You're confusing molten-salt reactors with molten-sodium reactors (different beasts). Molten fluoride is also reactive with water (hydrogen fluoride anyone?), but often MSR proposals don't involve water (they go for helium or CO2 gas turbines), and the ones that do separate steam far away from nuclear components, through intermediate coolant loops. Sodium reactors do the same thing. The risks really are manageable (in theory).
Radioactivity is dominated by short-lived fission products, not U-233/U-232 and company. U-232 is very radioactive, yes; but in a nuclear reactor, there exist vicious things far more radioactive than that. (Note that U-232 is a trace contaminant, but fission products are present in bulk amounts. U-232 is highlighted only because it's impossible to separate from U-233, a point of theoretical (and meaningless) debate involving nuclear weapons. Otherwise it's unimportant.)
It's relative. It's difficult to shield relative to U-235 (for example), which means that handling raw fuel is more difficult. (It requires robotic manipulators -- hot cells, "waldos" [0] -- unlike conventional fuels which can be handled manually [1]). This is barely relevant for MSRs, because there is no fuel fabrication step (no fuel pellets). It is a difficulty for solid-fuelled thorium reactors.
It's of no importance in nuclear reactors, because there there rest vastly greater amounts of vastly more radioactive monsters.
The reason people talk about U-232 is this confusing debate about nuclear weapons -- there's a weak (I think spurious) argument that thorium is weapons-resistant, because the U-232 gamma radiation makes it difficult to machine/work with weapons cores. It's really not relevant to molten-salt reactors.
U-232: I'm not sure that's really the good argument. The better argument is that it doesn't matter whether it is weaspons-resistant, because it is much easier to enrich U 235, even for U-poor countries. Is that argument also flawed? Unfortunately, I suspect some of the relevant knowledge is secret.
U-232: I'm not sure that's really the good argument. The better argument is that it doesn't matter whether it is weaspons-resistant, because it is much easier to enrich U 235, even for U-poor countries.
Yes, that's right. That's why the "debate" is spurious.
Radioactivity is dominated by short-lived fission products, not U-233/U-232 and company. U-232 is very radioactive, yes; but in a nuclear reactor, there exist vicious things far more radioactive than that. (Note that U-232 is a trace contaminant, but fission products are present in bulk amounts. U-232 is highlighted only because it's impossible to separate from U-233, a point of theoretical (and meaningless) debate involving nuclear weapons. Otherwise it's unimportant.)