Physics characteristics of the fixed bed nuclear reactor

•The burning-up fuel of 235U and the build-up of 239Pu density in the FBNR are determined.•The FBNR may operate at 218 MWth power for 2.73 years without on-site refueling.•At core heights over 120 cm, the FBNR can be controlled by change of its own core heights.•The kinetic parameters of the reactor change in process of its operation.

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 U235 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.