Abstract
In Fukushima accident on 2011, after the loss of both the emergency core cooling system and IC core cooling, primary containment vessel (PCV) pressure increased. Water level measurement drifted because of water evaporation in the reference leg. Radiation level increased at a turbine building (T/B). There was a hydrogen explosion the after the suppression chamber (S/C) wet venting. By using the FCVS technology, the such the risk reduction during severe accidents in NPPs were attained. But owing to the global warming, the risk of natural hazards are increased, such as typhoon, hard rain, hot summer, severe snowfall, melt snow in north pole and south pole. It is very important to reduce CO2 emission by best mix of utilizing renewable energy and the safety enhanced nuclear power plants.
