CEA : Clefs CEA n° 46 - Box - Pyrochemistry: a process for the future

Pyrochemical processes include metallurgical operations (extraction, making alloys, oxides, or even nitrides) carried out at high temperatures in non-aqueous media. In most cases, they are used when hydrometallurgy offers no solution, as is the case in the aluminum industry, for example, as aluminum does not have enough affinity for electrons (i.e. it is too electropositive) for it to be deposited by reduction of its cation in aqueous solution.

Pyrochemists use molten salt media, chiefly alkaline and alkaline-earth halogenides (LiCl-KCl, NaCl-KCl, NaCl-CaCl₂, etc.), and reducing or oxidizing alloys with a low melting point. Their very good resistance to irradiation, and the absence of neutron moderators, make these solvents attractive reaction media for the processing of nuclear objects in the civil or military fields. So, it could be possible to process uncooled, or slightly cooled, irradiated objects and increase the quantity of fissile material for a given volume. Not only would this enhance compactness, it would also make it possible to recover all the transuranic elements together (plutonium + minor actinides).

A research program has been proposed by the Nuclear Energy Division (CEA/DEN) to assess the potential of such processes as accurately as possible. The program covers two main aspects: special applications already identified, such as reprocessing transmutation targets as part of a multirecycling approach (see From the critical reactor to the subcritical hybrid system), and, as part of a wider approach, "integrated cycles" involving new systems (high-temperature reactors operating with highly refractory fuel).

"Salt/metal" two-phase block coming from experiments conducted to separate actinides from lanthanides by high-temperature extraction between a molten salt and a liquid reducing alloy.

"Salt/metal" two-phase block coming from experiments conducted to separate actinides from lanthanides by high-temperature extraction between a molten salt and a liquid reducing alloy.
Jérôme Lacquement/CEA
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	Pyrochemistry: a process for the future
	Pyrochemical processes include metallurgical operations (extraction, making alloys, oxides, or even nitrides) carried out at high temperatures in non-aqueous media. In most cases, they are used when hydrometallurgy offers no solution, as is the case in the aluminum industry, for example, as aluminum does not have enough affinity for electrons (i.e. it is too electropositive) for it to be deposited by reduction of its cation in aqueous solution. Pyrochemists use molten salt media, chiefly alkaline and alkaline-earth halogenides (LiCl-KCl, NaCl-KCl, NaCl-CaCl₂, etc.), and reducing or oxidizing alloys with a low melting point. Their very good resistance to irradiation, and the absence of neutron moderators, make these solvents attractive reaction media for the processing of nuclear objects in the civil or military fields. So, it could be possible to process uncooled, or slightly cooled, irradiated objects and increase the quantity of fissile material for a given volume. Not only would this enhance compactness, it would also make it possible to recover all the transuranic elements together (plutonium + minor actinides). A research program has been proposed by the Nuclear Energy Division (CEA/DEN) to assess the potential of such processes as accurately as possible. The program covers two main aspects: special applications already identified, such as reprocessing transmutation targets as part of a multirecycling approach (see From the critical reactor to the subcritical hybrid system), and, as part of a wider approach, "integrated cycles" involving new systems (high-temperature reactors operating with highly refractory fuel). "Salt/metal" two-phase block coming from experiments conducted to separate actinides from lanthanides by high-temperature extraction between a molten salt and a liquid reducing alloy. Jérôme Lacquement/CEA • • • • •		Liquid-cathode device used for electrolytic recovery of actinides from a molten salt bath. Jérôme Lacquement/CEA • • • • • Current conventional recovery methods (electrodeposition on solid and/or liquid cathodes, fractional precipitation, liquid-liquid extraction between molten salts and liquid alloys) are assessed for use in recovering minor actinides (Np, Am, Cm). These studies are conducted on a laboratory scale at the Atalante facility at the CEA/Valrhô-Marcoule center, using molten (500-800 °C) chloride and fluoride media. Michaël Lecomte and Jérôme Lacquement Nuclear Energy Division CEA/Valrhô-Marcoule