Updated, 14.05

THE OPERATOR of the Fukushima I power plant in Japan has confirmed that the facility’s nuclear reactor was not damaged in a major explosion at the facility this morning.

The walls and roof of one of the facility’s four containment buildings were destroyed following the explosion, which occurred at 3:30pm local time (6:30am Irish time) today.

The country’s official nuclear watchdog said the nature of the explosion had damaged the containment building only, saying the steel casing around the reactor itself safeguarded it from damage.

The Japanese government has confirmed, however, that quantities of cesium and radioactive iodine have been detected near the facility. The International Atomic Energy Agency said it would distribute iodine tablets to citizens living within affected regions near the plant.

A number of staff are known to be injured, Japan’s NHK TV reported, with one in particular trapped inside the cab of a crane mechanism. The staff had been working to try and cool the station’s nuclear reactor, after the damage from yesterday’s earthquake caused both the regular and backup cooling systems to collapse.

Some radioactive steam was to be released from the plant in order to try and ease the pressure on the overburdened reactor.

A professor in nuclear energy had told AP that “no Chernobyl was possible” at a light-water reactor like Fukushima, saying that the loss of coolant would mean nuclear reactions would slow to a halt in spite of the increased temperatures in the reactor.

The explosion at the containment building, however, caused radioactive emissions near the plant to rise significantly; hourly emissions from the plant, measured shortly after the explosion, were higher than the annual dosage considered ‘safe’.

The explosion is seen about 25 seconds into the following video:

Tokyo Electric Power Company, which operates the plants, said both the primary and backup cooling systems had been deactivated by the effects of the 8.9-magnitude earthquake that had struck the country yesterday.

It added that the explosion had occurred during an aftershock from the earthquake.

The plant is one of two stations in the city, which lies about 150 miles north of Tokyo; authorities have issued evacuation orders within a 20km radius around both plants.

Those evacuation zone were originally 2km, before being incrementally extended to 6km and then 10km as confirmation came of the radioactive leak.

Residents are still being urged to abandon their homes, and to avoid eating any food in the vicinity until further instruction.