Radioactive waste management
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 or other techniques. Societal issues are also included.
The scientific consensus is that disposal in deep geological formations represents an acceptable and safe method of long-term management of high-level and other hazardous radioactive waste. Likely candidate formations include clay, salt, and crystalline rock strata or deposits that have remained geologically stable for millions of years - having experienced no tectonic, volcanic or seismic activities - and that are likely to remain so for similar periods in the future.
Such a geological repository would consist of multiple containment barriers, each contributing to the required long-term isolation of the waste from the biosphere. Radioactive decay would ensure that, after the eventual degradation of these barriers, only small amounts of radioactivity would be present and the risks to man and the environment posed by the more mobile of these radionuclides migrating towards the surface would therefore be negligible. The depth and location of the facility would also considerably reduce the risk of inadvertent intrusion or access by humans. Crucially, following closure of the facility, no further human intervention would be needed, even though some degree of monitoring would probably continue in order to provide added reassurance. Such a facility would remain safe even in the event of future breakdown in societal structures, and its depth would protect it from natural events such as ice ages.
Geological disposal is based on the concept of multiple barriers, both engineered and natural, that work together to provide containment.
For disposal in hard rocks and clays, the basic engineered barrier components are the waste container (usually metal and often multi-layered) and a buffer of backfill material (clay or cement), which fills the space between the container and the rock.
These barriers work together to provide containment and safety:
- The container protects the waste and prevents any water reaching it for hundreds or thousands of years. By this time, the radioactivity will have decayed to very low levels.
- The buffer of backfill material protects the container, preventing water from flowing around it and mitigating any deep-earth movement. If is highly impermeable, like clay, and has the ability to bind any radionuclides that eventually escape from the container.
- Owing to the very slow rate of natural processes at depth, the bedrock and the geological environment of the repository can provide stable mechanical, chemical and hydrological conditions over very long timescales, allowing the engineered barriers to remain effective for considerably longer than if they were at the surface.
- If the engineered barriers do eventually become less effective, any eventual releases of residual radioactivity will be slowed down, or completely immobilised, diluted and dispersed by the rocks, soils and waters around and above the repository. There will be no impact on the surface natural environment.
In the case of direct disposal of spent fuel, an analogous series of barriers are present, ranging from the ceramic fuel itself to the multiple-fuel-bundle disposal canister and the backfill. As in the case of vitrified waste, the precise nature of these barriers will depend on the type of host rock.
All these engineered barriers together with the very long isolation provided by the chosen geological stratum will prevent radioactive substances reaching the surface of the earth in harmful quantities during the period over which the waste remains a hazard.
Euratom FP7 supports R&D in the areas of engineering studies and demonstrating repository designs, in situ characterisation of repository host rocks, understanding of the repository environment, studies on relevant processes (waste form, engineered barriers, bedrock and paths to the biosphere), development of robust methodologies for the repository performance and safety assessment, and investigation of governance and societal issues related to public acceptance.
A significant part of the programme will focus on engineering studies and design demonstration of effective technical solutions. Initially, these may include aspects such as safe on-site transport, feasibility of constructions and proof of long-term integrity of seals.
The feasibility of eventual waste recovery ('reversibility' or 'retrievability') and the impact on the integrity of the repository system may also be investigated.
These actions focus on the fulfilment of requirements for eventual licence applications (a licence from the national regulatory authority would be needed for the start of construction). However, the actions undertaken are broader than purely technical, including developing arguments for the safety case and studies on governance issues and enhancing public confidence.
Partitioning and Transmutation
When spent fuel is unloaded from a nuclear power reactor, only around 4% by weight is 'ultimate' radioactive waste (i.e. fission products). The rest is made up of unused uranium – most of the initial uranium is still present – and a small amount (1%) of plutonium, which was formed in the reactor. The uranium and plutonium can be recycled and re-used in fresh fuel, an industrial practice carried out in a number of reprocessing plants around the world.
Plutonium is particularly radiotoxic (it is an alpha-particle emitter) for very long periods of time. However, to further reduce the long-term toxicity of the 'ultimate' waste, the small quantities of other hazardous isotopes such as americium, neptunium, caesium, technetium and iodine can also be chemically separated (or partitioned) from the remaining waste before vitrification. The most toxic isotopes can then be converted into stable or short-lived isotopes by nuclear transmutation in fast-neutron reactors or accelerator-driven sub-critical systems.
This is collectively referred to as partitioning and transmutation (P&T). Because P&T aims to reduce the inventories of long-lived radionuclides in radioactive waste, the techniques could alleviate the problems linked to disposal of high-level radioactive waste in deep geological formations and enable optimal use to be made of these disposal facilities.
The primary objective is to provide a basis for the development of pilot facilities and demonstration systems for the most advanced partitioning processes and transmutations systems, with a view to reducing the volumes and hazard of high-level long-lived radioactive waste issuing from the treatment of spent nuclear fuel.
Apart from ways to reduce the volume and long-term toxicity of radioactive waste, research in this field will also explore the potential for new reactor concepts and fuel cycles to produce less waste during the operation of nuclear power plants. This is linked with Generation-IV systems research.
Partitioning processes for viable recycling strategies will need to be developed to full demonstration at pilot plant level. Initially, work may concentrate on extending the technically mature aqueous chemical separation processes that are compatible with both fuel fabrication and future fuel recycling strategies.
In parallel, the development of pyrochemical techniques for partitioning will continue in line with the roadmaps outlined for this technology under the Euratom Framework Programmes.
This research will lay the groundwork for future sustainable nuclear fuel-cycle strategies, whether involving transmutation in a dedicated waste-burning accelerator-driven system (i.e. a sub-critical reactor) or in future generation-IV power plants.
These techniques may allow the period over which high-level radioactive waste remains hazardous to be reduced from hundreds of thousands of years down to a few hundred years.