Pressure drop experiment with externally and internally cooled annular fuel bundles

Abstract

Canadian Nuclear Laboratories (CNL) has developed an externally and internally-cooled annular fuel (ICAF) bundle that is considered to have improved thermalhydraulic characteristics as compared to the fuel bundles used in the conventional pressurized heavy-water-moderated-and-cooled reactors (PHWRs), such as the CANDU® reactors. The ICAF bundle consists of 24 annular fuel elements (or rods) and a solid central rod. The coolant flows through both the internal and external channels of each annular fuel element; the total flow in the flow tube is split into the flow inside the internal channels of the annular elements and that in the outside subchannels of the fuel bundle. The most compelling argument for this design, compared to the conventional solid-rod design, is the significant reduction in maximum fuel temperature for equivalent linear element ratings, due to significantly-enhanced heat transfer from fuel surfaces to coolant. The primary objective of the ICAF bundle development is to achieve higher burnups and higher power densities using advanced fuel cycles, with comparable or improved thermalhydraulic safety margins. This paper presents the results of a pressure drop experiment performed to investigate the hydraulic behavior of the ICAF bundle. Experimental data were obtained for the pressure distribution, the bundle misalignment junction signature and the flow split. The data can be used to develop predictive models to be implemented into the thermalhydraulics analysis toolset, and to validate the toolset for safety analyses in establishing reactor operating power and evaluating safety margin.