Simulation of repository gas migration in a bentonite buffer

Abstract

The inventory of high-level radioactive waste in the UK is likely to be disposed of in a geological disposal facility, which will generate gases due to processes such as anoxic metal corrosion and water radiolysis. Such gases have the potential to migrate through the repository system and may be detrimental to the engineered barrier system by damaging the physical fabric of the buffer material through the build-up of pressure. An investigation into the migration of gases and the ranges of gas pressures expected in such a repository is presented. A model of gas transport is presented to simulate the transport of gases in conjunction with coupled thermo-hydro-chemical-mechanical processes. This model includes a boundary condition linking the corrosion behaviour to gas generation and water supply. A realistic range of gas generation rates has been established from available data alongside realistic ranges of material properties of a bentonite buffer. Numerical simulations were then undertaken for a range of realistic scenarios considering the corrosion processes and buffer properties.It was found that in all realistic cases, including realistic maxima and minima considered, the risk of pneumatic fracture was negligible.

Investigation on gas migration in saturated materials with low permeability

“…The critical pressure corresponding to the sudden increase of gas flow could be defined as the gas induced-dilatancy pressure, P dilatancy . In this regard, lots of contributions have been made for investigation of influences of the mechanical stress on gas migration (Hoseman et al, 1999;Marschall et al, 2005;Yu and Weetjens, 2009;Vardon et al, 2013;Ye et al, 2014). However, for almost all of these works, influence of the mechanical stress on gas migration is indirectly deduced from the measured variation of gas flow rate and several studies have established the relationship between the gas flow rate (or permeability) and the confining pressure, gas injection pressure or effective stress to reflect the influence of mechanical stress (Hoseman et al, 1999;Vishal et al, 2013a;Xie et al, 2015).…”

Editorial

“…The paper by Vardon et al (2014) tackles the important mediumand long-term safety consequences of the geotechnical burial of radioactive waste. The scenario investigated is the production of gas by anaerobic corrosion of the metallic waste containers and the consequences of this process for (a) the behaviour of the clay buffer medium surrounding these containers and (b) the satisfactory operation of the waste repository.…”