Sheathed-Thermocouple-Electrode Type Instrumentation for LMFBR Individual Subassembly Monitoring

Outlet temperature, channel flow-rate, boiling, fission-gas discharge and cover-gas entrainment can be detected from four wires of a pair of grounded-type sheathed chromel-alumel thermocouples inserted into the outlet open channel where magnetic flux traverses from a magnet circuit mounted inside the wrapper tube of individual subassembly of the liquid-metal-cooled fast breeder reactor. The modified conceptual design is presented. Use of magnet in the core environment for a period of time equal to the subassembly life seems hopeful according to reported informations. Simulation tests reveal its excellent stability and linearity just like an ordinary type. Calculated emf by an approximation is almost consistent with the measured. Shunt effect by the sheath is minor. Twenty-one proto-type magnet circuits are arraied in positions of the core-map. A continuous systematic arrangement is found to give nearly uniform flux density over the core. Two of them are built in a demonstration set, which is tested in sodium flow of up to 550°C. In actual use of the conceptual design, approximately 19 mV will be obtained against sodium flow of 10 m/sec at 650°C. Argon-gas is injected into stagnant and upflowing sodium. Significant noise is observed. Noise-amplitude monitoring is recommended for sensitive gas-void detection. In conclusion, this type is considered very promising in future LMFBR plants.