A significant reduction in the effectiveness of any spent fuel storage confinement system during use
This reportability notification addresses a potential unanalyzed condition of 18 Transportable Storage Canisters (TSCs) which are loaded with spent nuclear fuel (SNF). Seventeen of these TSCs are stored in Vertical Concrete Casks (VCCs) at the Haddam Neck Plant Independent Spent Fuel Storage Installation (ISFSI). One TSC is currently in transport operations and will be transferred to the ISFSI in the near future.
SNF clad temperature is affected by changes in the TSC internal environment that are encountered during fuel transfer operations. In order to maintain SNF clad temperatures within the analyzed limits, the time duration of certain fuel transfer activities are limited (for example, time in dewatering phase, time in vacuum drying phase and time in helium backfill phase).
The canister dewatering section of CY procedures allowed multiple blowdowns of the TSC while in the dewatering time clock. This is contrary to the NAC thermal analysis which assumes a water environment in the canister during the dewatering period. It appears that this condition is not consistent with current analysis assumptions and is therefore a potential unanalyzed condition.
NAC International (holder of the C of C) has been advised of this condition and is analyzing the
TSC loading conditions. VCC outlet temperatures are within acceptable limits and there is no evidence of unusual radiation exposure in the
ISFSI environs.
