Fluoride volatility processes

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). 

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. 

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. 

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... 

However, since the LMFR offers such an excellent opportunity for the application of cheap pyrometallurgical processing, this path has been explored quite extensively. In this section a fused chloride salt process for the remoi al of fission poisons is described. In following sections a fluoride volatility process and a noble fi.ssion product removal process are described. 

The chief advantages of the fluoride volatility process is that it will be operated batchwise and w ill give a complete, clean separation between the uranium and all the fission products. This allows comparatively easy control of the cleanup of the fuel and preparation of new fuel for the reactor. Since each step of this process is batch, the instrumentation would be comparatively simple and the operators would have complete independent control of each step. 

As is pointed out in Chapter 20, the easiest blanket to handle in the LMFR would be a 10 w/o thorium-bismuthide slurry in bismuth. Chemical processing of this blanket would be very similar to the core processes already described. The major problem consists in transferring the bred uranium and protactinium from the solid thorium bismuthide to the liquid bismuth phase, so that they can then be chemically processed. Two examples of proposed processes are shown in Fig. 22-11, which shows a process that can be used with the fused chloride salt FPS removal process, and in Fig. 24-19, which shows a flowsheet for a process to be used with the fluoride volatility process. 

Fig. 24-11. Annual fluoride volatility processing cost vs. plant throughput for 825-Mw-two-fluid LMFR.

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