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Seminar Recording: https://youtu.be/M7DEG62NsVQ

About the Event: In recent years, small modular reactors (SMRs, i.e. nuclear reactors with electric capacities less than 300 MW_elec) have received bipartisan, Congressional support on the pretense that their development will reduce the mass and radiotoxicity of commercially generated nuclear waste. However, these metrics are of limited value in planning for the safe management and disposal of this radioactive material. By analyzing the published design specifications for water-, sodium-, and molten salt-cooled SMRs, I here characterize their notional, high-level waste streams in terms of decay heat, radiochemistry, and fissile isotope concentration, each of which have implications for geologic repository design and long-term safety. Volumes of low- and intermediate-level decommissioning waste, in the form of reactor components, coolants, and moderators, have also been estimated.

The results show that SMRs will not reduce the size of a geologic repository for spent nuclear fuel, nor the associated future dose rates. Rather, SMRs are poised to discharge spent fuel with relatively high concentrations of fissile material, which may pose re-criticality risks in a geologic repository. Furthermore, SMRs—in particular, designs that call for molten salt or sodium coolants—entail increased volumes of decommissioning waste, as compared to a standard 1100 MW_elec, water-cooled reactor. Many of the anticipated SMR waste challenges are a consequence of neutron leakage, a basic physical process that reduces the fuel burnup efficiency in small reactor cores. Common approaches to attenuating neutron leakage from SMRs, such as the introduction of radial neutron reflectors, will increase the generation of decommissioning waste. The feasibility of managing SMR waste streams should be performed before these reactors are licensed, and future clean energy policies should acknowledge the adverse impact that SMRs will have on radioactive waste management and disposal.

About the Speaker: Dr. Lindsay Krall is a MacArthur post-doctoral fellow and a geochemist at SKB. Her post-doctoral research assesses the technical credibility of recent DOE programs related to SNF management, in particular those centered around deep borehole disposal and advanced nuclear reactors.