Glass - Back to the Future!

Presenting Author:
Miae Kim

article posted 6 April 2016

Miae Kim is studying for a PhD in materials science and engineering at Pohang University of Science and Technology, Republic of Korea where she already gained a masters in 2013. Before then she was at Yonsei University, earning a Bachelor of Ceramics Engineering degree.

Borate glasses with high rare-earth oxides waste loading

Miae Kim* & Jong Heo
Department of Materials Science and Engineering and Division of Advanced Nuclear Engineering, Pohang University of Science and Technology (POSTECH), Pohang, South Korea

Pyro-processing is being investigated to recover radioactive uranium and trans-uranium elements from the spent fuels of pressurized water reactors [1]. Previous researches to fabricate various wasteforms for lanthanide oxides wastes generated from pyro-processing reported low elemental released values (<104 g/m2) for lanthanide ions from the product consistency test (PCT) [2]. Current work reports the continuing effort on the enhancement of the waste loading and processability. Borate glasses are known for their low melting temperatures with high rare-earth oxide solubility compared to silicate glasses [3]. Borate glasses were investigated as potential wasteforms with high waste loading for immobilization of lanthanide ion wastes produced by pyro-processing. Processability of them was investigated by characterizing several important processing parameters for cold crucible induction melter (CCIM) process.

Figure 1. The specimens containing various concentrations of Nd2O3

The nominal composition (mol%) of the specimens prepared was (100-x)(0·25CaO–0·19Al2O3–0·56B2O3xNd2O3 (x=0, 10, 20, 30) (Figure 1). Maximum solubility of the rare-earth oxides in the glasses was evaluated as 22 mol% (56·8 wt%) when the batch was melted at 1300°C for 30 min. There is no significant loss of the starting components during melting processes. Processing temperature of these glasees were ~150°C lower than the melting points of competative lanthanide aluminosilicate glasses[5] with a slightly higher RE-loading[4]. PCT was performed on glass containing 20 mol% of RE. The normalized released amounts of Ca, Al and B were 10-3–10-4 g/m2day and the released concentration of Nd were below the limit of dectection of ICP-MS (<0·1 ppb). Thermal properties such as glass transition and crystallization temperatures was measured by DTA (Figure 2). Finally, the suitability to adjust to cold crucible induction melter (CCIM) such as viscosity (10–100 poise) and electrical conductivity (0·1–1 S/cm) was performed.

Figure 2. Differential thermal analysis of 0–30 mol% Nd2O3 containing glasses