Development of a fiber-optic temperature sensor for remote measurement of the water temperature in a spent nuclear fuel pool

A fiber-optic temperature sensor (FOTS) using an infrared optical fiber was developed and applied to remote and real-time measurements of the temperature of the water in a spent nuclear fuel pool (SNFP) at a nuclear power plant (NPP). In this study, metal caps were employed as the sensing probe of the FOTS owing to their high thermal conductivity. An infrared optical fiber, PIR AgCl:AgBr polycrystalline fiber, was used to transmit the infrared light emitted from the water at a certain temperature. The FOTS was used to measure the temperature of the water in oil bath by changing the temperature in 5 °C increments over the range from 30 to 70 °C. The temperatures measured by using the FOTS with a metal cap varied almost linearly over that range, which means that the FOTS with a metal cap can be used as an auxiliary monitoring system for measuring the temperature of the water in a SNFP water temperature.