[en] The basic concept of an innovative advanced marine reactor MRX has been established by design study toward the goals of light-weightiness, compactness, and safety and reliability improvement with adoption of several new technologies. The MRX is the integral-type PWR aimed for use of ship propulsion. Adoption of a water-filled containment makes the reactor light-weighted and compact greatly. The total weight and volume of the reactor are 1600 tons and 1210 m³, which are equivalent to halves of the Mutsu, although the reactor power of MRX is three times greater. An engineered safety system of the MRX is a simplified passive system, function of which is confirmed by the safety analysis to be able to keep the reactor integrity even in a case of accident. Reliability of the system is evaluated by the PSA and revealed to have two orders smaller core damage occurrence frequency than existing PWRs. The MRX can be applied to an energy supply system of electricity and heat co-generation. Concept of the nuclear energy supply system is designed to generate electricity, heat and fresh water. The nuclear barge is shown to be a possible nuclear energy supply system with advantage of being easily moveable. (author)