Breakthrough nuclear cooling system passes key test at Idaho lab

The MARVEL microreactor project at Idaho National Laboratory (INL) has successfully completed a critical three-month testing campaign of its innovative cooling system using the Primary Coolant Apparatus Test (PCAT), a non-nuclear facility designed to simulate the reactor’s thermal behavior. MARVEL features a unique sodium-potassium coolant and a natural circulation passive cooling mechanism that allows the reactor to cool itself without pumps, relying on natural convection. The PCAT tests confirmed the viability of this cooling approach, demonstrating stable natural circulation flow capable of safely managing up to 100 kilowatts of thermal power, with expectations that the actual reactor will perform even better due to enhanced heat removal capacity. In addition to validating the cooling system, the PCAT campaign rigorously tested INL’s thermal-hydraulic design and safety analysis software, RELAP5-3D, with experimental data closely matching the software’s predictions, boosting confidence in operational and safety assessments. However, the tests revealed higher-than-anticipated heat losses in