Spent fuel and high-level waste from reprocessing is highly radioactive and remains dangerous for thousands to hundreds of thousands of years and will require isolation in a deep geological repository. Also the ILW from reprocessing will require disposal in a geological repository. So far no such repository has been built. There is, however, an international consensus among the experts that disposal in a deep geological repository can be made in a safe way and that the long-term safety can be assessed (NEA, 1999a, 1999b, 2009; Witherspoon and Bodvarsson, 2006). Several countries are developing the design for a deep geological repository and are in the process of looking for a suitable site. Good progress is being made in Finland, France and Sweden. Finland and Sweden have decided to dispose of the spent fuel directly. Sites have been chosen and the licence is under prepara­tion. Operation is foreseen to start shortly after 2020. France will dispose of high-level vitrified waste and other long-lived reprocessing waste at depth in a clay formation in eastern France. The detailed siting is going on and operation is planned for around 2025. The progress of all these three projects will be very important as it will show the feasibility of disposal irrespective of whether the fuel is reprocessed or not.

The principles employed for geological disposal are fairly simple. The waste, which in itself is a solid that is resistant to dissolution and leaching, is placed in a tight container that is designed to remain tight for a long time and the container is placed in an environment that is benign for keeping the tightness. To ensure the latter, the siting looks for a geological medium that can be expected to remain mechanically and chemically stable for the long time periods required. In particular the chemical processes at depth, with small water movements, are very slow.

The safety of waste disposal is based on the multibarrier principle, i. e. the waste shall be surrounded by several barriers that are functioning inde­pendently of each other. This means that if one barrier fails, or our knowl­edge of the processes affecting the integrity of that barrier is not correct, the other barriers will ensure the long-term safety.

In Fig. 14.9 the disposal concept (KBS-3) developed in Sweden and Finland is shown. The spent fuel is encapsulated in copper canisters that are stabilized by an internal iron structure. The waste canisters are placed in boreholes at the bottom of tunnels at about 500 m depth in the granitic rock found in Sweden and Finland. In the boreholes the canisters are sur­rounded by bentonite clay, which provides a mechanical and chemical pro­tective buffer. At the end also the tunnels are backfilled with a mixture of bentonite and sand. This is the system that will be used for the first geologi-

cal disposal facilities that are considered in these countries for disposal of spent nuclear fuel. The barriers are:

• The fuel matrix itself, in which most of the radioactive elements are part of the matrix and are released only when the matrix is dissolved or cor­roded. The dissolution/corrosion rate is very low in the kind of water existing at the repository depth.

• The copper canister, which is highly corrosion resistant in the chemical environment created by the bentonite and the reducing groundwater at the repository depth. The iron structure in the canister ensures the mechanical stability of the canister against the pressures found at depth from the rock, the groundwater and the swelling bentonite clay.

• The bentonite clay, which reduces the inflow of corrodants from the ground water to the canister and also ensures that the outflow of radio­nuclides from the fuel, if the tightness of the canister is broken, is very slow. The bentonite also has a chemical buffering effect, keeping a stable pH.

• The surrounding rock, which has a low water flow and ensures that the transport of corrodants to the bentonite buffer and the canister is slow. The rock also provides mechanical stability around the canister. Finally the rock acts as a filter if the tightness of the canister is broken and radionuclides are transported out from the fuel through the canister and the bentonite. The filtering function has two components. First, the trans­port of water is very slow, thus providing time for radiological decay of the radionuclides, and second, the transport is further delayed by chemi­cal adsorption of the radionuclides at the surfaces of the cracks through which water and radionuclides are transported.

Similar disposal systems are being being considered in other countries but have to be adapted to the specific geological settings chosen and to the waste forms. Different geological media are being considered in different countries. In addition to hard rock like granite, also clay and salt formations as well as sedimentary rocks are being investigated. As noted above, a clay formation has been chosen in France, for example, and disposal in salt has been the main line of investigation in Germany. Also different canister materials are being considered.

The disposal of ILW could in principle be based on a simplified version of the basic principles for HLW disposal, as the main concern for this waste could be human intrusion disposal at less depth, e. g. 100 m is considered for ILW. A repository for ILW has been in operation in the USA since the mid-1990s. It is the Waste Isolation Pilot Plant (WIPP) in Carlsbad, New Mexico. Here the waste is disposed of in a dry salt formation in large salt rock chambers that are subsequently backfilled with crushed salt (Fig. 14.10). Another ILW repository is under construction in Germany at the Konrad mine.

An important component in the development of a deep geological dis­posal facility is the study of different technologies and processes in under­ground research facilities. Several such facilities have been developed around the world, e. g. the HADES facility in clay in Belgium, the URL in granite in Canada, the Aspo laboratory in granite in Sweden, and Grimsel in granite and Mont Terri in claystone in Switzerland.

Waste disposal is not only a technical question, it is a highly political and societal question and requires a strong commitment from society as well as from the industry. In several countries there have been political setbacks delaying programmes. The most spectacular ones have been in Germany and the USA. In Germany the development towards a repository in the Gorleben salt dome was well underway in the 1990s when it was halted by a political decision on a 10-year moratorium to investigate alternatives. At the time of writing this book (September 2010) discussions are underway to resume the work in Gorleben. In the USA a decision was made several

years ago to develop a repository at Yucca Mountain in Nevada. Following many years of costly investigations and the preparation of an extensive licence application, a political decision was, however, made in 2009 to bring the project to a halt, although at the time of writing the final fate of Yucca Mountain is not yet determined. These examples show that politics can easily cost much more than engineering.