Parametric analyses of diffusion of activated sources in disposal forms.

The primary objective of a low-level radioactive waste disposal facility is to isolate low-level radioactive waste from the public and the environment until the radionuclides in the waste have decayed to levels at which the hazard is negligible. Two fundamental concerns must be addressed when attempting to isolate low-level waste in a disposal facility on land. The first concern is isolating the waste from water, or hydrologic isolation. The second is preventing movement of the radionuclides out of the disposal facility, or radionuclide migration. Particularly, we have investigated here the latter scenario. Empirical curves describing the progression of the altered zone are obtained and they are used to define the correspondent altered thickness in the numerical calculations for a cement sample. Subsequent numerical analyses of diffusion of activated sources in waste disposals are considered for cemented containers. The adopted DAMAGE code takes into account a mass conservation equation and the linear momentum balance equation for the multiphase material. The mathematical model is based on the theory developed by Bazant for concretes and geomaterials; the fluid phases are considered as a unique mixture interacting with a solid phase. Short- and long-term diffusion analyses are performed for different characteristics of the grout and the results are presented in terms of radionuclides concentration. Indications on the minimum grout thicknesses able to resist to radioactive fluxes up to 1000 years are given.