Adsorption processes in nuclear fuel resource recovery

Abstract

The long term viability of nuclear energy as a significant source of power on a global scale is dependent upon the development of readily available, cost competitive, and environmentally sustainable nuclear fuel resources. Expanding the availability of nuclear fuels can be accomplished in two primary ways. First among these is the exploration of entirely new sources of nuclear fuels while the second would be to prolong the usable lifetime of fuel resources that are already available. The recovery of oceanic uranium is one potential, as of yet untapped, source of nuclear fuels that is attractive for both its vast scale and limited impact on the environment when compared to traditional mining techniques. For some time, amidoxime adsorbents have been considered the most promising materials for the recovery of uranium from seawater. Nevertheless, the low concentration of uranium in seawater and presence of many competitors to uranium make it quite difficult to recover uranium economically. Thus, one of the principal goals of this work is to investigate means of improving adsorption performance and reducing recovery costs through optimization of adsorbent design and synthesis. Prolonging the functional lifetime of nuclear fuel resources can effectively be achieved by reprocessing spent nuclear fuels. During reprocessing, however, a number of radioisotopes are volatilized and released in off-gas. Of these radioisotopes, iodine is the most important and must be removed from the off-gas stream before it can be released into the environment. Silver adsorbents are currently considered the promising materials for this application as a result of silver's ability to form strong bonds with iodine molecules. Despite this affinity for iodine, extended exposure to other off-gas species will reduce the adsorbent's iodine capacity, an effect known as aging. The underlying processes that produce the aging effect are, however, not known. As such, the other primary objective of this work is to analyze the aging effect and determine the processes governing aging. These processes will then be applied towards the development of predictive aging and adsorption models.