Information Notice 1988-37, Flow Blockage of Cooling Water to Safety System Components

Flow Blockage of Cooling Water to Safety System Components
	ML031150292
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	06/14/1988
From:	Rossi C; Office of Nuclear Reactor Regulation
To:	;
References
	IN-88-037, NUDOCS 8806080025
	Download: ML031150292 (10)
	v • d • e

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 June 14, 1988 NRC INFORMATION NOTICE NO. 88-37: FLOW BLOCKAGE OF COOLING WATER TO

SAFETY SYSTEM COMPONENTS

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is being provided to alert addressees to a potentially

generic problem involving flow blockage in safety-related piping interconnec- tions due to blofouling. This condition may occur and not be detected due to

stagnant water in system interconnecting piping which is not routinely flushed

or flow tested. The event described highlights the importance of maintaining

these lines free of clams, corrosion, and other foreign material. It is ex- pected that recipients will review the information for applicability to their

facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this information notice do not constitute

NRC requirements; therefore, no specific action or written response is required.

Description of Circumstances

On March 9, 1988, Catawba Unit 2 tripped from 20 percent power as the unitAswas

the

returning to full-power operation following the first refueling outage.

feedwater regulating valves were being placed in automatic, the B steam gener- ator (SG) feedwater regulating valve failed open. This caused a feedwater swing,ter

and, after the operator assumed manual control of the B steam generator feedwa

regulating valve, a high-high level in the D SG, which resulted in a main turbine

trip, a main feedwater isolation, and a main feedwater pump trip.

The Catawba auxiliary feedwater (AFW) system is safety grade, designed to start

automatically in the event of loss-of-offsite power, trip of gain feedwater

pumps, a safety injection signal, or low-low SG level. Three AFW pumps are

provided, powered from separate and diverse power sources. Two motor-driven

pumps are powered from two separate trains of emergency onsite electrical

power, each normally supplying two SGs. A turbine driven AFW pump is driven

by steam generated from either of twc SGs. The condensate storage system is

utilized for normal AFW supply and includes the main condenser hotwell, two

upper surge tanks per unit, and a shared AFW condensate storage tank (CACST).

however. the condensate storage system is not safety grade. Therefore, the

safety grade nuclear service water (PSW) system proviGes an assured backup

IN 88-37 June 14, 1988 water supply. The NSW system is supplied from either Lake Wylie or the standby

nuclear service water pond (SNSWP). In the event of partial or complete loss

of the condensate storage supply, as sensed by two out of three indications of

low suction pressure from any train, automatic swapover to the NSW system is

provided. The NSW system also provides assured makeup to several other systems, including the fuel pool cooling and component cooling systems.

Both motor-driven auxiliary feedwater (AFW) pumps automatically started upon

loss of the main feedwater pumps. An A train AFW pump low suction pressure

resulted in the automatic swapover of train A AFW pump suction from condensate

grade water to nuclear service water (NSW) causing valves RN 250A and CA 15A

to open. The attached Figure 1 provides a schematic of the AFW flow paths prior

to suction flow swapover, while Figure 2 provides the flow paths after swapover.

The A train AFW pump normally supplies AFW to SGs A and S. Meanwhile, levels in

SGs A and B were dropping. The low-low level set point was reached in SG A and

a reactor trip occurred. Approximately 13 minutes into the event, the operator

noted that the NSW valve to the AFW system (RN 250A) had opened. The valve was

closed immediately. However, at that time it was not noted that the A train AFW

pump suction line valve from the NSW system (CA 15A) also had opened and that

NSW had therefore been pumped into SGs A and B.

Approximately 20 minutes into the event, It was noted that the SG B level was

decreasing. Initial AFW flow had been normal (300 gpm per SG), but had de- graded to approximately 200 gpm to SG A and 100 gpm to SG B. The flow control

valve to SG A was fully open at this time. During shift turnover, approximately

35 minutes into the event, the oncoming shift found that valve CA 15A had also

opened. The main feedwater pumps were then restarted and the AFW system placed

on standby. Actions were Initiated to disassemble and inspect the AFW flow

control valves. When the A and B SG AFW flow control valves were disassembled, it was determined that the valves were clogged with Asiatic clam shells.

Discussion:

Fouling of service water systems has been recognized for some time as having

the potential for compromising system operability. Information Notice 81-21,

"Potential Loss of Direct Access to Ultimate Heat Sink," and Bulletin 81-03,

"Flow Blockage of Cooling Water to Safety System Components by Corbicula Sp.

(Asiatic Clam) and yjt1lus Sp. (Mussel)," Issued by the NRC Office of Inspection

and Enforcement (I ) addressed the potential for fouling of safety-related heat

exchangers by Asiatic clams, mussels, and debris from other shell fish. Infor- mation Notice 86-96, "Heat Exchanger Fouling Can Cause Inadequate Operability

of Service Water Systems," addressed similar fouling problems from buildup of

mud, silt, and corrosion in NSW piping. The AFW flow control valves at Catawba

have an anti-cavitation trim that can collect particles of clam shells and may

thus exacerbate flow degradation from fouling.

Duke Power Company has in place several programs and practices designed to

verify PSW flow to various systems and components. These include (i) periodic

flow balancing of the NSW system, (2)testing to verify heat transfer capability

of essertial heat exchangers served by the NSV! system, (3) periodic cleaning of

IN 88-37 June 14, 1988 heat exchangers based on differential pressure indications and. 4) visual exami- nation of heat exchangers and related piping during cleaning for the presence

of clams and unusual fouling conditions. Previous Inspection of the NSW system

dead leg piping for clams consisted of spot radiographic (RT) inspection of low

spots in the piping between the NSW and AFW systems. None of the RT inspections

revealed any clams. The valves in the NSW/AFW suction swapover lines had been

periodically stroke tested, but no flow through the lines was established.

As a result of the Catawba Unit 2 AFW swapover from condensate to NSW and the

introduction of raw NSW containing clams into the AFW system, Duke Power Company

initiated a program of flushes and inspections of dead legs between the NSW system

and various safety-related systems. The NSW system flushes and inspections per- formed included the NSW backup supply to AFW system piping, NSW emergency makeup

to component cooling system piping, and NSW backup to penetration valve injection

piping. Flushing also was planned on the NSW emergency makeup to spent fuel pool

cooling piping. Spot radiographic inspection indicated the presence of clams in

the piping to the component cooling and spent fuel pool cooling piping prior to

flushing. These locations were not previously radiographed.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact one of the techni- cal contacts listed below or the Regional Administrator of the appropriate NRC

regional office.

Charles E. Rss Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Thomas Peebles, RII

(404) 331-4196 Brian Bonser, RI!

(404) 331-4198 W. Lefave, NRR

(301) 492-0862 Attachment: List of Recently Issued NRC Information Notices

FIGURE 1 CATAWBA NUCLEAR STATION

AUXILIARY FEEDVATER

SYSTEA~

L

V 'tRAN 1SV

TRAIN

00' TRIN SVTCE

lVATER

t I

FIGURE 2 CATAWBA NUCLEAR STATION

AUXILIARY FEEDVATER

SYSTEA'

K; sa

3IER VATE

Attachment

IN 88-37 June 14, 1988 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

88-36 Possible Sudden Loss of RCS 6/8/88 All holders of OLs

Inventory During Low Coolant or CPs for PWRs.

Level Operation

88-35 Inadequate Licensee Performed 6/3/88 All holders of OLs

Vendor Audits or CPs for nuclear

power reactors.

88-34 Nuclear Material Control 5/31/88 All holders of OLs

and Accountability of or CPs for nuclear

Non-Fuel Special Nuclear power reactors.

Material at Power Reactors

87-61, Failure of Westinghouse 5/31/88 All holders of OLs

Supplement 1 W-2-Type Circuit Breaker or CPs for nuclear

Cell Switches power reactors.

88-33 Recent Problems Involving 5/27/88 All Agreement States

the Model Spec 2-T and NRC licensees

Radiographic Exposure authorized to manu- Device facture, distribute

or operate radio- graphic exposure

devices and source

changers.

88-32 Promptly Reporting to 5/25/88 All NRC material

NRC of Significant licensees.

Incidents Involving

Radioactive Material

88-31 Steam Generator Tube 5/25/88 All holders of OLs

Rupture Analysis or CPs for Westinghouse

Deficiency and Combustion

Engineering-designed

nuclear power plants.

88-30 Target Rock Two-Stage 5/25/88 All holders of OLs

SRV Setpoint Drift or CPs for nuclear

Update power reactors.

OL = Operating License

CP = Construction Permit

IN 88-37 June 14, 1988 heat exchangers based on differential pressure indications and, 4) visual exami- nation of heat exchangers and related piping during cleaning for the presence