There is no excuse for any new design to not be “walkaway safe”, so in the event of total loss of cooling power like at Fukushima, the reactor stays within the safe and stable portion of its operating envelope.
The total loss of cooling power at Fukushima resulted from a bad decision. Even after the coolant loop shutdown from the tsunami damage, there was still cooling power left - the shutdown reactor could have been flooded with seawater. Rather than immediately flood with seawater to prevent the meltdown, the decision was delayed because to do so would have permanently disabled the reactors. Probably the seawater flooding should have been enabled by the scram and initiated by the coolant loop shutdown, rather than subject to a fallible decision chain.