Thermal–Hydraulic Test and Analysis of the ENEA TF Conductor Sample for the EU DEMO Fusion Reactor

The ENEA conductor for the EU DEMO Nb
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Sn toroidal field (TF) magnets, cooled by supercritical He, features a rectangular cross section with two small pressure relief channels (“holes”), separated from the cable bundle by means of a flat spiral, twisted together with the last cabling stage. A well-instrumented short sample of the ENEA TF conductor has been tested in SULTAN at SPC, Villigen (Switzerland) in 2016, aimed at its thermal-hydraulic characterization, and the test results are presented here. A correlation for the friction factor in the small holes is derived, best fitting the results of a set of computational fluid dynamics simulations. The new correlation (combined with existing correlations for the He friction factor in the bundle region) is shown to allow a proper reproduction of the measured hydraulic characteristic of the conductor. The heat slug propagation tests are used to calibrate the hole-to-bundle heat transfer coefficient in the 4C thermal-hydraulic code and to estimate the characteristic length for the homogenization of the He temperature on the conductor cross section, following a localized thermal perturbation.