A porosity model to represent the influence of structures on a fluid flow - Application to a hypothetical core disruptive accident

Marie-France Robbe (1) , Fabienne Bliard (2)

1 DYN - Laboratoire d'études de DYNamique
2 SOCOTEC

In case of a Hypothetical Core Disruptive Accident (HCDA) in a Liquid Metal Fast Breeder Reactor, the interaction between fuel and liquid sodium creates a high pressure gas bubble in the core. The violent expansion of this bubble loads the vessel and the internal structures, whose deformation is important. An experimental programme was undertaken in France during the 80s to understand the HCDA physical process. Based on a 1/30 scale model of the SUPER-PHENIX reactor, the MARA programme involved ten tests of gradual complexity due to the addition of internal deformable structures. The numerical simulation of the HCDA mechanical effects on the reactor vessel has been carried out with the CASTEM-PLEXUS software. For this purpose, a specific constitutive law was added to this general ALE fast dynamics finite element code. In order to demonstrate the CASTEM-PLEXUS capability to predict the reactor behaviour, axisymmetrical computations of the MARA serie have been confronted with the experimental results. Whereas the CASTEM-PLEXUS results and the MARA tests with few internal structures are in a good agreement, the simulation of the last test (including all the significant internal components) is too conservative. The main reason comes from the fact that the CASTEM-PLEXUS model does not represent several non axisymmetrical structures which have a protective effect on the containment by acting as porous barriers, absorbing energy and slowing down the fluid impacting the containment. A new fluid constitutive law was developped to take into account the presence of the internal structures (without meshing them) by means of an equivalent porosity method. The structures are only described by means of three parameters: a porosity, a shape coefficient and a pressure loss. This paper briefly describes the porosity model implemented in the HCDA constitutive law of the CASTEM-PLEXUS code. The model is numerically validated on an analytical shock tube test. A parametric study assessing the solid parameter influence proves that the internal structures really have a shield effect on the fluid wave impacting the LMFBR vessel in case of a HCDA.

Mots clés: Hypothetical Core Disruptive Accident (HCDA); Liquid Metal Fast Breeder Reactor; vessel; fuel; sodium; explosion; SUPER-PHENIX reactor; MARA programme; mock-up; fluid constitutive law; modelling; equivalent porosity method; porosity; core disruptive accident; liquid metal reactor; internal structures; quali cation

Domaines: Physique mathématique [math-ph]; Modélisation et simulation; Mécanique des structures [physics.class-ph]; Mécanique des fluides [physics.class-ph]

Marie-France Robbe, Fabienne Bliard. A porosity model to represent the influence of structures on a fluid flow - Application to a hypothetical core disruptive accident. ICONE 7 - 7th International Conference on Nuclear Engineering, Apr 1999, Tokyo, Japan. pp.ICONE-7819. ⟨cea-03121989⟩