A small nuclear reactor at Idaho National Laboratory (INL) is moving closer to its first criticality test after engineers received a major part of its cooling system. The arrival of the primary coolant system gives researchers another major component to integrate into the reactor before initial testing, which the project currently expects to begin in December.
The reactor, Microreactor Applications Research Validation and Evaluation (MARVEL), is being led by Idaho National Laboratory for the U.S. Department of Energy. The project is intended to explore how small nuclear reactors operate and collect data that can potentially be used for the development of other advanced reactor designs.
The primary coolant system itself is responsible for carrying heat away from the reactor core when MARVEL is operating. The system uses a sodium-potassium alloy which is capable of remaining liquid at room temperature while also transferring heat at the high temperatures produced within the reactor. Unlike water-based cooling systems, which often require large amounts of pressure to keep the coolant in its desired state, the sodium-potassium coolant does not require pressurization to remain liquid.
The coolant system arrived at INL’s Transient Reactor Test Facility in mid-September where engineers will now work to integrate it with the rest of the MARVEL reactor. This process is another major step toward the initial testing of the reactor and eventually reaching criticality. Criticality is the point where a nuclear reactor is capable of maintaining a self-sustaining nuclear chain reaction.
However, reaching criticality does not immediately mean that the reactor will begin operating at full power. Instead, researchers will first use the reactor to collect information about its physics and behavior.
Before the primary coolant system arrived, the Department of Energy’s Idaho Operations Office approved MARVEL’s final documented safety analysis. This approval allows the project to move forward with a dry criticality configuration, which is a critical condition where almost no power is generated and coolant is not needed.
Dry criticality is important because it allows researchers to study the reactor’s physics before the reactor begins full thermal operation. The researchers can focus on how the reactor behaves while keeping the amount of power generation extremely low. This provides the team with another way to test the reactor in a controlled environment before moving toward higher levels of operation.
Abdalla Abou-Jaoude, the MARVEL microreactor lead, said that the approval allows the team to move toward the reactor’s initial criticality. The approved safety document could also be useful to other companies and organizations working with advanced nuclear reactors.
According to Abou-Jaoude, the team is open to sharing the document with industry stakeholders in the hopes that it can be used as a template for future projects.
INL nuclear safety engineer Doug Gerstner also said that the safety analysis represents years of engineering and safety analysis work. The approval provides a foundation for MARVEL to continue toward criticality while using the risk-informed approach that was developed for the project.
MARVEL’s purpose extends beyond simply testing one small nuclear reactor. The project is intended to act as a test bed where researchers and industry partners can study microreactor technology and collect information about how these systems operate. INL also plans to make key reactor information available so that other groups can learn from the project and use the data for future reactor development.
The reactor will also give researchers an opportunity to compare their calculations and predictions with measurements taken from an actual nuclear system. This can help researchers better understand the behavior of microreactors and potentially identify problems or improvements that could be applied to future designs.
As of now, the primary coolant system has arrived and the safety documentation has been approved, leaving engineers with another major step toward the reactor’s first criticality test. If MARVEL reaches initial criticality as planned, researchers will be able to begin collecting the data that the project was designed to produce and continue testing how small nuclear reactors can be used in the future.
