When the Fukushima Daiichi nuclear disaster began on 11 March 2011, reactor unit 4, 5 and 6 were all shut down. An explosion damaged the unit 4 four days after the 2011 Tōhoku earthquake and tsunami. Damages from the earthquake and tsunami on unit 5 and 6 are relatively minor. Reactors 5 and 6 were also shut down when the earthquake struck although, unlike reactor 4, they were still fueled. The reactors have been closely monitored, as cooling processes were not functioning well.