Michele Kearney's Nuclear Wire: Frequently Asked Questions and Answers About Decommissioning

Tuesday, October 30, 2012

Frequently Asked Questions and Answers About Decommissioning

Expert visits and training sessions are effective mechanisms for transferring latest knowledge in decommissioning techniques from one institution to another. (Photo: D. Calma/IAEA)

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What is decommissioning and why is it needed?
When we talk about decommissioning from the IAEA's viewpoint, we mean decommissioning facilities that use or store radioactive material. Decommissioning is the last phase in the lifetime of such facilities, following their design, construction, operation and permanent shutdown. It comprises different administrative and technical activities whose purpose is to remove or to minimize the residual hazards in the facility after it is shut down. Decommissioning thus enables the safe reuse of the site, as well as any buildings or parts of the facility for other nuclear, industrial or general purposes.
The decommissioning phase is usually assumed not to begin until after spent fuel or highly radioactive liquids are removed from the facility; it generally requires a detailed assessment of residual radioactivity or other hazardous material to be made beforehand. The main activities involved include: the decontamination of the plant and the buildings, as well as their segmentation into smaller units suitable for subsequent handling; the treatment and packaging of waste material; and the demolition of the remaining buildings. Decommissioning should lead to the complete or partial removal of the regulatory control that was in place during the facility's operation. It is therefore an essential step in ensuring that the legacy of the activities from which this generation has benefitted are not passed on to future generations.
What types of facilities are decommissioned?
The decommissioning process is applied to a wide range of facilities - from nuclear power plants, research reactors, spent fuel and radioactive waste stores, nuclear fuel cycle facilities and research facilities used for industrial, medical or educational purposes. Nuclear fuel facilities are used to extract and enrich uranium, as well as to fabricate or reprocess different kinds of fuel. The decommissioning of large power plants and fuel cycle facilities is in itself a complex industrial project, which may take several years, possibly decades to accomplish. In contrast, small medical, industrial or research facilities with limited amounts of materials and a low level of hazards can be decommissioned within months. Although the complexity, size, radionuclide inventory, hazard potential and protection requirements may be very different, the typical steps in the decommissioning process for all these facilities are essentially the same.
As an indication of the current global scale of decommissioning: there are approximately 100 nuclear power plants and approximately 200 research reactors that are undergoing or awaiting decommissioning, together with some tens of fuel cycle facilities (including several uranium enrichment facilities covering vast areas). In addition, there are many thousands of disused research laboratories and hot cells which require decommissioning, which were used for industrial, research and educational purposes.
What are the challenges associated with the decommissioning process?
Decommissioning is the safe deconstruction of a facility which is no longer needed. During the construction of a facility, all the materials are radiologically clean, but during the facility's operation a significant portion of the components, materials and structures become radioactive, thus radiological risks for workers during decommissioning represent the first challenge.
A systematic process known as radiological characterization is undertaken to estimate the radionuclide inventory of a facility that is to be decommissioned. This inventory forms the basis for planning the decommissioning activities, selecting technologies for decontamination, dismantling and demolition of the systems, structures and components of the facility. Adequate technologies to ensure safe and effective decommissioning are needed. They are sometimes simple and manual, but may sometimes be very sophisticated, computer or remotely controlled.
In addition, conventional industrial risks similar to any major deconstruction project also need to be considered. There is also the risk of releasing radioactive substances into the environment during the decommissioning activities, which requires that all the decommissioning activities have to be carefully planned, analyzed from the safety point of view and controlled by the application of different safety measures to minimize the exposure of the workforce, the general public and the environment. Continuous radiological monitoring of the workers, workplaces, materials, effluents and the environmental is performed during decommissioning to ensure that safety objectives are met.
During decommissioning large amounts of radioactive waste are generated in a relatively short time, so that adequate storage, treatment and disposal facilities need to be available to support this process. Some of the material generated during decommissioning is not radioactive and may be reused or recycled. During decommissioning constant, precise measurements are taken to separate radiologically clean materials from those that are radioactive.
Decommissioning is an expensive process and in this phase of its lifetime the facility no longer generates any income, therefore financing provisions for decommissioning need to be established while the facility is operational. In the case of nuclear power plants, funds are generally collected in special funds to be used for decommissioning, or operators are required to demonstrate that they have made appropriate provisions. In either case, oversight mechanisms are applied by the relevant Member State to ensure the adequacy of the funds that are set aside.
Decommissioning is quite a different activity from the operation of the facility. Many of the activities are unique, the situation at the facility is continuously changing as systems are dismantled gradually. The decommissioning hazard profile is not only different; it is not always as well characterized, as the operational hazard profile. Personnel training in decommissioning is therefore one of the key factors for successful decommissioning. Changes in the organizational and managerial structure are needed to ensure proper project management and to maintain the appropriate safety culture throughout the project.
What is the IAEA's role in decommissioning of facilities using radioactive material?
The IAEA assists Member States involved in decommissioning in a variety of different ways, including providing direct assistance in the form of expert missions, scientific visits and, in limited cases, the procurement of equipment for measurement of radiological hazards. The Agency also organizes various training courses and fellowships to provide decommissioning personnel experience in the use of relevant technologies. This assistance is provided through the IAEA's Technical Cooperation Programme with Member States.
In addition to direct assistance, the IAEA cooperates with Member States to collect experience from ongoing decommissioning programmes and, based on their analysis, prepares technical and safety reports outlining current good practices, with examples and experiences from completed or current projects. These experiences are also the basis for development of the IAEA safety standards, providing the Member States with the internationally agreed set of requirements for the decommissioning process, with guidance on how to ensure compliance with these requirements. Although compliance with the IAEA's safety standards is not mandatory for Member States, they do generally provide the basis for national legal and regulatory requirements, which should not be less demanding than the IAEA standards.
The IAEA also supports human resource development in decommissioning through its International Decommissioning Network (IDN), which is an active forum that exchanges knowledge and experience from ongoing projects. A broad cross-section of organizations - regulators and implementers from both advanced and less advanced programmes - are IDN members. IDN continually assesses Member States' assistance needs and its members regularly host workshops, training courses and scientific visits with the aim of sharing knowledge and experience throughout the member organisations and generally to improve skills relating to the planning and implementation of decommissioning programmes. Good practices in all aspects of decommissioning are discussed at IDN forums and workshops, where participants meet colleagues from other countries working on similar issues.