Development of a methodology for post closure radiological risk analysis of underground waste repositories. Illustrative assessment of the Harwell site. V.2

A probabilistic risk analysis (pra) is demonstrated for a number of ground water mediated release scenarios at the Harwell Site for a hypothetical repository at a depth of about 150 metres. This is the second stage of development of an overall risk assessment methodology. A procedure for carrying out multi-scenario assessment using available probabilistic risk assessment (pra) models is presented and a general methodology for combining risk contributions is outlined. Appropriate levels of model complexity in pra are discussed. Modelling requirements for the treatment of multiple simultaneous pathways and of site evolution are outlined. Further developments of pra systems are required to increase the realism of both the models and their mode of application, and hence to improve estimates of risk. (author)