ML20198P904
| ML20198P904 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/31/1997 |
| From: | Hammer M NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-04, GL-97-4, NUDOCS 9711120050 | |
| Download: ML20198P904 (6) | |
Text
Northern states Power Company Monticello Nuclear Generating Plant l
2807 W. County Road 75
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Monticello. MN 55362 l
October 31,1997 Generic Letter 97-04 US Nuclear Regulatory Com'aission Attn.: Document Control Desk Washington, DC 20555-0001 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Response to Generic Letter 97-04 Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps On October 7,1997, the Nuclear Regulatory Commission (NRC) issued Generic l.etter 97-04 regarding an issue which may have generic implications for Emergency Core Cooling Sptem pumps. The generic letter required a 30 day written response indicating: (a) whether or not the requested iaformatior, would be submitted, and (b) whether or not the requested information would be submitted within the requested time period. By this letter, Northern States Power Company (NSP) is fulfilling the P
required 30 day response by providing the requested 90 day information.
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For the Monticello Nuclear Generating Plant, the NPSH issues now identified in j$.
Generic Letter 97-04 were reviewed by the NRC prior to their issuance of 7'fC 6 )
Amendment No. 98 to the Monticello Facility Operating License on July 25,1997.
The information requested by the generic letter was provided to the NRC in submittals dated June 19,1997, July 16,1997, and July 21,1997 associated with License Amendment No 98, and a September 22,1997 letter which provided follow-up information. This infotmation is also provided in Attachment 1 to this letter. This letter therefore satisfies both the 30 and 90 day requested actions of Generic Letter 97-04.
Monticello is participating in a newly-established BWR Owner's Group (BWROG) effort which has the objective of reviewing current BWR industry NPSH calculational methodology. Should the BWROG recommend different NPSH calculational methodologies than NSP used to support License Amendment 98, NSP will evaluate
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9711120050 971031 PDR ADOCK 050002 '3
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e those differences. If the differences are significant, they will be incorporated into the NPBH calculation methodology for the final resolution of NRC Bulletin 96-03,
" Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling-Water Reactors."
This letter contains no new NRC ' commitments, nor does it modify any prior commitments. Please contact Samuel I. Shirey, Sr. Lir nsing Engineer, at (612) 295-1449 if you require further information, k
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Michael F. Hammer Plant Manager Monticello Nuclear Generating Plant attachments:
Affidavit to the US Nuclear Regulatory, Commission (1)
Generic Letter 97-04 Requested InformatiJn b
UNITED STATES NUCLEAR REGULATORY COMMISSION 6
l NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263 Response to Generic Letter 97 Assurance of Sufficient Net Positive Suction Head for Emergency Core Cool;ng and Containment Heat Removal Pumps Northern States Power Company, a Minnesota corporation, by letter dated October 31, 1997, provides the requested response to NRC Generic Letter 96-06, " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps' dated October 7,1997. This letter contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY By MJ/M4Mk/
Michael F. Hammer Plant Manager Monticello Nuclear Generating Plant On this 31 day ofOc.xobe c tan before me a notary pubiic in and for said County, personally appeared Michael F. Hammer, Plant Manager, Monticello Nuclear Generating Plant, and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and belief the statements made in it are true and that it is not interposed for delay.
- Sarnuel I. Shirey Notary Public - Minnesota
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~I buEU. SHIREY Sherburne County
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S C MINNESOTA l
_y;f,,NOTD" *' Uygg; My Commission Expires January 31,2000 Lg o
Attachm:nt 1 G:n:ric L tter 97-04 Requist:d inferm tion 4
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(1)'
Specify the general methodology used to calculate the head loss associated with the ECCS suction strainers.
Response
The head loss associated with the ECCS suction strainers was calculated using an empirical formula developed by the strainer manufacturer. The strainer manufacturer's empirical formula was based on the results of clean strainer head loss tests conducted on a prototype strainer, Monticello's current NPSH and ECCS suction strainer head loss calculations do not account for debris loading issues identified in NRC Bulletin 96-03.
(2)
Identify the required NPSH and the available NPSH.
Response
The required NPSH is specific to each pump type and is dependent on the flow rate at the time being evaluated. The available NPSH is dependent on the containment ovcrpressure credited, number of pumps operating, piping configuration and the suppression pool temperature at the time being evaluated. Therefore, the required NPSH and available NPSH for the limiting cases for pumps taking suction from the suppression pool following a DBA LOCA are provided in the table below.
Pump Time (seconds)
Required NPSH (ft)
AvailaNe NPSH (ft)
- 600*
27 28.7-B P: M*
600*
27
-29.1 B Core Spray" 33,535" 29 30.5 BRHR" 33,535" 26 31.3 The limiting short-term case for NPSH available assumes a single failure of the LPCI Loop Select Logic to select the unbroken reactor recirculation loop. In this case all four RHR pumps are assumed to be injecting into the broken recirculation loop. The RHR pumps and the core spray pumps are at maximum flow conditions with no credit for operator action to throttle their flow. Information for the RHR and core spray pumps with the least available NPSH is provided, other pumps are not limiting as they have more available NPSH.
The limiting long-term case for NPSH available assumes a single failure of a diesel generator and loss of offsite power. In this case ene RHR pump and one core spray pump with flow throttled to Technical Specification values is assumed.
Information for the B RHR pump and B core spray pump is provided since they have the least available NPSH, other pump combinations are not limiting as they have more available NPSH.
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Attachm:nt 1 G:n:ric Lctt:r 97-04 R;qusct d Inform tian (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.
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 evm. A was issued. The current design basis NPSH analysis was provided as Exhibit E of the June 19,1997, letter associated with l.icense Amendment 98 and a September 22,1997, letter which provided follow-up information. A safety evaluation was issued for License Amendment 98 on July 25,1997.
(4)
Specify whether containment overpressure (i.e. containment pressure above the i
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.
Response
Containment overpressure was credited in the calculation of available NPSH. The amount of overpressure needed (amount credited in the calculation of available NPSH) and the minimum overpressure available as a function of time after accident initiation is provided in the table below. Credit for the containment overpressure needed values listed below was approved in the Safety Evaluation Report dated July 25,1997, fcr Licence Amendment No. 98.
Time (seconds)
Containment Overpressure Minimum Containment
- Needed (psig)
Overpressure Available (psig)10-600 2.0 2.34 600 -2,000 2.0 4.60 2,000 -10,000 4.0 4.53 10,000-16,000 5.3 5.67 16,000 - 55,000 6.1 6.21 55,000 - 69,000 5.6 5.71 69,000 -85.000 5.0 5.10 85,000 -110,000 4.2 4.30 110,000 -140,000 3.3 3.49 140,000-200,000 2.3 2.37 200.000 - 330,000 1.0 1.12 2
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Attachm:nt 1 Gsn:ric Lctter 97-04 R:qu;;ted Inf rmati:n
-(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
The containment response analysis which provided the containment pressures for the calculation of available NPSH utilized inputs and assumptions that minimized containment pressure. See Exhibit D of the June 19,1997, letter associated with License Amendment 98.
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