Probing into the optimum preparation and the chemical durability of Sr0.5Zr2(PO4)3-SmPO4 dual-phase ceramics for nuclear waste forms via in-situ synthesis

Abstract

In this work, Sr0·5Zr2(PO4)3-SmPO4 dual-phase ceramics were prepared via in-situ synthesis process, which is a potential novel nuclear waste form for immobilizing the fission product 90Sr and the trivalent actinide radionuclides in high-level waste (HLW). And the preparation technology, microstructure and chemical durability of Sr0·5Zr2(PO4)3-SmPO4 dual-phase ceramics were systematically investigated. It was confirmed that the optimum microwave-sintering temperature (1050 °C) and heat preservation time (1.5 h) is estimated by Archimedes method. Besides, the as-prepared samples that were consisted of strontium zirconium phosphate (SrZP) and monazite showed the remarkable densification, in which the two crystalline phases were intermixed well with each other. Meanwhile, the formation and evolution of microstructure was also consistent with the variational rule of Sr0·5Zr2(PO4)3/SmPO4, indicating that there was not mutual reaction during the in-situ synthesis process. The PCT and MCC-1 experimental results demonstrated that the elemental normalized leaching rates of tested samples are all at a low level (LRSr∼10−4 g‧m−2‧d−1, LRZr∼10−8-10−6 g‧m−2‧d−1, LRSm∼10−7-10−5 g‧m−2‧d−1 and LRP∼10−4 g‧m−2‧d−1). It is indicated that Sr0·5Zr2(PO4)3-SmPO4 dual-phase ceramics possesses excellent chemical durability for HLW disposal.