Studies of tritium retention in JET, and de-tritiation

The author reports on studies of tritium retention in JET, and methods of de-tritiation: Analysis of samples removed from the first wall of JET - before the 2001 shutdown, a known quantity of 13CH4 was introduced (puffs) in order to follow the migration of carbon on a series of special tiles. Analyses were made of the films from various locations, and the resulting observations were presented, and further tiles were removed for analysis during the 2004 shutdown. Measurement of hydrogen retention during JET operations - deuterium retention was assessed for the tiles removed during the 2001 shutdown, and a trace tritium experiment was carried out in 2003. Development of techniques for improved temporal resolution of retention and deposition of hydrogen isotopes in JET - design and use of Quartz Micro-Balances (QMB) were described in detail (one prototype was installed in 2001, and additional units will be installed in 2004); details of these QMBs and results from studies in 2001-2004 have been published. Study of methods for in-vessel tritium inventory reduction - a photon-cleaning method was used to de-tritiate tiles in-situ. This procedure involves focusing intense UV and visible light from a flash-lamp by means of a parabolic reflector. Tiles of the inner divertor were treated at high power, and the deposited film was clearly seen to have been ablated from the surface, while a number of outer poloidal limiter tiles were to have been treated at lower power to out-gas the surface films without ablation (however, a problem developed with the lamp, so the treatment was carried out in the Beryllium Handling Facility at JET). Development of de-tritiation techniques for components removed from fusion devices - significant numbers of radioactive and Be-contaminated carbon tiles have been used in previous operational campaigns of JET and are now in storage. A promising technique has been evaluated that involves sweeping the flame of an oxy-gas burner across a divertor tile to reach a temperature of ∼ 1000K in ∼ 500 s. Decontamination factors (DF) of 850 were achieved for whole tiles. Several smaller pieces of tile have also been treated under various burner conditions, such as number of runs and final temperature - one piece of tile reached a DF = 2500