A research team led by Prof. Yoshiaki Oka of Waseda University has succeeded in developing a conceptual nuclear power reactor design of high plutonium breeding by light-water cooling for the first time in the world. The team devised a new fuel assembly where fuel rods are closely packed for reducing a reactor coolant to a fraction of fuel volume for high breeding. Prof. Oka succeeded in high plutonium breeding by light-water cooling through computational analysis.
Fast breeder reactors (FBRs) produce more fissile material than consuming while producing electric power. It is a "dream of nuclear power." The main line of FBR development has been liquid metal cooled fast breeder reactors (LMFBRs). It is, however, not yet commercialized because of the complexity of a plant due to the use of liquid sodium as a coolant.
A nuclear fuel cycle and FBRs are important for reducing the amount of spent nuclear fuel of light-water reactors (LWRs) and efficient utilization of uranium resources. Nuclear power utilization is in progress in developing countries. Commercialization of spent nuclear fuel reprocessing in advanced countries enhances nuclear security in the world.
Under the conceptual design, the breeding performance -- the compound system doubling time -- is 40 years. It means that the fissile material and electricity production of a group of FBRs double in 40 years. Energy demand is proportional to gross domestic product (GDP). The growth rate of GDP of seven advanced countries in the OECD is 1.4% in the past 10 years. It means that GDP and energy demand double in 50 years. The breeding performance meets the growth rate of energy demand in advanced countries.
The study will open the way for commercialization of FBRs and a nuclear fuel cycle for peaceful use of nuclear energy based on the mature light-water cooling technology. The result of the study was published in the January issue of "Journal of Nuclear Science and Technology" of Atomic Energy Society of Japan (AESJ).
Breeding characteristics increases with decreasing the water to fuel volume ratio. Tight fuel lattice with narrow gap between fuel rods was adopted for reduced moderation boiling water reactor (RMWR). For further decreasing the water to fuel volume fraction, a new fuel assembly of closely packed fuel rods was devised. The new fuel assembly and its fuel lattice consisting of three fuel rods are depicted in Fig.1. The coolant flows through the central hole of fuel lattice. The integrity or the leak tightness of the fuel rod is maintained as the conventional fuel rod where both ends of the fuel cladding tube are welded by end plugs.
The reactor design was carried out by computational methods for the cores with new fuel assemblies. The highest breeding characteristics are obtained for the core layout of the fuel assemblies in Fig. 2. The comparison of the characteristics with the RMWR is given in Table 1. The compound system doubling time is 43 years. It is substantially shorter than that of RMWR, 245 years.
Goal of breeding characteristics
The energy demand increases with the gross domestic product (GDP) . The growth rate of GDP of seven advanced countries of OECD is 1.4% per year in 10 years. With this growth rate, the GDP becomes double in 50 years and the energy demand does. The breeding characteristic of Table1 is 43 years, shorter than 50 years. It means that the fast breeder reactors with the new fuel assembly meet the goal of energy demand growth of advanced countries.
Future Research and Development items
Reactor design of boiling water reactor (BWR) condition, safety design and evaluation, development of the new fuel assembly including testing, demonstration with a prototype reactor.
High breeding with water cooling technology will open the way of commercializing nuclear fuel cycle and fast breeder reactors. It made it possible to reduce the amount of spent LWR fuels, to enhance the deployment and the security of peaceful uses of nuclear power in developing countries.