to which boron oxide (B2O3) had been added to achieve a pourable glass and minimize radionuclide volatilization. The most promising vitreous systems for future development were determined to be borosilicate based, e.g., CaO-Al2O3-B2O3-SiO2 and Na2O-CaO-Al2O3-B2O3-SiO2.

In 1970, the singular requirement for a waste form from the Office of Nuclear Waste Isolation1 (ONWI) was that it be a stable solid (DOE, 1981; Walton et al., 1983). By the mid-1970s, innovative proposals for producing stable solid waste forms were being offered—for example, supercalcine ceramics by Rustum Roy and colleagues at Pennsylvania State University (McCarthy, 1977; Roy, 1975, 1977, 1979); alumina-based tailored ceramics by Rockwell International Science Center (Jantzen et al., 1982b; Morgan et al., 1981); and titania-based SYNthetic ROCk (SYNROC) by Ted Ringwood and colleagues at the Australian National University and the Australian Nuclear Science and Technology Organisation (Reeve et al., 1984; Ringwood, 1978, 1985; Ringwood et al., 1978). The first systematic compilations of potential crystalline waste form phases were also made at this time (Haaker and Ewing, 1981).

There were extensive research and development (R&D) programs on nuclear waste forms during the late 1970s and early 1980s, resulting in the examination of a wide variety of single-phase and polyphase ceramics. By this time “low leachability” had become the main criterion for waste form comparisons (DOE, 1981; Walton et al., 1983), and such comparisons between crystalline ceramics and glass generated considerable controversy (Kerr, 1979a,b).

Beginning in 1978, there was intense study of alternative waste forms that culminated in a review (Garmon, 1981) that recommended borosilicate glass for immobilizing high-level radioactive waste (HLW) at the Savannah River Site (SRS) in South Carolina and West Valley in New York and also identified SYNROC/tailored ceramics as promising alternatives (Hench et al., 1981). Glass was considered to be a more proven technology, and there were questions about the maturity of production technologies for ceramic waste forms. Nevertheless, Hench et al. (1981) made a strong recommendation for continued research and development for ceramic waste forms, including SYNROC and titanate- and alumina-based ceramics. These alternative waste forms were later determined to be difficult to process, more costly to implement, and not as flexible for accommodating variations in waste composition as borosilicate glass (De et al., 1976; Dunson et al., 1982; Lutze et al., 1979; McCarthy, 1973; McCarthy and Davidson, 1975; Morgan et al., 1981; Ringwood et al., 1981; Schoebel, 1975), even though

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1 The Office of Nuclear Waste Isolation was located at the Battelle Memorial Institute. It conducted research and published technical reports on technical aspects of nuclear waste isolation.



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