Wendelstein 7-X has successfully finished its second major experimental run

Reflections on fusion history, current events, and predictions for the 'fusion powered future.
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Rich Feldman
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Re: Wendelstein 7-X has successfully finished its second major experimental run

Post by Rich Feldman »

Re. separation of isotopes. It'd be nice to see the numbers for heavy water next to those for uranium enrichment

They might represent two extremes of difficulty, among industrialized separation processes. In between are isotope products with special boron, nitrogen, oxygen, silicon, etc.

Dennis's point about thermodynamics is valid.
There is a theoretical minimum amount of work to make one gram (or one mole) of enriched uranium from the natural element.
And corresponding minimum to make a gram or a mole of heavy water from natural water.
How do the bottom lines compare, for D2O in a CANDU reactor (one time cost?) vs EU in a light water reactor?

Favoring heavy water: mass ratio of isotopes to be separated is 2:1 instead of 235:238.
Favoring uranium: desired isotope enrichment ratio is from 0.7% to 5%, instead of 0.03% to 99.some %.

Vemork Hydro plant in 1935 had heavy water production capacity of 12 tons per year.
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Ameen Aydan
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Re: Wendelstein 7-X has successfully finished its second major experimental run

Post by Ameen Aydan »

I think you guys interpreted what I said incorrectly. But I did give a bad explanation.

I wasn't trying to say that there will be new technologies. I have seen how uranium is enriched and how D2O is made. They are both a very hard process. Rather than coming up with new technologies, we just make the ones we already have better. Now that might not be the case with D2O, it is possible that we have reached the best possible production method. In that case, people will find ways to cut costs as production becomes more wide spread.

I once again, revisit the same example. Lithium batteries used to be pretty expensive and hard to find... 5 years ago. Now today, there are eBay seller essentially giving them away. Why? Not because we made any improvements to production method. Certainly not because we made new inventions that cut down costs. Rather, it's because the production became more wide spread and now the cheaper person will win.

So from this we see that in some instances, another amelioration was not actually needed, just a little competition.

I would also life to as you guys to please not mind if I made any mistakes here. I'm sourcing this from my mind... not so reliable.

Ameen Aydan
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Dennis P Brown
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Re: Wendelstein 7-X has successfully finished its second major experimental run

Post by Dennis P Brown »

In the article on deuterium enrichment via membranes, the process has to occur at liquid nitrogen temperatures (not exactly conducive for water to be directly processed - lol.) The process they describe takes a mixture of gases of hydrogen (H2)and deuterium (D2)and separates these. There are no sources for deuterium gas other than first removing the oxygen from water (very energy intensive.) This creates a mixture of the two gas phase - hydrogen and deuterium; then these must be cooled to -173 C using liquid nitrogen (again, rather energy intensive;) finally, pass this mixture through a membrane (some energy cost)- this results in a single increase of D2 to H2 by a factor of 12 (i.e. from 0.03% to 0.36%.)

They give no indication of how many times the process has to be done to get the 99.7% purity required for a heavy water reactor but it is not a linear process with increased number of passes (exchanges never are) - yields will not continue at that high of a value. So, does this process reduce the total energy required to create the deuterium for a reactor? Maybe but if it does, certainly not by much but until they try higher levels of enrichment, even that is a big question.

Ameen, again, no issue with mistakes - unlike you, I don't speak nor can I write in another language so you need offer no apologies! The issue is that mass production of a small, very singular part (i.e. a battery) isn't like making a vast and complex nuclear power plant. No amount of mass production can create a cost curve like a battery or even a car. That said, yes, deciding to build a thousand Candu type reactors over thirty years would bring down the average cost - but not by orders of magnitude (like a battery) and not even an order of magnitude. Labor costs can be reduced only so much, as can materials (Concrete and steel are as cheap as one can already make them and these are the bulk of the materials needed), land (fixed) and a vast infrastructure creation (fuel supply chain - fixed) all have innate costs that do not lend themselves to significant reductions by mass production or clever short cuts.

Really, the question isn't the cost of a fission reactor (either type) - frankly, that is a red herring. The issue is the total cost of carbon; if the long term effects and cost to society are included due to AGW (ignoring issues of coal ash storage (a serious problem), a fission reactor likely is very cost competitive to even a coal plant. The issue is one of absolute safety (this allows a plant closer to a city which saves a great deal of money in reduced power lines - a not insignificant cost factor - and improves overall net efficiency of the final electricity delivered by reducing transmission losses) and the Candu wins that hands down.
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