This article is about calculation of fuel burn-up and some physics parameters of the Fixed Bed Nuclear Reactor (FBNR), using spherical fuel elements similar to TRISO fuel, which is investigated by SRAC code. The fuel that was used is a uranium dioxide sphere (UO2) with U-235 enrichment of 5%. The main results of this study can be summarized as follows: (1) Variation of nuclear isotope densities and effective neutron multiplication coefficient in process of fuel burn-up is determined and the reactor can operate during the time of 2.73 years, without on-site refueling. The U235 burn-up reaches value 71.84% of its initial density at the end of the reactor fuel cycle. (2) When the core height is over 120 cm, the reactor control can be carried out by the movement of a core height level limiter, without the fine control rods in the core center. (3) The kinetic parameters of the reactor (the prompt-neutron lifetime and effective delayed neutron fraction) change in process of reactor operation. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.