Part 2 of 2 Parts (Please read Part 1 first)
     Dozens of SMR designs have been proposed. For this study, Krall analyzed the nuclear waste streams generated by three types of SMRs being developed by Toshiba, NuScale, and Terrestrial Energy. Each company chose a different design. Results from these case studies were corroborated by theoretical calculations and a broader design survey. This three-pronged approach allowed the authors to draw powerful conclusions.
     Rodney Ewing is the Frank Stanton Professor in Nuclear Security at Stanford and co-director of Stanford University’s Center for International Security and Cooperation (CISAC). CISAC is part of the Freeman Spogli Institute for International Studies at Stanford. Ewing is also a professor in the Department of Geological Sciences in the Stanford School of Earth, Energy and Environmental Sciences and a co-author of the Stanford study. He said, “The analysis was difficult because none of these reactors are in operation yet. Also, the designs of some of the reactors are proprietary, adding additional hurdles to the research.”
     Energy is produced in a nuclear reactor when a neutron splits a uranium atom in the reactor core. This generates additional neutrons that go on to split other uranium atoms, creating a chain reaction. However, some neutrons escape from the core which is called neutron leakage. The escaping neutrons strike surrounding structural materials, such as steel and concrete. These materials become radioactive when impacted by neutrons lost from the core.
     The new study found that SMRs will experience more neutron leakage than conventional reactors because of their smaller size. This increased leakage has an impact on the amount and composition of their waste streams.
     Ewing said, “The more neutrons that are leaked, the greater the amount of radioactivity created by the activation process of neutrons. We found that small modular reactors will generate at least nine times more neutron-activated steel than conventional power plants. These radioactive materials have to be carefully managed prior to disposal, which will be expensive.”
     The Stanford study also found that the spent nuclear fuel from SMRs will be discharged in greater volumes per unit energy extracted. The SMR waste can be far more complex than the spent nuclear fuel discharged from existing power plants.
     Allison Macfarlane is a professor and director of the School of Public Policy and Global Affairs at the University of British Columbia and a co-author of the study. She said, “Some small modular reactor designs call for chemically exotic fuels and coolants that can produce difficult-to-manage wastes for disposal. Those exotic fuels and coolants may require costly chemical treatment prior to disposal. The takeaway message for the nuclear industry and investors is that the back end of the fuel cycle may include hidden costs that must be addressed. It’s in the best interest of the reactor designer and the regulator to understand the waste implications of these reactors.”
     The Stanford study concludes that SMR designs are inferior to conventional nuclear power reactors with respect to radioactive waste generation, management requirements, and disposal options.
    One major problem is long-term radiation from spent nuclear fuel. The research team estimated that after ten thousand years, the radiotoxicity of plutonium in spent nuclear fuels discharged from the three study modules would be at least fifty percent higher than the plutonium in conventional spent nuclear fuel per unit energy extracted. Because of this high level of radiotoxicity, geologic repositories for SMR wastes need to be carefully chosen through a thorough siting process, the authors said.
     Ewing said, “We shouldn’t be the ones doing this kind of study. The vendors, those who are proposing and receiving federal support to develop advanced reactors, should be concerned about the waste and conducting research that can be reviewed in the open literature.”