A critical examination of the thermodynamics of water adsorption on actinide oxide surfaces

• Published in: Journal of nuclear materials 2003-10, Vol.322 (1), p.45-56
• Main Authors: Paffett, M.T, Kelly, Dan, Joyce, S.A, Morris, John, Veirs, Kirk
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Pollution; Radioactive wastes; Wastes
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/S0022-3115(03)00315-5

The reversible adsorption of water from actinide oxide surfaces is examined from several viewpoints in this article. A reinterpretation and critical look at the previously published thermodynamic values for desorption of water from PuO 2 [J. Phys. Chem. 77 (1973) 581] are reexamined in light of more recent mathematical treatments of thermal desorption data from high surface area materials. In addition, the time and temperature dependent process of water adsorption/desorption in closed system experiments is examined using chemical kinetics modeling. A simple experimental method and mathematical treatment of determining adsorption enthalpies based upon a closed system is also described. The desorption enthalpy for reversibly adsorbed water from PuO 2 is determined to be a function of adsorbate coverage with values ranging from 51 to 44 kJ mol −1 for coverages of one to several monolayers (MLs). Consistent desorption enthalpy values are obtained using either approach thus highlighting the importance of proper interpretation of adsorption parameters determined from high surface area powders. Reversible adsorption/desorption equilibrium of water with actinide oxide materials is discussed from the practical standpoint of storage and subsequent pressurization of containers. These results obtained from PuO 2 surfaces are consistent with desorption enthalpies of water from a low surface area UO 2 that has been measured using ultra-high vacuum thermal desorption mass spectroscopy to be 42.2 kJ mol −1.