Information Notice 1995-30, Susceptibility of Low-Pressure Coolant Injection Valves to Pressure Locking

Susceptibility of Low-Pressure Coolant Injection Valves to Pressure Locking

ML031060273
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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	08/03/1995
From:	Crutchfield D Office of Nuclear Reactor Regulation
To:
References
IN-95-030, NUDOCS 9508030050
Download: ML031060273 (8)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 August 3, 1995 NRC INFORMATION NOTICE 95-30: SUSCEPTIBILITY OF LOW-PRESSURE COOLANT

INJECTION AND CORE SPRAY INJECTION VALVES

TO PRESSURE LOCKING

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purgose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to the potential susceptibility of boiling-water

reactor low-pressure coolant injection (LPCI) and core spray injection (CSI)

gate valves to pressure locking. It is expected that recipients will review

the information for applicability to their facilities and consider actions, as

appropriate, to avoid similar events or problems. However, suggestions

contained in this information notice are not NRC requirements; therefore, no

specific action or written response is required.

Description of Circumstances

From May to July 1995, Georgia Power Company, the licensee for the Edwin I.

Hatch Plant, experienced several valve failures in both units during testing

of its inboard LPCI 24-inch flexible-wedge gate valves. These failures, which

are still under investigation for root causes, involved shearing of the motor

shaft and the pinion key, and overheating of the motor. Surveillance testing

of the valves was conducted at power and the downstream check valve leakage

which resulted in the reactor operating pressure on one face of the valve, may

have contributed to the failures. During the investigation of the root causes

for these failures and in responding to the NRC staff's inquiries, the

licensee realized that because of backleakage of the downstream check valves, reactor system pressure could cause the LPCI valves to be susceptible to

pressure locking during an accident. (See Discussion section of this

information notice for a description of 'pressure locking.')

The licensee reevaluated the operability of the LPCI valves and of the core

spray injection 10-inch flexible-wedge valves because of their similar valve

alignment. The licensee determined that one LPCI valve might not be capable

of opening under pressure-locking conditions and declared this valve

inoperable. The licensee installed a larger motor and different gearing in

this valve. The licensee also made a similar modification to the valve

located in the other train.

9508030050

• jc

IN 95-30

August 3, 1995 Discussion

Pressure locking may occur in flexible-wedge and double-disk gate valves when

fluid becomes pressurized within the valve bonnet and the actuator is not

capable of overcoming the additional thrust requirements resulting from the

differential pressure acting across both valve discs. This situation can

occur, for example, when a check valve exposed to high reactor coolant

pressure is in series with a gate valve. The check valve may meet leakage

requirements, but, over time, the pressure in the piping between the check

valve and the gate valve can increase. With time, the bonnet cavity pressure

and the pipe pressure will tend to equalize at the reactor coolant pressure.

If a large loss-of-coolant accident (LOCA) occurred, the pressure in the

piping would be rapidly reduced. This occurrence would trap high-pressure

fluid in the bonnet cavity. If no internal or external path is provided to

lower the bonnet pressure, the valve may become pressure locked.

Pressure locking can cause a power-operated valve to fail to open, resulting

in an inability of the associated safety train or system to perform its safety

function. Pressure locking represents a potential common-cause failure

mechanism that can render redundant trains of multiple safety systems

incapable of performing their safety functions.

The NRC staff and the nuclear industry have been aware of pressure-locking

problems in gate valves for many years. The industry has issued several event

reports describing failures of safety-related gate valves to operate because

of pressure locking. Several generic industry communications have given

guidance for identifying susceptible valves and for taking appropriate

preventive and corrective measures.

The NRC staff has provided information on pressure locking of gate valves to

the industry and has discussed the safety significance of the potential for

pressure locking of gate valves at public meetings.

• In March 1993, the NRC issued NUREG-1275, Volume 9, "Operating

Experience Feedback Report-Pressure Locking and Thermal Binding of

Gate Valves," which contains a discussion of the potential for

pressure locking of LPCI and CSI valves when leakage past their

check valves pressurizes the valve bonnet.

• A summary of a public workshop held by the NRC staff on February

4, 1994, is available in the NRC Public Document Room (Accession

Number 9403020090). This summary contains information on

evaluation of the potential for pressure locking and the actions

taken in response to the identification of susceptible valves.

The workshop proceedings will be issued soon as NUREG/CP-0146.

o In Enclosure 1 to Supplement 6 (March 8, 1994) of Generic Letter

(GL) 89-10, "Safety-Related Motor-Operated Valve Testing and

Surveillance," the NRC staff described an acceptable approach for

licensees to address the potential for pressure locking of motor- operated gate valves as part of their GL 89-10 programs.

KJ IN 95-30

August 3, 1995 The power-operated valves in the LPCI and CSI lines are designed to serve a

vital safety-related function. During a postulated large-break LOCA, as well

as under some small-break LOCA scenarios, the opening of these valves is

relied upon to provide a flow path for cooling water to the reactor core. If

these valves are unable to open because of pressure locking (or some other

common-cause problem), reactor fuel might be damaged during a LOCA.

Entergy Operations, Inc., has developed a methodology to predict the thrust

required to overcome pressure locking of flexible-wedge gate valves. However, the methodology is based on limited pressure-lock testing. The Georgia Power

Company applied this methodology in p:edicting the thrust required to overcome

pressure locking of their LPCI and CSI valves as the best available

information at the time. The licensee is considering making modifications to

these valves during the next outage. The Georgia Power Company also found

that care must be taken in adapting the Entergy methodology to valves in each

case, particularly with regard to the valve-specific forces across the hub of

flexible-wedge gate valves.

The NRC staff will, in the near future, issue a generic letter that will ask

licensees to verify that they (1)have performed or will perform evaluations

and appropriate analyses and (2)will take appropriate corrective actions, as

necessary, to ensure that safety-related power-operated gate valves that may

be susceptible to pressure locking are capable of performing their required

safety functions. A draft of this generic letter, *Pressure Locking and

Thermal Binding of Safety-Related Power-Operated Gate Valves," was published

in the Federal Register on April 26, 1995, (60 FR 15799) along with a request

for public comment. The staff is issuing this information notice in advance

of the generic letter because of the high safety significance of this issue

and to indicate the susceptibility of the LPCI and CSI gate valves to pressure

locking.

Related Generic Communications

On April 2, 1992, the NRC staff issued NRC Information Notice (IN)92-26,

'Pressure Locking of Motor-Operated Flexible Wedge Gate Valves," which

discusses the failure of an LPCI valve at the James A. FitzPatrick Nuclear

Power Plant as a result of pressure locking following a hydrostatic pressure

test of the LPCI piping. IN 92-26 also referenced earlier NRC staff documents

on pressure locking.

Recently, the NRC staff issued IN 95-14 (February 28, 1995), "Susceptibility

of Containment Sump Recirculation Gate Valves to Pressure Locking," and IN 95-

18 (March 15, 1995) and Supplement 1 (March 31, 1995), "Potential Pressure

Locking of Safety-Related Power-Operated Gate Valves," to alert licensees to

potential pressure locking of pressurized-water reactor containment sump

recirculation valves and safety injection valves identified at the Millstone

Nuclear Power Station and the Haddam Neck Nuclear Plant, respectively.

K-" IN 95-30

August 3, 1995 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

.Crutc fiel irector

Division of Reactor rogram Management

Office of Nuclear Reactor Regulation

Technical contacts: Thomas G. Scarbrough, NRR

(301) 415-2794 Howard J. Rathbun, NRR

(301) 415-2787 Edward H. Girard, RII

(404) 331-4186 Attachment:

List of Recently Issued NRC Information Notices

Xt achment

IN 95-30

August 3, 1995 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

94-66, Overspeed of Turbine- 06/16/95 All holders of OLs or CPs

Supp. 1 Driven Pumps Caused by for nuclear power reactors.

Binding in Stems of

Governor Valves

95-29 Oversight of Design and 06/07/95 All holders of OLs or CPs

Fabrication Activities for nuclear power reactors.

for Metal Components Used

in Spent Fuel Dry Storage

Systems

95-28 Emplacement of Support 06/05/95 All holders of OLs or CPs

Pads for Spent Fuel Dry for nuclear power reactors.

Storage Installations at

Reactor Sites

95-27 NRC Review of Nuclear 05/31/95 All holders of OLs or CPs

Energy Institute, for nuclear power plants.

"Thermo-Lag 330-1 Combustibility Evaluation

Methodology Plant Screening

Guide'

95-26 Defect in Safety- 05/31/95 All holders of OLs or CPs

Related Pump Parts due for nuclear power reactors.

to Inadequate Heat

Treatment

94-61, Corrosion of William 05/25/95 All holders of OLs or CPs

Supp. 1 Power Gate Valve Disc for nuclear power reactors.

Holders

95-25 Valve Failure during 05/11/95 All U.S. Nuclear Regulatory

Patient Treatment with Commission Medical

Gamma Stereotactic Licensees.

Radiosurgery Unit

95-24 Summary of Licensed 04/25/95 All holders of OLs or CPs

Operator Requalification for nuclear power reactors.

Inspection Program

Findings

OL

0 Operating License

CP = Construction Permit

IN 95-30

August 3, 1995 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

orig /s/'d by DMCrutchfield

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Thomas G. Scarbrough, NRR

(301) 415-2794 Howard J. Rathbun, NRR

(301) 415-2787 Edward H. Girard, RII

(404) 331-4186 Attachment:

List of Recently Issued NRC Information Notices

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DOCUMENT NAME: 95-30. IN

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DATE 08/01/95 0 8 /01/ 95 08/01/95 08/01/95 08/01/95 OFFICE SC/EMEB:DE C/EMEB/DE lE RIj l PECB:DRPM

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OFFICIAl RECORD COPY

V IN 95-XX

August xx, 1995 This Information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Thomas G. Scarbrough, NRR

(301) 415-2794 Howard J. Rathbun, NRR

(301) 415-2787 Edward H. Girard, Region II

(404) 331-4186 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\IN\INHATCH.UD3

• See previous concurrence

To rcelve a cony of this document. Indicate In the box: AC = Copy without ettachmentlenclosure 'E' = Copy with attachmentjenclosure 'N' - No copy

OFFICE PECB:DRPM I ADM:PUB SC/PECB:DRPM EMEB:DE EMEB:DE

NAME TGreene* Tech Editor* RDennig* TScarbrough* HRathbun*

DATE 08/01/95 08/01/ 95 08/01/95 08/01/95 08/01/95 OFFICE SC/EMEB:DE I C/EMEB/DE I D/DE I RII I PECB:DRPM

NAME. TChan RWessman* BSheron* EGirard* RKiessel*

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OFFICIAL RECORD COPY

- ~IN 95-XX

August xx, 1995 Recently, the NRC staff issued IN 95-14 (February 28, 1995), Susceptibility

of Containment Sump Recirculation Gate Valves to Pressure Locking," and IN 95-

18 (March 15, 1995), and IN 95-18, Supplement 1 (March 31, 1995), "Potential

Pressure Locking of Safety-Related Power-Operated Gate Valves," to alert

licensees to potential pressure locking of pressurized-water reactor

containment sump recirculation valves and safety injection valves identified

at the Millstone Nuclear Power Station and the Haddam Neck Nuclear Plant, respectively.

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Thomas G. Scarbrough, NRR

(301) 415-2794 Howard J. Rathbun, NRR

(301) 415-2787 Edward H. Girard, Region II

(404) 331-4186 Attachment:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\IN\INHATCH.UD3

• See previous concurrence

To rocelve a copy of this document. bidicate Inth box: 'C' - C0m wfthout attachniemtlencloavme 'E = Crnow vith mlttahmann11flEnfttm P0 - W

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OFFICE ECB:DR AIF I f EMEB:DE EB

NAME TGreene Tech Editor* j TScarbrohg M HRathbun fge

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OFFICIAL RECORD COPY