Tackling a tight fit at the Darlington Nuclear Generating Station

Darlington nuclear

AGF Access Group helps refurbishment efforts at the Darlington nuclear site access a challenging and time sensitive space

The Montreal-based AGF Access Group was recently recruited to help access a difficult space at Ontario Power Generation’s (OPG) Darlington Nuclear Generating Station.

Under its Winsafe brand, AGF was hired to provide a modular access solution for Canada’s largest clean energy project. 

The Darlington Nuclear Generating Station, located in Bowmanville, Ontario, is currently undergoing refurbishment. 

The project is joint venture led by SNC-Lavalin Group and Aecon Group.  

Part of the Darlington Nuclear Generating Station refurbishment requires the removal and replacement of 960 feeder tubes within each of the reactors’ cores. Each tube weighs up to 270 kg. In order to reach and replace the upper feeder tubes, the workers need safety and efficiency. 

Winsafe engineers created a new platform concept to meet the challenge of the constricted space and time constraints of the reactor core. They fabricated an extruded aluminum, lightweight, modular platform system that could quickly and easily be assembled by workers. 

“We never say no to projects, but when we first looked at the details of the Darlington refurbishment, it was a challenging request,” said Alex Di Domenico, vice president of major projects for AGF Access Group.

“Although the access portion was just a small piece of the overall puzzle, the project had unusual needs and traditional access equipment was not going to be the answer.”

New approach needed for Darlington

Historically for accessing this type of job, workers would weld steel platforms together while inside the reactor vault to make access feasible, and then later cut them out.

However, that approach was problematic at the Darlington Nuclear Generating Station due to limited space and access. Within the reactor vault, the extremely constrained space left little room for workers in bulky protective equipment to efficiently build and remove a high-capacity work platform to access the four-sided matrix of feeder tubes.

“Keeping the workers safe was our primary consideration. We also needed to be sure to minimize exposure to the radiation dose as much as possible,” said Emmanuel Piec, general manager of Winsafe. 

“We needed a design that would allow them to quickly put together the feeder platform without struggling with nuts and bolts in their protective gloves. By making the platform modular and almost completely tool-free, they could get it into place in the tight space quickly and safely.”

The two platforms, each consisting of two independent rectangular halves measuring roughly 9 metres in length and 6 metres wide, provide access to the faces of the two-sided reactor. 

Each platform has a weight capacity of 2,268 kg to support multiple workers and their tools, while they maneuvered and fit the tight and exacting tolerances for work with the heavy feeder tubes. 

A tight fit

The platform main structure, suspended from a series of fixed and relocatable steel rod hangers, needed to fit into an area that was only 23 cm deep, including peak deflection at maximum load.

The spans between platform hangers needed to be maximized, in order to minimize impeding movement of the long feeder tubes across the platform working surface. 

From the platform, the workers could remove and replace each of the tubes, using existing station mezzanines to get on and off the platform, and temporary step-up platforms as needed to reach the higher tubes. Feeder tubes and other materials were brought to the working area through a hoist-way located between the two corresponding platform halves.

“The space constraints surrounding this job were extremely challenging, but we came up with a solution which worked, and worked well,” Di Domenico said. “Given our experience in the nuclear industry, and our reputation for engineering ingenuity, we are a good fit for the project’s small, but crucial access challenge.”

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The feeder tubes in the first Darlington reactor were successfully removed on time and on budget, and most importantly, safely. 

As well, the design of the feeder platform was such that it could be easily dismantled and reassembled at the next reactor to do the same job.

OPG’s Darlington Refurbishment project, which began in October 2016 and involves the refurbishing of all four units, is scheduled for completion in 2026. 

The Darlington Nuclear Generating Station is one of the best-performing nuclear stations in the world. According to the Conference Board of Canada, the nuclear power station’s continued operation to 2055 will take the equivalent of two million cars off the road and will generate a total of $89.9 billion in economic benefits.