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

structures and components themselves should be de- signed to withstand the effects of the tornado, including General Design Criterion 2, "Design Bases for Protec- tornado missile strikes.

tion Against Natural Phenomena," of Appendix A,

"General Design Criteria for Nuclear Power Plants," to It is not necessary to maintain the functional cap-

10 CFR Part 50, "Licensing of Production and Utiliza. ability of all Seismic Category I stnpltufres because the tion Facilities," requires, in part, that structures, sys- probability of the joint occurrten f low-probability tems, and components important to safety be designed events (loss-of-coolant accid i.'t wi'f*%pesign Basis to withstand the effects of natural phenomena such as Tornado or smaller tornadQ or thquaki with Design tornadoes. without loss of capability to perform their Basis Tornado or smaller o sufficiently small.

safety functions. Criterion 2 also requires that thie design However, a source of', wt s"ii1 be available to bases for these structures, systems, and components provide long-term c0ecoolin reflect (1) appropriate combinations of the effects of normal and accident conditions with the effects of Similarly, .1Noot'&

- ssary

, to protect the radio- natural phenomena and (2) the importance of the safety active liquid w"i e'dup tanks since, even in the event functions to be performed. 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 missiles, and remain functional.l , . ,,  ; of a Design Basis Tornado are those necessary to ensure:

-" ' '.*"' 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 -l* 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 nn* 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 missiles.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission. U.S. Nuclear Regulatory Commission. Washinglon. D.C. 20M5. Attention. Docketing and Regulatory Guides ere issued to describe and make available to the public Service Section.

methods acceptable to the NRC staff of implementing specific paeis of the Commistion's regulations, to delineate techniques used by the staff in evelu. The guides ere Issued In the following ten broad divisions.

ating specific problems ot postulated accidents. or to provide guidance to appli.

c.nts. Rogulatoryv Guides are not substitutes fto regulatIons, and compliance 1. Power Reactor, 6. Products with them is not required. Methods and solutions different from those set Out In

7. Transportetion

2. Reseach and Teat Reactors the guides will be acceptable if they provide a basis for the findings requislte to 3. Fuels and Materials Facilities a. occupational Health the issuance or continuance at a permit or license by the Commission. 4. Environmental and Siting 9. Antitrust Review Comments and suggestions for Improvements In these guides are encouraged 5, Materials end Plant Protection 10. General at all times, and guides will be revised. as appropriate. to accommodate com- ments end to reflect new information or experience, However. comments on Copies of published guides may be obtained by written request Indicating the this guide, if received within about two months after its Issuance. will be par. divisions desired to the U.S. Nuclear Regulatory Commission. Washington, D.C.

trculatly useful in evaluating the need for an early revision 20566. Attention: Director. Office of Standards Development,

D. IMPLEMENTATION

.The appendix to this guide lists those structures, The purpose of this section is to provide information systems, and components, including their foundations to applicants regarding the NRC staff's plans for using and supports, that should be designed to withstand the this regulatory guide.

effects of a Design Basis Tornado (see Regulatory Guide 1.76), including tornado missiles, without loss of capa- Except in those cases in which the applicant proposes bility to perform their safety function. an acceptable alternative method for complying with specified portions of the Commission's regulations, the Those portions of structures, systems, or _.omponents method described herein will be used in the evaluation whose continued function is not required but whose of construction permit applications docketed after Feb- failure could reduce to an unacceptable safety level the ruary 15, 1977.

functional capability of any plant feature included in the items listed in the appendix should be designed and If an applicant wishes to use this regulatory guide in constructed so that the effects of the Design Basis daveloping submittals for applications docketed on or Tornado would not cause failure (for example, of the before February 15, 1977, the pertinent portions of the containment walls). 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.* gaseous radioactive waste and portions of structures housing these systems, including isolation valves, equip-

2. Those portions of the main steam and main ment, interconnecting piping, and components located feedwater systems in PWRs up to and including the between the upstream and downstream valves used to outermost isolation valves. isolate these components from the rest of the system, e.g., charcoal delay tanks in BWRs and waste gas storage

3. The reactor core and reactor vessel internals. tanks in PWRs.

4. Systems" or portions of systems that are re- 9. Systems or portions of systems that are required quired for (1) reactor shutdown, (2) residual heat for (1) monitoring systems important to safety and (2)

removal, (3) cooling the spent fuel storage pool, or (4) actuating and operating systems important to safety.

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 10. All electric and mechanical devices and circuitry auxiliary feedwater. between the process sensors and the input terminals of the actuator systems involved in generating signals that

5. The spent fuel storage facility to the extent initiate protective action.

necessary to preclude significant loss of watertight integrity of the storage pool and to prevent missiles from 11. Those portions of the long-term emergency core contacting fuel within the pool. cooling system that would be required to maintain the plant in a safe condition for an extended time after a

6. The reactivity control systems, e.g., control rod loss-of-coolant accident.

drives and boron injection system.

7. The control room, including its associated vital 12. Primary reactor containment and other safety- equipment, cooling systems for the vital equipment and related structures such as the control room building and life support systems, and any structures or equipment auxiliary building to the extent that they not collapse.

inside or outside the control room whose failure could The primary containment need not necessarily maintain result in an incapacitating injury to individuals occupy- its leaktight integrity under pressure loadings due to the ing the control room. pressure differentials developed by the tornado, but the structure should be designed to withstand penetration

8. Those portions of the gaseous radwaste treatment by tornado-borne missiles that could jeopardize safety- system that by design are intended to store or delay related structures, systems, and components within the containment.

• Asdeflned in §50.2 of IOCFR Part 50.

• "The system boundary Includes those portions of the system 13. The Class IE electric systems, including the required to accomplish the specified safety function and auxiliary systems for the onsite electric power supplies, connecting piping up to and including the first valve (includ- ing a safety or relief valve) that is either normally closed or that provide the emergency electric power needed for capable of automatic closure when the safety function is the functioning of plant features included in items 1.

required. through 11. above.

1.117-3