Monitoring stored nuclear waste with optical fibres
Nuclear power plants are not carbon-intensive sources of energy, but do present challenges in terms of nuclear waste management. To date, geological repositories are the most promising option for the safe storage of spent fuel. Long-term monitoring of repositories is considered essential given the risk of contamination of the water table. Fibre optic solutions are highly regarded given their reliability, accuracy and longevity. This prompted Euratom to fund an RTD project led by the Belgian Nuclear Research Centre (SCK-CEN). Working together with several optical sensing experts, SCK-CEN developed a fibre optic sensor capable of detecting abnormal levels of ionising radiation. The prototype produced during the project, entitled SOMOS, was comprised of special doped optical fibres. Harmful radiation was inferred from absorption at wavelengths between 1300 and 1500 nanometres. Fortunately, temperature effects were negligible while the dose-rate dependence was also shown to be less than 100Gy/h. SCK-CEN experimented with an Optical time domain reflectometer (OTDR) in an attempt to extend the sensor to a distributed set-up. While several important criteria, such as spatial resolution, sensitivity and dynamic range, were satisfied, the trials indicated the need for further research and development prior to deployment. Regardless, efforts such as SOMOS will ensure that geological repositories can be properly monitored over long periods of time.
