ML20248G864
| ML20248G864 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 06/01/1998 |
| From: | Dennis Morey SOUTHERN NUCLEAR OPERATING CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-04, GL-97-4, NUDOCS 9806050369 | |
| Download: ML20248G864 (6) | |
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Dan Morey S:uthern Nuclear yice President Op tating Company farley Project P0. Box 1295 Birmingham. Alabama 35201 Tel 205.992.5131 June 1, 1998 SOUTHE.RN co Energ to ServeYourWorld" Docket Nos.: 50-348 10 CFR 50.54 50-364 U. S. Nuclear Regulatory Commission ATTN.: Document Control Desk Washington, DC 20555-0001 Joseph M. Farley Nuclear Plant Revision to Aesponse to Generic Letter 97-04, " Assurance of Sufficient Net Positive
. Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" Ladies and Gentlemen:
NRC Generic Letter 97-04 requested addressees to provide information pertaining to the ECCS and containment spray pump NPSH calculations for the recirculation mode. The 90-day actions were completed by Southern Nuclear Operating Company (SNC), and the requested information was transmitted by SNC letter dated December 30,1997.
As a result of this information request, SNC identified needed changes and enhancemems to the existing calculations. SNC committed to complete these changes and enhancements by June 1,1998, and to revise the submittal if needed. This letter revises the December 30, 1997 SNC response to Generic Letter 97-04. Changes in the data are denoted.
Respectfully submitted, NM Dave Morey Suor to and bscr be em day of i
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1998
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Mr.L. A.Reyes, RegionII Administrator
' Mr. J. I. Zimmennan, NRR Project Manager Mr. T. M. Ross, FNP Sr. Resident Inspector 9806050369 9eo601 F PDR ADOCK 05000348 P
PDR:
4 ATTACHMENT
. Joseph M. Farley Nuclear Plant Revision to SNC Response to NRC Generic 1.etter 97-04
" Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps" Lican== were requested to review the current design-basis analyses used to determine the available NPSH for the emergency core cooling and containment heat removal pumps that meet either of the followmg criteria:
Pumps that take suction from the con.amment sump or suppression pool following a a.
design-basis LOCA or =~da y line break; or b.
Pumps used in " piggyback" operation that are necessary for recirculation cooling of the reactor core and contamment.
Licensees were requested to provide the information ou. lined below in items 1, 2, 3, 4, and 5 for each of their facilities. Each item is addressed below.
1.
Specify the general methodology used to calculate the head loss associated with the ECCS suction strainers.
The head loss associated with the ECCS suction strainers was determined by testing. A full scale model of Farley Nuclear Plant's (FNP's) containment sump recirculation intakes was developed in the mid-1970's to evaluate the adequacy of the intake design with regard to air-entraming and non-I air-entraining vortices. A description of the model testing of the containment sump recirculation intakes is found in FSAR Section 6C. Screen-grating losses for various configurations of blockage were determined from the use of piezometers. By means of the Farley specific contamment sump recirculation intake model, extensive testmg and data collection were conducted for numerous configurations and conditions to bound postulated posbLOCA conditions.
Both FNP Units employ four recirculation mtakes For Unit 1, there are two 14 inch diameter intakes for ECCS and two 10 inch d;
=a'ar intakes for containment spray. One 14 inch intake for ECCS (referred to as intake 1) and one 10 inch intake foi containment spray (referred to as intake
- 4) are each enclosed by a separate screen-grating cage. The other 14 inch intake for ECCS and 10 inch intake for contamment spray (referred to as intakes 2 and 3, respectively) are enclosed by a shared screen-gratmg cage. For Unit I, each of these intake configurations were modeled and tested For Unit 2, a full scale model of a single 14 inch diameter intake was tested i
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Attachment GL-97-04 Revision The' maximum measured head losses across the Unit I screen-grating cages under des gn flow conditions and with blockages as noted were as follows.
Intake No.
. Configuration Flow Measured Blockage (gpm)
Head Loss (ft)
(%)
1 RHR 5900 0.09 63.7 2 and 3 RHR & CS 8950 0.14 64.2 4
CS 3050 0.04 69.4 l
FNP Unit 2 containment sump recirculation intakes are similar to Unit 1, except each intake is i
located within a separate semen-gratmg cage. Since there are no shared screen-grating cages on Unit 2, the results for head losses across the screen-grating cage from the Unit I model are boundmg. These measured head losses are small when compared to the overall friction losses used i
in calculating the NPSH available and in some cases were neglected in the original calculations.
Updated system calculations include the effects of screen head losses. A boundmg value of.11 for a calculated 7715 gpm flowrate for intake 2 and 3 was used for RHR and CS NPSH calculations.
This value was calculated by adjusting the original measured data. (note 1) 2.
Identify the required NPSH and the available NPSH.
1 RHR Pumos For Unit 1, the required NPSH for the RHR pumps is 17 ft at a calculated limiting condition of 4415 gpm for hot leg recirculation. The available NPSH is 19.9 ft. (note 2) l For Unit 2, the required NPSH for the RHR. pumps is 17 ft at a calculated limiting condition of p
4400 gpm for cold or hot leg recirculation. The available NPSH is 18.2 ft. (note 2) l Charnine Pumps Testing of a spare charging pump established a required NPSH of 50 ft at a flow of 710 gpm. At the maximum calculated charging flow of 708 gpm (note 3), available NPSH was detennined to be 166 ft. (note 4) Ac available NPSH was determined based on a conservative configuration where l
one RHR pump provides flow to two charging pumps at a combined flow of 1340 gpm. The recirculation configuration is bounded by the injection mode and therefare is not included in the design-basis calculations. The design-basis is discussed in tim response to item 3.
L Caa*=3a-* Sorav Pumna l
l De required NPSH for the Unit 1 or 2 contamment spray pumps is 18 ft at 3400 gpm during recirculation. The available NPSH is 18.7 ft for Unit I and Unit 2. (note 5) 1 l -
Attachment GL-97-04 Revision
- 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 cvaluation was issued.
He current design-basis NPSH analyses differ for the RIIR and containment spray pumps. The differences are discussed below. The charging pump design-basis has not changed.
RHR Pumos He SER addressing the RHR NPSH analyses was issued for FSAR Amendments 40 (October 16, 1974) and 72 (March 7,1980). Updated calculations were performed for modifications on the RHR pumps.
FSAR Amendments 40 and 72 note the NPSH available and required for the RHR pumps at a flowrate of 4200 gpm during cold leg recirculation as follows.
Umt 1 Unit 2 NPSH available 20.6 ft 19.7 ft NPSH required 15.0 ft 15.0 ft Flowrate 4200 gpm 4200 gpm Time after accident Cold leg recire.
Cold leg recirc.
He results of subsequent calculations performed to address modifications to the RHR pumps are listed below. Rese values were included in updated FSAR Revision 11.
Unit 1 Unit 2 NPSH available 18.9 ft 17.4 ft i
NPSH required 17.0 ft 15.8 ft i
Flowrate 4415 gpm 4350 gpm Time after accident Hot leg recire.
Hot or cold leg recire.
During preparation for this response, the analysis of the RHR NPSH was reviewed due to disparities in the results for the units. The results of the reanalysis are summarized below. He FSAR description of NPSH available and required for the RHR pumps will be revised as needed.
Unit 1 Unit 2 NPSH available 19.9 ft (note 2) 18.2 ft (note 2) l NPSH requimi 17.0 ft 17.0 ft Flowrate 4415 gpm 4400 gpm Time after accident Hot leg recire.
Hot or cold leg recire.
Charming Pumos The FSAR describe; the most limiting condition for NPSH available. For the charging pumps, the end ofinjection mode is the most limiting condition. At the end of the injection mode when suction from the RWST is terminated (low RWST level), adequate net positive suction head is supplied from the containment sump by the booster action of the RHR pumps. Tne design-basis NPSH I
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Attachment GL-97-04 Revision required during injection mode for the charging pumps is 25 ft at 650 gpm. This description has not changed and remains the current design-basis. He NPSH required for the recirculation mode was calculated in preparation for this response. The results are given in response to item 2.
Containment Sorav Pumps FSAR Amendments 40 and 72 note the NPSH available and required for the containment spray pumps during recirculation as follows.
Unit 1 Unit 2 NPSH available 21.2 ft 20.9 ft NPSH required 37.5 ft 17.5 ft Flowrate 3050 gpm 3050 gpm The current design-basis described in updated FSAR Revision 14 identifies the NPSH available and required as follows.
Unit 1 Unit 2 NPSH available 19.3 ft 19.4 ft NPSH required 18.0 ft 18.0 fl Flowrate 3050 gpm 3050 gpm Reanalysis of the CS conditions produced the following results. CS pump flowrate increased due to lower calculated hydraulic resistance and updated test data for the CS pump model used at FNP.
The increased flowrate resulted in a small reduction in available NPSH. The results are tabulated below. The FSAR description of NPSH available and required for the RHR pumps will be revised as needed.
Unit 1 Unit 2 NPSH Available 18.7 ft (note 5) 18.7 ft (note 5) l NPSH Required 18.0 ft 18.0 ft Flowrate 3400 gpm (note 5) 3400 gpm (note 5) l 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.
Containment overpressure was not credited for either Unit in the calculation of available NPSH during the recirculation mode for the RHR, charging, and containment spray pumps. - _ _ _.
4 Attachment GL-97-04 Revision l
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.
Item 5 is not applicable to FNP, since containment overpressure was not credited in the calculation of available NPSH during the recirculation mode for the RHR, charging, and contamment spray pumps for either Unit.
Notes Regarding Changes i
NOTES:
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- 1. The measurements for ECCS suction stramers losses were taken at flowrates originally expected Reevaluation has resulted in increased CS flowrate and decreased RHR flowrate.
Strainer head losses have been adjusted to the net decreased flow at the shared screen.
- 2. Changes to RHR available NPSH have resulted from revised pump elevations, changes in CS flowrate and more conservative sump level assumptions.
- 3. Increased charging flow was calculated based on measured data.
- 4. Updated available NPSH based on recalculation of system resistance and tested RHR supply pressure.
- 5. CS pump flowrate increased due to lower calculated hydraulic resistance, while the NPSH required remained constant due to updated test data for the CS pump model used at FNP The increased flowrate, together with more conservative sump level assumptions, resulted in a small reduction in availabic NPSH.
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