A new rock mass classification system QHLW for high-level radioactive waste disposal

•A quantitative rock mass classification system QHLW for nuclear waste disposal is proposed.•The proposed system aims to identify the suitable rock volume of different scales for disposal.•Both the constructability and the long-term safety requirement of the repository are considered.•The thermal effect is firstly taken into account in rock classification system for HLW disposal.•The implementation indicated that it is a usable tool in identifying suitable rock for disposal.

In this paper, a new rock mass classification system named QHLW system is proposed with the purpose of evaluating the suitability of the host rock for high-level radioactive waste (HLW) disposal. In the system, the rock suitability evaluation of two different scales is considered, namely the repository and tunnel scales. The system is developed on the basis of Q-system, and considers both the long-term safety and constructability requirement of the host rock for disposal. Thus, some additional parameters, including the fracture zone, groundwater chemistry and thermal effect are also taken into account in light of their significant influence on the long-term safety of HLW disposal. The avoidance strategy is highlighted in the proposed system by excluding the rock volume with unfavorable conditions, particularly adjacent to the large scale fracture zones. In the proposed system, the Q′ index (the product of the first four parameters in Q-method) is considered as the basic constructability index. By incorporating the influence of other parameters, the QHLW system is established in which the suitability of host rock is classified into three classes at the repository and tunnel scales. As a preliminary validation, the system is applied to the Beishan area, a potential region for HLW disposal in China. Using the classification method at the repository scale, the most suitable disposal site in Xinchang block of the Beishan area is identified. The rock classification at the tunnel scale is also carried out along two deep boreholes. The proposed system is found to be a usable tool in identifying suitable rock volume of different scales for HLW disposal.