Deep geological disposal of nuclear waste in the Swedish crystalline bedrock

Transcription

1 Deep geological disposal of nuclear waste in the Swedish crystalline bedrock Claes Thegerström and Saida Laârouchi Engström, Stockhom/Sweden The Swedish solution Regulations and history The 1. Swedish reactor, Oskarshamn 1, was taken into commercial operation in The following year, the nuclear power utilities set up SKB (Swedish Nuclear Fuel and Waste Management Co). The initiative came from the Government, which wanted to have a single organisation to deal with nuclear fuel. The company s primary mission was at that time to coordinate the supply of nuclear fuel. Until then little attention had been paid to issues related to spent fuel and nuclear waste management. The general view was that spent fuel should be reprocessed and fuel from the first reactor was contracted for reprocessing at Windscale (Sellafield). According to that contract, the reprocessing wastes would be stored at Windscale, only the fissile elements (Pu and U) would be taken back for reuse in the reactors. Operational low- and medium level wastes from the reactors were collected and solidified at the plants but no long-term planning had been made concerning their storage and disposal. In 1976, Sweden got a new Government after an election campaign in which nuclear power was a major issue. Now a radical change took place in how nuclear waste management was viewed. The new Government s policy statement declared that the Address of the Authors: Claes Thegerström and Saida Laârouchi Engström Swedish Nuclear Fuel and Waste Management Company P.O.Box Stockholm/Sweden Revised version of a paper presented at the VGB Congress 2012, Mannheim, 10 to 12 October nuclear power utilities shall demonstrate an absolutely safe method for disposal of the spent fuel. Six months later the Stipulations Act was passed. It stated that the reactors under construction may only be started if certain stipulations are met. The law offered 2 alternatives for the spent nuclear fuel: reprocessing and final disposal of the high-level waste or final disposal of the nuclear fuel without reprocessing. The nuclear power utilities in Sweden now bore the responsibility for disposal of the waste from their electricity generation plants. Many reactors were in the process of being built or designed, and a solution had to be found otherwise they might not be taken into operation. Two agreements were signed in 1977 and 1978 with a French company for reprocessing of spent nuclear fuel from Swedish reactors. The agreement was submitted in support of an application for operating licences for 4 new reactors. The KBS project was commenced when the Stipulations Act came into force. (KBS stands for Kärnbränslesäkerhet = nuclear fuel safety). The goal of the project was to establish a method for disposal of nuclear waste. For several years, the project worked with vitrified waste from reprocessing. In the third project report, published in 1983, a method for direct disposal was presented. This means that the fuel is not reprocessed prior to final disposal. The report recommended a final repository in the Swedish crystalline bedrock, with barriers of natural materials. This is the method we are still working on. It is called the KBS-3 method and constitutes the basis for the application to build a final repository for the spent nuclear fuel which is to be submitted soon. In 1984 the Government decided that the KBS-3 method in its entirety has been found essentially acceptable with regard to safety and radiation protection. (Government decision of June 28, 1984.) This means that the Government accepted direct disposal as a feasible method and acknowledged that the geological conditions necessary for such disposal exist in Sweden. The new Nuclear Activities Act of 1984 gave the reactor owners full technical and financial responsibility for the waste. They gave in turn SKB the responsibility for all nuclear waste management. This meant that reprocessing was no longer required to be allowed to operate the reactors. From 1985, when an interim storage for spent fuel was taken into operation, there was a consensus based on political as well as industrial arguments to abandon the reprocessing strategy. Since the early 1980s, everyone who uses electricity generated from nuclear power also bears financial responsibility for management and disposal of the waste. This fee is still being charged today. For every kilowatt-hour of electricity generated from nuclear power, about 1 öre (a 10 th of a Euro cent) goes to the Nuclear Waste Fund. With that money research, development of technology, facilities, and all other investments related to nuclear waste management in Sweden are financed. A process for regular reporting and review of results and plans was also set up. This contributed significantly to the development of a high scientific quality of the work and an open and transparent review mechanism. The regular review of the SKB R&D-programmes every 3 years has had a significant influence on the programme in several aspects. To mention one example, the plan for step-wise implementation of a deep repository was introduced by SKB in the 1992 RD&D-programme following comments and suggestions by KASAM, the Swedish National Council for Nuclear Waste, on the 1989 R&D-programme. Other examples are the systematic evaluation of alternative strategies and methods for spent fuel management and final disposal reported in year 2000 following requests from safety authorities as well as municipalities involved in the siting feasibility studies. The Swedish system takes shape SKB has planned a system that can handle all kinds of radioactive waste that arises in a nuclear power plant. The waste is divided into different categories depending on its radiotoxicity. The largest portion in terms of volume, approximately 90 % of the waste, arises during the operation of a nuclear power plant. It is called operational waste. The final repository for the operational waste SFR (Slutförvaret för kortlivat radioaktivt avfall) is built at the Forsmark nuclear power plant, and was taken into operation in 1988 (Figure 1 and 2). The waste has to be isolated here for about

2 Fig. 1. Air photo of the SFR (Final Repository for Operational Waste, Slutförvaret för kortlivat radioaktivt avfall) at the Forsmark site. (Photo: SKB) tion of radioactive waste. Since the Swedish nuclear power plants are situated on the coast, the radioactive waste is transported by SKB s ship m/s Sigyn (Figure 3). Transportation safety is primarily guaranteed by the transport casks and containers which are designed to suit the type of waste to be shipped and to withstand extreme stresses. In the event of an accident they will retain their radiation-shielding properties. The establishing of these facilities has been an important step in the national programme for management of the radioactive waste. The programme provides however for management and disposal of all nuclear waste. The most important programme facilities that are still under development and remain to be built are the encapsulation plant and the final repository for spent fuel. They are the core facilities of the KBS-3 system. In addition we need to build a canister factory, which is not, however, a nuclear facility. The KBS-3 system and technical development Fig. 2. Transport down into the SFR. (Photo: SKB) years. After that its radioactivity is comparable to that which occurs naturally in the surrounding bedrock. Two tunnels, each a kilometre in length, lead down to the repository, which is located about 50 metres beneath the sea bed. There are 4 rock vaults and one silo. Radioactive waste arising from medical care, industry, and research is also disposed of here. The spent nuclear fuel will be kept in an interim storage for around 30 years prior to final disposal. This is done in the Central Interim Storage Facility for spent nuclear fuel Clab outside Oskarshamn. All handling of the fuel in Clab takes place under water. The water acts as a radiation shield while also cooling the fuel. The decay heat generated by the spent fuel is one reason for storing waste in interim-storages prior to final disposal. If the radioactivity in the fuel is allowed to decay, it will emit less heat in the deep repository, which is an advantage. 360 The existing Swedish system also includes a specially built ship for transporta- The Swedish method for disposing of radiocative waste, the KBS-3 method, entails encapsulating the spent nuclear fuel in copper canisters, which are embedded in bentonite clay at a depth of about 500 metres in the Swedish crystalline bedrock. The principle is based on the use of multiple protective barriers to isolate the fuel. The barriers prevent the radio nuclides from being transported to the ground surface and into the ecosystem via the groundwater. The first barrier is a copper canister with an insert of cast iron. The fuel assemblies are entirely encapsulated. In the early stages of the programme they were assumed to be encapsulated without fuel boxes and boron glass rods, which were disposed of separately. Nowadays, the fuel assemblies are assumed to be disposed of complete (including fuel boxes). Fig. 3. Transport of spent nuclear fuel from m/s Sigyn to Clab. (Photo: SKB)

3 Fig. 4. Parts from a copper canister proposed for the disposal of radioactive waste. (Photo: SKB) Cast iron protects the canister against external pressure. The copper protects against corrosion in the oxygen-free environment that prevails in a deep repository. As long as a canister is intact, no radio nuclides will escape. The second barrier is a layer of bentonite clay. The clay is a buffer that protects the canister against movements in the rock and holds it in place. The bentonite absorbs water while swelling. Due to this property, the water is bound in the clay and kept virtually immobile. The clay also acts as a filter. If a canister should be breached, most of the radio nuclides will remain in the canister. Most of the radio nuclides that do escape will be retained in the bentonite. The third barrier is the crystalline bedrock, which retards the transport of radio nuclides up to the ground surface. The primary purpose of the rock is to give the canister a stable and protective environment. The fuel itself can also be regarded as a barrier. It is ceramic in form and thereby highly insoluble in water. As a result, the radio nuclides are held in place for a long time. The work on research, development and demonstration of deep geological disposal of spent fuel has been an intensive one lasting for more than 25 years. Although the KBS-3 concept all over the time has been the basis for the work there has over the period also been a consolidation and broadening of the knowledge on conceivable ways of storing spent fuel in the Swedish bedrock. The KBS-3 method has continuously been modified and refined. Much of the technological development is performed in the Äspö Hard Rock Laboratory and in the Canister Laboratory, both located in Oskarshamn. Full-scale deposition tests are undertaken in the Äspö Hard Rock Laboratory at a depth of 340 to 460 metres in the bedrock. This is where the dress rehearsal prior to construction of the final repository is taking place. The scene is the 3.6 kilometre long and 460 metre deep tunnel that comprises SKB s underground research laboratory. (Figure 5) Here, in the nearly 2 billion year old crystalline bedrock, we are demonstrating how we plan to build the deep repository. Here we are also conducting various experiments to find out more about the method that will be used to isolate nuclear waste from man and the environment. There is no spent nuclear fuel down here. Otherwise it is very similar to the future final repository. Most things are in place: the canisters, the machines, the tun- nels, and the boreholes where the canisters will be emplaced. The development and testing of sealing methods for the canisters takes place in the canister laboratory. The plan is that the copper canisters for the fuel will be fabricated in a separate canister factory. The fuel will be taken from Clab to the encapsulation plant, where it will be dried and placed in the canister. Then a lid will be welded onto the canister and the canister will be inspected to make sure it is leak tight. The technology for encapsulation and inspection is being developed and tested in the Canister Laboratory. Here the technology for welding the lid onto the copper canister is being refined, and here the welded joints are checked to make sure they are really leak proof. The welded joints are examined by means of radiographic, ultrasonic, and eddy-current inspection. In the laboratory we also test equipment for the encapsulation plant. This facility will be built at roughly the same time as the final repository. Alternative methods Another important research area has been to follow and study various alternatives to the main line (deep disposal according to the KBS-3 method). A large number of alternative methods have been described and analysed in depth. The results of this analysis provide strong support for the choice of the KBS-3 method. The siting process Area survey studies Faced with the choice of locations for type area studies reconnaissance and surveys of nearly 1,000 sites scattered across the Fig. 5. Air photo of Äspö Hard Rock Laboratory. (Photo: SKB) 361

4 country were performed. On the basis of mainly geological, but also non-geological siting factors (including land ownership) were 8 sites chosen as suitable for drilling studies in the years 1976 to The intention was not to find a location for a repository, but obtaining data from large depth in different areas spread throughout the country. These data were necessary to have to get a picture of how the material qualities and conditions, such as hydraulic conductivity and groundwater redox status, vary. On the basis of some area survey type studies SKB concluded that it is possible to find many places in Sweden, where the geological conditions are suitable for the construction of a repository. This meant that other important factors, such as societal factors, could be taken into consideration in the choice of site. Feasability studies Since 1992 a stepwise process has been under way, aiming at finding a site for the final repository. By means of regional studies, we explored the general siting prospects in different parts of the country. These studies show that good prospects exist for finding suitable sites for a final repository at many places in the Swedish crystalline bedrock. However, geological conditions disqualified the Caledonide mountains in the north and parts of Skåne and Gotland in the south. For nearly 20 years ago the siting process for the final repository for spent nuclear fuel started. This was based on our view that a successful work requires that the safety of the site finally selected is met and that the municipality supporting the repository. The feasibility studies were conducted during the period 1993 to 2000 evaluated the siting prospects in a total of 8 municipalities: Storuman, Malå, Östhammar, Nyköping, Oskarshamn, Tierp, Älvkarleby, and Hultsfred. The purpose was to judge, on the basis of existing material, whether prospects existed for further siting studies for a final repository. The judgements were based on 4 factors: safety, technology, land and environment, how society can be affected by a repository. In 2000, we presented the Integrated account of site selection and programme prior to the site investigation phase. Three areas were prioritised for site investigations: Forsmark in the municipality of Östhammar, an area in the northern part of the municipality of Tierp, and the Simpevarp area in the municipality of Oskarshamn. The municipal councils in Östhammar and Oskarshamn consented to further investigations, while Tierp refused additional tests. Site-investigations In 2002, SKB initiated site investigations for siting of a final repository on 2 sites: the Simpevarp and Laxemar areas (Oskarshamn municipality) and the Forsmark area (Östhammar municipality). The site investigations covered studies of rock characteristics, including measurements from the surface, and in 1,000 meter deep boreholes. In addition, SKB made an inventory of natural and cultural values, and investigated how a repository might affect society. The investigations were concluded in After that we analysed the results of the site investigations, especially assessments of the long-term safety for a KBS-3 repository at Forsmark and Laxemar. The analysis revealed a clear advantage for Forsmark concerning long-term safety, so the choice became obvious In June 2009 SKB selected Forsmark as site for the final repository for Sweden s spent nuclear fuel. The Forsmark site offers rock at the repository level which is dry and has few fractures. These properties are of a major significance for long-term safety. In addition, a repository in Forsmark would require less space compared to a repository in Laxemar. This is an advantage, as less rock needs to be excavated and less material will be needed for backfilling. The facilities on the surface will be constructed in the existing industrial area, which reduces the environmental impact and provides access to the infrastructure of the area. Consultation and communication The consultation process Our goal is to obtain permits to site and build an encapsulation plant and a deep repository for spent nuclear fuel. Basically, 3 different permits/licences are required for both the final repository and the encapsulation plant (see below). We submitted applications for the encapsulation plant in 2006 and we filed the applications for the final repository and the complete system in March The licensing process begins with a consultation process the main purpose of which is to optimise the prospects of obtaining a good environmental impact statement (EIS). The consultation starts with an early consultation with the county administrative board and private individuals who are likely to be particularly affected. A much wider circle is later invited to the consultation: other government agencies, municipalities, members of the public, and non-governmental organisations who may be concerned. SKB is thus responsible by law to interact with the local population, the elected decision-makers in the municipality, the local and national NGOs, and the authorities involved on the local, regional, and national level. An EIS should be capable of being read and reviewed by a number of different target groups, each with different interests and backgrounds. This means that we have taken up a very wide range of questions for investigation, and also topics such as various kinds of impacts on the community, health impacts and other sorts of non-technical aspects. There has been constant feedback between ongoing investigations, surveys, design work, and consultations. As the siting investigations and design process progress and different surveys are carried out, the design of the facilities and their adaptation to their surroundings and impact on the environment is refined and improved. Results of investigations and surveys together with proposals for facility design have been presented at the consultation meetings, and the participants have been given an opportunity to offer their viewpoints on SKB s proposals. During the consultation, SKB solicits viewpoints regarding the scope of the environmental impact statement. When the site investigations are concluded and the necessary investigations have been completed, an EIS will be compiled for the site selected. External communication The communication activities described so far have made up the formal part of SKB s external communication. SKB will, however, also face a number of new communication challenges in addition to the work with the formal consultations. SKB has now been working in the site investigation regions for more than 10 years. We feel that the residents generally have trust in our work. SKB has occasionally commissioned opinion polls on people s attitudes towards a deep repository. One of the clearest tendencies is that people with the most knowledge about SKB and the final disposal method are the ones who are the most positive. This is particularly clear in the municipalities where we have performed feasibility studies and site investigations, and where the issue has been discussed for a long time. Around 4 out of 5 of the people in Oskarshamn and Östhammar are in favour of building a final repository if a suitable site will be found in their municipality. This is a confidence in our project that must be maintained. SKB s record of communication related activities includes a wide variety of experiences, and we have learned from all of them. Over time have we identified a number of basic conditions, which are fundamental for a stable and successful siting process. We will now meet new types of 362

5 communication challenges, but the key components of the stakeholder communication process are the same: The siting process shall be transparent and based on voluntary participation. It is easy to be suspicious of people who are not open about their plans, and it is very difficult to regain trust once it is lost. The municipalities must have the ultimate conclusion about our continued work within their boundaries. It is important to maintain a constant dialogue and to express it in comprehensible terms. It is not sufficient to simply supply a constant flow of information along a oneway channel. A clear division of responsibilities between stakeholders is a key question. The implementing party can not pretend to be a neutral player, and it is therefore important that another player adopts this role. Give the process the time that is needed try to avoid being in too much of a hurry. It takes time to build confidence, and one single attempt to speed up the process might ruin much more than you gain. Other opinions, anxieties and fears must be respected. A step-wise and adaptive approach to the implementation of the disposal system. Allow scope for possible changes or improvements to the project. You cannot be expected to know everything from the start, and constructive criticism should be welcomed. Despite all non-technical aspects of communication, the continued good performance of operating facilities and of R&D work to guarantee top-quality technical systems are a must. You must always be able to clearly demonstrate that the nuclear waste will be handled with care and skill. Submitting the applications The site selection is a milestone for the Swedish nuclear waste programme. In March 2011, when admitting the applications for permits to build the final repository for spent nuclear fuel in Forsmark and the encapsulation plant in Oskarshamn, another milestone was reached. Apart from the future repository, the application according to the Nuclear Activities Act also includes the existing interim storage facility in Oskarshamn, Clab. We have already applied for an encapsulation plant adjacent to Clab (Figure 6). Then, the application according the Environmental Code includes the whole system, which is the final repository, Clab and the encapsulation plant. The applications according to the Nuclear Activities Act and to the Environmental Code are formally the bases for 2 separate legal examinations, and we therefore had to draw up 2 different documents. The content of the documents are to a great extent Fig. 6. Storage pool for spent nuclear fuel in the Clab. (Photo: SKB) the same, but there are also important differences since there are a number of issues that are considered only according to one of the regulations. The Environmental Court will prepare the case and review it according to the Environmental Code. After some preparatory procedures they will hold a main hearing. Then they will give a statement to the Swedish Government which will request statements from the municipalities of Östhammar and Oskarshamn. The municipalities will accept or reject and have a right of veto. The Government will then make a decision on whether the final disposal system is permissible or not. If the application is accepted, the Environmental Court will hold a new hearing. Thereafter, the Court will grant permits and stipulate conditions pursuant to the Environmental Code. SSM, the Swedish Radiation Safety Authority (Strålsäkerhetsmyndigheten), will prepare the case in accordance to the Nuclear Activities Act and put forward a statement to the Government. If the Government grants the permit, the authority will subsequently stipulate conditions pursuant to the Nuclear Activities Act as well as to the Radiation Protection Act. The factual review started at the end of May In conjunction with this, the application documentation was also sent out to experts in a broad national referral, both by SSM and by the Land and Environmental Court. Environmental organizations, concerned municipalities and county administrative boards, universities and colleges, other authorities and more were allowed to give their opinions. At SSM, the work on the application is also divided up between its own personnel and hired external experts. The authorities can request supplementary information and clarification from SKB during the course of the entire process. SKB will also be able to respond to the statements of opinion that come in. The government also requested that an independent international review of the applications should be made. This was carried out by the OECD s Nuclear Energy Agency (NEA) between May 2011 and June The team of experts reviewed SKB s description of long-term radiation safety as well as the selection of site and method. In their final statement you can read From an international perspective, SKB s post-closure radiological safety analysis report, SR-Site, is sufficient and credible for the licensing decision at hand. SKB s spent fuel disposal programme is a mature programme - at the same time innovative and implementing best practice capable in principle to fulfil the industrial and safety-related requirements that will be relevant for the next licensing steps. Concluding remarks The selection of the site and the licence application is the result of over 30 years of technical research and development and close to 20 years of siting work. During the siting process we have conducted surveys throughout Sweden, feasibility studies in 8 municipalities and site investigations at Forsmark and Laxemar. We are now ready to change the emphasis of our work towards more of industrial accomplishment. At the same time we will, however, carry on and follow up our programme for communication and stakeholder involvement which we consider to have been a corner stone behind a successful development and siting work. 363