Nuclear Energy
Kairos Power is innovating the future by delivering a salt-cooled high-temperature nuclear reactor. During my Test Engineering internship, I completed an in-depth two-phase flow analysis on the molten salt coolant.
Kairos Power
Enabling the world's clean energy transition to improve people's quality of life while protecting the environment.
Non-Disclosure Agreement: I will only disclose non-proprietary information regarding my work at Kairos Power. All images are public knowledge.
A key parameter for flow characterization is void fraction percentage: the ratio of air to volume. A larger void fraction will decrease the heat transfer coefficient of molten salt, degrading the coolant's ability to remove heat from the fuel rods.
The Nuclear Regulatory Commission (NRC) requires a limit on the amount of void fraction present in the coolant. It was my job to develop a method to infer the void fraction within the coolant of Kairos Power's Hermes Test Unit Reactor.
Theoretical Model
Pictured left, I replicated methods from a verified source to predict two-phase flow behavior with non-fluid properties. The replication was accurate, and therefore I could apply such methods in the context of my experiment.
I had a theoretical method to infer the void fraction, but I needed to validate it...
Experimental Setup
For validation of the theoretical calculation, I created an experimental setup that I could physically extract void fraction data from.
Doing a test with water allowed me to visualize the flow and take pictures to get the true void fraction parameters of this experiment. I performed calculations to map the experimental data of water back to the conditions of molten salt.
To simulate the coolant pipes, I generated the void fraction in a tube, but surrounded it with a rectangular prism of water to reduce light refraction. It was a challenge to make the large assembly completely watertight.
Experimental Analysis
Once I had taken the photos, I followed the data collection process shown below. I ran a chosen time-resolved image through multiple image processing programs to cross-verify results and retrieve key flow characteristics—bubble count and radius contributing to the void fraction. With this data, along with additional [redacted] non-fluid properties, I could move forward to the final step of inferring the void fraction inside the molten-salt coolant.
Results
Bringing together the results, I now had a way to model the void fraction in the Hermes test unit reactor and provide experimental validation for that model. The figures below represent the error between the theoretical model and experimental data to pinpoint the most likely set of fluid parameters for a given scenario. Mapping these fluid parameters to the [redacted] data produced quantitative results on expected void fraction.
Conclusion
Preceding the end of my internship, I was able to run three tests with each part of the process included. While I am unable to provide quantitative analysis on the results of my experiments, I can say that I found success in many aspects of the model. The model had yet to be taken as solid proof, but I developed the foundation towards void fraction determination and analysis. I was happy to pass my results to the team, leaving my project in the hands of capable engineers that would go on to further analyze the feasibility of leveraging the model for requirement verification and closure.
Void fraction presence is due to argon gas entering through a free-surface vortex in the pump, and it is undesirable in molten salt coolant. To help Kairos Power establish information on this unavoidable phenomenon, I developed a method to predict whether or not the void fraction is at a concerning percentage.