Temperature and fission rate effects on the rim structure formation in a UO2 fuel with a burnup of 7.9% FIMA

Discussion About HBS Transformation in High Burn-Up Fuels

“…J.Nakamura shows that the crystallites size saturates around 200nm for local burn-up higher than 67 GWd/MtU (pellet average burn-up is 57 GWd/MtU). This is consistent with the value of 300 nm reported by M.Kinoshita [46].…”

“…Concerning the temperature threshold for rim formation [46] confirms a value of 1100°C. The limit of the restructured zone was found to be related to the starting of the high fission gas release zone.…”

“…We have also to account for two other difficulties: a radial instantaneous fission density profile very steep and therefore inaccurate in the rim zone, and an unknown local constraint. Lately from a very fine analysis of a high burn-up fuel performed at TUI, M.Kinoshita [46] gives a probably more accurate threshold around 7 % FIMA (about 70 GWd/MtU).…”

Evaluation of melting point of UO2 by molecular dynamics simulation

“…It is well known that UO 2 is exposed to high temperature and irradiation. Such conditions vary widely with position in the fuel, e.g., temperature gradient, high burn-up at the rim region [1], and also vary with loading time, e.g., accumulation of fission products and increase of oxygen partial pressure. As a result, the melting point of uranium oxide is affected by these factors.…”

A model for the influence of microstructure, precipitate pinning and fission gas behavior on irradiation-induced recrystallization of nuclear fuels

“…For example, several conflicting explanations have been put forward to account for evidence that xenon depletion, pore formation, and recrystallization begin at different local burnups [16]. In addition, a consensus has not been reached on the fission rate and temperature dependence of recrystallization [2,17], on the role of composition and fabrication parameters such as grain size [18], or on the role of stress [19]. This paper, presents a model for irradiation-induced recrystallization that links the observed microstructural evolution of the fuel, the role of fission gas bubbles, and the triggering event for recrystallization.…”