Leach rate expressions for performance assessment of solidified, low-level radioactive waste

Abstract Exact, analytical expressions for the diffusive leach rate of radioactive species from low-level, cylindrical, and rectangular-shaped wasteforms are obtained based on typical assumptions about the wasteform as are codified in the American National Standards Institute/American Nuclear Society ANSI/ANS 16.1 leachability standard of 1986. The new expressions are entirely analytical and model both the axial and the radial (for the cylindrical geometry) leach rate as a function of time, wasteform dimensions, diffusion coefficient of the species under study, and decay constant. Improved leach rate expressions for implementation in performance assessment codes of disposal sites are also provided along with an analysis of the associated errors. The numerical analysis utilizes parameter values applicable to strontium and faster-leaching nuclides from full-size, cement wasteforms under disposal conditions. With the decay constant set equal to zero, all the proposed expressions also apply to stabilized hazardous wastes and their disposal sites.