Basic nuclear chemistry research. A building block in the safe management of radioactive waste

Basic nuclear chemistry research provides building blocks covering various aspects of nuclear waste management: Within the demonstration of long-term safety of a repository for radioactive waste, it covers credible scenarios in which a contact of water and the respective waste form is assumed. Over the past few years, significant progress has been made in elucidating relevant chemical/geochemical processes. Thus, research performed over the past few years about the behavior of spent nuclear fuel has shown that, unlike earlier assumptions, corrosion of the waste matrices under oxidizing repository conditions can almost be excluded. In the presence of a corroding cask, many radionuclides are reduced to sparingly soluble or highly sorbent compounds, and the corrosion rate of the fuel proper is lower in the relevant scenarios than assumed so far. In a similar way, this applies to radionuclide releases from cemented low and intermediate-level radioactive waste. In the meantime, also processes have been understood much better which give rise to radionuclide retention in host rock, such as argillaceous rock. This has led to the development of geochemical models able also to take into account changes in geochemical conditions and resulting in conservative assumptions being relaxed. Various partitioning and transmutation (P and T) processes are currently under intense international discussion in an effort to separate selectively minor actinides (Am, Cm, Np) from the nuclear fuel for subsequent transmutation. Even if a P and T process were to become reality, a repository would still be needed. However, the share especially of longlived radiotoxic transuranium elements in the waste could be reduced by several orders of magnitude. Liquid-liquid extraction processes using highly selective extraction ligands, which are based on the existing technical-scale PUREX process, have reached a most advanced state. In addition, some countries also study electrochemical processes employing molten salt. Research is conducted into the development and improvement of extractands, extraction processes, but also to improve knowledge of the molecular aspects of chemical reactions. (orig.)