Removal of rare-earth fission products from molten chloride salt used in pyroprocessing by precipitation for consolidation into glass-bonded sodalite waste form

Abstract

As an alternative method to absorption into zeolite-A for removing rare-earth (RE) fission products (FPs) accumulated in spent molten chloride salt generated by the pyrometallurgical reprocessing of spent nuclear fuel, the precipitation of the RE FPs followed by consolidation into a glass-bonded sodalite waste form has been proposed to reduce the waste volume. Chemical forms of the precipitates generated by the addition of Li2O or Li2CO3 in LiCl-KCl melts containing chlorides of REs were identified. Then, the salt adhering to the Gd2O3 precipitate, which was generated by the addition of Li2O into LiCl-KCl molten salt containing GdCl3, was removed by vacuum distillation. The distillation product or its simulant (Gd2O3) was mixed with zeolite-A and fresh zeolite, and then consolidated into glass-bonded sodalite under uniaxial pressing at the maximum temperature and pressure of 915 °C and 1.3 × 105 Pa, respectively. Examinations of the consolidated products showed that a dense product was fabricated and that gadolinium existed as NaGd9Si6O26, as expected from the literature, or Gd2O3 in the products.