According to the agency and Kansai Electric, the pressure inside the accumulator in the reactor's
emergency core cooling system temporarily fell on Friday night, setting off an alarm.
According to the lab, jobs to be done include design modifications to the Advanced Test Reactor's
emergency core cooling system and the reactor's emergency power supply.
The external power supply was then shut down, disabling the
emergency core cooling system from injecting water at 4:36 p.m.
Once the reactors automatically shut down following the quake and if normal electrical power supplies are cut off, diesel generators are supposed to kick in to power an
emergency core cooling system to prevent meltdown of the nuclear reactor.
The company said the alarm light indicating the conditions of the pipe valve for the
emergency core cooling system did not function properly.
A pump that comprises the
emergency core cooling system failed on the evening of May 11, the day before the regular inspection by government officials.
* Natural circulation, coolant flow residual heat removal, and
emergency core cooling systems powered by natural forces--gravity.
The World Nuclear Association said pressure inside reactor 1 had been steadily increasing because the
emergency core cooling systems had not been active.
The earthquake and tsunami apparently caused damage to the
emergency core cooling systems at reactors 1, 2, and 4, while reactor 3 was apparently able to shut down without problems.
In August, a Public Citizen [215 Pennsylvania Ave., SE, Washington, DC 20003, (202) 546-4996] survey concluded that "between October 1996 and May 1999, 102 of the country's 111 reactors were operated outside the safety parameters established in their licenses." NRC inspectors found that reactor operators had ignored key safety rules governing
emergency core cooling systems and the cables controlling the nuclear reactors core.