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I was reading my handy-dandy nuclear energy book (from 1978, oh dear), and during it's discussion of uranium ore availability (judging 'ore' by prices of $80/kg and $130/kg), it mentions that 'if uranium prices eventually triple, the oceans become an orebody'. What was the 70s seawater-extraction technology they were talking about? How expensive WOULD uranium have to become to make seawater-extraction economical?

At the current performance of modern polyethylene fiber adsorbent, it would become cheaper than the alternatives if their price rose to ~ $210+ per kg of uranium. Further improvement is anticipated. The figure is estimated to drop to $130/kg of uranium extracted from seawater.

These figures are not very much when put in context. Nuclear fuel expense is a tricky topic because some cost figures are for the total with enrichment and fabrication expenses. But detailed calculations indicate that the total cost of nuclear electricity would rise by no more than several percent in event of having to resort to seawater extraction of uranium. Most of the generation expense is the capital cost of the power plants rather than the fuel.

A much more detailed discussion with references for the preceding is here.

Well I read most of your links, and nowhere do I see mentioned the cost of pumping the seawater through the filter medium. All filtering requires a flow, under pressure. The cost of production will never be lower than the cost of pumping all those billions of gallons of seawater needed to pull the microcopic amounts of Uranium per liter out of it.
This was covered in a science fiction story by A. C. Clarke, in "The man who ploughed the sea." Only about Gold, not Uranium.

Unless you are somehow proposing to use natural ocean currents as your pumping, or perhaps tides?

EmperorChrostas the Cruel wrote:Well I read most of your links, and nowhere do I see mentioned the cost of pumping the seawater through the filter medium. All filtering requires a flow, under pressure.

The process isn't described by your mental image of "filtering." It involves adsorbent fibers. For an analogy, think of branches of seaweed dangling and swaying in the natural flow of seawater with tides, etc.

There's a lot of flow of water and diffusion in the oceans (just like one might guess if observing a beach). One method is taking advantage of this natural convection.

I see one of the main URL links in my old post has become broken sometime during the year since it was written, but let's add another example:

Aquaculture of Uranium in Seawater by a Fabric-Adsorbent Submerged System
Volume 144 · Number 2 · November 2003 · Pages 274-278 [...]

The total amount of uranium dissolved in seawater at a uniform concentration of 3 mg U/m3 in the world's oceans is 4.5 billion tons. An adsorption method using polymeric adsorbents capable of specifically recovering uranium from seawater is reported to be economically feasible. [...]

We submerged three adsorption cages in the Pacific Ocean at a depth of 20 m at 7 km offshore of Japan. [...]

The total amount of uranium recovered by the nonwoven fabric was >1 kg in terms of yellow cake during a total submersion time of 240 days in the ocean. [...]

From here

That's a simple test rather than commercial-scale extraction, which isn't done so far since cheaper conventional mining still has sufficient inexpensive high-grade uranium ore available. Even when the best land-based ore is depleted, there are other sources before necessarily immediately going to seawater. For example, at least several times the amount of conventional uranium reserves is available within phosphate deposits at $60 to $100 per kilogram of uranium.

But uranium from seawater has particular long-term potential due to the billions of tons available, making it the simplest way to illustrate that the world will not run out of uranium.

There are multiple methods of obtaining the same goal. A different proposal here envisions putting an extraction system on barges towed by a ship. In that case, their anticipated cost is higher at 42000 yen per kg of uranium. Since about 107 Japanese yen equals an U.S. dollar, such would be about $390 / kg of uranium.

Even for that, it can be determined such would still result in less than 1 cent per kilowatt-hour total nuclear electricity generation cost increase.

That's even while neglecting the potential usage of breeder reactors to drop uranium consumption by two orders of magnitude and make total generation expense (mostly capital cost) even less affected by uranium expense.

Here's another example, with far less estimated expense, which takes advantage of tidal flow:

Experiments for Recovery of Uranium from Seawater by Harnessing Tidal Energy

[...] Thus operating estimated Cost per kg of uranium is just Rs 2500/kg [which is about $60 per kg in U.S. dollars]. [...]

Life of the remainder equipment is taken as 20 years to arrive at the annual fixed costs. This results in Rs. 900/kg [about $20/kg] of U recovered as the depreciation component of fixed cost. The 20 years lifetime average interest on the basis of 5% pa works out to 3.8% only. Or in other words the impact on the cost of uranium recovered is Rs. 1500/kg [about $40/kg]. Thus it is likely to be competitive with the current mining costs. [...]

From here.

The comments added in brackets are dollar conversion, from Indian rupees to U.S. dollars, currently 40:1.

While there's slight imprecision in using current exchange rates on an article from several years ago, that's really irrelevant. The general order of magnitude is what's important, and even their estimates would have some uncertainty.

Even if such wasn't quite as competitive with current mining costs as hoped, anything remotely like it would still be good enough if the highest quality land reserves were eventually depleted.

The really important observation beneath all of this is that enough uranium can be obtained to continue fueling even mere fission reactors for eons (even neglecting the thorium option). Such is one of the reasons to prefer more nuclear power over the current primary method of electrical power generation: coal power plants.

One of the advantages of uranium is that relatively so little is needed, unlike fossil fuels ... analogous to the vast difference between a few pounds of gasoline being sufficient for a car to drive around a city for a few minutes versus a few pounds of fissioning uranium having enough energy to blow up the city.

EmperorChrostas the Cruel wrote:This was covered in a science fiction story by A. C. Clarke, in "The man who ploughed the sea." Only about Gold, not Uranium.

Sci-fi stories aren't usually a reliable reference for accurate information, only sometimes a source of ideas, but, aside from chemical differences, gold is two orders of magnitude more uncommon in seawater than uranium.

The science in the story isn't invalid. The whole point of the story, was the flow of seawater is the limiting factor. That is in fact MY whole point. Unless you are using exsiting currents, or tides you must pump. No more, no less. True?
The passive absorbtion method you are proposing would need to be HUGE, to filter the required volume of seawater. Or a higher flow rate.

We are still left with X amount of Uranium per liter in seawater. It will take X amount of seawater flow to genrate X amount of Uranium. Do the math.

Note: I like this idea, it seems quite feasable. Until the Greens start popping in, and bitching about disrupting the natural ocean currents, F ing up the ecology, using the court for injunctions, ect....

Not to seem like a retard, Sikon, but what *is* the current price for uranium? Has it dropped through the 80s?

Stark wrote:Not to seem like a retard, Sikon, but what *is* the current price for uranium? Has it dropped through the 80s?

According to this the current price is sitting at $75.

That price J kindly quoted is per pound of U3O8.

Are the prices quoted in the OP on that basis, or are they per kg U?

If hte latter holds, here's my half-assed attempt at conversion, using atmoic masses from the IUPAC Periodic Table of the Elements, Nov 01 2004 edition.

Molar mass U: 238.02891(3) g
Molar mass O: 15.9994(3) g

Molar mass U3O8: 842.08193(249) g (assuming linear error propagation - quadratic drops the error by at most 10 ulp).

Fraction mass U per lb U3O8: 84.80015(26) %
Mass U per lb U3O8 (assuming 1 lb = 454g): 384.99267(119)g

As such, resulting conversion factor: 2.594752(1):1

Thus, given that spot price, price per kgU should be somewhere near 190 USD.