|Fig. 1: Amidoxime-impregnated braid that attract positively charged uranium ions in seawater. This amidoxime technology has the potential to harness the uranium ambient in seawater.  (Courtesy of the DOE)|
There are trace amounts of uranium in the world's ocean.  As uranium is the limiting ingredient necessary to harness nuclear power via nuclear reactors, and seawater makes up 70% of Earth's surface, the extraction of uranium from the oceans is a compelling prospect for countries that do not have natural mines of uranium.  Japan, China, and America are racing to optimize the uranium-extraction process from seawater in order to make the ocean a viable source. The uranium extraction process involves the electric attraction of positively charged uranium ions dissolved in water to plastic coated with amidoxime. [1,3-5] The uranium ions in the water will stick to the amidoxime; when the strands become saturated the plastic must be treated similar to how mined uranium must be refined before use in reactors.  Fig. 1 shows the adsorbent amidoxime braid developed by the Pacific Northwest National Laboratory; the fiber is attached to a plastic rod, which could theoretically be submerged in the ocean in mass to mine uranium. 
The Earth's oceans cover approximately 70% of Earth's surface.  The radius of the Earth is 6,371 km, and the average depth of the ocean is 3.7 km.  The total volume of the oceans is thus roughly
The oceans contain uranium at about 3 parts per billion by weight.  Since ocean water has mass denstiy of 1000 kg per m3, the total mass of uranium in the oceans is approximately
The global consumption of uranium metal prior to enrichment was approximately 56,585 tonnes in 2015 as reported by the Nuclear Energy Agency and the International Atomic Energy Agency.  The number of years the oceans could supply uranium at the 2015 burn rate is thus:
Additionally, nuclear energy presently provides about 4.5% of civilization's energy needs.  If one supplied all the world's energy with uranium out of the oceans with modern burn practices, the supply would last for
The above analysis shows that there is significant potential for the uranium suspended in the oceans to fuel modern society for three thousand years. Although it is unlikely that we will develop technology capable of capturing all of the uranium in the ocean, the research to create uranium extraction via amidoxime should be continued in order to transform ocean-uranium into a viable nuclear energy source. Uranium can be sourced in this manner all around the world, and its accessibility could transform the world's social and economic inequality due to the unequal distribution of fossil fuels throughout the world. Although uranium in seawater is not a completely renewable resource such as the wind and the sun, its great abundance makes it appear to be an unlimited resource, which could fuel our modern, energy-driven society.
© Charlotte Philp. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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