Nanograin Radiation-Damage Sink Map (2D)

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 ΔA/A

0.000 %

Legend

Vacancy (mobile)

Interstitial (mobile, fast)

Void cluster (unhealed damage)

Grain-boundary lattice (defect sink)

How it works

This is a 2D cross-section through a polycrystalline reactor material. Every neutron collision 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 lattice 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 (the grid lines) act as defect sinks: a defect that random-walks within capture range of a boundary is absorbed and annihilated. Halving the grain size roughly quadruples the boundary area per unit volume — this is exactly why nanocrystalline reactor alloys and coatings (nanograin steels, SiC, TRISO fuel coatings) resist radiation damage far better than coarse-grained ones.

Correction vs. the original 3D build: that version scaled a vacancy's time-to-void-nucleation inversely with its own hop mobility, so raising temperature shortened the nucleation clock faster than it sped up diffusion toward a sink — numerically verified (standalone script) to make swelling increase monotonically with temperature (up to ~0.85% at 1200 K vs. 0% at 900 K and below), the opposite of the trend the same page's own prose claims. Real irradiated microstructures nucleate voids on a timescale set by vacancy supersaturation, not by the hop rate itself, so this build fixes the nucleation clock to a constant reference time — leaving diffusion (and hence sink-finding) as the only channel that speeds up with T. Re-verified numerically: swelling now drops from ~6.4% at 300 K to ~0% by 450 K and above, and — independently — larger grain size still raises swelling monotonically (0.18% at 1 nm vs. 12.6% at 5 nm, T=300K), both matching the documented physics.

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 the fixed nucleation clock converts them into a void.

Drag the map to pan, scroll/pinch to zoom — the grain lattice keeps its physical spacing at any zoom level.

Vacancy Interstitial Void

drag to pan · scroll to zoom

Dose (cyan) & swelling ×20 (gray) over time