early on 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.