For example, one tonne of spent fuel has a thermal output of 1,300 W at the time of geological disposal.While some isotopes decay quickly, the amount of time some high-level waste remains dangerous is measured in thousands to hundreds of thousands of years Nuclear waste is usually split into low, intermediate and high level waste (LLW, ILW and HLW respectively).The main issue with the disposal of nuclear waste is its longevity.The diagram to the left shows the amount of time taken for HLW and spent fuel to decay to below the radioactivity of naturally occurring uranium ore (data for HLW here, for spent fuel here).
According to the IAEA, in 2008 there was almost 360,000 m of long-lived low and intermediate level waste (LILW) in storage waiting to be disposed of around the world.
While HLW is the most dangerous and the main candidate for geological disposal, some ILW can also be long-lived.
Short-lived intermediate and low level waste is often stored in surface facilities; the low level of the radiation and the short halflives mean that it is less dangerous.
Its radioactivity presents a danger to humans and other living beings, and therefore must be isolated from the biosphere until it decays to a safe activity level.
It includes spent fuel, along with any other material that has become radioactive, such as reactor parts.As well as being radioactive, it also produces large amounts of heat.