UWFDM-1395 Improvements to the Helium Flow Path in the US DCLL ITER Test Blanket Module

Computational fluid dynamics simulations have demonstrated flow problems within the helium flow path in the current US DCLL ITER test blanket module design. New geometry for the helium flow path has been designed that will improve flow evenness and simplify the overall helium flow path within the test blanket module while maintaining the overall test blanket module geometry. Global changes to the test blanket module geometry can be implemented based on these improvements. INTRODUCTION A Test Blanket Module (TBM) design based on the dual coolant lithium lead (DCLL) blanket concept has been developed by the US in support of the ITER Test Blanket Module program. The ferritic steel structure is cooled by flowing helium within the structural panels. A lead-lithium (PbLi) breeder is circulated through the TBM in the poloidal direction for tritium breeding and power extraction. Around the PbLi are silicon carbide (SiC) flow channel inserts (FCI), which reduce the MHD pressure drop on the flowing PbLi and thermally isolate the high temperature PbLi from the ferritic structure. The current design of the TBM involves a complex flow path for the helium coolant. Sections of the flow path are in series while others are in parallel. This causes some flow irregularities that are addressed in this paper. Potential design changes for the US TBM are presented for the following areas of concern: asymmetrical helium flow in the entry region, helium distribution in the headers between first wall passes, a point of local structural stress, a hot spot due to neutron and gamma heating, and the potential for uneven flow to the lead lithium internal cooling structure known as the grid plates and dividers. Design modifications that will resolve each of those problem areas have been made. The improvements include a new inlet section which alleviates asymmetric flow in the entry region, new header geometry options between the first wall passes, and a completely new grid plate/divider helium flow scenario. These changes can be incorporated into a global redesign of the TBM based on results of thermal hydraulic analysis. The global redesign greatly simplifies the helium flow path within the TBM. Further thermal hydraulic and flow analysis will be performed. PbLi HOT SPOT DUE TO NEUTRON AND GAMMA HEATING a. The Cause of the Hot Spot The TBM design routes the molten PbLi poloidally along the front of the TBM from the top to the bottom, where the PbLi turns toward the back of the TBM and flows upwards to the PbLi outlet. When the PbLi flow enters it splits into three separate channels before if flows poloidally. Should the operation of ITER be interrupted it may be desirable to have the capability to drain the PbLi from the TBM. Therefore when the current design was produced, based on the grid plate/divider geometry, a triangular “drain” opening was located at the front end, nearest the plasma, of the bottom of the grid plates/dividers to allow for the PbLi to drain to the center channel where the PbLi could be routed out of the TBM through the main PbLi drain.