The project involves replacing the plant’s steam generators and will add approximately 1,000 temporary jobs to the region.

The construction program will generate a total of approximately $300m in local spending, including wages, equipment, material and services purchased from local businesses, the company said.

SCE chairman and CEO Alan Fohrer said that the company decided to replace the plant’s steam generators when a cost-benefit assessment revealed the plan could save customers about $1bn during the plant’s current license period, which runs through 2022, when power generated by the plant was compared to the likely cost of replacement power.

Each new steam generator is 65ft tall, 22ft in diameter and weighs 640 tons, and the components produce steam that drives the plant’s huge turbines, generating enough electricity for about 1.4 million average homes.

The Unit 3 construction outage will last three to four months and will include steam generator replacement, refueling and maintenance.

Unit 2 is expected to continue normal operations during construction work on Unit 3.