ML18219D967

Letter Effect of Burnup on Allowable Peaking Factor

ML18219D967
Person / Time
Site:	Cook
Issue date:	02/09/1977
From:	Tillinghast J Indiana Michigan Power Co, (Formerly Indiana & Michigan Power Co)
To:	Rusche B Office of Nuclear Reactor Regulation
References
Download: ML18219D967 (12)

Text

NRC FORM,195 U.S. NUCLEAR REGULATORY CC" MISSION y-mp NRC DISTRIBUTION FoR PART 50 DOCKET MATERIAL Indiana & Michigan Pwr Co New York, NY 8 Tillinghast DOCKET NUMBER FILE NUMBER DATE OF. D)COMPT DATE RECEIVED g5.ETTE R HNOTORIZED

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'Effects of burnup on allowable 'peaking factor during Cycle 2 operation.....

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CO Donald C. Cook Nuclear Plant Unit 1 Docket No. 50-315 DPR No.

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Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.

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Dear Mr. Rusche:

This letter transmits information required by the NRC Staff in Revision 1 to the Safety Evaluation Report (SER) dated January 5,

1977 (Reference

1) concerning the effect of burnup on allowable peaking factor (Fg).

The SER revision required that we modify the allowable peaking factor of 1.95 for Cycle 2 operation which was calculated in accordance with the provisions of 10 CFR Part 50 using the Exxon Nuclear Corporation WREM-XX Evaluation Model (References 2,3, and 4) using methods specified in the SER revision.

These methods specified the mannex in which rupture pin pressure uncertainties are to be accounted for in the analysis.

These calculations were performed by Exxon Nuclear Company in accordance with requirements of Reference 1,

and the results showed that at the end of Cycle 2

(end of Cycle 1

for fuel supplied by Exxon) the rupture would be 690 psid (pounds per square inch differential pressure) with a resultant blockage of 28/o.

The F< associated with this blockage is 1.90 at a peak clad temperature of 2200'F.

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Mr. Benard C. Rusche Februaxy 9, 1977 The NRC staff also requested verbally that we determine the time during Cycle 2 that, the value of Pg would drop below 1.95 when the above uncertainties were taken into account.

Such a calculation was performed and it was determined that Pg would not dxop below 1.95 until the pin rupture exceeded 667 psid (differential pressure)

This will occur at a point in time corresponding to 80/o of the first cycle; i.e., at an average cycle burnup of 8500 MWD/MTU (peak pellet, burnup of 12,000 MWD/MTU).

The time when F< dropped below 1.95 was calculated assuming the fission gascontribution to rupture pressure varies linearly through the first cycle, from 0 psi at the beginning of the cycle to 60 psi at the end of the cycle.

Similarly, the uncertainty was assumed to vary from 0 to 60 psi during the cycle.

This burnup dependence may be applied to the Donald C. Cook Nuclear plant by applying a multiplier on F~ as a function of cycle life.

This multiplier is shown on the attached

curve, showing no multiplier is required to be applied to the 1.95 peaking factor until a burnup of 8500 MWD/MTU has been reached, and then showing the multiplier to vary, linearly between 1.0 and 0.9744, between 8500 and 10,800 MWD/MTU avexage cycle burnups; which when applied to the 1.95 peaking factor, yields a peaking factor of 1.90 at expected end-of-life.

This direct adaptation of the methods cited in Reference 1 was only used by Exxon due to the inadequate time the NRC staff had available for review of XN-65-51, Supplement 1

(Reference

5).

We anticipate that once the appropriate analysis is complete and reviewed by the NRC staff, that the burnup dependence on peaking factor indicated herein will not be required.

Very truly yours, JT:mam I

Sworn and subscribed to before me this 9th day of Februax'y 1977 in New York County, New York 3.

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S Vice, Pxesiden Notary Public DAVIDG. HUME NOTARY PUBLIC, Srete ol New Yorls No. 314608113 Qua!ified in New York Counly Commission Expires Mrrreh 30, 1977, cc:

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February 9, 1977 cc:

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W. Steketee R. Walsh R. C. Callen R.

W. Zurgensen Bridgman R. S. Hunter

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References Revision 1 to the Safety Evaluation Report on the Exxon Nuclear Company WREM-Based Generic PWR-ECCS Evaluation Model Update ENC-WREM-II for Conformance Requirements to 10 CFR "50 by the Office of Nuclear Reactor Regulation, January 5,

1977.

2) 3)

XN-76-27, "Exxon Nuclear Company NREM-Based Generic PWR ECCS Evaluation Model Update, ENC-WREM-XX," July 1976.

1 XN-76-27, Supplement 1,

"Supplementary Xnformation Relating to Exxon Nuclear Company WREN-Based Generic PWR ECCS Evaluation Model Update, ENC-WREM-XI, "

September 1976.

4)

XN-76-27, Supplement 2,

"Supplementary Information Relating to Exxon Nuclear Company NREM-Based Generic PWR ECCS Evaluation Model Update, ENC-WREM-XX, "

November 1976.

5)

XM-76-51, Supplement 1,

"Flow Blockage and Exposure Sensitivity Study for D. C.

Cook Unit 1 Reload Fuel Using ENC WREM-II Model, " January 1977.

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