Relevant: "For the kinds of radiation coming off spent nuclear fuel, every 7 centimeters of water cuts the amount of radiation in half."
On the picture, the fuel rods are indeed protected by a huge quantity of water above them. But what happens below them ? They seem to be in direct contact with the ground...
I would guess that in reality they are either suspended and/or there is enough concrete at the bottom
People tend to avoid casually tunneling under nuclear pools.