Analytic Thermal Model of an Optical Fiber Based Gamma Thermometer and its Application in a University Research Reactor

This paper describes and validates, by comparison with numerical modeling results, an analytical model of thermal transport in an optical fiber based gamma thermometer (OFBGT) that is appropriate for use in university research reactors. The maximum temperature difference between the thermal mass and the outer sheath (AT) for the OFBGT design that we have considered is approximately50°C, for the OFBGT in the Central Irradiation Facility of the Ohio State University Research Reactor (OSURR) with the reactor operating at full power (450 kW). The maximum value of AT that is predicted by the analytic model for the OFBGT design is smaller by approximately 1.1 °C than the value of AT which is predicted by the numerical model, for the same OFBGT design, but including all the details of the design. We have used the analytical model of thermal transport in an OFBGT to determine a normalized Modulation Transfer Function (MTF'(k)) for the OFBGT. We conclude that MTF? (kOSU) > 0.99, where kOSU is the spatial frequency for the axial dependence of the reactor power distribution in the OSURR.