ML19294A446

Responds to 781011 NRC Ltr.Forwards Results of Analysis Re LPCI Diversion Effects on ECCS Performancce for Subj Facil. Concludes That Peak Cladding Temps Caused by LPCI Diversion Are Below Limits of 10CFR50.46

ML19294A446
Person / Time
Site:	Black Fox
Issue date:	11/07/1978
From:	Ewing T PUBLIC SERVICE CO. OF OKLAHOMA
To:	Varga S Office of Nuclear Reactor Regulation
References
NUDOCS 7811130222
Download: ML19294A446 (15)

Text

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6212 DIN 8 -013 -292 PUBLIC SERVICE COMPANY OF OKLAHOMA A CENTR AL AND SOUTH WEST COMPANY Q"{f: ; E} O

. h:g'jNy PO BOX 201/ TULSA. OKLAHOMA 74102 /(918)583-3611 M Public Service Company of Oklahoma November 7, 1978 Black' Fox Station File: 6212.125.0500.21 LPCI Diversion Effects On ECCS Performance Docket STN 50-556 and STN 50-557 Office of Nuclear Reactor Regulation Division of Project Management Light Water Reactors Branch No. 4 U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attn: Steven A. Varga, Chief Gentlemen:

In response to your request of October 11, 1978, Public dervice Company of Oklahoma is submitting the results of en analysis performed to investigate the effects of LPCI diversion on ECCS performance for Black Fox Station Units 1 and 2.

The attached analysis will be cubmitted in Amendment 13 to the BFS PSAR, to be filed prior to Construction Permit issuance.

Very truly yours, T. N. Ewing Manager, BFS P ject TNE:so cc: See attached service list 7 81113 0W g(

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r.%r;N. CENTRAL AND SCUTH WEST SYSTEM

,S N ' Central Power and Light Pubhc Gerv;ce Cornpany of Oklaherna Southe stern Electnc Po Aer West Texas Ut+ ties

.i Corpus Chnst", Teus Tu sa Owoma sprevernet Lou:staru Atwne Tesas sk

BLACK FOX STATION SERVICE LIST XC: Mr. Cecil Thomas U.S. Nuclear Regulatory Commission Phillips Building 7920 Norfolk Avenue Bethesda, Maryland 20014 Mr. Jan A. Norris Environmental Projects Branch 3 U.S. Nuclear Regulatory Commission Phillips Building 7920 Norfolk Avenue Bethesda, Maryland 20014 Mr. William G. Hubacek U.S. Nuclear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76012 Mr. Gerald F. Diddle General Manager Associated Electric Cooperative, Inc.

P. O. Box 754 Springfield, Missouri 65801 Mr. Maynard Human General Manager Western Farmers Electric Cooperative P. O. Box 429 Anadarko, Oklahoma 73005 Michael I. Miller, Esq.

Irham, Lincoln & Beale One 1st National Plaza Suite 4200 Chicago, Illinois 60603 Mr. Joseph Gallo Isham, Lincoln & Beale 1050 17th Street N.W.

Washington, D.C. 20036 Robert A. Franden, Esq.

Green, Feldman, Hall & Woodard 816 Enterprise Bldg.

Tulsa, Oklahoma 74103

ANALYSIS OF LPCI DIVERSION EFFECTS ON ECCS PERFORMANCE FOR BLACK FOX STATION UNITS 1 AhT 2 November 2, 1978 DOCKET NOS: STN 50-556 STN 50-557

PURPOSE This analysis was performed to investigate the effect on the ECCS analysis for the Black Fox Nuclear Power Station of diverting low pressure coolant injection (LPCI) pumps to the containment spray mode ten minutes after a loss-of-coolant accident (LOCA) initiation. '

Automatic diversion of LPCI flow to containment spray has been provided in response to an NRC requirement to assure containment integrity for postulated high steam flow bypassing the suppression pool. Such flow diversion would occur only if a high containment pressure (>9 psig) signal is present af ter ten minutes. The assumption of sufficient bypassing to cause such a pressure has been shown by GE to be extremely conservative and unrealistic2 .

CONCLUSION The results show that the worst single failure /Dreak type combination is the high pressure core spray (HPCS) line break (approximately .02 ft2 )

assuming the failure of the low pressure core spray (LPCS) diesel generator (D/G) which powers one LPCS pump and one LPCI pump. This single failure / break type combination yields the highest peak cladding temperature (approximately 1985 F) of all the cases affected by LPCI diversion at ten minutes. The peak cladding temperatures experienced by the cases affected by LPCI diversion are below the limits established in 10 CFR 50.46 (2200 F). This temperature is also below the peak clad temperature (PCT) calculated for the break of a recirculation line (2038 F) which is not adversely affected by LPCI diversion at ten minutes.

INE00-10977 Drywell Integrity Study: Investigation of Potential Cracking in BWR/6 Mark III Containment ASSUMPTIONS

1) A maximum of two LPCI pumps (specifically LPCI "A" and LPCI "B")

can be fully diverted at ten minutes to the containment spray mode.

(NOTE: LPCI "A" shares an emergency diesel generator with the LPCS; LPCI "B" and "C" share an emergency diesel generator.' The pump associated with LPCI "C" cannot be diverted to containment sprays.) I

2) The standard FSAR assumption of one automatic depressurization system (ADS) valve failure combined with the worst additional single failure was retained because this assumption is built into the present model. This bounding assumption yields conservatively higher calculated peak cladding temperatures (PCTs) by approxi-mately 100 F. The PCT reported on Page ? does not include this assumption.

3) Approved Appendix K analysis models were used, except that some LPCI flow to the reactor vessel was stopped ten minutes after the accident.

GENERAL OBSERVATIONS FROM THE ANALYSES Only those accide'nt cases which are not reflooded to the hot node before ten minutes are affected by the assumed LPCI diversion. Once the core has been reflooded, only one ECCS pump is necessary to keep the core covered. Thus, the breaks affected include small breaks less than approximately 0.2 ft2 (depending on the break location) and outside steam line breaks (OSLB). The effect of the assumed LPCI diversion on the OSLB is small and is discussed in a later section of this report.

After reviewing the effect of diversion on the rest of the small breaks, general statements can be made to describe the results in the area of interest:

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1.

The calculated PCTs (no LPCI diversion) in the small break regions affected by LPCI diversion generally decrease with decreasing break size.

This follows from the fact that the core is uncovered for shorter periods and that the decay heat is lower at the time of uncovery as the break size increases.

2.

The maximum temperature for the assumed LPCI diversion case for any given break location occurs at approximately that break size where the LPCI system would normally inject flow into the vessel starting at 600 seconds (i.e. the assumed LPCI diversion time). Bigger breaks get some reflooding benefit from the LPCI pumps before diversion. Smaller breaks have the same ECC systems available as this maximum break, but the smaller break area has a lower calcu-lated PCT, as discussed previously. As an example, this worst break is indicated on Figure 1. A longer LPCI diversion time would have correspondingly smaller breaks where the maximum temperature would occur and hence lower calculated PCT.

3.

Diverting LPCI from its ECCS flooding function does not always result in higher PCTs.

When compared to no LPCI diversion, a reduction in PCT can be observed as a result of diverting LPCI if the LPCS is available.

The reduction of subcooled LPCI water results in a reflooding mixture (due largely to LPCS flow) of steam and water which has higher voids. Thus, in the case where little LPCI flow is available for reflooding, even though less ECCS flow is entering the vessel, the swollen level inside the lower plenum is higher and reflooding can occur sooner.

In such cases the calculated PCTs are extremely low and changes in PCT in either

. direction are insignificant.

4.

Because this investigation is primarily concerned with small breaks, the failure of the HPCS, for non core spray line breaks, is the worst sim;b failure for this study. If the HPCS were operable, the break sizes being analyzed would reflood earlier than ten minutes with the very small break sizes never uncovering.

The following break locations were considered: A) core spray line,

8) recirculation line, C) feedwater line, D) the steam line, and E) LPCI line. A brief summary of each analysis is provided below.

A.

Core Spray Line Break (HPCS Line) - It is conservatively assumed that no flow enters the vessel through the broken line independent of the break size. For this case, the failure of the diesel generator associated with LPCS and LPCI "A" is the worst single failure since all credit for core spray cooling is eliminated. The ECC systems remaining before diversions are 2 LPCI + ADS and 1 LPCI + ADS after diversion at ten minutes. Becuase in both cases the reflooding time ir based on only cooled LPCI flow reflooding the vessel, there is a longer reflooding time associated with the diverted case with reduced ECCS flow. The results of this investigation are shown in Figure 1. Because the temperature increase from the non-diverted case is a result of a loss of reflooding flow from 1 LPCI pump, intermediate cases (loss of part of the flow) will experience intermediate (lower) temperature increases.

This particular failure / break type combination was the most adversely affected by the assumed LPCI diversion. However, the peak cladding temperatures are still below the limit of 2200 F.

B.

Recirculation Line Break - For this break, the worst single failure is the HPCS failure, as described previously. The ECCS remaining before diversion are 3 LPCI + LPCS + ADS and, after diversion, 1 LPCI + LPCS + ADS. Since in the diverted case the remaining LPCI flow is not enough to significantly quench the voids in the lower plenum, the mixture in the lower plenum will reflood with a higher voided mixture. This higher void fraction for the diverted case more than offsets the reduction in ECCS flow entering the vessel due to this diversion of LPCI. Hence, there is a net reduction in PCT due to a shorter reflooding time and the recirculation line break without diversion which has already been reported is bounding relative to a line break with diversion. A representative break (.01 ft )2 was analyzed which confirmed these results.

The results of this investigation are shown in Table 1.

Intermediate cases (diversion of less than the full flow from two pumps) should result in smaller temperature decreases.

C. & D. Feedwater and Steam Line Breaks - For these breaks, the worst single failure is the HPCS failure, as described previously.

The ECCS remaining before diversion are 3 LPCI + LPCS + ADS and after diversion 1 LPCI + LPCS + ADS. For the diverted case, there will be a reduction in calculated PCT for the same reasons discussed for the recirculation line break. A representa-2 tive break (i.e. 01 ft ) was again analyzed which confirmed the anticipated results. The results of this investigation are shown in Table 1. For both cases, insignificant decreases in calcu-lated PCT result from LPCI diversion. The outside (isolated) steam line break was also considered with similar results.

E.

_LPCI Line Break - As in the case of the core spray line break, it is conservatively assumed that no flow enters the vessel through the broken line independent of the size. For this break, the worst single failure is the HPCS failure, as described previously. The ECCS remaining before diversion are 2 LPCI + LPCS + ADS and, after diversion, LPCS + ADS (if the break is in line "C") or LPCS + LPCI + ADS (if the break is in line "A"/or "B"). In either case there is insufficient LPCI flow to significantly quench the voids in the lower plenum.

Therefore, the core will reflood with a voided mixture. This higher void fraction more than offsets the reduction in ECCS flow entering the vessel due to diversion of LPCI. Hence, there is a net reduction in PCT due to a shorter reflooding time.

As above, the .01 ft2 break was analyzed which confirmed the anticipated results.

The results of both diverted cases are shown in Table 1.

RESPONSE TO QUESTION (1)

The system provided for diversion of LPCI flow is a safety grade system.

Consequently, it has a high reliability in performing its intended function. Postulation of a failure of this system to perform its function in combination with another single failure is not required under GDC 35 or 10 CFR 50.46.

RESPONSE TO QUESTION ON OPERATOR ACTION The operation of the ECC systems including diversion of LPCI to contain-ment sprays requires no operator action for at least 10 minutes following accident initiation. Ten minutes is the present licensing basis for operator manual action time following automatic actuation of the ECC system. There is no requirement either in 10CFR50.46 or GDC 35 for assuming no operator action 20 minutes after the initiation of the accident. Ten minutes continues to be the licensing basis used and supported by General Electric. It is also the basis for the containment performance evaluation as it has been for other BWR plants.

TABLE 1 THE EFFECT ON THE PCT OF DIVERTING LPCI FLOW AT 2

10 MINUTES FOR VARIOUS .01 FT BREAK TYPES BREAK PCT PCT TYPE NO DIVERSION WITH DIVERSION Recirculation Line 948 F 877 F Feedwater Line 917 F 836 F Inside Steam Line 920 F 831 F LPCI Line 834 F 804 F (1) 964 F (2)

NOTE: (1) PCT if break occurs in LPCI line "A" or "B" (2) PCT if break occurs in LPCI line "C"

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