Analysis of a control rod ejection accident in a boron-free small modular reactor with coupled neutronics/thermal-hydraulics code

Abstract

Design-basis accidents such as control rod ejection accident (REA) must be evaluated as part of a deterministic safety analysis for any reactor licensing process. In the present work, the behavior of a newly developed boron-free light-water small modular reactor (LW-SMR) core under REA-conditions is studied at the beginning of life using the coupled code PARCS/SUBCHANFLOW.The developed LW-SMR core can produce 330 MWth and contains 57 fuel assemblies. Generally, the REA happens due to a mechanical failure of the control rod drive mechanism housing such that the pressure difference between the primary-system and containment ejects a control rod assembly completely out of the reactor core. In this work, the REA analysis is performed at both critical HZP and HFP conditions. The impact of fuel-cladding gap-heat transfer model during the REA is also analyzed.This investigation showed that there is a high margin against fuel and cladding melting. In addition, the maximum fuel enthalpy is found to be far from fuel-cladding failure threshold. The performed simulations have shown that there is a significant impact of the models used to describe the fuel-cladding gap-heat transfer on the prediction of key safety parameters such as the maximum fuel enthalpy.