Failure Probability Study on Spent Fuel Transportation Cask Considering Several Key Parameters

There are many parameters that will affect the failure probability of the spent fuel transportation cask in a traffic accident. Especially cask collision speed with rocks or other vehicles, collision angle of the cask and the strength of the cask material are important parameters. And these key parameters are distributed probabilistically. Even only these factors are taken into consideration, there are so many cases of parameter combination that should be conducted for cask safety analysis. So, it is necessary to treat these parameters as probabilistic factors and also evaluate the total probability of cask failure with minimum cask crush analyses for estimation of the cask safety under wide ranges of traffic accident type. In order to minimize the number of crush analyses, the response surface method has been used. The probability density function for the collision speed has been developed based on the actual accident records. And this probability function is supposed to be normally distributed around the real data distribution. The angle of cask collision is another key factor for cask deformation. Crush angle ranges from horizontal (angle 0 degree) to vertical (angle 90 degree) and the probability density of the angle is supposed to be constant. The allowable limit for the maximum cask plastic strain is assumed to be the elongation of the cask material and its probability density has been postulated to be a normal distribution. Based on these probabilistic assumptions and response surface results made from minimum crush analyses, failure probability of the cask in a traffic accident is estimated. The response surface of the cask maximum plastic strain as a function of crush speed and angle is so complicated. Thick walled cask chosen as a typical cask for estimation has a peak failure probability density at an angle of 65.7 degree. And the probability of the cask failure in a traffic accident ranges from 0.0022% to 0.0042%. These probability values depend on cask design, crush speed and other factors. Failure probability estimation method using response surface method is effective to understand the safety of spent fuel transportation cask in a traffic accident.