Engineering firms SNC-Lavalin and Aecon have teamed up on a $600 million contract from the Ontario government to refurbish the Darlington nuclear power generating station.

Ontario Power Generation or OPG, the agency responsible for maintaining Ontario's power grid, announced the contract on Thursday. The job consists of eventually upgrading all four reactors at the Darlington facility.

The first phase of the contract involves planning how to remove 480 pressure and calandria tubes, along with 960 feeder pipes that run at the reactors. Phase two will be putting the plan into action.

The four reactors at Darlington have reached roughly half of their useful life, and the upgrade could give them several more decades of power generating potential.

Darlington now powers one out of every five homes in the province, but OPG wants to expand capacity at the site that could eventually see all four reactors putting out more than 5,500 megawatts of power — far and away the province's largest single power source.

The Darlington reactors are Candu technology, originally made by Atomic Energy of Canada Ltd., which SNC-Lavalin bought from the federal government last year. As soon as that deal was signed, SNC-Lavalin signed another deal to refurbish another Candu reactor, in Argentina.

The company is now waiting on another Ontario contract to possibly build two new Candu reactors elsewhere Ontario. There's no word when that decision will be made.

Work at Darlington is expected to begin in 2016 and create about 6,000 jobs, OPG said in a release.