Construction of Rostov reactor No. 1 began in 1977 and operations began in 2001. Construction of reactor No. 2 commenced in 1983 and finished in 2010. Unit 3 was connected to the electrical grid for the first time in December 2015.[1] Unit 4 underwent first criticality on 7 December 2017,[2] and put into commercial operation on 28 September 2018.[3] Units No. 3 and 4 are of an upgraded VVER-1000/320 subtype.[4]