Patent ID: 8831162

Claim:
A system, comprising: a reactor core; a γ-ray thermometer comprising: a container, a γ-ray heat generation detection section, a thermocouple thermometer, and a calibration heater, the γ-ray heat generation detection section contained in the container and located in the reactor core, the γ-ray heat generation detection section comprising: a cylindrical structural member contained in the container, the structural member provided with a heat insulator in the reactor core, part of the structural member that is located in the reactor core generating heat due to γ-rays, and a differential thermocouple contained in the structural member, the differential thermocouple including a hot junction located at a same vertical level as the heat insulator in the reactor core and a cold junction located at a vertical level lower than the heat insulator in the reactor core, the thermocouple thermometer contained in the structural member and located lower than a bottom of the reactor core, wherein the thermocouple thermometer measures the temperature of coolant flowing in the reactor core, and the calibration heater being installed inside the structural member, extending vertically at least between the γ-ray heat generation detection section and the thermocouple thermometer, and reaching the thermocouple thermometer; and an output signal processor receiving a signal output from the thermocouple thermometer and the differential thermocouple and computationally determining a local temperature of the coolant at the thermocouple thermometer.