Iron Phosphate Glass as an Alternative Waste-Form for Hanford LAW

Abstract

Although the current baseline Hanford flowsheet for immobilizing low-activity waste (LAW) assumes borosilicate-based glass, opportunities exist to improve or change this baseline to reduce the current schedule and cost requirements of accomplishing the mission of site cleanup. Development of an alternative glass-forming system can lead to this goal of cost and schedule reduction through enhanced waste loading and higher plant throughput. The purpose of this project is to investigate the ironphosphate glass system as an alternative for immobilizing Hanford LAW. Previous studies on the iron phosphate glass systems and their potential advantages for immobilizing Hanford LAW have been reviewed and technical uncertainties and data required before implementing this technology have been presented. A team of researchers and engineers from the MO-SCI Corporation, the Pacific Northwest National Laboratory, the Savannah River Technology Center, and the University of Missouri at Rolla has performed a series of tests to address some of the open questions about the potential use of iron phosphate glass for immobilizing Hanford LAW. The results of this team effort are summarized along with recommendations regarding the further laboratory study needs. Additional longer-term testing requirements for implementing the iron phosphate glass-based immobilization process at Hanford are also presented.

Vitrified metal finishing wastesI. Composition, density and chemical durability

“…Mazurin et al [34] collated a wealth of data on glass formation compositions for non-silicate glasses. Glasses based on the binary system P 2 O 5 -Fe 2 O 3 have recently received attention owing to their high chemical durability and their suitability as hosts for the immobilisation of certain nuclear wastes [35][36][37][38][39][40][41][42][43][44]. Investigations of third components in these glasses include ZnO [38,39], CaO [40], Na 2 O and K 2 O [41], PbO [42] and BaO [43].…”

“…The formation of vitreous products may still be possible with lower P 2 O 5 equivalents, but there would be a high likelihood of crystallinity. Crystalline phases in vitrified wastes can be beneficial [26,27,[29][30][31], although recent work indicated that crystallinity in certain iron phosphate glasses loaded with inactive simulated nuclear waste can reduce the chemical durability [44]. The merits of crystallinity are dependent upon the material application.…”

Immobilization of Hanford LAW in iron phosphate glasses

“…Leco analysis indicated that about 52% of the sulfate originally present (2.9 wt%) in the waste was retained in the glasses ( Table 2). The sulfate retention in iron phosphate glasses was previously found to depend on the glass composition [8] and melting conditions such as atmosphere and temperature [13].…”

“…The loading of this waste in a BS waste glass is largely determined by the allowable fraction of sulfate in the waste [4][5][6][7]. If the LAW waste loading was not limited by the sulfate content of the waste, then the amount of glass produced at Hanford could be reduced by as much as 50% [8].…”

Studies on the synthesis and characterization of cesium-containing iron phosphate glasses

“…A new group of phosphate glasses, iron phosphate glasses [5][6][7][8][9][10][11][12][13][14][15][16][17], known as IPG has been found to be suitable for vitrification of high level nuclear waste (HLW) rich in alkali oxides, sulphates and chrome oxides. For the same amount of waste immobilization, the density of iron phosphate vitreous waste form (3.2 g/cc) is 25% higher than that of BS waste form; consequently its volume is 25% lower than that of borosilicate waste form [9].…”