A sodium-cooled ultra-long-life reactor core having improved inherent safety with new driver–blanket burning strategy

• A self-controllable sodium-cooled ultra-long-life core was designed with a new axial blanket-driver-blanket configuration.
• The final core has cycle length of 53 EFPYs, small burnup reactivity swing of 773 pcm and high discharge burnup of 182 MWD/kg.
• Dummy rods in lower blankets coupled with upper sodium plenum give low sodium void reactivity which is essential for self-controllability.

In this paper, two sodium-cooled ultra-long-life reactor cores are designed by using new axial blanket-driver burnup strategy such that they have ultra-long-life longer than 40 EFPYs (Effective Full Power Years), high average fuel burnup of ∼180 MWD/kg, small burnup reactivity swing, and improved inherent safety in terms of self-controllability under unprotected accidents. An exploration on the arrangement of driver and blanket fuels revealed that axially blanket-driver-blanket (B-D-B) configuration with different thicknesses in inner and outer core regions is effective to achieve the design goals. The final core was determined through the reduction of sodium void worth with an upper sodium plenum above the core and with partial use of dummy rods in the lower blanket of the inner core, and through the reduction of burnup reactivity swing with the adjustment of driver and blanket heights and with partial use of dummy rods in outer driver region. The neutronic analysis shows that the final core has desirable features such as long life of 53 EFPYs, high average burnup of 182 MWD/kg, small burnup reactivity swing of 773 pcm, and satisfaction of all the conditions for self-controllability under unprotected accidents.