Effective management of trialkyl phosphine oxides waste via Gd2Zr2O7 ceramic

Abstract

The disposal of high-level liquid waste (HLLW) is critical for reprocessing in the nuclear industry. The trialkyl phosphine oxide (TRPO) process has been used for the extraction of HLLW; however, residual waste is inevitably generated during this process, and the TRPO waste should also be managed effectively. In this study, TRPO waste (four oxides) was directly immobilized via a Gd2Zr2O7 ceramic. Using a simple, traditional sintering method, the solid-solubility limit of the TRPO waste can reach 70 wt%. When the waste content is higher than 10 wt%, the structure of the matrix transforms from pyrochlore to fluorite. When the waste content is higher than 70 wt%, a ZrO2 phase is detected. Raman spectra confirmed the phase transition of the matrix from pyrochlore to fluorite, and the ZrO2 phase was also confirmed by the Raman fitting results. The highest Vickers hardness result is approximately 9.63 GPa for the matrix doped with 90 wt% TRPO waste. The leaching experiments showed that the leaching rates of Mo, Ru, and Pd were ∼10−5, ∼10−7, and ∼10−6 g m−2 d−1 after 35 d, respectively. These results demonstrate an efficient immobilization method to treat TRPO waste in Gd2Zr2O7 ceramics with a high solid-solubility limit.