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Annual Report

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Argonne National Laboratory has proposed a new extraction procedure to handle TRISO-coated fuels, the Fluoride Extraction Process, or FLEX. The FLEX process is designed to separate the uranium in the fuel from the actinides and most fission products by taking advantage of the unique properties of uranium hexafluoride (UF6). In the FLEX process, the used TRISO fuel is reacted with zirconium fluoride salt, forming UF6 and the fluoride salts of the actinides and fission products. At process temperatures, the UF6 volatizes into a gas, and is released from the molten salt mixture. This leaves behind the actinides and most fission products in a fluoride salt, which is subsequently processed using pyrochemical techniques to recover the actinides and other long-lived fission products for transmutation. The UF6 is then cooled, causing it to sublime into solid form, which is processed for disposal or reuse.

This research attempts to develop a waste form for disposing of the zirconium fluoride fission product waste stream. Fluorapatite, a naturally-occurring fluorinated calcium phosphate, has been identified as a potential matrix for the entombment of this waste stream. If the efficacy of fluorapatite-based waste storage can be demonstrated, then new and potentially more efficient options for handling and separating high-level wastes, based on fluoride-salt extraction, will become feasible.

The following are the specific research objectives:

  • To develop a waste matrix for the disposal of the fission product waste stream from the FLEX process
  • To develop a process to make synthetic fluorapatite that incorporates the FP-bearing ZrF4 salt
  • To develop a fundamental understanding of the chemistry of this new waste form in order to better predict its long term behavior in a repository environment
  • To develop a fundamental understanding of natural, fluoride-bearing mineral phases to use as natural analogs to bound the predicted behavior of the FLEX fission product waste stream.


Calcium phosphate; Fluorides; Phosphate minerals; Radioactive wastes — Storage; Separation (Technology); Zirconium compounds

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Radioactive wastes--Storage; Separation (Technology); Zirconium compounds


Chemistry | Oil, Gas, and Energy | Physical Chemistry

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