Information Notice 1995-14, Susceptibility of Containment Sump Recirculation Gate Valves to Pressure Locking

Susceptibility of Containment Sump Recirculation Gate Valves to Pressure Locking

ML031060320
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, 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, Crane
Issue date:	02/28/1995
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-95-014, NUDOCS 9502270218
Download: ML031060320 (8)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555-0001

February 28, 1995

NRC INFORMATION NOTICE 95-14:

SUSCEPTIBILITY OF CONTAINMENT SUMP

RECIRCULATION GATE VALVES TO PRESSURE LOCKING

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 to alert addressees to the potential susceptibility of containment sump

recirculation gate valves to pressure locking at nuclear plants.

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

On January 26, 1995, Northeast Nuclear Energy Co., the licensee for Unit 2 of

the Millstone Nuclear Power Station, determined that both containment sump

recirculation motor-operated gate valves may experience pressure locking

during a design-basis loss-of-coolant accident (LOCA) and fail in the closed

position.

This condition was discovered by the licensee after re-evaluation

of all Unit 2 valves to address weaknesses in their previous evaluation

criteria identified by the NRC Motor-Operated Valve Inspection at Millstone

Unit 1 in March 1994.

At Millstone Unit 2, failure of both of these valves

would make a water source for the emergency core cooling system (ECCS) and

containment spray unavailable during the recirculation phase of the LOCA (the

recirculation phase occurs not sooner than about 45 minutes after the start of

an event).

Millstone Unit 2 is a pressurized water reactor with two containment sump

recirculation valves (one in each of two parallel paths).

The sump piping

paths join piping from the refueling water storage tank (RWST) leading to low

pressure safety injection pump suction.

The Millstone Unit 2 containment sump

recirculation valves are parallel-wedge gate valves that are normally closed, leaving the containment sump side of the valve dry and exposed to the

containment.

The pump side of each valve is normally pressurized to

approximately 345 kPa [35 psig] due to the static head of the RWST.

The RWST

water may leak past the pumpside gate valve disc and may fill the valve bonnet

with water.

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IN 95-14 February 28, 1995 During a postulated LOCA at Millstone Unit 2, the sump side of each

containment sump recirculation valve could be exposed to sump water (reactor

coolant) with temperatures as high as 143 'C [289 OF] for some time prior to

the valve being required to open to allow ECCS and containment spray

recirculation cooling. Heating of the valve could heat the water trapped in

the water-filled valve bonnet. A pressure increase of 410 kPa per 0C [33 psi

per OF] is predicted.

The licensee has determined that a bonnet pressure of

1138 kPa [150 psig] (requiring only about a 3 'C [5 OF] temperature rise in a

water solid bonnet) may prevent the valve from opening.

Therefore, it might

not be possible to establish recirculation cooling following a LOCA.

Millstone Unit 2 has been in a cold shutdown condition since October 1994.

The licensee is considering various modifications to the valves to prevent

pressure locking to be implemented prior to restart.

Discussion

Pressure locking may occur in flexible-wedge and parallel-wedge 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 created across both valve discs by the pressurized

fluid.

For example, the fluid may enter the valve bonnet (1) during normal

open and close valve cycling, (2) when a fluid differential pressure across a

disc causes the disc to move slightly away from the seat, creating a path to

either increase the fluid pressure or fill the bonnet with fluid, or (3) for a

steamline valve, when differential pressure exists across the disc and the

valve orientation permits condensate to collect and enter the bonnet.

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 mode

that can render redundant trains of certain safety-related systems or multiple

safety systems incapable of performing their safety functions.

The industry has issued several event reports describing safety-related gate

valves failing to operate because of pressure locking.

Several generic

industry communications have given guidance for identifying susceptible valves

and for performing appropriate preventive and corrective measures.

In March 1993, the NRC issued NUREG-1275, Volume 9, "Pressure Locking and

Thermal Binding of Gate Valves." Further, the NRC staff held a public

workshop on February 4, 1994, to discuss the subject. A summary of the public

workshop is available in the NRC Public Document Room and contains both

information on evaluating the potential for pressure locking and actions taken

in response to the identification of susceptible valves.

The NRC staff

presentation at the workshop identified containment sump recirculation valves

as potentially susceptible to pressure locking.

In addition to pressure

locking events at U.S. nuclear power plants, the French experience was

documented in NUREG/CP-0137, "Proceedings of the Third NRC/ASME Symposium on

Valve and Pump Testing," in July 1994.

Related NRC generic communications are

listed later in this notice.

IN 95-14 February 28, 1995 The two primary safety issues related to the pressure locking scenario

described above are the potential loss of access to a water source for long- term reactor core cooling and the potential loss of a water source for

containment spray. During a postulated large-break LOCA or under some small- break LOCA scenarios, the opening of the sump valves is relied on to set up a

flow path from the sump to the safety injection and containment spray pumps.

In this alignment, the safety injection pumps recirculate the water between

the sump and the reactor for long-term core cooling and the containment spray

pumps draw water from the sump to provide containment spray for the control of

containment pressure, temperature, and fission products. If the sump valves

are unable to open due to pressure locking, the core may be damaged in a short

time. The containment pressure and temperature may also increase upon loss of

containment spray.

This could lead to containment failure.

The loss of

containment spray would also cause reduction of fission product scrubbing

inside the containment. Additionally, the safety injection and containment

spray pumps may be damaged by pump cavitation if the sump valves remain closed

and the RWST is emptied.

Related Generic Communications

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

"Pressure Locking of Motor-Operated Flexible Wedge Gate Valves."

IN 92-26 referenced earlier NRC staff documents on pressure locking.

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

alerted licensees to the issue of pressure locking of gate valves.

The staff

also 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.

IN 95-14 February 28, 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.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

Thomas G. Scarbrough, NRR

(301) 415-2794

Chu Y. Liang, NRR

(301) 415-2878

Eugene M. Kelly, Region I

(610) 337-5111 Attachment:

List of Reently Issued NRC Information Notices

Koe

Attachment

IN 95-14

February 28, 1995 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

95-13

95-12

95-11

95-10

Supp. 1

95-10

95-09

95-08

Potential for Data

Collection Equipment to

Affect Protection System

Performance

Potentially Nonconforming

Fasteners Supplied by

A&G Engineering II, Inc.

Failure of Condensate

Piping Because of Erosion/

Corrosion at a Flow-

Straightening Device

Potential for Loss of

Automatic Engineered

Safety Features

Actuation

Potential for Loss of

Automatic Engineered

Safety Features

Actuation

Use of Inappropriate

Guidelines and Criteria

for Nuclear Piping and

Pipe Support Evaluation

and Design

Inaccurate Data Obtained

with Clamp-On Ultrasonic

Flow Measurement Instruments

Radiopharmaceutical Vial

Breakage during Preparation

02/24/95

02/21/95

02/24/95 Al 1 for

holders of OLs or CPs

nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

02/10/95

02/03/95

01/31/95

01/30/95

01/27/95

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

All USNRC medical licensees

authorized to use byproduct

material for diagnostic

procedures.

95-07 OL = Operating License

CP = Construction Permit

IN 95-14

February 28, 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.

Snalfstdned by Beran IC.

Grimes

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

Thomas G. Scarbrough, NRR

(301) 415-2794

Chu Y. Liang, NRR

(301) 415-2878

Eugene M. Kelly, Region I

(610) 337-5111 Attachments:

List of Recently Issued NRC Information Notices

DOCUMENT NAME: 95-14.in

E-mailed to

E-mailed to

E.

E.

C.

J.

Kelly of Region I on 2/23/95 for review and comment.

Brown, AEOD, on 2/23/95 for review and comment.

Casto, Region II

Jacobson, Region III

T. Westerman, Region IV

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IN 95-XX

February 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.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

Thomas G. Scarbrough, NRR

(301) 415-2794

Chu Y. Liang, NRR

(301) 415-2878

Eugene M. Kelly, Region I

(610) 337-5111 Attachments:

1. Figure 1, Pressure Locking Flexible-Wedge Gate Valve

2. List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\\EJB1\\PRESSLOC.IN

E-mailed to

E-mailed to

E .

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Jacobson, Region III

Westerman, Region IV

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IN 95-XX

February 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.

Brian K. Grimes, Director

Division of Project Support

Office of Nuclear Reactor Regulation

Technical contacts:

Thomas G. Scarbrough, NRR

(301) 415-2794

Eugene M. Kelly, Region I

(610) 337-5111 Attachments:

1. Figure 1, Pressure Locking Flexible-Wedge Gate Valve

2. List of Recently Issued NRC Information Notices

DOCUMENT NAME:

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