4　Design Basis Flood

4.1　General Requirements

4.1.1　Water level，flood-peak flow，and flooding process shall be considered to determine the design basis flood.

4.1.2　All flood events that may affect the safety of the nuclear power plant during its service life shall be analyzed and evaluated to determine the design basis flood.

4.1.3　For various flood events，data of historical flood events in the bank area of the site and their frequency of occurrence shall be collected and investigated，and their reliability and completeness shall be analyzed.

4.1.4　To determine the design basis flood events，all characteristic elements and areas that affect the determination of design basis flood shall be fully analyzed.

4.1.5　To determine the design basis flood，the specific data of this site shall be used.Where such data is unavailable，data from other similar drainage basins may be used and a proper hydrometeorological model shall be established for comprehensive analysis.

4.1.6　Both the probabilistic method and deterministic method shall be used to determine the design basis flood with their results comprehensively analyzed and properly selected.

4.1.7　The design basis flood shall be comprehensively determined based on all severe flood events that may affect the safety of this site and their possible adverse combinations while considering the site specific features，expertise and engineering judgment.

The finalized design basis flood level shall not be lower than the hydrologically or historically recorded highest flood level.

4.1.8　The flood control standard for nuclear safety-related items shall be based on the design basis flood，and for those not related to nuclear safety shall conform to the current national standard GB 50660 Code for Design of Fossil Fired Power Plant.