Part 3. New way of thinking about safety

Safety-II, which is a safety concept implemented through dynamic measures, has been organized as a theoretical system with a new concept, as opposed to Safety-I, which is a conventional current-state-fixed safety concept. Resilience engineering is the methodology for realizing Safety-II. Examples of Safety-II are hydrogen explosion prevention at the Fukushima Daiichi Nuclear Power Station Units 5 and 6, and emergency evacuation at the Fukushima Daiichi Nuclear Power Station. Resilience engineering is a means and methodology for flexibly responding to the system performance that has changed (decreased) due to disturbance and for promptly recovering the performance. Regarding the defense in depth of nuclear reactor safety, before the Fukushima Daiichi Nuclear Power Station accident, the safety was considered perfect by the 1st to 3rd layers, and little consideration was given to the 4th and subsequent layers. In the case of a nuclear reactor, restoration is difficult, so impact mitigation and disaster prevention is the main focus from the 4th layer onward. Successful resilience engineering requires four abilities: countermeasure, monitoring, foresight, and learning. In order to enable flexible response and countermeasures, individuals should enrich their eyes to see the essence of things, ability to analyze situations, and a variety of potentials. Organizations should respect the judgment of the field, promote fair discussions, and refrain from the unfair pursuing of responsibility. (A.O.)