ML20247L854

Requests Addl Info Re GL 97-04, Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling & Containment Heat Removal Pumps

ML20247L854
Person / Time
Site:	Millstone
Issue date:	05/19/1998
From:	Andersen J NRC (Affiliation Not Assigned)
To:	Bowling M, Loftus P NORTHEAST NUCLEAR ENERGY CO.
References
GL-97-04, GL-97-4, TAC-MA0011, TAC-MA11, NUDOCS 9805260096
Download: ML20247L854 (14)

Text

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Mr. Martin L. Bowling,'Jr.' May 19, 1998 1 i Rtcov:ry Ofhcer - Ttchnical Ssrvicss j L Northe:st Nuclerr En:rgy Company-L ~'

1< c/o Ms. Patricia A. Loftus-Director Regulatory Affairs- 'i P. O. Box 128 - i Waterford, Connecticut 06385 ~l l- .

l

SUBJECT:

MILLSTONE NUCLEAR POWER STATION, UNIT 3 - GENERIC LETTER 97-04, j

" ASSURANCE OF SUFFICIENT NET POSITIVE SUCTION HEAD FOR l

' EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVA'. PUMPS" i

- REQUEST FOR ADDITIONAL INFORMATION (TAC NO. MA0011)

Dear Mr. Bowling:

1

' The staff issued Generic Letter (GL) 97-04, " Assurance of Sufficient Net Positive Suction Head l for Emergency Core Cooling and Containment Heat Removal Pumps" on October 7,1997. The GL requested that licensees provide information necessary to confirm the adequacy of the net a positive suction head available for emergency core cooling, and containment heat removal 'j

. pumps. By letter dated January 21,1998, Northeast Nuclear Energy Company (the licensee) l

. submitted its 90-day response to GL 97-04. The staff has reviewed your response and has l concluded that portions of your response.did not adequately address the requested information.

. Enclosed are examples of responses that the staff has found acceptable. Please note that the .

. enclosed examples are only guidelines of the type of information that the staff needs to conduct its review, and are included for your convenience. After reviewing the enclosed examples, please reevaluate your submittal, revise as necessary, and provide the revised response within l ' 60 days from the date of this letter.:

Should you have any questions, please contact me at (301) 415-1437.

. Sincerely,1 Origin = 3 signed by:

i James W. Andersen, Project Manager Special Projects Office - Licensing Office of Nuclear Reactor Regulation Docket No. 50-423

Enclosure:

Sample Responses . ,

cc w/ encl: See next page DISTRIBUTION-Docket Filet ACRS'

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SPO Reading JKudrick, NRR '

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LBerry DSkay 9 YO

. JAndersen k lf DOCUMENT NAME: G:%NDERSEN%0011.RAI g- ' To receive a copy of esis document, indicate in the box: "C." = Copy without enclosures *E" = Copy v#)qnclosures "N" = Np gd>y 0FFICE- SPO-L PMJ SPO-L:LA ( Q SRhl:NRR p SCS Q ( SP${Li[ D l NAME- JAndersen A

- LBerry .W \

RCinIso JKuq r S i\, PNMel i DATE 05/@/98 05/)4/98 ~ 05/j/98 05/J 3E lI 05/6 /98 9905260096 990519 # "FFICIAL RECOR COPY ' ( ,

PDR P

ADOCK 05000423 Pon 8

6 UNITED STATES

• . f j NUCLEAR REGULATORY COMMISSION o WASHINGTON, D.C. 200edHe01 May 19, 1998 g*****

Mr. Martin L Bowling, Jr.

Recovery Officer - Technical Services Northeast Nuclear Energy Company clo Ms. Patricia A. Loftus Director- Regulatory Affairs P. O. Box 128 Waterford, Connecticut 06385

SUBJECT:

MILLSTONE NUCLEAR POWER STATION, UNIT 3 - GENERIC LETTER 97-04,

" ASSURANCE OF SUFFICIENT NET POSITIVE SUCTION HEAD FOR EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVAL PUMPS"

- REQUEST FOR ADDITIONAL INFORMATION (TAC NO. MA0011)

Dear Mr. Bowling:

The staff issued Generic Letter (GL) 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" on October 7,1997. The GL requested that licensees provide information necessary to confirm the adequacy of the net positive suction head available for emergency core cooling, and containment heat removal pumps. By letter dated January 21,1998, Northeast Nuclear Energy Company (the licensee) submitted its 90-day response to GL 97-04. The staff has reviewed your response and has concluded that portions of your response did not adequately address the requested information.

Enclosed are examples of responses that the staff has found acceptable. Please note that the enclosed examples are only guidelines of the type of information that the staff needs to conduct its review, and are included for your convenience. After reviewing the enclosed examples, please reevaluate your submittal, revise as necessary, and provide the revised response within 60 days from the date of this letter.-

Should you have any questions, please contact me at (301) 415-1437.

Sincerely,-

L s W. Andersen, Project Manager l Special Projects Office - Licensing Office of Nuclear Reacter Regulation Docket No. 50-423

Enclosure:

Sample Responses cc w/ encl: See next page

______--___-____a

Millstone Nuclear Power Station

.. Unit 3 cc-Lillian M. Cuoco Esquire Joseph R. Egan, Esquire Senior Nuclear Counsel Egan & Associates P.C.

Northeast Utilities Service Company 2300 N Street, NW

! P. O. Box 270 Washington, DC 20037 Hartford, CT 06141-0270 Mr. F. C. Rothen Mr. Kevin T. A. McCarthy, Director Vice President - Work Services Monitoring and Radiation Division Northeast Utilities Service Company Department of Environmental Protection P. O. Box 128 79 Elm Street Waterford, CT 06385 Hartford, CT 06106-5127 Emest C. Hadley, Esquire Regional Administrator, Region i 1040 B Main Street U.S. Nuclear Regulatory Commission P.O. Box 549 475 Allendale Road West Wareham, MA 02576 King of Prussia, PA 19406 Mr. John Buckingham First Selectmen Department of Public Utility Control Town of Waterford Electric Unit Hall of Records 10 Liberty Square 200 Boston Post Road New Britain, CT 06051 Waterford, CT 06385 Mr. James S. Robinson, Manager Mr. Wayne D. Lanning Nuclear Investments and Administration Deputy Director of Inspections New England Power Company Special Projects Office 25 Research Drive 475 A!!endale Read Westborough, MA 01582 King of Prussia, PA 19406-1415 Mr. John Streeter Mr. M. H. Brothers Recovery Officer - Nuclear Oversight Vice President - Millstone Unit 3 Northeast Utilities Service Company Northeast Nuclear Energy Company P. O. Box 128 P.O. Box 128 Waterford, CT 06385 Waterford, CT 06385 Deborah Katz, President Mr. M. R. Scully, Executive Director Citizens Awareness Network Connecticut Municipal Electric P.O. Box 83 Energy Cooperative Shelbume Falls, MA 03170 30 Stott Avenue Norwich, CT 06360 Mr. David Amerine Vice President - Human Services Northeast Utilities Service Company P. O. Box 128 Water'ord, CT 06385

l Millstone Nuclear Power Station Unit 3 i Mr. Don Schopfer l cc: Wrification Team Manager Sargent & Lundy

- Mr. Allan Johanson, Assistant Director 55 E. Monroe Street Office of Policy and Management Chicago,IL 60603 Policy Development and Planning Division Mr. G. D. Hicks 450 Capitol Avenue - MS# 52ERN Director- Millstone Unit 3 Operations P. O. Box 341441 Northeast Nuclear Energy Company Har. ford, CT 06134-1441 P.O. Box 128 Waterford, CT 06385 Citizens Regulatory Commission ATTN: Ms. Susan Perry Luxton Senior Resident inspector 180 Great Neck Road Millstone Nuclear Power Station Waterford, CT 06385 clo U.S. Nuclear Regulatory Commission P. O. Box 513 The Honorable Terry Concannon Niantic, CT 06357 Nuclear Energy Advisory Council Room 4035 Mr. William D. Meinert Legislative Office Building Nuclear Engineer Capitol Avenue Massachusetts Municipal Wholesale Hartford, CT 06106 Electric Company P.O. Box 426 Mr. Evan W. Woollacott Ludlow, MA 01056 Co-Chair Nuclear Energy Advisory Council Attomey Nicholas J. Scobbo, Jr.

128 Terry's Plain Road Ferriter, Scobbo, Caruso, Rodophele, PC Simsbury, CT 08070 1 Beacon Street,-11th Floor Boston, MA 02108 Mr. John W. Beck, President -

Little Harbor Consultants, Inc.

< Millstone -ITPOP Project Office P.O. Box 0630 g Niantic, CT 06357-0630 Mr. B. D. Kenyon (Acting)

Chief Nuclear Officer- Millstone Northeast Nuclear Energy Company

. P.O. Box 128 ,

Waterford, CT 06385' i Mr. Daniel L Curry Project Director-Persons Power Group Inc.

2675 Morgantown Road Reading, PA 19607 I

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I I q#

Nuclear Station Response to NRC Generic. Letter 97-04 Per the above referenced generic Ictter, licensees were requested to provide information on five issues relating to net positive suction head fur Emergency Core Cooling System (ECCS)- pumps. The exact requests, and the specific responses, are included in the following:

1. SpecAfy the general methodology used to calculate the head loss associated with the ECCs ' suction strainers. -

In order to determine various flow and design issues relating to ECCS sump performance, contracted to construct a 1:3 scale model of the containment sump and to conduct extensive hydraulic testing. The general methodology used in calculating suction strainer and vortex suppressor head loss was the gathering of empirical data during test runs with various flow and screen blockage conditions, and compiling this data to determine a loss coefficient. The complete report is provided by the Report , " Assessment of Flow Characteristics within a Reactor Containment Recirculation Sump using a Scale Model". l l

, - The bounding case for suction screen head loss is given by l

maximum flow for the Residual Heat Removal (RHR) and  !

Containment Spray pumps. Using the loss coefficient determined by the above report for 50% strainer blockage, this maximum head loss was calculated to be . feet. Since the location of the sump screens is feet above the sump ,

floor, the suction pressure added by the elevation head  !

would more than compensate for the maximum head loss across the suction strainers. 1 The calculation for the limiting-case available net positive suction head for the ECCS and Containment Spray pumps i assumed a sump level of 0, and therefore no suction screen head loss was included. This is one of several '

conservatism contained in the minimum NPSH calculations.

The fellowing discussion on general NPSH calculation methodology is extracted from the FSAR, Section 6.3.2.14.

"The Emergency Core Cooling System is designed so that adequate net positive suction head is provided to system pumps in accordance with Regulatory Guide 1.1. To Enclosure

\ ..

Page 2 demonstrate that adequate NPSH is provided_for the ECCS pumps, it is not necessary to provide a graph of NPSH as a function of time; it is only necessary to demonstrate that the NPSH is adequate under the worst limiting conditions, Adequate net positive for_all pumps suction head is shown to be available as follows:

1

1. Residual Heat Removal Pumps The net positive suction head of the residual heat removal pumps is evaluated for normal shutdown operation, and for both the injection and recirculation modes of operation for the design basis l- accident.

The recirculation mode of operation gives the limiting NPSH requirement for the residual heat removal pumps, and the NPSH available is determined from the following equation:

NPSH[ actual] =

(h) containment pressure - (h) vapor pressure + (h) static head - (h)1oss To evaluate the adequacy-of the available NPSH, several l conservatism are applied:

a. No increase in Containment pressure from that present prior to the accident is assumed.

b. The Containment sump fluid temperature is assumed to be T even though the maximum temperature reached is approximately 'T.

c.

The static elevation head is calculated from the floor elevation of the sump (elevation '+ ")

instead of the of the RHR pump is available water. level. The

'+ " (Centerline of elevation discharge pipe).

d. The head loss is evaluated based on all pumps running at the maximum calculated runout flow with ,

conservatively assumed junction. factors.

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e. The required NPSM is based on one pump running at a maximum calculated runout flow of gpm.

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, ,. Page 3 )

2 '.

Safety Injection and Centrifugal Charging Pumps The. net positive suction head for the safety injection pumps and the centrifugal charging pumps is evaluated for.both the injection and recirculation modes of

! operation for the design basis accident. The end of the

( injection mode gives the limiting NPSH requirement for the safety injection pumps and the centrifugal charging pumps, and the NPSH available is determined from~the following equation:

NPSH[ actual) = (h) containment pressure . (h) vapor pressure + (h) static head - (h)1oss To evaluate the adequacy of the available NPSH, several conservatism are applied:

a. The Refueling Water Storage Tank (RWST) fluid temperature is assumed to be *F.

I

b. The static elevation head is calculated taking no credit for water'+

(elevation level").above the bottom of the RWST

c. The head loss is evaluated based on all pumps running at the maximum calculated runout flow with conservatively assumed junction factors.

L d. The required NPSH is based on one pump running at its maximum calculated runout flow."

l In summary, although head loss across the sump suction screens and vortex suppressor were not incorporated in the calculations for minimum available NPSH, the more limiting assumption of 0 sump level was used. If actual elevation and suction screen head loss were incorporated into the

! available NPSH calculation, results would be slightly higher

.than the current conservative values. ,

i i

2. Identify the required NPSH and the available NPSN.

Required NPSH and available NPSH (for the most limiting.

flows and operating modes) are given for the ECCS and containment spray pumps by the following table: i i

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,, Page 4 1

Required Available NPSH NPSH (feet) (feet)

Injection Cold Leg Pump Recire.

Min. RWST Minimum Level Sump Level Containment ^^

s ') (. ')

Spray A Containment Spray B Safety Injection A Safety ~

Injection B ,

Residual Heat Removal A Residual Heat Removal B Centrifugal Charging A Centrifugal Charging B

3. Apocify whether the current design-basis NPSH analysis differs from the most recent analysis' reviewed and approved by the NRC for which a safety evaluation was issued.

Current design-basis NPSH analysis is unchanged, and still accurately discussion in thereflected FSAR, as by the general methodology

. response. related in the issue 1 NRC in the This item was last formally reviewed by the SER.

4. Specify whether containment overpressure (i.e. ,

containment pressure above the vapor pressure of the sung or suppression pool fluid) .was credited in the calculation of available NPSH. Specify the amount of overpressure needed and the minimum overpressure available.

No amount of over,oressure was used 12. calculating available NPSH. Additionally, a barometric pressure of psia was used.

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j-Page 5 i

5. When containment overpressure is credited in the calculation of available NPSH, confirm that an appropriate containment pressure analysis was done to establish the minimum containment pressure.

N/A containment overpressure is specifically NOT credited in

's NPSH calculations for ECCS pumps.

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. NRC Recueg

1. Specify the general methodology used to calculate the head loss associated with the emergency core see!ing system (ECCS) suction sealners.

8829DR3 De basic methodology used for determining pump net positive suction head (NPSH) involves a comparison i of the difference between the total available suction head (absolute head measured at the pump impeller eye) l and the vapor head (absolute) of the pumped fluid. His basic methodology is reflected in the following equation:

NPSH = h,- h,,, + h,- h.

1 where:

1 l

b, = simospheric head, absolute pressure (in feet ofliquid) on the surthee of the

, liquid being pumped.

h, = vapor head, the head in feet corresponding to the vapor pressure ofliquid at the l temperature being pumped.

l h, = s'atic head, static height in feet that the liquid supply level is above the purnp impeller eye.

h. = friction head, all suction line losses (in feet) including all sump screen and form losses as well as friction losses through piping, valves and finings.

In applying this basic relationship to the ECCS and containment spray pumps for the sumn recirculation mode, the following conservative methodologies and assumptions were used to establish each term:

h, Absolute pressure on the surface of the liquid supply level. -

nis term is defined as the product of the containment pressure and the specific volume of the liquid l being pumped. De calculations assume that the containment pressure is atmospheric '

(14.7 psia). His assumption is consistent with NRC Regulatory Guide 1.1 which states that no I credit is to be taken for post accident containment pressurization. De specific volume of the sump fluid is conservatively assumed to be that of water at F. De assumed 'F water temperarare represents the maximum post-accident sump fluid temperature.

h,,, Vapor pressure ofliquid at the temperature being pumped.

His term is defined as the product of the saturation pressure for the temperature of the liquid being pumped and the specific volume of the liquid at that temperature. The ,

calculations l conservatively assume that the saturation pressure and specific volume of the sump fluid is that of ,

water at . 'F. De assumed 'F water temperature ..r.. / the maximum post-accident sump j fluid temperature.

1 h,, Static height of the pumped fluid above the pump impeller eye.

His term is dermed as the elevational difference between the su. face level of the fluid being pumped and the center of the pump impeller eye. De . calculations use the difference ATTACHMENT 2

between abe calculated conrinment sump level during meirculation and the ECCS and containment spray pump suction elevation for the static head. Containment sump levels are assumed to be conservatively low for both large break (LBLOCA) and small break (SBLOCA) loss ofeoolant accidents. Calculations which use methodologies and assumptions which minimize sump level have been performed for both accidents to confirm that the assumed containment sump levels are less than the calculated minimum sump levels.

h. = Friction head losses (in feet)in the suction line including Merion losses through piping, valves and finings as well as sup scree and fann losses.

His term is deAned as the head loss due to flow resistance encountered by the pumped fluid in the pump suction line. De calculations maximias the 6iction head loss by the conservative calculation and summation of the following parameters:

1. Sump screen and form losses which address head losses 6cm the sump inlet screen to the msidual heat mmoval and containment spray pump suction piping. This value was empirically established for based on scale model testing performed prior to plant operation. De testing measured pressum head losses for the actual sump configuration and established a corresponding loss coefficient for the sump configuration. The loss coefficient relates actual sump screen, form and suction piping entrance head losses to the fluid velocity in the pump suction piping. Dese losses were calculated for conservatively high pump flow rates. (Dese calculated losses assurne that the sump screen is Ave kom blockage. Sump screen blockage has been evaluated separately as described in the msponse to item 2.)

2. Suction line friction losses which consider the piping length, size (schedule), relative roughness, fitting resistance (i.e., piping elbows, reducers, see connections, gate valves and check valves) and fluid velocity. The calculations es2blish an equivalent pipe length for the actual length of straight pipe and all associated Attings and valves in the ECCS and containment spray pump suction piping. The maximum established equivalent piping length is corabined with conservatively high pump flow rates, actual pipe inside diameters and an empirically determined $iction factor to establish bounding suction line friction losses.

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NRC Reausst

,. 2. Identify the required NPSH and the available NPSH.

BEIRRRag The following is a summary of the available NPSH and the required NPSH for the ECCS pumps.

, Engna Avallable NPSH Renuired NPSH Excess NPSH l

1 ResidualHeat Removal (LBLOCA) .' A .A A Containment Spray (LBLOCA) A A ,A Residual Heat Removal (SBLOCA) A .A A (No Containment Spray)

Residual Heat Removal (SBLOCA) A A 9 (With Containtnent Spray)

Containment Spray (SBLOCA) A A .A Safety Irdection (LOCA) A A A (Hot Leg Recirculation)

Safetyinjection (LOCA) t A A 1 (Cold Leg Recirculation)

Centrifugal Charging (LOCA) A eA A l (Hot Leg Recirculation) '

Centrifugal Charging (LOCA) A A A (Cold Leg Recirculation)

During the containment sump recirculation mode of operation, the residualheat removalpumps and containment spray pumps take suction tom the containment sump. The safety injection pumps and the high pressure centrifugal charging pumps take suction kom the residual heat removal pump discha.ge. As indicated above, available NPSH has been evaluated for the residual heat removal pumps and the containment spray pumps when stiped to the containment sump. The gvallable NPSH has also been evaluated for the safety injection and high pressure centrifugal charging purnps when aliped to the residual beat removal pump discharge. No other ECCS pumps take suction tom the containment sump or are supplied by pumps which take suction tom the caamhent sump during the sump recirculation mode of

1. Peration.

Since there are sipificant differences between ECCS pump Ametional requirements and containment sump levels for the LBLOCA and SBLOCA recirculation mode of operation, the available NPSH has been evaluated for both accident conditions for the pumps directly aliped to the containment sump. Additionally, since the size and location of a SBLOCA will determine if the containment spray system will be activated, an evaluation ofAe available SBLOCA recirculation mode NPSH has been performed with and without actuation of the containment spray system for the pumps which take suction directly Dom the caamhan' stinp.

The safety injection pumps and high pressure centrifugal charging pumps have similar flow requirements for both the large break and small break loss-of wolant accidents. A single evaluation has been performed for both accidents when the pumps are operating stiped to the residual heat rt moval pump discharge piping.

l Since there are slight differences in the safety irdection and centrifugal charging pump flow disdstions between reactor coolant system cold leg irdection and hot leg injection, the available NPSH for the safety

' Iq)ection and centrifugal charging pumps has been evaluated for injection Eto both the reactor coolant system hot legs and coldlegs.

The available NPSH values for the midual best removal and containment spray pumps were established using the methodology described in the mponse to Item 1. The available NPSH values for the safety injection and centrifugal charging pumps were calculated in a similar manner whh output tom a hydraulic modelof the ECCS which conservatively establishes the pump suction pressure based upon operation of a single residual beat removal pump.

The required NPSH for each purnp was established Dom the equipment manufacturer's performance test curve for the required flow rate. The diference between the residual heat removal pump required NPSH for l

l LBLOCA and SBLOCA conditions is based upon the different pump performance requirennents. For a LBLOCA, the reactor coolant system pressurv decreases below the pump shutoffhead and a conserva large residual heat removal pump flow is assumed. For a SBLOCA, the reactor coolant system pressure remains above the pump shutoffbead and no hot leg or cold leg injection flow is provided by the realdual l best removalpumps.

The available NPSH values listed above assume that the sump serven is toe Dom post accident debris blockage. A separate evaluation of head losses associated with sump screen blockage has been performed.

j De evaluation uses an empirical relationship which establishes sump screen head loss as a Ametion of fluid velocity, sump semen mesh size and an empirical discharge coefficient established for rectangular mesh screens. This relationship was benchmarked for the sump configuration by comparison of predacted head losses to actual head losses measured during scale model testing for clean sump screens (no blockage) and 50% screen blockage. The evaluation established that with both trains ofresidual beat removal and containment spray pumps in operation at conservatively high flow rates, the increase in sump screen head loss from 0% screen blockage to 90% screen blockage would be . ft for a LBLOCA and ft for a SBLOCA. Given the excess NPSH values listed above and the results of a containment debri transport study which confirms that less than 90% screen blockage will occur under accident conditions, adequate NPSH is available to address worst case sump screen blockage.

NRC Reauest

3. Specify whether the current design-basis NPSH analysis differs 90m the most recent analysis reviewed and approved by the NRC for which a safety evaluation was med.

E8EtElf De original NRC approval of the available NPSH calculations for ECCS operation is documented in the initial plant safety evaluation report (Section 6.3.3 of NUREG. ., including Supplements I and 2).

Since the issuance of the initial plant safety evaluation report, the design basis NPSH calculations have been upgraded as part of the !?861987 Design Calculation Program performed in accordance with the Nuclear Performance Plan. Under the calculation upgrade program, the original calculations were given a general revision to include a clear purpose, verifiable input assumptions, uniform methodologies and clear acceptance criteria. The revised calculations were classified as " essential" and were subjected to an independent review to establish technical adequacy. While the Design Calculation Program was evaluated by NRC and found to be acceptable in the . Nuclear Perfonnance Plan safety evaluation report (Section 2.3 of NUREG< , Volume 2), the revised NPSH calculations produced under the program were not specifically addressed by NRC.

The technical changes made to the available NPSH calculations during the calculation upgrade program involved the addition ofconservatism to the assumed ECCS flow rates, the addition ofconservatism to the assumed containment sump bulk fluid temperature, the refinement of the containment sump level calculations to reflect revised containment spray flow paths twtweer. upper and lower containment and the evaluation of containment sump screen b!)ckage.

p...,.,

The changes made o add conservatism o abe assumed ECCS flow rates and containment sump bulk

" asmperature are consistent with the NRC evaluation in Section 6J.3 of NUREG- , Supplement 1. De bulk containment sump temperature was increased tom Y so .T to reflect the ==Imum expected esaperature. De containment sprey flow rate assumed in tbs analysis was increased to contain e level of conservatism similar to that cited for the residual beat removal pumps (i.e., a conservative flow rase above expected pump runout cand*iana).

De changes made to the sump level calculations for containment spray drainage were made to be consistent with the resolution of the "ECCS Water Loss Outside Crane Wall / Air Return Fan Operability" issue describedin Section 3.9 of NUREG- , Volume 2. De containment sump level calculations were revised so reflect plant modifications performed in 1988 1989 designed to drain containment sprey hventory diverted Dom the active sump back to the active sump.

De evaluation ofsump screen blockage was performed in accordance with the resokaion of the

" Containment Coatings"lasue described in Section 3.7 of NUREG. , Volume 2. De evaluations described in the response to Item 2. De evaluation confirms that edequate ECCS pump NPSH is available ,

for the maximum expected containment sump acreen blockage under accident conditions.

I Since the completion of the calculation upgrade prograra, the available NPSH calculations have been revised to reflect a 1991 modification to the containment spray system. De assumed containment spray flow rate was conservativelyincreased bom spm to spm as part of a desip change which evaluated system operation with a higher head containment sprey pump rotating element.

In summary, the current design basis NPSH analysis differs 6om the analysis reviewed and approved by the NRC as part of the original plant safety evaluation. De majority of the changes made to the analysis were performed as part of the Nuclear Performance Plan to address issues evaluated by the NRC safety evaluation contained in NUREG- , Volume 2. De balance of the changes were performed to support a plant modification which was evaluated under 10 CFR 50.59 criteria. The current design-basis analysis continues to meet the requirements ofNRC Regulatory Guide 1.1 for consideration ofsump bulk temperature and containment pressure.

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NRC Renuest

4. Specify whether containment overpressure (i.e., containment pressure above the vapor pressure of the sump or suppression pool fluid) was credited in the calculation of available NPSH. Specify the amount I of overpressure needed and the minimum overpressure available. I h

.I De ECCS and containment best removal systems at . are designed such that adequate NPSH is  ;

provided assuming the maximum expected sump fluid temperature ( Y)and noincrease in the assumed containment pressure (atmospheric or 14.7 psla) sute quent to a postulated loss-of-coolant accident. No credit is taken for containment overpressure in the calcuw% of available NPSH.

NRC Reaues:

5. When containment overpressure is credited in the calculation of available NPSH, confirm that an appropriate containment pressure analysis was done to establish the minimum containment pressure.

Eii:Rilag Since containment overpressure is not credited in the calculation of available NPSH, this question is not applicable to

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