Thermal-Hydraulic Analysis of the EU DEMO Helium-Cooled Pebble Bed Breeding Blanket Using the GETTHEM Code

The general tokamak thermal-hydraulic model (GETTHEM) has been updated to the most recent version of the EU DEMO helium-cooled pebble bed breeding blanket (BB) design. The GETTHEM results are first benchmarked in a controlled case against the results of 3-D computational fluid-dynamics computations, showing an acceptable accuracy despite the inherent simplifications in the GETTHEM model. GETTHEM is then applied to the evaluation of the poloidal hot spot temperature distribution in an entire BB segment, showing that the maximum temperature in the EUROFER structures overcomes the design limit of 550 °C by more than 50 °C in some blanket modules. A possible mitigation strategy is then proposed and analyzed, based on the idea of cooling the first wall in parallel with the breeding zone, showing that this solution would allow having the EUROFER in its working temperature range in the entire segment, although at the expense of a larger pressure drop.