ML20215M573

Forwards Preliminary Evaluation of Containment Study Transmitted w/ .Reevaluation of Combustible Gas Control & Core Debris Barriers,Per NRC Comments,Requested. Response to Encl Questions Also Requested by 861117

ML20215M573
Person / Time
Site:	Vermont Yankee
Issue date:	10/24/1986
From:	Bernero R Office of Nuclear Reactor Regulation
To:	Weigand G VERMONT YANKEE NUCLEAR POWER CORP.
Shared Package
ML20215M575	List: ML20215M573 ML20215M587
References
NUDOCS 8611030036
Download: ML20215M573 (3)

Text

f Y f 'o g UNITED STATES o NUCLEAR REGULATORY COMMISSION O y WASHINGTON, D. C. 20555

• % ...../ October 24, 1986 Mr. J. Gary Weigand, President and Chief Executive Officer Vermont Yankee Nuclear Power Corporation RD 5, Box 169 Ferry Road Brattleboro, VT 05301

SUBJECT:

VERMONT YANKEE CONTAINMENT STUDY This is in response to your letter dated September 2,1986, enclosing the Vermont Yankee Containment Study for our review. We acknowledge the extensive effort in generating the report in a short interval of 60 days.

We have reviewed the report in two parts. The first part relates to the review of your comparison of the Vermont Yankee design features to those of the reference plant in WASH-1400 and calculation of a Vermont Yankee specific containment conditional failure probability (CCFP). The second part deals with our review of your response to five generic NRC staff concerns related  :

to Mark I containments for Boiling Water Reactors (BWRs). l Your approach was to quantify the Vermont Yankee CCFP using the Peach Bottom analysis as a surrogate and modifying the accident sequence frequencies to reflect the specific design features and 14 year operating data base of Vennant Yankee, supplemented by industry experience where Vermont Yankee data was not available. The range of plant specific conditions were determined by  !

phenomenological analysis using Industry Degraded Core Rulemaking (IDCOR) )

group Modular Accident Analysis Program (MAAP), deterministic structural  !

capability calculations made for Browns Ferry and the Peach Bottom plants, and your staff's engineering judgement. Using the above approach, you have provided a best estimate CCFP value for Vermont Yankee containment of 7% for all sequences where containment may fail within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and where radionuclide releases include all noble gases and greater than 0.1% Iodines. You have, however, not provided an analysis of uncertainties in your methodology, in the

..phenomenological analysis using MAAP, and your engineering judgments.

Based on the staff's experience with other BWR Probabilistic Risk Assessment (PRAs) we believe that the CCFP of 7% may be fairly representative but is quite uncertain. It is our judgement that the CCFP based on your estimating techniques would have associated uncertainties as discussed in Enclosure 1.

We also believe that your evaluation has provided the staff with sufficient insights to conclude that the CCFP for Vermont Yankee may be lower than the 90% estimated from results of WASH-1400. Our assessment of the uncertainties leads us to believe that the Vermont Yankee CCFP is probably less than 50%.

That conclusion, that the CCFP is probably less than 50% and may be fairly estimated to be about 10%, brings out the very reason for the five generic NRC staff concerns related to Mark I containments. We believe that greater 8611030036 061024 DR ADOCK 0S00 1

l g e i

October 24, 1986 l

l assurance of containment performance in the face of core melt is desirable j and achievable. Therefore, our attention now is shifted to the second part i of your study.

l Our review of the second part of your report dealing with containment perform-ance enhancements has resulted in some preliminary conclusions and several questions. We find that the kind of enhancements proposed in your study are consistent with the type of improvements considered by the staff. You have indicated that further analysis should be performed to test the feasibility and effectiveness of the concepts discussed in your study. We agree.

Enclosure 1 is our preliminary assessment of your study. Our evaluation proposes further studies regarding combustible gas control and core debris barriers. We request that you reevaluate these two issues in the light of the staff comments. Enclosure 2 lists detailed staff questions. We request your response to the staff questions and comments by November 17, 1986.

Sincerely, n . m.

Robert M. Bernero, Director Division of BWR Licensing cc: See next page Distribution:

, Docket File NRC PDR Local PDR AD: DBL Rdg File l RBernero l

WHouston TSpeis ZRosztoczy OELD EJordan BGrimes l JPartlow l NThompson WHodges VRooney SNorris ACRS(10) *SEE PREVIOUS CONCURRENCES RSB: DBL (5520DocumentName: WEIGAND) WHodges*

j,g 10/24/86 0FC p%C3;,UBL :PSB: DBL :BWD2: DBL :AD/ DBL  : R0 M#:

. . . . . : . . . . . . . . . . . . : . . . . . . _ _ _ . . . : . . . . . . . . . . . . : . . . . . . . . . . . : _ _ _ . . . .,./. . . :: D / D NAME :MThadani :JHulman* :DMuller* :Glainas* :TSpe :R8ernero  :

___:.....,7......:....___....

DATE :10/Jy/86 :10/24/86  : 10/24/86 :10/24/86 :10f /86 :10/2786  :

, i Er. R. W. Capstick Vermont Yankee Nuclear Power Vermont Yankee Nuclear Power Corporation Station cc:

Mr. J. G. Weigand Mr. W. P. Murphy, Vice President &

President & Chief Executive Officer Manager of Operations Vermont Yankee Nuclear Power Corp. Vermont Yankee Nuclear Power Corp.

R. D. 5. Box 169 R. D. 5, Box 169 Ferry Road Ferry Road Brattleboro, Vermont 05301 Brattleboro, Vermont 05301 Mr. Donald Hunter, Vice President Mr. Gerald Tarrant, Commissioner Vermont Yankee Nuclear Power Corp. Vermont Department of Public Service 1671 Worcester Road 120 State Street Framingham, Massachusetts 01701 Montpelier, Vermont 05002 New England Coalition on Public Service Board .

Nuclear Pollution State of Vermont Hill and Dale Farm 120 State Street R. D. 2 Box 223 Montpelier, Vermont 0S602 Putney, Vermont 05346 Vermont Yankee Decommissioning Mr. Walter Zaluzny Alliance Chairman, Board of Selectman Box 53 Post Office Box 116 Montpelier, Vermont 05602-0053 Vernon, Vermont 05345 Resident Inspector Mr. J. P. Pelletier, Plant Manager U. S. Nuclear Regulatory Commission Vermont Yankee Nuclear Power Corp. Post Office Box 176 Post Office Box 157 Vernon, Vermont 05354 Vernon, Vermont 05354 Vermont Public Interest Mr. Raymond N. McCandless Research Group, Inc.

Vermont Division of Occupational 43 State Street

& Radiological Health Montpelier, Vermont 05602 Administration Building 10 Baldwin Street Regional Administrator, Region I Montpelier, Vermont 05602 U. S. Nuclear Regulatory Commission 631 Park Avenue Honorable John J. Easton King of Prussia, Pennsylvania 19406 Attorney General State of Vermont 109 State Street Montpelier, Vermont 05602 John A. Ritscher, Esquire .

Ropes & Gray l 225 Franklin Street Boston, Massachusetts 02110 I .

. _ _ _ _ . _ _ _ _ _ - _ _ _ _ _ _ . - - . . _ _ _ _ _ _ . _ _ _ _ . - _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ . _ _ . _ _ _ _ _ . _ _ _ _ _ _ _ . _ _ _ . _ _ , . _ _ _ _ _ _ _ . . . _ _ . . _