Leaching Behavior of HTR Fuel Elements and Fuel Particles in Salt Brine

[Automatically extracted and translated] For the safety analysis of the storage of HTR fuel elements in geological repositories, the release behavior of radionuclides during the post-operational phase of the repository must be known. Since it cannot be ruled out that brine may penetrate into remaining cavities of the sealed repository to a limited extent, the containers with fuel elements stored there may corrode and thus come into contact with saturated salt solution. It is assumed that activity will be released from the contamination of the fuel elements and from defective fuel particles in this case. However, the vast majority of the activity is enclosed by intact fuel particles and does not contribute to the release. The storage in the repository is to be carried out using borehole technology, with the MAW area with a temperature limit of 90°C, but also the area for vitrified waste with a maximum temperature of 200°C, being considered as the storage location from today's perspective. Due to the plastic behavior of the salt dome, the remaining cavities close, with high pressures (up to 300 bar) theoretically acting on enclosed brine quantities and storage containers with fuel elements, which can lead to partial mechanical destruction of the fuel elements. Crushing tests show that the fuel element matrix is destroyed, but the fuel particles remain largely intact. The present results were determined on mechanically intact fuel elements. Taking these boundary conditions into account, an investigation program was carried out to determine the release behavior of HTR fuel elements under repository conditions.