How UC Berkeley researchers are making nuclear reactors smarter
By Laura Shi, Ian Kolaja, and Eddie Bird
Nuclear reactors generate about 20% of electricity in the United States. Each reactor continuously produces a massive amount of electricity while emitting no greenhouse gases during operation. They also have a small land footprint at 12.71 acres per megawatt produced compared to other low carbon energy sources like solar and wind, which have footprints of 43.50 and 70.60 acres per megawatt produced, respectively (1). Nuclear reactors work by using the heat that comes from the splitting of atoms in uranium fuel rods to boil water, creating steam which then spins a turbine.
Many nuclear reactors currently in operation today are decades old. They are expensive to run, complex to operate, and hard to upgrade. Researchers both at the UC Berkeley nuclear engineering laboratories and in the nuclear industry are working to change this by designing smarter, cheaper, and more reliable reactors that utilize modern technology like automation. The increased adoption of nuclear power will, in turn, reduce greenhouse gas emissions and play an integral role in slowing down climate change.
An advanced reactor
Dr. Per Peterson is the principal investigator of the UC Berkeley Thermal Hydraulics Laboratory and the Chief Nuclear Officer of Kairos Power, a start-up dedicated to commercializing a brand new kind of reactor called the Pebble-Bed Fluoride High-Temperature Reactor (PB-FHR).
PB-FHRs use hundreds of thousands of golf-ball sized fuel pebbles instead of fuel rods. They’re cooled by molten salt instead of water. Because the fuel is embedded in thousands of tiny particles within the graphite shell, it’s nearly impossible to get uranium out of them. This means that there is a much smaller chance of nuclear material being stolen for nefarious purposes. PB-FHRs also operate at high temperature and low pressure. The high temperature makes them more efficient at generating electricity while having lower pressure eliminates the risk of launching radioactive material into the atmosphere if there is a containment breach.
The reactor is designed with the ability to handle accident conditions passively. The PB-FHR can cool itself down even when shut off because the coolant will continue to circulate through the system without the assistance of outside power. Additionally, the fuel physically cannot melt because of the high melting temperature of its outer graphite shell.
Automating reactor operation
Not only are PB-FHRs safer and cheaper, but they are also smarter. Graduate student Christopher Poresky is working on a project called the Advanced Reactor Control and Operations facility (ARCO). ARCO is an operator support system for an advanced reactor control room that is capable of detecting faults and notifying the operator of problems that they would not have been able to identify on their own. Poresky describes it as a “really smart check engine light.”
Fault detection in ARCO works by creating a “digital twin” inside the program. ARCO uses models to predict how the plant should behave and compares this with real-time measurements. By analyzing the difference between the output from the simulation and the measured values from the plant, the system informs the operator with a useful diagnosis of what is happening and how to respond. The system will not be fully automated; the operator will still be in control of the system while ARCO handles the numerical analysis.
“You really want to strike this balance of empowering people by automating the things they shouldn’t have to do but making sure they’re able to do the things they need to do,” Poresky says. “Operators will still be the decision-makers. Operators will still be critical thinkers and operators will still be the ones filling in the gaps.”
ARCO also uses automation to guide the operator. Current operation procedures are paper-based and involve numerous logical branches. This task flow can easily be programmed into ARCO, which will allow operators to focus on making sure the reactor is running smoothly, rather than being fixated on many laborious, routine tasks.
One of the key lessons learned at the Three Mile Island (TMI) nuclear accident was the danger of neglecting human-centered design in the control room. TMI occurred because of a valve that was stuck open. However, the instrumentation did not clearly indicate what the problem was, and the steps that the operators took escalated the problem to a partial core meltdown. While TMI led to no human casualties and minimal environmental effects, the reputation of nuclear power in the U.S. was greatly tarnished. Consequently, the nation’s investment in carbon-free electricity declined.
ARCO addresses this challenge by condensing all of the reactor data neatly onto a couple of computer screens. It employs “information automation” by showing the operator only information that is relevant to their task at hand. ARCO intends not only to make the reactor operation more efficient but also easier and more intuitive.
Researchers are working on cybersecurity research with ARCO to ensure that the system is resistant to hacking. Poresky is conducting experiments to study how well operators can respond when different parts of the facility are hacked, and they’re developing tools to let them fight back. One tool involves using a MIDI controller, which is normally used for producing music, as a back-up analog controller to override a compromised signal.
The biggest advantage of ARCO is its economic value. Currently, natural gas costs about six times as much as uranium fuel (2). However, because of the high operating costs of nuclear reactors, producing electricity with natural gas is cheaper. ARCO coupled with the efficient design of the PB-FHR makes tasks like maintenance and security less labor intensive; this would dramatically reduce the staffing needs of the reactor, giving PB-FHRs a competitive edge against natural gas plants by reducing their biggest cost.
“The market that Kairos Power is interested in meeting is the market to replace a very large amount of natural gas combined cycle plant generation that was deployed in the United States in the early 2000s,” says Peterson.
Replacing natural gas plants with PB-FHRs would dramatically reduce emissions. Developing and building new nuclear reactors at a faster rate is a powerful move towards stopping climate change, and ARCO makes this possible in a way that’s safe, affordable, and innovative.
The work engineers do shapes the world around us. But given the technical nature of that work, non-engineers may not always realize the impact and reach of engineering research. In E185: The Art of STEM Communication, students learn about and practice written and verbal communication skills that can bring the world of engineering to a broader audience. They spend the semester researching projects within the College of Engineering, interviewing professors and graduate students, and ultimately writing about and presenting that work for a general audience. This piece is one of the outcomes of the E185 course.
Connect with Laura Shi (BS NE ’22), Ian Kolaja (BS NE ‘19), and Eddie Bird (BS NE ‘21)
References
(1) Stevens, Landon. The Footprint of Energy: Land Use of U.S. Electricity Production. Strata Policy, 2017, pp. 1–25, The Footprint of Energy: Land Use of U.S. Electricity Production. https://www.strata.org/pdf/2017/footprints-full.pdf
(2) “Economics of Nuclear Power.” Nuclear Power Economics, World Nuclear Association, Apr. 2019, www.world-nuclear.org/information-library/economic-aspects/economics-of-nuclear-power.aspx.
