Out-of-Pile Anneal Experiment of PWR Fuel at Burn-Up of 39 MWd/kg U

概要

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Specimens obtained from the PWR type UO2 fuel with cladding at 39 MWd/kg U were provided for out-of-pile anneal. Obtained results are : (1) A transient fission gas release (FGR) from the out-of-pile, instantaneous triangular shape temperature (peak 980°C) was <0.5%. On the contrary, a transient FGR from in-pile referential test was about 4%. The difference was attributed to the flat temperature profile across fuel for the former and the concave temperature profile for the latter. Significant microcrackings in UO2 fuel periphery observed only in the in pile test might be the main cause of FGR enhancement. (2) Onset temperature of FGR of the provided specimen obtained from the anneal was about 1, 340°C. The maximum FGR was about 37% at 2, 000°C. Diffusion coefficient D (m2•s-1) was D=6.2 × 10-3 exp(-440, 000/RT) at temperatures, 1, 473 ?? T <1, 873 K. (3) FGR from holding at 1, 400°C/150 min was about 5 %, while FGR from cycling (30 cycles between 1, 400°C/5 min and 800°C/5 min) was 2.8%. No enhancement of FGR occurred by the cycling.