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

COMMISSION

June 1976 REGULATORY

GUIDE OFFICE OF STANDARDS

DEVELOPMENT

REGULATORY

GUIDE 1.117 TORNADO DESIGN CLASSIFICATION

A. INTRODUCTION

General Design Criterion 2, "Design Bases for Protec-tion Against Natural Phenomena," of Appendix A,"General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Licensing of Production and Utiliza.tion Facilities," requires, in part, that structures, sys-tems, and components important to safety be designed to withstand the effects of natural phenomena such as tornadoes.

without loss of capability to perform their safety functions.

Criterion

2 also requires that thie design bases for these structures, systems, and components reflect (1) appropriate combinations of the effects of normal and accident conditions with the effects of natural phenomena and (2) the importance of the safety functions to be performed.

structures and components themselves should be de-signed to withstand the effects of the tornado, including tornado missile strikes.It is not necessary to maintain the functional cap-ability of all Seismic Category I stnpltufres because the probability of the joint occurrten f low-probability events (loss-of-coolant accid i.'t Basis Tornado or smaller tornadQ or thquaki with Design Basis Tornado or smaller o sufficiently small.However, a source of', wt s"ii1 be available to provide long-term c0ecoolin Similarly, .1Noot'& -, ssary to protect the radio-active liquid w"i e'dup tanks since, even in the event of grosW c,X'i\hespills would be limited to small This guide describes a method acceptable to the NRC in It'luid4 foundations, which are designed for that staff for identifying those structures, systems, and r components of light-water-cooled reactors that should 4 be designed to withstand the effects of the Design Basis "Ný,.Strutures, systems, and components important to Tornado (see Regulatory Guide 1.76, "Design, .1;, saty that should be designed to withstand the effects Tornado for Nuclear Power Plants"), including toiado V41 mseadeif l .of a Design Basis Tornado are those necessary to ensure: missiles, and remain functional. , ,, ;-" ' 1. The integrity of the reactor coolant pressure

B. DISCUSSION

boundary.,, .. \ A V: Nuclear power plants should.be designed o'iat the 2. The capability to shut down the reactor and plants can be placed and maintained in a safe shutdown maintain it in a safe shutdown condition.

condition in the, event of ign Basis Tornado, as defined in Regulatory G Protection of struc- 3. The capability to prevent accidents that could tures, systems, and comp n sary to place and result in potential offsite exposures that are a significant maintain 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 substantially tiers to prfc-a.de sile trikes. For example, the from those now in use may require reevaluation with primary co or building, auxiliary build- respect to this objective.

ing, and co structures should be designed against collapse and s d provide an adequate barrier against The physical separation of redundant or alternative missiles.

Howeve , the primary containment need not structures or components required for the safe shutdown necessarily maintain its leaktight integrity under pressure of the plant is generally not considered an acceptable loadings due to the pressure differentials developed by method for protecting against tornado effects, including the tornado. If protective barriers are not installed, the tornado-generated missile

s. USNRC REGULATORY

GUIDES Regulatory Guides ere issued to describe and make available to the public methods acceptable to the NRC staff of implementing specific paeis of the Commistion'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 compliance with them is not required.

Methods and solutions different from those set Out In the guides will be acceptable if they provide a basis for the findings requislte to the issuance or continuance at a permit or license by the Commission.

Comments and suggestions for Improvements In these guides are encouraged at all times, and guides will be revised. as appropriate.

to accommodate com-ments end to reflect new information or experience, However. comments on this guide, if received within about two months after its Issuance.

will be par.trculatly useful in evaluating the need for an early revision Comments should be sent to the Secretary of the Commission.

U.S. Nuclear Regulatory Commission.

Washinglon.

D.C. 20M5. Attention.

Docketing and Service Section.The guides ere Issued In the following ten broad divisions.

1. Power Reactor, 2. Reseach and Teat Reactors 3. Fuels and Materials Facilities

4. Environmental and Siting 5, Materials end Plant Protection

6. Products 7. Transportetion a. occupational Health 9. Antitrust Review 10. General Copies of published guides may be obtained by written request Indicating the divisions desired to the U.S. Nuclear Regulatory Commission.

Washington, D.C.20566. Attention:

Director.

Office of Standards Development, C. REGULATORY

POSITION

D. IMPLEMENTATION

.The appendix to this guide lists those structures, systems, and components, including their foundations and supports, that should be designed to withstand the effects of a Design Basis Tornado (see Regulatory Guide 1.76), including tornado missiles, without loss of capa-bility to perform their safety function.Those portions of structures, systems, or _.omponents whose continued function is not required but whose failure could reduce to an unacceptable safety level the functional capability of any plant feature included in the items listed in the appendix should be designed and constructed so that the effects of the Design Basis Tornado would not cause failure (for example, of the containment walls).The purpose of this section is to provide information to applicants regarding the NRC staff's plans for using this regulatory guide.Except in those cases in which the applicant proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the method described herein will be used in the evaluation of construction permit applications docketed after Feb-ruary 15, 1977.If an applicant wishes to use this regulatory guide in daveloping submittals for applications docketed on or before February 15, 1977, the pertinent portions of the application wil' be evaluated on the basis of this guide.1.117-2 if ____________________________

APPENDIX MINIMUM STRUCTURES, SYSTEMS, AND COMPONENTS

TO BE PROTECTED

AGAINST TORNADOES 1. The reactor coolant pressure boundary.*

2. Those portions of the main steam and main feedwater systems in PWRs up to and including the outermost 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 heat removal, (3) cooling the spent fuel storage pool, or (4)makeup water for the primary system and all systems that are necessary to support these systems, e.g., service water, cooling water source, component cooling, and auxiliary feedwater.

5. The spent fuel storage facility to the extent necessary to preclude significant loss of watertight integrity of the storage pool and to prevent missiles from contacting fuel within the pool.6. The reactivity control systems, e.g., control rod drives and boron injection system.7. The control room, including its associated vital equipment, cooling systems for the vital equipment and life support systems, and any structures or equipment inside or outside the control room whose failure could result in an incapacitating injury to individuals occupy-ing the control room.8. Those portions of the gaseous radwaste treatment system 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 system required to accomplish the specified safety function and connecting piping up to and including the first valve (includ-ing a safety or relief valve) that is either normally closed or capable of automatic closure when the safety function is required.gaseous radioactive waste and portions of structures housing these systems, including isolation valves, equip-ment, interconnecting piping, and components located between the upstream and downstream valves used to isolate these components from the rest of the system, e.g., charcoal delay tanks in BWRs and waste gas storage tanks in PWRs.9. Systems or portions of systems that are required for (1) monitoring systems important to safety and (2)actuating and operating systems important to safety.10. All electric and mechanical devices and circuitry between the process sensors and the input terminals of the actuator systems involved in generating signals that initiate protective action.11. Those portions of the long-term emergency core cooling system that would be required to maintain the plant in a safe condition for an extended time after a loss-of-coolant accident.12. Primary reactor containment and other safety-related structures such as the control room building and auxiliary building to the extent that they not collapse.The primary containment need not necessarily maintain its leaktight integrity under pressure loadings due to the pressure differentials developed by the tornado, but the structure should be designed to withstand penetration by tornado-borne missiles that could jeopardize safety-related structures, systems, and components within the containment.

13. The Class IE electric systems, including the auxiliary systems for the onsite electric power supplies, that provide the emergency electric power needed for the functioning of plant features included in items 1.through 11. above.1.117-3