Evolution of helium from irradiated boron-containing materials with a graphite carbon base

Emel'yanov, I. Ya.; Grebennikov, R. V.; Moiseev, D. N.; Karasev, V. S.; Kislik, Vladimir S.; Shved, Yu. F.; Mel'nik-Kutsyn, Yu. P.; Lutsenko, N. M.; Demidov, P. I.; Sumets, N. G.

doi:10.1007/bf01375755

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“…In addition, large grains size B 4 C sample were used to render grain boundaries influence marginal. This study appears very complementary to previous works on He diffusion in B 4 C [8][9][10][11][12][13][14][15][16][17] , since it was possible to cover unexplored temperatures domain (600°C up to B 4 C melting point) and to investigate kinetics of He release from traps from ~1200°C.…”

Section: Introductionmentioning

confidence: 59%

“…The values of apparent activation energy of detrapping and frequency factors of He escape from He aggregates in B 4 C obtained in the present study have never been determined elsewhere. On the contrary, a few experiments [8][9][10][11][12][13]17 and recent DFT calculations [14][15][16] had studied interstitial He diffusion in B 4 C and have extracted E a and D 0 values from the results. These are gathered in Table 1 with the values determined in this work.…”

Section: Discussionmentioning

confidence: 99%

“…The next E a value we retrieved from literature data is that by Emel'yanov et al 11 in early 1970's. In their study, they heated B 4 C neutron irradiated samples (7 x 10 +18 n.cm -2 , and ~0.02 mol.% He in average) at different heating rates and deduced from the temperature difference of the maximum release rates an activation energy of 1.73 and 2.15 eV for sintering temperature of 1200 and 2400°C, respectively.…”

Section: Discussionmentioning

confidence: 99%

“…Experimentally, aggregation of He in the form of intra-and/or intergranular bubbles is commonly reported above 500°C, inducing anisotropic grain swelling and microcracking at both grain and grain boundaries scale. [4][5][6][7] As recently reminded by Motte et al 8 , knowledge of the diffusion mechanisms and kinetics of He in B 4 C is still scarce, even though considerable works were made [8][9][10][11][12][13][14][15][16][17] because of the numerous parameters to account for (reactor irradiated B 4 C vs. He implanted B 4 C vs. numerical simulations, B 4 C microstructure, He concentration and so on).…”

Section: Introductionmentioning

confidence: 99%

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Experimental determination of intragranular helium diffusion rates in boron carbide (B4C)

Horlait

Gosset

Jankowiak

et al. 2019

Journal of Nuclear Materials

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Boron carbide, B 4 C, is widely used as a neutron absorber in nuclear reactors. Since neutron absorption by 10 B leads to 4 He production, it appears necessary to study He behavior and its possible effects on the B 4 C ceramic. In this study, the diffusion characteristics of ion-implanted He in B 4 C (500 keV, fluences from 1 x 10 +13 to 2 x 10 +15 He.cm-2) were investigated mainly by Thermo-Desorption Spectroscopy (TDS) from 600°C up to B 4 C melting point. The experiments were done on dense B 4 C samples having large grains (30-60 µm) to render grain boundaries effects on He outward diffusion ineffective and thus to access intragranular He diffusion kinetics. From controlled temperature ramp experiments, it was notably observed that He release was realized in two main stages. A first He population was able to exit the material at moderate temperatures by interstitial diffusion. Then a second population was quantitatively released only over 1150°C. This was attributed to He atoms that, in their initial interstitial diffusion course at moderate temperatures from their implantation sites, got trapped in defect aggregates and/or He bubbles. As the nucleations of both these traps are expected to be related to helium and irradiation defect concentrations, the ratio of the two He populations was indeed found to be correlated with the implantation fluence. From the obtained He release curves, the apparent activation energies (E a) of He intragranular diffusion in B 4 C was determined (2.6-3.1 eV) in the 800-1100°C temperature range. This value appears slightly higher than the one determined at lower temperatures, hinting that a change in diffusion mechanism may occur around 800°C. The apparent E a of He detrapping from He bubbles (~2.5 eV) and from defect aggregates (~4 eV) were also determined for temperatures within 1200-1500°C.

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