05000387/LER-2011-004
| Susquehanna Steam Electric Station Unit 1 | |
| Event date: | 09-21-2011 |
|---|---|
| Report date: | 02-13-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3872011004R00 - NRC Website | |
EVENT DESCRIPTION
On December 6, 2011, Susquehanna Steam Electric Station declared the common "C" Emergency Diesel Generator (EDG) (EllS: EK) inoperable due to loss of firing from cylinder 8R during surveillance testing. LCO 3.8.1 was entered, the "E" Emergency Diesel Generator was substituted for the "C" EDG and the LCO exited. A review of past maintenance on the "C" EDG determined that the EDG was inoperable from the time maintenance was performed on September 21, 2011 until it was shutdown on December 6, 2011 because it could not have fulfilled its mission time.
CAUSE OF THE EVENT
The direct cause of the loss of firing was due to interruption of the spray pattern in the fuel injection nozzle and partial blockage. The root causes were determined to be:
1) the work package to install the delivery valve springs was insufficient, 2) the work crew proceeded using an inadequate work package, and 3) Quality Control (QC) activities were insufficient to prevent the incorrect reassembly of the fuel injector pump components.
ANALYSIS/SAFETY SIGNIFICANCE
This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications in that the "C" Emergency Diesel Generator could not fulfill its mission time in the event it was called upon to do so.
Actual Consequences "C" EDG was unknowingly inoperable and unavailable to perform its 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Probability Risk Assessment (PRA) mission time and its 30 day design bases mission time for a period of approximately 76 days. As a result, there were short periods of time when both units were unknowingly in elevated risk conditions without taking associated risk management actions.
Potential Consequences:
The potential consequence of the unavailability of the "C" EDG is an increase in core damage frequency and large early release frequency in the event of a Loss of Offsite Power combined with random failures of the remaining available EDGs, ultimately resulting in a high pressure containment challenge for the units. The increase in core damage frequency was less than 1.0 E-6 and the increase in large early release frequency was less than 1.0 E-7.
CORRECTIVE ACTIONS
The following corrective actions have been completed:
- The 12 fuel injection pumps, which contained the incorrectly installed delivery springs, have been replaced.
- The procedure on Work Package development has been revised to provide a clear standard for Human Factoring of work instructions.
The following corrective actions are planned:
- Revise the procedure governing Work Package Standards such that work packages are properly Human Factored and verified.
- Ensure that Human Factoring is part of the Maintenance Planner Qualification.
- Prior to performing work on of the remaining EDGs ensure the work packages meet the updated Human Factoring /Procedure Writing standards.
- Revise the procedure on "Hold and Notification Point Inspection and Documentation," to include guidance on the construct, formatting, wording, and use of notes and inspection steps in hold and notification point development. Ensure this guidance is consistent with procedure standards that have been established.
- Develop and implement an action plan to determine if potentially latent broken delivery valve springs exist on the A, D, or E EDGs. If broken springs are found in the investigation, then correct the condition.
No regulatory commitments are associated with this report.
ADDITIONAL INFORMATION
Failed Component Information:
Component: Delivery spring associated with the fuel injector pump Manufacturer: Bendix
Previous Similar Events:
None