Title: Measurement of gas permeability along the axis of a spent fuel rod
Authors: RONDINELLA VincenzoPAPAIOANNOU DimitriosNASYROW RamilGOLL WolfgangREHM Markus
Publisher: European Nuclear Society
Publication Year: 2015
JRC N°: JRC94524
ISBN: 978-92-95064-23-2
URI: http://www.euronuclear.org/events/topfuel/topfuel2015/transactions.htm
Type: Articles in periodicals and books
Abstract: Gas transport along the axis of irradiated fuel rods is an important process which determines homogeneous pressurization inside the rod. In case of failed rods, gas and/or liquid phase (water) axial transport is relevant for accident conditions (e.g. the effects of depressurization on fuel integrity and radionuclide release), and for spent fuel drying. The effects of increasing burnup on the mode of axial transport of gas are of particular interest. The closure of the pellet-cladding gap, which occurs at burnup around 45 GWd/tHM, removes a fast pathway for axial transport. This implies that gas or other mobile species will have to travel through cracks and other discontinuities in the fuel. This paper presents the results of axial gas transport measurements in a spent fuel rod. The permeability of nitrogen along the axis of a PWR ~52 GWd/tHM UO2 rod was investigated by applying a gas pressure difference and measuring the equilibration time across the fuel stack. The tests were performed in hot cell at ambient temperature (approximately 300 K). The pressure difference applied varied between 0.1 MPa and 1 MPa (1 and 10 bar) and the corresponding equilibration times varied between 930 s and 280 s, respectively. The derived permeability coefficient is of the order of 3•10-13 m2. These results confirm that axial transport of fluid occurs readily in spent fuel rod also when the pellet-cladding gap is closed. Further work is ongoing to investigate these properties in the context of spent fuel drying, storage and disposal, and to assess possible implications for in-pile behaviour under off-normal conditions.
JRC Directorate:Nuclear Safety and Security

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