ML20148E894

Discusses Effect of Fuel Rod Bowing on Departure from Nucleate Boiling on Thermal Margins.Requests That Util Provide for Future Ref List of Thermal Margin Credits, Applicable to Facility,Within 30 Days

ML20148E894
Person / Time
Site:	Yankee Rowe
Issue date:	01/04/1977
From:	Schwencer A Office of Nuclear Reactor Regulation
To:	Groce R YANKEE ATOMIC ELECTRIC CO.
References
NUDOCS 8010310685
Download: ML20148E894 (3)

Text

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- Doci:et No 50-29 JAN 4 c

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Yankee Atomic Electric Company i.j ATTN: Mr. P.obert H. Groce '

Licensing Engineer 20 Turnpike Poad Westboro, I4ssachusetts 01581 Gentlenen:

PE: YA!n'EE-i10WE ATOMIC POWER STATICH  ;

On August 9,1976, Westinghouse Electric Corporation presented data to b the !!P.C staf f which showed that previously developed nethods for accounting ,

for the effect of fuel rod bowing on departure frun nocicate boiling nay not contain adequate thernal margin when unheated rods (such as thimble Wr#'

tubes) are present. We have evaluated the inpact of the Westinghouse data pr on all operating pressurized water reactors (PWR's). flodels for treating the effects of fuel rod bowing on thermal-bydraulic perfomance have boon derived for all PWR's. The nodels are based on the propensity of the  ;:i individual fuel desit;ns to how and on the thermal analysis nothods used

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to predict the coolant conditions for both normal operation and anticipated l transients. l The reduction in departure from nucl. ate boilino ratio (Df:BR) due to fuel f.

rod ec' vim is assunnd to vary linearly with the reduction in clearance hetueen the fuel rods (or fuel rod and thimble rod) but can never be less l-than t hat due to the pitch reduction factor usea in the thermal analysis.

The r.axirr value of D!!0R reductin (at cont 1ct), obtained from the [ r experiocatal data was used to calculate the DC reduction vs the clearance reen: tion between fuel rods. Ad,iustnants were node for heat flux and 4 l

coolant prcssure differences between the data and pinnt cor,ditions in sent cases. 3; i  :

The clearance reduction is conservatively assumed to be niven by the J fellnwing equation.

"a*hS gl uhero O C is the ?. reduction in clearance G y Po is tqe rcpion as 3 rage or bundle cvorage burnup and a,b are enpirical constants fi ttad to data f e ry, 5,inil arlv decicnod fool rode..

n THIS DOCUMENT CONThlN '

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JEN 4 1; Yankee Atomic Electric Company .

These reductions in DiSR nay be treated on a region by region basis.

Credit nay be taken for the naroin between tne actual reactor coolant ,

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flow rate and the flow rate used in safety calculations. Credit may ~

also De taken for a difference between the actual core coolant inlet tenperature end that assteied in safety snelyses. In takinc credit for coolant flow or inlet temperature narein, the associated uncertainties in these quantities nest be taken into account. . . .

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Additional information on the derivation of the above reductions, as I well as nore extensive background information concerning rod bow, are j";

contained in the enclosure to this letter. -

Based on our review of the new rod bow data and the thermal margins available to offset the Dt:0R reduction, no change to the plant technical specifications is required for your facility at this tine.  ;

Because future changes in the themcl margin credits which you have p claimed to offset the CHDR i nduction for your facility may renuire I connensurate changes in the DhaR penalty, you are requested to provide, l within 30 oays, a list of the credits applicable to your facility for future reference on your docket. '

Sincerely, A. Schve'ncer, Chier' Operatino Reacters Cranch r1 Division of Onerating Peactors Ear 1ocures: DISTRIBlHION '

1. Interin SEr on Effects of Docket fuci Rod Bowing cn Therm l NRC PDR Nrcin Calculations for Local PDR t LioM Ueter reactors ORB #1 Reading '-

?. Sa~ple Technical Soccifications TJCarter ASchwencer cc v/ enclosures: See next page ABurger SMSheppard MFletcher OELD 01&E(3)

DEisenhut c TBAbernathy J RBuchanan ACRS(16)

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,  :. j Yankee Atomic Electric Company January 4,1977 j#

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Mr. Donal,d G. Allen, President .

Yankee Atomic Electric Company [. L 20 Turnpike Road E Westboro, Massachusetts 01581 '":7e; .

, 2, Greenfield Public Library i 402 Main Street Greenfield. . Massachusetts 01581 h

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