ML20198N812

Forwards 90-day Partial Response to GL 97-04, Assurance of Sufficient NPSH for ECC & Containment Heat Removal Pumps. Util Will Provide Further Clarifying Info by 980407,as Agreed to by NRR in 971212 Telcon

ML20198N812
Person / Time
Site:	Comanche Peak
Issue date:	01/14/1998
From:	Terry C, Walker R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-97-04, GL-97-4, TXX-98004, NUDOCS 9801210223
Download: ML20198N812 (12)

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Log # TXX 98004

==== M" File # 10035 L - Ref. # 10CFR50.54(f)

--- .--- GL 97 04 nlELECTRIC' January 14. 1998 C. lance Terry Gmup We Penidru U. S. Nuclear Regulatory Commiscion Attn: Document Control Desk Washington, DC 20555

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)

DOCKET NOS. 50 445 AND 50 446 RESPONSE TO GENERIC LETTER 97 04, " ASSURANCE OF SUFFICIENT NET POSITIVE SUCTION HEAD FOR EMERGENCY CORE COOLING AND CONTAINMENT HEAT REMOVAL PUMPS" REF: 1) Generic Letter 97 04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" dated October 7, 1997.

2) TU Electric Letter, logged TXX 97238. "Respose tc Generic Letter 97 04 . . . " from C. L. Terry to l' . Nuclear Regulatory Commission dated November 6 1997.

Gentlemen:

On October 7,1997, the NRC issued Generic Letter 97 04 " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps." Included in this letter was a request for both a 30 day and a 90 day response from al' addressees. TU Electric responded to the 30 day request in Reference 2. TU Electric committed to provide the information requested in the 90 day response by April 7, 1998.

Per conversation with members of NPR on December 12, 1997 TU Electric orally agreed to provide as much of the 90 day requested information as practical, during the week of January 12. 1998. TV Electric is providing the requested information as identified at this time in Attachment 2. TV Electric will provide _ further clarifying information by April 7,1998, as agreed-to by NRR in the phone conversation of December 12, 1997.

Pursuant to Section 182a of the Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f). TV Electric is submitting a response under affirmation (Attachment 1) to the requested information and requested actions as stated 1n Reference 1, i AUp i \

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TXX 98004 Page 2 of 2

• This communication contains the following commitment which will be completed as noted:

ACL Numt.et Commitment 97 116 TU Electric is providing the requested information as identified at this time in Attachment 2. TU Electric will provide further clarifying information by April 7, 1998, as agreed to by NRR in the phone conversation of December 12, 1997.

The ACL (Action Correspondence Log) number is used by TU Electric for the internal tracking of CPSE' commitments which are one time action requirements.

If you have any questions, please contact Randy Blankenship at (254) 897 5890.

Sincerely.

8. Y, Q C. l.. Terry By: On I

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RogeVD. Walker Regulatory Affairs Manager RTB/rb Attachments c- E. W. Herschoff, Region IV J. I. Tapia. Region IV T. J. Polich. NRR Resident Inspectors, CPSES l

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Attachment 1 to TXX 98004 Page 1 of 1  ;

l'NITED STATES OF AMERICA NilCLEAR REGULATORY COMMISSION In the Matter of )

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Texas Utilities Electric Company. ) Docket Nos. 50 445

) 50 446 l (Comanche Peak Steam Electric Station, )

Units 1 & 2) )  ;

AFFIDAVII ,

Roger D. Nalker being duly sworn, hereby deposes and says that he is Regulatory Affairs Manager of TU Electric, the 'icensee herein: that he is  !

duly 6uthorized to sign and file with the Nuclear Regulatory Commission this Response to Generic Letter 97 04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps": that he is familiar with the content thereof: and that the matters set forth therein are true and correct to the best of his knowledge, information and belief.

1. m e49A Roger V, Walker Regulatory Affairs Manager STATE OF TEXAS )

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COL,NTY OF h49Q O

Subscrihtd and sworn to before me, on this /N day of bmtMir ,

1998. (/ 0 CAROLYN L C0fENTIN0

.. } Notny Pubhc,5bte ct iern

> NotaryPplic i .( My Comm. Expres 04i04/98 *

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i Attachment 2 to TXX 98004 Page 1 of 9-GL 97 04 requested information regarding Net Positive Suction Head (NPSH) for the emergency core cooling and containment heat removal pumps that meet either of the following criteria:

(1) pumps that take suction from the containment sump or suppression pool following a design-basis LOCA or secondary line break, or (2) pumps used in " piggyback" operation that are necessary for rectrculation cooling of the reactor core and containment (that is, pumps that are supplied by pumps which take suction directly from the sump or suppression pool).

TU Electric submits that for Comanche Peak Steam Electric Station (CPSES) the following pumps are inclusive of these classifications for both units.

Emergency Core Coolina Pumos Suction Source Residual Heat Removal (RHR) Pump 01 Sump Residual Heat Removal (RHR) Pump 02 Sump Safety Injection Pump (SIP) 01 RHR 01 or RHR-02 Safety Injection Pump (SIP) 02 RHR 01 or RHR 02 Centrifugal Charging Pump (CCP) 01 RHR 01 or RHR 02 Centrifugal Charging Pump (CCP) 02 RHR 01 or RHR 5.

Containment Heat Removal Pumos Suction Source Containment ", pray Pump 01 Sump Containment Spray Pump 02 Sump Containment Spray Pump 03 Sump Containment Spray Pump 04 Sump With respect to the above 10 pumps for each unit CPSES presents the following responses as to the information requested per the generic letter.

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Attachment 2 to TXX 98004 Page 2 of 9 - ,

Jtem 1 - Specify the general methodology used to calculate the head loss associated with tne ECCS suction strainers.

Response

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

The basic equation for calculating NPSH is:

NPSH = h, h,,, + h, h ,,

where: ,

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

h,,, - head corresponding to the vapor pressure of the liquid at the temperature being pumped, s h ,, = static height that the liquid supply level is above or below the pump centerline or impeller eye.

h,, = 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 ims term is the containment pressure that is taken credit for in the analysis. CPSES assumes the pressure on the surface of the liquid is equal to the v~ essure of the liquid at the puaped fluid temperature. See t.... response to Question 4 for a discussion en the crediting of containment pressure in the NPSH analysis for CPSES.

h, head correrpondir'; to the vapor pressure of the liquid at the temperature being pumped.

This tern requires the determination of the t a perature of the fluid bein0 pumped. The temperature used in the limiting NPSH calculation is based on a conservative assessment using a sump fluid temperature equivaient to the saturated conditions in containment, at the containment pressure in the NDSH analysis.

CPSES assey s h,,, = h .

h, - static height that the liquid supply level is above or below the pump datum (e.g. centerline or impeller eye)

This term is simply the minimum static height of fluid above the pump reference point (typically pump centerline or impeller

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Attachment 2 to TXX 98004 Page 3 of 9-eye). The containment minimum flood analysis is used as a basis for the height of water on the containment floor (Elevation 808' 0") and in the sump (bottom elevation 802' 0') during the pump operating sequence.

hu - al' suction line losses including entrance losses and friction loss, .

This term involves suction line losses associated with the pump beina evaluated. The following parameters are considered in the NPSH calculation:

1. Suction line friction and entrance losses. The important parameters to consider here are the following:

+ Pipe roughness

+ Pipe aging effects

+ Length of piping e Fluid velocity (See Item 4 below)

+ Number and types of valves and fittings in the suction ciping

2. Head loss associated with the open area of a strainer / sump screen that is free of debris as confirmed by full scale model testing. The effect of sump screen blockage is considered in the architect / engineer analyses. The analyses by the Nuclear Steam Supply System vendor are performed at the floor level (below the screens) and do not include this head loss.

3. Suction line velocity head losses.

4. The maximum system flow rates through the strainers / sump and arrociated piping are determined for use in calcuiating friction losses. Higher flow rates create greater line losses. No design mode of operation reducet flow in the spray pump suction lines such that the flow rate is insufficient to maintain check valves in the full open position. There are no check valves in the RHR nump suction.

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Attachment 2 to TXX 98004 Page 4 of 9-Item 2 - Identify the r&qatred NPSH and the available NPSH.

Resoon g:

The following tabulation of NPSH analyses by the NSSS vendor provides the available NPSH (NPSH,), during recirculation, corresponding to flood level at containment elevation 808' 0" which is the flocr elevation ?t the top of the 6 foot deep containment emergency sumps. The actual NPSH, is greater and can be determined by adding the containment flood level above 808' 0" and correcting for head loss across the sump screens. The NPSH, is greater than the NPSH required (NPSH ).

Pumo GPE ESS ESL Harain Residual Heat Removal Pumps 4900* 20' 25' >5' Safety Injection Pumps 403* 9' 96.8' >87.8' Centrifugal Charging Pumps 409* 15' 62.5' >47.5'

• Corresponds to one RHR pump supplying two trains of SI and charging operating in parallel. The calculation [Ref. 7] is for the limiting case for RHR pump NPSH.

The following tabulation of NPSH analyses by the architect / engineer provides the NPSH,, during recirculation, corresponding to flood level at containment floor elevation 808' 0". The assumed RHR pump flow rate was conservatively selected as 5300 gpm. The RHR system is designed to limit the maximum flow durirg recirculation to 4900 gpm. The calculated RHR pump NPSH, also includes a head loss for 50% screen blockage equivalent to 0.5 feet taken from the full scale sump test [Ref. 6]. The calculated containment spray pump NPSH, includes a resistance coefficient to simulate 50% screen blockage equivalent to 0.52 feet at 7000 gpm taken from the full scale sump test [Raf. 6].

Pumo GPE ES& ESL Harain Residual Heat Removal Pumps 5300 23' 23,9' O.9' Containment Soray Pumps 3740* 17.l' 18.7' 1.6'

• Per pump The actual NPSH, is greater and can be determined by adding the containment flood level above 808'-0". The water height above elevation 808' 0" at transfer to ECCS recirculation. Hcces = 1.8' From the NSSS analysis above, the RHR pump margin is also at least 3' greater at the maximum flow of 4900 gpm.

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Attachment 2 to TXX 98004 Page 5 of 9' This yields NPSH margins for RHR as follows:

RHR Pumps - 0.9' + 3' + 1.8' = >5.7' and the ratio of NPSH availabla to WPSH required is:

NPSH, / NPSH, = [(23.9 + 1.8) / (20)] = 1.3 Yhe water h019ht above elevation 808' 0" at transfer to containment spray recirculation. Hess = 3.5', This yields NPSH margin for containment spray as follows:

Containnent Spray Pumps 1.6' + 3.5' = 5.1' and the ratio of NPSH available to NPSH required is:

NPSH, / NPSH, = [(18.7 + 3.5) / (17.1)] = 1.3

Attachment 2 to TXX 98004 Page 6 of 9-Item 3 - Specify whether the current design-basis NFSH analysis differs from the most recent analysis reviewed and approved by the NRC for which a safety evaluation was issued.

Response

As docueented in the CPSES FSAR [Ref.3] Appendix 1A(N) and 1A(B) and Sections 6.2.2.3.4 and 6.3.2.2.10 the NPSH analy>es for the ECCS and Containment Spray Pumps conform to RG 1.1. This acceptance criteria is reflected in the SER [Ref.4] Sections 6.2.2 and 6.3.2.

FSAR Table 6.2.21 shows the Containment Spray pump NPSH, (13 f eet) at 3000 gpm. FSAR Figure 6.2.2 2 shows the relationship of NPSH required and available as a function of flow. The NPSH, values were increased when new impellers were installed as a design modification fallowing issuance of the operating license.

FSAR Sectior 6.3 2.2.10 notes that the most limiting ECCS NPSH conditions are during injection with charging (and SI) poaps aligned to the Refueling Water Storage Tank (RWST) [see FSAR Table 6.3 1].

NPSH values during recirculation for ECCS are not provided in the FSAR.

The full scale contLinment sump testing (Ref. 6] discussed in SER and SSER section 6.3.4.2 was performed with design pump flows of 5300 for RHR and 3600 for containment spray.

As documented in Ref. 5 and SSER 9. Appendix L. Section 2.1.1. the NPSH margins were given as 4.23 feet for RHR Pumps anc 81 feet for the Containment Spray Pumps. The current NPSH margt- ., 5.7 feet and 5.1 feet, res)ectively, are similar. The NPSH analyses in Ref.

5 were based on t1e following:

RHR Pump Flow 5300 gpm Containment Spray Pump Flow 3900 gpm per pump Hinimum Containment Flood Level 814.8 feet As documented in SSER 17. Appendix A, Open Item F 5: the minimum water level for containment spray pump NPSH analysis (16345 ME(B)-

169) reviewed by the NRC was different than the 814.8 feet in Ref.

5 and was 810 feet. The SSER concluded that this was conservative.

The current minimum containment flood level analysis is 811' 6" for containaent spray NPSH analyses, which remains conservative to the NPSH analyses accepted in SSER 9. The current minimum containment flood level analysis is 809' 9.4" for the RHR Pumps.

Although there are differences in details of the current analyses, the basic methodology design margins and conclusions are still consistent.

Attachment 2 to TXX 98004 Page 7 of 9-Item 4 - Specify whether containment overpressure (1.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 of overpressure needed and the minimum overpressure available.

Resoonse:

In accordance with References 3 and 4 and Reg. Guide 1.1, no containment overpressure is credited in the calculation of available NPSH for any of the ECCS or containment heat removal pumps at CPSES.

Attachment 2 to TXX 98004 Page 8 of 9-Item 5 - When containment overpressure is credited in the calculation of available NPSH, confirm that an apprcpriate containment pressure analysis was done to establish the minimum containment pressure.

Resoonse:

Not applicable, see item 4.

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e Attachment 2 to TXX 93004

' age 9 of 9 h*FERENCES

1. Generic Letter 97 04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" dated October 7, 1997.

2. TU Electric Letter, logged TXX 97238. " Response to Generic Letter 97 04, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" from C.

L. Terry to U.S. Nuclear Re9ulatory Commission dated November 6, 1997.

3. CPSES Final Safety Analysis Report Amendment 94.

Appendix 1A(N), RG 1.1 Appendix 1A(B), RG 1.1, RG 1.79, RG 1.82 Section 6.2.2.3.4 Section 6.3.2.2.10 Section 6.3.4.2

t. NUREG 0797, Safety Evaluation Report related to the Operation of Comanche Peak Steam Electric Station, Units 1 and 2, July 1981.[SER]

Sections 6.2.2, 6.3.3.3 and 6.3.4.2, Supplements [SSERs]:

SSER 1, October 1981, Section 6.3.4.2 SSER 9. March 1985, Appendix L SSER 17 November 1988, Appendix A SSER 21, April 1989, Appendix L

5. " Evaluation of Paint and Insulation Debris Effects on Containment Emergency Sump Performance, Gibbs & Hill, Inc., Revision 1, October 1984.

6. "Model Testing of the Recirculation Containment Sump,' Western Canada Hydraulic Laboratories LTD., November 1981.

7. Calc. FSSE/SS-TBX 1192 (10/17/88)

8. Calc. ME(B) 325R0,CCN-4 (12/3/97): 2 ME 0147R0,CCN-1 (11/10/97)

9. Calc. ME CA 0232 4006R2 (8/21/97)

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