Is it safe to store high burn-up fuel?
Deep geological repositories are currently the preferred choice for long-term management of spent nuclear fuel. The safety of such underground facilities that exploit natural geology and man-made barriers to isolate radioactive waste is demonstrated quantitatively through performance assessment calculations. EU-funded scientists launched the project FIRST-NUCLIDES(opens in new window) (Fast / instant release of safety relevant radionuclides from spent nuclear fuel) to improve the current understanding of what happens with such barriers. The team focused on high burn-up spent uranium oxide fuel from pressurised and boiling water reactors. Burn-up has increased over the past years enabling nuclear plants to get more power out of fuel before replacing it. However, high burn-up makes the spent fuel hotter and more radioactive –two important considerations in designing storage facilities. Such waste is a source of significant release of radionuclides when a canister fails. Some of the released radionuclides show high solubility in groundwater while others undergo only marginal retention on their way to the biosphere. For safety analysis, researchers need to quantify there lease of these radionuclides. During the FIRST-NUCLIDES project, scientists gathered key input data via experimental investigations and modelling. The results include fission product distribution in fuel pellets, fission gas release after puncturing of spent fuel rods and fission gas and non-gaseous product release from spent fuel in the case of contact with water. The database created includes the largely unknown 'instant release fraction' values of iodine, chlorine, carbon and selenium. All these elements tend to form anionic species that are hardly chemically retained in repository barrier systems. The data and knowledge obtained should increase the confidence in predictions of the instant release of fission and activation products for spent uranium oxide fuel. In particular, the FIRST-NUCLIDES project has improved our understanding of its dissolution behaviour in view of licensing repositories set to be operational by 2025.
