The Nuclear Regulation Authority decided Wednesday to open a more thorough investigation into whether critical safety equipment at one of the reactors in the Fukushima No. 1 power plant was damaged before the complex was hit by tsunami in March 2011.

The decision was reached by a panel tasked by the NRA to look deeper into the cause of the Fukushima disaster and how it evolved to reconcile the differing conclusions reached by the three accident investigation commissions that probed the disaster.

The commission appointed by the government, which was responsible for nuclear oversight, reported that it was skeptical the magnitude 9.0 earthquake by itself caused the catastrophic damage that caused the cores of reactors 1 to 3 to melt.

The commission appointed by the Diet suggested the quake may have damaged the piping of an emergency cooling system called an isolation condenser at reactor 1. The report said several workers on the fourth floor of the building witnessed a water leak on the same floor, which houses two large tanks used by the isolation condenser and its piping, at the time of the quake.

The now-defunct panel also denied the possibility that the tremors caused radioactive water to slosh out of the spent-fuel pool on the fifth floor, although no on-site inspection has been carried out yet.

The third commission was independent and scathing in its findings.