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Nuclear Ship Mutsu

"Mutsu" was the first nuclear ship in Japan which was designed and constructed by Japanese independent technology. The first Japanese nuclear powered merchant ship "Mutsu" was put to sea for the first experimental voyage in 1974. The faulty design of the reactor shield caused radiation leak during the first power output experiment of Mutsu. While the engineers shut down the reactor before contamination became serious, the mass media's wording of "radioactivity" leak undermined the image of Mutsu. The officials originally reported the Mutsu accident to be "radiation leak". Radioactivity leak describes, for example, leak of uranium or primary coolant water. However, it ended up being reported as "radioactivity leak", which neither legal entity nor governmental agency corrected. It is always difficult to recover from negative publicity.

After accomplishing its objective, Mutsu was decommissioned in 1992. By that time in the world, Otto Hahn of West Germany and Savannah of the USA had already completed their experiments and research voyages. There is no plan to develop nuclear powered commercial ships, because construction of nuclear powered ships are economically inefficient unless the ships' size is larger than 100000t. People may wonder what significance the lengthy project had, spending more than 120 billion yen in 25 years. Looking back ta the history, the development of Mutsu was understandable considering the global trend at that time, the government acted too slowly to drop the nuclear powered ship program. Some may even say that Japan has a tendency to take no action even when it is necessary.

The town of Mutsu is known for the mass resistance movement against the mother port of the nuclear ship named "Mutsu", which was later modified into a weather ship - the nuclear reactor being removed out of the hull - after some hundred hours of experimental cruises. The reactor itself can be seen at the exhibition facility near the Mutsu port. Spent fuel from the Mutsu nuclear ship had been kept at the same place, but was later transported to the Japan Atomic Energy Research Institute (JAERI) in Tokaimura, Ibaraki Prefecture.

MIRAI is a conversion of the former nuclear powered ship MUTSU. The vessel's reactor was removed in 1995, non-reusable parts were dismantled and asbestos removed, and in 1996 the vessel was reborn as MIRAI. The research ship MIRAI was completed and delivered to Japan Marine Science Technology Center in September 1997 at Tokyo Shipyard of Ishikawajima Harima Heavy Industries Co., Ltd. and at Nagasaki Shipyard of Mitsubishi Heavy Industries Co., Ltd. MIRAI provides excellent navigational performance and resistance to ice. The vessel can conduct long-term observational studies over wide areas, and is used for oceanographic surveys primarily in the subtropic and subarctic regions of the Arctic, Pacific, and Indian Oceans. It is hoped that MIRAI will perform a role as an advanced international station for ocean-based, marine-Earth research as well as function as a base for transmitting various types of marine and Earth data.

Small reactors have merits such as higher safety and easy deployment for distributed energy supply such as district heating, desalination and hydrogen production. From this point of view, we are developing following reactor concepts. As of 2008-2009 the Nuclear Reactor Engineering Laboratory at Hokkaido University was evaluating a revised nuclear design of the reactor for the first Japanese Nuclear Ship Mutsu using the newest and proven nuclear fuel for the current PWRs to have long core life without on-site refueling. the modification of the reactor was initiated by taking into improvements and technology of the state of arts to fulfill the requirements such as (1) Longer core life without refueling. (2) Reactivity adjustment for load change without control rods or soluble boron, (3) Simpler operations for load changes and (4) Ultimate safety with sufficient passive capability. The new fuel rod has higher fuel enrichment for longer core life. So there is a need for a burnable poison to reduce high excess reactivity. The candidates as a burnable poison are Er and Gd. There is a reason to use Er. When the UO2 fuel enrichment of more than 5wt% is supposed to be used, facility alternations are needed from the point of the critical safety. The proposed core life time is about 10years and the proposed core has enough reactor shutdown margin.


Mutsu [Scombrops cheilodipteroides ] is a fish coming with the cold weather and lasting until late spring. The Mutsu one of the Percidae - is an edible fish of some size, which abounds on the Pacific shores of Japan, has pelagic eggs spawned in January and February, when it comes to shallower water from its usual haunts in two to three hundred fathoms on rocky or sandy ground. Like the young Cod, the young Mutsu are found swimming off the rocks in three or four fathoms, and are supposed to attain maturity in three or four years. It is used chiefly in the fresh state, and its roe is also much esteemed. In some respects it has a distinct flavour of the shad, and the flesh is very tender and delicate, albeit with very few bones to distract the attention from the flavor. Hand-line fishing for the mutsu (Scombrops chirudipteroidee) is prosecuted in the deep sea, in depths usually exceeding 300 fathoms. A fine 2-stranded silk or linen line is used; this is coiled in a shallow circular basket like those used for trawl lines.

The Emperor Komei died in 1867 and Mutsu Hito, not yet fifteen years old, ascended the throne amid the struggles of a civil war. His reign was well named Meiji (may-jee) meaning "enlightened progress" for it has brought wealth and prosperity to his people, along with the railroads and steamboats, telegraphs, telephones, electric lights, and other modern inventions. While foreigners called him Mikado and Emperor to his people the Meiji Emperor was something more, their revered Tenno, with more than 2500 years of history crowded into that title.

The province of Mutsu formerly extended beyond the northern shore of the main island, and included the territories of the daimio of Matsumae. After having defeated Fujiwara Yasuhira in 1189, the militant Yoritomo divided the great provinces of Mutsu and Dewa among several of his favorite officers. In 1868, after the rebellious daimios of Oshin and Dewa had submitted to the Mikado, those two provinces, which far exceeded in extent any others in the country, were subdivided, for obvious political reasons. In 1869 the province of Mutsu (Mutsunoku, or Oshin) was divided into five, namely Iwaki, Iwashiro, Rikuzen, Rikuchiu and Mutsunoku.

Mutsu Bay is a large bay at the northern end of Honshu Island, Japan. Mutsu Bay covers about 1660 km. Scallop culture has been greatly enhanced since the 1950s due to the success in collecting natural scallop spat. An important contribution to the technique of spat collection was made by a Mutsu Bay fisherman, who fastened a small-mesh onion-bag around the cedar leaves, allowing the scallop larvae to enter the mesh and settle on the cedar leaves. Lantern nets are used extensively in Mutsu Bay, Japan, where they were first developed, and have been widely and successfully adopted elsewhere.



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Page last modified: 18-01-2020 19:10:10 ZULU