The wetwell is connected to the drywell by a number of wide pipes.
FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi
2.
So long as power was available, pumps would circulate hot fluid from the reactor to the wetwell where it would be condensed.
FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi
3.
Both the drywell and the wetwell are surrounded by a secondary containment vessel (or shield building) also built from reinforced concrete about a meter thick.
FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi