Immobilization of Cs and Sr within perovskite-type Ba0.7-ySry(La, Cs)0.3ZrO3 glass/ceramic composite waste forms

Abstract

The disposal of radioactive Cs and Sr in high-level radioactive waste is a problem that needs to be considered in the nuclear industry. Currently, it is difficult to immobilize Cs and Sr simultaneously into a durable host phase, especially at low temperatures to avoid volatilization of Cs. Thus, perovskite-type Ba0.7-ySry(La, Cs)0.3ZrO3 (y ≤ 0.6) polycrystalline was synthesized by sol-gel technique at low temperatures and developed as a host to immobilize Cs and Sr. The polycrystalline powders were further fixed in glass matrix to form the glass/ceramic composite waste forms. The results show that Cs and Sr can be immobilized effectively in the lattice positions of Ba0.7-ySry(La, Cs)0.3ZrO3 at a low temperature (900 °C), without volatilization of Cs during the immobilization process. The glass/ceramic composite waste forms with a crystalline-amorphous phase inlaid structure, prepared with glass content of 40 wt% and sintering temperature of 800 °C, have low porosity, good compactness, and high hardness. The leaching rates of Cs and Sr in the waste forms can reach the order of 10−3 - 10−4 g m−2 d−1 after 14 days. This result provides an ideal host of Ba0.7-ySry(La, Cs)0.3ZrO3 for simultaneous immobilization of Cs and Sr at low temperatures, and combines the advantages of traditional glass solidification and promising ceramic solidification.