Analysis of twisted tape solutions for cooling of the residual ion dump of the ITER HNB

The ITER HNB residual ion dump is exposed to a heat load about 17 MW on the dump panels with a peak power density of 7 MW/m2. Water flows through cooling channels, 2 m long and 14 mm diameter, realized by double side deep drilling. Unavoidable manufacturing deviations could generate a discontinuity at the channel length center. It is necessary to verify the influence of issues such as cavitation, fluid stagnation, low boiling margins, among others, in the cooling performance. Assuming worst case conditions, analytical and CFD methods showed a subcooled boiling operation with high safety margins to the water critical heat flux. Additionally, by analysing several thermo-hydraulic parameters, the twisted tape cross sections were optimized. Per cooling channel, two twisted tapes are inserted from the sides of the panels, thus, a study of a separation gap between them at the channel length center presented an optimal distance. This paper demonstrates that common machining techniques and drilling tolerances allow the manufacturing of panels able to withstand safely the required beam operation heat loads, even under worst case operation scenarios.