Residue and waste management during decommissioning

Radioactive residues as well as dismantled radioactive plant components will accumulate during the decommissioning of nuclear facilities. According to Section 9a of the Atomic Energy Act, these must either be safely recycled (for example by clearance or reuse in another facility licensed under nuclear or radiation protection law) or disposed of in an orderly manner as radioactive waste. Only a few percent of the total mass of the controlled area of a nuclear power plant must be disposed of as radioactive waste.

Clearance

Clearance is an administrative act effecting the release of radioactive substances from nuclear supervision. It is regulated by the Radiation Protection Ordinance. Clearance ensures that the effective dose that might occur for individuals would only be in the range of 0.01 millisievert (10 microsievert) per year. This is a very small additional exposure compared to natural radiation exposure in Germany (2.1 millisieverts per year on average).

Measuring facility used for clearance of batches of residual material from the decommissioning of the Greifswald nuclear power plant (KGR). Source: EWN GmbH

Unrestricted clearance

In the case of unrestricted clearance, the relevant authority will conduct the necessary administrative steps to release the residual substances from nuclear regulatory supervision, so that they can then be reused, recycled or disposed of as ordinary waste without any restrictions.

Materials are only awarded unrestricted clearance if measurements show that they do not exceed the clearance threshold for unrestricted clearance as laid down in the Radiation Protection Ordinance. This means their release shall not cause individual members of the population to be exposed to an effective annual radiation dose of more than 0.01 millisievert..

Specified clearance

Specified clearance applies when the future use, recovery or disposal of the released substances is restricted (e.g. in the case of a specific clearance of scrap metal for recycling by melting down or a maximum quantity for delivery to a landfill).

Disposal as radioactive waste

Materials which can neither be recycled nor cleared must be disposed of as radioactive waste. An estimated 5,000 cubic metres of conditioned decommissioning waste is created by the decommissioning of a single nuclear power plant. Decommissioning waste is waste with negligible heat generation. The waste must be stored at an interim storage facility until the Konrad repository for low- and intermediate-level radioactive waste becomes available.

Before the radioactive waste is delivered to an interim or final storage facility, it must be treated (conditioned), packaged and labelled accordingly. The general aim of waste treatment is to reduce the volume of waste and to bring the waste into a defined (i.e. conditioned) state. Solid waste, for example, is compacted in order to reduce the volume of waste. Combustible waste is sent for incineration, which leads to a reduction in the volume of raw waste to ash volume by a factor of up to 50. Liquid waste is converted into solid products, for example through drying/evaporation or cementation.

Statutory transport regulations must be observed when transporting conditioned waste to an interim storage facility. An essential requirement is that only specially authorised transport containers or tested packaging may be used for the transport of all radioactive materials.

Reactor pressure vessel from Rheinsberg nuclear power plant: consignment in interim storage facility north (Zwischenlager Nord - ZLN). Source: EWN GmbH

Decay or cooling storage

In the case of decay storage, materials are stored for longer periods of time. The process of radioactive decay means that the activity of these materials gradually decreases.

Decay storage is used for dismantled scrap metal, for instance, as well as for large components such as reactor pressure vessels or steam generators. The decay of the activity of these (large) components means that:

• easier handling and treatment of the waste at a later point in time, and
• if necessary, disposal by release is more likely to be successful.

Decay storage thus offers an opportunity to reduce the total volume of radioactive waste during the decommissioning phase of a nuclear facility.

The interim storage facility north (Zwischenlager Nord - ZLN) operated by EWN GmbH is used, among other things, as a storage facility for the decay storage of radioactive residual materials and waste that occur during plant decommissioning and dismantling.