Although uranium-235 is the typical fuel for commercial fission reactors on account of it being fissile, it’s relatively rare relative to the fertile U-238 and thorium (Th-232). Using either of these fertile isotopes to breed new fuel from is thus an attractive proposition. Despite this, only India and China have a strong focus on using Th-232 for reactors, the former using breeders (Th-232 to U-233) to create fertile uranium fuel. China has demonstrated its approach — including refueling a live reactor — using a fourth-generation molten salt reactor.
The original research comes from US scientists in the 1960s. While there were tests in the MSRE reactor, no follow-up studies were funded. The concept languished until recently, with Terrestrial Energy’s Integral MSR and construction on China’s 2 MW TMSR-LF1 experimental reactor commencing in 2018 before first criticality in 2023. One major advantage of an MSR with liquid fuel (the -LF part in the name) is that it can filter out contaminants and add fresh fuel while the reactor is running. With this successful demonstration, along with the breeding of uranium fuel from thorium last year, a larger, 10 MW design can now be tested.
Since TMSR doesn’t need cooling water, it is perfect for use in arid areas. In addition, China is working on using a TMSR-derived design in nuclear-powered container vessels. With enough thorium around for tens of thousands of years, these low-maintenance MSR designs could soon power much of modern society, along with high-temperature pebble bed reactors, which is another concept that China has recently managed to make work with the HTR-PM design.
Meanwhile, reactors are getting smaller in general.
Thorium seems to be quite promising. From what I’ve gathered (mostly from youtube), the reason to use Uranium was chosen long ago because it can produce stuff to make bombs, and that was a big thing 50 years ago. And once the Uranium reactors were working relatively well, nobody wanted to cough up the cash to do the research to make other reactor types mature for production. Sometimes I wonder how such cost calculations are made. It seems that handling of the radio active “waste” is simply left out of the equation when designing a reactor.
As I see it, we’ve really just made the first baby steps of what can be done with nuclear reactors. Probably a lot of other reactor types can be designed and made too. Those are probably less “energy efficient” or more expensive, but that may be worth it if they can be used to “burn” radio active waste into shorter lived isotopes.
But I’m not a nuclear chemist, and getting an overview of what would be viable combinations is a bit beyond me. I also don’t have enough pocket money to fund research in that direction. But still, good to read that some progress is being made.
Using uranium as a fuel was not because you could make a bomb out of it, that seems to be an urban myth. Uranium-235 is relatively easy to source, compared to other fuels, and operates within reasonable circumstances. Thorium requires very high temperatures and corrosive liquid salts which makes uranium a very good step in between.
Thorium however is much safer and the waste is radioactive during a relatively short period so that will surely be the future. But without uranium, we wouldn’t have had nuclear energy.
Oh the power generation was definitely a byproduct of “need bigger reactor to produce more plutonium”. Look at the history of the UK’s Atomic bomb and where the slogan “Energy too cheap to meter” came from and you’ll find they’ll relatively readily admit that by now.
Now that said, molten salt reactors pose unique (and possibly unsolved) corrosion problems, but you can have Thorium in a not-molten-salt-reactor (think that might be what India is going for?)
Umm … Thorium isn’t what is fissioned in a thorium reactor. Its the U-233 that it is bred into. The daughter products produced by U-233 and U-235 have about the same waste products and the decay of waste is about identical. You essentially have a uranium reactor either way. I also wouldn’t consider introducing fluorine based salts making anything safer.
The reasons the uranium breeder was chosen over the thorium breeder were that the breeding ratio for a U-Pu fast-neutron breeder reactor is quite high, and the technology needed for U-Pu fast breeders was much more developed.
Fast breeders of either kind are not very suitable for producing weapons material. For that, low-temperature, thermal-neutron production reactors are the preferred option. At the time when breeders were under active development, the U S. was scaling back their production reactor fleet, except those producing tritium, because they had a surplus of weapons material except for tritium.
The impetus for development of breeder reactors in the 1960s and 1970s were the beliefs that the world would need more than 1000 power reactors by the year 2000 and that the supply of natural uranium would be unable to supply the needed fuel. By the late 1970s it was clear that there was much more uranium ore available than previously believed and that the world would probably not have more than about 350-400 reactors by 2000.
Conventional uranium-fueled reactors are much less expensive to operate than breeders so long as there is ample natural uranium, so the motivation to pursue breeders of any description went away. The world currently has about 440 operating power reactors, Currently known uranium reserves appear to be sufficient to operate about 800 reactors for about a century, so there is unlikely to be much economic motivation for breeders anytime soon.
In thorium breeders, the breeding ratio is quite low if the thorium is in fixed fuel assemblies because too much of the intermediate isotope between thorium-232 and uranium-233, protactinium-233, is consumed in non-fission reactions if it is left in the neutron field while it transforms. Using a liquid fuel allows the protactinium-233 to be chemically separated and sequestered out of the neutron field until it has transformed into uranium-233. The problem with liquid-fueled reactors is that the highly radioactive fission products are released into the circulating fluid, making the reactor essentially unmaintainable except remotely using robotics. If or when there is an economic imperative for breeders, it is more likely that they will be uranium-based, fixed-fuel designs cooled with liquid sodium rather than thorium-based, liquid-fueled designs cooled with molten salts.
Fast breeders…
Hot daughters…
Nuclear chemists are horny bastards!
You can tell by the names they pick for things.
i’m not an expert on any of this stuff but my impression is that the “handling of waste is simply left out of the equation” story is kind of interesting
in many conventional reactors, a low-enriched-uranium fuel is like loose pellets(?) stuffed inside of hollow rods, and the hollow rods are made out of zirconium or something exotic like that (neutron transparent). and then they’re surrounded by water (neutron moderator and absorber), and then also with graphite (neutron moderator) and control rods made out of like boron or something (neutron absorber). to the extent that they can control the reaction, it’s by varying the geometry of the neutron absorbers and moderators…moderators in the neutron path genrerally make it react faster, and absorbers make it react slower.
that much is pretty simple but what happens inside of the rods complicates the whole thing. various reaction byproducts accumulate inside the rods. when a neutron hits uranium, it breaks down into a whole spectrum of products. some of them are “nuclear poisons”, which means they basically act as neutron absorbers without creating more neutrons…they stop the chain reaction. many of them are themselves radioactives, with a huge range of half-lives, so some of them break down in minutes or days and some take years or centuries. so they represent a neutron source that can enhance the nuclear chain reaction.
so my point is, the reactor designers are actually intensely interested in waste products, because they trap those waste products inside the reactor and have to account for them as a major operational concern. one of the causes of the chernobyl disaster was they didn’t follow the protocols for throttling the reactor up and down, and it resulted in a relatively high concentration of nuclear poison, which they then tried to overcome in an impatient fashion by removing all of the control rods. once the poison started to ‘burn off’ (absorbed as many neutrons as it could, i guess), the reaction rate increased very quickly.
so the conventional design is very focused on the waste as an operational concern…with the trade off that after it’s done operating, they aren’t as concerned about the waste. by comparison, with liquid-fuel reactors, it is possible and necessary (??) to filter out the waste products during operation. that filtering is complicated and that’s one reason those reactors are less common / more experimental. once the waste products are filtered and sorted, i think dealing with them actually becomes more easy.
so everyone’s concerned with waste, just in different ways.
Since TMSR doesn’t need cooling water, *
A puny little 2MW demonstration reactor that does not make steam to run through turbines to generate electricity might not need water cooling.
But try scaling that up to a 1 GWe power plant. It *could be air cooled (and has been with conventional power plants), but you pay a price in both capital cost and efficiency. If you’re a government with an agenda, the additional cost might be acceptable.
Arggh. Sorry about the rogue italics. An edit button, please, HaD.
This is a case where size doesnt matter.
Traditional nuclear power plants use water directly to cool the core, contaminating the water with radioactive isotopes.
These thorium reactors remove heat from the core with molten salt. The molten salt is then used to heat water to run turbines. As long as the heat exchanger doesnt fail crossmizing the molten salt and the water there is no pathway for contamination.
Additionally, the turbines system is typically operated in a closed loop so that the steam is condensed and reused over and over again. There is no giant tower billowing steam in these systems. So even if there was a failure that caused the system to become contaminated, so long as there was no failure of the outer pressure containment shell there would be no environmental discharge to be concerned about.
As for efficiency and cost, TMSR run at 40-50% thermal efficiency vs LWRs 30%. TMSRs are also projected to have lower capital costs both in construction and operation.
…traditional reactors also have two water loops, to keep the irradiated water separate from the rest of the operations. MSR’s just use much higher temperature fluids in the inner loop, which does help the thermal efficiency (as well as bringing other benefits), at the cost of technical complications.
but yeah, waste heat requiring cooling is very likely to be a thing in a production-scale plant. that’s a factor deriving from the operating parameters of the power-generating turbines, and MSR’s aren’t intended to redesign those. that’s how you condense the steam so as to run it through the heat exchanger and then the turbines again.
(…i suppose you could redesign the outer loop while at it, if you wanted to take on that much technological risk. make it run on fully supercritical water, maybe, since you’ve the heat to spare. but i’d be more likely to settle for one technological innovation at a time, myself.)
The material used for core cooling is not relevant, since it’s always used closed-loop. Whether it’s helium, carbon dioxide, sodium, heavy water, molten salt, or even ordinary water, it’s not a consumable. Likewise the intermediate steam turbine loop isn’t relevant either: That hyper-pure water is also re-used.
Water is not plentiful in the Gobi desert, but saying the 2 MW demonstration reactor “doesn’t need cooling water” is disingenuous (or just naive). Size very much matters here. 2 MW can be dumped in ambient air without too much trouble. But a large power reactor very much wants a cheap way to dump the 2-4 GW of waste heat it produces. Trying to do that without water is costly.
It’s a question of what is the largest unit size that can still run air-cooled with reasonable performance AND how many of those you need to build to reach economic plant size AND whether it’s cheaper to just run a single big reactor.
The huge reactors we have now are a product of each being a “prototype” of its own kind, with decades of lead-in time for evaluation, permitting, protesting, politics etc. which favors large unit sizes to make the money count. Size creates issues with safety, since the power density of the reactors cannot be easily contained in a meltdown, which creates the need for elaborate safety mechanisms which further increase cost and time to permit operation, which further increases the economical unit size etc. etc.
SMRs are a thing that’s coming to leverage the economy of mass production, being simpler to make, easier to contain in an accident, re-using manufacturing processes and designs, certifications and permits, lower bureaucracy, less financial risks…. so it’s not a given that you can’t build an air-cooled nuclear power plant in the middle of the desert.
To point, even where we have traditional reactor “families”, wherever you build one, the local authorities like to put their own spoons in the pot and invent extra regulations and interfere with designs by demanding that they should do things this way or that way.
They’re all like the Doble Steam car where every single vehicle was hand-made by craftsmen down to the nuts and bolts, and no car had matching parts because the Doble brothers kept tinkering with the designs even as they were producing the cars.
The thermal efficiency difference is smaller than you say: it is 33-34% for LWRs and 40-43% for plants operating at the temperatures claimed for TMSRs.
just to flesh this out a little
my understanding is that the core water in a traditional plant only contains isotopes from the fuel in the case of a mechanical failure of the sheathing on the fuel rods. the radioactive materials in the core water are isotopes of the water itself…hence, tritium, the result of bombarding hydrogen with neutrons (and, imo, a fairly benign product, due to its short half-life). the reactor has to allow the neutrons to flow through the water, because it uses the water as a neutron moderator. but it doesn’t have to let the water touch the fissile material or its byproducts.
i think molten salt reactors can use a neutron absorber / shield / mirror between the fuel and the water, because the water isn’t needed as a neutron moderator
Popular Mechanics wrote about Thorium Reactors in 2010, and there were several articles before that. This is nothing new.
Yeah,when I was a kid, back in the ’60s, I read an episode in in a comic of “Mandrake the Magician” where Mandrake foils an attempt by evildoers to corner a supply of Thorium for evil purposes. It impelled me to look up articles, books, and encyclopedia entries that described Thorium and its uses in Thermonuclear power. (I miss print copies of the Reader’s Guide.)
knowing it is possible is old. knowing progress is being made is new
Since thorium is associated with lanthanides (such as europium used in phosphors, and neodymium in magnets), which China mines massively, and is actually a dangerous, (mildly) radioactive substance in mine waste, separating out and using that thorium to create energy is win-win technology. Now, if there were only more trustworthy ways to dispose of the eventual, highly radioactive, waste…
Fast Neutron Reactors. They burn waste out of existence.
if they solve the various problems of filtering waste products out of the molten salt, then it is much easier to deal with (or use) small streams of specific waste products instead of a massive stream of mostly uranium with trace quantities of much scarier substances, effectively inseperably mixed in.
You sound just like pure Russian troll. Not many people in the world knows what Andoria was and where it came from.
My comment was reply to comment glorifying RBMK reactor that is no longer visible to me.
bummer it was deleted because the RBMK design is pretty neat. instead of having a giant pressure vessel full of water, the water runs in pipes through the reactor. it’s neat because it’s easy to understand why it is so much less expensive to build and scale, and also because it’s easy to imagine why it has such a marginal neutron flux that it has to operate at the edges of tolerance. i think i’m glad it’s no longer being built but i think paying attention to the design of it is educational.
Check out the security: First, it’s in the middle of desert, 50 km from the nearest town, and has FOUR gated fence perimeters, including a prison-style isolation zone. Why so much security for a little research reactor?
I once had a Thorium nuclear power plant in my neighbourhood (but no molten salt there):
https://en.wikipedia.org/wiki/THTR-300
.
That illustrates the real problem with nuclear power. Can you trust the operators when things go wrong?
Murphy dictates that things always go wrong at some stage.
Unintended Consequences dictate it will be something that wasn’t anticipated.
Currently, the dunning-kruger hypothesis is under attack, but I think it’s interesting to look at something like the contrapositive of it: for any problem, there will be a bunch of people who know they aren’t smart enough to try to solve the problem, a bunch of people who think they can solve the problem and are right, and a bunch of people who think they can solve the problem but they can’t actually. (That’s the D-K population.) As the problems get harder, those populations change, with the number of people who can actually solve the problem shrinking. At some problem complexity, everyone will either say “oh that’s too hard” or unknowingly be in the D-K population group. I think designing long-term commercially viable nuclear energy may be a problem of this sort.