Bruce Power has started loading fuel into its Unit 6 reactor in its work to return the unit to service.
The project is on track to resume service later this year.
Unit 6 is the first of six units that will be refurbished between 2020 and 2033.
As Bruce Power is looking to get the unit back online, the Canadian Nuclear Safety Commission has approved the loading of fuel into the reactor core for the first time in almost four years.
The 480 fuel channels will be refueled with 5,760 fuel bundles over the next few weeks.
The fuel bundles produce the same amount of electricity as 40,000 kg of coal or 400,000 cubic metres of natural gas.
After the fuel bundles are loaded, it will be followed by the heat transport system fill and pressurization, as well as other lead-out activities.
Once inspections are completed, Unit 6 will return to the electricity grid in the fourth quarter of this year.