Sodium–aluminum–iron phosphate glasses as legacy high level waste forms

Glass Crystalline Materials as Advanced Nuclear Wasteforms

“…This is achieved by quenching the melt at high cooling rates about 500 • C/h, whereas at cooling rates of 50 • C/h or less, crystalline phases appear [38]. Crystallisation of glass can occur after the melt is drained into canisters due to residual heat [6,7]. Often T g is taken as the temperature at which the melt viscosity is 10 12 Pa•s (10 13 Poise) [39] although the glass transition is a quasi-equilibrium second order phase transformation, and the glassy state of matter differs topologically from that of molten state [40].…”

“…Partial glass devitrification occurred when cooling rates about 30-50 • C/h close to that of HLW vitrification facilities were used [6]. On melt pouring from the EP-500 Joule-heated ceramic melter, the temperature of the container with vitrified HLW decreases within 17 h from 700 to 500 • C [7], that is, the cooling rate was just about 10-15 • C/h. The question therefore remains open about the state of vitrified HLW stored at "Mayak" PA since 1987 as it can be a relative homogeneous glass, although glass with crystalline phases or even a fully crystallized material are also possible variants.…”

“…Considering the processing rates of vitrification facilities [2][3][4][5][6], the current mass of vitrified HLW can be estimated at about 35,000-36,000 tonnes, of which almost 80% are A-B-Si, and the rest are Na-Al-P glasses. Vitrification of HLW is, however, not the optimal method of immobilisation due to the relative low radionuclide loading of glasses and their susceptibility to crystallisation, which can begin immediately after the melt pouring into canisters due to the residual heat of the melt [6,7]. Partitioning of HLW radionuclides onto groups can provide a better solution for their immobilisation by incorporation within crystalline lattice of silicates, titanates, zirconates, and phosphates.…”

Effect of Gamma Irradiation on Structural Features and Dissolution of Nuclear Waste Na–Al–P Glasses in Water

“…Crystallization of AlPO 4 can begin in the melt in the furnace with a Na 2 O content of less than 5 mol% and then continue when the melt (glass) cools down after pouring into canisters. In general, phosphotridimite and alkaline aluminum (iron) phosphates are typical products arising from the partial or complete crystallization of phosphate glass matrices [35][36][37][38][39][40][41][42][43][44][45]. At high contents of light rare earths (the Ce group), lanthanide phosphate with the structure of monazite appears, REE solubility in the aluminum-phosphate melt is determined as few wt.% [11,42,43].…”

“…This can be caused by undetectable structural changes such as radiation-induced annealing that occurs in some other type of glasses [22]. Much higher effect on the deterioration of properties of the aluminum-phosphate vitreous waste form, including their solubility in hot water, is observed due to glass crystallization in temporary storage and after ultimate disposal in deep underground repository [11,14,15,[36][37][38][39][40][43][44][45].…”