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Selector-Valve Failed Fuel Detection and Location System for Japan Sodium-Cooled Fast Reactor

The Japan Sodium-cooled Fast Reactor (JSFR) is studied as an advanced loop-type sodium-cooled reactor. A selector-valve (SV) mechanism is adopted in the design of JSFR for its failed fuel detection and location (FFDL) system. JSFR has only two FFDL units for 562 core fuel subassemblies to reduce construction cost by decreasing the reactor vessel diameter. Consequently, one SV-FFDL unit must handle about 300 subassemblies. Because of the large number of subassemblies per unit, it is predicted that the total duration for measuring all the fuel subassemblies becomes long. In addition, JSFR adopts an upper internal structure (UIS) with a slit above the core. In order to detect the fission products from the subassemblies below the slit, additional sampling nozzles for the FFDL are set in the UIS around the slit. In previous water experiments and numerical simulation, the sampling performance for the subassemblies under the UIS slit has been evaluated to be lower than those under the normal UIS position. In this paper, the outline of the FFDL system is shown, which can be applied to a large number of fuel subassemblies in a compact reactor vessel. The detection capability of the FFDL system was studied to achieve the design conditions. Operation modes and procedures of the FFDL system were also investigated.