05000325/LER-2009-004
| Docket Number | |
| Event date: | 09-20-2009 |
|---|---|
| Report date: | 11-19-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| Initial Reporting | |
| ENS 45368 | 10 CFR 50.72(b)(2)(i), Tech Spec Required Shutdown |
| 3252009004R00 - NRC Website | |
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Introduction Initial Conditions On September 13, 2009, at 1950 hours0.0226 days <br />0.542 hours <br />0.00322 weeks <br />7.41975e-4 months <br /> Eastern Daylight Time (EDT), Emergency Diesel Generator (EDG) [EK] 4 was removed from service for routine maintenance and surveillance testing and both units entered TS 3.8.1, Required Action D.4, which required the inoperable EDG to be restored to operable status within 7 days (i.e., on September 20, 2009, at 1950 hours0.0226 days <br />0.542 hours <br />0.00322 weeks <br />7.41975e-4 months <br />). Both units entered TS 3.8.1, Condition H at 1950 hours0.0226 days <br />0.542 hours <br />0.00322 weeks <br />7.41975e-4 months <br /> on September 20, 2009. Per Required Action H.1, the units were required to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> (i.e., 0750 hours0.00868 days <br />0.208 hours <br />0.00124 weeks <br />2.85375e-4 months <br /> on September 21, 2009) followed by Mode 4 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> (i.e., 0750 hours0.00868 days <br />0.208 hours <br />0.00124 weeks <br />2.85375e-4 months <br /> on September 22, 2009) per Required Action H.2.
Unit 1 was in Mode 1, at approximately 32 percent of rated thermal power (RTP), when a preplanned manual scram was inserted at 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br /> EDT on September 20, 2009. Unit 2 was in Mode 1, at approximately 30 percent of RTP, when a preplanned manual scram was inserted at 0421 hours0.00487 days <br />0.117 hours <br />6.960979e-4 weeks <br />1.601905e-4 months <br /> EDT on September 21, 2009. The only safety-related equipment which was inoperable at the time the units were shutdown was EDG 4. Unit 1 and Unit 2 systems necessary to support plant shutdown were operable.
Reportability Criteria The TS required shutdown was due to inoperability of EDG 4. This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(A), due to the completion of a plant shutdown required by the plants' TSs. The NRC was notified of the initiation of a plant shutdown required by TSs at 1708 EDT on September 20, 2009 (i.e., Event Number 45368).
Event Description
On September 13, 2009, at 1950 hours0.0226 days <br />0.542 hours <br />0.00322 weeks <br />7.41975e-4 months <br /> EDT, EDG 4 was removed from service to perform scheduled six year preventive maintenance and surveillance testing. This maintenance included draining of the mechanical governor control (EGB) governor oil system and a complete refill.
On September 19, 2009, at 0942 hours0.0109 days <br />0.262 hours <br />0.00156 weeks <br />3.58431e-4 months <br /> EDT, EDG 4 was started for a maintenance run. The EDG started normally but then shut down after approximately 45 seconds. Troubleshooting identified a problem with the control air pressure regulating valve (i.e., 2-DSA-PRV-1251) and the valve was replaced. Following the valve replacement, at 2125 hours0.0246 days <br />0.59 hours <br />0.00351 weeks <br />8.085625e-4 months <br /> EDT, another EDG 4 start was attempted, but the diesel failed to start, reaching only 138 rpm. Potential causes of the failure were binding of the fuel racks, internal EGB fault and failure of the input drive to rotate the governor. Subsequent testing narrowed the apparent cause of the EDG failure to start to the EGB mechanical governor. The EGB was removed from the governor and shipped to Engine Systems Incorporated (ESI) for failure analysis.
Event Description (continued) Bench testing of the EGB revealed that the electric pilot valve was stuck and required mechanical agitation to free it. The EGB was removed from the bench assembly and the sub-governor assembly was removed from the EGB. The electric portion of the pilot valve assembly was removed and inspected. Binding was observed along the shaft and small metal particles were observed in the affected area of the shaft.
Particulate matter was found on the electrical pilot valve upper land region where the compensating bushing is located. After particle removal, the pilot valve stroked freely. The mechanical pilot assembly was disassembled and no binding was observed. No abnormal wear was observed. This confirmed that the cause of the diesel failure to start was due to the internal binding of the electric portion of the pilot assembly within the EGB.
To restore EDG 4 operability, a replacement governor was readied for installation on EDG 4. All components associated with replacement EGB were inspected for foreign material. The EGB, the new servo boost cylinder, and the new oil cooler as well as all connecting tubing were flushed with filtered oil prior to installation on EDG 4. On September 25, 2009, governor replacement was completed and successful post-installation tuning and post-maintenance testing, demonstrated that the EDG 4 is fully capable of performing its intended safety function. EDG 4 was declared operable at 1615 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.145075e-4 months <br /> EDT on September 27, 2009.
Event Cause The select cause of this event is failure to prevent intrusion of foreign material into the EGB during vendor performed maintenance. The most likely source of the foreign material is introduction during previous vendor performed EGB repairs prior to its installation on EDG 4. The purchase orders for these repairs were reviewed and they only contained standard requirements for assurance of quality. Specific requirements for preventing foreign material intrusion or flushing were not included. As a result, the vendor-performed maintenance activities did not provide adequate documentation that foreign material exclusion (FME) practices and cleanliness flush requirements were performed during maintenance on the EGB.
BSEP maintenance controls are considered a contributing cause to this event. Site maintenance activities could also have introduced the foreign material. Lack of specificity in procedures for EGB maintenance created the potential for undetected foreign material to be introduced.
Safety Assessment The safety significance of this event is considered minimal. At the time of this event EDG 4 was inoperable for maintenance. Based on prior successful operation and the analysis of potential paths for foreign material to move to the pilot assembly, it is highly likely that the foreign material that impacted EDG 4 performance was dislodged from its previous location and moved to the pilot assembly during the governor Safety Assessment (continued) oil change performed with the other maintenance on the engine. Therefore, it is reasonable to conclude that EDG 4 would have performed as required, in response to an actual event, prior to being removed from service for routine maintenance and surveillance testing on September 13, 2009.
Corrective Actions
The following corrective actions have been identified.
- Standard purchase order requirements for foreign material exclusion and establishing cleanliness were established in ESI purchase orders.
- BSEP procedures that address EGB maintenance and governor oil addition or removal will be revised to add adequate FME control and cleanliness requirements. These revisions are currently scheduled to be completed by January 8, 2010.
Previous Similar Events
A review of LERs and corrective action program condition reports for the past three years identified the following similar events.
- LER 1-2007-002, dated May 30, 2007, "Technical Specification Required Shutdown Due To Emergency Diesel Generator 4 Inoperability," documents an event where Unit 1 was shutdown due to the inability to return EDG 4 to operable status within the 7-day completion time of Required Action D.4 of TS 3.8.1. The extended out-of-service time was due to multiple equipment issues, including two failed refurbished governors and latent design problems discovered during the Allen- Bradley relay replacements only after extensive post-maintenance testing. Each individual equipment issue was manageable within the allowed outage time, but the number and sequence of discovery was such that the cumulative effect of these issues precluded EDG 4 recovery within the allowed out-of-service time. The failure of the two refurbished governors in this event was attributed to the centering spring assembly. As such the corrective actions, applicable to the governors, associated with LER 1-2007-002, could not-have reasonably been expected to prevent the condition reported in this LER.
- LER 1-2006-007, Supplement 1, dated January 26, 2007, "Operations Prohibited by Technical Specifications Due To Inoperable Emergency Diesel Generator 1," documents an event where EDG 1 was inoperable for 15 days, 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> and 17 minutes. This was caused by inadequate post- maintenance closeout inspections, which resulted in foreign material being left in the lube oil Previous Similar Events (continued) system. The corrective actions to prevent recurrence associated with LER 1-2006-007, Supplement 1, focused on FME controls for the EDG lube oil sumps and could not have reasonably been expected to prevent the condition reported in this LER.
Commitments No regulatory commitments are contained in this report.