RD & Technical Report D-Programme 2001 D-Programme TR-01-30 RD&D-Programme 2001 Programme for research, development and demonstration of methods for the management and disposal of nuclear waste September 2001 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel and Waste Management Co Box 5864 SE-102 40 Stockholm Sweden Tel 08-459 84 00 +46 8 459 84 00 Fax 08-661 57 19 +46 8 661 57 19 TR-01-30 ISSN 1104-8395 Graphium Norstedts Tryckeri, 2001 RD&D-Programme 2001 Programme for research, development and demonstration of methods for the management and disposal of nuclear waste September 2001 Preface The Nuclear Activities Act requires a programme for the comprehensive research and development and other measures that are required to manage and dispose of nuclear waste in a safe manner and to decommission and dismantle the nuclear power plants. To meet this requirement, SKB is now presenting RD&D-Programme 2001. The pro- gramme presents SKB’s plans for the period 2002–2007. The period of immediate con- cern is 2002–2004. The level of detail for the three subsequent years is naturally lower. The programme provides a basis for designing systems for safe management and dis- posal of the radioactive waste from the nuclear power plants. SKB’s plan is to imple- ment deep disposal of the spent fuel in accordance with the KBS-3 method. In the RD&D-Programme we describe our activities and planning for this line of action and the work that is being conducted on alternative methods. Review of the programme can contribute valuable outside viewpoints. The regulatory authorities and the Government can clarify how they look upon different parts of the programme and stipulate guide- lines for the future. Municipalities and other stakeholders can, after studying the pro- gramme, offer their viewpoints to SKB, the regulatory authorities or the Government. In December 2000, SKB presented proposals for sitings of the deep repository and the background material on which the choice was based, as well as programmes for inves- tigations on these sites. In June 2001, SKI and Kasam submitted their statements of opinion to the Government following an extensive review. Pending the Government’s decision, SKB has nothing new to add as far as the siting process is concerned. This RD&D-Programme differs from the preceding ones in that it concentrates on questions relating to research and technology development. Questions pertaining to siting of our facilities will be elaborated on in greater detail in conjunction with appli- cations to authorities and related environmental impact statements. This programme is also structured differently than the previous programmes. We take our point of depar- ture in the regulatory requirements on long-term safety and link them to the develop- ment of the safety assessment methodology and the research on the long-term pro- cesses in the repository. The programmes for safety and research are then linked together with the programmes for development of methods and instruments for the site investigations and the design of the deep repository, the encapsulation plant and the canister. In conclusion, the programmes for alternative methods, decommissioning and other long-lived waste are also explained. It is our hope that such a structure and such an approach will provide a clearer picture of which factors are most important for safety in the repository and in which areas we are concentrating our efforts. Stockholm in September 2001 Swedish Nuclear Fuel and Waste Management Company Peter Nygårds Tommy Hedman President Head of Safety and Technology 3 4 Summary The preceding RD&D-Programme from 1998 was supplemented in December 2000 by an integrated account of method, site selection and programme prior to the site investigation phase. Since the latter account lies close in time, SKB has chosen to concentrate RD&D-Programme 2001 on research and technology development. View- points offered on previous RD&D-programmes and comments from the review of the SR 97 safety assessment comprise important input for RD&D-Programme 2001. It has not been possible or appropriate in this report to take into account all the viewpoints that have emerged in the regulatory authorities’ statements regarding the supplement to RD&D-Programme 98 presented in June. Many of the review comments will there- fore be dealt with in the continued work with the site investigation programmes. An overall goal for SKB is to start the initial operation of a deep repository for spent fuel in 2015. This presumes that site investigations have been commenced at the beginning of 2002 and that the different phases have been executed without major changes. Regular operation should then be able to commence in the early 2020s before the storage pools in CLAB are full, thus avoiding further expansion. The encapsulation plant should be ready to start roughly one year before the deep repository is finished. Future RD&D-programmes will probably place the emphasis slightly differently depend- ing on different phases and permit applications. RD&D-Programme 2004 is expected to give a central role to the canister and the encapsulation technology. In RD&D- Programme 2007, the deep disposal technology and continued work on alternative disposal methods may be important topics. All of this is shown by the overall timetable presented in Chapter 1. The timetable also includes conducting safety assessments of the deep repository when data from the site investigations are available. These assessments should provide a basis for site selection and will be preceded by preliminary safety judgements based on data from the initial site investigation phase. The methods used to analyze long-term safety are being developed based on the lessons learned from SR 97. Central parts of the safety assessment are system descriptions, along with choice and analysis of scenarios. This is now being further adapted and developed for the purpose of dealing with data from the site investigations. SR 97 used a simplified method for risk calculations, which has now been evaluated and improved with the aid of newly-developed analytical models. Safety assessment, research and repository design are closely interrelated. The design of the repository is a premise for safety assessment. The research contributes knowl- edge regarding what changes may take place in the long term in the repository. Con- versely, the results of a safety assessment can be used to improve the repository design and – not least – to prioritize different research areas. We have used this to build up the structure in large parts of the report. Instead of presenting the research arranged according to discipline, as is customary, we have tied it to the processes that are of importance for the long-term safety of a deep repository for spent fuel. It is our hope that it will be easier to determine why research is being done, where sufficient knowl- edge already exists, and which areas require further studies. 5 The spent fuel is the waste that is to be isolated in the deep repository. Various processes will with time alter the conditions in the fuel and in the voids of the canister. Many of these process only occur if the isolation of the canister is breached and water enters the canister. Radiolysis of water is an example of such a process, which can in turn influence the chemical conditions in the canister. Water in the canister can also cause corrosion of the fuel’s cladding tubes. If water comes into contact with the fuel it can lead to dissolution of radionuclides. Dissolved radionuclides can diffuse in the water and thereby escape from a damaged canister. Fuel dissolution is therefore an important process for showing what might happen if a canister fails to isolate the fuel, which is a part of the safety assessment. Fuel dissolution is a priority area in RD&D- Programme 2001. The canister is an important barrier in the repository. It consists of different parts. Outermost is a shell of copper, and the insert is of cast iron – outer corrosion resist- ance combined with inner strength. Corrosion resistance and strength are important properties. Processes that affect these properties are therefore urgent fields of knowl- edge. Large resources are being devoted to studies of copper corrosion and stress corrosion cracking (SCC) in the copper canister. Corrosion inside a canister is also dealt with in the event that water should enter. The study of strength that was used for SR 97 needs to be brought up to date. Strength needs to be calculated using more realistic material data for the cast iron insert. SKB will also investigate the long-term safety of a canister type with a slightly thinner shell but a heavier-duty insert. The buffer of bentonite clay is supposed to protect the canister mechanically against minor rock movements. It is also supposed to retard solute transport. Corroding substances should be kept from reaching the canister, and if the canister is damaged the buffer is supposed to retard the migration of radionuclides. After the buffer and canister have been placed in the deposition hole, the buffer will reach a stable water- saturated state. This may take ten years or so. At the same time, the canister emits heat which has to be conducted out to the rock via the buffer. It is important to be able to predict the state of the buffer after it has been saturated with water, which is the stable state in the very long term. The initial evolution of the buffer is therefore studied in the Äspö HRL and by means of models. The water-saturated state is also investigated. Important processes in the latter case are effects of saline water and gas transport.