ACCIDENT CONDITION MODELS IN THE DIONISIO 2.0 CODE

ALEJANDRO SOBA; MARTIN LEMES; GOLDBERG, EZEQUIEL; LOZA PERALTA, MATÍAS E.; EMILIO GONZALEZ; ALICIA DENIS

Workshop; FUMAC; 2019

This document summarizes the work carried out with the DIONISIO code in the frame of theFUMAC Research Project.The more challenging task implied in the proposal of expanding the application range of fuelsimulation codes to accident conditions is the depiction of the fuel rod environment. It can exhibit awide variety of thermal-hydraulic conditions substantially different to those existing under normaloperation, thus affecting heat removal from the rod. But a detailed description of the different regimesthe coolant may exhibit is an enormous work that constitutes the specific purpose of the thermalhydrauliccodes. Several famous and reliable codes exist that perform this task. Nevertheless, andwithout attempting to solve the complete problem in its many details, a subroutine was developed forthe DIONISIO code that performs a simplified analysis of the coolant in a PWR, restricted to the morerepresentative situations. Keeping the focus on the simulation of fuel behavior, the thermal-hydraulicmodulus is intended to provide to the code the boundary conditions necessary to reproduce accidentsituations. Empirical expressions have also been incorporated to the subroutine dedicated to accidents,that predict ballooning and burst phenomena. Experiments of the FUMAC database, in addition toseveral of the FUMEX II and III data sets, have been simulated with DIONISIO using the LOCAsubroutines.Moreover, due to the fast cladding oxidation and the associated dissociation of water moleculesthat can take place under accident conditions, the hydrogen content in the cladding material can exhibita considerable increase. This can trigger severe material damage during a sudden rod cooling. Due toits importance regarding materials safety criteria, a modulus dedicated to hydrogen uptake simulationwas developed and is presently under intensive examination.