Core design and safety system of advanced marine reactor MRX

An advanced marine reactor called MRX has been designed to obtain a more compact and lightweight reactor with enhanced safety. The reactor is an integral PWR with adopting a water-filled containment vessel, in-vessel type control rod drive mechanisms and an emergency decay heat removal system by natural convection. The design of fuel element is based on well developed PWR fuel-technology. The core design has been made with satisfying the following conductions specific to marine reactors: (a) To maintain non-criticality in low temperatures without use of a soluble poison even under the condition that one of the control rod clusters which has the largest reactivity worth is withdrawn from the core. (b) To operate the reactor with a sufficient power level for steerage way even in the case that one of the control rod cluster which has been largest worth cannot be withdrawn from the core. (c) To keep enough residual reactivity for overriding Xe poisoning at the EOL. (d) To keep the lifetime of 8 years for fuel assembly with the refueling frequency of 4 years. The engineered safety is accomplished by a simplified system which consists of an emergency decay heat removal system (EDRS) and a containment water cooling system (CWCS) operated by natural convection. The EDRS transfers decay heat from the core to the containment water. The CWCS is used for heat removal of containment water to the atmosphere. The LOCA analysis showed that the core flooding is maintained passively even taking into account the ship inclination. (author)