System design study of a small lead-bismuth cooled reactor

Chikazawa, Yoshitaka  ; not registered; not registered

Small sized fast breeder reactors have a potential to use a power source applicable to diversified social needs. In the Feasibility Study of JNC, we will make a concept of small sized fast breeder reactor with various requirements of economical competitiveness, reactor safety, very long lived core, etc. The design requirements for a small lead-bismuth cooled fast breeder reactor in Fiscal Year 2001 (FY2001) were defined as follows; (1)electric power: 50 MWe, (2)fuel type: mixed nitride fuel, (3)reactor type: tank type (no secondary cooling system), (4)coolant circulation system: natural circulation, (5)fuel exchanging system: handling of each fuel subassembly, and (6)core life: 30 years. In order to reduce construction cost of the plant, the concept of a fuel exchanging system was changed to a conventional subassembly handling type as comparing a whole-core handling type in a study in FY 2000. And balance of power of the coolant system was reevaluated. Though a reevaluated diameter of the reactor vessel (3.85 m) was larger than that of a previous design (3.7 m) in FY2000 because of a change of the core size, the total mass of nuclear steam supply system was reduced from 324 tons to 259 tons with simplified reactor structure owing to no requirement of a whole-core handling mechanism. The constitution of a decay heat removal system was chosen which was a system of one PRACS and ONE RVACS driven by natural circulation in order to satisfy a heat removal condition of Category IV in Japanese Standard. The construction cost of the plant was estimated at 800,000 yen/kWe which was much higher than the target value, that is, 350,000 yen/kWe (5.5yen/kWh), because of a scale demerit coming from a low power and a usage of heavy reactor components for lead-bismuth coolant. But it would have some possibility to reduce the construction cost with an increasing of a reactor power, a common use of some BOP components among reactors and a learning effect of construction.