Modeling and Simulation of Fission Products Activity under Severe Accident Conditions for Pressurized Water Reactor /

Abstract

Pressurized water reactors produce energy by fission process and this process is controlled by using different techniques like control rods, soluble poison like boric acid etc. Due to loss of coolant in reactor pressure vessel (RPV), the fission reaction becomes uncontrol due to which reactor core heats up to beyond limit causing the core to melt down and a large amount of fission products release to containment building and to environment. These fission products are very harmful for human and environment. The quantification of theses fission products is necessary for reactor safety. For this purpose, a 1000MWe pressurized water reactor is chosen and a mathematical model is developed and simulation is carried out using MATLAB software. A program is developed in which deposition process, resuspension process, recirculation rates, exhaust leakage rates are used, which analyze each isotope by keeping in view containment air and surface. The results show that activity of noble gases on the containment surface increases at constant rate and decreases in the containment air with respect to time. While the activity of fission fragments first increase rapidly then decreases instantaneously on the containment surface as well as in the air. But magnitude of fission products activity on the containment surface is less as compared to the air. In addition, I-134 is studied for various core damage percentage, air borne activity, zirconium oxidation, mixing rates, exhaust leakage rates, recirculation rates and containment spray flow rates. The results reveal that two orders of magnitude activity decreases upon activation of spray system during accident. The developed mathematical model is validated by conducting a comprehensive comparison of results with published work. This model can also apply to evaluate the containment performance during nuclear accident.