Navigating the intricacies of a nuclear reactor building is no small feat, especially when it comes to large-scale maintenance and engineering. These buildings, often several decades old, pose significant challenges for engineers. Originally constructed with minimal thought to the removal of massive internal components, their outdated designs now require meticulous planning, careful collaboration, and innovative solutions to meet the strict safety standards of nuclear facilities.
Mammoet, a company specializing in heavy lifting and transport solutions, was called upon five years ago by Framatome, a leader in nuclear technology, to assist in the complex task of removing and replacing four steam generators from nuclear power plants in France. This marked the beginning of a five-year challenge that would push the boundaries of precision engineering and demonstrate the strength of careful planning and execution.
One of the primary hurdles in this operation was the necessity to remove these generators in one piece, given the risk of contamination. Additionally, removing the generators intact meant less downtime for the power plant—a critical factor in nuclear operations. However, the challenge lay not only in the weight of these massive components—each generator stretching 25 meters in length, 6.5 meters in diameter, and weighing a staggering 520 tons—but also in the confined spaces of the reactor buildings themselves.
The polar crane, the main piece of equipment used for such operations inside nuclear reactors, lacked the capacity to lift the steam generators on its own. As a result, Mammoet’s team, consisting of experts from France and their main engineering offices in Schiedam, Netherlands, had to design a unique set of handling equipment. This set-up needed to maneuver the massive generators safely and efficiently within extremely tight tolerances, often within mere hundreds of millimeters.
Olivier Vanesse, Nuclear Activities Manager and Project Director from Mammoet France, shed light on the complexity of the task: “The facilities and infrastructures inside the reactor buildings are such that you cannot simply make a basic tailing operation. You need to be able to steer the steam generator, you need it to rotate. There are a number of steps that need to happen in order to move each of them through the main hatch. So that’s a difficult operation.”
To address these challenges, Mammoet developed a four-part system: a lifting trolley installed on the polar crane for lifting and tailing, a supporting mast to reinforce the crane, a device for down-ending and tailing the generators, and skidding tracks for maneuvering the generators in and out of the reactor building. Due to the complexity and unprecedented nature of the task, this equipment had to be designed, prototyped, manufactured, and rigorously tested to meet stringent regulatory standards set by EDF, the operator of these nuclear plants.
Adding another layer of sophistication to the project, the team utilized advanced 3D computer-rendered models of the reactor building. These models allowed them to virtually navigate the site, taking precise measurements and adjusting their designs accordingly. “The 3D scans were really useful to us and very accurate,” said Olivier. “We had scans, as well as high-resolution photos, and were able to make virtual visits to take measurements and see the equipment going inside the reactor building.”
This detailed preparation led to the successful completion of the first project at Flamanville FA1, validating the efficiency of Mammoet’s equipment and procedures. The innovative approach not only showcased their engineering prowess but also set a precedent for future maintenance operations in France’s nuclear power plants. With this success, Mammoet and Framatome have established a reliable method and specialized equipment to handle the complex replacement of steam generators, ensuring continued efficiency and safety in one of the world’s most challenging engineering environments.