title: Direct Measurement of Surface Dissolution Rates in Potential Nuclear Waste Forms: The Example of Pyrochlore.
abstract: The long-term stability of ceramic materials that are considered as potential nuclear waste forms is governed by heterogeneous surface reactivity. Thus, instead of a mean rate, the identification of one or more dominant contributors to the overall dissolution rate is the key to predict the stability of waste forms quantitatively. Direct surface measurements by vertical scanning interferometry (VSI) and their analysis via material flux maps and resulting dissolution rate spectra provide data about dominant rate contributors and their variability over time. Using pyrochlore (Nd2Zr2O7) pellet dissolution under acidic conditions as an example, we demonstrate the identification and quantification of dissolution rate contributors, based on VSI data and rate spectrum analysis. Heterogeneous surface alteration of pyrochlore varies by a factor of about 5 and additional material loss by chemo-mechanical grain pull-out within the uppermost grain layer. We identified four different rate contributors that are responsible for the observed dissolution rate range of single grains. Our new concept offers the opportunity to increase our mechanistic understanding and to predict quantitatively the alteration of ceramic waste forms.
authors.affiliation: ‡Earth Science Department, Rice University, 6100 Main Street, Houston, Texas 77005, United States.
authors.forename: Cornelius
authors.initials: C
authors.lastname: Fischer
authors.affiliation: §Institute of Energy and Climate Research, Nuclear Waste Management and Reactor Safety (IEK-6), Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Sarah
authors.initials: S
authors.lastname: Finkeldei
authors.affiliation: §Institute of Energy and Climate Research, Nuclear Waste Management and Reactor Safety (IEK-6), Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Brandt
authors.affiliation: §Institute of Energy and Climate Research, Nuclear Waste Management and Reactor Safety (IEK-6), Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Bosbach
authors.affiliation: ‡Earth Science Department, Rice University, 6100 Main Street, Houston, Texas 77005, United States.
authors.forename: Andreas
authors.initials: A
authors.lastname: Luttge
keywords: dissolution rates; nuclear waste management; pyrochlore; rate spectra; rate variability; reactive surface portions; vertical scanning interferometry; zirconates