Many experiments during the Tritium Trace Experimental (TTE) campaign at JET presented almost optimal conditions to study tritium transport with the technique of neutral particle analysis. The low tritium background, the small tritium influxes from the wall and the purity of deuterium neutral beam injection all contributed to very high contrast of the neutral tritium fluxes due to T2 puffing. In particular, in these favourable conditions it was possible to obtain a more than satisfactory signal to noise ratio even with reduced T2 puffs, i.e. injecting an amount of particles so small that it did not alter the main plasma parameters, ideal for perturbative transport studies. The fluxes of neutral particles leaving the plasma were detected with JET low energy NPA, called ISEP (Ion Separator) since it was explicitly designed to simultaneously measure all the hydrogen isotopes. It has been observed for the first time that the delay from the beginning of the T2-puff to the peak of the tritium neutral fluxes increases with the particle energy. Since the fluxes of higher energies are emitted from the deeper plasma layers, the measured dependence of the delay on the particle energy can be interpreted as propagation of the tritium ions into the plasma. DOUBLE code simulating the neutral particle fluxes emitted by plasma is applied to reconstruct the tritium ion density profile and its temporal evolution (within the range 0.4 ­ 0.9 a, where a is the minor radius). The diffusive and convectional transport coefficients have been obtained by the fitting of the transport model with the reconstructed tritium profiles. The coefficients are compared against the neoclassical values.The results are extended to the plasma conditions of ITER relevance since the neutral particle diagnostics are supposed to be one of the basic methods to measure the fuel mixture in the next step device. In the light of the obtained results at JET, the evaluation of the diagnostic performance in ITER is refined.