Manufacturing of a HCLL cooling plate mock up

Abstract

The European DEMO blankets and associated test blanket modules (TBM) are made of a set of components cooled by flowing helium at 80 bar pressure. Hot isostatic pressing (HIP) is one of the very few processes that allow manufacturing such components exhibiting complex cooling channels. In HIP technology, the parts used to manufacture components with embedded channels are usually machined plates, blocks and tubes. Achievable geometries are limited in shape because it is not always possible to figure the channels by bent tubes. This occurs, for example, when channels present sharp turns, the cross section of the channels is rectangular or the rib between channels is so small that very thin tubes would be required. In these cases, bending is unpractical. The breeder unit cooling plates (CPs) of the helium cooled lithium lead (HCLL) blanket have eight 4 mm × 4.5 mm parallel channels that run following a double U scheme. Turns are sharp and the wall thickness is small (1 mm), so the manufacturing process described above cannot be used. An alternative process has been developed which has many advantages. It consists of machining grooves in a base plate, then closing the top of the grooves using thin welded strips, and finally adding a plate by HIP. There is then no need for the use of tubes with associated bending and deformation issues. The final component contains welds, but it must be stressed out that these potentially brittle zones do not connect the channels to the external surface because they are covered by the HIPed plate. Furthermore, the welds are homogenised during the HIP operation and further heat treatments. This paper describes the design of a simplified cooling plate (CP) mock up and its fabrication using this so-called weld + HIP process.