Idaho National Labs
Feb 21, 2018
2:32 - Introduction to Nuclear
Bret Kugelmass: How did you get involved in the nuclear space?
Hans Gougar: Hans Gougar studied physics in his undergraduate studies at the University of Wisconsin and started out teaching high school physics. Five years in, while teaching in London, England, Gougar met his wife-to-be, Mary Lou, and they found a common interest in the nuclear curriculum. Hans Gougar ended up at Penn State where he studied nuclear engineering with a focus on advanced nuclear power. Nuclear energy is the manipulation of matter on a fundamental, nuclear level to generate electricity, perform medical procedures, and power water and space vehicles. It has only been a little over 100 years since humans were able to probe the interior of the atom, the nucleus. While at Penn State, Mary Lou obtained a fellowship to work on a dissertation that required her to work in Idaho at Argonne West and Hans got a job at Idaho National Lab. He started out working on the Advanced Test Reactor, then was asked to help out on a new pebble bed project at the Laboratory. The U.S. had seen the pebble bed work going on in South Africa and there seemed to be a resurgence in interest in high temperature reactors around the world. Exelon, a utility in Eastern U.S., committed to investing in and building this technology. The lab said they would look into the technology and see how they could help out. An internal project was set up in conjunction with MIT.
7:51 - Pebble Bed Reactors
Bret Kugelmass: What is pebble bed technology and how do high temperature reactors work?
Hans Gougar: Pebble bed reactors run at the highest temperature of any other type of power reactor and operates between 700-1,000 degrees Celsius outlet temperature. The high temperature is allowed by the structure of the reactor. Instead of having oxide fuel rods in metal cans with water flowing through it, as in light water reactors, high temperature reactors have very small, millimeter size uranium oxide particles that are coated with various layers of silicon carbide, high density carbon, and other materials. Thousand or millions of these particles are encased in either a graphite pebble, about the size of a billiard ball, or a compact, cylindrical-shaped element encased in larger blocks. Like a gumball machine, a cavity is filled with the pebbles, which contain thousands of fuel particles. The coatings on the pebbles are highly robust and it is very difficult to break them in the conditions inside the reactor. A uranium oxide or carbide kernel is surrounded by a low density, spongy buffer material that can absorb and hold onto fission products, a high density layer of pyrolytic carbon, silicon carbide, the main fission product retaining barrier, and finally one more layer of pyrolytic carbon. The multilayer system is very effective at keeping nuclear stuff inside. When this is embedded in graphite, it creates another barrier, but any excess heat that may be generated during an off-normal incident gets absorbed by the graphite and transmitted away out of the core without harming or allowing the fuel particles inside to undergo any damage. Helium is used as the coolant in the pebble bed system since it doesn’t corrode anything and is very inert neutronically and chemically. The helium carries the heat away where you can do something useful with it, whether that is high efficiency electricity generation or industrial processes that are driven by heat.
13:33 - Resurgence of Pebble Bed Technology
Bret Kugelmass: Worldwide, where are we now with pebble bed technology?
Hans Gougar: Pebble bed technology was first developed in the 1970’s and 1980’s in Germany. In the U.S., prismatic high temperatures reactors were built, including Fort St. Vrain. The technology faded out and was competing with light water technology that had the major support from the government and the industry at the time. In the 1990’s, interest surged after the accidents at Three Mile Island and Chernobyl. China and Japan had just finished building small, engineering scale reactors that are still operable today and used for experimental data collection. The Japanese have plans to use their test reactor to explore power conversion systems like a gas turbine or hydrogen production, but they are not meant to generate revenue or electricity. A number of scientists in South Africa in the 1990’s decided they could adopt this technology and was right for their market and mining industry. They started a government-funded project called the Pebble Bed Modular Reactor (PBMR). Hans and Mary Lou Gougar decided to take the opportunity to see the industry from a different perspective and spent a little over a year helping out at PBMR in South Africa.
17:56 - Pebble Bed Research at INL
Bret Kugelmass: When did you return to Idaho National Lab and what has been their focus since then?
Hans Gougar: Hans Gougar left the Pebble Bed Modular Reactor (PBMR) project in South Africa and returned to Idaho National Lab (INL) in 2009. INL has four main research areas within the high temperature reactor project, originally called the Next Generation Nuclear Plant. The main focus was on improving the particle and standing up a commercial provider for the fuel, since the entire fuel infrastructure in the U.S. was focused on the light water reactor. INL is looking at new grades of graphite, qualifying them, and understanding how they behave inside the reactor environment. There are metallic components inside the vessel itself and the metals that are useful or qualified for use in nuclear applications cannot easily withstand those higher temperatures, so new metals need to be found, qualified, and made available to the industry. INL also works on simulation design and analysis methods that are needed to license such a machine. The regulator and investors must be convinced that the reactor temperature is known throughout and how much fission is taking place. They also want to know about its behavior if something goes wrong and off-site cooling is lost. In the early days, German pebble bed reactors used loss of coolant as a shut down mechanism. The primary coolers and blowers would be turned off, increasing the temperature a little bit, but by natural feedback mechanisms, would turn itself off and cool itself down. The affinity for neutrons by the nuclear fuel is very temperature sensitive. As you raise the temperature of the fuel, it is less likely to absorb neutrons and cause fission.
22:39 - Qualification Process for New Fuels and Materials
Bret Kugelmass: What are some challenges of pebble bed technology?
Hans Gougar: Pebble bed reactors face the same challenge of cost of other nuclear power plants. There is no constant feedback and product improvement, limiting the opportunity to learn and innovate. Reactors must go through the same licensing process and come up with the same supply chain for fuel and components. It is a multibillion dollar adventure and investors are hesitant to get in. Hans Gougar and the Idaho National Lab (INL) are working with the Nuclear Regulatory Commission (NRC) to modify the regulations so they are not light water specific, but are more generic in nature. The NRC must be able to understand the technology first and then define the appropriate limits and operating regimes for the system. INL provides an independent auditing or confirmation expertise to the NRC and startup companies. The bulk of INL’s work has been on basic fuel and material qualifications. INL fabricates the fuel, puts it in the test reactor, and burns it to a crisp to understand how it behaves and how well it retains the fission products. This data is supplied to the vendors and the regulator. In the U.S., the primary configuration is a prismatic reactor. Instead of a gumball machine setup, the reactor has cylindrical fuel elements, about the size of a pinky finger. These cylinders are stacked inside of a larger graphite blocks stacked together and helium is blown through them.
27:56 - Future Deployment of High Temperature Nuclear Plants
Bret Kugelmass: Where do you see the future work of your work, INL, and pebble bed nuclear technology going?
Hans Gougar: Pebble bed technology is poised for major deployment, but the U.S. must relearn how to build nuclear power plants inexpensively. These plants are highly engineered, complex machines. To build one on-time and on-schedule according to your designer’s specs is a tremendous architectural engineering effort. Costs in the U.S. have gone up in the areas of engineering procurement construction (EPC), labor, and supply chain. If you can build a machine that is inherently safe, it allows to you have a lower cost machine, but it is still very complex and expensive. People are concerned about carbon footprints and fossil fuels. Natural gas is keeping our economy going, but eventually prices might spike again depending on local supply conditions. If gas prices get around $8-9 per million BTU, a high temperature reactor can compete in both the electricity and process heat marketplace with natural gas.