Session: 17-05-01: Steam Turbine Generators & Auxiliaries

Paper Number: 173512

Radiolytic Hydrogen Generation From Aluminum-Clad Spent Nuclear Fuel: Insights From Molecular Dynamics Simulations 

The production of potentially flammable gases through radiolysis in the oxyhydroxide layer of aluminum cladding is a significant issue in the long-term storage of spent nuclear fuel. Aluminum-clad SNF is extensively used in research reactors due to its favorable properties, such as high thermal conductivity and strong resistance to corrosion. Once removed from the reactor, this fuel is typically stored underwater, where it undergoes corrosion over time. This corrosion leads to the formation of an oxyhydroxide layer on the aluminum surface, which retains water. A certain amount of residual water persists even after vacuum drying or forced helium dehydration. When exposed to gamma radiation emitted by the ASNF during dry storage, the water within this layer can undergo radiolysis, resulting in the generation of hydrogen gas. This hydrogen production is of particular concern because it can accumulate within sealed storage canisters, potentially increasing internal pressure and posing safety hazards, such as flammability and structural stress. Therefore, understanding the mechanisms and rates of hydrogen generation is essential for improving the safety and reliability of nuclear fuel storage systems. This research focuses on predicting the quantities of hydrogen and oxygen produced due to gamma radiation interacting with the oxyhydroxide layer, using molecular dynamics (MD) simulations to capture the system’s reactive behavior at the atomic level.

In this study, aluminum 6061 alloy is used to model the cladding material. This alloy is composed of approximately 98.4% aluminum, 1% magnesium, and 0.6% silicon. The oxyhydroxide layer is represented by gibbsite (Al(OH)₃), a compound with a layered structure consisting of octahedral sheets of aluminum hydroxide, modeled in the presence of water. Simulating gamma radiation in MD involves translating the energy deposited by gamma-ray interactions into atomic-scale events. Specifically, gamma rays generate energetic electrons, which then transfer energy to atoms in the material, displacing them from their lattice positions and creating what are known as Primary Knock-on Atoms. In the simulation, this is achieved by imparting high kinetic energy to selected atoms, mimicking the recoil effect caused by electron collisions.

The study explores how variations in the thickness of both the aluminum 6061 and gibbsite layers, as well as changes in radiation dose, influence the production of hydrogen and oxygen. While experimental studies have been conducted in this area, computational investigations at the molecular level remain limited. The outcomes of this research are expected to enhance our understanding of radiolytic gas generation and contribute to the development of safer, more radiation-resistant materials for nuclear fuel storage. Detailed findings will be presented in the upcoming technical session.

Presenting Author: Sheikh Ferdous Penn State Harrisburg

Presenting Author Biography: Dr. Ferdous is currently working as an Assistant Professor in mechanical engineering at Penn State Harrisburg. Before joining Penn State Harrisburg, he was an Assistant Professor at Indiana State University. Dr. Ferdous has over a decade of computational experience using molecular dynamics simulations to study the mechanics of various materials, including ceramic composites, metals, biomaterials, and polymer composites. His teaching interests include capstone design, mechanics of materials, machine design, materials science, kinematics, and engineering economics. The core theme of Dr. Ferdous’s research is the development of multiscale computational models to understand the mechanical performance of advanced structural and biological materials.

Authors:

Sheikh Ferdous Penn State Harrisburg
Donna Guillen Idaho National Laboratory