Effect of Gamma-Ray and Neutron Heating as Interfering Input for the Measurement of Temperature Using Optical Fiber Sensor System

This paper accounts for gamma-ray and neutron heating of an optical fiber/capillary tube temperature sensor by including current sources in the fiber and capillary tube in the electrical analog of the capillary tube/fiber sensor system. The resulting model is examined to determine the conditions for which gamma-ray and neutron heating of the capillary tube/fiber sensor system is a significant interfering input for the measurement of the steady-state temperature of the medium in which the capillary tube/fiber sensor system is immersed, or the temperature of the component to which the capillary tube/fiber sensor system is attached. The model predicts that gamma-ray and neutron heating may result in a discrepancy, on the order of tens of degrees centigrade, in the sensed temperature, in comparison to the temperature of the medium, for a bare fiber in stagnant air for a power reactor. However, for the case of bonding of a capillary tube/fiber sensor system to metal, or the placement of the sensor in a liquid for which the heat transfer coefficient exceeds approximately 1 × 10
⁺⁴
(W/m
²
· K), the discrepancy in the sensed temperature is predicted to be negligible for power reactor neutron and gamma-ray absorbed dose rates.