Nuclear Waste
Nuclear waste refers to the fission products of a nuclear reactor.
The image below shows the possible products, coloured by the likelihood that they will be produced.

This graph shows the toxicity of nuclear waste (in Sievert/ton) as a function of time:

Implications
If the USA was powered entirely by nuclear energy, each person would be responsible for ~40g of nuclear waste per year.
- Compared to ~10,000 kg per year per person of CO₂ #Greenhouse Gas Emissions