Mammoet’s Creative Stator Offloading Plan Was Well Grounded
July 7, 2021 - Canada produces 82% of its electricity from greenhouse-gas-free sources. Nuclear power accounts for about 15% of Canada’s total electric output.
The Darlington Nuclear Generating Station, located east of Toronto on the shore of Lake Ontario, has been on line since the early 1990s. It generates enough power for two million homes.
Following three decades of plant operation, Darlington’s owner, Ontario Power Generation, announced a 10-year plan to refurbish the facility.
The ambitious project involved the replacement of major components, which will extend the life of the facility for 30 more years. It signifies a commitment to keep Ontario running on a reliable and clean supply of power long into the future.
Mammoet colleagues have been on site at Darlington for close to 40 years, having helped haul heavy components for its construction back in 1982. More recently, as the facility prepares to extend operations to 2055, Mammoet engineers have helped to move a wide range of modules, including heat exchangers, transformers, and generators.
This familiarity with the site allowed Mammoet to view this challenge from an entirely new angle.
A crucial part of the plant’s refurbishment was delivery of an additional stator – a stationary component that helps convert rotational energy into electrical energy. Stators are large and heavy, so delivering one safely requires a lot of logistical planning.
GE was commissioned to manufacture Darlington’s new stator. Assembly took place at its facilities in Poland before the unit was shipped to Canada. GE entrusted Mammoet to transport the precious cargo to Darlington’s East Warehouse, where the stator would be stored.
Sites like Darlington produce electricity by harnessing the immense thermal energy created through nuclear fission. The heat emitted in these reactions is used to heat large quantities of steam, which flows through blades, causing them to rotate.
A shaft connects the blades to large magnets in each generator. When the magnets rotate within copper coils inside the stator, they generate electricity. Over time, heat and vibration cause stators to become less efficient, so they eventually need to be replaced.
Darlington’s new stator began the 4,970-mi. journey from its factory in Poland by rail. It then travelled on a cargo ship across the Atlantic to Lake Ontario.
At the nearby Port of Oshawa, the stator was offloaded onto a barge already loaded with the SPMTs required to carry it onto land. However, disembarking the barge at Darlington posed a serious challenge.
Although the power station was equipped with its own dock close to the generator warehouses, it had not received cargo for several decades. During that time, tons of silt had built up at quayside. As a result, the barge simply could not reach a position parallel with the quay.
The obvious solution was to dredge the dock until the water was deep enough for the barge to dock safely so that the SPMTs could drive sideways off it. But that would’ve added a great deal of extra time and administration to the project.
Permits from local authorities would’ve been required, delicate environmental issues would’ve needed to be considered, and dredging would’ve carried carry a significant price tag. The project needed to be carried out in a tight timeframe following the melting of the winter ice, so delay was not an option.
During their routine site inspection, the Mammoet team - along with local barge operator McKeil - came up with an idea that would eliminate the need for dredging. It was proposed that the stator should be offloaded from the ocean-going transport vessel onto a shallow-draft transport barge for the last water-borne leg of its journey.
The barge could be floated close enough to the quay that 49’ ramps could connect it with dry land - but at a roughly 45° angle relative to the quay edge. These ‘ro-ro’ ramps would allow the Mammoet team to drive their load off the front of the barge and land it over the corner of the quay instead of the side.
To secure the barge in that position, Mammoet’s engineers mobilized two heavy prime mover tractors and a 55-USt counterweight as bollards. Once the barge was safely moored at the Darlington quayside, water would be pumped into the barge slowly, intentionally grounding it.
This extra ballast would allow the barge to settle gently onto the mud below its keel, providing additional stability to supplement this unconventional mooring approach. A dive survey was carried out by the team to confirm that the method was feasible.
The deck of the barge would thereby create a stable platform of similar height to that of the adjoining dockside roadway. The team could then place the ro-ro ramps between the barge and the dockside, allowing access for the SPMT to safely offload the unit and drive it along the route to its temporary home in the site’s warehouses.
The plan was widely acknowledged as a sound and elegant operational solution. With an in-depth insight into the intricacies of the operation, the team confidently executed the load-in and watched as the stator arrived safely in its new home.
“The movement of the generator stator from Poland to our Darlington Nuclear Station’s East Warehouse was our first major lift and material movement for our Unit 3 Darlington Refurbishment Project,” explained Bill Owens, senior vice president, nuclear refurbishment execution, Ontario Power Generation.
“The detailed planning and the expertise in the project execution were truly remarkable. I had the opportunity watch the stator being transported from the barge in Lake Ontario and onto land, then moved into our East Warehouse and it was an impressive display of teamwork and skill by everyone involved.”
This approach ensured delivery of a crucial plant component while preventing ecological damage to the quay and saving on the prohibitive costs of dredging the harbor. Though the approach here was unconventional, Mammoet was able to draw upon both the expertise of its many global engineering centers and the world’s largest fleet of heavy transport equipment to deliver an innovative yet practical solution.