Two years ago, Japan shut down all of its nuclear reactors. On Tuesday morning, one of them kicked back into gear.

Japan imposed a ban on nuclear-power generation in September 2013 in response to the meltdown of several reactors at the Fukushima Daiichi plant following a devastating tsunami in 2011. The nuclear disaster spewed radioactive materials into the air and nearby water, and forced 100,000 people to evacuate their homes.

The disaster was the worst since the Chernobyl explosion in 1986, and it led Japanese regulators to rethink safety standards for the nation’s more than 40 commercial nuclear reactors. The reactor that restarted Tuesday, at the Sendai Nuclear Power Plant in southern Japan, is the first to come back online since officials announced new standards in June 2013.

The Sendai reactor will start generating electricity by Friday, according to the plant’s operator, Kyushu Electric Power Company. It will reach full capacity by the start of next month. Its relaunch opens the door for other utility companies to apply to restart reactors, and applications for 25 reactors at 15 plants have already been submitted. But they face a long and expensive process—more than $100 million was poured into the Sendai plant to meet regulation requirements.