Professor, Nuclear Engineering
University of Illinois
Apr 12, 2019
Bret Kugelmass: Where did you grow up?
James Stubbins: James Stubbins grew up in Berkeley, California, when his father worked at Lawrence Berkeley Lab (LBL) as a research scientist, and then later, Cincinnati, Ohio when his father took a faculty position at the University of Cincinnati. Stubbins completed his bachelor’s degree in nuclear engineering at the University of Michigan and, due to Stubbins’ likelihood to get drafted during the war, had trouble finding work. Stubbins started grad school in Cincinnati and ended up not getting drafted. After graduation, Stubbins spent a year and half at a German nuclear research center, Forschungszentrum Karlsruhe, which later became Karlsruhe Institute of Technology, and then worked on nuclear materials at the University of Oxford and the Harwall Lab in the United Kingdom. Stubbins then moved on to General Electric where he worked on high temperature gas-cooled reactor technology.
Bret Kugelmass: What is the relationship between the commercial sector, the nuclear industry, and the government?
James Stubbins: James Stubbins’ program at GE was purely research-based, at a time in which the Energy Research and Development Administration (ERDA) managed nuclear research while the Nuclear Regulatory Commission (NRC) regulated commercial nuclear power. ERDA was one of the organizations that later formed the Department of Energy. General Atomics developed the Fort Saint Vrain Reactor, a gas-cooled reactor in Colorado. The design was based on the Peach Bottom Reactor, but to a scale ten times larger, which created many unintended design challenges. Higher flow rates and a much larger core caused the core to shake, requiring a stabilization girdle. Since the reactor was built in Colorado, where there are no rivers to use for heat sync, a high temperature reactor which exchanges waste heat to air could be used. In nuclear plant turbines, the heat from the reactor increases the pressure of the gas, allowing it to be run through a turbine to extract energy. Fort Saint Vrain was running a steam cycle with the goal of using it for an efficient energy conversion cycle, such as from coal or iron ore.
Bret Kugelmass: Why didn’t high temperature nuclear reactors become more popular earlier on?
James Stubbins: James Stubbins, who specializes in material science, sees the limit of very high temperature systems is the life of the materials in the components. High oxidation environments put an oxide scale on the surface, protecting against further corrosion and acts as a thermal barrier, but requires the parts and components to be replaced or rebuilt after experiencing creep. In a gas-cooled reactor, any oxygen in the system burns the carbon out of the core, so helium is used instead to protect the turbine blades from corrosion. A closed cycle system uses a gas as a heat transfer medium such as helium, which can withstand high temperatures. Hydrocarbons from oils in the system, like lubricated parts in the turbines, and there is always some air ingress. The challenge for these future plants is that carbon does not form a film on metal, but instead diffuses into the metal and changes the properties.
Bret Kugelmass: Does a new metal alloy have to be developed for turbine blades in high temperature gas-cooled nuclear reactors?
James Stubbins: James Stubbins visualizes the development of a new metal alloy for use in high temperature gas-cooled nuclear reactors as a evolutionary process, rather than inventing something new. Material scientists analyze existing materials, then use the results to develop an alloy that works for this purpose. Japan has completed the alloy development cycle for use at a temperature of 950 Celsius. There is nothing to prevent the carbonization in these systems, which limits the material life and material degradation must be planned into the design. Scientists are trying to determine the ideal temperature, but plant efficiency is lost as the system temperature is lowered. Gases are not a good temperature conversion medium due to their low heat capacity and low density, compared to water, liquid metal, or molten salt, therefore pressure must be increased to keep high temperatures. One project Stubbins worked on with the Atomic Energy Commission analyzed what materials could be used for high temperature nuclear-powered planes.
Bret Kugelmass: What other materials work have you studied in the nuclear field?
James Stubbins: James Stubbins has performed a lot of research on in-reactor materials that see a lot of radiation, such as fuels. Cerium, CeO2, is an atom that look similar to Uranium, so radiation effects can be performed on the atom without having Uranium present and understanding how the atom would respond. Some radiation effects performed include heavy ions and neutrons. Stubbins has also analyzed material that has gone through the Advanced Test Reactor at Idaho National Laboratory and also, in the past, looked at materials irradiated at the Fast Flux Test Facility, which is now decommissioned. The effort is to extend the performance behavior of materials to higher temperatures, higher doses, or higher stresses. Smaller, more compact reactors may require all of these increases in stress on materials. Stubbins analyzes what happens inside the material, and is currently utilizing the Advanced Photon Source at Argonne National Lab, which utilizes high power x-rays, to watch materials break apart. This allows researchers to paint a cohesive picture of the material response.
Bret Kugelmass: Is the alloy metal a mixture or is it like a molecule?
James Stubbins: James Stubbins studies the effects of irradiation on materials such as alloy metals. Alloy metals are like a mixture in which the atoms are next to each other without atom-to-atom bonding, but small clumps of elements may form. Most metals have a lattice structure, and when a neutron comes in, it knocks atom out of their arrangement. Very energetic neutrons can cause atoms to knock other atoms out of order in a chain reaction. There is some residual damage, but often the atoms can fall back into a vacant place and restore the structure. The number of times the atoms in the structure are knocked out of place is analyzed for types of metals and the radiation environment they are in. Pressure vessels are forged, produced a better quality product, and are very thick and must withstand high pressures. They are intended to last a long time, instead of being a disposable component.
Bret Kugelmass: Did you come to the University of Illinois after working at G.E.?
James Stubbins: After working for G.E., James Stubbins joined the faculty at the University of Illinois Nuclear, Plasma, and Radiological Engineering department. Right after the Three Mile Island incident, many reactors had to go be modified due to upgraded safety analysis regulations and lots of non-destructive testing on welds and other materials. This time in the U.S. also had very high interest rates due to inflation, so the nuclear industry took out loans at rates between 15-20% to support these upgrades. In the 1990’s, Stubbins saw undergraduate student numbers at the University decrease sharply, but was able to maintain graduate student population with high quality research programs. The nuclear industry at the time did not invest in university nuclear studies, other than some fuel development, but schools had very low budgets and funding. Stubbins became department head in 1999 and has seen a reinvestment in universities and nuclear programs, allowing the undergraduate population to grow. The University currently has 16 faculty with diverse backgrounds, allowing students to get involved in fields such as medical imaging, plasma technology, and fusion research.
Bret Kugelmass: What do you down the line for you and the world in the nuclear space?
James Stubbins: James Stubbins is hopeful for the materials development space in the future of nuclear technology. Materials scientists today have better facilities for analyzing how materials behave and can tell more about the interactions. Additive manufacturing is changing the way materials are formed, allowing different compositions in layers of a structure to meet different needs.
- Technical challenges of scaling up high temperature nuclear power plant designs - The relationship between nuclear power generation efficiency and reaction temperature - The effects of oxidation and carbonization on turbine blades in different nuclear reactors - How nuclear reactor designs plan for long-term material degradation in critical components - Modern methods of analyzing effects of radiation on metal alloys - How the impacts of neutrons on metal lattice structures drive material design - Performance criteria for critical components of nuclear plant materials - How today’s nuclear industry is reinvesting in nuclear-related education and research.