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 – 45 µm of the ‘plasma-facing’ surface, however, possible tritium presence up to 100 µm cannot be excluded. During temperature programmed desorption at 4.8 K/min in the flow of purge gas He + 0.1% H2 the tritium release started below 475 K, the most intense release occurred at 725 – 915 K and the degree of detritiation of > 91% can be obtained upon reaching 1075 K. The total tritium activity in the samples was in range of 2 – 32 kilo Becquerel per square centimetre of the plasma-facing surface area.