ML20198B686

Forwards 90-day Response to GL 97-04, Assurance of Sufficient NPSH for ECC & Containment Heat Removal Pumps,

ML20198B686
Person / Time
Site:	Peach Bottom, Limerick
Issue date:	12/30/1997
From:	Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-97-04, GL-97-4, NUDOCS 9801070035
Download: ML20198B686 (14)

Text

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10 CFR 50.54 (f)(GL P' ')4)

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PECO NUCLEARL nco om e-v -

• $s ctm Bodeva,d i A unir of PECO Emcr Wayne PA 190875691  ;

December 30,1997 l q

Docket Nos. 50-277:  ;

50-278 50-352.

353 License Nos. DPR DPR - NPF NPF-85 U. S. Nuclear Regulatory Commission -

Attn: Document Control Desk I

Washington, DC 20555_

SUBJECT:

Peach Bottom Atomic Power Station, Units 2 and 3 Limerick Generating Station, Units 1 and 2 90 Day Response to Generic Letter 97JM

REFERENCE:

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) Letter from G. A. Hunger Jr. (PECO Energy Company) to

<- USNRC dated November 4,1997.

Dear NRC Officials:

On October 7,1997, the U. S. Nuclear Regulatory Commission issued the referenced (;eneric letter regarding a subject which may have generic implications for degrading performance of the Emergency Core Cooling System (ECCS) and Containment Heat Removal System pu;nps. The generic letter

- _ _ required,'within 90 days, Licensees provide the information outline ' below for

. each of their facilities. New Net Positive Suction Head (NPSH) analyses were neither requested nor required.

~ -1. Specify.the general methodology used to calculate the head loss associated

- with the ECCS suction strainers. f f

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LDecember 30,'1997 ,

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2. .ldentify the required NPSH and the available NPSH. i

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

. 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 of overpressure needed and the minimum overpressure available. _

l

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

In order to provide a clear and logical response to this request, PECO Energy has provided responses for Limerick Generating Statien and Peach Bottom Atomic Power Station in Attechments 1 and 2 respectively. As discussed in -

Reference 2) letter, the PECO Energy response is based upon the BWR Owners' Group (BWROG) NPSH Committee 90 day response template and the agreements rea :hed during interactions between the BWROG and the NRC staff  !

regarding the content of the template and the BWR responses. Although the 2 ' discussion of the specifics of the analyses and calculations provides an accurate description of the present state of each, PECO Energy may revise them in the . ,

future in accordance with the approved revision processes and the applicable regulatory requirements, without mod 3 cation of this response. Information (e.g.,-

calculations, analyses) referred to in this response % contained in docketed correspondence or is available for your review.

Very truly yours, fbff G. A Hunger, Jr.,

Director-Licensing 4 ,

Attachments, Affidavit l l

cc: - H. J. Miller, Administrator, Region I, USNRC j A. C_. McMurtray, USNRC Senior Resident inspector, PBAPS l

A. L. Burritt, USNRC Senior Resident inspector, LGS  ;

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I COMMONWEALTH OF PENNSYLVANIA:

ss.

COUNTY OF CHESTER  :

J. B. Cotton, being first duly sworn, deposes and says:

That he is Vice President of PECO Energy Company; that he has read the enclosed 90 day response to Generic Letter 97-04 for Peach Bottom Atomic Power Station Operating Licenses DPR-44 and DPR-56 and Limerick Generating Station Operating Licenses NPF-39 and NPF-85, and knows the contents thereof; and that the statements and matters set forth therein are true a and correct to the best of his knowledgo,information and belief.

An/$b f&

Vfce Prepident i

Subsciibed and swom to before me thisfoMday of k1997.

/ /

Notary Pitblic NOTARIAL SEAL carol A. WALToN.Notory Putits uv n xp re Y #

^

v. x ATTACHMENT 1

~ '

NRC Generic Letter 97-04 90 Day Response for Limerick Generating ' Station =

Introduction:

The general equation used to calculate the available Net Positive Suction Head

(NPSHA) fer the ECCS pumps at Limerick Gencrating Station (LGS) is as follows:

NPSH, = h, - h, + h,, - h, where:

h, = absolute pressure on the surface of the suppression pool-water supply. For LGS, this does not include containment

" i overpressure.

h, = head corresponding to the vapor pressure of the suppression pool water supply at the temperature being pumped. For LGS, at limiting conditions, this corresponds to the vapor pressure for water at a temperature that bounds the maximum post LOCA bulk average suppression pool water temperature, h , = static head corresponding to the elevation difference between the suppression pool water supply surface and the centerline of the pump suction. For LGS, this term considers the effect of long and short term suppression pool water level d.rawdown following a Design Bases Accident (DBA)

Loss of Coolant Accident (LOCA), starting from minimum

. Technical Specification (TS) we.ter level.

h, = friction and entrance losses from the suppression pool to the pump suction (See item 1 below).

[

I For LGF an analysis has been performed which identifies the point at which the -

most limiting NPSH margin occurs. This analysis considers the combined effects

. of suppression pool level, pump flow, suppression pool temperature and drywell pressure. The most limiting condiCon occurs where the minimum margin between NPSH4 and sequired Net Positive Suction Head (NPSHa) exists. This minimum NPSH margin occurs at the point when the suppression pool bulk -

- average temperature reaches its maximum for LGS.

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ATTACHMENT 1~  ;

e - NRC Generic Letter 97-04 190 Day Response for Limerick Generating Station  :

1) .- Specify the General methodology used to calculate the head loss

- associated with the ECCS suction strainers.

r

- Response The head loss of the ECCS suction strainers is one component of the hi

- term in the NPSH equation. This term represents all of the entrance and "-

friction losses between the suppression pool and the ECCS pump suction. l For LGS, the suction line losses considered and their bases are as

[

3:

follows:

Loss Component - Basis of Value Strainer Losses Entrance losses are small and included

. In the strainer loss term. The design specification for the suction strainer

! - requires no more than 2.0 psid across >

~

the strainer at 50% fouled for the pump _

design flowrate and temperature.

Vendor tests verified the actual pressure drop across the suction strainer at 50%

c fouled is less than this design maximum pressure drop.

The strainer losses assumed in the LGS 4 ECCS pump NPSH calculations are

greater than both the test results at 50%

fouled and the design basis losses at 50% fouled. This additional safety--

margin is included for operability considerations.

Piping Friction Losses Piping friction losses for LGS are calculam using the formula for piping losses contained in Crane Technical Paper 410. : This formula considers the -

actuallength and diameter of the ECCS pump suction piping as shown on the piping isometric drawings'as well as the

piping roughness. To account for the effects of pipe aging, the friction factor for cast iron is used instead of -r commercial steel pipe for the Residual 2

=,. _

.- r

ATTACHMENT 1 NRC Generic Letter 97-04 90 Day Response for Limerick Generating Station

_ Heat Removal (RHR) system calculation -

. and the straight pipe lengths were q increased by 40% for the Core Spray-4 (CS) system calculation.

, Pipe Fitting Losses Fitting losses for LGS are calculated using the formulas for various fittings-

[ found in Crane Technical Paper 410.

The number and type of fittings to be -

l considered were determined from the -

piping isometric drawings for the ECCC pump suction lines. -There av no flow dependent valves in the RHR or CS -

4 pump suction lines at LGS.

I a-Flow Rates The suction line losses were computed for a variety of flow conditions including

both short term pump runout flows and j long term system flow rates.

The suction line loeses have also been verified to be acceptable during i pump, valve and flow testing.

2) Identify the required NPSH and the available NPSH.

Response

NPSH margins have not been calculated for each ECCS pump at LGS,

, because there ia little difference in NPSHn or NPSH4 between different pumps in either the RHR or CS systems. The suction line losses were assessed for each RHR and CS pump to determine the bounding suction line in each system. Likewise, the pump curve r each RHR and CS

- pump were examined to determine which p> .iad the bounding NPSHa in each system. The bounding NPSH, and NPSHa were then combined to evaluate NPSH margin.

- An analysis was performed for the bounding configuration for each .

. system, and the ilmiting NPSH margin was found to occur concurrent with the suppression pool maximum bulk average temperature condition. This condition occurs several hours fol!owint, a DBA LOCA with pump flows at long iarm design values.

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' ATTACHMENT 1 NRC Generic Letter 97-04 90 Day Response for Limerick Generating Station The limit lng NPSH value for each system is given below:

Pumo Reauired NPSH (ft.) Available NPSH (ft.)

RHR 6.0 8.0 CS 10.0 12.0

3) . Specify whether the curreni c ign-basis NPSH analysis differs from the most recent analysis reviewed and approved by tne NRC for which a safety evaluation was issued.

Response

A summary of the NPSH analysis for the LGS RHR system was submitted as part of the Licensing submittal for the Power Rerate Project.

The NRC issued a Safety Evaluation Report for this submittal. In addition the NRC issued a Safety Evaluation Report for the original analysis contained in the LGS Updated Final Safety Analysis Report (UFSAR) Section 6.3.2.2.4. For the CS system, the NPSH analysis has never formally been reviewed by the NRC.

For the RHR system. the current design-basis NPSH analysis does differ from the most recent analysis reviewed and approved by the NRC for which a safety evaluation was issued. Additional conservatism is included in the current design-basis NPSH analysis that was not included in the LGS UFSAR or Power Rerate Project Submittal discussion. This additional conservatism includes accounting for pipe aging, conservative flowrate and addit onal pressure drop across the suction strainers.

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 of overpressure needed and the minimum overpressure available.

Response

LGS is committed to Regulatory Guide 1.1 (Safety Guide 1). Although substantial overpressure is expected following a DBA LOCA or secondary line break, LGS conservatively takes no credit for containment overpressure.

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ATTACHMENT 1 NRC Generic Letter 97-04 90 Day Response for Limerick Generating Station 6 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,

Response

Not applicable for LGS. Although substantial overpressure is expected following a DBA LOCA, LGS takes no credit for containment overpressure.

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j ATTACHMENT 2 ,

NRC Generic Letter 97-04, .

^ '

-90 Day Response for Peach Bottom Atomic Power Station

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l 1

Introduction:

LThe general equation used to calculate the available Net Positive Suction Head - i (NPSHx) for the ECCS pumps at Peach Bottom Atomic Power Station (PBAPS) H is as follows:-

f l NPSH4 = h, - h, + h, - h,  ;

I where:

h, = absolute pressure on the surface of the torus water supply.

For PBAPS, this includes containment overpressure. (See item 4 below) l

- h, = head corresponding to the vapor pressure of the torus water supply at the temperature being pumped. For PBAPS, at limiting conditions, this corresponds to the vapor pressure

. for water at the maximum post LOCA bulk average torus water temperature.

, I 4 h, = static head corresponding to the elevation difference between the torus water supply surface and the centerline of the pump suction. For PBAPS, this term considers the i l

effect of long and short term torus water level drawdown

. following a DBA LOCA, starting from minimum TS water l level. '

hr friction and entrance losses from the torus to the pump suction (See item 1 below).

For PBAPS, an analysis has been performed which identifies the point at which the most limiting NPSH margin occurs. This analysis considers the combined effects of tcrus level, pump flow, torus temperature and drywell pressure. The most limiting condition occurs _where the minimum margin between NPSH4 and l required Net Positive Suction Head (NPSHa) exists. This minimum NPSH margin occurs at the point when the torus temperature reaches its maximum for

'PBAPS.

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ATTACHMENT 2 NRC Generic Letter 97-04, 90 Day Response for Peach Bottom Atomic Power Station

1) Specify the General methodology used to calculate the head loss associated with the ECCS suction strainers.

Response

The head loss of the ECCS suction strairers is one component of the h, term !n the NPSH equation. This term represents all of the entrance and friction losses between the torus and the ECCS pump suction. For PBAPS, the suction line losses considered and their bases are as follows:

Loss Component Basis of Value Strainer Losses For Unit 2, the strainer losses were calculated using formulas from The Handb_o_pk of Hydraulic Resistance by Idelchek. 2 For Unit 3, the strainer losses were calculated by the strainer supplier (ABB) using a correlation based on prototypical testing conducted at the Electric Power Research Institute (EPRI) Non-Destructive Examination (NDE) center.

Both Units considered entrance losses in calculating strainer losses.

Strainer losses are calculated based on the debr:s load sufficient to causo 50% blockage of the Unit 2 strainers. This deoris load produces a negligible head loss on the Unit 3 strainers.

Unit 3 strainers have been replaced in response to NRC Bulletin 96-03. However, the f'nal Bulletin response htu not been cubmitted.

These values will be revisad consistent with the final Bulletin response, to reflect the head loss associated with the debris bed assumed in the Bulletin response.

Piping Friction Losses Piping friction losses for PBAPS are calculated using the formula for piping losses contained in Crane Technical Paper 410. This 2

ATTACHMENT 2 NRC Generic Letter 97-04, 90 Day Response for Peach Bottom Atomic Power. Station formula considers the actual length and -

diameter of the ECCS pump suction piping as shown on the piping isometric drawings as well as the piping roughness. To account for the effects of pipe aging, the friellon factor for cast iron is used instead of commercial steel pipe.

Pipe Fitting Losses Fitting losses for PBAPS are calculated using the formulas for various fittings found in Crane Technical paper 410. The number and type of fitting to be considered were determined from the piping isometric drawings for the ECCS pump suction lines. There are no flow dependent valves in the RHR or CS pump suction lines s "BAPS.

Flow Rates The suction line losses were computed for a variety of flow conditions including both short term pump runout flows and long term system flow rates.

The suction line losses have been verified to be acceptable during pump, valve and flow testing for Unit 2 and strainer post installation testing for Unit 3.

2) Identify the required NPSH and the avai!able NPSH.

Resnonse NPSH margins have not been calculated for each ECCS pump at PBAPS, because there is little difference in NPSHn or NPSH4 between different pumps in either the RHR or_ CS systems. The suction line losses were evaluated for each RHR and CS pump to determine the bounding suction line. Likewise, the pump curves for each RHR and CS pump were examined to determine which pumps had the bounding NPSHn. The bounding NPSH4and NPSHa were then combined to evaluate NPSH margin. The bounding configuration was found to be RHR Unit 2.

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ATTACHMENT 2 NRC Generic Letter 97-04, 90 Day Response for Peach Bottom Atomic Power Station -

An analysis was performed for the bounding configuration, and the limiting

' NPSH margin was found to occur concurrent with the torus maximum bulk average temperatum condition. The Limiting NPSH value is given below:

E9mn Reauired NPSH (ft.) Available NPSH (ft.)

Unit 2 RHR 26 30.03

3) Specify 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.

89f22019)

A summary of the NPSH analysis fcr PBAPS was submitted as part of the Licensing submittal for the Power Herate Pro, lect. A summary of key inputs to this analysis (containment pressures, temperatures) was also -

submitted in our rasponse to RAI 6 on the Rerate submittal by our letter 4

dated July 20,1994. A safety evaluation was issued for this submittal.

Our current design basis does differ f9. this previously submitted information. The analysis for power relats did not consider the effects of the use of containment sprays or leakage. Our current design basis

- considers the effects of both contahment sprays and leakage. Also, the rerate analysis u v d values for piping Icsses which bound the actual-piping configurations for both RHR and CS. Our current design basis uses piping iosses watch correspond to actual piping configuration for the most limiting ECCS suction line (RHR Unit 2). In accordance with ongoing discussions with the NRC staff, the current design basis analysis will be submitted as part of our closure of NRC Bulletin 96-03.

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 of overpressurs needed and the minimum overpressure available.

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_ ATTACHMENT 2_

NRC Generic Letter 97-04, n 90 Day Respoisse for Peach Bottom Atomic Power Station-

. l

Response

Containment overpressure has always been credited in the calculation of.

available NPSH for the ECCS pumps at PBAPS. The amount of ,

overpressure needed and the minimum overpressure available as a function of time after accident initiation is shown in the attached graph.

l These values are calculated based on the limiting RHR pump (Unit 2 RHR), since this represents the most limiting NPSH conditions. This 3 analysis assumes all ECCS pumps start at time zero and containment l - sprays are initiated concurrently. The analysis also assumes that the i containment sprays instantaneously reduce the containment airspace

- temperature to the spray temperature. Drywell leakage at the Tech Spec.

limit of 0.5% per day is also assumed.~ These values are for the current licensing basis debris load and do not account for head loss associated

- with revised accident debris loads calculated in response to NRC Bulletin 96-03. A new rec #ed overpressure analysis will be included in our final response to NFsC Bulletin 96-03.

t

~ 5. When contalrimet overpressure is credited in the calculation of availa'.sle.

- NPSH, confirm that an appropriate containment pressure analysis was done to establish the minimum containment pressure.

Response

Containment overpressure has always been credited in the calculation of available NPSH for the ECCS pumps at PBAPS. An appropriate

. containment pressure analysis was performed to establish the minimum containment pressure. This containment overpressure analysis assumes all ECCS pumps start at time zero and containment sprays are initiated -

concurrently. The analysis also assumes that the containment sprays instantaneously reduce the containment airspace temperature to the spray temperature. Drywell leakage at the Tech Spec, limit of 0.5% per -

, day is also assumed. This analysis assumes the current licensing basis debris load and does not account for head loss associated with revised

' accident debris lcr.ds calculated in response to NRC Bulletin 96-03.- A

. new required overpressure analysis will be included in our final response to NRC Bulletin 96-03.

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. * *O ATTACHMENT 2 NRC Generic Letter 97-04, 4 '

90 Day Response for Peach Bottom Atomic Power Station

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