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GDC 2 Design Bases for Protection against Natural Phenomena

“Design bases for protection against natural phenomena: Structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiche without loss of capability to perform their safety functions. The design bases for these structures, systems, and components shall reflect: (1) Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated, (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena and (3) the importance of the safety functions to be performed.”

To comply with the requirements of this GDC, the applicants are required to consider the effects of extreme natural phenomena as summarized below:

Earthquakes: criteria for defining safe shutdown earthquake (SSE) are developed from the site-related factors (see Appendix A of 10 CFR Part 100 and SRP Section 2.5.2), and Criteria provided in Appendix S of 10 CFR Part 50. The staff reviews the site-related factors in Section 2 of Standard Review Plan (Ref. 3), and Design methodology in Section 3.7 of SRP. The staff has developed several regulatory guides [e.g., RG 1.60 (2010) [18], RG 1.61 (2007) [19] to help the applicants and licensees to develop the plant-specific design and analysis.

Hurricanes, Tornadoes: the safety-related plant structures (including containment structures) are designed to withstand hurricane-related winds and low probability tornado effects as discussed in SRP Sections 3.3.1, 3.3.2, and in RG 1.76 (2007) [20]. The safety-related structures are designed to withstand a spectrum of tornado generated missiles, as stipulated in RG 1.76 [20].

Probable Maximum Flood (PMF): the applicants are required to consider the effects of PMF as stipulated in SRP Sections 2.4.3, and 3.4.2, and potential for upstream dam failure as stipulated in SRP Section 2.4.4.

Probable Maximum Surge (PMS) and Seiche Flooding: the applicants are required to consider the potential effects of PMS and Seiche flooding as stipulated in SRP Section 2.4.5.

Probable Maximum Tsunami (PMT): The applicants are required to consider the coastal sites likely to be subjected to PMT based on the historical records with sufficient margins as discussed in SRP Section 2.4.6.

Containment structures are appropriately designed for the applicable natural phenomena in combination with the applicable design basis loadings. Detailed discussion of the loads and load-load combinations is provided in Chapter 3 of this book. Detailed discussion of “Beyond Design Basis Natural Phenomena” is provided in Chapter 8 of this book.

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