Core characteristics of an OTTO refueling pebble bed reactor and comparison with a multi-pass scheme

Paper in proceeding, 2012

This paper presents the core characteristics of a once-through-then-out (OTTO) refueling scheme of a pebble bed reactor and compares with a reference multi-pass scheme. In order to control the axial power profile of the OTTO scheme, the core was loaded by new fuel pebbles designed with burnable poison. However, using burnable poison will result in the decrease of fuel burnup performance as well as other core parameters. Thus, the fuel and burnable poison designs were carried out to maximize the average discharged burnup while maintaining a limited power peak and ensuring core criticality. Numerical calculations have been performed based on the 400 MWt pebble bed modular reactor (PBMR-400). The results show that the OTTO scheme using the newly designed fuel pebbles can achieve the average discharged burnup of 75 GWd/t which is about 21% less than that of the multi-pass scheme (95 GWd/t), whereas the other neutronic characteristics are comparable.