The system cooling water which contained spent - but still highly radioactive - nuclear fuel rods failed and it took engineers some 30 hours to repair the damage.
Workers at the Fukushima Daiichi plant are attempting to remove highly radioactive water from a reactor building to allow repair work to the cooling systems knocked out on 11 March.
In early April, the cooling system at one of the pools containing spent - but highly radioactive - fuel rods in reactor number three broke down for about three hours.
The nuke has had its share of scary moments, including a cooling tower collapse, and, more recently, discoveries of leaks of the radioactive hydrogen isotope tritium.