Scoping calculations for the near-field evolution in a geological repository for high-level radioactive waste in Boom Clay in the Netherlands

摘要

The central objective of the OPERA research programme, recently initiated by the Dutch radioactive waste management organisation COVRA, is the development of initial conditional safety cases for generic repositories in the Tertiary Boom Clay and Zechstein rocksalt formations in the Netherlands. The generic disposal concept for high-level radioactive waste (HLW) in Boom Clay pursued in this context is based on the Belgian supercontainer concept. In this concept, the engineered barrier system (EBS) makes extensive use of cementitious materials as buffer within the waste container, as backfilling grout, and in the construction material for the disposal gallery linings. Thus the near-field chemistry will be governed by the degradation of cementitious materials under repository conditions in the long-term and a highly-alkaline near-field will develop post closure. In this paper we present results of scoping calculations aiming at the evolution of the geochemical conditions in the near-field, performed in the context of the evaluation of the corrosion behaviour of and the radionuclide release from vitrified HLW and spent research reactor fuel under disposal conditions. The overall aim of this project is to provide a coherent picture of the radionuclide release from HLW disposed in a generic repository in Boom Clay in the Netherlands, to increase the understanding of waste form evolution and the radionuclide migration behaviour in the near-field, and to develop radionuclide source terms to support the post closure safety assessment.