As innovative means to recover actinides from irradiated fuels, pyrochemical processes are proposed. In the Japan Atomic Energy Research Institute (JAERI), the feasibility of applying molten-salts processes to nitride fuels containing transuranium elements for transmutation is investigated. In the course of study, experiments and analyses have been made on the high-temperature chemistry of M­N­Cl systems, the effects of oxygen impurities, and the implications of the divalent state along with the normal trivalent state of lanthanides and actinides. Thermodynamic calculation and the electrochemical measurements are compared in a few aspects of dissolution and precipitation of nuclear materials in molten halides.