Verification and validation of the high-resolution code nTF with VVER-1000 hot zero power monte carlo calculations and experimental data

Novel codes allow the prediction of parameters with increased resolution, in comparison to conventional approach, sometimes using meshing smaller than size fuel pin. Optimally, complex geometric structures, like ones included VVER core e.g. corner stiffeners, would be modeled explicitly by novel neutronic codes. In this paper, performance deterministic neutron transport code nTF is studied for geometries. The verified standalone Monte Carlo reference solutions a range Hot Zero Power (HZP) models, from 2D pincells 3D full VVER-1000, described X2 benchmark. Several modeling options and approximations are optimize model. updated version nTF, including all necessary modifications improve its capabilities, presents good agreement simple configurations critical state core. Specifically state, RMS pin power difference 1.5% eigenvalue 74 pcm respect solution. Any resulting discrepancies analyzed, more significant use lattice CASMO5-VVER that employs similar methods as nTF. optimized model validated experimental data benchmark, produced HZP start-up tests. differences results measured simulated benchmark remain within accuracy limits set utilities literature verification most cases. related discussed detail.