(A) study on natural circulation soluble-boron-free small modular reactor

Abstract

This study investigates the feasibility of designing a high-performance and stable natural circulation Soluble-Boron-Free (SBF) Small Modular Reactor (SMR) core. A Truly Optimized PWR (TOP) lattice concept was implemented to the core to maximize the neutron economy and improve the inherent safety parameters of the SBF SMR. It is demonstrated that the TOP lattice increases the thermal power of the natural circulation SBF SMR core. The pan-shape cylindrical Centrally-Shielded Burnable Absorber (CSBA) was proposed to be the main reactivity control in the SBF SMR core. In addition, the zoned erbia (Er2O3) admixed to the fuel pellet was implemented to the TOP lattice to lower both the pin power peaking and the excess reactivity. In this study, the two-batch fuel management was adopted. The CSBA was axially zoned into three zones, while the fuel enrichment was axially zoned into two zones to obtain a stable axial power distribution. The out-in fuel loading and radially zoned CSBA were implemented to achieve a flat radial power distribution. It is shown that the excess reactivity can be lowered to less than 1,000 pcm throughout the reactor operation, and the targeted cycle length (> 2 years) can be achieved. In addition, by utilizing the Mode-Y logic in the rodded depletion, the reactor criticality can be attained throughout the reactor operation with an acceptable Axial Shape Index value, and the reactor design is proven to be stable. Moreover, the shutdown margins of the SBF SMR core at the Cold-Zero-Power (CZP) condition are achieved by introducing a pseudo checker-board control rod pattern with the extended fingers.