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Management of radioactive waste
The primary task in this research area is to coordinate the development of concepts and processes that can address the key outstanding issues in radioactive waste management and disposal. More specifically, the Seventh Euratom Framework Programme (Euratom FP7) supports research on this topic as to its concrete and practical applications, such as repository design or all aspects linked to the geological disposal of nuclear waste.
Furthermore, it finances activities that demonstrate the technologies and safe disposal of spent fuel and long-lived radioactive waste in geological formations (deep geological disposal) and that investigate ways to reduce the amount and hazard of the waste by partitioning and transmutation link 1 or other techniques. Societal issues are also included.
The basic principle
The basic principle of radioactive waste management is that neither current operations nor their potential consequences should expose any individual now or in the future to a level of risk or harm that is unacceptable by today’s strict international radiation protection standards.
Any waste that contains more than specified trace amounts of radioactive elements is termed ‘radioactive waste’. All industries generate waste during product manufacture, while radioactive waste is generated by many industrial practices, as well as by hospitals and research facilities.
However, the largest producer is the nuclear industry, generating radioactive waste at all stages of the production and use of reactor fuel, from the mining and processing of uranium ores to the management of the irradiated or spent fuel after it is removed from the reactor. In addition, decommissioning of power stations and other nuclear facilities produces significant amounts of mainly low-level waste (e.g. structural steelwork that has been irradiated with neutrons).
Radioactive waste is broadly classified as low-, intermediate- or high-level waste. These are generic qualitative classifications and are indicative of the intensity of radiation emitted by the waste. The higher the level, the more substantial are the protective measures required during handling, transport, storage and disposal.
High-level waste may contain several billion becquerel (Bq) per cm3 of waste compared with only a few tens of Bq per cm3 in the case of low-level waste. 1 Bq is equivalent to one radioactive decay per second. By way of comparison, milk contains 50–80 Bq per litre and the human body on average 130 Bq per kg. The type of radiation emitted is also important, with the most penetrating forms requiring greater thicknesses of shielding material in order to protect the workforce and public.
Another criterion of waste classification is its decay time. The hazard posed by radioactive waste decreases over time, owing to radioactive decay. Depending on its composition, waste can remain radioactive and thus a potential hazard for months, years or much longer periods of time (thousands of years). However, the more intense the radiation, the more rapid is the decay.
The accepted management strategy for the vast majority of radioactive waste is to concentrate and contain or confine it over the period during which it presents a potential environmental or health hazard.
Low- and intermediate-level waste is directly processed into solid waste. This solid waste is disposed of in dedicated disposal facilities on the surface or in shallow rock chambers. Such disposal facilities have existed for over 20 years in several Member States. In other Member States siting of such facilities is in progress.
At present, the nuclear power industry temporarily stores spent nuclear fuel either near the reactor sites or in centralised storage facilities. The fuel is generally kept in deep water-filled pools in order to ensure cooling and to provide shielding from the intense radiation. However, depending on national practice, spent fuel is not necessarily considered as waste. Spent fuel can be reprocessed and the unused uranium and plutonium recycled into new fuel elements.
Reprocessing is a complex industrial process that chemically separates the unused fuel from the much smaller but highly radioactive waste fraction. This high-level waste is then vitrified by mixing it with molten glass, which cools and solidifies to produce a resistant and durable waste form. These vitrified residues and spent fuel not destined for reprocessing have been accumulating in storage facilities for decades, though now a more permanent management solution is close to implementation.
A common European view on the most appropriate disposal option for these very hazardous radioactive wastes has been developing over recent decades. It recognises deep geological disposal as the most viable and safest long-term solution.
The successful research carried out under previous Euratom framework programmes is enabling current activities in FP7 to be truly implementation-oriented. The objective is to demonstrate that the technology is ready for deployment and can be delivered safely and economically.
Research in progress
Geological disposal link 2 comprises the disposal of waste hundreds of metres underground in engineered repositories specially constructed in geologically stable rock layers. The scientific community considers this to be the safest way to manage the spent fuel and hazardous long-lived radioactive waste. Research in this area involves engineering studies and demonstration of waste repository designs as well as aspects such as radionuclide migration and gas generation. In situ characterisation of repository host rocks, both generic and in site-specific underground research laboratories, are ongoing, as well as other studies on repository environment.
Partitioning and transmutation link 3 (P&T) are methods that aim at reducing the amount and/or radiotoxicity of long-lived radioactive waste, thereby minimising the timescale required for isolation and optimising the space requirements underground. Partitioning is the advanced chemical separation of the most hazardous radionuclides from high-level waste and transmutation is their nuclear conversion into stable or short-lived nuclides. Research in this area could form the basis for the development of pilot facilities and demonstration systems for the most advanced P&T systems, involving sub-critical and/or critical link 4 nuclear reactors (in particular generation-IV designs). Research is also exploring the potential of concepts that produce less waste in nuclear energy generation, such as the more efficient use of fissile material in existing reactors.