America, Japan and China are racing to be the first nation to make nuclear energy completely renewable. The hurdle is making it economic to extract uranium from seawater, because the amount of uranium in seawater is truly inexhaustible. James Conca at Forbes describes the latest developments with uranium seawater extraction.
And it seems America is in the lead. New technological breakthroughs from DOE’s Pacific Northwest (PNNL) and Oak Ridge (ORNL) national laboratories have made removing uranium from seawater within economic reach and the only question is – when will the source of uranium for our nuclear power plants change from mined ore to seawater extraction?
Nuclear fuel made with uranium extracted from seawater makes nuclear power completely renewable. It’s not just that the 4 billion tons of uranium in seawater now would fuel a thousand 1,000-MW nuclear power plants for a 100,000 years. It’s that uranium extracted from seawater is replenished continuously, so nuclear becomes as endless as solar, hydro and wind.
The latest technology builds on work by researchers in Japan and uses polyethylene fibers coated with amidoxime to pull in and bind uranium dioxide from seawater (see figure above). In seawater, amidoxime attracts and binds uranium dioxide to the surface of the fiber braids, which can be on the order of 15 centimeters in diameter and run multiple meters in length depending on where they are deployed
Advances by PNNL and ORNL have reduced the cost by a factor of four in just five years. But it’s still over $200/lb of U3O8, twice as much as it needs to be to replace mining uranium ore.
Over the last twenty years, uranium spot prices have varied between $10 and $120/lb of U3O8, mainly from changes in the availability of weapons-grade uranium to blend down to make reactor fuel.
So as the cost of extracting U from seawater falls to below $100/lb, it will become a commercially viable alternative to mining new uranium ore. But even at $200/lb of U3O8, it doesn’t add more than a small fraction of a cent per kWh to the cost of nuclear power.
Marine testing at PNNL showed an ORNL adsorbent material had the capacity to hold 5.2 grams of uranium per kilogram of adsorbent in 49 days of natural seawater exposure — the crowning result presented in the special issue. The Uranium from Seawater program continues to make significant advancements, producing adsorbents with even higher capacities for grabbing uranium. Recent testing exceeded 6 grams of uranium per kilogram of adsorbent after 56 days in natural seawater — an adsorbent capacity that is 15 percent higher than the results highlighted in the special edition.
Uranium is dissolved in seawater at very low concentrations, only about 3 parts per billion (3 micrograms/liter or 0.00000045 ounces per gallon). But there is a lot of ocean water – 300 million cubic miles or about 350 million trillion gallons (350 quintillion gallons). So there’s about 4 billion tons of uranium in the ocean at any one time.
However, seawater concentrations of uranium are controlled by steady-state, or pseudo-equilibrium, chemical reactions between waters and rocks on the Earth, both in the ocean and on land. And those rocks contain 100 trillion tons of uranium. So whenever uranium is extracted from seawater, more is leached from rocks to replace it, to the same concentration
Oak Ridge National Laboratory researchers developed a fiber to adsorb uranium from seawater. Researchers at the Pacific Northwest National Laboratory exposed the fibers to Pseudomonas fluorescens and used the Advanced Photon Source at Argonne National Laboratory to create a 3-D X-ray microtomograph to determine that the fiber structure was not damaged by the organism.
Scientists envision anchoring hundreds of lengths of U-extracting fibers in the sea for a month or so until they fill with uranium. Then a wireless signal would release them to float to the surface where the uranium could be recovered and the fibers reused. It doesn’t matter where in the world the fibers are floating. Source: Andy Sproles at ORNL
Scientists from two DOE labs, Oak Ridge National Laboratory in Tennessee and Pacific Northwest National Laboratory in Washington, led more than half of the 30 papers in the special issue. ORNL contributions concentrated on synthesizing and characterizing uranium adsorbents, whereas PNNL papers focused on marine testing of adsorbents synthesized at national labs and universities.
“Synthesizing a material that’s superior at adsorbing uranium from seawater required a multi-disciplinary, multi-institutional team including chemists, computational scientists, chemical engineers, marine scientists and economists,” said Sheng Dai, who has technical oversight of the ORNL uranium from seawater program. “Computational studies provided insight into chemical groups that selectively bind uranium. Thermodynamic studies provided insight into the chemistry of uranium and relevant chemical species in seawater. Kinetic studies uncovered factors that control how fast uranium in seawater binds to the adsorbent. Understanding adsorbent properties in the laboratory is key for us to develop more economical adsorbents and prepare them to grab as much uranium as possible.”
That teamwork culminated in the creation of braids of polyethylene fibers containing a chemical species called amidoxime that attracts uranium. So far, testing has been conducted in the laboratory with real seawater; but the braids are deployable in oceans, where nature would do the mixing, avoiding the expense of pumping large quantities of seawater through the fibers. After several weeks, uranium oxide-laden fibers are collected and subjected to an acidic treatment that releases, or desorbs, uranyl ions, regenerating the adsorbent for reuse. Further processing and enriching of the uranium produces a material to fuel nuclear power plants.
SOURCES- James Conca at Forbes, Industrial and Engineering Chemistry Research.