Tim Meyer wrote:
I'm pretty sure neutrons are WAY too precious for anything other than burning Pu-239 in a way to produce U-233 for the LFTR-23; where Kirk said in the subject report, one LFTR-49 for three LFTR-23s—impressive! But the goal is to get AWAY from U-238 (U-235) and move away from the higher actinides. I thought that was one of the great benefits of thorium! This is the "Energy from Thorium" Thorium Energy Alliance is it not? Thorium is about three times more abundant than uranium. That speaks for itself.
Getting away from needing uranium as fuel is certainly "A goal" but not necessarily "THE goal". There are a number of problems with using uranium as an energy source, weapon proliferation fears is probably on the top of that list. It will be difficult to remove ourselves completely from needing uranium as a nuclear fuel because uranium-235 is the only naturally occurring isotope that is fissile. We might be able to remove the need to enrich uranium with the use of heavy water reactors and other technology, that should reduce fears of nuclear weapon proliferation.
Just so I'm clear here I will say that there is nothing inherently wrong with having the ability to produce nuclear bombs. We live our lives of freedom and comfort because past generations developed nuclear bombs. It becomes a problem when madmen get their hands on the technology as then they become a much greater threat, just as if they had access to any other weapon of mass destruction. This is a genie we cannot put back in the bottle, so long as people know that nuclear bombs are possible, and people have access to dirt or seawater, there will be a threat that someone will extract the uranium and do something evil with it.
Also, I'm not saying that LFTR49 is a bad idea, it's a very good idea. As an engineer I tend to think of ways to "fix" things, even if those things aren't broke. LFTR49 produces neutrons for the bombardment of thorium, producing U-233, an excellent idea. I'm just playing on this theme to see if other valuable products could be made from this. This is a forum dedicated to the uses of thorium for energy but we can't narrow ourselves with this too much or we'd be ignoring the value of thorium as a source of medical isotopes. It's not too far of a leap to think of other variations on this technology, such as the production of Pu-239 for starting more LFTR49 reactors, feeding military power reactors, producing fuel for solid fuel reactors, etc. Thorium is more abundant than uranium so using thorium over uranium is preferable. Even better would be to utilize both as a fuel since that opens us to even more energy possibilities.
This brings to mind an alternative use for the U-233 produced. We have a lot of solid fuel reactors still. I expect that not only will these be operational for a very long time yet but more will be built. What of taking the U-235/U-238 mix of isotopes from the spent fuel and mixing it with some of the U-233 produced to make new solid fuel rods? One big thing holding back MSR technology is that the solid fuel people see it as a threat for their business model. If this can be sold as a means to recycle the spent solid fuel into new solid fuel then this might be more popular.
Another big reason we cannot free ourselves from uranium as a fuel completely is its value as a feedstock for Pu-238. We can get to Pu-238 from thorium but that takes a lot more valuable neutrons than if you start with natural uranium. This leads into my next point on alternative materials for neutron bombardment.
Tim Meyer wrote:
I'm a little concerned about placing a lot of eggs in the targeted alpha therapy basket. I bet there are other and more vital medical isotopes the LFTRs would supply?
I'm sure there are plenty we could dream up. Tc-99m comes to mind as that is what was used for my bone scans. I'll disagree with the "eggs in one basket" here since it sounds like what is being proposed is two paths for the usage of the U-233 produced with LFTR49. One use is as a fuel for LFTR23, the other is as a source for valuable decay products of which one has a potential use for targeted alpha therapy.
With a two fluid reactor design we can think up all kinds of variations on a theme where the core fluid is fissioning and producing heat and neutrons for a blanket salt. This blanket can contain thorium to produce U-233, U-238 to produce Pu-239, or any of a number of elements to produce fuel and non-fuel isotopes. So long as the balance of neutrons is maintained there's a lot of possibilities.
I believe that Flibe Energy succeeded with LFTR49 where Transatomic failed with WAMSR was with an understanding of the chemistry needed. It takes an understanding of nuclear fission to keep those neutrons where they need to be but without the chemical processing beforehand that balance becomes difficult or impossible. WAMSR keeps the chemistry simple but then made the neutron balance hard. LFTR49 added complexity to the chemistry which made the neutron balance easier.
I won't even pretend I understand all the chemistry and nuclear physics here but I do understand algebra. If you put 2 neutrons in and get back 1.9 then you come up negative. If you put 2 neutrons in and get 2.2 back then that little extra can be used in a lot a different ways. Using those neutrons for U-233 production is a great idea. What I was pondering with my previous post was using them to produce more Pu-239, which has a lot of peaceful and not so peaceful uses. I see potential for variations on this theme to produce all kinds of valuable isotopes, or maybe even use it to destroy isotopes that are difficult to dispose of by other means.
I'll wrap up my thoughts here by getting back to where I started, it seemed to me that the article was too quick to get to the conclusion that the uranium extracted from spent LWR fuel could be just thrown away. That uranium is valuable as a fuel. Put it in a HWR/CANDU. Mix in some U-233 to enrich it and put it back in a LWR. Just generally hit it with more neutrons so we can get things like Pu-239 (fuel), Pu-238 (RTG), Tc-99m (bone scans), Am-241 (smoke alarms), Co-60 (industrial radiography), and so on.
At a minimum perhaps we could be satisfied with using uranium for it's density and not just toss it in a hole. That density would come in real handy for weighing things down, radiation shielding, and armor. Don't throw it away.
Tim Meyer wrote:
What if a ten-mile-wide asteroid were headed for Earth right now?
I imagine it'd go something like this...
https://www.youtube.com/watch?v=iVL-xa4aZUo