Vitrification is a process of converting a material into a glass-like amorphous solid which is free of any crystalline structure, either by the quick removal or addition of heat or by mixing with an additive. In this photo, nuclear waste has been combined with glass-forming materials, vitrified, and is being poured into a container, after which it will be sealed. The final waste form resembles obsidian and is a non-leaching, durable material that effectively traps the waste inside. The waste can be stored for relatively long periods in this form without concern for air or groundwater contamination.Photo credit: Pacific Northwest National Laboratory