Spent fuel storage casks

Purpose: To determine the amount of leakage in a cask by detecting the pressure change in two spaces partitioned by the cover and the packing in the cask and confirm the extent packing failure. Constitution: A first cover is disposed for closing in an airtight manner an opening in communication with a hollow chamber containing fuel assemblies. A second cover is disposed for making the first cover and the first space having a predetermined volume airtight. An outer cover is disposed for making the second cover and the second space having a predetermined volume airtight. After evacuating the first space, the valve is closed to confine. High pressure gases such as nitrogen are enclosed in the second space. Under the state, the pressure for the first space and the second space are measured and monitored. It can be detected for the absence or the presence of packing failures due to the pressure change and the amount of leakage and the extent of failure (degree of cracks in the packing) due to the pressure rise rate. If there is no abnormality, the inside of the first space is evacuated about once per year. (Kawakami, Y.)