The Nuclear Incident at the Paks Nuclear Power Plant, Hungary. Annex I. Case study that considers the guidance and recommendations provided in this Safety Guide (Russian Edition)

The Paks nuclear power plant in Hungary comprises four 440 MWe water cooled, water moderated power reactors that supply about 40% of the electricity to the country. Units 1–4 went into commercial operation between 1983 and 1987. On 10 April 2003, an incident occurred in the course of operations to clean fuel assemblies during a scheduled maintenance shutdown for Unit 2. Thirty fuel assemblies had been removed from the Unit 2 reactor and placed in a fuel cleaning tank approximately 10 m under water in a shaft adjacent to the fuel pool. The external surfaces of the fuel assemblies were being cleaned, using a specially designed chemical cleaning process, to remove depositions of magnetite from the fuel assembly cladding. At 21:53 on 10 April 2003, workers detected an increase in the activity of ⁸⁵Kr, from a measurement system installed in the cleaning circuit. At about the same time, the instruments measuring the activity concentrations of noble gases in the reactor hall indicated that the 'emergency level' had been reached. The timeline of the different events during the incident is shown.