The reactor core of Darlington 2 in Canada has now been rebuilt, owner and operator Ontario Power Generation (OPG) has announced, celebrating the installation of all its fuel channels. It is the first in a programme of ten reactor refurbishments.

Workers celebrate the rebuilding of Darlington 2's core (Image: OPG)

Candu reactors feature a large horizontal calandria vessel with 480 tubes through which cooling water flows at high temperature. Each one has two end fittings which allow it to be isolated so the fuel bundles it contains can be replaced without having to shut down the whole reactor. Refurbishment to prolong the life of the power plant requires all this as well as thousands of auxiliary components to be dismantled.

"Fuel channel installation, and the planning and coordination necessary to complete it in an efficient way, was extraordinarily challenging," said Mike Allen, OPG senior vice president for nuclear refurbishment.

"We literally had to rebuild the reactor core to the highest safety and quality standards," said Allen. "We couldn’t have done this without a strong and integrated OPG-CanAtom team."

The rebuilding work started in June 2018.

The Organisation of Canadian Nuclear Industries said that now the fuel channels had been installed, feeder installation in unit 2 continues. The next steps include loading fuel in the third quarter of this year and bringing systems back into service so that the unit can restart in early 2020. The planned refurbishment outage sequence at Darlington 2 is to be completed before the start of work on unit 3, to allow the implementation of lessons learned. OPG plans to start work on unit 3 in February 2020, on unit 1 in July 2021 and unit 4 in January 2023.

Ten reactors are being refurbished in a joint effort by the Canadian nuclear industry. All ten refurbishments - which require approval from the government of Ontario, the owner of OPG and therefore the reactors - are to be completed by 2033.