SUMMARY

This study aims to perform a radiation hazard and shielding analysis for a new Cryomodule Repair and Maintenance Facility (CRMF) that will be built at the SLAC National Accelerator Lab (SLAC). CMRF is part of the Linear Coherent Light Source-II-High Energy (LCLS-II-HE) and LCLS-II projects, part of the world's first high-energy X-ray free-electron laser. CMRF aims to support their operation; the repair and testing of cryomodules can occur onsite at SLAC instead of being shipped across the country, which is a significant project and operational risk for LCLS-II and LCLS-II-HE. During normal operation at CMRF, the cryomodule can accelerate electrons up to 168 MeV and will be operated in a shielded enclosure inside the CMRF.
At such high energy, several radiation risks must be considered. This study will investigate the radiation hazards to radiation workers from prompt radiation, residual radiation, air activation, and groundwater activation. The goal was to ensure that while the cryomodule was in operation, the dose rate at 30 cm outside the bunker was less than five µSv per hour (0.5 mrem/h). When the cryomodule is turned off, the dose rate inside the bunker should be less than five µSv per hour to allow entry to the bunker. Furthermore, this document will cover the development of efficient shielding strategies to ensure the safety of personnel working at the CMRF and the environment. FLUKA, a Monte Carlo radiation transport code, was used for the radiation hazard and shielding analysis.
The radiation hazard analysis indicated insufficient shielding design, resulting in an excess dose to workers. Therefore, a shielding analysis was performed, investigating two distinct shielding methods. A finalized shielding plan was developed adhering to the dose rate limit of five µSv per hour for radiation workers during regular operation. The results will be used to implement radiation safety guidelines for CMRF by the Radiation Protection Department at SLAC.