Comprehensive assessment of the Ispra BWR and PWR subchannel experiments and code analysis with different two-phase models and solution schemes

Abstract

This paper presents subchannel code results for a selection of the subchannel experiments performed at the Joint Research Centre of the CEC at Ispra with 16-rod BWR and PWR bundles at prototypical conditions. Three different well-known subchannel codes (COBRA-IIIC, CANAL, THERMIT) have been applied, each of which is representative of widely used two-phase flow methodologies (homogeneous, drift-flux, 2-fluid modelling) and numerical solution schemes. Their degrees of agreement with the measured subchannel exit mass flow and enthalpy distributions are reported as well as their limitations due to the lack of details in modelling two-phase flow rod bundle transport phenomena and/or numerical solution schemes both in transverse and axial directions. It is conclusively demonstrated that the extra expenditures of using advanced codes such as THERMIT effectively pay off when stringent requirements for optimizing LWR fuel rod bundles should be met.