Oxidative Stability of Tc(I) Tricarbonyl Species Relevant to the Hanford Tank Waste

Technical Report · Thu Dec 17 00:00:00 EST 2015

DOI:https://doi.org/10.2172/1378053· OSTI ID:1378053

Chatterjee, Sayandev ^[1]; Hall, Gabriel B. ^[1]; Levitskaia, Tatiana G. ^[1]; Walter, Eric D. ^[1]; Washton, Nancy M. ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Technetium (Tc), which exists predominately in the liquid supernatant and salt cake fractions of the nuclear tank waste stored at the U.S. DOE Hanford Site, is one of the most difficult contaminants to dispose of and/or remediate. In the strongly alkaline environments prevalent in the tank waste, its dominant chemical form is pertechnetate (TcO₄^-, oxidation state +7). However, based on experimentation to-date, a significant fraction of the soluble Tc cannot be effectively separated from the wastes and may be present as a non-pertechnetate species. The presence of a non pertechnetate species significantly complicates disposition of low-activity waste (LAW), and the development of methods to either convert them to pertechnetate or to separate the non-pertechnetate species directly is needed. The challenge is the uncertainty regarding the nature and stability of the alkaline-soluble, low-valence, non pertechnetate species in the liquid tank waste. One objective of the Tc management project is to address this knowledge gap. This fiscal year (FY) 2015 report summarizes experimental work exploring the oxidative stability of model low-valence Tc(I) tricarbonyl species, derived from the [Tc(CO)₃]⁺ moiety. These compounds are of interest due to their implied presence in several Hanford tank waste supernatants. Work in part was initiated in FY 2014, and a series of samples containing non-pertechnetate Tc generated ex situ or in situ in pseudo-Hanford tank supernatant simulant solutions was prepared and monitored for oxidation to Tc(VII) (Levitskaia et al. 2014). This experimentation continued in FY 2015, and new series of samples containing Tc(I) as [Tc(CO)₃]⁺•Ligand was tested. The monitoring method used for these studies was a combination of ⁹⁹Tc NMR and EPR spectroscopies.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Environmental Management (EM)
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1378053
• Report Number(s): PNNL-25076; EMSP-RPT-033; EY4049110
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES