Synergistic Irradiation, Corrosion, and Microstructural Evolution in Nuclear Materials: On-Demand Oral Presentations
Sponsored by: TMS Structural Materials Division, TMS: Nuclear Materials Committee
Program Organizers: Djamel Kaoumi, North Carolina State University; Michael Short, Massachusetts Institute of Technology; Peter Hosemann, University of California, Berkeley; Stephen Raiman, University of Michigan; Raluca Scarlat, University of California, Berkeley; Aaron Kohnert, Los Alamos National Laboratory; Ryan Schoell, Sandia National Laboratory; Philip Edmondson, The University of Manchester; Celine Cabet, Commissariat a l'Energie Atomique

Monday 8:00 AM
March 14, 2022
Room: Nuclear Materials
Location: On-Demand Room

Radiation Stability of Nanostructured Ytrium Stabilized Zirconia: Santanu Ghosh1; 1IIT Delhi
     For a systematic understanding of the dependence of radiation tolerance on specific energy loss, yttria stabilized zirconia (YSZ) with different grain sizes (tens of nano-meters to few microns) were irradiated under different conditions (single beam irradiation with high energy (Se>>Sn) ions at 300 K and 1000 K, single beam irradiation with low energy (Sn>>Se) ions at 300 K & simultaneous dual beam irradiation with high and low energy ions at 300 K). The low and high energy ions were chosen to mimic the damage produced by alpha recoils and fission fragments respectively, and thus the irradiations at 1000 K and the dual beam irradiations helped to better simulate typical nuclear reactor environment. The damage for all grain sizes was found to be reduced at 1000 K. This damage reduction was significantly more for the nano-crystalline samples. Results are explained in the framework of thermal spike model.

Ni Oxidation by CO2 and Its Impact on D2 Ingress: A Nanoscale Study by In-Situ Atom Probe Tomography: Sten Lambeets1; Elizabeth Kautz1; Karen Kruska1; David Senor1; Daniel Perea1; Arun Devaraj1; 1Pacific Northwest National Laboratory
    Tritium production depends on the proper functioning of the dedicated Tritium-Producing Burnable Absorber Rods (TPBARs) which are sensitive to degradation. Under the operating conditions, the zirconium alloy (zircaloy) getter acts to absorb and store tritium. However, zircaloy is susceptible to contamination. Contaminants, such as CO2, can promote unwanted oxidation. Hence, the zircaloy is protected with a Ni coating that prevents oxygen atoms migration while remaining open to tritium diffusion. Oxidation of the Ni coating may lead to structural and chemical changes that compromise tritium diffusion. Using an in-situ atom probe tomography (APT) approach, we track composition evolution of Ni when exposed to 50mbar of deuterium (as tritium surrogate) and CO2 at 350oC. Data reveal how CO2 dissociative adsorption leads to Ni oxide layer formation, but also how the simultaneous presence of CO2+D2 may prevent the oxide formation but lead to a carbon-rich layer formation. Both layers negatively impact deuterium diffusion.

Quantifying Radiation Enhanced Diffusion in Model Oxides with Isotopic Tracers and Atom Probe Tomography: Kayla Yano1; Aaron Kohnert2; Tiffany Kaspar1; Sandra Taylor1; Steven Spurgeon1; Hyosim Kim2; Yongqiang Wang2; Blas Uberuaga2; Daniel Schreiber1; 1Pacific Northwest National Laboratory; 2Los Alamos National Laboratory
    Corrosive degradation of structural alloys in reactors is mitigated by thin protective oxide layers that separate the metal from a corrosive media. Irradiation can dramatically affect this protectiveness by generating a non-equilibrium point defect population that fundamentally alters atomistic transport through the irradiated oxide. However the direct impact of irradiation on ion transport is as yet broadly unexplored. In this work embedded isotopic tracers (18O and 57Fe) are used to monitor and quantify atomic transport in model irradiated oxide systems with atom probe tomography. Combining these observations with a chemical-rate theory model provides insights on fundamental transport mechanisms and rates. These results show orders of magnitude increases in anion diffusivity in both proton irradiated hematite and argon irradiated chromia. Preliminary work on Fe cation diffusion, transport across oxide heterolayers, and transport upon phase transformations will also be discussed.

Defects and Disorder in Swift Heavy Ion-irradiated, Fluorite-derived Complex Oxides: Devon Drey1; Eric O'Quinn1; Will Cureton1; Igor Gussev1; Maik Lang1; 1University of Tennessee at Knoxville
    Oxides that adopt the fluorite structure constitute an important class of materials in nuclear systems, in which they are subject to extreme conditions such as high temperatures, corrosive fluids, and highly ionizing radiation. Fluorite-derived oxide ceramics are used as nuclear fuels (UO2), corrosion resistant coatings (Ln-doped ZrO2), and geological nuclear wasteforms (Ln2(Zr,Ti)2O7 pyrochlore). Despite their structural simplicity, fluorite-derived oxides can accommodate atomic disorder without losing crystallinity. A thorough understanding of the defect morphology in fluorite-derived oxides is necessary for their use in next generation nuclear systems. By combining state-of-the-art swift heavy ion irradiation with advanced neutron and X-ray scattering techniques we show that defect formation in these materials is decidedly complex. The local structure of highly disordered and radiation amorphized pyrochlore is very similar despite having different long-range structures. Furthermore, radiation resistance in these materials is dependent on the structural length scale being investigated and the level of pre-existing disorder.

Effect of Phosphorus (P) on Precipitation and Segregation Behavior in Neutron Irradiated Reactor Pressure Vessel Steels: Mukesh Bachhav1; Emmanuelle Marquis2; Anshul Kamboj2; Megha Dubey3; G. Robert Odette4; 1Idaho National Laboratory; 2University of Michigan; 3Boise State University; 4University of California
    RPV steels undergo embrittlement which may limit pressure vessel lifetimes. In low Cu steels embrittlement is linked to the formation and growth of nanoscale Mn-Ni-Si (MNS) precipitates with increasing fluence. The effects of Cu, Ni. Mn and Si concentration on the MNS precipitation is well studied and models are available to predict the corresponding embrittlement over extended plant lifetimes. However, there is very limited understanding on the effect of P on the MNS precipitation. In this work, we studied the individual and synergic effect of P, Cu and Ni on the MNS precipitation. Seven RPV steels with systematic variations in Cu, Ni, and P contents were neutron irradiated to a fluence of 1.4 x 10^20 n/cm2 at 290C in the UCSB ATR-2 experiment. Atom probe tomography (APT) revealed the role of P in the nucleation of MNS precipitates.