Subchannel modelling capabilities of RELAP5-3D (c) for wire-spaced fuel pin bundle

The paper deals with the presentation of a subchannel modeling approach developed with RELAP5-3D for lead and lead-bismuth eutectic (LBE) cooled wire-wrapped fuel bundle. For the modeling assessment, the code-to-experiment analysis is performed using experimental data from the NACIE-UP facility, hosted at ENEA Brasi-mone Research Center. Three relevant thermal hydraulic phenomena must be accounted in case of wire-wrapped fuel bundle: pressure drops along bundle, crossflow between adjacent subchannels, and sweeping mixing induced by helical wire. Furthermore, in case of liquid metal system, the effect of radial thermal conduction must be evaluated. All these phenomena are considered in the modeling methodology. A thermal hydraulic nodalization of the whole facility has been developed, with particular attention to the fuel pin bundle simulator (modelled with a detailed subchannel approach). The main outcomes of the activity are the assessment of satisfactory capabilities of the proposed subchannel modeling and the identification of some open issues to be investigated in the future works.