They are not safe. They lack their own biological shield, and thus require the core section to be buried underground, as can be seen in various demo images. Even then, I suspect you wouldn't want to be too close while operating. They also lack other safety systems a commercial nuclear power station reactor has, having only a single control rod. This makes sense for an extraterrestrial reactor, as transporting mass to Mars is very expensive.
>They also lack other safety systems a commercial nuclear power station reactor has, having only a single control rod.
They also have a very strong negative thermal reactivity coefficient, meaning that as the reactor gets hotter it produces much less power. [0] From what I understand, with any reasonable amount of cooling this reactor won't melt down even with the control rod entirely removed, where "reasonable amount of cooling" means "not left to float in a vacuum with no radiators". (Also, if you remove the neutron reflector it'll stop working)
Granted, you'd probably want a bit more shielding before putting one in your basement. But it's not going to melt down.
