Sandwich-type cooling pipes of the first wall of future fusion nuclear reactors (ie. DEMO) will likely have tungsten be brazed to a Reduced Activation Ferritic Martensitic (RAFM) steel. Under incoming High Heat Flux (HHF) (1-5 MW/m2), the mismatch in thermal expansion between tungsten and steel results in significant thermal stresses in the brazing region favouring the growth of cracks, damaging the structural integrity of such pipes. Finite element analysis has been performed of the brazed joints in these cooling pipes under HHF. Thermal stresses and resulting plastic strains are estimated both the braze interlayer and parent materials. The thickness of parent materials in the piping design is demonstrated to have significant impact on stresses, plastic strains and therefore on the joint fracture. 
As images of brazed joints reveal, brazing processes are very likely to induce cracks in the edge region of joints. In simulations, a crack is therefore introduced in the brazing alloy where simulated stresses and strains are found to be the highest. J-integrals on loading and C(t) during creep dwell are calculated for the crack growing from an edge to the centre of the considered piping assembly. The results are discussed in relation to the current sandwich-type piping design of the DEMO reactor.&nbsp;

Prediction of J-Integrals at Defects in W-9CR Steel Sandwich-Type Cooling Pipes

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

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