For category B waste (low or medium-level and long-lived waste), the disposal solution must offer protection for periods of time that exceed all those contemplated within the framework of conventional industrial projects (several tens or even hundreds of thousands of years). It is only after these extremely long periods of time that the radioactivity of this waste will be reduced by natural decay and reach a value that is only a fraction of the natural radiation to which we are all permanently exposed. The solution recommended internationally, which is the reference solution in Belgium, is deep disposal.

Internationally, scientists believe that deep disposal in stable geological layers is an appropriate solution for the long-term management of radioactive waste. Among the host formations generally considered are salt (layer or dome), crystalline rock (granite) and clay. More and more countries, however, opt for clay (Switzerland and France among others).

In Belgium, the matter has been the subject of regular discussion for over 25 years. The research carried out by ONDRAF/NIRAS, with the collaboration of SCK·CEN (the Belgian nuclear research centre in Mol) and several engineering offices and universities, must determine whether disposal in the poorly indurated layers of clay (such as the Boom clay in the north-east of the country) can guarantee protection of man and his environment in the long term. The salt rock used in Germany in particular is not found in the Belgian subsoil. Granite formations, such as those used for the disposal in Sweden and Finland lie more than 2,000 meters deep. They have never been explored. Boom clay has been stable for several million years so it should remain so for the periods required for radioactive waste to become harmless.

Although all conclusions are positive, research will continue for several years before a concrete decision will be taken on the way and the place where the waste will be actually disposed of. Besides the technical research, a social dialogue must be started on the way Belgium intends to manage its category B waste in the long-term.

	a socially acceptable solution
	the principle of multiple safety function
	the concept of deep disposal (for category B waste)
	the results of the research carried out so far?

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A socially acceptable solution

The SAFIR 2 report was limited to scientific and technical aspects. It evaluated confidence in the safety, feasibility and the soundness of the disposal system studied. However, a long-term radioactive waste management solution must not only be safe and technically feasible, it must also be acceptable to society and ONDRAF/NIRAS was particularly conscious that even if a solution were scientifically correct, it could not go ahead without political consensus and social acceptance.

In the case of category A waste, this is the reason why the deep disposal solution and the way in which this waste will be disposed of are being discussed by local partnerships.

In the case of category B and C waste, it is ONDRAF/NIRAS's opinion that social dialogue between all concerned should be encouraged to the full. This is why, in coming years, the ONDRAF/NIRAS Research & Development programme will try to re-establish equality between the technico-scientific and societal dimensions. In concrete terms, this means that the participation of society will take the form of real dialogue which is open to all parties involved. Indeed, a decision-making process must be put in place that is capable of responding to society's expectations. Clearly, ONDRAF/NIRAS, will have to establish structures representing society as a whole that will be in a position to influence the continuation of the Research & Development programme.

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The principle of multiple safety function

In order for the radioactivity contained in the waste to reduce without harming man or the environment, the disposal solution must provide optimum protection in accordance with the principle of multiple safety function. This principle consists in using a series of successive and complementary barriers each with its own function within the scope of the long-term safety of the repository (impermeability, corrosion resistance, dissolution, solubility, retention, diffusion, leaching, etc.). The various natural or man-made barriers must, each in their own way, contain the radioactive substances and slow their migration in the long term.

The barriers will be selected and designed in such a way that the overall performance of the disposal system does not depend on any single barrier alone. This ensures that even in the event a barrier did not function entirely as intended (because of unexpected or unlikely events), a sufficient safety margin would still be guaranteed.

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The concept of deep disposal (for category B waste)

The generic concept of deep disposal studied in Belgium takes the form of a network of concrete underground galleries (1) hollowed out in a poorly indurated layer of clay (2) in which the waste would be buried. These galleries would be linked together by one or more main galleries (3) accessible by shafts (4).

Deep disposal is being considered for the three categories of waste. While the overall repository architecture is identical for all classes of waste, certain barriers would differ depending on the class of waste to be disposed of. The principle of multiple safety function also applies to a deep disposal. Which are the different barriers for category B waste? (Attention: the concept for the disposal of category B waste is currently being designed. The illustration below dates from June 2004. It can change with time.)

First, the drums of conditioned waste are enclosed in groups in a big concrete container. Cement mortar is poured into the container to fill the spaces between the drums. The waste package obtained in this way facilitates transportation of the waste to the galleries of the repository and its recovery if necessary. It also forms the first barrier between the waste and the biosphere. The repository would take the form of a network of underground concrete galleries in which the waste package are buried. When all the galleries are full, the repository is entirely closed off with backfilling material. The repository infrastructure is thereby completely isolated from the outside world.

The main barrier on which the safety of the repository depends is the geological layer in which this facility could be built, that is to say, a layer of poorly indurated clay. Given its low permeability and high capacity for retaining radionuclides, this barrier alone would be sufficient to guarantee a high degree of both short-term and long-term safety.

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The results of the research carried out so far?

The SCK·CEN (Belgian Nuclear Research Centre) began research in 1974 to determine whether radioactive waste can be buried in Boom clay and an underground research laboratory named HADES was set up (at a depth of over 200 meters) in the early 80s to study this clay as a potential host formation. Since its creation in 1980, ONDRAF/NIRAS has managed and coordinated the Belgian Research & Development programme in close collaboration with the SCK·CEN and with financial support from the European Commission. In 1995, this collaboration led to the creation of an Economic Interest Group known as EIG PRACLAY. In 2000, EIG PRACLAY was renamed EIG EURIDICE.

The Belgian Research & Development programme is a methodological programme dedicated to determining whether it is technically and economically possible to come up with a safe solution for the deep geological disposal of radioactive waste. This programme, which is necessarily multidisciplinary and progressive, can be divided into three phases:

• phase one (1974 - 1989)
• phase two (1990 - 2000)
• phase three (2001 - ...)

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For further information:
• See our page on the SAFIR 2 report
• Heading EIG EURIDICE
• The SCK·CEN site

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