Fluoride volatilization

Research Opportunities. The presence of a long-lived fluorescing state following either 532 nm or 1064 nm excitation of PuF6(g) provides a valuable opportunity to study the extent to which electronic energy in a 5f electron state is available in photochemical and energy transfer reactions. Such gas phase bimolecular reactions would occur in a weak interaction limit governed by van der Waals forces. Seen from the perspective of potential photochemical separations in fluoride volatility... 

Powdered niobium metal, 20.0 g. (—200 mesh), and tin(II) fluoride, 52.0 g. (40 mesh),t are mixed in a molybdenum crucible in an Inconel- or nickel-pipe reactor approximately 3 in. in diameter and 10 in. long and heated to 400-500°C. in a stream of dry nitrogen. The niobium(V) fluoride volatilizes from the reaction mixture and condenses on the water-cooled lid of the reactor, which leaves metallic tin in the crucible. The yield of niobium(V) fluoride is 21.1 g., or 95% of theoretical. A very small amount of blue niobium oxyfluoride (composition of variable oxygen and fluorine content) often forms as an impurity because of the presence of minute amounts of oxygen. Anal. Calcd. for NbFs Nb, 49.44 F, 50.56. Found Nb, 49.43 F, 50.2. 

Process studies on fluoride volatility method have been carried out for the purpose of evaluating feasibility for the reprocessing of FBR fuels (33). Process concept investigated is shown in Figure 9. It aimed at a simple and advanced process for continuous operation. Experiments are mainly made on the fluorination and purification using bench-scale fluid-beds and traps. 

Although promising data have been acquired for the fluoride volatility process, the technical feasibility has not been demonstrated yet. Aside from chemical problems, many technological problems such as process stability due to powder handling and remote maintenance, are still remained unsolved. In order to solve these problems, head-end process studies as voloxidation have been started. Here, stress is put on the environmental protection of... 

However, nonaqeuous processes were found to have a number of disadvantages, which have discouraged their widespread use. (1) Except for fluoride volatility processes, separations are incomplete, fuel is not completely decontaminated, and refabrication must be done remotely. 

The three types of nonaqueous processes on which most development work has been done are (1) pyrometallurgical processes, involving high-temperature processing of metallic fuels (2) pyrochemical processes, involving high-temperature processing of oxide or carbide fuels and (3) fluoride volatility processes, in which elements in fuel are converted to fluorides, which are then separated by fractional distillation. 

Barghusen, J. J., et al. Fluid-Bed Fluoride Volatility Processing of Spent Reactor Fuel Materials, in Progress in Nuclear Energy, series III, Process Chemistry, vol. 4, Peigamon, New York, 1970, p. 347. 

Schmets, J. J. Reprocessing of Spent Nuclear Fuels by Fluoride Volatility Processes, Atomic Energy Rev. 8(1) 3 (1970). 

The various processes available for fuel reprocessing are aqueous solvent extraction, precipitation, ion exchange, fractional distillation, pyrometal-lurgy, and fluoride volatility. Most of the commercial development experience has come from the solvent-extraction method for separation of uranium, plutonium, and fission products. 

Nonaqueous Processes 74.4.2.1 Volatility Process Fluoride Volatility... 

Fluoride volatility processes utilize the high volatilities of the hexafluoride of plutonium and uranium to separate them from FPs and were investigated primarily for the reprocessing of irradiated oxide fuels (Cleveland, 1979, 504-508 Selvaduray, 1978, 258-259 ... 

Fluoride volatility process. (Adapted from Qeveland, J.M. 1979. The Chemistry of Plutonium, 653. La Grange Park, IL American Nuclear Society.)... 

Trevorrow, L., J. Fischer, and J. Riha. 1963. Laboratory investigations in support of fluid bed fluoride volatility processes. III. Separation of gaseous mixtures of uranium hexafluoride and plutonium hexafluoride by thermal decomposition, 14. Argonne, IL Argonne Natl. Lab. United States Atomic Energy Commission [Published by the Atomic Energy Commission and Its Contractors], ANL-6762. 

Uhlif, J., M. Marecek, and J. Skarohlid. 2012. Current progress in R D of fluoride volatility method. Procedia Chemistry 7 110-115. 

An alternative method for production of UFg (the fluoride volatility process) for enrichment facilities from uranium ore concentrates was developed by Honeywell and is practiced at its Metropolis plant. Figure 1.11 schanaticaUy compares this process with the classic process described earlier. 

In principle, the fluoride volatility process has fewer stages and is simpler than the conventional process. It consists of reduction of the UOC (yellow cake) to UO2 with hydrogen (derived from cracking anunonia) followed by hydro-fluorination to produce UF4 (green salt) and then fluorination to produce UF (hex). In principle, uranium ore concentrates may be directly fluorinated to produce UFg, but this process consumes large amounts of fluorine and is not applied commercially. 

FIGURE 1.11 Comparison of two processes for production of UF from uranium ore concentrates the classic process and the Honeywell fluoride volatility process. (Adapted from http //www.converdyn.com/product/different.html, accessed July 26, 2014.)... 

The main methods used for reprocessing of SNF flowsheet were reviewed in a 120 pages report by the Nuclear Energy Agency (NEA 2012). The three main processes are the so-called hydrometallurgy processes (PUREX and UREX), pyromet-allurgy processes and its variations, and the fluoride volatility process (quite like the method used at the uranium conversion facilities discussed in Chapter 1). The report reviewed in detail several of these processes that are deployed in different facilities for various types of spent fuel (NEA 2012). In this section, we shall try to briefly present an overview of the main points and the analytical aspects. 

There remains the question of how to come by the first core loading without separation of Pu. One possibility [XX-8, XX-33] is to use LWR spent fuel as the feed material and to remove from it only part of the uranium and part or all of the FP. For example, if the LWR spent fuel contains 1% Pu and minor activities (MA), it is necessary to remove approximately 90% of the uranium to make a fuel with 11 to 12 % of Pu and MA by weight. This could hopefully be done using a highly proliferation-resistant process, possibly a combination of an AIROX process and a fluoride volatilization process or a simplified version of the UREX process. Another feed option that could be considered is the spent fuel from MOX fuelled LWRs. The transuranium isotopes (TRU) content in such spent fuel can be approximately half of that needed for ENHS like reactors. Hence, only -50% of the uranium need be extracted along with FP to make fuel for ENHS like reactor. The latter is likely to offer a more economical fuel cycle. 

The earliest reported polymerization of vinyl fluoride involved heating a saturated solution of VF in toluene at 67°C at 600 MPa for a period of 16 hours. In another study, benzoyl peroxide was the polymerization initiator. A polymer was produced with a density of 1.39 g/cm which could be dissolved in hot dimethylformamide, chlorobenzene, and other polar solvents. A great many initiators and vinyl fluoride polymerization conditions have been studied. Examples ofbulk f ] and solution[ ][ F[i04] pp lymerizations have been reported. Aqueous suspension or emulsion techniques have been generally preferable over other methods.Vinyl fluoride volatility required the use of moderately high pressures during the polymerization. Photopolymerization of VF, aided by a free-radical initiator, has also been accom-... 

In this plant it is assumed that the core and blanket salts will be reprocessed by the fluoride volatility process [1] to remove UFo. The L Fg will be ri duced by a fluorine-hydrogen flame proce.ss [2] and returned to the reactor core. The lilanket salt with its removed will be returned to the blanket, since the buildup of (i.ssion products in the blanket. salt will... 

---