Information Notice 1993-92, Plant Improvements to Mitigate Common Dependencies in Component Cooling Water Systems

Plant Improvements to Mitigate Common Dependencies in Component Cooling Water Systems

ML031070168
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:	12/07/1993
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-93-092, NUDOCS 9311190459
Download: ML031070168 (7)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

December 7, 1993 NRC INFORMATION NOTICE 93-92:

PLANT IMPROVEMENTS TO MITIGATE COMMON

DEPENDENCIES IN COMPONENT COOLING WATER

SYSTEMS

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

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

notice to alert addressees to potential problems resulting from common

dependencies in component cooling water (CCW) systems. Such dependencies on

loss of the CCW system were found to be contributors to the core damage

frequency at several nuclear power plants. 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.

Background

On November 23, 1988, the NRC issued Generic Letter 88-20, Oindividual Plant

Examination for Severe Accident Vulnerabilities,O requesting that each nuclear

power plant perform a systematic examination to identify any plant-specific

vulnerabilities to severe accidents and report the results to the Commission.

As stated in the letter, licensees are expected to expeditiously correct any

identified vulnerabilities. This notice provides insights gained from the

individual plant examination (IPE) process regarding improvements in plant

design or operational practices and procedures to mitigate potential problems

resulting from common dependencies in CCW systems.

Description of Circumstances

CCW systems provide cooling for reactor coolant pump (RCP) seals, and in many

cases also supply cooling water to emergency core cooling system (ECCS)

components.

Consequently, failure of the CCW system could cause a loss of RCP

seal cooling leading to an RCP seal loss of coolant accident (LOCA) and could

also disable the necessary accident mitigation systems. Several licensees

have identified these common dependencies as contributors to the total plant

core damage frequency in their IPEs. The following cases illustrate the

measures taken by several utilities to mitigate the consequences of such

accidents.

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IN 93-92

December 7, 1993 Turkey Point Units 3 and 4

The Turkey Point IPE documented a potential accident sequence caused by

an unisolable rupture of the CCV system that could occur while the

B charging pump is out of service. In this scenario, cooling to the RCP

seals would be lost, as would cooling to the A and C charging pumps. If

the charging pumps are run without CCW, they are predicted to fail.

This scenario would, according to the IPE, cause an RCP seal LOCA

because all means of providing seal cooling would be lost from either

the normal CCW system supply or the alternate seal injection supply from

the charging pumps. Additionally, because the CCW system supplies

cooling to the low and high head safety injection pumps, these pumps

also would fail.

Thus, an unmitigated RCP seal LOCA would occur.

This finding led the licensee to modify the A and C charging pumps in

1991 so that the service water system can be aligned as an alternate

cooling water supply to any of the charging pumps.

(The B charging pump

had been similarly modified in 1976.) Thus, a loss of the CCW system

alone would not disable all of the ECCS components required for LOCA

mitigation. This modification reduced the contribution of this sequence

to the total core damage frequency. However, during an NRC Operational

Readiness Assessment Team inspection at the facility, procedural

deficiencies were identified that could have prevented this modification

from performing its intended function. The licensee corrected the

deficiencies.

H.B. Robinson Steam Electric Plant. Unit 2

During development of the Robinson IPE, the licensee identified an

accident sequence that could be initiated by a total loss of the CCW

system. The configuration at Robinson is similar to that at

Turkey Point in that the CCW system supplies cooling to both the RCP

seals and the charging pumps. Thus, loss of the CCW system could lead

to an RCP seal LOCA coincident with the inability to provide high

pressure makeup.

This discovery led the licensee to implement procedural revisions that

allow the alignment of an alternate cooling supply to the charging pumps

by connecting the firewater system to existing fittings on the charging

pump couplings. This procedural revision reduced the estimated core

damage frequency contribution for the sequence.

Watts Bar Nuclear Plant. Unit I

Before performing the IPE, the licensee modified a procedure to align a

backup cooling water supply to the IA-A centrifugal charging pump (CCP)

via the emergency raw cooling water (ERCW) system. The CCPs depend on

the CCW system for normal cooling to the pump lube oil and gear oil

coolers. The CCV system also supplies cooling to the residual heat

removal pumps, safety injection pumps, containment spray pumps, and the

IN 93-92 December 7, 1993 RCP thermal barrier coolers. In the IPE, the licensee credited operator

actions associated with aligning the ERCW backup during a total loss of

CCW system scenario. The IPE indicated that alignment of the ERCW

system to the CCP reduced the Incremental core damage frequency.

A recent NRC Emergency Operationg Procedure team inspection at the

facility identified procedural deficiencies that could have prevented

this alignment from performing its intended function. The licensee is

developing measures to correct these deficiencies.

Diablo Canyon Nuclear Power Plant. Units I and 2

At Diablo Canyon Units 1 and 2, the CCW system provides cooling to the

charging pumps, which supply cooling water to the RCP seals. While

developing the probabilistic risk assessment, the licensee discovered

that loss of the CCW system could result in loss of the charging pumps

and the RCP seals and could lead to an RCP seal LOCA. To mitigate this

consequence, the licensee provided an alternate means of cooling the

charging pumps from the fire water system on loss of the CCW system.

Rose connections and dedicated hoses were provided and operational

procedures were changed to facilitate this alternate means of cooling.

As a result, the licensee indicated that the core damage frequency

associated with loss of the CCW system was reduced.

Donald C. Cook Nuclear Plant. Units I and 2

The CCW system for the Cook Nuclear Plant provides cooling to the RCP

seals and various primary plant components.

Loss of the CCW system

leading to an RCP seal LOCA was identified as a dominant contributor to

the core damage frequency. The licensee is currently investigating

changes to operational procedures to instruct the operator to open the

cross-tie valve of the chemical and volume control system of one unit to

the opposite unit early in the accident response to provide RCP seal

cooling and to prevent seal damage.

Discussion

As indicated above, several licensees have identified, through the IPE

process, that a common dependency in the CCW system to provide cooling for RCP

seals and ECCS components could result in a significant contribution to the

core damage frequency. Licensees found that changes in plant operational

practices and procedures or cost-effective improvements in design could reduce

the calculated core damage frequency.

IN 93-92

December 7, 1993

This information notice requires no specific action or written response. If

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

the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts:

J. L.

(404)

Shackelford, R11

331-0338

H. T. Drouin, RES

(301) 492-3917 Attachment:

List of Recently Issued NRC Information Notices

K>

Attachment

IN 93-92

December 7, 1993 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

91-21, Supp. 1

Inadequate Quality

Assurance Program of

Vendor Supplying

Safety-Related Equipment

12/07/93

All holders of OLs or CPs

for nuclear power reactors

and all recipients of

NUREG-0040, 'License Con- tractor and Vendor Inspec- tion Status Report' (White

Book).

89-77, Supp. 1

Debris in Containment

Emergency Sumps and

Incorrect Screen

Configurations

12/03/93 All holders

for nuclear

of OLs or CPs

power reactors.

93-91

93-90

93-89

Misadjustment Between

General Electric 4.16-KV

Circuit Breakers and Their

Associated Cubicles

Unisolatable Reactor

Coolant System Leak

Following Repeated

Applications of Leak

Sealant

Potential Problems with

BWR Level Instrumentation

Backfill Modifications

Status of Motor-Operated

Valve Performance Pre- diction Program by the

Electric Power Research

Institute

Fuse Problems with

Westinghouse 7300

Printed Circuit Cards

12/03/93

12/01/93

11/26/93

11/30/93

11/04/93

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 boiling water reactors.

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for nuclear power reactors.

93-88

93-87 OL - Operating License

CP - Construction Permit

IN 93-92 December 7, 1993 This information notice requires no specific action or written response. If

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

the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

orig /s/'d by EKGrines

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: J. L. Shackelford, RII

(404) 331-0338

M. T. Drouin, RES

(301) 492-3917 Attachment:

List of Recently Issued NRC Information Notices

• See Drevious concurrence

OFC

OGCB:DORS

ADM:PUB

RII:OB

C/OB/RII

D/DRS/RII

NAME

• MHarper

• Tech Ed

Shackelford

TPeebles

AGibson

DATE

08/04/93

08/05/93

09/01/93

09/01/93

09/01/93 OFC

SPSB:DSSA

C/SPSB

D/DSSA

C/SAIB:RES

D/DSIR

NAME

Schiffgens

WBeckner

AThadani

CAder

WMinners

DATE

09/09/93

09/9/93

3/93

11/04/93

1 1/05/93 OFC

• C/OGCB

NAME

GMarcus

DATE

11/23/93

12/27I93

OFFICIAL RECORD COPY

FDCUMENT NAML:

93-9Z.IN

i;

I

IN 93-XX

November 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

the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical /ontacts:

J. L.

(404)

Shackelford, R11

331-0338 M. T.

(301)

Drouin, RES

492-3917 Attachment:

List of Recently Issued NRC Information Notices

• See previous concurrence

OFC

OGCB:DORS

ADM:PUB

RII:OB

C/OB/RII

D/DRS/RII

NAME

• MHarper

• Tech Ed

• Shackelford

• TPeebles

• AGibson

DATE 1 08/04/93

08/05/93

09/01/93

09/01/93

,09/01/93 OFC

SPSB:DSSA

C/SPSB

D/DSSA

C/SAIB:RES

D/DSIR

NAME

• Schiffgens

• WBeckner

• AThadani

• CAder

• WMinners

DATE , 09/09/93

109/09/93

[09/13/93

11/04/93

111/05/93 OFC

C/OGCB

D/DORS

NAME

GMarcus G

BKGrimes

DATE I 11 /f/93

1 11/

/93

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OFFICIAL RECORD COPY

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