Advanced modelling of complex boron dilution transients in PWRs – Validation of ATHLET 3D-Module against the experiment ROCOM E2.3

Abstract Inherent boron dilution in PWRs constitutes one of the key issues in nuclear safety research. This issue has been widely investigated analytically and experimentally through several test facilities in Germany. Besides the knowledge gained on the matter, the experimental research has contributed to the creation of large databases for the validation of computational tools used in nuclear safety analyses, such as system and computational fluid dynamic (CFD) codes. In this paper, the multidimensional features of the thermal–hydraulic system code ATHLET are assessed based on the results from the boron dilution experiment E2.3, carried out at the ROCOM test facility. The aim of the present paper is twofold; first contributing to the validation of the 3D-Module of ATHLET, as well as assessing the numerical diffusion introduced by the code during the calculation of boron transport and fluid mixing in the developed pseudo multidimensional vessel throughout the progression of the boron dilution event. Overall, the obtained results with ATHLET 3.1A are satisfactory and meet the validation exercise goals, namely in downcomer annulus and lower plenum. However, the limitations of the code to simulate fluid mixing in the cold legs lead to some deviations in the results at the vessel inlet nozzles.