Coupled RELAP/PARCS Full Plant Model Assessment of a Cooling Transient in Trillo Nuclear Power Plant (NUREG/IA-0255)

Abstract

This report presents the methodology to change from a 0-D kinetics core in a RELAP5/Mod3.3 full plant model of Trillo NPP to a coupled RELAP5/PARCS 3-D core. The coupled plant model is assessed against a real cooling transient that deformed the core power axial profile. The coupled steady state core model was adjusted to a CASMO/SIMULATE calculation by condensing the cross-sections with the SIMTAB methodology. The need of information exchange between RELAP and PARCS during the transient was the reason for two modifications of the coupling between both codes. The CASMO/SIMULATE calculation of the initial core conditions correspondent to the date of the transient was performed by Iberdrola Ingeniería. The SIMTAB methodology used to build the PARCS input file, the automated tools for core input files mapping and the RELAP/PARCS modifications of control rod and boron content were performed by the Nuclear Engineering Group belonging to the Institute for Industrial, Radiophysical and Environmental Safety (ISIRYM) at the Universitat Politècnica de València (UPV). The modifications to the RELAP5 full plant model to couple the 3-D PARCS core, the steady-state adjustments of PDDs, and the transient calculation and analysis were performed by the Thermo-Hydraulic group of Almaraz-Trillo NPPs. The results of the transient show an almost perfect agreement with plant data for all the compared variables. The comparison of in-core parameters evolution with plant data is also very good and the 3-D simulation allows to perform a more detailed analysis of core behaviour. This report was prepared by the Thermo-Hydraulic group of Almaraz-Trillo NPPs (CNAT), with the help of the Polytechnic University of Valencia. The Asociación Española de la Industria Eléctrica (UNESA, Electric Industry Association of Spain) and Almaraz-Trillo NPPs AIE sponsored this work.