One of the world’s largest nuclear facilities recommenced operations on January 21. The Tokyo Electric Power, or TEPCO — the same utility that operated the Fukushima plant — restarted the first reactor, Unit 6, at its Kashiwazaki-Kariwa complex in Niigata Prefecture on the main South island, reports The New York Times. The restart was delayed by a day after a safety alarm failed to sound during a test over the weekend. 

Fifteen years ago, an 8.9-magnitude earthquake sent a tsunami crashing into the coastline of Japan, and disabled the power supply and cooling of three reactors at its Fukushima Daiichi power plant, causing a nuclear accident that saw all three cores largely melted in the first three days. Japan shut down all its 54 reactors in the wake of the 2011 disaster.

The Times says Japan, like many others, is turning to nuclear power to meet massively increased demand for carbon-free, round-the-clock electricity to power chip factories and the data centers needed for artificial intelligence. As a result, the world’s fourth largest economy is accelerating the pace at which it is restarting reactors that have been mothballed for more than a decade.

Read More: To Support AI Development, the U.S. Needs to Rebuild Its Domestic Uranium Supply Chain

Before the Fukushima disaster, Japan had one of the world’s most extensive nuclear programs but, since the accident, only 15 of its 33 operational reactors have restarted, largely because of a rigorous approval process from local and prefectural governments.