Development of helium leak detector for canister. Part. 1. Leak evaluation tests and analysis by vertical small canister model

We develop a helium leak detector using temperature information of the canister for the concrete cask. In order to realize the detector, it is necessary to evaluate its sensitivity by tests and analysis. Therefore, gas leak tests were performed on a small pressurized vessel with 12 electric heaters. The vessel is a one-eighteenth scaled model of the storage canister in the concrete cask. The diameter of the vessel is 100 mm and the height is 260 mm. Inner pressure (from 1atm to 5atm), heat rates (from 11.9W to 47.8W) and the kind of fluid in the vessel (air or helium) were changed as parameters. Phenomenon that the temperature at the top of the vessel decreases and the temperature at its bottom increases during gas leak was observed in these tests. The phenomenon was valid by numerical analysis. In these tests using helium gas, the temperature in the vessel was lower than that in the test using air even under the same condition of the heat rate, which is because heat conductivity of helium is high. The temperature inside the vessel was hardly depended on the inner pressure in these tests. (author)