Monte Carlo Burn-up Calculation of the PBMR Core with Pebble Flow Velocity

PBMR core has the fuelling scheme that fresh fuel elements are added to the top of the reactor while the burned fuel pebbles are removed from the bottom of reactor. The discharge rate of fuel pebble in the fuelling system is actually 2936 pebbles per day for PBMR. In the previous study, the burn-up calculation was carried out assuming the velocities of the pebbles are all the same in the whole core region. The pebble velocity is the function of the pebble position within the core. It is important that the pebble velocity should be accurately analyzed, because the difference of the velocity affects the criticality and the flux distribution. A method to calculate the relative velocity of the pebble flow was developed in the previous study. The burnup calculation was pursued with MONTEBURNS 2.0 code in this study, after the pebble velocity calculation by using the method