IFMIF High Flux Test Module and Test Cell - Design and Design Validation

The International-Fusion-Material-Irradiation-Facility (IFMIF) is an accelerator driven neutron source to create a displacement rate per full power year of 20-50 dpa/fpy in fusion DEMO reactor candidate materials within the High-Flux-Test-Module (HFTM). Besides the displacement damage IFMIF also provides helium and hydrogen production rates that reflect within the uncertainties the values expected in a DEMO Fusion reactor. Within the limited volume of 0.5 litres more than 1000 qualified specimens can be irradiated simultaneously. They are housed in capsules, which are inserted in rigs. The rigs are installed within the HFTM container. The subdivision into 12 rigs allows the simultaneous irradiation at different temperature levels between 300 and 600 oC or more. However the limited space within the HFTM requires a sophisticated arrangement of the specimen, equipment for temperature control and heat removal through narrow channels. Helium is chosen as coolant as it will not be activated nor it is corrosive. The coolant pressure is limited to 0.3 MPa in order to keep the mechanical constraints on the container walls low. Neutronic calculations with the extended Monte Carlo code McDeLicious provide the nuclear heat density in the container, rig and capsule walls as well as in the specimens. In addition heat from electric heaters is used to keep the specimens at the envisaged temperature levels with tolerances of ± 15 oC. This tolerance requires a highly reliable prediction of heat removal and pressure loss in the above mentioned narrow channels. The CFD code STAR-CD has been used for thermo hydraulic lay out. As the coolant conditions are not covered reliably by available experiments, a dedicated experimental helium loop (ITHEX) has been built up. Within an annular test channel local friction factors and heat transfer in a developing flow were measured. The experimental results lead to the conclusion, that the k-ε-Low-Reynolds turbulence model is well suited for the HFTM design. A second experiment for analysing the influence of the inlet transition from the inlet plenum into the narrow channels has been performed. To this end a special LDA (Laser Doppler Anemometry) system was built up with a probe volume of less than 50 μm width. More results on dedicated experiments will be presented. The so far validated thermo hydraulic simulations with STAR-CD provide the input for the stress analyses for the HFTM container and internals. The crucial manufacturing techniques are tested. We, therefore, are confident, that the sophisticated HFTM design is feasible. (author)