There have been a few different types of reactors that have claimed to be able to run on thorium, many of these the molten salt type, which have their own share of problems. Breeder reactors are able to utilize it as well, but currently breeders are primarily used to deal with used uranium fuel and the only few in operation are in Russia.
I don't think I'm missing any "finer points", it's that the only reactors currently in production that can run on thorium are HWR's like the CANDU and there's no real point in Canada, because of the amount of uranium we have.
I've not heard of a "candle" type reactor, but the reason you have to mix it with something else is the reason I outlined earlier, and that's because thorium isn't fissile, it's fertile, so it needs to be mixed with something that is fissile, like plutonium or uranium in order to undergo fission.
No, it means it needs to be mixed with a fissile isotope so that fission can commence. Yes, that can be spare weapons material, like plutonium from warheads, but it can also be dirtier plutonium from used fuel or even uranium.
No it isn't, not in the form of used fuel without reprocessing. It's a pain in the butt, because it has to be stored and the US has no DGR, so it just gets stored in cooling ponds until it can go into casks, which then sit around. That's the case at every plant in the US.
The US could also reprocess that waste (PUREX for example) and run it in their existing reactor fleet. Nobody has been willing to invest the money to build a reprocessing plant, that's the issue.
Yes, there are always waste products. The CANDU fuel cycle, which in most instances uses natural uranium, has a "lesser" waste stream than an LWR or BWR, but you can also run a MOX or a DUPIC cycle where you use spent LWR/BWR fuel in the CANDU. China is doing this at Qinshan with the two C6's located there.
The US already used surplus weapons material (warheads) in reactor fuel after the cold war. The burned tons of former Soviet weapons material this way, which is why US uranium production tanked during that time period.
The issue isn't government cooperation, it's somebody being willing to spend the money to build something. PUREX is a tried and true reprocessing technique for LWR and BWR fuel, used extensively by France, they even reprocess used fuel for the Japanese, but the US doesn't have a single PUREX facility.
Anybody handing SNF or anything radioactive needs to be approved by the appropriate regulatory body. So while the ability to factory assemble a given reactor type might sound wonderful, they still are required to be monitored by and compliant with the nuclear standards, which immediately torpedoes the simple and cheap part because then you are into permits, monitoring, regulation, approvals, oversight, site visits...etc.
This is why these things are typically operated by large utilities who have the money to jump through these hoops and regulatory hurdles.
So was the CANDU. It didn't require enrichment, which only countries pursuing atomic weapons (like the US and the Soviets) had. We had developed a number of different designs that were supposed to vary suitability for different sized markets. Ultimately, the anti-nuclear movement coupled with Chernobyl killed that.
There's actually a new twist on the "pre-fuelled" reactor design here in Canada. It's the USNC/GFP MMR, which is basically a reactor and power unit about the size of a shipping container designed to power remote communities. The fuel load is designed to last ~20 years at which point you swap out the reactor portion for a fresh one.
This is the first design slated to be built at Chalk River.
Bombs typically aren't made with reactors anyways. All you need is a gas centrifuge. That's why North Korea has nuclear weapons and no nuclear reactors.
www.osti.gov
