Nuclear Ship Mutsu - 1974 Incident
On 28 August 1974, the ship's reactor attained criticality for the first time in the testing area 800km east of cape Shiriya in Aomori. At around 17:00 on September 1, the alarm went off as it detected an increase in radiation when its crew brought the reactor up to 1.4% of full capacity. The mass media reported this incident saying, "Nuclear powered ship Mutsu leaked radioactivity". Concerned about the dangers posed by the ship to the community and the fishing industry, the community (the town Mutsu and Aomori Prefecture) and the fishing industry, refused to allow the ship to return to the harbor, although they once had accepted the reactor test.
On October 14, a compromise was reached and the government, the local government of Aomori, the town of Mutsu and the Aomori Prefectural Fishery Cooperation signed an agreement on Mutsu's entrance into its home harbor and withdrawal from its current home harbor. The ship returned to the port of Ohminato on October 15.
Radiation leaked from the shielding ring. The alarm went off as it detected fast neutrons leaking out of the reactor shielding (streaming). The faulty design of the reactor shield was due to lack of experience. Only few models of reactor shields had been designed in Japan at that time, and there were few experienced reactor shield designers. The engineers made poor judgments about the capacity shielding with hard to calculate complex shapes. Although Westinghouse Electric Company (U.S.A.) had reviewed the design of the reactor shield as requested and had warned about the possibility of "streaming", the designer made no correction to the original design. Because the ship and its reactor were commissioned to different independent companies, radiation shielding was not designed in a cohesive and integrated way. The efficiency of the shielding was not examined comprehensively.
The mass media reported radioactivity leak, instead of radiation leak. This made the community and the whole Japan fear radiation contamination of seafood (scallop) and produced an image of Mutsu to be "the nuke-leaking ship". Officials and investigators inherited this terminology "radioactivity", fueling bitter protests and general public distrust. It caused a significant delay in the project while the government tried to persuade harbor authorities to allow the ship to berth.
On 18 March 1975, the Atomic Energy Commission established the Nuclear Powered Vessels Council to discuss the future development of nuclear powered ships, as well as to review the Mutsu's development plan and the role of the Japan Nuclear Ship Research and Development Agency. On June 10, the Atomic Energy Commission publicly stated its disappointment in the government agency's inadequate judgment and inefficiency that invited the public's distrust, granted that the reactor was shut down before contamination became serious. It supported the Investigation Commission's recommendations and promised to implement them in the development plan as swiftly as possible. It also expressed support for the continuation of the nuclear powered ship program, the efforts in elevating the level of technology of Japan Nuclear Ship Research and Development Agency, and a thorough review and overhaul by a governmental agency.
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