General Atomics looks to silicon carbide for modular tokamak breeding blanket

July 15, 2022, 12:00PMNuclear News
This fusion tokamak cutaway illustrates how the GAMBL concept would be incorporated into a fusion pilot plant. The SiC-tungsten composite wall provides superior heat-removal capabilities and durability, and a modular approach enables fabrication using existing technologies. (Image: GA)

Researchers at General Atomics (GA) are proposing a breeding blanket made of modular silicon carbide–based components to withstand the intense conditions in a high-power fusion power plant. The GA modular blanket (GAMBL) concept is described in an article published this month in the journal Fusion Engineering and Design, and was introduced by GA in a July 13 press release.

Harsh conditions: A tokamak’s breeding blanket must absorb neutrons, produce heat, and create tritium to make the fusion fuel cycle self-sufficient, but those tasks also leave the blanket materials subject to neutron activation. Silicon carbide (SiC) represents an advance over reduced-activation steel and conventional steel for components like the blanket because it has lower activation properties and thermal strength.

According to GA, uncertainties about SiC’s material properties and its ability to contain high-pressure helium coolant have limited its applications in fusion designs. GAMBL addresses those limitations by using engineered SiC-tungsten materials for interior surfaces of the tokamak for superior heat-removal capabilities and durability, and also features modular components to permit fabrication using existing technologies.

“The approach to design structures between metallic alloys and ceramic-composite components is very different,” said Yutai Katoh, interim director of the Materials Science and Technology Division and program director for Fusion Materials at Oak Ridge National Laboratory. “Because of this, the fusion energy community has been reluctant to seriously pursue reactor designs using SiC composites. GAMBL is the type of effort that is needed if we want to maintain options for fusion reactors that offer cost competitiveness and public acceptance.”

Upping efficiency: “Current near-term designs for prototype fusion reactors rely on steels, but SiC-based materials have unique advantages such as low activation, high-temperature strength, and an ability to couple to a highly efficient power conversion system,” said Mark Tillack, who led the GAMBL design team.

GAMBL’s simplified cooling system and absence of steel means the system can deliver temperatures above 1,000°C to generate electricity more efficiently and economically, compared with designs using low-activation steel, which are limited to temperatures of about 500°C, according to GA.

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