Minor actinides represent the long-term radiotoxicity of nuclear wastes. As one of their potential incineration options, partitioning and transmutation in fission reactors are seriously considered worldwide. If implemented, these technologies could also be a source of nuclear fuel materials required for sustainability of nuclear energy. The objective of this research was to evaluate performance characteristics of Very High Temperature Reactors (VHTRs) and their variations due to configuration adjustments targeting achievability of spectral variations. The development of realistic whole-core 3D VHTR models and their benchmarking against experimental data was an inherent part of the research effort. Although the performance analysis was primarily focused on prismatic core configurations, 3D pebble-bed core models were also created and analyzed. The whole-core 3D models representing the prismatic block and pebble-bed cores were created for use with the SCALE 5.0 code system. Each of the models required the Dancoff correction factor to be externally calculated. The code system DANCOFF-MCThe whole-core/system 3D models with multi-heterogeneity treatments were validated by the benchmark problems. Obtained results are in agreement with the available High Temperature Test Reactor data. Preliminary analyses of actinide-fueled VHTR configurations have indicated promising performance characteristics. Utilization of minor actinides as a fuel component would facilitate development of new fuel cycles and support sustainability of a fuel source for nuclear energy assuring future operation of Generation IV nuclear energy systems. was utilized to perform the Dancoff factor calculations.