1) 00:56

Bret Kugelmass: How did you enter the nuclear space?

Katy Huff: Katy Huff grew up in rural Texas and was inspired by her mother, a mechanical engineer for GE in power systems, to pursue engineering. Huff spent the last two years of high school at the Texas Academy of Math and Science on the campus of the University of North Texas in Denton, Texas. For her undergraduate degree in physics, Katy Huff attended the University of Chicago, with a specific interest in its history in nuclear energy. As a graduate student at the University of Wisconsin, Huff worked on fuel cycle analysis, which looks at the life cycle of nuclear fuel from the moment it is dug out of the ground, how it is used in the reactor, and what is done with spent fuel.

2) 07:49

Bret Kugelmass: What do you know about the history of nuclear fuel fabrication?

Katy Huff: Katy Huff teaches fuel cycle analysis at the University of Illinois. In the past, nuclear fuel was enriched with gaseous diffusion, then technology transitioned to centrifugal diffusion, with the possibility of using laser isotope enrichment in the future. These processes separate Uranium-235, the fissionable atom, from Uranium-238, which can be fissionable; enrichment is increasing the ratio of Uranium-235 to Uranium-238. The biggest impact on fuel price trends is whether there is a surplus of enriched uranium. There are different levels of enrichment. Three to five percent enriched is typical light water level enrichment. Under 20% is still low enriched uranium, but reactors tend not to use this level of enrichment, with the exception of new reactor technologies in development. This power density is beneficial in smaller reactors and where high heat capacity plants. High enrichment fuel allows passive safety impacts related to fuel temperature feedback, which is a design aspect that allows a reactor to react to rises in temperature by reducing power levels, giving the plant an inherent safety feature that is not dependent on an operator.

3) 14:10

Bret Kugelmass: What are the drivers of negative temperature coefficients?

Katy Huff: Katy Huff analyzes the connection between advanced fuels and inherent safety features in newer nuclear reactors. Expansion, which decreases the probability of interaction, and doppler effect, which is a broadening of the range of energies when neutrons strike an atom, are two drivers of negative temperature coefficients in a nuclear reactor. Some advanced fuels have other passive safety features. New solid fuel shapes have altered heat transfer and how fuel melts by redirecting cooling in a spiralized way. New liquid fuels have heat transfer benefits which also allows fuel to expand quickly and provide negative temperature coefficients. In a typical light water reactor, heat in the fuel pellets travels to the edge of the pellets through conduction, the cladding is heated by the boundary condition on the fuel, and eventually transferred to the cooling system. Rapid heat transfer to the coolant allows stable fuel temperatures, reducing the risk of melting.

4) 22:04

Bret Kugelmass: Does the high temperature gradient between the fuel pellets and the cladding and the small distance create a problem?

Katy Huff: Katy Huff teaches methods and reasoning of improving the efficiency of heat transfer in a nuclear reactor system. Newton’s Law of Cooling says the higher the temperature gradient, the faster the heat will move. With advanced fuels that can reach higher temperatures, the higher temperature gradient allows a higher heat transfer behavior, which contributes to the ability to move the heat out of the fuel and into the coolant. It is easier to select a fuel for a reactor design than to design a reactor around an advanced fuel, since there are so many factors that affect design combinations. In academia, many computational tools are available to explore transfer methods, such as neutron transport, thermal hydraulics, and coupled multiphysics. Katy Huff’s group works with the Idaho National Labs by adding applications to model and simulate advanced reactors that don’t have appropriate computational tools yet. These tools assist students in implementing new methods and continuously programming to analyze reactor physics and options for design and technology in a reactor. The University of Illinois at Urbana-Champaign is home to Blue Water, the largest and fastest university supercomputer which allows Huff and her team to run simulations, but it not able to run all simulations due to security regulations.

5) 29:48

Bret Kugelmass: What research have you done on the back end of the nuclear fuel cycle?

Katy Huff: Katy Huff is interested in reprocessing strategies and disposal assessments in relation to the back end of the nuclear fuel cycle. A significant portion of Huff’s research has been related to simulating how reprocessing might work in the long term timeframe. Huff employs a fuel cycle code from the University of Wisconsin, used in her dissertation, which is an agent-based simulator for the nuclear fuel cycle. This program can assess which type of materials leave a nuclear reactor and with four different processes, what materials result. Reprocessing is when fuel, which is at the end of its usable life, is chemically dissolved to extract uranium, and possibly plutonium. Reprocessing is expensive, but some countries like France, have committed to the process with the belief that the benefits are greater than the costs. Dependent on the values of a nation, a country could incorporate externalities into economics through taxes, incentives, or national infrastructure.

6) 35:54

Bret Kugelmass: What are fission products?

Katy Huff: Katy Huff researches disposal assessments, and risks and benefits of methods and limitations. Some isotopes are of special interest to scientists due to their mobility in an environment, such as cesium or iodine, which basically have no solubility limit in water. However, these isotopes are particularly damaging to people and the environment, and solubility is more of a risk than a benefit due to long term storage and risks of entering water supply through accidental drilling. Katy Huff believes in continuing to hold the nuclear industry to a high safety and environmental standard, even if it is a higher standard than other energy sources. The economics of externalities can fix a market, such as carbon tax which would allow nuclear to compete with other technologies that do not produce energy without carbon emissions. While nationwide or international carbon credits or taxes do not yet exist, some states, like Illinois, have ensured that clean energy is being rewarded.

7) 44:45

Bret Kugelmass: What topics should the next generation of nuclear engineers be thinking about and focusing on?

Katy Huff: In a future of science and computationally enable lifestyles, Katy Huff believes in keeping the nuclear industry at the forefront of computing development. Nuclear energy and nuclear engineering, especially reactor physics, have been at the forefront of what algorithms are created. All of the supercomputers and large scale calculating have been created to complete nuclear energy calculations.

7-10 Bullets

• What is a nuclear fuel cycle and how is it analyzed? - How a surplus of enriched uranium impacts nuclear fuel prices - The connection between high enrichment nuclear fuel and inherent safety features - How negative temperature coefficients affect nuclear heat transfer - Computational tools for analyzing the nuclear fuel life cycle and transfer methods - Costs and benefits of nuclear waste reprocessing and how nations manage it - Long term safety considerations for nuclear waste disposal of different isotopes - Competitive advantages of nuclear energy and its impact on computational science.