ML20005B949

Forwards Safety Evaluation of SEP Topic XV-13 Re Spectrum of Rod Drop Accidents.Evaluation Will Become Basic Input to Integrated Safety Assessment for Facility & May Be Revised Should Plant Design or NRC Criteria Be Modified

ML20005B949
Person / Time
Site:	Millstone
Issue date:	09/09/1981
From:	Crutchfield D Office of Nuclear Reactor Regulation
To:	Counsil W NORTHEAST NUCLEAR ENERGY CO.
References
TASK-15-13, TASK-RR LSO5-81-09-030, LSO5-81-9-30, NUDOCS 8109160174
Download: ML20005B949 (4)

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September 9,1981 Tilip -

Docket No. 50-245 i

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Mr. W. Counsil, Vice President EdLE*g 7 4 Nuclear Engineering and Operations

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Q9 Northeast Huclear Energy Company T, %

Post Office Box 270 Hartford, Connecticut 061:i1

SUBJECT:

HILLSTONE 1 - SEP TOPIC XV-13, SPECTRUM OR R0D DROP ACCIDENTS In your letter dated June 30, 1981, you submitted a safety assessment report on the above topic. The staff has reviewed your assessenent and our conclusions are presented in the enclosed safety evaluation report. This report completes this topic evaluation for Millstone 1.

The enclosed safety evaluation will be a basic input to the integrated safety assessment for your facility. The essessment may be revised in the future if ycur facility design is changed or if NRC criteria relating to this topic are modified before the integrated assessment is completed.

Sincerely, e

Dennis H. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing

Enclosure:

As stated cc w/ enclosure:

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111LLSTONE 1 Docket No. 50-245 Mr. W. G. Counsil cc Will,s.: H. Cuddy, Esquire Conne,t; ut Energy Agency Day, Berry & Howard ATTN. Asristant Director Counselors at Law Rei.earch and Policy One Constitution Plaza Development Hartford, Connecticut 06103 Department of Planning and Energy Policy Natural Rest-urces Defense Council 20 Grand Street 91715th Street, N. W.

Hartford, Connecticut 06106 Washington, D. C.

20005 Northeast Nuclear Energy Coinpany ATTN: Superintendent Mil? stone Plant P. O. Box 128 Waterford, Connecticut 06385 Mr. Richard T. Laudenat Manager, Generation Facilities Licensing Northeast Utilities Service Company P. O. Box 270 Hartford, Connecticut 06101 Resident Inspector c/o U. S. NP.C P. O. Box Drawer KK Niantic, Cor.necticut 06357 Wate: ford Public Library Rope Ferry Road, Route 156 Waterford, Connecticut 06385 First Selectman of the Town of Waterford Hall of Records 200 Boston Post Road Waterford, Connecticut 06385 John F. Opeka Systems Superintendent Northeast Utilities Service Company P. O. Box 270 Hartford, Connecticut 06101 U. S. Environmental Protection Agency Region 1 Office ATTN: EIS C0ORDINATOR JFK Federal Building Boston, Massachusetts 02203 x

J TOPIC: XVA3, SPECTRUM OF R0D DROP ACCIDENTS FOR MILLSTONE UNIT i l

INTRODUCTION The rod drop accident in a boiling water reactor occurs when a rod blade becomes disconnected from its drive and is stuck in the upper portion of the core. The drive is then withdrawn 'eaving the rod behind. At some later time, the rod blade bccomes unstuck and falls rapidly out of the core.

If the control rod has sufficient worth the potential for localized fuel damage exists.

EVALUATION l

In order to limi'.he worth of a potential dropped rod, a rod withdrawal sequence is defined and enforced, in Millstone Unit 1, by a Rod Wortn Minimizer, a computer based device which blocks rod motion if an attempt is made to withdraw an out of sequence rod. The analysis of the rod drop event is then done for the maximum potential dropped rod under tha assump-tion that the sequence is followed.

The analysis of the rod drop accident is made generically. That is, curves of peak fuel enthalpy as a function of dropped rod worth are drawn for what are believed to be conservative values for certain parameters. These parameters include the Doppler coefficient of reactivity, the shape of the scram curve, the rod drop speed and the scram insertion time.

For each cycle the input parameters are compared to those in the generic analysis and if all are conservative then the generic analysis is accepted.

If any parameter is nonconservative, then a cycle specific analysis is performed or use is made of sensitivity studies performed around the base case generic analysis.

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The basic generic analysis which has been used is described in General Electric Topical Reports NED0-10527, " Rod Drop Accident Analysis for Large Boiling Water Reactors" and Supplements 1 and 2 to that report.

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The bounding analysis procedure is described in NED0-24011-A, " Generic Reload Fuel Application." Both of these reports have been reviewed and approved by the staff and the methods and procedures are used on all currently operating BWR/3s, 4s, and 5s.

CONCLUSION C:, the basis that the same models and procedures are employed at j

Millstone Unit I as at current generation boiling water reactors to analyze the red drop accident, we conclude that this analysis meets present day requirements and is acceptable.

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