Pilgrim Nuclear Station began powering down Sunday morning so that it can refuel for the last time.

According to a station spokesman, Entergy is investing $54 million during the refueling outage and bringing in more than 800 temporary workers to assist the plant’s 620 full-time workers. They plan to “upgrade, replace and inspect hundreds of pieces of equipment,” Pilgrim spokesman Patrick O’Brien said.

“Operators at the Pilgrim Nuclear Power Station have commenced power reduction, marking the start of the facility’s biennial and final refueling outage. This is the 21st and final refueling outage at Pilgrim,” O’Brien said in a statement.

It’s not clear when the plant will power up. Pilgrim is scheduled to shut down for good on May 31, 2019.

Citing the plant’s record and rating by the Nuclear Regulatory Commission, critics of the plant have been repeatedly calling for it to close down.