Characterization of removable coatings for graphite-moderated nuclear reactors decommissioning

In this study the behavior and characteristics of two removable coatings to be deposited on a nuclear grade graphite substrate were analyzed, with the aim to evaluate their possible application on graphite bricks during dismantling operations of graphite-moderated nuclear reactors.Indeed, nowadays many shut-down reactors are still in decommissioning phase, and effective measures should be taken to guarantee safe dismantling operations. One option could be the use of coating application techniques, which mitigate the risk of graphite dusts spreading and loose contamination, protecting clean surfaces.Tested coatings, both polymeric mixtures, were selected according to their previous application history, availability in commerce and easiness in handling, whereas substrates used were non-irradiated nuclear Virgin Atcheson Graphite Ordinary Temperature (AGOT) graphite samples from L-54M Politecnico di Milano research reactor, which is in decommissioning phase. Thermal characterization of the coatings was carried out before deposition using a Thermogravimetric and Differential Thermal Analysis (TGA-DTA) equipment, tests were performed to obtain a preliminary estimation of the drying time and degradation conditions. After deposition, mechanical properties, such as hardness, of the coating were assessed. The preliminary experimental campaign showed that coating painting could be a feasible option to prevent the spread of highly contaminated graphite dusts during decommissioning of graphite components of nuclear reactors, thus ensuring clean and safe working conditions.