Release of tritium from the JET vacuum vessel after high power discharges

Measurements have been made of the tritium recovery from the JET pumping system both after high power neutral beam injection where the tritium is produced from D(d, p)T reactions and after tritium is injected into the torus in the first tritium experiment (FTE). The tritium has been detected using a liquid scintillation counter which has allowed measurements to be made over a wide range of concentrations. The recovery rate has been found to follow a power law R=At −n over the period from 10 to 3000 s after each discharge. The value of n varies from 0.8 when tritium is first introduced into the plasma to ∼0.5 many discharges later. This effect is attributed to a change in the depth distribution of the tritium in the surface.