05000362/LER-2002-002
| San Onofre Nuclear Generation Station (Songs) Units | |
| Event date: | 09-09-2002 |
|---|---|
| Report date: | 11-19-2002 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3622002002R00 - NRC Website | |
1 FACT JTY NAME San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 2 DOCKET NUMBER 05000-362 6 LER NUMBER PAGE (3) 2002 — 002 — Event Date: � September 9, 2002 Discovery Date: � September 24, 2002 Reactor Vendor Power (on 9/9/02) Power (on 9/24/02) Description of the Event.
Combustion Engineering 100 percent 100 percent Combustion Engineering 100 percent 100 percent On September 9, 2002 (event date), the Unit 3 Containment Emergency Fan Unit [BK] 3ME402 failed to start. The failure to start was traced to the breaker [BKR] installed in position 3B0611 (that powers 3ME402). The breaker was removed for evaluation and subsequent testing verified that the breaker would not close when given a close signal. On September 24, 2002, (discovery date) SCE concluded that the breaker had failed immediately after its last close operation on August 24, 2002.
Based on the specific failure mode (see the Additional Information section), SCE reviewed the performance history of the breaker installed in position 3B0611 and recognized that a similar period of inoperability of 3B0611 and 3ME402 may have existed from June 1, 2002, to June 29, 2002. As described in the Additional Information section, this breaker had functioned correctly on several occasions between May 7, 2002 and August 24, 2002.
TS 3.6.6.1 requires two trains of containment cooling to be operable when the plant is in Modes 1 through 3. With one containment cooling train inoperable, action "C" of TS 3.6.6.1 requires the inoperable train to be restored to operability within 7 days. Because containment emergency fan 3ME402 had been inoperable for longer than 7 days on a least one occasion, SCE is submitting this report in accordance with 10CFR50.73(a)(2)(i)(B) for a condition prohibited by the plant's Technical Specifications.
Cause of the Event:
The inoperability of 3ME402 was caused by the inability of the closing springs for breaker installed in position 3B0611 to fully charge through the end of the charge cycle. Asea Brown Boveri (ABB) addressed this failure mode in a 10CFR21 report sent to the Nuclear Regulatory Commission (NRC) on May 6, 2002.
Corrective Actions:
1. SCE replaced the operating mechanism for the failed breaker with a mechanism that is not susceptible to the failure mode discussed in the Part 21 notification.
On September 11, 2002, the breaker was reinstalled in position 3B0611 and 3ME402 was returned to service.
2. Additional actions planned in response to the Part 21 notification are described in the Additional Information section.
1 FACILITY NAME 6 LER NUMBER 2 DOCKET NUMBER PAGE (3) and 3 05000-362 2002 — 002 — 00
Safety Significance:
San Onofre has two trains of emergency containment cooling systems. Each train has one containment spray header (CS)[BE] and two loops of containment emergency coolers. Thus, there are six individual components between Train A and Train B that can provide post accident containment cooling as follows:
Train A Train B 1) Containment Spray Pump P012 4) Containment Spray Pump P013 2) Emergency Cooler E399 5) Emergency Cooler E400 3) Emergency Cooler E401 6) Emergency Cooler E402 Best estimate calculations completed for Edison's Individual Plant Examination (IPE) concluded that any one of the above six components is sufficient to ensure containment pressure and temperature limits can be maintained. The increased core damage and large, early release risk due to 3ME402's inoperability was calculated to be 4.8E-7 and 2.6E-8, respectively. This calculation was based on actual component unavailability and plant operations when 3ME402 was inoperable (between August 24, 2002 and September 9, 2002), and when 3ME402 may have been inoperable (between June 1, 2002 and June 29, 2002). Therefore, SCE concludes that this event was of low safety significance.
Additional Information:
- In the last two years, there have been no previous events involving the same underlying cause as this event.
- ABB Part 21 Notification:
On May 06, 2002, ABB provided to the NRC a Part 21 Notification for K-Line mechanism failures to charge and close on demand. ABB indicated that this failure mode may exist in K-Line circuit breakers manufactured or having undergone mechanism repair, refurbishment or replacement between January 1, 1988 and December 31, 1998 and recommended utilities address this issue at the next available maintenance interval.
In response to the Part 21 report, SCE reviewed plant records and following verification by ABB, determined that there are 23 breakers of this type installed in safety-related applications in Units 2 and 3. SCE has replaced 5 of these breakers and the remaining breakers are planned for either replacement of the operating mechanism or change out with a breaker not susceptible to this failure mode.
6 LER NUMBER PAGE (3) 1 FACILITY NAME San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 05000-362 2002 — 002 -- 00
- Evaluation of 3B0611 The breaker installed in position 3B0611 was overhauled on December 7, 2001 and installed in position 3B0611 on May 7, 2002. On June 29, 2002, 3B0611 failed to close during surveillance testing for 3ME402. Investigation revealed a secondary contact wire was pinched. Following the wire replacement, the breaker was successfully cycled three times. Because SCE considered that the cause of the failure had been identified and corrected, the breaker was not removed for analysis. 3ME402 was started successfully on June 1, 2002, July 28, 2002 and August 24, 2002.