Kirk Sorensen wrote:
...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.