[nine_k]

The idea is that you are not going to have a meltdown even in a badly malfunctioning reactor.

[thaumasiotes]

Is it? It's not at all difficult to stock enough seawater to flood a terrestrial plant. What's distinguishing the submarine?

[phone[phone]]

A submarine (when submerged) has a large body of water for heat to radiate out into.

A (previous generation) terrestrial plant already has systems that can dump ludicrous amounts of water onto the core, but they all rely on there being power to operate pumps. A nuclear submarine that can dump in sea water does not need this - the body of water it is in is cold enough (relative to the heat in the core) that it will naturally carry heat away.

[HPsquared]

Smaller size than commercial power station reactors, easier to keep cool.

[thaumasiotes]

This contradicts the comment I responded to, though. The scenario is that we've already failed to keep it cool.

[moloch-hai]

There is less of it to cool.