Thermal-hydraulic modeling and severe accident radionuclide transport

The evaluation of radionuclide transport within a nuclear reactor plant and then to the external environment after an accident that involves severe damage to the fuel rods requires an appropriate evaluation of the thermal-hydraulic conditions that influence both the chemical equilibria among the involved species and the radionuclide retention phenomena. The ENEL Code for the Analysis of Radionuclide Transport (ECART) computer program has been developed for the purpose of unifying reactor cooland and containment system analysis and represents the current state of the art of light water reactor severe accident aerosol codes. New aerosol transport models, like physical resuspension and transport under two-phase flow within the reactor coolant system, are included. The code comprises three modules that deal with aerosol transport, chemical equilibria, and thermal hydraulics, respectively. The recently developed thermal-hydraulic module has been applied to the analysis of transients typically addressed by the code to obtain first indications about the adequacy of the adopted models and about the need for further improvements. A thorough assessment is now needed to achieve confidence in the modeling capabilities of the module. The three modules are presently coupled in the integrated ECART code. The obtained code will be further assessed by application to relevant severe accident scenarios.