ML20198J876
| ML20198J876 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 01/05/1998 |
| From: | Drawbridge B NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| AR-97024647, GL-97-04, GL-97-4, NYN-98001, NUDOCS 9801140232 | |
| Download: ML20198J876 (7) | |
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(603) 474-9521 The Northeast Utilities System January 5,1998 Decket No. 50-443 NYN-98001 AR 97024647 United States Nuclear Regubtory Commission Attention: Document Control Desk Washington, DC 20555 0001 Seabrook Station 90-Day Response to Generie Letter 97-04 This letter provides North Atlantic Energy Service Corporation's (North Atisntic) 90-day response to Generic 1.etter (GL) 97 04, " Assurance of Sufficient Net Positive Suction licad for Emergency Core Cooling and Containment IIcat Removal Pumps." The response provides the requested information regarding the adequacy of the net positive suction head available for emergency core cooling and containment heat removal pumps.
Should you have any questions regarding this response, please contact Mr. Terry L. liarpster, Director of Licensing Services, at (603) 773 7765.
Very truly yours, NORTil A. NTIC ENER SERVICE CORP.
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13ruce L. DIawbridge
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Director-Services i
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II. J. Miller, Region _I Administrator f
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C. W. Smith, Project Manager R. K. Lorson, NRC Senior Resident inspector 1
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STATE OF NEW HAMPSlilRE Rockingham, ss.
January 5,1998 s
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I Then personally appeared before me, Bruce L. Drawbridge, Director - Senices. North Atlantic
- Energy Senice Corporation that he is duly authorized to execute ux! file the foregoing information in the name and on the behalf of Nov.h Atlantic Energy Senice Corporation and that the statemcots therein arc truc to the best of his knowledge and belief.
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Susan J. MesN, Notary Public My Commission Expiresi December 22,19%,
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Response b USNRC Gen:ric Lett:r 97-04
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" Assurance of Sufficient Net Positive Suction llead for Emergency Core Cooling and Containment Ileat Removal Pumps" i
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' Introduction Generic Letter (GL) 97-04, " Assurance of Sufficient Net Positive Suction Head for Emergency Co;c Cooling and Containment lleat Removal Pumps," was issued to request licensecs to confirm the adequacy of the net positive cuction head available for emergency core cooling and containment heat removal pumps. His response provides the requested information for Scabrook Station
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Response to Reauested Information item 1:
"Specify the general methodology used to calculate the head 8e associated with the ECCS suction strainers."
EnPRIE nc Alden Research Laboratories of the Worcester Polytechnic Institute peiformed an extensive hydraulic model test program of the containment recirculation sumps. The objective of the testing program was to verify the adequacy of the containment sump design by atsuring the absence of severe vortices or other flow irregularitics that could potentially affect the operation of the Emergency Core Cooling System (ECCS) and Containment Building Spiay (CBS) Pumps during post Loss of Cooling Accident (LOCA) ECCS operation.
The model was designed and constructed to a uniform scale of 1:4 to include the sump and areas adjacent to the containment building. The structures lowted in the vicinity of the sump that could influence pump flow were included in the model, up to the maximum potential water level in the Containment Building following a LOCA. The tests incorporated various pump and flow combinations under difTerent postulated restrictions, such as screen blockage (up to 50%
blockage). Prior to projecting the model results to the actual containment sump performance, detailed studies were conducted concerning the possible scale effects of modeling vortices. To further assure the Scabrook Station sump design was acceptable, additional testing was performed utilizing higher fluid temperatures and higher flow rates (velocitics) in the model than indicat xl by the Froude scaling criteria.
The hydraulic model study was documented in Alden Research LaboratoryAVorcester Polytechnic Institute Report entitled " Investigation of Vortexing and Swirl Within a Contaimuent Recirculeion Sump Using a liydraulic Model - Scabrook Nuclear Power Station" dated January 1980.
Additionally, Alden Research Laboratory evaluateu the efTect of pipe swirling flows on pipe friction losses. This study was documented in Alden Research LaboratoryAVorcester Polytechnic Institute Report titled "The EfTect of Swirling Flow on Pipe Friction Losses" dated February 1980. These reports were transmitted to the USNRC to respond to RAI 440.44, via PSNH letter SBN 197, dated November 1981.
The losses measured in the hydraulic model of the Seabrook Station containment sump accounts for the etTects that would alter the magnitude of the pressure to thirty pipe diameters downstream 1
Response to USNRC Gencric Lett:r 97-04
" Assurance of Sufficien! Net Positive Suction llead for Emergency Core Cooling and Containment IIeat Removal Pumps" from the entrance. He effect of the screen loses and its swirl (rotational flow pattems) are includ:d in the Residual lleat Removal (RiiR) and CBS pump NPSH calculations.
i ne available NPSil for the purups taking suction from the containment sump was calculated based on the following equation:
NPSilA = P, + P. - P, 1
where.
P. = Pressure at pump suction from the computer flow model P. = 14.69 psia P, = Vapor pressure at saturation The pressure at the pump suction (P. ) was calculated based on a steady state computer simulation of system operation. The computer simulation took into account the minimum post LOCA water level in the containment, suction line losses including entrance losses, piping and pipe component losses, sump screen losses (assuming 50% screen blockago, and friction losses attributed to swirl.
Piping roughness was also taken into consideration and included in the model. The available NPSil was calculated using maximum design basis flows for both the CBS and RHR pumps.
He most limiting available NPSil for the pumps that are " piggy backed" ofTof the RilR pumps occurs prior to the realignment to ECCS cold leg recirculation. The RilR discharge provides the suction source for the Safety injection, (SI) and Charging (CS) pumps during the ECCS Recirculation phase, thus providing a greater available NPSH to cach pump than is available during ECCS i Vection. The minimum available NPSH has been calculated based on the Refueling Water Storage Tank (RWST) environmental conditions and assuming an empty RWST. The minimum NPSil for the Si pump was calculated using the same computer flow model used to calculate the CBS and RilR performance during ECCS injection. Maximum system flows were used to determine the most limiting available NPSH. The available NPSH for the CS pumps was calcule. icd assuming maximum injection flow rates. The calculations accounted for minimum RWST level and atmospheric pressure, suction line losses including entrance losses, piping and pipe compona.. losses. Consideration of piping roughness was also included in the calculation.
Resoonse to Reauested Information item 2:
" Identify the required NPSH and the available NPSH."
Bnponsgr The most limiting pump alignment for available NPSH for the CBS and RHR pumps occurs during ECCS recirculation. The RHR and CBS pumps share a common suction flow path, the Containment Sump, during this mode of operation. The available NPSH was calculated f
- assuming maximum design basis flows, ia order to maximize fnction losses, for both the CBS and RHR pumps. He calculation further assumes a containment sump temperature of 212' Fahrenheit. The guidance provided in NRC Regulatory Guide 1.1 (Safety Guide 1), " Net Positive 2
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,7, Response t2 USNRC Gen:ric L:tt:r 97-04
" Assurance of Sufficient Net Positive Suction llead for Emergency Core Cooling and Containment IInt Removal Pumps" Suction Head for Emergency Core Cooling and Containment Heat Removal System Pumps" was follow.d in calculating the available NPSH. NUREG-0800, Standard Review Plan Section 6.2.2 further clarified Regulatory Guide 1.1 by stating that the analysis should be based on the assumption that the containment pressure equals the vapor pressure of the sump water. No increase in containment pressure frc.n that present prior to the postulated accident was credited in the Seabrook Station analysis, i.e.,
atmospheric pressure was assumed, no containment overpressure was used in the calculation.
The most limiting pump alignment 7egarding available NPSH for the Si and CS pumps occurs prior to the switchover to ECCS recirculation operation when the pumps are taking suction from the Refueling Water Storage Tank (RWST). The calculated available NPSH is the bounding case (lowest NPSH available). During ECCS recirculation operation, both the Si and CS pumps are supplied from tha discharge of the RHR pumps. ECCS recirculation ope:ation is not the limiting case for these pumps.
The required NPSH and the limiting available NPSH for the pumps are listed below:
Pumps Required NPSH Available NPSH (ft)
(ft)
CBS P-9A/B, Containment Building Spray Pumps 20.5 21.04 RH-P-8A/B, Residual Heat Removal Pumps 19.5 22 CS-P-2A/B, Charging Purnps 28 40-SI-P-6A/B, Safety injectic.n Pumps 16 40.5 Resnanse to Reauested Information Item 3:
"Speify 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."
Response: The current design basis NPSH analysis does not differ from the most recent analysis reviewed and approved by the NRC for which a safety evaluation was issued. The most recent Staff approved analysis was evaluated in the Seabrook Station SER, March 1983.
Response to Reauested Information Item 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 ofoverpressure needed and the minimum overpresoarc available" Empomg_ As described in the response to question 2, no containment overpressure was credited in the calculation of available NPSH. The calculation of the available NPS3 is consistent with the guidance provided)n NRC Regulatory Guide 1.1 (Safety Guide 1), " Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal System Pumps" and NUREG-0800, "Standaro Review Plan" Section 6.2.2.
NUREG-0800 further clarifies Regulatory Guide 1.1 by stating that the analysis should be based on the assumption that the containment pressure equals the vapor pressure of the rump water. No increase in containment pressure from that present prior 3
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Respose to USNRC Generic Lett:r 97-04
" Assurance of Sufficient Net Positive Suction llead for Emergency Core Cooling and Containment Ileat Removal Pumps" 9
to the postulated accident was credited in the Seabrook Station analysis (i.e., atmospheric pressure was assumed, no containment overpressure was used in the calculation.)
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Response to Reauested Information item 5:
"When containment overpressure is credited in the calculation of available NPSH, condrm that mi appropriate containment pressure analysis was done to establish the minimum containment pressure."
BCEP2pg_ As discussed above in the responses to questions 2 and 4, no containment overpressure was used to calculate the available NPSil for the pumps that take suction from the containment sumps.
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