MRX (Marine Reactor X)
The basic concept of an innovative advanced marine reactor with a passive safety system, MRX (Marine Reactor X) has been established for the primary application to ship propulsion. The design goals of the reactor system, to be lightweight and compact, and to be enhanced in safety and reliability, are achieved with adoption of new technologies. The MRX was of the integral-type PWR with 100 MW of thermal output. Adoption of a water-filled containment makes the MRX extremely lightweight and compact.
In preparation for commercial use of nuclear ships, the research and development of the next-generation improved-type ship reactor was under way at the Japan Atomic Energy Research Institute in the early 1990s. This effort was based on results from the "MUTSU" project. For a nuclear ship to be commercially viable, improved economy and reliability was needed. Hence, a light, compact, reliable, and safe ship reactor was being developed. It must require only a small crew for operation and maintenance. By 1995, design studies had been made that address a loop-type PWR, similar to that in "MUTSU," and an integrated-type PWR with steam-generators built into the reactor vessel. Through the studies, the design of an integrated PWR has been selected.
It is named MRX (Marine Reactor X). The conceptual design and R&D for the main equipment (like the control rod drive mechanism) and the safety system of MRX were ongoing. This reactor is designed to have a thermal output of 100 MWt. This would be suitable for a near-future fast cargo ship (like a container ship) or an ice-breaker. It can be much smaller in comparison with a conventional reactor having the same power. Furthermore, the design is expected to be applicable for a reactor for future ultra-high speed cargo vessels crossing the Pacific Ocean with speeds as fast as 50 knots.
JAERI has advanced the research and development to the improved marine reactor aiming at realization of the future marine reactor together with the research and development by “Mutsu”. In the case of the marine reactor, the requirements for the output, the load conditions, and the automation of the operation are different depending on the kind of ship to be used, and the research and development of two kinds of improved marine reactors, i.e., a large marine reactor MRX (Marine Reactor X) and a deep-sea reactor DRX (Deepsea Reactor X) have been advanced for the installation onboard an ice-breaking observation ship and a deepsea scientific research ship which are expected to be realized soon.
The conceptual design has already been established on MRX and DRX, and the development of the element technology such as the fundamental test or the like on the passive safety technology, and the development of the element equipment such as the reactor containment built-in type control rod driving device are advanced in parallel. Consideration has been given to how to advance the design and Studies on the engineering level including demonstration of the establishment of the conception, acquisition of the thermal hydrostatic data necessary for developing the detailed design, demonstration of the reliability of the new concept and the operational and maintenance performance.
The MRX is the marine reactor to simultaneously achieve the high safety, miniaturization and weight reduction of the system by employing the integral type PWR, the reactor built in type control rod driving device, the water-filled type containment, and the decay heat removing system by the natural circulation.
The total weight and volume of MRX is about 1600 tons and 1210 m3, which is half that of the first Japanese nuclear ship, Mutsu', reactor, although the reactor power of MRX is three times greater than that of the 'Mutsu' reactor. Numbers of active components in the reactor system are greatly reduced, compared with loop type PWRs, by adopting an integral type reactor and the passive system. Safety was evaluated by both experiments and analyses. Core damage occurrence frequency estimated by probability safety analysis (PSA) is of two orders smaller than those of existing PWRs.
The engineering examination of the MRX was completed in 1996 for the present. Feasibility study on economics is conducted by comparing the total operation costs of a nuclear container ship installing the MRXs with a diesel engine ship. The nuclear ship has the advantage for greater speed and larger amounts of cargo carried.
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