Development, Characterization, and Testing of a SiC-Based Material for Flow Channel Inserts in High-Temperature DCLL Blankets

Abstract

Flow channel inserts (FCIs) are the key elements in the high-temperature dual-coolant lead-lithium blanket, since in this concept the flowing PbLi reaches temperatures near 700 °C and FCIs should provide the necessary thermal and electrical insulations to assure a safe blanket performance. In this paper, the use of a SiCsandwich material for FCIs consisting of a porous SiC core covered by a dense chemical vapor deposition-SiC layer is studied. A fabrication procedure for porous SiC is proposed and the resulting materials are characterized in terms of thermal and electrical conductivities (the latter before and after being subjected to ionizing radiation) and flexural strength. SiC materials with a wide range of porosities are produced; in addition, preliminary results using an alternative route based on the gel-casting technique are also presented, including the fabrication of hollow samples to be part of future lab-scale FCI prototypes. Finally, to study the corrosion resistance of the material in hot PbLi, corrosion tests under static PbLi at 700 °C and under flowing PbLi at ∼10 cm/s and 550 °C, with and without a 1.8-2T magnetic field, were performed to materials coated with a 200-400-µm-thick dense SiC layer, obtaining promising results.

Controlling the electrical resistivity of porous silicon carbide ceramics and their applications: A review

“…During the sintering stage, Y 2 O 3 reacts with the SiO 2 layer on the surface of SiC and forms a Y‐Si‐oxycarbonitride liquid phase, which causes N 2 to dissolve and results in the formation of nitrogen‐doped (N‐doped) SiC 26,29,147 . The results obtained from various studies on the effect of oxide additives on the electrical properties of porous SiC are summarised in Figure 3 26,31,37,41,57,63,76,139,148,149 …”

“…In such fusion reactors, lead‐lithium (Pb‐Li) liquid is used for multiple purposes, for example, as a coolant, neutron multiplier, and tritium breeder to sustain the thermonuclear reaction 76,186 . During the operation, plasma is generated as a result of the thermonuclear reaction, and the temperature of the Pb‐Li coolant rises owing to the generated heat 41,187 . To avoid excessive heating of the steel structure, He is used to cool the housing (steel structure), as shown in Figure 13A.…”

“…Usually, the electrical resistivity of SiC ceramics increases with an increase in the porosity (%). 41,63 Pores create hurdles in the flow of charge carriers, thus, increasing the electrical resistivity (as shown in Figure 1A). In some exceptional cases, a change in the microstructure may decrease the electrical resistivity of porous structures, as reported by Ihle et al 57 This decrease in the electrical resistivity is due to the enlarged grain size of porous SiC as compared to that of dense SiC.…”

“…Porous SiC ceramics exhibit a room temperature electrical resistivity of the order of 10 -1 -10 6 Ω⋅cm. 30,31,37,41,57,[76][77][78][79] For example, the electrical resistivities of porous SiC ceramics sintered with 10 vol.% AlN-Y 2 O 3 and 7wt.% Y 2 O 3 -La 2 O 3 are 1.3 × 10 -1 Ω⋅cm at 30.3% porosity 31 and 5.3 × 10 1 Ω⋅cm at 9.9% porosity, 37 respectively. The electrical resistivity of ceramics generally increases with an increase in the porosity.…”

“…39,40 In contrast, the substrate material used for handling electronic devices is required to have high electrical resistivity (≥10 14 Ω ⋅ cm). 29,36 To realise the use of SiC for advanced functional applications, such as in dual coolant lead lithium blankets (DCLL) of fusion reactors (as flow channel inserts [FCIs]), 41,42 substrate materials for thermoelectric energy conversion, 43,44 electromagnetic interference (EMI) shielding materials, 45,46 heating elements, 32,47 and heatable filters 28,31 for cleaning the contaminated air in hospitals, it is imperative to control its electrical properties.…”