The older four units are small-sized pressurized heavy water reactors of 220 MW gross.

[3] On 19 January 2011, unit 4 with 220 MW capacity was connected to the southern power grid at 01:56 hours.

The unit, fueled by indigenous uranium, will supply electricity to Karnataka, Andhra Pradesh, Kerala, Tamil Nadu and Puducherry.

[4] In December 2018, it got the distinction of setting a world record of continuous operation among all nuclear power plants.

As on 10 December 2018, KGS-1, which was synchronized to India's Southern grid on 13 May 2016, continues to operate for a record number of 962 days.