Development of computational methods and their applications for the analysis of nuclear power plants

Journal article, 2009

A specificity of nuclear reactors is their multiphysics and multiscale character. The multiphysics nature comes from the interdependency between different fields governing the physics of such systems (neutron transport, heat transfer and fluid dynamics). The coupling between physical phenomena across various characteristic lengths, varying from the microscale to the macroscale, requires a multiscale treatment. Specific modelling techniques at the system level are thus required for the simulation of nuclear reactors and are presented in this paper. The use of such techniques for both time-independent and time-dependent simulations are dealt with, and examples of such simulations are presented. Time-independent simulations are mostly carried out for in-core fuel management purposes, i.e., for designing a core loading that allows running the reactor in a safe and economical manner. For the time-dependent simulations, two classes of problems are encountered. If the system undergoes small stationary fluctuations whereas the mean values of the variables remain constant, linear theory can be used to find the governing equations of such fluctuations. Due to the stationary character of the fluctuations, such calculations are more easily performed in the frequency domain. If the system undergoes large fluctuations and/or if the mean values of the variables are changing with time, the equations are to be solved in the time domain.