Tritium Experience in JT-60 DD Plasma Operation

Effluent of tritium in vacuum exhaust in JT-60 through the stack to environment always remains a level below detectable level (<10⁻⁵Bq/cm³ at the stack, <10⁻⁷Bq/cm³ at the site boundary). Though tritium concentration of drain water is below the limit of regulations of the local agreement and the law, small tritium contamination in the facility drain and in the rain drain of stack appeared occasionally. For a scheduled maintenance work of the in-vessel components, following an annual deuterium plasma discharge campaign, a 4-week no-deuterium (H or He) plasma discharge campaign and the succeeded ventilation by room air allow to reduce tritium on the interior surface of in-vessel components. This cleaning up shots and air introduction allowed workers to enter into the vacuum vessel. Air blow well tends to remove surface tritium elements and would be necessary before disassembly and replacement of components on vacuum pumping lines.