## 2 Overview of Microreactors
### Microreactor Designs
This design allows the reactor to be easily transported by truck, ship, or aircraft. This portability feature is particularly advantageous for meeting energy needs in remote areas and providing emergency power supplies [159; 160; 161; 162]. The reactor is equipped with passive cooling systems that do not require water, facilitating regulatory approval processes. Kaleidos aims to provide a resilient power supply with minimal on-site infrastructure requirements. Once installed, the reactor can immediately operate at full capacity and provide long-term, reliable energy production. Additionally, Kaleidos can provide clean electricity and heat during energy production, making it suitable for various industrial and commercial applications [159; 160; 161; 162]. Table 2 provides a detailed comparison of various features of microreactors. This table includes different microreactor designs and compares their power output, operational duration, fuel type, coolant type, and general characteristics. The reactors listed in the table include eVinci(tm), Aurora, Holos Generators, Xe-Mobile, NuScale, SEALER, U-Battery, MMR(tm), and Kaleidos. The power output (MWe) of these reactors ranges from 0.2 to 100, with operational durations extending from 3 to 30 years. Fuel types among these reactors include HALEU TRISO, metallic fuel, UO or UN, and TRISO/FCM(tm). The coolant types include liquid sodium, helium, carbon dioxide, and pressurized water. For instance, the eVinci(tm) microreactor offers a power output of 0.2-5 MWe and can operate for at least 3 years. It features high-temperature heat pipes and a compact design that ensures reliability. The Aurora microreactor can generate 1.5 MWe of power and operate autonomously for 20 years. It uses metallic fuel and liquid sodium as a coolant and has the capability to burn nuclear waste. The Holos Generators microreactor offers scalable power options ranging from 1 to 100 MWe and features a simple design similar to a turbojet engine, providing high efficiency [25]. Table 2 thus highlights the diverse capabilities and specifications of different microreactor designs, showcasing their potential applications and the advanced technologies they incorporate. This comprehensive comparison underscores the versatility and adaptability of microreactors in addressing various energy needs across different settings. Table 3 highlights the distinct advantages and disadvantages associated with various microreactor designs. Each microreactor presents unique benefits tailored to specific needs and challenges. For instance, the eVinci(tm) microreactor, developed by Westinghouse Electric Company, boasts a high-temperature heat pipe and a compact design, making it reliable for long-term operation without refueling for over three years. However, the limited operational data and high initial costs present notable challenges. Similarly, the Aurora microreactor by Oklo Inc. offers long autonomous operation (up to 20 years)  
Figure 9: Overview of the Kaleidos microreactor developed by Radiant Nuclear [161]. and the capability to burn nuclear waste, yet it remains in the developmental stage with insufficient technical data and requires additional safety measures for the sodium coolant. Other designs, like the Holos Generators and Xe-Mobile, emphasize high efficiency and portability, respectively, but face challenges related to their innovative designs and increased costs for sophisticated control systems [25].