ML20092N463

Requests Rev to SER Section 6.2.3,reflecting Max 10 Minute Drawdown Time to Achieve 1/4 Inch of Water Pressure in Secondary Containment post-LOCA.FSAR Will Be Revised

ML20092N463
Person / Time
Site:	Fermi
Issue date:	06/26/1984
From:	Jens W DETROIT EDISON CO.
To:	Youngblood B Office of Nuclear Reactor Regulation
References
EF2-68-233, NUDOCS 8407030166
Download: ML20092N463 (7)

Text

{{#Wiki_filter:_ d b W:yne H. J:ro II Vice Presdent ,Ji Nuclear Operations 2000 Second Avenue t [ fS5fIeDEE'"*** June 26, 1984 l EF2-6d,233 l l Director of Nuclear Reactor Regulation l~ _ Attention: Mr. B. J. Youngblood, Chief l L Licensing Branch No. 1 i U. S. Nuclear Regulatory Commission Washington, D.C. 20355

Dear Mr. Youngblood:

p

Reference:

(1) Fermi 2 NRC Docket No. 50-341 I

Subject:

Secondary Containment Drawdown Time I f SER Section 6.2.3 states, in part, that the SGTS will take six minutes to drawdown the secondary containment' pressure l to minus one-quarter inch of water following a DBA-LOCA with l coincidental loss of all off-site power. The six minute drawdown time was - based on the response to question 042.28 of FSAR Appendix E.5. The analysis that was performed in l the response to question 042.28 assumed a maximum outdoor temperature of 105'F, which was the worst case for the internal environmental pr, file. Ilowever, this is not the most limiting case for ds wdown time. As ambient air temperature' decreases, more mass leaks into_the secondary containment and thus, more mass must be removed to attain design negative pressure. The secondary containment pressure response analysis has j been reperformed using an outdoor temperature of -10'F + (Attachment 1). The analysis shows that in order to draw- -down the secondary containment in six minutes following a { f DB A LOC A, the secondary containment would have to be made unreasonably leak tight and the SGPS would have to operate at or beyond its maximum design flowrate of 4000 CFM. I -11owever, by operating - the SGTS at 3800 CFM, a negative one-quarter inches of water pressure is predicted to be i achieved in ten minutes _ based on the limiting case. At this flow rate, the steady state secondary containment pressure will ne well below minus'one-quarter inches of water. It I should be noted that the drawdown time under t non-environmentally extreme conditions will oe much less than ten minutes. s

4 Mr. B. J. Youngblood June 26, 1984 EF2-68,233 Page 2 The Fermi 2'SER assumes a secondary containment drawdown Jtime of six minutes'(Section 6.2.3). A radiological con-sequence, analysis using cnis time is discussed in SER Section 15.2.3.1. An extrapolation of this analysis was made to assess the effects of-the increase in drawdown time. The post LOCA thyroid dose at ' the site boundary would be increased approximately thirty percent but would reinain well within the guidelines of 10CFR100. This dose is based on very conservative assumptions. The FSAR is being revised to reflect a maximum ten minute drawdown time to achieve minus -one-quarter inch of water pressure in the secondary containment post LOCA. Your expe-dited -review and concurrence is requested. Please coordi-nate a' revision to the SCR with our technical specification reviewer to support the proof and review process. If you have any questions, please contact Mr. O. Keener Earle (313) 586-4211. Sincerely, f / ll / cca Mr. P. M. Byron Mr. M. D. Lynch M Mr. D. Hoffman USNRC, Document Control Desk Washington, D.C. 20555 t . a

f f 11r. B. J. Youngblood June 26, 1984 EF2-68,233 Page 3 bec: F. E. Agosti* L. P. Bregni W. F. Colbert* O. K. Earle W. R. Ilolland R. S. Lenart* E. Lusis P. A. Marquardt T. D. Phillips* 11. Tauber A. E. Wegele Approval Control

• O.

K. Earle (Bethesda Office)* M. S. Rager* NRR Chron File

• With attachments i

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s . - SECONDARY CONTAIMENT PRESSURIZATION DURING UBA LOCA The Standby Gas Treatment System (SGTS) provides. uuf ficient flow to maintain the secondary containment pressure at or below -0.25 inches of water, thus ensuring that any airborne radioactive saaterial in the secondary containiaent is not released to tne surrounding atmosphere without passing ~< 4 througn the SGTS filters. In the event of a DBA-LOCA, loss of off-site power is assumed; consequently, there is a delay period from the start of the event to the activation of the SGTS and the emergency area coolcru. L During the delay period, the secondary containment pressure increases above -0.25 inches of water due to heat generated by eraergency equipment and other sources. Upon initiation of the SGTS and emergency area coolers, a short period of time is required to reduce the secondary containment pres-L sure to a negative pressure at or below -0.25 inches of water. 'The purpose of this calculation is to generate the secondary containment pressure response during a DBA-LOCA and to deteriaine the period of time where the secondary containment L pressure in above -0.25 inenes of water. i The iaethod of analysis, assumptionu and results are described below. METilOD OF ANALYSIS AND ASSUMPTIONS The computer codo !!VAC (Reference 1) wau used to generate. the accondary containment pruusure response. All iaajor assumptions are given below: I 1. No credit was taken for exfiltration froia the accondary I containment. 2. Infiltration to the secondary containment wau included in the pressure response analysis. 3. No heat transfer was allowed to the outdoor atmosphere. 4. lle a t transfer to interior secondary coattainnioint walls, floors and ceilings was included. l S. Ilea t transfer fro,a the torus room to the accondary con ta in.aen t to based on flow through the preusure relieving doors in the corner room basement walls. Only one SGr3 filter train is availabic with a minimum u. voluuetric flow rate of 3000 CPM.

C Y, e ~:m. i 7., Off-site power is lost at the start of the DBA-LOCA event. 8. The activation of the SGTS is delayed by 33 seconds and the activation of the emergency area coolers is delayed by 38 seconds. 9. The RIIR pump rooms and the core spray and RCIC pump rooms in the reactor building sub-basement are treated separately from the main secondary containment volume. j These rooms have their own emergency coolers to handle emergency equipment and lighting heat loads. n Because the heat loads and cooling are confined to c .s partially enclosed volumes at the very bottom of the secondary containment, the area coolers will absorb the 3 heat loads within the confines of the corner rooms. / 10. The heat loads from the RIIR, core spray and RCIC pump rooms will not affect the main secondary containment volume prior to the initiation of the area coolers. The RIIR pumps are activated 13 seconds after the start of the DBA-LOCA event. The emergency coolors are activated at 38 seconds. For the heat loads to affect the main volumo, the pumps, piping, and subsequently the corner room atmospheres must heat up. After the corner room atmosphores have heated up, the only mode of heat tranfor to the main volume is by natural con-voction. Considering that natural convection is a rather slow process, no significant heat transfer to the main secondary containmont volume from the corner rooms is expected during the 25 seconds from the intiation of the R!in pumps to the initiation of emergency cooling. 11. An outdoor temperature of -10*F was used in the analysis. Results The secondary containment response due to a DBA-LOCA is shown in Figure 1. During the first 33 seconds, the pres-sure increases to a slightly positive valuo. With the acti-vation of the SGPS at 33 seconds and the activation of the area coolers at 38 seconds, the prosaure decreases to near atmospheric. At 40 seconds. pressure relieving doors on the common wall betwoon the torus room and the corner rooms open and allow l heated torus room air to entor the rest of socondary con-tainment. Thin stop input of heat into the secondary con-tainment appearn as a sharp pressuro spike on Figure 1. i ~ } h e D

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