Information Notice 2000-20, Potential Loss of Redundant Safety Related Equipment Due to Lack of a High-Energy Line Break Barriers

Potential Loss of Redundant Safety Related Equipment Due to Lack of a High-Energy Line Break Barriers

ML003760571
Person / Time
Issue date:	12/11/2000
From:	Marsh L Operational Experience and Non-Power Reactors Branch
To:
References
IN-00-020
Download: ML003760571 (5)

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

December 11, 2000

NRC INFORMATION NOTICE 2000-20:

POTENTIAL LOSS OF REDUNDANT SAFETY-

RELATED EQUIPMENT BECAUSE OF THE LACK

OF HIGH-ENERGY LINE BREAK BARRIERS

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 the discovery of several high-energy line break (HELB) concerns about

redundant safety-related equipment at D. C. Cook Nuclear Plant, Units 1 and 2. A failure of

redundant safety-related equipment may result in risk-significant configurations. It is expected

that the recipients will review the information for applicability to their facilities and consider

corrective actions, as appropriate. However, suggestions contained in this information notice

are not NRC requirements; therefore, no specific action or written response is required.

Background

As a result of the numerous safety issues identified at Cook 1 and 2 since August 1997, the

NRC analyzed the risk significance of Cook issues using the Accident Sequence Precursor

(ASP) program methodology. Of the 141 issues analyzed, four were found to be accident

sequence precursors since their conditional core damage frequencies were greater than

1.0x10-6/year. Two of these four issues involved postulated HELB scenarios that may lead to

failure of redundant safety-related systems (see Licensee Event Reports (LERs) 316/98-005 and 315/99-026 for details).

Within these two issues there are three scenarios that are described below:

ÿ

A break in a Unit 2 main steam line or main feedwater line could degrade the ability of

the component cooling water (CCW) pumps of both units to perform their function. All

five CCW pumps for Cook 1 & 2 are in the same room. The pumps are not qualified for

the harsh environment of a HELB. Therefore, all of the pumps may fail on exposure to

the high humidity and high temperatures caused by a main steam line or a main

feedwater line break in the pipe chase adjoining the room.

ÿ

A break in the high-pressure feedwater heaters or associated piping near the door to the

switchgear room could degrade the ability of both trains of 600V safety-related buses.

The door between the switchgear room and the turbine building is normally open and

may not close in the event of a HELB. Both trains of 600V safety-related buses are in

the switchgear room and the buses are not qualified for a harsh environment.

Therefore, both trains of safety-related 600V buses may fail on exposure to the high

humidity and high temperatures of a HELB.

ÿ

A HELB in the turbine building could degrade the ability of all three auxiliary feedwater

(AFW) pumps. The door to the turbine-driven AFW pump is normally open and may not

close in the event of a HELB. The two motor-driven AFW pumps are in rooms whose

ventilation intake is from the turbine building. AFW pumps are not qualified for a harsh

environment. Therefore, all AFW pumps may fail on exposure to the high humidity and

high temperatures of a HELB in the turbine building.

Discussion

Conditions conducive to a risk-significant configuration:

Four conditions must coexist to produce a risk-significant configuration like that at Cook. These

four conditions are (1) lack of a HELB barrier between the redundant trains of a system that is

needed to mitigate accidents, (2) the lack of environmental qualification for the redundant

components of trains located in the same area, (3) the presence of high-energy piping in

adjacent areas, and (4) the lack of a HELB barrier between adjacent piping and the redundant

safety system trains.

Relationship of the risk-significant configuration to regulatory guidance:

Section 3.6.1 of the Standard Review Plan (SRP) and NRR Plant Systems Branch Technical

Position SPLB 3-1 (formerly APCSB 3-1) provide regulatory guidance on the plant design for

protection against postulated piping failures outside containment. When SPLB 3-1 is used as a

guide to meet the requirements of the General Design Criterion 4 of 10 CFR Part 50,

Appendix A, the method used to conform with that regulatory guidance depends upon when the

construction permit applications were tendered and the operating licenses issued. Section B.4 of SPLB 3-1 provides details on the dependence of its applicability to the dates on which

construction permits were tendered or operating licenses were issued.

Generic Letter 87-11, issued on June 11, 1987, transmitted Revision 2 of the Mechanical

Engineering Branch (MEB) Technical Position MEB 3-1. This revision provided additional

guidance on locations where pipe breaks should be postulated. Revision 2 of MEB 3-1 allows

the elimination of pipe-whip restraints, jet-impingement shields (placed to mitigate the effects of

arbitrary intermediate ruptures), and other related changes. However, the revision does not

relieve licensees from the need to conform to the guidance relating to HELB effects on essential

systems and components. Essential systems and components are systems and components

required to shut down the reactor and mitigate the consequences of a postulated piping failure, without offsite power. Even though application of Revision 2 of the MEB 3-1 pipe break criteria

may not require postulating breaks near areas that house the redundant equipment and

installing pipe restraints, licensees are expected to comply with their licensing basis and

regulatory commitments for postulating a crack at the location most damaging to the essential structures and systems. For example, the Giambusso letter of 1972 (NUREG-0800,

Standard Review Plan 3.16.1, Appendix B, Rev. 2, October 1999) specifies that where pipes

carrying high-energy fluids are routed near structures and systems necessary for safe

shutdown of the plant, supplemental protection of those structures and systems shall be

provided to cope with the environmental effects (including the effects of jet-impingement) of a

single postulated open crack at the location most damaging to those essential structures and

systems.

NUREG-1728, Assessment of Risk Significance Associated With Issues Identified at

D. C. Cook Nuclear Power Plant, Volumes 1 & 2 were published in October 2000. This report

documents the results of an analysis of the risk significance at D. C. Cook Nuclear Power Plant, Units 1 & 2 since August 1997. This NUREG may be accessed electronically at the NRCs

Public Electronic Reading Room at www.nrc.gov/NRC/ADAMS/index.html.

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, the appropriate regional office, or the appropriate Office of Nuclear Reactor Regulation

(NRR) project manager.

/RA/

Ledyard B. Marsh, Chief

Events Assessment, Generic Communications

and Non-Power Reactors Branch

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical contacts:

S. D. Weerakkody, RES

Y. C. Li, NRR

301-415-6374

301-415-2772 E-mail: sdw1@nrc.gov

E-mail: ycl@nrc.gov

C. D. Petrone, NRR

301-415-1027 E-mail: cdp@nrc.gov

Attachment: List of Recently Issued NRC Information Notices essential structures and systems. For example, the Giambusso letter of 1972 (NUREG-0800,

Standard Review Plan 3.16.1, Appendix B, Rev. 2, October 1999) specifies that where pipes

carrying high-energy fluids are routed near structures and systems necessary for safe

shutdown of the plant, supplemental protection of those structures and systems shall be

provided to cope with the environmental effects (including the effects of jet-impingement) of a

single postulated open crack at the location most damaging to those essential structures and

systems.

NUREG-1728, Assessment of Risk Significance Associated With Issues Identified at

D. C. Cook Nuclear Power Plant, Volumes 1 & 2 were published in October 2000. This report

documents the results of an analysis of the risk significance at D. C. Cook Nuclear Power Plant, Units 1 & 2 since August 1997. This NUREG may be accessed electronically at the NRCs

Public Electronic Reading Room at www.nrc.gov/NRC/ADAMS/index.html.

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, the appropriate regional office, or the appropriate Office of Nuclear Reactor Regulation

(NRR) project manager.

/RA/

Ledyard B. Marsh, Chief

Events Assessment, Generic Communications

and Non-Power Reactors Branch

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical contacts:

S. D. Weerakkody, RES

Y. C. Li, NRR

301-415-6374

301-415-2772 E-mail: sdw1@nrc.gov

E-mail: ycl@nrc.gov

C. D. Petrone, NRR

301-415-1027 E-mail: cdp@nrc.gov

Attachment: List of Recently Issued NRC Information Notices

DISTRIBUTION: IN File

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OFFICE

REXB

Tech Ed

DLPM

EMEB

SPSB

RES

C:REXB

NAME

CPetrone

PKleene

JStang

EImbro

RBarrett

PBaranowsky*

LMarsh

DATE

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10/10/00*

11/18 /00*

11/ 30 /00*

12/4 /00*

12/5 /00

12/ 11 /00

OFFICIAL RECORD COPY

______________________________________________________________________________________

OL = Operating License

CP = Construction Permit

Attachment LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

_____________________________________________________________________________________

Information

Date of

Notice No.

Subject

Issuance

Issued to

______________________________________________________________________________________

2000-19

Implementation of Human Use

Research Protocols Involving

U.S. Nuclear Regulatory

Commission Regulated

Materials

12/05/2000

All medical use licensees

2000-18

Substandard Material Supplied

by Chicago Bullet Proof

Systems

11/29/2000

All 10 CFR Part 50 licensees and

applicants. All category 1 fuel

facilities. All 10 CFR Part 72 licensees and applicants

2000-17 S1

Crack In Weld Area of Reactor

Coolant System Hot Leg Piping

At V.C. Summer

11/16/2000

All holders of OL for nuclear

power reactors except those who

have ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel

2000-17

Crack In Weld Area of Reactor

Coolant System Hot Leg Piping

At V.C. Summer

10/18/2000

All holders of OL for nuclear

power reactors except those who

have ceased operations and have

certified that fuel has been

permanently removed from the

reactor vessel

2000-16

Potential Hazards Due to

Volatilization of Radionuclides

10/5/2000

All NRC licensees that process

unsealed byproduct material

2000-15

Recent Events Resulting in

Whole Body Exposures

Exceeding Regulatory Limits

9/29/2000

All radiography licensees

2000-14 Non-Vital Bus Fault Leads to

Fire and Loss of Offsite Power

9/27/2000

All holders of OL for nuclear

power reactors

2000-13

Review of Refueling Outage

Risk

9/27/2000

All holders of OL for nuclear

power reactors

2000-12

Potential Degradation of

Firefighter Primary Protective

Garments

9/21/2000

All holders of licenses for nuclear

power, research, and test

reactors and fuel cycle facilities