No abstract

After decades of RD&D, mature concepts for the geological disposal of long lived and high level radioactive waste exist and some are close to being implemented. Underground Research Laboratories (URLs) have made an essential contribution to this progress. They enable in situ characterization and testing of host rocks and the demonstration of technologies and component performances at representative scales and under realistic geological conditions. They also offer a tool for training personnel and show aspects of the geological disposal concepts to stakeholders, including the public. In this paper we will present the different types and roles of URLs and we will discuss how the RD&D role of URLs has evolved and how it is likely to evolve in the near future.

Passive safety systems in a nuclear reactor allow to simplify the overall plant design, beside improving economics and reliability, which are considered to be among the salient goals of advanced Generation IV reactors. This work focuses on investigating the application of a self-actuated, gravity-driven shutdown system in a small lead-cooled fast reactor and its dynamic response to an initiating event. The reactor thermal-hydraulics and neutronics assessment were performed in advance. According to a first-order approximation approach, the passive insertion of shutdown assembly was assumed to be influenced primarily by three forces: gravitational, buoyancy and fluid drag. A system of kinematic equations were formulated a priori and a MATLAB program was developed to determine the dynamics of the assembly. Identifying the delicate nature of the balance of forces, sensitivity analysis for coolant channel velocities and assembly foot densities yielded an optimal system model that resulted in successful passive shutdown. Transient safety studies, using the multi-point dynamics code BELLA, showed that the gravity-driven system acts remarkably well, even when accounting for a brief delay in self-actuation. Ultimately the reactor is brought to a sub-critical state while respecting technological constraints.