Jae Hwan Yang

Waste Form of Silver Iodide (AgI) with Low-Temperature Sintering Glasses

This study focuses on the fabrication and characterization of waste forms of silver iodide (AgI) using low-temperature sintering glasses. We investigated the glass composition of bismuth-phosphate-zinc oxide, which enables low-temperature sintering to fabricate waste forms of AgI. We confirm that novel waste forms were fabricated with Bi2O3-P2O5-MxOy glasses, where MxOy is a metal oxide, such as ZnO, CaO (or CaCO3), MgO, or Na2O (or Na2CO3), at sintering temperatures of 600–650°C. The samples were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), inductively coupled plasma-atomic emission/absorption spectrometry (ICP-AES/AAS), and ion chromatography (IC) used for product consistency testing (PCT). Our findings indicate that chemically durable waste forms of AgI were formed and that the loss of iodine during heat treatment was effectively suppressed by a low sintering temperature.

A new route to the stable capture and final immobilization of radioactive cesium

Radioactive Cs released from damaged fuel materials in the event of nuclear accidents must be controlled to prevent the spreading of hazardous Cs into the environment. This study describes a simple and novel process to safely manage Cs gas by capturing it within ceramic filters and converting it into monolithic waste forms. The results of Cs trapping tests showed that CsAlSiO4 was a reaction product of gas-solid reactions between Cs gas and our ceramic filters. Monolithic waste forms were readily prepared from the Cs-trapping filters by the addition of a glass frit followed by thermal treatment at 1000°C for 3h. Major findings revealed that the Cs-trapping filters could be added up to 50wt% to form durable monoliths. In 30-50wt% of waste fraction, CsAlSiO4 was completely converted to pollucite (CsAlSi2O6), which is a potential phase for radioactive Cs due to its excellent thermal and chemical stability. A static leaching test for 28 d confirmed the excellent chemical resistance of the pollucite structure, with a Cs leaching rate as low as 7.21×10-5gm-2/d. This simple scheme of waste processing promises a new route for radioactive Cs immobilization by synthesizing pollucite-based monoliths.

Al2O3-containing silver phosphate glasses as hosting matrices for radioactive iodine

ABSTRACT Al2O3-containing silver phosphate glasses were synthesized to investigate the feasibility of phosphate glasses for the immobilization of radioactive iodine (129I) present in spent nuclear fuel. Characterizations were performed by X-ray diffraction, Fourier transformed infrared spectroscopy, and scanning electron microscopy coupled with energy dispersive spectroscopy to examine structures, bonding properties, surface morphology, and elemental distribution of the synthesized glasses. The principal results showed that iodine became more strongly immobilized in the phosphate glasses with the addition of Al2O3, which was confirmed by the decrease of iodine leaching rates with approximately one order of magnitude. The present study would be helpful to decide whether Al2O3-containing silver phosphate glasses could be used as a candidate matrix to incorporate 129I.