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The hiding place: Inside the world's first long-term storage facilty for highly radioactive nuclear waste
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- Authors
- Robert Macfarlane
- Published
- Jul 26 2019
- Word count
- 5235 words
This post is a two-fer - I arrived at the linked article via The New Yorker's "Is Nuclear Power Worth the Risk?".
There's no question we need to achieve extremely low or net zero carbon dioxide emissions, within a few decades. Assuming that some amount of nuclear power must remain part of the global energy mix for peak demand and baseload support of renewable sources, we need both better risk education and a truly trans-generational approach to considering costs, benefits, and risks.
While we condemn governmental bodies that make risk decisions without informed public consent, there's greater moral hazard in decisions made on behalf of our great-to-the-nth-power grandchildren, or the biosphere as a whole.
Projects like Onkalo are only addressing past unmitigated risk, not providing sufficient storage for a new generation of nuclear power byproducts. [Yes, I know thorium molten-salt reactors aren't supposed to waste as much, but there aren't any in commercial production yet, and commercial fusion remains decades away.] They also assume that better, safer technology for nuclear waste reprocessing won't become available.
Just for fun I'll explain how molten salt reactors and thorium is supposed to improve on this rather bleak situation.
The chief difference is that molten salt reactors burn up their fuel evenly. This does not happen in current solid fuel reactors. The fuel pellets are similar to ceramics and operate at extremely high temperatures. The outside of the pellets is consumed, but fuel burn decreases the deeper into the pellet you go. It's just not possible to burn up more than a few percent of the pellet's uranium, and some of the worst radioactive byproducts (the actinides) build up inside the pellets.
We could reprocess these pellets and continue to burn them, except that's an expensive operation and paying for it breaks the profit margins, so we don't do it.
In a liquid fuel environment, you don't have this problem. The burn up is evenly distributed since all of the fuel is in constant motion within the reactor. There's no place for byproducts to hide or build up.
We end up trading the solid fuel burn up problem for issues with corrosion of the reactor materials and there's a lot of plating as some of the byproducts build up in the inside, so this is no silver bullet. Corrosion and plating are two of the chief challenges designing MSRs, and it's why the various companies working on this use different salt mixtures and are investing in materials research.
Using thorium improves things further because it's got a lot less of the actinides in the fuel cycle and decay chain. It's just cleaner.
The theory is you leave it all in the reactor being constantly bombarded by neutrons until they've blasted everything into lead or near-lead at the end of the decay chain, and only then do you remove the spent fuel.
I've seen two estimates for the thorium waste in this scenario. The first claims the waste will have a half-life of three hundred years, and the second claims we can get that down to one hundred if we design the reactor specifically to burn up the waste. This is the design ThorCon in Canada is pursuing - a waste burner.
These reactors can use the uranium spent fuel pellets as a fuel source, with some basic reprocessing to get it out of solid fuel form. It's still a dirtier fuel, but burning it up all the way is more important. Every estimate I've seen estimates between 90% to 97% volume reduction in the waste itself. That shouldn't be surprising because most of this 'waste' is unspent fuel because of the solid fuel design, it's got nothing at all to do with the nuclear reaction itself.
After you're done, you have a brutish nuclear slag material that's radioactive and unsafe to be around for several hundred years. That's an improvement over the ten thousand years for the current waste, and combined with the volume reduction it would make the current problem more manageable.
The next step is to reprocess this into glass, either borosilicate or iron phosphate. Once it's locked into the glass, you're now dealing with hot glass bricks. They don't break down, they don't leak into the environment. By the time the glass goes, it'll be long after the radiation risk is past.
You can pile all of the world's waste into vaults like this, or just dump it into the deepest sea trench you can find. It can't get out of the glass and contaminate the water.
That's the rosy pitch you get from thorium molten salt advocates. It's not based on any crazy stuff that hasn't been done before, so it's likely to be right, but there are also likely to be many caveats in building a working system that follows this process. There will be hidden costs and challenges.
We'll still need these storage facilities. We just won't need them to last longer than human civilization has if the waste has been neutered this way. If we'd had these in the past, right now the bricks of spent fuel from late 1700s reactors would be on sale as souvenirs, and no longer even able to register above background radiation levels on a geiger counter.
If you're interested in this particular waste management aspect of thorium molten salt, keep your eye on SALIENT. Proving out the waste reduction is part of their planned study program. They'll be able to answer the question with proper research and testing within a decade.
Thanks for the detailed response, and for passing on the SALIENT link. My biggest concern with MSR's is the thermally hot, corrosive liquid loop.
My knowledge of radioactive liquid systems, as found in reprocessing anyway, is that they can create hard-to-dispose highly contaminated secondary bulk waste in the form of piping, valves, cladding, etc., not to mention the various chemical residues. The shorter decay lifetime for thorium cycle will help, but the dirty parts aren't as compact as fuel rods.
Yep, all nuclear reactors - including fusion - will produce that sort of waste material. It isn't hot for long after it leaves the reactor, some number of decades depending on the nature of the reactor. Turnover for these materials is between six and twenty years depending on the design, so there isn't a lot of bulk there to manage as the parts don't change that often. I expect they'll just bury those parts in a cement coffin.
There's been a lot of interest in high end ceramics for this because they don't plate out materials as easily or corrode, but it's proving difficult to find ceramics that can withstand neutron bombardment at those temperatures. They may prove less prone to becoming radioactive than metals. They get brittle fast, though, so we've got to invent a new kind of ceramic that doesn't embrittle so easily to go that route.
I don't believe aneutronic fusion reactors would produce any radioactive waste, although even if we had a reliable way of sourcing fuel, those are decades behind D-T reactors.
Edit: I've since learned aneutronic reactors do produce some neutrons (just not in the main branch) due to secondary reactions. Neutron production is less than 0.1% that of a neutronic reactor, but some shielding would be necessary, and some small volume of waste would be produced.
This is from an article on bulletin of atomic science.
If you're fucking around with nuclear energy, you're going to be dealing with radioactive waste one way or another. It's a problem inherent to the technology. It's also not nearly as big a deal as people make it out to be - we just do things poorly in existing reactor designs.
That's all about neutronic fusion reactors, I was talking about aneutronic fusion reactors. The mechanism of waste generation in a neutronic fusion reactor, i.e. a D-T or D-D reactor, is basically neutron bombardment transmuting the elements comprising the reactor vessel into their radioactive isotopes. This will happen in any neutronic fusion reactor, since by definition they use fusion reactions that release most of their energy in neutrons, but as was mentioned, the isotopes generated have half lives measured in years or decades, so it's not much of a concern.
In aneutronic fusion reactions (e.g. D-3He or B-p+), as the name implies, neutrons are not generated as part of the fusion process. Instead, the reaction's energy is released in charged particles like protons, that can easily be directed with magnetic fields, and even converted directly into electricity without needing a heat engine. If there's a mechanism for aneutronic reactors to generate waste, I'm not aware of it.
Edit: I've since learned aneutronic reactors do produce some neutrons (just not in the main branch) due to secondary reactions. Neutron production is less than 0.1% that of a neutronic reactor, but some shielding would be necessary, and some small volume of waste would be produced.
Funny you should mention that; there's a patent in the family backstory for some of the early research on aneutronic fusion (crossed-field with some nifty toroidal looping features and later, MHD power extraction). The project lost funding, and I don't know what's become of related research. But I do remember being baby-sat at the lab, with interesting tasks like, "yell when that part glows blue". Presumably, it didn't involve spare neutrons.
That sounds promising. Avoiding the neutron problem is a big deal. I did some reading and this class of fusion easily beats molten salt reactors across the board for cost and power without the waste issue. I'm surprised I don't see this talked about more often. It seems more practical.
It sort of is and it sort of isn't. It's more practical in that aneutronic fusion reactors can do without shielding and a heat engine, and produce no waste, but it's much less practical in that aneutronic fusion reactions are four to ten times harder to ignite than the D-T reaction, which itself is only on the edge of viability for economical power production. For that reason, I'd be immensely skeptical of anybody claiming to be able to build a breakeven capable aneutronic fusion reactor for less than hundreds of billions of dollars, as they should be able to apply similar techniques to make getting power from neutronic fusion child's play.
Aneutronic fusion is an energy source for the next century IMO. For now, we should be focusing on getting D-T reactors into production; for all their shortcomings, tokamak based power plants using the ARC design could be built inside a decade, and we need them on the grid as soon as possible.
Reasons for skepticism about alternative fusion approaches, including aneutronic reactors, are enumerated here.
It's been claimed that you cannot produce any fusion reaction without at least some byproduct neutrons, thus generating durable radioactive waste. It's just a question of how hot, how long, and how much.
That's a great article, definitely saving it for future reference. Did not know that about neutron generation, I'll update my comments up the chain.
People forget our grid is built to distribute power from central large stations to the rest of the grid. It's not like the internet, able to route energy from wherever it comes in to wherever it's needed - yet. Large power plants are going to be around for a long time, at least until we do a total rebuild of the power grid.
Um, that's all true, but was there a way it relates to the thread? Seems a bit out of the blue to bring up.
I was just thinking that large fusion plants are a very good fit for the current grid.