Synroc development—Past and present applications

Abstract

Synroc has evolved over the last 40 years from the titanate full-ceramics developed in the late 1970s to a technology platform that can be applied to produce glass, glass–ceramic, and ceramic waste forms and where there are distinct advantages in terms of waste loading and suppressing volatile losses.A first of a kind Synroc plant for immobilizing intermediate level waste arising from Mo-99 production is currently in detailed engineering at ANSTO.Since the year 2000, Synroc has evolved from the titanate full-ceramics developed in the late 1970s to a technology platform that can be applied to produce glass, glass–ceramic, and ceramic waste forms and where there are distinct advantages in terms of waste loading and suppressing volatile losses. Furthermore recent efforts have focused strongly on waste form development for plutonium-bearing wastes in the UK, for different options for the immobilization of Idaho calcines and most recently developing an engineered waste form for the intermediate level wastes arising from 99Mo production, for the Australian Nuclear Science and Technology Organisation (ANSTO). A variety of other studies are currently in progress, including engineered waste forms for spent fuel and investigating the proliferation risks for titanate-based waste forms containing highly enriched uranium or plutonium. This paper also attempts to give some perspective on Synroc waste forms and process technology development in the nuclear waste management industry.

Hot Isostatically Pressed (HIPed) fluorite glass‐ceramic wasteforms for fluoride molten salt wastes

“…GC2B showed substantially higher Sb and Mo release rates for all time‐points, although the release rates for Mo and Sb in both samples were higher than those expected for these elements in the metallic form. For example, Mo releases of 0.4 g/m 2 /d are observed in Synroc‐C where Mo metal is present within the wasteform 35 . Given that SEM‐EDS analyses suggested the formation of Sb/Mo alloy in both samples, the enhanced release of Sb and Mo may be a result of the increase in the F ‐ ion content of the leach solution within the static leach experiment, or may indicate incomplete conversion to the Sb and Mo metallic form, particularly for GC2B.…”

New insights into phosphate based materials for the immobilisation of actinides

“…The fabrication of ceramic waste forms was historically one of the main drawbacks compared to waste glasses, because the melting points of ceramic materials often exceed 2000°C. However, in the last two decades tremendous progress was made in fabrication methods of ceramic waste forms that can be expanded to the industrial scale [134]. Generally, waste forms can be fabricated by sintering, uniaxial hot pressing (HUPing), isostatic hotpressing (HIPing) and melting.…”

“…These advantages include: (i) no notable emissions of volatile radionuclides in the high temperature consolidation step due to the closed processing system, (ii) less secondary waste and (iii) flexible processing conditions. Several industry-scale HIPing systems are currently being set up for the processing of actinide-rich radioactive wastes [134]. However, at HIPing conditions (high temperatures, up to 2000°C and high pressure, 100-200 MPa), the waste form and the stainless steel container may interact, this interaction has already been demonstrated to be non-detrimental for several types of ceramic waste forms [140][141][142].…”

Structure and stability of alkali gallates structurally reminiscent of hollandite

“…Crystalline ceramic wasteforms, particularly SYNROC 4 and titanate/alumina‐based ceramics, have received a lot of attention due to their ability to incorporate a broad spectrum of chemical species within available lattice sites, potentially higher waste loadings, and resistance to hydrothermal leaching 5‐7 . Among the ceramic materials studied are hollandite‐type structures, generally A x M 8 O 16 .…”