ML20235E682

Summary of 720105 Meeting W/Ge & Util Re Rod Drop Accident Analysis.Bnl Consultants Studied Rod Drop Accident for Number of Months & Found That GE Using Incorrect Scram Function (Linear Ramp) in Rod Drop Accident

ML20235E682
Person / Time
Site:	Vermont Yankee, 05000000
Issue date:	01/07/1972
From:	Dunenfeld M US ATOMIC ENERGY COMMISSION (AEC)
To:	Rosen M US ATOMIC ENERGY COMMISSION (AEC)
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References
FOIA-87-40 NUDOCS 8707130049
Download: ML20235E682 (3)

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! January 7, 1972 l

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I Horris Rosen, Chief, Systems Performance Branch j

MEETING WITh VERHONT YAIKEE ON BOD DR0p ACCIDENT on January 5,'1972 we met with Vermont Yankee and.GE to discuss the rod drop i accident analysis, about which we have recently developed esacerns. ~E. Rich-ings, M. Dunenfeld, W Minners, and other AEC personnel were present, as were C. Le11ouche, M. Levine, and H. Easts, sur BIE. consultants. We do met attempt to present complete meeting notes or attendance here, (These will be contained in the DEL meeting minutes) but to Briefly sammarize the important aspects of

, what occurred.

I We have had our ea= =1 tants at REL studying the rod drop accident for a num-bar of months. We have known that GE was using an incorrect scram function (a linear ramp) in the rod drop accident, but were not concerned because GE studies showed insensitivity of the analysis to the time (and therefore shape) of the scram.

! A few months ago, however, Le11ouche deter =fnad the proper rod insertion-reactivity function and found that it was sufficiently delayed that tne fuel enthalpy in large rod worth accidents (2.5% or greater) exceeded our limit of 280 calories / gram. GE's analyses have always shown enthalpies below this limit.

' We discussed our findings with GE physics personnel last November, encountered Technical objections, and performed further analyses at BEL which still showed

! there is a problem. We had another telephase conversation with GE on the a l

matter during the monthly meeting at BML on December 20, 1971.

l The problem came to a head for Vermost Yankee because we cannot provide an l j unqualified acceptance of the rod drop analysis in response to interrogations for the hearing, in view of our concern.

At the subject meeting, GE presented pre 14=f nary results of the red drop  ;

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accident using a new model, with almost the correct scram function and several new input data assumptions, which show acceptable results. If, however, the l proper FSAR input data were used in this new model, the results would met be acceptable, and would show enthalpies well in excess of 280 calories /gs.

Further, correct analyses of existing reactors would show unacceptable enthal-pies. To interpret this differently, GE evidently found that Lellesche's work was correct, and would like t;o claim certain input parameter changes which would still give them the right answer.

8707130049 FOIA e70623 pDR PDR l THOMAse7-40 j

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, I i I. Horris Rosen t

One of the important input parameter changes claimed is the rod drop velocity

{ which would be reduced to 2.8 ft/sec from the former value of 5 ft/sec. OE I states that they have abundant data supporting the redeced value, which will be disclosed in a report awaiting internal approval before release. As in-l portant is that CE needs to use measured or expected scram times rather than.

those permitted by technical specifications (about twice the expected time).

They have always used expected scram times in their analysis but an issue was

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I not made of this beesuse it was not believed that the seren time was important.

l Now that it is, CE was informed that they would have to see the tech spec numbers.

1 They can therefore use a reduced value of the scram time if they are willing to make a tech spec change.

There were several other input parameter changes believed to be of minor in-portance, which we will review further. There is a small disagreement yet

!' about the seram-reactivity function which CE will evaluate. We agreed to j

provide copies of RNL analyses to CE to help in this evaluation. CE further

' will consider what to do about the scram time. Details of the 10% of full power drop accident have yet to be evaluated by CE. At least six months work is expected before a complete submittal is forthcoming from CE.

i It is perhaps worthwhile to note that provision of a safety grade rod worth mininizer woula permit CE to claim sufficiently reduced rod worths for rod drop accidents to overcome the problems we have described.

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Marvin Dunenfe&d Systems Performance Branch s Division of Reactor Standards j cc

E. G. Case, DRS S. kanauar. DR W. Minners, DEL

! Distribution:

Suppi DE Reading DRS Raading SPB Reading bec: M. Dunenfeld l

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DRS SPB I

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HDUNEh7 ELD: pad j 1/7/72 l l

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b Excerpted fm 141st ACRS Meeting Summary -- Jan. 6-8, 1972 EXECUTIVE SESSION 1.2.4 BWR Rod Drop Enthalpy in Excess of Limit Dr. Okrent reported information to the effect that work at BNL has dis-closed that an incorrect function has been used by G.E. for calculating fuel enthalpy resulting from a control rod drop. The correct calcula-tion indicates that the enthalpy limit (280 cal /gm) is exceeded for fast rod ejection (5 ft/sec).

Appropriate changes in the Technical Specifications may be an acceptable solution to the problem. The matter is being followed by the Regulatory ,

Staff. It was agreed that this should be discussed with the Staff.

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