The inspectors identified a
Severity Level IV noncited violation of
10 CFR 50.59 for the failure to obtain NRC approval prior to implementing a change to the facility that resulted in a departure from a method of evaluation described in the final safety analysis report used in establishing the design bases. Specifically, the licensee implemented a change that assumed the unprotected dry
cooling towers would not be impacted during a tornado event. This change was implemented based on the inappropriate use of a
Tornado Missile Risk Evaluation method of evaluation not previously approved by the NRC. The licensee implemented this change to compensate for a licensee identified analysis error that adversely affected the
ultimate heat sink capability following a tornado event. The licensee entered this deficiency into their corrective action program for resolution. The cause of this finding is related to the crosscutting element of human performance
The finding is greater than minor in that it affected the
mitigating systems cornerstone attribute of equipment availability and function during a design bases tornado event. Regional and
NRR staff determined that the change made by the licensee resulted in a departure from a method of evaluation described in the final safety analysis report used in establishing the design bases and that the change would require NRC approval under
10 CFR 50.59 guidance. In accordance with the
NRC Enforcement Manual, violations of
10 CFR 50.59 are not processed directly through the
significance determination process. Therefore, this issue was considered applicable as traditional enforcement. Although the
significance determination process is not designed to assess significance of violations that potentially impact or impede the regulatory process, the technical result or condition of a
10 CFR 50.59 violation can be assessed through the
significance determination process. The inspectors and the Region IV reactor analyst discussed the significance of this finding. A
significance Determination Process Phase 1 screening was performed and the finding was determined to have very low safety significance because there was no actual loss of mitigating system safety function per
Generic Letter 91-18 guidance.
