Overpressurization transient in a BWR [boiling water reactor] with multiple failures in safety systems

After the accident at Chernobyl, the Finnish Centre for Radiation and Nuclear Safety, which is the Finnish Nuclear Energy Authority, enlarged the scope of reactivity-initiated accident analysis beyond that for design bases accidents to determine the real safety margins of nuclear power plants. In this connection, boiling water reactor (BWR) overpressurization events with multiple failures in safety systems have also been studied. Analyses have been performed at TVO 1 nuclear power plant, which is a 2,160-MW(thermal) BWR in Finland. The most probable overpressurization incident, pressure controller failure, was chosen for analysis. In this event, all turbine control valves close simultaneously, initiating an overpressurization transient in the pressure vessel. The objective of these overpressurization analyses was to find out how much reactivity it is possible to inject during an overpressurization transient with multiple failures in the safety systems