05000362/LER-2002-003
| San Onofre Nuclear Generation Station (Songs) Unit 3 | |
| Event date: | 10-16-2002 |
|---|---|
| Report date: | 12-11-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3622002003R00 - NRC Website | |
1 FACILITY NAME 6 LER NUMBER 2 DOCKET NUMBER PAGE (3) t Combustion Engineering Plant:
Reactor Vendor Event Date:
Event Time:
Mode Power (percent):
BACKGROUND:
October 16, 2002 0152 PDT 1 100 San Onofre Unit 3 has two turbine driven Main Feedwater Pumps (MFWP). Each pump normally provides about 50 percent of full-load feedwater flow to the two steam generators. A separate lube oil support system provides bearing oil, hydraulic oil, and control oil for each of the two MFWP/MFWPTs. Each lube oil system contains three pumps (2 AC, 1 DC). The AC-powered lube oil pumps can supply 100 percent of required oil. Typically, one AC-powered lube oil pump is in service with the other AC-powered pump serving as a standby that will start automatically if needed. This auto start feature is periodically tested locally. The DC pump auto-starts on low bearing oil pressure or loss of both AC pumps.
DESCRIPTION OF THE EVENT:
Early, on October 16, 2002, Unit 3 was at 100% power and plant operators (Utility, licensed and unlicensed) were conducting MFWPT protective device testing in accordance with procedure S023-2-1.1. During this work, operators performed an auto-start test of the standby Lube Oil Pump P109 for MFWPT K006. After confirming operation of both AC-powered lube oil pumps, at tripped. In accordance with plant Abnormal Operating Instruction (A01) S023-13-24, plant operators manually actuated the Emergency Feedwater Actuation System (EFAS). All three Auxiliary Feedwater (AFW) pumps started and provided feedwater to both Steam Generators (SG). Plant operators also initiated a power reduction to approximately 75% power in accordance with the A01. This action allowed operators to secure feeding both steam generators by AFW at 0157, five minutes into the transient. At 0218, operators reset EFAS.
AT 0902 PDT on October 16, 2002, Southern California Edison (SCE) made an 8-hour telephone notification to the NRC Operations Center (Log No. 39292) in accordance with 10CFR50.72(b)(3)(iv)(A) for a valid Engineered Safety Features (ESF) actuation of EFAS. SCE is providing this 60-day follow up report in accordance with 10CFR50.73(a)(2)(iv)(A).
6 LER NUMBER PAGE (3) 1 FAC1_ITY NAME 2 DOCKET NUMBER 05000-362 2002 — 003 — 00
CAUSE OF THE EVENT:
Based on engineering judgment, SCE believes that there are two possible causes of the MFWPT trip:
1. A spurious trip occurred due to an inadequately latched turbine trip reset mechanism, or 2. A low oil pressure condition occurred due to a malfunctioning oil pressure regulator or check valve.
Either of these conditions would have resulted in the observed MFWPT trip.
SCE's investigation is ongoing. To complete the cause evaluation, the MFWPT lube oil system and associated control systems will require disassembly. This work is planned for the next scheduled refueling outage (January, 2003). SCE will complete the cause evaluation and implement appropriate corrective actions at that time. A supplemental LER will be submitted if the cause is significantly different than noted above.
CORRECTIVE ACTIONS:
Pending identification and repair of malfunctioning component(s), the MFWPT AC lube oil pump auto-start tests for all MFWPTs have been suspended (Unit 2 and Unit 3). Additionally, the on-line lockout and trip exercise testing for MFWPT K006 has been suspended.
SAFETY SIGNIFICANCE:
The MFWPs are not essential for safe shutdown of the plant. The SONGS 2/3 UFSAR, Sections 15.2.2.5 and 15.10.2.2.5, credits the AFW system for maintaining an adequate heatsink during a transient in which an instantaneous and complete loss of feedwater occurs. The event reported herein, where one feedwater pump was lost and all safety systems functioned correctly is bounded by the UFSAR safety analysis identified above. Therefore, SCE concludes that this event was of very low to no safety significance.
ADDITIONAL INFORMATION.
In the past three years, SCE has not reported any ESF actuations that resulted from feedwater transients.