Ensuring an ongoing supply of power in a low carbon economy is one of the major national and international challenges that almost every country faces. Investments in alternative and renewable energy technologies have risen steadily over the last decade, particularly since the ratification of the 2030 Paris Agreement. Although reasonable progress has been made as a result of this, even the most developed renewable energy technologies, for example, solar, wind and hydro, cannot satisfy the rapidly growing energy demand of the world. Arguably a non-renewable energy source, nuclear energy may be one clean energy answer for the future. More specifically, small-scale nuclear energy holds considerable potential. Such potential exists in the form of light water small modular reactors (LW-SMRs). These SMRs have the capability to meet the energy independence and the energy security needs of many countries while reducing capital and operating expenditure and environmental and physical footprint. The modularity aspect of this technology allows for varied application, from large towns to rural regions that currently rely on individual generators. It also creates the opportunity of cogeneration with already existing conventional power generation technology to diversify power generation and increase grid stability. LW-SMRs are not a new idea; in fact, they have been used to power U.S. aircraft carriers and submarines for almost 60 years. This case study will address the advantages and disadvantages of the LW-SMR, using the market leader NuScale as an example. NuScale in Oregon, United States, is arguably the most experienced and influential LW-SMR nuclear energy company when it comes to the factory fabrication of LW-SMRs.
Since the Paris Agreement was ratified in 2016 , the aim of the Paris Agreement is to limit the global temperature increase to below 2°C, with a preference to keep the warming below 1.5°C. Significant changes will have to be implemented to achieve this goal. While there has been a minimal number of large projects executed since the agreement due to time frame challenges, a large variety of sustainable and renewable energy projects have been put into motion all over the world. Global energy demands are expected to increase rapidly due to strong economic growth in many developing countries . Owing to a range of issues such as intermittent energy production, cost feasibility and scaling limitations, there are inherent difficulties in transitioning to a grid system where most of the electricity is supplied by renewables . This is worrisome, considering that it is predicted that the world market for electricity generation is expected to increase by 80% over the next 25 years . While these renewable energy systems are continually improving, baseload power generation must be achieved by alternative means. The solution may just be nuclear energy, specifically through the utilisation and optimisation of small modular reactors (SMRs).
Nuclear power plants generate flexible, continuous and reliable energy with zero carbon emissions. Approximately 11% of the world’s electricity demand is met using nuclear power. In some countries, up to 70% of the power requirement is achieved using nuclear power . The aim of LW-SMRs is to reduce the problems associated with conventional (large-scale) nuclear reactor plants, such as the high capital and operational costs, safety issues and the disposal of radioactive waste.
SMRs, as the name suggests, are a form of small-scale nuclear energy production. They operate according to the same fundamental principles as large-scale nuclear reactors but have recently been deemed to be more affordable and flexible while remaining equally efficient as large-scale reactors. Owing to this, over the last couple of decades, many new projects (50+ ) have been undertaken to facilitate the adoption of SMRs. This case study will address the influential factors for such projects by taking into consideration the advantages and disadvantages associated with the development, implementation and optimisation of small-scale nuclear energy. An SMR world leader, NuScale Power, will be used as an important point of reference. This report will focus primarily on LW-SMRs to allow for direct comparison.
What Are SMRs and What Are They Used For?
SMRs are defined as nuclear reactors producing 300 MW (or less) of electrical power . SMRs are designed around the idea of modularisation, and their compact design allows for their factory fabrication and manageable transportation to destinations for installation. SMRs are mainly used to produce heat energy from nuclear fission for generating electrical power in a single or multi-module (depending on energy requirement) nuclear power plant. Most existing SMR operations are third-generation light water reactors, while fourth-generation reactors with inherent safety features such as NuScale are currently being developed . Safety features include having a small nuclear fuel inventory, being a seismic category 1 design, utilising natural circulation and incorporating automatic shut down and self-cooling features . In extreme events where power is disconnected from the facility, the increased strength and number of safety barriers can prevent a nuclear meltdown. Fission energy is used to heat circulating high-pressured water to subcritical levels, which is used to boil low-pressured water in a secondary loop. Produced steam is passed through a turbine and condensed in a recycled stream. While other thermodynamic fluids have been investigated to replace the water in the primary loop, water remains the most cost-efficient option .
Existing SMR Operations
While the modularity component of the SMR is still in development, there are a variety of different small reactors under development, construction and in operation all around the world. The most popular of these are the pressurised light water reactors. Those in operation include the CNP-300 (300 MW) pressurized water reactor (PWR) in China, the pressurized water reactor (PHWR)-220 (220 MW) in India and the EGP-6 (11 MW) at Siberia. The EGP is a light water graphite reactor and is essentially a pilot plant that will be decommissioned in 2019 . There are also 5 SMRs under construction (all PWRs) and 10 reactor projects ready for near term deployment . The CNP-300 and PHWR-220 have been in operation since 1994 and 1973, respectively. China has since exported their CNP-300 design to Pakistan for development and implementation . India is also now looking to export the PHWR-220 design. Countries such as Vietnam, Thailand and Malaysia have expressed interest in the SMR design .
Case Study: NuScale
The goal of NuScale Power is to provide sustainable and scalable advanced nuclear technology to produce electricity, heat and water to improve the quality of life for people around the world. Formed in 2007, NuScale has been deemed the market leader in SMR fabrication technology since 2013 by the Department of Energy . NuScale was established with the sole purpose of completing and commercialising the design for a small-scale reactor that uses conventional light water-cooling methods—the NuScale Power Module (NPM). The design specification for the NPM will be determined by 2020, with factory construction beginning in 2022 and the first NPM being delivered by 2025 . This time line was established over the course of 8.5 years following 130 meetings, 2 million labour hours (800 people), 1,000 documents (12,000 pages) and a US$505 million total investment.
The NPM produces 60 MWe of power, and like most SMRs, it is small enough to be manufactured in a factory and transported and installed on-site. The design allows for flexible and independent power production and can be operated in parallel to achieve demand (up to 12 modules providing 600 MWe gross output) . These modules are predicted to have a 60-year lifetime .
NuScale’s SMR is the first and only SMR under design certification review by the U.S. Nuclear Regulatory Commission (NRC). The 12th of December 2019 marked the completion of Phase 4 of the review of the Design Certification Application. The final phase, Phase 6, is targeted for completion in early September . NuScale has also applied to Canada’s nuclear regulator for a pre-licensing vendor design review . This is not a step in the NRC application process but is an optional service to assess the vendor’s (NuScale) reactor technology. This additional submission allows the NuScale design to be reviewed by another highly experienced nuclear regulator.
Advantages of the SMR
The design and development of SMRs are taking place in many parts of the world. There are many reasons for this, and those include, but are not limited to, their ability to be fabricated in a factory, their small environmental footprint, the ease of their transportation, their flexible operations, their economies of installation and maintenance and their low associated greenhouse gas emissions.
Nuclear power is a key player in decarbonising the energy production system . While SMRs might be more expensive per unit of power produced compared to large nuclear reactors, they can play a vital role in providing electricity in conjunction with renewables . Owing to the intermittent nature of many renewable energy sources, combining renewables with nuclear power can constitute one of the cheapest ways of achieving a low-carbon energy production system, and it can reduce emissions more compared to energy production systems relying entirely on renewable sources . While renewable energy, as well as nuclear, typically has a low carbon footprint, many renewable sources generally produce less power output per MW of installation, are less reliable, and require transmission, storage and backup generation capacity .
The carbon emission from nuclear power generation across its full life cycle is approximately 23 g CO2/kWh , which is around 4 times higher than wind power plants  but at the same time significantly less than that of many solar power plants . However, when comparing this to coal-fired power plants, which make up approximately 30% of the world’s energy production , there are significant emission reductions to be made by replacing these with nuclear power plants considering the emission intensity of coal-fired plants can be as large as 1,000 g CO2/kWh . While efforts are underway to reduce emissions associated with fossil fuel systems by introducing technologies such as carbon capture and storage (CCS) , the average emission associated with these technologies today and in the near future still ranges from 400 to 970 g CO2/kWh, [19, 21]. Therefore, utilising SMRs to replace fossil fuel-driven power plants, and especially those of low efficiency, could be one of the quickest ways to reduce carbon emissions associated with energy production.
Being a relatively small module, the SMR can be fabricated in a streamlined manner in a factory. By being manufactured off-site, not only can economies of scale be taken advantage of, but the burden of on-site construction can be significantly reduced. The median construction time for large-scale reactors in 2018 was 8.5 years. This is slower than previous years, which can largely be attributed to the high number of first of a kind (FOAK) reactors being constructed . This involves a considerable amount of time and resource investment. As these statistics were retrieved from data obtained for 441 operational reactors, it is deemed to be a representative average. SMRs, however, can be built on-site in under 4 years (excluding module construction at the factory). This is considerably less than the time required to construct large reactors. There is further potential to reduce the construction time of SMRs to 3 years following the FOAK .
In comparison to other forms of energy generation technologies, nuclear power plants occupy significantly less land area . While large-scale nuclear power plants occupy around 25% of the area of coal-fired power plants, small-scale nuclear power reactors have an even smaller footprint. Their modular form allows for installation underground, underwater, or on ships . The NuScale module weighs 590 tons, has a 2.7 m diameter and is 20 m long , making transportation via railcar, barge, or special trucks and on-site installation relatively easy. The overall footprint of the facility (720 MW) has been predicted to be only 34.5 acres . A conventional large-scale reactor (550 MW production) on the other hand requires over 500 acres . The difference in these physical footprints is immense, with SMR sites requiring significantly less land clearing.
Flexible Operation and Dispatchability
Load following refers to situations in which a power plant ramps electricity production up or down to meet supply and demand. The flexibility of a power system is determined by its load-following capability. The “long-term future of nuclear power will depend on its ability to adapt to the new world of flexible power systems and low marginal cost renewable electricity” . A significant downside to large reactors and most forms of renewable energy is their lack of flexibility to do exactly that. Their power supply is often surplus, and demand exceeding their design capacity cannot be met. Conversely, SMRs have been shown to load follow effectively with a 57 MW wind farm, proving their ability to play a crucial role in cogeneration with both renewable and non-renewable energy generation . The number of modules connected to the grid can also vary . During peak demand, more modules can be initialised and connected to the grid. While this reaction-driven process is not instant and cannot react to sudden changes in demand, forecasted demand can be met. For example, one or more additional modules can be connected during the summer period. The number of modules installed at the nuclear power plant should be determined according to scenario cash flow modelling. For a city to be entirely dependent on the modules, the output must satisfy the peak demands. It may prove to be more economical for a combination of energy generation methods to be utilised. When the SMRs are introduced to an established electricity supply network, existing technology can be incorporated into the new combination grid supply.
While still achieving cost parity, SMRs can produce anywhere between 5 MW and 300 MW of electricity . The lower this production, the more flexible the capacity becomes. Taking the case of NuScale, one 60 MWe alone can provide enough power for up to 60,000 homes . The number of modules implemented can be quickly increased according to the electricity demand of the city. This makes it a convenient option for either rural or urban areas, particularly those with poor resource availability and storage possibilities for solar and wind operations. Hydro storage in the form of dams, lakes and reservoirs is currently the most prevalent economic and environmental storage technology. Hydro storage is built on water flowing between two bodies of different elevation, where water is released from the upper water body to generate electricity and then pumped back with surplus electricity produced from intermittent technologies . However, many towns and cities do not have topographic environment for this technology and therefore cannot economically store energy generated from intermittent renewable technology. It is these locations where SMR technology would be most suitable.
Disadvantages of SMRs
Most of the issues that follow the SMR proposals are closely linked with those of large-scale nuclear energy. This includes the substantial initial costs, particularly those related to a continuous SMR production factory, the issue of nuclear waste and the finite amount of recoverable uranium.
High Initial Costs
In 2013–2014, NuScale projected their overnight capital cost (OCC, a standard concept used to compare construction costs of power plants) for a 540 MWe plant to US$5,078/kWe. The levelized cost of electricity (LCOE, typically measured as $/MWh) was furthermore estimated at US$100/MWh . At that time, NuScale, which was one of the first producers to receive grants from the Department of Energy in the United States to develop SMRs, was one of the pioneers in producing SMRs commercially. Typically, FOAK development is usually significantly more expensive, and costs are expected to decrease as technologies mature and components, systems and facilities can be shared . As technological development has advanced, the OCC has been significantly lowered, and in 2018, NuScale estimated their OCC to have reduced by more than 50% and for the LCOE to be 18% less than originally thought . This can be compared to the OCC of commercial large-scale reactors, which, when constructed in the United States between 1968 and 1978, ranged from 1,800 kW to 11,000/kW , and is currently estimated to average at US$6,317 kW . It is important to note that like large-scale reactors, large SMR facilities also have an added risk of construction overruns. Rural single module applications however may not incur this economic barrier. Nuclear reactors, regardless of their kind, are currently being outperformed by some types or renewables such as wind power (1,319/kW) and solar PV ($1,331/kW) .
Until fabrication has stabilised and production is well understood, the LCOE of SMR-generated power will be 30% more costly than that of the energy produced by a large-scale nuclear reactor . Furthermore, current cash flow modelling suggests that the cost of a natural gas plant with CCS is less than that of an SMR plant on a per output basis . Cost parity, however, is expected to be achieved once 10 units are deployed on a yearly basis . This cost parity is a result of high learning rates (8–10% ) and moving the building activity away from the plant site, where the time and resource-consuming construction of the SMR is external to the plant. The cost of achieving such an output is expected to be several hundred billion dollars . Manufacturers need promised investors, with approximately 30–50 ordered modules . Such investment requires a U.S. national, and more importantly, a worldwide commitment to decarbonise the energy system. Such investors will arise if the direct or indirect cost of emitting carbon dioxide grows from US$40 to US$100 over the next decade [35, 36].
The large water requirements for all thermoelectric plants arise from the cooling and condensing stages of the process. After passing through the turbine, the remaining steam and saturated water need to be cooled before recirculating through the reactor. This is achieved using large heat exchangers with a counterflow of cool service water. The more heat that needs to be removed, the more service water will be required, and the more water-intensive the whole process becomes. NuScale has estimated a water requirement rate of 740 gallons/MWh , comparable to large-scale nuclear energy, coal, oil and gas-fired plants which range from 580 to 850 gallons/MWh . As this water does not come into contact with the reactor water, the effluent is pollutant-free, with the reactor water remaining inside the reactor . Nuclear reactors have a high-water use compared to most renewable energy sources, such as wind and solar, which both require an almost insignificant amount of water during their life cycle . The high consumption of water associated with nuclear reactors is primarily due to the considerable evaporation occurring during the cooling process, resulting in water being lost from the system.
Like large nuclear reactors, a significant issue involving SMRs is the management of spent fuel (often referred to as nuclear waste). While many safety controls are in place, the removal of a single expired module from a set involves more risk than removing spent fuel from a large nuclear reactor due to the added complexity of refuelling multiple modules. In each case, the power plant is shut down, but the SMR facility will need to have a variety of additional decommissioning steps that can isolate the expired reactor from those that remain. The upfront costs of such are substantial but reduce the cost of decommissioning at the end of the module’s life cycle . Being a relatively new technology, reliable data on SMR decommissioning costs are scarce. The average price of decommissioning Nuclear Energy Agency (NEA)-membered nuclear reactors in 2003 was found to be US$320/kWe , or US$480/kWe in today’s terms according to the rise in the Chemical Engineering Plant Cost Index . This cost per input is comparable to those of recently decommissioned large-scale U.S. nuclear power plants (1,358, 527 and US$266/kWe) . This translates to US$24 million per PWR NPM. This is considerably larger than the decommissioning costs of coal- (US$100/kWe) and gas-powered plants (US$200/kWe). All decommissioning costs are relative to a plant size of 500 MW .
Once removed from the immediate power generation facility, the spent nuclear fuel follows one of two pathways. It is prepared for long-term storage, or the dangerous fission products, such as 90Sr, 137Cs, 99Tc and 129I, can be separated and the remaining elements reprocessed . Regardless, nuclear waste needs to be disposed of. By reprocessing the spent fuel, not only can a portion be reused, but the half-life of the remnant is reduced significantly . Owing to the high cost of reprocessing and relatively low cost of nuclear fuel, however, the spent uranium is usually stored in underground concrete bunkers, where transportation is completely automatic . Although there are many suitable geological locations for safe storage of spent fuel, the question of where this fuel should be stored remains a highly political issue.
Proliferation of Nuclear Weapons
The issue of proliferation of radioactive material will always be a concern for the nuclear energy industry. It has been argued that having SMRs at more sites increases security and proliferation risks, particularly due to staggered refuelling. Each underground module is individually refuelled every 2 years to ensure energy security . While the uranium fuel is transported and handled much more frequently than that of a large reactor, the miniscule quantity and enrichment significantly reduces the attraction of an attack or sabotage. NuScale’s enrichment of 5% is considerably lower than that of other reactors that operate using high-assay low-enriched uranium that can be enriched up to 20% . This resilient plant design is achieved through the application of defence in-depth principles which reduce vulnerability to site and transport sabotage .
A Finite Supply of Nuclear Fuel
While somewhat abundant now, it was initially forecasted in the early 2000s that the world’s uranium supply would approach depletion around the mid to late 21st century. This prediction has since been re-evaluated due to the substantial overestimation of uranium demand and increased reactor efficiencies. It was initially predicted that a much larger number of reactors would be in operation by now. This assumption was made before the Treaty on the Prohibition of Nuclear Weapons was signed (2017) and the Fukushima disaster. This disaster created the impression that using nuclear energy was very dangerous. The reputation of nuclear power has since improved as it is one of the only feasible methods of combating climate change . Opinions differ about how much uranium is likely to be mined in the future. Bedford  has predicted that its rate of production will increase for at least the next 200 years. On the other hand, Dittmar  has estimated that its level of production has already peaked and that there will be a significant shortage in production by 2030. This highlights the considerable uncertainty surrounding future uranium availability, thereby also questioning the future market price of the commodity.
Electrification of remote areas remains an issue, and renewables such as solar, wind and hydro have the potential to fill parts of this gap. Diversification of energy production methods can be useful in many areas due to the risks associated with the reliance on a single source of energy. However, not all locations have the potential to utilise these technologies due to a lack of the required natural resources for their operation. SMRs have the potential to replace non-renewable energy production systems in geographically and geologically suitable location, which can both diversify and lower the carbon emission associated with the traditional grid system .
Remote high latitudinal areas without potential for hydropower may be a suitable target market for NuScale and other SMR producers due to the dispatchability of the technology as well as its capacity to produce baseload power. Many existing smaller off-grid systems are currently powered by diesel generators, which are associated with high emissions and are exposed to price fluctuations occurring in the global oil market . Although the NuScale facility is not applicable, the implementation of single module in these low-demand areas could reduce the reliance on individual generators, as mini grids can be implemented at a local scale as an alternative to an expensive expansion of the existing regional network to remote locations. This can reduce costs associated with grid development and maintenance and reduces the transmission loss.
One of the main drawbacks of LW-SMRs and other water-dependent nuclear power plants is the high water consumption, making this type of technology unsuitable in locations of water scarcity . This can, however, be worked around by installing coastal or floating SMRs, which can use seawater as a means of cooling. An example of such an SMR is the floating nuclear reactor constructed in Murmansk, Russia, that was shipped to Pevek, Chukotka, in late 2019 . Although operating costs for the plant in Pevek are high, it has been estimated to be significantly cheaper compared to that of extending the grid network to this remote region .
SMRs can furthermore be combined with other generation sources that are better suited for peak generation or alternatively can be used alone in remote industrial areas where there is little temporal variance in energy demand. Cogeneration with gas-fired power plants has been deemed the most suitable energy generation combination due to the high economic returns and low environmental impact . Rural mini grids can be self-sufficient with cogeneration where demand that exceeds the electricity supply from SMRs can be met by firing up these additional small-scaled power plants. Besides, SMR technology can be coupled with storage in the form of hydro-storage or possibly batteries. This provides greater flexibility in meeting energy and emission requirements and can be useful in areas where environmental conditions do not support solar and wind power.
With a rapidly growing demand for energy and a quickly approaching global emission target, new alternative power production technologies must be developed and put into immediate action. While considerable improvements in innovative renewable technologies such as solar and wind energy have been made, they cannot combat global warming on their own. Instead, a clean, reliable and carbon-free energy source to satisfy baseload power needs to be adopted. For these exact reasons, nuclear is an increasingly attractive alternative to fossil fuels. Owing to the significantly reduced capital and operational costs, operational flexibility and low emissions, it is believed that SMRs can play a key role in mitigating the worst emissions associated with energy production. Of the technologies today capable of supplying baseload power, SMRs have the smallest environmental footprint. While unprocessed spent fuel cells will need to be stored somewhat indefinitely, the quantity of such produced per megawatt delivered compared to the emissions produced using coal- and gas-fired plants is arguably negligible.
NuScale Power has forecast the deployment of their FOAK SMR, the NPU, to occur during 2026. Considering the time frame between this and the receipt of a design certification (September 2020) is 6 years, it is imperative that action is soon taken by other interested parties. Global adoption of SMRs is unlikely to be achieved with the currently limited number of projects being developed. Rather than merely waiting until NuScale Power and other nuclear companies prove their success, investors and government need to assess the potential of SMR production possibilities and consider placing advance orders for these.
Case Study Questions
What is a small modular reactor and how does it differ from large-scale nuclear reactors from an economic, social and environmental perspective?
Where would SMRs be most applicable?
What changes can be made to make nuclear energy more sustainable in terms of both resource management and waste generation?
Can nuclear power be considered a sustainable energy generation technique? Can it be accurately compared to renewable technologies such as wind and solar?
Can SMRs alone meet the energy demand of an economy now and in the future? If so, is this sustainable and what barriers exist?
Is it possible to further reduce the negative environmental effects and externalities of nuclear energy using SMRs?
Primary author: Liam Darby led the process of conceptualisation, analysis, original draft, review and editing.
Second author: Amanda Hansson assisted in general editing and further research as well as recalibrating the case study.
Third author: Clement Tisdell aided in structuring, significant editing and in refining the scope of the case study. He undertook extra research and suggested changes to the draft as well.