Applicability of the UV-stimulated oxidation to tritium cleanup

The rate of the UV-stimulated HT oxidation was studied in H2(HT)-O2-O3 atmospheres with excess O3. The concentration of HTO increased linearly with UV irradiation time. The formation rate of HTO was estimated to be 3.4 x 10-2 Bq cm-3 s-1, which was about 14000 times greater than that of the UV-stimulated HT oxidation in the H2(HT)-O2 atmosphere. Namely the excess O3 greatly assisted the UV-stimulated HT oxidation. The HTO formation obeyed the half order kinetics to hydrogen pressure and 0.7 order with respect to photon flux. Computer simulation consisting of 33 elementary reactions was employed to make clear the mechanism of the HT oxidation. The computer simulation reproduced the same hydrogen pressure and photon flux dependences as the experimental results. It was revealed that the main path for HTO formation is as follows: (1) HT oxidation is initiated by photolysis of O3 to O(1D) radicals; (2) O(1D) radicals react with H2(HT) to form OH(OT) radicals; and (3) OH(OT) radicals produce H2O(HTO) by the reaction with H2(HT). On the basis of computer analysis, it is concluded that the considerable increase in the rate of HTO formation is due to the increase in O(1D) production in the presence of O3. The present results suggest that the O3-assisted UV-stimulated HT oxidation is expected to be applicable to non-catalytic oxidation of tritium in thermonuclear fusion reactors. 8 refs., 6 figs., 1 tab