Modeling of two-phase flow and heat transfer in nuclear reactors; overview of recent advances

Due to the complexity of multiphase flow phenomena, including both modeling and computational issues, a one-dimensional modeling framework has been typically used sofar in the analysis of boiling channels und systems. The growing range of applications and the needs for belfer understanding multiphase phenomena in nuclear technology, which include but are not limited to, the next generation reactors, require that analytical and computational tools be developed extending far beyond the current generation codes. The necessary innovations should encompass modeling concepts, numerical methods and computalional structure. It is interesting to note that in addition to technical advancements affecting operation and safety of nuclear installations, new mechanistic models and codes will also have significant direct impact on cost effectiveness. This is due to the fact that computer simulations using physically-based models will eventually reduce the experimental efforts which are needed today mainly to obtain data for new correlations being developed for specific designs and operating conditions. Furthermore, a better understanding of the physics of multiphase flows should help to design future experiments and develop new instrumentation and experimental techniques. The objective of this paper is to present an overview of the recent progress made in the modeling and computer simulations of two-phase flow in heat transfer in nuclear reactor systems and components.