Three Mile Island was expensive, but nobody was injured. TMI had a big, strong containment vessel. Although they had a meltdown, the containment did its job and held.

Fukushima had too small a containment vessel. It was only slightly larger than the reactor pressure vessel, and it failed to contain the pressures of the meltdown.

Chernobyl had no containment at all.

Instead of all these "modular reactor" excuses for weaker containment vessels, such as NuScale, what's needed is more work on making very large pressure vessels cheaply. There's been progress in robotic welding of thick sections.