“One of my concerns with the Yang climate plan is I think he probably just Googled "advanced nuclear," took a look at the top hits online, and ran with that,” says Kieran Dolan, a nuclear engineering graduate student at MIT’s Nuclear Reactor Lab.

"So why does everyone who knows nothing about reactors think thorium is the beez kneez, while everyone who knows something about reactors laughs at them?" One of the advantages of growing up in a nuclear weapons lab is you end up hanging out with the kids of people who... know stuff about fission.

"Because from an energy-in, energy-out standpoint we have no reason to expect that thorium reactors are viable," is the answer I've gotten three times from three different Ph. D nuclear physicists.

It's like that time my Chem 141 professor, who was slummin' and bored because he was supposed to be doing inorganic research, decided to spend an hour telling us why all this talk of "silocon-based life" in sci fi was bullshit as a roundabout way to explain electron shells: carbon is so much more amenable to energy transport that silicon-based life would move at about the same pace as crystal-forming and without access to liquid water any silicon-based life would be competing with carbon-based life because there's no reason to ever expect that a stellar environment would create silicon without creating carbon first.

They don't tell you this about biodiesel, either: it's less energy-dense than diesel and the energy necessary for creating it is an externality that you don't have to deal with when putting it in your tank but you do have to deal with when arguing for it as an energy solution. It's like hydrogen fuel cells. Yay! You made a car run on hydrogen! Great! Where'd the hydrogen come from? Oh yeah? Oil? And how much energy did it take to crack the hydrogen loose? Really? And how much more energy-efficient would it have been to turn it into super-unleaded? Yeah, I know, theoretically you could have electrolytically cracked it from sea water using wind, solar, unicorn farts and rainbows but you didn't, did you?

The pragmatic arguments against thorium reactors usually focus on "we don't build them because you don't get plutonium out of them which we need for nuclear weapons" but you get U-233 which you can totally use in a pinch. This could well be why India is pushing hard into thorium, but it isn't: India is pushing hard into thorium because they have a lot of thorium within their borders. Even then they've been on the verge of making one work for about sixteen years now.

The real argument against thorium reactors is that once you account for energy life cycles, the efficiency of production is below breakeven. Nobody really wants to bring this up because once you account for energy life cycles the efficiency of uranium reactors ain't so great either, which is one of the reasons the United States hasn't made any new ones in quite a while. Thus, thorium reactors remain perpetually just beyond the horizon: a promising technology if only we'd sink the billions and billions and billions of dollars that China and India have. Because, see, just because attempts at thorium reactors have failed for the past 40 years (compare with Fermi's pile) doesn't mean they will continue to fail. If we hold our heads right and squint just so, they'll save the world.

To transition the United States from fossil fuels to green energy, Yang wants the government to invest $50 billion in the development of thorium molten-salt nuclear reactors—and he wants them on the grid by 2027.

Yeah let's take an unproven technology with radically-unsafe byproducts that depends on hypothetical metallurgy and scatter it across the countryside as quickly as we can! Why? Because the nerds don't wanna hear anything bad about thorium and if the hippies like solar we better endorse something else so we can differentiate ourselves.