In advanced fuel cycles, it is likely that fast spectrum, high temperature reactors will be utilized to transmute actinide isotopes that are inefficiently transmuted in light water moderated reactors. Many such reactors will utilize metallic fuels and electrometallurgical processing might become a practical alternative to aqueous processing methods like solvent extraction and ion exchange. The solution chemistry of actinides and fission products is significantly different in the molten salt/molten metal media used for such processing.

Dry processing (pyrometallurgy) has historically found use in electrolytic production of some metallic products, notably for refining very electroposi­tive elements and strong reducing agents like alkali metals. Potassium and sodium metals were first prepared in 1807 by using melt electrolysis of respectively potash and soda. [11,12] Today melt electrolysis (alkali chlo­ride) remains the only process for production of metallic sodium or lithium. Molten salt refining is also appropriate for aluminum, which is obtained by

electrolytic decomposition of aluminum oxide in molten cryolite (Hall — Heroult process). [13]

Pyrochemical processing involves dry chemical reactions at high tem­perature where reactions occur in solid, liquid and gas phases. Oxidation — reduction, volatilization (of halide or metal), slagging (melt refining, molten salt extraction, carbide slagging), liquid metal (melt refining, liquid metal extraction, liquation, precipitation), and electrolytic processes are the most common types. Implicit in this chemistry is the requirement of conducting separations operations when the metals or metal salts are in a fluid condi­tion, which typically occurs only at moderate to high temperatures. A sub­category of such media are the so-called room temperature ionic liquids (RTILs) which by convention form molten salts below 100°C. This new category of materials would appear to offer the greatest promise for elec­trometallurgical partitioning, but is still quite new, thus most important details of metal ion coordination chemistry in these media are unknown.

Pyrometallurgy operates in a quite different manner from solvent extrac­tion. Such dry processing offers some advantages, but also suffers limita­tions. The first significant attempts at actinide metal production in molten salts started with the Manhattan Project in the 1940s. [14] Significantly, Kolodney confirmed that uranium and plutonium could be electrodeposited from molten chlorides. [15] The literature on U and Pu electrorefining in molten salts has been reviewed by Willit et al. [16] Basic chemistry and technologies developed in Russia have been described by Bychkov and Skiba. [17] Molten alkali and alkaline-earth chlorides have been most extensively studied for plutonium conversion and separation. Three pro­cesses are in use thorough the world at significant scale-up: (i) DOR process (direct oxide reduction) which consists in PuO2 reduction by calcium in Ca-based chloride salt, (ii) MSE process (molten salt extraction) for 241Am removal from weapon-grade plutonium by MgCl2 in alkali chloride salt, (iii) ER process (electrorefining) for high plutonium purification using molten alkali and/or alkaline earth chloride electrolyte. [18]