This paper deals with a study of water splitting by gamma rays in the presence of some double perovskites A2MM’O6 and also Sr2Fe1-xTa1 xO6. The irradiation is performed using 60Co as a source with 3·104 Ci activity and 8.3 kGy/h dose rate, which simulated the radioactive wastes, resulted from reprocessing of spent nuclear fuel elements much more active: 108-109 Ci. The stable products of radiolysis, as well as the other chemical species are measured by mass spectrometry. The calculated radiation yield (GH2) generally decreases in the order: Sr2Fe1-xTa1 xO6 (x=0.5; 0.4; 0.3; 0.1) > Ca2AlTaO6 > Sr2AlTaO6 > Ba2AlTaO6, under the given experimental conditions; the yield was higher in the presence of these catalysts than in their absence.