Ceramic Matrix Composites Based on Lanthanum Orthophosphate for Disposal of High-Level Radioactive Waste

Abstract

Ceramic matrix composites for solidification and disposal of actinide-rare-earth fraction of high-level waste (HLW) were prepared by sintering of nanosized powders of 0.8LaPO₄–0.2Al₂O₃, 0.8LaPO₄–0.2Y₂O₃ and 0.8LaPO₄–0.2ZrO₂ obtained from 0.8LaPO₄ · nH₂O–0.2Al(OH)₃, 0.8LaPO₄ · nH₂O–0.2Y(OH)₃ and 0.8L-aPO₄ · nH₂O–0.2ZrO(OH)₂ precursors. These powders-precursors were synthesized via sol-gel technique. After heat treatment at 850°C powders of 0.8LaPO₄–0.2Al₂O₃, 0.8LaPO₄–0.2Y₂O₃ and 0.8LaPO₄–0.2ZrO₂ were obtained. Further powdered compositions were stepwise sintered to prepare ceramic composites which were supposed to be used as matrices for storage of HLW. Rate of La³⁺, Al³⁺, Y³⁺ and Zr⁴⁺ leaching from ceramic matrix composites in strength aqueous solutions of NaCl and Na₂SO₄ simulating underground brine typical for proposed location of HLW geological repository was estimated.