Why Should We Save the Uranium-233?
I have appealed many times on this blog to our public leaders to save the precious resource that is uranium-233. I have explained in an earlier blog post why the uranium-233, if used in a liquid-fluoride thorium reactor (LFTR) represents “unlimited” energy, because it can “catalyze” the consumption of abundant natural thorium and the inventory of U-233 remains even at the end of the reactor lifetime.
But why save this particular 1000 kg of U-233? If we’re going to start hundreds of LFTRs, there isn’t enough U-233 to start all of them, and we’ll have to use other sources of fissile material. So why worry about this batch of U-233?
Reason #1: Destroying the U-233 is a waste of money.
The Department of Energy is estimating that the cost of “downblending” U-233 with depleted uranium (predominantly U-238) followed by “disposal” at the Waste Isolation Pilot Plant (WIPP) in New Mexico will cost approximately $380 million dollars. This is the estimate as of December 2006, and it came from an article in the Knoxville News-Sentinel that is no longer available, but the text can be viewed on the thorium-forum. $380 million is a LOT of money, money that’s being used to destroy U-233 rather than develop the LFTR technology that turns it into unlimited energy.
Reason #2: LFTR runs better when it is started with U-233 than any other fissile fuel.
The LiF-BeF2 dissolves uranium better than plutonium, and if you start LFTR on U-233 you start it the way that it will be running in the long run. It takes a lot of neutron absorptions for U-233 to turn into something other than uranium. You have absorb one (U-234), two (U-235), three (U-236), and finally four (U-237, decaying to Np-237) neutrons before you form your first transuranic nuclide. By contrast, if you were to start LFTR on highly-enriched uranium (which would be a very attractive way to dispose of HEU that was produced for nuclear weapons) you only have to absorb two neutrons to get to Np-237. Plus, HEU has a certain amount of U-238 in it, and U-238 is only one neutron absorption away from forming a transuranic isotope (Pu-239). Obviously starting on plutonium, you’ve already put a lot of transuranics in the reactor to begin with.
This may sound a bit confusing, so I’ve made an image to try to graphically depict what happens in the reactor when you start on different fuels. U-233 fissions more favorably, its products have more opportunities to fission, and it has further to go before it forms a transuranic.
Reason #3: U-233 allows us to prove “thorium burning” in a prototype reactor.
One of the basic underlying assumptions of the LFTR is that we can “burn” thorium, in other words, we produce enough U-233 to replace that consumed. By starting a prototype reactor on U-233, we can actually show this in a real-world case early on, rather than trying to extrapolate backwards from a HEU or plutonium startup. It is going to be important to demonstrate that LFTR can really burn thorium, and a U-233 start is the only conclusive way to demonstrate this.
Reason #4: The aged U-233 contains valuable decay products that could save lives.
The U-233 in the DOE’s inventory has had 30+ years to decay. That means that some special isotopes like actinium-225 and bismuth-213 have had time to form in the stored U-233. These actinides, which can ONLY be formed through U-233 decay (not fission) have shown that they could be very promising isotopes for certain types of radiotherapies that could save thousands of lives every year. Even the Inspector General of the DOE has appealed to save the U-233 to save lives.
To summarize, saving the U-233 saves money, lets us demonstrate LFTR’s ability to burn thorium, and could save lives. Please appeal to your congressional leadership to save this precious resource.