Study on concrete cask for practical use. Development of the detecting method of helium leak from canister

In Japan, it is planed to construct interim storage facilities taking account of dry storage away from reactor in 2010. A concrete cask is economical, but data for its safety analysis have not been sufficient yet. The design of spent fuel canisters used in the concrete cask storage is demanded to be able to be inspected for maintaining the containment capability during storage. For this purpose a method has been reported to detect helium leak from a canister utilizing a phenomenon of temperature change of the canister side surface due to the loss of effect of helium convection in the canister. However, this method is not considered reliable enough. In the present study, it was found that the difference in the temperatures of the centers of the top and the bottom on the canister surface (defines as ΔTBT) increased remarkably when the helium leaked. It was proposed that helium leak could be detected by observing over the change of ΔTBT. Moreover, this method enables to detect helium leak at early stage by monitoring both ΔTBT and air temperature of the inlet. (author)