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

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

Preliminary study on oxidation of nuclear grade graphite

A test methodology has been defined in order to assess the risk of bulk-oxidation of nuclear graphite with a focus on particular operations, such as cutting of graphite components during decommissioning of nuclear reactors. Graphite is used for its properties in nuclear reactors, as a fuel element matrix, moderator, structural and reflector material. The experimental tests have been performed using a horizontal TGA-DTA furnace and both isothermal and nonisothermal tests were performed on non-irradiated specimens. In isothermal tests, testing temperature range was 550 – 750 °C, the selected temperature has been reached heating the furnace under N2 atmosphere at 5 °C/min, then oxidation has been evaluated at constant temperature in air (100 mL/min) for at least 180 min. Non-isothermal tests have been performed either under N2 atmosphere or air and samples have been heated at 5 °C/min from 30 to 950 °C. As several properties may affect the oxidation resistance of nuclear graphite, such as impurities, grain size, pore structure, graphitization degree, antioxidation treatments, the testing protocol has been preliminary applied to non-irradiated graphite samples from two different graphite reactors. Preliminary experimental results revealed the excellent ability of the tested graphite samples for oxidation resistance with lower oxidation rates and longer oxidation times compared with some literature results