Energy From Thorium Discussion Forum

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PostPosted: Oct 01, 2014 6:57 am 
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Next: transport energy need.

The uranium absorbers are placed some distance offshore. They need to be hauled in and out of a harbor for production (floating production is possible but may increase cost more than transport savings so may not be economical).

Mid size freight ship, short distance, typical 250 kJ/ton-km.

25 kg of absorber times 10 times 20 km (10 km off shore moorings) is 5 ton-km. 1.25 MJ.

EDIT: removed error, 1.25 MJ not GJ... transport energy is nil in large scale operations...


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PostPosted: Oct 01, 2014 11:28 am 
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An other good topic, good work Cyril.

So if I correctly understood for now you have an energy input of 3.25 GJ per kg of seawater Uranium (the transports are neglected) but you have not taken into account all the energy inputs yet ( what is "electric grafting" ? Do you talk about electro magnets which retain the polymers ? Or is it something else ?)

You assume 10 possible recycling, is that pessimistic ?

The uranium's concentration is only 3.3 micrograms per liter of seawater and we can just burn around 0.7 % of it (for CANDU and LWR using MOX if I am correct) and we have a thermal efficiency of 35 %.

So we use around 0.24 % of the energy contained in this 3.3 micrograms per liter and you still have this difference between energy input and output. That's incredible, only nuclear power can do this kind of thing. Nuclear power is amazing.


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PostPosted: Oct 01, 2014 11:48 am 
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Yes, we are up to 3.25 GJ/kg U just for making the absorbent. Including hauling the braids out and into harbor it is 3.251 GJ. Completely trivial transport energy (if we assume large scale operation).

We have to make a holding cable and anchor for the braid but it is not much weight compared to the membrane and if it is stainless steel cable then it is lower energy per kg than the absorbent.

The major item left open I think is the electro grafting. This is an energetic process where we shoot electron or such into the polymer, this slams off a hydrogen atom, leaving a void. The void can now be occupied by uranium. This is how the absorbent is activated. The process should be quite energy intensive, on the other hand the mass of hydrogen atoms to slam off is small. Can't find any data on this at all.

10 recycling seems pessimistic. I don't know if the process is recycling or just washing off (re-use rather than re-cycle). It could be better if we only have to wash the polymer. It would be even better if we didn't have to do the grafting again. Not sure about any of this.

Quote:
So we use around 0.24 % of the energy contained in this 3.3 micrograms per liter and you still have this difference between energy input and output. That's incredible, only nuclear power can do this kind of thing. Nuclear power is amazing.


Amen.


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PostPosted: Oct 01, 2014 1:17 pm 
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It's good to check out what other researchers have written. Chiefly there is the Ugo Bardi work:

http://www.fraw.org.uk/files/limits/bar ... s_2010.pdf

Bardi comes up with a low EROEI of 2.5 or so. Unfortunately for Bardi this is based on a number of completely false assumptions:

1. The transport energy of the membranes is equivalent to the energy needed to catch fish. That's patently silly; fish swim away and you have to wade through huge distances to catch a kg of fish, carrying a huge drag force fishing net along. The uranium absorbent beds, by contrast, won't go anywhere! There is no need to drag huge fishing nets along which increases energy usage. It is more appropriate to consider the energy needed in bulk shipping freight transport. We go 10 km out of the harbor, pick up a thousand tonnes of braids, then 10 km back again. No nets to drag along, no long distances. No fisherman could catch a thousand tonnes of fish with 20 km of distance travelled and no nets out!
2. 300 kg of of absorbent is needed for every kg U. That means Bardi assumes zero re-use and zero recycling credit! That's even more silly than the fishing energy input assumption.

Bardi set out to prove ocean extraction of resources doesn't work, and made silly assumptions accordingly.

I'm not aware of any other significant research on EROEI for seawater uranium extraction. All we have I think is the misleading Bardi paper. Its probably not very useful to determine EROEI in the first place; this is still a technology that is rapidly developing and in its current primitive form is too expensive to be widely used yet. The recent work on MOFs that show a factor of 3-4 improvement in uranium harvesting just proves this.


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PostPosted: Oct 01, 2014 1:38 pm 
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Thanks a lot Cyril.

In fact I think we should do the EROI of the entire cycle, it will speak more to the people. So we must take into consideration enrichment and fuel fabrication. Once the uranium is removed from the polymers, what is his chemical form ? Uranium dioxide ? Pure metal ? We will maybe have to take into account the energy of some eventual chemical transformation steps before having UF6 for centrifugation. Unfortunately I am very busy these last times, I found this paper (which I didn't read, only the EROI which is 16 :mrgreen: ), maybe it will interest you:

http://www-pub.iaea.org/iaeameetings/cn216pn/Thursday/Session13/180-Schneider.pdf

I believe I have seen some articles in the past where the EROI was 22, I will check that later.


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PostPosted: Oct 01, 2014 1:53 pm 
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Quote:
So we must take into consideration enrichment and fuel fabrication.


Yes, but these are essentially independent of the source of the uranium. I've already looked at enrichment and fuel fabrication, it amounts to around 0.1% of the electric output of the uranium if put into modern LWR.

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Once the uranium is removed from the polymers, what is his chemical form ?


They make yellowcake (U3O8). The same processes as used today.

Removing the uranium from the polymer involves elution via acid, likely at least 0.1 M HCl. I'll calculate the energy needed to make the acid later.

Thanks for the ref I'll go check it out.


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PostPosted: Oct 02, 2014 2:28 am 
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If we have breeders only then it doesn't matter where the uranium comes from. Any source will do. As Cole Porter has said, "anything goes".

The attraction of seawater uranium is that you can have converter reactors only and still not worry about mining constraints.

It is very useful to determine the EROEI for this scheme. If we have breeders EROEI will be off the scale, no need to calculate that.


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PostPosted: Oct 02, 2014 4:35 am 
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Ok, the electronuclear grafting process, according to Fab's link, is optimal at 300 kiloGrays exposure. That's 300 kJ/kg. What is the efficiency of electricity to accellerated particles? If it is 10% then this is 3 MJ/kg, 75 MJ for 25 kg abs. (75 MJ/kgU)

This is very small. Even if we have to graft each time again it is still only 750 MJ, 0.75 GJ/kgU. Much smaller than the polymer production and recycling energy need.


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PostPosted: Oct 02, 2014 11:09 am 
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It is worth noting that the transport energy is potentially avoidable.
You coudl always use a sailing boat to retrieve the absorbers if you wanted.

Additionally there are locations with strong tidal races (for example the Menai Straits near Anglesey) that would potentially allow absorber frames to be lifted out of the water using a cableway whilst still providing the required huge water flow over them.


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PostPosted: Oct 02, 2014 12:31 pm 
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jagdish wrote:
I would like to have them remove uranium from drinking water to safe levels.


Why? There aren't meaningful water supplies contaminated with dangerous amounts of uranium. This is a completely marginal application of a technology.


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PostPosted: Oct 02, 2014 12:34 pm 
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E Ireland wrote:
It is worth noting that the transport energy is potentially avoidable.
You coudl always use a sailing boat to retrieve the absorbers if you wanted.

Additionally there are locations with strong tidal races (for example the Menai Straits near Anglesey) that would potentially allow absorber frames to be lifted out of the water using a cableway whilst still providing the required huge water flow over them.


Why bother? If my numbers are accurate within a factor of 10, then transport energy costs are so trivial there isn't any point in optimizing this part of the system.

The most important improvements are to be had in increased uranium uptake per kg of absorbent (eg, MOFs). Once we get to a certain uptake/kg I suspect the cost difference with market uranium will become small enough that government investment in production will kick off the technology. Then economy of scale should do the rest.


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PostPosted: Oct 02, 2014 3:20 pm 
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Typical value for long soaking periods with efficient braid type absorbents would be 4 kgU/1000 kg absorbent. 250 kg absorbent need per kg.

One question. Is there a significant effect from having a bunch of these absorbents next to each other as would be necessary for the scale we're talking about to power the world? That number may be accurate for a single strand, but what about a million of them near each other? They might be competing for the nearby uranium. One would need to look at how fast uranium diffuses through ocean water, and the flow rates of the ocean, and mixing from ocean flows. Have you looked into this? I recall reading some objections to uranium extraction from ocean water based on this problem. I'd like to know if it's a real problem or fiction.


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PostPosted: Oct 03, 2014 1:27 am 
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Joshua Maurice wrote:
Quote:
Typical value for long soaking periods with efficient braid type absorbents would be 4 kgU/1000 kg absorbent. 250 kg absorbent need per kg.

One question. Is there a significant effect from having a bunch of these absorbents next to each other as would be necessary for the scale we're talking about to power the world? That number may be accurate for a single strand, but what about a million of them near each other? They might be competing for the nearby uranium. One would need to look at how fast uranium diffuses through ocean water, and the flow rates of the ocean, and mixing from ocean flows. Have you looked into this? I recall reading some objections to uranium extraction from ocean water based on this problem. I'd like to know if it's a real problem or fiction.


Good question!

Lets try to put some numbers on this.

If we have braid absorbents with say 25 kg of absorbent per meter (they are vertical braids) that catch 4 gramsU/kg in 100 days then we capture 100 grams U, 1 gram/day/meter abs.

If the braids are spaced 10 meters apart (we don't want them to entangle so may need even more) then we get 10 m2 of horizontal flow area for our 1 gram/day. With a 0.1 m/s average flow this is 1 m3 seawater/second/meter abs. 3600 m3/h, 86400 m3/day.

So with these assumptions (granted they are just assumptions) we get 1 gram out of 86400 m3 of seawater in collection efficiency.

With 0.0033 grams/m3 seawater our seawater flow contains 285 grams U.

Our area based collection efficiency is 0.35%.

This is so low, you can put many braids behind each other before this becomes a problem. Also the absorption capacity is limited by saturation of the absorption sites more than the concentration of available uranium. So if you have a big array then all you have to do is wait a little longer before collecting...

My guess is a good size facility would not be in the millions of braids, but ten thousand. This should be enough to supply a single large LWR. That's 100x100 braids, 1 km2. Expansion would then occur perpendicular to the dominant sea current so that you won't deplete the flow excessively. Similar to wind turbine farm siting, except for wind turbines the problem is much more severe (halve the wind speed = 1/8 the power).


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PostPosted: Oct 03, 2014 2:22 am 
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Hmm no wait, the braids can be made quite long apparently so we'd need less. We'd need 1000 braids of 200 meter long with 25 kg/m absorbent to continuously fuel an ESBWR or EPR assuming 3 harvests per year.


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PostPosted: Oct 03, 2014 10:43 am 
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Fab's link has more good stuff. One thing is the other heavy elements that end up in the absorbent. The absorbent quite likes Mg, Ca, and Na which is expected on their abundance in sea water. But vanadium really stands out. For every kg of uranium absorbed there's almost 4 kg of vanadium. Vanadium is quite valuable, around $25/kg today. Though it is too bad the vanadium competes for the same absorption capacity as the uranium, selling the vanadium would help bring this concept closer to economic viability. The current economic value of the vanadium would be higher than the value of the uranium in the absorbent!


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