Part 2 of 2 Parts (Please read Part 1 first)
The main concern about any nuclear power reactor is the possibility that the core could melt down in a disaster. The main advantage of TRISO fuel is that it is just not possible for it to melt down.
Each TRISO particle has a core of uranium, carbon and oxygen. This core is about the size of a seed from a poppy. It is surround by three layers of carbon and ceramic-based materials. The structure that results from this encapsulation not only prevents any of the radioactive fission products from being released but it can also resist neutron irradiation, corrosion, oxidation and high temperatures which are the most common sources of risk in nuclear power reactors.
TRISO fuel particles have been irradiated and subjected to more than three hundred hours of testing at temperatures up to eighteen hundred degrees Celsius or three thousand degrees Fahrenheit. These tests exceeded the worst-case projections for nuclear accident conditions. The TRISO particles showed minimal damage at most with full fission product retention. Paul Demkowicz is the technical lead for post-irradiation examination of TRISO fuel. He said, “The ability of the fuel to retain fission products at such high temperatures translates directly to enhanced safety of the reactor. This sort of test data is important input for reactor design and reactor licensing.”
TRISO fuel particles were first developed in the United Kingdom in the 1960s as part of the Dragon Reactor project. This was an experimental high-temperature gas-cooled reactor. By 2002, the U.S. Department of Energy (DoE) had already invested significant effort into the improvement of TRISO fuel and significant progress was made. By 2009, a test of improved TRISO fuel established an international record by achieving a nineteen percent maximum burnup during a three-year test as the Idaho National Laboratory. This is three times the burnup rate of conventional light water reactors. The burnup rate for nuclear fuel is a measure of how much energy can be extracted from a primary nuclear reactor fuel. These tests established the efficiency and long-life capability of TRISO reactors. The DoE has expressed interest in producing and burning TRISO fuel in commercial nuclear power reactors and the private sector nuclear industry has shown interest. TRISO is not a far-off new technology. It is almost ready for the marketplace.
There are already two experimental reactors that use TRISO fuel. These are the HTR-1 reactor in China and the High-temperature engineering test reactor in Japan. The DoE’s Advanced Reactor Technologies (ART) program is currently carrying out advanced TRISO fuel research. Some vendors including X-energy and Kairos Power have show solid interest in using TRISO fuel in their reactors. They are especially interested in TRISO fuel utilization in small modular reactors and microreactor designs. There are various projects around the globe that are developing high-temperatures and molten salt nuclear reactors which can use TRISO fuel. By 2019, three companies were selected by the U.S. Department of Defense (DoD) to develop TRISO nuclear reactor prototypes. These companies are X-energy, BWX Technologies and Westinghouse Government Services.
These trends could indicate a shift in the planning for nuclear power plants. Up until now, the focus has been on building huge nuclear power plants that power entire cities. Now we have companies working on smaller and more robust nuclear power reactors that would be used to provide power for smaller areas without the risks of the full-sized reactors in use today. X-energy CEO Clay Sell said that TRISO reactors are also well suited for applications in the military and in the exploration and exploitation of space.