Verification of Monte Carlo Code MCS Coupled with CTF and FRAPCON

Abstract

MCS is an in-house Monte Carlo neutron transport code under development at Ulsan National Institute of Science and Technology (UNIST) since 2013. In previous studies, MCS has been coupled separately to either the sub-channel code CTF or the steady-state fuel performance code FRAPCON to build a Monte Carlo based multi-physics coupled code system for large scale light water reactors (LWR) applications. However, the fidelity of those separate coupling attempts was limited as the MCS-CTF coupled system could not simulate well the physical effects linked to the fuel thermal conductivity and fuel gap conductance and the MCS-FRAPCON coupled system was limited to the use of a single closed channel enthalpy model. To achieve higher fidelity and overcome those limitations, the full CTF-FRAPCON coupling has been implemented into MCS code to make full use of good features including in CTF the simulation of transverse cross flow between neighboring sub-channels and in FRAPCON a burnup-dependent fuel thermal conductivity formulation and an iterative determination of the fuel pellet-cladding gap thermal conductance. A CTF + FRAPCON coupling interface has been developed and a simple single rod case has first been tested to verify the accuracy and efficiency of this full coupling system. Then, the MCS based multi-physics coupled system was applied to the BEAVRS benchmark, a whole core model solved with 3D pin-by-pin power density and thermal-hydraulic (T/H) feedbacks exchange between neutron transport solver and T/H solvers. The obtained results prove the practical capability of this new Monte Carlo based steady-state multi-physics coupled code system to tackle 3D LWR whole core analysis with high fidelity.