10 CFR Part 50, Appendix B, Criterion III, Design Control required, in part, that design control measures shall provide for verifying or checking the adequacy of design reviews, by the use of alternate or simplified calculation methods, or by the performance of a suitable testing program.
Generic Letter (GL) 2008-01 required, in part, licensees to evaluate the potential impact of vortexing on tanks and recirculation
sumps. Contrary to the above, since December 2008, the licensee failed to verify the adequacy of design for the casing cooling system to meet
Generic Letter (GL) 2008-01 vortex evaluation requirements. Specifically, the licensee identified that the 1990 calculation accounted for vortexing in usable volume, but did not verify that the low-low level setpoint accounted for this required submergence. A detailed risk assessment was performed in accordance with NRC
Inspection Manual Chapter 0609 Appendix A using the NRC North Anna standardized plant analysis risk (
SPAR) model. The major analysis assumptions included: Non-recoverable common cause failure to run of the outside recirculation spray pumps caused by vortexing of the casing cooling pumps, a one year exposure period, North Anna site specific performance testing restoration values for the Inside Recirculation Spray pumps. Seismic and high wind conditions external event risk was included. The risk evaluation concluded that the violation represented a risk increase in core damage frequency of < 1 E-6 /year, a GREEN finding of very low safety significance. This issue is in the licensees
CAP as CR533387, Casing Cooling Tank Low Level Setpoint does not Account for Vortexing. The instruments were recalibrated and tested to the required setpoint.
