Leaching study of nuclear melt glass: Part I

Abstract

Ground samples of three nuclear melt glasses from underground nuclear explosions at the Nevada Test Site (NTS) were leached at 25/sup 0/C with natural ground water from NTS. Using our dynamic single-pass flow-through leaching system we monitored the release of radionuclides from the glasses during 420 days of leaching. We continually flowed the ground water over the melt glass at flow rates of 185 ml/day for half of the samples and 34 ml/day for the rest. Leachate solutions were collected continuously, and composite samples, collected on days 1, 2, 3, 6, 11, 32, 38, 70, 120, 230 and 420, were analyzed using low-background Ge(Li) gamma spectrometers. For most of the radionuclides the leach rate decreased smoothly throughout the experiment. Except for /sup 95/Zr, /sup 144/Ce, and /sup 155/Eu, there was no difference between the fast (185 ml/day) and slow (34 ml/day) flow-rate leach rates. The measurable leach rates ranged from a high of 1 x 10/sup -2/ g-glass/m/sup 2/ day for /sup 22/Na (slow flow-rate, day 1 in glass No. 2) to a low of 1 x 6/sup -6/ g-glass/m/sup 2/ day for /sup 54/Mn (slow flow-rate, day 420 in glass No. 2). Most of the leach-rate values were about 5 x 10/sup -4/ g-glass/m/sup 2/ day initially, decreasing to 5 x 10/sup -6/ g-glass/m/sup 2/ day after 420 days of leaching. The leach rates had not leveled off by the end of the experiment and were, in general, continuing to decrease. From the activities in the leachate solutions, we determined the percent of the pre-leach activity leached from the melt glasses during the experiment. Only /sup 124/Sb, in one fast flow-rate channel of glass No. 2, exceeded 3% of the initial activity leached. The majority of the samples released less than 1% of the pre-leach activity for a given radionuclide. The percent activity released from the samples leached at the fast and slow flow rates were nearly equal.