Canada’s Bruce Power will go ahead with refurbishment of six reactor units at its Candu nuclear power plant in Ontario, after signing an amended "multi-year investment" agreement with the province’s Independent Electricity System Operator (IESO), which is governed by an independent board, whose chair and directors are appointed by Ontario’s government.

The agreement is due to come into force on 1 January 2016, and will allow Bruce Power to "immediately invest in life-extension activities for units 3 to 8 and support a long-term refurbishment programme that will commence on unit 6 in 2020, optimising the operational life of the site."

Ontario’s energy ministry said the contract means refurbishment work will begin in 2020, rather than the previously estimated schedule of 2016, to "maximise the value" of existing units. Bruce Power will invest around $13bn of its own funds and will take full risk of cost overruns .

"Bruce Power will bear the risk of delivering these projects on time and budget with upside sharing for better than planned performance with the IESO. The price of these refurbishments will be finalised prior to each project through a defined, transparent process in the agreement," it said.

It is estimated the six refurbishments in the agreement will cost about $8bn, in addition to $5bn in a range of other life-extension activities from 2016-53. In the short-term, between 2016 and 2020, the company will be investing about $2.3bn as part of this plan. The refurbishment of each unit will add about 30-35 years of operational life, while other life-extension investments will add a combined 30 reactor years of operational life to the units, pre-refurbishment. Bruce Power said this approach "provides additional benefit in terms of sequencing refurbishments and optimising asset life."

In 2005, Bruce Power entered into the Bruce Power Refurbishment Implementation Agreement to enable the restart of Bruce units 1 and 2, to return the site to its full operating capacity of eight units (6300MW). This has allowed Ontario to phase out coal-fired power generation.

The company said it is Ontario’s lowest cost source of nuclear, currently generating over 30% of the province’s electricity at 30% below the average residential cost of power. Extending the operational life of the Bruce Power units will ensure Ontario families and businesses have long-term price stability, it added.