Feasibility Study of Sheathed-Thermocouple-Electrode Flowmeter for LMFBR Individual Subassembly

Abstract

A very local disturbance in a subassembly could propagate to gross failure over the core in large liquid metal cooled fast breeder reactor plants. The recent practice is to install a number of thermocouples in the outlet of each subassembly, but the protection thus provided is limited in extent. Probe type eddy current flowmeters are under development in many countries but the accuracy, simplicity and stability do not at present provide satisfaction.
A unique proposal of "sheathed-thermocouple-electrode flowmeter" is hereby presented. A pair of magnets and pole-pieces mounted inside a subassembly shell gives a transverse magnetic field in the outlet open channel. A pair of grounded type sheathed CA thermocouples is inserted into this field. The electromotive forces emerging from the four wires of the thermocouple pairs, by combination, should provied useful information on the outlet temperature, channel flow rate, sodium boiling, fission gas release resulting from pin failure, and cover gas entrainment. Essentially it requires no additional sacrifice on the part of reactor and fuelhandling designs compared with current outlet thermocouple installations. A preliminary feasibility study has been made of this new type of flowmeter, and ample proof has been obtained of its practicability.