Decommissioning strategies and dismantling techniques
There are two basic strategies for decommissioning a nuclear installation: immediate dismantling or dismantling following safe enclosure, known as deferred dismantling.
The German Atomic Energy Act (AtG) originally considered both strategies as equivalent. This changed with the Act on the Reorganisation of Responsibility in Nuclear Waste Management stipulating that nuclear power plants have to be decommissioned and dismantled without delay if their license has expired or their power operation has been terminated and the operators are obligated to contribute to the fund pursuant to Section 2 (1) sentence 1 of the Act on the Nuclear Waste Management Fund. Therefore, safe enclosure is no longer an option for nuclear power plants. Temporary exceptions to this may be approved by the competent authority in individual cases for plant components insofar and as long as this is necessary for radiation protection reasons.
Irrespective of the decommissioning strategy, in general the permanent shutdown is followed by a post-operational phase before the start of the actual decommissioning. During this period, the fuel assemblies may be removed or the operational media and waste disposed of, insofar as this is covered by the operating licence for the nuclear power plant. Decommissioning and dismantling activities may commence once the decommissioning licence has been granted.
Dismantling of a nuclear power plant
Nuclear power plants are dismantled stepwise.
Broadly speaking, the dismantling of a nuclear power plant proceeds as follows:
- Step 1: Dismantling of plant components no longer required for the residual operation and removal of the spent fuel elements as soon as possible
- Step 2: Dismantling of higher activated components, e.g. the reactor pressure vessel and the biological shield
- Step 3: Decontamination of buildings and release of the entire facility (buildings and site) from regulatory control
- Step 4: Conventional demolition or re-use of the building.
When decommissioning, it is important to use mature, reliable techniques that satisfy the requirements of safety, radiation protection and swift project implementation. Techniques are required for various processes: decontamination, dismantling, disassembling and other techniques including activity measurements and waste conditioning.
The following criteria among others apply when selecting individual techniques:
- radiation protection aspects, with the goal of keeping the exposure of staff to a minimum
- suitability and effectiveness of the technology,
- possible clearance of material that is radiologically acceptable,
- reducing the volume of radioactive waste and
- space-related aspects.
The selected techniques and their application are licensed and supervised by the competent Land authority. Technical experts support the authorities in this process.