Calculating External Dose Increase from Partial Loss of Lead Shielding in a Spent Fuel Cask

In this work, a stainless steel-lead-stainless steel (SS-Pb-SS) transportation cask containing spent nuclear fuel is assumed to be damaged with a consequent loss of some lead photon shielding. One possible scenario is a collision during transit that subjects the cask to a severe impact on its end which causes the lead layer to ?slump?, thus leaving a gap in the lead shield layer. The factor by which the external photon dose rate increases due to the partial loss of shielding is calculated. This analysis compares the effective shielding of damaged and undamaged casks and estimates this factor F (increase in dose rate) at receptor points away from the cask. The analysis uses analytical point-kernel methods with radiation buildup factors and dose response functions to approximate the increase in dose rate. Representative values of F are computed and presented as functions of position relative to the cask.