Fracture modes of ITER tungsten divertor monoblock under stationary thermal loads

Panayotis, S.; Hirai, T.; Barabash, V.; Amzallag, C.; Escourbiac, F.; Durocher, A.; Komarov, V.; Martinez, Jean-Marc; Merola, M.

doi:10.1016/j.fusengdes.2017.08.009

Cited by 39 publications

(12 citation statements)

References 20 publications

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“…extensive ongoing studies [11][12][13][14][15][16]. Until now, the fatigue crack initiation heat flux factor threshold for the transients was identified to be ∼6 MW m −2 s 0.5 for double forged tungsten with the elongated grains oriented parallel to the heat-loaded surface.…”

Section: Introductionmentioning

confidence: 99%

Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle transient heating

Morgan

Vermeij

et al. 2021

Nucl. Fusion

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Section: Introductionmentioning

confidence: 99%

Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle transient heating

Morgan

Vermeij

et al. 2021

Nucl. Fusion

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“…This presents problems for the ITER operation as recrystallisation leads to a modification of material properties including a reduction in hardness, strength and thermal shock resistance [3]. Recrystallisation in tungsten has also been observed to lead to the pre-mature formation of macro-cracks on the surface [4,5], accelerating material damage by grain ejection or melting. However, a more detailed understanding of the recrystallisation kinetics of tungsten exposed to conditions expected in the reactor divertor is essential to predict the material lifetime and potential impact on the ITER operation.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of retarded recrystallisation in helium plasma-exposed tungsten

et al. 2019

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Recrystallisation has been identified as a critical issue for the ITER divertor but currently the synergistic effects of heat and particle bombardment on tungsten recrystallisation are still unclear. In this study, tungsten was exposed to helium plasma under a range of sample temperatures (573 K-1073 K) and ion fluences (10 24 -10 25 m −2 ) followed by annealing at a range of temperatures (1373 K-1673 K). It is quantitatively found that larger helium nanobubbles form at higher sample temperatures during plasma exposure due to increased nanobubble mobility and coalescence. The retardation of recrystallisation showed the opposite trend, with less recrystallisation occurring in samples exposed at lower temperatures and with smaller nano-bubbles. This result is attributed to the Zener drag force from the helium nano-bubbles opposing grain boundary movements during annealing with the effect of the force being inversely proportional to bubble size. Ion fluence is not found to affect the extent of recrystallisation at any temperature. The presence of the sub-surface helium nano-bubbles increased the microstrain in the tungsten which was eliminated during subsequent annealing as a clear sign of the recovery stage proceeding.

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“…Macrocracking has been observed due to near-surface recrystallization to a depth of 1-2 mm [60]. The cracking correlates with susceptibility to recrystallization, and the cracks may be of concern as a risk for leading edge melting [66]. The fast recrystallization kinetics found here would also imply recrystallization to a deeper depth more quickly than expected from previous furnace annealing studies [57,58].…”

Section: Implications For Iter Divertor Operationmentioning

confidence: 51%

ITER monoblock performance under lifetime loading conditions in Magnum-PSI

et al. 2020

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The ITER divertor will be exposed to extremely high plasma fluences over its lifetime, and it is known that plasma exposure can lead to a variety of particle-induced surface-morphology and microstructure changes in tungsten. However, no data exists at fluences comparable to those expected over extended ITER operations (10 30-31 m -2 ) and so it is uncertain how these changes will evolve and affect the divertor performance over such long timescales. Six monoblocks were exposed to high flux plasma comparable to partially-detached plasma conditions in the ITER divertor in Magnum-PSI. Different exposures used different plasma species (H, He, D or D+He) and aimed to replicate conditions similar to those during different phases of the ITER staged approach. The highest fluence achieved was 10 30 D m -2 , comparable to around one year of ITER Fusion Power Operation. Post-mortem analysis by Nuclear Reaction Analysis revealed very low deuterium retention throughout the blocks, while surface analysis showed no cracking or damage, but did observe helium fuzz growth at low ion energies of 8-18 eV, below typically assumed ion energy requirements for such growth to occur. Metallographic sectioning revealed recrystallization up to 2.2 mm below the surface of monoblocks exposed at peak surface temperatures of up to 1580 °C for different durations up to ~20 hours. Finite Element Method analysis coupled to metallographic and Vickers Hardness identification of the boundary of the recrystallized region identified a faster recrystallization process compared to literature expectations, reinforcing that recrystallization dynamics is an important criterion for tungsten grade selection for the ITER divertor. Overall, no major damage or failure was identified, indicating that the design is capable of fulfilling its steady-state performance requirements under high flux, high fluence plasma loading conditions in the ITER divertor.

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Fracture modes of ITER tungsten divertor monoblock under stationary thermal loads

Cited by 39 publications

References 20 publications

Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle transient heating

Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle transient heating

Temperature dependence of retarded recrystallisation in helium plasma-exposed tungsten

ITER monoblock performance under lifetime loading conditions in Magnum-PSI

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