05000259/LER-2012-010
| Browns Ferry Nuclear Plant Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2592012000R00 - NRC Website | |
I. PLANT CONDITION(S)
At the time of discovery, Browns Ferry Nuclear Plant (BFN), Unit 1, was in Mode 4 at zero percent rated thermal power during a refueling outage.
II. DESCRIPTION OF EVENT
A. Event:
On November 22, 2012, at 0600 Central Standard Time (CST), during a BFN, Unit 1, refueling outage, Sense Line A3 Excess Flow Check Valve (EFCV) [CKV], 1-ECKV-068-0065B, failed to meet the acceptance criteria of surveillance 1-SR-3.6.1.3.8(4), Instrument Line Excess Flow Check Valve Operability Test. The valve was replaced and retested. Again, the valve failed to pass the surveillance requirement.
Further troubleshooting identified both failures resulted from the valve being incorrectly installed in a reverse orientation in the system. The valve was originally installed in a reverse orientation on October 15, 2006. Prior to BFN, Unit 1, restart, procedure 1-SR-3.6.1.3.8(4) was performed on March 19, 2007, and acceptance criteria was documented as being satisfied for this valve.
This configuration would not have reduced flow downstream of the check valve in the event of a sensing line rupture outside of primary containment. The check valve was replaced and installed in its correct orientation on November 23, 2012. The surveillance was successfully completed on November 27, 2012. Due to this condition, 1-ECKV-068-0065B was inoperable from October 15, 2006, until November 27, 2012.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
There were no inoperable structures, components, or systems that contributed to this event.
C. Dates and Approximate Times of Major Occurrences:
October 15, 2006 Check valve 1-ECKV-068-0065B installed.
March 19, 2007, 0430 Central Daylight Time (CDT) November 22, 2012, 0600 CST November 22, 2012 Check valve 1-ECKV-068-0065B initially failed 1-SR-3.6.1.3.8(4). Test engineer reperformed test and signed off acceptance criteria.
Surveillance 1-SR-3.6.1.3.8(4) was performed on 1-ECKV-068-0065B.
Valve failed acceptance criteria.
Check valve 1-ECKV-068-0065B was replaced. The new check valve was installed in the same orientation as the previous valve.
November 22, 2012, 2235 CST Surveillance 1-SR-3.6.1.3.8(4) was performed on 1-ECKV-068-0065B.
Valve failed acceptance criteria.
November 23, 2012 Check valve 1-ECKV-068-0065B was determined to be installed in a reverse orientation and was replaced under WO 112971469.
November 27, 2012 Check valve 1-ECKV-068-0065 passed the acceptance criteria in 1-SR-3.6.1.3.8(4).
D. Other Systems or Secondary Functions Affected
There were no other systems or secondary functions affected.
E. Method of Discovery
On November 22, 2012, at 0600 CST, during a BFN, Unit 1, refueling outage, Sense Line A3 EFCV, 1-ECKV-068-0065B, failed to meet the acceptance criteria of surveillance 1-SR-3.6.1.3.8(4), Instrument Line Excess Flow Check Valve Operability Test.
F. Operator Actions
There were no operator actions.
G. Safety System Responses
There were no safety system responses.
III. CAUSE OF THE EVENT
A. Immediate Cause
The immediate cause was determined to be the incorrect installation of the check valve in a reverse orientation.
B. Root Cause
The root cause of the condition was identified to be inadequate procedural guidance in Mechanical Corrective Instruction MCI-0-000-CKV002, Maintenance of Marotta Instrument Line Check Valves. Procedure MCI-0-000-CKV002 does not contain a step to ensure the valve was installed correctly, or an independent step to verify correct installation.
C. Contributing Factors
There were no contributing factors.
IV. ANALYSIS OF THE EVENT
The WA is submitting this report in accordance with 10 CFR 50.73(a)(2)(i)(B), as any operation or condition which was prohibited by the plant's Technical Specifications.
The BFN, Unit 1, Technical Specifications (TS) Limiting Condition for Operation (LCO) 3.6.1.3 requires that each Primary Containment Isolation Valve (PCIV) be Operable in reactor Modes 1, 2, and 3, and when the associated instrumentation is required to be Operable per LCO 3.3.6.1, "Primary Containment Isolation Instrumentation." Since 1-ECKV-068-0065B was inoperable in an applicable Mode, the unit should have been in Condition C of TS 3.6.1.3. The TS 3.6.1.3 Required Action C.1 requires the affected penetration flow path to be isolated by use of at least one closed and de-activated automatic valve, closed manual valve, or blind flange within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> for EFCVs. The TS 3.6.1.3 Required Action C.2 requires verification, once per 31 days, that the affected penetration flow path is isolated. If Required Actions and associated Completion Times for Condition C are not met, then Condition E is entered and requires the unit be in Mode 3 (Hot Shutdown) within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and in Mode 4 (Cold Shutdown) within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
Because 1-ECKV-068-0065B was inoperable from October 15, 2006, until November 27, 2012, BFN operated with an inoperable PCIV for longer than allowed by the TS.
Check valve 1-ECKV-068-0065B is normally open to allow process indication downstream to monitor system parameters. A sensing line rupture downstream of the check valve would cause the check valve to seat due to excess differential pressure and substantially reduce the leak. With the valve installed in a reverse orientation, process parameters were still accurately monitored because the valve would not reduce flow. In the event of a sensing line rupture downstream of the check valve, the valve would have failed to perform its function.
Check valve 1-ECKV-068-0065B was installed on October 15, 2006, in preparation for the BFN, Unit 1 restart. The valve was installed in accordance with MCI-0-000-CKV002, Maintenance of Marotta Instrument Line Check Valves. Since work order history shows that this is the last time the valve had been worked on prior to the November 22, 2012, failure, it is evident that the check valve was incorrectly installed in a reverse orientation at that time. Due to the design of Marotta instrument line check valves, it is possible to install the check valve in a reverse orientation. The work instruction does not require the technician to ensure the valve is installed with the correct orientation, nor does it require the installation to be independently verified. This was determined to be the root cause of the event.
Surveillance 1-SR-3.6.1.3.8 is required to be performed on a representative sample of EFCVs once per 24 months such that each EFCV is tested at least once per 120 months. The surveillance is divided into 5 representative samples and the surveillance procedures are numbered 1-SR-3.6.1.3.8(1) through 1-SR-3.6.1.3.8(5). Prior to BFN, Unit 1, restart, all BFN, Unit 1, EFCV were tested. During the BFN, Unit 1, restart EFCV testing, on March 19, 2007, 1-ECKV-068-0065B was tested by a technician in accordance with 1-SR-3.6.1.3.8(4). The valve initially failed the test. A test engineer reperformed the test and incorrectly indicated that, while the valve did not perform as the other EFCVs that were tested, the results were still acceptable. The surveillance was not performed again until November 22, 2012.
On November 22, 2012, 1-ECKV-068-0065B failed to meet the acceptance criteria of surveillance procedure 1-SR-3.6.1.3.8(4). The valve was replaced in the same orientation it was found and retested. Again, the valve failed to pass the surveillance requirement. Both failures resulted from the valve being installed in a reverse orientation in the system.
A review of completed surveillance procedures 1-SR-3.6.1.3.8(1) through 1-SR-3.6.1.3.8(5), performed during the BFN, Unit 1, restart, was conducted to determine if the test engineer who signed off on the incorrectly installed valve also signed off on any other valves. It was determined that during this time period, the test engineer in question only signed off on the acceptance criteria in 1-SR-3.6.1.3.8(4) for 1-ECKV-068-0065B. Therefore, the incorrect installation of 1-ECKV-068-0065B was not discovered on March 19, 2007, due to an isolated human performance error made by the test engineer.
Extent of Condition The extent of condition covers check valves that were installed incorrectly. If additional instrument line check valves or other check valves installed at BFN were also installed in a reverse orientation or with another installation defect, it is likely that surveillances such as 1-SR-3.6.1.3.8(4) would identify this condition. The population of BFN, Unit 1, EFCVs, not tested since 2007, will be tested during the next BFN, Unit 1, refueling outage scheduled for Fall 2014.
Extent of Cause The extent of cause covers procedures that perform maintenance on check valves. The root cause identified inadequacies in MCI-0-000-CKV002. The corrective action to prevent recurrence is to revise MCI-0-000-CKV002. Mechanical maintenance identified seven additional procedures that perform maintenance on check valves. These seven procedures will be evaluated to ensure direction is adequate for correct installation of check valves.
V. ASSESSMENT OF SAFETY CONSEQUENCES
The safety consequences of a failure of an EFCV associated with an instrument line break are not significant and have been previously evaluated by General Electric (GE) and reviewed and accepted by the Nuclear Regulatory Commission (NRC) for the BFN in support of a revision of the Technical Specifications Surveillance Requirements for EFCVs.
The purpose of EFCVs installed in boiling water reactor instrument lines, which penetrate the primary containment boundary, is to limit the release of fluid in the event of an instrument line break. At BFN, EFCVs are not required to close in response to a containment isolation signal and are not postulated to operate under post-Loss-of- Coolant-Accident (LOCA) conditions. At BFN, EFCVs are not needed to mitigate the consequences of an accident because an instrument line break coincident with a design basis LOCA would be of a sufficiently low probability to be outside the design basis.
The radiological consequences evaluated by BFN for an instrument line break do not credit the EFCVs for isolating the break. The evaluation assumes a discharge of reactor water through an instrument line with a 1/4 inch orifice during the detection of the instrument line break and subsequent reactor pressure vessel (RPV) cool down and depressurization sequence. For a radiological material release directly to the secondary containment with the primary containment initially intact, a failure of an EFCV would be bounded by the Main Steam Line Break Analysis of BFN Updated Final Safety Analysis Report, Section 14.6, "Analysis of Design Basis Accidents - Uprated.
The operational impact of an EFCV failing to close during the rupture of an instrument line connected to the RPV boundary is based on environmental effects of a steam release in the vicinity of the instrument racks. The environmental impact of the failure of instrument lines connected to the RPV pressure boundary is the released steam into the reactor building. The magnitude of a release through an instrument line would be within the pressure control capacity of reactor building ventilation systems and that the integrity and functional performance of secondary containment following an instrument line break would be met. The BFN analysis confirmed that an instrument line rupture outside primary containment will not result in over pressurizing secondary containment. The separation of instrument lines and equipment in the reactor building is expected to minimize the operational impact of an instrument line break on other equipment due to jet impingement. The BFN analysis assumes plant shutdown and cool down occur after the line break.
Because the failure of an EFCV associated with an instrument line break has been analyzed and its consequences have been found to be radiologically bounded and environmentally manageable, WA concludes that there was no significant reduction in the protection of the public as a result of this event.
VI. CORRECTIVE ACTIONS - The corrective actions are being managed by TVA's corrective action program.
A. Immediate Corrective Actions
Sense Line A3 EFCV, 1-ECKV-068-0065B, was replaced and passed acceptance criteria of 1-SR-3.6.1.3.8(4) on November 27, 2012.
B. Corrective Actions to Prevent Recurrence
1. Revise MCI-0-000-CKV002, Maintenance of Marotta Instrument Line Check Valves to include steps to ensure proper installation of check valves and to independently verify installation.
2. Review and revise, as necessary, BFN mechanical maintenance check valve procedures to ensure adequate direction for correct installation of check valves.
VII. ADDITIONAL INFORMATION
A. Failed Components
The failed component was Sense Line A3 EFCV, 1-ECKV-068-0065B, on the Reactor Recirculation System [AD]. The EFCV was manufactured by Marotta Scientific Controls, Inc.
B. Previous Similar Events
A search of LERs for BFN, Units 1, 2, and 3, for approximately the past five years identified LER 50-296/2010-003-02, Multiple Test Failures of EFCVs. The Corrective Actions (CA) for LER 50-296/2010-003-02 included the following.
1. Consider replacing each of the instrument line EFCVs with an orifice.
2. Initiate frequency revision in Maximo to administratively revise each Unit's SR-3.6.1.3.8 series to change performance frequency from 120 months to 72 months.
3. Trend performances of each Unit's SR-3.6.1.3.8 series over the next three cycles.
The first CA was presented to the Change Control Board (CCB). The CCB did not approve replacing EFCVs with an orifice. The second CA has been implemented, and the third CA is still in progress.
A search on similar conditions of Problem Evaluation Reports (PERs) for BFN, Units 1, 2, and 3, for approximately the past five years identified PERs 222850, 241921, and 646463.
C. Additional Information
The corrective action document for this report is PER 646600.
D. Safety System Functional Failure Consideration:
In accordance with NEI 99-02, this issue is not considered a safety system functional failure.
E. Scram With Complications Consideration:
This condition did not include a reactor scram.
VIII. COMMITMENTS
There are no commitments.