[digikata]

The overall concept is good, but there could be things that go wrong in the real world. How fast the heat ramps up vs the failsafe plug in the vessel melting, or the chance of some material failure shedding debris which could potentially plug the drain path.

[ChuckMcM]

Actually if you read the Oakridge reports those cases are considered. For reference this reactor would have both survived and shut down cleanly in both the Chernobyl (over driving the reaction) and Fukishima (30m tsunmai + 9+ earthquake) situations.