## 2 Overview of Microreactors
### Microreactor Designs  
There are various microreactor designs listed by the World Nuclear Association (WNA) and currently under development by different developers, with more designs being explored. An example of this is the eVinci(tm) microreactor by Westinghouse Electric Company (Cranberry Township, PA, USA) (Figure 1), merging space reactor technology with commercial nuclear system design [94; 95; 96; 97]. This high-temperature heat pipe reactor can produce 200 kW to 5 MW of electrical power for more than three years without the need for refueling. Utilizing High-Assay Low-Enriched Uranium (HALEU) TRISO fuel, it features a straight \begin{table}
\begin{tabular}{l l} \hline \hline
**Database** & **Search Strategy** \\ \hline \multirow{3}{*}{**Google Scholar**} & (“Microreactor” OR “Nuclear fuel” OR “HALEU” OR “Nuclear energy” OR “Small Modular Reactor (SMR)” OR “blockchain” AND PUBYEAR \(>\) 1980 AND PUBYEAR \(<\) 2025) \\ \hline \multirow{3}{*}{**Web of Science**} & (“Microreactor” OR “Nuclear fuel” OR “HALEU” OR “Nuclear energy” OR “Small Modular Reactor (SMR)” OR “blockchain” AND PUBYEAR \(>\) 1980 AND PUBYEAR \(<\) 2025) \\ \hline \multirow{3}{*}{**Scopus**} & (“Microreactor” OR “Nuclear fuel” OR “HALEU” OR “Nuclear energy” OR “Small Modular Reactor (SMR)” OR “blockchain” AND PUBYEAR \(>\) 1980 AND PUBYEAR \(<\) 2025) \\ \hline \multirow{3}{*}{**ScienceDirect**} & (“Microreactor” OR “Nuclear fuel” OR “HALEU” OR “Nuclear energy” OR “Small Modular Reactor (SMR)” OR “blockchain” AND PUBYEAR \(>\) 1980 AND PUBYEAR \(<\) 2025) \\ \hline \multirow{3}{*}{**ProQuest**} & (“Microreactor” OR “Nuclear fuel” OR “HALEU” OR “Nuclear energy” OR “Small Modular Reactor (SMR)” OR “blockchain” AND PUBYEAR \(>\) 1980 AND PUBYEAR \(<\) 2025) \\ \hline \multirow{3}{*}{**Engineering Village**} & (“Microreactor” OR “Nuclear fuel” OR “HALEU” OR “Nuclear energy” OR “Small Modular Reactor (SMR)” OR “blockchain” AND PUBYEAR \(>\) 1980 AND PUBYEAR \(<\) 2025) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Search strategies in databases. forward and safe design. The use of heat pipes eliminates the need for reactor coolant pumps and auxiliary systems, resulting in a compact and dependable reactor [94; 95; 96; 97; 98; 99; 100]. The eVinci(tm) microreactor benefits from its high-temperature heat pipe technology, which removes the need for reactor coolant pumps and related systems, offering a compact and reliable design. It can function for over three years without refueling and is inherently safe due to its strong negative temperature coefficient. Additionally, it features flexible load following, capable of automatically adjusting the heat load. However, operational performance data are limited since it is still under development, and initial production and installation costs may be high. The Aurora microreactor designed by Oklo Inc. (Santa Clara, CA, USA) (Figure 2) is intended to generate approximately 1.5 MWe of electricity and operate autonomously for 20 years [25; 44; 77; 82]. This configuration, employing metallic fuel in heat pipes with liquid sodium, is designed to consume nuclear waste from light water reactors [94; 101; 102; 103; 104; 105]. The US Idaho National Laboratory provides Oklo with access to reprocessed used nuclear fuel to test the Aurora concept [94; 101; 102; 103; 104; 101]. The advantages of the Aurora microreactor include its ability to operate for 20 years without refueling and its capability to burn nuclear waste from light water reactors. The design features metallic fuel and a liquid sodium coolant in a compact configuration. However, due to the use of sodium, additional safety measures may be required, and sufficient technical and operational performance data are not yet available. The Holos-Quad microreactor, developed by Holos Generators (Manassas Park, VA, USA) (Figure 3), combines commercial technologies with safer, melt-resistant fuels, functioning similarly to a turbo-jet engine [111; 112; 113; 114; 115]. This reactor employs TRISO fuel and features a straightforward design.