REACTOR WATER-LEVEL METER

PROBLEM TO BE SOLVED: To provide a reactor water-level meter capable of measuring a water level without being influenced by variations in a reference water level in a reference level device.SOLUTION: A liquid level forming pipe portion 4 of a measurement pipe LP is connected to a gas phase part in a reactor pressure vessel (RPV) 1 and a liquid layer part at a bottom face of the RPV 1, and the liquid level forming pipe portion 4 is constituted so as to form a liquid level therein. By using an optical fiber temperature sensor 5, a temperature difference arising between the gas phase part and the liquid layer part in the liquid level forming pipe portion 4, and a height position at which the temperature difference is generated are detected. Then, on the basis of the detected height position, a water level of cooling water in the liquid level forming pipe portion 4 (that is, a water level of cooling water in the RPV 1) is calculated.