The measurement of temperatures above 1000 °C is both difficult and yet vital for the success of a wide range of industrial processes, including nuclear fuel production and essential nuclear safety testing. In the nuclear sector, measurements can be required up to 2500 °C and the nuclear waste often needs long term, continual and reliable observation.
The harsh environment which is synonymous with the nuclear industry makes it difficult, if not impossible, to use traditional temperature sensors. Conventional sensors undergo mechanical and chemical changes which cause calibration drift and errors in measurement, and frequent replacement is not possible.
Using temperature sensors based on fundamental thermometry, like a Johnson noise thermometer, avoids this problem. The main development challenge is to extract the tiny Johnson noise signal from ambient electrical noise influences using compact electronics.
Monitoring of the UK’s nuclear waste inventory can be improved by periodic non-contact temperature measurements. Identification of ‘hot spots’, where high radioactivity exists is critical. Thermal imaging can remotely measure the surface temperature, provided the surface emissivity is known. This is often not the case. Imaging phosphor thermometry can be used to determine the surface temperature at a number of key locations independently of the emissivity. By combining thermal and phosphor imaging, it is possible to measure surface temperature accurately.