Hacker News Reader

Comment by mbil | Hacker News Reader

I don't know anything about nuclear energy, but a friend who works in nuclear tech told me that the reason thorium as an energy source hasn't been embraced is because its byproduct can be used for weapons. That doesn't look to be exactly accurate (based on a few minutes of googling), but there might be some truth to it.

http://phys.org/news/2012-12-thorium-proliferation-nuclear-w...

View on HN

The reverse is actually true. Nobody uses Thorium since you can't make bombs out of them. Thorium is very unsuited to weaponize since one of the byproducts of the fuel process (U-232) decays in to a hard gamma-emitter. This not only makes the material dangerous to handle, it will also wreak havoc with bomb electronics, will require heavy shielding and be very easy to detect.

Due to its unsuitability for bombs, the militaries of the world (in the '50s) didn't invest into researching Thorium. Industrial inertia (and sunk costs) and Uranium being good enough lead us to where we are today.

It is 'technically' possible to make a U-233 bomb but the effort required is so far above U-235 bombs that for any nation able to do the former, it's much easier and cheaper to do the latter.

Emitting hard gammas seems like it would be troublesome for a power plant as well.

It's a much easier problem to solve in a plant setting than it is in something that would be suitably sized for use as a bomb

A nuclear power plant has thousands of tons of shielding. There are also no timing critical electronics sitting right next to the fuel.

U233 can be used to make bombs, but when you make U233 in a reactor, the progenitor to U233 is Pa233, this has a half life of 27 days. Inside the reactor, Pa233 gets hit by neutrons and one of them will knock another neutron loose so you get Pa232, then you get U232.

U232 makes a very heavy gamma ray that makes it difficult to work with the resulting U233, that is, you get killed trying to make a bomb from it. Also the fabrication of solid U233 is difficult because of the U232 contamination.

If Thorium is used in an LWR the neutron exposure on the Pa233 is enough that the U233 produced is hard to work with. If you had a special reactor like the ones they use to make weapons grade plutonium you could make weapons grade U233.

As for the various liquid salt reactors, it all depends on whether or not and how effectively Pa is removed. The Pa + neutron reaction hurts the breeding ration by consuming both Pa and neutrons. To maximize the breeding ratio it would be desirable to separate out the Pa and put it somewhere away from neutrons where it can decay to U233. If you had a process for this that was incredibly efficient than you could make weapons grade U233.

From what I understand it is the opposite, that because it was much easier to turn uranium byproducts into nuclear warheads it was the technology that won out over thorium.

We have used thorium reactors in the past but having radioactive molten salt is pretty rough on the components and drastically diminishes the life of the reactor.

Reply on news.ycombinator.com