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Radioisotope Fractionation and Secular Disequilibrium in Performance Assessment for Geologic Disposal of Nuclear Waste

Published online by Cambridge University Press:  21 March 2011

William M. Murphy  and
David A. Pickett
William M. Murphy
Affiliation:
Department of Geosciences, California State University, Chico, CA 95929-0205
David A. Pickett
Affiliation:
Center for Nuclear Waste Regulatory Analyses (CNWRA), Southwest Research Institute, San Antonio, TX 78238-5166
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Abstract

Two potential applications of radioisotope fractionation and decay-series secular disequilibrium in performance assessment for geologic repositories for nuclear waste are preferential radionuclide release in source term analysis and characterization of system closure as a measure of the capacity of the geologic system to isolate waste. A primary mechanism of radioisotope fractionation is selective release and mobility of alpha decay products because of nuclear recoil effects, which is evident in natural system data. Preferential release of radioisotopes from nuclear waste forms or solubility limiting solid phases could affect repository performance; however, consequences of differential radioisotope releases are neglected in performance assessments. Decay-series disequilibria are useful also to characterize open/closedsystem behavior in natural systems. Systems that are closed on time scales that are long relative to the half-lives of decay chain nuclides achieve secular equilibrium characterized by unit activity ratios among series nuclides. For geologic disposal of nuclear waste, measures focused on chemical system closure could capture the essential characteristics of the natural system with respect to radionuclide isolation and could be based quantitatively on uranium and thorium decay series secular equilibria/disequilibria.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 713: Symposium JJ – Scientific Basis for Nuclear Waste Management XXV , 2002 , JJ8.7
Copyright
Copyright © Materials Research Society 2002

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