Low-alkaline cementitious grout for high-level nuclear waste disposal

The stratum disposal system for high-level nuclear waste mainly involves the use of natural bedrock, called the natural barrier, and over pack and the buffer, those are designated as the artificial barrier. Grouting technology is indispensable for the environment that the crack and the underground water flow of the bedrock bring about mass transport, also ratio active component. However, typical cementitious grout material is strongly alkaline and the alkalinity that it imparts to the barrier material, especially to mineral substances in the bedrock or buffer, is suspected to compromise the performance of the barrier system over the long term. In order to avoid this undesirable alkaline influence, we have developed a procedure for reducing the alkaline state in cementitious materials by employing high volumes of additives such as pozzolanic materials. In this paper, we discuss the basic properties of low-alkaline cementitious grout, and explain how to select and mix appropriate proportions of grout to accomplish the end-objective, i.e., develop an efficient stratum disposal system. We also elaborate on progress achieved in research on this topic over the last two years. (author)