A design for the DCLL inboard blanket S. Smolentsev, M. Abdou, M. Dagher - UCLA S. Malang – Consultant, Germany 2d EU-US DCLL Workshop University of California, Los Angeles November 14-15, 2014

Following the 1st EU-US workshop in 2013, UCLA started a small project on DCLL DEMO blanket design and analysis The design uses the layout of the European DEMO1 plant and is based on the LT DCLL blanket concept as a low-risk solution. DEMO1 is a near-future technology pulsed machine (2-hr pulse). DEMO2 is the next steady-state design based on foreseeable advances in physics and technology. DEMO1 is a large, high aspect ratio (major radius = 9 m, minor radius = 2.25 m, aspect ratio = 4.0), low power density machine. The average NWL of DEMO1 is MW/m 2. The LT concept can be viewed at present as an important intermediate step on the pathway towards a more attractive HT blanket system. The present effort is limited to inboard (IB) blanket.

The blanket maintenance scheme is based on the concept of Vertical Maintenance System The blanket segments can be replaced through the vertical port at the top of the vacuum vessel. The port is also used for routing of all necessary pipes. To replace the segments, the port is opened and the pipes coming from the segments are cut. Then, the central OB segment located under the opening is extracted vertically using a crane. Two other OB segments are moved toroidally towards the port and then extracted through the port in the same way as the central OB segment extracted. The two IB segments have to be moved first radially and then toroidally to reach a position under the vertical port opening to allow for their vertical extraction.

US IB DCLL blanket design Long (~10 M) poloidal banana- shape segments to match the vertical maintenance scheme PbLi Tin/Tout=350°C/ 450°C to avoid corrosion problems The poloidal flow velocity is 0.38 m/s The sandwich-type (steel-alumina steel) FCI as electrical insulator. He Tin/Tout=350°C/ 450°C The magnetic field used in the analysis is 10 T

PbLi flow path PbLi enters the inlet manifold of the blanket segment through the inlet pipe at the top and then distributed into 5 rear poloidal blanket ducts where it flows downwards. At the bottom of the segment the LM makes a U-turn and flows upwards through the 5 front ducts facing the plasma. It is collected in the outlet manifold at the top of the segment from which it is extracted from the blanket through the vertical outlet pipe.

Identification of key R&D and blanket analysis tasks One of the main goals of the ongoing work is to use the proposed design to identify key R&D tasks for IB DCLL blankets. Four important tasks can be identified. First, the MHD pressure drop needs to be evaluated for the whole blanket system, including the blanket itself and access pipes, in which MHD flows experience high MHD pressure drop due to 3D MHD effects when the liquid crosses the magnetic field lines at the edge of the TF coils. Of particular importance is the 3D MHD pressure drop in the manifolds and those caused by the electric current leaking from the bulk flow at the FCI junctions. Second, detailed velocity simulations have to be performed for the bulk poloidal flows (inside the FCI box) and those in the thin gaps between the RAFM walls and the FCI. These velocity distributions will be used in the corrosion and tritium permeation analysis to make sure that the proposed design complies with the corrosion and tritium leak limits. Third, it is important to investigate if the PbLi flow distribution in the inlet manifold leads to sufficiently equal flow rates in the parallel poloidal ducts. Here, some design optimizations are possible using the length of the entry expansion zone as an optimization parameter. Fourth, there is a need to model the tritium transport in the PbLi primary loop to check if the maximum tritium partial pressure in the blanket can be maintained at a sufficiently low level (typically < 1 Pa), which would assure no need for tritium permeation coatings in the blanket. This task will also require analysis of the performance of the tritium extraction system, which at present is based on a vacuum permeator concept.

Concluding remarks The proposed blanket design does not show many details as the main goal of the current work is to introduce the most important design features needed for the next MHD/Thermofluids R&D and blanket analysis. That is why the main focus of the current design work is to specify the PbLi routes, while helium routing in the first wall and other RAFM structures have not been shown. Also, any details of the high temperature shield and attachment of the blanket segments to the rest of the structure have not been worked out yet.