Assessment of the Evolution with Time of the Instant Release Fraction of Spent Nuclear Fuel in Geological Disposal Conditions

Abstract

ABSTRACTUnder the geological disposal conditions, spent nuclear fuel (SNF) is expected to evolve during the first thousands years while being maintained isolated from the biosphere before water comes in. Under those circumstances, several driving forces would lead to the progressive intrinsic SNF transformations within the rod which would basically modify the physical and chemical state of the fuel and the subsequent release of radionuclides in solution. In this paper, we briefly summarize the mechanisms we estimate to be significant and propose a new framework for the quantitative assessment of the radionuclide (RN) inventory we estimate to be associated to the classically referred to “Instant Release Fraction” (IRF). We hence demonstrate that in this framework, significantly high IRF values have to be expected for the long term due mainly to the presence of athermal diffusion processes.