Application study on low alkaline cementitious materials for deep geological repository of high level radioactive wastes. Phase 1. Requirements for use of cementitious materials in deep geological repository system (Joint research)

Deep geological repository of high level radioactive wastes (HLW) will be constructed at the depth of more than 300m below the surface. Use of cementitious material for rock support, tunnel lining, and grouting is essential for the repository system and possibly causes increase of surrounding groundwater pH due to cement hydrates leaching from the materials. Since this hyperalkaline condition may lead to degradation of engineered barrier materials such as a metal overpack and also the surrounding host rock as natural barrier, there is concern that it gives significant impact on long-term safety performance of the repository system. Because of these backgrounds, developments of low alkaline cementitious materials have been conducted both at home and abroad. Through studies on application of the low alkaline cementitious materials into rock support and tunnel lining so far, JAEA is now planning to conduct an in-situ test for shotcreting at the tunnel of the Horonobe Underground Research Laboratory. On the other hand, CRIEPI has studied and developed cementitious materials for disposal of radioactive wastes including HLW. The JAEA-CRIEPI joint research project on low alkaline cementitious materials for deep geological repository is aiming to identify key issues for further improvement of performance and technologies of the low alkaline cementitious materials by integrating experience and expertise in this area, which are accumulated in both organizations. This report summarizes requirements and their expected performance for use of cementitious materials in repository system taking account of surrounding conditions in each stage of repository program in order to reflect them to further development of the low alkaline cementitious materials. (author)