| FUGEN PLANT DESCRIPTION AND | ||
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Plant Description |
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Fugen is 165MWe nuclear power station (heavy water moderated, boiling light water cooled, pressure tube type). Its power output is the smallest among the nuclear power plants operating in Japan, but is the only plant to load MOX fuel. As the reactor uses heavy water*1 to moderate neutrons, its core structure is different from that of LWR. But, other than that, it has a similar system to Boiling Water Reactor (BWR) in that the steam generated at the core directly turns the turbine for power generation. The heavy water as moderator is kept in a calandria tank of approximately eight meters in diameter. In the tank, 224 pressure tubes, 12 centimeters in diameter, are installed vertically. One fuel assembly is set in each pressure tube, where light water flows as a coolant. The pressure tubes are surrounded by calandria tubes to make a double-tube structure so that the heavy water as moderator and light water as coolant are completely separated. Carbon dioxide gas flows in the space between the pressure tube and the calandria tube to mitigate the heat transfer from the fuel side to the heavy water side and to detect the leakage of coolant. Heavy water is cooled by circulation to maintain its fixed temperature (49 degrees centigrade at reactor entrance) in the core. Furthermore, boric acid is added to the heavy water to control the reactivity in the core. Helium is used as a cover gas for maintaining the purity of heavy water. Totally, there are 49 control rods, which are inserted from the reactor top into the heavy water via guide tubes installed in the calandria tank. There are 224 fuel channels in the reactor cooling system, which consists of two independent reactor cooling loops with 112 channels for each. Coolant is supplied to the core through an inlet feeder tube that distributes coolant to each channel from a lower header of each loop. In the core, the cooling water is heated up to two phase flow, which enter a steam drum via an outlet riser tube. After water-steam separation in the steam drum, the steam goes directly to a turbine, and the heated water, along with feedwater, returns to the lower header through four down comers pressurized by two recirculation pumps. * 1: Heavy water: In heavy water hydrogen atoms (H) are replaced by deuterium atoms (a hydrogen isotope), and its specific gravity is 1.1. Since heavy water has a small neutron absorption, it is used as a moderator and coolant. Natural water contains 0.015% heavy water and enriched to make heavy water (99.65% or higher) appropriate for reactor's moderation. Heavy water is enriched and produced using chemical reaction and properties differences between heavy water and light water. (e.g. different boiling points, electrolysation facility) |
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Schematic Diagram of Fugen's System
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