Upscaled heat transfer coefficients for a liquid metal-cooled fast nuclear reactor

•Application of the Volume Averaging Method (VAM) to upscale the energy point model.•Calculation of heat transfer effective coefficients for a Liquid Metal-cooled Fast Reactor.•Solution of three closure problems (boundary-value problems) to obtain the closure variables.•Derivation of the upscaled model with two equations and nine effective coefficients.•The average temperature with the upscaled model resembles that with the pin-scale direct model. [Display omitted] In this paper, we calculate the heat transfer effective coefficients for a Liquid Metal-Cooled Fast Reactor. We upscaled the local energy equation of a fuel pin and its surrounding liquid metal (cooler fluid) to the whole fuel assembly representing the entire nuclear reactor core. Such an upscaling procedure was carried out within the volume averaging framework. The upscaled model contains two coupled energy equations, and jointly three closure problems are presented which assist to numerically compute the effective coefficients. The closure problems consist of boundary-value problems, whose solution must be carried out in a representative geometry of fuel assembly. The closure problems were solved to obtain the closure variables, with which the effective coefficients related to conductivity and convection heat transfer were obtained. The upscaled model results were compared with the more-intensive numerical solution of the pin-scale mathematical model. An acceptable agreement was found validating the mathematical structure of the upscaled model, the closure problems, and the definitions of effective parameters.