The US Department of Energy’s (DOE) Marvel microreactor project has cleared more milestones as researchers at Idaho National Laboratory (INL) prepare the plant for initial startup tests this winter.

The microreactor’s primary coolant system, or PCS, arrived at INL in mid-September, completing fabrication and delivery of a key component and pushing the microreactor a step closer to achieving criticality – a stable nuclear chain reaction that’s an important step toward full operation.

The coolant system arrived at INL’s transient reactor test facility, where it will now be integrated with the reactor’s other systems before it achieves criticality, which is anticipated in December.