Not bad. I do worry about the containment vessel not being much bigger than the reactor. That was part of the problem at Fukishima. When the reactor overheated and turned the cooling water to steam, the pressures were too high and the containment was breached.
Three Mile Island had a big containment vessel, and when they had a partial meltdown, the containment held.
I think the whole idea with NuScale reactors is that if you take away external power and scram the reactor, there's enough water in the pool to handle the decay heat. After the water boils away, the decay heat is supposed to be small enough that passive air cooling will keep it safe.
The containment pressures in a NuScale reactor are supposedly lower according to slides I found on the IAEA website. The containment is initially vacuum and apparently the initial pressure pulse of a pressure vessel failure will be contained and the steam will rapidly equilibriate.
Three Mile Island had a big containment vessel, and when they had a partial meltdown, the containment held.