[en] This paper describes major research subjects and approaches on reactor safety for commercialization of fast reactors including recriticality issue in core disruptive accident sequences. To achieve the research objective for these major subjects, a new in-pile safety experimental program named SERAPH (safety engineering reactor for accident phenomenology) is proposed, and the conditions of the proposed tests and the major requirements for the facility are formulated. 13 refs., 5 figs., 1 tab