Thermodynamics of MgCl2 in plutonium electrorefining

Thermodynamic calculations have been carried out on reactions occurring during the electrorefining of plutonium. The use of MgCl2 to introduce Plutonium ions into the NaCl-KCl melt is shown to be ineffective; the expected Pu3+ concentration being 3xlO-6 mole fraction at 1000K. The Law of Mass Action probably accounts for the known success of plutonium electrorefining; the magnesium distilling from the reaction melt. On the reduction of Pu3+ at the cathode, calculation shows sodium will only be reduced when the Pu3+ concentration is below 10-11 mole fraction at 1000K. Experimentally sodium formation is observed. The role of water in the salt used in electrorefining is discussed and the importance of its elimination reiterated. (author) 2 tabs., 9 refs