05000250/LER-2008-002
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) |
| 2502008002R00 - NRC Website | |
On February 28, 2008 during a Short Notice Outage, the Unit 3 containment was purged. The purge was terminated February 29, 2008 at 03:52. On March 1, 2008, a local leak rate test (LLRT) was performed around 00:00 on Penetration [PEN] 35 (POV-3-2600 and POV-3-2601). The containment [EIIS: NH] purge supply valve POV-3-2600 [EIIS: V] and the penetration failed the test with a leakage of about 45,000 standard cubic centimeters per minute (sccm). The acceptance criteria was less than or equal to 16,500 sccm. The valve POV-3-2600 failed its LLRT because the valve disc was not fully closed. A successful LLRT was performed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of discovery on 3/1/08 at about 14:10 hours.
Unit 3 was in a Short Notice Outage (SNO) in mode 3 at the time of discovery. The LLRT was not due; however, it was performed as an augmented surveillance because of the valve history and the need to perform a purge during the SNO. The condition is presumed to have existed while purging was in progress during Mode 3. The penetration is considered to have been inoperable from 2/28/08 at 00:25 hours when the penetration was opened in Mode 3, until the successful LLRT on 3/1/08 at 14:10 hours. Assuming this, the penetration and valve were inoperable for about 61 hours7.060185e-4 days <br />0.0169 hours <br />1.008598e-4 weeks <br />2.32105e-5 months <br />, exceeding the allowed 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> outage time of Technical Specification 3.6.1.7.b. This condition is reportable in accordance with 10CFR50.73(a)(2)(i)(B).
CAUSE OF THE EVENT AND CORRECTIVE ACTIONS
Subsequent investigation determined corrosion in the actuator bearing surfaces may have created friction that prevented the actuator from delivering the seating torque needed to provide an adequate seal. Condition Report 2008 7337 was initiated to evaluate the event and identify corrective actions.
Immediate corrective actions included cycling POV-3-2600, performing a "snoop" check on the POV-3-2600 purge supply isolation valve disc/seat and stem/packing as well as placing administrative controls on fuses [FU] for POV-3- 2600 and POV-3-2601 with instructions not to operate until Mode 5. Following the immediate actions, the penetration retested satisfactorily. Snooping for indications of areas of leakage (which would act as a seat lubricant), additional pressurization of the penetration (up to approximately 60 psig), and waiting time most likely allowed the actuator spring force to position the disc a small amount further into the seat, resulting in an acceptable leakage of about 8,500 sccm.
The failure of POV-3-2600 was most likely due to inadequate preventive maintenance. Corrective actions include diagnostic testing to confirm the suspected cause and identify any other potential contributing causes, inspection of valve internals, and additional Work Order instructions to periodically grease the actuator.
ANALYSIS OF EVENT
The containment purge supply isolation valves are Safety Related, Quality Group B valves. Their safety related functions include preventing the unrestricted release of radioactivity from the containment to the outside environment following a LOCA. This is a function common to all containment penetrations. They also isolate the containment following a LOCA to maintain sufficient backpressure such that emergency core cooling systems will function properly. The failure of the POV-3-2600 purge supply outer isolation valve to fully close during the LLRT for Penetration 35 on 3/1/2008 is considered a Maintenance Rule functional failure of the valve because it could not perform its required isolation function from the time the penetration was opened for containment purging. However, 3 3 previous LLRT results of Penetration 35 last performed on 10/5/07 showed the penetration was operable prior to containment purge. The probability of an event resulting in core damage and a release of radioactivity to the containment building is low during the period of time that the valve and penetration were assumed inoperable (about 61 hours7.060185e-4 days <br />0.0169 hours <br />1.008598e-4 weeks <br />2.32105e-5 months <br />) with the reactor in Mode 3. There was no impact on the health and safety of the public due to the event.
ADDITIONAL INFORMATION AND PREVIOUS EVENTS
There were no previous failures of POV-3-2600. A review of industry operating experience for the past five years did not reveal similar events due to the same failure mechanism. There was however, a previous failure of Turkey Point Unit 4 POV-4-2602 to close during an LLRT (documented in Licensee Event Report 2006-001-00 submitted January 29, 2007). The failure of containment purge exhaust valve POV-4-2602 to close was also attributed to increased friction in the actuator due to corrosion. The Preventive Maintenance (PM) process for all of the purge valves was evaluated and determined to be ineffective. One of the corrective actions implemented new lubrication PMs. The effectiveness of the new PMs is still being evaluated under the monitoring program. No corrective actions, including the lubrication PMs had been performed on POV-3-2600. All eight (8) containment purge valves were placed into (a)(1) of the maintenance rule for continued monitoring of the PM program. Once the monitoring proves that the PM program is effective, the valves will be returned to (a)(2) status. Because the corrective actions from CR 2006-34852 have not yet been implemented for POV-3-2600, the condition is not considered a repeat condition from a Maintenance Rule perspective.
component function identifier (if appropriate)].
MANUFACTURER DATA
The valves are made by Henry Pratt, model R1A5. The actuators are model T420-SR3-S made by Bettis. The identical valves and actuators are used in the other 48" purge supply valves (both units 3 and 4).