05000219/LER-2013-002
| Oyster Creek, Unit 1 | |
| Event date: | 10-06-2013 |
|---|---|
| Report date: | 12-5-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2192013002R00 - NRC Website | |
Plant Conditions Prior To Event
Event Date: October 06, 2013 Event Time: 1130 EDT Unit 1 Mode: Startup Power Level: 20%
Description of Event
Reactor Startup from the 1M30 Maintenance Outage began at 0019 hours2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> on 10/05/13. Criticality was achieved at 0520 hours0.00602 days <br />0.144 hours <br />8.597884e-4 weeks <br />1.9786e-4 months <br />. Reactor power was raised to approximately 25% power to perform turbine over speed testing with condenser vacuum at approximately 28.8" H2O. ABN 14 was entered at 1050 on 10/06/2013 due to degrading condenser vacuum. Reactor power was lowered to approximately 20% in an attempt to stabilize plant conditions.
At 1130, a manual reactor SCRAM was inserted when condenser vacuum degraded below 23" H2O. All control rods were inserted, and condenser vacuum continued to degrade until stabilizing just above 20" H2O. Therefore, the main condenser remained available for decay heat removal.
Following the reactor SCRAM, operations and maintenance personnel identified an approximate 1" hole on Y-1-26, B' Condenser Steam Inlet Expansion Joint on the south side of B' Condenser. It was confirmed to be an active leak and subsequently the source of condenser vacuum degradation. A temporary leak repair was performed.
Cause of Event
An approximate 1" hole on Y-1-26, `B' Condenser Steam Inlet Expansion Joint on the south side of `B' Condenser was the cause of the degrading condenser vacuum. It was confirmed to be an active leak and subsequently the source of condenser vacuum degradation.
Analysis of Event
The basic function of the expansion joint, Y-1-26 (Sola Basic Industries, model 97-5516) is to provide a flexible pressure retaining connection to absorb motion in a system caused by thermal expansion and low levels of vibration. The need to be flexible requires the expansion joint to be fabricated from 1/32" (wall thickness) commercial grade stainless steel A240 type 304.
Inspection of the hole showed a circumferential fracture from end to end of one of the three expansion joint convolutions. The fracture was found to be thick-lipped with ratchet marks. There was also a tangential crack perpendicular to fracture as well as a 1/32" — 1/16" indentation that was suggestive of impact damage. The indentation was approximately 1 — 1.5" diameter quarter circle. The end of the indentation stopped at the upper half of the fracture. A review of photos of the failure done by Exelon Power Labs showed that the fracture was most likely caused by fatigue cracking. A contributory cause of the failure was also noted to be the impact damage at the fracture site.
During 1M30 V-3-20 valve rework was performed which necessitated entering the North water box approximately 20 feet North of Y-1-26 expansion bellows. However, due to the location of the valve it was unlikely that damage was caused from the work performed. Work history of expansion bellows Y-1-26 documents visual inspections of the bellows done on a 1R frequency. The last inspection was performed up to and including 1R23, November 2010, with no defects noted. The damage likely occurred after the 1R23 inspection. Since that time, work activities performed around Y-1-26 expansion bellows, such as the Condenser Waterbox Inspection PM complete Analysis of Event Continued on October 2012 during 1R24, likely resulted in an unseen accidental impact of tools or equipment.
Corrective Actions
A temporary leak repair was performed on the 1" hole on Y-1-26, 'B' Condenser Steam Inlet Expansion Joint on the south side of 'B' Condenser. A replacement of the Y-1-26 Expansion Bellows is planned for a future outage.
Previous Occurrences
There have been no similar Licensee Event Reports associated with this component failure submitted at OCNGS in the last two years.
Component Data Component IEEE 805 System ID IEEE 803A Component Expansion Joint SM EXJ