ML18038A658

Forwards Safety Evaluation Accepting Licensee Responses to Generic Ltr 83-28,Items 4.5.3, Reactor Trip Reliability Sys for All Domestic Operating Reactors. Contractor Rept Also Encl

ML18038A658
Person / Time
Site:	Nine Mile Point
Issue date:	06/22/1989
From:	Slosson M Office of Nuclear Reactor Regulation
To:	Burkhardt L NIAGARA MOHAWK POWER CORP.
References
CON-IIT07-438-91, CON-IIT7-438-91 GL-83-28, NUREG-1455, TAC-54002, TAC-71822, NUDOCS 8906280217
Download: ML18038A658 (7)

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1 Docket Nos. 50-220 and 50-410 Dune 22, 1989 Mr. Lawrence Burkhardt III Executive Vice President, Nuclear Operations Niagara Mohawk Power Corporation 301 Plainfield Road

Syracuse, New York 13212

Dear Mr. Burkhardt:

DIS UTION PDI-1 Rdg SVarga CVogan MSlos son VMcCree EJordan ACRS (10)

JJohnson, RI NRC PDR Local PDR BBoger RCapra DOudinot OGC BGrimes BMozafari

SUBJECT:

SAFETY EVALUATION FOR GENERIC LETTER 83-28, ITEM 4.5.3, REACTOR TRIP RELIABILITY-ON-LINE FUNCTIONAL TESTING OF THE REACTOR TRIP SYSTEM (TAC NOS.

54002 AND 71822)

V Generic Letter 83-28, Item 4.5.3, required confirmation from all licensees and applicants that on-line functional testing of the reactor trip system, including independent testing of the diverse trip feature, was being performed.

By letter s dated November 8, 1983, February 2, 1984., April 30, 1984, July 31, 1984, July 2, 1985 and December 31, 1985 for Nine Mile Point'nit 1 and April 10, 1984, December 20, 1985 and April 15, 1986 'for Nine'ile Point Unit 2, you submitted responses to Generic Letter 83-28,'tem '4.5.3.

Therein you indicated your endorsement of the BWR Owners'roups Report NECD-30844, as being applicable to Nine Mile Point Units 1 and 2.

The NRC staff, with the assistance of our contractor, Idaho National Engineering Laboratory, has reviewed your responses and the BWR Owners Group's report.

We conclude that the existing intervals for, on-line functional testing at Nine Mile Point Units 1 and 2 are consistent with achieving high reactor trip system availability.

The enclosed safety evaluation and contractor's report (EGG-NTA 8341) provide the details and basis for our conclusion.

Therefore, we consider Generic Letter 83-28, Item 4.5.3 to be complete.

This completes a'll staff activities related to TAC Nos.

54002 and 71822.

S incerely,

Enclosures:

1.

Safety Evaluation Report 2.

Technical Evaluation Report cc w/enclosures:

See next page t TACS 54002 5 71822]

ORIGINAL SIGNED BY Marylee M. Slosson, Project Manager Project Directorate I-1 Division of Reactor Projects I/II pool POI-1 PDI-1 CVogan MSlosson: r 6/gl /<>

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/g Mr. Lawrence Burkh III Niagara Mohawk Power Corporation Cce Hr. Troy B. Conner, Jr., Esquire Conner 8 Wetterhahn Suite 1050 1747 Pennsylvania

Avenue, N.W.

Washington, DC 20006 Nine NPoint 1/2 Mr. Kim Dahlberg Unit 1 Station Superintendent Nine Mile Point Nuclear Station Post Office Box 32

Lycoming, New York 13093 Mr. Frank R. Church, Supervisor Town of Scriba R.

D. 82

Oswego, New York 13126 Mr. Richard Abbott Unit 2 Station Superintendent Nine Mile Point Nuclear Station Post Office Box 32

Lycoming, New York 13093 Mr. James L. Willis General Supt.-Nuclear Generation Niagara Mohawk Power Corporation Nine Hi'le Point Nuclear Station Post Office Box 32

Lycoming, New York 13093 Charlie Donaldson, Esquire Assistant Attorney General New York Department of Law 120 Broadway New York, New York 10271 Resident Inspector U. S. Nuclear Regulatory Commission Post Office Box 126

Lycoming, New York 13093 Mr. Paul D. Eddy State of New York Department of Public Service Power Division, System Operations 3 Empire State Plaza

Albany, New York 12223 Mr. Gary D. Wilson, Esquire Niagara Mohawk Power Corporation 300 Erie Boulevard West

Syracuse, New York 13202 Mr. Peter E. Francisco, Licensing Niagara Mohawk Power Corporation 301 Plainfield Road

Syracuse, New York 13212 Regional Administrator, Region I U. S. Nuclear Regulatory Comnission 475 Allendale Road King of Prussia, Pennsylvania 19406 Mr. Richard Goldsmith Syracuse University College of Law E. I. White Halle Campus

Syracuse, New York 12223 Ms. Donna Ross New York State Energy Office 2 Empire State Plaza 16th Floor Albany, New York 12223 Mr. Richard M. Kessel Chair and Executive Director State Consumer Protection Board 99 Washington Avenue

Albany, New York 12210

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ENCLOSURE I SYSTE SAFETY EVALUATION REPORT GENERIC LE EACTOR TRIP TORS

1.0 INTRODUCTION

On February 25, 1983, both of the scram circuit breakers at Unit 1 of the Salem Nuclear Power Plant failed to open upon an automatic reactor trip signal from the reactor protection system (RPS).

This incident was terminated

. manually by the operator about 30 seconds after the initiation of t'e automatic trip signal.

The failure of the circuit breakers was determined to be related to the sticking of the undervoltage trip attachment.

Prior to this incident, on February 22, 1983, at Unit 1 of the Salem Nuclear Power Plant, an automatic trip signal was generated based on steam generator low-low level during plant startup.

In this case, the reactor was tripped manually by the operator almost coincidentally with the automatic trip.

Following these incidents, on February 28, 1983, the NRC Executive Director for Operations (EDO), directed the staff to investigate and report on the generic implications of these occurrences at Unit I of the Salem Nuclear Power Plant.

The results of the staff's inquiry into the generic implications of the Salem Unit 1 incidents are reported in NUREG-1000, "Generic Implications of the ATWS Events at the Salem Nuclear Power Plant".

As a result of this investigation, the Commission (NRC) requested (by Generic Letter 83-28 dated July 8, 1983) all licensees of operating reactors, applicants for an operating

license, and holders of construction permits to respond to generic issues raised by the analyses of these two ATWS events.

The licensees were required by Generic Letter 83-28,'tem 4.5.3 to confirm that on-line functional testing of the reactor trip system (RTS), including independent testing of the diver se trip features, was being performed at all plants.

Existing intervals for on-line functional testing required by Technical Specifications were to be reviewed to determine if the test intervals were adequate for achieving high RTS availability when accounting for considerations such as:

(I) uncertainties in component failure rates; (2) uncertainties in common mode failure rates; (3) reduced redundancy during testing; (4) operator error during testing; and (5) component "wear-out" caused by the testing.

2.0 DISCUSSION The NRC's contractor, Idaho National Engineering Laboratory (INEL), reviewed the licensee Owners Group availability analyses and evaluated the adequacy of the existing test intervals, with a consideration of the above five items, for all plants.

The results of this review are reported in detail in EGG-NTA-8341,

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"A Review of Reactor Trip System Availability Analyses for Generic Letter 83-28, Item 4.5.3 Resolution," dated March 1989 and summarized in this report.

The results of our evaluation of Item 4.5.3 and our review of EGG-NTA-8341 are presented below.

.The Babcock

& Wilcox (BKW), Combustion Engineering (CE), General Electric (GE),

and Westinghouse (W) Owners Groups have submitted topical reports either in response to GL 83-28, Item 4.5.3 or to provide a basis for requesting Technical Specification changes to extend RTS surveillance test intervals (STI).

The owners groups'nalyses addressed the adequacy of the existing intervals for on-line functional testing of the RTS, with the considerations required by Item 4.5.3, by quantitatively estimating the unavailability of the RTS.

These analyses found that the RTS was very reliable and that the

. unavailability was dominated by common cause failure and human error.

The ability to accurately estimate unavailability for very reliable systems was considered extensively in NUREG-0460, "Anticipated Transients Without Scram for Light Water Reactors",

and the ATWS rulemaking.

The uncertainties of such estimates are large, because the systems are highly reliable, very little experience exists to support the estimates, and common cause failure probabilities're difficult to estimate.

Therefore we believe that the RTS unavailability estimates in these studies, while useful for evaluating test intervals, must be used with caution.

NUREG-0460 also states that for systems with low failure probability, such as the

RTS, common mode failures tend to predominate, and, for a number of

reasons, additional testing will not appreciably lower RTS unavailability.

First, testing more frequently than weekly is generally impractical, and even so the increased testing could at best lower the failure probability by less than a factor of four compared to monthly testing.

Secondly, increased testing could possibly increase the probability of a common mode failure through increased stress on the system.

Finally, not all potential failures are detectable by testing.

In summary, NUREG-0460 provides additional justification to demonstrate that the current monthly test intervals are adequate to maintain high RTS availability.

3.0 CONCLUSION

All four vendors'opical reports have shown the currently configured RTS to be highly reliable with the current monthly test intervals.

Our contractor has reviewed these analyses and performed independent estimates of their own which conclude that the current test intervals provide high reliability.

In addition, the analyses in NUREG-0460 have shown that for a number of reasons, more frequent testing than monthly will not appreciably lower the estimates of failure probability.

Based on our review of the Owners Group topical reports, our contractor's independent

analysis, and the findings noted in NUREG-0460, we conclude that the existing intervals, as recommended in the topical reports, for on-line functional testing are consistent with achieving high RTS availability at all operating reactors.