The global push for commercial fusion is largely justified by complex Levelized Cost of Energy models that promise to undercut fossil fuels and advanced fission. However, within the spreadsheet architectures of companies pursuing the Deuterium-Tritium fuel cycle lies a massive, deliberately obfuscated operational expenditure: the cost of catastrophic material embrittlement. The physics of D-T fusion produces a relentless torrent of 14.1 MeV neutrons, and these subatomic projectiles systematically destroy the physical structure of the reactor from the inside out.

When a 14.1 MeV neutron strikes the crystalline lattice of a steel alloy or tungsten divertor, it displaces atoms from their structural positions. This damage is quantified in Displacements Per Atom (dpa). In a commercial D-T power plant operating at high availability, the first wall and divertor will endure dozens of dpa per year. Over time, this leads to severe swelling, loss of ductility, and catastrophic embrittlement of the plasma-facing components.

When a 14.1 MeV neutron strikes the crystalline lattice of a steel alloy or tungsten divertor, it displaces atoms from their structural positions.

Simultaneously, high-energy neutrons trigger transmutation reactions within the structural alloys, generating microscopic bubbles of hydrogen and helium gas deep within the metal. This gas accumulation exacerbates the swelling and induces micro-cracking. Under the extreme thermal cycling and disruption heat fluxes—which can reach 100,000 MW/m2 for a fraction of a millisecond—these embrittled components will rapidly fail.

The commercial reality of this physics is devastating. To prevent a catastrophic vacuum breach, a grid-connected D-T reactor will require the frequent, scheduled replacement of its entire internal structure. For context, in ITER-class D-T systems, highly irradiated structural components like the divertor may require full replacement up to eight times over a standard twenty-year operational lifespan.

Replacing an activated, highly radioactive divertor cassette cannot be done by human hands. It requires months of downtime, utilizing highly bespoke, radiation-hardened remote handling robotics to slowly dismantle and rebuild the reactor core. The sheer capital cost of these replacement components, combined with the devastating loss of revenue during the months-long shutdown, thoroughly destroys the long-term plant economics. Any LCOE model claiming $40/MWh while relying on a D-T fuel cycle is functionally ignoring this multi-billion-dollar maintenance reality.

The private fusion sector must face a harsh engineering truth: building a reactor that successfully contains a burning D-T plasma is an incredible scientific achievement, but it is a terrible business model. Utilities will not purchase power plants that systematically destroy their own infrastructure. The path to NOAK commercialization requires materials that can survive, and the only way materials survive is by eliminating the 14.1 MeV neutron.