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:*                                   UNITED STATES


COMMISSION
NUCLEAR REGULATORY COMMISSION


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


NOTICE 93-58: NONCONSERVATISM
WASHINGTON, D.C. 20555 July 26, 1993 NRC INFORMATION NOTICE 93-58:   NONCONSERVATISM IN LOW-TEMPERATURE OVERPRESSURE


IN LOW-TEMPERATURE
PROTECTION FOR PRESSURIZED-WATER REACTORS
 
===OVERPRESSURE===
PROTECTION
 
FOR PRESSURIZED-WATER
 
REACTORS


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


licenses or construction
,
 
permits for pressurized- water reactors.,


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


Commission (NRC) is issuing this information
notice to alert addressees to a nonconservatism in the low-temperature


notice to alert addressees
overpressure protection (LTOP) setpoint calculation for Westinghouse


to a nonconservatism
facilities. It is expected that recipients will review the information for


in the low-temperature
applicability to their facilities and consider actions, as appropriate, to


overpressure
avoid similar problems. However, suggestions contained in this information


protection (LTOP) setpoint calculation
notice are not NRC requirements; therefore, no specific action or written


for Westinghouse
response is required.


facilities.
Description of Circumstance


It is expected that recipients
On October 29, 1992, the Texas Utilities Electric Company, the licensee for


will review the information
Comanche Peak Steam Electric Station, reported that its existing low


for applicability
temperature overpressure protection may not have provided the required margins


to their facilities
of safety against reactor vessel brittle fracture under certain overpressure
 
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.
transients.


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


for Byron, Zion, Diablo Canyon, Kewaunee, Sequoyah and Point Beach nuclear stations.Discussion
Canyon, Kewaunee, Sequoyah and Point Beach nuclear stations.


In reactor units designed by Westinghouse, overpressure
Discussion


protection
In reactor units designed by Westinghouse, overpressure protection of the


of the reactor vessel at low temperature
reactor vessel at low temperature conditions is provided by a cold


conditions
overpressure mitigation system (COMS). This system compares pressure and


is provided by a cold overpressure
temperature inputs against a preset setpoint curve and relieves the pressure


mitigation
when the setpoint is reached. This protection is necessary because, while at


system (COMS). This system compares pressure and temperature
low temperatures during plant startup and shutdown conditions, certain


inputs against a preset setpoint curve and relieves the pressure when the setpoint is reached. This protection
transients could cause the reactor coolant system pressure to exceed the


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


because, while at low temperatures
protection against brittle fracture. A spurious start of a safety injection


during plant startup and shutdown conditions, certain transients
pump, reactor coolant pump, or other operational errors could activate this


could cause the reactor coolant system pressure to exceed the reactor vessel pressure-temperature (P-7) limitations
system. During such events, the P-T limitations are maintained by opening the


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


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


against brittle fracture.
9307190131      RD3                                        -R


A spurious start of a safety injection pump, reactor coolant pump, or other operational
IN 93-58 July 26, 1993 The transmitters that provide pressure signals to the COMS are located at the


errors could activate this system. During such events, the P-T limitations
primary system hot leg piping of the reactor vessel. During low temperature


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


by opening the pressurizer
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


power-operated
the difference in elevation of the sensor to the core region was not


relief valves (PORVs) or safety relief valves in the residual heat removal (RHR) suction lines to relieve system pressure.9307190131 RD3 -R
considered. The resulting pressure difference between the sensor and the


IN 93-58 July 26, 1993 The transmitters
vulnerable location in the reactor vessel could be as high as 790 kPa


that provide pressure signals to the COMS are located at the primary system hot leg piping of the reactor vessel. During low temperature
(100 psig), depending on the number of reactor coolant pumps in operation and


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


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
originally developed by Westinghouse did not take these factors into


for the difference
consideration.


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


of the sensor to the core region was not considered.
methods to compensate for this pressure increase: 1) reduce the maximum


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


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


between the sensor and the vulnerable
heatup/cooldown curves by a value equal to the plant specific difference in


location in the reactor vessel could be as high as 790 kPa (100 psig), depending
pressure from both flow loss and elevation difference when the reactor coolant


on the number of reactor coolant pumps in operation
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


and the location of the pressure-sensing
temperature without drawing a steam bubble in the pressurizer, or 4)
demonstrate that the available margin in the LTOP calculation, taking into


taps. The LTOP setpoint curve that was originally
account instrumentation uncertainty, is sufficient to offset the plant- specific pressure difference.


developed
The Westinghouse letter describes interim administrative controls as well as


by Westinghouse
calculational methods to verify setpoint adequacy for addressing the LTOP


did not take these factors into consideration.
concern. The staff notes that the administrative restrictions described in


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


has sent a letter to licensees
to address the concern only until LTOP setpoints are verified to be adequate


recommending
or are revised appropriately in technical specifications.


one of the following methods to compensate
Although the information in this notice addresses the cold overpressure


for this pressure increase:
mitigation system at Westinghouse designed plants, aspects of this issue may
1) reduce the maximum allowable


relief valve setpoint by an amount equivalent
also be applicable to other PWRs.


to the plant-specific
r *s


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


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


in pressure, 2) maintain RCS pressure below the heatup/cooldown
one of the technical contacts listed below or the appropriate Office of


curves by a value equal to the plant specific difference
Nuclear Reactor Regulation (NRR) project manager.


in pressure from both flow loss and elevation
Brian K. Grimes, Director


difference
Division of Operating Reactor Support


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
Office of Nuclear Reactor Regulation


without drawing a steam bubble in the pressurizer, or 4)demonstrate
Technical contacts:  Thomas Koshy


that the available
(301) 504-1176 Chu-Yu Hang


margin in the LTOP calculation, taking into account instrumentation
(301) 504-2878 Attachment:  List of Recently Issued NRC Information Notices


uncertainty, is sufficient
. t


to offset the plant-specific pressure difference.
0
                                                              Attachment                    4>
                                                              IN 93-58 July 26. IM                      us


The Westinghouse
Page I of I


letter describes
LIST OF RECENTLY ISSUED


interim administrative
. 0)
                                      NRCINFORMATION NOTICES                                  (I)
                                                                                                0
    Information                                  Date of


controls as well as calculational
Notice No.              Subject                Issuance    Issued to


methods to verify setpoint adequacy for addressing
0.


the LTOP concern. The staff notes that the administrative
93-57          Software Problems            07/23/93    All holders of OLs or CPs


restrictions
Involving Digital                        for test and research


described
Control Console Systems                  reactors and nuclear power


in approaches
at Non-Power Reactors                    reactors


(2) and (3) are intended by Westinghouse
93-56            Weakness in Emergency        07/22/93    All holders of OLs or CPs


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


are verified to be adequate or are revised appropriately
Found as Result of                        reactors.


in technical
Steam generator Tube


specifications.
Rupture


Although the information
93-55            Potential Problem with        07/21/93    All holders of OLs or CPs


in this notice addresses
Main Steamline Break                      for pressurized water


the cold overpressure
Analysis for Main Steam                    reactors.                      0  _
                    Vaults/Tunnels


mitigation
93-54          Motor-Operated Valve          07/20/93    All holders of OLs or CPs


system at Westinghouse
Actuator Thrust                            for nuclear power reactors.


designed plants, aspects of this issue may also be applicable
Variations Measured


to other PWRs.
with A Torque Thrust


r
Cell and A Strain Gage


* s IN 93-58 July 26, 1993 This information
93-53            Effect of Hurricane          07/20/93    All holders of OLs or CPs


notice requires no specific action or written response.
Andrew on Turkey Point                    for nuclear power reactors.


If you have any questions
Nuclear Generating


about the information
Station and Lessons


in this notice, please contact one of the technical
Learned


contacts listed below or the appropriate
93-52          Draft NUREG-1477,              07/14/93    All holders of OLs or CPs


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
'Voltage-Based Interim                    for pressurized water        2
.)                Plugging Criteria for                      reactor (PWRs).               2 Steam Generator Tubes'                                                  t      o


===Reactor Support Office of Nuclear Reactor Regulation===
93-51          Repetitive Overspeed          07/09/93    All holders of OLs or CPs          Lno
Technical


contacts:
8 Tripping of Turbine-                       for nuclear power reactors.  0    o, Driven Auxiliary Feed-                                                                   co
Thomas Koshy (301) 504-1176 Chu-Yu Hang (301) 504-2878 Attachment:
List of Recently Issued NRC Information


Notices
water Pumps                                                            W    U      Z UJ


.t Attachment
93-50          Extended Storage of            07/08/93    All licensees authorized                  _A3>
                                                                                                          4 Sealed Sources                            to possess sealed sources.


IN 93-58 July 26. IM Page I of I LIST OF RECENTLY ISSUED NRC INFORMATION
Z. i


NOTICES Information
cc


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


Digital for test and research Control Console Systems reactors and nuclear power at Non-Power
CO0
                                                                                          2C


Reactors reactors 93-56 Weakness in Emergency
-i1X


07/22/93 All holders of OLs or CPs Operating
o


Procedures
CP - Construction Permit


for pressurized
LU              0.


water Found as Result of reactors.Steam generator
zw


Tube Rupture 93-55 Potential
IN 93-58 July 26, 1993 This information notice requires no specific action or written response. If


Problem with 07/21/93 All holders of OLs or CPs Main Steamline
you have any questions about the information in this notice, please contact


Break for pressurized
one of the technical contacts listed below or the appropriate Office of


water Analysis for Main Steam reactors.Vaults/Tunnels
Nuclear Reactor Regulation (NRR) project manager.


93-54 Motor-Operated
Ordginal sgnei by


Valve 07/20/93 All holders of OLs or CPs Actuator Thrust for nuclear power reactors.Variations
Brian IL. W=me


Measured with A Torque Thrust Cell and A Strain Gage 93-53 Effect of Hurricane
Brian K. Grimes, Director


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


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


Interim for pressurized
Technical contacts:    Thomas Koshy


water Plugging Criteria for reactor (PWRs).Steam Generator
(301) 504-1176 Chu-Yu Liang


Tubes'93-51 Repetitive
(301) 504-2878 Attachment:    List of Recently Issued NRC Information Notices


Overspeed
*See previous concurrence


07/09/93 All holders of OLs or CPs Tripping of Turbine- for nuclear power reactors.Driven Auxiliary
OFC    OEAB:DORS        ADM:PUB          SC/OEAB:DORS      C/SRXB:DSSA


Feed-water Pumps 93-50 Extended Storage of 07/08/93 All licensees
NAME    TKoshy*          Tech Editor*      EGoodwin*        RJones*
l DATE    06/04/93        05/10/93          05/21/93           06/04/93 I  OFC


authorized
NAME


Sealed Sources to possess sealed sources.OL -Operating
C/EMCB:DE


License CP -Construction
l JStrosnider*
                            C/OEAB:DORS


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.
AChaffee*
                                              OGCB:DORS


IN 93-58 July 26, 1993 This information
JLBirmingham*
                                                                C/OGCB:DORS


notice requires no specific action or written response.
GHMarcus*
          1 DATE    05/24/931      06/08/93            06/17/93          06/17/93
[OFC                      __                __                C


If you have any questions
lNAME    W ames


about the information
lDATE    07/-vf/93
[OFFICIAL RECORD COPY]                                                  $&        d.


in this notice, please contact one of the technical
DOCUMENT NAME: S:\DORSSEC\93-58.IN              emw& aA                  1'r-    . a4 Iq 1A~k~AM'x


contacts listed below or the appropriate
,ng      ?w


Office of Nuclear Reactor Regulation (NRR) project manager.Ordginal sgnei by Brian IL. W=me Brian K. Grimes, Director Division of Operating
ar


===Reactor Support Office of Nuclear Reactor Regulation===
4k, kxd)sL*K e4W            4
Technical
                                                            . '_ . .-.      .  __71Z11l9 3


contacts: Thomas Koshy (301) 504-1176 Chu-Yu Liang (301) 504-2878 Attachment:
IN 93-XX
List of Recently Issued NRC Information


Notices*See previous concurrence
June xx, 1993 This information notice requires no specific action or written response. If


OFC OEAB:DORS
you have any questions about the information in this notice, please contact


ADM:PUB SC/OEAB:DORS
one of the technical contacts listed below or the appropriate Office of


C/SRXB:DSSA
Nuclear Reactor Regulation (NRR) project manager.


NAME TKoshy* Tech Editor* EGoodwin*
Brian K. Grimes, Director
RJones*l DATE 06/04/93 05/10/93 05/21/93 06/04/93 I OFC C/EMCB:DE


C/OEAB:DORS
Division of Operating Reactor Support


OGCB:DORS
Office of Nuclear Reactor Regulation


C/OGCB:DORS
Technical contacts:   Thomas Koshy


NAME l JStrosnider*
(301) 504-1176 Chu-Yu Liang
AChaffee*
JLBirmingham*
GHMarcus*DATE 05/24/931
06/08/93 06/17/93 06/17/93[OFC 1 __ __ ClNAME W ameslDATE 07/-vf/93[OFFICIAL


RECORD COPY]DOCUMENT NAME: S:\DORSSEC\93-58.IN
(301) 504-2878 Attachment:   List of Recently Issued NRC Information Notices


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
*See previous concurrence


notice requires no specific action or written response.
OFC      OEAB:DORS        ADM:PUB        l SC/OEAB:DORS    C/SRXB:DSSA


If you have any questions
l NAME    TKoshy*          Tech Editor*      EGoodwin*      RJones*      l


about the information
[ DATE


in this notice, please contact one of the technical
OFC


contacts listed below or the appropriate
NAME


Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating
l 06/04/93 l C/EMCB:DE


===Reactor Support Office of Nuclear Reactor Regulation===
JStrosnider*
Technical
                          l 05/10/93 C/OEAB:DORS


contacts: Thomas Koshy (301) 504-1176 Chu-Yu Liang (301) 504-2878 Attachment:
AChaffee*
List of Recently Issued NRC Information
                                          l 05/21/93 OGCB:DOR  Ltj


Notices*See previous concurrence
JLBirmingam
 
OFC OEAB:DORS
 
ADM:PUB l SC/OEAB:DORS


C/SRXB:DSSA
06/04/93 C/OGCB:DORS


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


C/OEAB:DORS
l


OGCB:DOR Ltj C/OGCB:DORS
l
 
lNAME JStrosnider*
AChaffee*
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
DATE     05/24/93         06/08/93         06/16/93         06/ 7/93 lOFC      D/:DORS       l               l               l   _     _
  NAME    BKGrimes       l


RECORD COPY]DOCUMENT NAME: S:\DO RS SEC\LTOPREV1.IN
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      SC/OEAB:DORS C/SRXB:DSSA


ADM:PUB SC/OEAB:DORS
NAME    TKoshyA-        Tech Editor* EGoodwin*    RJones*
  DATE  6  4 /93        05/10/93    05/21/93    06/04/93
[OFC      C/EMCB:DE      C/OEAB:DORS  C/OGCB:DORS  D/DORS


C/SRXB:DSSA
NAME    JStrosnider*    AChaffee*    GMarcus      BGrlimes


NAME TKoshy A- Tech Editor* EGoodwin*
DATE   05/24/93     106/08/93       / /93       /   /93
RJones*DATE 6 4 /93 05/10/93 05/21/93 06/04/93[OFC C/EMCB:DE
[OFFICIAL RECORD COPY]
DOCUMENT NAME: S:\DORSSEC\LTOP.IN


C/OEAB:DORS
*See previous concurrence


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


D/DORS NAME JStrosnider*  
NAME   TKoshy          Tech Editor*   EGoodwin*       RJones/
AChaffee*  
  DATE   60 /zI/93      05/10/93        05/21/93     1     y/93 OFC    C/EMCB:DE      C/OEAB:WDORS    C/OGCB:DORS    D/DORS
GMarcus BGrlimes DATE 05/24/93 1 06/08/93 / /93 / /93[OFFICIAL


RECORD COPY]DOCUMENT NAME: S:\DORSSEC\LTOP.IN
NAME   JStrosnider*   A      ee      GMarcus        BGrimes
 
*See previous concurrence


[OFC OEAB:DORS
DATE  105/24/93      j 0 /6        /93            J


ADM:PUB SC/OEAB:DORS
/ /93            j


C/SRXB:D S l NAME TKoshy Tech Editor* EGoodwin*
[OFFICIAL RECORD COPY]
RJones /DATE 60 /zI/93 05/10/93 05/21/93 1 y/93 OFC C/EMCB:DE
DOCUMENT NAME: G:\TXK\LTOP.IN


C/OEAB:WDORS
OFC      OEAB:DORS    ADM:PUB      SC/OEAB:DORS C/SRXB:DSSA ,
  NAME    TKoshy &      Tech Editor* EGoodwin    RJones


C/OGCB:DORS
DATE    05/tQ/93      05/10/93    05/ l93    e  e        I    193
[OFC


D/DORS NAME JStrosnider*
NAME
A ee GMarcus BGrimes DATE 105/24/93 j 0 / 6 /93 J / /93 j[OFFICIAL


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


OFC OEAB:DORS
_  C/EMCB:DE


ADM:PUB SC/OEAB:DORS
JStrosnide


C/SRXB:DSSA
05/24/93 IC/OEAB:DORS


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


C/OEAB:DORS
05/  /93 C/OGCB:DORS


C/OGCB:DORS
GMarcus


D/DORS NAME JStrosnide
05/  /93 D/DORS


I AChaffee GMarcus BGrimes DATE 05/24/93 05/ /93 05/ /93 05/ J93[OFFICIAL
BGrimes


RECORD COPY]DOCUMENT NAME: G:\TXK\LTOP.IN
05/  J93
[OFFICIAL RECORD COPY]
DOCUMENT NAME: G:\TXK\LTOP.IN


d. I-}}
d.     I-}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Revision as of 03:22, 24 November 2019

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.

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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

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0

Attachment 4>

IN 93-58 July 26. IM us

Page I of I

LIST OF RECENTLY ISSUED

. 0)

NRCINFORMATION NOTICES (I)

0

Information Date of

Notice No. Subject Issuance Issued to

0.

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. 0 _

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 2

.) Plugging Criteria for reactor (PWRs). 2 Steam Generator Tubes' t o

93-51 Repetitive Overspeed 07/09/93 All holders of OLs or CPs Lno

8 Tripping of Turbine- for nuclear power reactors. 0 o, Driven Auxiliary Feed- co

water Pumps W U Z UJ

93-50 Extended Storage of 07/08/93 All licensees authorized _A3>

4 Sealed Sources to possess sealed sources.

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cc

OL - Operating License

CO0

2C

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o

CP - Construction Permit

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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.

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

  • See previous concurrence

OFC OEAB:DORS ADM:PUB SC/OEAB:DORS C/SRXB:DSSA

NAME TKoshy* Tech Editor* EGoodwin* RJones*

l DATE 06/04/93 05/10/93 05/21/93 06/04/93 I OFC

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1 DATE 05/24/931 06/08/93 06/17/93 06/17/93

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IN 93-XX

June xx, 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 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

l NAME TKoshy* Tech Editor* EGoodwin* RJones* l

[ DATE

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NAME

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DATE 05/24/93 06/08/93 06/16/93 06/ 7/93 lOFC 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

OFC OEAB:DORS ADM:PUB SC/OEAB:DORS C/SRXB:DSSA

NAME TKoshyA- Tech Editor* EGoodwin* RJones*

DATE 6 4 /93 05/10/93 05/21/93 06/04/93

[OFC C/EMCB:DE C/OEAB:DORS C/OGCB:DORS D/DORS

NAME JStrosnider* AChaffee* GMarcus BGrlimes

DATE 05/24/93 106/08/93 / /93 / /93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: S:\DORSSEC\LTOP.IN

  • See previous concurrence

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

NAME TKoshy Tech Editor* EGoodwin* RJones/

DATE 60 /zI/93 05/10/93 05/21/93 1 y/93 OFC C/EMCB:DE C/OEAB:WDORS C/OGCB:DORS D/DORS

NAME JStrosnider* A ee GMarcus BGrimes

DATE 105/24/93 j 0 /6 /93 J

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[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 RJones

DATE 05/tQ/93 05/10/93 05/ l93 e e I 193

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DOCUMENT NAME: G:\TXK\LTOP.IN

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