B14713, Nonproprietary Version of Response to NRC Questions on RCS Flow Reduction Evaluation

Nonproprietary Version of Response to NRC Questions on RCS Flow Reduction Evaluation

ML20067C809
Person / Time
Site:	Millstone
Issue date:	12/31/1993
From:	WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
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ML19303F924	List: B14713, Nonproprietary Version of Response to NRC Questions on RCS Flow Reduction Evaluation ML20067C795 ML20067C800
References
B14713, NUDOCS 9403040219
Download: ML20067C809 (4)

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Occket No. 50-423 B14713 Attachment 2 Westinghouse Class 3 Response to NRC Questions on RCS Flow Reduction Evaluation January 1994 9403040219 940110 gDR ADOCK0500g3

Westinghouse Class 3 RESPONSES TO NRC QUESTIONS ON RCS FLOW REDUCTION EVALUATION December 1993 Westinghouse Electric Corporation Nuclear Energy Systems P.O. Box 355 Pittsburgh, Pennsylvania 15230

• 1993 Westinghouse Electric Corporation All Rights Reserved

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Table 1

. Millstone Unit 3 4% TDF Reduction Evaluation for N Loop Oceration Available DNB Margin Available DNB Margin EVENT Correlation Before TDF Reduction After TDF Aeduction qqgg

1. Loss of Flow WRB-2 (RTDPI 2, Feedwater Malfunction WRB.2 tRTDP)

3. Excessive Load increase WRB 2 tRTCP)

J. Loss of Load / Turbine Trip WRB 2 lRTDP)

5. RCCA Withdrawal at Power WRB.2 (RTDP)

6. Inadvertent St Actuation WRB 2 (RTCP)

7. RCS Depressurization WRB 2 (RTDP)

8. RCCA Misalignment (Dropped RCCA Bank)

WRB 2 IRTDP)

9. Steamline Break W-3 inon RTOP) 10.RCCA Withdrawal from Subentical W 3 (non-RTOP)

Overoressure Considerations I

1. Loss of Load Plant specific sensitivities performed for a 4% TDF reduction Turbine Trip confirm that the LOL/TT pressunzation rate is [ 1" to small changes in RCS flowrate The maximum RCS pressure reached assuming a 4% TDF reduction [ 1" from the current Millstone 3 licensing basis analysis.

2. Locked Rotor Although plant specific sensitivities were not performed for this event.

sensitivities performed for other plants indicate that a reduction in flow is I 1" with respect to maximum RCS pressures. Furthermore, the Millstone Unit 3 licensing-basis locked rotor analysis shows that there is about ( }' margin to the limit (2750 psia) for N loop operation which is more than sufficient to offset any penalty associated with a lower RCS flow.

3. Feedline Break NRC personnel also expressed concerns about the peak secondary side pressure reached dunng a FLB event with reduced RCS flow. Ths Millstone Unit 3 licensing basis FLB analysis uses a conservative model for SG safety valve relief thrcugh the 3 intact SG. The safety valves are conservatively assumed to open at 110% of the SG design pressure.

This prevents the pressure in the SG from exceeding the design pressure limit as long as the valves have sufficient relief capacity. Since the total relief capacity of these valves is not exceeded, this modelis considered appropriate.

Dose Considerations

1. Locked Rotor 6% rods-in-DNB continues to apply after the 4% flow reduction.

-W- 9 F ==  ?-P-

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Response to NRC Question on Niillstone Unit 3 4c7 c TDF reduction The potential offsite doses due to a steam generator tube rupture event for Niil in FSAR) are compared in the following table with the corresponding offsit the FSAR).

e dose limits (page 15.6-9 in Offsite Radiological Doses Thyroid Dose (tem)

Whole Body Dose (rem)

Calculated Limit Calculated Limit Pre accident iodine spike 2.1 300 0.019 2 hr Exclusion Area Boundary 25 Pre accident iodine spike 0.24 300 0.0012 8 hr Low Population Zone 25 Concurrent iodine spike 0.34 30 0.018 2 hr Exclusion Area Boundary 2.5  !

Concurrent iodine spike 0.076 30 0.0011 8 hr Low Population Zone 2.5 As shown in the table above, a significant amount of margin exists between the cur doses and the limits. The 4% thermal design flow reduction was determined to result in of offsite radiological doses. Since, there is ample margin to the limits to support even a sub increase in the offsite radiological doses, it is apparent that the offsite dose will sdll be be with a 4% thermal design flow reduction. Therefore, the conclusions of the hiillstone Unit 3 F the radiological doses remain below 10CFR100 guidelines with a pre accident iodine c spike an of 10CFR100 guidelines with a concurrent iodine spike remain valid-1 l

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