Effect of Surface Finish on Nuclear Glass Dissolution Rate

Abstract

ABSTRACTThe influence of the surface finish on nuclear glass dissolution was investigated. Seven different surface finishes were tested: a specimen as cut, three specimens polished with 220, 600 and 4000 mesh SiC paper and one with 1 μm diamond powder, a flame-polished specimen and a thermal rupture specimen.The initial glass corrosion rates were measured after 7 and 28 days of Soxhlet leaching at 100°C. The surface finish of each glass coupon was also assessed by three-dimensional analysis before and after leaching for 28 days. Leaching solution analyses showed that the mean apparent leach rate for the first 7 days was highly dependent on the surface finish: the measured rates ranged from 3.8·g.m-2d-1 for the as-cut specimen to 1.3 g·m-2d-1 for the flamepolished specimen. The differences in the leach rates diminished considerably after 28 days of leaching: the mean rate measured between 7 and 28 days for the as-cut and polished specimens was identical (1.7 g·m-2d-1), but was still lower for the remaining two specimens. Three-dimensional surface analysis showed that leaching revealed surface defects (superficial microcracks) produced by cutting or polishing. These effects were less perceptible on the flame-polished or thermally ruptured specimens. The actual surface area of the cut and polished specimens exceeded the apparent geometrical area.In another experiment, the leach rates measured for as-cut specimens and flamepolished specimens were measured over periods of five months or more using a thermogravity balance placed above the Soxhlet device. The experiment confirmed the existence of an initial period during which the dissolution rate for the as-cut specimen was much higher than the mean corrosion rate.