Contamination in Unit 2 appeared to be due to a partial meltdown of the reactor core

"As officials scrambled to determine the source of the radioactive water, Chief Cabinet Secretary Yukio Edano said the contamination in Unit 2 appeared to be due to a partial meltdown of the reactor core."

TEPCO 3/28/2011:
The water inside the reactor 2 turbine room was measured at 1,000 millisieverts an hour.

Greenpeace 3/28/2011:
Greenpeace said its experts had confirmed radiation levels of up to 10 microsieverts per hour in a village 40 km (25 miles) northwest of the plant. It called for the extension of a 20-km (12-mile) evacuation zone.

Yukio Edano 3/28/2011:
As officials scrambled to determine the source of the radioactive water, Chief Cabinet Secretary Yukio Edano said the contamination in Unit 2 appeared to be due to a partial meltdown of the reactor core.