Plutonium treaty and uranium MOX
Russia Withdraws From Cold War Plutonium Deal With US
Russia withdraws from 25-year-old weapons-grade plutonium agreement
The Russians are exiting the Plutonium Management and Disposition Agreement (PMDA) with the United States. To be honest, the treaty has been pretty dead for a long time now, largely since the United States abandoned their strategy to make uranium-MOX fuel from surplus weapons-grade plutonium that was once nuclear warheads.
You see, it’s rather easy to disposition surplus weapons-grade uranium, since it’s just highly-enriched uranium. You simply downblend it with natural uranium, throwing away all of those glorious separative work units (SWU) that you once paid so dearly for, usually with power generated from burning coal. Sure, it’s wasteful but you can do it, and we did do it, for many years.
But dispositioning plutonium is not easy. There is no such thing as “natural” plutonium, because we’ve made every atom of the stuff. There’s nothing with which to “downblend” plutonium. If you want to get rid of it, you’ll need to fission it, and that will need to be done in a nuclear reactor.
The US had elected to make mixed-oxide (MOX) fuel. But they elected to make their MOX fuel with uranium, and uranium makes more plutonium when you irradiate it. So you were digging the ditch even as you were trying to fill it in. A much better idea, both then and now, would have been to make thorium mixed-oxide fuel (Th-MOX) and that way you wouldn’t make more plutonium as you consumed it. The short video gives you the overall idea.
At any rate, this treaty and the MOX plan have been discussed on this blog since it started up in 2006. But very little real progress has taken place, unfortunately.
All ttue, unfortunately
I think there could be a problem with combining oxides of Pu239 and Th232 into mixed-oxide (Thorium-MOX) fuel pellets for conventional solid-fueled, water-cooled power reactors.
My understanding is that using Thorium-MOX fuel pellets in place of conventional 4 percent enriched uranium fuel pellets would not create used fuel containing new plutonium; instead, the used fuel thus created would contain new U233.
In other words, U233 would no longer be considered a “precious” commodity, but would become a potentially troublesome “legacy” component of widely used solid reactor fuel, similar to the way plutonium is today.
Managing the development and production of Thorium-MOX solid fuel and the transportation and reprocessing of used Thorium-MOX fuel assemblies would likely present a challenging nuclear infrastructure problem. It seems that using reactor-grade Plutonium directly as a “kickstarter” fuel for Thorium MSRs could be simpler, depending on the time to availability of prototype reactors.
I think that the first thing we need at this point is a flexible used-fuel disassembler that would enable us to disassemble used fuel from standard power reactors, extracting unused uranium, TRUs, and fission products, all of which can be dispatched to internal or external service providers. Unused uranium can be sent to enrichment plants or Uranium-MOX providers; TRUs can be sent to Uranium-MOX or Thorium-MOX providers, or used internally to make molten salt fuel for LFTRs or fast Thorium MSRs; and fission products can be either sent to radiological medical providers or disposed in medium-term (300-500 year) borehole deposits. And so on.
Kirk Sorensen presented an interesting talk at UTK that outlined, among other things, how salt-based electrochemistry could be used in a spent fuel dissembler:
https://energyfromthorium.com/2023/12/13/utk-colloquium-2023/
World Nuclear News featured an interesting article showing how the Moltex Waste-to-stable-salt (WATSS) system uses molten salt electrochemistry and physics for the separation of used fuel into recyclable components such as enrichment-ready uranium and reactor-grade plutonium. Also, the WATSS system is onsite with a CANDU reactor and a prototype molten salt fast reactor:
https://www.world-nuclear-news.org/articles/moltex-requests-pre-licensing-consultation-for-recycling-process
So, I would say there’s actual progress going on out there.