Exploration of configurations of wave energy converters to mechanically drive a seawater uranium harvester

Abstract

Nuclear power accounts for about 20% of the electricity generated in the United States today [29], but conventional reserves of terrestrial uranium are estimated to be depleted within the century [19]. Fortunately, an estimated 4.5 billion tonnes of uranium exists as ions in the ocean [281, and a system of adsorbent polymers has been designed to extract the uranium. A proposed machine to harvest seawater uranium, the Symbiotic Machine for Ocean uRanium Extraction (SMORE), is fixed to a floating wind turbine and requires 550 kW to power four nets of shell enclosures containing the adsorbent and the chemical processing required to remove the uranium and reuse the polymer [161. Given the high energy density of ocean waves, this thesis explores the potential of wave energy converters to provide the power requirements of SMORE. Each net requires 92 kW of power, or about 1100 kNm to drive continuous movement at 0.087 rad/s. This thesis found that harnessing that amount of power would require a heaving buoy of 11.5 m diameter and 1 m height, though the large geometry and range of motion caused structural concerns. In contrast, a pitching buoy of 4.7 m diameter and 2 m height could provide the same amount of power, and the structure could be more easily reinforced with only one moving body. Various configurations of pitching buoys are discussed as well. While this thesis defined a first order approximation of a future system, the modeling of realistic sea states and several mechanical optimizations need to be explored further. The integration of some electronics to power the chemical processing tanks and optimize the response control of the buoy may also provide benefit at a small increase in cost. Using a wave energy converter reduces not only the power load on the turbine, but also may decrease the incident wave loads and stabilization requirements of the turbine [13]. Further cost analysis is required, but a future implementation of this wave energy converter could add great value to both the uranium harvesting system and floating wind turbine.