[en] In order to contribute for the establishment of new system with environmentally harmonized, more safe and efficient use of nuclear energy, research activities in the area of limiting heat transfer for nuclear energy science have been conducted, which are classified into four areas; nuclear energy system research, boiling research, mixed flow research and neutron radiography research. They are related with each other and 'phase transformations' phenomena are common keyword. Main research items are characteristics of multiphase flow in narrow channels, mechanistic modeling of multiphase flow phenomena and critical heat flux, multiphase fluid under severe accident conditions in a nuclear reactor and development of high-frame-rate imaging and qualification with the use of neutron radiography and their application to visualization and assessment of fluid phenomena. (T. Tanaka)