Designing of comprehensive risk analysis system for multiple layers of defense-in depth concept

A systematic and comprehensive risk analysis system has been under development for enhancing safety of nuclear power plant throughout the whole process of design, operation and maintenance and even for nuclear emergency and post-accident management. The major subject of this paper is to correlate this risk analysis system with the defense in depth concept proposed by IAEA. The discussions are made on how all defense in depth layers are organized, with highlighting on the system configuration for both the fourth and fifth layers of the defense in depth from the learned lessons of Fukushima Daiichi accident occurred in March 2011 in Japan. (author)