Date of Award

8-19-2024

Document Type

Open Access Thesis

Department

Computer Science and Engineering

First Advisor

Xinyu Huang

Abstract

The amount of hydrogen in a nuclear reactor can have a profound impact on its performance and safety when it is absorbed into or released from fuel rods. Hydrogen pickup in modern fuel cladding materials has been minimized by alloying additions and microstructural texture engineering, but these materials are still susceptible to hydrogen release during high temperature oxidation. The nuclear accident at the Fukushima Daiichi power plant in 2011 resulted in hydrogen gas production and subsequent explosions which led the United States Department of Energy to initiate a program to develop enhanced nuclear fuel cladding materials. New cladding materials include chromium (Cr) coatings applied to the outer surface of traditional zirconium-alloy fuel cladding.

The high temperature performance of Cr coated cladding has been extensively studied, but few studies have investigated the hydrogen pickup behavior. This work is targeted at answering three questions: (1) Does the Cr coating protect against hydrogen pickup compared to traditional uncoated zirconium-alloy cladding materials, or does the coating create a diffusion pathway for hydrogen to enter the cladding since it prevents the formation of a protective ZrO2 layer? (2) Does the coating microstructure influence hydrogen pickup? (3) How does the hydrogen pickup change in the presence of a localized through-coating scratch? (4) How does the hydrogen pickup change when samples are oxidized?

Hydrogen permeation studies were carried out for a variety of Cr coated cladding materials with different deposition methods (physical vapor deposition and cold spray), coating thicknesses (10-25 µm), and coating conditions (as-fabricated, scratched, and oxidized). Cladding materials were subjected to a pure hydrogen gas environment with varying initial hydrogen pressures, targeting two hydrogen concentrations of 100 and 300 ppm. Cr coated cladding greatly suppressed hydrogen uptake when compared to unoxidized zirconium-alloy cladding in all cases. In general, cladding with a thicker Cr layer reduced the amount of hydrogen ingress into the bulk zirconium matrix with all Cr coatings reducing hydrogen flux by 1-2 orders of magnitude and reducing the average hydrogen pickup fraction by up to 59%. Coatings with an expected denser microstructure showed lower hydrogen permeation when compared to other coatings. The hydrogen uptake slightly increased in defective coatings with a through-coating scratch but was still significantly lower when compared to uncoated and unoxidized cladding materials. Oxidized Cr samples proved to be the most effective barrier to hydrogen permeation.

Hydrogen pickup, mobility, and overall impact on cladding materials are highly complex phenomena. It will take many years of experimental studies, operational experience, materials characterization, and theoretical modeling to fully understand. The work here provides an initial but important start at understanding how evolutionary nuclear fuel cladding materials such as composite Cr coated zirconium alloys behave with the introduction of hydrogen. The results here are being used to support ongoing coating development efforts.

Rights

© 2024, Jorie Lyn Walters

Download

Share

COinS