Robert D. Mariani

Ab initio molecular dynamics study of the properties of cerium in liquid sodium at 1000 K temperature

For liquid-sodium-cooled fast nuclear reactor systems, it is crucial to understand the behavior of lanthanides and other potential fission products in liquid sodium or other liquid metal solutions such as liquid cesium-sodium. In this study, we focus on lanthanide behavior in liquid sodium. Using ab initio molecular dynamics, we found that the solubility of cerium in liquid sodium at 1000u2009K was less than 0.78 at. %, and the diffusion coefficient of cerium in liquid sodium was calculated to be 5.57u2009×u200910−9 m2/s. Furthermore, it was found that cerium in small amounts may significantly alter the heat capacity of the liquid sodium system. Our results are consistent with the experimental results for similar materials under similar conditions.

An Electromotive Force Measurement System for Alloy Fuels

The development of advanced nuclear fuels requires a better understanding of the transmutation and micro-structural evolution of the materials. Alloy fuels have the advantage of high thermal conductivity and improved characteristics in fuel-cladding chemical reaction. However, information on thermodynamic and thermophysical properties is limited. The objective of this project is to design and build an experimental system to measure the thermodynamic properties of solid materials from which the understanding of their phase change can be determined. The apparatus was used to measure the electromotive force (EMF) of several materials in order to calibrate and test the system. The EMF of chromel was measured from 100°C to 800°C and compared with theoretical values. Additionally, the EMF measurement of Ni-Fe alloy was performed and compared with the Ni-Fe phase diagram. The prototype system is to be modified eventually and used in a radioactive hot-cell in the future.Copyright

Investigation of Tin as a Fuel Additive to Control FCCI

One method to control fuel-cladding chemical interaction (FCCI) in metallic fuel is through the use of an additive that inhibits FCCI. A primary cause of FCCI is the lanthanide fission products moving to the fuel periphery and interacting with the cladding. This interaction will lead to wastage of the cladding and eventually to a cladding breach. Tin is being investigated as a potential additive to control FCCI by reacting with the fission product lanthanides. The current study is a scanning electron microscopy (SEM) characterization of a diffusion couple between U-10Zr-4.3Sn (wt%) and the 4 most abundant lanthanide fission products. As the lanthanides move into the fuel, they are interacting with and breaking down the Zr5Sn3 precipitates that formed during fresh fuel fabrication. This reaction produced Ln-Sn precipitates and δ phase (UZr2), which is conducive to normal fuel operation and increased burnups.

Development of Self-Healing Zirconium-Silicide Coatings for Improved Performance Zirconium-Alloy Fuel Cladding

Article history: Received 21 December 2016 Revised 19 February 2017 Accepted in revised form 6 March 2017 Available online 07 March 2017 The air oxidation behavior of zirconium-silicide coatings for three stoichiometries, namely, Zr2Si, ZrSi, and ZrSi2, at 700 °C has been investigated. These three coatingswere deposited on a zirconium-alloy substrate using amagnetron sputter process at a low temperature. Argon gas pressure was observed to have a profound effect on the coating microstructure, with lower pressures favoring a denser and more protective microstructure. Coatings of ZrSi2 stoichiometry clearly showed superior oxidation resistance presumably due to the formation of a thin protective oxide layer, consisting of nanocrystalline SiO2 and ZrSiO4 in amorphous Zr-Si-O matrix. The thermal stability of the coatings was evaluated by annealing in an argon environment, and this also assisted in eliciting the effects of oxidation-induced inward Si migration. Thicker coatings of ZrSi2 were prepared and evaluated for oxidation resistance at 700 °C for longer exposure times, aswell as at 1000 °C and 1200 °C. Once again the thin oxide layer provided for significant oxidation resistance. Pre-oxidizing the samples at 700 °C prior to 1000 °C and 1200 °C oxidation tests substantially reduced the extent of oxidation. Insights into the fundamental mechanisms of the oxidation behavior of zirconium-silicide coatings were obtained using a combination of scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. One potential application of these coatings is to enhance the oxidation resistance of zirconium-alloy fuel cladding in light water reactors under normal and accident conditions.

Behaviors of Ce, Pr, and Nd in liquid cesium by ab initio molecular dynamics simulations

The fuel cladding chemical interaction (FCCI) phenomenon is potentially the main factor restricting the application of metallic fuels in liquid sodium cooled fast reactors. The understanding of the lanthanide (Ln) transport behaviors in liquid Cs filled pores in U-Zr fuel is essential for understanding FCCIs. By using ab initio molecular dynamics, fundamental properties of the metallic system Cs-Ln, such as density of states and coordination number, have been studied. Then, the Ln diffusivities in liquid cesium and the solution viscosity were calculated. For validating the model, the viscosity of the pure liquid Cs which has been well measured is also calculated at three temperatures, which indicates the present model has a high accuracy in calculation of viscosity and self-diffusivity of Cs in liquid Cs.The fuel cladding chemical interaction (FCCI) phenomenon is potentially the main factor restricting the application of metallic fuels in liquid sodium cooled fast reactors. The understanding of the lanthanide (Ln) transport behaviors in liquid Cs filled pores in U-Zr fuel is essential for understanding FCCIs. By using ab initio molecular dynamics, fundamental properties of the metallic system Cs-Ln, such as density of states and coordination number, have been studied. Then, the Ln diffusivities in liquid cesium and the solution viscosity were calculated. For validating the model, the viscosity of the pure liquid Cs which has been well measured is also calculated at three temperatures, which indicates the present model has a high accuracy in calculation of viscosity and self-diffusivity of Cs in liquid Cs.