ML20198E782
| ML20198E782 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 01/06/1998 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-04, GL-97-4, NUDOCS 9801090217 | |
| Download: ML20198E782 (5) | |
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l CnAkLos 11.CosE Incitimore Ocs and Electric Company i
Vice President Cahen Cliffs Nuclear Power Plant g
Nuclear Energy 1650 Cahen Cliffs Parkway Lusby, Maryland 20657 410 495-4455 January 6,1998 U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION:
Document Control Desk '
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SUBJECT:
Calurt Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50 318 90-Day Response to Generic Letter 97-04: Assurance cf Sufficient Net Positive Suction llead for Emergency Core Cooling and Containment Heat Removal
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REFERENCES:
(a)
NRC Gen:ric Letter 97-04: Assurance of Sufficient Net Positive Suction llead for Emergency Core Cooling and Containment Ileat s
Removal Pumps, dated October 7,1997 (b)
Leder from Mr. C.11. Cruse (BGE) to the Document Coritrol Desk (NRC), dat:d November 5,1997, 30-Day Response to Generic Letter 97-04: Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps (C)
"flandbook of Ilydraulic Resistance," Idlechik, l.E., Second Edition, Hemisphere Publishing Corporation,1986 The purpose of this letter is to forward our 90-day response to Reference (a). A 30-day response was forwarded by Reference (b). He generic letter requests that within 90 days from the date of the generic letter, each addressee submit a written response to five questions. The information requested is related to the current design basis analyses used to determine the 'available Net Positive Suction Head (NPSH' for
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the emergency core cooling and containment heat removal pumps that take suction from the containment sump. The questions and responses are provided below.
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l Document Control Desk January 6,1998 fage 2' Qutailoti:
Specify the general methodology used to calculate the head loss associated with the Emergency Core Cooling System (ECCS) suction strainers.
Respanac_1:
1 Determination of the 'available NPSil' for any pump requires that the hydraulic friction losses aetween the suction source and the inlet of the pump be computed. For the ECCS, the hydraulic friction loss, or head loss, associated with flow across the ECCS suction strainer is a portion of the total hydraulic friction loss between the suct%n source (i.e., containment sump) and the inlet of the dCCS pumps.
For the high pressure safety injection and low press tre safety injec6 ion pump evaluations, The hydraulic resistance coefficient of the ECCS sump was obtained from NUREG/CR-2759 and NUREG/CR-2760, which were studies of Containment Emergency Sump Performance. The resistance coeffici:nts listed in tb NUREGs include both strainer losses and r.ipe entrance losses. The data from these reports showed a range of sump resistance coefficients between 0.9 and 1.2 for sumps of similar configuration to that tt Calvert Cliffs (i.e., vertical outlet, protruding pipe entrance). A resistance coefficient of 1.2 was conservatively selected. The containment spray pump analysis t.tilized a sump resistance coefficient of 0.78, coiresponding to a standari pipe entrance value. Even though this value is lower, the impact on the total friction losses, and hence on 'available NPSil', is inconsequential. It is noted that the 0/i8 value did not incorporate any allowances for the effect of sump blockage on the sump resistance factor, llowever, Baltimore Gas and Electric Corr iy (f5GE) was cognizant of this issue and did informal sensitivity studies, which showed that 50n sump blockage did not have a noticeable effect on the sump resistance coefficiert.
Baltimore Gas and Electric Company has recently completed a separate calculation to determine the friction loss across the ECCS suction strainer. This :alculation analyzes the specific strainer geometry at Calvert Cliffs where the entrance to the ECC3 recirculation headers is enclosed within a containment sump cage. His sump cage consists of screen, grating, and various structural steel members. The hydraulic friction losses associated with flow passing through this sump cage was computed using formula and methodologias from Reference (c). Separate formulas were used to compute the hydraulic friction loss associated with flow passing through the grating and screening, respectively, and the results were summed to obtain a total friction loss.
These formulas require knowledge of the fluid flow velocity across the grating and screening, which in turn depends on the available flow area through these layers, in determining the available flow area, the sump cage is assumed to have 50% flow area blockage from debris. This assumption is censistent with industry practice, and is conservative when applied to Calvert Cliffs based on the low approach velocity to the sump, and the sump design.
The results of the evaluation demonstrate that the hydraulic friction losses across the sump cage are not significant even with 50% blockage of the surface area, and therefore, the resistance coefficients from NUREG/CR-2759 and NUREG/CR-2760 are still appropriate.
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Document Control Desk January 6,1998 Page 3' Question 2 Iden2y the required NPSil and the available NPSil.
Etaponse 2:
The ' required NPSil' and 'available NPSH' for each of the ECCS pumps, as documented in the existing calculations of record, are as follows:
Purup
'Reauired NPSH'
'Available NPSil' High Pressure Safety injection (at 607 gpm) 19.5 feet 22.5 feet low Pressure Safety injection (at 3000 gpm) 12.5 feet 23.0 feet Containment Spray (at 1642 gpm) 18.5 feet 24.3 feet He ' required NPSil' values come irom the venh sump performance curves provided by the vendor, except fer the HPSI pumps which, for the f1w, mn of interest, were augmented by onsite testing from St Lucie, whose llPSI pumps are of wim design to those at Calvert Cliffs. Use of this augmented test data is conservative because de 'w.u.rd NPSil' increased slightly.
Consistent with Safety Guide 1, the 'availauie NPSH' is provided by the static head of the water column between the water level in the lower level of containment, and the inlet to each of the pumps.
He 'available NPSil' is reduced by hydraulic friction losses (including sump strainer losses) between the containment sump and the suction of the ECCS pumps.
The evaluated HPS! flow of 607 gpm was based on procedural limits on the indicated Post-Recirculation Actuation Signal high pressure safety injection flow with instrument uncertainty incorporated accentingly. The containment spray flow of 1642 gpm is the maximum flow predicted by the existing calculation of record under Post-Recirculation Actuation Signal conditions, ne low pressure safety injection pumps are taken out-of-service when a Recirculation Actuation Signal is received; however, this pump may take suction from the containment sump later in the accident response for core flush duties, end for alternate shutdown cooling in the event that the conditions to enter shutdown cooling cannot be met. He core flush flow rate is only 150 gpm, while the shutdown coolint, flowrate is 3000 gpm. The evaluation of'available NPSH' to ' required NPSH' is, therefore, performed at the higher flowrate of 3000 gpm.
A new calculation is in progress, and though this calculation is not yet complete, the following table is believed to be a more accurate representation of the actual NPSH margin for each pump.
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Document Control Desk
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January 6,1998 Page 4' Eump
'Reouired NPSH'
'Available NPSH' liigh Pressure Safety injection (at 620 gpm) 19.5 feet 22.0 feet Low Pressure Safety injection (at 3000 gpm) 12.5 feet 22.0 feet Containment Spray (at 1525 gpm) 21.0 feet 24.5 feet A comparison of the two tables shows little 6:fference in NPSH values, and in both cases the
'available NPSil' is greater than the ' required NFSH'. The calculation currently in progn:ss will be
- completed by March 15,1998.
Ilutationl 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.
Resammel:
Subsequent to the issuance of the original license, the calculations of record have been updated to reDect the appropriate plant inputs, operating conditions, and industry operating experience. However, the theory and methodology of the analyses used to demonstrate adequate NPSH for the ECCS pumps has not changed.
. Question 4:
Specify whether containment overpressure (i.e., containment pressure above the 5apor pressure of the sump ct suppression pool Guid) was credited in the calculation of 'available NPEH'. Specify the amount of overpressure needed and the minimum overpressure available.
Response 4:
Containment overpressure is not credited in the evaluation of 'asilable NPSH'.
Ouestion 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.
Response 5:
This question is not applicable. See response en Question 4.
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Document Control Desk
7 January 6,1998 -
Page5'-
Should you have questiore regarding this matter, we will be pleased to discuss them with you.
Very truly yours,
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C. H. Cruse Vice President. Nuclear Energy 1
STATE OF MARYLAND
- TO WIT:
COUNTY OF CALVERT 1, Robert E. Denton, being duly sworn, state that I am Senior Vice President - Generation, Baltimore Gas and Electric Company (BGE), and that I am duly authorized to execute and file this response on behalf cf BGE. To the best of my knowledge and belief, the statements contained in this document are true ara correct. To the extent that these statements are not based on my personal knowledge, they are based upon information provided by other BGE employees and/or consultants. Such information has been reviewed in accordance with company practice and I
- to be reliable.
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swop before e a Notar H'ublic in and for the State of Maryland and County of Subscribe a
'D
,this
. day ot\\A4upw,1998.
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WITNESS my lland and Notvial Seal:
Notary Public 9
My Commission Expires:
dALLBAW /, NdOM U
Ddele CHC/SJR/ dim cc:
R. S. Fleishman, Esquire H. J. Miller, NRC J. E. Silberg, Esquire Resident Inspector, NRC A. W. Dromerick, NRC R. I. McLean, DNR Director, Project Directorate I 1, NRC -
J. H. Walter, PSC i