One-dimensional model for containment in AP1000 nuclear power plant based on thermal stratification

Abstract

Passive containment cooling system operating based on natural circulation is innovatively used in AP1000 nuclear power plant to improve safety. However, the overall heat and mass transfer will decrease and the heat transfer through the containment shell will be slow due to stable stratification which will occur if the forced convection mixing is not sufficiently strong enough to disrupt the stable fluid layers, so it is important for system design and accident analysis to evaluate whether the circulation can establish or not in the containment accurately and efficiently. Many researches indicate that the gradients of such parameters in horizontal direction are so small that can be ignored, in this paper, one-dimensional model is developed for AP1000 containment based on thermal stratification theory, natural circulations in and outside the containment are both included. Based on the results, the thermal stratification and circulation exist simultaneously, the pressure in the containment can be kept at the safe level, and positive pressure gradient in the vertical direction affords the force of circulation. The steam and air with higher temperature concentrating at the top will strengthen the heat and mass transfer because the cooling capacity of top head is higher than of other parts.