A microscopic, modelistic approach was carried out to elucidate the electrochemical reduction of a nuclear waste solution in a packed bed electrode. The interfacial surface reactions within the packed bed were taken into account and the particle-particle contact resistance through oxide films was found to be big enough to effect the potential distribution throughout the bed. On the basis of equations developed here, the contribution of the resistance of the oxide film to the potential and current distribution throughout the bed was compared with the macroscopic homogeneous approach.