Lessons learnt from the reliability analysis of the personnel safety and access control system of a tokamak fusion experiment

Pulsed Tokamak experiments give rise to significant direct radiation even in the pre-tritium phase. A fundamental safety requirement is the provision of high integrity personnel access control systems to protect site, operational staff and the public from the risk of exposure to high radiation. The paper discusses the radiation hazards during the early hydrogen/deuterium operation and the different levels of installed safeguards which included diverse safety systems in the form of conventional hard wired interlocking and programable logic controllers. The form of a detailed reliability analysis assessing the risk of individual exposure to high radiation (for both the public off-site and staff on-site) is discussed together with the lessons learnt and some of the design changes implemented. An interesting feature is the impact of human reliability in the analysis and how a recently developed technique (HEART) provided an estimation of error rates. The confidence gained in addressing the reliability of personnel and public protection against radiation hazards under normal operating conditions provides an important foundation for the safety analysis of fusion plant with significant tritium inventory. (author). 4 refs, 2 figs, 1 tab