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The high temperature engineering test reactor (HTTR) is a block-type high-temperature gas-cooled reactor (HTGR) developed by Japan. The HTTR is a graphite-moderated and helium-cooled HTGR with a thermal power of 30 MW and a maximum outlet temperature of 950°C. HTTR uses UO2 fuel with enrichment vary from 3,4% to 9,9%. Neutronic calculations are performed by PIJ and CITATION modules on SRAC2006 code system with JENDL-4.0 as the nuclear data library. In this study, two models are used for the cell-burnup calculations. Microscopic cell in the fuel compact is defined in model 1, whereas it is not defined in model 2. The core geometry used in these calculations are triangular-z and hexagonal-z. The neutronic analysis includes several parameters such as effective multiplication factor (k-eff), conversion ratio, changes in atomic density for fissile and fertile materials, neutron spectrum, power density distribution, and power peaking factor. The results show a quite different neutronic parameters with model 1 and 2. Model 1 achieved the first criticality at the enrichment of 6,3%, whereas model 2 at 6,7%. The conversion ratio tends to increase during burnup and greater in model 2. Both core geometries show similar results with greater k-eff in the triangular-z geometry. The maximum power density is located at the fuel block with an enrichment of 6,7%.