---
type: claim
domain: energy
description: "No fusion device has demonstrated tritium breeding ratio above 1 and if first-generation plants cannot breed fast enough the entire fleet is constrained by a shrinking natural supply produced as CANDU fission byproduct"
confidence: likely
source: "Astra, fusion power landscape research February 2026; IAEA materials analysis"
created: 2026-02-17
depends_on:
- Commonwealth Fusion Systems is the best-capitalized private fusion company with 2.86B raised and the clearest technical moat from HTS magnets but faces a decade-long gap between SPARC demonstration and commercial revenue
related:
- plasma-facing materials science is the binding constraint on commercial fusion because no facility exists to test materials under fusion-relevant neutron bombardment for the years needed to qualify them
reweave_edges:
- plasma-facing materials science is the binding constraint on commercial fusion because no facility exists to test materials under fusion-relevant neutron bombardment for the years needed to qualify them|related|2026-04-19
sourced_from:
- inbox/archive/2026-02-17-astra-fusion-power-landscape.md
---

# Tritium self-sufficiency is undemonstrated and may constrain fusion fleet expansion because global supply is 25 kg decaying at 5 percent annually while each plant consumes 55 kg per year

D-T fusion requires tritium. Global supply is approximately 25 kg, produced primarily as a byproduct in CANDU fission reactors. Tritium has a 12.3-year half-life, so the existing supply naturally decays at roughly 5 percent per year. A single commercial fusion plant at 100 MW consumes approximately 55 kg per year.

Each plant must therefore breed its own tritium from lithium blankets surrounding the plasma, achieving a tritium breeding ratio (TBR) greater than 1.0. No fusion device has demonstrated tritium self-sufficiency at any scale. The physics is understood, but the engineering integration of breeding blankets with plasma operations, heat extraction, and neutron management has never been tested in an integrated system.

**Update (2025-2026):** MIT PSFC's LIBRA project is the first to demonstrate reproducible and scalable tritium breeding in molten salts with a robust tritium accountancy system using D-T neutrons. ARC-class tokamaks are designed to use molten salt Liquid Immersion Blanket (FLiBe) to breed tritium. This is early-stage work but represents the first concrete experimental program attacking the breeding integration challenge.

This creates a bootstrap problem: the first few plants can draw on existing CANDU-produced supply, but fleet expansion requires demonstrated breeding. If early plants achieve TBR of only 0.95 instead of the required 1.05+, the tritium shortfall compounds exponentially across a growing fleet.

The tritium constraint is one reason Helion Energy's approach (D-He3 fuel) and TAE Technologies' long-term target of proton-boron fusion (aneutronic, no tritium needed) are strategically interesting despite being technically harder. They sidestep the supply chain constraint entirely.

## Evidence
- Global tritium supply: ~25 kg, decaying at 5%/year (12.3-year half-life)
- Single 100 MW plant consumption: ~55 kg/year
- No demonstrated TBR > 1.0 in any fusion device
- MIT PSFC LIBRA project: first reproducible tritium breeding in molten salts

## Challenges
If LIBRA and similar programs demonstrate TBR > 1.05 in integrated systems, the constraint relaxes significantly. Alternative fuel cycles (D-He3, p-B11) eliminate the constraint entirely but face harder plasma physics.

---

Relevant Notes:
- [[Commonwealth Fusion Systems is the best-capitalized private fusion company with 2.86B raised and the clearest technical moat from HTS magnets but faces a decade-long gap between SPARC demonstration and commercial revenue]] — CFS/ARC design depends on successful tritium breeding via FLiBe blankets

Topics:
- [[space exploration and development]]