NUREG-0138, Exemption from GDC 17 Requirements Re LPCI Swing Bus Design
| ML20072Q752 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 12/07/1990 |
| From: | Boger B Office of Nuclear Reactor Regulation |
| To: | COMMONWEALTH EDISON CO. |
| Shared Package | |
| ML20072Q755 | List: |
| References | |
| RTR-NUREG-0138, RTR-NUREG-138 NUDOCS 9012270380 | |
| Download: ML20072Q752 (5) | |
Text
._ __
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION in the Matter of COMMONWEALTH EDISON COMPANY Docket Nos. 50-254 and 50-265 (QuadCitiesNuclearPowerStation, Units 1 and 2 EXEMPTION 1.
The Commonwealth Edison Company (CECO or the licensee) is the holder of Operating License No. DPL-29 which authorizes operation of Quad Cities Nuclear PowerStation(QCNPS) Unit 1,andOperatingLicenseNo.DRP-30whichauthorizes operation of Unit 2.
These licenses provide, among other things, that QCNPS Units 1 and 2, are subject to all rules, regulations, and Orders of the Commission now or hereafter in effect.
The station is comprised of two boiling water reactors at the licensee's site located in Rock Island County, Illinois.
II.
In September 1987, the Fermi 2 plant 'aas found to be "ulnerable to a total Low Pressure Coolant injection (LPCI) fai'. e resu' ting from a single fai,1ure of DC control power in one divisio.
In rt lewing ti.e desigo modifications proposed to correct this vulnerability, the staff relooked at the LPCI swing bus design.
The original Quad Cities (a BWR-4 plant) design utilizes the swing bus configuration to provide power to the valves required for low Pressure Coolant Injection (LPCI)fromeitheroftworedundantstandby(onsite)powersources.
Under Regulatory Guide (R.G.) 1.6 for Class IE electric power systems, a swing bus concept does not satisfy the single failure criterion as it can potentially 1
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cause redundant emergency diesel generators to be paralleled resulting in the loss of redundant emergency power sources (common mode failure). Since a swing bus could compromise this independence requirement of reu.ndant Class 1E power sources and their load groups, automatic bus transfer schemes are not permitted between redundant safety trains. The swing bus configuration violates General Design Criterion (GDC) 17 of Appendix A to 10 CFR Part 50 requirements as the onsite electrical power systems do not have the desired independence to ensure performance of their safety functions.
111.
The swing bus design was permitted in the past to accommodate the design of the ECCS/LPCI mechanical system, valve arrangement, loop selection logic, etc. The staff acknowledged and approved the LPCI swing bus design weakness in Section 3.6.2 of the Quad Cities Safety Evaluation Report, dated August 25, 1971.
However, an Exemption to GDC-17 had never been issued.
Furthermore, the LPCI swing bus design weakness had been identified as one of fifteen technical issues in NUREG-0138, issued November 1976. The staff discussion had been provided in the NUREG under Issue No. 3 entitled,
" Acceptability of Swing Bus Design of BWR-4 II Plants."
It stated that, "The swing bus design approved for use in the BWR-4 plants does not satisfy the single failure criterion or the independence requirements of GDC-17."
It further stated that, "the swing bus design was accepted in construction II The staff found that the LPCI swing bus design has been used in both BWR-3 and -4 product lines, therefore, this issue applies to both BWR-3 and -4 plants.
l
permit (CP) review of the BWR-4 product line prior to development of R.G. 1.6."
As a result, the staff did not require that the BWR-4 product line be changed to eliminate the swing bus design, except for scme plants when such a change was required to meet the ECCS criteria of 10 CFR 50.46.
For those plants that chose not to perform an analysis of a complete LPCI f ailure coincident with LOCA analysis, the licensees were either required to remove the swing bus design or to commit to do so.
In some cases, plants were allowed to modify the LPCI swing bus design into a split-bus design so that it could take credit for a portion of the LPCI flow in LOCA analysis.
Although the LPCI swing bus has never satisfied R.G. 1.6 recommendations, the staff accepted the swing bus design in NUREG-0138 principally because the ECCS acceptance criteria can be met without any LPCI function. Nevertheless, for those BWR-3 and -4 plants that retained their swing bus design, the staff suggested the following alternative recommendations which are considered comparable to meetir.g R.G.1.6 recommendations:
A.1)
Only loads associated with LPCI function, i.e., LPC: valve motors may be connected to the swing bus so as to confine single failures within the swing bus.
2)
Thebustransferscheme(circuitry)mustmeettheapplicable portions of IEEE Standard 279, such as the single failure criterion, testability, and quality of components to reduce probability of propagating electrical faults between divisions.
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4 3)
Proper coordination of circuit protective devices must be provided to lessen probability of propagating faults into non-LPCI portions of the electrical division. This requires that the design provide both an adequate number of circuit breakers and proper breaker coordination.
B. Splitting the swing bus into two buses to obtain partial ECCS credit.
R.G. 1.6 prohibits the use of the swing bus as it does not satisfy the staff position regarding sufficient independence to satisfy GDC 17.
- However, the staff has determined that reasonable independence can be assured with the implementation of either the above alternate recommendations. Quad Cities has implemented the first of the alternate recommendations which brings the design to a level of safety comparable to that of meeting GDC 17. On this basis, the staff did not consider that the increase in independence provided by a change in the swing bus design to satisfy R.G.1,6 was justified for Quad Cities.
IV.
Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12:
(a)(1) and (a)(2)(ii) the Exemption from GDC 17 is authorized by law, will not present an undue risk to the public health and safety, and is consistentwiththecommondefenseandsecurity,and(2)applicationofthe regulation in the particular circumstances.is not necessary to achieve the underlying purpose of the rule. The Commission has reexamined its 1976
- discussion (IssueNo.3)inNUREG-0138andthetechnical. basis,and continues to concur with the general technical assessment, therein, that alternative' recommendations set out above provide an equivalent level of safety
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e as that which be achieved without a swing bus design. Accordingly, the Comission hereby grants the Lxernption from GDC 17 of Appendix A to 10 CFR Part 50.
Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant impact has been prepared and published in the Federal Register (55 FR 50524). Accordingly, based upon the environmental assesstsent, the Comissicn h65 cctermined thbt the granting of this exemption tu r, not have a sigr,1ficant effect on the quality of the human environt..uit.
This exemption is offectivt upon issuance.
FOR THE NUCLEAR REGULATORY COMMISSION Cruce A. Boger, Director Division of Reactor Projects !!!/IV/V Office of Nuclear Reactor Regulation Dated at Rockville, Maryland this 7th day of December,1990
December 7, 1990 h.
3 Docket Hos. 50-254 DISTRIBUTION:
and 50-265 UBU el Files BBoger PDill-2 r/f JZwolinski RBarrett L01shan Mr. Thomas J. Kovach CMoore TMurley/FMiraglia Nuclear Licensing Manager JPartlow CRossi Conrnonwealth. Edison Company-Suite 300 OGC-WF1 EJordan OPUS West !!!
GHill(8)
ACRS(10) 1400 OPUS Place GPA/PA OC/LFMB Downers Grove, Illinois 60515 PDill-2 Gray NRC & Local PDRs JClifford
Dear Mr. Kovach:
SUBJECT:
EXEMPTION FROM THE TECHNICAL REQUIREMEf4TS Of GEf4ERAL DESIGil CRITER10N 17 Of APPENDIX A TO 10 CFR PART 50 FOR THE QUAD CITIES LPCI SWING BUS DESIGN (TAC N05. 69420 AND 69421)
The Low Pressure Coolant injection (LPCI) swing bus design at Quad Cities.
Units 1 and 2, was found acceptable in the Quad Cities Safety Evaluation Report, issued August 25, 1971. The design was reexamined and again found acceptable in tiUREG-0138, published November 1976.
Both documents acknowledge that the design does not meet General Design Criterion (GDC) 17 of Appendix A to 10 CFR Part 50.
Enclosed is the Exemption from GDC 17.
A copy of this Exemption is being filed with the Office of the federal Register.
Sincerely, OriginalSigned By:
l l
Richard J. Barrett, Director l
Project Directorate 111-2 Division of Reactor Projects Ill/lV/V j
Office of Nuclear Reactor Regulation
Enclosure:
Exemption cc w/ enclosure:
See next page DOCUMENT NAME:
[69420AND69421 EXEMPTION)
- SEE PREVIOUS CONCURRENCE
/
Office:
- LA/PDill-2 CAPM/PDlll-2 PD i
3-2
- 0GC ADR3/DRP345 CMoore RBa rett CBarth JZwolinski 09/21/90 h(D'L01shan/tg Surname:
o/28/90
,, / 47 /90 10/29/90
\\'v/ % /90 Date:
Office:
D/DRP34 e
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s.
Mr. Thomas J. Kovach Quad Cities Nuclear Power Station Conucnwealth Edison Company Units 1 and 2 CC:
Mr. Stephen E. Shelton Vice President towa-Illinois Gas and Electric Ccmpany P. O. Box 4350 Davenport, Iowa 52808 Michael 1. Miller, Esq.
Sidley and Austin One First National Plaza Chicago, Illinois 60690 Mr. Richard Bax Station Manager Quad Cities Huclear Powcr Station 22710 206th Avenue North Cordova, Illinois 61242 Resident inspector U. S. Nuclear Regulatory Commission 22712 206th Avenue North Cordova, 111inois 61242 Chairman Rock Island County Board of Supervisors 1504 3rd Avenue Rock Island County Office Bldg.
Ro;k Island, Illinois 61201 Illinois Department of Nuclear Safety Office of Nuclear Facility Safety 1035 Outer Park Drive Springfield, Illinois 62704 Regional Administrator, Region Ill U. S. Nuclear Regulatory Commission 799 Roosevelt Road, Bldg. f4 Glen Ellyn, Illinois 60137 Robert Neumann Office of Public Counsel State of Illinois Center 100 W. Randolph i
Suite 11-300 Chicago, Illinois 60601
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i UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION 4
In the Matter of COMMONWEALTH EDISON COMPANY Docket Nos. 50-254 and 50-265 (QuadCitiesNuclearPowerStation, Units 1 and 2 EXEMPTION 1.
TheCommonwealthEdisonCompany(CEcoorthelicensee)istheholderof Operating License No. DPR-29 which authorizes operation of Quad Cities Nuclear Power Station (QCNPS) Unit 1, and Operating License No. DRP-30 which authorizes operation of Unit 2.
These licenses provide, among other things, that QCNPS Units 1 and 2, are subject to all rules, regulations, and Orders of the Commission now or hereafter in effect.
l The station is comprised of two boiling water reactors at the licensee's site located in Rock Island County, Illinois, j
II.
i in September 1987, the Fermi 2 plant was found to be vulnerable to a total Low Pressure Coolant Injection (LPCI) failure resulting from a single failure of DC control power in one~ division.
In reviewing the design modifications proposed to correct this vulnerability,'the staff relooked at the LPCI swing bus design.
The original Quad Cities (a BWR-4 plant) design utilizes the swing bus--
configuration to provide power-to the valves required for low Pressure Coolant Injection (LPCI)fromeitheroftworedundantstandby(onsite)powersources.
Under Regulatory Guide (R.G.) 1.6 for Class 1E electric power systems, a swing l
bus concept does not satisfy the single failure criterion as it can potentially i
e s!-
L,/
1 cause redundant emergency diesel generators to be paralleled resulting in the loss of redundant emergency power sources (comon mode failure). Since a swing bus could compromise this independence requirement of redundant Class IE power sources and their load groups, automatic bus transfer schemes are not permitted between redundant safety trains. The swing bus configuration violates General Design Criterion (GDC) 17 of Appendix A to 10 CFR Part 50 requirements as the onsite electrical power systems do not have the desired independence to ensure performance of their safety functions.
111.
The swing bus design was permitted in the past to accomodate the design of the ECCS/LPCI mechanical system, valve arrangement, loop selection logic, etc. The staff acknowledged and approved the LPCI swing bus design weakness in Section 3.6.2 of the Quad Cities Safety Evaluation Report, dated August 25, 1971. However, an Exemption to GDC-17 had never been issued.
Furthermore, the LPCI swing bus design weakness had been identified as one of fifteen technical issues in NUREG-0138, issued November 1976. The staff discussion had been provided in the NUREG under Issue No. 3 entitled,
" Acceptability of Swing Bus Design of BWR-4 II Plants."
It stated that, "The swing bus design approved for use in the BWR-4 plants does not satisfy the single failure criterion or the independence requirements of GDC-17."
It further stated that, "the swing bus design was accepted in construction 1/
The staff found that the LPCI swing bus design has been used in both BWR-3 and -4 product lines, therefore, this issue applies to both BWR-3 and -4 plants.
s permit (CP) review of the BWR-4 product line prior to development of R.G.1.6."
As a result, the staff did not require that the BWR-4 product line be changed to eliminate the swing bus design, except for Scme plants when such a change was required to meet the ECCS criteria of 10 CFR 50.46.
For those plants that chose not to perform an analysis of a complete LPC1 f ailure coincident with LOCA analysis, the licensees were either required to remove the swing bus design or to commit to do so.
In some cases, plants were allowed to modify the LPCI swing bus design into a split-bus design so that it could take credit for a portion of the LPCI flow in LOCA analysis.
Although the LPCI swing bus has never satisfied R.G. 1.6 recommendations, the staff accepted the swing bus design in NUREG-0138 principally because the ECCS acceptance criteria can be met without any LPCI function.
Nevertheless, for those BWR-3 and -4 plants that retained th ir swing bus design, the staff suggested the following alternative recommendations which ar's considered comparable to meetir.g R.G. 1.6 recommendations:
A.1)
Only loads associated with LPCI function, i.e., LPCI valve motors may be connected to the swing bus s0 as to confine single failures within the swing bus.
2)
The bus transfer scheme (circuitry) must meet the applicable portions of IEEE Standard 279, such as the single failure criterion, testability, and quality of components to reduce probability of propagating electrical faults between divisions.
9 I
-4 3)
Proper coordination of *ircuit protective devices must be provided to lessen probability of propagating faults into non-LPCI portions of the electrical division. This requires that the design provide both an adequate number of circuit breakers and proper breaker coordination.
B. Splitting the swing bus into two buses to obtain partial ECCS credit.
R.G. 1.6 prohibits the use of the swing bus as it does not satisfy the staff position regarding sufficient independence to satisfy GDC 17. However, the staff has determined that reasonable independence can be assured with the implementation of either the above alternate recommendations. Quad Cities has implemented the first of the alternate reconmendations which brings the design to a level of safety comparable to that of meeting GDC 17. On this basis, the staff did not consider that the increase in independence provided by a change in the swing bus design to satisfy R.G.1.6 was justified for Quad Cities.
IV.
Accordingly, the Commission has determined that, pursuant to 10 CFR 50.12:
(a)(1) and (a)(2)(ii) the Exemption from GDC 17 is authorized by law, will not present an undue risk to the public health and safety, and is consistent with the common defense and security, and (2) application of the regulation in the particular circumstances is not necessary to achieve the underlying purpose of the rule. The Commission has reexamined its 1976 discussion (Issue No. 3) in NUREG-0138 and the technical basis, and continues to concur with the general technical assessment, therein, that alternative recommendations set out above provide an equivalent level of safety
~. - -...
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j-l, 5-l as that which be achieved without a swing bus design. Accordingly, the
[
Coreission hereby grants the Lxercption from GDC 17 of Appendix A to 4
l Pursuant to 10 LFR 51.21, 51.32, and 51.35, an environment:1 assessment and finding of no significant impact has been prepared and published in the l
Federal Register (55 FR 50624). Accordingly, based upon the environmental as:,essirent,-the Comrrissich has determined that the granting of this exemption i
uni hot have a sigriificant effect on the quality of the human environt.uit.
This exemption is Lifettivt upon issuance.
l FOR THE NUCLEAR REGULATORY COMMISSION
. Druce A. Boger, Director Division'of Reactor Projects !!!/IV/V Office of Nuclear Reactor Regulation l
Dated at Rockville Maryland -
this 7th day of December,1990 I
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