RV Mirai is a prominent Japanese oceanographic research vessel, notable for its unique history as a former nuclear-powered general cargo ship, originally named Mutsu. Launched as a nuclear vessel, Mutsu’s reactor was completed on 25 August 1972, with fuel loaded shortly thereafter. The vessel’s initial testing phase was marked by controversy; after a planned pier-side test was canceled due to protests, the ship was eventually sent into open ocean for testing, departing Ōminato on 26 August 1974. The reactor attained criticality on 28 August, and by 1 September, the reactor was brought to 1.4% capacity. During this testing, a minor shielding inadequacy allowed some neutrons and gamma rays to escape, a concern identified by Westinghouse Electric Corporation but not addressed prior to testing. Although no significant radiation exposure occurred, the incident sparked political controversy and local protests, leading to a blockade by fishermen that lasted over 50 days. The government ultimately permitted Mutsu to return to port on the condition it be relocated, and it was moved to Ōminato on 15 October 1974. Between 1978 and 1982, modifications were carried out to improve the reactor shielding, and the ship’s home port was moved to Sekinehama in 1983. After an extensive overhaul completed in February 1991, Mutsu fulfilled its original testing objective of traveling 82,000 kilometers. The vessel was decommissioned in 1992 after over 25 years and a program cost exceeding 120 billion yen (~US$1.2 billion). In 1995, the reactor was removed and the vessel was decontaminated. Subsequently, Mutsu was transformed into RV Mirai, an ocean observation vessel. Key sections of the original ship—including the reactor room, control room, bridge, bow, and propeller—were converted into a museum at the Mutsu Science Museum, where visitors can explore the controls and view the reactor vessel through viewing ports. The nuclear material is stored nearby at a facility operated by the Japan Atomic Energy Agency. Mirai’s transformation from a nuclear cargo ship to a scientific research vessel underscores its maritime significance, reflecting advances in nuclear technology and Japan’s commitment to oceanographic research.

This description has been generated using GPT-4.1-NANO based on the Vessel's wikidata information and then modified by ShipIndex.org staff.