Gas migration from low-level radioactive waste repositories in hard rocks

A mathematical model is used to describe the migration of gas from radioactive waste repositories. Calculations are presented for rock properties characteristic of the Forsmark area. In Sweden, the repository of medium- and low-level radioactive waste is in fractured hard rock formations at a depth of --50 m below sea level. Chemical reactions in the stored waste produce hydrogen, which displaces the water from the fractures and migrates toward the surface, where it is finally released into the atmosphere. The lateral gas movement is considered negligible, and computations are performed under the assumption of vertical flow. Rock permeability was determined by flow tests in vertical boreholes. Calculations were performed for two cases: a constant gas flow rate corresponding to a gas production of 33000 kg/yr and a constant pressure corresponding to a gas cushion of 0.5m