Determination of pressure loss coefficient of the hot duct break of the CEA ALLEGRO 2009 concept using a CFD technique

Abstract

ALLEGRO is a demonstration reactor of the GEN IV GFR2400 gas fast reactor concept which is currently in the pre-conceptual design phase. In the present ALLEGRO design, the hot duct (leg) – which connects the reactor with the main heat exchanger – is located inside the cold duct. For this reason, the break of the hot duct does not lead to a classical loss of coolant accident (there is no depressurization of the system), but a core by-pass occurs, which may threaten the integrity of the core. The peak cladding temperature (PCT) highly depends on the pressure loss between the hot and the cold ducts at the break. In this study, by an original approach we aimed to estimate the value of the pressure loss coefficient between the hot and the cold ducts by using the ANSYS FLUENT CFD (Computational Fluid Dynamics) code as a numerical tool. The results showed that if the break is located in the hot duct halfway between the reactor vessel and the main heat exchanger, the pressure loss coefficient value falls in the range of 1.05–1.15 for break sizes up to 100%. Considering the primary importance of the hot duct break pressure loss coefficient, further studies are proposed to assess the worst case break geometry.