The evolution of the microstructure of Cr16–Ni19 steel under irradiation in the low enrichment zone of a fast neutron reactor. The effect of neutron irradiation conditions on the structural and phase state

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Abstract

Microstructural studies of samples made from various sections of fuel element shells were carried out after irradiation in the low enrichment zone of a fast neutron reactor with a sodium coolant to damaging doses of over 100 dpa. At different sites, the rate of generation of atomic displacements varied from 0.5×10–8 to 1.6×10–6 dpa/s, the irradiation temperature ranged from 370 to 630°C. The structural and phase state of the shell samples is investigated, the evolution of the composition and morphology of the secretions of the second phases and the austenitic matrix is shown.

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About the authors

V. L. Panchenko

JSC “Institute of Nuclear Materials”

Author for correspondence.
Email: panchenko_vl@irmatom.ru
Russian Federation, Zarechny, Sverdlovsk region, 624250

I. A. Portnykh

JSC “Institute of Nuclear Materials”

Email: panchenko_vl@irmatom.ru
Russian Federation, Zarechny, Sverdlovsk region, 624250

A. E. Ustinov

JSC “Institute of Nuclear Materials”

Email: panchenko_vl@irmatom.ru
Russian Federation, Zarechny, Sverdlovsk region, 624250

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Supplementary files

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2. Fig. 1. Microstructure of Cr16-Ni19 h.d. steel in the initial (unirradiated) state: (a) cellular dislocation structure; (b-d) segregation of Cr, Mo, Ti at the grain boundary (marked with black arrows); (e) - distribution profile of Cr, Ni, Mo, Ti across the grain boundary (dashed line).

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3. Fig. 2. Dislocation structure of Cr16-Ni19 h.d. steel after irradiation, Tobl ~ 370°C, G ~ 1.1 ∙ 10-8 sleep/s: (a) relatively homogeneous dislocation mesh; (b) stripe contrast on Frank loops with packing defect, dark-field STEM image.

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4. Fig. 3. SEM of grain boundary and dislocations in Cr16-Ni19 h.d. steel after irradiation at ~ 370°C: (a, c, e) respectively grain boundary section (dark-field STEM image), mixed map and distribution profile of Cr, Mo, Ni, Si across the boundary (the position of the boundary is marked by a dashed line in the diagram), G ~ 1. 1 ∙ 10-8 sleep/s; (b, d, e) respectively the dislocation forest (light-field STEM image), mixed map and distribution profile of Si, Ni, Cr through the Franck loop and dislocation (dashed and dotted lines in the diagram) in the grain volume, G ~ 0.6 ∙ 10-8 sleep/s.

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5. Fig. 4. Morphology of intermetallides in the grain volume in Cr16-Ni19 h.d. steel after irradiation, Tobl. ~ 450°C, G ~ 1. 3 ∙ 10-6 sleep/s: (a) coffee bean-type contrast on coherent γ'-phase emission; (b) G-phase emission on vacancy pores; (c, d) direct resolution of the austenite lattice and the corresponding FP with decoding; (e, f) direct lattice resolution at the γ' particle and the corresponding FP with decoding, the reflexes forbidden for the HCC lattice are visible (in parentheses); (g, i) direct lattice resolution in the vicinity of the interphase boundary and the corresponding FP with decoding, the {022} planes of the G-phase are parallel to the {111} planes of austenite.

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6. Fig. 5. Second-phase emission and RIS in the grain volume in Cr16-Ni19 h.d. steel after irradiation, Tobl ~ 450°C, G ~ 1.3 ∙ 10-6 sleep/s: (a) grain section with second-phase emission, light-field STEM image; (b, c) γ'- and G-phase particles on Ni and Si distribution maps; (d-e) τ-carbides (M23C6) on Cr, Mo and V distribution maps.

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7. Fig. 6. Second-phase efflorescence and RIS at the grain boundary in Cr16-Ni19 h.d. steel after irradiation, Tobl ~ 450°C, G ~ 1. 3 ∙ 10-6 sleep/s: (a) section of the grain boundary with second-phase separations, dark-field STEM image; (b) grain-organic τ-carbide particle in the Cr distribution map; (c, d) G-phase particles and thin line of RIS along the grain boundary in the Ni and Si distribution maps; (e, f) RIS of Ti and P in the second-phase separations.

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8. Fig. 7. Formation of second phases and segregations at the periphery of primary carbonitride in Cr16-Ni19 h.d. steel after irradiation, Tobl ~ 450°C, G ~ 1.4 ∙ 10-6 sleep/s: (a) dark-field STEM image; (b-h) distribution maps of Ti, Cr, Ni, Mo, Si, V, P respectively in the analysed foil section.

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9. Fig. 8. Identification of phases formed on primary carbide (Fig. 7) in Cr16-Ni19 h.d. steel by direct lattice resolution, Tobl ~ 450°C, G ~ 1.3 ∙ 10-6 sleep/s: (a, b) direct lattice resolution in the vicinity of the primary carbide-intermetallide interface and the corresponding FP with decoding; (c, d) direct lattice resolution on M23C6 carbide and the corresponding FP with decoding.

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10. Fig. 9. Microstructure of Cr16-Ni19 type steel h.d., characteristic for the medium-temperature irradiation range, Tobl ~ (490-550)°C, G ~ (1.5-1. 6) ∙ 10-6 sleep/s: (a) grain boundary bends caused by local migration; (b) the boundary region with low-angle disorientation and reduced dislocation density is bounded on the right by a dislocation wall; (c) the intergrain boundary with a chain of second-phase precipitates; (d) prismatic τ-carbide and G-phase particles.

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11. Fig. 10. Phosphides in the grain volume of Cr16-Ni19 type steel grains h.p., Tobl ~ 490°C, G ~ 1.5 ∙ 10-6 sleep/s: (a, b) light-field STEM image and phosphorus distribution map of the analysed area; (c, d) HP SEM and corresponding FP with transcription on one of the M2P-type phosphide particles (GPU, a ~ 0.587 nm, c ~ 0.346 nm).

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12. Fig. 11. Morphology of carbide-intermetallide particle conglomerates in the structure of Cr16-Ni19 h.d. type steel from the mid-temperature range, Tobl ~ 525°C, G ~ 1. 6 ∙ 10-6 sleep/s: (a, b) light-field STEM image and corresponding composite distribution map of Cr and Ni; (c-d) HP SEM on the conglomerate particles marked with arrow (b) and corresponding FPs with identification of carbide (e) and intermetallide (f) lattice reflections.

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13. Fig. 12. Cellular dislocation structure of Cr16-Ni19 h.d. type steel characteristic for high-temperature irradiation range, Tobl. ~ 590°C, G ~ 0.6 ∙ 10-6 sleep/s: (a) light-field STEM image of the triple junction of grains, polygonisation dislocation walls are visible; (b) map of nickel distribution in the investigated area, RIS at grain boundaries, dislocations and small-angle dislocation boundaries.

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14. Fig. 13. Morphology of precipitates in Cr16-Ni19 h.d. type steel characteristic of the lower edge of the high-temperature irradiation range, Tobl. ~ 570°C, G ~ 1.3 ∙ 10-6 sleep/s: (a) light-field STEM image, τ-carbide, M2P phosphides and Frank loops (FLs) are marked; (b-d) distribution maps of Cr, Ni, Ti. Fine Ni3Ti and G-phase particles in conglomerates with τ-carbides are marked; (e, f) distribution profiles of Cr, Ni, Si, Mo, Ti, P elements through the three-layer conglomerate τ + G + τ and M2P phosphide enriched in Si and Ti.

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15. Fig. 14. Fine TiC reflections in Cr16-Ni19 h.d. steel, Tobl ~ 630°C, G ~ 0.6 ∙ 10-6 sleep/s: (a) morphology of fine carbides; (b) distribution profile of Ti, C, Ni, Si elements through the secondary titanium carbide particle; (c, d) TEM VR and corresponding PD with decoding obtained on the coherent carbide particle. The identified reflections belong to the [-1 -1 0] zone axis of the austenitic matrix; circles encircle the corresponding TiC reflections with lattice parameter a ~ 0.433 nm.

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16. Fig. 15. Loves phase in Cr16-Ni19 type steel h.d. in the region of maximum irradiation temperatures, Tobl ~ (625-630)°C, G ~ (0.6-0. 8) ∙ 10-6 sleep/s: (a, b) morphology and FP with high-resolution image interpretation of the Loves phase (λ) formed at the periphery of the primary carbonitride M (C,N) particle; (c, d) STEM image in the vicinity of the triple grain junction and the corresponding composite distribution map of Cr and Mo, the grain-boundary separations of the Lavez phase and τ-carbide and the intra-grain separations of the Lavez phase on the primary carbonitrides are marked; (e, f) cross-sectional distribution profiles of Fe, Mo, Cr, Ni, Si through the Lavez phase particles (e) and τ-carbide (f).

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17. Fig. 16. Dependences of dislocation density (a), average size and concentration of Frank loops (b) on irradiation temperature in Cr16-Ni19 h.d. steel.

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18. Fig. 17. Relative change of concentration of basic elements in austenitic matrix as a function of irradiation temperature in samples of fuel element cladding #1 (a) and #2 (b) made of Cr16-Ni19 type steel.

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