ML20084F697

RO 250-75-1 Re Apparent Discrepancy Between Measured Control Rod Worth & Vendor Predictions.Cause Not Stated.Fuel Vendor Recalculated Predictions & Results Are Now Consistent W/Util Predicted Values

ML20084F697
Person / Time
Site:	Turkey Point
Issue date:	04/14/1975
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Rusche B Office of Nuclear Reactor Regulation
References
RO-250-75-1, NUDOCS 8304210244
Download: ML20084F697 (3)

Text

. P.C. BOX 3100 MIAMI. f tORIDA 33101

.-...-g FLORtDA PO'AER & LIGHT COMPANY April 14, 1975 Mr. Benard C. Rusche, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Rusche:

UNUSUAL EVENT NO. 250-75-1 TURKEY POINT UNIT NO. 3 APPARENT DISCREPANCY BETWEEN MEASURED -

CONTROL ROD WORTH AND VENDOR PREDICTIONS A. DESCRIPTION OF EVENT During physics tes. ting following Unit 3 Cycle II refueling, a comparison of measured control rod worths to the predicted worths, furnished by the vendor indicated ' discrepancy of approximately 19% for total control rod bank worth. The measured val-ucs were lower than predicted which gave some concern as to required shutdown margin at beginning-of-cycle. Further testing verified that adequate shutdown margin existed so normal operation of the unit was initiated.

B. APPAR$NT CAUSE AND ANALYSIS OF EVENT An investigation into the apparent discrepancy was initiated by Florida Power & Light Company to determine its cause and extent.

The fuel vendor was requested to reconfirm the predicted values for Cycle II operation. In addition, Florida Power & Light Company engineers performed independent calculations of beginning-of-cycle physics parameters. The Florida Power & Light Company calculations indicate that the measured control rod worths are within 6% of predicted values for beginning-of-cycle conditions.

Further, end-of-cycle calculations indicate that adequate shut-down margin will be available.

C. CORRECTIVE ACTION The fuel vendor has recalculated his predictions and the results, included as Table 1, are consistent with Florida Power &-Light Company predicted values. Based on this recalculation and our a: ~~'

'i 8304210244 750414 PDR ADOCK 05000250 S PDR TAWhM't&JtuT" ^

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Mr. Benard C. Rusche, Director Page Two April 14, 1975 L- independent calculations, adequate control rod capability and {

L-shutdown margin exist throughout Cycle II.

Very truly yours,

l II pM A. D. Schmidt

.Vice President .

Power Resources PJW/cpc Enclosure ,

cc: Mr. Norman C. Moseley ,

Jack R. Newman, Esquire 6

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'O. O 1 TABLE 1 i

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TURKEY POINT UNIT NO. 3 - CYCLE 2 l

END OF CYCLE SHUTDOWN REQUIREMENTS AND MARGINS 1

I REVISED ITEM CYCLE 1 CYCLE 2 Control Rod Worth at HZP (%Ap)

" 'All Full Length Rods Inserted 7.71 7.23

. All Full Length Rods Inserted Less Worst Stuck Rod (F-14) 6.47 6.01 (1) Less 10% S.82 5.41 Control Rod Requirements (%Ap)

Power Defect (Combined Doppler, Tavg, Void and Redistribution ertects) 3.07 2.61 Rod Insertion Allowance 0.70 0.70 (2) Tota,1 Requirement 3.77 3.31 Shutdown Margin [(1) - (2)] (%Ap) 2.05 2.10 Required Shutdown Margin (%Ap) 1.77 ,

1.77 Excess 0.28 0.33 The revised control rod worth is based on the end of Cycle 1 critical boron and an adjustment to the radial reflector cross-section to provide better agreement with power distribution measure- .

ments. The revised power defect is based on a more accurate evaluation at the Cycle 2 plant operating conditions for a core average moderator temperature of 567.3*F at a system pressure of 1,900 psia, as pre-viously documented in the Unit No. 3 Design Report.

Based on this revised analysis, the calculated N-1 rod worth at BOC II is within 6.7% of the measured value. In addition, at BOC II the reanalysis provides good agreement between the calculated and measured power distribution and the HFP and HZP critical boron concen-trations.

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