European Clearinghouse: Incidents related to reactivity management. Failure modes and corrective actions

This work is part of the European Clearinghouse on Nuclear Power Plant Operational Experience Feedback (NPP OEF) activity carried out at the Joint Research Centre/Institute for Energy (JRC/IE) with the participation of nine EU Regulatory Authorities. It investigates the 1999 Shika-1 criticality event together with other shortcomings in reactivity management reported to the IAEA Incident Reporting System in the period 1981-2008. The aim of the work was to identify reactivity control failure modes, reactor status and corrective actions. Also initiating factors and associated root causes were investigated and are reported elsewhere. None of the events analysed had radiological consequences outside the power plant. In some of them, criticality was reached for a short time. Most of the events resulted in changes in procedures, material or staff and management training. This paper summarises the action taken at power plants and by the regulatory bodies in different countries to avoid repetition of similar events. It identifies insights that might be useful to reduce the likelihood of operational events caused by shortcomings in reactivity management.