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Present and future activities of nuclear desalination in Japan Akio Minato*, Mitsuyoshi Hirai** *Central Research Institute of Electric Power Industry 1-6-1, Ohtemachi, Chiyoda-ku, Tokyo 100-8126 Japan **Water Re-use Promotion Center 3-5-4, Nihonbashi-Ningyocho, Chuo-ku, Tokyo 103-0013 Japan In Japan, 52 nuclear power plants are now being operated. And following start of operation of the most recently completed plant in 1996, they supply about 33 % of the total electricity. All technologies related to design, construction and operation of the nuclear power plant domestic at the present time. Regarding the desalination technology, the first MSF (Multi Stage Flash) desalination plant with the capacity of about 2,600 ton/day has started its operation for the potable water supply into the cool mine at Kyushu Island. The heat energy source of its plant was supplied from the fossil fire plant. Recently, a seawater desalination plant with Reverse Osmosis (RO), of which capacity is 40,000 ton/day, is now being operated at Miyakojima Island in Okinawa and 50,000 ton/day seawater desalination plant with advanced RO (recovery ration of about 60 %) is now under construction at the north region of Kyushu Island. The object of both plants is to supply a potable water. Subsequently, many desalination plants have been constructed to supply potable water and industrial water. The total capacity of seawater desalination plants has reached about 140,000 ton/day as of today. Furthermore, the export of the desalination technologies has increased and Japanese industries contribute about 20% of the desalination plants in Middle East region in the design, operation, construction and maintenance at the present time. Thus, Japan has a mature technology in both nuclear power and desalination. Seawater desalination plants are installed with several nuclear power plants in order to satisfy the regulation for nuclear plant installation. This has been done where there is a limited source of water due to the geological condition. These desalination plants are being operated to ensure supplemental water by using a thermal or electrical energy from own nuclear power plant. ME (Multi Effect) desalination plant with a capacity of 1,300 ton/day started its operation at Ohi Nuclear Power Plant of Kansai Electric Power Company from 1976. At present, small desalination plants (MSF, MED or RO) with a unit capacity of about 1,000 ton/day are now being operated at several nuclear power plants, such as Takahama nuclear power plant of Kansai, Ikata nuclear power plant in Shikoku and Genkai nuclear power plant in Kyushu [1]. Some special design or technology is applied in the desalination plants (Distillation or Reverse Osmosis) that are installed in support of the nuclear power plant system. The distillation system was designed so that a postulated failure event in the desalination system does not affect the operation of nuclear power plant, A steel vessel covers the graphite vessel of RO module. Each desalination plant is not operated continuously during a year because the major function of the plant is to ensure the supplement water for the nuclear power plant. Regarding the maintenance of desalination plant, some piping was exchanged due to the corrosion by high temperature seawater, however, each desalination plant are being operated without any trouble as of today. The installation experience, operating conditions and maintenance experience from the nuclear desalination will be described in this paper. Recently, the development of innovative and/or small reactor design, which does emphasis safety feature, is promoted in Japan, in order to apply to the seawater desalination and to install in the developing countries. An advanced RO system with less energy consumption technology is also being developed. Furthermore, some Japanese industries and universities are now very interesting in the nuclear desalination [2,3,4]. Present and future activities related to nuclear desalination in Japan will be described in this paper. References �Operating Experience Gained with Nuclear Desalination Plants by Japanese Electric Power Companies�, IAEA-SM-347/15, IAEA, Nuclear Desalination of Sea Water, Proceeding of s Symposium Taejon, Republic of Korea, 26-30 May, 1997 �A Challenge to Global Environmental Issues by Small Reactor - Nuclear Desalination and Prevention of Desertification -�, 3rd International Symposium on Global Environment and Nuclear Energy Systems, Tokyo Institute of Technology, Oct., 1999 �A proposal for reusable type small PWR for sea water desalination�, K. Shimamura, K. Inoue, Y. Uchiyama, A. Minato, IAEA-SR-218/13, International Seminar on Status and Prospects for Small and Medium Sized Reactors, IAEA-SR-218, Egypt, 27-31 May, 2001 "A distinctive coupling concept of small natural circulation BWR and RO desalination system�, K. Kataoka, H. Heki, IAEA-SR-218/13, International Seminar on Status and Prospects for Small and Medium Sized Reactors, IAEA-SR-218, Egypt, 27-31 May, 2001