carbonyl C and N of amide moiety was of principal importance. The coupling of Co^3+/2+ is also recommended because of hydraulic advantages.