Effect of Irradiation Temperature on the Growth of Helium Bubbles in Boron Carbide

Hollenberg, G.W.; Mastel, B.; Basmajian, J.A.

doi:10.1111/j.1151-2916.1980.tb10195.x

Cited by 34 publications

(20 citation statements)

References 7 publications

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“…The goal was, however, mainly phase stability and not the properties of isolated defects, nor their role in mass transport kinetics. In spite of a number of experimental works devoted to helium bubbles [11,12,13,14,15,16,17,18,19,20,21] and the related question of helium kinetics [20,22,23,24], not much is known on self-diffusion.…”

Section: Introductionmentioning

confidence: 99%

The influence of irradiation induced vacancies on the mobility of helium in boron carbide

Gillet

Roma

Crocombette

et al. 2018

Journal of Nuclear Materials

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Boron carbide, used as a neutron absorber, undergoes nuclear reactions producing relevant quantities of He. The understanding of He kinetics at the atomic scale in the material is still in its infancy, in spite of decades of experimental work devoted to the characterization of He containing, irradiated, boron carbide samples. The interplay of He itself with intrinsic defects created by irradiation on kinetics is still almost completely unknown. In this paper we present an exhaustive study of vacancies and substitutional helium impurities in boron carbide using Density Functional Theory. Analyzing the stability and mobility of these defects allows us to consider diffusion mechanisms other than the known interstitial mechanisms. We find that vacancies trap He interstitials, raising the activation energy of 2D diffusion to approximately 2 eV. The trapping mechanism is different according to the charge state of the vacancy : in p-type conditions, when vacancies are neutral or positive, He diffuses via a dissociative mechanisms and is trapped in a substitutional position; in n-type conditions, negative vacancies trap He atoms traveling in an adjacent {111} plane by a charge transfer driven distorsion. No favorable vacancy assisted diffusion mechanism was identified for substitutional He atoms, except the dissociative one previously mentioned. Other possible vacancy diffusion mechanisms, which we also analyzed, are hindered by the high activation energy of vacancy self-diffusion.

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Section: Introductionmentioning

confidence: 99%

The influence of irradiation induced vacancies on the mobility of helium in boron carbide

Gillet

Roma

Crocombette

et al. 2018

Journal of Nuclear Materials

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“…Figure 1. Microstructure of the material and TRIM calculation for the implantation of 500 keV (incidence 15°) 4 He in B 4 C (here for 1 x 10 +14 He/cm²).…”

Section: Methodsmentioning

confidence: 99%

“…Moreover its characteristics make it a serious candidate for neutron absorption application in future Gen-IV reactors 2 . When submitted to a neutron flux, 10 B atom mostly undergoes the (n,α) absorption reaction leading to the formation of 7 Li and 4 He. As a consequence, in fast neutron reactors, a spent B 4 C would accumulate up to ~10 mol.% of He 3 .…”

Section: Introductionmentioning

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%

“…To this aim an experimental study on the He diffusion in B 4 C was carried out in simplified conditions, i.e. 4 He was implanted in B 4 C at a low concentration in order to minimize structural defect and bubbles formations. In addition, large grains size B 4 C sample were used to render grain boundaries influence marginal.…”

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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LMFBR Core Materials

Roberts

1981

Structural Materials in Nuclear Power Systems

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Effect of Irradiation Temperature on the Growth of Helium Bubbles in Boron Carbide

Cited by 34 publications

References 7 publications

The influence of irradiation induced vacancies on the mobility of helium in boron carbide

The influence of irradiation induced vacancies on the mobility of helium in boron carbide

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

LMFBR Core Materials

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