ML20198J637

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

ML20198J637
Person / Time
Site:	Davis Besse
Issue date:	12/29/1997
From:	Jeffery Wood CENTERIOR ENERGY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2507, GL-97-04, GL-97-4, NUDOCS 9801140177
Download: ML20198J637 (6)

Text

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419-24% 2300 Mo3 Prtyktent. Nuclear - far 419321R337 Docket Number 50-346 Licens'e Number NPF-3

- Sebial Number 2507 December 29, 1997 United States Nuclear Regulatory Commission

- Document Control Desk -

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- Washington, D. C. 205554001

Subject:

Response to NRC Generic Letter 97-04: Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps-Ladies and Gentlemen:

On October 7,1997, the Nuclear Regulatory Commission (NRC) issued GL 07-04, requesting that licensees for nuclear power plants review their current design-basis analyses used to determine the avaGgble net positive suction head (NPSH) for the emergency core cooling (including core spray and decaf heat removal) and containment heat removal pumps that meet either of the following criteria:

(1) pumos that take suction from the contairment sump or suppression pool follow-ing a design-basis loss of coolant accident (LOCA) or secondary line break, or (2) pumps used in " piggyback" operation that are necessary for recirculation 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).

Based on this review, licensees vere requested to provide the information outlined below:

1. Specify the general methodology used to calculate the head loss associated with the Emergency Core Cooling System (ECCS) suction strainers. I 9901140177 97g 5 7 % @s'~}(6 ( \

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2. ; Identify the required NPSH and the available NPSH.-

i 3. Specify whether the current design-basis'NPSH analysis differs from the most 0 recent analysis reviewed and approved by the NRC for which a safety evaluation:

was issued. E  ;

4DSpecify whether containment overpressure (i.e., containment pressure above the .

vapor pressure of the sump or suppression pool fluid) was credited in the i calculation of availabls NPSH. Specify the amount of overpressure needed and the minimum ' overpressure available. -  :

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.

t Toledo Edison (TE) has reviewed the current design-basis analyses used to -

determine the available net poaitive suction head for the emergency core cooling.

and containment heat' removal pumps at the Davis Besse Nuclear Power Station ,

(DBNPS). The information requested by Generic Letter 97-04 follows:

NRC Reauest.h 1

Specify the general methodology used to calculate the head loss associated with the ECCS suction strainers. ,

TE Resoonse 1:

The methodology used to calculate the head loss associated with the ECCS suction strainers was previously provided to the NRC by letter dated May 7,1976 in its -

Enclosure S. The following summarizes the methodology previded:

The ECCS Sump suction strainer consists of a wire mesh-covered steel grating box l' fitted over a concrete sump. The head Icss across the ECCS sump suction strainers -

L was calculated to be approximately 0.05 ft. These calculations were based on the - ,

following assumptions:

'. The horizontal screen crea covering the top of the sump was not credited.

- . Fifty percent of the vertical wire mash area was assumed to be blocked. t

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i . Tha wire mesh covering the entrance to the containment sump was assumed to be-I

constructed of rounded wire.

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• The transition from the wire mesh to the grating was modeled as a c 2dden enlargement.

The dimensions below were used for the calculations.

Wire Mesh Gratine Inner Edce Height 2' 0" 1' 10 %"

Width-Large Eud 6'4 1/16" 6'2 9/16" Width Small End 4'75/8" 4'61/8" Length 14'3" 14" The results of the calculations were verified by a scaled ECCS Emergency Sump test and an actual pump suction line test. These tests showed that the predicted

. values were conservative since, in all cases, the actual hetd losses were less than the calculated head losses.

NRC Reauest 2:

Identify the required NPSH and the available NPSH.

TE Response 2:

The required and available NPSH from the ECCS Emergency Sump is provided in the following table. Since containment overpressure is not credited and maximium injection rates are used, the table represents the most liming cases.

NPSH NPSH NPSH NPSH required available required available Train #1 Train #1 Train #2 Train #2 g Decay Heat / Low Pressure 11 ft. 13.4 ft. 9.5 ft. 12.2 ft.

Injection Pumps Containment 11 ft 15.8 ft. 11ft 14.9 ft Spray Pumps High Preseure 28 ft. >> 28 ft.* 28 ft. >> 28 ft.*

Injection Pumps

• : The High Pressure Injection (HPI) Pump takes suction from the discharge of the Decay Heat / Low Pressure Injection (DH/LPI) Pump when operating in the recirculation mode. Abundant NPSH is provided both due to the cooling provided by the DHR coolers and the pressure boost from the DHR pump.

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J The basis used for the NPSH cal 6ulations during the post-LOCA phase are  :

Ldescribed in DBNPS Updated Safety Analysis' Report Section 0.3.2.14, " Net Positive l Suction _ Head Requirements".

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. . The regtdred and available NPSH values in the table are based on a total flow in a single train of 5500 gpm ( LPI @ 4000 gpm, Containment Spray @ 1500 gpm).-

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. Available NPSH is based on pip e and fitting losses calculated ming Crane - 1 Technical Paper Number 410.

.-- Pressure above the water surface of the sump is equal to the vapor pressure of l the fluid at the pump inlet. Containment overpressure is not credited. .

.: NPSH calculations are in accordance with Safety Guido 1, " Net Positive Suction

' Head for Emergency Core Cooling and Containment Heat Removal System Pumps."

NRC Information Notice No. 87-63 (TE letter Log 1-1716), " Inadequate Net Positive Suction Head in Low Pressure Safety Systems," identified that several plants had -i experienced higher-than-expected flow rates in low pressure safety systems that could occur following a LOCA. Higher-than-expected flow rates in the pump ,

discharge lines could then lead to lower than calculated suction line pressures and, consequently, to inadequate NPSH. The DBNPS staff performed calculations, which 1 showed that with a 20% reduction in the resistance coefficient values provided in Crane Technical Paper Number 410, the assumed flows in the NPSH calculations of 4000 gpm for DH/LPI and 1500 gpm for Containment Spray were reasonable and the calculated NPSH available was adequate.

In the case of a single failure where the discharge of one DH/LPI Pump would be lined up to supply bo_th trains oflow pressure injection, procedural limi;s (DB-OP-02000, "RPS, SFAS, SFRCS Trip or SG Tube Rupture") are in place to limit total flow to a maximum of 4000 gpm.

~ NRC Reouest 3:

Specify whether the current design-basis NPSH analysis differs from the most recent anglysis reviewed and approved by the NRC for which a safety evaluation -

was issued.

TE Resoonse 3:

! The current design-basin NPSH analysis does not differ from what was reviewed

'and approved by the NRC in the original DBNPS Final Safety Analysis Report

. (FSAR).1 In addition, the~ DBNPS NPSH calculations for the HPI and LPI Pumps in piggyback configuration and for the LPI Pumps clone were reviewed during the'  ;

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- NRC_ Davis-Besse Design Engineering Inspection (Inspection Report No. 50-346/97---

' 201, dated September 4,1997 (TE letter Log 5122)) conducted in the Spring of.1997 and found to be satisfactory.

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NRC Re.nutEt.1 -

Specify whether containment overpressure (i.e , containment pressure above the .

. vapor pressure of the sump or suppressio'n pool fluid) was credited in the calculation tof available NPSH.- Specify the amount of overpresente needed and the minimum overpressure available.  :

TE Response 4:

' Containment overpressure was not credited in the DBNPS NPSH analysis. 1 NRC Reauest 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 pressme.

TE Resoor.se 5:

Containment overpressure was not credited in the calculation of available NPSH, .

therefore', this aequest is not applicable to the DBNPS.

Should you have any questions or require additionalinformation, please contact

. Mr. James L. Freels, Manager-Regulatory Affairs, at (419) 321-8466.'

F Ve truly yours, FWK/lgi

cc: 'A. B.' Beach, Regional Administrator, NRC Region III S. J. Campbell,-DB-1 NRC Senior Resident Inspector A. G. Hansen, DB-1 NRC/NRR Project Manager

Utility Radiological Safety Board : .

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Q :. ., w a# Docket Number 50-346 License Number NPF-3 Serial Number 2507 -

. Enclobure '

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RESPONSE

5 TO NRC GENERIC LETTER 97-04 FOR THE s

DAVIS-BESSE NUCLEAR POWER STAT!ON UNIT NUMBER 1 .,

This letter is submitted pursuant to 10 CFR 50.54(0 and contains information

- pursuant to NRC Generic Letter 97-04, " Assurance of Sullicient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" -

. for the Davis-Besse Nuclear Power Station, Unit Number 1, By: ' __

JoTn[. Wood, Vice President - Nuclear l

Sivorn to and subscribed before me thia 29th day of December,1997.

Yue yh)d Notary Public, Stifte of Ohio-Nora Lynn. Flood-- My Commission erpires September 4, 2002.

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