Montreal-based AGF Access Group, Inc. has been selected to provide a modular access solution manufactured under its Winsafe brand for Canada's largest clean energy project: the Ontario Power Generation's (OPG) Darlington Nuclear Generating Station in Southern Ontario, a joint venture refurbishment project led by SNC-Lavalin Group, Inc. and Aecon Group, Inc.
Part of the Darlington Station refurbishment requires the removal and replacement of 960 feeder tubes within each of the reactors' cores, with each tube weighing up to 600 pounds. 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.
Alex Di Domenico, Vice President, Major Projects said: "We never say no to projects, but when we first looked at the details of the Darlington refurbishment, it was a challenging request. 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."
Historically for accessing this type of work, workers would weld steel platforms together while inside the reactor vault to make access feasible, and then later cut them out, but that approach was problematic in this environment with 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, 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 30 feet in length and 20 feet wide, provide access to the faces of the two-sided reactor. Each platform has a weight capacity of 5,000 lbs. to support multiple workers and their tools while they maneuver and fit -up the tight and exacting tolerances for work with the heavy feeder tubes.
The platform main structure, suspended from a series of fixed and relocatable steel rod hangers, needed to fit into an area that was only nine inches 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 hoistway 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," said Di Domenico. "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."
The feeder tubes in the first reactor were successfully removed on time, on budget, and most importantly, safely. Additionally, 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. Ontario Power Generation's (OPG) Darlington Nuclear Generating Station is one of the most 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.