In order to remove decay heat of the severe damaged cores of Unit 1–3, TEPCO injected cooling water into the reactors. As the reactors appear to have holes around the bottom, the water dissolved the water-soluble fission products, which then accumulated in the basement of the turbine building (the adjacent diagram #2) through any leaks from the water-injected reactor buildings (#1). Since the accumulated radioactive water was a risk, TEPCO tried to transfer it.
