Validation of the axial expansion reactivity worth for a metal-fueled Sodium-cooled Fast Reactor via a physical experiment

For a metal-fueled SFR (Sodium-cooled Fast Reactor), the negative feedback of the reactivity due to the thermal expansion of fuel has been a principal safety mechanism to guarantee passive reactor shutdown after undercooling accidents. In this paper, an experimental model of the fuel axial expansion reactivity in a metal-fueled SFR was proposed and measured values using the BFS-109-2A critical assembly was compared with calculated values using as-built MCNP models based on the ENDF/B-VII.0 library. The energy-dependent axial expansion reactivity components of the BFS-109-2A model showed good agreement with those of the target core. The difference in the calculation/experiment ratio between the as-built MCNP models and measurements vary from −10.2% to 2.6% for the axial expansion reactivity, meanwhile the suggested axial expansion model showed a 25% discrepancy comparing to the target core.