Speaker
Description
The European Spallation Source (ESS) is developing the Contamination Alarm for Target (CAT) system as a Level 3 defence-in-depth measure for worker protection. CAT is intended to detect contamination leaking from the target helium coolant loop into surrounding utility areas and, when a defined threshold is exceeded, trigger evacuation through the facility's existing fire alarm system. Tritium detection is currently the leading candidate, as it can be distinguished more reliably from the helium background than the other approaches considered.
CAT has an overall reliability target of 10⁻² PFD for the complete detection-to-alarm function. The detection subsystem will be designed according to IEC 61511, while the alarm subsystem will follow the applicable fire alarm standard, since it will be integrated with the existing facility system. This avoids introducing a separate alarm system, but means that the two parts are governed by different standards and involve different technologies and organisational ownership.
Several questions remain regarding the reliability of the overall function. These include how to allocate the PFD target between the two subsystems, how to identify and mitigate common-cause failures across the system boundary, and how to ensure that the interface between the two systems does not become a weak point.
This paper presents the current CAT requirements, constraints, and design options. It also discusses the reliability questions raised by combining subsystems developed under different standards, and seeks feedback from the accelerator reliability community, including experience from similar detection-to-alarm systems.