Boron dilution sequence analysis in NuScale SMR with asymmetrical feedwater injection using TRACE

Within the McSAFER H2020 project framework, the “Universidad Politécnica de Madrid” (UPM) research group has developed a 3D-TRACE model of a NuScale Power Module in order to assess the impact of the asymmetrical phenomena that could appear during different accidental sequences. In this study, a Boron Dilution scenario is analyzed assuming a difference of a 10% in the flow rates between both feedwater injection trains. The reactor core is modeled by means of a Cartesian 3D-VESSEL component applying a one-to-one ratio between the fuel assemblies and the channels implemented in the VESSEL. The rest of the RCS except the pressurizer region is modeled using two cylindrical VESSEL components. Finally, the results show that an adequate core-cooling condition is maintained during the whole transient and that the acceptance criteria for the Boron Dilution sequence are met as it is presented in the Safety Analysis Report of the NuScale Standard Plant.