Calculation of Surface Dose-Rate Profile of a Cask by Monte Carlo Method

It is important to obtain the dose-rate profile of a cask surface or I m from the cask for evaluating the maximum dose-rate easily and precisely. So far two dimensional SN codes, such as DORT(Rhoades and Childs 1988) are used for this purpose, but the Monte Carlo code is a much better tool for the calculation of complicated geometrical shapes like a cask because any three-dimensional configuration can be modeled with the Monte Carlo code. The only problem in getting a dose-rate profile using the Monte Carlo code is the definition of estimators ; however, this is a serious problem. For example, if a thousand estimators are required, almost the same amount of additional geometry input is necessary to define the estimators when using the conventional method. It means that the calculation model becomes extremely complicated, and the complicated model makes the CPU time much longer. In this paper, a technique is presented to obtain surface dose-rate profiles of a cask surface or 1m from the cask by Monte Carlo code within a reasonable CPU time.