DEUTERIUM RELEASE MEASUREMENTS IN THE BERYLLIUM PHASE OF JET AND DETERMINATION OF TRITIUM CONTENT IN THE EXHAUST-GAS

In this work the results of gas balance measurements during the beryllium phases of JET are presented and compared with similar data from the carbon phase. Gas balance calculations are carried out by measuring the gas release after a discharge and comparing it to the total fuelling. These measurements give direct information on the in-vessel retention of hydrogen isotopes. After the introduction of beryllium the fuelling requirements of a typical discharge increased by a factor of congruent-to 2 and the measured gas release increased substantially. The average deuterium recovery after a non-disruptive shot is congruent-to 35-50% of the input. This percentage increases to congruent-to 80% for long term measurements. The deuterium inventory in the walls is similar for C and Be. Some tritium release measurements are presented. The fraction of tritium recovered, both following the discharge and on the long term, is about half of the measured fraction of deuterium. The analysis of D and T release data leads to the observation that surface effects dominate the gas release after the discharge.