Decommissioning begins to be addressed at an early stage of a nuclear power plant programme. As noted in Table 20.3, the Safety Analysis Report includes a decommissioning concept including provisions for safety, the differing approaches to decommissioning, and planning of work. The end state for decommissioning, depending on national legal and regulatory requirements, encompasses partial or full decontamination and/or disman­tlement, with or without restrictions on further use of the site. The IAEA has developed basic safety requirements that must be satisfied during the planning and implementation of decommissioning, for the termination of practices and for the release of facilities from regulatory control (IAEA, 2006a). Chapter 24 describes the various aspects of decommissioning and the experience already gained.

There are three general approaches that could be followed to achieve a decommissioning end state. In all three cases, a facility is eventually released for other uses, either with or without regulatory restrictions, but the time frames are different. The first approach is immediate dismantlement, where radioactive contaminants are removed or reduced to a level that permits the facility to be released. For this approach, the decommissioning project would need to be initiated shortly after the end of plant operations. It requires timely completion of the decommissioning site activity and removal of radioactive material from the NPP to a licensed facility, followed by processing for either long-term storage or disposal. The second approach is deferred dismantling or safe storage. In this case, any SSCs that have radio­active contaminants are either processed or placed in a condition where they can be safely stored and maintained. Subsequently, the SSCs are decontaminated and/or dismantled such that the facility’s radioactivity returns to levels that allow the facility to be released. The third approach is entombment. For this approach, the radioactive SSCs are safely encased until the radioactivity decays to a level such that the facility can be released from regulatory control.

Whatever approach is taken, the licensee must ultimately develop a final decommissioning plan for regulatory approval. The development of this information will likely require a preliminary period of work before the decommissioning plan can be finalized and be submitted to the regulator. The plan might encompass the strategy, the current state of the plant includ­ing radiological characteristics, the schedule, implementation and manage­ment of the plan, how the waste will be managed, and a description of the end state and how it will be verified.

The licensing submission will also require a safety assessment that may include some of the topics in Table 20.2. The assessment would cover the decommissioning activities given in the plan and any potential abnormal events that could occur. The occupational exposures and the potential releases to the environment, and the health and safety of the public, would be addressed, including the mitigation and prevention strategies. The IAEA recommendations for the development and review of the decommissioning safety assessments are given in a Safety Guide (IAEA, 2009b), where it is stated:

Decommissioning activities are performed with an optimized approach to achieving a progressive and systematic reduction in radiological hazards, and are undertaken on the basis of planning and assessment to ensure the safety of workers and the public and protection of the environment, both during and after decommissioning operations.

The site can be released from regulatory control once the licensee has completed the decommissioning work and has met the regulatory require­ments. Recommendations for meeting these requirements are the subject of an IAEA Safety Guide (IAEA, 2006b). The Guide is directed to both the regulatory body and the licensee, and covers the release of sites or parts of sites from regulatory control after a practice has been terminated.