Abstract
Despite being regarded as a well-established field, temperature measurement continues to pose significant
challenges for many professionals in the metrology industry. Thermal imagers enable fast, non-contact
and a full field measurement, however there is a lack of metrological development to support their use.
Here, thermal imagers have been examined for the monitoring of special nuclear material containers; the
surface temperature is an important parameter for store management decisions. Throughout this research:
a selection of thermal imagers were calibrated and made traceable to the International Temperature Scale
of 1990; laboratory observations of a proxy steel plate were made; initial measurement of nuclear material
storage containers were made; then a deployment to an inactive store was demonstrated. For this technique
to be feasible, uncertainties less than 10 °C would be required.
During the laboratory calibration of an uncooled and cooled thermal imager against blackbody reference
sources, across the measured temperature range of 10 °C to 100 °C the uncertainties were less than 3.20 °C
(k = 2) and 0.50 °C (k = 2) respectively. Here k is the uncertainty coverage factor. When these calibrations
were applied to the plate, regions of steel and higher emissivity coating were evaluated. These uncoated
regions were measured with a thermal imager to demonstrate temperature differences compared to surface
mounted thermocouples of 8.3 °C and uncertainties up to 30.1 °C (k = 2). For the coated regions this
temperature difference was reduced to 1.8 °C with uncertainties up to 6.8 °C (k = 2).
Extending this approach to store containers – each instrumented with internal heaters and thermocouples
– yielded poor comparability between thermocouples and an external thermal imager. Using a revised
container instrumentation, deployment of two uncooled thermal imagers to an inactive store to observe
the container was completed. From this measurement campaign the surface temperature determined using
a thermal imager for a container ranged from 4.9 °C (k = 2) to 20.5 °C (k = 2). These results demonstrate
the feasibility of thermal imagers being deployed to nuclear material stores for the assessment of radioactive
material behaviour in storage containers