Information Notice 1993-58, Nonconservatism in Low-Temperature Overpressure Protection for Pressurized-Water Reactors: Difference between revisions

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{{#Wiki_filter:* UNITED STATES NUCLEAR REGULATORY
{{#Wiki_filter:*  


COMMISSION
===UNITED STATES===
NUCLEAR REGULATORY COMMISSION


===OFFICE OF NUCLEAR REACTOR REGULATION===
===OFFICE OF NUCLEAR REACTOR REGULATION===
WASHINGTON, D.C. 20555 July 26, 1993 NRC INFORMATION
WASHINGTON, D.C.


NOTICE 93-58: NONCONSERVATISM
20555


IN LOW-TEMPERATURE
===July 26, 1993===
NRC INFORMATION NOTICE 93-58: NONCONSERVATISM IN LOW-TEMPERATURE OVERPRESSURE


===OVERPRESSURE===
PROTECTION FOR PRESSURIZED-WATER REACTORS
PROTECTION


FOR PRESSURIZED-WATER
==Addressees==
All holders of operating licenses or construction permits for pressurized- water reactors.
 
,
 
==Purpose==
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information


REACTORS
notice to alert addressees to a nonconservatism in the low-temperature


==Addressees==
overpressure protection (LTOP) setpoint calculation for Westinghouse
All holders of operating
 
facilities. It is expected that recipients will review the information for
 
applicability to their facilities and consider actions, as appropriate, to


licenses or construction
avoid similar problems. However, suggestions contained in this information


permits for pressurized- water reactors.,
notice are not NRC requirements; therefore, no specific action or written


==Purpose==
response is required.
The U.S. Nuclear Regulatory


Commission (NRC) is issuing this information
===Description of Circumstance===
On October 29, 1992, the Texas Utilities Electric Company, the licensee for


notice to alert addressees
Comanche Peak Steam Electric Station, reported that its existing low


to a nonconservatism
temperature overpressure protection may not have provided the required margins


in the low-temperature
of safety against reactor vessel brittle fracture under certain overpressure


overpressure
transients.


protection (LTOP) setpoint calculation
The same concern was later reported by the licensees for Byron, Zion, Diablo


for Westinghouse
Canyon, Kewaunee, Sequoyah and Point Beach nuclear stations.


facilities.
Discussion


It is expected that recipients
In reactor units designed by Westinghouse, overpressure protection of the


will review the information
reactor vessel at low temperature conditions is provided by a cold


for applicability
overpressure mitigation system (COMS).


to their facilities
===This system compares pressure and===
temperature inputs against a preset setpoint curve and relieves the pressure


and consider actions, as appropriate, to avoid similar problems.
when the setpoint is reached.


However, suggestions
===This protection is necessary because, while at===
low temperatures during plant startup and shutdown conditions, certain


contained
transients could cause the reactor coolant system pressure to exceed the


in this information
reactor vessel pressure-temperature (P-7) limitations established for


notice are not NRC requirements;
protection against brittle fracture. A spurious start of a safety injection
therefore, no specific action or written response is required.Description


of Circumstance
pump, reactor coolant pump, or other operational errors could activate this


On October 29, 1992, the Texas Utilities
system.


Electric Company, the licensee for Comanche Peak Steam Electric Station, reported that its existing low temperature
During such events, the P-T limitations are maintained by opening the


overpressure
pressurizer power-operated relief valves (PORVs) or safety relief valves in


protection
the residual heat removal (RHR) suction lines to relieve system pressure.


may not have provided the required margins of safety against reactor vessel brittle fracture under certain overpressure
9307190131 RD3
-R


transients.
IN 93-58 July 26, 1993 The transmitters that provide pressure signals to the COMS are located at the


The same concern was later reported by the licensees
primary system hot leg piping of the reactor vessel. During low temperature


for Byron, Zion, Diablo Canyon, Kewaunee, Sequoyah and Point Beach nuclear stations.Discussion
operation of the reactor coolant pumps, dynamic pressure in the reactor vessel


In reactor units designed by Westinghouse, overpressure
would be higher (by the amount of flow loss in the core and vessel outlet)
than that sensed in the hot leg. Additionally, the static head correction for


protection
the difference in elevation of the sensor to the core region was not


of the reactor vessel at low temperature
considered. The resulting pressure difference between the sensor and the


conditions
vulnerable location in the reactor vessel could be as high as 790 kPa


is provided by a cold overpressure
(100 psig), depending on the number of reactor coolant pumps in operation and


mitigation
the location of the pressure-sensing taps. The LTOP setpoint curve that was


system (COMS). This system compares pressure and temperature
originally developed by Westinghouse did not take these factors into


inputs against a preset setpoint curve and relieves the pressure when the setpoint is reached. This protection
consideration.


is necessary
Westinghouse has sent a letter to licensees recommending one of the following


because, while at low temperatures
methods to compensate for this pressure increase: 1) reduce the maximum


during plant startup and shutdown conditions, certain transients
allowable relief valve setpoint by an amount equivalent to the plant-specific


could cause the reactor coolant system pressure to exceed the reactor vessel pressure-temperature (P-7) limitations
calculated difference in pressure, 2) maintain RCS pressure below the


established
heatup/cooldown curves by a value equal to the plant specific difference in


for protection
pressure from both flow loss and elevation difference when the reactor coolant


against brittle fracture.
pumps are in operation, 3) restrict the number of reactor coolant pumps and, therefore, the flow loss error that can be operated below a defined RCS


A spurious start of a safety injection pump, reactor coolant pump, or other operational
temperature without drawing a steam bubble in the pressurizer, or 4)
demonstrate that the available margin in the LTOP calculation, taking into


errors could activate this system. During such events, the P-T limitations
account instrumentation uncertainty, is sufficient to offset the plant- specific pressure difference.


are maintained
The Westinghouse letter describes interim administrative controls as well as


by opening the pressurizer
calculational methods to verify setpoint adequacy for addressing the LTOP


power-operated
concern.


relief valves (PORVs) or safety relief valves in the residual heat removal (RHR) suction lines to relieve system pressure.9307190131 RD3 -R
The staff notes that the administrative restrictions described in


IN 93-58 July 26, 1993 The transmitters
approaches (2) and (3) are intended by Westinghouse to provide interim actions


that provide pressure signals to the COMS are located at the primary system hot leg piping of the reactor vessel. During low temperature
to address the concern only until LTOP setpoints are verified to be adequate


operation
or are revised appropriately in technical specifications.


of the reactor coolant pumps, dynamic pressure in the reactor vessel would be higher (by the amount of flow loss in the core and vessel outlet)than that sensed in the hot leg. Additionally, the static head correction
Although the information in this notice addresses the cold overpressure


for the difference
mitigation system at Westinghouse designed plants, aspects of this issue may


in elevation
also be applicable to other PWRs.


of the sensor to the core region was not considered.
r


The resulting
* s


pressure difference
IN 93-58 July 26, 1993 This information notice requires no specific action or written response. If


between the sensor and the vulnerable
you have any questions about the information in this notice, please contact


location in the reactor vessel could be as high as 790 kPa (100 psig), depending
one of the technical contacts listed below or the appropriate Office of


on the number of reactor coolant pumps in operation
Nuclear Reactor Regulation (NRR) project manager.


and the location of the pressure-sensing
===Brian K. Grimes, Director===
Division of Operating Reactor Support


taps. The LTOP setpoint curve that was originally
===Office of Nuclear Reactor Regulation===
Technical contacts: Thomas Koshy


developed
(301) 504-1176 Chu-Yu Hang


by Westinghouse
(301) 504-2878 Attachment:


did not take these factors into consideration.
===List of Recently Issued NRC Information Notices===


Westinghouse
. t


has sent a letter to licensees
Attachment


recommending
IN 93-58 July 26. IM


one of the following methods to compensate
Page I of I


for this pressure increase:
===LIST OF RECENTLY ISSUED===
1) reduce the maximum allowable
NRC INFORMATION NOTICES


relief valve setpoint by an amount equivalent
Information


to the plant-specific
Date of


calculated
Notice No.


difference
Subject


in pressure, 2) maintain RCS pressure below the heatup/cooldown
Issuance


curves by a value equal to the plant specific difference
Issued to


in pressure from both flow loss and elevation
93-57 Software Problems


difference
07/23/93


when the reactor coolant pumps are in operation, 3) restrict the number of reactor coolant pumps and, therefore, the flow loss error that can be operated below a defined RCS temperature
===All holders of OLs or CPs===
Involving Digital


without drawing a steam bubble in the pressurizer, or 4)demonstrate
for test and research


that the available
Control Console Systems


margin in the LTOP calculation, taking into account instrumentation
reactors and nuclear power


uncertainty, is sufficient
at Non-Power Reactors


to offset the plant-specific pressure difference.
reactors


The Westinghouse
93-56 Weakness in Emergency


letter describes
07/22/93


interim administrative
===All holders of OLs or CPs===
Operating Procedures


controls as well as calculational
for pressurized water


methods to verify setpoint adequacy for addressing
Found as Result of


the LTOP concern. The staff notes that the administrative
reactors.


restrictions
===Steam generator Tube===
Rupture


described
93-55 Potential Problem with


in approaches
07/21/93


(2) and (3) are intended by Westinghouse
===All holders of OLs or CPs===
Main Steamline Break


to provide interim actions to address the concern only until LTOP setpoints
for pressurized water


are verified to be adequate or are revised appropriately
Analysis for Main Steam


in technical
reactors.


specifications.
Vaults/Tunnels


Although the information
93-54 Motor-Operated Valve


in this notice addresses
07/20/93


the cold overpressure
===All holders of OLs or CPs===
Actuator Thrust


mitigation
for nuclear power reactors.


system at Westinghouse
===Variations Measured===
with A Torque Thrust


designed plants, aspects of this issue may also be applicable
===Cell and A Strain Gage===
93-53 Effect of Hurricane


to other PWRs.
07/20/93


r
===All holders of OLs or CPs===
Andrew on Turkey Point


* s IN 93-58 July 26, 1993 This information
for nuclear power reactors.


notice requires no specific action or written response.
===Nuclear Generating===
Station and Lessons


If you have any questions
Learned


about the information
93-52 Draft NUREG-1477,
07/14/93


in this notice, please contact one of the technical
===All holders of OLs or CPs===
'Voltage-Based Interim


contacts listed below or the appropriate
for pressurized water


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
Plugging Criteria for


===Reactor Support Office of Nuclear Reactor Regulation===
reactor (PWRs).
Technical


contacts:
Steam Generator Tubes'
Thomas Koshy (301) 504-1176 Chu-Yu Hang (301) 504-2878 Attachment:
93-51 Repetitive Overspeed
List of Recently Issued NRC Information


Notices
07/09/93


.t Attachment
===All holders of OLs or CPs===
Tripping of Turbine- for nuclear power reactors.


IN 93-58 July 26. IM Page I of I LIST OF RECENTLY ISSUED NRC INFORMATION
Driven Auxiliary Feed- water Pumps


NOTICES Information
93-50
Extended Storage of


Date of Notice No. Subject Issuance Issued to 93-57 Software Problems 07/23/93 All holders of OLs or CPs Involving
07/08/93  


Digital for test and research Control Console Systems reactors and nuclear power at Non-Power
===All licensees authorized===
Sealed Sources


Reactors reactors 93-56 Weakness in Emergency
to possess sealed sources.


07/22/93 All holders of OLs or CPs Operating
OL - Operating License


Procedures
CP - Construction Permit


for pressurized
0
4>
us


water Found as Result of reactors.Steam generator
0)
.


Tube Rupture 93-55 Potential
(I)
0
0.


Problem with 07/21/93 All holders of OLs or CPs Main Steamline
2
0 _
2t


Break for pressurized
o


water Analysis for Main Steam reactors.Vaults/Tunnels
Lno


93-54 Motor-Operated
0 o, W


Valve 07/20/93 All holders of OLs or CPs Actuator Thrust for nuclear power reactors.Variations
U


Measured with A Torque Thrust Cell and A Strain Gage 93-53 Effect of Hurricane
2C


07/20/93 All holders of OLs or CPs Andrew on Turkey Point for nuclear power reactors.Nuclear Generating
cc


Station and Lessons Learned 93-52 Draft NUREG-1477, 07/14/93 All holders of OLs or CPs'Voltage-Based
CO


Interim for pressurized
0
LU


water Plugging Criteria for reactor (PWRs).Steam Generator
.)
8 co


Tubes'93-51 Repetitive
Z UJ


Overspeed
_ 4A3>
Z. i


07/09/93 All holders of OLs or CPs Tripping of Turbine- for nuclear power reactors.Driven Auxiliary
-i1X


Feed-water Pumps 93-50 Extended Storage of 07/08/93 All licensees
o


authorized
zw


Sealed Sources to possess sealed sources.OL -Operating
0.


License CP -Construction
IN 93-58 July 26, 1993 This information notice requires no specific action or written response.


Permit 0 4>us 0) .(I)0 0.2 0 _2 t o Lno 0 o, W U 2C cc CO 0 LU.)8 co Z UJ_ 4 A3>Z. i-i1X o z w 0.
If


IN 93-58 July 26, 1993 This information
you have any questions about the information in this notice, please contact


notice requires no specific action or written response.
one of the technical contacts listed below or the appropriate Office of


If you have any questions
Nuclear Reactor Regulation (NRR) project manager.


about the information
===Ordginal sgnei by===
Brian IL. W=me


in this notice, please contact one of the technical
===Brian K. Grimes, Director===
Division of Operating Reactor Support


contacts listed below or the appropriate
===Office of Nuclear Reactor Regulation===
Technical contacts:


Office of Nuclear Reactor Regulation (NRR) project manager.Ordginal sgnei by Brian IL. W=me Brian K. Grimes, Director Division of Operating
===Thomas Koshy===
(301) 504-1176 Chu-Yu Liang


===Reactor Support Office of Nuclear Reactor Regulation===
(301) 504-2878 Attachment:
Technical


contacts: Thomas Koshy (301) 504-1176 Chu-Yu Liang (301) 504-2878 Attachment:
===List of Recently Issued NRC Information Notices===
List of Recently Issued NRC Information
*See previous concurrence


Notices*See previous concurrence
OFC


OFC OEAB:DORS
OEAB:DORS


ADM:PUB SC/OEAB:DORS
ADM:PUB
 
SC/OEAB:DORS


C/SRXB:DSSA
C/SRXB:DSSA


NAME TKoshy* Tech Editor* EGoodwin*  
NAME
RJones*l DATE 06/04/93 05/10/93 05/21/93 06/04/93 I OFC C/EMCB:DE
 
TKoshy*  
Tech Editor*  
EGoodwin*  
RJones*
l DATE
 
06/04/93  
05/10/93  
05/21/93  
06/04/93 I
 
OFC
 
C/EMCB:DE


C/OEAB:DORS
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NAME l JStrosnider*  
NAME
 
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AChaffee*  
JLBirmingham*  
JLBirmingham*  
GHMarcus*DATE 05/24/931  
GHMarcus*
06/08/93 06/17/93 06/17/93[OFC 1 __ __ ClNAME W ameslDATE 07/-vf/93[OFFICIAL
DATE
 
05/24/931  
06/08/93  
06/17/93  
06/17/93
[OFC 1  
__  
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lNAME
 
W ames
 
lDATE
 
07/-vf/93
[OFFICIAL RECORD COPY]
DOCUMENT NAME: S:\\DORSSEC\\93-58.IN
 
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emw& aA Iq 1A~k~AM'x$& d.1'r- .a4 4k, kxd).'_ ..-.,ng ?w ar sL*K e4W 4._ _71Z11l9 3 IN 93-XX June xx, 1993 This information
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notice requires no specific action or written response.
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ar


about the information
sL*K e4W


in this notice, please contact one of the technical
4
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contacts listed below or the appropriate
_ _71Z11l9 3


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
IN 93-XX


===Reactor Support Office of Nuclear Reactor Regulation===
June xx, 1993 This information notice requires no specific action or written response.
Technical


contacts: Thomas Koshy (301) 504-1176 Chu-Yu Liang (301) 504-2878 Attachment:
If
List of Recently Issued NRC Information


Notices*See previous concurrence
you have any questions about the information in this notice, please contact


OFC OEAB:DORS
one of the technical contacts listed below or the appropriate Office of


ADM:PUB l SC/OEAB:DORS
Nuclear Reactor Regulation (NRR) project manager.
 
===Brian K. Grimes, Director===
Division of Operating Reactor Support
 
===Office of Nuclear Reactor Regulation===
Technical contacts:
 
===Thomas Koshy===
(301) 504-1176 Chu-Yu Liang
 
(301) 504-2878 Attachment:
 
===List of Recently Issued NRC Information Notices===
*See previous concurrence
 
OFC
 
OEAB:DORS
 
ADM:PUB
 
l SC/OEAB:DORS


C/SRXB:DSSA
C/SRXB:DSSA


l NAME TKoshy* Tech Editor* EGoodwin*  
l NAME
RJones* lDATE l 06/04/93 l 05/10/93 l 05/21/93 06/04/93 l[ OFC l C/EMCB:DE
 
TKoshy*  
Tech Editor*  
EGoodwin*  
RJones*  
l
 
DATE
 
l 06/04/93 l 05/10/93 l 05/21/93  
06/04/93 l
 
[
 
OFC
 
l C/EMCB:DE


C/OEAB:DORS
C/OEAB:DORS


OGCB:DOR Ltj C/OGCB:DORS
OGCB:DOR
 
Ltj C/OGCB:DORS
 
l
 
NAME


lNAME JStrosnider*  
JStrosnider*  
AChaffee*  
AChaffee*  
JLBirmingam
JLBirmingam


HMarcus L DATE 05/24/93 06/08/93 06/16/93 06/ 7/93l OFC D/:DORS l l l _ _NAME BKGrimes l DATE 06/ /93 _ l[OFFICIAL
HMarcus
 
L


RECORD COPY]DOCUMENT NAME: S:\DO RS SEC\LTOPREV1.IN
DATE
 
05/24/93
06/08/93
06/16/93
06/ 7/93 l OFC
 
D/:DORS
 
l
 
l
 
l
 
_
_
NAME
 
BKGrimes
 
l
 
DATE
 
06/ /93
_
l
 
[OFFICIAL RECORD COPY]
DOCUMENT NAME: S:\\DO RS SEC\\LTOPREV1.IN


*See previous concurrence
*See previous concurrence


OFC OEAB:DORS
OFC
 
OEAB:DORS
 
ADM:PUB


ADM:PUB SC/OEAB:DORS
SC/OEAB:DORS


C/SRXB:DSSA
C/SRXB:DSSA


NAME TKoshy A- Tech Editor* EGoodwin*  
NAME
RJones*DATE 6 4 /93 05/10/93 05/21/93 06/04/93[OFC C/EMCB:DE
 
TKoshy A-  
Tech Editor*  
EGoodwin*  
RJones*
DATE
 
6 4 /93  
05/10/93  
05/21/93  
06/04/93
[OFC
 
C/EMCB:DE


C/OEAB:DORS
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D/DORS NAME JStrosnider*  
D/DORS
 
NAME
 
JStrosnider*  
AChaffee*  
AChaffee*  
GMarcus BGrlimes DATE 05/24/93 1 06/08/93 / /93 / /93[OFFICIAL
GMarcus
 
BGrlimes


RECORD COPY]DOCUMENT NAME: S:\DORSSEC\LTOP.IN
DATE
 
05/24/93
1
06/08/93
/
/93
/
/93
[OFFICIAL RECORD COPY]
DOCUMENT NAME: S:\\DORSSEC\\LTOP.IN


*See previous concurrence
*See previous concurrence


[OFC OEAB:DORS
[OFC
 
OEAB:DORS
 
ADM:PUB
 
SC/OEAB:DORS
 
C/SRXB:D S
 
l


ADM:PUB SC/OEAB:DORS
NAME


C/SRXB:D S l NAME TKoshy Tech Editor* EGoodwin*  
TKoshy
RJones /DATE 60 /zI/93 05/10/93 05/21/93 1 y/93 OFC C/EMCB:DE
 
Tech Editor*  
EGoodwin*  
RJones /
DATE
 
60 /zI/93  
05/10/93  
05/21/93  
1 y/93 OFC
 
C/EMCB:DE


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D/DORS NAME JStrosnider*  
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A ee GMarcus BGrimes DATE 105/24/93 j 0 / 6 /93 J / /93 j[OFFICIAL
 
NAME
 
JStrosnider*  
A
 
ee
 
GMarcus
 
BGrimes
 
DATE
 
105/24/93 j 0 / 6  
/93 J
 
/ /93 j
 
[OFFICIAL RECORD COPY]
DOCUMENT NAME: G:\\TXK\\LTOP.IN
 
OFC
 
OEAB:DORS
 
ADM:PUB
 
SC/OEAB:DORS
 
C/SRXB:DSSA ,
NAME
 
TKoshy &
Tech Editor*
EGoodwin


RECORD COPY]DOCUMENT NAME: G:\TXK\LTOP.IN
RJones


OFC OEAB:DORS
DATE


ADM:PUB SC/OEAB:DORS
05/tQ/93
05/10/93
05/ l93 e


C/SRXB:DSSA
e
 
193 I


, NAME TKoshy & Tech Editor* EGoodwin RJones DATE 05/tQ/93 05/10/93 05/ l93 e e 193 I[OFC _ C/EMCB:DE
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BGrimes
 
DATE


I AChaffee GMarcus BGrimes DATE 05/24/93 05/ /93 05/ /93 05/ J93[OFFICIAL
05/24/93  
05/ /93  
05/ /93  
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[OFFICIAL RECORD COPY]
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RECORD COPY]DOCUMENT NAME: G:\TXK\LTOP.IN
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{{Information notice-Nav}}
{{Information notice-Nav}}

Latest revision as of 10:47, 16 January 2025

Nonconservatism in Low-Temperature Overpressure Protection for Pressurized-Water Reactors
ML031070245
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: 07/26/1993
From: Grimes B
Office of Nuclear Reactor Regulation
To:
References
IN-93-058, NUDOCS 9307190131
Download: ML031070245 (9)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555

July 26, 1993

NRC INFORMATION NOTICE 93-58: NONCONSERVATISM IN LOW-TEMPERATURE OVERPRESSURE

PROTECTION FOR PRESSURIZED-WATER REACTORS

Addressees

All holders of operating licenses or construction permits for pressurized- water reactors.

,

Purpose

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

notice to alert addressees to a nonconservatism in the low-temperature

overpressure protection (LTOP) setpoint calculation for Westinghouse

facilities. It is expected 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 are not NRC requirements; therefore, no specific action or written

response is required.

Description of Circumstance

On October 29, 1992, the Texas Utilities Electric Company, the licensee for

Comanche Peak Steam Electric Station, reported that its existing low

temperature overpressure protection may not have provided the required margins

of safety against reactor vessel brittle fracture under certain overpressure

transients.

The same concern was later reported by the licensees for Byron, Zion, Diablo

Canyon, Kewaunee, Sequoyah and Point Beach nuclear stations.

Discussion

In reactor units designed by Westinghouse, overpressure protection of the

reactor vessel at low temperature conditions is provided by a cold

overpressure mitigation system (COMS).

This system compares pressure and

temperature inputs against a preset setpoint curve and relieves the pressure

when the setpoint is reached.

This protection is necessary because, while at

low temperatures during plant startup and shutdown conditions, certain

transients could cause the reactor coolant system pressure to exceed the

reactor vessel pressure-temperature (P-7) limitations established for

protection against brittle fracture. A spurious start of a safety injection

pump, reactor coolant pump, or other operational errors could activate this

system.

During such events, the P-T limitations are maintained by opening the

pressurizer power-operated relief valves (PORVs) or safety relief valves in

the residual heat removal (RHR) suction lines to relieve system pressure.

9307190131 RD3

-R

IN 93-58 July 26, 1993 The transmitters that provide pressure signals to the COMS are located at the

primary system hot leg piping of the reactor vessel. During low temperature

operation of the reactor coolant pumps, dynamic pressure in the reactor vessel

would be higher (by the amount of flow loss in the core and vessel outlet)

than that sensed in the hot leg. Additionally, the static head correction for

the difference in elevation of the sensor to the core region was not

considered. The resulting pressure difference between the sensor and the

vulnerable location in the reactor vessel could be as high as 790 kPa

(100 psig), depending on the number of reactor coolant pumps in operation and

the location of the pressure-sensing taps. The LTOP setpoint curve that was

originally developed by Westinghouse did not take these factors into

consideration.

Westinghouse has sent a letter to licensees recommending one of the following

methods to compensate for this pressure increase: 1) reduce the maximum

allowable relief valve setpoint by an amount equivalent to the plant-specific

calculated difference in pressure, 2) maintain RCS pressure below the

heatup/cooldown curves by a value equal to the plant specific difference in

pressure from both flow loss and elevation difference when the reactor coolant

pumps are in operation, 3) restrict the number of reactor coolant pumps and, therefore, the flow loss error that can be operated below a defined RCS

temperature without drawing a steam bubble in the pressurizer, or 4)

demonstrate that the available margin in the LTOP calculation, taking into

account instrumentation uncertainty, is sufficient to offset the plant- specific pressure difference.

The Westinghouse letter describes interim administrative controls as well as

calculational methods to verify setpoint adequacy for addressing the LTOP

concern.

The staff notes that the administrative restrictions described in

approaches (2) and (3) are intended by Westinghouse to provide interim actions

to address the concern only until LTOP setpoints are verified to be adequate

or are revised appropriately in technical specifications.

Although the information in this notice addresses the cold overpressure

mitigation system at Westinghouse designed plants, aspects of this issue may

also be applicable to other PWRs.

r

  • s

IN 93-58 July 26, 1993 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 Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Thomas Koshy

(301) 504-1176 Chu-Yu Hang

(301) 504-2878 Attachment:

List of Recently Issued NRC Information Notices

. t

Attachment

IN 93-58 July 26. IM

Page I of I

LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

93-57 Software Problems

07/23/93

All holders of OLs or CPs

Involving Digital

for test and research

Control Console Systems

reactors and nuclear power

at Non-Power Reactors

reactors

93-56 Weakness in Emergency

07/22/93

All holders of OLs or CPs

Operating Procedures

for pressurized water

Found as Result of

reactors.

Steam generator Tube

Rupture

93-55 Potential Problem with

07/21/93

All holders of OLs or CPs

Main Steamline Break

for pressurized water

Analysis for Main Steam

reactors.

Vaults/Tunnels

93-54 Motor-Operated Valve

07/20/93

All holders of OLs or CPs

Actuator Thrust

for nuclear power reactors.

Variations Measured

with A Torque Thrust

Cell and A Strain Gage

93-53 Effect of Hurricane

07/20/93

All holders of OLs or CPs

Andrew on Turkey Point

for nuclear power reactors.

Nuclear Generating

Station and Lessons

Learned

93-52 Draft NUREG-1477,

07/14/93

All holders of OLs or CPs

'Voltage-Based Interim

for pressurized water

Plugging Criteria for

reactor (PWRs).

Steam Generator Tubes'

93-51 Repetitive Overspeed

07/09/93

All holders of OLs or CPs

Tripping of Turbine- for nuclear power reactors.

Driven Auxiliary Feed- water Pumps

93-50

Extended Storage of

07/08/93

All licensees authorized

Sealed Sources

to possess sealed sources.

OL - Operating License

CP - Construction Permit

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Nuclear Reactor Regulation (NRR) project manager.

Ordginal sgnei by

Brian IL. W=me

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts:

Thomas Koshy

(301) 504-1176 Chu-Yu Liang

(301) 504-2878 Attachment:

List of Recently Issued NRC Information Notices

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

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts:

Thomas Koshy

(301) 504-1176 Chu-Yu Liang

(301) 504-2878 Attachment:

List of Recently Issued NRC Information Notices

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