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Non-nuclear energy

Geological disposal

Fission and radiation protection
Fusion
   

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.

Multiple barriers

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.

Research objectives

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.

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