The U.S. Department of Energy (DoE) (Washington, DC, USA) is including U.K. company Modular Walling Systems Ltd. (MWS) (Renfrewshire, Scotland, United Kingdom) as part of a new multi-million-dollar funding program to help make advanced nuclear construction faster and more affordable. Their proprietary steel composite system, known as Steel Bricks, features modules that can be manufactured to have different plate material on either side of a wall to better meet certain corrosion requirements in nuclear power plants.
The MWS system is fabricated in the United Kingdom by structural steelworks manufacturer Caunton Engineering (Newthorpe, England, United Kingdom). Hailed as a second-generation steel composite structure, the proprietary system is described by DoE as essentially being “high-tech LEGO pieces,” which could significantly reduce the amount of construction labor required to build nuclear reactors at a given site.
The system is one of three development projects that will be funded by the U.S. DoE’s Advanced Construction Technology (ACT) initiative.1 GE Hitachi Nuclear Energy, a world-leading provider of nuclear power plant technology, is leading a team to explore these technologies and ensure that they are tested to meet nuclear requirements. To that end, Steel Bricks was identified as a major component for GE Hitachi’s next-generation BWRX-300 small modular reactor (SMR), which targets a market estimated to be worth $1.2 trillion globally.
“The Steel Bricks system is a ‘first of a kind’ concept in the fast-emerging world of steel composite construction,” says Stewart Gallocher, founding director of MWS. “It provides not just the walls and suspended floors or roofs in steel composite, but most importantly a basemat. This takes away the need for conventional foundations, eliminating the traditional Achilles heel of this form of construction, which are the weak points of the basemat-to-wall connection.”
“Many attempts have been made during the past 25 years to devise simple, safe, and rapid fabrication methods to internally connect steel faceplates,” he adds. “But most have lacked commercial application, due to being too expensive and labor intensive. We can now successfully deliver a solution which is technologically proficient, all while providing significant cost and time saving benefits. This could mark a major leap forward for advanced nuclear construction in its global drive to become a cost-effective, green, and sustainable alternative to carbon-based energy provision.”
Historically, most buildings and containment structures in nuclear power plants have been built from reinforced or post-tensioned concrete, according to MWS.2 This has placed a heavy reliance on cast, in situ construction, which has led to lengthy site operations to assemble the shuttering and reinforcing steel and strip the shuttering after the concrete cures. Attachments to the walls and floors, which are used to support electrical and mechanical equipment such as piping and cable trays, generally require the installation of embedded steel plates in the walls or concrete expansion anchors into walls, floors, and ceilings.
“Installing embedded steel plates is difficult, because anchor rods and their end plates need to be inserted within very dense reinforcement, requiring the displacement of the reinforcement bars,” MWS explains. “If post-installed anchors are permitted, then this can also be a time-consuming process that involves first locating the reinforcing bars in the concrete to avoid cutting them. This is followed by drilling into the concrete and inserting anchors for bolting steel plates to the concrete surface to attach supports.”
That is where steel-concrete composite (SC) construction comes into play. SC construction, according to MWS, is a form of modular construction that comprises two steel faceplates, which are internally connected to create a sandwich panel. The faceplates provide permanent shuttering during concrete infill pouring, and they also generate strength through composite action, once the concrete has cured.
“Our Steel Bricks system, with trademark diaphragm holes running through the webs, has been assembled in such a way that the concrete is poured through holes in the roof, flowing down the walls and filling the basemat before coming back up the walls and lining the ceiling—all in one continuous pour,” Gallocher says.
Because of their size, small reactors are particularly suited to modularization, with the potential for a repeat volume of standard components. According to MWS, the modular SC construction process eliminates temporary formwork and all that comes with it, such as rebar fixers and lay-down areas. Sourcing an SC modular core through a steelwork contractor also reduces the supply chain, the company explains, and off-site manufacturing in factory-controlled conditions offers more quality control than can often be achieved on site, given weather concerns. The modular panels have the ability to be erected in confined spaces, or from one side.
The MWS modular solution is made by folding two pre-cut steel plates into L-shaped sections, which are joined to form a U shape. The two separate Ls design enables the system to have the potential benefit of a different plate material on either side of a wall, e.g., stainless steel (SS) on one side and carbon steel (CS) on the other. “With Steel Bricks, there are far fewer components and no need for proprietary steels or equipment,” the company explains. “With simple manufacturing techniques, multiple fabricators can be employed simultaneously, thereby speeding up off-site production.”
According to the company, the modules can be manufactured as required for certain parts of a nuclear power plant, where they could provide the required corrosion resistance. Furthermore, there are no bimetallic corrosion concerns, as the CS/SS joint is embedded in concrete.
The U-shaped bricks can be welded together, end-to-end and vertically, to create larger modules. No tie bars or reinforcing bars are required, since these are replaced by the diaphragm, which is integral to the system.
In manufacturing the floor modules, the system can have holes in the top flange, which allows the concrete to rise above the plate to form a concrete finish—similar to conventional reinforced concrete floors, the company explains. Supports for electrical and mechanical equipment can be easily welded to the plate’s external face.
The system has far fewer internal components than many other solutions, according to the company. A standard panel is at approximately 12 m in length, with a depth of 0.8 m and a height of 1.8 m. These cores are slimmer than their concrete counterparts, according to MWS, which increases the lettable floor area and the site’s capital value.
“It offers a much simpler design from a manufacturability standpoint than traditional steel composite structures,” says Brian Johnson, vice president of GE Hitachi and product director for BWRX 300.
Going forward, the DoE funding will allow for the further development of the Steel Bricks system and its application for advanced SMR design. Full-size specimens will be fabricated in the United Kingdom and tested at Purdue University in West Lafayette, Indiana, USA, in late 2021.
“Construction costs and schedule overruns have plagued new nuclear builds for decades,” says Kathryn Huff, acting U.S. assistant secretary for nuclear energy. “By leveraging advanced construction technologies, we can drive down costs and speed the pace of advanced nuclear deployment—much needed steps to tackle global climate change and meet President Biden’s goal of net-zero carbon emissions by 2050.”
Other projects delivered as part of the ACT initiative include vertical shaft construction and advanced monitoring coupled with digital twin technology. The initial phase will focus on technology and development, as well as preparation for a small-scale demonstration, with a goal of delivering completed projects in the next three years.
Additional details on the program and its investments, which is being run through the DoE’s National Reactor Innovation Center, are available at the agency’s web site.
Sources: MWS, www.steelbricks.co.uk; U.S. DoE, www.energy.gov.
1 “Three Ways to Make Nuclear Power Plants Faster and More Affordable to Build,” U.S. Office of Nuclear Energy Articles, July 8, 2021, https://www.energy.gov/ne/articles/3-ways-make-nuclear-power-plants-faster-and-more-affordable-build (Aug. 30, 2021).
2 “Multi-Million Dollar Investment Program Announced for U.K. Steel Construction System,” Modular Walling Systems News Releases, July 8, 2021, https://www.steelbricks.co.uk/News.aspx (Aug. 30, 2021).