Volume 70, Issue 1-2

Being an integral part of the life of all nuclear facilities, the decommissioning of these facilities is an important task to the owners as well as to the regulators and authorities. This applies not only to large nuclear facilities such as power plants and fuel cycle facilities but is also referring to the multitude of small nuclear applications in medicine, industry and research. The article provides an overview of the statutory and legal framework, the regulatory body and the licensing procedure for the decommissioning and dismantling of nuclear facilities in Germany. Furthermore, the respective international regulatory framework as it is laid down in the Joint Convention and the IAEA Safety Standards is outlined and a brief description of the current activities of WENRA is given.

Worldwide, 104 power and prototype reactors, 382 research reactors and 247 facilities of the nuclear fuel cycle have been shut down and are in different phases of decommissioning or decommissioning has already been completed. With 18 shut down power and prototype reactors, 11 shut down research reactors with a power of more than 50 kW th and with 10 shut down facilities of the nuclear fuel cycle Germany belongs to those countries with a lot of experience in decommissioning. This pertains not only to the number of shut down installations but also to the variety of different types. Further countries with a high degree of experience in decommissioning are among others the United States of America, the United Kingdom and France.

At the end of their useful life nuclear facilities have to be decommissioned. The strategy selection on how to decommission a facility is a highly important decision at the very beginning of decommissioning planning. Basically, a facility may be subject to (a) immediate dismantling; (b) deferred dismantling after a period of “safe enclosure” or (c) entombment where a facility is turned into a near surface disposal facility. The first two strategies are normally applied. The third one may be accepted in countries without significant nuclear activities and hence without disposal facilities for radioactive waste. A large number of factors has to be taken into account when a decision on the decommissioning strategy is being made. Many of the factors cannot be quantified. They may be qualitative or subject to public opinion which may change with time. At present, a trend can be observed towards immediate dismantling of nuclear facilities, mainly because it is associated with less uncertainty, less local impact, a better public acceptance, and the availability of operational expertise and know how. A detailed evaluation of the various factors relevant to strategy selection and a few examples showing the situation regarding decommissioning strategy in a number of selected countries are presented in the following article.

A variety of technologies is available for the decontamination and dismantling of nuclear facilities. All over the world, these technologies as well as conditioning processes of decommissioning waste are further developed. So far, they have been mainly applied to the dismantling of research and prototype facilities. Dismantling of reactors of higher power has started with the nuclear power plants of Greifswald and Würgassen among others. The present paper shall present the state of the art of decontamination and dismantling techniques as well as of post-treatment processes of radioactive decommissioning waste. From the technical point of view, the most complex step is the remote dismantling of activated and highly contaminated components. The prototype facilities of Forschungszentrum Karlsruhe, which are currently being dismantled, cover all types of plants. Their status of dismantling and the experience gained from using decommissioning technologies that are also suited for power facilities shall be illustrated. Further developments and adaptations of individual techniques, e. g. thermal and mechanical cutting methods, as well as of the complete systems technology, including carrier system, manipulator system, and tools, are reasonable and indispensable for managing the variety of dismantling tasks and, not least, for reducing their operation times and costs of use.

Clearance in Germany is far advanced. A complex regulatory framework exists in the Radiation Protection Ordinance (RPO/Strahlenschutzverordnung, StrlSchV) since 2001 which has replaced previous recommendations on clearance issued by the German Radiation Protection Commission (Strahlenschutzkommission, SSK). A number of options exist both for unconditional clearance (e. g. of all kinds of materials with no restrictions on the destination or future use) and for clearance for a specific purpose (e. g. recycling of metal scrap). For each clearance option there is a set of nuclide specific clearance levels which have been derived on the basis of the 10 Sv/a individual dose criterion using complex radiological models which are tailored to the respective material cycles (metal scrap, buildings, building rubble, waste for disposal, sites). The clearance levels have been thoroughly reviewed by the SSK. An extensive comparison to sets of clearance levels used in other countries or issued as guidance by international bodies revealed that the correspondence between values is between good and acceptable taking into account country-specific approaches and special assumptions which would not necessarily pertain to German situations. Clearance is a major factor in the material management, especially of nuclear installations undergoing decommissioning. The variety of clearance options leaves the operator of a nuclear installation sufficient flexibility for optimisation of the material management. Clearance is of particular importance in a country like Germany where the estimated costs for a future repository are very high and the interim storage facilities for radioactive material are limited and costly. While the licensee is responsible for his material management, the issuance of a clearance permit is done by the regulatory body upon application. The regulators may choose to use the clearance levels and regulations as stipulated by the RPO, or to impose site-specific regulations on the licensee. The actual clearance measurement, i. e. checking the compliance of the residual radionuclide content in or on a particular material, building or site with the clearance levels, is performed under the responsibility of the licensee's appointed radiation protection officer, with additional checks usually made by the regulator or an independent expert acting on his behalf. After compliance verification, the material will be reused, recycled or disposed of according to the clearance option, being then subject to the conventional waste legislation.

More than ten nuclear power plants in Germany have been decommissioned or are under dismantling. Objectives, strategies, preparatory work, licensing, technical dismantling and safety considerations are explained from the utility point of view, using the Stade (KKS) decommissioning as an example. Challenges with respect to characterisation, logistics and economy are discussed.

Gas-cooled reactors represent an important part of the world's nuclear programme. A wide spectrum of designs has been developed and tested. The majority of these test reactors and 1 st generation of power reactors has been shut down and is now in different stages of decommissioning. This is also the case for the pilot power reactors of the types High Temperature Gas-cooled Reactor (HTGR) and Heavy Water Gas-cooled Reactor types (HWGCR). Gas-cooled reactors show major generic design characteristics different from Light Water Reactors (LWR), hence influencing the choice of decommissioning strategy, waste/material management and also to a certain extent the decommissioning techniques and procedures applied. The most important issue influencing the decommissioning is the presence of large amounts of graphite in most of these reactors. The majority of the shut-down reactors is located in the UK and in France and major decommissioning programmes are under way in these countries. Interesting decommissioning work has also been carried out in Germany and in the USA. Most reactors are in a stage of safe enclosure. However, decisions have been taken recently to perform direct complete dismantling, notably in France, Italy and, to a certain extent, in Germany.

The decommissioning is the final phase in the life cycle of a nuclear reactor. In case of finishing the operation after the foreseen lifetime the decommissioning is planned long-dated with regard to the options “immediate dismantling”, “safe enclosure” and “entombment”. In case of an accident the operational phase was mostly finished immediately depending from the possible options for managing the damaged facility. With regard to the accidents in the nuclear power plants Three Mile Island Unit 2 (USA), Lucens Experimental Reactor (Switzerland), A-1 (Slovakia) and Chernobyl-4 (Ukraine) this article presents a short description of these accidents and of the related decommissioning projects. The examples demonstrate that in principle these projects represent variations of the above mentioned options. It has, however, to be noted that the realisation of the entombment of the destroyed unit Chernobyl-4 is unique with regard to the essential high complexity related to the first and the second Sarcophagus.

Four Siemens-owned German fuel cycle facilities are being decommissioned at the Hanau and Karlstein sites. Decommissioning of one of these facilities has already been completed. The facilities comprise three fuel fabrication plants and a facility for post-irradiation investigations of fuel assemblies. In each case the actual decommissioning phase was preceded by clean-out. Extensive preparatory investigations and planning, including licensing procedures, had been necessary. In some cases new measuring techniques and systems had to be developed and waste processing systems erected. In addition to providing a general survey of the different conditions and procedures involved, the MOX facility is used in this paper as an example for presenting these activities in greater detail. This includes the concept of immediate conditioning of radwaste for maintenance-free long-term interim storage (storage for several decades until a repository is available) in such a way as to also meet the requirements for shipment and final disposal without any need for further actions. A number of lessons have been learned and recommendations derived from the many years of decommissioning work at the four facilities.

Concerning the decommissioning of facilities related to reprocessing of spent nuclear fuel and processing and disposal of radioactive waste, i. e., facilities for waste conditioning or storage, specific features prevail. Such facilities are generally optimised for the handling of radioactive substances and, therefore, are frequently highly contaminated, but do not contain any activated material. One main concern of their decommissioning will usually be the decontamination of extended surfaces of process equipment and building structures. Depending on the extent and success of the decontamination, dismantling tasks might have to be remotely performed. Based on a survey of the number of such facilities, typical issues associated with their decommissioning were found to be well presented by focussing on the examples of the decommissioning of the two prototype spent fuel reprocessing plants at Dessel/Belgium and Karlsruhe/Germany. Such issues are mainly associated with the presence of alpha-contamination of the process equipment and large building structures. Experience gained from solving associated problems is discussed.

The use of nuclear energy for military as well as for peaceful purposes was and remains closely connected with the mining and processing of uranium ore and, to a lesser extent, of thorium ore. Mining and processing of radioactive ores are characterised by the generation of huge amounts of radioactive residues, massive impacts upon ecosystems, landscape reshaping (or devastation in some places), and the monostructural socio-economic orientation of human settlement areas. However, a great number of the mines and mills commissioned during the cold war have been already closed, either for deposits being depleted of economically recoverable resources or on political grounds. The specifics of uranium/thorium mining and milling make high demands on the decommissioning and rehabilitation of the facilities which in addition to radiological aspects would have to address issues such as water pollution control and soil conservation, future site re-use, landscaping, and infrastructure development. The present paper gives an overview of the state of decommissioning and rehabilitation. Radiological specifics and their integration into the decommissioning and rehabilitation management are demonstrated for the rehabilitation of uranium mining legacies in Saxony and Thuringia.

On October 9, 2003, the German Ministry of Economics and Labor signed an agreement with the Russian Federation's former Ministry of Atomic Energy for support in eliminating the nuclear weapons that the Russian Federation has pledged to reduce through the dismantlement of decommissioned nuclear submarines. This treaty, which is binding under international law, implements the Global Partnership against the Spread of Weapons and Materials of Mass Destruction as agreed to at the G8 Summit in Kananaskis in 2002. The core element of the German-Russian project is the creation of a long-term interim storage facility for 120 nuclear submarine reactor compartments near Murmansk in northwestern Russia and the preparation of the reactor compartments for interim storage. This technically demanding project, which began not without some problems, has developed in a positive manner since the end of 2003. The provisions in the treaty and its supplementary documents, which were internationally publicized, have generally proven to be successful.