The current generic radioactive waste disposal concept in the Netherlands is designed to be situated in a Boom Clay stratum at approximately 500 m depth. The location of such a repository has not been decided and, as such, the design contains many uncertainties. The impact of these uncertainties are important to the feasibility of the repository design and construction, with respect to both stability and consequential f nancial performance. The objective of this study is to develop an approach that uses probabilistic methods to quantify uncertainties, and utilises PLAXIS to assess the geomechanical repository behaviour during and after construction. In addition, the new Thermal module in PLAXIS has been utilised to provide an initial assessment of the temperature changes in the Boom Clay. This research project was undertaken as part of the OPERA research programme.