He migration in implanted UO2 sintered disks

Helium thermal diffusion in a uranium dioxide matrix

“…At high fluence and for temperature of 1100°C we thus deduced by extrapolation a diffusion coefficient of about 2.0 · 10 À17 m 2 s À1 . This value is slightly lower but still in good correlation with the value determined by [27] using a more accurate numerical solution of Fick's equation based on NRA spectral data for samples implanted at a depth of about 2 lm.…”

Diffusion of helium in the perfect and non perfect uranium dioxide crystals and their local structures

“…The experimental points, obtained by [8][9][10][11], lie between the theoretical dependencies. This is not surprising, because the samples used for measurement were the mixture of local diffusion coefficients.…”

“…So, depending on Table 1). ⁄, j, N, d, -experimental values of diffusion coefficients obtained successively in [8][9][10][11].…”

“…So, for example the authors [10] obtained the value of diffusion coefficient equal to D = 6 Â 10 À13 cm 2 s À1 , and in [11], after annealing at 1100°C during 25 min its value decreased below 2 Â 10 À14 cm 2 s À1 Defects in the obvious way reduce the values of the potential barrier. In the work [1] the height of the potential barrier between interstitial positions and oxygen and uranium vacancies were estimated theoretically.…”

Specific outcomes of the research on the spent fuel long-term evolution in interim dry storage and deep geological disposal

“…Studies on unirradiated UO 2 to determine the helium solubility [16][17][18] and its diffusion coefficient [19] indicate a low solubility limit of He (<1 at.%) and a thermal diffusion coefficient lower than 10 À26 m 2 s À1 for temperatures below 573 K. The present state of knowledge suggests that in a first step, helium should accumulate in intragranular bubbles possibly causing microcracks. This phenomenon should accelerate the helium release to grain boundaries and by increasing 1.5 · 10 À19 6.0 · 10 À20 5.5 · 10 À21 125 Te [6] 1.6 · 10 À19 2.0 · 10 À20 1.3 · 10 À21…”