TRISO fuel primer

TRISO Fuel

TRISO (tri‑structural isotropic) fuel is built around a fuel kernel (commonly UO₂, sometimes UC/UCO) protected by engineered layers deposited via FCVD. The layered architecture supports fission product retention within the particle under demanding conditions.

Download primer Fabrication & qualification

Particle structure

A TRISO particle consists of a kernel coated with four layers (applied via FCVD):

1
Porous carbon buffer
Absorbs fission product recoils and accommodates swelling.
2
Inner pyrolytic carbon (IPyC)
Dense protective pyrocarbon layer.
3
Silicon carbide (SiC)
Ceramic barrier supporting retention and structural integrity.
4
Outer pyrolytic carbon (OPyC)
Dense outer protective layer.
Thousands of TRISO particles are incorporated into a graphite matrix to form compacts or spherical fuel elements (“pebbles”), depending on reactor concept.

Certification is the critical path

TRISO credibility is earned through qualification evidence, including irradiation testing, retention performance, and documented QA/QC. Certified fuel materially de-risks system certification programs.

Request a briefing for controlled-disclosure materials.

Manufacturing steps (overview)

A simplified view of the principal steps described in the KNE primer:

1
Kernel manufacturing
Droplets formed and cooled to create kernels (program-specific material choices).
2
Coated particle manufacturing
Buffer + IPyC + SiC + OPyC applied; coated particles are <1 mm.
3
Fuel-form manufacturing
Compacts or pebbles formed in graphite matrix; integrity verified.
4
Vigorous QA/QC
Quality checks at each step; rejects may be recycled where appropriate.
Scale-up: batch to continuous (high level)

Early production is often batch-oriented. At higher throughput, criticality safety and process stability can drive “safe geometry” designs and more continuous manufacturing philosophies, with stronger in-line controls.

Kernel choice (UO₂ vs UCO)
Kernel selection impacts performance trade-offs. UCO is often used to support higher performance margins by limiting free oxygen release under certain conditions.
Yield and defect economics
Commercial viability depends on high yields and low defect rates; QC discipline is not optional in TRISO commercialization.
Tooling evolution
Scale-up frequently shifts from modified off-the-shelf equipment toward purpose-built process tooling.
For detailed readiness milestones, contact KNE.