Fission Gas Release from Externally Restrained Uranium Dioxide Fuel

Abstract

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 37GWd/t in a BWR. The irradiated fuels were annealed at temperatures of 1,500–1,800°C and external pressures of 10–150MPa. 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.

KEYWORDS:

• LWR type reactors
• nuclear fuels
• LWR fuel
• uranium dioxide
• densification
• swelling
• bubble growth model
• hydrostatic pressure
• high temperature
• high pressure
• annealing
• temperature dependance
• temperature range
• pressure dependance
• pressure range
• burst