Heat removal characteristics of vault storage system with cross flow for spent fuel

Since the amount of spent fuel to be stored is expected to steadily increase in Japan, a use of large-scale dry storage facilities is considered to be a promising method in practice at reasonable economic cost. The present study is concerned with the heat removal experiment of vault storage system adopting cross flow with passive cooling, using a 1/5 scale model. The results show that the flow pattern of air in the storage module strongly depends on the ratio of the buoyancy to the inertia force. A simple method to estimate air flow patterns in the storage module was proposed, where the Ri (Richardson) number was considered as the most representative parameter. Then the heat transfer rate from a storage tube to cooling air was estimated, which could apply to the design of a full-scale vault storage system with cross flow, in which dozens of storage tubes were placed. The acquired information was also used to optimize heat removal design of the vault storage system in the present study. (orig.)