On the other hand, Japan has a precious experience of the nuclear ship "Mutsu". "Mutsu" navigated 81,860km in total (about 2.2 turns around the earth) in eight test services from July, 1990 to December, 1991 using the atomic power, and recorded the total running time of 3,508 hours of its nuclear reactor, and 81.12 million kWh in the integrated thermal output of the nuclear reactor. The maximum design thermal output of the nuclear reactor was 36 MW, the normal thermal output was 32 MW (the maximum continuous shaft output was 10,000 HP, the normal shaft output was 9,000 HP), and the recorded mean rate of operation to the normal thermal output was as high as 83%. The burnup of the uranium 235 of about 3.2kg (equivalent to about 4,000tons in terms of heavy oil) during this period is of about one ball for the baseball in volume. This experiment showed that the marine nuclear reactor can be stored in the space of the dimensions (130m (length) x 19m (breadth) and 13m (depth)) of "Mutsu" without radiation exposure.
In the world, 434 sets of land-based nuclear reactors (370 million kW in total) are in operation as of the end of December, 1996. 390 nuclear-propelled war-ships are under service, and 599 nuclear reactors therefor are in operation. This means that the safety has been proven. The economy for the marine nuclear reactor is left unknown; however, the experiences obtained with the land-based nuclear reactors are remarkably different from those before 45 years when "Mutsu" was planned. The cost will be reduced by designing a standard nuclear reactor using a light water reactor, completing the safety examination once, and manufacturing a large number of reactors of the same type through the type approval system. In considering the experiences that 51 land-based reactors have been operated in Japan without serious accidents, the successful construction and operation of "Mutsu", and the world-leading nuclear reactor manufacturing technology, we feel that Japan bear the responsibility for the challenge to the practical use of the nuclear ships for the world.
However, we do not believe that the use of the atomic power of the nuclear fission type should be continued permanently. It is natural that the fission products of the long life time can not be continuously formed forever. The nuclear fission type atomic power is a kind of "stopgap" to get over the first half of the 21st century until connecting to the age of hydrogen energy similar to natural gas.
Incidentally, there appears a sign of rushing into the age of the fuel cell earlier than expected. The car industry has taken the lead, and the polymer electrolyte type fuel cell will be put into practice in 2010. The stack for passenger cars of 50kW class has been manufactured, but it is doubtful to mount 1,000 stacks on the ships from the viewpoint of the reality. Methanol will be used for the fuel for the time being, but there is a possibility in cyclohexane. The feasibility study should be started immediately whether or not cyclohexane is applicable to ships from the aspects of the economy, the dimensions, the weight, etc. In the second half of the 21st century, there will be an age when a large volume of hydrogen will be produced by the natural energy and the nuclear fusion. If it comes true, the main engines of ships will surely be the fuel cell, and the age of the electric-propelled ship will come.
