2024 年 23 巻 4 号 p. 101-117
A 9 m drop test is required for type B nuclear fuel casks to simulate one of the transport accident conditions. Japanese regulation requires the evaluation of maximum damage and the condition inducing such damage in each cask following vertical, horizontal, corner, and inclined drop tests. For the inclined drop test, licensees are asked to clarify the effect of the secondary impact caused by falling in the case of a cask with high aspect ratio (length/diameter). However, in previous studies on a slap-down drop test for dual-purpose casks with a low aspect ratio (around 2.3) dropped at a small angle of inclination, it has been reported that acceleration due to the secondary impact acting on the main body significantly exceeds the primary impact acceleration. For this reason, we conducted a 9 m horizontal drop test and three slap-down drop tests (9 m −4 deg., 9 m −8 deg., and 9.4 m −8 deg.) using low-aspect-ratio (1.8) dual-purpose casks as 1/2.3-scale models to confirm the effects of slap-down drops on such casks. The drop height and slap-down angle were used as parameters for comparing the results of the horizontal drop test with those of the three slap-down drop tests. As a result, it was clarified that the maximum impact acceleration is higher in the slap-down drop tests than in the horizontal drop test even in the case of a low-aspect-ratio cask, and it increases to about 1.8 times the maximum in the case of the 9 m −8 deg. drop test condition. The significant effect of the slap-down drop was demonstrated, and therefore, the examination of the slap-down drop of the low-aspect-ratio cask is necessary in determining the condition that induces the maximum damage.
