Oxidation of UN/U2N3-UO2 composites: an evaluation of UO(2 )as an oxidation barrier for the nitride phases

Composite fuels such as UN-UO2 are being considered to address the lower oxidation resistance of the UN fuel from a safety perspective for use in light water reactors, whilst improving the in-reactor behaviour of the more ubiquitous UO2 fuel. An innovative UN-UO2 accident tolerant fuel has recently...

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Bibliographic Details
Published in:Journal of nuclear materials 2021-02, Vol.544
Main Authors: Costa, Diogo Ribeiro, Hedberg, Marcus, Middleburgh, Simon C., Wallenius, Janne, Olsson, Pär, Lopes, Denise Adorno
Format: Article
Language:English
Subjects:
Accident tolerant fuel
alpha-U2N3
oxidation resistance
thermogravimetric analysis
UN microspheres
UN-UO2 composite
UO2 fuel
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Summary:Composite fuels such as UN-UO2 are being considered to address the lower oxidation resistance of the UN fuel from a safety perspective for use in light water reactors, whilst improving the in-reactor behaviour of the more ubiquitous UO2 fuel. An innovative UN-UO2 accident tolerant fuel has recently been fabricated and studied: UN microspheres embedded in UO2 matrix. In the present study, detailed oxidative thermogravimetric investigations (TGA/DSC) of high-density UN/U2N3-UO2 composite fuels (91-97 %TD), as well as post oxidised microstructures obtained by SEM, are reported and analysed. Triplicate TGA measurements of each specimen were carried out at 5 K/min up to 973 K in a synthetic air atmosphere to assess their oxidation kinetics. The mass variation due to the oxidation reactions (%), the oxidation onset temperatures (OOTs), and the maximum reaction temperatures (MRTs) are also presented and discussed. The results show that all composites have similar post oxidised microstructures with mostly intergranular cracking and spalling. The oxidation resistance of the pellet with initially 10 wt% of UN microspheres is surprisingly better than the UO2 reference. Moreover, there is no significant difference in the OOT (similar to 557 K) and MRT (similar to 615 K) when 30 wt% or 50 wt% of embedded UN microspheres are used. Therefore, the findings in this article demonstrate that the UO2 matrix acts as a barrier to improve the oxidation resistance of the nitride phases at the beginning of life conditions.
ISSN:0022-3115
1873-4820
DOI:10.1016/j.jnucmat.2020.152700