Microstructure and leaching durability of glass composite wasteforms for spent clinoptilolite immobilisation

The chemical durability of glass and graphite–glass composite doped with cesium oxide

“…7) show that the normalised leach rates of the major glass elements were based on the sequence Si < B < Cs. The value of NL Cs was increased by two orders of magnitude from 0.2 Â 10 À6 g/cm 2 /day to 2.05 Â 10 À5 g/cm 2 /day at temperature rising from 298 K to 363 K. The value of NL cs (0.77 Â 10 À6 g/cm 2 /day) at 313 K was lower than NL cs (0.907 Â 10 À6 g/cm 2 /day) obtained by Joui et al [18] at the same temperature, using ASTM C1220-98. Conversely, the value of NL Cs from GGC obtained from Fig.…”

“…The containers were kept in a multi scale temperatures oven at different temperatures: 298 K, 313 K, 323 K, 333 K, 343 K, 353 K and 363 K. The ratio of the surface area of matrix to the volume of water (SA/V) was adjusted to be 10 m À1 by filling a suitable leachant volume. The SA:V ratio was obtained from a similar study, using the ASTM-C1220 leach test for examining the chemical durability of glass, containing ion exchange resin doped with Cesium (Cs-Clino) [18]. The authors reported that the cumulative leach rate of Cs was 0.037 Â 10 À6 g/cm 3 and the corresponding normalised leach rate (NL) was 0.915 Â 10 À6 g/cm 2 /day which is within the permissible limit.…”

“…The cumulative concentrations (C i ) in water were measured in g/cm 3 from each container after 28 days. The concentrations of an element (i) were converted to their normalised leach rates (NL i ) in the given equation [18].…”

“…It should be noted that some studies neglected the volatilisation of cesium vapour during the sintering process in glass [18], thus causing a significant errors when calculating the initial concentration of Cs in the glass. Other studies used TiO 2 as a network modifier to suppress the volatilisation of Cs from borosilicate glass [19].…”

Glassy Wasteforms for Nuclear Waste Immobilization

“…GCMs include the following: (1) glass ceramics in which a glassy waste form is crystallized in a separate heat treatment [7,78] ; (2) GCMs in which, e.g., a refractory waste is encapsulated in glass such as hot-pressed lead silicate glass matrix encapsulating up to 30 vol pct of La 2 Zr 2 O 7 pyrochlore crystals to immobilize minor actinides [9] ; (3) GCM formed by pressureless sintering of spent clinoptiloite from aqueous waste processing [10] ; (4) some difficult wastes such as the French HLW U/Mo-containing materials immobilized in a GCM termed U-Mo glass formed by cold crucible melting that partly crystallize on cooling [11] ; (5) yellow phase containing wastes are immobilized in Russia in a yellow phase GCM containing up to 15 vol pct of sulfates, chlorides, and molybdates [12] ; and (6) GCM that immobilizes ashes from incineration of solid radioactive wastes. [13] Note that alkali-rich wastes at the Hanford site are also immobilized in glassy wasteforms with high crystal contents that characterize them as GCMs.…”