Laventine, D. and Boxall, C. and Chombakkadath, M. and Orr, R. and Taylor, R. (2019) Analysis of water absorption onto ceria and thoria thin films by direst mass and contact angle measurements : 14th International Nuclear Fuel Cycle Conference, GLOBAL 2019 and Light Water Reactor Fuel Performance Conference, TOP FUEL 2019. In: 14th International Nuclear Fuel Cycle Conference, GLOBAL 2019 and Light Water Reactor Fuel Performance Conference, TOP FUEL 2019, 2019-09-22 - 2019-09-26, The Westin Seattle.
Full text not available from this repository.Abstract
Plutonium oxide (PuO2) is one of the most highly radioactive products of the nuclear fuel cycle and its storage poses particular challenges due to the high temperatures produced by its decay and the production of gases from, inter alia, surface adsorbed water entrained with the PuO2 during the packaging process. Its high radiotoxicity necessitates the use of actinide oxides in similar oxidation states, such as CeO2 and ThO2, as model systems to allow the comprehensive study of its interaction with water under storage conditions. We have developed a method which enables direct gravimetric measurement of the adsorption of microgram amounts of water onto CeO2 and ThO2 thin films, also with masses in the microgram range. Additionally sessile contact angles of water droplets deposited onto the same films have been measured to provide a correlating measure of the affinity of the oxide surface with water. Porous CeO2 and ThO2 films were deposited from a surfactant based precursor solution onto thin GaPO4 crystal and glass substrates. The absorption of water onto the CeO2 or ThO2 coating at different relative humidities was then studied in a closed reactor using crystal nanobalance gravimetry, wherein changes in crystal resonant frequency due to absorbed mass are directly and linearly related to mass changes occurring at the crystal surface. Using this method, we have determined the enthalpy of absorption of water onto CeO2 to be 49.7 kJmol-1 and onto ThO2 to be 54.6 kJmol-1 at 75°C, 11 and 15 kJmol-1 greater than the enthalpy of evaporation. Sessile contact angle measurements on the same films provide values for CeO2 and ThO2 of 56° and 27° respectively - indicating that water shows a greater affinity for the ThO2 surface than CeO2, an observation consistent with the hierarchy of water adsorption enthalpies derived here These enthalpies are within the range predicted for the reversible absorption of water onto PuO2, confirming this method allows for the investigation of water absorption onto plutonia using microgram samples. The significantly higher enthalpy of water absorption for thoria over ceria, and the correspondingly smaller water droplet contact angles indicates a high variation in water-absorbing properties of commonly used plutonia analogues, further emphasizing the need for studies on active PuO2 samples. Copyright © GLOBAL 2019 - International Nuclear Fuel Cycle Conference and TOP FUEL 2019 - Light Water Reactor Fuel Performance Conference.All rights reserved.