Study of core characteristics on fuel and coolant type. Results in FY1999

Feasibility studies (F/S) have been undertaken since July, 1999 in order to determine promising concepts of a commercialized fast reactor cycle system and to define the related necessary R and D tasks. In the phase I(FYs of 1999-2000) of this F/S, a number of conceptual candidates are selected from the following 5 viewpoints: a) ensuring safety, b) economic competitiveness to future LWRs, c) efficient utilization of resources, d) reduction of environmental burden, e) enhancement of nuclear non-proliferation. As for this study based on the above viewpoints, core characteristics of many kinds of reactors have been surveyed and classified in the combinations of fuel (MOX, metal and nitride) and coolant (sodium, lead, lead-bismuth, carbon dioxide and helium) types and power output scales. As a result, R and D items to be performed have been proposed, and a data base to select candidate reactor concepts has been constructed. The intermediate results obtained in the first FY of the phase I are as follows: (1) There are many years of experience for the MOX fuel compared with metal and nitride fuels. However, metal and nitride fuels are excellent for breeding and doubling time. (2) The metal fuel has the cladding temperature limit corresponding to the core outlet temperature of 510-530degC, due to the fuel-clad compatibility problem which is lower than in the MOX fuel case. A new cladding material should be developed to achieve the higher temperature. (3) The nitride fuel has the demerits due to estrangement of nitrogen under accident conditions and also due to the necessity of enrichment of 15N. (4) Some high burnup experience has been accumulated for the metal fuel and even less for the nitride fuel. Experiential evaluation of high-burnup behaviors and accumulation of high-burnup fuel irradiation experiences are indispensable for making these fuels a general high-burnup fuel concept. (5) From the core characteristics, there is no difference among sodium, heavy-metal and gas coolants. (author)