Moving toward the goal of having an operational molten salt nuclear reactor in the next decade, Southern Company and the Idaho National Laboratory have completed the inaugural run of a first-of-its-kind test bed to foster rapid development of the technology.
As next-generation nuclear reactors, known as Gen IV power plants, are developed, it is looking more and more likely that they will be of the molten salt variety. These plants swap out radioactive fuel rods and a water-coolant system with a salt slurry mixed with nuclear fuel and offer myriad benefits over their older brethren.
Such reactors are safer than old-school nuclear power plants, for example, because they operate at much lower pressures, making structural stress and failure in the event of an accident less of an issue.
Molten salt nuclear reactors (MSR) also have unique passive methods of preventing nuclear disasters. Some plants are equipped with what's known as a "freeze plug" in the reactor chamber. In the event of a power failure, the system keeping this chunk of salt in a frozen state fails, causing the plug to dissolve. This, in turn lets the salt/fuel slurry drain passively into underground tanks where it safely cools. On the other hand, if a reactor overheats, the expansion in the slurry spreads out the nuclear fuel making it harder for fission to continue, effectively shutting the plant down.
Additionally, molten nuclear reactors are more efficient than their predecessors, and are even potentially able to use waste materials that weren't completely spent in other nuclear processes. They also produce less waste that tends to decompose faster than traditional spent fuel rods and, because of their relatively small size, then can be deployed modularly as needed.
Combating corrosion
All that being said, one of the big challenges of MSRs is that hellishly hot molten salt tends to wreak havoc with whatever it comes into contact with.
Enter the joint project between Idaho National Labs (INL), Southern Company and TerraPower. That project, known as the Molten Chloride Reactor Experiment (MCRE), achieved a major milestone just last month, when it announced that it had used a prototype furnace to create a fuel based on denatured uranium at the rate of 18 kg (39 lb) per batch. That's a far cry from the three and a half tonnes the reactor will eventually need to reach criticality, but it's a start, and the fuel is being produced with 90% efficiency
Now the MCRE project has revealed the successful completion of its Molten Salt Flow Loop Test Bed, which aims to develop a reactor that can withstand the corrosive effects of molten salt.
This closed system is made from stainless steel with a slurry of lithium chloride-potassium chloride salts inside (yes, that is indeed the whole complicated name). As the salts circulate in the system, scientists are able to adjust properties of the slurry – such as temperature – without stopping the flow. This, in effect, means that they can study next-gen nuclear fuels as they circulate in real time.
Five different sensors are able to analyze different stats such as the salts' surface tension and fluid density as well as monitor the level of corrosion in the system and the amount of heat transfer at any one point. By watching how the properties of the salt affect the materials they contact, the research team hopes to dial in the perfect match between fuel slurry and containment system.
“Most test loops focus on testing the structural materials,” said Ruchi Gakhar, lead scientist at INL’s Advanced Technology of Molten Salts department. “After a few hours of operation, they dismantle the loop to study how the materials have degraded.”
“In contrast, our loop at INL is unique because it serves as a test bed for advanced electrochemical sensors and bubbler instruments,” he added. “These instruments allow us to monitor and investigate material performance in real-time while the loop is still operational. This approach has not been implemented or explored in flow loops at other institutions.”
You can learn more about the molten salt test loop in the following video form INL.
Source: Idaho National Laboratory