## 2 Overview of Microreactors
### Microreactor Designs
The Kalinos microreactor is designed to be a fully portable unit housed within a shipping container, allowing for easy transportation by truck, ship, or aircraft. This portability feature is particularly  
Figure 5: Overview of the micro NuScale power module developed by NuScale Power [143]. advantageous for meeting energy needs in remote areas and providing emergency power supply [159; 160; 161; 162]. The reactor is equipped with passive cooling systems that do not require water, simplifying the regulatory approval processes. The design aims to provide a robust power supply with minimal on-site infrastructure requirements. Once installed, the reactor can begin operating at full capacity immediately, offering long-term, reliable energy production. Additionally, the Kalinos design includes the capability to provide clean electricity and heat during energy production, making it suitable for various industrial and commercial applications [152; 153; 154; 155; 156; 157; 158; 163; 164; 165]. Figure 6: Overview of the SEALER microreactor developed by LeadCold [150]. Figure 7: Overview of the U-Battery developed by Urenco [151]. The MMR(tm) (Micro Modular Reactor) developed by Ultra Safe Nuclear Corporation (Seattle, WA, USA) (Figure 8) is an advanced nuclear reactor designed for high efficiency and safety. This reactor is cooled by helium gas and uses graphite as a moderator to control the nuclear reactions. The MMR(tm) is capable of producing 5 megawatts of electrical power (MWe) and is designed to operate for 20 years without the need for refueling, making it highly reliable and low-maintenance [166; 167; 168; 169; 170]. The reactor utilizes TRISO (tristructural isotropic) and FCM(tm) (Fully Ceramic Microencapsulated) fuels, which are known for their robustness and high safety margins. These fuels allow the reactor to maintain stability at high temperatures and ensure safe operation under various conditions [168; 169; 170; 171; 172]. In addition to its efficient fuel use, the MMR(tm) incorporates a molten salt storage system and a steam turbine generator to convert thermal energy into electrical energy. This combination allows for flexible heat transfer and high-temperature stability, which are essential for efficient power generation and safe operation [166; 167; 168; 169; 170]. Despite its many advantages, the MMR(tm) also faces some challenges. It is still in the development stage, which means that further research and testing are required to fully commercialize the technology. Additionally, the operational costs of the MMR(tm) can be relatively high compared to more established energy sources. However, the potential benefits of this reactor, such as its long operational life without refueling and its high safety standards, make it a promising option for future energy needs [168; 169; 170; 171; 172]. The MMR(tm) is particularly suited for applications in remote areas or regions with limited access to conventional energy sources. Its compact size and modular design allow for easy transportation and installation, making it a versatile solution for various energy demands [166; 167; 168; 169; 170; 171; 172]. Overall, the MMR(tm) developed by the Ultra Safe Nuclear Corporation represents a significant advancement in nuclear technology, offering a reliable, safe, and efficient source of low-carbon energy [170; 171; 172; 173; 174]. The Kaleidos microreactor developed by Radiant Nuclear (El Segundo, CA, USA) (Figure 9) is an innovative solution for portable nuclear power generation [159; 160; 161]. This reactor utilizes high-temperature gas-cooled reactor (HTGR) technology, using helium gas as the coolant and TRISO fuel [159; 160; 161; 162]. TRISO fuel is superior in terms of safety features, being resistant to meltdown. Kaleidos is designed to produce 3 MWt of thermal  
Figure 8: Overview of the MMR(tm) developed by the Ultra Safe Nuclear Corporation [175]. power and approximately 1 MWe of electric power [159; 160; 161; 162]. The Kaleidos microreactor is fully portable and housed in a transport container.