Energy From Thorium Discussion Forum

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PostPosted: Feb 05, 2014 11:37 am 
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It would be quite easy to extract water from wells too. The traditional disadvantage of wells is that they can be easily drained, but this is not an issue with heavy water production.

Co-locating heavy water production with a demineralized or distilled water production plant can also make sense, because purification costs are avoided. The resulting light water tails, depleted of deuterium, can be sold normally as distilled water.


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PostPosted: Feb 05, 2014 2:14 pm 
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"Heavy Water: a Manufacturers' Guide for the Hydrogen Century" - The past and future of heavy-water technology in Canada, by heavy-water expert Dr. Alistair I. Miller of Atomic Energy of Canada Ltd. (PDF format, 340 kb)

http://media.cns-snc.ca/Bulletin/A_Miller_Heavy_Water.pdf

Quote:
AECL is currently working on more efficient heavy-water production processes based on wet-proofed catalyst technology. CECE and CIRCE are based on electrolytic hydrogen and reformed hydrogen, respectively. CIRCE could be on the sidestream of a fertilizer or hydrogen-production plant, for example. AECL currently has a prototype CIRCE unit operating at a small hydrogen-production plant in Hamilton, Ontario. These catalyst technologies are more environmentally benign than the gas-extraction process they would replace.


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PostPosted: Feb 05, 2014 4:23 pm 
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Well, if we take the future H2 market to be 100 Mtons/year then there would be some 31 kton deuterium in there, over 60 GWe/year worth of CANDU D2O need.

That's substantial, quite probably enough for any aggressive buildout of D2O reactors.

Now the question is how much of the H2 market is suitable for a CIRCE piggybacking. Electrolysis would be perfectly compatible, but is only some 4% of the hydrogen market (and contrary to hydrogen advocates assertions, the share of electrolysis is decreasing because electrolysis is the most expensive hydrogen production method). 4% is not enough, under 3 GWe/year. The other streams would be very very dirty (CO, NOx, heavy metal, the nasties). Compared to H2O based deuterium extraction, where you can play with clean drinking water or distilled water. If CIRCE is dependent on electrolysis dreams then it is a pretty bleak outlook.


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PostPosted: Feb 05, 2014 7:13 pm 
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CIRCE is apparently the subset of these technologies which is applied to systems such as Steam Methane Reformers.
CECE is the application to electrolysis.

And an all nuclear system will likely use low cost electrolysers as load dumps.


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PostPosted: Feb 05, 2014 8:03 pm 
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Apparently technology derived from CECE can also be used to drastically reduce moderator concentrations of Tritium fairly cheaply, concentrating it to ~80% tritium to allow it to be stored.

It incidentally slashes carbon-14 release by replacing 17O enriched oxygen with natural oxygen, reducing production of 14C via (n,a) reactions.

Apparently a CANDU loses roughly 2t/HW a year, which means a 100GWe ~136 reactor park would lose some 275t of heavy water per year from a total inventory of 62,150t.

Which along with, admittedly slower, energy demand growth will mean that the plants won't all be rendered useless after the 'dash phase' although production rates would drop off drastically.


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PostPosted: Feb 06, 2014 8:58 am 
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So that's a replacement market of only 0.5% only. That means you can shut down 199 out of every 200 heavy water plants. That's the end of the heavy water industry. In the interest of sustainability it is rather excellent of course, but it is bad news for the heavy water industry. If the reactor builders or operators/utilities buy and own the heavy water plants, this is not so bad.

I have to ask though, where does this 2 tonnes/year go to? Tritium emissions limits are very strict so it can't go outside plant. Where does it go? If it is leakage through seals and then capture through dehumidifiers then the heavy water gets degraded with light water moisture in the air whilst being mostly contained. Ok, this loss path makes sense to me. But if so then canned rotor pumps and canned valving (or operationally valveless PHT) would eliminate this source completely. 2 tonnes/year is worth more than half a million dollars. Re-enriching the leakage moisture that is recovered would make economic sense compared to enriching fresh water.


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PostPosted: Feb 06, 2014 11:43 am 
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Well the water upgraders fitted to the dehumidifier circuits don't reject pure light water, they end up rejecting about 1-2% heavy water (in light water).
That probably accounts for quite a bit.

If energy growth continues at a couple of percent per annum then the heavy water plants might carry on, it depends on whether capital costs or operating costs are dominant - if the former then they might carry on operating until they are life expired and end up with an enormous stockpile of heavy water.

If we built 100GWe in fifteen years they might continue to ~30 years age before shutting down.
Giving us an enormous stockpile for new reactors and so on. (leaving a stockpile of some 53900t after accounting for ~30 years of losses - which is pessimistic - which would be worth approaching $16bn at today's prices)

I was assuming that the ownership of the heavy water plants would be integrated with the reactors themselves for this very reason.

EDIT:

Additionally, if we assume that 136 CANDUs with a ~90% capacity factor have a thermal output of 283GWt, and that SEU fuel can reach 20GWd/t, then such a reactor fleet would require ~4660t of 1.2% enriched fuel per year.
If we set tails concentration low (at 0.1%) then we would require 8390t of natural uranium and 3.3 million SWU.
That is a fairly small plant in modern terms, certainly smaller than the George Besses II facility.


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PostPosted: Feb 06, 2014 8:12 pm 
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HW moderator is quite different from the graphite.
Indian designers played around with carbon-and water moderated design before opting for HW in the AHWR. None has been built so far though it has not been formally abandoned. Light water coolant reduces HW losses but increases neutron losses and needs higher enrichment.
Apparently the un-moderated designs are better but got a bad name due to sodium fires. Perhaps it is time to look for better coolants for both fast and thermal designs. Safety and economics are both important. FLiBe could get into cost and availability problems.
Has anyone studied the suitability of BeF2-MgF2, either as solvent or as coolant?


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PostPosted: Feb 06, 2014 9:02 pm 
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There have been studies in producing intermediate and fast spectrum reactors by taking a PWR and filling it with heavy water instead of light water, which reduces the moderating power significantly.


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PostPosted: Apr 11, 2015 8:38 pm 
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Quote:
So I ask, is there any way to get a primarily graphite moderated pressure tube reactor core that does not have a positive void coefficient?


I was looking at documentaries concerning the first reactors for nuclear weapon production these last times.

The Hanford N reactor (built in USA at the Hanford site, for producing weapon grade plutonium) is a pressure tube reactor, graphite moderated, and cooled by light water. It has overall negative void ( by diminushing the carbon/fissile ratio they let the light water play a bigger part in the moderation, making the overall void coefficient negative) but it used slightly enriched uranium ( between 0.95 % and 1.25 % enrichment) whereas the reactors B, D and F used natural uranium ( but they had positive void if I am not mistaken ).

The Hanford N reactor also has a dedicated cooling system for the moderator. Its power was 4000 MWth thermal, these plutonium production reactors were very powerfull, the quantities of Pu produced must be large.

Maybe it is possible to make a natural uranium, graphite moderated reactor, with a negative void by using heavy water coolant.

Some characteristics of the Hanford N reactor are in the following document comparing Hanford N with Chernobyl's RBMK :
http://www.gao.gov/assets/80/75765.pdf

It is interesting also to see that the Hanford N reactor was plagued by the Chernobyl accident in the public opinion just because these 2 reactors were very similar althought the Hanford N reactor had overall negative void contrary to Chernobyl's RBMK.


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