TRISO fuel

Nuclear fuel made of tiny uranium kernels, each sealed in layered carbon and ceramic coatings that act as its own containment.

• Each particle is under a millimetre across: a uranium kernel inside porous carbon, dense carbon, silicon carbide, then more dense carbon.
• The silicon carbide layer holds in radioactive fission products up to about 1,600 °C, above what reactors reach even if cooling is lost.
• Thousands of particles are pressed into graphite pebbles or blocks for high-temperature gas- or salt-cooled reactors.
• Downsides: little uranium per volume, costly manufacture, reliance on uranium enriched to about 15–20%, and few production lines.