Extracting uranium from seawater is closer to becoming an economic reality which could guarantee the future of nuclear power, scientists said today.
The world's oceans hold at least four billion tons of the precious metal.
But for the past four decades, the goal of mining seawater for uranium has remained a dream because of the technical difficulties and high cost.
Today, a report presented to a scientific meeting showed that fast progress is being made towards turning the oceans into a uranium reservoir.
Improvements to the extraction technology have almost halved production costs from around 560 dollars (£355) per pound of uranium to 300 dollars (£190).
Dr Robin Rogers, from the University of Alabama, told the annual meeting of the American Chemical Society in Philadelphia: "Estimates indicate that the oceans are a mother lode of uranium, with far more uranium dissolved in seawater than in all the known terrestrial deposits that can be mined.
"The difficulty has always been that the concentration is just very, very low, making the cost of extraction high. But we are gaining on that challenge."
The standard extraction technique, developed in Japan, uses mats of braided plastic fibres embedded with compounds that capture uranium atoms.
Each mat is 50 to 100 yards long and suspended 100 to 200 yards under the water. After being brought back to the surface, the mats are rinsed with a mild acid solution to recover the uranium. They are then dunked in the water again in a process that can be repeated several times.
The new work involves making cheaper and more efficient versions of the mats and the compounds that latch onto uranium.
A team led by Dr Rogers is exploring the use of waste shrimp shells from the seafood industry to produce a biodegradable mat material.
Dr Erich Schneider, from the University of Texas, another speaker at the American Chemical Society symposium, said the aim was to establish seawater uranium as an "economic backstop" that will sustain the nuclear power industry.
Nuclear power plants are built to operate for 60 years or longer and involve a huge investment, he told the meeting. Before committing themselves to building nuclear plants, energy companies had to be sure they can source reasonably priced uranium for many decades to come.
"This uncertainty around whether there's enough terrestrial uranium is impacting the decision-making in the industry, because it's hard to make long-term research and development or deployment decisions in the face of big uncertainties about the resource," said Dr Schneider. "So if we can tap into uranium from seawater, we can remove that uncertainty."
Seawater extraction of uranium may also have environmental advantages, the meeting heard.
Traditional uranium mining produced contaminated wastewater and posed health risks for miners.