ML19316A307

Responds to NRC .Discusses Manner in Which Postulated Effect of Rod Bow on DNBR Is Factored Into thermal-hydralic Performance Requirements of Future Reload Fuel Cycles

ML19316A307
Person / Time
Site:	Oconee
Issue date:	05/03/1977
From:	Parker W DUKE POWER CO.
To:	Case E, Schwencer A Office of Nuclear Reactor Regulation
References
770502, NUDOCS 7912050877
Download: ML19316A307 (3)

Text

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DATE oF OOCUMENT Duke Power Company 5/2/7.7 Mr Edson G. Case Charlotte, North Carolina oxys Receiveo William O. Parker, Jr.

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OESCKsPTION ENCLOSURE Ltr. consisting of info. pertaining to the manner in which the postulated effect of rod bow on DNBR is factored into the thermal-hydraulic performance requirements of future reload fuel cycles....

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,,,,n Mr. Edson G. Case, Acting Director

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U. S. Nuclear Regulatory Commission

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Attention:

Mr. A. Schwencer, Chief p,..

Operating Reactors Branch #1

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Docket Nos. 50-269, -270, -287

Dear Mr. Case:

The following information pertains to the manner in which the postulated effect of rod bow on DNBR is factored into the thermal-hydraulic per-formance requirements of future reload fuel cycles of Ococee Units 1, 2, and 3 and is submitted in response to your letter of March 25, 1977.

l On Septeeber 17, 1976, Babcock & Wilcox Company (B&W) submitted to the NRC (lettar of K. E. Suhrke to D. F. Ross) an interim rod bow evaluation for the Mark B fuel assembly design representative of Oconee fuel. This interim evaluation is based on extensive bow measurements performed on irradiated fuel assemblies from Oconee Unit 1 discharged after end-of-Cycle 1 and end-of-Cycle 2.

A correlation relating the magnitude of bow and fuel assembly burnup was obtained in the same form as that by the NRC.

The empirical constants of the correlation were adjusted to encompass the cold-to-hot adjusted measured data at the 95 x 95% upper tolerance limit. The resulting equat_ ion for the maximum rod bow magnitude is Ob(mils) = 11.5 + 0.069 vBu.

The rod bow DNBR penalty assigned for future reload fuel cycles of Oconee units is consistent with this bow equation and results in a DNBR penalty of approximately 6% for fuel burnups equivalent to three cycles of operation.

The thermal-hydraulic sign analyses of future reload cycles are based on closed vent valve cc-iguration and without the effect of densification power spike on DNBR but including the customary flow area reduction factor.

Thus, considering 1% DNBR margin credit for the flow area reduction factor, the additional thermal margin to be provided for rod bow DNBR penalty is 5%.

The procedure now employed for future reloads, in general, is to

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1 Mr. Edson G. Case Page 2 May 2, 1977 explicitly provide a minimum of 5% DNBR margin in ti e design analyses that h

establish the RPS setpoints based on minimum DNBR requirements - that is,

those setpoints previously based on a minimum DNBR of 1.3 would now be based on a minimum DNBR of 1.365 (1.05 x 1.3).

An exception to this would be the flux-flow ratio for Cycle 3 of Units 2 and 3 wherein thermal margin credit for 1-3% excess RCS flow will be claimed to demonstrate the required DNBR margin.

(The RCS flow for Units 2 and 3 are 111.5% and i

110%, respectively, compared to thermal design flow of 106.5%.)

It should be noted that the actual setpoints would have varying degrees of additional thermal margin.

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The procedure described above represents the manner in which the rod bow DNBR penalty is accounted for in the upcoming Cycle 4 of Unit 1 or Cycle 3 of Units 2 and 3, and unless otherwise stated, this procedure would be used for all future reloads of Oconee units.

Ve truly yours,f l

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