05000247/LER-2013-004
| Docket Number | |
| Event date: | 09-11-2013 |
|---|---|
| Report date: | 11-12-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2472013004R00 - NRC Website | |
Note: The Energy Industry Identification System Codes are identified within the brackets {}.
DESCRIPTION OF EVENT
On September 11, 2013, during an engineering walkdown of Service Water (SW){BI} temperature control valve SWN-TCV-1103 {TCV}, eight pin hole leaks were discovered at approximately 17:30 hours, in the Primary Auxiliary Building {NF} pipe chase in SW piping {PSP} that supports three Radiation Monitors (RM) (IL]. All leaks had minor corrosion product buildup as well as staining of the piping and staining of the floor.
Seven leaks were on socket welds and one was on an elbow with all located in the ASME Section XI Code boundary. The affected SW piping and the essential SW header were declared inoperable and Technical Specification (TS) 3.7.8 (SW System) was declared not met at 17:30 hours, which also required entry into TS 3.0.3. SW valves SWN-61 and SWN- 55A were closed isolating the leaking piping restoring operability of the SW header and TS 3.7.8 declared met at 17:54 hours. The tagout boundary for leak isolation required placing Radiation Monitor (R) R-49, R-46, and R-53 to standby rendering them non- functional and required that compensatory action be taken. TS 3.0.3 was exited on September 11, 2013, at 17:57 hours. Radiation Monitor R-49 monitors the liquid blowdown from the secondary side of the steam generators (SGs). Samples from the bottoms of all four SGs are mixed in a common header and the common sample is monitored. R-46 and R-53 monitor the SW return from all five containment fan cooler units. The condition was recorded in the Indian Point Energy Center (IPEC) Corrective Action Program (CAP) as Condition Report CR-IP2-2013-03759.
An investigation revealed that the original SW pipe serving R-46, R-53 and R-49 was cement lined carbon steel (CS) small bore piping. The CS piping experienced general corrosion pitting at socket weld locations where protective cement lining could not be applied leaving susceptible material exposed to the corrosive Hudson River water that is used for SW. The CS piping was replaced with 300 series Stainless Steel (SS) in the late 1980's. Pin hole leaks were first identified in the replacement SS SW piping in 2008 as part of an extent of condition of ASME Code piping with 300 series SS material.
The pitting corrosion of SS series 300 SS pipe material is well understood by the industry and at Indian Point and generally does not challenge the structural integrity of the pipe. Series 300 SS is susceptible to general corrosion pitting in a brackish water (chloride) environment. A walkdown on September 11, 2013 identified eight pin hole leaks in SW piping serving monitors R-46, R-53 and R-49. The leaks were at the following locations; at the second elbow upstream of valve SWN-57, first elbow downstream of valve SWN-944, second elbow upstream of valve SWN-944, upstream pipe fitting of valve SWN-658, second elbow downstream of valve SWN-61, first elbow downstream of valve SWN-61, second elbow in overhead where piping penetrates the SW pipe chase ceiling, and the horizontal elbow in overhead prior to the vertical run down to the mixing nozzle. There was no active leakage identified. The leak locations would not allow for Ultrasonic Testing (UT) or to obtain thickness readings. Without the ability to characterize the flaw size, structural evaluations could not be performed in accordance with code case requirements and the piping was declared inoperable. All ASME Section XI Code SS piping weld deficiencies identified in 2008 were weld repaired and a corrective action prepared to track replacement of the 300 series SS pipe with highly corrosion resistant material (AL6XN). Pipe replacement was scheduled for the spring 2010 outage but was deferred to 2012 because of higher risk work and inspections had not identified any degraded conditions. The pipe replacement scheduled for 2012 was again deferred to 2014 for higher risk work. No mitigation strategy was documented. Procedure EN-DC-336 (Plant Health Committee) Revision 4 had a requirement to document the evaluation of risk and required interim actions for high priority long term projects. Revision 4 became effective December 15, 2011.
Cause of Event
The apparent cause was procedure EN-DC-336 (Plant Health Committee) was not followed to document a risk assessment or mitigating (bridging) strategy when the pipe replacement was rescheduled from the 2R20 outage. A bridging strategy would document the risk of deferring pipe replacement and identify interim actions that could be taken (more frequent targeted inspections). The direct cause of pin hole leaks in the SW piping is because Series 300 SS piping is susceptible to corrosion pitting in a brackish water (chloride) environment. In 2008 pin hole leaks due to crevice crack corrosion was identified and a modification developed to replace the piping with material immune to brackish water corrosion. In 2008, the Unit Reliability Team (URT) appropriately ranked the risk for replacement in 2010. Subsequently, the piping replacement was de- scoped from the 2010 outage and rescheduled to 2012, and then rescheduled again to 2014 due to no indication of leakage and higher risk work.
Corrective Actions
The following corrective actions have been or will be performed under Entergy's Corrective Action Program to address the cause and prevent recurrence:
- The affected piping will be weld repaired and returned to operable.
- Full pipe replacement with highly corrosion resistant material (AL6XN) is scheduled for the 2014 refueling outage.
- A review and assessment of the Site Integrated Project Database (SIPD) will be performed to identify any additional potential risks for not having documented risk assessments of items meeting the risk criteria.
- The Modification Project Review Committee (MPRC), Engineering Change Review Group (ECRG), Plant Health Committee (PHC), and System Engineering staff will be briefed on the need to consider requesting a bridging strategy when required high or medium risk ranked work is rescheduled beyond the operating cycle.
Event Analysis
The event is reportable under 10 CFR 50.73(a)(2)(1)(B). The licensee shall report any operation or condition which was prohibited by the plant's TS. This condition meets the reporting criteria because the essential SW header was declared inoperable as a result of discovering pin hole leaks in ISI Class 3 SW piping for the RM system. TS 3.7.8 LCO requires three pumps and required flow path for the essential header to be operable. The LCO requires associated piping, valves and instrumentation and controls required to perform the safety related function to be operable. The piping discovered with through wall leaks is ISI Class 3 piping and is not operable with this condition.
During previous operation for an unknown period of time of up to approximately 6 months the subject piping contained through wall leaks as evidenced by corrosion product buildup at certain welds, staining of the piping directly below the welds, and staining of the floor below the welds. This previously unrecognized condition required TS 3.0.3 entry and corrective actions to return the piping header to operable. Failure to comply with the TS LCO and perform required actions is a TS prohibited condition.
There was no safety system functional failure reportable under 10 CFR 50.73(a)(2)(v).
A designated essential header was available and the leaks would not have prevented the SW cooling function for affected heat loads.
A similar condition was discovered in 2008 as a result of a walkdown that identified SW system leaks in RM piping in the SW pipe chase and recorded in CR-IP2-2008-04268 on September 17, 2008. The 2008 leak was not in the same location. The plant did not enter TS 3.0.3 as the piping was isolated for ultrasonic examination prior to determining the pipe was inoperable. The condition was recorded as "no reportability determination required" therefore, past reportability was not assessed and no LER was submitted. The condition in 2008 would not now require an LER as the past reporting criteria of three years has been exceeded. CR-IP2-2013-04346 recorded this finding.
Past Similar Events
A review was performed of the past three years of Licensee Event Reports (LERs) for events reporting a TS violation due to inoperable SW piping caused by leaks and none were identified.
Safety Significance
This event had no significant effect on the health and safety of the public. There were no actual safety consequences for the event because there were no accidents or events during the degraded condition. No active leaking was identified.
There were no significant potential safety consequences of this event. The leaks in SW piping were within the capability of the SW system to provide adequate SW flow to SW loads. The degraded piping was on the discharge of the heat loads therefore any failure would not prevent the SW cooling function. Any failure of the degraded piping as a result of a transient, accident or event could result in potential flooding. SW leaking in the PAB area would drain to the PAB sump. Any flooding condition could be identified and mitigated as the PAB sump has a high level alarm that actuates an alarm on the PAB sump alarm panel in the unit 2 NPO office and at the Waste Disposal Panel (Flood 15 foot Elevation, Flood 68 foot Elevation). Alarm Response Procedure ARP-014 (PAB Flooding) requires operator acknowledgement of the alarm, notification of the Control Room and initiation of action to eliminate the cause of the flooding.
Procedure 2-ARP-004 (Waste Disposal Panel) also includes actions to respond to WDP PAB Sump Pump Hi level alarm. The ARP actions include isolation of any source of flooding. The SW piping leaks were downstream of the isolation valves which would allow operators to isolate the leak once alerted. In addition to PAB Sump level alarms, periodic operator rounds (Nuclear Rounds) include Waste Disposal Alarm Panel tested/verification thereby providing another means to identify SW piping leakage.