Various small modular reactor (SMR) designs are being developed with the aim of expanding the market potential of nuclear energy. However, an important part of the overall implementation is yet to be completely developed: how to manage spent nuclear fuel.
Increasing nuclear power generation is considered by many as one of the key elements in curbing CO2 emissions and meeting climate goals. SMRs, often defined as reactors with power production capacities up to 300 megawatts, are seen as a feasible way to help achieve these aims.
SMRs are attractive for several reasons. Their small size and the potential for serial production offer the promise of making them easier to finance and faster to build than traditional, large power plants. They are also touted as being safer than large reactors due to smaller thermal capacities and radioactive inventories as well as passive safety features.
The development of SMRs benefits from the technology developed for larger power plants and demonstration reactors, and the skills honed while operating these facilities. However, one key issue to be addressed is how to most effectively manage spent SMR fuel, which is high-level radioactive material.
Known fuels get a head start
Spent nuclear fuel needs to be cooled, treated, packaged and stored, and finally disposed of in a repository unless it is reprocessed. Finland, for example, has a clear concept and design for disposing of used fuel from its currently operating large power plants. It will likely be the first country in the world to operate a deep geological repository (ONKALO).
Although it may be a tempting idea to use the constructed repository for disposal of spent fuel from SMRs as well, there are numerous technical and economic issues to be addressed to account for the variation in SMR designs and material properties. Existing concepts for waste management will certainly give a head start to the implementation of SMRs based on currently operating reactor technology for which waste management routes exist.
The majority of large commercial nuclear power reactors are light water type reactors (LWRs) as are the most advanced SMR designs. In addition to light water type reactors, there are several different non-LWR designs being developed. These advanced modular reactors (AMRs) operate at higher temperatures and will use more exotic fuels, such as TRISO fuel, HALEU, molten salts and others, for which specific treatment and disposal routes are not yet available.
Spent fuel management calls for individual solutions
Dedicated waste management paths need to be developed for each small reactor type, even when using the well-known light water technology. This means that there is a need to characterize actual used fuel taken from a reactor operating under normal conditions. As irradiated fuel from SMR/AMR designs is not yet available or fully understood in terms of long-term safety, VTT conducts numerical simulations based on assumed reactor operating parameters and fuel designs. These analyses allow VTT, vendors, and potential buyers or operators to evaluate the disposability of SMR/AMR spent fuel, by assessing the impact of the operational inventory on the detailed design and safety case of a deep geological repository. This work is carried out in collaboration with international experts and SMR/AMR developers, such as in IAEA groups, the NEA WISARD project and Euratom collaborative projects.
In addition to reactor type, another essential factor in nuclear waste management is the location of each reactor. If SMRs/AMRs are widely dispersed over a given national jurisdiction, used fuel will likely need to be transported to a centralized facility for treatment, packaging and final disposal. The transport of nuclear fuel, both fresh and used, is already commonplace with established regulations and infrastructure existing for this purpose. However, in the case of widely dispersed SMRs across a country, transport networks may need to be expanded and interim storage facilities constructed.
Additional challenges will arise from the use of SMRs. For example, in Finland, SMRs are being considered for district heating. As such, even small municipalities may be interested in SMRs. New siting opportunities and ownership models raise questions regarding the fulfillment of spent fuel management responsibilities.
It's important to realize that spent fuel management is a critical part of a nuclear power investment whether the project includes dozens of reactors or just one. To reach an optimal solution, spent fuel management methods and costs need to be considered in the initial planning.
