One of the first studies dealing with the production of nuclear waste for small standard reactors.
Nuclear power is a major component of decarbonizing our economy, but large nuclear reactors are often complex and expensive. To make nuclear power more available and attractive, developers have introduced multiple designs of Small Modular Reactors (SMRs) that have greater flexibility and offer lower upfront costs. Various types of SMRs with advanced reactor design features are currently under development in the United States and worldwide.
The researchers believe that SMRs can be deployed at a variety of scales for locally distributed electricity generation. SMR has approximately one-tenth to one-third of the power output of LWRs, which are the most common type of nuclear reactor in commercial operations in the United States. SMR techniques and economics have been studied extensively; However, there is less information about their effects on nuclear waste. “We are just beginning to study the properties of nuclear waste in SMRs,” said Chief Nuclear Engineer Taek-Keum Kim of the US Department of Energy’s Argonne National Laboratory.
Kim and colleagues from Argonne and the US Department of Energy’s Idaho National Laboratory recently published a report that seeks to measure the potential nuclear waste attributes of three different SMR technologies using metrics developed through an extensive process during a comprehensive assessment of nuclear fuel cycles published in 2014. Commercially operational SMRs have not yet been made, and several companies have collaborated with the DOE to explore various possibilities for SMRs, and all three designs studied in the report are slated to be up and running by the end of the decade.
One type of SMR, called VOYGR and being developed by NuScale Power, is based on the existing conventional pressurized water reactor design but scaled down and made modular. Another type, called Natrium and being developed by TerraPower, is sodium-cooled and runs on mineral fuel. The third type, called Xe-100 and developed by Energy X, is cooled by helium gas.
In terms of nuclear waste, Kim said, each reactor offers advantages and disadvantages over large light water reactors. “It is not correct to say that because these reactors are smaller in size, they will have more problems proportioning the nuclear waste, simply because they have a larger surface area compared to the core volume,” he said. “Each reactor has its pros and cons depending on vacuum combustion, uranium enrichment, thermal efficiency, and other design features of the reactor.”
One prominent factor affecting the amount of nuclear waste a reactor produces is called combustion, and it refers to the amount of heat energy produced by a given amount of fuel. Kim said the Natrium and Xe-100 reactors have much higher burnouts than the LWRs. Higher combustion is associated with less nuclear waste production because the fuel is converted more efficiently into energy. These designs also have a higher thermal efficiency, which indicates how efficiently the heat produced by the reactor is converted into electricity. The VOYGR pressurized water reactor design, due in part to its smaller size, has slightly lower combustion and thermal efficiency compared to a larger pressurized water reactor.
The attributes of spent fuel differ somewhat between designs, as the VOYGR is similar to LWRs, Natrium produces more concentrated waste with different long-lived isotopes, and the Xe-100 produces a lower density but greater volume of spent fuel.
“Finally, when it comes to nuclear waste, SMRs are roughly comparable to conventional pressurized water reactors, with potential benefits and weaknesses depending on which aspects you are trying to design for,” Kim said. ? “Overall, there appear to be no additional significant challenges to SMR nuclear waste management compared to large commercial LWR waste.”
The research was funded by the Department of Energy’s Office of Nuclear Energy through the Systems Analysis and Integration Campaign.