Incinerators burn waste at high temperatures.  The main purpose of incinerating radioactive waste is to reduce waste volume, since a large proportion consists of bulky organic items such as contaminated paper, clothes, timber, and plastic.

This organic waste is burnt resulting in most of the original volume breaking down into a gas and the residual material turning into ash.  The gas is treated and filtered before being released to atmosphere.  The ash is then sent for disposal.  Burning can result in a volume reduction factor of greater than 100 but is normally between 30 and 70.

The off-gas will contain small particles of ash that need to be trapped – typically in bag filters.  This secondary waste is called “fly ash” and will need to also be treated prior to disposal.