The JET 2019-2020 scientific and technological programme exploited the results of years of concerted scientific and engineering work, including the ITER-like wall (ILW: Be wall and W divertor) installed in 2010, improved diagnostic capabilities now fully available, a major Neutral Beam Injection (NBI) upgrade providing record power in 2019-2020, and tested the technical & procedural preparation for safe operation with tritium. Research along three complementary axes yielded a wealth of new results. Firstly, the JET plasma programme delivered scenarios suitable for high fusion power and alpha particle physics in the coming D-T campaign (DTE2), with record sustained neutron rates, as well as plasmas for clarifying the impact of isotope mass on plasma core, edge and plasma-wall interactions, and for ITER pre-fusion power operation. The efficacy of the newly installed Shattered Pellet Injector for mitigating disruption forces and runaway electrons was demonstrated. Secondly, research on the consequences of long-term exposure to JET-ILW plasma was completed, with emphasis on wall damage and fuel retention, and with analyses of wall materials and dust particles that will help validate assumptions and codes for design & operation of ITER and DEMO. Thirdly, the nuclear technology programme aiming to deliver maximum technological return from operations in D, T and D-T benefited from the highest D-D neutron yield in years, securing results for validating radiation transport and activation codes, and nuclear data for ITER.

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The ITER-Like-Wall project has been carried out at the Joint European Torus (JET) to test plasma facing materials relevant to ITER. Materials being tested include both bulk metals (Be and W) and coatings. Tritium accumulation mechanisms and release properties depend both on the wall components, their location in the vacuum vessel, conditions of exposure to plasma and to the material itself. In this study, bulk beryllium limiter tiles, plasma-facing beryllium coated Inconel components from the main chamber, bulk tungsten and tungsten coated carbon fibre composite divertor tiles were analysed. A range of methods have been developed and applied in order to obtain a comprehensive overview on tritium retention and behaviour in different materials of plasma facing components (PFCs). Tritium content and chemical state were studied by the means of chemical or electrochemical dissolution methods and thermal desorption spectroscopy. Tritium distribution in the vacuum vessel and factors affecting its accumulation have been assessed and discussed.

Novel method for determining the depth profile of tritium in metallic samples has been demonstrated. Tritium accumulation in the fusion reactor materials is considered as a radiological issue due to its radioactivity. Therefore, tritium behavior prediction and estimation of its overall retention in fusion devices is of high importance. Proposed method in this study allows to measure depth profile of tritium in the metallic samples after exposure to tritium containing plasma, tritium gas or after irradiation with neutrons resulting in the tritium formation. In the method, successive layers of metal are removed using appropriate etching agent in the controlled regime and amount of evolved gases measured by the means of chromatography (gas composition and release rate) and proportional gas flow detector (tritium). Results on tritium profile in neutron irradiated, plasma exposed and tritium gas loaded beryllium have been reported and possible applications of the method for other metallic samples have been tested within this research.