05000361/LER-2008-007
| San Onofre Nuclear Generating Station | |
| Event date: | 08-22-2008 |
|---|---|
| Report date: | 11-14-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3612008007R00 - NRC Website | |
Event Date:
August 22, 2008 Reactor Vendor:
Combustion Engineering Mode: Mode 1 — Power Operation Power: 99 percent
Description of Event
San Onofre Unit 2 has two Emergency Diesel Generators (EDGs) [EK] to provide emergency AC power if normal AC power is unavailable. Technical Specification (TS) 3.8.1 requires two EDGs be operable during Modes 1-4. If one EDG is inoperable, TS 3.8.1, Condition B, requires performance of Surveillance Requirement (SR) 3.8.1.1, AC Sources Verification, within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> of entering Condition B, and once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter. TS 1.3, Completion Time, specifies that completion time begins at the time the condition is entered (i.e., when the EDG is declared inoperable).
On September 18, 2008 (date of discovery), during review of historical operator logs, SCE identified that past operating practice was not always in verbatim compliance with TS 1.3. Specifically, for planned periods of EDG inoperability, Operators (Utility, Licensed) performed SR 3.8.1.1 within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> prior to declaring an EDG inoperable, and once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter. In these cases where an EDG was declared inoperable for planned maintenance, operators did not perform SR 3.8.1.1 within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after declaring the EDG inoperable. This practice existed since initial plant startup, and was consistent with SONGS original TS. However, it does not comply with SONGS Improved TS implemented on August 5, 1996. While this practice has existed since plant startup, the most recent occurrence of this noncompliance occurred on August 22, 2008 (event date).
Cause of the event
The cause of this event was an inadequate procedure which was not consistent with the improved TS. SONGS procedure S023-3-3.23, Attachment 7, directed Operators (Utility, Licensed) to perform TS SR 3.8.1.1 prior to declaring an EDG inoperable. This practice, was, and is still considered conservative and has been in place since original plant startup. During implementation of the improved TS (implemented on August 5, 1996), SCE failed to recognize this practice was not in verbatim compliance with TS 1.3, Completion Time, which specifies that completion time begins at the time the condition is entered (i.e., at the time the EDG is declared inoperable).
Although Operators acted prudently in performing SR 3.8.1.1 prior to removing an EDG from service, SR 3.8.1.1 must also be performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after declaring the EDG inoperable in order to be in verbatim compliance with TS 1.3.
Completed Corrective Actions
The applicable SR 3.8.1.1 implementing procedure, S023-3-3.23, Attachment 7, "AC Sources Verification," was revised on October 10, 2008, to clearly specify the SR must be performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after declaring an EDG inoperable.
SCE reviewed other TS SRs and found no similar examples.
Planned Corrective Actions
S023-2-13, "Diesel Generator Operation," is being revised to clearly specify S023-3-3.23, Attachment 7, must be performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> after removing an EDG from service.
A formal cause evaluation is currently being conducted. This LER will be updated if the cause evaluation reveals any new significant causes or corrective actions.
Safety Significance
SR 3.8.1.1 was successfully completed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> prior to declaring an EDG inoperable and also once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> after entering TS 3.8.1, Condition B. SCE concludes that, while this practice was not in verbatim compliance with the TS, there was no safety significance to this event.
Previous Occurrences
LERs 2-1996-009 and 2-1997-001 describe historical examples of failure to adequately implement Improved TS SRs.