Potential Multi Canister Overpack (MCO) Cask Drop in the K West Basin South Loadout Pit

The purpose of this calculation note is to document the probabilistic calculation of a potential drop of a multi-canister overpack (MCO) cask or MCO cask and immersion pail on a per lift basis at the K West Basin south loadout pit. This calculation note supports both initial cask loading system alignment activities and normal operations. To perform normal operations in the basin, an MCO cask needs to be lifted four different times. A probabilistic calculation of the potential for a drop will be used for the MCO lifts required during operations. The point estimate value calculated for the probability of a potential drop in the south loadout pit is 1.5 x 10-5 per lift. The probability of 1.5 x 10-5 per lift is approximately a factor of two smaller than the midpoint of the crane load drop failure data provided in NUREG-0612, Control of Heavy Loads at Nuclear Power Plants. The point estimate value for the frequency of potential drops in the south loadout pit is 6.0 x 10-5 per MCO, based on four lifts per MCO. With an MCO-drop accident frequency limit of 0.01 per year, the number of MCOs that can be handled in the south loadout pit must be limited to 165 MCOs per year