[Gravityloss]

Note that this very different to the molten salt LFTR design. With solid fuel it is very hard to prevent protactinium capturing neutrons, which means problems for breeding and waste and probably operational constraints as well. The LFTR is such a beautiful consistent design but it is very different from ordinary reactors.

Also the title is inaccurate as different thorium reactors have been designed, built and operated. See MSRE and THTR-300 for example.

[warfangle]

The big problem with a molten salt LFTR is the materials necessary for the plumbing. Any metal will become brittle as it is exposed to the radiation emitted from the reactor core. And manufacturing ceramics into the precision pieces called for is not a solved problem.

LFTR designs are fantastic, amazing, and solve a lot of problems. There is a lot of materials science to be done to make them viable, though.

[JohnHaugeland]

You're confusing issues from pressurized reactors with LFTRs. The reason manufacturing ceramics for pressurized reactors is hard is the pressure and size involved. LFTR can be run at normal pressure at small scale; you can use a kiln as the pressure vessel if you want to.

Also, no, not any metal gets brittle; inconel and hastelloy handle radiation quite well for decades at a time, as does good old fashioned nickel. Beyond that, most reactor pressure vessels are a layer of metal then a layer of something that's really good at radiation, then the real pressure vessel, so that the interior layer's brittleness isn't very important.

We built and ran LFTRs commercially in the 1950s in New York State and Pennsylvania, before computers became a commercially realistic thing. They provided our grandparents no significant technical challenge.

The actual big problem with LFTR is primarily regulatory. The design hasn't been vetted to modern safety standards, which costs hundreds of millions of dollars, and the entities who are nuclear-aware and have that kind of money to throw around tend to be the existing nuclear companies, who can't switch to any other technology because they're deep in the Gilette Razor model, and anything that took out their existing fuel contracts would immediately bankrupt them.

There is /zero/ materials science needed to make a LFTR. I don't know where you got that idea. They're substantially easier than what we make today. The average auto body shop can pull it off.

[warfangle]

>You're confusing issues from pressurized reactors with LFTRs.

Nope, pretty sure I'm not. I'm well aware that LFTRs run at low (even sub-atmosphere) pressures.

>We built and ran LFTRs commercially in the 1950s in New York State and Pennsylvania

We never ran LFTRs commercially. If you know otherwise, please cite. I only know of two experimental reactors at the Oak Ridge facility: the Aircraft Reactor Experiment and the Molten-Salt Reactor Experiment.

> I don't know where you got that idea.

I got that idea from some pretty simple facts about nickel alloys (like Hastelloy N) under neutron bombardment.

When you bombard nickel with neutrons, you produce helium. When the helium builds up irregularly, the alloy becomes brittle. You can dope Hastelloy N with titanium or niobium to even out the distribution of helium deposits (this is what ORNL did) but that brings the maximum temperature down to 650C.

As well, tellurium (one of the fission products of a LFTR reactor) corrodes the grain boundaries of Hastelloy N. You can reduce this effect by doping it with niobium and keeping the UF4/UF3 ratio to less than 60.

You have to trade off lower temperatures with whether or not you want to deal with beryllium toxicity. You can replace BeF2 with a eutectic lithium fluoride/thorium fluoride composition, but that requires an increased temperature of the reactor salts. There are other problems with using beryllium, though - it produces lithium-6, which is a strong neutron poison.

You also have to filter out noble element deposits, because they don't form fluorides.

There are also serious design challenges with modifying current turbines to work with supercritical CO2 or helium. You can use supercritical steam instead, but it isn't nearly as efficient.

You also have to worry about tritium diffusion. It's small enough that it leaks through the heat exchangers.

There are issues with the rapid expansion/contraction the graphite moderator, but some are working on graphite pebble designs.

Once you throw the corrosive salts, strange reaction byproducts, and neutron bombardment into the mix, I highly doubt that 'the average body shop' could pull off the fabrication of a LFTR style molten salt reactor that could run safely for longer than a week.

[Gravityloss]

I was surprised to hear from GE that a CO2 working fluid power plant using turbine waste heat is a thing nowadays. They have a contractor, Echogen, who provides that part.

http://www.cospp.com/articles/print/volume-14/issue-01/featu...

http://www.echogen.com/documents/why-sco2-can-displace-steam...

In ships, when fuel costs just keep on rising, that starts making sense. (There are other reasons why it might not be good though.) On land power plants, it might make natural gas electricity more competitive against coal with this better efficiency.

Though I don't see the keyword supercritical on the Echogen site yet...

[warfangle]

Oh neat, I didn't know about that either.

[JohnHaugeland]

You are quoting verbatim as fact from an unsourced blog post you provide in another comment. That blog post says what you're claiming as fact are /rumors/. It points out beside the issue things like that a heat generation experiment that wasn't hooked up to dynamos didn't generate electricity, in literally the same paragraph as claiming they produced too much heat (so use some of it?)

In the meantime, it refers to hypotheticals as its only criticisms, many of which are mutually contradictory, many in ways as obvious as the above.

On top of that, one of the best bullshit detectors that has ever existed is watching for basic quality of language, and this guy has not yet mastered the wily apostrophe.

With apologies, I'm not going to be your unpaid research assistant tonight. You made a claim without evidence. I dismissed it without evidence. You seem to believe the burden of proof is now on me. Sorry; I have other things to do which are more important to me, and you flat out ignored several of the things I said, so I'm comfortable doing the same (like when you claimed that building ceramic housings was a challenge, and I thought you were confused about Japan Steelworks; you have provided no explanation for believing that ceramic containers, which Hitachi uses extensively, are out of our reach.)

Similarly, your story about grain boundaries is compelling, at least if you don't consider lining the reactor. But then you go on to observe that a 50s reactor ran for four years without a problem on 50s metallurgy, and don't seem to think that that's a problem for your concern.

Finally, that's true, you don't want to be around irradiated fluorine. But if you would rather be near a failed coal plant than a failed lftr, my interpretation is that you don't know much about what happens in either a fluorine leak or a coal plant explosion. Fluorinated uranium rain two countries away? Buddy, not even six blocks away. What makes that shit dangerous is how violently and universally it reacts. There would be less uranium and fluorine in the rain than in to day's seawater.

Helen Caldicott off, please. Either do the envelope math or stop pretending it's anything more than blog fuelled FUD.

[warfangle]

> You made a claim without evidence

So did you :)

[warfangle]

I wanted to add a couple additional points, separate from my other response:

Everything at Oak Ridge did _not_ provide our grandparents with insignificant technical challenges. Not only for the points (in my other response) about neutron bombardment making the Hastelloy N brittle, but also:

- The cooling circuit glowed red hot. This indicates that it was close to its thermal creep zone; we didn't know much about thermal creep back then. [0]

- The MSRE reactor spent a good portion of its life down for maintenance. [0]

- The tritium release is not a small problem: of an estimated 2.0TBq of tritium produced, 6-10% diffused from the fuel system into the containment cell atmosphere, and another 6-10% was released from the heat removal system. And these were lower than expected. You really don't want your LFTR to be leaking tritium everywhere. [1]

- The decontamination of the experiment was really, really hazardous. Not only were they dealing with nuclear waste; they were dealing with nuclear waste and fluorine gas. You really don't want to be anywhere near elemental fluorine gas. This was all because ORNL didn't defuel and store the salts correctly; it's mostly been rectified in modern designs[1]. But it goes to show how horrifyingly dangerous the components are. As bad as a nuclear spill would be, you have to remember that these aren't your run of the mill molten salts. They're highly toxic salts spewing out gamma, beta, and alpha radiation. I'm trying to imagine what it would be like if Chernobyl released these kinds of chemicals in its radiation plume. I don't think I can imagine something that horrifying. Toxic rain over Germany doped with uranium hexafluoride and plutonium? I'd rather have coal power. And I hate coal power.

Of course, all of this is me being extraordinarily cautious. I was really, really excited about LFTR design when I first heard about it. But the more I learn, the more I'm convinced that we really don't have the materials to safely operate one of these things on a commercial scale.

0. http://daryanenergyblog.wordpress.com/ca/part-8-msr-lftr/ 1. http://en.wikipedia.org/wiki/Molten-Salt_Reactor_Experiment#... (throughout)

[msandford]

I wish I had dug in further. I am substantially less excited now.

[swatkat]

The one mentioned in the article is Heavy Water Reactor with Thorium fuel. Here's its whitepaper: http://www.barc.gov.in/reactor/ahwr.pdf