ML20039F773
| ML20039F773 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 01/08/1982 |
| From: | Tauber H DETROIT EDISON CO. |
| To: | Kintner L Office of Nuclear Reactor Regulation |
| References | |
| EF2-55-988, NUDOCS 8201130331 | |
| Download: ML20039F773 (5) | |
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'h YE44=< a January 8, 19 g 9 g ' EF2 - 55,988 Mr. L. L. Kintner U. S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation Division of Licensing Washington, D. C. 20555
Dear Mr. Kintner:
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. responses to NRC Staff questions received by Detroit' Edison regarding the Fermi 2 seismic reassessment report. Sincerely, / r/ W / Attachment .f g cc: Mr. B. Little II l hg 9 AD o PDR
- ~ Attachment to8 EF2-55,988 QUESTION #1 RSB reviewed the Fermi 2 seismic 1 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 verious systems required-for safe shutdown, except for residual heat removal-(RHR). .For-RHR the applicantilicted' Division II'since the common suction _line isolation valvest are supplied by Division l II. But in table 5 2-1 of the-report, the RHR service water (SW) Division II to support RHR Division II is i not included. We require' additional clarifications i 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 I & II DC power supply (batteries, which have been generically qualified). The Division I & II loops of the RHR system are con._ nected by a 20" diameter header just downstream of the 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 utilices the Division I RHR heat exchanger, the corresponding Division I side of the RHRSW system was also reassessed. See attached sketch for further clarification. 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 hi n pressure. E This results in a rise of suppression pool temperature. The statement about torus cooling not 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 i discussion dealing with torus cooling should be r revised to accurately reflect what. actions are required. 4 J 4
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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-i 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 344 F coolant temperature. In accordance with Tech. Spec. limits,_the cooldown rate-is to be kept at 1000 F/HR, providing approximately 2 hours 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, conser-vative heat balance shows a temperature rise of 790 F without tcrus cooling and 660 F with 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
During 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 j with a seismic event substantially larger than asLthe-DBE. Detroit Edison was especially counselled and directed to concentrate their efforts on evaluation of-highest stressed components and on. critical elements sto assure-that a single heat removal path is available. .. ~.,
The' reassessment.was to be based on Detroit Edison's judgement to select structures, systems and components based on previous analyses and test results conducted for the Design Basis Earthquake criteria. In crder to complete the reevaluation in an orderly and logical fashion, the cold shutdown path was defined by iden-tifying the scenario 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 tofgeneric design pro-vided for the DBE. For large-bore piping, the'reeva-luat.2n 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. I e i 1
Attachment to: EF2-55,988 QUESTION #1 CLARIFICATION SKETCII DIV.[ n DN H RPV ( l... L.. _ / DIV I-Ac "';l, OlV.it-AC FOO9 ~ } F608 . CROSS " TIE 3 g DIV. H-DC / 1 F008 FOIO g l 20"l HEADER I i 1 f b DIV. I DIV. E RHR RHR n' HTX. HTX. p s- - h- -g- .-{ pJ p/ rd t' DIV. I DIV.E RHRSW RHRSW FLOW PATH . - - -.}}