Fission Gas Release from Externally Restrained Uramium Dioxide Fuel

概要

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In order to examine the fission gas release behavior under restraint conditions, an out-of-pile high pressure annealing technique was applied to UO2 fuels irradiated to 37 GWd/t in a BWR. The irradiated fuels were annealed at temperatures of 1,500–1,800°C and external pressures of 10–150 MPa. The fractional release of 85Kr was evaluated by β-activities in small amounts of gas that were intermittently collected from the high pressure furnace. The fission gas release was almost completely suppressed by strong external restraint pressures of 100–150 MPa in the temperature range of 1,500–1,800°C, and the critical pressure for the onset of burst release due to rapid bubble growth and tunnel formation was found to be in the range of 40–60 MPa at 1,500°C. This type of burst release was very similar to that observed during the power-down stage in the irradiation tests of high burnup fuels.
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