There's a big difference between a dam and a pool; the pool is supported by the ground, and even if you bash holes in it, the water still has to find somewhere to go. Also, pools are not typically built from concrete and stainless steel.
The safety requirement here is not "doesn't leak", it's "holds most of the water for 30 days (after which water is not required)". You would have to get an implausibly-large leak, during a situation where nobody can add more water for a month.
I don't lack imagination; my imagination just has enough structure to distinguish between realistic and unrealistic scenarios.
We should be orders of magnitude more worried about all the carbon dioxide we're dumping into the atmosphere, than the failure modes of an engineered hole in the ground.
Thinking that nuclear safety just comes down to digging a big hole and filling it with water is such a gross over simplification that I honestly can't believe you are arguing in good faith.
Maybe a particular reactor design could use such a mechanism as one failsafe, but that alone is not enough, and no design is perfect, and the people operating it are not perfect.
I think some of the risks of nuclear are acceptable, I am actually very pro nuclear, but we should acknowledge them instead of pretending they don't exist. The only way risk can be properly managed is if it's acknowledged.
They didn't just drop a reactor in a pool; they also eliminated a bunch of pumps and other failure-prone components from the system.
I would prefer to see inherently safe designs like LFTR gain traction, but NuScale has one of the few designs likely to be built in the near term, where you could SCRAM and take a vacation without causing a meltdown. That is a major advancement in safety; let's not let perfect be the enemy of good.
The safety requirement here is not "doesn't leak", it's "holds most of the water for 30 days (after which water is not required)". You would have to get an implausibly-large leak, during a situation where nobody can add more water for a month.