Product Consistency Testing of Hot Isostatically Pressed Iodine-containing Waste Forms

摘要

PCT was conducted on the successfully pressed samples, and the results from the analysis of the leachate are shown in Table 2. A value of "ND" indicates a value below the reporting limit, and this is desirable as it indicates no measurable release of the selected element from the waste form. Sample 2-7 was found to have released substantially more of each element measured than other samples; it is recommended that this sample be replicated to confirm these results. Out of the 12 samples tested, six had no measureable release of iodine. From Samples 2-1, 2-2, and 2-3, it can be seen that the amount of iodine leached from the material decreased substantially as pressing temperature was increased from 525℃ to 900℃. Sodium release from these samples also followed this trend. Further increase of the pressing temperature to 1100℃ for the same sample composition (Sample 2-21) did not result in measurable improvement in leach rate (leached iodine remained below the reporting limit of 1 mg/L, and leached silver rose to slightly above the reporting limit of 5 μg/L). Samples 2-11 and 2-21, both composed of NaZ powder and Agl (3:1), were pressed at 900℃/100 MPa and 1100℃/175 MPa, respectively. No measurable improvement in leach rate was observed for the higher temperature and pressure used for Sample 2-21. This result, combined with the data from Samples 2-1, 2-2, and 2-3, indicates that the majority of the benefit arising from increased temperature may be realized at 900℃ and that further elevation may not result in a more durable waste form. PCT of the pressed samples resulted in iodine release below detection limit for six of twelve samples. This is promising and indicates that a durable waste form may be produced through HIPing even if transformation of the zeolite to a distinct mineral phase does not occur. From PCT results, it was determined that future pressing should be conducted at a temperature of 900℃. The ultimate goal of investigations into HIPing of Ag°Z-I is to produce a pellet that can be demonstrated to have high iodine retention and be considered a promising candidate for long-term stability and disposition of iodine-containing zeolite sorbents. Continued fundamental research and development into this process will focus on incorporation of pure zeolite minerals in the initial sample composition and will ensure that transformation from zeolite to sodalite is stoichiometrically favorable through the addition of alumina.