Aerosol Physics Considerations for Using Cerium Oxide CeO₂ as a Surrogate for Plutonium Oxide PuO₂ in Airborne Release Fraction Measurements for Storage Container Investigations

Abstract

Cerium oxide (CeO2) dust is recommended as a surrogate for plutonium oxide (PuO2) in airborne release fraction experiments. The total range of applicable particle sizes for PuO2 extends from 0.0032 µm (the diameter of a single PuO2 molecule) to 10 µm (the defined upper boundary for respirable particles). For particulates with a physical particle diameter of 1.0 µm, the corresponding aerodynamic diameters for CeO2 and PuO2 are 2.7 µm and 3.4 µm, respectively. Cascade impactor air samplers are capable of measuring the size distributions of CeO2 or PuO2 particulates. In this document, the aerodynamic diameters for CeO2 and PuO2 were calculated for seven different physical diameters (0.0032, 0.02, 0.11, 0.27, 1.0, 3.2, and 10 µm). For cascade impactor measurements, CeO2 and PuO2 particulates with the same physical diameter would be collected onto the same or adjacent collection substrates. The difference between the aerodynamic diameter of CeO2 and PuO2 particles (that have the same physical diameter) is 39% of the resolution of a twelve-stage MSP Inc. 125 cascade impactor, and 34% for an eight-stage Andersen impactor. An approach is given to calculate the committed effective dose (CED) coefficient for PuO2 aerosol particles, compared to a corresponding aerodynamic diameter of CeO2 particles. With this approach, use of CeO2 as a surrogate for PuO2 material would follow a direct conversion based on a molar equivalent. In addition to the analytical information developed for this document, several US national labs have published articles about the use of CeO2 as a PuO2 surrogate. Different physical and chemical aspects were considered by these investigators, including thermal properties, ceramic formulations, cold pressing, sintering, molecular reactions, and mass loss in high temperature gas flows. All of those US national lab studies recommended the use of CeO2 as a surrogate material for PuO2. Definitions Activity Median Aerodynamic Diameter (AMAD) ICRP Definition-Fifty per cent of the activity in the aerosol is associated with particles of aerodynamic diameter greater than the AMAD. Aerodynamic Diameter-The diameter of a hypothetical (spherical) particle of unit density (1.0 g/cc) that has the same (terminal) settling velocity as the particle under consideration.

Organophosphorus-Modified Lanthanide Nitrates as Potential Actinide Oxide Aerosol Surrogates

“…Two samples ( Tb and Ho ) had both the easily interconverted metaphosphate and phosphate phases present, which was surprising based on the fact that the literature on potential PUREX aerosol efforts has focused on metal oxide behavior. In particular, cerium oxide (CeO 2 ) is often sprinkled over paper “trash” to mimic contaminated waste . Traditional efforts have merely focused characterizing the percent of transferred metal; , however, this may be an erroneous approach due to the actual formation of phosphates from the PUREX route.…”

Thermal and mechanical properties of CeO2

“…Many recent examples exist to demonstrate such efforts to characterize PuO 2 and mixed actinide oxides such as (U,Pu)O 2 . Cerium dioxide has historically been considered as a surrogate due primarily to its 3+ and 4+ valence states, which match the readily accessible oxidation states of Pu . Assessment of material properties using Ce rather than Pu relieves the operational constraints inherent to work with transuranic elements.…”

Defect equilibria and thermophysical properties of CeO2‐x based on experimental data and density functional theory calculation result

“…1 In research and development for advanced nuclear fuels, cerium oxide has been used as a surrogate material for PuO 2 in various experiments because both materials have very similar mechanical and thermal physical properties. [2][3][4][5] Both oxides of CeO 2 and PuO 2 have a fluorite crystal structure and are nonstoichiometric compounds that are stable over the hypo-stoichiometric composition range. In addition, chemical, thermal and mechanical properties are very similar in both materials.…”