Thermal impact of waste emplacement and surface cooling associated with geologic disposal of high-level nuclear waste

This article is a study of the thermal effects associated with the emplacement of aged radioactive high-level wastes in a geologic repository, with emphasis on the following subjects: waste characteristics, repository structure, and rock properties controlling the thermally induced effects; thermal, thermomechanical, and thermohydrologic impacts, determined mainly on the basis of previous studies that assume 10-yr-old wastes; thermal criteria used to determine the repository waste loading densities; and technical advantages and disadvantages of surface cooling of the wastes prior to disposal as a means of mitigating the thermal impacts. Waste loading densities determined by repository designs for 10-yr-old wastes are extended to older wastes using the near-field thermomechanical criteria based on room stability considerations. Also discussed are the effects of long surface cooling periods determined on the basis of far-field thermomechanical and thermohydrologic considerations. Extension of the surface cooling period from 10 yr to longer periods can lower the near-field thermal impact but have only modest long-term effects for spent fuel. More significant long-term effects can be achieved by surface cooling of reprocessed high-level waste.