[wuschel]

Hi, interesting answers.

1) Could you tell me more about replenishment of Uranium in seawater, or point me towards your source?

Wouldn't it mean that we would reach a maximum saturation of Uranium in the ocean after some time (with precipitation of excess Uranium in the form of salts)?

Have you seen / access to estimates of Uranium electrode deposition cost from water? Are they cost competitive in any way in comparison to other energy systems that will be employed in the future?

At the end, you would need to use electrical energy converted from another source to gain Uranium. For me, that scenario is a bit 'fishy'.

[acidburnNSA]

Thanks, and sure. You're right to be skeptical. The renewability of uranium isn't a widely accepted idea and unfortunately is hard to definitively prove experimentally due to the hilariously long time scales. So we're left with less rigorous claims of this to treat rationally more than scientifically. Also, haha: 'fishy'!

Here's a good source: http://www.mdpi.com/2071-1050/4/11/3088/htm And it points to an older one: http://tmtfree.hd.free.fr/albums/files/TMTisFree/Documents/E...

From the first:

"One additional aspect of nuclear sustainability—noted long-since by Bernard Cohen—is that a significant fraction of the nuclear fission energy resource is in fact completely “renewable” in the same sense as wind and solar energy [32]. Wind and rain constantly erode the Earth’s crust, which contains an average uranium concentration of 3 parts per million. Rivers then carry this dissolved uranium into the oceans, at a rate of approximately 10,000 MT per year [33]. In a breeder reactor energy system, this is a sufficient rate to supply the world’s entire electricity demand at the present time more than five times over—or is roughly one quarter of what’s needed to supply a continual 100 TW to a hypothetical global civilization of 10 billion persons which is energy supply-replete by any contemporary measure.

As the crust is being eroded by rivers, it is constantly replaced by new layers of rock being pushed upward by plate tectonic processes. The supply of uranium in the Earth’s crust is effectively inexhaustible, on the order of 40 trillion metric tonnes, a factor of 10,000 more than is present in the oceans. At present erosion rates, this source of uranium would last on the order of 4 billion years, similar to the timespan over which the Sun will become a red giant.

Therefore, this assured source of “continually mined-by-Nature and oceanically presented” uranium will last as long as life on Earth does—even if burned at rates sufficient to supply a large fraction of a fully-developed human civilization—and represents an astronomical amount of nuclear energy, one that is in fact truly renewable and inexhaustible by any human measures."

EDIT: As for increasing concentrations of uranium in the sea, it's already in equilibrium so the incoming stuff that leaches in through rivers is leaching back into the rocks, giving us the equilibrium concentration we observe today. The point here is that if we start extracting it that concentration is not expected to drop because we can't offset the balance very much.

[wuschel]

Hi,

thank you very much for your detailed elaboration on the subject, and the references. I was not aware of the bigger, geologic perspective:

   ~ 3 mg Uranium in 1 m^3 ocean water. 

Makes sense, when one thinks about the relative ratio of chemical elements on earth. I guess, as always, it is the demonstration of chemical enrichment procedures that is the key here, and there is currently no economic incentive to do such a thing. Although, I have not looked into current fuel production procedures. How expensive is 1g (sufficiently) pure Uranium fuel?

The sentence that our energy requirements could be covered with breeder reactor systems for 50K years made my smile, though. It will be probably the lack of higher "level fuels" such as proteins and carbohydrates that give us headaches, first.

Please note that I am not at all hypercritical regarding nuclear energy. There is a lot of industrial and green propaganda out there, and it is sad to see that we scientist are loosing the battle in media. Too often, rigorous scientific explanations in not sexy enough for us apes.