Aluminium Seals in a Nuclear Plant

Aluminium can be used to envelope many things—including old nuclear reactors.
7 April, 2017
Almost 60 years ago, the United Kingdom built the Bradwell nuclear power station near Dengie, along the Essex seacoast east of London.
The Bradwell facility generated power for decades, but ceased operation in 2002 and began a long decommissioning process scheduled for completion in late 2018.

The Bradwell site has a special role in the nuclear power industry, because it's considered a "lead and learn" site for understanding the best practices to decommission plants and the process behind their phase-out. It's not something that's usually top of mind for the public, but behind the scenes are experts grappling with how to close down and replace old nuclear plants. Scott Raish, the closure director at Bradwell, has noted that it's the first of its kind. There's never been a road map needed for that before, but now first-generation nuclear facilities all over the world are being replaced with new utilities.
What that means for the industry is that Bradwell is categorized as a "safe store," which keeps the decaying material in place while avoiding the costs of radioactive waste disposal and facility removal.

At Bradwell, the 60 TWh of electricity produced during the facility's lifetime now means at least 80 years of standing silent and still. It will take decades for radiation levels to decay naturally, so Magnox – the reactor operators – have to prepare and seal the site. Part of that process involved wrapping reactors and related site buildings in a giant aluminium cocoon that is designed to last for the next century.
The metal-envelope sheets are 40 meters high, 40 meters deep and run 85 meters long. They are made of a weathertight aluminium cladding manufactured by Kalzip, installed by more than 900 workers who managed 28,000 individual fittings on the behemoth project.

The aluminium sheathing, according to nuclear energy contracting specialist Mott McDonald, will protect the neighboring Essex communities and the environment from an "unpredictable" decay process. In what is essentially a case study for the industry, aluminium sheets also will seal off the now-decontaminated pond cooling and storage systems.
The pond cleanup alone took four years, and illustrates the methodical and precise work involved in the stages of decommissioning Bradwell. A 3D laser scan assessment first was completed to produce a model of the existing 30-hectare site, accurate to within a millimeter, to ensure the sheathing will work.

The assessment looked at the structural integrity of the existing buildings, and how adding aluminium envelopes would hold up under heavy snow or wind. Engineers also looked inside too, checking to see how a permanent aluminium shield would impact the interior and its contents – buildings that will be shrouded for the span of a few human generations before it will one day be safe for their demolition.
The design challenge included a need to keep future workforce needs to a minimum and reduce the need for ongoing maintenance. So the aluminium sheathing system at Bradwell also relies on a passive ventilation system that will reduce condensation, and the risk of corrosion, so that the buildings will only require an inspection every five years. Security needs will remain throughout the life of the project.

A similar solution is planned for a second Magnox facility in Scotland, which historically has relied heavily on nuclear power generation. The Hunterston A power plant – opened by Queen Elizabeth in the same construction era as Bradwell – also is in the process of decommissioning.
Banner image: Maldon Standard