ML20210N857

Forwards Addl Info Re Proposed Core Uprating,Per 860414 Request.Figures Re Core Melt Mixture Level,Upper Plenum Pressure,Break Flow & Core Steam Flow Included

ML20210N857
Person / Time
Site:	North Anna
Issue date:	04/30/1986
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Harold Denton, Rubenstein L Office of Nuclear Reactor Regulation
References
86-250, NUDOCS 8605050278
Download: ML20210N857 (12)

Text

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l VIuGINEA ELucTunc Ann Pownu Coxi Axy i

Hicunown.Va uulNIA M:5261 i

W.I..MTWWABT I Vice Pasesomwr m usan oessarm=s April 30, 1986 ,

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. Mr. Harold R. Denton, Director Serial No.86-250 1

Office of Nuclear Reactor Regulation N0/DJV/aca j Attn: Mr. Lester S. Rubenstein, Director Docket Nos. 50-338 i PWR Project Directorate No. 2 50-339 j Division of PWR Licensing-A License Nos. NPF-4

) U.S. Nuclear Regulatory Commission NPF-7 l Washington, D.C. 20555 i.

Gentlemen:

4 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT NOS. 1 AND 2 REQUEST FOR ADDITIONAL INFORMATION i CORE UPRATING

! Your letter dated April 14, 1986 requested additional information j regarding the proposed core uprating for North Anna Units 1 and 2.

t Virginia Electric and Power Company's response to this request is provided i

in Attachment 1. If you have any further questions on this matter please contact us.

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f Very truly yours,

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[ .J.tI l W. L. Stewart i

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Attachment l 1. Response to NRC Request for Additional Information i

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8605050278 060430 i PDR ADOCK 05000338

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Vamosna ELacterc ano Powan Courant to Mr. !!arold 11. Denton i

l I cc: Dr. J. Nelson Grace i Regional Administrator 1

NRC Region II I

Mr. Larry King h1C Resident Inspector North Anna Power Station a

i Mr. Charles Price

) Department of He'alth 109 Governor Street I l

Richmond, Virginia 23219 Mr. Leon B. Engle

NRC North Anna Project Manager l PWR Project Directorate No. 2 i

Division of FVR Licensing-A i

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ATTACMENT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION 84M625GLD506

'l NRC REQUEST FOR ADDITIONAL INFORMATION Page 24 of Attachment I to your letter of February 6,1986 refers to a two-inch small break LOCA analysis for a plant similar to North Anna, provide this analysis or an available reference and justify that this plant is similar.

1

RESPONSE

Results from the two-inch SBLOCA analysis for a plant similar to North Anna, referred to on page 24 of Attachment 1, is provided below along with justification for applicability tc North Anna.

Objective of the Analysis The objective of the reference analysis was to determine for a 3-loop Westinghouse plant how much time would elapse before the core would become uncovered for a two-inch equivalent diameter SBLOCA, in the event that accumulators and pumped SI were not available for injection into the RCS.

Methodology The two-inch SBLOCA analysis was performed with the Westinghouse WFLASH SBLOCA Evaluation Model described in! Reference 1.

Plant Characteristics The analysis was performed for a 3-loop plant which is similar to North Anna Units 1 & 2. A comparison of the two plants is shown in Table 1.

The minor differences between the two plants and their impact on the applicability of tnis analysis to North Anna are discussed in a later section.

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Initial Conditions and Assumptions The two-inch break transient was initiated from 102% full power conditions. The ECCS system (accumulators and pumped SI) was assumed to be inoper3ble and consequently was not modeled. The analysis was performed with all assumptions required by Appendix K of 10CFR50.46.

Analysis Results The analysis results are summarized in Figures 1 through 4. As shown in Figure 1 the core uncovery began at 1327 seconds (22.12 minutes) after the initiation of the two-inch break.

Applicability of the Analysis to North Anna Units 1 & 2 Examination of Table 1 shows that the 3-loop reference plant used in the analysis described above is very similar to North Anna Units 1 & 2. The minor differences between the two plants and their impact on the applicability of these results of North Anna are discussed below.

The uprated North Anna Units have a full power rating which is 4.43%

higher than the reference plant. This full power difference is insignificant when the results of this analysis are extrapolated to hot standby or hot shutdown initial conditions and their corresponding decay heat levels, For example, at the time o core uncovery the decay heat level of the. reference plant full power analysis is approximately 65.86MWt (2.3% of full power), whereas when North Anna is in a hot standby or hot shutdown mode of operation the decay heat level is expected to be no more than 40.37MWt (1.36% of full power) or 35.25MWt (1.19% of full power), respectively. Consequently, the 22.12 minute time frame to core uncovery calculated for the full power case is a conservative minimum estimate for the time to core uncovery for SBLOCA's that may initiate from hot standby or hot shutdown initial conditions.

Based on a comparison of power levels alone, it is expected that a more realistic time to core uncovery for hot standby or hot shutdown initial conditions would be greater than 36 minutes.

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The two plants employ different model steam generators. The differences between the models is largely due to different secondary side feedwater and steam separator design features which have insignificant impact on the plant's response to a SBLOCA.

Both plants contain 17x17 fuel, however, the reference plant was analyzed with Optinized Fuel Assembly (0FA) fuel, whereas, North Anna has standard fuel. This fuel difference accounts for a small portion of the core volume difference between the two plants (the majority of the core volume difference is due to differences in ba rrel-ba f fle design). The differences in power density between the two fuel types has an insignificant impact on the thermal-hydraulic response of the RCS during a SBLOCA.

A comparison of the reactor vessels shows that the volume distribution is slightly different between the two plants, but that the total vessel volume differs by only 1.17%. The volume distribution difference between the two plants is primarily the result of different barrel-baffle and upper head design configurations. The differences in volume distribution below the top of the core will be insignificant prior to core uncovery.

An examination of the volume above the core, i.e. the upper head and upper plenum volumes, shows that North Anna has approximately 8% more volume above the core. As a result, for the North Anna Units, 8% more water (as compared to the reference plant) must boil-off or be lost through the break before core uncovery will occur. Consequently, the elapsed time to core uncovery for North Anna would be longer than the 22.12 minutes calculated for the reference plant.

Susunary and Conclusion As a result of geometric and power level differences, the 3-loop plant modeled in the reference SBLOCA analysis provides a conservative representation of the North Anna Units response to a two-inch SBLOCA from hot standby or hot shutdown conditions. Therefore it is concluded that application of these results for the assessment of North Anna is conservative and justified.

84M625GLD506

References

1. Skwarek, R. J., Johnson, W. J., and Meyer, P.E., " Westinghouse Emergency Core Cooling System Small Break October 1975 Model",

WCAP-8970 (Proprietary) and WCAP-8971 (Non-Proprietary), April 1977.

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TABLE 1 PLANT COMPARISON Parameter Reference Plant North Anna Reactor Power (MWt) 2775 2898 No. of Loops 3 3 Steam Generator Type Model F Model 51 Pump Type 93A7000 93A7000 Fuel Type 17x17 0FA 17x17 Std.

Total Vessel Vol. (Ft**3) 3683.00 3726.22 Upper Head Vol. (Ft.**3) 611.82 439.22 Upper Plenum Vol. (Ft.**3) 816.90 1097.70 Core Volume (Ft.**3) 769.87 538.03 Lower Plenun Vol. (Ft.**3) 900.22 917.44 Downcomer Volume (Ft.**3) 584.19 733.33 84M625GLD506 I

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