Fukushima Daiichi nuclear disaster (Unit 3 Reactor) 13 March an official of the Japan Nuclear and Industrial Safety Agency (NISA) told at a news conference that the emergency cooling system of Unit 3 had failed, spurring an urgent search for a means to supply cooling water to the reactor vessel to prevent a meltdown of its reactor core. At 05:38 there was no means of adding coolant to the reactor, owing to loss of power. Work to restore power and to vent excessive pressure continued. At one point, the top three meters of the uranium/mixed oxide (MOX) fuel rods were not covered by coolant. At 07:30 JST,
Corium (nuclear reactor) nuclear fuel (the uranium oxide fuel has a melting point of 2865 ˚C, thus the physical nature of the damaged fuel has not been fully determined but it is assumed to have become molten) to melt and form corium. The reactor core isolation cooling system (RCIC) was successfully activated for Unit 3; however, the Unit 3 RCIC subsequently failed, and at about 09:00 on March 13, the nuclear fuel had melted into corium. Unit 2 retained RCIC functions slightly longer and corium is not believed to have started to pool on the reactor floor until around 18:00 on March 14.