On 3 September 2026 at 10.15 Hando Tohver will defend his doctoral thesis “Open-source modeling approaches for radioactive waste management in nuclear newcomer countries” .
Supervisors:
Siiri Salupere, PhD, Research Fellow in Radiation Protection, Institute of Physics, University of Tartu, Estonia.
Marti Jeltsov, PhD, Researcher, High Energy Physics and Theoretical Physics, National Institute of Chemical Physics and Biophysics, Estonia.
Marily Jaska, MSc, Head of Radiation and Nuclear Energy Unit, Environmental Management and Radiation Department, Ministry of Climate, Estonia.
Opponent:
Szabolcs Czifrus, Associate Professor, Director, Institute of Nuclear Techniques, Budapest University of Technology and Economics
Summary
The world is rapidly moving away from fossil fuels and nuclear energy is gaining popularity, particularly in the form of small modular reactors. These are a good option for smaller countries whose electricity grids are too small for large power plants. However, nuclear newcomer countries face a serious challenge: how to safely manage radioactive waste without any prior experience? Since the hazardous nature of radioactive waste rules out a trial-and-error approach in waste management, radiation transport must be modeled in detail using computer simulations before any decisions are made. The most accurate programs are, however, only available to experienced nuclear states due to security and export restrictions. This doctoral thesis shows that a solution exists in the form of freely available open-source software: EGSnrc and OpenMC produce results of equal accuracy to export-restricted codes when evaluating the radiation shielding of waste containers, making these open-source codes a suitable choice for countries building up their nuclear capabilities. Using these tools, it was demonstrated that oil shale ash, an industrial byproduct generated in Estonia, is a suitable concrete additive for waste containers, and that adding basalt-boron fibers significantly improves protection against neutron radiation. Beyond material shielding analysis, a new software tool called Wastimate was developed during this work to help plan waste management across the entire lifecycle of a nuclear plant. Using Wastimate, it was shown that smart co-packaging of older and newer fuel assemblies can shorten the overall waste management timeline by up to a decade. In summary, early-stage waste management studies, from container materials to facility planning, are entirely achievable using open-source tools, benefiting both Estonia and other countries embarking on the path of nuclear energy.
