Criticality of the thorium burnup in equilibrium state

•Impact of F2Be, Na, Pb coolants on the burnup of thorium in fast reactor.•The maximal keff, and burnup and CR in an equilibrium state are study.•Analytical and Monte Carlo method of calculation of keff in an equilibrium state.•The maximal keff and burnup are increasing functions of average neutron energy.•The keff > 1 and CR > 1 are possible simultaneously but in a non-equilibrium state.

The effective neutron multiplication factor (keff) as a function of burnup for different volume coolant (CoR) and fuel (FR) to cell ratio is presented. Additionally the Conversion Ratio (CR) of Th-232 to U-233, concentration of U-233, fissile and fission products calculation as a function of burnup are presented. The assembly is a critical reactor which makes volumes of coolant and fuel changes possible. In addition, an analytical model of calculation of keff as a function of U-233 and a poison concentration in equilibrium state are presented. One can achieve the criticality of Thorium Breeder Reactor (TBR) for enough high average neutron energy which one can obtain in Fast Breeder Reactor (FBR) only. The maximal value of CR and burnup for case of keff ≥ 1 achieves 1.4 and 360 GWd/MTU, correspondently. The calculations were done with a MCNPX 2.7 code using F2Be, Na and Pb coolants.