Decommissioning of nuclear facilities requires strict protocols to ensure that all sources of ionizing radiation are safely disposed of. Each country has a regulator with ultimate responsibility for the management of the decommissioning process. External contractors are frequently utilised for the actual work. In every country there are national laws and codes that must be followed. It is essential that contractors understand the detailed nature of such laws and codes.
There are 656 nuclear power plants in the world: 72 are under construction; 436 are operational; 147 are shut down and 1 is in long term shutdown.
The International Atomic Energy Agency (IAEA) has defined three options for decommissioning which have been internationally adopted:
Immediate dismantling (DECON): Dismantling can begin immediately.
Safe Enclosure (Safestor): Effectively places the facility in safe storage until ready for dismantling.
Entombment: Encase completely, unsafe to dismantle.
The problem with older plants is that they did not factor in decommissioning to their design. Modern nuclear power plant design requires decommissioning facilitation to be an integral part of the design. This means that older facilities are more difficult and therefore more expensive to dismantle. Decommissioning costs are falling as experience is gained. Costs per kWe produced will fall further in the future due to the integration of decommissioning constraints into the initial design.
Different nuclear technologies used for the shutdown power plants:
The technology used in the original design will have a direct impact upon the cost of decommissioning. For example:
Western PWR’s cost $200 – $500/kWe
BWR’s cost $300 – $550/kWe
GCR’s can cost up to $2600/kWe for the UK Magnox reactors
The International Atomic Energy Agency (IAEA) recommend that an evaluation of the various decommissioning options should be performed by considering a wide range of issues, with special emphasis on the balance between the safety requirements and the resources available at the time of implementing decommissioning. Cost–benefit or multi attribute type analyses provide systematic means for such an evaluation. These analyses should utilize realistic estimates of both costs and radiation doses. It should be ensured that the selected option meets all the applicable safety requirements. The selection of a preferred decommissioning option should be made by analysing components such as:
- Compliance with laws, regulations and standards which should be applied during decommissioning.
- Characterization of the installation, including the design and operational history as well as the radiological inventory after final shutdown and how this changes with time.
- Safety assessment of the radiological and non-radiological hazards.
- The physical status of the nuclear installation and its evolution with time, including, if applicable, an assessment of the integrity of buildings, structures and systems for the anticipated duration of the deferred dismantling.
- Adequate arrangements for waste management, such as storage and disposal.
- Adequacy and availability of financial resources required for the safe implementation of the decommissioning option.
- Availability of experienced personnel, especially staff of the former operating organization, and proven techniques, including decontamination, cutting and dismantling, as well as remote operating capabilities.
- Lessons learned from previous, similar decommissioning projects.
- The environmental and socio economic impact, including public concerns about the proposed decommissioning activities.
- The anticipated development and use of the installation and the area adjacent to the site.
The IAEA recommend that the following list is taken into consideration for the final decommissioning plan:
- A description of the nuclear reactor, the site and the surrounding area that could affect, and be affected by, decommissioning.
- The life history of the nuclear reactor, reasons for taking it out of service, and the planned use of the nuclear installation and the site during and after decommissioning.
- A description of the legal and regulatory framework within which decommissioning will be carried out.
- Explicit requirements for appropriate radiological criteria for guiding decommissioning.
- A description of the proposed decommissioning activities, including a time schedule.
- The rationale for the preferred decommissioning option, if selected.
- Safety assessments and environmental impact assessments, including the radiological and non-radiological hazards to workers, the public and the environment; this will include a description of the proposed radiation protection procedures to be used during decommissioning.
- A description of the proposed environmental monitoring programme to be implemented during decommissioning.
- A description of the experience, resources, responsibilities and structure of the decommissioning organization, including the technical qualification/skills of the staff.
- An assessment of the availability of special services, engineering and decommissioning techniques required, including any decontamination, dismantling and cutting technology as well as remotely operated equipment needed to complete decommissioning safely.
- A description of the quality assurance programme.
- An assessment of the amount, type and location of residual radioactive and hazardous non-radioactive materials in the nuclear reactor installation, including calculation methods and measurements used to determine the inventory of each.
- A description of the waste management practices, including items such as: Identification and characterization of sources, types and volumes of waste; Criteria for segregating materials; Proposed treatment, conditioning, transport, storage and disposal methods; The potential to reuse and recycle materials, and related criteria; Anticipated discharges of radioactive and hazardous non-radioactive materials to the environment.
- A description of other applicable important technical and administrative considerations such as safeguards, physical security arrangements and details of emergency preparedness.
- A description of the monitoring programme, equipment and methods to be used to verify that the site will comply with the release criteria.
- Details of the estimated cost of decommissioning, including waste management, and the source of funds required to carry out the work.
- A provision for performing a final confirmatory radiological survey at the end of decommissioning.
Let’s take a closer look at the work that goes into decommissioning a nuclear reactor. The reactor in question is the research reactor WWR-M located at the Institute for Nuclear Research in Kiev, Ukraine.
To complete the scheduled dismantling tasks the following sequence of the work and controls were
- Decontamination of areas and equipment to facilitate dismantling.
- Preparation of the temporary storage areas for the location of dismantled and separated parts.
- Dismantling of the equipment at the reactor upper part in the reactor hall.
- Dismantling of the metal layer on the thermal column cover and the thermal column shield.
- Dismantling of the thermal column’s first disc.
- Dismantling of Beryllium reflector.
- Dismantling of reactor vessel (extraction of the vessel in one piece, without separation).
- Dismantling of the armature rod drives.
- Dismantling of the ion exchange and electrophoresis filters.
- Dismantling of primary circuit.
- Dismantling of primary circuit’s fixing units.
- Dismantling of biological concrete shield.
- Dismantling of spent fuel cooling pool.
- Removal of contaminated components: which can be removed after dismantling of other components.
- Removal of clean auxiliary equipment for the final radiation survey.
- Dismantling of non-contaminated structures.
- Removal of contaminants from all areas and premises.
- Cleaning of adjacent areas (where necessary).
- Classification of radioactive substances for unlimited re-use or final disposal.
- Conditioning and transfer for final disposal of radioactive waste generated during the dismantling process.
- Classification of radioactive waste packaging.
- Restoration of the reactor site (if necessary) depending on the plans for future use.
- Execution of the final radiation survey inside the reactor building and the sanitary protective zone.
Each of the above stages requires careful and detailed preparation and planning. Missing out on a stage risks environmental exposure to ionizing radiation.
This article gives a brief insight into the level of detail required for safely decommissioning a nuclear power facility. Additionally, if this is being carried out in a foreign environment the risks escalate due to the language barrier.
Constructive Translations is in a position to help clients overcome the language difficulties. Rigorous translations carried out according to BS EN 15038 or certified translations will guarantee accurately translated documents.