Countries in the second group will have, in addition to disused sealed sources and NORM, three main types of radioactive waste: (a) resulting from the operation of nuclear power plants; (b) produced during decommissioning; and (c) spent fuel or, in those cases where fuel is sent away for reprocessing, vitrified fission products.

The first type, NPP operational waste, typically consists of low-level waste (LLW) and short-lived intermediate-level waste (ILW-SL). LLW mostly consists of contaminated items such as discarded items of plant, clothing and paper. Short­lived ILW mostly arises from operations to clean up and recycle process water. These produce spent ion-exchange resins and (especially in former Soviet countries) evaporator concentrate (also known as evaporator bottoms or salt cake). LLW and ILW-SL are often grouped together under a single heading designated by the acronym LILW.

Radioactive decommissioning wastes fall into two categories: contaminated items and activated metals. The former typically consists of cooling circuit components, such as steam generators and pipework that have not been exposed to a neutron flux. Where the geometry is sufficiently simple, it may be possible to decontaminate these components so that the materials may be released for recycling. Activated metals mostly occur in the reactor pressure vessel and its contents where neutrons have been captured by stable isotopes of metals such as iron, nickel and cobalt to produce radioactive species. In terms of activity, the activated wastes constitute by far the greater part of the total.

Depending on national policy, spent fuel may be considered to be either a waste or a resource. In the first case, the fuel elements themselves will be disposed; this is known as ‘direct disposal’ and is followed, for example, in Sweden, Finland and the USA. If spent nuclear fuel is thought of as a resource (as it has been in Belgium and the Netherlands) then it will probably be sent abroad for reprocessing. The recovered uranium and plutonium may be returned as mixed oxide (MOX) fuel while the waste products are packaged as vitrified fission products. Both spent nuclear fuel and vitrified wastes generate significant quantities of heat. One of the advantages of reprocessing spent fuel is the considerable reduction in the volume of waste, albeit with a corresponding increase in specific activity and hence, heat output. Because most of the platonium has actinides have been removed, vitrified waste decays more rapidly — in terms of both heat output and radiotoxicity — than spent fuel and this is a significant benefit to the long term safety case.