Thermoelectrics for nuclear fusion reactors: opportunities and challenges

Nuclear fusion energy holds great promise for being the ultimate solution to the ever-expanding energy needs of modern civilization. Based on the ideal operating temperature ranges of the plasma-facing armour materials and molten salt coolant in tokamak fusion reactors, there is a significant unutilized temperature gradient of similar to 973-1273 K that can be potentially harvested by thermoelectric (TE) devices, without affecting the efficiency of the existing molten salt's heat cycle. In this review, we assess the potential suitability of various high temperature TE materials, such as Si1-xGex, n-type La3-xTe4, p-type Yb14(Mg,Mn)Sb11 zintl compounds, p-type B4C and other borides, for applications on plasma-facing surfaces of nuclear fusion reactors. The practical considerations of plasma-facing TE devices in fusion reactors were also discussed in detail, where potential overlaps between material modifications for enhancing TE properties and neutron irradiation resistance in materials were identified, together with compromises in TE device design parameters. Lastly, transverse TE materials, especially high temperature goniopolar Re4Si7 were also discussed in relation to their potential for Ettingshausen refrigeration for liquid He-free cooling of magnetic field coils. With the continued development of improved fusion reactor designs and structural materials, more opportunities for TE material applications are bound to open up, catalysing the advancement of TE material development for applications under extreme conditions. In this review, we discuss the promising applications and practical considerations of thermoelectrics to harvest the unutilized thermal gradient between the plasma-facing surfaces and the molten salt coolant loop in tokamak fusion reactors.