The inspectors reviewed Dominions
MR (a)(1) evaluation for the vital switchgear cooling system following the determination that two air conditioners (A/C-3 B51, and A/C-4 B61) had insufficient refrigerant charge as documented in CR-06-01138, dated November 21, 2006. The evaluation concluded that there was no functional failure because, in accordance with MP-24-MR-FAP710, Maintenance Rule Functional Failures and Evaluations, the failures were considered design deficiencies that could not have been prevented by post-modification testing or predictive maintenance. The inspectors reviewed Dominions
MR procedure, CRs, and work orders applicable to the maintenance on the switchgear cooling system. In order to fully understand whether prior opportunities existed to prevent the A/C unit failures, the inspectors will conduct additional interviews and investigation into the maintenance rule and design control processes. As such, this issue remains an unresolved item (
URI) pending further NRC investigation into prior A/C unit maintenance practices and review of Dominions maintenance rule and design control processes for these A/C units. (
URI 05000336/2007002-01, Maintenance Rule (a)(1) Evaluation of Unit 2 Vital Switchgear Emergency Cooling Failure).
