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Fluoride volatility is a method for the extraction of elements which form volatile fluorides. It is being studied for reprocessing of nuclear fuel, either of the conventional fuel rods used in today's LWRs, or as an integral part of a molten salt reactor system.
Additional recommended knowledge
Uranium oxides react with fluorine to form gaseous uranium hexafluoride, most of the plutonium reacts to form gaseous plutonium hexafluoride, a majority of fission products (especially electropositive elements: lanthanides, strontium, barium, yttrium, cesium) form solid fluorides dropping to the fluorinator bottom, and only a few of the fission product elements (the transition metals niobium, ruthenium, technetium, molybdenum, and the halogen iodine) form gaseous fluorides that accompany the uranium and plutonium hexafluorides, together with inert gases. Distillation is then used to remove the other volatile metal fluorides and iodine fluorides from the uranium hexafluoride .
The nonvolatile residue of alkaline fission products and minor actinides is most suitable for further processing with 'dry' electrochemical processing (pyrochemical) Nuclear reprocessing#Non aqueous methods. The lanthanide fluorides would be difficult to dissolve in the nitric acid used for aqueous reprocessing methods, such as PUREX, DIAMEX and SANEX, which use solvent extraction. Fluoride volatility is only one of several pyrochemical processes designed to reprocess used nuclear fuel.
The Řež nuclear research institute at Řež in the Czech Republic tested screw dosers that fed ground uranium oxide (simulating used fuel pellets) into a fluorinator where the particles were burned in fluorine gas to form uranium hexafluoride. 
Volatility, valence, and chemical series
Valences for the majority of elements are based on the highest known fluoride.
Roughly, fluoride volatility can be used to remove elements with a valence of 5 or greater: Uranium, Neptunium, Plutonium, Metalloids (Tellurium, Antimony), Nonmetals (Selenium), Halogens (Iodine, Bromine), and the middle Transition metals (Niobium, Molybdenum, Technetium, Ruthenium, and possibly Rhodium). This fraction includes the actinides most easily reusable as nuclear fuel in a thermal reactor, and the two long-lived fission products best suited to disposal by transmutation, Tc-99 and I-129.
Left behind are Alkali metals (Cesium, Rubidium), Alkaline earth metals (Strontium, Barium), Lanthanides, the remaining Actinides, remaining Transition metals (Yttrium, Zirconium, Palladium, Silver, Cadmium) and Poor metals (Tin, Indium). This fraction contains the fission products that are radiation hazards on a scale of decades (Cs-137, Sr-90, Sm-151), four long-lived but less dangerous fission products (Cs-135, Zr-93, Pd-107, Sn-126), most of the neutron poisons, and the higher actinides (Americium, Curium, Californium) that are radiation hazards on a scale of hundreds or thousands of years and are difficult to work with because of gamma radiation but are fissionable in a fast reactor.
Fluorides by boiling and melting points
Missing: Pd 46, La 57, Pr 59, Pm 61, Eu 63 and up
Missing top fluorides: TcF7 AgF4 XeF6 LaF3 CeF4 PrF4 PmF3 EuF3 GdF3 TbF4
Inert: Kr 36, Xe 54
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Fluoride_volatility". A list of authors is available in Wikipedia.|