It’s water. We actually know how to keep water from leaching into the environment. It may be a hard job, but it is emminently doable. Impermeable membranes, set into, and if necessary below the foundation, then you collect the water, purify it, and recirculate it.
It’s the same job normally done by the reactor vessel. If the vessel isn’t water-tight, make the next barrier water-tight.
Might not even have to do that. If there are simply cracks in the substructure, you just have to provide a lower-resistance path for the water, like through an active pumping system. Collect the water before it reaches the cracks, then throw in sealant, and you might cut off all the leakage, or 99.9% of it.
Still don’t know what has made the vessel leak. Could be melts, but it also could be broken pipes that enter and exist the containment.
Nice thing is that they are able to collect more data now that things are stable, and the data is helping them understand the problem, which will lead to better solutions.
No need to read further. Come back when you actually have a grasp of the situation. It is unprecedented.