Space Nuclear Systems
Idaho National Labs
Feb 28, 2018
2:52 - Space Nuclear Reactors
Bret Kugelmass: How did you get into the nuclear space?
Shannon Bragg-Sitton: Shannon Bragg-Sitton grew up in Albuquerque, New Mexico, located near Kirtland Air Force Base, Sandia National Lab, and Los Alamos National Lab. Her first job as a high school student was working on space nuclear reactors. In the early 1990’s, the U.S. purchased six non-nuclear electrically heated test units for space reactors from the former Soviet Union. They were brought over to the U.S. to configure, test, and see if there was a desire them in the U.S. space program. Bragg-Sitton, fascinated by the technology and by space, worked alongside many Russians and interpreters on the space reactors. This inspired her to enter a Bachelor's program in nuclear engineering. These space reactors used the reactor to produce electricity, which then drove electric propulsion systems. Other systems were nuclear thermal propulsion systems, in which the reactor coolant, typically hydrogen, was used as the propellant. These types of power sources open up opportunities to space travel, exploration, and discovery that is much beyond what current systems can do. In and after graduate school, Bragg-Sitton focused on nuclear electric propulsion systems with NASA. When something really difficult, like space travel, is combined with something challenging, like nuclear, it takes time to get projects through to completion.
7:16 - Contributions to National Lab Programs
Bret Kugelmass: What did you do after your time at NASA?
Shannon Bragg-Sitton: When Shannon Bragg-Sitton worked at NASA, she was actually an employee of Los Alamos National Lab on loan to NASA. Her alma mater, Texas A&M, asked her to come back as faculty in the nuclear engineering program. Texas A&M has the largest undergraduate population in nuclear engineering and is the only university to operate two research reactors. Bragg-Sitton spent three years at Texas A&M developing programs and classes in space nuclear systems and plasma physics. She decided to return to the National Laboratory to get back into the fundamental aspects of developing space nuclear systems. In her current position, Bragg-Sitton still maintained ties with several universities and working with students on committees and PhD projects, but was more in a position where she could help define programs and establish the way forward for nuclear energy. In the past seven years at the National Lab, she has worked on advanced nuclear fuel, advanced energy systems, small modular reactors, advanced reactors, and ways in which those systems can supply the nation’s energy needs in a different way. Light water reactors produce electricity and provide resilient baseload power, but throw away a lot of thermal energy. Baseload supply power is being stressed by outside factors of renewable energy and natural gas and needs to operate more flexibility or modify their power to meet the volatility of renewable energy. Solar and wind energy are non-dispatchable energy sources, since they are only available when the sun and wind are available. Energy storage helps protract this out, but not in the long term and seasonal storage. A majority of the solar and wind resources are in specialized locations. Intermittency and transmission are two major challenges in the electricity market. Emissions coming from resources used for energy is also a consideration. However, electricity is only one piece of the puzzle. The energy sectors include electricity, industrial energy, transportation, and residential heating. Some industrial processes burn carbon resources to create the heat necessary to drive these processes, such as in plastic production.
15:31 - Nuclear Renewable Hybrid Energy Systems
Bret Kugelmass: What is your Nuclear Renewable Hybrid Energy Systems program?
Shannon Bragg-Sitton: Shannon Bragg-Sitton wants nuclear power reactors to work in coordination with renewable technologies coming online in certain regions. Nuclear can technically modify the power output within certain constraints. A reactor operates best when it is at its nominal operating power level running steady state. Instead of changing that, some energy produced could go to the electricity sector and the excess heat not needed for electricity can be sent to other things, such as industrial processes or district heating. Waste heat can be used in district heating to send steam to the region. Higher quality heat can drive industrial processes and water desalination. The most commercially available option for water desalination is reverse osmosis, which is driven solely by electricity. Bragg-Sitton’s program is managed under the Office of Nuclear Energy in the Department of Energy. Her program has a collaborative sister program in the Office of Energy Efficiency and Renewable Energy, whose focus in hybrid energy systems is in hydrogen. Hydrogen at Scale looks at large-scale production of hydrogen through the use of clean energy sources. Hydrogen can be used as a transportation means in fuel cell vehicles and is an entry into other industrial processes, such as upgrading biofuels. Bragg-Sitton’s program looks at how to integrate hydrogen production into a nuclear system, such as with low temperature electrolysis or high temperature electrolysis and how they can be operated flexibly. She started looking at preliminary analysis using simplified models, then looking into more dynamic and higher fidelity models to determine how to move energy around. Each subsystem has different response times and power changes. A control system architecture must allow this energy to be lined up and balanced, but models must be validated. Models are moved into a laboratory where systems can be put together with controlled heat sources to mimic the behavior and thermal energy input. In the integrated systems laboratory, there is a dynamic load and acts like users on the grid to see the variation of electricity demand. Actual solar panels and wind turbines are integrated into the lab and computer systems represent a microgrid. Real time digital simulators emulate the power systems on the grid. These pieces are physically put together for hardware in-the-loop testing to understand how the systems behave.
25:33 - Implementation of Hybrid Energy Systems
Bret Kugelmass: As you progress your research, who are the eventual stakeholders for this technology that might implement it in the real world?
Shannon Bragg-Sitton: When Shannon Bragg-Sitton first started the program, the focus was on advanced reactor technologies which operate at higher temperatures than light water reactors, bringing higher efficiency. The program looked for benefits at lower temperature light water reactors and started getting interest from the current fleet of light water reactors which are being operated by utilities that are currently seeing economic challenges for their reactors. Bragg-Sitton is working with a number of operating utilities at existing plants and has done a number of initial analyses for advanced reactor developers and developers of light water small modular reactors to look at the feasibility of the systems. The user community, such as fuel cell producers, are also brought in to talk about fabrication and distribution using hydrogen. Bragg-Sitton maintains a utility advisory committee for her Hybrid Energy Systems program, relying on operators to share how they’d realistically accomplish integration in a current operating reactor, without impacts to safety systems, regulations, and licenses. The National Laboratory is coming up with the ideas and working with industry directly for them to advise on strategies for implementation.