RV Mirai (2007-12-27).jpg
Mirai on 27 December 2007
Name: Mutsu
Namesake: Mutsu, Aomori
Ordered: 17 November 1967[1]
Builder: Ishikawajima-Harima Heavy Industries, Tokyo, Japan[1]
Yard number: 2107[1]
Laid down: 27 November 1968[1]
Launched: 12 June 1969[1]
Completed: 4 September 1972 (fuel loaded)
Decommissioned: 1992
Fate: Rebuilt as the research vessel Mirai
Name: Mirai
Namesake: Japanese for "future"
Owner: Japan Agency for Marine-Earth Science and Technology[2]
Builder: Mitsubishi Heavy Industries, Shimonoseki, Japan (new stern section)[1]
Completed: 1 October 1997[1]
Status: In service
General characteristics (as Mutsu)
Type: General cargo ship
Length: 130 m (427 ft)
Beam: 19 m (62 ft)
Draught: 6.9 m (23 ft)
Depth: 13.2 m (43 ft)
Installed power: 36-megawatt Mitsubishi pressurized water reactor
Propulsion: Steam turbine, 10,000 shp
Speed: 17 knots (31 km/h; 20 mph)
Crew: 80
General characteristics (as Mirai)[1][3]
Type: Research vessel
  • 8,706 GT
  • 3,419 NT
Length: 128.5 m (422 ft)
Beam: 19 m (62 ft)
Draught: 6.9 m (23 ft)
Depth: 10.5 m (34 ft)
Ice class: 1A
Installed power: 4 × Daihatsu 6DKM-28 (4 × 1,838 kW)
  • 18.3 knots (33.9 km/h; 21.1 mph) (maximum)
  • 16 knots (30 km/h; 18 mph) (service)
Range: 12,000 nautical miles (22,000 km; 14,000 mi)
  • 34 crew
  • 46 research personnel

RV Mirai is a Japanese oceanographic research vessel. She was originally built as the nuclear-powered general cargo ship Mutsu,[4] but never carried commercial cargo.[5]


Development and construction

Mutsu (1972–1996)

The reactor was completed on 25 August 1972, and fuel was loaded on 4 September.[6] When officials announced that the first test run was to be run at the pier in Ōminato, local protests forced them to reconsider.[6] Eventually it was decided to test the ship in the open ocean, 800 kilometres (430 nmi) east of Cape Shiriya.[6] The ship departed Ōminato on 26 August 1974, and the reactor attained criticality on 28 August.[6]

Radiation accident

As the crew brought the reactor up to 1.4% of capacity at 5pm on 1 September 1974,[6] there was a minor shielding inadequacy that permitted the escape of neutrons and gamma rays[4] from the reactor shielding enclosure.[6] Westinghouse had reviewed the design and warned of this possibility, but no changes were made to the design.[6] There was no significant radiation exposure, but it became a political issue, with local fisherman blocking her return to port for more than 50 days.[4] The government finally came to an agreement with the local government and fishermen; the Mutsu was allowed back to port on condition that it was to find a new home port, and the ship returned to Ōminato on 15 October.[6]

In Sasebo, between 1978 and 1982, various modifications were made to the reactor shield of the Mutsu, and its home port was moved to Sekinehama in 1983.[6] Following an overhaul, the Mutsu was completed in February 1991.[6] She then completed her original design objective of travelling 82,000 kilometres (51,000 mi) in testing, and was decommissioned in 1992.[6] Over 25 years the programme had cost more than 120 billion yen (about US$ 1.2 billion).[6]

Mirai (1996–present)

After removing the reactor in 1995 and decontaminating the vessel, Mutsu was rebuilt as the ocean observation vessel Mirai.[4][7]

Mutsu Science Museum

The reactor room, control room, bridge, bow, and propeller were converted into a museum and are open to the public at the Mutsu Science Museum.[8] Visitors can interact with the controls in the control room and view the reactor vessel through several viewing ports. Reactor room image 1 Reactor room image 2 Reactor vessel through viewing port image Control room image Bridge image

The nuclear material from the ship is stored across the street from the museum at a facility operated by the Japan Atomic Energy Agency.[5]

See also

  • Savannah, the world's first nuclear-powered cargo ship
  • Otto Hahn, a German nuclear-powered cargo ship
  • Sevmorput, a Soviet and later Russian nuclear-powered cargo ship


  1. ^ a b c d e f g h "Mirai (6919423)". Sea-web. Retrieved 18 August 2019.
  2. ^ a b "Mirai (6919423)". Equasis. French Ministry for Transport. Retrieved 18 August 2019.
  3. ^ "Oceanographic research vessel Mirai". Japan Agency for Marine-Earth Science and Technology. Archived from the original on 2009-11-21.
  4. ^ a b c d OECD Nuclear Energy Agency (2001), Investing in Trust: Nuclear Regulators and the Public : Workshop Proceedings, Paris, France, 29 November - 1 December 2000, OECD Publishing, p. 30, ISBN 978-92-64-19314-7
  5. ^ a b http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/27/029/27029493.pdf
  6. ^ a b c d e f g h i j k l Nakao, Masayuki, Radiation Leaks from Nuclear Power Ship "Mutsu" (PDF), Japan Science and Technology Agency (JST)[permanent dead link] Good overview of the construction, leak, and lessons learnt.
  7. ^ "MIRAI < Research Vessels and Vehicles < Research Vessels, Facilities and Equipment < About JAMSTEC < JAMSTEC". Jamstec.go.jp. Retrieved 2016-07-17.
  8. ^ "むつ科学技術館のホームページへようこそ!!". Jmsfmml.or.jp. Retrieved 2016-07-17.