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Decommissioning of nuclear facilities

At the end of their useful lifetime nuclear facilities will be shut down and have to be decommissioned subsequently. Some of them are shut down prematurely, for example because of technical or economical reasons (accident, backfitting needs) or because of political implications (phase out of nuclear energy). A considerable amount of experience is already available in the decommissioning of nuclear facilities. Many of them have already been completely dismantled. Others are in the process of being dismantled and further ones are earmarked for shut down and subsequent decommissioning. At present, most of the facilities undergoing decommissioning are smaller ones, for example research facilities and prototype plants. Nevertheless, a considerable number of commercial facilities is in the process of decommissioning. Experience shows that decommissioning can be done safely and without undue radiological exposure. The regulatory framework for decommissioning and dismantling of nuclear facilities is an important element of providing safety and occupational and public protection when nuclear facilities are decommissioned. Such a framework includes independent authorities, appropriate licensing procedures and provisions for the release of materials, buildings and sites from regulatory controls. Decommissioning technology is available. This has been demonstrated in practice. A wide range of methods and techniques is being applied. Research and development is effectively contributing to improving existing techniques and to developing new ones which are superior for example in terms of safety, economics or effectiveness. Different types of facilities are to be decommissioned, for example reactors, fuel fabrication facilities, waste management facilities and fuel reprocessing plants. Each of them has specific characteristics which have to be taken into account when decommissioning is planned and carried out. Major differences occur even among the various types of reactors. Considerable differences do exist for example, among light water reactors (LWRs). In the case of the pressurised water reactors (PWR) it is primarily the reactor building that contains radioactive materials whereas in the case of the boiling water reactor (BWR) it is also the turbine hall. Gas cooled reactors, for example Magnox reactors, are very different from LWRs. Not only are they very much bigger in size but they are also designed to use graphite as moderator. The management of graphite as a radioactive waste is regarded to be a particularly difficult issue in the decommissioning process. Promising solutions have been put forward recently. Selecting a decommissioning strategy is a very important step at the very beginning of the decision making process. In the past “deferred dismantling” after a period of safe enclosure of about 30 years and up to 100 years was often selected for various reasons, in particular to take advantage of the radioactive decay. Today the trend is more towards “immediate dismantling”, because it is associated with less uncertainties, has less local impact, has a better public acceptance and makes use of existing operational experience and know how. On the other hand, it turned out that the radioactive decay does not substantially simplify the decommissioning process. Decommissioning of a reactor after an accident, for example Three Mile Island (USA), is a very special task. It cannot be standardised because decommissioning depends very much on the accident scenario and the consequences of the respective event. The cleanup of existing situations is another very important subject. Many of these are legacies associated with military activities, often originating from the early days of nuclear weapons production. The cleanup of weapons test sites and the dismantling of nuclear submarines are legacy examples. In several instances the mining and milling of uranium ore is also related to military programmes. The cleanup of such sites, whether civilian or military, is a real challenge from a work-related as well as from a financial point of view. Many commercial nuclear facilities of the first generation will be taken out of operation in the near future peaking in about 20 years from now. This shows that decommissioning of nuclear facilities which is already an important business will be a growing industry and it will be even more important in the future than it is today. Editorial