> Practically, it's the PWR- Pressurised Water Reactor. I say practically as there are always new developments, like Thorium-Salt reactors that made the headlin

> Practically, it's the PWR- Pressurised Water Reactor. I say practically as there are always new developments, like Thorium-Salt reactors that made the headlines a while back, but these are the reactors that are producing the majority of nuclear electricity and haven't had a single major accident. Three Mile Island was a PWR. Of course, it wasn't a major accident in the sense that no significant radioactivity escaped the plant, but it was a major economic hit for the operator, and gave an unfortunate boost to various anti-nuclear groups. I think in practice, BWR's are considered about equally safe as PWR's. Yes, Fukushima was BWR's, but it's uncertain if same vintage PWR's with equivalent safety equipment would have fared any better. > They contain less fissile material in the reactor core Compared to what? A fast reactor of equivalent size, sure, but this isn't really the thing holding fast reactors back.. > they are purely Boron moderated No, they are water moderated. Boron, which is an efficient neutron adsorber, is used to control the reactivity during the burnup. That is, with fresh fuel rods the boron concentration in the water is higher to compensate for the higher reactivity of the fuel. There is ongoing research to design LWR's without boron, in order to avoid the corrosion issues and the equipment needed for controlling boron concentration. One way is to have rods filled with DU, which are slowly pulled out (and the volume replaced by water) as burnup proceeds. This approach has its own downsides, but, we'll see.