It is now believed leaks seeping into the soil, fresh water and the sea are continuous. Radiation has found its way into local produce, milk and tap water as far as Tokyo, 220km (140 miles) to the south.
Theories on main sources of leaked radiation
Reactor 2: Cooling problems damaged the core. It is thought radioactive steam is flowing from the core into the reactor housing and leaking through cracks. Contaminated material may have escaped through the damaged walls of the water-filled suppression chamber beneath the reactor.
Radioactive water in a tunnel underneath the reactor and the turbine (see diagram below) is preventing workers from gaining access. This tunnel emerges at the front of the building as a trench - just 55 metres from the sea.
BBC News - Japan's nuclear reactor: radioactive leaks