In a high-energy lepton collider such as the Future Circular Collider (FCC-ee) at CERN, several phenomena create a challenging radiation environment for accelerator components and equipment including cables and electronics. This paper examines synchrotron radiation (SR), dominating at the highest beam energies (ttbar) for two different optics schemes. Recent developments in the design of photon stoppers and dedicated radiation shielding are presented, highlighting progress towards a more realistic configuration while maintaining acceptable annual ionizing dose levels. The study covers the contribution of the collider ring and the impact on the attached alcoves, housing radiation sensitive equipment. The absorbed power in accelerator components and the surrounding tunnel environment is evaluated for various operation modes to ensure compliance with the thermal load limits of the ventilation system. Furthermore, radiation and particle fluence levels dominated by photo-neutron production are quantified for the electronics bunkers located below the beamline. These results are used to assess the feasibility of employing radiation-tolerant, commercial-off-the-shelf electronics in these areas.

MolFlow is a test-particle Monte Carlo code for ultra-high vacuum simulations, primarily intended for use in the field of particle accelerators. This contribution gives an overview of updates made to the code in recent years. The graphical user interface has been improved and a new feature has been added for extracting simulation results along user-defined 3D paths. Additionally, the code can now count the number of particles present on a surface at a specified time. Furthermore, the calculation of particle residence time (sojourn time) has been updated to allow for temperature variations during a particle's residence on a surface. This enables simulations of surface decontamination through heating (bakeout). Finally, MolFlow can now simulate particle collisions with static background gases using the hard-sphere collision model.

The design of the Future electron--positron Circular Collider (FCC-ee) vacuum system integrates vacuum engineering, impedance mitigation, and surface functionalisation to achieve compatibility with high beam currents and sustained operational stability. Based on these design principles, this contribution presents an overview of the principal vacuum components and outlines the studies conducted to evaluate and optimise their electromagnetic and vacuum performance. Particular emphasis is placed on the interplay between material properties, surface treatments, and component geometry, as well as on the distribution and integration of vacuum elements and transitions within the accelerator. Impedance studies were performed to evaluate the electromagnetic impact of representative vacuum components. The main findings are summarised, highlighting the achieved performance and outlining directions for further optimisation.