http://www-ns.iaea.org/tech-areas/emergency/ines.asp
Coolant within Unit 3 is covering about half of the fuel rods in the reactor, and Japanese authorities believe the core has been damaged. High pressure within the reactor’s containment led operators to vent gas from the containment. Later, an explosion destroyed the outer shell of the reactor building above the containment on 14 March.
Following the explosion, Japanese officials expressed concerns that the reactor’s containment may not be fully intact. White smoke has been seen emerging from the reactor, but on 19 March it appeared to be less intense than in previous days.
Efforts to pump seawater into the reactor core are continuing.
Of additional concern at Unit 3 is the condition of the spent fuel pool in the building. There are indications that there is inadequate cooling water level in the pool, and Japanese authorities have addressed the problem by dropping water from helicopters into the building and spraying water from trucks. Spraying from trucks continued on 20 March. There is no data on the temperature of the water in the pool.
On 18 March, Japan assigned an INES rating of 5 to this Unit.