Flow Optimization Studies for the ITER Shield Modules

A 3-d, 4-channel prototypical model representing a subset of an ITER neutron shield module was analyzed using computational fluid dynamics. We used this model to optimize the radial gaps in the coaxial flow drivers along with the depth of the radial holes or channels in the stainless steel modules. In addition to redirecting the flow first to the back of the module and then to the front, the flow drivers increase the pressure drop in the radial tubes to allow for more uniform flow distribution from the back-drilled manifolds. They also increase the fluid velocity near the wall for improved heat transfer. We sized the flow drivers to allow for 2, 3 and 4-millimeter (mm) gaps along the annuli. The depths of the radial channels below the manifold were 10, 15, 20, 25, and 30 mm for each of the 2, 3, and 4 mm radial gaps. The objective of the study was to ascertain if a fixed 90-mm length on the bottom flow driver could be utilized for radial channels of varying depth below the back-drilled manifold and still provide adequate cooling for the neutron thermal load. Our group also performed an optimization of the gap around the tee-vane in the shield module front header. Tee-vane gaps of 1, 2 and 3 mm were studied to assess the flow bypass and wall velocities at the end of the model. In this article, we present the results of a full matrix of flow simulations using the CFdesign CFD package. The study indicates that a 90-mm-long flow driver with a 4-mm radial gap can keep the steel around the radial tubes sufficiently cool up to 30 mm beneath the back-drilled manifold. We also discovered that flow bypass through the end gap on the tee-vane is relatively small and has little effect on cooling of the front cover plate for gap sizes as large as 3 mm.