05000457/LER-2010-001
| Braidwood Station | |
| Event date: | 1-5-2010 |
|---|---|
| Report date: | 04-16-2010 |
| 4572010001R00 - NRC Website | |
Background:
Plant Operating Conditions Before The Event:
Event Date: February 15, 2010 Event Time: 1443 CST Unit: 2 MODE: 1 Reactor Power: 100 percent Unit 2 Essential Service Water: Normal operating temperature and pressure
Description of Event:
On January 29, 2010, an equipment operator observed le.akage from a braided hose that runs from the casino of the 2A SX pump to its inboard seal. The hose provides couiiiiy and flush ling functions to the pump seal. The initial report indicated the leak rate was sixty drops per minute from a fitting. The size of the leak did not prevent the 2A SX pump from delivering required flow to safety related loads. Additionally, the leak was not affecting any components on the 2A Essential Service Water (SX) [Bl] pump or any other equipment in the area. Because the initial inspection indicated the leak was from a fitting, it was not considered pressure boundary leakage, and the pump was determined to be operable in the prompt operability determination. Technical Specifications (TS) Limiting Condition Operation 3.7.8 Condition A for the 2A SX pump was not entered.
On February 2. 2010, the 2A SX pump was run so that Plant and Design Engineering could perform an inspection of the flexible hose while the pump was running and while it was idle. Zero leakage was observed during this inspection. However, it was conservatively decided to proceed with replacement of the hose during a 2A SX strainer work window that commenced later on Febi uary 2, 2010. It was also decided that the flexible hose would be submitted for failure analysis after removal.
The flexible hose was replaced during the work window and sent to a vendor for failure analysis. The work window was exited on February 4, 2010, and the 2A SX train was declared operable.
On February 15, 2010, the station was provided the failure analysis results, which concluded the hose contained a pinhole leak approximately seven inches from one end of the hose. The leak was caused by external wear from rubbing contact with the braided wire jacket. Similar non-through wall wear was observed at several other locations along the length of the hose. The hose's application makes it susceptible to vibration-induced movements that promote wear.
The failure analysis results represent pressure boundary leakage of an ASME Section III Class 3 code line. As such, the pump should have been declared inoperable at the time the leak was identified (January 29, 2010) until the pump was restored to operable status following the 2A SX strainer work window (February 2. 2010). The amount of time would have exceeded the allowed outage time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and resulted in a condition not allowed by TS. The event is being reported pursuant to 50.73(a)(2)(i)(B), as a condition prohibited by TS 3.7.8 Condition C.
The pressure boundary leakage was discovered upon receipt of the failure analysis results (February 15, 2010).
No additional structures. systems. or components were inoperable at the start of this event that contributed to the event.
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Cause of Event
The failure analysis concluded the following: Pressure testing indicated the flex hose contained a pinhole leak approximately seven inches from one end of the hose. The leak was caused by external wear from rubbing contact with the braided wire jacket. Similar non-through wall wear was observed at several other locations along the length of the hose. The hose's application makes it susceptible to vibration-induced movements that promote wear.
D.Safety Consequences:
The line provides seal flushing and cooling functions. The required flow through the line must circulate around the primary ring (seal face) through a mating ring (seat) at no less than 0.4 gallons per minute (gpnn) in order to remove heat generated, or failure may occur. Based on a review of the failure analysis report and engineering judgment, the flex hose would have supported operation of the pump. The through-wall flaw was the result of fretting of the inner bellows by the outside stainiess steel braiding and was loc..:alized. Based on ille localized ilaidie df the degradation mechanism and the robustness of the flexible hose design when compared to actual operating conditions, the degraded condition would not have resulted in a catastrophic failure of the hose. As a result, the increase in plant risk was minimal.
There were no actual safety consequences to this condition.
E. Corrective Actions:
The corrective actions include:
- The braided hose has been replaced.
- A cushioning bronze inner braid on the SX seal water flexible hoses will be installed (i.e., flexible hose that is supplied with a bronze braid between an inner hose and an outer stainless steel braided jacket).
A 6-year replacement preventive maintenance program (PM) will be implemented for the SX seal water flexible hoses. The 6-year frequency was chosen based upon the time from installation to the experienced failure (approximately eight years).
Operator training will be provided, related to ASME code applicability and system design and on short term LCO actions requiring assistance from other groups.
. Previous Occurrences:
There have been no previous, similar events identified at the Braidwood Station.
Component Failure Data:
Manufacturer� Nomenclature� Model�Mfg. Part Number Senior Flexonics Inc.
�Flexible Hose Assembly� J43350-6 1/2" x 42"-J43350-6 1.11.;,.. I c ;[..� ILL�url�(: