Accumulation and release of tritium in actively cooled structures exposed to high fluences of energetic particles (at energies up to 160 keV in JET) have been studied during the recent DT experiments (DTE1). This retention of tritium is of importance in terms of tritium accountability, activation and decontamination of components, and as a possible source for contamination of the cooling water. To develop an understanding of the underlying physics and to benchmark predictive models for tritium retention, release and migration is a prime condition for ignition devices which have to handle large quantities of tritium safely. Exchange between implanted and incident particles of different isotope (D and T) may be observed experimentally from the beamline neutron emission during pulses in which beams are not injected into torus but impinge on the calorimeter (Async pulses). It was previously shown [1] that neutron emission data could successfully be described by a "local mixing model" [2-3] taking into account the stopping function for the incident particles.