Development of an Approach for Monitoring Intermediate Level Nuclear Waste Using Thermal Imaging and Gamma Testing of Thermal Imager

The temperature measurement of intermediate level nuclear waste containers is vital to monitor their long-term condition. Thermal imaging has a number of advantages for this application compared to single spot radiation thermometers, and, as such, it was selected to monitor intermediate level waste containers. In order to achieve a low measurement uncertainty, a robust temperature calibration is required, and it is important to have a good level of confidence in the emissivity of the surface being measured. The infrared emissivity of the container materials was therefore measured and corrected for. The third consideration is the impact of gamma radiation on the thermal imager and how any radiation damage will affect the measured temperature. The implementation of a calibrated instrument and emissivity correction was validated using temperature controlled, 1:10 scale model 3 m3 box containers within a climatic chamber. The surface temperature of the scale containers was determined to an uncertainty of ±6.5°C (
$k =2.1$
) for the container walls, ±3.5°C (
$k =2.1$
) for the container lid, and ±1.5°C (
$k =2.1$
) for the container vents. The radiation testing of multiple thermal imagers indicated no calibration drift due to radiation exposure and provided the maximum achievable lifetime in terms of total radiation dose, with this being 598 ±35 Sv (
$k =2$
). The techniques used to operate within a gamma environment and determine the temperature of the 1:10 scale 3 m3 box containers were therefore successful.