NRC Generic Letter 1989-22
UNITED STATESt BNUCLEAR REGULATORY COMMISSIONWASHINGTON, D. C. 20555October 19, 1989TO: ALL LICENSEES OF OPERATING REACTORS AND HOLDERS OF CONSTRUCTIONPERMITS*SUBJECT: POTENTIAL FOR INCREASED ROOF LOADS AND PLANT AREA FLOOD RUNOFF DEPTHAT LICENSED NUCLEAR POWER PLANTS DUE TO RECENT CHANGE IN PROBABLEMAXIMUM PRECIPITATION CRITERIA DEVELOPED BY THE NATIONAL WEATHERSERVICE (GENERIC LETTER 89-22)This letter is to inform you that the NRC staff has adopted for future plantsthe latest probable maximum precipitation (PMP) criteria published by theNational Oceanic and Atmospheric Administration (NOAA), National WeatherService (NWS) to establish acceptable design configurations for safety-relatednuclear power plant facilities. The staff has been using the PMP concept inplant flood design for well over 15 years. The criteria appear in RegulatoryGuides, ANSI Standards, and Standard Review Plans (NUREG-0800) and were basedprimarily on procedures established in the 1940s and 1950s by the U.S. ArmyCorps of Engineers and National Weather Service (NWS).Since 1977, more recent PMP criteria have been published by the NationalOceanic and Atmospheric Administration (NOAA), National Weather Service.These criteria are to be used to evaluate the degree of licensee compliancewith the General Design Criterion 12 App A to 10 CFR Part 50. The newcriteria are contained in NOAA/NWS Hydrometerological Reports (HMR) No. 49(1977), No. 51 (1978), No. 52 (1982), No. 53 (1980) and No. 55 (1984). One ofthe more significant changes in the new HMRs is that they now provide PMPestimates for drainage areas as small as 1 square mile and for durations assmall as 5 minutes. The previous reports generally only provided PMP estimatesfor areas of 10 square miles or greater and durations of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or more.There were empirical methods to subdivide the 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> duration to smallerincrements, but there was never any methodology to estimate PMP for areas lessthan 10 square miles. Thus, the 10 square mile PMP values were used for siteand roof drainage design. Current 1 square mile short duration PMP estimatesare larger than those previously used.Staff has revised (Revision 3) Sections 2.4.2, Floods,' and 2.4.2, 'ProbableMaximum Floods (PMF) on Streams and Rivers," of the Standard Review Plan(NUREG-0800) to formally incorporate the latest NWS reports into the licensing1* Five plants, Byron, Braidwood, Vogtle, South Texas, and River Bend, fullymeet the new PMP Criteria and the licensees for these five plants may dis-i letter.91 180273t C
Generic Letter 89- 22 -2 -October 19, 1989review process. In general, the latest NWS criteria call for higher rainfallintensities over shorter time intervals and smaller areas than have beenpreviously considered. In some cases, such events could result in higher siteflooding levels and greater roof ponding loads than have been used in previousdesign studies.This information is provided for your review and determination of appropriateaction, if any. No submittal is required.Sincerely,Jades G. PartlowAssociate Director for ProjectsOffice of Nuclear Reactor RegulationEnclosure:List of Most Recently IssuedGeneric Letters
Technical Contact:
_____ _ __ _S. Chan, ESGB/NRR492-0830
LIST OF RECENTLY ISSUED GENERIC LETTERS<_>GenericDate ofT 1 ciiand-Issued Toc.. I; , 4_.Letter NO. uu vLL ------ -89-2289-21POTENTIAL FOR INCREASED ROOF 10/19/89LOADS AND PLANT AREA FLOODRUNOFF DEPTH AT LICENSEDNUCLEAR POWER PLANTS DUE TORECENT CHANGE IN PROBABLEMAXIMUM PRECIPITATIONCRITERIA DEVELOPED BY THENATIONAL WEATHER SERVICE(GENERIC LETTER 89-22)REQUEST FOR INFORMATION 10/19/89CONCERNING STATUS OFIMPLEMENTATION OF UNRESOLVEDSAFETY ISSUE (USI) REQUIREMENTSPROTECTED AREA LONG-TERM 09/26/89HOUSEKEEPING89-2089-19ALL LICENSEES OFOPERATING REACTORS ANDHOLDERS OF CONSTRUCTIONPERMITS (EXCEPT BYRONBRAIDWOOD, VOGTLEOSOUTH TEXAS, AND RIVERBEND)ALL HOLDERS OFOPERATING LICENSESAND CONSTRUCTIONPERMITS FOR NUCLEARPOWER REACTORSALL FUEL CYCLEFACILITY LICENSEESWHO POSSESS, USE,OR PROCESS FORMULAQUANTITIES OFSTRATEGIC SPECIALNUCLEAR MATERIALALL LICENSEES OFOPERATING REACTORS,APPLICANTS FOROPERATING LICENSESAND HOLDERS OFCONSTRUCTION PERMITSFOR LIGHT WATERREACTOR NUCLEARPOWER PLANTSALL HOLDERS OFOPERATING LICENSESOR CONSTRUCTIONPERMITS FOR NUCLEARPOWER PLANTSREQUEST FOR ACTION RELATED TO 09/20/89RESOLUTION OF UNRESOLVEDSAFETY ISSUE A-47 "SAFETYIMPLICATION OF CONTROLSYSTEMS IN LWR NUCLEARPOWER PLANTS" PURSUANT TO10 CFR 50.54(f)89-18RESOLUTION OF UNRESOLVEDSAFETY ISSUE A-17, "SYSTEMSINTERACTIONS IN NUCLEARPOWER PLANTS09/06/89ACCESSION NUMBER IS 890907002989-17PLANNED ADMINISTRATIVECHANGES TO THE NRC OPERATORLICENSING WRITTEN EXAMINA-TION PROCESS -GENERICLETTER 89-1709/06/89ALL HOLDERS OFOPERATING LICENSESOR CONSTRUCTIONPERMITS FOR PWRSAND BWRS AND ALLLICENSED OPERATORS89-16INSTALLATIONWETWELL VENTLETTER 89-16)OF A HARDENED(GENERIC09/01/89ALL GE PLANTS
Generic Letter 89- 22-2 -October 19, 1989review process. In general, the latest NWS criteria call for higher rainfallintensities over shorter time intervals and smaller areas than have beenpreviously considered. In some cases, such events could result in higher siteflooding levels and greater roof ponding loads than have been used in previousdesign studies.This informationaction, if any.is provided forNo submittal isyour review and determination of appropriaterequired.Sincerely,ORIGINAL SIGNED BY JAMES G. PARTLOWJames G. PartlowAssociate Director for ProjectsOffice of Nuclear Reactor RegulationEnclosure:List of Most RecentlyGeneric Letters
Technical Contact:
S. Chan, ESGB/NRR492-0830DISTRIBUTION:Central FilesNRC PDR IPD4 ReadingP. O'ConnorF. HebdonG. HolahanF. MiragliaC. BerlingerJ. Partlow1K It1 VIaWY/ 14;~~IFTPD4JDRSP/PM :PD4/,DJS/ :A 4/UKIU+rA /U :AA UI r'qq, :A---___: ------- o---a-h---n-- -r a :C ___ inge :J) -----a_NAME :PO'Connor:bj:FHe n :G olahan olahan :' twDATE_ :--------- ---/---/8- _--/89 _______/89 -- _ _______ -__ _- : ---------DATE :1 /X7)/89 :/2L1/89 :lf /%V /89 V' A% /89 : 8al9 M /§/89 : l 5/89fOFFICIAL RECORD COPYDocument Name: GENERIC LETTER/PD4 DOCUMENT NAME:GENERIC LETTER/PD4ORIGINATOR NAME *:P. O'Connor x23026SECRETARY NAME:Beverly/Celeste x21340SUBJECT:GENERIC LETTER 89-XX RE: DESIGN FOR PROBATENAMEE MAXIMUMDATE_ -°\ lokh1°c\I I\F/Z/7 j1.2.3.4.5.7.7.P. O'ConnorF. HebdonG. HoIahan3tj-'CA2G. HolahanF. MiragliaC. BerlingerJ. PartlowSecretary -DispatchPLEASE DO NOT REMOVE THIS SHEET FROM PACKAGE* CAN THIS DOCUMENT BE DELETED FROM SYSTEM? YESSHOULD THIS DOCUMENT BE ARCHIVED? YES ---- NO_NO