Japanese Nuclear Propulsion 1 - The Mutsu Episode

Mutsu photo (Courtesy http://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/tayu/ACT95E/06/0601.htm)

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Mutsu Diagram (Courtesy) 

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S has located a chapter in Japan's history that is surprising. That Japan developed and utilised "dual-use" nuclear reactor propulsion to power the ship Mutsu (see Wikipedia and IAEA) in the 1970s to 1992.

In Comments in mid June 2016 S identified Japan’s one public example of a nuclear propulsion for a ship.

Japan's Atomic Energy Agency (JAEA) built a nuclear propelled ship, the Mutsu, nearly 50 years (1968-1970). Mutsu's had a 36 MW Mitsubishi pressurised water reactor (PWR). The reactor was completed in August 1972. Low enriched (less than 20% U235) Uranium was loaded into the reactor in September 1972.

Minor radiation (neutrons and gamma rays) emanated from Mutsu's reactor during workup assessments, at sea, in September 1974. This was misinterpreted by the Japanese press as a leak of radioactive substances. The ray "leakage" was only equivalent to twice as much as the usual "radiation" from an old-style television picture tube.

With this press coverage the Mutsu's future became a high profile anti-nuclar issue. Local fisherman blocked Mutsu's return to her home port for more than 50 days.

“The Japanese 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.

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. Following an overhaul, the Mutsu was completed in February 1991. She then completed her original design objective of travelling 82,000 kilometres in testing, and was decommissioned in 1992. Over 25 years the programme had cost (about US$ 1.2 billion).” [quite a modest sum for reactor development.]

But Mutsu had a second life - after its reactor was removed in 1995 it was renamed the (non-nuclear) Mirai.

During and after the Mutsu experience Japan's Atomic Energy Agency has not planned, built or purchased a nuclear propelled ship.

S Comments

Building nuclear submarines is technically possible for Japan and many in the Japanese Navy (JMSDF) would be happy having Japanese nuclear propelled submarines. But public and political anti-nuclear sensitivities in general and memories of the Mutsu, have blocked any serious thought of Japanese nuclear propelled submarines. Even if the Japanese Navy built nuclear submarines, no local governor of a Japanese prefecture would permit such a submarine to enter a port. 

Pete's Comment

This is also noting that Japan's major submarine bases are Kure (in Hiroshima Prefecture) and Yokosuka (near extremely populated Yokohama-Tokyo). It is odd that US nuclear propelled submarines and the US Seventh Fleet supercarrier share the Yokosuka base - but that is a nuclear political paradox.

An isolated naval base in Japan would probably need to be built to permanently base Japanese nuclear submarines. Australia has a similar problem in that Fleet Base East (Sydney Harbour) could not serve as the number two base (including emergency porting) for any future Australian nuclear submarines.

The military value of a Japanese civilian ship reactor is that it represents a dual-use technological testbed for future miniaturisation and increase in power output (100 MW would be a submarine minimum). This is a necessary preliminary for a mature submarine reactor. Though the French Rubis class SSN had a 48 MW reactor - that was for an unusually small 2,400 tonne SSN with only 14 x heavyweight weapon shots.

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Next week S and Pete will complete Japanese Nuclear Propulsion 2 - further down the technological track towards a Japanese submarine reactor capability.

S and Pete