Analysis of the OECD/CSNI ISP-42 PANDA integral test facility by the RELAP5/Mod3.2.2 code

The present document deals with RELAP5/Mod3.2.2 analysis of the International Standard Problem (ISP-42) exercise performed in PANDA facility installed at Paul Scherrer Institute. PANDA is a large-scale thermal-hydraulic test facility suitable for the simulation of passive containment for Advanced Light Water Reactors. The work focuses on phases A, B and C of the ISP-42 experiment, including the break in the main steam line, the Passive Containment Cooling System Start-Up, the Gravity Driven Cooling System and the normal operation in case of LOCA. Techniques for the optimal nodalisation development have been proposed and tested and a detailed nodalisation was set-up at the University of Pisa, in order to model 3-D flow paths with a 1-D code. The comparison between pre-test predictions and experimental data is discussed and RelapS proved to be suitable also for containment active. A trial quantification of the accuracy of the calculations, submitted to the ISP-42, by an experimental tool for code assessment, the Fast Fourier Transform Based Method (FFTBM), has been implemented for the phase A, providing a simple index of code accuracy and a list of merit of the participating organizations at ISP-42.