On the application of advanced modeling tools to the SLB analysis in NuScale. Part I: TRACE/PARCS, TRACE/PANTHER and ATHLET/DYN3D

Nowadays, there is a growing interest in the Small Modular Reactors (SMRs) technology due to their enhanced safety level and reasonably reduced manufacturing and construction costs. However, modeling tools should be able to deal with the special features inherent to their design such as the modeling of the helical Steam Generators. In this work, a Steam Line Break sequence in the NuScale reactor has been simulated using several modeling tools based on a full-plant thermohydraulic model for a system code coupled with a 3D nodal diffusion code for describing the core physics. To do so, four different models have been developed by four different organization for the coupled codes TRACE/PARCS, TRACE/PANTHER and ATHLET/DYN3D. In that sense, a very reasonable agreement is reached among the steady-state parameters of the plant computed by each participant and the ones presented in the Design Standard Application Report of NuScale. Regarding the simulation of the SLB transient, it should be noted that after 100 seconds of simulation, it can be said that remarkable differences are to be seen among the results for the time behavior of the core temperatures. Those differences are attributable to differences in the heat transfer within the helically coiled steam generators. Important differences have been also found in the decay heat removal system performance, so it is concluded that further investigation and model development is needed for the phenomena occurring in the steam generators and the decay heat removal heat system.