LLW is defined as waste that contains only limited amounts of long-lived radionuclides, but still requires robust isolation and containment for periods up to a few hundred years. It is suitable for disposal in engineered near­surface facilities. ILW has a radioactivity content that requires disposal at greater depths, of the order of tens of metres to a few hundred metres. Disposal of ILW was discussed in Section 14.4.6.

Disposal facilities for LLW have been in operation for more than 20 years in several countries around the world. Some of the earlier disposal facilities had a very simple design and the waste was essentially disposed of in trenches above the water table and with a watertight cover. The more modern disposal facilities have a more engineered design with several bar­riers against release. Two different types can be distinguished, engineered surface facilities and engineered facilities in rock chambers. Both types of facilities can superficially be described as disposal in a house that should remain tight for water intrusion, but which still has control over any water coming out from the house. In all cases the multiple barrier approach is being used to ensure long-term containment of the radioactive elements.

Two examples of near-surface engineered facilities are the Centre de Stockage de l’Aube (CSA) in France and El Cabril in Spain, which have been in operation since the early 1990s. Similar facilities are in operation or under construction in several other countries, e. g. Japan, China and Belgium.

In CSA the disposal is made in large concrete structures (25 x 25 x 8 m) that are built on the surface (Fig. 14.13). The conditioned waste packages are placed in the concrete structures and subsequently surrounded by con­crete. When one concrete structure is filled a reinforced concrete lid is cast, including an impermeable cover. The disposal operations take place under a temporary roof that can be moved from disposal structure to disposal structure. Underneath the concrete structure there is a channel system for collection and control of any water that might come out of the structure.

Each concrete structure can house about 2500 m3 of conditioned waste. The whole CSA site is designed for 1,000,000 m3. After completion of the dis­posal the concrete structures will be covered by clay and earth and grass will grow on top of the mounds thus made (Fig. 14.14). The site is intended to be surveyed, including control of any effluents, for at least 300 years, i. e. approximately 10 half-lives for cesium-137 and strontium-90. The long-term safety of the disposal (>300 years) is based on the low content of long-lived radioelements, the characteristics of the waste form and packages, the watertight concrete structure and finally the surrounding geology with a low water flow.

LLW disposal facilities in rock chambers at about 100 metres depth are in operation at Olkiluoto and Loviisa in Finland and Forsmark in Sweden (SFR). Other similar facilities are under construction in Korea. In some countries disposal of LLW is planned at greater depth, e. g. in Germany (Konrad) and Canada (Bruce).

In SFR the repository has been placed between 50 and 100 metres below ground level. It consists of several different rock chambers that have been adapted to the type and activity level of the waste (Fig. 14.15). Some very low-level waste is disposed of directly in the rock chambers with no extra barriers than the waste package itself and the rock, while the more active LLW is placed in a large concrete silo (50 m high, 50 m diameter) and sur­rounded by concrete. Between the concrete silo wall and the rock a buffer of bentonite clay is introduced to further reduce any leakage. The multiple barriers are thus the waste form and package, the concrete structures, the bentonite clay and the rock. The facility has been built with the intention of making it possible to abandon it without further surveillance once it has

been filled. Whether this will happen in reality is of course a decision to be taken by future generations.

Very low-level waste (VLLW) is defined as waste that does not meet the criteria for exemption, but has such low activity content that it does not need a high level of containment and isolation. It is thus suitable for dis-

posal in near-surface landfill-type facilities. An example of such a disposal facility is Morvilliers in France (Fig. 14.16). These types of facilities should also be part of the infrastructure needed in any individual country introduc­ing nuclear power plants. They will be needed at the time of dismantling a power plant.

14.6 Conclusions

The management of radioactive waste has sometimes been seen as the Achilles heel of nuclear power production. It will require very long-term considerations also for the period after the nuclear power production has been stopped. Some of the radioactive wastes are very hazardous and will require very careful handling and management. They are also long-lived and will require isolation over hundreds to hundreds of thousands of years. The volumes to be handled are, however, quite small and the utmost care can be exercised without significantly increasing the cost of nuclear power production (a few percent of the production cost) or putting undue burdens on the future. All countries with nuclear power plants have an active pro­gramme to responsibly manage their radioactive waste by treatment, con­ditioning and storage today and by operating or developing disposal facilities for tomorrow. Preparations for disposal of low-level waste from reactor operation should be considered from an early phase of planning nuclear power as these types of waste will occur from the start of the reactor. They should be part of the infrastructure necessary for starting a nuclear power programme. Also the future handling of the spent nuclear fuel should be considered at an early stage, although construction of facili­ties will only be needed decades later.

In this chapter several examples of the management principles, strategies and methods have been described. It should be clear that the final choice of strategy will depend on the national conditions, e. g. size and prospects of the nuclear power programme, industrial capacity and geological condi­tions. It will often be too early for a country considering the introduction of nuclear power to decide from the beginning what strategies should be chosen, e. g. concerning reprocessing and recycling and concerning disposal. It is, however, very important that good comprehension of the options is developed early and to see how different options could be implemented in the specific country. It is also very important to ensure from the start of nuclear power production that funding will be available to take care of the waste (including decommissioning of the power plants) when needed, taking into account that many of these costs will appear long after the power production has stopped. It should be realized that introduction of nuclear power implies an undertaking for a hundred years or more.