Technetium Chemistry in HLW: Role of Organic Complexants

Hess, Nancy J. ; Blanchard, David L., Jr. ; Cho, Herman M. ; Xia, Yuanxian ; Campbell, James A. ; Rai, Dhanpat ; Conradson, Steven D.

Pacific Northwest National Laboratory (U.S.)

关键词: Sludges;    Uranium;    Half-Life;    37 Inorganic, Organic, Physical And Analytical Chemistry;    Wastes;   

DOI  :  10.2172/839063
RP-ID  :  EMSP-81921--2004
RP-ID  :  839063

美国|英语

来源: UNT Digital Library

【 摘 要 】

Tc contamination is found within the DOE complex at those sites whose mission involved extraction of plutonium from irradiated uranium fuel or isotopic enrichment of uranium. At the Hanford Site, chemical separations and extraction processes generated large amounts of high level and transuranic wastes that are currently stored in underground tanks. Technetium is thought to have followed U in bismuth phosphate, REDOX and PUREX extraction campaigns and the Cs and Sr isotope recovery efforts. The waste from these extraction processes is currently stored in underground High Level Waste (HLW) tanks. However, the chemistry of the HLW in any given tank is greatly complicated by repeated efforts to reduce volume and recover isotopes. These processes ultimately resulted in mixing of waste streams from different processes. As a result, the chemistry and the fate of Tc in HLW tanks are not well understood. This lack of understanding has been made evident in the failed efforts to leach Tc from sludge and to remove Tc from supernatants prior to immobilization. Although recent interest in Tc chemistry has shifted from pretreatment chemistry to waste residuals, both needs are served by a fundamental understanding of Tc chemistry. The fate of Tc in the insoluble salts that constitute tank residuals is of paramount importance due to the long half-life and environmental mobility of Tc. Knowledge gaps include determination of the Tc oxidation state, the stability of reduced Tc solution species, and interactions with possible organic complexants in HLW. The objective of this renewal proposal is to continue to pursue fundamental understanding of Tc solution chemistry that provides the basis to make knowledgeable decisions and predictions of Tc behavior during retrieval operations and in tank residuals.