= Solution
\b[<Synroc> immobilises waste <ions> in selected durable crystalline hosts], rather than trying to put the whole inventory into one universal site. The underlying philosophy is that <minerals> retaining analogous elements over geological times suggest useful <crystal structures> for engineered containment. These natural analogues motivate the choice; their survival does not prove that every synthetic composition, damaged microstructure or groundwater environment will behave identically. This was the rationale of the original mineral-analogue proposal.<Immobilisation of high level nuclear reactor wastes in SYNROC by A. E. Ringwood and others>[Nature 278, 219–223, abstract and mineral-analogue argument]{ref}
A representative <Synroc-C> assemblage includes <zirconolite>, $\mathrm{CaZrTi_2O_7}$, as an <actinide> host; a <hollandite waste-form phase>, represented by $\mathrm{BaAl_2Ti_6O_{16}}$, whose tunnels accommodate large <cations> such as <caesium>; and a <perovskite waste-form phase>, $\mathrm{CaTiO_3}$, which can accept <strontium> on <calcium> sites and other constituents with suitable <charge compensation in a crystal>. Titanium-oxide phases provide additional accommodation and composition flexibility. The actual phases are <solid solutions>, not simply pure end-member <minerals> mixed with an inert waste powder.<Crystal chemistry and phase manipulation in Synroc by E. R. Vance and others>[Key Engineering Materials 48–50, 717–721; ANSTO abstract identifying the multiphase titanate assemblage]{ref}
Manufacture combines a characterised waste feed with selected oxide-forming precursors, converts the mixture to a suitable powder or <calcination> product, and consolidates it while forming the host phases. <hot pressing> and <hot isostatic pressing> are consolidation approaches; the latter uses pressure acting approximately equally in all directions. The objective is a dense <ceramic> with the intended phase assemblage and low connected <porosity>, contained in an appropriate <radioactive waste package>. Verify density and phase composition, use <microscopy> to find segregated constituents or pores, and test <leaching> of the actual product. Successful densification alone does not establish radionuclide retention.<ANSTO Synroc Radioactive Waste Treatment Technology by the Australian Nuclear Science and Technology Organisation>[Institutional technology overview, waste-form design, characterisation and hot isostatic pressing]{ref}
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