05000482/LER-2008-007
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 05-11-2008 |
|---|---|
| Report date: | 07-10-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 4822008007R00 - NRC Website | |
PLANT CONDITIONS PRIOR TO EVENT:
MODE — 3 Power — 000
BACKGROUND:
Each Residual Heat Removal (RHR) system [EIIS Code: BP] can provide flow to all four Reactor Coolant System (RCS) [EIIS Code: AB] Cold Leg lines. Both RHR systems can be lined up, via cross connect valves, to a common discharge header and provide flow to RCS Hot Legs Loop 2 and 3.
EVENT DESCRIPTION:
On 5/10/2008, Wolf Creek was in Mode 3 returning to power operation at the end of Refueling Outage 16. At 2248 on 5/10/2008, the control room operators became aware that the 'D' Safety Injection Accumulator [EIIS Code:
BQ-ACC] was not maintaining level and attempts at seating check valves were unsuccessful at stopping the leakage from the accumulator. Intially, leakage through the safety injection test lines was suspected. Actions were taken to identify the source of the leakage.
At 0123 on 5/11/2008, a potential leakage path through check valve EPV8818D, 'B' RHR to RCS Cold Leg Loop 4 Check Valve [EllS Code: BP-V] was identified. Leakage past this check valve would explain the accumulator level decrease and the recently observed pressure increase on the 'B' RHR discharge header. Other check valves continued to be investigated for potential leakage paths.
At 0300 on 5/11/2008, the control room was notified that relief valve EJ8842, RHR To Safety Injection System (SIS) Relief Valve [EIIS Code: BP-RV], which provides flow to the RCS Hot Leg loops 2 and 3, had a leak of approximately 200 drops/minute. Both trains of RHR were declared inoperable and Technical Specification 3.5.2 was entered with an action to be in Mode 4 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
At 0409 on 5/11/2008, the leakage from the relief valve was determined to be due to a failure of the bellows. The RHR cross connect valves, to the common RHR discharge header, were closed to depressurize the header and to reduce the leakage. Technical Specification 3.0.3. was entered, with 0300 as the starting time, and actions taken to commence cool down to Mode 4. Mode 4 was entered at 0725 on 5/11/2008.
Relief valve EJ8842 was replaced at approximately 1330 on 5/11/2008.
Efforts to seat the check valve EPV8818D were made through 5/13/2008. The check valve was successfully seated on 5/13/2008.
BASIS FOR REPORTABILITY:
Both trains of RHR were declared inoperable. This event is reportable under 10 CFR 50.73(a)(2)(v)(B) as an event or condition that could have prevented fulfillment of a safety function needed to remove residual heat.
This event was also reported on 5/11/2008 under 10 CFR 50.72(b)(3)(v)(B) as an event or condition that could have prevented fulfillment of a safety function needed to remove residual heat, as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> report.
ROOT CAUSE:
The over-pressurization which lead to leakage from EJ8842, RHR TO SIS Relief Valve, was caused by excessive check valve leakage from 'D' Safety Injection Accumulator through RHR Check Valve EPV8818D into the RHR Train Discharge Header.
CORRECTIVE ACTIONS:
The corrective action to address this issue is to rework valve EPV8818D. Work orders have been written to conduct this work. The action will be completed prior to restart at the end of Refueling Outage 17.
SAFETY SIGNIFICANCE:
The event was of low safety significance. Both RHR trains were available and could have provided flow to the RCS in the event of an accident. The leakage through the relief valve wasn't sufficent to prevent flow from the RHR to the RCS Hot Legs. After the cross connect valves were closed, isolating the line with the leaking relief valve, both RHR trains could still provide flow to the RCS through the RCS Cold Legs.
OPERATING EXPERIENCE/PREVIOUS EVENTS:
Events occurring at Wolf Creek since 2000 were examined. Wolf Creek has experienced leakage through check valves and failures in relief valves in this time period. However, these failures have not led to their associated safety systems being declared inoperable.