Concept of Shielding Characteristics for Spent Fuel Shipping Casks

Abstract

By introducing a concept of shielding characteristics, a new method is proposed for shielding calculations of spent fuel shipping casks. The method separates ordinary shielding calculation into two steps. One method calculates the radiation current leaking from the unshielded cavity region; the other method synthesizes the radiation dose rate outside the cask arising from the leaked current, the response functions for the radiation dose rate at the outer cask surface, and the functions for the radiation current reflected from the inner surface of the cask wall. In the synthesis, the effect of the coupling of the currents reflected between the cask wall and the cavity region is taken into account. The validity of the proposed method is confirmed by applying the method to an analysis of the measured data obtained for a CRIEPI cask. Response functions, the established characteristic functions for radiation shielding capabilities, are calculated for several typical actual casks. Calculated results are summarized for the convenience of applying the proposed method to actual cases.