University of Minnesota Duluth
University of Minnesota Department of Chemistry and Biochemistry
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Friday, September 22, 2017; 3:00 p.m.; LSci 175

 

Department of Chemistry & Biochemistry Welcomes:

 

Dr. Nathalie A. Wall, Associate Professor, Department of Chemistry,
Washington State University

“Tc Chemistry for Nuclear Waste Management and Nuclear Forensics”

 

Technetium-99 is a pure beta emitter with a 213,000 year half-life and a cumulative yield from 235U and 239Pu thermal neutron induced-fission of approximately 6%. Fundamental understanding of 99Tc chemistry is therefore critical for forensics analysis, waste treatments, and disposal of spent nuclear fuels.  Technetium exists primarily in the IV and VII oxidation states in natural environment. Tc(VII) species dominate in oxidative conditions, while Tc(IV) is most prevalent under anoxic and mildly reducing conditions.  As pertechnetate, TcO4-, Tc(VII) exhibits high aqueous mobility and solubility upwards of 11 M in neutral waters.  Conversely, Tc(IV) features a high propensity for sorption onto mineral surfaces and very low solubility, on the order of 10-8 M in neutral waters.

 
From the standpoint of environmental science, 99Tc is a particular problem at storage sites such as the Hanford reservation, where an estimated 500 Ci of 99Tc travelled to the vadose zone above groundwater reserves, due to the high mobility of Tc(VII); reduction processes to convert Tc to its lower and less soluble oxidation state, Tc(IV), has therefore been proposed as a remediation and disposal tool.  With regards to nuclear forensics, technetium constitutes an interesting high yield fission product that can provide valuable information in a post-detonation scenario.  However, little thermodynamic information has been available for either application and accurate predictions for Tc mobility in the environment for waste management or forensics sampling have been challenging.


We will present an overview of our findings on Tc chemistry, including thermodynamic data for Tc(IV) complexation in aqueous solutions with ligands of relevance for nuclear waste managements and nuclear fuel cycle, Tc(IV) solubility, potential stable analogs for Tc, and Tc solid-state chemistry data.