Evolution of thermo-physical properties and annealing of fast neutron irradiated boron carbide

Gosset, Dominique; Kryger, B.; Bonal, J.P.; Verdeau, Caroline; Froment, Karine

doi:10.1016/j.jnucmat.2017.11.027

Cited by 16 publications

(10 citation statements)

References 25 publications

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“…In particular, the interplay of helium and the point defects created by neutron irradiation, and their mobility, is crucial in order to understand and control the formation of helium bubbles, which ultimately control internal strain [5] and the lifetime of control rods [2].…”

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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“…Maruyama et al [3] demonstrated that the thermal conductivity of boron carbide decreases rapidly to 1/3 of the unirradiated value as early as the burnup of ~5×10 26 cap/m 3 , and then further decreases gradually to 1/10 at about 35×10 26 cap/m 3 . Some other neutron irradiation investigations have also verified the abrupt degradation of thermal conductivity of boron carbide at the very beginning of the irradiation process [5][6][7].…”

Section: Introduction mentioning

confidence: 76%

“…It can be deduced simply that 5×10 26 cap/m 3 of neutron captures can only produce 0.455 at% 10 B burnup of the total boron in a fully dense boron carbide pellet, which implies that the boron carbide pellet would endure an extremely high thermal gradient during most of its service life due to the thermal conductivity degradation. The high thermal gradient will result in a large thermal stress in pellets, and thus lead to an extensive cracking [7,8].…”

Section: Introduction mentioning

confidence: 99%

“…They also assessed the contributions of the defect scattering and Umklapp processes to the degradation, and came to a conclusion that the contribution of the former, especially the point defects, was remarkably higher than that of the latter. However, Gosset et al [7] assumed that the helium bubbles as well as the high micro-strains induced, rather than the irradiation defects, might serve as phonon scattering centers. In our previous work [9], we tried to quantitatively estimate the effect of irradiation-induced point defects on the thermal conductivity of boron carbide by a classical phonon scattering model.…”

Section: Introduction mentioning

confidence: 99%

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Thermal conductivity of boron carbide under fast neutron irradiation

Zhi

Wei

et al. 2022

J Adv Ceram

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Due to the complex products and irradiation-induced defects, it is hard to understand and even predict the thermal conductivity variation of materials under fast neutron irradiation, such as the abrupt degradation of thermal conductivity of boron carbide (B4C) at the very beginning of the irradiation process. In this work, the contributions of various irradiation-induced defects in B4C primarily consisting of the substitutional defects, Frenkel defect pairs, and helium bubbles were re-evaluated separately and quantitatively in terms of the phonon scattering theory. A theoretical model with an overall consideration of the contributions of all these irradiation-induced defects was proposed without any adjustable parameters, and validated to predict the thermal conductivity variation under irradiation based on the experimental data of the unirradiated, irradiated, and annealed B4C samples. The predicted thermal conductivities by this model show a good agreement with the experimental data after irradiation. The calculation results and theoretical analysis in light of the experimental data demonstrate that the substitutional defects of boron atoms by lithium atoms, and the Frenkel defect pairs due to the collisions with the fast neutrons, rather than the helium bubbles with strain fields surrounding them, play determining roles in the abrupt degradation of thermal conductivity with burnup.

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“…All in all there are few reasons to suspect that He diffusion mechanism in B 4 C gets modified around the temperature of 800°C. Interestingly, annealings at such temperature of neutronirradiated B 4 C was reported to allow the "healing" of the c cell parameter 45,50,51 . The three publications reporting such results did not put forward a hypothesis on what phenomenon caused this lattice change.…”

Section: Discussion Of He Diffusion and Releasementioning

confidence: 99%

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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Evolution of thermo-physical properties and annealing of fast neutron irradiated boron carbide

Cited by 16 publications

References 25 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

Thermal conductivity of boron carbide under fast neutron irradiation

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

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