Core neutronics and safety characteristics of a boron-free core for Small Modular Reactors

Abstract

This work presents the safety-related neutronics and thermal-hydraulics features of a reactor core designed to fit into a Small Modular Reactor (SMR) moderated and cooled by light water. The core design process is conducted in an iterative manner to optimize its performance from safety perspective. The optimized core is operated without boron in the moderator and is characterized by enhanced safety features as a result of (1) avoiding concerns related to boric acid induced corrosion of a reactor pressure vessels internals; and (2) eliminating the probability of boron dilution accidents. The optimization studies are performed with an advanced multi-physics simulation tools including both neutronics (deterministic, Monte Carlo) coupled with a subchannel thermal-hydraulics code. With an intensive core design iteration process and through using such multi-physics tools, a reactor core with sufficient thermal margins, a cold shutdown margin, and a reduced power peaking factor is obtained. In this paper, the core design approach, core features, and the verification of the core analysis method are discussed in details. Finally, it has been concluded that the developed and optimized core fulfills all safety requirements and design objectives.