Efficient Synthesis of Resilient Nuclear Waste Forms

The first chapter serves as an introduction to nuclear science. Nuclear weapons are briefly discussed, but more focus is given to the intricacies of fission and traditional nuclear reactors. In order to better understand nuclear waste, a comprehensive guide to radioactive decay is presented. During this section, there is an emphasis on how each decay mode interacts and affects matter. This is especially important for anyone handling radioactive material so that the related dangers and principles of shielding can be better understood. Additionally, a short introduction to nuclear waste is presented, leading into the focus of Chapter 2. The second chapter follows research into whether the complexation between radionuclides and methylene diphosphonic acid (MDPA) can serve as a reliable nuclear waste form. In this section, nuclear waste repositories are discussed in more detail. Some common ways to simulate radiation damage in materials is covered; however, almost all of this subsection focuses on doping experiments. Monazite is briefly discussed, due to its similarity with MDPA and its favorable properties for radiation stability. Additionally, hydrothermal techniques are described, as they are the primary synthesis technique used with this research. Over the span of 281 days, powder x-ray patterns were collected for the 239PuMDPA complex (t1/2: 24,110 yr) in order to track crystallinity and any phase transitions. During this period, no clear decline was seen in the crystallinity, indicating the complex’s durability over time in the presence of low-level alpha decay. The emergence and disappearance of intense x-ray diffraction peaks could indicate the formation of crystal defects and subsequent α-annealing. The stability of the crystals under extreme pressures was studied using a diamond anvil cell. Up to pressures of 4.48 GPa, the crystals remain completely stable, indicating that in a geologic repository, this waste form should remain stable due to the pressures present. Beyond 6.19 GPa, a phase transition within the crystal structure might occur. Future experiments using Raman spectroscopy should be performed to verify the presence of a phase transition. It was found that thermal annealing of the 239PuMDPA samples led to a loss of long-range order; however, the MDPA ligand remains undamaged. While the sample remains crystalline, its ability to immobilize radionuclides could be diminished.