Darlington Nuclear’s newly refurbished Unit 1 now producing life-saving Cobalt-60 isotopes
At a glance
- The recently refurbished Unit 1 reactor at OPG’s Darlington Nuclear Generating Station is now producing critical life-saving Cobalt-60 isotopes for the world.
- The medical isotope is used to sterilize 30% of the world’s single-use medical devices, as well as certain food products.
- OPG plans to modify Darlington’s three other units to allow them to also produce the isotope to help secure a stable, reliable global supply.

Newly returned to service from refurbishment, Darlington Nuclear Generating Station’s Unit 1 is once again generating clean, low-carbon power for Ontario – and now producing life-saving Cobalt-60 medical isotopes.
During refurbishment activities, OPG made modifications to the unit to allow it to produce the critical medical product, which is used to sterilize 30% of the world’s single-use medical devices, such as syringes, gloves, and implants. The isotope is also used to treat certain foods to rid them of harmful bacteria and insects, providing safety and security for the global supply chain and consumers around the world.
Darlington’s three other units will be similarly modified over the course of the refurbishment of Unit 4, the final unit to be overhauled in the Darlington Refurbishment project, as well as during planned maintenance outages on Units 2 and 3.
What is an isotope? Isotopes are nuclear species of the same chemical element, with specific properties that may be of use for varying applications. Think of it like the various trims of a specific car make and model. Several isotopes, including Cobalt-60, are created in OPG’s nuclear stations and offer important medical and industrial applications due to their ability to emit high-intensity gamma rays. About 40 million nuclear medicine procedures are performed each year with the help of isotopes. |
After three years of activation in the Unit 1 reactor, Darlington’s new supply of Cobalt-60 will be harvested during a maintenance outage and delivered to Nordion, an Ottawa-based health sciences company, to be packaged and distributed to gamma sterilization facilities around the world.
For decades, Ontario’s CANDU reactors and their production of Cobalt-60 isotopes have helped ensure a healthier and safer quality of life for millions around the world. We are now proud to continue this legacy at our Darlington Nuclear station, which will be a critical source of this invaluable product for decades to come.Nicolle ButcherPresident and CEO, OPG

Currently, about 50% of the world’s Cobalt-60 is supplied by Ontario’s nuclear reactors, with the isotope being first produced in the province in 1971 at OPG’s Pickering Nuclear Generating Station. Darlington’s new capability will ensure a stable and reliable supply of Cobalt-60 for the world as Pickering ends commercial operation in the coming years and prepares for its potential refurbishment, while also supporting growth in demand.
“Cobalt-60 is essential to the safety of the healthcare industry and to our mission of Safeguarding Global Health®,” said Riaz Bandali, President of Nordion. “OPG has been a trusted partner in this mission for more than 50 years, and we are proud of what we have accomplished together at Darlington.”
“OPG's production of Cobalt-60 represents an important contribution to medical sterilization and cancer treatment,” added Kirsten Burgomaster, Health System Executive at Lakeridge Health and Regional Vice President of the Central East Regional Cancer Program. “This initiative supports Lakeridge Health’s commitment to patient safety and high-quality care across Durham Region. It highlights the ongoing role of nuclear energy in enhancing public health, from patient care to cancer therapy.”
Cobalt-60 is just one of several isotopes OPG produces to help support the well-being of society.
OPG subsidiary Laurentis Energy Partners currently produces Molybdenum-99 isotopes at Darlington’s Unit 2 using a proprietary Target Delivery System, designed and commissioned in partnership with BWXT Medical, that allows harvesting of the isotope while the reactor is still in operation. Molybdenum-99’s decay product, Technetium-99m, is used in more than 40 million medical procedures each year to detect illnesses like cancer and heart disease.
Laurentis soon hopes to use the same system to produce Yttrium-90 isotopes, a potentially life-saving product instrumental in treating several diseases, primarily liver cancer.
From the mine to hospitals: How Cobalt-60 is produced

- The Cobalt-60 life cycle begins with the mining of Cobalt-59, a naturally-occurring non-radioactive material. The element is removed from the ground and processed into pure Cobalt-59 powder, which is then compressed into slugs.
- These slugs are assembled into bundles to form Cobalt adjuster rods, which are then shipped to OPG’s Darlington Nuclear station.
- Here, the rods are inspected before being loaded into the reactor core of Darlington’s Unit 1. During a planned maintenance outage of the unit, Cobalt adjuster rods are placed into the reactor core.
- This unit has been converted to use Cobalt adjuster rods, rather than stainless steel rods. Adjuster rods serve a vital function and are part of the Reactor Regulating System.
Workers prepare to clean a shipping flask loaded with Cobalt-60 bundles at Pickering Nuclear GS. - Over the course of about 36 months, the rods are bombarded by neutrons in a process called irradiation and the Cobalt-59 changes at the atomic level to become Cobalt-60.
- During a unit outage, harvesting of the mature Cobalt-60 adjuster rods begins.
- The irradiated rods are carefully extracted using special equipment and loaded individually into a protective flask container.
- The loaded flasks are then transported from the reactor building to the irradiated fuel bay, which looks like a large swimming pool.
- Each Cobalt-60 adjuster rod is then removed from its flask and carefully lowered into the fuel bay to be inspected, measured, and organized into Cobalt-60 bundles.
Cobalt-60 produced at OPG's nuclear stations is used to sterilize medical equipment. - Finally, the Cobalt-60 bundles are loaded underwater into a shipping flask, a purpose-built flask for transportation of Cobalt-60, which is then craned out of the bay and into a decontamination room, where it is dried and purged with argon gas.
- Now ready for shipping, the prepared flasks are loaded onto a trailer and delivered to the processing facility at Nordion, an Ottawa-based health sciences company. Here, the Cobalt-60 is processed for industrial or medical use and shipped to the customer.
How does Cobalt-60 benefit healthcare?
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