Phosphor thermometry for nuclear decommissioning and waste storage

Abstract

Reliable surface thermometry of stored nuclear waste containers is essential for both health monitoring and corrosion modelling. In this paper we investigate the feasibility of using phosphor thermometry for long-term temperature monitoring of nuclear waste containers and storage racks. Two strands of research were conducted. Firstly, two thermographic phosphors (ruby and manganese-doped magnesium fluorogermanate [MFG]), mixed with six different binders were coated onto stainless steel (316L) substrates and exposed for one month to gamma radiation (γ-ray) and sodium hydroxide (NaOH) solution. Secondly, a hybrid fibre-optic phosphor thermometer, capable of measuring these samples, was constructed and tested. The instrument can measure temperatures using both the luminescence decay time and intensity ratio techniques. Following γ-ray and NaOH exposure, no significant degradation in phosphor appearance or performance was observed. The MFG/silicone binder combination gave the best results. The hybrid phosphor thermometer demonstrated for MFG/silicone binder that: the intensity ratio technique gave the lowest measurement standard deviation (σ(T) < 0.1 °C) but suffered minor drift with thermal cycling. the decay time technique (650 nm emission) did not show any drift and was capable of a measurement standard deviation of σ(T) ≤ 0.3 °C.