Nanograin Radiation-Damage Sink Simulator

Irradiation Setup

Grain size 2.5 nm

Dose rate 0.30 dpa/s

Temperature 600 K

Live Readouts

Dose

0.000 dpa

Active defects

Void swelling ΔV/V

0.000 %

Legend

Vacancy (mobile)

Interstitial (mobile, fast)

Void cluster (unhealed damage)

Grain-boundary lattice (defect sink)

How it works

Every neutron collision inside a reactor material knocks an atom off its lattice site, creating a Frenkel pair: a vacancy (empty site) and a self-interstitial (displaced atom wedged between sites). Both diffuse randomly through the crystal with an Arrhenius mobility:

D(T) = D₀ · exp(−Eₘ / kᵦT)
Eₘ(vacancy) ≈ 0.30 eV,  Eₘ(interstitial) ≈ 0.10 eV
→ interstitials migrate far faster than vacancies at the same T

Grain boundaries act as defect sinks: a defect that random-walks within capture range of a boundary is absorbed and annihilated. The areal sink strength of a boundary network scales with grain size d̄ as:

k²_GB ≈ 6 / d̄²   (sink strength, per unit volume)

Halving the grain size roughly quadruples the sink strength — this is exactly why nanocrystalline reactor alloys and coatings (nanograin steels, SiC, TRISO fuel coatings) resist radiation damage far better than coarse-grained ones. If a vacancy survives too long without finding a sink, it is treated here as clustering into a nanoscale void — the microscopic origin of irradiation-induced volumetric swelling. The swelling readout is illustrative (scaled for visibility over a short simulated run), but the qualitative trend — smaller grains and higher temperature both suppress swelling, higher dose rate accelerates it — matches real reactor-materials science.

Grain size — sets the spacing of the grain-boundary lattice (more/fewer sinks).
Dose rate — how fast new Frenkel pairs are generated (neutron flux).
Temperature — raises defect mobility, letting more defects reach a sink before clustering.

Vacancy Interstitial Void

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