Thermal Treatment of Fuel Residues and Problematic Nuclear Wastes

Problematic nuclear wastes and fuel residues plague the nuclear industry worldwide. In this
Thesis thermal treatment is demonstrated through the development of various simulated
nuclear wasteforms and surrogate materials from a variety of nuclear waste topics.
Development of vitreous wasteforms for the treatment of intermediate level Magnox sludge
from the Storage Ponds at Sellafield is discussed in this Thesis with both low activity uranium
and surrogate materials. Magnesium borosilicate glasses were found to have comparable
durability with current UK high level waste (HLW) glass whilst incorporating the whole
spectrum of waste anticipated into a single composition. Highly metallic feeds could be
incorporated into the wasteform with no adverse effects on the dissolution of such samples. If
implemented, this composition could result in a 25% volume reduction in waste to be disposed
saving approximately £82 million compared to the current baseline plan.
Ascertaining the long-term integrity and safety of fuel residues arising from nuclear
meltdowns, such as the Chernobyl and Fukushima accidents, through thermal synthesis of low
activity simulants is explored in this Thesis. Two simulant Chernobyl ‘lava-like’ fuel
containing materials (LFCM) were developed recreating the typical morphology and
microstructure found in real samples, including a World first to successfully document
formation of Chernobylite from a glass melt whilst aqueous durability was analogous to that
of UK borosilicate HLW glass.
Investigating how thermal treatment of americium waste built-up in stockpiles of civil
plutonium is outlined in this Thesis. A novel cerium niobite, a simulant for americium, was
synthesised with the crystal structure and suitability as a wasteform assessed. One potential use
for an americium ceramic could be as a power source in a radioisotope thermoelectric generator
(RTG); however it was determined an Am structured niobite for this application would be
unsuitable, due to the phase transformation this material exhibited at elevated temperatures.
This work opens avenues for further research on other potential materials.