Decoupling the Functional Requirements of an Adsorbent for Harvesting Uranium from Seawater through the use of Shell Enclosures

摘要

In the case of ocean deployment of an offshore system for harvesting uranium from seawater, adsorbent materials will need to withstand the harsh environment of the ocean as well as the likelihood of rough handling during transport and deployment. Currently, adsorbent polymers with high tensile strength tend to have poor uranium adsorption capacity. However, the mechanical requirements of an offshore uranium harvesting system can be decoupled from the chemical requirements through the use of an exterior shell enclosure surrounding an adsorbent polymer. Furthermore, the adsorbent polymer may be wound into a ball with filaments extending radially outward from the center core. This study proved the mechanical feasibility of winding an adsorbent polymer into a filament ball to meet the annual uranium needs of a 5-MW nuclear reactor. With the structural strength of the system now provided by a shell enclosure instead of the adsorbent itself, the strength of various shell designs under vertical distributed loading was investigated. It was found that the factor of safety increased as the number of faces of the shell enclosure decreases. The cube shell likely appears to be the strongest, with a factor of safety of 8.03, because its vertical walls were the most effective at resisting vertical loads. Further investigation should be done into the performance of the shell geometries under point loads. Additionally, the performance of a spherical shell under similar loading conditions should be studied for comparison. Given that adequate seawater flow to the adsorbent interior is crucial to the total uranium adsorption of the device, the impact of four different hole geometries on the strength of the cube shell was also studied. It was determined that the vertical rectangular slits resulted in the highest factor of safety of 29.01, which follows on in the view that vertical geometries should resist vertical loads better. However, given that the loads on the shells will be random, it is likely that the large square holes, with the second highest factor of safety of 21.76, will prove to be the strongest in practice. Additional analysis needs to be conducted to determine which hole geometry is best for adequate seawater flow to the adsorbent interior. Future work should also focus on determining the distance between the filament ball and the shell enclosure for the optimal fluid flow and resulting uranium adsorption.