ML20041C878

Forwards Revised Responses to Questions Re Seismic Reassessment Rept for Review of Equipment Necessary to Achieve Safe Shutdown & Cooldown

ML20041C878
Person / Time
Site:	Fermi
Issue date:	02/24/1982
From:	Tauber H DETROIT EDISON CO.
To:	Kintner L Office of Nuclear Reactor Regulation
References
EF2-55-988, NUDOCS 8203020628
Download: ML20041C878 (4)

Text

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r3 Mr. L. L. Kintner U. S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Licensing Washington, D. C. 20555 4

Reference:

Enrico Fermi Atomic Power Plant, Unit 2 NRC Docket No. 50-341

Subject:

Fermi 2 Seismic Reassessment:

Review of Equipment Necessary To Achieve Safe Shutdown and Cooldown Attached are our revised responses to NRC Staff questions received by Detroit Edison regarding the Fermi 2 seismic reassessment report.

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EF2-55,988 i

QUESTION #1 RSB reviewed the Fermi 2 seismic reassessment report for completness of the list of shutdown equipment spe-cified by the applicant.

In table 5.2-1 of the report titled " Principal and Auxiliary Systems Required for Safe Shutdown ~and Cooldown", the applicant listed only Division I of the various systems required for safe shutdown, except for residual heat removal (RHR).

For RHR the applicant listed Division II since the common i

suction line isolation valves are supplied by Division II. But in table 5.2-1 of the report, the RHR service water (SW) Division II to support RHR Division II is not included. We require additional clarifications from the applicant with regard to exclusion of RHR SW Division II from the list.

RESPONSE

The RHR Shutdown cooling outboard. isolation valve is powered from the Division II DC power supply l

(batteries, which have been generically qualified).

i The Division I & II loops of the RHR system are con-nected by a 20" diameter header just downstream of the i

shutdown cooling suction isolation valves.

Therefore, flow can be diverted to the Division I RHR heat exchanger through the use of this common header.

Downstream of the RHR pumps, the Division I loop was selected for the flow path to be reassessed. Because this path utilizes the Division I RHR heat exchanger, the corresponding Division I side of the RHRSW system was also reassessed.

See attached sketch for further clarification.

l QUESTION #2 In table 5.1.1 of the report a scenerio for seismi-cally induced loss of offsite power is given.

The reactor is isolated and SRVs open on high pressure.

This results in a rise of suppression pool temperature. The statement about torus cooling not i

being required is incorrect.

In a telecon with the aplicant on November 13, 1981, the applicant agreed that the statement was incorrect. The section of the discussion dealing with torus cooling should be revised to accurately reflect what actions are required.

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RESPONSE

From a review of the shutdown scenario presented in table 5.1-1 of the Supplementary Seismic Reevaluation Report EF2-53,332, Rev. 1 dated July 15, 1981 it indi-cates that suppression pool cooling is not essential to safely shut the plant down, utilizing the RHR shutdown cooling mode with one heat exchanger.

However, the Division I heat exchanger is available for suppression pool cooling following the reactor scram until the vessel is sufficiently depressurized (to below 110 PSIG) to clear the interlock for RHR Shutdown Cooling Mode Operation.

The 110 PSIG reactor vessel pressure corresponds to about 344c F coolant temperature.

In accordance with Tech. Spec. limits, the cooldown rate is to be kept at 1000 F/HR, providing approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> of vessel depressurization via the SRVs and the RCIC operation for inventory control.

A heat balance for this shutdown mode with and without suppression pool cooling was performed to determine the torus temperature rise.

This simplified, concer-vative heat balance shows a temperature rise of 79 F without torus cooling and 660 F wit.k torus cooling provided during vessel depressurization.

QUESTION #3 During the telecon we were also told that the seismic reassessment analysis was done only for one division of each essential system.

The applicant should provide justification for analyzing only one division of each essential system.

RESPONSE

Euring the initial discussions with the NRC Staff and management representative, particular emphasis was placed on the need for a " reassessment" to be con-ducted within a 6 week time span to provide additional information regarding the Fermi 2 plant's capacity and seismic design margins to safely shut the unit down with a seismic event substantially larger than as the DBE.

Detroit Edison was especially counselled and directed to concentrate their efforts on evaluation of highest stressed components and on critical elements to assure that a single heat removal path is available.

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The reassessment wa.s to be based on Detroit Edison's judgement to se 2,

structures, systems and components based on previ.

's analyses and test results conducted for the Design Bae's Earthquake criteria.

In order to complete the reevaluation in an orderly and logical fashion, the 7old shutdown path was defined by iden-tifying t.

ocenario in Table 5.1-1 and then selecting the equipment required to function.

In general, the functional and structural similarity of the divisional equipment allows the conclusion of the reassessment of one division to be applied to both.

In those areas where actual geometry differences exist, such as pipe routing, electrical tray, conduit and instrument tubing, a generic analysis was undertaken to establish the seismic margins in respect to generic design pro-vided for the DBE.

For large bore piping, the reeva-luation resulted in actual reduction of seismic stress, hanger loads and equipment nozzle loads, due to very conservative application of damping (0.5%) in the original analysis for the DBE.

The latter results were confirmed via an NRC audit of the mechanical equipment and large bore piping reevaluation.

(Ref.

NRC letter dated 9/3/81 from L. L. Kintner.)

The reevaluation identified certain components that require corrective actions as listed on Table 5.4-1 of Report No. EF2-53,332, Rev.

1.

It was not our intent to limit these corrective actions to only those com-ponents located in Division 1.

Table 5.4-1 is intended to be a generic listing of components that require corrective actions, i.e.

it includes 4 diesel generator fuel oil storage tanks serving both divisions.

Attachment to:

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