For the first time, hydrogen catalytic effects of fission product alloy particles nondestructively extracted from spent nuclear fuel were demonstrated. The redox sensitive radionuclides at oxidized forms Se(IV), Tc(VII), U(VI), Np(V) and Pu(VI) were found to be stable in a solution saturated with a gas mixture (Ar + 10% H-2 + 0.03% CO2) but rapidly immobilized in the same solution when contacted with the particles. In comparison, a synthetic alloy sample with similar elemental composition as the alloy particles generated in nuclear fuel displayed a smaller, but unequivocal catalytic effect. The smaller catalytic effect of synthetic alloy was apparently enhanced by a P-radiation source. The information obtained in this work contributes to improved understanding of the redox chemistry of radionuclides in nuclear waste geologic repository environments and, in particular, of the catalytic properties of these unique alloy particles. (C) 2009 Elsevier B.V. All rights reserved.