SUMMARY

Microreactors contain material and geometric features not characteristic to operating reactors. The usage of control material at the core periphery and the distance between absorber and fissionable assemblies allows for environmental effects to significantly affect multigroup data of a region given its boundary condition and location within the core. A microreactor design consisting of eighteen identical fuel assemblies surrounded by control drums rotated to determine reactivity is derived from literature with closed gaps in temperature data. This design is analyzed using the continuous-energy Monte Carlo code SERPENT 2 under six sets of environmental effects – four involving a single assembly with independently imposed radial and axial boundary conditions, and two involving a whole core model with drums rotated to minimize or maximize reactivity.

The results generated include eigenvalues, pin power distributions, scattering kernels up to third order, and multigroup cross sections for capture, scattering, fission, and neutron production in selected regions in the problem sets. The dependence of these data on local environment imposed by a set of boundary conditions at assembly interfaces is investigated. The stylized benchmark model contains essential reactor physics qualities to significantly effect local multigroup cross sections of a given material at both differing axial or radial location within the core as well as core environment effects imposed by differing boundary conditions. These reference data can therefore benchmark computational methods and tools for multigroup cross section generation or core calculations based on pin power density.