NRC-97-0143, Provides 90 Day Response to GL 97-04, Assurance of Sufficient Net Positive Suction Head for ECC & Containment Heat Removal Pumps

Provides 90 Day Response to GL 97-04, Assurance of Sufficient Net Positive Suction Head for ECC & Containment Heat Removal Pumps

ML20198B165
Person / Time
Site:	Fermi
Issue date:	12/30/1997
From:	Gipson D DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-97-0143, CON-NRC-97-143 GL-97-04, GL-97-4, NUDOCS 9801060216
Download: ML20198B165 (8)

Text

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Douglas R. Gipson Senior Vice PresMent,Nmlear Generation fermi 2 61m North Dixie !!wy, Newport. Michigan 45166 Tel111rs3201 rat al3AscAla s

Detroit Edison December 30,1997 NRC-97-0143 U. S. Nuclear Regulatory Commission Attn.: Document Control Desk Washington, D. C. 20555

References:

1)

Femti 2 NRC Docket No. 50-341 NRC License No. NPF-43 2)

NRC Generic Letter 97-04: " Assurance of Sufficient Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps", dated October 7,1997 3)

Detroit Edison Letter to NRC," Detroit Edison's 30-Day Response to NRC Generic Letter 97-04", NRC-97-0114, dated November 5,1997 4)

NRC Inspection Report No. 50-341/97011, dated October 29, 1997.

Subject:

Detroit Edison's 90-Day Response to NRC Gen:ric Letter 97-04 7

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In Reference 2, the NRC requested 30 day and 90 day responses to provide the information outlined in the " Requested Information" Section of the Generic Letter (GL) 97-04. Reference 3 provided Detroit Edison's 30 day response and committed ~ N /

Detroit Edison to provide a 90 day response. Detroit Edison is a participant in the Boiling Water Reactor Owners' Group (B'VROG) Net Positive Suction Head (NPSH) Committee which will review current BWR industry NPSH calculation methodology and recommend a consistent approach for adequately addressing NPSH issues. This letter provides Detroit Edison's 90 day response to Generic Letter 97-04 which is based on the format recommended by the BWR Owners' Group NPSH Committee. No commitments are being made by this letter.

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9901060216 971230 PDR ADOCK 05000341 PDR A DTE Energy Company p

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USNRC NRC-97-0143 Page 2 Detroit Edison was requested to review the current design-basis analyses used to determine the available NPSil for the Emergency Core Cooling (including Core Spray and Residual lleat Removal) and Containment Heat Removal pumps that meet either of the two criteria given in the " Requested Information" Section of GL 97 04.

Based on this review, Detroit Edison was requested to provide responses to the five questions outlined in the " Requested Information" Section of GL 9b04. The enclosure to this letter provides detailed Detroit Edison response to these five questions, as reauested by GL 97-04.

Additionally, as part of a recent Engineering and Technical Support inspection, the

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NRC reviewed the calculations related to Residual Heat Removal (RHR) and Core Spray strainer head loss and NPSH requirements. This NRC inspection is documented in the inspection Report 50-341/97011 (Reference 4). The subject inspection report stated that the calculations provided sufficient justification to show adequate net positive suction head available for the RHR and core spray pumps under all modes of operation and concluded that there was adequate net positive suction head available for the RHR and core spray pumps.

If you have any questions, please contact Mr. Norman K. Peterson, Director, Nuclear Licensing at (313) 586-4258.

Sincerely, f

Enclosure cc:

A. B. Beach B. L. Burgess G. A. Harris A. J. Kugler

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1, DOUGLAS R. GIPSON, do hereby affirm that the foregoing statements are based on facts'and circumstances which are true and accurate to the best of my knowledge.

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DOUGLAlfR. GIPSON Senior Vice

• resident dl/KbOI997 before me On this-day of 3 personally appeared Douglas R. Gipson, being first duly sworn and says that he

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- Enclosure to NRC-97-0143 Page1 j)ctroit Edison's 90-Day Response to NRC Generic Letter 97-04.

" Assurance of Sufficient Net Positive Suction Head for Emereeney Core Cooline and Containment IIcat Removal Pumns". dated October 7.1997

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Detroit Edison has reviewed the current design basis analyses used to determine the available NPSH for the Emergency Core Cooling (including Core Spray and Residual Heat Removal) and Containment iicat Removal pumps at Fermi 2 that meet either of the following two criteria: (1) pumps that take suction from $e containment sump or suppression pool following a design-basis Loss of Coolant Accident (LOCA) or secondary line break, or (2) pumps used in " piggyback" operation that are necessary for recirculation cooling of the reactor core and containment (i.e., pumps that are supplied by pumps which take suction directly from the sump or suppress' en pool).

7 Based on this review D.:troit Edison's detailed response to the five questions 3

ou6ined in the " Requested Information" Section of the Generie Letter 97-04 is given below,in the format recommended by the BWR Owners' Group NPSH Committee:

NRC GL 97-04 Ouestion No.1: "Specify the general methodology used to calculate the head loss associated with the ECCS Suction strainers."

Detroit Edison Response:

As diserssed in the Fermi 2 Updated Safety Analysis Report (UFSAP.), the head loss through the ECCS suction strainers is computed based on the assumption that ont y 50 % of the flow area is available, or 50 % plugging of the strainers is assumel The basis for this assumption is the original Chicago Bridge and Iron Company's ECCS Suction Strainer Pressure Drop Study conducted by the Colorado State University during 1973 - 1974, which verified that the computed value for the pressure loss through 50% clogged strainer is reasonable.

The equation used for computing the Net Poitive Suction Head Available (NPSHs) foi various accident scenarios pertaining to the operation of the Emergency Core Cooling and Containment Heat Removal pumps is the standard formula from " Cameron Hydraulic Data," is as follows:

NPSH = h, + h,, - h,, - h,,

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I 4

Enclosure to NRC 97-0143 Page 2 :

where:

NPSH = Net Positive Suction Head Available in feet ofliquid (waten).

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h, = absolute pressure (in feet ofliquid) on the surface of the liquid supply level corrected at the inlet water temperature.

(Note: Detroit Edison does not take credit for containment overpressure and therefore, the above term is equivalent to the atmospheric pi, tre in absolute units.) -

h,, = Static height in feet at which the liquid supply level is abt.e the pump datum.

(Note: The static height is based on the minimum suppression pool / torus

- s.cr level above the centerline of the pump suction. The assumed water level in the suppression pool is equivalent to the ninimum level provided in the Fenni 2 Technical Specifications, Section 3.6.2.1.a.l.)

h,, = Head in feet corresponding to the vapor pressure of the liquid at the e

temperature it is being pumped.

(Note: The subject temperature is the highest temperature attained in the accident scenario being analyzed.)

h,, = All suction losses in feet including entrance losses and friction losses e

through pipe, valves fittings, etc..

(Note: The suction losses in the computations include losses through the existing ECCS suction strainer assuming 50% plugging as stated eerlier.)

NRC GL 97-04 Ouestion No. 2: " Identify the required NPSH and the avaliable NPSH."

Detroit Edison Response:

The required NPSH is specific to each pump type and is dependent on the flow rate ihr each accident scerario beiag evaluated. Since Detroit Edison is not taking any c'ontainment overpressure credit, the available NPSH is primarily dependent on the piping configuration and the suppression pool temperature for the particular scenario being evaluated.

Enclosure to NRC-97-0143 Page 3 The required NPSil and availaole NPSil for the limNng cases for pumps taking suction from the suppression pool following a DBA LOCA are provided in the table below:

Pump Worst Case Scenario Required NPSH Available NPSH (ft)

(11)

Core Spray Accident System 17 20.4 (South Loop Injection At Rated Pump D)

Core Spray (Long Term)

RIIR Pump B Containment Cooling 13 17.2 Mode (Drywell Spmy)

RilR Pump B Suppression Pool 13 17.2 Cooling Mode

(~orus Spray)

L Note 1: Core Spray System Pumps: The limiting case for the least NPSH available for the various accident scenarios analyzed is for the South Loop Core Spray Pump D taking suction from the Suppression Pool with the pump discharging into the Reactor Pressure Vessel during the long term accident system injection mode at rated flow.

Note 2: Although the four Cere Spray pumps were manufactured similarly, their individual characteristic curves have slight differences. For each mode the most conservative pump, with highest NPSH required (Pump D for South Loop and Pump C for North Loop), was used for the analysis.

Note 3: Drywell Cooling ivfode and Suppression Pool Cooling Mode of the RHR System Pumps: The limiting cases for the least NPSH available for the variots accident scenarios analyzed are those with one RiiR system Pump operating with the Heat Exchanger in sersice, taking suction from the Suppression Pool with the pump discharging into the drywell spray loop nozzles or the suppression pool spray sparger, during the long term accident system injection rnode at rated flow.

Enclosure to NRC 97-0143 Page 4

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Note 4: The computations for the NPSH available utilizes the minimum suppression pool water level provided in the Fermi 2 Technical Specifications.

NRC GI,97-04 Ouestion No. 3: "Specify whether the current design-basis NPSil analysis differs from the most recent snalysis reviewed and approved by the NRC for w hich a safety evaluation w as issued."

Detroit Edison Response:

The current design basis NPSil analysis for Fermi 2 does not differ from the h

most recent NPSil analysis reviewed and approved by the NRC during the initial licensing of Fermi 2. This analysis was found acceptable by the NRC in Section 6.2.2 of the Fermi 2 Safety Evaluation Report NUREG- 0798, dated July 1981.

Additionally, as part of a comprehensive onsite Engineering and Technical Support inspection completed on September 22,1997, the NRC reviewed the

}5 calculations related to RHR and core spray strainer head loss and Net Positive M.

Suction 11ead requirements. This NRC Engineering and Technical Support inspection is documented in the Inspection Report 50-341/97011 dated October 29,1997 (Reference 4). Section E2.6.b " Observations and Findings" of the subject inspection report states that the calculations provided sufficient justification to show adequate net positive suction head available for the RliR and core spray pumps under all modes of operation and concluded that there was adequate net positive suction head available for the RHR and core spray pumps.

NRC GI,97-04 Ouestion No. 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."

Detroit Edison Response:

Detroit Edison does not take credit for containmerit overpressure, i. e.,

containment pressure above atmospheric pressure, at Me calculations show that the available NPSH is greater than the required NPbH in all the accident scenarios anaiyad for the ECCS pumps taking suction from suppression pool.

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f Enclosure to NRC-97-0143 Page 5 NRC GL 97-04 Ouestion No. 5: "When containment overpressure is credited

. In the calculation of available NPSil, confirm that an appropriate containment pressure analysis was done to establish the minimum containment pressure."

Detroit Edison Response:

This question is not applicable to Fermi 2 as Detroit Edison does not take credit for containment overpressure.

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