Development of passive safety systems for Next Generation PWR in Japan

Our countryʹs energy demand is expected to increase steadily into the future. When the situation of our country, which is not rich in energy resources, is taken into account, it seems that the importance of nuclear power generation will be heightened. Based on such a background, the basic policy for nuclear power generation is ʹfrom light water reactors to fast breeder reactorsʹ. However, considering that light water reactors have become common, the recent outlook for the supply and demand for uranium resources, development trends of fast breeder reactor technology, etc., the light water reactor is expected to remain dominant in our country until at least the second half of the 21st century. Therefore, five PWR utilities in Japan (Hokkaido, Kansai, Shikoku, Kyushu, and Japan Atomic Power), Mitsubishi Heavy Industries Ltd and Westinghouse Electric Corporation have jointly started researching the Next Generation PWR (N.G.P) which is expected to be the leading nuclear power plant, taking place of APWR [T. Magari, Development of Next Generation PWR in Japan, Proceedings of the 10th Pacific Basin Nuclear Conference, 1996; K. Fujimura, et al.. Proceedings of the Second International Symposium on Global Environment and Nuclear Energy Systems, 19963. In this program, construction is targeted to start from 2010 based on expected future environmental conditions. Now, the capacity of more than 1500 MWe class PWR concept is investigated and a plant concept which has innovative features of a hybrid safety systems, i.e. an optimum combination of active and passive safety systems, and horizontal steam generators for core cooling at the accidents is developed as a promising candidate. The plant concept and the results of the investigation are presented in this paper.