ML20217F117

Informs That During 466th Meeting of ACRS on 990930-1002, Proposed Resolution of GSI B-55, Improved Reliability of Target Rock Srvs, Was Reviewed.Conclusion & Recommendations Are Listed

ML20217F117
Person / Time
Issue date:	10/08/1999
From:	Powers D Advisory Committee on Reactor Safeguards
To:	Travers W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
References
REF-GTECI-B-55, REF-GTECI-PV, TASK-B-55, TASK-OR ACRS-R-1858, NUDOCS 9910200228
Download: ML20217F117 (2)

Text

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October 8.1999 Dr. William D. Travers Executive Director for Operations U.S. Nuclear Regulatory Commksion Washington, D.C. 20555-0001

SUBJECT:

PROPOSED RESOI.UTION OF GENERIC SAFETY ISSUE B-55, "lMPROVED RELIABILITY OF TARGET ROCK SAFETY RELIEF VALVES" During the 466* meeting of the Advisory Conimittee on Reactor Safeguards, September 30-

' October 2,1999, we reviewed the proposed resolution of Generic Safety issue (GSI) B-55,

" Improved Reliability of Target Rock Safety Relief Valves." During our review, we had the benefit of discussions with representatives of the NRC staff. We also had the benefit of the document referenced.

Conclusion and Recommendation We agree with the staff's proposed resolution of GSI B-55.

The staff should perform a statistical analysis to ensure that the apparent improvement in performance of the two-stage valves is significant and confirms its conclusion.

Backaround The boiling water reactor (BWR) pressure relief system is designed to prevent over-pressurization of the reactor coolant pressure boundary. This protection is accomplished I

through the use of a plant-unique combination of safety valves (SVs), power actuated relief valves (PARVs), and dual function safety relief valves (SRVs) that have both a mechanical self-actuating setpoint function and a power-actuated function. The majority of the SRVs in older BWRs were manufactured by Target Rock.

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. Some SRVs have exhibited anomalies, such as:

Spurious actuation Upward setpoint drift i

Excessive blowdown 180022 Owe 7 9910200228 991008 Arg PDR ACRS R-1858 PDR i

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The' BWR' Owners Group and the individual BWR licensees have i.mproved the performance of l

the SRVs by installing lon-beam implanted platinum disks or Stellite 21 disks to improve seating l

and installing additional pressure switches to actuate these valves using pneematic power.

l Based on recent performance data, the staff has concluded that both the Stellite 21 and the ion-beam implanted platinum disks are performing better than the former Stellite 6B disks with a l

lower rate of occurrence of high setpoint drift beyond that allowed by plant Technical Specifications. The conclusion concerning the relative performance of the different disk materials would be more persuasive if it were supported by an appropriate statistical analysis of the data.

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In addition, the staff stated that the affected BWR plants have sufficient margin to l

accommodate upward valve setpoint drift as high as 10 percent. In view of the improvement in valve performance, the margin available to accommodate upward setpoint drift and other options such as pressure switches, the staff does not plan to initiate any nevt regulatory actions.

We agree with the proposed resolution of GSI B-55. The activities being pursued by the licensees under existing regulatory requirements are sufficient. There is no need to impose any additional regulatory requirements.

Sincerely,

)*h?A ustup Dana A. Powers l

Chairman t

Reference:

E mail to John T. Larkins, ACRS, from Charles Hammer, Office of Nuclear Reactor Regulation, NRC,

Subject:

. ACRS Briefing of Generic Safety issue B-55," improved Reliability of Target Rock Safety Relief Valves," dated September 2,1999.

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