ML18053A474
| ML18053A474 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 08/05/1988 |
| From: | Virgilio M Office of Nuclear Reactor Regulation |
| To: | Berry K CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| References | |
| TAC-59123, NUDOCS 8808110176 | |
| Download: ML18053A474 (4) | |
Text
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UNITED STATES NUC~EAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 Docket No. 50-255 Mr. Kenneth W. Berry Director, Nuclear Licensing Consumers Power Company 1945 West Parnall Road Jackson, Michigan 49201
Dear Mr. Berry:
August 5, 1988
SUBJECT:
ANTICIPATED TRANSIENTS WITHOUT SCRAM (10 CFR 50.62 ATWS RULE)
Consumers Power Company provided information concerning the Pali sades* Pl ant proposed design conformance to the requirements of the subject rule by submittal dated June 30, 1987.
The ATWS rule requires that the equipment/
systems installed to prevent and/or mitigate the consequences of ATWS events be electrically independent of the existing reactor protection system (RPS) to ensure that faults within nonsafety-related ATWS circuits cannot degrade RPS circuits, and to minimize the potential for common mode failures _(CMF) that could affect both RPS and ATWS circuits.
Electrical independence of the diverse scram system (DSS) from the existing RPS should be provided from the sensor outputs up to and including the final actuation device.
Electrical independence of the diverse auxiliary feedwater system (AFWS) actuation circuitry and diverse turbine trip system (OTT) from the existing RPS should be provided from the sensor outputs up to the final actuation device.
The matrix relays in the proposed Palisades DSS design receive power from the same 120 Vac vital instrument buses that provide power to the RPS.
The use of shared power supplies for RPS and DSS components is not in conformance with the requirements of the ATWS rule.
It is the*NRC staff's understanding that Consumers Power Company had intended to use the existing RPS power supplies to provide.power to the ass matrix relays because _of their high reliability, and --
considers the use of electrically independent supplies that may be somewhat less reliable to be poor.engineering practice.
The intent of the ATWS rule is to require systems/equipment that are diverse (i.e., hardware/component diversity) from the existing RPS components, and which are capable of preventing and/or mitigating the consequences.of an ATWS event.
This diversity ensures that a CMF _of identical components within the existing RPS that prevents a reactor trip by normal means will not also prevent the diverse ATWS prevention/mitigation systems from performing their design functions.
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'Mr. Kenneth The ATWS rulemaking process as documented in SECY 83-293, "Amendments to 10 CFR 50 related to Anticipated Transients WithOut Scram (-ATWSJ Events, 11 recognized that existing RPSs were highly reliable.
The largest contributor to RPS unreliability was shown to be a CMF of identical components.
The diverse equipment to be installed for the prevention and/or mitigation of ATWS events, although required to perform in a reliable manner, was not required to be procured and installed as safety-related (Cla:ss lE) equipment because it was determined that nonsafety-related diverse equipment (if properly maintained) had a sufficient degree of reliability to reduce the probability of unacceptable consequences from an ATWS event, PfATWS)' t~ ~n a~ceptable le~el.. Providing power to both the RPS and ATWS prever'lti6n/m1t1gat1on system circuits from a common source results in an interface between the systems that is difficult to.
analyze and could potentially be a mechanism for CMFs to affect both systems (e.g., degraded voltage or frequency conditions).
The ATWS rule requires that the power supplies for ATWS prevention/mltigation systems be electrically independent frbm the existing RPS power supplies to 1) prevent faults within nonsafety~related ATWS circuits from degrading the safety-related RPS, and
- 2) prevent interactions between the systems that could potentially compromise the added diversity by providing a means for CMFs to affect both the RPS and the DSS equipment inst~lled to prevent unacceptable plant conditions given failure of the RPS.
The NRC staff has not approved any designs that share power supplies between RPS and ATWS circuits, except where the ATWS circuits are designed, procured and installed as a fully redundant and independent 4 channel safety-related (Class lE) system (thus, exceeding ATWS.rule requirements), and where an analysis has
- been provided that demonstrates that a CMF of the shared power supplies (including sustained degraded voitage or frequency conditions) cannot adversely affect both the RPS and ATWS prevention/mitigation functions.
In these special case~, the lower level power supplies (e.g., + 15 Vdc logic power supplies) are required to be diverse.
It is the staff 1s understanding that the DSS at Palisades will be a nonsafety-related system.
Therefore, this is to inform you that the proposed power supply design for Palisades does not meet the requirements of the ATWS rule and to advise you as to what the NRC staff has found acceptable for other facilities.
Sincerely,
- ori g*i*na 1 *signed* by" Martin J. Virgilio, Director Project Di~ectorate III-1 Division of Reactor Projects - III, IV, V & Special Projects cc:
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@~JS.EJ-ElLESJ GHOLAHAN EJORDAN NRC & LOCAL PDRs ACRS (10)
RlNGRAM DCRUTCHFJELD BGRIMES SNewberry OGC PD31 PLANT GRAY TWAMBACH RKENDALL, ICSB/DEST OFFICE:
SURNAME:
DATE:
LA/PD3lf.ERSP Ringram -
08/J /88
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TWambath/rl
~V1rg1~io 08/ tfl88 08/ ~ /88 OFFICIAL RECORD COPY
Mr. Kenneth The ATWS rulemaking process as documented in SECY 83-293, "Amendments to.
10 CFR SO related to Anticipated Transients Without Scram (ATWS) Events, 11 recognized that existing RPSs were highly reliable.
The largest contributor to RPS unreliability was shown to be a CMF of identical components.
The diverse equipment to be installed for the prevention and/or mitigation of ATWS events, although required to perform in a reliable manner, was not required to be procured and installed as safety-related (Class lE) equipment because it was determined that nonsafety-related diverse equipment (if properly maintained) had a sufficient degree of reliability to reduce the probability of unacceptable consequences from an ATWS event, PrATWS)' to an acceptable level.
Providing power to both the RPS and ATWS pre~entlOn/mitigation system circuits from a common source results in an interface between the systems that is difficult to analyze and could potentially be a mechanism for CMFs to affect both systems (e.g., degraded voltage or frequency conditions).
The ATWS rule requires that the power supplies for ATWS prevention/mitigation systems be electrically independent from the existing RPS power supplies to 1) prevent faults ~ithin nonsafety-related ATWS circuits from degrading the safety-related RPS, and
- 2) prevent interactions between the systems that could potentially compromise the added diversity by providing a means for CMFs to affect both the RPS and the DSS equipment installed to prevent unacceptable plant conditions given failure of the RPS.
The NRC staff has not approved any designs that share power supplies between RPS and ATWS circuits, except where the ATWS circuits are designed, procured and installed as a fully redundant and independent 4 channel safety-related (Class lE) system (thus, exceeding ATWS rule requirements), and where an analysis has been provided that demonstrates that a CMF of the shared power supplies (including sustained degraded voltage or frequency conditions) cannot adversely affect both the RPS and ATWS prevention/mitigation functions.. In these special cases, the lower level power supplies (e.g., + 15 Vdc logic power supplies) are required to be diverse. It is the staff's understanding that the DSS at Palisades will be a nonsafety-related system.
Therefore, this is to inform you that the proposed power supply design for Palisades does not meet the requirements of the ATWS rule and to advise you as to what the NRC staff has found acceptable for other facilities.
- III, cc:
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Mr. Kenneth W. Berry Consumers Power Company cc:
M. I. Miller, Esquire Sidley & Austin 54th Floor One First National Plaza Chicago, Illinois 60603 Mr. Thomas A. McNish, Secretary Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Judd L. Bacon, Esquire Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137 Jerry Sarno Township Supervisor Covert Township 36197 M-140 Highway Covert, Michigan 49043 Office of the Governor Room 1 - Capitol Building Lansing, Michigan 48913 Mr. Gerald B. Slade Plant General Manager Palisades Plant 27780 Blue Star Memorial Hwy.
Covert, Michigan 49043 Resident Inspector c/o U.S. Nuclear Regulatory Commission Palisades Plant 27782 Blue Star Memorial Hwy.
Covert, Michigan 49043 Palisades Plant Nuclear Facilities and Environmental Monitoring Section Office Division of Radiological Health P.O. Box 30035 Lansing, Michigan 48909