Decommissioning Strategies: Status, Trends and Issues

This annex summarizes what decommissioning is, alternative decommissioning strategies, the status of decommissioning projects around the world, and the factors that influence choices among decommissioning strategies. After a nuclear power reactor is turned off for the last time, the initial steps toward decommissioning are not unfamiliar. The fuel is moved to the spent fuel storage pond where it will cool down for at least a few years, after which it will be moved to away-from-reactor (AFR) storage or sent for reprocessing. During those initial years, the workforce will most likely be relatively unchanged, and the systems to cool the spent fuel storage pond and ensure water quality will operate as before. Systems ranging from the reactor's instrumentation and control to heating and ventilation will all be kept running. Subsequent steps will depend on the choice that has been made among the decommissioning strategies described in this annex. But the initial steps of powering down the reactor, disconnecting the turbine, and removing spent fuel will be familiar from maintenance and refuelling shutdowns experienced during the reactor's operating life. While the spent fuel is cooling, the reactor's cooling fluids will be removed from the primary and secondary cooling loops, and the loops may be cleaned by running cleaning fluids through them. At this point, the reactor is in a state of 'cold shutdown', but many systems will continue running, including ventilation and radiation monitoring. If the selected strategy is immediate dismantling, removal of the spent fuel away from the reactor building is a significant milestone. The reactor workforce can then be reduced and dismantling can begin. Dismantling will likely start with the turbine and other relatively uncontaminated components. Many components, such as pumps, valves and pipes, may have been replaced or removed for maintenance during the reactor's lifetime, and their removal for the final time will not be very different. The contamination level of each component will have to be measured and carefully recorded, but this again is not new. All dismantling will be done inside temporary tents or other containment structures to ensure that contamination is not spread. As components are dismantled, they may be either stored on-site or shipped to their final disposal site. The sort of final disposal sites that are available will also determine whether large components are cut up or disposed of intact. Steam generators and even reactor pressure vessels have been disposed of intact. They are …