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STA02-rueckbau
STA02-rueckbau

Decommissioning nuclear power plants

New allocation of roles between operators and state

The German Act on the Reorganisation of Responsibility in Nuclear Waste Management, which came into effect in June of 2017, has re-designated the responsibilities for decommissioning and dismantling nuclear power plants as well as the disposal of nuclear waste. According to the act, the power plant operators are in charge of decommissioning and dismantling the nuclear power plants, including the disposal of materials as well as packaging the radioactive waste appropriately. The German government is responsible for organising and funding interim and final storage of the waste.


What is post-operation, decommissioning, dismantling?

The post-operational phase starts once a nuclear plant has stopped generating electricity for good and it ends when the decommissioning and dismantling licence is issued.

Decommissioning requires special licences based on the operator's decommissioning plans. These plans include a detailed and exhaustive list of all plant components inside areas where material was exposed to radioactivity – as well as the radioactive inventory. The sequence of the planned dismantling activities must be laid out, decontamination techniques and planned disposal channels need to be described. An important task during the planning stage is to develop a concept for treating and packaging radioactive waste. At that point in time, all relevant measures, e.g. the start date for disposing of the fuel elements, must be covered without exception by the operating licence (that is still valid).

“Decommissioning” is frequently used synonymously with “switching off”. Decommissioning, as stipulated by the Atomic Energy Act, only starts once an approval procedure has been completed and a decommissioning and dismantling licence has been granted. Dismantling can only start once the decommissioning and dismantling licence has been granted. The period of time that the licence is valid for ends once the plant is released fully from the requirements of the Nuclear Energy Act.

During the dismantling phase the plant components are disassembled. Any radiation that is still present in the inventory of the plant and the plant components that were exposed to radioactivity can be reduced using suitable decontamination measures before or after disassembly. Most of the material can be decontaminated to such an extent that it can be released into the materials cycle under supervision by the relevant authority. Securely sealing in any radioactivity is a key safety target during decommissioning and dismantling of the plant and is ensured through continued operation of vital plant elements such as ventilation systems. The decommissioning and dismantling licence that is issued for each plant on an individual basis stipulates the maximum permitted limits for releasing radioactive material with exhaust air and wastewater. By filtering exhaust air and treating wastewater, in practice these emissions remain well below those limits.  


Procedure for granting a decommissioning and dismantling licence

In order to obtain approval for starting the dismantling process for nuclear facilities in Germany, a decommissioning and dismantling licence pursuant to section 7 paragraph 3 of the Nuclear Energy Act must be granted. To apply for the licence, a set of prescribed documents and data must be presented to the relevant authority of the federal state where the plant is located. The documents need to describe, among other things, the planned dismantling procedure and techniques, the expected environmental impact and radiation protection measures. An environmental impact study is also part of the process and the public must be consulted. People can object to plans and the objections are then heard and considered during a hearing facilitated by the authority responsible for issuing the licence, with the applicant present. The authority has the submitted documents assessed by an expert body, usually TÜV, before granting the licence for decommissioning and dismantling the plant, possibly after requesting changes or additional measures. The Federal Ministry for the Environment, as the federal body responsible for monitoring the process, is also being included during the last step of the procedure and in turn consults advisory groups, e.g. the Waste Management Commission.

Therefore, it may take several years before a decommissioning and dismantling licence is granted. After the licence has been granted and accepted, the plant can be decommissioned and dismantled.


Our integrated dismantling process (Integrierter Rückbauprozess – IRP)

In Germany, some operators, including RWE, have already gained comprehensive experience in solving the technically and organisationally complex task of decommissioning and dismantling nuclear power plants. Planning and implementing the process requires specialised knowledge that exists within RWE, due to the considerable number of projects that have been successfully completed to date. This knowledge is consistently being expanded, incorporating the latest developments and innovations.

Planning a timely and, moreover, safe dismantling process is an ambitious task requiring new techniques. To this end, RWE has looked at all steps of the dismantling process in great detail and across all its nuclear power plant sites – from applying for the dismantling licence to being released from the requirements of the Nuclear Energy Act. The result is RWE’s integrated dismantling process (Integrierter Rückbauprozess – IRP) for the operational implementation and organisational management of the procedure. IRP sub-divides the task of dismantling the plant into smaller work packages. Similar to the processes in the automotive industry, they are processed step by step, almost like on an assembly line. The individual dismantling activities are coordinated and interlinked. This approach makes the dismantling process manageable and safe.

In a first step, the planners divide the plant into areas that involve similar activities and dismantling volumes. Then they estimate the workload for each dismantling activity and record the result in a “timetable”. The material is then categorised (e.g. cable, panelling, pipelines, pumps) and disassembled separately. The material must be broken down to such a level that it can be cleaned (decontaminated) and released – i.e. leave the controlled area – in a transport box. Based on their individual characteristics, the dismantled components then need to pass through a set sequence of processing and treatment stations. As a result, an industrial logical sequence of standardised processes comes about, because each residual material is allocated to a predefined material stream. At the Lingen, Biblis and Gundremmingen sites, state-of-the-art facilities for processing and treating dismantled materials are being set up – our dismantling factories.

The objectives of RWE's industrialised dismantling process are as follows:

  • Reduce radioactive waste
  • Minimise conventional waste
  • Return dismantled components into the materials cycle.

Which technologies are used in the dismantling process?

When a power plant is dismantled, mainly conventional, established dismantling and disassembly techniques are used. All components of the plant must be removed and broken down further into smaller pieces in order to prepare them for the residual material and waste management process.

However, dismantling such a plant also requires specialised technical solutions. Disassembling smaller metal parts that are only slightly or not at all contaminated, e.g. pipes, as well as heavily contaminated parts with thick walls, e.g. reactor pressure vessels, requires specialised procedures. Some of this work must be carried out remotely or under water in order to protect the workers and avoid any radioactivity escaping.

Various tried and tested thermal and mechanical cutting techniques can be used. Mechanical techniques include sawing, rope sawing, milling cutting, angle grinding, shearing and water-abrasive cutting. Thermal cutting methods are oxyfuel cutting, plasma cutting and electric arc cutting.

As an alternative to on-site cutting, large components such as steam generators may be transported to specialised dismantling companies for further processing.


Decontamination and release

Minimising waste is one of the key requirements during the dismantling of nuclear power plants. Only a small proportion of the total mass of a nuclear power plant is contaminated or activated during operation. Decontamination processes can be used to clean up material to such an extent that it can be released from the requirements of the Atomic Energy Act without restrictions and returned to the materials cycle or released for specific use or disposal, e.g. disposed of as conventional construction waste or burned in a waste incinerator.

Decontamination is particularly important during two stages in the dismantling process. Before the dismantling work starts, cycles and spaces are decontaminated in order to minimise the amount of radiation the workers are exposed to. During this process, it is frequently the case that not just the radionuclides that were deposited on the surface of the material are removed but also a thin layer of the material itself. Plant components that have already been dismantled are often decontaminated again so that they can be subsequently released from the requirements of the Atomic Energy Act and then be disposed of. 


Release

Every nuclear power plant has a controlled area that is subject to particularly strict release regulations with regard to the material located there. Literally every bit of concrete and every bolt from the controlled area must undergo a detailed testing procedure (clearance), tightly monitored by the relevant regulatory authorities. Substances that remain within the legal radioactivity limits can be returned to the materials cycle or disposed of after their formal unrestricted release.


Disposal

Like all industrial installations, power plants also consist of a multitude of different materials that must be recycled or disposed of in different ways. Which procedure will be used depends, first of all, on whether the material in question is located in the plant's controlled area, where it may have been exposed to radioactivity, or outside that area.

Most of the waste that occurs during the dismantling process is not any different from materials found in other industrial plants. Concrete, glass, cables, different types of steel or plastic make up around 90 per cent of the substance of a nuclear power plant. Here, the same principles as those for domestic waste apply. Whatever can be recycled is recycled, the rest is disposed of conventionally, just like domestic waste, for example.

For residual materials from a nuclear power plant's controlled area – that do not need to be stored in a permanent storage facility as radioactive waste – there are only two possible paths after radiological decontrolling measurement. If they get unrestricted clearance, these materials are returned into the materials cycle or disposed of conventionally. Waste material with specific clearance is always classified as waste and is either incinerated or goes into landfill.

Waste that cannot be released is packaged as radioactive waste in specialised containers and handed over to the state authorities for final storage.