In nuclear reactors a number of radioactive waste products are produced as the fuel is used up. Prominent among them are plutonium, strontium, cesium and barium which are produced by fission of uranium and neutron irradiation.
There are two types of nuclear wastes — high-level waste which will be radioactive for thousands of years and low-level waste which is less radioactive. When the fuel elements are first removed from the reactor, they are allowed to cool long enough for the radioactivity of the fission products to decay to acceptable levels, a process usually involving their immersion in water for a month or so. The waste is then sent to nuclear reprocessing plants where useful uranium and plutonium are separated for reuse.
Some low-level waste is pumped straight into the sea. High level waste is sealed in concrete and steel tanks and stored deep underground. High level waste is also now being converted to glass. This involves dissolving the spent fuel in acid, converting it into a glassy form, enclosing it in metal containers, and burying it underground. But scientists have not yet found out how to make the rubbish completely safe.
