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Deep geologic repository progress—2025 Update
Editor's note: This article has was originally published in November 2023. It has been updated with new information as of June 2025.
Outside my office, there is a display case filled with rock samples from all over the world. It contains a disk of translucent, orange salt from the Waste Isolation Pilot Plant near Carlsbad, N.M.; a core of white-and-bronze gneiss from the site of the future deep geologic repository in Eurajoki, Finland; several angular chunks of fine-grained, gray claystone from the underground research laboratory at Bure, France; and a piece of coarse-grained granite from the underground research tunnel in Daejeon, South Korea.
Alice Y. Ying, Mark S. Tillack
Fusion Science and Technology | Volume 19 | Number 3 | May 1991 | Pages 990-995
Blanket Technology | doi.org/10.13182/FST91-A29471
Articles are hosted by Taylor and Francis Online.
Laminar heat transfer in self-cooled liquid metal blankets can be enhanced by increasing the aspect ratio of the ducts. To determine the potential benefits of elongated rectangular ducts, numerical simulations of MHD fully-developed flow and developing heat transfer were performed. Results show that as the aspect ratio increases (i.e., the ratio of the side wall to Hartmann wall length), the peak velocity and side layer flow quantity increase, which leads to enhancement of the average heat transfer coefficient along the side layer. The pressure gradient decreases with increasing elongation, providing an added benefit. However, results of the heat transfer analysis also indicate that the non-uniformity along the heated wall and the peak wall temperature both increase as the aspect ratio increases, due to smaller velocities in the corners and near the interface between the side layer and the core. The net benefit to reactor blanket design is therefore uncertain, because designs are usually constrained by the peak structure temperature. At fixed velocity, elongated ducts always have higher peak temperatures. However, the reduction in pressure gradient allows the designer to increase the average velocity, which improves thermal performance due to lower bulk temperature rise as well as higher wall heat transfer coefficient. Calculations show that peak temperatures can be reduced relative to the square duct case with lower pressure gradient by optimizing the velocity. Elongated ducts may suffer from larger pressure stresses due to geometric factors. Thermal stresses are also likely to increase, owing to the increased thermal gradients in the walls. Overall, it is difficult to guarantee that elongation will provide improved performance without a more detailed design analysis.