Abstract
Calcium-aluminoborate (CAB) glasses were developed to sequester new waste compositions made of several rare-earth oxides generated from the pyrochemical reprocessing of spent nuclear fuel. Several important wasteform properties such as waste loading, processability and chemical durability were evaluated. The maximum waste loading of the CAB compositions was determined to be ~56.8 wt%. Viscosity and the electrical conductivity of the CAB melt at 1300 °C were 7.817 Pa·s and 0.4603 S/cm, respectively, which satisfies the conditions for commercial cold-crucible induction melting (CCIM) process. Addition of rare-earth oxides to CAB glasses resulted in dramatic decreases in the elemental releases of B and Ca in aqueous dissolution experiments. Normalized elemental releases from product consistency standard chemical durability test were <3.62·10−5 g·m−2 for Nd, 0.009 g·m−2 for Al, 0.067 g·m−2 for B and 0.073 g·m−2 for Ca (at 90, after 7 days, for SA/V = 2000m−1); all meet European and US regulation limits. After 20 d of dissolution, a hydrated alteration layer of ~ 200-nm-thick, Ca-depleted and Nd-rich, was formed at the surface of CAB glasses with 20 mol% Nd2O3 whereas boehmite [AlO(OH)] secondary crystalline phases were formed in pure CAB glass that contained no Nd2O3.
Highlights
Pyrochemical reprocessing technologies have been developed to recycle radioactive uranium and trans-uranium elements from spent nuclear fuels[1,2]
Borate glasses are well-known for their low TM, high r5">5] are converted to oxides (REOs) solubility and moderate chemical durability, for calcium aluminoborate (CAB) glasses though borate glasses are generally less durable than silicate glasses[11,12,13]
We investigate the applicability of using calcium-aluminoborate (CAB) glasses for immobilization of REO wastes produced by pyrochemical reprocessing
Summary
Pyrochemical reprocessing technologies have been developed to recycle radioactive uranium and trans-uranium elements from spent nuclear fuels[1,2] During these recycling processes, new families of radioactive wastes are generated. It can accommodate up to 55 wt% of combined fission product (alkali + alkaline earth + lanthanide) with good chemical durabilities This glass has high crystallization tendency when more than 35 wt% of REO was added. REO wastes generated from the pyrochemical processing contain highly concentrated REOs and it is necessary to develop a new family of glasses with high REO solubilities. We present our findings related to processability, waste loading, and in particular, durability, by using high-resolution techniques to observe the glass dissolution mechanisms of borate glasses
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