ABSTRACT
This chapter outlines severe reactor accident phenomena and shows some of the complexities associated with them. To increase our confidence in the performance of safety systems and procedures during severe accidents, we must elucidate a variety of physical and chemical processes, including core damage progression, fuel-coolant interactions, natural convection, aerosol processes, hydrogen behaviour, core–debris/concrete interactions, fission product chemistry, and the performance of engineered safety features. The transport of fission product aerosols both within the primary circuit and in the containment is governed largely by natural convection. The releases associated with severe fuel damage will depend on such parameters such as the composition of the hydrogen/steam mixture in the core, the extent of chemical reactions of fission products with the sheath and control/structural materials, and the concentrations of fission products. The efficiency of such pools to attenuate fission product transport would depend on particle sizes, steam mass fractions, and pool temperatures.
