Journal of the American Ceramic Society, Vol.103, No.10, 5454-5469, 2020
Hot Isostatically Pressed (HIPed) fluorite glass-ceramic wasteforms for fluoride molten salt wastes
Molten pyroprocessing salts can be used to dissolve used nuclear fuel from a reactor allowing recovery of the actinides. Previously, ANSTO have demonstrated hot isostatically pressed (HIPed) sodalite glass-ceramic wasteforms for eutectic (Li,K) Cl salts containing fission products, but this system cannot be used for the analogous molten alkali fluoride salts (eg, FLiNaK), which have utility in the application of the next generation of nuclear reactors. In this work, a novel glass-ceramic composite wasteform has been prepared by HIPing, as a candidate for the immobilization of fission product-bearing FLiNaK salts. The wasteform has been tailored to immobilize the high fluoride content of the waste within fluorite, whereas the waste alkali elements are incorporated in a durable sodium aluminoborosilicate glass, with total waste loadings of similar to 17-21 wt% achieved. It was also demonstrated that the speciation of Mo- and Sb-simulated fission products was altered by adding Ti metal due to a controlled redox environment. The resulting candidate wasteform has been studied by X-ray diffraction and scanning electron microscopy, including the HIP canister-wasteform interaction zone, and its performance assessed via leaching studies using the PCT and ASTM C1220 leaching protocols. Dr Vance very much enjoyed the challenge of wasteform design for problematic nuclear wastes, for which fission product-bearing FLiNaK salts are a clear example. His ability to hone in on a wasteform solution with viable waste loadings that meet performance requirements was testament to his nearly 40 years experience in nuclear waste immobilization. The samples discussed in this work represent the last wasteform materials that he prepared.