[en] In order to prepare for the future needs of new research reactors, a project has been launched, of which goal is the development of a high performance research reactor. As one of the initial stage activities, various kinds of core configurations have been considered and preliminary analyses on them was carried out to figure out the highest performance concept. The calculation results was compared with the nuclear design requirements established based on IAEA reports and the experiences of HANARO design and operation. A rod type of U-Si fuel with low enriched uranium was used as a fuel for the core of new core configurations considered. It is because the U-Mo dispersion fuel which is internationally under qualification seems to need several more years to be qualified for actual use while the rod-type U-Si fuel has been partly qualified. The core configurations considered in this report may be classified two category; cores with and without flow tubes. Namely a compact core, multi core, and Al block core are categorized into the core concept with flow tube, and that without flow tube includes a core with one or three in-core irradiation holes and the annular core concepts. The analyses showed that we could get the thermal flux level of up to 2.8E13 n/cm²·s/MW in the core and 2.2E13 n/cm²·s/MW in the reflector with reasonable amount of excess reactivity. This would be one of highest flux levels that LEU fuel research reactors can provide