CNN:

An explosion at an earthquake-damaged nuclear plant was not caused by damage to the nuclear reactor but by a pumping system that failed as crews tried to bring the reactor's temperature down, Chief Cabinet Secretary Yukio Edano said Saturday.

The next step for workers at the Fukushima Daiichi plant will be to flood the reactor containment structure with sea water to bring the reactor's temperature down to safe levels, he said. The effort is expected to take two days.

If you are in the nearby region, including in the Pacific West or Oceana—right now you should consider taking a multivitamin—better yet, a potassium iodide supplement. Radioactive cesium and iodine, if released in significant quantities into the environment, can replace non-radioactive potassium and iodine in the body.