A Neutronic Investigation of a High Performance Two-Batch Natural Circulation Soluble Boron Free Small Modular Reactor

Abstract

A high-performance natural circulation Soluble-Boron-Free (SBF) Small Modular Reactor (SMR) design is pursued by utilizing a Truly-Optimized PWR (TOP) lattice and a new innovative Burnable Absorber (BA) design. The TOP lattice enhances the neutron moderation by increasing the hydrogen-to-uranium ratio. In this study, the TOP lattice is achieved by reducing the fuel pellet diameter while preserving the fuel pin pitch and Fuel Assembly (FA) dimensions. Two cylindrical Centrally-Shielded Burnable Absorber (CSBA) are utilized to control the excess reactivity during the reactor operation. Furthermore, a combination of erbia (Er O ) and gadolinia (Gd O ) admixed 2 3 2 3 to the fuel are introduced to the fuel rod surrounding the guide tube to lower the pin power peaking and early excess reactivity. The CSBA designs are zoned radially and optimized to obtain a flat radial power distribution and small burnup reactivity swing, less than 1,000 pcm. The fuel enrichment is zoned axially to obtain a stable axial power during the SBF reactor operation. Moreover, a pseudo checker-board Control Rod (CR) pattern with an extended Control Element Assembly (CEA) is proposed for a sufficient shutdown margin at cold zero-power conditions. All calculations are performed with Monte Carlo Serpent 2 code utilizing the ENDF/B- VII.1 library.