Conceptual design study of JSFR (1) - Overview and core concept -

The major concept for FBR in Japan and its core concept will be shown in the full paper. The abstract of the core concept is shown as follows; The Japan Sodium-Cooled Fast Reactor (JSFR) at the commercialized stage should have excellent prospects in operation and maintenance as well as the economy. The conceptual core design study on JSFR has been performed from view points of safety, economics, resource utilization, environmental burden reduction, and nuclear proliferation resistance. The major consideration in core design studies is concentrated on the following requirements. From the safety consideration of hypothetical accidents, core coolant void reactivity should be low enough to prevent the prompt criticality in the initiating phase of Core Disruptive Accident (CDA), and measures of early discharge of molten fuel should be considered in the core and fuel design to prevent the recriticality in the transition phase of CDA. The core design is aiming at the core coolant void reactivity of 6$ or less, the core specific power of 40kW/kg -MOX or more and the core height of 100cm or less in order to avoid the excess positive reactivity insertion in the initiating phase of Unprotected Loss of Flow (ULOF) events. The newly designed FAIDUS (Fuel Assembly with Inner Duct Structure) type subassembly concept is adopted in fuel design of JSFR. The inner duct is installed at corner of subassembly and a part of upper shielding elements removed in FAIDUS. In the transition phase of CDA, the molten fuel enters the inner duct channel and goes out from core region passing through the upper shielding. The FAIDUS type assembly is expected to have superior performance for molten fuel release at CDA. For the reduction of fuel cycle cost due to the economical competitiveness requirement, the target of core average discharge burnup is 150GWd/t, and the total average discharge burnup (including blankets) 60∼80 GWd/t. The high burnup contributes to reducing the fuel mass capacity in the fuel cycle facilities like reprocessing plants and fuel fabrication plants. Cladding and wrapper tube materials of JSFR are ODS (Oxide dispersion strengthened) martensitic steel and PNC-FMS (ferritic/martensitic steel), respectively, which withstand neutron dose of high burnup fuel. Ferritic/martensitic material is selected because of its dimensional stability up to high neutron dose. ODS martensitic steel is selected because of its excellent high temperature strength as well as its dimensional stability. From a viewpoint of uranium resource utilization, core should have flexible breeding capability. The target for the maximum breeding ratio of JSFR is 1.1-1.2. The high breeding core with breeding ratio of 1.2 is achieved by changing of fuel specifications under the same fuel assembly size as the low breeding core and the same core layout. Figure-1 shows the core layout. The core of JSFR is composed of 288 inner core fuel subassemblies, 274 outer core fuel subassemblies,96 radial blanket fuels and 57 control rods. The major fuel specifications of the low breeding core are as follows. The fuel pin diameter is 10.4mm, number of fuel pin per subassembly is 255, outer flat-to-flat width of wrapper tube is 201.6mm and fuel subassembly pitch is 206.0mm. The fuel pin length is 2690mm. This paper describes the current study for core and fuel design in JSFR. It shows the core and fuel specifications and core layout of JSFR, and describes the evaluated results of neutronic and thermal hydraulic characteristics and fuel integrity such as CDF