ML20248J657

Forwards Response to GL 97-04, Assurance of Sufficient Net Positive Suction Head for ECC & Containment Heat Removal

ML20248J657
Person / Time
Site:	Wolf Creek
Issue date:	12/18/1997
From:	Muench R WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ET-97-0143, ET-97-143, GL-97-04, GL-97-4, NUDOCS 9801020093
Download: ML20248J657 (6)

Text

- _ - - - _- - - - - _-____ _ _____

<e i

t LF CREEK W@)NUCLEAROPERATING CORP RK.hard A. Muench Vce President Engineering December 18, 1997 ET 97-0143 U. S. Nuclear Regalatory Commirsion ATTN: Document Control Desk Mail Station Pl-137 Washington, D. C. 20555

Reference:

NRC Generic Letter 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Contajnment Heat Removal," dated October 7, 1997

Subject:

Docket No. 50-(82: Final Response to NRC Generic Letter 97-04 Gentiemen:

Attached is Wolf Creek Nuclear Operating Co rper ation's thCNOC) response tc Generic Letter 97-04, " Assurance of Sufficient Net I'ositive Suction Head for Emergency Core Cooling And Containment Heat Removal." The reference requested addressees to submit information necessary to confirm the adequacy of the net positive suction head (NPSH) available for emergency core cooling and containment heat removal pumps. WCNOC has evaluated the reference as it applies to Wolf Creek Generating Station (WCGS), and has reviewed plant information to address the requests made in the Generic Leiter. Based on the reviews completed to develop this response WCNOC has reasonable assurance that thtre is sufficient NPSH for emergency core cooling and containment heat removal pumps.

If you have any questions concerning t his response, please contact me at (316) 364-8831, extension 4034, or Mr. Michael J. Angus, at extension 4077.

Very truly yours, s j 9001020C7 971218

/

DR ADO A 0500 2 Richard A. Muonch /

Attachment RAM /jad g g)/

n /

cc: W., D. Johnson (NRC) , w/a E. W. Merschoff (NRC), w/a J. F. Ring..ald (NRC). w/a K.'M. Thomas (NRC), ;/a a# I.! I.l! l.ll. .I! I.ll. .I PO. Box 411 i Burhngton, KS 66839 i Phone' (316) 364-8831 An Equal Opportuvity EmrAoyer M l' HC: VET

STATE OF KANSAS )

) SS COUNTY OF COFFEY )

Richard A. Muench,-of lawful age, being first duly sworn upon oath says that he is Vice President Engineering of Wolf Creek-Nuclear Operating Co@ oration; that he has read the foregoing document and knows the content thereof; that he has executed that sans for and on behalf of said Corporation with full power and authority to do so; and that the facts _therein rtated are true and correct to the best of his knowledge, information and belief.

By -

k/46" Richard . Muench Vice P ident Engineering SUBSCRIBED and sworn to befores me this fk day of hdrdf", 1997.

Lt$u 0- O.)-t JULIE A. DALE Notny Pubsc. St of r :

Expirat.on Date b

Attechm:nt to ET 97-0143 5

14g2 1 of 4 Final Response to Generic Letter 97-04

" Assurance of Sufficienc Net Positive Suction Head for Emergency Core Coolir2g

. and Containment Heat hemoval" Scope b

The scope of the subject Generic Letter es it applies to Wolf Creek Generating Station (WCGS) includes the Residual Heat Removal Pumps (KrtRPs ) , Safety Injection Pumps (SIPS), Centrifugal Charging Pumps (CCPs), and the Containment Spray Pumps (CSPs).

The RHRPs, SIPS, CCPs, and CSPs take s_ction from the Refueling Water Storage Tank (RWST) during the injectie- phase. Following receipt of a lo-lo-1 RWST signal, the RHRPs are 41ned up to take suction from the containment recirculation sumps and provide coolant to the suction of the SIPS , CCPs, and inject into the cold legs of the Reactor Coolant System (cold leg recirculation). When the suction of the SIPS and CCPs are switched over from RWST to the discharge of the RHRPs, the RHRPs provide the necessary suction head to each of the CCPs and SIPS. Upon receipt of a lo-lo-2 RWST _ level signal, suction of the CSPs are switched over f rom the BWST to the contal.tment recirculat. ion sumps.

Ro;1uested Information Following are the five areas of information requested by Generic Letter 97-04,

" Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling And Containment Heat Removal." Based on the reviews completed to develop this response, Wolf Creek Nu: lear Operating Corporation has reasonable assurance that there is sufficient NPSH for the emergency core cooling and containment  ;

heat removal pumps.

1. General Methodology used to calculate the head loss associated with the ECCS suction strainers.

The general methodology used at WCGS to calculate the head loss associated with the ECCS suction strainer / containment recirculation sump is as follows:

The basic equation for calculating NPSH is:

N PS d =h. - hy.p + h t- hr Where:

h. = absolute pressure cn the surface of the liquid supply level, hy.p = head corresponding to the vapor pressure of the liquid at the temoerature being pumped.

ha = static height that the liquid supply level is above or below the pump centerline or impeller eye.

hr = suction line losses including entrance losses and friction losses.

Additional detail on each of the terms is provided below, h, - absolute pressure on the surface of the liquid supply level

'his term is the containment preuure that is taken credit for in the analysis. See the response to Question 4 for a

Attcchment to ET 97-0143 i

p ga 2 of 4 discussion on the crediting of containment pressure in the NPSH analysis for WCGS.

h,,, - head corresponding to the vapor pressure of the liquid at the temperature being pumped This term requires that the temperature of the flujd being pumped to be determined. The temperature used in the limiting NPSH calculation is based on the post-LOCA maximum fruid temperature predicted. See the response to Question 4 for a discussion on utilized maximum vapor pressure, h.s - static height that the liquid supply level is above or below the pump centerline or impeller eye This term is the minimum static height of fluid above the pump centerline or the impeller eye. The accident analysis is used as a basis for the height of water on the containment floor and in the sump during the pump ,

operating sequence.

hr - all auction Aine losses including lossas associated with sump screens and suction pipe entrance This term involves suction line losses associated with the pump being evaluated. The following parameters are considered when calculating he:

A. Suction line frictional losses are determined based on expected system flow rates. The important factors in cale':lating line frictional losses are:

. Length of piping

. Number and type of fittings a 1d valves in the suction piping

. Fluid velocity

. Pipe roughness B. Entrance loss to the suction piping C. Head loss associat9d with the containment recirculation sump screens At WCGS, he was originally calculated based on adding the suction line frictional losses and suction piping entrance losses. A very conservative Entrance Loss Coefficient (K) of 0.46 was usad to calculate the piping entrance loss.

This utilized entrance loss coefficient was twice the actual coefficient needed for determining the piping entrance losses. The performance of the containment recirculation sumps was verified with a 1:2.98 scale hydraulic model. The hydraulic model test determined that in one Containment Spray or Residual Heat Removal suction line with 50 percent sump screen blockage, the entrance loss coefficient was about 0.35 which included the sump screen losses. Therefore, it was concluded that the overall suction line losses were conservatively calculated and sump screen losses with 50 percent blockage were accounted for vis adoption of a very high entrance loss coefficient for the suction piping.

Attcchment to ET 97-0143 s

P"cge 3 of 4

2. Required HPSH and the Available HPSH The table below provider the required and available NPSH for each of the four pumps within the scope of the generic letter. These are the limiting values that have been reported in the Updated Safety Analysis Report (USAR). See response to question 3.

s e Required ;NPSHn h f t)l /Nailabis!NPSH (ft)"

"EiiRUal-Heat Removal. Pump' 21.0' 0 4,800 gpm i1. N @ 4,800 gpm

_. 4.c ..m.., m ._. . _ . . . . . . . .

(during reeir_cu1ation)

'5AGEy}EjidEE"is~rsii""""~~ ~55"If'~"F"556 gpm 44* 0 660 gpm

~

( du ring _inj ect i on ) '

Cent.rilugal "EISUdIEUIP ump ["1~f 8.0' O 556~5j~5 44' 0 550 gpm 4..a.... .. . . _ . . . . _ .

(during _ injection _)

• Containmist spray Pump 16.b' J 57556~gpm "YI.Ti"~5""57550 gpm (during recirculation)

The most limiting NPSH available margin for the SIPS and CCPs is at the point of swap-over to the recirculation mode when the elevation head in the 1

RWST is a minimum. During the recirculation mode, the available suction pressure for these pumps is increased significantly based on the supplied pressure from the RHR pumps.

Reported values are based on existing ar.alyris. During review of the calculations for adequacy, weaknesses were identified. However, the net impact on the values being reported is insignificant as i t. relates to available NPSH versus required NPSH.

As noted above, the limiting available NPSH for the RHRPs and CSPs occurs during recirculation phase of the ECCS operatloa and for the SIPS and CCPs occur during injection phase of the ECCS operation. Wolf Creek calculations were performed to ensure that the pressure drops and available static head for each pump was within the NSSS Vendor guidelines. 'I hi s would assure that each pump will have adequate available NPSH for safe operation. The results showed that for each case, combination of the pressure drops and static elevations met the provided guidelines.

When the SIPS and CCPs piggy back on the RHR pump during recirculation, the available NPSH for the remaining cases can be conservatively estimated as follows:

1 Required NPSHg' (f t).

~

Available HPSHO (ft)'

^

I

~556E{Iniection: Pump" 16.0' O 660 gpm 137 O 660' diam

. ,. a..e hl '

. _ .w d _ . . . . . . . . . . .

"~

Centr [fuga Gdharg M U 6Ep- 17.0' 5~~555~gpm 125'~~ 8 SSF drE~~

This estimate is based on 14.7 psia atmospheric pressure, RWST water vapor pressure at 100*P, maximum allowable head loss for Westinghouse supplied componants, and a minimum RHR pt.mp developed head (for conservatism).

l 1

l

Attcchment to ET 97-0143

,- Paga 4 of 4-

3. Differences between current design-basis NPSH analysis and most recent analysis reviewed and approved bi the NRC f or which a safety evaluation was  :.

. i's sued .

There have been no modifications to the ECCS and the Containment Spray Systems at WCGS that would impact the results of the previous NPSH calculations. Therefore, the current design basis NPSH analyses are the same as those most recent analyses that were reviewed and approved by the NRC with the following clarifications

• The current USAR indicates that the required NPSH for the Safety '

Injection Pump at a nominal flow rate of 660 gpm is 25 ft. This requirement is based on the original pump design specification sheet as included in tne pump vendor manual. However, the provided pumps exceed this requirement and the pump performance test curves indicate that only 16 ft of NPSH is required at the given rominal flow.

• The current USAR indicates that the required NPSH for the Centrifugal Charging Pump at a nominal flow rate of 550 gpm is 28 ft. This requirement is based on the original pump design specifications sheet as included in the pump vendor manual. However, the provided pumps exceed this requirement and the pump performance test curves indicate that only 17 ft of NPSH is required at the given nominal flow.

The above stated required NPSH for the Safety Injectica and Centrifugal Charging Pumps are within the boundaries of the required NPSH as described in the current USAR.

4. Use of containment overpressure in the calculation of availrble NPSH.

WCNOC has not taken any credit for containment overpressure in its available NP6H calculations. A saturated sump model was used where it was conservatively assumed that the containment a'rhient pressure was equal to the sump water vapor pressure.

S. Confirmation that appropriate containment pressure analysis was done to establish the minimum containment pressure.

This item is not applicable to WCGS since credit was not taken for any containment overpressure.

_ _ _ _ _ - _ - - _ - . _ _ - _ . . _ . _ - _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ - _ _ - _ _ _ _ _ _ - _ - _ _ - _ _ _ _ _ _ - _ - _ - _ _ _ _ _ _ - _ _ - - - _ _ - . _ _ - - - - _