With mankind confronted by an energy crisis and climate change, nuclear power is back on the scene. But despite excellent energy efficiency and low CO2 emissions, nuclear fission still leaves us with the delicate problem of radioactive waste. A typical European response in this area is the Belgian model.

By 2008, the UK began the return to nuclear power by calling for the construction of new reactors. Sweden joined the movement in February 2009 by reviving its atomic energy program, on hold since 1980. In its wake, Paris announced an agreement with Italy to build the first four nuclear power plants there. And all this without any real mass protest. According to a Eurobarometer survey in 2008, almost 44 % of Europeans support nuclear power, compared with 37 % in 2005. Energy dependence and climate change today appear more tangible than a hypothetical nuclear accident, and of more immediate concern than the future manage ment of nuclear waste.

Varying definitions

According to the World Nuclear Association, some 237 nuclear reactors will be built across the world between now and 2030. With 80 % of nuclear waste coming from these reactors, the issue of waste management is more relevant than ever. The remaining 20 % comes from medical applications (detection and treatment of pathologies), agricultural use (elimination of bacteria) and scientific research.

But what is radioactive waste? According to the International Atomic Energy Agency (IAEA), it is “any matter for which no use is foreseen, and which contains radionuclides in concentrations greater than the values that the authorities regard as permissible”.

An EU directive exists defining radiation protection standards, but the actual management of nuclear waste remains a national competence. A joint convention of 1997 simply states that each country will manage its own waste.

“This is a working definition”, says Jean-Paul Minon, Director General of the Organisme national des déchets radioactifs et des matières fissiles enrichies (ONDRAF) (BE). “Like with municipal waste, it is the owner who decides what is of no use. In Belgian hospitals, the radioactive sources used in cobalt therapy are decommissioned as soon as their irradiation power has decreased by half, because this means longer exposure times for patients, even though these sources can clearly still save many lives. We gladly donate them to third world countries, providing they pick up the cost of transport.”

Answer A, B or C?

Since the 1950s, the international community has allowed the disposal of radioactive waste into the environment, mainly in the Atlantic Ocean, where more than 100 000 tonnes of radioactive waste have been dumped in concrete drums. This controversial practice was abandoned in 1982 in favour of other methods of disposal. Currently, it is the interplay of two parameters, the half-life (see box) and the activity of the waste, which determines the appropriate form of management. In the Belgian model, which is representative of what happens in most Member States, nuclear waste is divided into three categories, A, B and C, on which the nature of the container, the type of storage and the permitted exposure time depends.

Class A waste is permanently stored on the surface. As Jean-Paul Minon explains, the volumes to be managed remain reasonable. “For a country of 10 million inhabitants like Belgium, where 55 % of the electricity consumed is of nuclear origin, Class A waste represents 72 000 m³ over the 40-year lifetime of the power stations, including their decommissioning.” This waste is packed in steel drums and stored on the Belgoprocess site in Dessel (BE), pending final destination. The shielding and thickness – between 25 and 80 cm – of the reinforced concrete walls guard against any outward emission.

“We can therefore ensure the safe management of such waste on the surface”, says Jean- Paul Minon, “because its activity level will be down to that of natural background radiation after only 300 years. But this is not true for Class B and Class C waste, where storage periods may extend over hundreds of thou sands of years. These time spans, unmanageable on a human scale, force us to consider deep-layer geological storage.

Test digging

“There is a widespread popular conception that countries already bury their radioactive waste”, notes ONDRAF spokesperson Émile Biesemans. “But this is absolutely not the case. European countries are still carrying out tests in this area to ensure the feasibility of this type of storage. We can consider that Europe has begun tackling the question in time, because Class C waste requires a long period of cooling – at least 60 years – in a tank or on the surface before geological storage”.

Right now the EU has 10 out of the world’s 14 underground laboratories. One of the first, built in 1980, is the HADES – High-Activity Disposal Experiment Site - underground laboratory based in Mol (BE). The scientific research centre is located some 225 metres underground in a layer of Boom clay, seen as a potentially appropriate host geological formation for longlife highly radioactive waste. The site hosts various European programmes examining the hydrogeological, geomechanical and geochemical feasibility of deep storage. The results are allowing scientists to fine-tune their forecasts and their evaluations of the short and longterm modelling.

Hot stuff!

In 2010, a 10-year thermal experiment entitled PRACLAY – Preliminary demonstration test for clay disposal of high-level radioactive waste – will be initiated at Mol. The project’s scientific coordinator, Xiangling Li, is busy defining its objectives. “The high activity vitrified waste that it is planned to store permanently in this way continues to give off heat for hundreds of years. Which is why we are trying to verify, on as long a time-scale as possible, that this heat does not cause major disruptions of the soil, endangering the stability of the excavation and the containment and insulation capabilities of the Boom clay. Preliminary tests in the lab, on-site on a reduced scale and by simulation suggest that Boom clay is an excellent candidate. We are optimistic that this live experiment will confirm our predictions”.

The technological and scientific importance of this project, which is being undertaken with national and European funding, goes well beyond the borders of Belgium. The sharing of knowledge advocated by the scientific teams will be beneficial to countries like France or Switzerland, which have similar geological formations. Certain technical aspects will also be valuable to other EU countries wishing to establish similar storage areas in crystal rock or in salt mines. “It is even possible that our expertise will open up new avenues for the absorption of atmospheric CO2, since the geological storage of this gas is based on similar techniques,” says Xiangling Li.

An effective shield?

Prior to burial, high-activity liquid waste from the reprocessing of spent fuel is vitrified, i.e. trapped inside a glass matrix. This structure should considerably slow the radioactive emissions. “At least that’s what we want to check”, says Elie Valcke, who heads up the CORALUS (Corrosion of alpha-active glass in underground storage conditions) project. “Between 2000 and 2003, we inserted into the Boom clay four test tubes containing several vitrified nonradioactive and highly radioactive test samples, in direct contact with different types of fill. In 2004, two tubes were extracted, one maintained at 30 °C for 3.3 years, and the other at 90 °C for 1.3 years. The results are quite positive since the loss of mass due to the dissolution of the glass was only 0.2 % for the first tube, and 2 % for the second. In both cases, all radioactivity released by the glass wall was stopped by the filling material, including 99.9 % within a radius of just five millimetres.” The scientific team believe that analysis of the last tubes, scheduled to be extracted in 2009 (6.5 years at 90 °C) and 2014 (10 years at 30 °C), will confirm the effectiveness of vitrification.

Jean-Paul Minon is keen to emphasise that even if Class A waste will be stored permanently on the surface from 2016 onwards, no decision concerning the final disposal of Class B and Class C waste has been, taken in Belgium. “Even if the feasibility of deep-layer storage has been demonstrated, the ultimate decision will be not only political but also social. Dialogue with the public has become inevitable. And that’s good. Between now and then, it’s possible that new solutions will be envisaged. Some people believe, for example, in evacuating radioactive waste into space, but our launchers are far from being reliable enough to consider it seriously.”

Marie-Françoise Lefèvre

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The ABC of radioactivity

Radioactivity is a spontaneous process in which unstable atomic nuclei decay, emitting energy and forming stable nuclei of lower mass. This energy takes the form of alpha or beta radiation, often accompanied by gamma radiation. Alpha radiation relates to very heavy nuclei, like that of uranium. It corresponds to the ejection of two protons and two neutrons, or, in other words, a helium nucleus. Beta radiation comes from nuclei presenting an excess of neutrons or protons. Excess neutrons are converted into protons with an emission of electrons, or, conversely, protons into neutrons with an emission of positrons. Gamma radiation, finally, is an emission of highenergy photons that accompanies these nuclear transformations.

Depending on the nature of the nucleus, radioactive processes can vary enormously in time. We call the half-life of an element the time required for the radioactivity of a sample to be divided by 2. For example, a block containing 1 mg of 60Co – with a half-life of 5.2 years – will contain no more than 0.5 mg after 5.2 years, 0.25 after 10.4 years and so on.

The activity of a source is the number of radioactive disintegrations per second and is measured in becquerels (Bq). The dose, a unit directly linked to the biological effects of radiation, is expressed in sieverts (Sv). Thus, death is almost certain to follow exposure to more than 10 Sv, while the radioprotection level acceptable to the public is around 0.001 Sv per year. In general, below 0.005 Sv per hour, waste is considered as low-activity, between 0.005 and 2 Sv per hour, it is considered a mediumactivity, and above this as high-activity waste.

Nuclear safety bodies

While competence for policies for the management of radioactive waste lies at national level, various international bodies exist to disseminate best practices.

IAEA:The International Atomic Energy Agency is a body of the United Nations Security Council. Its primary role is to encourage the safe and peaceful use of nuclear energy. The IAEA has set up the programme of safety standards for radioactive waste (RADWASS) which lists the standards to be met.

UNSCEAR:The United Nations Scientific Committee on the Effects of Atomic Radiation is tasked with assessing the levels and effects of radiation exposure and communicating its findings to governments, and with supporting the development of national security measures.

ICPR:The International Commission on Radiological Protection is an independent organisation that promotes public dissemination of the science of radiation protection and provides safety recommendations on radiation.

NEA:The Nuclear Energy Agency assists member countries of the Organisation for Econo mic Cooperation and Development (OECD) in maintaining the necessary scientific platforms for the safe economic and environmentally friendly use of nuclear energy.