Structure, tritium depth profile and desorption from ‘plasma-facing’ beryllium materials of ITER-Like-Wall at JET

Abstract

Tritium depth profile and its temperature programmed desorption rate were determined for selected samples cut out of beryllium tiles removed from the Joint European Torus vacuum vessel during the 2012 shut down. A beryllium dissolution method under controlled conditions was used to determine the tritium depth profile in the samples, whereas temperature programmed desorption experiments were performed to assess tritium release pattern. Released tritium was measured using a proportional gas flow detector. Prior to desorption and dissolution experiments, the plasma-facing surfaces of the samples were studied by scanning electron microscopy and energy dispersive X-ray spectroscopy.Experimental results revealed that > 95% of the tritium was localized in the top 30 – 45µm of the ‘plasma-facing’ surface, however, possible tritium presence up to 100µm cannot be excluded. During temperature programmed desorption at 4.8K/min in the flow of purge gas He+ 0.1% H2 the tritium release started below 475K, the most intense release occurred at 725 – 915K and the degree of detritiation of > 91% can be obtained upon reaching 1075K. The total tritium activity in the samples was in range of 2 – 32kilo Becquerel per square centimetre of the plasma-facing surface area. Keywords: ITER-Like-Wall, Beryllium, Tritium, Fuel accumulation, Depth profile, Thermal desorption