Thorium MSRs: In Space

[Accelerando]

Apparently there's hubbub on the Internet about Thorium reactors and how they can provide plentiful power to human civilization for some time to come. While I don't know too much about that, I was curious about their potential for powering human infrastructure in space. Bases, villages, spaceships, deep space exploration, propulsion systems, what have you.

Why? Yesterday I set out to turn Gabyalufix's nuclear reactors into functioning Electrical Energy Generators, but quickly realized i have not the faintest idea of how spacecraft reactors would be constructed  especially thorium ones about which I am very curious  despite hearing not a few times of how they would be extremely helpful if not vital to long-term space missions. I could have posted this in General Add-on Affairs, but I figured you off-topic braniacs would have more to say about such things.

Finding clear information about reactor design on the Internet seems difficult. The only tried and tested space reactor I know of is TOPAZ, a 300kg vessel that could produce 5-10kW of power. A forum post on this site suggests that a 1MW reactor could be constructed using a few hundred kilos of plutonium and a few hundred more to build the reactor itself, but that's not quite the data I'm after (although I'd love to hear more on the subject if you know about it).

How much better could modern or near-future molten salt reactor technology make this, realistically speaking? How well do TOPAZ, or other existing systems, measure up to the requirements for a crewed journey to Jupiter, Saturn, or Mars? I have heard that the VASIMR engine will require a reactor capable of 1kg/kW power generation in order to get flying faster than chemical rockets in an appreciable amount of time. Correct me if I'm wrong on any of this.

Be civil, and stuff!

[RedDwarfIV]

One MSR has, I believe, already been built that can sit on the flatbed trailer of an artic' lorry. And it's a completely self-contained power generation unit. Something like that could probably fit in the Space Shuttle.

[colmo]

One of the main nice things about MSRs is the passive safety - the reactor contents drain off in the event of an emergency. I'm not sure how this would work in zero gravity.

[RedDwarfIV]

It is one of the nice things, yes, but its only one of the plethora of reasons why MSRs are useful. I'm sure some kind of battery powered pump would be effective.

[colmo]

I'm guessing not requiring cooling rods, and thus saving a load of weight, is another advantage.