Structural integrity of Cs and Sr immobilized lacunar apatite phosphate simulated ceramic wasteform Na0.9Cs0.1Pb3Sr(PO4)3 under heat and aqueous flow

•Lacunar apatite phosphate[NaPb4(PO4)3]hostis chosen for possible combined immobilization of Cs and Sr species.•Simulated wasteform of the formula Na0.9Cs0.1Pb3Sr(PO4)3 was investigated for its thermal and chemical stability studies.•Mechanism of leaching behaviour of the wasteform was explored. Lacunar apatite host, NaPb4(PO4)3was converted into a ceramic wasteform with the incorporation of Cs and Sr ions. The systematic substitution yielded the wasteform composition Na0.9Cs0.1Pb3Sr(PO4)3 with 8.52 wt% of Strontium and 1.29 wt% of caesium. The wasteform was subjected to continuous heating in the temperature range 298–973 K and aqueous flow to study the thermal stability and chemical durability respectively. The wasteforms response was studied by powder X-Ray diffraction analysis (Room temperature and High temperature), electron microscopic & elemental analysis and normalized mass loss (NLi) & leach rate (LRi) calculations. The average thermal expansion coefficient (αavg) value of 14.4 ± 1.1 × 10−6 K−1 and the leach rates of immobilised Cs, LRCs (10−6–10−8 gm−2d−1) and Sr, LRSr (10−3–10−4 gm−2d−1) demonstrate the structural integrity of the phase. The anisotropic nature of thermal expansion and the mechanistic feature of leaching are discussed. [Display omitted]