Applying laboratory methods for durability assessment of vitrified material to archaeological samples

Laboratory testing used to assess the long-term chemical durability of nuclear waste forms may not be applicable to disposal because the accelerated conditions may not represent disposal conditions. To address this, we examine the corrosion of vitrified archeological materials excavated from the near surface of a ~1500-year old Iron Age Swedish hillfort, Broborg, as an analog for the disposal of vitrified nuclear waste. We compare characterized site samples with corrosion characteristics generated by standard laboratory durability test methods including the product consistency test (PCT), the vapor hydration test (VHT), and the EPA Method 1313 test. Results show that the surficial layer of the Broborg samples resulting from VHT displays some similarities to the morphology of the surficial layer formed over longer timescales in the environment. This work provides improved understanding of long-term glass corrosion behavior in terms of the thickness, morphology, and chemistry of the surficial features that are formed.

Ab Initio Investigation of Helium Mobility in La2Zr2O7 Pyrochlore

The α-decay of incorporated actinides continuously produces helium, resulting in helium accumulation and causing security concerns for nuclear waste forms. The helium mobility is a key issue affecting the accumulation and kinetics of helium. The energy barriers and migration pathways of helium in a potential high-level nuclear waste forms, La2Zr2O7 pyrochlore, have been investigated in this work using the climbing image nudged elastic band method with density functional theory. The minimum energy pathway for helium to migrate in La2Zr2O7 is identified as via La–La interstitial sites with a barrier of 0.46 eV. This work may offer a theoretical foundation for further prospective studies of nuclear waste forms.

Rapid Synthesis and Chemical Durability of Gd2- x Nd x Zr2O7 (0.0 ≤ x ≤ 2.0) Sub-Micron Ceramics as Nuclear Waste Forms

In this work, Nd3+ was used as a surrogate and it was incorporated into Gd2Zr2O7 nanocrystalline ceramics to simulate the immobilization of trivalent actinide elements. A series of Gd2 − xNdxZr2O7 (0.0 ≤ x ≤ 2.0) nanocrystalline powders were fabricated by solvothermal method, and then Gd2 − xNdxZr2O7 sub-microncrystalline ceramics were prepared by sintering via self-propagating chemical furnace plus quick pressing (SCF/QP). All powders are in defective fluorite structure, and Nd doping hardly change the powder grain size. After analyzing the sintered ceramics, it can be found that the transition from defective fluorite structure to pyrochlore structure occurs when x ≥ 1.5. The sample density decreases with elevated Nd content, while the grain size gradually enlarges. Besides, the normalized release rates of Nd and Zr elements in the Nd2Zr2O7 waste form are kept in low values (below 10− 5 g•m− 2•d− 1), which exhibits its excellent aqueous stability.