Document: NRC Regulatory Guide
Document ID: 4f130c35-25dc-4950-b437-3801efdab5f6
Document Type: regulatory_guide
Title: Protection Against Extreme Wind Events and Missiles for Nuclear Power Plants (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1435/ML14356A107.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.117
CFR Part: 
CFR Title: 

Content:
ng offsite exposures to exceed an appropriate fraction of 10 CFR Part 100 guidelines. Protection of designated structures, systems, and components may generally be accomplished by designing protective barriers to preclude extreme wind damage. For example, the primary containment, reactor building, auxiliary building, and control structures should be designed against collapse and should provide an adequate barrier against missiles. However, the primary containment need not necessarily maintain its leak-tight integrity. If protective barriers are not installed, the structures and components themselves should be designed to withstand the effects of the extreme winds, including tornado and hurricane missile strikes. The physical separation of redundant or alternative structures or components required for the safe shutdown of the plant is generally not considered acceptable by itself for protecting against extreme wind effects, including generated missiles. This is because of the large number and random direction of potential missiles that could result from wind effects, as well as the need to consider the single failure criterion. As stated in GDC 2, “SSCs important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions. The design bases for these SSCs shall reflect … appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena.” An applicant or licensee does not need to assume simultaneous occurrence of low probability events (e.g., loss-of-coolant accident with a design basis tornado) because the joint occurrence is sufficiently small. However, applicants and licensees should consider subsequently-occurring low probability events (e.g. loss-of-coolant accident followed by a design bases tornado). For this reason, equipment used to provide long term core