Do you know where your core is?
More like
Do you know where your cores are ?
Ground water radiation level spikes are not a good indicator that they do.
Wherever it is it has to be tracked down and found.
If this is the 4th floor pictured, then the reactor containment and core are below. There was no fuel in the unit 4 reactor core - it was off line for maintenance and evaluation. The spent fuel pool is, I think, on this floor. They generally onload and offload fuel into the reactor from the top through a large access "lid". The crane removes the fuel, and then sets it down into the spent fuel pool on the same floor. Pretty efficient design providing a 45 foot tsunami doesn't wipe out all of your power supplies.