This research aims to develop capability of on-site staffs that can respond to beyond "design basis accident (DBA)" in the sophisticated socio-technical system, in which ensuring safety has been more complicated. Fukushima Daiichi nuclear accident is therefore considered as the actual case of "beyond DBA". The authors focused on the actions to prevent the accident progression undertaken by on-site staffs, which were hardly evaluated in existing accident analyses and reports. With reference to

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... e concept of resilience engineering, "Responding" of the four cornerstones was particularly analyzed. Based on the precedent studies, causal factors of modeling "Responding" where pointed out the importance of "Attitude" that is a new lesson learned from on-site response at the accident. In addition, new lessons learned on improvement of skills indicated the limit of the concept of risk removal type safety as a safety goal that human is defined as "a safety hazard element". This led the necessity of the success expansion type of safety as a new safety goal that human is defined as "a resource necessary for system flexibility and resilience". Focusing on "Responding" on-site enabled to deduce core competence by extracting causal factors. Thus, new lessons learned successfully derived introduced for human resource development of the next generation to lead technologies in the society.