REDUCTIVE VERSUS OXIDATIVE ALTERATION OF URANIUM(IV) DIOXIDE, PATHWAYS AND IMPLICATIONS FOR SPENT NUCLEAR FUEL ALTERATION

Alteration pathways of uranium(IV) dioxide are key to understanding the fate of spent nuclear fuel in disposal conditions

Depending on the prevailing redox environment, UO₂(s) alteration may proceed via oxidative or reductive dissolution.

In the past a substantial effort was placed to unravel the mechanisms and alteration products resulting from the oxidative alteration of spent nuclear fuel. This was particularly relevant for the Yucca Mountain repository situation but also in the case that the radiolytic production of oxidants dominated the dynamic redox balance at the spent fuel surface. The information collected was the result of dedicated laboratory experiments but also of substantial natural analogue information on the alteration pathways of natural uraninite[1].

Recently, the paradigm for the redox environmental conditions of spent nuclear fuel disposal has shifted towards the prevalence of reducing conditions, mainly due to the imposition of a high partial pressure of hydrogen by the anaerobic corrosion of the steel containers. The long-term stability of uranium dioxide under these conditions has been discussed in the light of the evidences from the Cigar Lake uranium ore deposit[2].

These has clear implications for the potential alteration pathways of UO₂under reducing conditions and recent work has brought the attention towards coffinite as a potential alteration product under reducing conditions[3]. In addition, recrystallization of the uranium(IV) dioxide matrix could have implications for radionuclide containment within the spent fuel matrix.

The presentation will attempt to put into perspective the implications for the diverse alteration pathways of the uranium dioxide matrix depending on the redox conditions and the consequences for spent nuclear fuel disposal.

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[1] Spent nuclear fuel

J Bruno, RC Ewing - Elements, 2006

[2] The long-term effect of hydrogen on the UO₂ spent fuel stability. Findings from the Cigar Lake Natural Analogue Study-Applied Geochemistry 2014, 49, 178

[3] Thermodynamics of formation of coffinite. X. Guo and 12 coworkers. www.pnas.org/cgi/doi/10.1073/pnas.1507441112

Session No. 16

T134. Radiation Effects, Mineralogy, and Materials Science of Actinides I: In Honor of Rodney C. Ewing, 2015 Roebling Medalist

Sunday, 1 November 2015: 8:00 AM-12:00 PM

Room 317 (Baltimore Convention Center)

Geological Society of America Abstracts with Programs. Vol. 47, No. 7, p.58

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