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Comment by fatbird | Hacker News Reader

I've seen several thorium-boosting articles like this, and none of them say why research and industrial development selected for uranium over thorium. Is it just because the initial research into power came out of weapons research?

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There are numerous different reasons. Thorium proponents often gloss over a lot of the difficulties of the system, leading to a false sense of how easy it would be to make such reactors. One of the biggest problems is that a Thorium reactor is actually a U-233 reactor, which is bred from the Thorium, and U-233 is not so easy to work with. It emits a huge amount of gamma radiation, which is highly penetrating and dangerous for human life.

To work with U-235 or Plutonium you only need a glove box, but to work with U-233 you cannot have humans physically close to the material, you need waldos and closed circuit cameras and so forth. This naturally increases the cost of working with the fuel. But wait, it gets worse. As I said, gamma radiation is highly penetrating and heavily ionizing, which means that it damages delicate materials quite easily. Especially seals, made out of rubber or silicone or what-have-you, and electronics. This makes fuel cycle handling hugely challenging and also makes reactor construction rather challenging as well.

Now, likely we could overcome these problems but they are nevertheless huge problems.

One of the big reasons why Uranium/Plutonium reactors have caught on is because you can use 1950s technology to build reactors and process fuel. That's not the case with Thorium/U-233.

This pretty much nails it, that is why things have to be very different with Thorium and the combination "very different" and "nuclear" leads to an over abundance of caution.

One of the reasons the travelling wave reactor is "interesting" is that starts and ends with 'low grade' radioactive material, and works very much like a 'brushfire' which burns fuel ahead of it and leaves behind fully utilized fuel. The downside is that it doesn't really "stop" in the sense that you start one of these candles burning and for the most part it goes 10 years and then sputters out, you can harvest the energy or not but you can't really turn it off. (at least not in the early designs)

So much of the engineering issues with Thorium are mastering the fuel cycle and that is something the US DoE hasn't spent a whole lot of time investigating. Its an interesting question what we could do with a 1950's attitude toward researching nuclear power uses and 2010's level of technology.

LFTRs are not all that difficult. It is a WHOLE lot simpler than a Traveling Wave reactor!

We have different definitions of "difficult" I suspect.

The Thorium fuel cycle produces U232, that stuff kills at a distance, through walls. What that means is that there are a number of scenarios, one of which Fukishima just went through, where the core gets uncovered and rather than leaking Cesium it shoots gamma rays everywhere killing anything trying to get near it. That is not the case with the U238 fuel cycle.

Not saying it can't be dealt with, just saying its different, and by being different it is dangerous in different ways.

"The Thorium fuel produces U232..." Yup, which is one of its nicest features. It means that the U233 is unlikely to be used for weapons. And since it never leaves the well shielded containment area in a LFTR, there is no hazard.

If the kettle is breached in the LFTR, the salt will probably just condense on any small break and seal it. If the break is large, the salt drains into a drain tank which is still in the shielded containment volume. No worries, mate! Oh, and since there is no significant pressure and no volatile chemicals like liquid sodium, there are no forces trying to disperse the materials. Inherently MUCH safer than any PWR or LMFR.

Has anyone considered using molten lead as a "seal"? I imagine you could reduce the number of places that need seals and then have it set up so that everything that needs to get into the sealed box passes through a small pool of lead that is kept molten. So long as everything around the lead has a melting operating temperature tolerance greater than 621 F it should be able to function through a molten lead seal.

Thorium is kind of like diesel, it doesn't work well in a spark ignition engine. Thorium doesn't work very well in a solid fuel reactor. Liquid Fluoride Thorium Reactors (LFTRs, pronounced "lifters") on the other hand work very nicely. All the "reasons" you mention apply to solid fuel reactors, not LFTRs. The man who invented both preferred the LFTR.

It's not the U-233 itself that emits gamma, but the U-232 it tends to be contaminated with. This can be avoided by chemically separating protactinium during the decay chain from thorium, but the U-232 is often considered desirable as a anti-proliferation measure.

By using liquid fuel and transmuting in place, you never handle U-233, contaminated or not. After reactor startup (which requires a good neutron source), you just keep feeding more thorium to the reactor and removing fission products.

One thing thorium proponents tend to omit is that there was a German thorium reactor which was considered to be in regular service (i.e., non-experimental). It suffered an incident and was shutdown several years thereafter as the costs of dealing with the incident and ensuring safety overwhelmed the operating company and forced it to seek a government bailout.

So there is some negative experience with Thorium. And the Germans are not willing to try again. Since the Germans that designed that reactor have the most experience with Thorium, and they are not trying again this should give a bit of a pause for others.

However, China is licensing those German designs and will try similar reactors in the coming years so we will see how that goes.

See :

http://en.wikipedia.org/wiki/THTR-300

http://en.wikipedia.org/wiki/Pebble_bed_reactor#Thorium_High...

Thorium has issues in a solid fuel reactor. The LFTR is the way to go.

It can not be stress enough that the reactor must be a molten salt reactor. The molten salt provides the stability, safety, and efficiency gains that a normal light water reactor can NOT match.

Long story short.

For breeder reactors getting neutron balance on to critical level is very challenging. You need one neutron to breed fertile material into fissile and another neutron to split the fissile nucleus. Usually 2-2.5 neutrons are released in fissions of U-235, U-233 (bred from thorium-232) or U-239 (bred from U-239), but some of the neutrons are absorbed by other materials in reactor, some other neutrons are leaked out from the reactor core etc. I would say this is the main reason, why breeder reactors are not common.

U-235 is the only fissile isotope available on earth so it was a natural choice for power generation.

Thorium in a LFTR breeds almost as well in a stable thermal spectrum reactor as U238 does in a twitchy fast spectrum reactor. And a LFTR doesn't have nearly the neutron loss mechanisms that solid fuel reactors typically do.

One reason also very much overlooked is that the entire nuclear industry makes the majority of its money from fuel fabrication. Making the bundles of fuel rods for PWRs and BWRs is a recurring, reliable source of income for the lifetime of the plant and any innovation into thorium or other models would take away that cash cow.

To clarify your point: utilities aren't usually in the fuel fabrication business, but some engineering firms are, like Westinghouse. They provide the designs, expertise during and after construction and fuel. And there's only a couple of vendors, so if you want to open up a nuclear power plant it's on their terms.

Yes. You're right. Utilities are told by the regulations to pay the engineering firms so that they can operate. I wish they had more choice other then the big ones but no one seems to be able to enter the market.

That's true that thorium would upend the ceramic uranium pellet market if if was a prevalent design, but it's not. The fuel fabrication business is tiny compared to most other segments of the energy market. It's probably not even the main revenue stream for a company like Areva. Remember, the nuclear industry is not a vertical industry like oil that takes the product from the ground to the service pump. It's a scattering of smaller service companies, small mining companies, and construction that are dwarfed in size in comparison to fossil fuel companies.

It's really, really complicated, since nearly all R&D came from huge government funding and that means politics.

A lot of it is that it came out of weapons research, and u-235 and Pu-239 were well understood from weapons research.

[edit] Also, plutonium fast breeder reactors looked very attractive in the '50s since they could use U-238, with just Plutonium feedstock, and also produced material usable for weapons. It turned out that 1) it's Not That Easy and 2) we don't need more atomic weapons.

>> we don't need more atomic weapons

Speak for yourself, the Pentagon, UK, France, Russia, China, India, Pakistan, Israel, North Korea, possibly others still replacing and/or building tons of those.

Partially. Also, the first really "working" nuclear reactor was built for a submarine. However, every modern nuclear reactor uses essentially the same design. This has resulted in some...idiosyncrasies in this design.

Yup. One of the good things about the light water reactors that everybody uses is that you can make them relatively small. That's a big deal when you're deciding what sort of reactor to put on a submarine. And then everybody who knew how to make a nuclear power plant only knew how to make a light water reactor, and then lock-in happened.

The other obvious advantage to having a light water reactor on a submarine is that water is something you can easily find a lot of out in the ocean.

The other obvious advantage to having a light water reactor on a submarine is that water is something you can easily find a lot of out in the ocean.

Well, you have to at least de-salinate the water and filter it before you use it in the reactor. If, in an emergency, you need to pump in salt water, you're going to ruin the equipment via corrosion.

The movie 'K-19 The Widowmaker' got into this a bit.

  If, in an emergency, you need to pump in salt water,
  you're going to ruin the equipment via corrosion.

Well, yeah, but is that any worse than if you have a different reactor design? Considering that, in a meltdown scenario, corroded equipment is not your biggest problem, it seems you would want to at least have the option. But most of what I know about subs comes from reading "The Hunt for Red October".

That's true only if you needed to replace water in the primary loop, but that's not likely. Seawater is only in the 3rd outer condenser loop in a PWR design.

Liquid Fluoride Thorium Reactors were based on a design for an AIRCRAFT reactor! Talk about having to be SMALL! :)

That's not really true, is a huge difference between using Sodium vs Lead vs light water vs heavy water vs gas for the primary coolant loop.

http://en.wikipedia.org/wiki/Heavy_water_reactor

http://en.wikipedia.org/wiki/Light_water_reactor

http://en.wikipedia.org/wiki/Liquid_metal_cooled_reactor

http://en.wikipedia.org/wiki/Lead-cooled_fast_reactor

http://en.wikipedia.org/wiki/Gas-cooled_reactor

The real link has a lot more to due with how cheap uranium was to mine / refine and how much refined uranium was needed for weapons programs. At this point we could stop all uranium mining for the next 50+ years without any problems and by changing designs that could stretch out to something like 1000 years. Fuel is simply not the problem.

the initial research being for weapons is probably part of it, though uranium-233 (from thorium) was used during a 1955 nuclear bomb test. [1]

thorium reactors are also "breeder" reactors. they initially require an external source of neutrons to start the reaction, then the thorium breeds into uranium-233 and the reaction can become self-sustaining. so thorium by itself is actually an impossible place to start.

[1] http://en.wikipedia.org/wiki/Uranium-233

Good point; compare to the first 5 US reactors, the Chicago Pile and the plutonium breeding Oak Ridge X-10, and Hanford B, D and F reactors. All graphite moderated (very pure graphite, BTW, something the Nazi's couldn't get), all using natural, as in unenriched uranium (at least initially). That was obviously handy for bootstrapping prior to enough Highly Enriched Uranium (HUE, mostly U-235) being available from Oak Ridge's separation plants, which I gather the first major use of was for the Little Boy gun assembly bomb.

That initial charge can be the Trans-Uranics (TRUs) from spent nuclear fuel. That way we can transition into the Thorium Age while cleaning up after the Uranium Flirtation! ;)

Really, the greatest reason has to do with organizational momentum. Think of how office politics work when different groups have competing ideas for the same solution. Those with expertise and time invested into their way are going to protect and defend their turf. Thorium lost that battle.

The argument that it wasn't good for weapons integration doesn't hold water as a commercial power reactor would not be used in that fashion at all. The DOE's production of plutonium 239 comes from specialized irradiated u238 rods exposed for 4 weeks or so - totally different production method and process that a PWR power reactor would use.

There is a Google Tech Talk on this very subject by Kirk Sorensen. He's a big thorium proponent so apply salt as you see fit but his talk seems fairly well cited.

http://www.youtube.com/watch?v=bbyr7jZOllI

This is only one of MANY good presentations by Sorenson and others on LFTRs and what we can do with them.

I'm not in the industry, but I believe uranium reactors produce plutonium as a byproduct. Plutonium is useful to make bombs.

Not reactor grade plutonium. Creating a pure Pu239 product depends on a specialized Pu239 production reactor with special methods. Extracting a pure Pu239 product from used reactor fuel would not be an attractive option for making a bomb. Not when you can produce a better product with a better/different method.

The same type of reactor can be used to make weapons grade Plutonium. Just ask Iran why they removed a fuel bundle from one of their reactors after just a few weeks rather than years.

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