ML19347F170

Clarifies Purpose & Scope of Mark I Containment long-term Program in Response to Util Re Torus Mod at Facility.Completion Dates Should Not Be Modified Until Schedular Uncertainties Have Been Quantified

ML19347F170
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	04/29/1981
From:	Eisenhut D Office of Nuclear Reactor Regulation
To:	Rich Smith VERMONT YANKEE NUCLEAR POWER CORP.
References
NUDOCS 8105150383
Download: ML19347F170 (2)

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k Docket No. 50-271 g

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, f Q /Sggh Mr. Robert L. Smith Licensing Engineer 6

Yermont Yankee Nuclear Power D

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1671 Worcester Road c

Framingham, Massachusetts 01701

SUBJECT:

IMPLEMENTATION OF THE MARK I CONTAINMENT LONG-TERM PROGRAM

Reference:

Letter from R. L. Smith VYNPC to D. G. Eisenhut USNRC, dated February 23, 1981

Subject:

TORUS Modification at Vemont Yankee The purpose of this letter is to reiterate the purpose and scope of the Mark I program, to provide clarification of the NRC Order and forwarding letter of January 13, 1981, and to respond to your letter referenced above.

As you are aware, the purpose of the Mark I containment long-term program is to define the design basis loads that are appropriate for the anticipated life of each BWR Mark I facility and to restore the original intended design safety margins for each Mark I containment system. Extensive experinental and analytical programs conducted by the Mark I Owner's Group resulted in load definition and structural assessment techniques, as set forth in the " Mark I Containment Program Load Definition Report," NEDO-21888, dated December 1978, and the " Mark I Containment Program Structural Acceptance Criteria Plant Unique Analysis Application Guide," NED0-24583-1, dated October 1979. The methodology in these reports as modified by the staff's Acceptance Criteria (described in NUREG-0661) provides a conservative and unifom basis for detemining if any structural or other plant modifica-tions are needed to restore the original intended margin of safety in the containment design.

Although the plant-unique analysis work has been underway for some time, the staff recognizes there are still analyses that must be completed before all of the plant modification designs can be confirmed. The current schedules for completion of the Mark I modifications already reflects revised commitments by most licensees in anticipation of additional modifi-cations that are typically associated with supports for piping attached to the suppression chanber and the supports on internal structures. Most schedules included consideration of the amount of difficulty expected to be encountered in transferrina the techniques developed in the Mark I long-term program to the plant unique analyses.

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- ; APR 2 9 1981 With due regard to these uncertainties, the schedules reflected in the Mark I Orders were already " revised" schedules and were approved by the Con-mission in order to ensure a timely completion of this program and restoration of the margins of safety in the containment design. We do not believe that it is appropriate to modify such completion dates until schedular uncertainties have been quantified and until there is a justifiable basis for establishing a new revised schedule. Every reasonable effort should be made to achieve the completion dates established by the Order before the staff will consider extensions to those completion dates.

In addition, several licensees have requested staff review of plant-specific applications of the generic Mark I criteria. We do not believe that such reviews are necessary. It is our opinien that the generic Mark I criteria, as described in NUREG-0661, provides sufficient guidance to conduct the plant-unique analyses and that only our post-implementation audits of the plant-unice analyses are required.

In the event that an exception to the generic criteria must be taken to achieve the completion schedule, you should advise the staff of any exceptions by letter as soon as practical, stating your sound engineering basis for that exception, and you should describe the exception in detail in the plant-unique analysis report. We intend to review such exceptions only in our post-implementation audi t.

If you believe further consideration of your completion schedule is warranted after completion of the plant-unique analysis, you should formally submit a detailed schedule that includes the schedule for design, procurement, and installation of planned plant modifications, the schedule for plant outages and fuel burnup estimates, a description of the resources devoted to Mark I-related activities, and a qualitative estimate of the relative safety significance of the modifications that have not yet been installed.

Sincerely, Original signed by g-nn 5. 21sanhd Darrell G. Eisenhut Director i

Division of Licensing Office of Nuclear Reactor Regulation cc: Sea next page Distribution:

Docket File B. Siegel NRC PDR Project Manager ORB #2 Reading OELD D. Eisenhut ISE (3)

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