engleski

Vitrification of High Chrome Oxide Nuclear Waste in Iron Phosphate Glasses

A simulated high level waste containing 4 mass % chrome oxide, whose overall composition is representative of the high chrome oxide wastes at Hanford WA, was easily vitrified in a phosphate glass at temperatures ranging from 1150 oC, for waste loadings of 55 mass %, to 1250 oC for waste loadings of 75 mass %. Even at these high waste loadings, these iron phosphate glasses had an excellent chemical durability The total elemental mass release, determined by the Product Consistency Test, for either glassy or deliberately crystallized wasteforms that contained 70 or 75 mass % waste was less than 1.5 and 2.0 g/m2, respectively. The corrosion rate of glasses containing 70 or 75 mass % waste loading was less than 0.2 and 3.5 g/m2/day as determined by the Vapor Hydration Test (VHT). When these glassy wasteforms were deliberately crystallized (48 h at 650 oC), the corrosion rate remained unchanged for the wasteform containing 70 mass % waste and increased only slightly to 14.4 g/m2/day for the crystallized wasteform containing 75 mass % waste. The best chemical durability was achieved when the O / (Si+P) atomic ratio was between 3.5 and 3.8. These iron phosphate glasses were also resistant to crystallization although trace amounts of crystalline Cr2O3 were present in wasteforms containing more than 70 mass % waste. No crystallization peaks were observed when the glasses containing 70 or 75 mass % waste were reheated to 750 oC during DTA. Similarly, no crystallization was detectable by XRD when a melt containing 70 mass % waste was cooled at 2 oC per minute in the melting furnace to room temperature (with a 2 h hold at 870 oC). It is concluded that 10 to 45 mass % of the total HLW at Hanford WA, especially that containing high percentages of chrome oxide, could be vitrified with a phosphate glass to form a wasteform that would meet all of the current chemical durability requirements by simply adding 25 to 35 mass % phosphate to the waste and melting the mixture at 1150 to 1250 oC for a few (< 6 ) hours.

Iron phosphate glasses ; Nuclear waste disposal

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