an introduction to the effect of neutron irradiation on the microstructure and properties of structural alloys

1. 1 An Introduction to the Effect of (Neutron)Irradiation on the Microstructure and Properties of Structural Alloys

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3. 3 Causes � - fast neutron displacements (measured in dpa or fluence) - transmutation damage (specially He and H) coupled with: - thermal, stress and chemically-driven processes Consequences - - Dimensional instability: creep (stress), swelling & growth (unstressed) - Reduced ductility (embrittlement) - Reduced creep failure time - Lower fracture resistance in the presence of cracks - Enhanced environmentally-assisted cracking

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8. 8 Grains consist of single crystals (bcc, fcc and hcp) Grains of different orientations separated by grain boundaries several alloying elements (typically = 4) plus impurities alloy constituents - primary matrix phase - precipitate phases with distinct compositions and crystal structures defect structures: dislocations, gas bubbles, cavities (voids), vacant lattice sites(vacancies), interstitials microstructure depends - composition, - method of fabrication (e.g., cold-worked, annealed) and - service conditions (e.g., temperature, irradiation)

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10. 10 not at equilibrium; microstructure evolves: - thermodynamic driving forces - rates (kinetics) controlled by �temperature �irradiation �chemical environment � stress property degradation (damage): - embrittlement - swelling - deformation

11. 11 Point defects: vacancies and interstitials created by radiation undergo reactions and aggregation (clustering) Microstructure provides both sources of and sinks for point defects Like defects cluster and anti-defects annihilate (recombine)

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15. 15 Point-defect Reactions & Aggregation Radiation produces vacancies (V) & self-interstitial atoms (I) V - an unoccupied crystal lattice site I - atom not on a lattice site (usually 2 atoms around one site) Clustering reactions: V + V V2, V + Vn Vn +1, I + I I2, I + In In +1, Recombination & annihilation reactions: V + I 0, I + Vn Vn -1, V + In In �1 Cluster-cluster coalescence reactions: Vn + Vm Vn+m, In + Im In+m, In + Vm Vm-n + In-m Similar clustering reactions for: solute-solute; solute-point defect; gases (including He and H produced by transmutations)

16. 16 Point-defect Reactions With Sinks Sinks include: point-defect clusters, surfaces, grain boundaries and dislocations Point defects can change the sink (cluster growth and dislocation climb) or loose identity (free surface) Mobile clusters can interact with sinks Equal fluxes of V and I annihilate each other at unchanged sinks Net flux of V or I to dislocations causes climb (V-up, I-down) Net flux of V causes void growth Net flux of I causes loop growth In the void-swelling regime, loops and voids grow together

17. 17 Light-water reactors (PWR and BWR) - core internals and reactor pressure vessel Magnetic-fusion energy - limiter, divertor, first wall, structural materials � Inertial-fusion energy - neutron + ion debris on chamber walls, laser-material interactions �� Generation IV reactor concepts - supercritical-water reactor - gas-cooled fast reactor - very-high-temperature reactor, gas-cooled - sodium (or lead) - cooled fast reactor - molten-salt reactor

18. 18 PWR components

19. 19 Core barrel, baffle & former

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25. 25 materials challenges - Radiation damage - High thermal heat fluxes - Sputtering/blistering of plasma-facing materials - Chemical compatibility - Low induced radioactivity

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