Toward Gamma Ray Immune Fibre-Optic Phosphor Thermometry for Nuclear Decommissioning

Abstract

AbstractTemperature measurement of stored nuclear waste is important for long-term monitoring. Conventional sensors can degrade in ionizing radiation from induced transmutations and their frequent replacement is inconvenient. A thermometer based on suitable phosphors can overcome some problems, but the optical signal needs to be transmitted through an optical fibre and processed remotely away from the dangerous area. This requires that the optical fibre itself be suitably resistant to radiation-induced damage. Here, we report transmission measurements through a type of hollow-core fibre based on anti-resonance and with transmission windows at wavelengths suitable for use with the thermographic phosphor magnesium fluorogermanate whilst subjected to gamma radiation. Its performance is compared to commercially available standard fibres (single mode and radiation hard fibres) at dose rates equivalent to decades of use in a storage facility. Transmission was unchanged for the anti-resonant fibre at the phosphor emission wavelength and it was successfully incorporated into a fibre thermometer that worked from $${20}\,^{\circ }\hbox {C}$$ 20 ∘ C to $$200\,^{\circ }\hbox {C}$$ 200 ∘ C . Performance at the phosphor excitation wavelength needs to be improved by modification to the hollow-core fibre design, but we show that a hybrid of single mode and anti-resonant fibres can already be made into a thermometer with suitable gamma immunity.