ML20198G470
| ML20198G470 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 01/05/1998 |
| From: | Horn J NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-04, GL-97-4, NLS970226, NUDOCS 9801130043 | |
| Download: ML20198G470 (13) | |
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PM llCR L. IO lA A $8WI Nebraska Public Power District ""at%==T" e m u n m =x m m a a m u n w a a m aw a a n ,n - w w a m a nn a m u m m m ma NLS970226 January 5,1998 U.S. Nuclear Regulatory Commission Attention: Documen: Control Desk Washington, D C. 20555 0001 Gentlemen:
Subject:
Response to NRC Generic Letter 97-04 Cooper Nuclear Station, NRC Docket 50 298, DPR-46
Reference:
- 1. NRC Generic i etter 97-04 dated October 7,1997. " Assurance of Suflicient Net Positive Suction licad for Emergency Core Cooling and Contaiament Ileat Removal Pumps"
1997," Response to NRC G neric Letter 97-04" On October 7,1997, the Nuclear Regulatory Commission (NRC) issued Generic Letter 97-04 (Reference 1) regarding an issue which msy have generic implications for Emergency Core Cooling System (ECCS) and containment heat removal system pumps. The generic Ictter required, within 90 days, that licensees provide the information outlined below:
- 1. Specify the general methodology used to calculate the head loss associated with the ECCS suction stainers.
- 2. Identify tiie required Net Positive Suction licad (NPSil) and the available NPSil.
- 3. Specify whether the current design-basis NPSli ar.alysis differs from the most recent analysis reviewed and approved by the NRC for which a safety evaluation was issued. ,
- 4. Specify whether contairunent overpressure (i c., containment pressure above the vapor /
pressure of the sump or suppression pool fluid) was credited in the calculation of available NPSil. Specify the amount of overpressure needed and the minimum overpressure avcilable.
- 5. _ When containm;nt overpressure is credited in the calculation of available NPSil, confirm that an appro .inte containment pressure analysis was done to establish the minimum containment pressuie.
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' NLS970226 i January 5,1995 * !
Page 2 0f 3 j liy this letter, as committed to in Reference 2, the Nebraska Public Power District (District)is l providing the tquired 90 day response. l t
Should you have any questions concerning this matter, please contact me. !
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nlor ' ice President, Energy Supply f I
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cc: Regional Administrator i USNRC - Region IV q Senior Project Manager !
USNRC - MRR Project Directorate 1%1 ;
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NLS970226 - ,
January 5,1998 Page 3 of 3.-
STATE OF NEBRASKA )
)
NEMAllA COUNTY ')
O. R. Ilorn, being first duly sworn, deposes and says that he is an authorized representative of the
.. Nebraska Public Power District, a public corporation and political subdivision of the State of-Nebraska; that he is duly authorized to submit this correspondence on behalf of Nebraska Public Power District; and that the statements contained herein are true to the best of his knowledge and -
belief.
m' / _
l 0. . liorn Subscribed in my presence and sworn to before rne this [ day otil1Utty , 1998.
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At:schment I to NLS970226 P' age I of 9 Response to NRC Generic latter 97-04 Cooper Nuclear Station, NRC Docket 50 298, DPR-46 On October 7,1997, the Nuclear Regulatory Commission (NRC) issued Generic Letter 97 04 regarding an issue which may have generic implicatioru for Emergency Core Cooling System (ECCS) and containment heat removal system pumps. The following information is provided for Cooper Nuclear Station (CNS) in response to the generic letter.
Note that the informatio i provided encompasses the Residual licat Removal (RilR) and Core Spray (CS) pumps, and excludes the fligh Pressure Coolant injection (IIPCI) pump. While the llPCI pump can take suction from the suppression pool, the normal suction is from the Emergency Condensate Storage Tanks. In addition, during a Design Basis Accident Loss of Colant Accident (DBA LOCA), the llPCI system will isolate due to low steam line pressure at less than or equal to 60 seconds into the event, which is well before the suppression pool temperatures begin to show a significant increase.
Item 1 - Specify the general methodology used to calculate the head loss associated with the ECCS suction stainers, Respamc:
The head losses associated with the ECCS suction strainers are included in the cumulative head losses for the everall ECCS suction strainer / suction piping configuration. These cumulative values were developed through analysis using plant startup data collected at each ECCS pump inlet under two difTerent test flow configurations with half of the suction strainers hooded to simulate panially blocked strainera, These flow configurations were:
- ECCS Design Flow (7700 gallons per minute (gpm) for the RilR pumps and 4720 gpm for the CS pumps).
- ECCS Recirculation Flow (2500 gpm for R11R and 1200 gpm for CS).
The relationship between the cumulative head losses and net positive suction head (NPSil)is described below.
The basic equation for calculating NPSI-I is:
NPSil = h, - ly + h,, - h,,
Where:
p_
i;
f ', -
Attachment I to NLS970226 l' age 2 of 9 h, a Absolute pressure on the surface of the liquid supply level h, . = IIead corresponding to the vapor pressure of the liquid at the temperature o being pumped h, = Static height that the liquid supply levelis above or below the pump
. centerline or impeller eye hr, = - Suction line losses including entrance losses and friction losses Additional detail on each of the terms is provided below.
h,'= Absolute pressure on the surface of the liquid supply level This term is based on values of suppression pool pressures and temperatures obtained from l
computer analyses of containment response during a DBA-LOCA event ' Absolute pressures are subsequently converted to head based on the following equation:
- h, = 144 x P, x V, .
Where:
144 = Conversion factor from square inches to square feet
= Suppression pool pressure (psia)
P,,,
- V, = Specific volume for water at the suppression pool bulk temperature (fP/lb)
Alsa see the response to Item 4 for a discussion on the crediting of contairmient pressure in the NPSil analysis for CNS.
h,, = liend corresponding to the vapor pressure of the liquid at the temperature being _
pumped This term is obtained from the Steam Tables based on the temperature of the fluid being -
pumped and assumes the maximum bulk fluid temperature predicted using the DBA-LOCA containment analyses described above. Absolute pressures are converted to head in 'he same fashion used for h..
' General Electric Report GENE-637-045-1293 dated January 1994, " Containment Analyses in Support of an increase in the RHRS Heat Exchanger Tube Plugging Margin for Cooper Nuclear Station" L
h .
.4 i
. Attachment I to NLS970226 :
l' age 3 of 9 h, = Static height that the liquid supply level is above or below the pump centedine or impeller eye l This term is simply the minimum static height of fluid above the pump reference point
- (typ.cally pump centerline or impeller eye). This is based upon the minimum rent ression pool water volume allowed by Technical Specifications 3.7.A.I.a.
hs = Suction line losses including entrance losses and friction losses For CNS; this term has been determined analytically using plant startup data taken at each ECCS pump inlet.
' Item 2 - Identify the required net positive suction head (NPSH,) and the net positive i suction head available (NPSH ).
BIspa'15c:-
The available NPSH is dependent on the wetwell pressure, the number of pumps operating, the piping configuration, and the suppression pool bulk fluid temperature at the most limiting condition. Pressures above atmospheric are credited. The required NPSH is based on criteria specified by the pump manufacturer, In general, values for required Containment Pressure (P,)
and NPSII, are calculated using the following equations:
NPSH, = 144 x ( P,- P,) x V, + h,- hi Note: As used in GENE-637-045-1293, NPSil, was read from pump curves and this equation <
was solved for P,.
And NPSH, = 144 x ( P. - P,) x V, + h, - ha Where:
144 = Conversion factor from squarc nches to square feet P, = Containment pressure required for the applicable ECCS pump NPSH, as specified by the manufacturer (psia)
P, = Vapor pressure based on the maximum bulk fluid teniperature predicted (psia)
= Available wetwell pressure (psia)
P.
Attachment 1 to NLS970226
- Page 4 of 9 V, =- Specific volume of the water based on the maximum bulk fluid temperature predicted (R'/lb) h, = Static height that the liquid supply level is above or below the pump 1 centerline or impeller eye (feet) _
h3 = Suction line losses including entrance losses and friction losses (feet) ;
Based on data and analysis documented in GENE-637-045 1293, the following values are -
provided:
- The pressure required, P,, is 18.59 psia and 15.81 psia for the RHR and CS pumps, respectively.
- The maximum bulk fluid temperature predicted is 195.9 degrees Fahrenheit. Accordingly, P, equals 10.5 psia and V, equals 0.016608 n'/lb.
- The available wetwell pressure, P., is 22.46 psia.
- The static height, h,,, is 12.96 feet for both the RHR and the CS pumps.
- The suction line losses, h3 , are 4.63 and 8.55 feet of water for the RiiR and CS pumps, respectively (at flows of 7700 and 4720 gpm, respectively).
Accordingly, the values for NPSH, and NPSH, are tabulated as follows:
PUMPS NPSH, NPSH, CS; A or B Pump 17.05 ft - 32.98 A.
RHR; A, B, C, or D Pump 27.62 ft 36.90 fl.
Item 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.
Rus'onic:
While information has been provided on NPSH, no design-basis NPSH analysis has been provided to the NRC for which a safety evaluation was issued. However, an overview of the current design-basis and the various licensing submittals detailing NPSH considerations is as follows:
-Attachment 1 to NLS970226 Il age 5 of 9
- 1. Amendment 11 to the Final Safety Analysis Report (FSAR), Question 6.4 The first NPPD response to discussions about ECCS NPS!! containment back pressure requirements is found in the submittal of Amendment 11 to the Final Safety Analysis Report (FSAR) F. The response to Question 6.4 states that there are times that the containment pressure must be above atmospheric in order to maintain the NPSH requirements for the core standby cooling system pumps under the long-term usage design basis analysis conditions. A plot of minimum containment pressure and pressures for ECCS '.' ump NPSH requirements versus time aller the DBA-LOCA was provided as FSAR Figure 6.4-1,
- 2. Technical Specification Amendment No. 82 The most recent information presented to the NRC for review was st.bmitted as a part of the technical basis for a change to Technical Specification 3.7.A.I.c3 ' This amendment allowed an increase in the rnrximum suppression pool temperature during normal operation from 90 to 95 degrees Fahrenheit.
The basis for the temperature increase was provided by General Electric Report NEDC-24360-P ',4 which was included as part of the aforementioned amendment request. Section 6.2 therein addressed the effect of the temperature increase on the ECCS Pump NPSH requirements. This report showed a long term maximum bulk temperature of 184 degrees Fahrenheit, and calculated the NPSh to be 47.3 and 46.6 feet of water for the RHR and CS pumps, respectively.
- 3. Current Design Basis The ECCS NPSH containment back pressure requirements currently described in the Updated Safety Analysis Report (USAR) are based on calculation GENE-637-045-1293
- performed in support of Design Change 91-144,"RHR Heat Exchanger Tube Plugging Margin."
2 Letter to L. M. Muntzing (USAEC) from R. E. Reder (NPPD) dated May 30, 1972," Amendment No. I1 to License Application, Filed on July 27,1967, For Cooper Nuclear Station, Filed Under AEC Docket No 50-298"
' Letter to USNRC from J. M. Pilant (NPPD) dated June 10,1982, " Proposed Change to Technical Specifications, Suppression Pool Temperature, Cooper Nuclear Station, NRC Docket No. 50-298, DPR-46" General Electric Report NEDC-24360-P dated August 1981," Cooper Nuclear
- Station Suppression Pool Temperature Response" 8
General Electric Report GENE-637-045-1293 dated January 1994," Containment Analyses in Support of an Increase in the RHRS Heat Exchanger Tube Plugging Margin for Cooper Nuclear Station"
-Attachment I to NLS970226 -
Page 6 of 9 -
GENE-637-045-1293 concludes that adequate NPSil margins are maintained for both RilR and CS pumps throughout the DBA-LOCA. Tabulated results from the analysis indicated a long term maximum bulk fluid temperature of 195.9 degrees Fahrenheit, coinciding with a wetwell pressure of 22.46 psia, and pressures of 15.81 psia and 18.59 psia required for CS and RIIR pump NPSil requirements, respectively.
- 4. ECCS Suction Strainer Replacement The most recent assessment of ECCS NPSil was performed in support ofModification Package 96-132, "ECCS Strainer Replacement," which installed modified ECCS suction strainers in response to NRC Bulletin 96-03 6', Calculations supporting the current design basis (i.e., GENE-637-045-1293) were not revised as a result of this modification since the new suction stainers were shown to have head losses less than or equal to the suction strainers previously installed.
- Item t - Specify whether containment overpressure (i.e., containment pressure above the vapor pressure of the sump or suppression pool fluid) was credited in the ca'culation of available NPSH. Specify the enount of overpressure needed and the minimum overpressure available.
Ronanic:
CNS does credit containment overpressure in the calculation of NPSH, for use with the RHR and CS pumps. The term h,in the NPSH, calculation represents pressure values at various suppression pool temperatures during accident conditions. Analysis for long term DBA-LOCA conditions indicate that there are times that the containment pressure must be above atmospheric in order to maintain the NPSH requirements for the core standby cooling system pumps. The analysis currently in the US AR is based on calculation GENE-637-045-1293.
The relationship between pressures required for ECCS pump NPSH and minimum containment pressure is shown on USAR Figure VI-5-15 and is based on data contained in Table C-1 of calculation GENE-637-045-1293. The amount of pressure needed varies with the temperature of the suppression pool. Five data points are listed in the table below and are used to demonstrate the relationship between pressures required and pressure available.
6 NRC Bulletin 96-03 dated May 6,1996," Potential Plugging of Emergency Core l
Cooling Suction Strainers by _ Debris in Boiling-Water Reactors" l
Attachment I to NLS970226 l iage 7 of 9.
SUPPRESSION - CS PUMP HHR PUMP WETWELL POOL REQUIRED REQUIRED PRESSURE TEMPERATURE PRESSURE PRESSURE (degrees F) (psla) (psia) (psia) 95 6.20 9.06 14.70 152.3 9.24 12.06 21.04-175.4 12.05 14.84 19.50 190.7 14.71 17.49 21.69 195.9 15.81 18.59 22.47 i As overpressure is considered to be the containment pressure above atmospheric (and not the pressure above the vapor pressure) 7', the previous table can be reformatted as follows to show the overpressure needed and the overpressure available.
SUPPRESSION CS PUMP ltIIR PUMP OVERPRESSURE POOL REQUIRED REQUIRED AVAILAHLE TEMPERATURE OVERPRESSURE OVERPRESSURE (degrees F) (psi) (psi) (psi) 95 0.00 0.00 0.00 152.3 0.00 0.00 6.34 175.4 0.00- 0.14 4.80 190.7 0.01 2 79 6.99 I95.9 0. I 1 3.89 7.77 This clarification was provided by the NRC as described in letter to NEI Administrative Pciuts of Contact from D. J. Modeen (NEI) dated December 5, i 1997, "NEl Workshop on NR.C Generic Letter 97-04, ' Assurance of SutTicient !
Net Positive Suction Head for Emergency Core Cooling and Containment Heat
. Removal Pumps'"
r= !
Attachment I to NLS970226 Page 8 of 9 Item 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.
Essaos As previously noted, calculation GENE-637-045-1293 was initiated to support Design Change 91-144 and is the basis for USAR figure VI 5-15, titled " Minimum Containment Pressure for Operation of ECCS Pumps." This calculation contains several assumed conservatisms which assure the minimum containment pressure has been established. ' An overview of these conservatisms is provided below:
- The reactor is initially at 102 percent of rated thermal power per Regulatory Guide 1.49. The .
~ ANS 5.1 decay heat model is used assuming an exposure of 25,700 MWD /st.
- OITsite power is assumed lost at the initiation of the accident and is not restored during the entire event.
- Only one on-site diesel generator is available during the entire event. Consequently, only one CS pump, RilR pump (Containment Cooling mode), and RIIR Service Water Booster pump are assumed available. A heat transfer coefficient value of 177 Btu /(sec-degrees Fahrenheit) is used for the P'RS heat exchanger with this configuration to conservatively represent the 15 percent maximt..n allowable tube pluggt.
The service water temperature used for cooling remains at 90 degrees Fahrenheit throughout the transient.
- At the initiation of the accident the suppression pool has the minimum Technical Specification water volume of 87,650 cubic feet and its temperature is at the Technical Specification limit of 95 degrees Fahrenheit.
To minimize the mass of non-condensable gases in the drywell, the bulk temperature is assumed to be 150 degrees Fahrenheit together with 100 percent humidity at the time of the accident. This assumption is conservative since a smaller condensable gas mass will result in lower containment back pressure for the NPSH evaluation.
The initial containment pressure is O psig to minimize non-condensable gas mass in the containment.
- A containment gas leakage rate of approximately 5 percent per day is assumed, which corresponds to about 10 times the Technical Specification leakage limit.
s c .
Attachment I to NLS970226 Page 9 of 9 The discharge from the RIIR heat exchanger always returns to the pool via the drywell and torus sprays to minimize the containment pressure by spraying cold wer into the containment air space.
. Suppression pool cooling by the RiiR heat exct ager is initiated at 600 seconds into the event.
- During the event the portion of feedwater in the feedwater system that is higher in temperature than the peak pool temperature is assumed to return to the reactor vessel.
- lleat loss from the torus shell surface to the reactor building air space is neglected.
The power required to operate the CS and RHR pumps is added to the containment heat load by increasing ti = water temperature at the pump discharge accordingly.
Further, the Emergency Onerating Procedures (EOPs) include graphs for RilR and CS NPSil limits which are based on available overpressure. Thus, the EOPs provide the necessary information to assure that NPSli requirements are maintained during accident conditions.
In summary, the overpressure requirements have been developed using conservrtisms which assure the minimum containment pressure has been established, and are maintained during accident conditions through the EOPs.
1
a' l' ATTACHMENT'3 LIST OF NRC COMMITMENTS l e
Correspondence No: NLS970226 The following table identifies those actions committed to by the District in- this document. Any. other actions discussed in the submittal represent intended or planned actions by the District. They are described to the NRC for the NRC's information and are not regulatory commitments. Please notify the Licensing Manager at' Cooper Nuclear Station of any questions regarding this document or any associated regulatory commitments.
COMMITTED DATE COMMITMENT OR OUTAGE None.
-n t
l l PROCEDURE NUMBEt 0.42 l REVISION NUMBER 5 l PAGE 9 OF 13 l