The astronomical high sea level and low sea level with a recurrence interval of 100 years are selected for the design of circulating cooling water system.

For coastal NPP sites, Design Basis Flood (DBF) level design shall consider the credible combinations of astronomical tides, storm surges (tsunamis), seiches, sea level rise, and wind-generated waves, etc.

A recurrence interval of 1,000 years for 10 min rainstorm intensity is selected for the drainage system design in Nuclear Island (NI) and Balance of Plant (BOP), and design basis shall checked against 10 min Probable Maximum Precipitation (PMP), which exceeding a recurrence interval of 10,000 years.

The design basis for the structure design of NI building is selected as a 3 s gust wind with a recurrence interval of 100 years at 10 m height.

Take a tornado with a 10⁻⁷ annual exceedance probability as the safety related building structure design basis.

The maximum/minimum safety design air temperature are selected as the hourly dry-bulb air temperature that is not guaranteed for 2 h in the hottest 4 months/coldest 3 months over the years, or the wet-bulb air temperature correspondingly.

The average value of the 7th highest/lowest daily average water temperature each year (denoted as T7) are selected for normal operation, and the highest/lowest water temperature in history are selected for accident condition.

Snow load with a recurrence interval of 100 years is selected for the structure design of NI building.