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Following refurbishment, Darlington Unit 2 reconnects to the grid

image credit: Fish-eye view of Unit 2 turbine hall. Credit: Ontario Power Generation
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Journalist Independent Journalist and Analyst

DW Keefer is a Denver-based energy journalist who writes extensively for national and international publications on all forms of electric power generation, utility regulation, business models...

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  • Jun 8, 2020

Ontario Power Generation’s Darlington Nuclear Generating Station Unit 2 reconnected to the grid in early June following a three-year refurbishment.

Unit 2 was the first of four reactors to be refurbished. Work began in October 2016 and involved dismantling and then reassembling the reactor. Major component replacement included reactor fuel channel assemblies and primary heat transport feeder piping.

All 960 feeder tubes as well as 480 channel fuel channels and 480 calandria tubes were removed as part of the project. Safety improvements included installation of a third emergency power generator to provide multiple layers of back-up in case of power loss. Additionally, fire protection systems were inspected and updated to regulatory codes and standards.

Following completion of major work earlier this year, the unit achieved First Criticality in early April. That demonstrated that the reactor could maintain a sustained fission chain reaction to create the heat needed to produce electricity.

Prior to the Covid-19 pandemic, the project team was on track to begin Unit 3 refurbishment in April. Ontario Power decided to defer the planned start and now plans to resume field work in June and begin the refurbishment itself in the third quarter of 2020.

Refurbishment of Darlington 3 is expected to be complete in 2024. Work on unit 1 is to begin in 2022 and unit 4 in 2023, with the entire refurbishment project scheduled for completion by the end of 2026.

The CANDU (Canada Deuterium Uranium) is a pressurized heavy-water reactor design. CANDU reactors were first developed in the late 1950s and 1960s by a partnership between Atomic Energy of Canada Limited, the Hydro-Electric Power Commission of Ontario, Canadian General Electric and other companies.

There are around 30 CANDU reactors in use around the world along with 13 "CANDU-derivatives" in India, developed from the CANDU design. South Korea, China, Argentina, Romania and Pakistan all operate CANDU reactors.




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