"I guess they will use this for deep space probes? like old RTGs ?"
Actually a bit safer.
U235 is a low level Alpha emitter. They can be stopped by a pair of rubber gloves (watch the SNAP10a assembly video on YT). It's cold to the touch. It doesn't warm up till the chain reaction is started in LEO.
The PuO pellets inside an RTG are glowing red hot from the moment they are made. PuO is a very poor thermal conductor so they have to be small otherwise the gradient across the pellet is enough to crack it.
You can't stop PuO vigorously fissioning. With KRUSTY you remove the reflector and it's an inert lump of metal, even in sea water, which is quite a good moderator (part of the reason this reactor is a fast neutron spectrum design which does not use a moderator).
Biting the hand that feeds IT
