Effect of Surface Roughness of Cask Flange and Sealability of Metal Gasket (2) Flange Surface of Serration Process and Precision Polishing

A rubber gasket is used as the sealing material for the hermetic boundary of spent nuclear fuelcasks. However, instead of a rubber gasket, a metal gasket is used as the sealing material for the hermetic boundary of a storage and shipping cask for the long-term storage of spent nuclear fuel due to the requirement for stable sealing performance for an extended period of time. A metal gasket is placed between the flanges that form the hermetic boundary of the cask. Generally, in Japan, aluminum, which is softer than the flange material, is used as the surface material of the metal gasket in contact with the flange. When the metal gasket is compressed, the aluminum is de-formed to fit the surface roughness of the flange and brought into close contact with the flange surface. Thus, the gap between the flange and the metal gasket is eliminated to provide good sealing performance. In a previous paper (PATRAM2013) [1], we reported the results of an investigation of the sealing performance of aluminum as the surface material to provide the sealing performance of the metal gasket and showed that the behavior of the sealing performance largely depends on the surface processing of the flange.In this study, to further seek for the better sealing performance of the aluminum, we conducted a test with different shapes of spiral grooves formed by the serration process, which is effective for large flanges. We found that there was a range of shapes that gave good sealing performance, and we determined this range. The sealing performance of smaller serrated flange tends to decrease. However, we considered whether the sealing performance can be improved by precision polishing to reduce the surface roughness of the flange to extremely low level. We also found that the above procedure can improve the sealing performance with an actual metal gasket.