SMR’s – small size, big opportunity?

Materials World magazine
1 Mar 2017

Small nuclear reactors are attracting the attention of Government officials, regulators and energy leaders to meet the demands of a looming energy crisis. Richard Wain and Rob McCluskey argue the case for compact modular plants in the energy mix. 

Alongside renewable energy, nuclear power is an attractive energy solution because it produces virtually no greenhouse gas emissions. Developed and industrialised countries are seeking to meet their environmental obligations through the use of low-carbon power generation, but they also need security of supply. Wind and solar power are viable options from an emissions perspective but being subject to the elements cannot always be relied upon for a guaranteed power output. Gas-fuelled power stations are being considered, but, in the UK’s case, more than half of the natural gas needed has to be imported, meaning the UK is reliant on other countries to meet demand.

Nuclear has several advantages including consistency of output, low carbon emissions and secure, independent power. For emerging markets, modern nuclear power is being considered as part of a balanced mix. But developing and producing nuclear energy has never been simple or cheap. The industry continues to operate to the highest and most stringent safety requirements. Additionally, large nuclear power stations can be extremely expensive to develop and deliver. As a result, their construction is often politically charged.  

Decisions surrounding energy policy are not made quickly and, as seen in the UK, large nuclear plants are not quick to bring to market. So although the technology is attractive, the scale of the projects can be daunting. Distributed power solutions have become much more prevalent in the last 20 years with many local communities and authorities now contributing to how and where their energy is provided. Until now, these distributed energy plants have usually been diesels or gas turbines, but could smaller, cheaper and more localised nuclear power be used in supplying a modern power grid?

Viable alternative solutions

With energy demand increasing, compact nuclear plants that can support the grid, be easily built and respond flexibly to peaks in power demand could come to the fore. According to Paul Stein, Director of Research and Technology at Rolls-Royce, ‘Traditional (large nuclear) plants are bespoke projects and are not getting any cheaper. Small modular reactors (SMRs) could be made in factories and assembled on site, speeding up the work.’ 

The idea of small nuclear reactors has never really been promoted or considered a viable option until recently. However, more energy suppliers are now exploring the market for potential growth opportunities. For around 60 years, Rolls-Royce has been designing and developing small nuclear reactors, although its focus has been solely to power the nuclear submarines of the Royal Navy. Major power stations can generate up to 1,600MW, whereas SMRs would typically provide around 100–400MW of power. But some designs are smaller than this. Harry Holt, President of Nuclear for Rolls-Royce, UK, said, ‘The UK needs a strong intellectual property position for SMRs. An SMR programme presents a once in a lifetime opportunity for UK nuclear companies to be involved in the design, manufacturing and building of the next-generation reactors. The UK Government has the chance to maximise British content, creating and sustaining high-tech, high-skills employment, reinvigorating the UK supply chain and positioning the country as a global leader in innovative nuclear technologies. SMRs present tremendous opportunities in international export markets.’

From R&D to market

The advantage of SMRs for the UK is safe, reliable and affordable low-carbon electricity as the country strives to reach its 2050 de-carbonisation commitments to reduce greenhouse gases by 80% compared to 1990 levels. Additionally, these smaller reactors could be considerably cheaper to produce as, once the design is approved and licensed for use, they could be factory-built, bringing about the benefits from the economies of volume production. If export sales were subsequently achieved, these savings would be even greater.

The case for SMRs became the subject of a UK Government-backed competition to find the right design when, in 2015, the UK stated its intention to invest £250 million into R&D funding for SMRs. Rolls-Royce is proposing to produce the optimum design solution and lead a UK supply chain for the delivery of the system. If successful, it will secure UK business with a potential export market of £250–£400bln, a scale of opportunity that is difficult to ignore. Matt Blake, Rolls-Royce Chief Engineer of SMRs said, ‘Development of a UK SMR promises to be one of the largest national engineering collaborations. The Rolls-Royce SMR project will use a broad range of interdisciplinary technical expertise to deliver a commercially viable, sustainable solution to energy security.’

Materials and manufacturing

The materials selected for use in the UK SMR design will be essential to achieve the reactor’s desired performance, with capital cost, speed of manufacture and in-service reliability being important considerations. The experience gained over the long history of the global nuclear industry has led to a set of mature, well-understood materials that provide excellent in-service performance.   

Typically, pressurised water reactor (PWR) primary systems make extensive use of low-alloy steels to provide the combination of strength and ductility necessary for large pressure vessels. Where required, austenitic stainless steel cladding is applied to provide corrosion resistance. Stainless steels are also used extensively in piping applications, while nickel-based alloys are commonly used for steam-generator tubing. Zirconium alloys are used for fuel cladding because of their resistance to corrosion and relative neutron transparency, key to reactor efficiency.  

In the secondary systems, steel containing small amounts of chromium to minimise susceptibility to flow-assisted corrosion are increasingly replacing traditional carbon steels. Titanium alloy is now the material of choice for condenser tubing because of its corrosion performance in cooling water environments such as seawater. Away from the reactor plant itself, reinforced concrete and structural steel make up the majority of the containment structure.  

The main materials challenge – and opportunity – for a UK SMR will be to access the benefits of new manufacturing methods consistent with economies of volume, while ensuring that the vast wealth of experience gained with these materials remains applicable. In some areas new manufacturing methods could also bring advantages to in-service performance and safety analysis. For example, conventional grades of pressure vessel steel could be specified, but, through the use of modern steelmaking practices, it is expected that much cleaner material can be obtained that is low in undesirable residual elements. This brings about performance benefits in terms of improved resistance to ageing of the material due to irradiation and long-term exposure to elevated temperatures.

Rolls-Royce has also played a part in gaining acceptance of hot isostatically-pressed (HIP) 316L stainless steel into the American Society of Mechanical Engineers boiler and pressure vessel code. HIP material offers mechanical properties and corrosion performance similar to that of forgings, yet can be produced in a near-net shape form, reducing the number of finishing operations required. In replacing castings, HIP has a lower defect rate, bringing such benefits as reduced re-work and more straightforward safety analysis. Other net-shape manufacturing technologies, such as laser powder bed fusion, offer similar benefits by enabling parts with complex shapes to be made more quickly and efficiently than is possible when more traditional methods are used.

Improved welding and cladding technologies new to the nuclear industry are also required. Electron beam (EB) welding can produce welds much faster than traditional arc-welded joints, with the potential to produce weld microstructures much closer to that of the parent material. Similarly, new cladding methods are also being evaluated. Methods such as blown powder laser cladding have the potential to offer advantages over conventional methods, requiring less material, time and energy to produce. Advantages in terms of structural integrity assessment of the clad and substrate interface could also be facilitated by these improved methods.

In the same way, the availability of materials and components as part of the capability of the supply chain must also be considered. The role of the supply chain is critical to the success of the UK SMR programme. Consolidating and simplifying the range of materials and product forms across the whole power station delivers the advantages of economies of scale, reduced capital cost and improves the resilience of the supply chain. 

Good quality evidence is required to support safety claims and demonstrate the performance of the materials intended for use. This has led to thinking about the approach for measuring material properties and performance. For example, can established test methods and practices for measuring the mechanical properties of nuclear pressure vessel forgings be modified to get better quality data from fewer tests?  

There is no single major development in the field of materials that will deliver the improvements required for the UK SMRs to be viable. However, the collective impact of these many small developments will be to significantly reduce costs and improve performance, while reinvigorating the UK supply chain and developing intellectual property for UK institutions.

Export opportunities 

There are hurdles to overcome before a series of SMRs located across the UK are rolled out to meet the country’s energy supply needs. The licensing process is likely to take some years and the UK will face competition from other countries with exportable nuclear technology, including the USA and France. There are a number of export market opportunities, such as Central and Eastern Europe and the Middle East. SMRs could be deployed en masse in the next decade and remain in service until the end of the Century, providing power and socio-economic benefit to the global community. The design of the reactor and the power station is being developed with global application in mind, where local partners can benefit in the application of this technology. SMRs, if approved, could be relatively quick to bring to market – around five years in terms of construction – with major components  transported by truck, train or barge to all of the potential sites identified. However, the UK has a looming energy crisis and needs to find answers. Rolls-Royce has submitted proposals to the UK Government for a 220MW-capable SMR that could be doubled in output to 440MW if required. Together with timely and firm political decision-making backed by a determination to drive regulatory support, this could lead to the first power-generating SMRs in the UK within 12 years. 

Dr Rob McCluskey is the lead Materials Technologist for the Rolls-Royce Small Modular Reactor. He has worked for the company’s nuclear businesses for five years, supporting the design and manufacture of pressurised water reactors for the Royal Navy’s submarine fleet, as well as supporting the generic design assessment process for new-build civil nuclear projects.  

Richard Wain is the Materials and Chemistry Design Manager for Rolls-Royce’s Small Modular Reactor. He has worked for Rolls-Royce’s nuclear businesses for more than 20 years, and has extensive experience of design, construction, commissioning and in-service support of PWRs for the Royal Navy’s submarine fleet and licensing of civil reactors.