[acidburnNSA]

Thanks for posting. I'm in the nuclear industry and would like to try to address some of these issues if you don't mind.

1. Uranium in seawater is replenished by erosion through streams at a rate faster than we could ever burn it. It is effectively totally sustainable and even renewable on a 4+ billion year time frame, even without breeder reactors. But really, breeder reactors will become a thing when uranium gets expensive enough to warrant them. The reactors that were attempted so far just weren't needed because it turned out we had way more uranium that we originally thought.

2. With passive cooling systems, even seismically active regions can be powered by nuclear. Also, there are exciting possibilities for offshore nuclear, floating 10km out to sea where tsunami wavelengths are huge. Cooling is guaranteed and huge shipyards can do the construction. I agree that it's clear from Fukushima that designs requiring active cooling are no good in such places.

3. There are teams of nuclear engineers and other reactor designers in San Francisco right now at the American Nuclear Society meeting whose goal is to reduce the price of nuclear so that corporations can make a profit from them without compromising safety. I believe it can be done.

4. The Finns are about done with their deep geologic repository [1] and it's looking great. We definitely know how to dispose of nuclear waste. It's just a matter of political will and outreach. The tradeoff you have to keep in mind is that you can get all your primary energy for literally your entire life while personally producing 2 soda cans of nuclear waste. Compare that to fossil fuel (2 million times more waste) or to the vast energy harvesting resources for wind and solar (concrete bases, fiberglass, steel, silicon, glass, semiconductor processing, etc.) and you see that nuclear is extremely low footprint and that's its magic.

I sympathize with your concerns and am working to mitigate them. Biggest hurdle in my mind is standardizing designs. I dream of coordinating an open source reactor design effort some day.

[1] https://en.wikipedia.org/wiki/Onkalo_spent_nuclear_fuel_repo...

[jacquesm]

> Uranium in seawater is replenished by erosion through streams at a rate faster than we could ever burn it.

Isn't there a substantial energy cost associated with collecting that Uranium?

The same goes for gold, there is a huge amount of gold in seawater and yet, nobody has been able to extract it in a way that left money on the table after the process had run.

[acidburnNSA]

Great question, and one that I don't have a quantitative reply to on hand. The thing with uranium is that it is so unimaginably energy dense that with the success we've seen so far in seawater extraction technology, it's hard to imagine the energy required for extraction being anything but minuscule in comparison. Obviously there's a limit of concentration where this becomes not true but my understanding is that we are not near that limit.

Here's a summary of some recent work on seawater uranium extraction: https://www.forbes.com/sites/jamesconca/2016/07/01/uranium-s...

And here's a special edition of Industrial and Chemical Engineering dedicated to the topic: http://pubs.acs.org/toc/iecred/55/15#UraniuminSeawater

[jacquesm]

Thank you for the links and the answer.

[mseebach]

This article suggests a total cost of $1000-$1500 which is ~20x the cost of mined uranium (and 40x less the cost of gold). It does not mention energy as a significant driver of this cost.

http://scienceandglobalsecurity.org/archive/2013/06/the_cost...

[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.

[seb1204]

I also had my fair share with nuclear power plant design and power plant design in general in the past. From that time I have kept a rather moderate/positive view of the technology. However 'we' seem to be implementing it so badly that I am concerned. The total (from end to end) are unknown and even based on what is known not fully accounted for.

While you point out that there are technical solution to the challenges I strongly believe Countries/Corporations/Governments are not willing or capable of operating these plants to a safe standard and earn money doing so.

The whole issue of decommissioning and deconstruction is only in its infancy and already a huge money drain on the backs of the people and not the Corporates who earned money for 30 years running the plant. I think we should speak of deconstruction and not of demolition. Demolition is mainly smashing buildings to pebbles with a big steel ball, for nuclear power plants that is not the case. See [1] or [2] - sorry both in German

Re 1. Until the technology has actually been built and scaled up we won't know what technical details and challenged await us. I don't see that as a reason to not do it but rather a call for caution on over-optimistic timeline.

Re 2. Indeed many aspects of the reactors have been improved on paper/in theories. See for example the European Pressurized Reactor [3]. The first 3 plants to that nature are riddled with technical detail problems and budget overruns, see [4]. When I was at Unit learning about EPR most lecturers where approaching retirement or already past retirement. The nuclear power industry - at least for the German part - has had the issue of very few skilled successors. This might have a big role in the building of the actual new types of plants. 35-45 years ago when the current old plants where built there was a large pool of experts - engineers, construction, QA/QC - they are all retired now.

Re 3. That is good, and there surely are technical solutions but I am very sure they are no easy find. Just think about the discussion of material selection for certain vessels in light of the current material embitterment news from Belgium Power plants [5]. I'm not saying that these issues are insurmountable but that the process to get to an agreed (experts and governments) new solution is slow and painful with no ETA.

Re 4. In Germany at least the search for a repository was driven by politics into the wrong direction. This should have been driven buy science and technology people. By now the topic is so far down the drain so that changing course is political suicide. Another point regarding the waste is the discussion of marking the nuclear wasted depositories for >1000 or rather 10000 years. Interesting YC discussion here [6]

[1] http://www.focus.de/finanzen/eon-spaltet-akws-ab-muessen-jet... [2] https://www.handelsblatt.com/unternehmen/industrie/milliarde... [3] https://en.wikipedia.org/wiki/EPR_(nuclear_reactor) [4] https://en.wikipedia.org/wiki/Olkiluoto_Nuclear_Power_Plant [5] https://en.wikipedia.org/wiki/Nuclear_energy_in_Belgium#Hydr... [6] https://news.ycombinator.com/item?id=14530978