05000362/LER-2004-001, Manual Reactor Trip Due to Sea Grass at Intake Structure

Manual Reactor Trip Due to Sea Grass at Intake Structure

ML041900070
Person / Time
Site:	San Onofre
Issue date:	07/02/2004
From:	Waldo R Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 04-001-00
Download: ML041900070 (4)

LER-2004-001, Manual Reactor Trip Due to Sea Grass at Intake Structure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3622004001R00 - NRC Website

text

SOUTHERN CALIfORNIA EDISONt An EDISON INTERNATIONVtLt Company Dr. Ravmond WV.

Waldo Station Manager San Onofre July 2, 2004 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555-0001

Subject:

Docket No. 50-362 Licensee Event Report No. 2004-001 San Onofre Nuclear Generating Station, Unit 3 Gentlemen:

This submittal provides Licensee Event Report (LER) San Onofre Nuclear Generating Station, Unit 3 2004-001 for a manual trip of Unit 3 due to degraded circulating water pump suction resulting from heavy influx of sea grass.

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,

, 4JX LER No. Unit 3 2004-001 cc:

B. S. Mallett, NRC Regional Administrator, Region IV C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 & 3 P.O. Box 128 San Clemente, CA 92672-0128 949-368-8725/PAX 88725 Fax 949-368-6183 waldorwvsongs.sce.com 4,lt

Abstract

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.U.S. NUCLEAR REGULATORY COMMISSION (7-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION

1. FACILTY NAME

2. DOCKET NUMBER I.

LER NUMBER PAGE 3 S

No SEOUENTIAL 00 2f San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 NUMBER RENO2o3 1 2004 1-001 -

00 2o Plant:

San Onofre Nuclear Generating Station (SONGS) Unit 3 Event Date:

June 4, 2004 Reactor Vendor:

Combustion Engineering Mode:

Mode I - 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 [SCN]

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 [RCT].

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) [Jl] 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.U.S. NUCLEAR REGULATORY COMMISSION (7-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION L. LER NUMBER PAGE (3)

San SENUENTIAL REV NO San Onofre Nuclear Generating Station (SONGS) Unit 3 05000-362 NL)MBER 13 of 3 I

2004 1-001 -

I00

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 Sectionsl5.2.1.3 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

Additional Information

In the recent past, SCE has not reported reactor trips resulting from degraded circulating water pump suction or loss of condenser vacuum.