The capability of the ESCOT pin-level nuclear reactor core thermal-hydraulic (T/H) code is extended for the multiphysics analysis of hexagonal geometry cores, and its performance is assessed by a code-to-code comparison with COBRA-TF (CTF). ESCOT is an accurate yet fast core T/H solution aimed at high-fidelity and high-resolution multiphysics core analysis in the framework of massively parallel computing platforms. The coupling of ESCOT with the nTRACER direct whole-core calculation code is enhanced for the hexagonal geometry handling needed for VVER core analysis. The lateral momentum terms, the turbulent mixing coefficient values, and the parallelization algorithms are modified to handle hexagonal geometry. The newly implemented ESCOT features are verified by comparing single-assembly and full-core steady-state standalone and coupled solutions for the VVER-1000 benchmark X-2 with CTF results.

The ESCOT and CTF results show differences within an acceptable range in both standalone and coupled calculations. The computing time superiority due to the use of the drift flux model (DFM) of ESCOT over the CTF two-fluid model is corroborated with a speedup factor of 1.5. The use of the DFM together with the axial-radial parallelization capability of ESCOT makes ESCOT an ideal alternative to replace the simplified built-in T/H solver in nTRACER as the coupled simulation results demonstrate.