Information Notice 1995-18, Potential Pressure-Locking of Safety-Related Power-Operated Gate Valves

Potential Pressure-Locking of Safety-Related Power-Operated Gate Valves
	ML031060248
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:	03/15/1995
From:	Grimes B; Office of Nuclear Reactor Regulation
To:	;
References
	IN-95-018, NUDOCS 9503140317
	Download: ML031060248 (11)
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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 March 15, 1995 NRC INFORMATION NOTICE 95-18: POTENTIAL PRESSURE-LOCKING OF SAFETY-RELATED

POWER-OPERATED GATE VALVES

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

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

notice (IN)to alert addressees to a recent analysis demonstrating the

potential susceptibility of safety injection valves to pressure-locking. It is

expected that recipients will review this additional information for

applicability to their facilities and consider actions, as appropriate, to

avoid similar problems. However, suggestions contained in this information

notice are not NRC requirements; therefore, no specific action or written

response is required.

Background

IN 95-14, 'Susceptibility of Containment Sump Recirculation Gate Valves to

Pressure Locking," dated February 28, 1995, was written in response to the

determination by the licensee of the Millstone Nuclear Power Station that both

of the Unit 2 containment sump recirculation motor-operated gate valves may

experience pressure-locking during a design-basis loss-of-coolant accident

(LOCA) and fail to open. The failure of both of these valves would make a

water source for the emergency core cooling system and the containment spray

unavailable during the recirculation phase of the LOCA. The circumstances at

Haddam Neck discussed in this supplement were identified as a result of

licensee action in response to this previous Millstone determination.

Description of Circumstances

On March 9, 1995, the Connecticut Yankee Atomic Power Company reported that

seven motor-operated gate valves in the safety injection systems at the Haddam

Neck Nuclear Power Plant were susceptible to pressure-locking to the extent

that the operability of valves may have been jeopardized. These

susceptibilities were detailed as follows:

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9503140317 I

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I , A- ' IN 95-18 March 15, 1995 1. Four high-pressure safety injection admission valves (SI-MOV-861A

through 861D; see Attachment 1).

These normally closed valves are susceptible to pressure-locking

following a postulated LOCA in which the pressure in the reactor coolant

system (RCS) drops substantially before the safety injection actuation

signal initiates the opening of the valve. These valves are also

susceptible tc pressure locking caused by the heating of fluid captured

in the valve bonnet when the valves are stroked during the startup of

the plant.

2. Two low-pressure safety injection admission valves (SI-MOV-871A and

871B; see Attachment 2).

These normally closed safety injection valves are susceptible to

pressure-locking following a postulated LOCA where the pressure in the

RCS drops substantially before the safety injection actuation signal

initiates the opening of the valve.

3. One common low-pressure safety injection isolation valve (SI-MOV-873;

Attachment 2).

This normally open valve would be closed during transfer to the

recirculation mode following a LOCA if either SI-MOV-871A or B failed to

close. Once this isolation valve was closed, it would be susceptible to

pressure-locking as a result of temperature increase of fluid in the

bonnet caused by high containment temperature. This condition could

prevent the reopening of the valve should it be required for entrance

into the two-path long term recirculation mode.

The Haddam Neck plant has been shut down for refueling since January 28, 1995.

The licensee plans to modify the susceptible valves before restarting the

plant. A modification being considered includes venting both the bonnet space

and the packing gland seal leakoff back to the RCS to prevent pressure- locking. In addition, the licensee is considering procedural changes to

minimize valve unseating forces.

Discussion

The licensee had previously evaluated these valves for possible pressure- locking and thermal-binding and had concluded that the valves were not

susceptible to these problems. However, recent diagnostic testing has shown

that the friction coefficients, the unseating forces, and the methodology

previously used were nonconservative. The reexamination of the analysis by

the licensee, using the test results, indicated that these valves may become

inoperable due to pressure-locking problems.

As noted in IN 95-14, the NRC staff and the nuclear industry have been aware

of disk binding problems of gate valves for many years. The industry has

issued several event reports describing the failure of safety-related gate

valves to operate because of pressure-locking or thermal-binding of the valve

, IN 95-18 March 15, 1995 disks. Several generic industry communications have given guidance for both

identifying susceptible valves and performing appropriate preventive and

corrective measures. In Enclosure 1 to Supplement 6 of Generic Letter 89-10,

Safety-Related Motor-Operated Valve Testing and Surveillance,* dated March 8,

1994, the NRC staff discussed pressure-locking and thermal-binding of motor- operated gate valves.

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

when fluid entrapped in the bonnet becomes pressurized and the actuator is

incapable of overcoming the additional thrust requirements needed to overcome

the increased friction resulting from the differential pressure on both valve

disks from the pressurized fluid. IN 95-14 discusses several of ways in which

fluid may enter the valve bonnet. Thermal binding of gate valves can result

from contraction of a valve body as a result of cooling after a gate valve has

seated. Like pressure locking, thermal binding can increase the forces that

are necessary to unseat the valve. These mechanisms represent potential

common-cause failure modes that can render redundant trains of safety-related

emergency core cooling systems incapable of performing their safety functions.

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.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts: Thomas Scarbrough, NRR

(301) 415-2794 Donald Kirkpatrick, NRR

(301) 415-1849 Attachments:

1. Haddam Neck High Pressure Safety Injection

2. Haddam Neck Low Pressure Safety Injection and Heat Removal System

3. List of Recently Issued NRC Information Notices

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Haddam Neck Low Pressure Safety Injection (LPI) and

Residual Heat Removal (RHR) Systems

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K>iAttachment 3 IN 95-18 March 15, 1995 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

95-17 Reactor Vessel Top Guide 03/10/95 All holders of OLs or CPs

and Core Plate Cracking for boiling water reactors.

95-16 Vibration Caused by 03/09/95 All holders of OLs or CPs

Increased Recirculation for boiling water reactors.

Flow in a Boiling Water

Reactor

95-15 Inadequate Logic Testing 03/07/95 All holders of OLs or CPs

of Safety-Related Circuits for nuclear power reactors.

95-14 Susceptibility of Con- 02/28/95 All holders of OLs or CPs

tainment Sump Recircula- for nuclear power reactors.

tion Gate Valves to

Pressure Locking

95-13 Potential for Data 02/24/95 All holders of OLs or CPs

Collection Equipment to for nuclear power reactors.

Affect Protection System

Performance

95-12 Potentially Nonconforming 02/21/95 All holders of OLs or CPs

Fasteners Supplied by for nuclear power reactors.

A&G Engineering II, Inc.

95-11 Failure of Ccndensate 02/24/95 All holders of OLs or CPs

Piping Because of Erosion/ for nuclear power reactors.

Corrosion at a Flow- Straightening Device

95-10 Potential for Loss of 02/10/95 All holders of OLs or CPs

Supp. 1 Automatic Engineered for nuclear power reactors.

Safety Features

Actuation

95-10 Potential for Loss of 02/03/95 All holders of OLs or CPs

Automatic Engineered for nuclear power reactors.

Safety Features

Actuation

OL - Operating License

CP - Construction Permit

IN 95-18 March 15, 1995 susceptible valves and performing appropriate preventive and corrective

measures. In Enclosure 1 to Supplement 6 of Generic Letter 89-10, "Safety- Related Motor-Operated Valve Testing and Surveillance," dated March 8, 1994, the NRC staff discussed pressure-locking and thermal-binding of motor-operated

gate valves.

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

when fluid entrapped in the bonnet becomes pressurized and the actuator is

incapable of overcoming the additional thrust requirements needed to overcome

the increased friction resulting from the differential pressure on both valve

disks from the pressurized fluid. IN 95-14 discusses several ways in which

fluid may enter the valve bonnet. Thermal binding of gate valves can result

from contraction of a valve body as a result of cooling after a gate valve has

seated. Like pressure locking, thermal binding can increase the forces that

are necessary to unseat the valve. These mechanisms represent potential

common-cause failure modes that can render redundant trains of safety-related

emergency core cooling systems incapable of performing their safety functions.

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. original signed by

Brian K. Grimes

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts: Thomas Scarbrough, NRR

(301) 415-2794 Donald Kirkpatrick, NRR

(301) 415-1849 Attachments:

1. Haddam Neck High Pressure Safety Injection

2. Haddam Neck Low Pressure Safety Injection and Heat Removal System

3. List of Recently Issued NRC Information Notices

DOCUMENT NAME: 9514SP1.IN *See previous concurrence

OFFICE OECB:DOPS ADM:PUB SC/OECB:DOPS EMEB:DE C:SRXB/DSSA

NAME DKirkpatrick* Tech Editor* EGoodwin* TScarbrough* RCJones*

DATE 03/13/95 03/13/95 03/14/95 03/14/95 03/14/95

. . _, , .

OFFICE IC/EMEB:DE IOECB:DOPS IC/OECB:DOPS IEMEB:DE

NAME RWessman* RKiessel* AChaffee*- PChen* ,

DATE 03/14/95 03/14/95 03/ 14 /95 1 03/14/95 1 03/// /95 OFFICIAL RECORD COPY

IN 95-14, Supp. 1 March xx, 1995 susceptible valves and performing appropriate preventive and corrective

measures. In Enclosure 1 to Supplement 6 of Generic Letter 89-10, "Safety- Related Motor-Operated Valve Testing and Surveillance,' dated March 8, 1994, the NRC staff discussed pressure-locking and thermal-binding of motor-operated