Going modular11 July 2019
Delivering a new generation of reactors will require a host of innovative techniques and advanced technologies, including modular manufacturing, as Miguel Garcia and Tim Chapman explain.
THE CURRENT GENERATION OF GIGAWATT-scale nuclear new build projects face significant hurdles in financing and delivery, so attention has turned to new kinds of nuclear reactor that promise to reduce cost and risk.
These include small modular reactors (SMR), based on existing Generation III+ technology but a fraction of the size. They also include new designs of advanced modular reactor (AMR) covering a range of Generation IV technologies — salt and lead-cooled reactors; small high-temperature reactors for off-grid and industrial co-generation use; and compact tokamaks for nuclear fusion.
The one thing that all these designs have in common is that they are modular. The reactors and their surrounding systems are designed to be made in factories as large assemblies, which are shipped to site and fitted together with the minimum of fuss. As well as reducing construction risk and helping deliver new power stations to schedule and cost, modularisation should allow the supply chain to use lessons learned from other sectors to drive down costs, and exploit new manufacturing techniques that are not approved for current reactor designs.
Off-site modularisation techniques are widely used in other safety-critical industries, but adapting them for nuclear applications will require intensive development to prove to regulators that they do not introduce any additional safety risks.
The Fit For Modules (F4M) project was designed to lay the groundwork for adopting off-site modularisation across the nuclear sector. Supported by the UK government through the Nuclear Innovation Programme (NIP), the project was led by shipbuilder Cammell Laird with support from the Nuclear Advanced Manufacturing Research Centre (Nuclear AMRC) and industry partners including Arup, Laing O’Rourke, Frazer-Nash Consultancy and Westinghouse.
The initial phase of the project, completed in 2018, set out how modularisation can reduce project risks and costs while improving quality and safety. The team also produced a roadmap of how modular construction techniques could be developed to support new reactor designs.
Modularisation requires the capability and capacity to deliver modules complete with all electrical, mechanical, piping, control systems and structural elements, which can be fully commissioned and validated before they are delivered to site.
In contrast, current new projects rely on on-site build, which can drive costs up by limiting productivity and introducing construction site risk. Schedules are often at the mercy of external factors such as the weather.
Modularisation can avoid many of these problems. In one example studied by the F4M team, partially building a storage tank farm off-site was estimated to save 40% compared with constructing the entire facility on-site.
Complex modules will increase the scope for innovative approaches throughout the supply chain. If the specifications for modules are based on functionality and system performance, rather than detailed specifications for each component, top-tier suppliers can propose solutions that use new ideas and approaches. Developing module designs in parallel will also allow small suppliers to deliver innovative solutions that help reduce lead-time and cost.
At the start of the F4M collaboration, Nuclear AMRC led an investigation into the principles of modularisation, covering six core areas of a product life cycle: design, manufacturing, operations, maintenance, disassembly and disposal.
Each of these areas can benefit from modularisation. The most successful modularised systems are those that have embraced a modularised philosophy from initial concept design onwards. The key lies in defining the design parameters that determine how modules will fit together, connect and communicate. These interfaces depend on coupling and cohesion.
Coupling refers to the degree of interdependence between the modules. Two modules are considered to be coupled if, for the overall system to work correctly, a change to one module requires a change to the other. Good modular design requires that coupling is minimised. Cohesion refers to how tightly bound the internal elements of the module are to one another. Greater cohesion should reduce coupling, and the design should aim to maximise cohesion from the start. This can be challenging, and one of the goals of F4M was to assess the practical obstacles to effective design for modularisation.
A system with high cohesion and low coupling will minimise the complexity of the interfaces between modules, permitting easier maintenance and disassembly. Modules can also be upgraded during service, simplifying maintenance and reducing through-life costs.
There are potential pitfalls and obstacles. Modularisation can increase design cost, due to the attention that has to be paid to interfaces between modules that will be manufactured by different partners. It can reduce flexibility in construction management, and introduces a risk of damage to assemblies during transport to site.
Modularisation also requires a strong supply chain.
If suppliers are unable to meet the requirements for on-time delivery of complex systems with fine design tolerances, project schedules can be hit hard. Small errors in manufacture can drive up costs if modules have to be transported back to the factory for rework.
Roadmap for modules
F4M researchers at Cammell Laird and Nuclear AMRC hosted a series of industry workshops to address the challenges associated modular construction, as regards people and culture; process and methods; and technologies and techniques. They consulted end users, government, regulators and project financiers to assess the challenges associated with large capital projects.
To better understand the regulatory issues around modular construction, consortium members Laing O’Rourke and Arup assessed the safety case implications in a potential loss-of-coolant accident, with independent peer review by Frazer-Nash.
The resulting roadmap identified a need for R&D projects to develop capabilities and understanding in seven areas:
- Structures — design for manufacture, mechanical handling, intelligent fixtures and asset tracking.
- Processes — design for assembly, control & instrumentation, fluid mechanics, certification and post-transfer validation.
- Digitally-enabled quality assurance — design and formulation of an end-to-end digital platform, with virtual and augmented reality connectivity, to underpin the quality assurance requirements.
- Concurrent engineering — to develop and demonstrate the processes.
- Leadership assessment — with competence framework and collaboration programme.
- Infrastructure delivery — with participation of the Institution of Civil Engineers’ cross-sector ‘Project 13’ initiative.
- Transport — to optimise processes and infrastructure for dispatch, transit, receipt and installation.
These pilot studies should be followed by a year-long scale-up phase, to identify any remaining capability gaps and establish a supplier quality oversight group to ensure the supply chain can consistently meet all quality assurance requirements. A final roll-out phase should then provide further development of key programmes, including risk and opportunity management.
F4M is one of the projects funded by the NIP, the UK’s first public investment in future nuclear fission for a generation. In the first phase, announced in late 2016 and now nearing completion, government’s Department for Business, Energy and Industrial Strategy committed £20 million to develop advanced manufacturing and materials capabilities and support the development of new advanced reactors. A second phase of projects is due to be announced soon.
Two other NIP projects led by the Nuclear AMRC are developing new tools and techniques that could halve the production time and cost for pressure vessels and other large components for new designs of reactor.
The ‘Simple’ project (Single Manufacturing Platform Environment) aims to integrate a range of machining, fabrication and inspection operations onto a single manufacturing platform. Doing more on one machine will reduce the need to move large components between work areas, helping ensure accuracy and quality control throughout the manufacturing process.
In the first phase, the Nuclear AMRC team have worked with partner organisations to successfully demonstrate an integrated welding and monitoring tool. Combining a range of sensors with a mechanised arc welding head, the tool will allow automated in-process inspection of welds, improving quality and reducing the risk of weld failure. The team
and industry and research partners are also addressing a series of challenges in forming, machining and assembling large components and modules through the Inform project (Intelligent Fixtures for Optimised and Radical Manufacture).
Recent work involves new techniques to scan raw components shaped by forging or near-net processes, and using the data to generate optimised toolpaths and ensure perfect alignment during machining. The team is also developing conceptual designs for future factories that could significantly reduce cost and lead times for major nuclear assemblies.
The centre has also played a key role in other advanced manufacturing and materials research funded by the first phase of NIP, including a study of advanced joining technologies led by Frazer-Nash, and the Mattear project (Materials and Manufacturing Technology Evaluation for Advanced Reactors) led by Wood.
Other work at the company includes a collaboration with the US Electric Power Research Institute (EPRI). The four-year project, funded by the US Department of Energy and with industrial partners on both sides of the Atlantic, aims to reduce the time needed to produce a SMR pressure vessel from around two and a half years to less than 12 months. In the first phase, Nuclear AMRC is developing electron beam welding techniques for vessel sections made from metal powder using hot isostatic pressing.
Author information: Miguel Garcia, Modules Technical Lead, Nuclear AMRC; Tim Chapman, Communications Manager, Nuclear AMRC