Li4SiO4 pebbles reduction in He+0.1% H-2 purge gas and effects on tritium release properties

Lithium orthosilicate reduction was examined by Temperature Programmed Reac tion (TPR) and Temperature Programmed Desorption (TPD) methods performed in He (or Ar) + H-2 purge gas flowing through pebble bed specimens. The param eters governing the kinetics and the steady-state of the reduction process to Li4SiO4-x were determined at 800 degrees C. The level x of the O-vacancy concentration at steady-state (of the order of 1.5 x 10(-3) mole fraction) was found to be compatible with the impurities content in the specimens. P ebble pre-annealing treatments were found to affect the microstructure and the reduction mechanism. Post-irradiation tritium release by TPD tests were performed on both stoichiometric and reduced pebbles with similar results. Tritium release properties of this breeder system seem to be independent f rom the material reduction state(x). (C) 2000 Elsevier Science B.V. All rig hts reserved.