Simulation tools incorporated to DIONISIO in the frame of the FUMAC project

LEMES, MARTÍN; DENIS, ALICIA; SOBA, ALEJANDRO

Shenzhen

Workshop; Modelling of Fuel Behaviour in Design Basis Accidents and Design Extension Conditions; 2020

Several models were integrated to the DIONISIO code within the framework of the IAEA Research Project ?FuelModeling in Accident Conditions (FUMAC)?, to take account of accidental conditions, in particular the loss of coolantaccidents (LOCA). A specially designed thermal-hydraulic subroutine provides a simplified description of the rod environmentin normal or accidental conditions. The heat transfer coefficients that account for the different coolant regimes, in single ordouble phases, are activated as the corresponding conditions occur. The simulation of a considerable number of experimentshas shown that, despite its simplicity this subroutine gives adequate predictions of the conditions in a vertical cooling channel,quite similar to those given by the thermal-hydraulic codes. The description of the fuel rod atmosphere is improved with theincorporation of this subroutine since it provides fairly realistic boundary conditions for the simulation of the fuel rod behavior,without requiring the intervention of external specific codes. Models of high temperature oxide growth (ZrO2) and hydrogencapture and release by the cladding in steam were also included. Moreover, the model of cladding creep predicts the conditionsfor ballooning and eventually, those for catastrophic failure (burst) and its localization. The calculation scheme makes apartition of the rod length into a number of segments defined by the user. In each segment the local conditions are consideredto calculate, with the synchronous work of all the subroutines, the physical and chemical parameters in one representativepellet. Then, a description of the whole rod is obtained by coupling all the segments. This strategy has yielded accuratesimulations of a wide variety of cases, either in normal or LOCA type conditions. Exhaustive comparisons were carried outwith several thermal-hydraulic codes (COBRA-IV, RELAP5-Mod3.1, SOCRAT, ATHLET-Mod 1.1) and with a number ofexperiments like those of the IFA?650 series (-1,-2,-9,-10,-11), PUZRY, QUENCH-L0/L1 (for which a new working schemewas specially developed in DIONISIO), CORA-15, IAEA-SPE-4, among others.