ML20198A889
| ML20198A889 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 12/26/1997 |
| From: | Mccoy C SOUTHERN NUCLEAR OPERATING CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-04, GL-97-4, LCV-1119-A, NUDOCS 9801060125 | |
| Download: ML20198A889 (11) | |
Text
m....
C. K. Mch Southe nNocher Vice Presdent Oper: ting Compa:y.lic.
Vogtte Project 40 invemess f. enter Padway i
l P0. Box 1295 Bamingham.Nabama 35201 Tel 205992 7122 Iax 205992 0403 SOUTHERN h COMPANY Energy to serre %ur World" December 26, 1997 LCV-lll9-A Docket Nos. 50-424 50-425 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Vogtle Electric Generating Plant RESPONSE TO GENERIC LETTER 97-04 D ATED OCTOBER 7.1997 Ladies and Gentlemen:
On October 7,199'i, the Nuclear Regulatory Commission issued Generic Letter 97-04 regarding the performance of the Emergency Core Cooling System and Containment Heat Removal Systems. The Generic Letter required an initial response within 30 days and requested a written summary report within 90 days.
Southern IJuclear provided a 30 day response in letter LCV-1119, dated October 30,1997.
The Generic Letter requested a 90 day response which provided the following information:
- 1) Specify the general methodology used to calculate the head loss associated with the ECCS suction strainers.
- 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.
- 4) Specify whether containment overpressure (i.e., containment pressure above the vapor pressure cf 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.
- 5) When containment overpressure is credited in the calculation of available NPSH, confirm that an appropriate containment pressu;e analysis was do.; to establish the minimum containment pressure.
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LCV-1119-A Southern Nuclear's response for Vogtle Electric Generating Plant is provided in the Enclosure to
'i this letter.- Additionally, in reviewing the calculations,'some inconsistencies were noted in flow.
values usal in particular scenarios. We are reevaluating these calculations and wih advise if there is a significant change to the current design bases.
Should you require any additional information regarding this response, please contact my office.
Sincere >y, C. K. McCoy.
Sworn to and subscribed before me this Mdayof kchlM41997 M4c44). 64L' Notary Public MyCommissionExpires:b % 9 hh I
J CKM/PAH/gmb Enclosurei Assurance of Sufficient NPSH for ECCS and CS Pumps cc:
Southern Nuclear Operating Comoany Mr. J. B. Beasley Mr.' M. Sheibani NORMS U. S. Nuclear Regulatory Commission-Mr. L. A. Reyes, Region II Administrator Mr. D. II. Jaffe, NRR, Senior Project Manager Mr. John Zeiler, Senior Ib sident Inspector, Vogtle a
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Eccl:sure Vogtle Electric Generating Plant Response to GL 97-04 dated October 7,1997 Assurance of Sufficient NPSil for ECCS and CS System Pur.ms
- Reauested Actions from GL 97-04
- 1) "Specify the general methodology used to calculate the head loss associated with the ECCS suction strainers."
SNC Response The general methodology,2 used to calculate the net positive suction head (NPSH) i associated with the emergency core cooling system (ECCS) pumps and the containment spray system (CSS) pumps is as follows:
The basic equation for calculatirig NPSH is:
NPSH = h. - h, + h. - h t, where:
m h. = absolute pressure at the supply liquid's surface.
h, = vapor pressure of the liquid at the temperature of the pumped liquid.
h. = static head between the level of the liquid supply and the pump's suction.
ht= suction line losses, including the containment sump screens as applicable.
The emergency sump screen head loss is calculated using equation (2) in section 5.5 of 3
NUREG-0897, Revision 1, October 1985.
balculation X4C1204V01, Revision 1, Emergency Core Cooling Pumps Suction Line Losses and NPSH, dated
.luly 5,1984.
- Calculation X4Cl204V05, Revision 3, Containment Emergency Sump Perforn.ance, dated June 14,1996.
8 Serkiz, A. W.," Containment Emergenc;i Sump Performance," NUREG-0897, Revision 1, NRC, published October 1985.
I
E clos:re Vogtle Electric Generating Plant Response to GL 97-04 dated October 7,1997 Assurance of Sufficier 1 NPSH for ECCS and CS System Pumos The head losses due to fibrous debris blockage of the sump screens is calculated by:
All=
a (Q + A)'(V + A)'
- where, AH=
Sump screen blockage losses (R 110) 2 Q=
recirculation flow rate (R'/sec)
V=
volume ofinsulation debris deposited on screen (fl')
A=
cffective (wetted) screen area 68.3 for "NUKON" insulation a =
1,79 for "NUKON" insulation b
=
1.07 for "NUKON" insulation '
c =
5 "A"is further dermed as follows:
2 A u = cfrective open screen area per containment emergency sump (A ) 2)
Ar = total screen cross section area per containment emergency sump (R The equation then becomes:
All=
a (Q + A.n)" (V + A1)*
- 2) " Identify the required NPSil and the available NPSil."
s SNC Remonte I
Residual Heat Removal PumpJi The residual heat removal (RIIR) system is designed so that adequate net positive suction head (NPSH) is provided to the RHR pumps, in accordance with Regulatory Guide 1.1.
To demonstrate that adequate NPSH is provided for the RHR pumps, it is only necessary to demonstrate that the NPSH is adequate under the worst limiting conditions. The net positive suction head (NPSH) of the RHR pumps was evaluated for normal plant cooldown operation and for both the injection and recirculation modes of operation for the design basis accident (DB A).
ScrLiz, A. W.," Containment Emergency Sump Performance," NUREG-0897, Revision 1, NRC, published October 1985.
- Calculation X4Cl204V05, Revision 3, Containment Emergency Sump Performance, dated June 14,19%
2
~
E: clos:re Vogtle Electric Generating Plant Response to GL 97-04 dated October 7,1997 Assurance of'Semcient NPSII for ECCS and CS System Pumns The recirculation mode of operation gives the limiting NPSil requirement for the RHR pumps, and the NPSH available is determined from the following equation:
NpSH = h. - h, + h. - h.i To evaluate the adequacy of the available NPSH, the debris generation from a high energy line break within the containment and the resultant impact on the RIIR pump performance was evaluated using the following.
A. The minimum flood level inside th containment, based on the refueling water storage tank (RWST) water discharged dming injection and switchover to recirculation, plus the water volume of three accumulator tanks, is at elevation 177 feet and 0 inches.
B. The RIIR pump suction elevation is 123 feet and 3 inches.
C. The calculated maximum line losses that inchide losses through pipe fittings, valves, entrance and exit are 16.98 feet at 4500 gallons per minute, RHR pump mn-out flow.
D. The quantity ofinsulation debri; generated by the double-ended rupture of the reactor coolant system hot leg at its connection to the steam generator, the limiting case, is 172.0 cubic feet.
E. The volume of the debris deposited on each of the two RHR trash guard-screen cages is 31.7 percent of the total debris generated. This is based on the ratio ofindividual pump flowrate to total recirculation flowrate, which also includes the two containment spray pumps.
F. The maximum RHR emergency sump screen head loss, assuming 31.7 percent of the total debris generated is evenly deposited on the trash guard-screen cage, is 15.11 feet.
G. The vapor pressure of the pump liquid is assumed to bc in equilibrium with the containment ambient pressure (e.g., no credit is taken for sub-cooling of the sump fluid).
h.=h, The NPSli equation for the recirculation mode when suction is taken from the containment emergency sump becomes:
NPSH = h. - h w w - h m.m. w
- FR AR Paragraph 6.3.2.2.4, Revision 7. September 1997.
' Calculation X4Cl204V05, Revision 3, Containment Emergency Sump Performance, dated June 14,19%.
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E clostre Vogtle Electric Generating Plant Response to GL 97-04 dated Octobu 7,1997 Assurance of Sumcient NPSil for ECCS and CS Sv: tem Pumos Using the above values, the calculated RHR pump available NPS11 is 21.6 feet. The RHR pump required NPSH st 4500 gallons per minute is 19 feet. Therefore adequate available NPSH margin is provided for proper RHR pump operation.
fdmitinment Spray Pumpj The containment spray system is designed so that adequate net positive suction head (NPSll)is provided to the containment spray pumps,in accordance with Regulatory Guide 1,1, To demonstrate that adequate NPSliis provided for the' containment spray pumps, it is only necessary to demonstrate that the NPSH is adequate under the worst limiting conditions. NPSH for the containment spray pumps is evaluated for both the injection and recirculation modes of operation for the DB A. The recirculation mode of operation gives the limiting NPSH requirement for the containment spray pumps, and the NPSH available is determined from the following equation:
- NPSil = h. - h y +h,-h.t To evaluate the adequacy of the available NPSH, the debris generation from a high energy line break within the containment and the resultant impact on the containment spray pump performance was evaluated using the following. "
A. The minimum flood levelinside the containment based on the refueling water storage tank (RWST) water discharged during injection and switchover to recirculation, plus the water volume of three accumulator tanks, is at 177 feet and 0 inches.
B. The containment spray pump suction elevation is 121 feet and 5 inches.
C. The calculated maximum line losses that include losses through pipe fittings, valves, entrance and exit are 6.93 feet at 2600 gallons per minute, containment spray pump design flow.
D. The quantity ofinsulation debris generated by the double-ended rupture of the reactor coolant system hot leg at its connection to the steam generator, the limiting case, is 172.0 cubic feet.
- Vogtle FSAR Paragraph 6.2.2.2.2.3.2, Revision 7, September 1997.
' Calculation X4Cl204V05, Revision 3, Containment Emergency Sump Performance, dated June 14,1996.
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E: clos:re Vogtle Electric Generating Plant Response to GL 97-04 dated October 7,1997 Assurance of Sufficient NPSil for ECCS and CS System PumDs E. Hydraulic model studies performed on a scale model of the Plant Vogtle containment emergency sump configuration showed that the approach velocities to the four sumps during two train operation was essentially the same. Therefore, it is assumed for the containment spray system that the volume of debris transported and deposited on one sump screen is one quarter of the total debris generated by the postulated pipe break event. This is conservative for the containment spray pumps since their flow is less than the RHR pumps.
F. The maximum containment spray emergency sump screen head loss, assuming 25 percent of the total debris generated is evenly deposited on the trash guard-screen cage,is 14.93 feet.
G. The vapor pressure of the pumped liquid i.i assumed to be in equilibrium with the containment ambient pressure (e.g., no credit is taken for sub-cooling of the sump fluid):
h.=h, Tbc NPSH equation for the recirculation mode when suction is taken from the containment emergency sump becomes:
NPSH = h. - h w w - h,,.%
Using the above values, the calculated containment spray pump available NPSH is 33.7 feet. The required NPSH at 2600 gallons per minute is 15 feet. Therefore, adequate available NPSH margin is providad for proper containment spray pump operation.
Safety Iniection and Charging Pumgi The NPSH for the safety injection and charging pumps was evaluated for both the injection and recirculation modes of operation for the design basis accident (DBA). These pumps piggy-back onto the RHR pumps during the recirculation mode of operation. The end of the injection mode of operation gives the limiting NPSH available (minimum static head). The NPSH available was determined from the elevation head and vapor pressure of the water in the refueling water storage tank (RWST), which is at atmospheric pressure, and from the pressure drop in the suction piping from the tank to the pumps.
The NPSH evaluation for the charging and safety injection pumps with suction from the RWST is based on the pump being analyzed at its rur-out flowrate.
" Hydraulic Model Studies of Flow Conditions to Containment Emergency Sumps," Final Report for A. W.
Vogtle Plant, October,1985.
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Ercios:re Vogtle Electric Generating Plant Response to GL 97-04 dated October 7,1997 Assurance of Su4icient NPSH for ECCS and CS System Pumos When a predetermined low RWST level is reached, the safety injection and charging pumps are manually aligned to take suction from the RHR pump discharge headers. The NPSH requirements of the safety injection and charging pumps are satisfied by the discharge head of the RHR pump (s) during the recirculation mode of system operation.
NPSH Summary The following results are from the current design-basis NPSH analysis " for the containment spray pumps and the residual heat removal pumps, including the containment emergency sump performance.
Recirculation Mode NPSH NPSH NPSH Available Required Margin Limiting Case (feet)
(feet)
(feet)
Containment Spray 33.7 15 18.7 Pumps Residual Heat 21.6 19 2.6 Removal Pumps l
l
" Calculation X4Cl204V05, Revision 3, Containment Emergency Sump Perfonnance, flated June 14,19%.
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E clos:re Vogtle Electric Generating Plant i
Rerponse to GL 97-04 dated October 7,1997
- Assurance of Sumcient NPSH for ECCS and CS System P_umm The following results are from the current design-basis NPSH analysis " for the SI and
)
charging pumps during the injection mode. The results for the Si and charging pumps in the recirculation mode have been approximated. "
NPSH NPSH NPSH Available Required Margin Limiting Case (feet)
(feet)
(feet)
Centrifugal 81.8 40 41.8 Charging Pumps (Injection Mode)
Centrifugal 250 40 210 Charging Pumps (approx.)
(approx.)
(Recirculation Mode)
Safety Injection 62.6 30 32.6 Pumps (Injection Mode)
Safety Injection 250 30 220 Pumps (approx.)
(approx.)
(Recirculation Mode)
" Calculation X4Cl2o4V01, Revis;on 1, Emergency Core Cooling Pumps Suction Line Losses and NPSH, dated July 5,1984.
" Calculation X4Cl204V06, Revision 0, System Head Curves for RHR, CCP, SI, CS, and AFW Pumps, dated October 31,1990.
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l E:clostre Vogtle Electric Generating Plant Response to GL 97-04 dated October 7,1997 Assurance of Sufficient NPSH for ECCS and CS System Pumns
- 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."
SNC Response The results of the most recent analysis submitted " to the NRC regarding the containment sump analysis indicated that there was adequate NPSH availabic for the containment spray and residual heat removal pumps to perform their safety function while drawing suction from the containment sumps.
For both cases evaluated, using a conservative estimate of the quantity of debris generated and transport, it was found that the available NPSil for the RHR and CS pumps exceeded the required NPSil for proper pump operation. The minimum available NPSH margin for the CS pumps (even distribution case) was 18.4 feet and for the RHR pumps (uneven distribution case) was 2.2 feet.
This conclusion is based on the theoretically worst case where 100% of the insulation debris generated by the break is assumed to be completely shredded and migrate onto the containment emergency sump screens. The head loss due to the maximura theoretical debris blockage provides margin above the minimum NPSH requirements for the RHR and CS pumps.
The current design-basis NPSH analy" sis differs from the most recent analysis reviewed and approved by the NRC. The analysis indicates that the minimum available NPSH margins are greater than the values reviewed and approved by the NRC. Specifically, the minimum available NPSH margin for the CS pumps (even distribution case) increased to 18.7 feet, and for the RHR pumps (uneven distribution case) increased to 2.6 feet. The analysis was finalized, shortly aller the initial analysis was submitted to the NRC, and as a result the minimum available NPSH margins increased. The current analysis continues to comply with the ir.ethodology from NUREG-0897 ", Revision 1, October 1985.
" GN-690,"SER Open item 3: Containment Sump Analysis," Letter to U. S. Nuclear Regulatory Commission from Georgia Power Company, dated August 23,1985.
" Calculation X4Cl204V?$, Revision 3 Containment Emergency Sump Performance, dated June 14,19%.
" Serkii., A. W.," Containment Emergency Sump Performance," NUREG-0897, Revision 1, NRC, published =
October 1985.
8 l
^
Eqct:sure t
Vogtle Electric Generating Plant Response to GL 97-04 dated October 7,1997 Assurance of Sufficient NPSil for ECCS and CS System Pumps
- 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."
SNC Response A saturated sump modelis used in calculating " the NPSH available to the system pumps.
That is, the containment atmospheric pressure is conservatively assumed to be equal to the vapor pressure of the liquid in the recirculation sumps, ensuring that credit is not taken for containment pressurization during the transient.
- 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 "
fiF.C Response Containment overpressure (e g., containment pressure above the vagor pressure of the sump or suppression pool fluid) was not credited in the calculation of available NPSH to the system pumps. Therefore, the containment pressure analysis was not reviewed in response to this generic letter.
" Calculation X4Cl204V05, Revision 3, Containment Emerge.cy Sump Performance, dated June 14,1996.
" Calculation X4Cl2o4V05, Revision 3, Containment Eme.gency Sump Performance, dated June 14,19%.
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