Regulatory Guide 1.117

Tornado Design Classification.

ML13350A280
Person / Time
Issue date:	06/30/1976
From:	NRC/OSD
To:
References
FOIA/PA-2015-0456, FOIA/PA-2015-0458 RG-1.117
Download: ML13350A280 (3)

U.S. NUCLEAR REGULATORY COMMISSIONJune 1976REGULATORY GUIDEOFFICE OF STANDARDS DEVELOPMENTREGULATORY GUIDE 1.117TORNADO DESIGN CLASSIFICATIONA. INTRODUCTIONGeneral Design Criterion 2, "Design Bases for Protec-tion Against Natural Phenomena," of Appendix A,"General Design Criteria for Nuclear Power Plants," to10 CFR Part 50, "Licensing of Production and Utiliza.tion Facilities," requires, in part, that structures, sys-tems, and components important to safety be designedto withstand the effects of natural phenomena such astornadoes. without loss of capability to perform theirsafety functions. Criterion 2 also requires that thie designbases for these structures, systems, and componentsreflect (1) appropriate combinations of the effects ofnormal and accident conditions with the effects ofnatural phenomena and (2) the importance of the safetyfunctions to be performed.structures and components themselves should be de-signed to withstand the effects of the tornado, includingtornado missile strikes.It is not necessary to maintain the functional cap-ability of all Seismic Category I stnpltufres because theprobability of the joint occurrten f low-probabilityevents (loss-of-coolant accid i.'t BasisTornado or smaller tornadQ or thquaki with DesignBasis Tornado or smaller o sufficiently small.However, a source of', wt s"ii1 be available toprovide long-term c0ecoolinSimilarly, .1Noot'& -, ssary to protect the radio-active liquid w"i e'dup tanks since, even in the eventof grosW c,X'i\hespills would be limited to smallThis guide describes a method acceptable to the NRC in It'luid4 foundations, which are designed for thatstaff for identifying those structures, systems, and rcomponents of light-water-cooled reactors that should 4be designed to withstand the effects of the Design Basis "Ný,.Strutures, systems, and components important toTornado (see Regulatory Guide 1.76, "Design, .1;, saty that should be designed to withstand the effectsTornado for Nuclear Power Plants"), including toiado V41mseadeif l .of a Design Basis Tornado are those necessary to ensure:missiles, and remain functional. , ,, ;-" ' 1. The integrity of the reactor coolant pressureB. DISCUSSION boundary.,, .. \ A V:Nuclear power plants should.be designed o'iat the 2. The capability to shut down the reactor andplants can be placed and maintained in a safe shutdown maintain it in a safe shutdown condition.condition in the, event of ign Basis Tornado, asdefined in Regulatory G Protection of struc- 3. The capability to prevent accidents that couldtures, systems, and comp n sary to place and result in potential offsite exposures that are a significantmaintain the plant , e tdown condition may fraction of the guideline exposures of 10 CFR Part 100,generally be acco.'lishe y esigning protective bar- "Reactor Site Criteria." Designs that differ substantiallytiers to prfc-a.de sile trikes. For example, the from those now in use may require reevaluation withprimary co or building, auxiliary build- respect to this objective.ing, and co structures should be designed againstcollapse and s d provide an adequate barrier against The physical separation of redundant or alternativemissiles. Howeve , the primary containment need not structures or components required for the safe shutdownnecessarily maintain its leaktight integrity under pressure of the plant is generally not considered an acceptableloadings due to the pressure differentials developed by method for protecting against tornado effects, includingthe tornado. If protective barriers are not installed, the tornado-generated missiles.USNRC REGULATORY GUIDESRegulatory Guides ere issued to describe and make available to the publicmethods acceptable to the NRC staff of implementing specific paeis of theCommistion's regulations, to delineate techniques used by the staff in evelu.ating specific problems ot postulated accidents. or to provide guidance to appli.c.nts. Rogulatoryv Guides are not substitutes fto regulatIons, and compliancewith them is not required. Methods and solutions different from those set Out Inthe guides will be acceptable if they provide a basis for the findings requislte tothe issuance or continuance at a permit or license by the Commission.Comments and suggestions for Improvements In these guides are encouragedat all times, and guides will be revised. as appropriate. to accommodate com-ments end to reflect new information or experience, However. comments onthis guide, if received within about two months after its Issuance. will be par.trculatly useful in evaluating the need for an early revisionComments should be sent to the Secretary of the Commission. U.S. NuclearRegulatory Commission. Washinglon. D.C. 20M5. Attention. Docketing andService Section.The guides ere Issued In the following ten broad divisions.1. Power Reactor,2. Reseach and Teat Reactors3. Fuels and Materials Facilities4. Environmental and Siting5, Materials end Plant Protection6. Products7. Transportetiona. occupational Health9. Antitrust Review10. GeneralCopies of published guides may be obtained by written request Indicating thedivisions desired to the U.S. Nuclear Regulatory Commission. Washington, D.C.20566. Attention: Director. Office of Standards Development, C. REGULATORY POSITIOND. IMPLEMENTATION.The appendix to this guide lists those structures,systems, and components, including their foundationsand supports, that should be designed to withstand theeffects of a Design Basis Tornado (see Regulatory Guide1.76), including tornado missiles, without loss of capa-bility to perform their safety function.Those portions of structures, systems, or _.omponentswhose continued function is not required but whosefailure could reduce to an unacceptable safety level thefunctional capability of any plant feature included in theitems listed in the appendix should be designed andconstructed so that the effects of the Design BasisTornado would not cause failure (for example, of thecontainment walls).The purpose of this section is to provide informationto applicants regarding the NRC staff's plans for usingthis regulatory guide.Except in those cases in which the applicant proposesan acceptable alternative method for complying withspecified portions of the Commission's regulations, themethod described herein will be used in the evaluationof construction permit applications docketed after Feb-ruary 15, 1977.If an applicant wishes to use this regulatory guide indaveloping submittals for applications docketed on orbefore February 15, 1977, the pertinent portions of theapplication wil' be evaluated on the basis of this guide.1.117-2 if ____________________________APPENDIXMINIMUM STRUCTURES, SYSTEMS, AND COMPONENTSTO BE PROTECTED AGAINST TORNADOES1. The reactor coolant pressure boundary.*2. Those portions of the main steam and mainfeedwater systems in PWRs up to and including theoutermost isolation valves.3. The reactor core and reactor vessel internals.4. Systems" or portions of systems that are re-quired for (1) reactor shutdown, (2) residual heatremoval, (3) cooling the spent fuel storage pool, or (4)makeup water for the primary system and all systemsthat are necessary to support these systems, e.g., servicewater, cooling water source, component cooling, andauxiliary feedwater.5. The spent fuel storage facility to the extentnecessary to preclude significant loss of watertightintegrity of the storage pool and to prevent missiles fromcontacting fuel within the pool.6. The reactivity control systems, e.g., control roddrives and boron injection system.7. The control room, including its associated vitalequipment, cooling systems for the vital equipment andlife support systems, and any structures or equipmentinside or outside the control room whose failure couldresult in an incapacitating injury to individuals occupy-ing the control room.8. Those portions of the gaseous radwaste treatmentsystem that by design are intended to store or delay*Asdeflned in §50.2 of IOCFR Part 50.*"The system boundary Includes those portions of the systemrequired to accomplish the specified safety function andconnecting piping up to and including the first valve (includ-ing a safety or relief valve) that is either normally closed orcapable of automatic closure when the safety function isrequired.gaseous radioactive waste and portions of structureshousing these systems, including isolation valves, equip-ment, interconnecting piping, and components locatedbetween the upstream and downstream valves used toisolate these components from the rest of the system,e.g., charcoal delay tanks in BWRs and waste gas storagetanks in PWRs.9. Systems or portions of systems that are requiredfor (1) monitoring systems important to safety and (2)actuating and operating systems important to safety.10. All electric and mechanical devices and circuitrybetween the process sensors and the input terminals ofthe actuator systems involved in generating signals thatinitiate protective action.11. Those portions of the long-term emergency corecooling system that would be required to maintain theplant in a safe condition for an extended time after aloss-of-coolant accident.12. Primary reactor containment and other safety-related structures such as the control room building andauxiliary building to the extent that they not collapse.The primary containment need not necessarily maintainits leaktight integrity under pressure loadings due to thepressure differentials developed by the tornado, but thestructure should be designed to withstand penetrationby tornado-borne missiles that could jeopardize safety-related structures, systems, and components within thecontainment.13. The Class IE electric systems, including theauxiliary systems for the onsite electric power supplies,that provide the emergency electric power needed forthe functioning of plant features included in items 1.through 11. above.1.117-3