Power Generation

By Ian Parker, freelancer, ianparkerwriter@aol.com

The world’s electricity needs will continue to rise in the coming years, especially with trends such as the focus on Artificial Intelligence (AI), which is very power hungry; the production of green hydrogen gaining popularity; as well as the ongoing move away from burning other fuels that pollute – with predictions suggesting that some countries will experience a doubling of their electricity needs in a few years.

A number of green energy solutions will be employed, including nuclear – which is enjoying a resurgence in the form of Small Modular Reactors (SMRs), rather than the large stations currently in operation. SMR units tend to be built in factories and then assembled on-site, resulting in a wide range of joining systems being required that must have high integrity. 

UK company Thomas Smith Fasteners explains: “Fasteners are an essential component in the nuclear industry. Nuclear facilities, such as power plants and research reactors, require fasteners that can withstand extreme temperatures, pressures, radiation and corrosion. Fasteners hold together critical components and ensure the safe and efficient operation of nuclear reactors.”

The company adds: “In the nuclear industry, fasteners are used for a variety of applications, including structural support for critical components such as fuel rods, reactor vessels, as well as other equipment. Fasteners are also used in cooling systems to attach pipes and fittings. These systems are designed to reduce the temperature in the reactor and maintain safe operating conditions. Fasteners made of stainless steel or other high performance alloys are commonly used to resist corrosion and withstand high temperatures. It is paramount that the correct fastener is chosen.”

US company Lincoln Structural Solutions reports its nuclear fasteners are specialised components used in the construction and maintenance of nuclear power plants and other facilities that handle nuclear materials. These fasteners, such as bolts, nuts, screws, and washers, are critical for ensuring the structural integrity and safety of nuclear installations.

According to the company, key characteristics and requirements of nuclear fasteners include:

• Material selection: They are made from high grade materials such as stainless steel, nickel alloys, or other corrosion resistant materials to withstand the harsh environments within nuclear facilities.
• High strength and durability: These fasteners must endure extreme temperatures, pressures and radiation levels without degrading
  or failing.
• Precision manufacturing: Nuclear fasteners are produced
  with high precision and tight tolerances to ensure a perfect fit and reliable performance.
• Certification and standards: They must meet stringent industry standards and certifications, such as those set by the American Society of Mechanical Engineers (ASME) and the Nuclear Regulatory Commission (NRC), to ensure they are suitable for nuclear applications.
• Quality assurance: Extensive testing, including mechanical testing, non-destructive testing (NDT), and sometimes even radiographic testing, is performed to guarantee the reliability and safety of
  these fasteners.
• Traceability: Each fastener typically comes with detailed documentation tracing its manufacturing process, materials and testing history to ensure full accountability and quality control.

Learning from the past

Part of the impetus for SMRs has been the nuclear accidents of the past, which have driven the need for increased safety. This can be provided by the smaller SMRs that have automatic safety systems, compared with the manned systems of the older stations, which have sometimes failed. The nuclear accidents at Three Mile Island, USA (1979); Chernobyl, Soviet Union (1986); and Fukushima, Japan (2011) set fission power back a long way.

The Three Mile Island (TMI) accident began with failures in the non-nuclear secondary system, followed by a stuck-open pilot operated relief valve (PORV) in the primary system, which allowed large amounts of water to escape from the pressurised isolated coolant loop. The mechanical failures were compounded by the initial failure of plant operators to recognise the situation as a loss-of-coolant accident (LOCA). 

TMI training and operating procedures left operators and management ill prepared for the deteriorating situation caused by the LOCA. During the accident, those inadequacies were compounded by design flaws, such as poor control design, the use of multiple similar alarms, and a failure of the equipment to indicate either the coolant inventory level or the position of the stuck-open PORV. This led to a partial meltdown of the TMI-2 reactor.

In Chernobyl, tests were being run to simulate reactor cooling during a blackout, but attempting to shut down the reactor in these conditions led to a power surge that resulted in a steam explosion and a core meltdown, destroying the containment. In Fukushima, an earthquake and tsunami damaged all of the back-up energy sources so the reactor couldn’t be cooled after shutdown and again the containment was ruptured. 

In August last year, a report was published on bolt failures in a conventional nuclear power station in Shandong, China. The shaft of the electric isolation valve at the outlet of the seawater tank pump in a nuclear power plant fractured due to bolt failure, resulting in detachment and loss of the electrical switching function. Upon disassembly, it was discovered that all connecting bolts on the frame were fractured. Macroscopic examination, chemical composition analysis, hardness testing, metallographic examination, scanning electron microscope (SEM) observation, as well as energy spectrum analysis were performed on the fractured bolts. Results revealed significant deviation from design specifications for stainless steel austenite in terms of their chemical composition; instead they consisted of low alloy steel (40Cr). High strength bolts exposed to marine environments are susceptible to corrosion induced stress cracking or hydrogen embrittlement leading to fracture. 

The smaller SMRs with their automatic safety systems are far less likely to suffer accidents of this nature, or any accidents at all, and the nuclear industry points out that it deals with all its waste. Other older technology electricity generating stations release most their waste into the environment. 

Nothing new

Small fission reactors are not new, they’ve been operating in submarines, aircraft carriers and ice breakers since the 1950s, but they don’t have the same level of safety controls as modern SMRs due to space, weight and cost limitations. The SMRs in design and development now have passive safety features, which do not require human intervention.

Today, more than 80 SMR designs are under development in 19 countries, but only Russia and China have them operating. The most common technology is pressurised water, but other designs include generation IV, thermal-neutron, fast-neutron, molten salt and gas cooled reactors. In each case, the last line of defence is the containment, which needs top quality fasteners. 

In the UK, Rolls-Royce SMR Ltd is developing a 470 MW reactor that can power a million homes. Many big nuclear stations in the UK are nearing end of life and the Rolls-Royce’s SMRs can occupy the same sites. Some 90% of the SMR is made in a factory and transported to the installation site by road or rail. The required site is only about 12 acres, about a tenth of the size of a conventional nuclear station. 

Factories making Rolls-Royce’s SMRs could be positioned in many locations around the UK, supporting the government’s levelling up ambitions and helping its aim of having 24 GW of nuclear energy by 2050. Rolls-Royce is already looking at sites in North Wales and West Cumbria, close to decommissioned stations or nuclear sites. The company says it could generate 40,000 jobs and generate GB£52 billion (€62 billion) in economic benefit. 

Rolls-Royce currently has  Memorandum of Understandings (MoUs) with Estonia, Turkey, and the Czech Republic, and development funding of GB£490 million is already in place. Investors include Rolls-Royce Group, Constellation Energy Corp (USA), BNF Resources UK Ltd and Qatar Investment Authority. 

Rolls-Royce SMR in detail

At the heart of each Rolls-Royce SMR is a Pressurised Water Reactor (PWR) using well understood technology that is operating in hundreds of nuclear reactors and safely powering millions of homes around the world. The SMR’s PWR is a symmetrically arranged, three-loop, close coupled reactor producing 1,358MWt of heat. The plant design provides multiple layers of safety, redundancy and back-up systems –
meeting the highest standards of safety, security, safeguards and environmental protection.

The heat generated in the nuclear core is transferred to the water flowing over the fuel. This water is prevented from boiling by keeping the whole primary system at a high pressure, making the heat transfer much more efficient. The heated water then flows through to one of the three steam generators that passes the heat to the lower pressure secondary side, which is allowed to boil, making the steam that passes through a turbine that powers the generator, pushing electricity through to the grid.

While the basic elements of the Rolls-Royce SMR are typical of most PWRs operating today, there are some very modern innovations. The company has adopted an industry leading boron-free primary circuit design, which has allowed toxic and corrosive boric acid to be eliminated from all duty systems – drastically reducing overall plant water consumption but, more importantly, eliminating this hazardous waste source from daily operations.

The reactor core is protected from external risks and the impact of any ground movement. Internally, the reactor is protected by safety systems that can operate independently of any human intervention – so that the core is put into a safe state with no external intervention for up to three days.

Modular construction is well established in industries such as oil, gas and shipbuilding – where engineering, fabrication and assembly of modules is carried out in a controlled factory environment, using advanced manufacturing techniques, before being transported to site for assembly. The approach results in significant advantages over ‘traditional’ on-site construction, including improved quality control, shorter construction times and increased safety.

Rolls-Royce states its SMRs will operate at very high-levels of availability (>92%) for at least 60 years, providing long-term stable clean energy, to support both on-grid electricity, as well as a range of off-grid clean energy solutions. It will support the decarbonisation of industry and the production of clean fuels to enable the energy transition in the wider heat and transport sectors.

For nuclear power to be widely adopted and meaningfully contribute to the global effort to decarbonise, it needs to be commercially investable and reliably delivered. The global challenge around decarbonisation is huge, with an increasing demand for clean, affordable electricity set to increase, driven by:

Increasing electrification of systems, including transport and heating.

• A growing hydrogen economy, where clean forms of hydrogen generation need clean electricity at large scale.
• The emergence of eFuels and synthetic aviation fuels to enable decarbonisation of transport.
• An increasing demand for energy, driven by population growth and increasing global development.
• An increasing demand for constant forms of power to support a decarbonising electricity grid and growing technology industries, such as data centres.

All this must be done with the highest level of nuclear safety. The UK has one of the world’s most rigorous and respected independent regulatory regimes. The nation’s independent nuclear regulators (the Office for Nuclear Regulation, the Environment Agency and Natural Resources Wales) work together to ensure that any new nuclear power stations built in the UK meet high standards of safety, security, safeguards, environmental protection, and waste management, through a process called Generic Design Assessment (GDA).

The Rolls-Royce SMR has successfully completed Step Two of the GDA, which the company says confirms Rolls-Royce’s position as the leading SMR vendor in Europe.

Great British nuclear

Rolls-Royce SMR Ltd is currently engaged in the Great British Nuclear (GBN) SMR technology selection process, which will select the best SMR technologies from around the world to deliver low carbon nuclear power and support the UK transition to net zero. “A successful outcome for Rolls-Royce in the GBN process will support the UK government’s mission to deliver growth and become a clean energy superpower”, reports the company.

It will unlock investment at home creating long-term jobs, supply chain growth and a skills programme to train future generations in STEM subjects. It will enable export success, attracting foreign direct investment into the UK and enabling overseas success – capitalising on the Rolls-Royce SMR’s ‘first mover advantage’. It will bring power to the grid as quickly as possible – helping secure Britain’s energy independence and achieving net zero.

The Rolls-Royce SMR module development facility – housed within University of Sheffield’s Advanced Manufacturing Research Centre’s existing Factory 2050 facilities – will produce working prototypes of the individual modules that will be assembled into SMR power plants. The first phase is worth GB£2.7 million and will be part of a wider GB£15 million plus package of work that will further de-risk and underpin the Rolls-Royce SMR programme.

The company aims to produce a repeatable factory built power station, that relies on tried and tested nuclear technology, resulting in lower risk, reduced capital and a shorter build time than conventional nuclear power plants. A whole power plant approach focused on standardisation, repeatability and commodity supports the increasing demand for low carbon energy.

Partners and suppliers are critical to the success of the Rolls-Royce SMR, not least fastening system providers. The Rolls-Royce SMR supplier approval process is based on several assessments including quality management system, manufacturing capability, as well as planning and control. These assessments will be conducted and will form part of the process of becoming an approved supplier to the Rolls-Royce SMR. The company requests that its suppliers commit to the code of conduct and integrate these principles into their own supply chain.