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Singapore has set an ambitious target of achieving net-zero emissions by 2050, prompting the exploration of low-carbon alternatives to reduce its dependence on fossil fuels and to diversify its energy mix. Singapore currently derives 86% of its energy consumption from petroleum and other liquids, with natural gas accounting for 13%. However, it must import two-thirds of its crude oil and imports natural gas through pipelines as well as liquefied natural gas. This large amount of energy imports not only cause Singapore to lose a significant amount of foreign currency reserves but also poses a risk to the country’s energy security.

Nuclear energy is not weather-dependent and requires relatively little fuel to generate a significant amount of power. Meanwhile, stockpiling of uranium for nuclear power is a viable solution in enhancing Singapore’s long-term energy security. The Energy 2050 Committee has therefore identified Small Modular Reactors (SMRs) as a viable option to decarbonise the power sector and increase energy security.

Despite the potential benefits of nuclear energy for Singapore, establishing a nuclear plant in such a densely populated country poses a certain set of challenges and risks. The risks associated with nuclear energy are not solely technological but also sociological and environmental. Many conservationists remain opposed to its use due to concerns about the high risks it potentially poses to the population, the environment, and neighbouring countries. Risks include casualties and health risks due to radioactive exposure, security threats such as terrorist attacks, and environmental contamination. A comprehensive risk analysis provides insights into the risks and benefits of nuclear energy in a densely populated country, which can be used to make informed decisions about its use. It is crucial to thoroughly consider, assess, and evaluate all potential hazards before embarking on nuclear projects. This should be carried out by forming a team of trained experts, including scientists, engineers, and specialists from various fields to provide insights into nuclear energy technology, procedures, programmes, control measures, and risks, and act as advisors to the government on nuclear safety matters.

Key factors for ensuring safe nuclear energy operation are strict governance, robust safety procedures, and effective measures. By combining these elements with the latest advancements in nuclear technology and plant design, the probability of nuclear accidents can be significantly reduced.

Bowtie analysis of operating SMRs

The operation of a nuclear power plant is associated with several hazards that can have serious consequences for public health and the environment. Natural hazards, such as earthquakes, severe weather, wildfires, and flooding, are well documented. Human errors in nuclear plant design, maintenance, and operation are also reported that can cause the failure of critical equipment. In addition, nuclear power plants are also vulnerable to intentional harm caused by sabotage, terrorism, and cyberattacks.

The economic impact of a nuclear disaster can extend beyond the immediate area, causing damage to property, businesses, and investments and can have an impact on the health and well-being of neighbouring communities. This is particularly relevant for neighbouring countries such as Malaysia and Indonesia. Given the consequences, fear of a nuclear disaster can if not managed properly, lead to widespread scepticism of nuclear energy, which can have further societal and psychological effects.

Based on the identified hazards and potential consequences, a qualitative bowtie diagram, Figure 1, provides a visual representation of the potential treats to a nuclear power plant, the potential consequences, and the suggested barriers to prevent or mitigate those consequences.

Comparative analysis on reactor types

To further enhance the broad-based control measures depicted in the bow-tie diagram, it is crucial to gather and thoroughly analyse data from past incidents. This process enables the identification of causes of such incidents, the detection of patterns and trends, and the development of effective solutions to mitigate the risks.

The study aimed to identify the types of reactors that have contributed the most to nuclear accidents, as well as the common causes of safety system failures. However, the committee noted that such incidents primarily involved large conventional reactors and may not accurately reflect the safety risks associated with the SMRs that Singapore is considering. SMRs are gaining traction as a preferred option in the energy market due to their potential to provide flexible, affordable, and low-carbon energy. However, given their relatively recent emergence and unique design, there is currently limited data available on SMR nuclear accidents. To address this gap, this study relied on a database of nuclear events to expand the available information and develop sound recommendations for the Singapore government.

According to the analysis, Pressurized Water Reactors (PWRs) were found to be the most common type of reactor involved in nuclear events, accounting for 784 (62%) out of 1,256 incidents, followed by Boiling Water Reactors (BWRs) with 382 (30%) events. Further analysis revealed that the causes of nuclear events varied between them.

According to this data, design residuals are the leading cause of nuclear events for both PWRs and BWRs. Therefore, it is important to consider inherently safer designs when setting up SMRs in Singapore, and foreseeable operational risks must be addressed during the design stage. To prevent operator errors, design verification and testing can be conducted to ensure that operations are robust and that systems can safeguard operations from operator error.

While Singapore is unlikely to experience natural disasters such as earthquakes or tsunamis that could trigger a nuclear accident, tremors from earthquakes in neighbouring countries can occasionally be felt on the island. Thus, it is still recommended to design and build SMRs that can withstand tremors and other natural hazards to increase safety margins. This is also a requirement by the Nuclear Regulatory Commission for all nuclear plants in the United States, following lessons from the 2011 Fukushima Daiichi accident.

SMR retrofitting for Singapore

To ensure the continued safety and reliability of nuclear facilities, as well as to gain valuable experience and test new technologies, the implementation of a pilot project to retrofit SMRs prior to the construction of full-scale nuclear facilities is recommended. By retrofitting SMRs with advanced safety features and monitoring systems, we can evaluate their performance in a controlled environment and make any necessary improvements before scaling up to larger facilities.

SMRs require an Emergency Planning Zone (EPZ) with a radius of less than 0.3 km. The existing power stations in Singapore are located in industrial areas away from densely populated residential areas. The approximate distances between the power stations and the densely populated areas show that any of the three power stations can be retrofitted with SMRs while maintaining a safe distance from densely populated areas. Using Hierarchical Clustering analysis, the Senoko Power Station has been identified as the most suitable candidate for the initial conversion, with the potential to retrofit the other two stations in the future.

The selection of the Senoko Power Station as the primary candidate for SMR retrofitting is based on several factors, including its age of over 30 years and its reliance on oil that emits high levels of carbon dioxide. After a thorough evaluation of the power station’s various plants, the Hitachi 1983 Steam Thermal Plant, specifically either G7-243MW or G8-250MW, has been identified as the most suitable option for retrofitting with SMRs. To ensure the safe and efficient operation of the retrofitted plant, it is recommended to use an Integrated Pressurized Water Reactor (iPWR) for the project. This type of land-based, water-cooled SMR has a power range of 151 MWe to 250 MWe and can be matched with either the G7-243MW or G8-250MW oil-based plant for a one-to-one retrofitting capacity. Several models, including NUWARD, W-SMR, or mPower, are suitable for this project.

The retrofitting of SMRs may also present several construction and operational risks, which can be mitigated through the use of digital twin software and machine learning. The implementation of digital twin software and machine learning to simulate and evaluate the performance of SMRs will be an essential component of the SMR retrofitting process, allowing for thorough testing and optimisation of the technology prior to deployment. Digital twin models can help identify and prevent potential safety hazards, such as runaway reactions or loss of containment, by providing a virtual environment to test and optimize the technology. Machine learning techniques, such as supervised learning, can be utilised to ensure the safe operation of SMRs by detecting anomalies and predicting potential failures. Unsupervised learning, on the other hand, can optimise the maintenance and life cycle costing of all equipment by analysing patterns and identifying areas for improvement. Incorporating digital twin software and machine learning into the SMR retrofitting process can ensure the safe and efficient operation of these reactors. This approach will allow us to identify and resolve potential issues early on, minimising risk and ensuring the long-term sustainability of the facility.

Inherent safe design of SMRs

Based on comparative analysis, design errors have been identified as the leading cause of nuclear events. To mitigate this risk, it is imperative that the proposed Integrated Pressurized Water Reactor (iPWR) for Singapore is designed to be inherently safe, with a range of advanced features including:

  • The ability to operate for more than three days without operator intervention for any design basis accidents and loss of electrical power supply under normal and emergency conditions.
  • State-of-the-art fully digital Nuclear Instrumentation & Controls (I&C) powered by internal batteries for safe state monitoring without internal or external electrical power supply for up to three days.
  • Process I&C that keeps the reactor in operation while maintenance I&C, which is independent from process I&C, remotely logs and implements predictive-based maintenance. The system data is under the control of a dedicated team in a remote-control room to protect the system from cyber-attacks.
  • Active and passive safety management of core meltdown accidents with corium.

 

Another passive approach to nuclear safety is the use of in-vessel retention of the melted core, which can contain a core melt accident within the plant, thereby eliminating the need for evacuation measures for the surrounding area. This enables a smaller emergency planning zone to be established within the plant boundary. Additionally, the semi-buried (25m) underground nuclear configuration offers protection against potential acts of terrorism or malicious commercial plane crashes, as well as against the release of radioactive materials. This feature provides an added layer of protection against accidents and risks, ensuring the safety of the plant and the surrounding environment.

Emergency preparedness

Despite the safety measures put in place, accidents may still occur. Therefore, it is crucial to have a comprehensive on-site and off-site emergency response plan that can manage a credible nuclear plant emergency scenario in a highly populated country like Singapore. The plan must consider the challenges, limitations, and risks associated with the operation of a nuclear facility.

An off-site emergency response plan is a particularly critical component for ensuring the safety of the population and the environment in the event of a nuclear incident in Singapore. The plant operator and local government must work together to ensure that the necessary measures are taken to safeguard the population from potential threats and hazards related to the plant’s operations. To ensure the success of an off-site emergency response plan for a nuclear plant operating in Singapore, it is also crucial to engage with the local community and provide them with the necessary information about the plant’s operation, safety measures, and emergency response plans.

Managing a nuclear emergency in Singapore poses numerous challenges. Limited land space area makes it challenging to find a suitable evacuation site, while the high population density makes it difficult to safeguard the population. Limited resources and logistic issues, including a shortage of medical and emergency specialists and professionals, equipment, space, infrastructure, and supplies, further complicate responding to a nuclear emergency. Coordination and collaboration with local and neighbouring nations also present challenges, the different objectives and priorities of each party can lead to delays in establishing a unified approach, making the decision-making process difficult. Therefore, further research is necessary to address these challenges and develop effective strategies for managing a nuclear emergency in Singapore.

The Singapore government is recommended to establish legal requirements related to nuclear safety, operations, and emergencies, and drive international nuclear research collaborations to exchange knowledge and experience in the nuclear safety field and gain access to nuclear facilities. The government should also nurture a nuclear workforce to meet future demands of the sector through a competency progression model and engage the public on nuclear energy through awareness campaigns, seek their feedback for better collaborations, and understanding for future sustainability of energy management.

Next steps for nuclear Singapore

To prepare for a full-fledged nuclear facility by 2050, this study recommends a pilot project to retrofit an SMR into an existing power station. The implementation of inherently safe Integral Pressurized Water Reactor (iPWR) SMR is highly recommended due to its ability to contain emergencies within the site boundaries, putting large-scale emergency evacuation concerns to rest.

While the majority of past nuclear incidents may not be highly relevant in Singapore’s context, they do highlight the importance of establishing legal requirements related to nuclear safety, operations, and emergencies. This is necessary to ensure that Singapore is adequately prepared and equipped to respond to potential nuclear incidents. In addition, driving international nuclear research collaborations can facilitate the exchange of knowledge and experience in the nuclear safety field, further enhancing the country’s preparedness and response capabilities.

The Singapore government is also recommended to nurture a nuclear workforce to meet future demands of the sector through a competency progression model and engage the public on nuclear energy through awareness campaigns and feedback mechanisms for better collaboration and understanding towards the sustainable management of energy. A nuclear task force may work with the government to establish legal requirements, drive nuclear research collaborations, educate the public, and nurture a nuclear workforce.

By implementing these recommendations, Singapore can move towards a more sustainable energy future with a safe and reliable nuclear power source.

Authors: Eio Wee Kwang, Kerk Boon Hock, Muhammad Sarhan Samad, Ng Swee Wah, Ho Li Min Sarah, and Loh Tzu Yang, Department of Chemical and Biomolecular Engineering, College of Design and Engineering, National University of Singapore

This article first appeared in Nuclear Engineering International magazine.