Regular Article

Safety-related investigations designing a soluble-boron-free small modular reactor core at equilibrium

Karlsruhe Institute of Technology (KIT), Hermann-vom-Helmholtz-Platz-1, Eggenstein-Leopoldshafen 76344, Germany

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Received: 16 June 2025
Received in final form: 6 October 2025
Accepted: 19 November 2025
Published online: 6 February 2026

Abstract

Many water-cooled SMRs (WC-SMRs) are being developed and their deployment is being considered in different countries world-wide, with some designs considering no soluble boron in the coolant. The elimination of soluble boron in the coolant of WC-SMRs offers advantages such as an enhanced negative moderator temperature coefficient, reduced corrosion, and simplified chemical systems, etc. leading to the growing interest in Soluble-Boron-Free (SBF) SMR-designs. Without soluble boron, excess reactivity control relies on burnable absorbers and control rods, potentially increasing power peaking factors and requiring careful core design to ensure safety margins. This study starts with an academic SBF Karlsruhe Small Modular Reactor (KSMR) core designed with a fresh fuel loading in order to find an optimal equilibrium cycle following a two-batch refueling strategy by optimizing fuel enrichment, burnable absorber rod configuration, and Gd₂O₃ content using CASMO5 and SIMULATE5. A Golang-based tool, named CoreOptimizer, was developed to automate the input file generation, simulation execution and output data extraction, enabling efficient core optimization. The resulting core design meets safety and performance criteria. This paper describes the optimization process, the applied tools and discusses the key neutronic and safety characteristics of the optimized equilibrium core design.