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

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, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	07/26/1993
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-93-058, NUDOCS 9307190131
Download: ML031070245 (9)

• 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

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.

Z. i

cc

OL - Operating License

CO0

2C

-i1X

o

CP - Construction Permit

LU 0.

zw

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

NAME

C/EMCB:DE

l JStrosnider*

C/OEAB:DORS

AChaffee*

OGCB:DORS

JLBirmingham*

C/OGCB:DORS

GHMarcus*

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

[OFC __ __ C

lNAME W ames

lDATE 07/-vf/93

[OFFICIAL RECORD COPY] $& d.

DOCUMENT NAME: S:\DORSSEC\93-58.IN emw& aA 1'r- . a4 Iq 1A~k~AM'x

,ng ?w

ar

4k, kxd)sL*K e4W 4

. '_ . .-. . __71Z11l9 3

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

OFC

NAME

l 06/04/93 l C/EMCB:DE

JStrosnider*

l 05/10/93 C/OEAB:DORS

AChaffee*

l 05/21/93 OGCB:DOR Ltj

JLBirmingam

06/04/93 C/OGCB:DORS

HMarcus L

l

l

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

/ /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 RJones

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

[OFC

NAME

DATE

_ C/EMCB:DE

JStrosnide

05/24/93 IC/OEAB:DORS

AChaffee

05/ /93 C/OGCB:DORS

GMarcus

05/ /93 D/DORS

BGrimes

05/ J93

[OFFICIAL RECORD COPY]

DOCUMENT NAME: G:\TXK\LTOP.IN

d. I-