Darlington nuclear unit 1 offline for last planned O&M outage prior to 2022 refurbishment

Photo courtesy Ontario Power Generation

By Rod Walton, Power Engineering & POWERGEN+ content director

The tireless Darlington Nuclear Generation Station’s Unit 1 is getting a short break prior to its upcoming makeover.

Earlier this month, Ontario Power Generation took Darlington Unit 1 offline for a planned inspection and maintenance outage. These outages typically take a couple of weeks, much shorter that used to be norm.

Brevity, however, is not the reactor unit’s norm these days. Last September, the 878-MW  Darlington Unit 1 set a record for continuous operation of a nuclear power reactor when it went 963 days without a stoppage. It’s last time offline prior to that was January 26, 2018.


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“Unit 1’s record-setting run highlights the excellent work carried out by our dedicated nuclear professionals throughout the pandemic to ensure Ontarians and front-line workers battling COVID-19 can count on a steady supply of power 24 hours a day, seven days a week,” said Sean Granville, OPG’s Chief Operating Officer. “It also highlights the effectiveness of our preventive maintenance programs, and the overall reliability of our nuclear fleet.”

The outage team will now inspect Unit 1’s equipment, including fuel channels, and carry out maintenance in areas that aren’t normally accessible during unit operation. The outage scope also includes upgrading the unit’s reactivity control systems and completing preparatory work required prior to refurbishment.

The current planned outage is the final inspection and maintenance break before Darlington Unit 1 gets a refurbishment in 2022.

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That project is part of a 10-year upgrade plant announced by OPG several years ago. Units 2 and 3 were the first to be taken offline for a refurbishment expected to take about three years each.

Under the plan, the Darlington units are shut down, defueled and islanded to disconnect the reactor from the rest of the plant. What follows include containment pressure testing, disassembly of feeder tubes, the fuel channel and the Calandria tube, which is made of zirconium and surrounds the pressure tube to form a tight leak seal of the vessel.

Prior to Darlington Unit 1’s record-setting operational run, the previous record was 962 days set by the Kaiga power station in India more than two years ago.

All four of Darlington’s nuclear reactor power units were commissioned in the 1990s. Together they offer than 3 GW in carbon-free generation capacity and operate with CANDU pressurized heavy water reactors (schematic pictured here).

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(Rod Walton is content director for Power Engineering, POWERGEN International and the online POWERGEN+ series which resumes next week with sessions focused around utility workforce, operations and maintenance and asset management. He can be reached at 918-831-9177 and rod.walton@clarionevents.com).

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