THERMAL-HYDRAULIC MODELING AND SEVERE ACCIDENT RADIONUCLIDE TRANSPORT

The evaluation of radionuclide transport within a nuclear reactor plan t 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 equi libria among the involved species and the radio nuclide retention phen omena. The ENEL Code for the Analysis of Radionuclide Transport (ECART ) computer program has been developed for the purpose of unifying reac tor coolant 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 transpo rt under two-phase flow within the reactor coolant system, are include d. The code comprises three modules that deal with aerosol transport, chemical equilibria, and thermal hydraulics, respectively. The recentl y developed thermal-hydraulic module has been applied to the analysis of transients typically addressed by the code to obtain first indicati ons about the adequacy of the adopted models and about the need for fu rther improvements. A thorough assessment is now needed to achieve con fidence 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 sc enarios.