ML20235E659

Draft Summary of 720105 Meeting W/Ge & Util Re Rod Drop Accident.Ge Did Not Attempt to Defend Old Scram Function W/ Old Methods & Input

ML20235E659
Person / Time
Site:	Vermont Yankee, 05000000
Issue date:	01/07/1972
From:	Richings H US ATOMIC ENERGY COMMISSION (AEC)
To:	Rosen M US ATOMIC ENERGY COMMISSION (AEC)
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References
FOIA-87-40 NUDOCS 8707130041
Download: ML20235E659 (3)

Text

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t l January 7, 1972

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j Horris Rosen, Chief Systems Perfromance Branch l

l SITd!ARY5,OF JAMUARY WEET1HC WITH CE AND YEINGMT varrrr ON THE ROD DROP ACCIDENT 1972 Background i' j As part of their program to study various aspects of reactor physics and core

' related transients, our BNL consultants, principally C.1411enche, have been j working on the BWR rod drop transients for the past six months and more. j q While ganarally agreeing with the CE results in most areas, one area of the j t

analysis began to emerge as highly suspect. This was the scram functions

{ used in the CE analysia, i.e. the reactivity as a function of time 1meerted by the scram bank. This involves bank worth, more importantly beak insertion l

' time, and even more importantly reactivity insertions as a immetion of bank position. The BNL work indicated that GE had been highly neo-conservative in this area, and, contrary to past CE response to questions which indicated i

little sensitivity to scram, that for the larger dropped rod worths peak enthalples would be much larger and well beyond our 280 cal /sm limit.

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As a result of theaa and continuing studies, conversations were initiated

{ with CE, via telephone, in November and December. These conversations in-j dicated that CE (R. C. Stirn) admitted that the scram functions used in the SAR analysis were not completely defensible but that CE had been doing new j

calculations over the past year or se (which would not be completed for

' another several months) which still give results within limits. They did not wish to present their calculations until some time in the spring (or later).

'We learned in mid-December of questions from a Vermont Yankee intervenor which could, in effect, require us to state at this time our agreement with GE on the SAR analysis methods., input and results. Vermont Yankee was in-formed of our present difficulty in being able to do this and they requested a meeting with us, CE, and our BNL consultants to discuss the situation.

Meeting CE (R. C. Stirn, J.' 'A. Woolley) did not attempt to defend the old scram func-tion with the old methods and input. Rather, they presented available re-suits from their new calculations. These results and expected results from i

8707130041 870623 I

PDR FOIA THOMAS 87-40 PDR

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i Horris Rosen future calculations were intended to show that CE still meets the required i

limits (e.g. 280 cal /gn) for this accident. N mew calculation invole new l analysis methods (models) and new input data and parameters. The extent of I,. the change is such that a whole new (extensive) submittal and evalestion (extensive) would be required for full acceptance. -The fellowing are some of the major new areas to be awa=f w along with some comments.

Model - The type of model is not changed, (i.e. adiabatic, point kenttics) just elaborated (e.g. 2D multigroup calculations, better data input). 2D-

space-time calculation (e.g. TWICL) still are not done as cheeks. BHL thinks I such checks are necessary.

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Scram reactivity function - Emactivity insertion as a function of bank posi-i tion still must be input to the code. The shape that CE now uses, while improved over the previous linear function, BNL does not believe is correct or sufficiently conservative.

Scram time - CE is using a " measured" scram bank insertion time rather than l Isch Spec inscreion times. This in not considered to be satisfactory, i

kod drop velocity - GE is now using drop velocities less than 3 ft/see rather than the previous 5 ft/sec. This is said to be justified by more recent tests

! than those given in the velocity limiter report. This has not been submitted

as yet. Rasults are sensitive to this persmater.

Rod reactivity worths - CE has calculated new and somewhat lower rod worths i

I for the various configurations of interest, e.g. the 3.8% af at 10% power rod worth has dropped to about 3.0.

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Based oc the hML work to date we believe that using the presently " justified"

{ input assumptions (e.g. 5'it/sec drop velocity, Tech Spec scram time, plus BNL scram function) the peak enthalpy for the 2.5a > sero power cases would i be in excess of 350 cal /sm and the 3.8op10: power (esse in excess of 500 cal /ga. It seems not unlikely that using the parameters CE would now like l to use (perhaps along with better use of voids in the calenlation) that re-L suits from " correct" calculat6 ens would be under 280 cal /sm. The timing on j the formal written presentation of this information and its evaluations is l  ; at present, however, not evident. As of now there is no resolutions on how l

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i Morris Rossa the Vermont Yankee situation is to be handled.

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l Howard J. Richings Systema Performance Aranch Division of Imacter Standards j cc: E. C. Case DES i

S.11anauer. DR W. Minners, DEL  !

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Distribution

i Suppl l DR Reading

DRS Reading SPB Reading bec

H. J. Richings I

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DRS SPB ERICHINGS: pad 1/7/72

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