COUPLED TRANSIENT ANALYSIS OF A CORE WITH FUEL ASSEMBLY BOWING WITH A HYBRID CTF/DYN3D MODEL

Fuel assembly bowing is a known phenomenon observed in many PWR reactors all over the world. The relevant to safety as it can lead increased water gaps between assemblies which results higher pin peaking factors. goal of present study assess effect not only for stead-state nominal conditions but also during transient. selected transient loss one reactor coolant pump be limiting especially regarding Departure from Nucleate Boiling (DNB) criterion. This focuses on an extreme case where simulated core hot by keeping gap constant whole active length. resulting cross-sections and form functions obtained 2d infinite lattice model are used nodal diffusion code DYN3D applying its pin-by-pin reconstruction method. For simulation, coupled with thermal-hydraulics subchannel CTF SALOME platform. Several modelling options compared: geometry neutronics (TH); mixed: gap, TH geometry; both TH. confirm that should considered models order reduce conservatism.