Powering the Future: Constructing Small Modular Reactor Power Stations for Sustainable Energy

Powering the Future

Constructing Small Modular Reactor Power Stations for Sustainable Energy

Richard Skiba

Copyright © 2024 by Richard Skiba

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This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional when appropriate. Neither the publisher nor the author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, personal, or other damages.

Skiba, Richard (author)

Powering the Future: Constructing Small Modular Reactor Power Stations for Sustainable Energy

ISBN 978-1-7637696-7-0 (Paperback) 978-1-7637696-8-7 (eBook) 978-1-7637696-9-4 (Hardcover)

Non-fiction

Contents

Introduction

Chapter 1: Introduction to Small Modular Reactors (SMRs)

Understanding Small Modular Reactors

Evolution of Nuclear Technology

Benefits of SMRs in Modern Power Generation

SMRs vs. Traditional Nuclear Reactors

Key Players and Developers in the SMR Industry

Chapter 2: Feasibility and Site Selection for SMR Power Stations

Key Factors in SMR Site Selection

Environmental Impact and Regulatory Requirements

Assessing Geographical and Geological Considerations

Engaging Local Communities and Stakeholders

Case Studies: Site Selection in Different Regions

Chapter 3: Design and Engineering of SMR Power Stations

Core Design Principles of SMRs

Safety Features and Redundancies in SMR Design

Modular Construction Techniques for SMRs

Engineering Challenges and Solutions

Key Components and System Integrations

Chapter 4: Regulatory and Licensing Framework for SMRs

Understanding International and National Nuclear Regulations

Licensing Process for SMR Construction and Operation

Compliance with Safety and Environmental Standards

Case Study: Licensing an SMR in Various Jurisdictions

Future Trends in Nuclear Regulatory Policies

Chapter 5: Construction Process of SMR-Based Power Stations

Planning and Timeline for SMR Construction

Modular Assembly and On-Site Integration

Quality Control in SMR Construction

Workforce Training and Skill Requirements

Overcoming Construction Challenges

Chapter 6: Infrastructure and Systems for SMR Power Stations

Cooling Systems and Heat Management

Electrical Distribution and Grid Connectivity

Safety and Monitoring Systems

Waste Management Infrastructure

Emergency Response and Contingency Planning

Chapter 7: Economic and Financial Aspects of SMR Projects

Cost-Benefit Analysis of SMR Implementation

Funding and Investment Models for SMR Projects

Projected Return on Investment and Break-Even Points

Financial Risks and Mitigation Strategies

Long-Term Economic Impact of SMR Power Stations

Chapter 8: Environmental Impact and Sustainability of SMRs

Carbon Footprint and Emissions Reductions

Waste Management and Fuel Recycling Options

SMRs in the Context of Sustainable Energy Go

SMRs and Integration with Renewable Energy

References

Introduction

S

mall Modular Reactors (SMRs) represent a significant advancement in nuclear technology, designed to produce less power than traditional large nuclear reactors. Conventional reactors typically generate over 1,000 megawatts of electricity (MWe), whereas SMRs usually produce less than 300 MWe per module [1, 2]. This reduced power output, combined with their modular design, enhances their versatility, allowing them to be deployed in a variety of applications and locations that may not be suitable for larger reactors [3].

The modular design of SMRs is one of their defining features, facilitating standardized manufacturing and potentially accelerating construction timelines. This modularity allows for the combination of multiple units to scale power production according to demand, thus providing flexibility in energy supply [2]. Furthermore, the compact size of SMRs necessitates less land and infrastructure, making them particularly suitable for remote or space-constrained areas [4]. Enhanced safety is another critical characteristic of SMRs; they incorporate passive safety systems that utilize natural processes such as gravity and convection to cool the reactor, which significantly reduces the risk of overheating and catastrophic failures [5]. This safety feature is particularly advantageous for deployment in isolated regions, islands, or small communities, where traditional reactors may not be feasible [6].

Economically, SMRs present several advantages. Their smaller initial investment costs make them more accessible, especially for countries or companies that may lack the capital for large-scale nuclear projects [7]. The modular construction and factory assembly processes streamline the building phase, potentially lowering overall costs and reducing construction timelines [7]. Additionally, the smaller physical footprint and enhanced safety measures of SMRs can mitigate their environmental and ecological impacts compared to conventional reactors [8].

In terms of applications, SMRs are poised to play a crucial role in the transition to clean energy. They can complement renewable energy sources in regions where renewables are limited by geographical or intermittency challenges [4]. Various countries and companies are exploring the potential of SMRs as a sustainable, low-carbon energy solution, emphasizing their capability to meet future energy demands while supporting global climate goals [8]. Their adaptability for diverse applications, including electricity generation, desalination, district heating, and industrial heat supply, further underscores their potential as a versatile energy source [9].

Interest in Small Modular Reactors (SMRs) has been expanding across various sectors, especially among those focused on energy, environmental sustainability, and economic development. SMRs represent a cleaner, low-carbon energy option, appealing to environmental advocates and policymakers who are working to reduce greenhouse gas emissions. These groups may find SMRs valuable because they offer an alternative to fossil fuels and can complement renewable sources like wind and solar. Learning about SMRs enables policymakers to design informed energy strategies and incentives, making SMRs a vital topic of interest for those shaping the future of sustainable energy.

For energy professionals and utility companies, SMRs offer flexibility and cost-effectiveness in delivering reliable power. Their ability to fill in when renewable sources fall short makes SMRs critical for maintaining grid stability and meeting fluctuating energy demands. Additionally, industries in remote locations, like mining operations and oil refineries, often require independent, dependable power sources. Understanding SMRs provides decision-makers in these sectors with potential solutions to power their operations without relying on distant grids.

Academics and researchers in fields such as nuclear physics, environmental science, and sustainable development also have an interest in SMRs. They study SMRs to explore technical capabilities, limitations, safety protocols, and their potential impact on global energy systems. This research not only advances academic knowledge but also supports the development of sustainable technologies and energy resilience solutions.

Several groups are particularly interested in the practical aspects of constructing SMRs. Nuclear engineers, mechanical and electrical engineers, and technicians in nuclear fields have a direct role in SMR design and construction. Knowledge of SMR technology allows these professionals to enhance their skills and align their expertise with emerging energy solutions. Construction and infrastructure firms, too, find SMRs appealing as they demand specialized skills in nuclear construction. For these firms, SMRs present a new growth area in clean energy infrastructure, especially as the demand for sustainable projects rises.

Government and military organizations often have strategic interests in SMR technology. Military bases in remote areas, for example, need reliable, independent power, and SMRs offer a potential solution. Defence and government agencies interested in energy security may find it worthwhile to understand SMR construction and implementation to support their missions and achieve energy independence. Similarly, energy and utility companies view SMRs as a potential long-term investment for diversifying their energy offerings, especially as public demand for clean energy options grows. SMRs could help these companies meet low-carbon energy goals and offer flexible power solutions.

Entrepreneurs and investors are also drawn to the potential of SMRs in the clean energy market. As interest in sustainable energy expands, understanding SMR construction and its regulatory landscape allows these stakeholders to make informed investment decisions in SMR technology and related projects.

This book provides content for learning about SMRs and their construction and suits those looking to contribute to the clean, reliable energy landscape. With the world increasingly focused on sustainable practices, SMRs offer a unique and scalable solution that bridges the gap between traditional energy sources and renewable options.

Chapter 1

Introduction to Small Modular Reactors (SMRs)

Understanding Small Modular Reactors

Overview

S

mall Modular Reactors (SMRs) represent a significant evolution in nuclear technology, characterized by their reduced size and power output compared to traditional nuclear reactors. Typically, SMRs generate up to 300 megawatts of electricity (MWe), contrasting with conventional reactors that can exceed 1,000 MWe. This smaller scale allows for modular construction, where components are manufactured in factories and then transported to the installation site, enhancing adaptability and deployment flexibility across various settings [2, 10, 11]. The modularity of SMRs not only facilitates faster construction timelines but also enables them to be deployed in locations with limited space, making them suitable for remote areas or regions with constrained infrastructure [11, 12].

The design of SMRs incorporates several features that enhance their appeal. Their modular nature allows for the assembly of smaller, standardized units, which can be combined to meet specific power generation needs. This flexibility is particularly advantageous in meeting diverse energy demands efficiently [11, 13]. Furthermore, SMRs typically require less supporting infrastructure than larger reactors, which contributes to their lower environmental impact and makes them a more sustainable option for nuclear energy [12, 13]. The compact design also allows for their integration with renewable energy sources, providing stable power in areas where grid access is limited [14].

Safety is a paramount concern in nuclear energy, and SMRs are designed with advanced safety features, including passive safety systems that utilize natural processes such as gravity and convection to maintain core cooling. This design minimizes the risk of overheating and enhances safety even in emergency situations where external power may be unavailable [11, 14]. The inherent safety characteristics of SMRs, coupled with their ability to operate independently or alongside renewable energy sources, position them as a viable solution for providing reliable, low-carbon power to small communities and industrial sites [15, 16].

The economic advantages of SMRs are also noteworthy. Their smaller size translates to lower initial capital investments, making nuclear energy more accessible to smaller markets and developing regions [17]. Additionally, the modular construction approach reduces construction times compared to traditional nuclear plants, further enhancing their economic viability [12, 13]. As countries increasingly seek clean energy solutions, SMRs are gaining traction as a complementary technology to renewable energy sources, capable of providing consistent power while supporting global sustainability goals [14, 15].

SMR Operation Principles

Small Modular Reactors (SMRs) represent a significant advancement in nuclear technology, utilizing nuclear fission to generate heat, which is subsequently converted into electricity. Similar to traditional nuclear reactors, SMRs operate by splitting uranium or other fissile materials in a controlled chain reaction. This process releases substantial amounts of heat, which is captured by a coolant, typically water, that circulates around the nuclear fuel. However, SMRs are distinct from conventional reactors in several key aspects, including their design, size, and safety features, which enhance their operational flexibility and efficiency across various applications.

The defining characteristic of SMRs is their electrical output, which is generally less than 300 MWe. This smaller scale allows for a variety of innovative designs that can be constructed more quickly and with lower financial risk compared to larger reactors. For instance, the integral pressurized water reactor (iPWR) is currently a leading design for near-term licensing and deployment, showcasing the modular construction and passive safety features that are hallmarks of SMR technology [11, 18, 19]. These reactors are particularly advantageous in locations lacking robust transmission or distribution infrastructure, as they can provide localized power generation for large population centres and specific industrial applications [3, 20, 21].

At the core of Small Modular Reactors, nuclear fuel is typically composed of uranium dioxide pellets that are encased in long fuel rods, arranged in assemblies within a reactor vessel. When fission occurs, uranium atoms split, releasing neutrons and energy. These neutrons can then collide with other uranium atoms, triggering further fission reactions, thereby establishing a self-sustaining chain reaction. This process is critical for the operation of nuclear reactors, including SMRs, as it generates the heat necessary for electricity production [5].

The heat generated from fission is absorbed by a coolant circulating around the fuel rods. This coolant, often water or a liquid metal such as sodium, plays a vital role in transferring heat away from the reactor core to prevent overheating and maintain safe operational conditions [22]. The heated coolant is subsequently directed to a steam generator or heat exchanger, where it transfers heat to water or another fluid, converting it into steam. This steam is then utilized to drive a turbine connected to an electrical generator, effectively converting thermal energy into mechanical energy, which is subsequently transformed into electricity [23].

SMRs are designed to produce approximately 300 megawatts of electricity (MWe) per module, although multiple modules can be installed together to meet larger power demands [24]. After passing through the turbine, the steam is condensed back into water and returned to the heat exchanger in a closed loop. This closed-loop system allows for the continuous recycling of water, ensuring a consistent and efficient cycle for electricity generation [25]. The integration of advanced heat exchangers is essential for optimizing this process, as they enhance heat transfer efficiency and contribute to the overall safety and reliability of the reactor system [26].

The operational principles of SMRs hinge on the effective management of nuclear fission reactions, the efficient transfer of heat through advanced cooling systems, and the conversion of thermal energy into electrical power. The design and implementation of these systems are important for maximizing the efficiency and safety of nuclear power generation [27].

Small Modular Reactors (SMRs) represent a significant advancement in nuclear reactor design, particularly due to their incorporation of passive safety systems. These systems leverage natural processes, such as gravity and convection, to maintain core cooling without the need for active mechanical controls or external power sources. For instance, the passive safety features of SMRs allow for gravity-fed coolant circulation, which can effectively cool the reactor core even during emergencies when external power or human intervention is unavailable. This design significantly mitigates the risk of overheating or meltdown, as it reduces reliance on pumps and other active cooling mechanisms that are prone to failure [5, 28, 29].

The development of passive safety systems in SMRs has its roots in the lessons learned from past nuclear accidents, such as those at Three Mile Island and Fukushima. These incidents highlighted the necessity for designs that inherently minimize risks. The concept of passive safety was formalized in the 1980s and has since evolved into the modern designs seen in SMRs today, which are engineered to be inherently safe and capable of managing decay heat without operator action [5, 29]. For example, the Westinghouse SMR incorporates an integral pressurized water reactor (iPWR) design that houses all components within a single pressure vessel, further enhancing safety and simplifying the reactor's overall design [28].

In addition to their passive safety features, SMRs are characterized by their compact design. Many models integrate the reactor core, steam generator, and containment systems into a single module, which simplifies the reactor architecture and reduces the number of components that could potentially malfunction [11, 29]. This compact structure not only enhances safety but also allows for installation in various environments, including below ground or within specially designed containment pools. Such design choices provide additional protection against external threats, including natural disasters and security breaches [30, 31]. The compact nature of SMRs also facilitates easier transportation and deployment, making them suitable for a wider range of applications, including those in developing regions with limited infrastructure [11, 29].

Furthermore, the passive cooling mechanisms employed in SMRs, such as natural circulation and convection, are designed to operate effectively without the need for electrical power. This is particularly crucial in scenarios where power loss occurs, as demonstrated by the incorporation of passive containment cooling systems in designs like the AP1000 [32, 33]. The ability of these systems to maintain cooling through natural processes not only enhances the safety profile of SMRs but also aligns with the growing emphasis on sustainability and resilience in nuclear power generation [34].

Figure 1: Illustration of a light water small modular nuclear reactor (SMR). U.S. Government Accountability Office from Washington, DC, United States, Public Domain, via Wikipedia.

Figure 1 shows a simplified diagram of a Small Modular Reactor (SMR) system, depicting its main components and the process of converting nuclear fission into electricity. The SMR is housed within a containment structure, designed to ensure safety and isolate the reactor from the external environment in case of any operational issues. Inside this containment structure lies the reactor vessel, where the nuclear fission reaction takes place. The reactor vessel contains the reactor core, made up of fuel rods with fissile material, such as uranium, which undergoes controlled fission reactions to generate heat.

Above the reactor core, the diagram shows the pressurizer. The pressurizer maintains the reactor's pressure, keeping the coolant water at high temperatures without boiling. This high-pressure environment enables efficient heat transfer from the reactor core to the coolant circulating through the system. The coolant absorbs the heat produced by the fission reactions in the core and flows upwards and out of the reactor vessel.

The heated coolant is then directed to a steam generator. In this component, the heat from the coolant is transferred to a separate loop of water, turning it into steam. This separation ensures that the water producing steam remains free of radioactive contamination. The steam generator, therefore, acts as a heat exchanger, allowing heat transfer without direct contact between the radioactive coolant and the steam that will eventually drive the turbine.

The steam produced by the steam generator flows into a turbine, where it expands and spins the turbine blades. The turbine is connected to a generator, which converts the mechanical energy from the turbine's rotation into electrical energy. This generated electricity is then transmitted through power lines to the grid, where it can supply power to homes, industries, and other infrastructure. The image illustrates this by showing the generator connected to an electrical transmission tower and a city, symbolizing the end-use of the generated power.

Once the steam has passed through the turbine and released its energy, it is condensed back into water and returned to the steam generator in a closed-loop system. This closed-loop design allows the steam to be reused, conserving water and maintaining efficiency in the power generation process.

A small figure of a six-foot-tall person is included in the diagram for size comparison, indicating that the containment structure housing the SMR is compact relative to traditional nuclear reactors. This compact design is a key characteristic of SMRs, allowing them to be deployed in a wider range of locations, including remote or space-limited sites. The compact size and modular nature of SMRs are crucial for their flexibility and scalability in different energy settings.

Nuclear Fission

Nuclear fission is a process in which the nucleus of a heavy atom, such as uranium or plutonium, splits into two smaller nuclei, releasing a significant amount of energy in the form of heat and radiation. This process occurs when a neutron collides with the nucleus of a fissile atom, causing it to become unstable and split as shown in Figure 2. Nuclear fission is the fundamental reaction used in nuclear power plants and atomic bombs, although the controlled environment in a nuclear power plant allows it to be used safely for energy production.

Figure 2: Nuclear reaction. Nuclear Regulatory Commission, CC BY 2.0, via Flickr.

The fission process begins when a neutron is absorbed by the nucleus of a fissile atom, like uranium-235 or plutonium-239. The absorption of this neutron destabilizes the nucleus, causing it to stretch and eventually split into two smaller nuclei, known as fission fragments. Alongside this splitting, two or three additional neutrons are usually released, along with a large amount of energy. This energy comes from the strong nuclear force, which holds the protons and neutrons together in the nucleus. When the nucleus splits, some of this binding energy is released as kinetic energy of the fission fragments and the emitted neutrons. This kinetic energy is then converted into heat as the particles collide with surrounding atoms.

The emitted neutrons from the fission event can collide with other nearby fissile nuclei, causing further fission reactions in a self-sustaining chain reaction. This chain reaction is the basis for generating energy in nuclear reactors. In power plants, materials like uranium-235 are arranged in such a way that the chain reaction can be carefully controlled. Control rods, typically made from materials that absorb neutrons like boron or cadmium, are used to regulate the reaction rate. By adjusting the position of these control rods, operators can slow down or speed up the fission process, thereby controlling the amount of heat generated.

Figure 3: Illustration of a typical nuclear fission reaction. MikeRun, CC BY-SA 4.0, via Wikimedia Commons.

Figure 3 illustrates the process of nuclear fission, specifically showing how a uranium-235 nucleus undergoes fission when struck by a neutron. This chain of reactions is fundamental to the operation of nuclear reactors, as it releases a significant amount of energy. The illustration shows the sequence of steps involved in a single fission event and highlights the products of this process.

In the initial stage, a neutron (represented as n in the diagram) collides with a uranium-235 nucleus. Uranium-235 is a fissile isotope, meaning it can undergo fission when struck by a neutron, especially a slow-moving, or thermal, neutron. Upon absorbing the neutron, the uranium-235 nucleus becomes highly unstable and temporarily forms uranium-236 .

This unstable uranium-236 nucleus cannot hold together for long and soon splits into two smaller, more stable nuclei, known as fission fragments. In this example, the fission of uranium-236 produces two specific fragments: barium-144 and krypton-89 . These nuclei are lower in atomic number and more stable than uranium, but they are still radioactive and will eventually decay to achieve stability.

In addition to the barium and krypton nuclei, the fission reaction releases a significant amount of energy, primarily in the form of kinetic energy of the fission fragments, which eventually translates into heat. This heat is what nuclear reactors capture to produce steam and generate electricity.

Moreover, the fission process releases additional neutrons—typically two or three—as shown in the image. These neutrons are crucial for sustaining the fission reaction in a chain reaction. When released, these neutrons can go on to strike other uranium-235 nuclei, causing further fission events. In a controlled environment, such as a nuclear reactor, this chain reaction is carefully managed to produce a steady output of energy. In an uncontrolled environment, such as a nuclear bomb, the chain reaction accelerates rapidly, resulting in a massive energy release.

Figure 4: Illustration of a nuclear fission chain reaction. MikeRun, CC BY-SA 4.0, via Wikimedia Commons.

Figure 3 captures the essential elements of nuclear fission: the absorption of a neutron by a uranium-235 nucleus, the formation and subsequent splitting of an unstable uranium-236 nucleus, the production of fission fragments (barium and krypton in this case), the release of additional neutrons, and the substantial energy release. This process is foundational to nuclear energy, as the energy from repeated fission events is harnessed to generate electricity in nuclear reactors. The careful control of this reaction is what differentiates peaceful nuclear power generation from the explosive power of nuclear weapons.

Figure 4 illustrates a chain reaction process in nuclear fission, showing how a single fission event can initiate a series of subsequent fission reactions. This cascade effect is central to the function of nuclear reactors and atomic bombs, as it demonstrates how the energy release from fission can be sustained and amplified. The diagram specifically uses uranium-235 nuclei to show this process, highlighting the fission fragments and additional neutrons produced in each reaction.

At the beginning of the chain reaction, a neutron collides with a uranium-235 nucleus, transforming it into uranium-236 , which is highly unstable. This instability causes the uranium-236 nucleus to split into two smaller nuclei, known as fission fragments, along with the release of additional neutrons. In this case, the fission fragments include elements like barium-144 , krypton-89 , and cesium-137 , among others. These fission fragments vary depending on the specific fission event, as uranium-235 can split in multiple ways, producing different pairs of elements each time.

Each fission event also releases additional neutrons, typically two or three per reaction. These neutrons are critical for sustaining the chain reaction, as they can go on to collide with other nearby uranium-235 nuclei, inducing further fission reactions. In the image, these subsequent reactions are depicted branching out from the initial fission event, with each new uranium-235 nucleus undergoing fission after being struck by a neutron. This process creates a branching pattern, with each generation of reactions leading to more fission events, releasing more energy and more neutrons in an exponential manner.

The fission fragments shown in the diagram include a variety of elements, such as rubidium-96 , strontium-90 , xenon-144 , and iodine-131 . These fission products are radioactive and will eventually decay into stable isotopes over time, but their immediate byproducts contribute to the radioactivity of spent nuclear fuel, which requires careful handling and storage.

The released neutrons and the energy produced in each fission event are fundamental to both nuclear power generation and nuclear weapons. In a nuclear reactor, this chain reaction is carefully controlled to maintain a steady rate of fission, with only one of the released neutrons from each fission event continuing the reaction to the next uranium-235 nucleus. Control rods made of neutron-absorbing materials, such as boron or cadmium, are used to capture excess neutrons and regulate the reaction rate, preventing it from accelerating uncontrollably.

However, in an atomic bomb, the chain reaction is designed to proceed without control, allowing each fission event to trigger multiple subsequent reactions. This creates a rapidly accelerating chain reaction, releasing a massive amount of energy in a very short time, resulting in an explosion.

Overall, Figure 4 illustrates the self-sustaining nature of a nuclear chain reaction, showing how the fission of uranium-235 nuclei can lead to successive reactions that produce energy and additional neutrons. This process underpins the operation of nuclear reactors, where the reaction rate is controlled for safe energy production, as well as nuclear weapons, where the chain reaction is allowed to proceed uncontrolled for explosive force. The branching effect shown in Figure 4captures the exponential nature of the chain reaction, highlighting both the power and the importance of careful management in nuclear fission technology.

The heat produced by nuclear fission is harnessed to produce electricity. In a nuclear reactor, the fission reaction heats a coolant—usually water—that flows around the reactor core. This heated coolant is then used to generate steam, which drives a turbine connected to a generator, converting the thermal energy from fission into electrical energy. In contrast, in an atomic bomb, the fission reaction is uncontrolled, allowing a rapid, exponential chain reaction that releases a massive amount of energy almost instantaneously.

Fission reactions also produce radioactive waste, as the fission fragments are typically unstable and emit radiation as they decay into stable forms. The handling and disposal of these radioactive byproducts are critical considerations in nuclear power, as they require secure storage for long periods to prevent environmental contamination. The energy released by fission is substantial; just a small amount of uranium can produce more energy than several tons of coal or oil, making it an efficient but complex energy source.

One of the challenges in nuclear fission is managing the reaction rate to maintain a stable output of energy. In a power reactor, this is achieved by maintaining a critical state, where each fission event, on average, leads to exactly one more fission event, ensuring a steady release of energy. If the chain reaction accelerates uncontrollably, it could lead to overheating, which is why safety measures such as cooling systems, containment structures, and emergency shutdown procedures are integral to nuclear reactor design.

Managing the reaction rate in nuclear fission is essential for ensuring a stable and controlled energy output in nuclear reactors. Fission, the process of splitting atomic nuclei, releases energy and produces neutrons that can initiate further fission reactions in adjacent nuclei. This chain reaction must be meticulously regulated to prevent fluctuations in energy output, which could lead to hazardous conditions, such as overheating or reactor core damage [35]. The objective is to achieve a critical state where, on average, each fission event results in exactly one subsequent fission event, thereby maintaining a steady and manageable energy release [35].

If the reaction rate surpasses this critical state, where each fission event leads to more than one subsequent event, the chain reaction can escalate uncontrollably, resulting in a condition known as supercriticality. This scenario poses significant risks, including overheating of the reactor core, potential fuel melting, and damage to the reactor structure, which could lead to radiation release if containment measures fail [35]. To mitigate these risks, nuclear reactors are equipped with various systems designed to monitor and control the reaction rate with precision [35].

A primary safety feature in nuclear reactors is the implementation of control rods, which are composed of materials that absorb neutrons, such as boron or cadmium. By adjusting the position of these control rods—either inserting or withdrawing them from the reactor core—operators can regulate the number of neutrons available to sustain the chain reaction. This mechanism allows for the slowing down of the reaction rate, ensuring that it does not accelerate uncontrollably [35]. Operators must be adept at positioning these rods to maintain the desired critical state, adjusting for any changes in reactor conditions or power demand [35].

In addition to control rods, effective cooling systems are vital for managing the heat generated during fission. These systems circulate coolant, typically water, around the reactor core to absorb and dissipate heat produced by the fission process. A failure in the cooling system could lead to a dangerous rise in core temperature, risking core damage and potential meltdown [35]. Therefore, cooling systems are designed with redundancies and backup measures to ensure reliable operation, even in the event of primary system failure [35].

The containment structure surrounding the reactor is another critical safety feature. This robust, sealed building is designed to prevent the escape of radioactive materials in case of an accident. In the unlikely event of a malfunction or breach within the reactor, the containment structure serves as a final barrier, protecting the environment and public from radiation exposure [36]. Typically constructed from thick concrete and steel, the containment building is engineered to withstand extreme conditions, including potential explosions and natural disasters [36].

Finally, emergency shutdown procedures, commonly referred to as SCRAM systems, are implemented as an immediate safety response if the reactor exhibits signs of instability. A SCRAM system rapidly inserts all control rods fully into the core, effectively halting the fission process by absorbing the majority of neutrons and stopping the chain reaction [35]. This rapid shutdown mechanism is crucial for preventing overheating or other dangerous scenarios when the reactor's automatic control systems detect criticality issues or equipment malfunctions [35].

The combination of control rods, cooling systems, containment structures, and emergency shutdown procedures constitutes a comprehensive safety framework for managing the fission reaction rate in nuclear reactors. By maintaining a steady and controlled chain reaction, these systems ensure the safe and efficient operation of nuclear power plants, allowing for reliable energy generation while minimizing the risk of accidents. Properly balancing the fission reaction rate is therefore fundamental to nuclear reactor design, facilitating sustained power generation without compromising safety [35].

SMR Safety Systems

Safety is a paramount concern in nuclear energy, and SMRs are designed with enhanced safety features that differentiate them from traditional reactors. Many SMR designs incorporate passive safety systems that do not rely on active mechanical systems to maintain safety during abnormal conditions. This design philosophy stems from lessons learned in the nuclear industry, particularly after incidents such as the Three Mile Island accident, which highlighted the need for inherently safe reactor designs [29, 37]. The passive safety features of SMRs allow them to operate with a reduced risk of catastrophic failures, making them an attractive option for both developed and developing regions [3, 38].

Small Modular Reactors (SMRs) are emerging as a pivotal innovation in nuclear energy, primarily due to their advanced safety systems designed to enhance reliability and minimize the risk of accidents. Unlike traditional large-scale nuclear reactors, SMRs incorporate both active and passive safety features that contribute to their inherent safety profile. These systems are engineered to prevent overheating, manage radiation containment, and ensure safe shutdown processes, thereby reducing the necessity for human intervention during emergencies [11, 16, 29].

A key aspect of SMR safety is the implementation of passive safety systems. These systems leverage natural phenomena such as gravity, convection, and conduction to maintain reactor cooling without relying on external power or mechanical components. For instance, in the event of a power loss, passive cooling mechanisms can continue to operate autonomously, utilizing gravity-driven coolant flow to avert overheating [39, 40]. This contrasts sharply with traditional reactors, where active cooling systems are vulnerable to failure during power outages or mechanical malfunctions. The reliance on passive systems in SMRs significantly enhances their resilience during emergencies, thereby providing a robust alternative for maintaining core temperatures [16, 28].

Moreover, the modular design of SMRs contributes to their safety by confining critical components within a single, compact unit. This configuration reduces system complexity and minimizes potential failure points, which are often exacerbated by human error or equipment malfunction [11, 41]. By integrating the reactor core, cooling systems, and containment structures into a single module, SMRs facilitate easier maintenance and repair processes, as components can be isolated without impacting the entire system [42, 43]. Additionally, the capability to install SMRs below ground or within protective containment pools offers an extra layer of security against external threats such as natural disasters or security breaches [44].

Containment systems in SMRs are meticulously designed to prevent the release of radioactive materials during accidents. These systems typically feature multiple barriers, including a steel-lined containment vessel encased in thick concrete walls, which provide substantial shielding against radiation leaks [45, 46]. Furthermore, the smaller fuel quantities used in SMRs compared to traditional reactors inherently reduce the potential scale of any radioactive release. Some designs even utilize coolants like molten salt, which are less prone to vaporization under high temperatures, thereby further mitigating the risk of pressurized releases [5, 39].

Automatic shutdown capabilities are another critical safety feature of SMRs. Many designs are equipped with systems that can detect abnormal conditions, such as overheating, and initiate an immediate shutdown sequence autonomously. This SCRAM system rapidly inserts control rods into the reactor core, effectively halting the fission process and allowing passive cooling systems to maintain safe temperatures [16, 47]. The simplicity and fewer components in SMR designs enhance the reliability and speed of these shutdown systems, which can act within seconds during emergencies [40, 41].

Fail-safe designs are integral to SMR technology, reducing risks associated with human error and unexpected events. SMRs often utilize straightforward, intuitive control systems that minimize the likelihood of operator mistakes. Additionally, many designs operate at low pressures, which are less likely to fail catastrophically compared to high-pressure systems, further enhancing their safety profile [11, 39, 40]. This layered approach to safety, which combines both passive and active systems with redundancies, positions SMRs as exceptionally resilient against potential disruptions [16, 48].

Modular Functionality

The modular nature of SMRs means they can be built in factories under controlled conditions and then transported to their operational sites. This approach enables faster and more efficient construction than traditional, large-scale nuclear plants, which must often be built on-site. Because of their smaller size and lower power output, SMRs are suitable for diverse applications beyond traditional power generation. They can provide energy to isolated or remote communities, supplement renewable energy sources in areas with inconsistent power supply, and even be used for industrial processes, desalination, or hydrogen production.

SMRs generate electricity through nuclear fission, using a compact, modular design that incorporates passive safety features and integrated systems for heat exchange and containment. This design enhances the safety, efficiency, and adaptability of SMRs, making them a versatile solution for reliable, low-carbon energy in various settings. Their unique construction and operation make SMRs a promising component of the future energy landscape, bridging the gap between traditional nuclear power and the needs of modern, sustainable energy systems.

Small Modular Reactors (SMRs) can be combined in parallel to generate more megawatts of electricity (MWe), creating what is known as a multi-module nuclear power plant. This modular approach allows for scalability in power generation to meet specific energy needs, enabling a plant to start with a small number of SMRs and add more modules over time as demand increases. However, SMRs are not typically combined in series; rather, they are connected in parallel. Here’s how it works and why this design is beneficial:

Parallel Configuration of SMRs

In a parallel configuration, each SMR operates independently and feeds its generated electricity to a shared power grid or distribution system. Each reactor module has its own reactor core, cooling system, steam generator, and turbine, functioning as a self-contained unit. By connecting multiple SMRs in parallel, a nuclear facility can increase its total power output, with each module contributing a set amount of megawatts to the overall generation capacity.

For instance, if each SMR module produces 77 MWe, then a multi-module plant with 6 SMRs operating in parallel would have a total generating capacity of around 462 MWe. This modularity provides flexibility, allowing power plant operators to add or remove modules based on demand or maintenance requirements without affecting the operation of other modules.

Parallel operation in SMRs works as follows:

Independent Operation and Redundancy: Each SMR module operates independently, with its own control and safety systems. This design allows each module to be shut down or serviced without affecting the rest of the plant. If one module needs maintenance, the other modules can continue to supply power, providing reliability and redundancy that large reactors lack.

Shared Electrical Output: The power generated by each SMR module is directed to a common electrical bus, which consolidates the power output and delivers it to the grid. By using multiple modules, the combined output of the plant can meet a wide range of power demands. For example, an SMR facility could add modules over time to reach a desired capacity, scaling up as energy needs grow or replacing older modules without disrupting the overall power supply.

Load Following and Flexibility: SMRs configured in parallel provide load-following capabilities, meaning they can adjust output to meet varying demand. In times of lower demand, some modules can be operated at reduced power or temporarily shut down. During peak demand, additional modules can be brought online to provide extra power. This flexibility is especially beneficial for integrating with renewable energy sources like wind and solar, which are intermittent. SMRs can provide consistent power when renewable sources fluctuate, ensuring grid stability.

Centralized and Efficient Cooling: Although each module has its own cooling system, SMR plants often use a centralized cooling infrastructure that serves all modules. The cooling system can be designed to scale with the number of modules, allowing a single plant to efficiently manage heat from multiple reactors. This centralized cooling system streamlines operation and maintenance, as it consolidates cooling infrastructure for multiple reactors.

Combining reactors in series is not practical in nuclear power design. In a series configuration, each reactor would depend on the output of the previous one, creating interdependencies that could compromise safety and reliability. In nuclear reactors, each module needs to operate as an independent unit with direct access to its coolant and safety systems. A series setup would complicate the design, making it more difficult to control individual reactor operations, manage safety, and ensure that all modules can be safely isolated if necessary.

Moreover, SMRs are designed to produce electricity directly from each module’s steam cycle, driving its own turbine-generator setup. In a series configuration, the heat or steam from one reactor would need to pass through another reactor, which is not feasible due to the temperature, pressure, and complexity of reactor operations.

The benefits of parallel SMR configurations include:

Scalability: Parallel configurations allow plant operators to scale up power generation incrementally. New modules can be added as demand increases, making it easier to expand capacity compared to a single large reactor.

Flexibility: Parallel operation supports load-following, allowing operators to adjust power output based on real-time demand. Some modules can be run at reduced power or shut down when less electricity is needed.

Enhanced Safety and Reliability: The independence of each module allows for easy isolation in case of issues. If one SMR needs maintenance or encounters an issue, the remaining modules can continue operating without interruption, enhancing reliability.

Simplified Maintenance and Reduced Downtime: Since each SMR is a self-contained unit, maintenance can be performed on individual modules without affecting the operation of the entire plant. This setup minimizes downtime and enhances operational flexibility.

Cost-Effective Expansion: SMRs can be deployed in stages, spreading out costs over time rather than requiring a large upfront investment. This staged approach makes it easier for utilities and governments to finance projects.

An example of a multi-module SMR plant is the proposed NuScale Power Plant. Each NuScale Power Module produces 77 MWe, and up to 12 modules can be combined within a single plant, generating a total output of 924 MWe. This setup enables the plant to adjust its output according to grid demand and provides redundancy by ensuring that each module can be independently operated, maintained, or shut down without impacting the others.

Figure 5: Diagram of a NuScale reactor. NuScale, CC BY-SA 3.0, via Wikimedia Commons.

As an example of application of multiple SMRs, to estimate the number of Small Modular Reactors required to power cities of various sizes, we need to look at average power consumption rates for cities of these populations. Power consumption can vary significantly depending on factors such as climate, industrial activity, and lifestyle, but we can use approximate per capita power consumption values to make a rough estimate.

Assumptions for Calculation:

Average power consumption per person in developed countries: Approximately 4 kW per person (combining residential, commercial, and industrial demand).

Output of a typical SMR: Modern SMRs typically produce between 50 MWe to 300 MWe per unit. For this calculation, we’ll use a commonly referenced SMR output of 100 MWe per unit for simplicity.

Using these assumptions:

4 kW per person is approximately equivalent to 4 MW per 1,000 people.

The total power requirement can be calculated by multiplying the population by 4 MW per 1,000 people.

We then divide this total power requirement by the output of one SMR (100 MWe) to determine the number of reactors needed.

Calculating for each city:

1. City of 100,000 People (e.g., Fairfield, California, US)

Total Power Requirement = 100,000 people × 4 MW per 1,000 people = 400 MW

Number of 100 MWe SMRs needed = 400 MW ÷ 100 MWe = 4 SMRs

So, it would take approximately 4 SMRs to power a city of 100,000 people.

2. City of 1,000,000 People (e.g., Austin, Texas, US)

Total Power Requirement = 1,000,000 people × 4 MW per 1,000 people = 4,000 MW

Number of 100 MWe SMRs needed = 4,000 MW ÷ 100 MWe = 40 SMRs

Therefore, around 40 SMRs would be needed to power a city of 1,000,000 people.

3. City of 5,000,000 People (e.g., Melbourne, Victoria, Australia)

Total Power Requirement = 5,000,000 people × 4 MW per 1,000 people = 20,000 MW

Number of 100 MWe SMRs needed = 20,000 MW ÷ 100 MWe = 200 SMRs

Thus, 200 SMRs would be required to meet the power needs of a city of 5,000,000 people.

4. City of 10,000,000 People (e.g., Nagoya, Japan)

Total Power Requirement = 10,000,000 people × 4 MW per 1,000 people = 40,000 MW

Number of 100 MWe SMRs needed = 40,000 MW ÷ 100 MWe = 400 SMRs

For a large metropolis of 10,000,000 people, approximately 400 SMRs would be needed.

Summary of Results

Considerations

Redundancy and Load Management: In practice, a few additional SMRs might be added to account for redundancy, maintenance, and peak demand periods, so the actual number could be slightly higher.

Variability in Power Demand: Power demand per capita varies between cities and countries, so a city with significant industrial activity or extreme climate conditions may require more SMRs.

SMR Output Variability: Some SMRs are designed to produce more (up to 300 MWe), meaning fewer reactors would be needed if using higher-output models.

These numbers provide a general estimate, but actual deployment would depend on detailed assessments of the city's specific power needs and the SMR models used.

these calculations make a compelling argument for the potential of Small Modular Reactors (SMRs) in addressing the power needs of cities of varying sizes. The results highlight several key advantages and applications of SMRs, especially in terms of scalability, flexibility, and suitability for diverse environments. Here’s a deeper look at how these numbers support the case for SMRs and what they reveal about their applications:

1. Scalability and Flexibility: The calculations show that SMRs can be deployed in modular units to match the specific power demands of a city. For a smaller city of around 100,000 people, only a few SMRs would be necessary, while a metropolis of 10 million people would require many more. This modular approach allows for incremental, flexible power generation that can grow alongside a city’s population and industrial demands. Unlike large traditional nuclear plants, which are often built to produce thousands of megawatts at once, SMRs can be added over time, providing a tailored solution for both urban and rural areas.

2. Suitability for Smaller or Remote Communities: The basic analysis suggests that SMRs are particularly well-suited to smaller cities and remote communities that may not need the vast output of a full-sized nuclear plant. For example, a small city or isolated area could rely on a few SMRs to provide steady, reliable power without requiring the high investment and large infrastructure footprint associated with traditional nuclear plants. This makes SMRs a practical solution for regions with limited access to large power grids or those looking to achieve energy independence, such as island communities or areas where renewable sources alone may not be reliable.

3. Complementary to Renewable Energy Sources: SMRs can act as a stable, low-carbon energy source that complements renewable sources like wind and solar. In cities with fluctuating energy demands or variable renewable output, SMRs can provide consistent baseload power, helping to balance the grid when renewables are not generating. Their modular design allows utilities to add SMRs as needed, potentially reducing reliance on fossil fuels and ensuring grid stability as renewables continue to expand. For larger cities looking to decarbonize, SMRs could provide the dependable power necessary to offset