RELIABILITY ANALYSIS OF THE ESS TARGET SAFETY SYSTEM

摘要

The European Spallation Source (ESS) will be a 5 MW neutron spallation research facility where an energetic proton beam incident upon a helium-cooled tungsten target is converted to neutron beams, see [1] for more detail. The Target Safety System (TSS) is part of the overall radiation safety plan for the ESS Target Station. As such, in case of an abnormal event, the TSS will protect the public from exposure to unsafe levels of radiation, prevent the release of radioactive material beyond permissible limits, and bring the neutron spallation function into a safe state. The TSS is a safety interlock system consisting of two redundant trains, one based on relays and the other based on safety PLCs. The radiation safety functions for the ESS target were derived from the hazard and accident analyses of target station systems and areas. By analyzing the accident scenarios quantitatively, the radiation dose consequences to the public were determined. The dose consequences combined with the probability of occurrence identifies the level of risk for each event, and defines the appropriate risk reduction required for the TSS Safety Instrumented Functions (SIF) in order to achieve a tolerable level of risk. Analysis of the hardware reliability of the TSS will be presented. This is identified as the safety integrity level (SIL), and describes the Probability of Failure on Demand (PFD) of each SIF, including input devices, logic modules, and final element devices. The results from the SIL verification illustrate that based on the current architecture the TSS SIFs meet the SIL target.