Reactor core monitor in FBR type reactor

Purpose: To simplify the method of controlling control rods for the measurement of power distribution and enable the monitor for various states in a reactor core. Constitution: In FBR type reactors, power distribution has been monitored by disposing a coolant temperature meter and a flowmeter at the inlet of the reactor core and at the exit of the fuel assembly. Although it is possible to determine radial power distribution but obtain no axial information in this method, which has been determined by reactor core calculation using a calculation model. In this invention, the power distribution is determined by fixing the insertion state of the control rods and displacing materials giving fluctuation in the power distribution (external disturbance generating material) at the inside of the fuel rod. That is, a guide pipe is disposed to the inside of the control rod and an external disturbance material comprising control rod constituent material B4C capable of displacement is disposed at the inside of the guide pipe. The material is moved in each of the axial directions of the guide pipe to cause power change in the reactor core region in adjacent with the external disturbance material. Then, the axial power distribution in the reactor can be determined by measuring the change of the assembly channel power caused by the power change. (K.M.)