05000272/LER-2013-001
| Salem Generating Station - Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown |
| 2722013001R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse — Pressurized Water Reactor (PWR/4) Reactor Coolant System (RCS){AB} Pressurizer Spray Valve {AB/PCV} Containment Fan Cooler Unit {BK} * Energy Industry Identification System {EIIS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: August 22, 2013 Discovery Date: August 22, 2013
CONDITIONS PRIOR TO OCCURRENCE
Salem Unit 1 was in Operational Mode 1 operating at 100% reactor thermal power. No additional structures, systems or components were inoperable at the time of the discovery that contributed to the event.
DESCRIPTION OF OCCURRENCE
On August 22, 2013, Salem Unit 1 was in Mode 1 operating at 100% power. At 1016, operators received Containment Fan Cooler Unit {BK} leak detection alarms indicating vapor leakage to the Containment atmosphere and entered the abnormal operating procedure for Reactor Coolant System (RCS) leakage. Unit 1 entered Technical Specification Action Statement (TSAS) 3.4.6.2(b) at 1029 when unidentified RCS leakage was estimated at 3.5 gallons per minute (gpm). TSAS 3.4.6.2(b) requires a reduction of RCS unidentified leakage to within the limit of 1 gpm within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or be in at least Hot Standby (Mode 3) within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown (Mode 5) within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
At 1252, a completed RCS leakrate calculation confirmed an unidentified RCS leak rate of 3.6 gpm.
At 1310, an inspection team inside Containment identified the leakage source as packing leakage on Pressurizer Spray Valve 1PS1 {AB/PCV}.
At 1400, a completed RCS leakrate calculation indicated an unidentified RCS leak rate of 4.3 gpm.
At 1510, Containment atmospheric pressure reached its Technical Specification limit of 0.3 psig. Unit 1 entered TSAS 3.6.1.4 for Containment internal pressure which requires a reduction of Containment atmospheric pressure below the limit of 0.3 psig within one hour or be in at least Hot Standby within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Cold Shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.
Efforts to isolate Pressurizer Spray Valve 1P51 were unsuccessful and at 1628, operators commenced turbine load reduction at a rate of 30% per hour in accordance with operating procedures. At 1636, Unit 1 commenced containment pressure relief in accordance with procedures. Containment pressure was reduced to less than 0.3 psig and Unit 1 exited TSAS 3.6.1.4 at 1647.
A 4-hour notification was made to the NRC at 1708, under the requirements of 10 CFR 50.72(b)(2)(i) for "The initiation of any nuclear plant shutdown required by the plant's Technical Specifications.
Containment pressure relief was completed at 1730 with a final containment atmospheric pressure of 0.13 psig.
Unit 1 entered Hot Standby conditions at 2005.
At 2212, Pressurizer Spray Valve 1P51 was isolated and estimated unidentified RCS leakage rate was observed to decrease. An RCS water inventory balance completed on August 23, 2013 at 0102 indicated an unidentified RCS leak rate of 0.08 gpm. Unit 1 exited TSAS 3.4.6.2.b at 0159 after review of the RCS leak rate calculations.
CAUSE OF OCCURRENCE
The most probable cause of the Pressurizer Spray Valve 1P51 packing failure was due to a loss of packing consolidation. Initial examination of the valve indicated a packing torque of less than 10 ft.-lbs.
which is less than the specified required value of 16 ft.-lbs.
PREVIOUS OCCURRENCES
A review of LERs for Salem Units 1 and 2 for the previous three years did not identify any similar events.
SAFETY CONSEQUENCES AND IMPLICATIONS
There were no safety consequences associated with this event. The 3.6 to 4.3 gpm RCS leakage rate at normal operating temperature and pressure was well within the capacity of the normal RCS charging and makeup system. Therefore, by definition, this event was not a Small Break Loss Of Coolant Accident (LOCA). All identified consequences were bounded by UFSAR analyses for a Small Break LOCA. No Engineered Safeguards actuations were necessary as a result of this leak. RCS leakage throughout the event remained well below Emergency Plan entry requirements of greater than or equal to 10 gpm unidentified leakage or greater than or equal to 25 gpm identified leakage.
Operators responded appropriately to indications of increased RCS leakage and all safety systems operated as required. The plant completed an orderly shutdown and the leak was isolated. Leakage from Pressurizer Spray Valve 1P51 and any associated gaseous activity which came out of solution systems. Radiation release rates for containment pressure relief remained well below the Offsite Dose Calculation Manual (ODCM) limits and personnel exposures were considered routine and within normal operating limits.
A review of this event determined that a Safety System Functional Failure (SSFF) as defined in NEI 99-02, Regulatory Assessment Performance Indicator Guideline did not occur. This event did not prevent the ability of a system to fulfill its safety function to either shutdown the reactor, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident.
CORRECTIVE ACTIONS
1. Pressurizer Spray Valve 1P51 was manually isolated following plant shutdown and the valve packing torque was adjusted to its required 16 ft.-lbs. An evaluation determined that Salem Unit 1 could operate safely until the next refueling outage with one Pressurizer Spray Valve isolated. Pressurizer Spray Valve 1PS1 will remain manually isolated until plant conditions allow further investigation and repair.
2. Prior to the Unit 1 startup, Operations shift crews received just-in-time training for startup and power operation transients with one Pressurizer Spray Valve isolated.
3. Pressurizer Spray Valve 1P51 valve utilizes composite end rings in its packing configuration. An extent of condition review was made of the Salem Unit 1 and 2 Air Operated Valve Program Category 1 and 2 Air Operated Valves that utilize composite end rings in the same packing sequence. Category 1 valves are active Safety Significant valves that are high risk and Category 2 valves are active Safety Related Valves that do not have high safety significance. The review of as- left packing loads determined that the gland stress was adequate to prevent packing failure on all valves reviewed with the exception of 21AF11, Auxiliary Feedwater Level Control Valve. A local torque check will be performed on 21AF11 as plant conditions permit.
4. A boron leak evaluation was performed to determine any adverse impact to Pressurizer Spray Valve 1PS1 surrounding areas inside Containment. The evaluation concluded that it would be acceptable to clean the leakage residue from the Pressurizer enclosure in the next Unit 1 refueling outage.
5. A causal analysis is in progress to determine the causes and necessary corrective actions associated with the packing failure of Pressurizer Spray Valve 1PS1.
COMMITMENTS
No commitments are made in this LER.