Information Notice 2000-20, 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 PUBLIC
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OFFICE REXB Tech Ed DLPM EMEB SPSB RES C:REXB
NAME CPetrone PKleene JStang EImbro RBarrett PBaranowsky* LMarsh
DATE / /00 10/10/00* 11/18 /00* 11/ 30 /00* 12/4 /00* 12/5 /00 12/ 11 /00
OFFICIAL RECORD COPY
Attachment LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
______________________________________________________________________________________
2000-19 Implementation of Human Use 12/05/2000 All medical use licensees
Research Protocols Involving
U.S. Nuclear Regulatory
Commission Regulated
Materials
2000-18 Substandard Material Supplied 11/29/2000 All 10 CFR Part 50 licensees and
by Chicago Bullet Proof applicants. All category 1 fuel
Systems facilities. All 10 CFR Part 72 licensees and applicants
2000-17 S1 Crack In Weld Area of Reactor 11/16/2000 All holders of OL for nuclear
Coolant System Hot Leg Piping power reactors except those who
At V.C. Summer have ceased operations and have
certified that fuel has been
permanently removed from the
reactor vessel
2000-17 Crack In Weld Area of Reactor 10/18/2000 All holders of OL for nuclear
Coolant System Hot Leg Piping power reactors except those who
At V.C. Summer have ceased operations and have
certified that fuel has been
permanently removed from the
reactor vessel
2000-16 Potential Hazards Due to 10/5/2000 All NRC licensees that process
Volatilization of Radionuclides unsealed byproduct material
2000-15 Recent Events Resulting in 9/29/2000 All radiography licensees
Whole Body Exposures
Exceeding Regulatory Limits
2000-14 Non-Vital Bus Fault Leads to 9/27/2000 All holders of OL for nuclear
Fire and Loss of Offsite Power power reactors
2000-13 Review of Refueling Outage 9/27/2000 All holders of OL for nuclear
Risk power reactors
2000-12 Potential Degradation of 9/21/2000 All holders of licenses for nuclear
Firefighter Primary Protective power, research, and test
Garments reactors and fuel cycle facilities
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit