Helical coil steam generator (HCSG) is a specific type of shell and tube heat exchanger known for having higher heat transfer coefficient than many other designs. For this reason, they are considered in Small Modular Reactor (SMR) and High Temperature Reactor (HTR) designs. Investigation of flow behavior in HCSGs is important for better design. In this paper we present our study on modeling of the coolant flow in the primary side of the HCSG. We used Nek5000, open source, high-order spectral element CFD code developed in Argonne National Laboratory. Nek5000 accepts only hexahedral mesh, which makes very challenging the meshing process for the complicated HCSG geometry. Tet-to-hex meshing strategy was applied to by-pass the geometric complexities. Tetrahedral mesh was created first, and then each tetrahedral element was converted to four hexahedral elements. Boundary layers were extruded to fit the exact geometry. In this study large eddy simulation (LES) was performed at Reynolds number of 9000 based on the inlet velocity and the tube diameter. The employed sub-grid scale model for the LES relies on explicit filtering.