05000361/LER-2002-007
| San Onofre Nuclear Generation Station (Songs) Unit 2 | |
| Event date: | 11-04-2002 |
|---|---|
| Report date: | 12-31-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(Iv)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3612002007R00 - NRC Website | |
6 LER NUMBER PAGE (3) 1 FACLITY NAME —007 — 00 Reactor Vendor
Description of the Event
Combustion Engineering On November 4, 2002 (event date), with the Unit 2 at about 18 percent power, plant operators were returning the unit to full power operation following an unscheduled shutdown (see number 84/10900/0673) {EIIS Component Code PCV} began operating erratically, and ultimately stopped moving at 47 percent open and caused pressurizer pressure to decrease. Attempts to close the spray valve were unsuccessful. At 1638 PST, Reactor Coolant System (RCS) pressure decreased below TS 3.4.1 minimum allowed pressure of 2025 psia and at 1644 PST, plant operators (utility, licensed) manually tripped the reactor. At 2215 PST, Southern California Edison (SCE) made a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> telephone notification to the NRC Operations Center (Log No. 39343) in accordance with 10 CFR 50.72((b)(2)(iv)(B) for a manual actuation of the Reactor Protection System. SCE is providing this follow-up report in accordance with 10 CFR 50.73(a)(2)(iv)(A).
Cause of the Event:
The cause of pressurizer spray valve's behavior has not yet been determined. Testing and observation suggest internal binding (Cause Code. X). This valve will be disassembled during the next refueling outage.
Corrective Actions:
On November 4, 2002, spray valve PV-0100A was isolated when the inlet and outlet manual block valves were closed. Some testing of this valve was performed and then the valve was left isolated with the manual inlet and outlet valves closed.
The second pressurizer spray valve (2PV0100B) will be used for the remainder of the operating cycle. This valve was tested on November 5, 2002 and the test results and observation indicate the valve is operating as expected.
A causal evaluation and applicable corrective actions will be performed following the valve disassembly as part of the corrective actions program.
Safety Significance:
The pressurizer spray valves are not safety related, are not included within the Technical Specifications and are not required for accident mitigation purposes. The requirement for these valves to function is not credited in any of the Chapter 15 analysis. A malfunction of these valves, causing increased spray flow, is considered in the design of the Core Protection Calculator (CPC) system. Protection for this malfunction is provided by the CPC DNBR trip. Therefore, SCE concludes that this event was of low to no safety significance.
1 FACUTY NAME 6 LER NUMBER 2 DOCKET NUMBER PAGE (3) An assessment of the conditional core damage probability (CCDP) and the conditional large early release probability (CLERP) for the November 4, 2002 event, determined that the Unit 2 CCDP and CLERP were 3.4E-7 and 1.6E-8, respectively. The assessment was based on the reported actual component unavailability and system alignments at the time of the event.
Additional Information:
Spray valves have previously experienced galling in the anti-rotational device Design changes were implemented to correct this condition by removing the anti-rotation device from the internal bellows.