05000275/FIN-2011003-02
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Finding | |
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Title | Unplanned Loss of Preferred Offsite Power Due to Less than Adequate Work Planning |
Description | The inspectors identified a self-revealing finding following the unplanned loss of 230 kV preferred offsite power to Unit 1 due to inadequate work planning. On May 17, 2011, Unit 1 lost preferred offsite power after a technician began cutting a hole in a startup bus control panel using a reciprocating saw. The reciprocating saw induced vibration on the control panel and caused the phase differential protection relay to actuate which separated the startup bus from preferred offsite power. All three Unit 1 emergency diesel generators automatically started after offsite power was lost to the plant vital loads. Procedure AD7.DC8, Work Control, stated that when performing nonroutine work, including modifications on electrical or instrument equipment, the equipment shall be isolated to prevent any unintended equipment actuations. The licensee had authorized the cutting work while the Unit 1 startup bus was in service. The licensee took corrective action to restore offsite power and entered the finding into the corrective action program as Notification 50402706. The inspectors determined that the failure to adequately evaluate the effect of the cutting activity on the energized plant equipment was a performance deficiency. This performance deficiency was more than minor because the finding was associated with the Mitigating Systems Cornerstone human performance attribute and affected the cornerstone objective to ensure the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. The senior reactor analyst utilized Table 3.7 from the plant specific risk-informed notebook and determined that the risk based on Phase 2 estimation was Green. Additionally, the analyst performed a bounding analysis that corroborated the Phase 2 result based on three complete losses of preferred power during the refueling outage with a total exposure time of 2.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />. Using the standardized plant analysis risk model for Diablo Canyon Units 1 and 2, the analyst quantified the conditional core damage probability for any initiator resulting in a consequential loss of offsite power as 1.2 x 10-4. Given these conditions, the analyst noted that the change in core damage frequency could be approximated as the product of these two values (3.9 x 10-8). This indicated that the subject finding was of very low risk significance (Green). This finding has a crosscutting aspect in the area of human performance associated with the work control component, in that Pacific Gas and Electric failed to appropriately plan work activities by incorporating risk insights, job site conditions, and plant structures, systems, and components. |
Site: | Diablo Canyon ![]() |
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Report | IR 05000275/2011003 Section 1R18 |
Date counted | Jun 30, 2011 (2011Q2) |
Type: | Finding: Green |
cornerstone | Mitigating Systems |
Identified by: | Self-revealing |
Inspection Procedure: | IP 71111.18 |
Inspectors (proximate) | I Anchondo C Alldredge N Greene L Micewski M Peck L Carson S Garchow L Willoughby G Miller W Sifre C Osterholtz |
CCA | H.5, Work Management |
INPO aspect | WP.1 |
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Finding - Diablo Canyon - IR 05000275/2011003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Diablo Canyon) @ 2011Q2
Self-Identified List (Diablo Canyon)
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