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

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 degrees 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 degrees 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.