EFFECT OF SURFACE ROUGHNESS OF CASK FLANGE AND GASKET DIAMETER TO SEALABILITY

In regard to spent fuel storage and transportation casks, metal gasket is selected as sealing material from the standpoint of long-term storage. When cask flange is made of stainless steel, aluminum is chosen as gasket material because it is more flexible than stainless steel. Sealability is obtained by gasket deformation and contact with rough surface of flange. Therefore, it is known that gasket sealability is not kept when flange roughness is larger. In the case of flange with serrations, sealability can be obtained when the flange roughness is larger than another type of flange. It is thought that leakage directly crossing the gasket is relatively small, because serrations were grooved in circumferential direction, however it has not been clearly resolved yet. In this study to clarify the effect of metal gasket stress to leakage seal test was conducted as the first step to measure gasket stress and leak rate using flange with serrations and the interspaces between gasket and flange was estimated. As second step, seal test was conducted with flanges that had different serrations dimensions, and correlation between flange surface profile and leak rate was found. Additionally static/ dynamic impact test results according to JNES and NUPEC test were presented as basic characteristics of the gasket. As a result of the test, it was found that fluid leaked through the interspaces was smaller when gasket diameter was larger. Therefore it was estimated that the larger gasket diameter obtained the longer total length of the interspaces and the larger gasket pressure loss. We found that leakage of fluid could be predicted by measuring gasket stress, its diameter and flange profile.