| 07-02-2004 | On June 4, 2004, at 0445 PDT, plant operators manually tripped the Unit 3 reactor due to degraded circulating water pump suction caused by heavy influx of sea grass across the traveling screens during very low tide conditions. At the time of the reactor trip, Unit 3 was at approximately 80 percent power.
Safety systems responded as expected.
Southern California Edison (SCE) reported this event to the NRC Operations Center (Log No. 40791) at 0821 EDT in accordance with 10 CFR 50.72(b)(2)(iv)(B) for actuation of the Reactor Protection System (RPS) [JC]. This follow-up Licensee Event Report is provided in accordance with 10 CFR 50.73(a)(2)(iv)(A).
A traveling screen panel was repaired and broken shear pins replaced. The traveling screen system was tested and returned to service.
Circulating water pumps are not essential for safe shutdown of the plant and do not provide a safety function.
The SONGS 2/3 UFSAR Sections 15.2.1.3 and 15.10.2.1.3 credit the Auxiliary Feedwater System and ADVs for maintaining an adequate heatsink during a transient in which an instantaneous and complete loss of condenser vacuum occurs. Therefore the event reported herein is bounded by the UFSAR safety analysis identified above. |
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Event Date: June 4, 2004 Reactor Vendor: Combustion Engineering Mode: Mode 1 — Power Operation Power: 100 percent
Description of Event
On June 4, 2004, Unit 3 was operating at 100 percent power. Around 0400 PDT, plant operators (utility, licensed) noticed increasing differential pressure across the intake traveling screens [SON] and received a high differential pressure alarm. At 0434, the resulting reductions in circulating water pump [P] suction pressure required operators to begin reducing reactor power. At 0435, operators secured one circulating water pump. Circulating water pump suction continued to degrade as indicated by circulating pump amperage, which began fluctuating. At 0445, with the Unit at approximately 80 percent power, operators manually tripped the reactor [ROT].
Southern California Edison (SCE) reported this event to the NRC Operations Center (Log No. 40791) at 0821 EDT in accordance with 10 CFR 50.72(b)(2)(iv)(B) for actuation of the Reactor Protection System (RPS) [JC]. This follow-up Licensee Event Report is provided in accordance with 10 CFR 50.73(a)(2)(iv)(A).
After the reactor trip, the steam bypass control system (SBCS) [JI] permissive channel began operating erratically. Approximately fourteen minutes after the trip, Operators switched from full auto SBCS operation to atmospheric dump valves (ADVs) [V] to remove decay heat. This action is in accordance with operation procedures and operator training. The SBCS issue was determined to be unrelated to the sea grass influx event.
SONGS Unit 2 was unaffected by this event. The Unit 2 intake conduit structure is located separately from the Unit 3 intake conduit and was not impacted by heavy influx of sea grass.
Unit 3 Salt Water Cooling system was unaffected by this event.
Cause of the Event
Plant operators manually tripped the reactor due to degraded circulating water pump suction caused by heavy influx of sea grass across the traveling screens during very low tide conditions.
Traveling rakes and screens are intended to prevent debris from entering the circulating water pumps and the shear pins provide overload protection to the screens. During this event, the rakes and screens were unable to keep up with the unusually heavy influx of sea grass and, as designed, shear pins broke and the screens ceased to operate.
Corrective Actions
1. SCE repaired a traveling screen panel [PL] and replaced broken shear pins. The system was tested and returned to service.
2. The SBCS permissive controller was replaced. The system was tested and returned to service.
3. SCE will review operations procedures and training to determine if enhancements can be made in response to similar events.
4. SCE will review design changes to the current traveling screen system to determine if upgrades are warranted.
Safety Significance
Circulating water pumps are not essential for safe shutdown of the plant and do not provide a safety function. The SONGS 2/3 UFSAR Sections15.2.1.3 and 15.10.2.1.3 credit the Auxiliary Feedwater System and ADVs for maintaining an adequate heatsink during a transient in which an instantaneous and complete loss of condenser vacuum occurs. Therefore the event reported herein is bounded by the UFSAR safety analysis identified above and is of low to no safety significance.
Additional Information
In the recent past, SCE has not reported reactor trips resulting from degraded circulating water pump suction or loss of condenser vacuum.
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| 05000362/LER-2004-001 | Manual Reactor Trip Due to Sea Grass at Intake Structure | 10 CFR 50.73(a)(2)(iv)(A), System Actuation | | 05000362/LER-2004-002 | Station ManagerEDISON' San Onofre
An EDISON INTERNATIONALS Company
May 8, 2006
U.S. Nuclear Regulatory Commission
Document Control Desk
Washington, D.C. 20555-0001
Subject:DDocket Nos. 50-362
Licensee Event Report No. 2004-002-01
San Onofre Nuclear Generating Station, Unit 3
Reference: Raymond Waldo (SCE) letter to NRC Document Control Desk, "Licensee
Event Report No. 2004-002", dated August 9, 2004.
Dear Sir or Madam:
In the letter referenced above, SCE provided a Licensee Event Report (LER) in
accordance with 10CFR50.73(a)(2)(i)(B) to report violations of Technical Specifications
due to an incomplete post-maintenance calibration of Logarithmic Power Level-High
Channel "A". When this LER was first submitted, SCE's cause evaluation was in
progress. SCE is revising this LER to incorporate the updated findings from the cause
evaluation.
Any actions listed are intended to ensure continued compliance with existing
commitments as discussed in applicable licensing documents; this LER contains no new
commitments. If you require any additional information, please so advise.
Sincerely,
a-sLi
LER No. 3-2004-002-01
cc: B. S. Mallet NRC Regional Administrator, Region IV
C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 & 3
P.O. Box 128
San Clemente, CA 92674-0128
949-368-9263/PAX 89263
Fax 949-368-6183
breigdp@songs.sce.com
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(7-2001) COMMISSION Estimated burden per response to comply with this mandatory information collection request: 50 hours.
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1. FACILITY NAME 2. DOCKET NUMBER 3. PAGE
San Onofre Nuclear Generating Station (SONGS) Unit 3 05000362 1 OF 3
4. TITLE
Incomplete post-maintenance calibration of Logarithmic Power Level-High Channel "A" results in Technical
Specification Violations. | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications | | 05000361/LER-2004-003 | | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
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