Traveling Wave Reactor: Hype or magical energy source?

I was watching Bill Gates give a TED talk on this power technology (vid can be seen here along with a text snippet).

Sounds great but going with the notion that anything that sounds too good to be true I looked around for more info. The best cite (from a reputable source) I found was this article published by MIT.

The short version is the Traveling Wave Reactor uses U-238 as its main fuel source rather than U-235 required by conventional reactors (actually it needs a little U-235 to get going but somewhere in my reading they suggested a single U-235 re-processing plant could supply the whole world if these reactors were used).

The reactor kind of burns like a candle. The reaction moves along the tube converting U-238 into plutonium which is nearly instantly used to produce energy. Apparently this “candle burning” progresses pretty slowly and a single reactor could run for 50 years or more before needing replacement.

The upside to all this is it can use the massive stockpiles of U-238 we (literally) have lying about for fuel (they suggest we have stockpiles sufficient for over 1,000 years of electricity). Further, it seems the waste products are less than a typical reactor and some of the nastier stuff leftover can be recycled back into a new reactor.

Unfortunately I have not been able to find much detail on the downside to this. Everyone likes to trump the upside.

I would think people would be falling over themselves to develop this if it delivers on its promise but since it is flying low on the radar I have to wonder where the gotchas are. Cheap energy with zero carbon footprint and no dirtier than current reactors?

Below I am copying a post in the comment section to the MIT article which details the waste leftover. No idea how reliable that is so take it with a grain of salt.

Anyway, anyone here have the SD on this?

Mostly just chiming in to see what others think. I’ve read about these before, and I think the downsides are related to the intensity of the radiation which necessitates more shielding (I might be misremembering though). But that’s just engineering. I think the technology is promising, but then so are several other fission technologies that are also in development. The biggest challenge, at least here in the US, is to actually get new designs developed and tested and get the intentional regulation blockages freed up so that we can actually look at some of this stuff wrt to actually building full scale working systems.

I’d go with ‘neither’. :slight_smile:


Without getting into a gazillion minor technical details that could make this not work once you actually tried it, I will say this.

At a very broad level, it doesnt violate any rules of physics, nor the very general principles of how nuclear power works in the first place.

I don’t know much about this design specifically, but it sounds like a sort of breeder reactor, and the problems with breeder reactors in general are more political than technological.

Not fully understanding the tech it seems one would be hard pressed to get Pu out of this to use for nefarious purposes. It seems the Pu is created then used almost right away. Even if you stopped the reaction how much Pu would be sitting there? Not to mention you’d have to cart the whole reactor away, cool it for a few years then extract the Pu embedded in U-238.

Sounds like way more hassle than other methods.

Is anyone else imagining a glowing Blue Screen of Death?

I hope that this design gets through to testing - we have to do better than current nuclear reactor designs, and many breeder technologies produce considerably less radioactive waste material than current systems.


I should add I understand that the ban on breeder reactors are a political decision and not a technical one.

Never understood how they thought plutonium could be nabbed by terrorists with these things though.

I’ve often wondered why no one had ever built a continuously self-breeding reactor, and apparently this is it. As said upthread, not inherently implausible, the only question is whether the design works as advertised.

I note the design runs significantly hotter than your typical reactor and uses liquid sodium as a coolant. Neither of these things is in its favor in terms of making it safer, easier to make, cheaper, or more reliable.

I love the general concept, but the very first thought that pops into my mind is “is there anyway to NOT use liquid sodium?”.

True, sodium, especially really hot sodium, is a lot more reactive than graphite. I hadn’t looked at the details; that looks like a big one.

Meh , liquid sodium is nothing once you are dealing with radioactive stuff like this. Liquid potassium is used in many chemistry labs daily. I’ve never seen liquid sodium used, but it’s just hotter. By the time you have a large release of sodium, you likely have much bigger problems. It won’t stay metallic sodium for long.

I want to say that the primary problem with breeder reactors is economics, not politics. There are proliferation concerns to be sure, but fuel costs are not a huge part of running a reactor. I understand that a doubling in the price of fuel would only lead to a five percent increase in the cost of electricity from a typical plant.

To my way of thinking, what we ought to be pushing in terms of nuclear power are passively safe designs which produce as little waste as possible. Hybrid fusion-fission reactors (uses neutron flux from a Q < 1 fusion reactor to cause fission in a subcritical pile) are my latest love interest, but they are really still at the concept stage. Physicists at my alma mater developed something they call Diverter X technology which allows them to bombard waste from conventional reactors with large amounts of neutrons generated by a Tokamak to actively destroy it, but I don’t believe the technology was developed with power production in mind.


I did a little background reading after seeing this thread, and having to use liquid sodium as a coolant would indeed seem to be an issue. Is there a fail-safe method of shutting the reactor down if the coolant is lost? I didn’t find that mentioned anywhere.

I think that by the time you have a coolant leak, a sodium fire is the least of your problems. There is nothing inherently difficult about liquid sodium. It is used all of the time in chemistry. I have no idea if the birch reduction is used in commercial synthesis, since there are a number of substitutes, but all of them are equally reactive.

Based on the thread title, I was hoping someone had proposed seagoing nuclear reactors that extracted uranium from seawater as their fuel, endlessly plying the Seven Seas like whaling ships of old keeping the streetlamps lit with whale oil.

I was wondering about how they’d shut it down as well, for maintenance even if not for an emergency. They say the material is in “hexagonal pillars”, so maybe they can raise half of them up to slow the reaction, then lower them to restart it. That might also give them the ability to adjust the power output somewhat, which you’d think they’d want to be able to do.

Reactors of this type are designed to be passivly safe. Risk of coolant loss is very low, because the entire reactor is submerged in a pool of liquid metal at ambient pressure that can’t escape. The fuel is self-limiting and unable to generate enough power to melt itself when the reactor is operating. If the primary coolant pumps are lost due to loss of power or mechanical failure, the decay heat of the fuel is removed by natural convection flow of the coolant.

There’s nothing inherently difficult about solid graphite, either, but it’s still not something you want in your reactor.

Solid graphite is not necessarily a problem if the reactor temperature is above the annealing temperature of the graphite. This prevents the build-up of Wigner energy, and is the process used in pebble bed reactors.

Looking around, I came across this article. From the abstract:

That’s a pretty good trick, if it works. I don’t have access to the full article, but I wonder how it could handle a blackout, where it couldn’t supply any electric power for a few days.