Analysis of fission gas release and gaseous swelling in UO2 fuel under the effect of external restraint

Multiscale Modelling for the Fission Gas Behaviour in the Transuranus Code

“…Subsequent to the intersection and associated venting of the gas to the grain boundaries, new bubbles can be generated in the neighbourhood of the grain face and/or existing ones will grow until they intersect again. Such a sudden contribution to release is consistent with the empirical bulk contribution proposed in the COSMOS code [14,15] during power increases. They considered an instantaneous empirical additional release fraction from the bulk of the grains when certain local temperature and burn-up conditions were fulfilled.…”

“…Bubble movement can provide an explanation for the sudden increase of the effective diffusion coefficient during transients, although there is an alternative explanation [16] based on the intersection of growing bubbles with the grain boundaries, which is consistent with the sudden increase of the release fraction from the grains as proposed by Verwerft [17] and implemented in the COSMOS code [14,15].…”

“…It is known that the application of the effective diffusion coefficient during high temperature and transient conditions leads to a systematic underestimation of the release fraction (e.g., [8,11]). This has been overcome by introducing artificially thermal resolution of gas [7,12], or by increasing the empirical diffusion coefficient during transients [13], or by adding an additional empirical release term from the grains [14,15].…”

Dissolution experiments of commercial PWR (52 MWd/kgU) and BWR (53 MWd/kgU) spent nuclear fuel cladded segments in bicarbonate water under oxidizing conditions. Experimental determination of matrix and instant release fraction

“…FIAP1: it is an initial rapid release that comprises the initial oxidation degree of the SNF surface [30,31] ), this fact produces higher cracking of the fuel [50][51][52] and, consequently, higher surface available for corrosion. Therefore, the PWR SNF presents an "apparent" higher dissolution rate.…”

FUEL PERFORMANCE CODE COSMOS FOR ANALYSIS OF LWR UO2AND MOX FUEL

“…A full description can be found in [4], and this paper only gives a brief summary for the fission gas release model.…”