Deformation and reflood of a fuel rod assembly
during a loss-of-coolant accident
IRSN developed the DRACCAR computer software in support of the safety analysis of pressurised water reactors (PWR). This software simulates loss-of-coolant accidents (LOCA) such as the loss of coolant in the reactor core or in a spent fuel storage tank. During the course of such an accident, the coolant vaporises and the fuel rods dry out, which leads to an increase in their temperature, to cladding swelling and failure. This swelling could be responsible for major blockage in part of the core and thus can prevent the back-up systems from cooling the core.
The 3D multi-rod software is designed to model a fuel assembly so as to assess rod cooling and the blockage rate caused by deformed rods, by taking into account mechanical and thermal interactions between rods.
The software can:
Provide a consistent interpretation of the entire experimental database
for a « single-rod » configuration or a « rod-bundle » configuration
with either real or simulator fuel ;
Transpose onto a reactor scale the phenomena involved, using validated
models in experimental data, in order to determine what kind of
research still needs to be conducted ;
Carry out safety studies.
Phebus LOCA test © IRSN An eight of a 17x17 PWR fuel assembly
The models developed for this software cover:
Oxidation of cladding and Zircaloy guide tubes, as well as hydriding
which can change mechanical properties ;
Thermomechanical behaviour of cladding (deformation and failure),
including bowing ;
Thermal-hydraulics on the scale of an assembly (to couple with
appropriate software), including a reflood model ;
Fuel relocation and release of fission gases.
Validation and future developments
A first version - DRACCAR V1 - was delivered in March 2008 and validated on the basis of available experimental data (EDGAR, PHEBUS LOCA, PERICLES, REBEKA, HALDEN, etc.). A second version (V2) will be available some time in 2012 and will be coupled to the numerical simulation platforms PLEIADES and NEPTUNE developed in partnership with the CEA, EDF and IRSN.
Scientific community and collaborations
This tool is developed in partnership with EDF and is integrated since 2009 into a European platform of the 7th FP1. It will benefit from a high-level scientific environment thanks to various collaborative agreements with research organisations such as the CNRS Laboratoire d’Energétique et de Mécanique Théorique et Appliquée (Nancy), and the Institut de Mécanique des Fluides (Toulouse) for the local-scale development of models which will be integrated into the next version of the software (V2).