There are thousands of tons of spent nuclear fuel in cooling pools around the world that must be permanently disposed of. Phil Stauffer and researchers at the Los Alamos National Labs have been collaborating with the U.S. Department of Energy (DoE) and other national laboratories are seeking a long term solution to the permanent disposal of spent nuclear fuel.
Stauffer says, “Deep salt formations that already exist in the United States are one candidate for long-term disposal. This 'high-level' nuclear waste can create a lot of heat, in addition to the radioactivity that must be contained. We need to develop a clear path to dispose of this waste."
There are many salt deposits underground around the world. They have been found to be “self-healing”, have very low permeability and they conduct heat very well. All of these features are important to the release of the heat generated by nuclear waste. It is believed that salt formation can make an excellent barrier to the long-term release of radioactive materials into the environment.
The United States and Germany are currently disposing of low and intermediate radiative waste in permanent geological repositories in salt deposits. These wastes do not create as much heat as spent nuclear fuel. Because of this, additional studies have been required to determine the safety and efficacy of salt deposits for the spent nuclear fuel.
While salt is a formidable physical barrier, salt is also subject to chemical processes that might affect its ability to safely store spent nuclear fuel. How salt deposits react to the presence of water, heat and other geological factors needed to be exhaustively researched.
Recent thermal underground testing began by the creation of a full-scale mock-up of a spent nuclear fuel waste canister which was heated for a year. This is the first such test since the late 1980s in the U.S.
At the same time as the canister test, the U.S. Department of Energy research team is running a project to investigate generic waste repositories. One of the issues being studied is how water migrates towards heat sources buried in salt. The project is called the BATS project which stands for “Brine Availability Test in Salt”. It is part of the work of Stauffer and his team. His team began working on a pilot test several years ago.
The researchers have drilled boreholes into salt deposits and done heater tests on these salt-surrounded holes. This research has provided important insights which are being used to make waste disposal decisions. These tests are being conducted underground in big tunnels in old salt mines.
Phase 1s (shakedown) started in the summer of 2018 and ran for a year. Stauffer said, “The lessons learned, and insights gained in this initial testing, are proving vital to the design and implementation of the next, larger-scale experiment.” Researchers have also been using computer models to predict the results expected from some of the tests. Stauffer also said, “Long term modeling can be used to develop the appropriate initial pressure and other important factors for the boreholes.”
Phase 1 began in January of this year and is scheduled to run for several month. It will involve more complex data collection. Fiber optic cables, electrical resistivity tomography and real-time isotopic measurements on the waters that evaporate from brine. Data from the next experiment will be used to refine models and shared with the international nuclear research community. Plans call for increasing the scale of the heater experiments to eventually explore the availability of brine to spent nuclear waste canisters in an arrangement representing a possible future high-level nuclear waste repository.