ML20205Q756

Summary of 990318 Meeting W/Util & ABB/C-E in Rockville,Md Re GL 97-04, Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling & Containment Heat Removal Pumps. List of Attendees & Presentation Matl Encl

ML20205Q756
Person / Time
Site:	Fort Calhoun
Issue date:	04/19/1999
From:	Wharton L NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
GL-97-04, GL-97-4, TAC-M99992, NUDOCS 9904220053
Download: ML20205Q756 (34)

Text

April.19, 1999 LICENSEE: Omaha Public Power District j i

FACILITY: Fort Calhoun Station i

SUMMARY

OF MEETING ON RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RELATED TO GL 97-04, " ASSURANCE OF SUFFICIENT NET POSITIVE SUCTION HEAD FOR EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVAL PUMPS" (TAC NO. M99992)

On March 18,1999, a meeting was conducted at the NRC headquarters office in Rockville, Maryland with NRC staff, Omaha Public Power District (OPPD), and their contractor, Asea Brown Bovari- Combustion Engineering (ABB-CE). The meeting was held to discuss staff l concerns with a Fort Calhoun Station 10 CFR 50.59 safety evaluation regarding credit for subcooling in the calculation of net positive suction head (NPSH) for the containment spray and high pressure safety injection pumps. OPPD submitted the 10 CFR 50.59 safety evaluation calculation associated with the NPSH available for the containment spray and the high pressure safety injection pumps in recirculation phase.

4 OPPD and ABB-CE presented information to address staff concerns expressed in a letter dated February 23,1999. The letter detailed the staff's assessment of OPPD's GL 97-04 and RAI i responses. The major areas of concern were OPPD's use of the CONTRANS containment performance analysis computer code and their evaluation of the plant modification options.

OPPD indicated that some additionalinformation was available regarding assumptions and sensitivities in the overpressure analysis. The staff requested that OPPD provide the additional information in response to the meeting. The staff expects to be able to complete its review and resolve all GL 97-04 concerns based on the proposed submittal.

Original Signed By L. Raynard Wharton, Project Manager, Section 2 ,

Project Directorate IV & Decoinmissioning I Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-285 DISTRIBUTION:

See next page Attachments: 1. List of Meeting Attendees I

2. Meeting Presentation Material cc w/atts: See next page Document Name 1 1

OFC /EQiV-2 PDIV-2 PDIV-2/SC , l NAME bhadon EN SDembek DATE 4 /19 /99 4 /19 /99 4//Tb  !

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~ OFFICIAL RECORD COPY 9904220053 990419 PDR ADOCE M000285 P PDR ,

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DISTRIBUTION FOR MARCH 18.1999 MEETING

SUMMARY

WITH OMAHA PUBLIC POWER DISTRICT l HARD COPY Docket File PUBLIC l PDIV Reading l RWharton

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ACRS l

l E-MAIL l

SCollins/RZimmerman (SJC1/RPZ)

BSheron (BW"d JZwolinski/SE. sack SRichards EPeyton RLobel RCaruso DSkay JBongarra BBateman ,

JWermiel I KKavanagh j JKudrick '

FOrr l DLange, EDO KBrockman, Region IV DGraves, Region IV i

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e cua o/ I,y Oi UNITED STATES 5 8 NUCLEAR REGULATORY COMMISSION f WASHINGTON, D.C. 20066 4001

% / April 19, 1999 LICENSEE: Omaha Public Power District I t

l FACILITY: Fort Calhoun Station  !

SUMMARY

OF MEETING ON RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RELATED TO GL 97-04,

• ASSURANCE OF SUFFICIENT NET i POSITIVE SUCTION HEAD FOR EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVAL PUMPS" (TAC NO. M99992)

)

On March 18,1999, a meeting was conducted at the NRC headquarters office in Rockville, j Maryland with NRC staff, Omaha Public Power District (OPPD), and their contractor, Asea Brown Boveri- Combustion Engineering (ABB-CE). The meeting was held to discuss staff concerns with a Fort Calhoun Station 10 CFR 50.59 safety evaluation regarding credit for subcooling in the calculation of net positive suction head (NPSH) for the containment spray and  !

high pressure safety injection pumps. OPPD submitted the 10 CFR 50.59 safety evaluation calculation associated with the NPSH available for the containment spray and the high pressure  ;

safety injection pumps in recirculation phase.

ll OPPD and ABB-CE presented information to address staff concerns expressed in a letter dated February 23,1999. The letter detailed the staff's assessment of OPPD's GL 97-04 and RAI responses. The major areas of concern were OPPD's use of the CONTRANS containment performance analysis computer code and their evaluation of the plant modification options.

OPPD indicated that some additional information was available regarding assumptions and sensitivities in the overpressure analysis. The staff requested that OPPD provide the additional information in response to the meeting. The staff expects to be able to complete its review and resolve all GL 97-04 concerns based on the proposed submittal.

1 L. Raynard Wharton, Project Manager, Section 2 Pro;ect Directorate IV & Decommissioning Division of Licensing Project Management Office of Nuclear Reactor Regulation  ;

Docket No. 50-285 Attachments: 1. List of Meeting Attendees )

2. Meeting Presentation Material cc w/atts: See next page ,

I Ft. Calhoun Station, Unit 1 cc w/atts:

Winston & Strawn Mr. S. K. Gambhir l l

ATTN: Perry D. Robinson, Esq. Division Manager - Nuclear Operations I 1400 L Street, N.W. Omaha Public Power District Washington, DC 20005-3502 Fort Calhoun Station FC-2-4 Adm. l Post Office Box 399 1 l Mr. Jack Jensen, Chairman Hwy. 75 - North of Fort Calhoun l

Washington County Board Fort Calhoun, Nebraska 68023-0399 of Supervisors l Blair, Nebraska 68008 Mr. Wayne Walker, Resident Inspector U.S. Nuclear Regulatory Commission Post Office Box 309 Fort Calhoun, Nebraska 68023 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011 Ms. Cheryl Rodgers, LLRW Program Manager Environmental Protection Section Nebraska Department of Health 301 Centennial Mall, South P.O. Box 95007 Lincoln, Nebraska 68509-5007 Mr. J. M. Solymossy Manager - Fort Calhoun Station Omaha Public Power District Fort Calhoun Station FC-1-1 Plant Post Office Box 399 Hwy. 75 - North of Fort Calhoun Fort Calhoun, Nebraska 68023 Mr. Mark T. Frans Manager - Nuclear Licensing Omaha Public Power District Fort Calhoun Station FC-2-4 Adm.

Post Office Box 399 Hwy. 75 - North of Fort Calhoun l Fort Calhoun, Nebraska 68023-0399

a ATTENDANCE LIST MEETING WITH OMAHA PUBLIC POWER DISTRICT MARCH 18.1999 )

OMAHA PUBLIC POWER DISTRICT R. Phelps J. Ressler M. Frans ABB - COMBUSTION ENGINEERING l M. Gancarz D. Whipple G. Singh R. Schneider NRC l

R. Wharton l R. Lobel R. Caruso l D.Skay J. Bongarra B. Bateman J. Wermiel K.Kavanagh J. Kudrick F. Orr

I i

l I

ATTACHMENT 2 MEETING PRESENTATION MATERIAL I

I

l OPPD/NRC MEETING l Net Positive Suction Head (NPSH) Calculations for ,

Containment Spray Pumps - Fort Calhoun Station )

l March 18,1999 I

1. INTRODUCTIONS II. MEETING PURPOSES (OPPD) lli. BACKGROUND (OPPD - 5 Min.)

IV. CONTRANS METHODOLOGY (ABB-CE - 30 Min.)

V. EVALUATION OF PLANT MODIFICATION OPTIONS (OPPD -15 Min.)

. Operator Action to Throttle Spray Flow e Fixed resistance Addition to Spray System

. Summary i

VI. HPSI PUMP QUESTIONS (OPPD - 5 Min.)  ;

Vll. DISCUSSION OF LICENSING DETAILS (OPPD/NRC - 30 Min.)

Vill.

SUMMARY

/ CONCLUSIONS (OPPD/NRC - 5 Min.)

i l

l MEETING PURPOSE

1. Provide the technical bases that Fort Calhoun analyses of available NPSH for LOCA events ensure ample margin to meet NPSH requirements.

i

2. Provide additional details to demonstrate that ECCS system modifications to increase the available NPSH margin are not appropriate.

3. Resolve licensing details to allow OPPD and NRC to move forward and l

close the NPSH issue in Generic Letter 97-04.

l l

l

I Bac <grounc /F iS':ory e 1971 FSAR stated that NPSH was in compliance with AEC Safety Guide 1 e 1992 Events:

As-built hydraulic calculations of spray system performed as part of design basis reconstitution Spray pump flow could be higher than that used in SAR discussion of NPSH LER 92-016 issued (May 1992) 1 .

ABB-CE reviewed 27 available containment analysis l l

cases -- Case OSNVBV97 identified as having lowest l amount of sump subcooling OPPD implemented partial credit for sump subcooling l

and revised USAR accordingly l OPPD formally notified NRC of commitment change i relative to AEC Safety Guide 1 (Sept.1992)

NRC Inspection Report closed LER 92-016 (Dec.

1992)

• Generic Letter 97-04 OPPD response described 1992 events related to spray pump NPSH

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l Chronology of CONTRANS .TIodifications to 1999 Time Frame

• 1 i CONTRANS Revision No. :' Approval Date Change

! Description r

l i Revision 0 l April.1974 I Original submittal. {

Revision 1 i June,1975 I NRC Approved model. j Revision ID February,1977 Extended ranges for EBASCO l designs.

Revision 2, Cyber 855 June,1987 Different Mainframe Computer-Mainframe FORTRAN IV version I l

Revision 2. CDC 7600 March,1991 First FORTRAN V version. EQ Mainframe Option based on NUREG-0588.

CONTRANS2 Version NPL, March,1991 An interim FORTRAN V version.

l CDC 990 Mainframe i Version 2. MOD 1 CDC 990 March,1991 An updated version - Output format Mainframe changes and an option per NUREG-0588 guidelines. For EQ application during a MSLB.

CONTRANS2 MOD 1. March.1991 Minor changes for the Workstation.

Apollo Domain DN10000, 400 Series etn2ml .ccw January,1993 Component Cooling Water ! Intake ,

Apollo Domain DN10000, Cooling Water (CCW/ICW) model ,

9000/400 Series developed for a ABB plant for response to Generic Letter 89-13.

ctalml.cew. purge March,1995 Containment Purge model.

HP-UX 9000/700 Series (Interim Version) etn2ml.cewrwp April,1995 Component Cooling Water / Raw Water (CCW/RW) model developed -

HP-UX 9000/700 Series for OPPD for response to Generic (Interim Version)

Letter 89-13.

etn2ml.062097 June,1997 Option to use alternate decay heat ,

HP-UX 9000/800 Series methods, additional plotfiles, and a l chane in computer platform. i workstation January,1998 Component Cooling Water / Service j ctnmp2.797 li Water (CCW/SW) model developed i HP-UX 9000/800 Series workstation for a ABB plant to support Generic '

Letter 89-13 and start-up issues.

(Interim Version)

- All modifications performed in accordance with ABB QA procedures.

c l

OPTION 1 l

Reduce NPSH a By Ooerator Action to Throttle Soray Flow

• Local manual throttling after RAS is not feasible due to radiation conditions and no suitable manual valves.

• Existing spray header AOVs can be throttled remotely if instrument air is available.

1

• Instrument air system is not safety grade, so enabling throttling with existing AOVs would require a safety-grade airlgas source (i.e., modification is required to enable operator action to throttle spray flow).

• A backup bottled gas supply would require a very large number of bottles due to constant-bleed devices in the AOVs' pneumatic loops.

• A dedicated air supply (compressor) system for the )

AOVs would place additional electrical load on the i emergency diesel generators.  ;

i e The AOVs could be replaced with MOVs, but those l would add load on the diesels. l l

l

• Modification costs likely to exceed $500,000.  ;

l 1 l l

OPTION 1 Reduce NPSH a By Ooerator Action to Throttle Spray Flow

• Timing of operator action is a concern (i.e., at RAS, not before or after RAS). l

• New operator action introduces human element risk --  !

conflicting priorities, wrong action, wrong time, etc.

i

• New procedural step (s) would be an Operator Work- '

Around, prompting another modification request to eliminate the OWA.

CONCLUSION:

Not a feasible option.

OPTION 2 '

i Reduce NPSH a By Fixed Resistance in Soray Pioing

• Would reduce recirculation phase spray pump flow to desired level without operator intervention.

i l e Would also reduce injection phase spray pump flow.

l e Requires modification of both spray headers.

1 e New containment pressure analysis required because l of lower spray flow.

l e Total cost of modification and new containment pressure analysis estimated to exceed $400,000.

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Discussion of Ootion 2 - Fixec Resis':ance e Reduction of spray flow during injection phase will decrease peak pressure mitigation capacity of the containment spray system -- counter to safety.

e LOCA containment peak pressure may not have sufficient margin below design limit to accommodate the resulting reduction in delivered spray flow.

I e Analysis shows substantial degree of sump subcooling present for large break LOCA event. (Modification would increase NPSH margin.)  !

e Analysis also shows small margin between LOCA containment peak pressure and containment design pressure. (Modification would decrease this margin.)

CONCLUSION:

It is preferable to credit sump subcooling rather than reduce the spray system's capacity to mitigate LOCA containment peak pressure.

6 TEXT DISCUSSION i

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BACKGROUND / HISTORY e FSAR and Safety Guide 1 Section 6.2.1 of the Fort Calhoun FSAR (circa 1971) states that NPSH for the ECCS pumps is in compliance with AEC Safety Guide 1. The FSAR's NPSH values did not utilize subcooling head in l computing NPSHA.

l e 1992 Events As-built hydraulic calculations of the Containment Spray system were developed as part of the Design Basis Reconstitution effort. It was discovered that CS pump flow rate could be higher (on a per-pump basis) than the pump flow value used in the FSAR's discussion of NPSH. This was due to single failure possibilities leaving fewer than three spray pumps operating.

The new information indicated that for certain spray system alignments (i.e., I pump 1 header, or 2 pumps 2 headers), a NPSH deficiency could exist for the spray pumps in the recirculation phase if subcooling head is excluded from the NPSH computation. This was reported to the NRC in LER 92-016, dated May 18,1992.

After reviewing options, OPPD decided to implement a partial credit for sump water subcooling.

ABB-CE reviewed the containment analysis cases available at the time and identified Case OSNVBV97 as having the smallest degree of sump subcooling. A subcooling credit of about 9 fe:t was used, which was about 25% of the minimum available subcooling head for Case OSNVBV97 l during the post-RAS phase of a large LOCA. The 9-foot credit provided positive NPSH margin for the spray pumps.

OPPD kept NRC informed ofits actions and intentions. LER 92-016 stated that the USAR would be revised to reflect the subcooling credit and the USAR was changed accordingly. OPPD formally notified the NRC of the commitment change relative to Safety Guide 1 in letter LIC-92-291R dated September 18,1992. NRC Inspection Report 5-285/92-30, dated December 31,1992, subsequently closed LER 92-016.

e GL 97-04 Response Generic Letter 97-04 asked questions about ECCS pump NPSH. In its Dec. 31,1997 response to the Generic Letter, OPPD described the 1992 events related to the containment spray pumps. NRC's follow-up questions have led to the March 18,1999 meeting with the NRC staff.

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OPPD / NRC Meeting, March 18, 1999 ABB CENP Presentation

Background:

In the 1992 timeframe, ABB CENP utilized an existing containment response simulation generated with the CONTRANS computer code to support a Net Positive Suction Head (NPSH) calculation of the OPPD containment spray pumps. The  !

CONTRANS simulation supplied the amount of available pressure head. This was defined as the minimum differential pressure between the containment vapor space and the saturation pressure at the sump temperature. When converted to feet, this represented about 36 feet of pressure head. At the time, only 9 feet was required to demonstrate adequate NPSH. Since only 25% of the available margin was used, OPPD

& ABB determined that further, more limiting CONTRANS simulations would not be pertinent.

Recently, the NRC has questioned: 1.) The adequacy of the existing analyses results for the NPSH calculation and 2.) the validity of the methodology utilized. For Item #2.

this directly reflects on the use of the CONTRANS computer code for this application.

A meeting was called by the NRC to address these issues.

Obiectives:

The objective of the meeting is to 1.) confirm the adequacy of the existing analyses for Containment Spray Pump NPSH and 2.) demonstrate the validity of the methodology q used to determine the available margin.  !

l Technical Basis for Sub-Cooline Credit:

In 1992, out of an available matrix of 27 cases, a best estimate maximum safeguards scenario was found to be the most limiting with respect to the minimum differential l pressure between the total pressure of the containment vapor space and the saturation l pressure based on the containment sump temperature. As mentioned before, only 9' of l the available 36' was required to satisfy the NPSH criteria. l Since the NRC questioned the use of the best estimate scenario rather than a worst case biased calculation, ABB CENP has mn a limited set of sensitivity cases. These cases are for illustration purposes and have not been formally verified. These comprise a minimum pressure case and a maximum sump temperature case. Inputs for these cases were largely biased based on guidance provided in Attachment A to the 1986 Safety Evaluation Report (SER) for the ECCS LBLOCA EM methodology. These input

- changes were composed of changes to the initial containment conditions, heat transfer to the containment heat sinks, and the use of maximum containment fan cooler and i

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containment spray heat removal performance. Other changes to maximize sump temperature included a change to the separation of break Gow into steam and liquid i input.

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The results of these additional " biased" cases showed that the use of 9 feet remains a small fraction of the available pressure head. This is presented in the attached plot.

Time Independent Acoroach:

A review of the previous figure indicates that the muumum containment pressure (in head of water) is in the range of 33-36 ft. This confirms that substantial margin exists relative to the small (about 9 ft) overpressure credit considered in the AOR.

The time independent approach was selected for the AOR since:

1. The minimum available NPSH was selected for the AOR reference margin estimate.

2. Total available margin was large.

3. The required NPSH, as provided from the manufacturer, is dependent on volumetric flow pumped and not temperature.

4. Temperature affects due to elevation and friction losses in suction piping is small compared to available margin.

I The level of margin was further confirmed with recent sensitivity studies biasing results to establish a minimum containment pressure and maximum sump temperature.

In all cases signi5 cant margin is available.

Use of CONTRANS Containment Performance Analysis Cnmouter Code: l To address the NRC's concern regarding the use of CONTRANS to support minimum pressure applications, ABB CENP has reviewed both the CONTRANS SER and the ECCS LBLOCA EM SER. Both refer to CONTRANS as an acceptable modeling tool.

To illustrate this (work has not been formally verified), ABB CENP benchmarked containment parameters for CONTRANS versus the ECCS minimum pressure code and found that essentially identical results could be achieved solely by the selection of input.

This con 5rmed that the governing equations in the code are identical. l l

CONTRANS has evolved since the original approval in 1976. Several changes were made which were necessary due to computer platform changes Equipment Quali5 cation (EQ) requirements (such as that provided in NUREG-0588 and IN 84-90) and to support Generic Letter 89-13 issues. One rarely used modification also allowed l CONTRANS to model a hole in containment due to purge valves. In each case. the i original solution could be veri 5ed by simply turning off these options. Each change l was verified and documented in accordance with ABB's Quality Assurance procram. A summary of the changes is provided in the attached Table. l l

l Summary:

1 The CONTRANS containment results were shown to be valid for application to the NPSH calculations. CONTRANS can be biased to produce maximum or minimum containment pressure results by proper input selection. Additionally, the current version of CONTRANS can produce identical results to the original version approved in 1976 with appropriate input selection. While several options have been added to address current day issues, these have been verified and validated in accordance with ABB's Quality Assurance Procedures. The use of CONTRANS continues to be within its SER.

The use of CONTRANS in performing additional sensitivity analyses has confirmed that original use of 9 feet of overpressure is conservative relative the calculated available margin.

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• PLeANT MODIFICATION OPTIONS Option 1: Operator Action to Throttle Spray Flow l

l Local manual operator action to throttle containment spray flow after RAS is not feasible. Radiation l conditions in rooms containing spray piping would preclude personnel access to reposition manual valves.

In addition, the manual valves on the spray header piping are gate valves which are generally not suitable for throttling service.

Each of the two containment spray headers has an air-operated valve (AOV) which can be throttled remotely from the control room ifinstrument air is available. Instrument air is not a safety-grade system, so a safety-grade air / gas supply would need to be provided to enable remote throttling with the existing AOVs. A modification is therefore required to give the operators the capability to remotely throttle spray flow.

The AOV3' pneumatic loops have constant-bleed devices. For that reason, a safety-grade backup bottled gas supply would require a very large number of bottles to facilitate long-term indefinite spray throttling, which is not practical.

Air could be supplied to the AOVs by a dedicated safety-grade air compressor system. Such a system would l require emergency electrical power which would place additional electrical load on the emergency diesel generators. (The diesel generators presently have very little margin to accept extra loads.)

The existing AOVs could be replaced with motor-operated valves (MOVs), but again this would add more electrical load to the emergency diesel generators. MOVs also tend to be heavier than AOVs and the effect on piping system loading would have to be addressed (possible pipe support modifications).

Costs of the above-mentioned modifications would likely exceed $500,000.

Timing of the operator action is a concern. Throttling would be needed as soon as the recirculation phase l starts, but not before. Operators would have to have their " hand on the controls," watching and waiting for RAS to happen. This is an undesirable additional burden on the operators in a post-accident situation. Any new procedural provision for throttling spray flow also introduces human element risk that was not there previously. The operator could do the wrong action, do it at the wrong time, be distracted away from more important matters, etc.

The new proceduralized operator action would be characterized as an Operator Work-Around (OWA). It is desirable to eliminate OWAs and avoid their creation whenever possible. A design-driven OWA such as this is highly likely to prompt another modification request to eliminate the OWA. It is not justifiable to implement a modification to enable spray flow throttling, only to create a new OWA and another modification to eliminate it.

I Based on the above, it is concluded that operator action to throttle spray flow is not a feasible option.

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i Op' ion 2: Fixed Rcsistance Addition to Spray System '

1 l Adding a fixed hydraulic resistance (e.g., orificing) to the containment spray system would place pump Aw l and NPSHR in a range where NPSHA would be adequate without crediting subcooling head, all without j having to rely on operator action to reduce spray flow.  !

l At this point it is important to be aware of the required hydraulic performance from a spray pump to meet accident requirements, and how this is affected by a fixed resistance modification.

The NPSH assessment in USAR 6.2.1 is based on a spray pump flow of about 3100 gpm. This pump flow ,

I correlates to one of two possible spray system operating alignments: 1 pump feeding i header or 2 pumps t feeding 2 headers. Since the 2P/2H alignment must be addressed. hydraulic resistance would have to be added to both spray headers.

1 l At present there is a subcooling head credit of about 9 feet in the NPSH computation. This could be eliminated if spray pump NPSHR was reduced by 9 feet. This can be done by introducing enough hydraulic resistance to reduce the maximum pump flow to about 2500 gpm.

Note: The graphs are for illustrative purposes to show the magnitude of the effect on the spray system. The j graphs are based on estimate-type computations and are not based on formalized calculations.

The hydraulic resistance for the containment spray system is higher during the injection phase of a LOCA than during the recirculation phase. During the injection phase, the spray pumps are taking suction from an atmospheric tank and discharging to a pressurized containment. During the recirculation phase, the suction source is the same as the discharge (i.e., containment building), so the containment backpressure on the discharge side is the same as the containment pressure acting on the suction side.

The LOCA containment peak pressure analysis of record credits a delivered spray flow of 1885 gpm, to be delivered by one spray pump feeding one spray header. The actual flow output from the pump has to be more than 1885 gpm, to account for flow losses through a missing spray nozzle, blocked spray nozzles, and the l pump minimum recirculation line back to the SIRWT. When these are considered, the total required pump I flow is 2190 gpm. The pump must achieve this flow when pumping against a 60 psig containment, so the i I

required pump performance point is 2190 gpm at 379 feet TDH. This operating point is then adjusted to account for the uncertainty of flow and pressure instruments used to measure pump hydraulic performance.

After these adjustments, the required pump operating point to meet the LOCA containment pressure analysis is 2270 gpm at 389 feet TDH. This represents an intersection point between a pump performance curve and the injection phase system resistance curve.

If the system hydraulic resistance is increased to limit the maximum pump flow at 2500 gpm in the recirculation alignment, then the effect will be a steepening of the system resistance curve for the injection phase. The net result is that delivered spray flow will be reduced by more than 300 gpm during the injection phase of a LOCA.

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t The reduction in delivered spray flow during the injection phase would require a new containment pressure analysis. Given the present peak pressure (58.96 psig for limiting case of record), it is very questionable whether it can be kept below 60 psig with a 300 gpm reduction in delivered spray flow.

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Option 2: Fixed Resistance Addition to Spray System (continued) l The cost of a fixed resistance modification, including the analysis to support it, is estimated to exceed  ;

$400,000.  !

Since the operator throttling option has been discounted as a feasible option, a fixed resistance modification is the only possible modification option to eliminate the subcooling credit. It is also clear that such a modification will significantly reduce the delivered spray flow during the injection phase of a LOCA.

Reducing deliverable spray flow during the injection phase of a large LOCA is contrary to safety. i l

It is therefore a choice between a fixed resistance modification and implementing a subcooling credit for l NPSH. Analysis shows a substantial degree of sump subcooling is present during the recirculation phase of a large LOCA event. Analysis also shows a relatively slim margin of LOCA containment peak pressure below the 60 psig limit. Based on that, it is clearly preferable to implement a subcooling credit for NPSH l rather than intentionally decrease the capacity of the containment spray system to mitigate containment peak pressure.

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HPSI PUMP QUESTIONS

• The subcooling credit is applied to the HPSI pumps as well as the spray pumps for the sake of ,

consistency. These pumps all take suction from the same place. It is not physically possible for I subcooling head to exist for the spray pumps and not for the HPSI pumps. To list subcooling credit i for spray pumps and not HPSIs would be confusing.

e USAR 6.2.1 is governing with respect to NPSH and should not be interpreted as being in conflict with the HPSI pump " max flow" value in USAR Table 6.2-2. USAR Table 6.2-2 is intended to give the  !

reader a general description of equipment (i.e., original spec data) and not represent any mode-specific l HPSI pump operating point.

o HPSI pump NPSH is adequate without the subcooling credit anyway. HPSI pumps have a much lower NPSH requirement than the containment spray pumps.

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