Xenon-133 diffusion and trapping in single-crystal uranium dioxide

Abstract

The diffusion of 133Xe in single‐crystal UO2 was studied following the recoil injection of the 133Xe from an external fissionable source. This technique was selected to minimize the diffusion path to a free surface and decrease the possibility of gas‐atom trapping during the diffusion anneals. Gas release results consistent with classical diffusion solutions were obtained over the entire heating cycle for each release curve and no “burst effect” was observed. The results were consistent with D = 2.88 × 103 exp [(−4.78 ± 0.15) eV/kT] cm2s−1 over the temperature range 1065 to 1300 °C. Increasing the recoil concentration to 3 × 1012 fission fragments cm−2 (3 × 10−8 fission atom fraction) produced anomalies in the gas release curves which probably resulted from gas‐atom trapping. Using parameters measured elsewhere for rare gas trapping in UO2 and CaF2, it was shown that many of the rare gas diffusion coefficients reported in the literature for UO2 appear to be too low as a consequence of gas‐atom trapping.

Uncertainty and sensitivity analysis of fission gas behavior in engineering-scale fuel modeling

“…The subsequent review of Matzke [43] demonstrated a scatter of about two orders of magnitude, depending on the considered temperature, between different experimental data sets including those from Matzke [44], Miekeley and Felix [45], and Carter et al [46]. Prussin et al [47] pointed out an uncertainty of at least two orders of magnitude for the lattice diffusion coefficient of Xe in UO 2 , based on various post-irradiation annealing measurements including those from Matzke [44,48], Miekeley and Felix [45], Carter et al [46], and Turnbull et al [41]. Lattice diffusion coefficients of stable fission gases from White and Turnbull [49][50][51] measured in the Halden gas flow rigs also indicated a scatter of approximately two orders of magnitude, depending on the considered temperature, between different measurements.…”

Predicting the probability for fission gas resolution into uranium dioxide

“…Neither Kr or Xe are soluble in UO 2 [31][32][33][34][35][36][37]. This provides the driving force to move these species from the lattice into bubbles or to escape from the fuel entirely.…”

“…This provides the driving force to move these species from the lattice into bubbles or to escape from the fuel entirely. In reality, however, the constant generation of fission gasses in the lattice, the thermal diffusion of Xe and Kr at reactor temperatures [32,37,38] and dynamic effects such as radiation cascades occurring within the fuel [1,14,25,[38][39][40][41][42][43][44] will all contribute to produce a gas atom population that is distributed between sites within the crystalline lattice and gas bubbles of varying sizes. The bubbles therefore act as reservoirs, absorbing gas atoms from the lattice and returning them through processes such as radiation-enhanced resolution [1,14,25,[38][39][40][41][42][43][44][45].…”

First-principles theory for helium and xenon diffusion in uranium dioxide

“…The atomic transport processes of fission products and He in UO 2 are therefore of great interest for understanding the performance of UO 2 as a nuclear fuel. The diffusion characteristics of fission products have been the subject of extensive research [8][9][10][11]. From a detailed lattice structural analysis of the fission gas diffusion in UO 2 at low gas concentrations, Matzke et al [2,9,12] have reported that some of the fission gases diffuse by proceeding via a vacancy cluster but not a single vacancy.…”