Information Notice 1995-18, Potential Pressure-Locking of Safety-Related Power-Operated Gate Valves
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UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C.
20555
March 15, 1995
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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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
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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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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
95-16
95-15
95-14
95-13
Reactor Vessel Top Guide
and Core Plate Cracking
Vibration Caused by
Increased Recirculation
Flow in a Boiling Water
Reactor
Inadequate Logic Testing
of Safety-Related Circuits
Susceptibility of Con- tainment Sump Recircula- tion Gate Valves to
Pressure Locking
Potential for Data
Collection Equipment to
Affect Protection System
Performance
Potentially Nonconforming
Fasteners Supplied by
A&G Engineering II, Inc.
Failure of Ccndensate
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
03/10/95
03/09/95
03/07/95
02/28/95
02/24/95
02/21/95
02/24/95
02/10/95
02/03/95
All holders of OLs or CPs
for boiling water reactors.
All holders of OLs or CPs
for boiling water 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 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.
95-12
95-11
95-10
Supp. 1
95-10
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
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DATE
03/14/95
03/14/95
03/ 14 /95 1 03/14/95 1 03//
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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
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.
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: G:\\DON\\HDNPLOCK.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
03-1495
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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, OSafety- 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 disfgate 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
discs from the pressurized fluid. IN 95-14 discusses several )g) 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
3. List of Recently Issued NRC Information Notices
Removal System
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IN 95-14, Supp. 1
March xx, 1995 Discussion
Pressure-locking may occur in flexible-wedge and parallel disc gate valves
when fluid becomes pressurized within the valve bonnet 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
discs from the pressurized fluid. IN 95-14 discusses a number of ways in
which fluid may enter the valve bonnet. Another mechanism for locking valves, not identified at Haddam Neck, is the thermal contraction of a valve body as a
result of cooling after a gate valve has seated. This effect 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 cooling systems incapable of performing their safety
functions.
The pressure-locking or thermal-binding of the safety injection admission
valves could prevent both high-pressure and low-pressure coolant from promptly
reaching the reactor vessel following a LOCA.
In addition, the similar
failure of a safety injection isolation valve after closure, such as the
failure discussed here, could prevent two-path recirculation of the sump water
following a LOCA.
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
DOCUMENT NAME:
G:\\DON\\H NPLOCK.IN
- See
previous concurrence
OFFICE OECB:DOPS
ADM:PUB
SC/OECB:DOPS
EMEB:DE
NAME
DKirkpatrick
Tech Editor*
EGoodwin 9 TScarbrough
DATE
/
/95
03/13/95
_3 /
_
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/95 OFFICE C/EMEB:DE
OECB:DOPS
C/OECB:DOPS
D/DOPS
NAME
RWessman
RKiessel
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BGrimes
DATE
I
/95 I
/95
/
/95 I
/95
OFFICIAL RECORD COPY
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IN 95-14, Supp. 1
March xx, 1995 Discussion
Pressure-locking may occur in flexible-wedge and parallel disc gate valves
when fluid becomes pressurized within the valve bonnet 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
discs from the pressurized fluid. IN 95-14 discusses a number of ways in
which fluid may enter the valve bonnet. Another mechanism for locking valves, not identified at Haddam Neck, is the thermal contraction of a valve body as a
result of cooling after a gate valve has seated. This effect 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 cooling systems incapable of performing their safety
functions.
The pressure-locking or thermal-binding of the safety injection admission
valves could prevent both high-pressure and low-pressure coolant from promptly
reaching the reactor vessel following a LOCA. In addition, the similar
failure of a safety injection isolation valve after closure, such as the
failure discussed here, could prevent two-path recirculation of the sump water
following a LOCA.
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
3. List of Recently Issued NRC Information Notices
Removal System
DOCUMENT NAME:
G:\\DON\\HDNPLOCK.IN
- See previous concurrence
OFFICE OECB:DOPS
ADM:PUB
SC/OECB:DOPS
EMEB:DE
NAME
DKirkpatrick
Tech Editor*
EGoodwin
TScarbrough
DATE
'>/3/ /95
03/13/95
/
/95
/
/95 OFFICE
C/EMEB:DE
OEA
C/0ECB:DOPS
D/DOPS
NAME
RWessman
RKiessel
AChaffee
BGrimes
D
/
/95
///
/95
1
_/ /95 OFFICIAL RECORD COPY