ML20236F507
| ML20236F507 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 10/23/1987 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Tarrant G VERMONT, STATE OF |
| References | |
| NUDOCS 8711020174 | |
| Download: ML20236F507 (2) | |
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' bi sitr. Gerald & Tarrant, ComissionerL M
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Department'of Public Service'
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State Office Buil_ ding....
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Dear.Gerry:
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This is a follow-up to our telephone conversatiioniofL0ctober).21?andlyourj N
letter;to me' dated September 1, 1987, regarding containment lsafetye
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iWearecontinuihgto.developia;-resolutiontojhe51ssuefofl:whh11mprovement's)
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are needed for BWR Mark 11 containmentstof.the' type:found at~~ Vermont Ya'nk'ee.:
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.Last ~ year the NRC, under the leadership of Mr. Harold 'Dentoniand.Mr. Robert:
-1 Bernero,. had proposed several improvements; to, Mark?IJcontainmentif that wepe e
thought;to provide edditional assurance that thel consequences.oftaLsevere'co s 1
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damagiaccident would. be substantially mitigated. ! After a; goodideal-;offstudy'.
and' peer review,-they concluded last'Aprilethat' "On-the~one handFtheilndu.stry.:
analysts say that changestare not justified'.70n theLother hand the Researchi q
scientists-indicateithat the changes are'no_t effective'.." >In other.words, the.L 1
technical consensus on the proposed improvements) evaporated, even amonglthe; 1
s NRC staff.
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Primarilyduetothosedevelopments,ourfscheduleforfdeveloping' recommended' d
improvements for Mark I containments has slipped.
-are now the following:
Our ksy planning' milestones cm !
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November 1987 -
Planifor Developing lRe' solution-auly 1988-Preliminary l Recommendations September 1988 --
. Final recommendations' to Comission; With regard to the: containment venting issue, we havefasked: Vermont' Yankee andv
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d other' licensees.to proceed with caution.1 When backfitting design;changesito" y
H such an important safety structure as the containment,7 t-is essential that
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all:the ramifications.be considered carefully.;:It was for this reason that wei L
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'sent the enclosed letter to:VermontsYankee.asking thatithey;considerca1...
d number of questions in their evaluation of a containment vent for/the pla_nt.;
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-I-have instructed my staff to keep you/ informed'of all Eey-. developments on fi s
~this issuerelated to. Vermont Yankee.
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Thomas E. Hurley, Director Office,ofNuclearfReactorTReg'ulation/-
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Enclosure:
d mq Ltr to R..W. Capstick fm S. Varga dtd 8/24/87 si d
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J.. Gary Weigand,.. Vermont Yankee-
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,. : 10-23-87.-
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1 August-24 198'7-Docket No.: 50-271 H
l Mr. ;R. W. Capstick
' Licensing Engineer.._
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Vermont Yankee' Nuclear Power Corporation 1617 Worcester Road Framingham,. Massachu setts ' ' 01701
Dear'Mr. Capstick:
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SUBJECT:
': VERMONT YANKEE: CONTAINMENT SAFETY INITIATIVE;(TAC N0." 62753)l
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On June ~25,1987,: Vermont. Yanke'e Nuclear Power Corporation L(VYNPC) submitted a -
status update and: design description for the Vermont Yankee Containment'= Safety; Initiative. We are: studying with interest your' plans to. proceed with.,
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' improvements -related to containment spray, and :look' forward to receiving more infonnation. about -your. containment venting. plans.
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..I Because we consider there-are' sev'eral unanswered. questions: concerning the. _.
j containment venting issue, we 1 ppreciate your thoughtfu1Ede11 berate; approach.'
We' note that you intend a thorough rereviewcof containment vent-~designiand.
implementation issues, and that you will notify us ofLthe results-of your:
review by March 1,11988.. We have,enclos'edfa list-of several considerations.
related to containment venting analysis that we woul.d like you> to ' consider in conducting your: review.
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Should you.have any questions regarding this please contact: the NRR Pmject -
L Manager, V. Rooney (301-492-8344).
Sincerely,'
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- Steven A..- Varga', Director.
Division of, Reactor Projects:I/II.
Office of Nuclear Reactor Regulation As stated o
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CONTAINMENT VENTING' CONSIDERATIONS
Athoroughreviewof; con'siderationsinvolvedincont'ainmentventindwould'.
include:
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1).. A' comprehensive analysis of accident. sequences,-with their. estimated.
frequency 'of occurrence,. for..which the vent.would be : called upon'. to -
't operate.:
2)
- An estimate of the' fraction of.those. sequences where'the vent would be,
m operated but where the accident would, have been.tenninated short'.of,
- containment failure without. vent operation:
a). elhetric power returnhd to service -
b) equipment returned to service i.
c) mis-diagnosed. situation corrected by operators 3)
A comprehensive analysis.of sequences:that i
(a) could be improved by correct use'of.the vent, or (b) could be-initiated or made worse by incorrect operation of the vent l L
4)
An analysis of sequences-that could lead to containment failure by.
l operation of the vent ~followed by excessive pressure differential l
(buckling).
5)
Analysis of the probability of vent failure when called upon.
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Analysis 'of maintenance or surveillance errors on the.. vent system that I
could induce accidents..
7)
An estimate of. the radioactivity._ released for"all sequences when the vent 1
could be opened, including both correct usage according to procedcres. 3nd incorrect usage due to human' error or eouipment malfunction.
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