Depleted Uranium Disposal

[NNadir]

Probably the best solution for U-238 in the short term is to use it as a diluent for U-233.

NO! NO! HELL NO!

I really can't see the rationale for this statement.

It seems to me very clear that the best use for U-233 is to recover the lost energy potential of U-238.

Given the huge reserves of mined U-238, for which very little has to be done, it makes sense to convert it all to plutonium, which is, in my view, easily accomplished by using U-233 in this sort of matrix.

One sees these schemes like CORAIL that actually dilute fissionable nuclei with things like zirconium. I basically don't believe that any neutron should be wasted in this fashion.

In fact, I would like to see what I call "mature" uranium, which is a mixture of U-232, U-233, U-234, U-235, U-236 and U-238. Three of these nuclei are extinct, and really U-234 is not present in significant amounts in natural uranium.

I note that this kind of uranium is completely and totally proliferation resistant, since any attempt to separate isotopes from it is certain to fail on grounds of expense.

I am not, I note, speaking of dilution as a means of so called disposal, but as a means of accessing more plutonium, which I believe the world needs. I am recommending it as an option in a mature thorium cycle, after several hundreds of tons of U-233 have accumulated. In fact there is a good argument for doing it well before hundreds of metric tons of U-233 have accumulated.

[dezakin]

You can extract energy from lead with a large particle accelerator to shatter it too, but I wouldn't bother converting all the lead piping from old Rome to fuel anytime in the near future. Using DU as breeder reactor fuel has an opportunity cost far higher than mining fresh uranium, tailings enrichment, or using LFTRs.

The best thing to do with the stuff is just use it for industrial applications that allready exist. Like sailboat keels.

And really the notion of diluting U233 with U238 is just madness. It took a hell of a lot of effort to breed it to begin with, and given its an ideal start charge for LFTRs, its just offensive to think about it. The fact that they're actually doing it with the MSRE U233 is even more painful.

[NNadir]

You can extract energy from lead with a large particle accelerator to shatter it too, but I wouldn't bother converting all the lead piping from old Rome to fuel anytime in the near future. Using DU as breeder reactor fuel has an opportunity cost far higher than mining fresh uranium, tailings enrichment, or using LFTRs.

The best thing to do with the stuff is just use it for industrial applications that allready exist. Like sailboat keels.

And really the notion of diluting U233 with U238 is just madness. It took a hell of a lot of effort to breed it to begin with, and given its an ideal start charge for LFTRs, its just offensive to think about it. The fact that they're actually doing it with the MSRE U233 is even more painful.

This is only true if one has only a few tons of U-233 with which to work.

If one wants sailboat keels, lead works quite well.

I think we are claiming that the MSR is the only type of reactor worth building. I have never felt this way. I think we want a flexible fleet containing many types of reactors for differing missions. I have, for instance, long been a fan of heavy water reactors. I cannot think of a better approach to running these types of reactors than U-233 in a U-238 matrix, maybe a ternary alloy with thorium, if one insists.

Some people act as if U-233 is going to spring from the forehead of the nuclear industry like the Goddess Diana from the head of Zeus.

This is not the case. We need to unlock the thorium and that means having neutrons. For a rapid scale up of nuclear energy on the scale required for all of humanity, this involves not thorium, but plutonium.

That’s what’s on the table and available for use.

We have on this planet probably only a few thousand metric tons of plutonium, at best, closer to one thousand than to two thousand most likely.

We need more of it. The obvious place to get it is depleted uranium.

I see this path: Pu-239/240 + Th => U-233, at first in trivial amounts. U-233 + U-238 => Pu-239 in larger amounts. The available fleet to do this in a breeding scenario is the world’s fleet of HWR, as located in Canada, Romania, India and South Korea. (OK, Argentina and Pakistan too.)

We might best accumulate U-233, by the way, not with MSR’s to begin with, but with traditional PWR’s but with Radkowsky type configured PWR’s burning (ideally) weapons grade plutonium and then reactor grade plutonium. Whatever the status of Thorium Power (and I don’t know the status) the idea was a perfectly sound one.

To do this, we need not do anything fancy.

We can – and should – have high purity U-233. I understand that. But I am thinking long term, longer than my own lifetime. The question was “what to do with depleted uranium.” My answer was to treat it as an available energy resource.

With our mined supplies of thorium and uranium including so called "depleted uranium," we need not have another energy mine for the lifetime of anyone now living.

We should not lose sight of the forest for the trees as they say.

[Lars]

For your purposes u235 will work just as well as u233 and is much much more available. I suspect we will end up using mostly u235 to generate start charges for our reactors. This may be done using thorium "fuel" rods in LWR's or HWR's burning u235 (or Pu239) and generating u233. Or it might be done in a LFTR extracting generated u233 from the blanket and adding make up fissile to the core.

[dezakin]

The question was “what to do with depleted uranium.” My answer was to treat it as an available energy resource.

With our mined supplies of thorium and uranium including so called "depleted uranium," we need not have another energy mine for the lifetime of anyone now living.

We should not lose sight of the forest for the trees as they say.

The issue is simply that using DU for fuel has a far higher opportunity cost than all other options. It doesn't make sense to do.

[Kirk Sorensen]

I think we are claiming that the MSR is the only type of reactor worth building.

Nobody's claiming that. For crying out loud, the whole nuclear engineering world is working on every other kind of reactor EXCEPT the MSR. But here, we have a community of people who come and discuss this reactor by their own choice and many of us try to push it. The U-233, in its present form, would advance this cause tremendously. Why on earth would we want to destroy that option?

[NNadir]

I think we are claiming that the MSR is the only type of reactor worth building.

Nobody's claiming that. For crying out loud, the whole nuclear engineering world is working on every other kind of reactor EXCEPT the MSR. But here, we have a community of people who come and discuss this reactor by their own choice and many of us try to push it. The U-233, in its present form, would advance this cause tremendously. Why on earth would we want to destroy that option?

Again, I am not here arguing for "destroying that option." I am not calling for diluting current U-233, now in stock. I am calling for the use of future U-233 as a tool to recover the energy of depleted uranium.

I hope that's clear.

[Lars]

There is no (nor will there ever be) a surplus of 233U . When we do have it one could use it (or 235U or 239Pu) together with a fertile (232Th or 238U) to have a virtually limitless supply of energy. The proper combination of fissile and fertile depends very much on the availability and reactor design. For a thermal design the natural choice is 232Th / 233 U. For a fast design the natural choice would be 238U / 239 Pu.

One could do almost any combination for startup - this will be driven by availability of fissile and anti-proliferation restrictions.

There is amply 238U and 232Th. The question of fertile supply is totally minor.

[Kirk Sorensen]

...and to continue Lars' thought, U-233 is the ideal material for unlocking the energy potential of thorium. It's better than U-235, it's better than Pu-239. Thorium, in turn, is easier to extract energy from than U-238. Significantly easier. From the perspective of minimizing opportunity costs, we should:

1. Burn plutonium in a fast reactor (ideally chloride-based) to convert blanket thorium to U-233. Plutonium will perform better in the fast reactor than U-233, whereas U-233 will perform far better in the thermal reactor than plutonium.

2. Use the U-233 so bred to start lots of LFTRs.

In the distant future that Lars is so fond of simulating, I don't see much of a need for plutonium at all. The plutonium generated during the 20th century will be consumed in the 21st century to generate the U-233 that starts the LFTRs that then power the 21st through 29th centuries... :)

(then the Borg get us, for our thorium of course)

[jaro]

The issue is simply that using DU for fuel has a far higher opportunity cost than all other options. It doesn't make sense to do.

A CANDU-MSR with agressive on-line processing would be very close to breeder status, using NU.

If we wish to dispose of DU, then mixing it with spent LWR fuel can be done so as to produce a fuel with NU-equivalent reactivity.

The result is the same as starting on fresh NU, only you get to cut into two waste issues -- DU and LWR SNF.

[DV82XL]

If we wish to dispose of DU, then mixing it with spent LWR fuel can be done so as to produce a fuel with NU-equivalent reactivity.

What a terrible waste of SWU's downblending is. Huge amounts of energy lost on material that could be used in its present form (and that includes the HEU that is being diluted) or kept for future use, as a token sacrifice to nonproliferation.

This is going to be seen as an act of utter and unexplainable stupidity by future generations.

[jaro]

How is it different from mixing fissiles with thorium, if the end result is the same -- total fuel burn.

Moreover, in using LWR SNF, there is no need for enrichment plants, or for traditional SNF reprocessing plants that separate Pu.

What more could you want ?

[Kirk Sorensen]

How is it different from mixing fissiles with thorium, if the end result is the same -- total fuel burn.

Mixing fissiles with thorium is totally different because there is no fissile form of thorium. Hence fertile and fissile can be separated easily by chemical means.

[jaro]

Mixing fissiles with thorium is totally different because there is no fissile form of thorium. Hence fertile and fissile can be separated easily by chemical means.

That is important in system designs requiring fissile separation from fertile.

In other designs, we don't care, unless we happen to be nuke weapons proliferators.

[NNadir]

...and to continue Lars' thought, U-233 is the ideal material for unlocking the energy potential of thorium. It's better than U-235, it's better than Pu-239. Thorium, in turn, is easier to extract energy from than U-238. Significantly easier. From the perspective of minimizing opportunity costs, we should:

1. Burn plutonium is a fast reactor (ideally chloride-based) to convert blanket thorium to U-233. Plutonium will perform better in the fast reactor than U-233, whereas U-233 will perform far better in the thermal reactor than plutonium.

2. Use the U-233 so bred to start lots of LFTRs.

In the distant future that Lars is so fond of simulating, I don't see much of a need for plutonium at all. The plutonium generated during the 20th century will be consumed in the 21st century to generate the U-233 that starts the LFTRs that then power the 21st through 29th centuries...

(then the Borg get us, for our thorium of course)

Well, all that stuff imagined, it would be well to consider the case of the first nation that will, as a practical matter, be the most active in moving to a thorium fuel cycle.

That, of course, will be India.

I’m a big fan of India’s commercial power reactor program and one of my very, very, very favorite papers discussing India’s approach is Jagannathan’s paper in Energy Conversion and Management “Reactor physics ideas to design novel reactors with faster fissile growth.”

Let’s get real. Most, if not all, of the growth in U-233 inventories for the next 20 or 30 years is going to take place as a practical matter in solid fuel matrices. That may not be the ideal case, but it is the realistic case.

It is very clear to me at least that the world’s largest inventory of uranium-233 for the next several decades is going to be in India.

Jagannathan’s paper makes several subtle points that I think people overlook. One of these is that the accumulation of fissiles in solid matrices is hardly linear, but is in fact, a function of the ratio of fission to capture in the fissile nuclei.

Rod Adams was good enough to post a figure from this paper on the internet in one of my Kos diaries before the dumb anti-nuke fundie Tim Lange and I had a mutually agreed parting of the ways.
Here’s the figure..

Thus the accumulation of fissile nuclei reaches, asymptotically, a maximum concentration either in thorium or in depleted uranium. Ultimately there is a point at which capture + fission exactly matches capture in the i-1th (fertile) nuclei, as a practical matter, again, limited to U-238 and Th-232, although at some point in the future it may be practical to discuss Pu-240 in this context.

(I personally regard Pu-241 as a great nuclei that has not achieved the appreciation it deserves.)

I fully and freely grant that this situation may be avoided with fluid fuels, but as a practical matter, for two or three decades, that situation is not going to be obtained realistically.

On the other hand, we should start breeding now. I’m no fan of Donald Rumsfeld’s to be sure, but to paraphrase his idiotic remarks during his manufactured war, one needs to fight with the nuclear fleet one has, and not the one that one wishes one had.

The best nuclear fleet in the world for producing U-233 is India’s. They will do it because they must do it. If anybody needs U-233 in the next century, India will be the provider of it. If you look carefully, you will see that India may in fact be using mixed isotope, U-233/U-238 uranium. Reading between the lines it is clear that they intend to produce exactly this kind of U-233.

I think we can and should convert our PWR fleets to something like the Radkowsky configuration to help things along. That is certainly one option for isotopically more pure U-233, but realistically, it’s going to be chock full of U-234 as well.

One of the interesting figures in this paper which I highly recommend if one wishes to think about rapid scaling of nuclear energy – something I regard as a moral imperative in these times – is the graph of eta vs neutron energy for the big three nuclei, U-233, U-235 and Pu-239.

It is very clear from a glance at this that in many ways plutonium-239 is the best possible breeding nuclei among the three in terms of neutron economy.

Pu-239 has a higher value of value of eta from 0.001 MeV to 0.05 MeV than does U-235, and only slightly lower than U-233. Here is something that I think most people don’t know, and I certainly didn’t appreciate: From 1 to 5 eV, the eta value for plutonium-239 is significantly superior to that of U-233, roughly 2.5 in that range. (In that range, U-233 is actually pretty poor, hovering around 2, and actually falling below 2 in that area. From about 20 keV to 2 MeV there are simply no nuclei (except, as I happen to know, Pu-241) that can approach Pu-239’s eta value. At 1 MeV, the value of eta of Pu-239 is nearly 3. You just can’t beat it.

U-233 at that energy has an eta value of about 2.5, a breeder, but not one quite at the level of Pu-239.

In fact, U-233 only comes close to Pu-239 with trans-fission neutron energies, i.e. fusion neutrons, not that anyone is actually ever going to have fusion neutrons, ever in my view.


Look, U-233 is a great nuclei. It really is. But the truth is that’s it’s too slow an accumulator for us to rely totally upon in the next century when rapid breeding may become an imperative under what are sure to be emergency conditions.

There is absolutely no good reason to reject plutonium. I think it’s a key component of the future, if there is, in fact, to be a future at all. We need plutonium, more of it, lots more of it. That’s what I personally want for all of that depleted uranium, a raw material for Pu-239.

Let me say something else: My personal bailiwick, besides chemical transformations of heat into chemical fuels via the reduction of carbon oxides, notably carbon dioxide, is fast fluid reactors. I have said this before and I will say it again. I just don’t like chloride as a counterion in fast fluid reactors.