ON UNIVERSAL FORM FOR ACTINIDE WASTES IMMOBILIZATION

摘要

A possibility to use an iron-based garnet for Pu-containing waste immobilization has beensuggested on the basis of crystal-chemical analysis. Research of synthetic garnets in the system:CaO – Fe2O3 – Al2O3 – ZrO2 – Gd2O3 – UO2 was carried out in order to check up the suggestion.Experiments were performed in air medium at 1400 – 1500 oC and 1 atm. All studied garnetshave shown a high ability to incorporate Gd and Zr in their structure, while incorporation ofuranium was found to be greatly dependent on the overall composition of the phase. Solubility ofuranium varied from 16-18 wt.% to 0.6-0.8 wt.%. The highest solubility was observed in Ca-Zr-Fe garnet, the lowest one – in the silica-containing phases. Addition of Gd into the system tendsto decrease maximal U content in the phase to 3-6 wt.%. Analysis of garnets formula calculatedfrom their chemical compositions leads to conclusion that U enters both the eight-coordinated Asitesand the six-coordinated B-sites of the structure, while Gd occupies the A-sites and Zr fillsthe B-sites only. Corrosion products such as Cr and especially Ni have low content in the garnets(about 2.4 wt.% Cr2O3 and lower than detection limit of 0.3 wt.% for NiO) and are predominantlydistributed into oxide phases. The studies of irradiation stability of the materials is planned inorder to compare features of the garnet ceramics with the other prospective waste forms.