JAEA is now conducting “Fast Reactor Cycle Technology Development (FaCT)” project for commercialization before 2050s. A demonstration reactor for Japan Sodium-cooled Fast Reactor (JSFR) is planned to start operation around 2025. In the FaCT project, conceptual design study on the demonstration reactor has been performed since FY2007 to determine referential reactor specifications for the next stage of design work of licensing and construction study. Plant performance as a demonstration reactor for the 1.5 GWe commercial reactor JSFR is being compared between 750 MWe and 500 MWe plant designs. In this paper, the current status of the conceptual design study for the demonstration reactor plant is summarized.
A conceptual design study of Japan sodium-cooled fast reactor (JSFR) is in progress as the ''Fast Reactor Cycle Technology Development (FaCT)'' project in Japan. A selector-valve type failed fuel detection and location (FFDL) system is applied to the JSFR design that has an upper internal structure (UIS) with a slit above the core and several sampling nozzles for the FFDL are set in the UIS around the slit to detect the fission product (FP) from the subassemblies below the slit. Therefore, mixing process in the UIS of complicated geometry should be known and appropriate arrangement of the sampling nozzles in the UIS is needed. A water experiment using a 1/5-scale model was carried out to investigate the mixing process in the UIS and concentration distribution of FP simulant. Experimental results showed that the sampling nozzles set in the UIS detected the FP simulant concentration within the criteria of FFDL signal detection, even in case of failed subassemblies under the UIS slit. In addition, identification of the failed fuel subassembly under the UIS slit was achieved by means of comparing concentration profiles in the UIS. Therefore, the suitable sampling nozzle arrangement was obtained for JSFR. A numerical simulation using a CFD code was carried out and the simulation method was validated based on the experimental data of the FP simulant concentrations. The simulation results showed that the simulation predicts the FP concentration distributions.
An advanced loop-type sodium-cooled fast reactor has been developed by the Japan Atomic Energy Agency. The upper internal structure (UIS) above the core is a key component where control rod guide tubes are housed. A radial slit is set in the UIS to simplify the fuel-handling system and to reduce the reactor vessel diameter. A high-velocity upward flow is formed in the UIS slit. This slit jet influences thermal hydraulic issues in the reactor vessel. A water experiment was carried out to understand the flow field in the UIS, which is composed of the control rod guide tubes and several horizontal perforated plates with a slit. A refractive index matching method was applied to visualize the flow in such a complex geometry. Velocity measurement using particle image velocimetry showed that the velocity in the UIS slit was accelerated by the multiple slits and kept at a high value at the mid-height of the reactor upper plenum. A numerical simulation was carried out for this complex geometry of the UIS to obtain an adequate simulation method. A comparison between the experimental and analytical velocity profiles showed that the numerical simulation is highly applicable.
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