Energy From Thorium Discussion Forum

Any thoughts?


http://www.nucleartownhall.com/blog/deb ... ment-26350

Martin Burkle Says:
July 31st, 2010 at 9:58 am
LFTR Cost Problems
I think that fuel costs are a small consideration for our current reactors (maybe 10% of the operating costs). The real incentive for building LFTR would need to be construction costs. It is my opinion that whatever is saved by operating at atmospheric pressure and smaller reactor size is offset by the reprocessing systems required to make LFTR work.

Remember that scale matters! Never have the onsite repressing methods worked at the scale needed for a production site.

Can anyone estimate the cost of PRODUCTION repressing on site? Will there be a hot room with manipulators? What will the procedure be when the distiller gets clogged? How do you test to see if the neutron absorbing gas is being removed correctly? What is the procedure to fix the pump to move the working fluid back into the reactor. There are a hundred questions like this that need to be considered and a risk needs to be assigned to each. Once this is done the costs will skyrocket.

The 1980 layout of a LFTR plant had much more floor space for the reprocessing than the reactor. Remember, all the the reprocessing space is highly radioactive. It looks to me like the radioactive floor space is about the same for the LFTR as for the AP1000 therefore the cost will not be much different.

PS. Is it true that highly radioactive material would need to be shipped to a new site so that the new site could be started? Doesn’t this present a large public relations problem? Maybe even a large cost?

I don't know "Martin Burkle" but my hunch is that he's confusing PUREX-type reprocessing with the simple fluorination/reduction approach we'd use in a two-fluid LFTR.

I suspect the folks at INL and Savannah River understand how to engineer systems that can be maintained despite high radiation fields. And at SR, the canyons were a production environment for the weapons complex. Like most engineered systems of consequence and reliability, one thinks through what can fail and how to repair it.

Hopefully you can clarify the issue on the debate forum.

posted a lengthy response. In essense, there are plenty of details to be worked but they aren't deal killers.

I'm not a scientist. However, it would seem to me that without even building a LFTR, it should be possible on a small scale to test reprocessing techniques using materials that are not radioactive but chemically similar to the actual radioactive materials. I don't understand the need to guess. Obviously when using the real materials, i.e., the ones which are radioactive, shielding would be required, but there have been decades of experience in handling radioactive materials. However, I may be entirely off-base because my degree is not an a scientific field.

Nice response.

Precisely the low investment sort of task that we should be doing now - for LFTR but also for other promising technologies. It is a modest scale investment that could significantly reduce the uncertainities involved with picking a technology to move forward with.

Charles, We are pumping helium at a rate of 11 scfm. Krypton-85 has a 10+ year half-life so we are talking about storing it for 100 years. We can't simply store all the gas until the radioactivity dies away. We will have to do some separation. Earlier separation means we need smaller tanks to store the full flow of gas but is made more challenging by the heat from decay being so intense. ORNL planned on storing all the gas for 47 hours before separating some of the gas (20%) in charcoal beds, and finally separating the helium from the xenon and krypton after 90 days worth of storage. They planned on converting tritium to water by running the gas through a mesh of CuO. I don't specifically recall if they planned on separating the xenon and krypton (I don't think so). I'd like to try to pull out the tritium earlier because the greens have made such a fuss over tritium that what was acceptable in the 1960's would not be acceptable today.

Why would pulling out the tritium earlier be a problem? Couldn't it be used to reduce the CuO as it emerged from the reactor and then immediately be condensed? I don't know enough about it to know whether that would be practical and, if the heat from the decaying nobel gasses were excessive, I suppose that condensing the H2O vapor could present a problem before decay occurred. I wonder what would be done with the Cu; perhaps it would be oxidized again so that it could be used to oxidize more tritium. It would be nice if something like a heat recovery wheel would work, but perhaps preventing radiation leakage would rule it out.

ORNL's plan was to separate Kr & Xe from He and T. Then pass the He and T through a 2" diameter 4' tube packed with CuO wool at 800C. Then cooling the gas down would cause the tritated water to separate from the helium. They only did this after a long time. Hence the tritium was given much more time to go through the HX walls. A tube would last a few years. They did not say what happened next but it seems natural to think of recharging the Cu with hot oxygen.

I hestitate to pass the whole gas through the Cu tubes. The heat given off from Xe decay would be pretty tough to cool down far enough. Worse, I imagine the decay products from Xe would collect on the Cu wool and create problems. The cooled tritiated water would then also contain a mix of decay fission products - some of which are still radioactive.

So, I would hope to use the mass difference between the light elements He & T (mass of 4 and 6 assuming T2) and the heavy elements Kr and Xe (83-140 or so) to mechanical separate the light from the heavy gases. Then we could pass the light elements through the Cu tubes. Passing the full volume of He/T through the tubes would only require 6 2" diameter tubes so this isn't a big deal - the tubes should last > 15 years this way. Then as you mention I think it is likely we could recharge them with oxygen.

I need to find someone (or some paper) to see how hard it is to separate these gases. I don't want a real gas centrifuge since that will run afoul of proliferation concerns (enrichment). But perhaps given the massive differences in mass and the modest separation quality requirements we could get away with something simple like a coil of tubing to exploit acceleration differences between the light and heavy gases.

That's very different from what I expected. It seems that the amount of tritium is very tiny, perhaps even so tiny that the only concerns are political. Some environmental organizations might be upset even if radiation exposure were only 0.00001% above the background level. I wonder why they are not upset about the radiation in coal ash.

It is unclear why a centrifuge would be a problem. It's not as though it would be used to enrich uranium, and presumably the concerns regarding centrifuges are only to prevent enriching uranium. On the other hand, regulatory agencies are not always very rational. Conceivably it might be practical to separate the gasses by distillation. Surely they would liquefy at a temperature well above what it required to liquefy helium. Liquid helium is available because it is used to chill the magnets for NMR (MRI) imaging machines and could be used to liquify the gasses from the reactor. Or perhaps new specific-purpose technology could be developed. If the gasses were pre-chilled, perhaps with liquid N2, then possibly the magneto caloric effect could be used to liquefy them. There must be several ways to do it.

I really hope that LFTRs can be produced soon; they would solve so many problems. If they were already common, then the concern about Iran's nuclear program might not even exist. Obviously they would then have no reason to be enriching uranium except for weapons so probably they wouldn't have dared to implement an enrichment program. Meanwhile, there are other rogue nations that might do what Iran is doing.

The legal limit is 10 Curies/day. LFTR produces 2400 Curies/day. The peak leak rate at Vermont Yankee was 2.5 million picocuries / liter at 100 gallons per day (if I recall correctly) or 1 milliCurie. So just to meet legal limits we need to collect 99.6% of the tritium. To meet the practical political requirements we need to be 1000x better. Not reasonable but the likely reality.

A centrifuge could be OK - especially if it doesn't look like one used for uranium enrichment and doesn't use any technology that could concievable be converted. Probably this is true - if I recall correctly uranium gas centrifuges require some pretty exotic materials to achieve the separations needed to make it reasonable. As long as what we are doing can't help anyone trying to enrich uranium (or teach them anything useful about enriching uranium) it should be fine.

Not that complicated. Using liquid nitrogen will liquify the xenon and krypton and not the helium and hydrogen (tritium) so nothing exotic is necessary.

A centrifuge? No, one would not use a centrifuge to separate hydrogen from xenon and krypton.

One good possibility is a palladium-silver filter:



(I believe T2 should be included, and G&E forgot about the existence of T when writing this. Strictly, H2, HD, D2, HT, DT, and T2.)



(N.N. Greenwood & A. Earnshaw, "Chemistry of the Elements", Butterworth Heinemann, Oxford, UK, 1998, p. 1151)

These other metals, that strongly and irreversibly bind hydrogen, may offer other good options:



(How fire can be domesticated)