Tokyo Electric Power Company restarted Reactor No. 6 of the Kashiwazaki-Kariwa Nuclear Power Plant in Niigata Prefecture on January 21.

The plant, which is the largest nuclear generating station in the world by net electrical power according to Niigata Prefecture, is the first one to be restarted by TEPCO since the March 2011 Fukushima Daiichi nuclear disaster.

Reactors at Kashiwazaki-Kariwa Nuclear Power Plant were shut down in March 2012 following the March 11, 2011 nuclear accident that was triggered by Magnitude 9.0 earthquake and tsunami.

Reactor No. 6 was originally scheduled to be restarted on January 20. However, an alarm system failure had postponed the restart.

It was restarted at 7:02PM on January 21.

TEPCO said that the reactor reached criticality at 8:28PM , where a self-sustaining nuclear fission reaction occurs.

Commercial operation of the reactor will begin on February 26 after checking the integrity of its turbine and generator.

Concerns and opposition to restarting the plant remain as TEPCO was responsible for the unprecedented nuclear accident and subsequent scandals.