1998

Vanttola, Timo

The Reactor Safety (RETU, 1995-1998) research programme concentrated on search of safe limits for nuclear fuel and the reactor core, accident management methods and risk management of nuclear power plants. The total volume of the programme was 100 person years and funding FIM 58 million. This symposium report summarises the research fields, the objectives and the main results obtained. In the field of operational margins of a nuclear reactor, the behaviour of high burnup nuclear fuel was studied both in normal operation and during power transients. The static and dynamic reactor analysis codes were developed and validated to cope with new fuel designs and complicated three-dimensional reactivity transients. Advanced flow models and numerical solution methods for the dynamics codes were developed and tested. Research on accident management developed and validated calculation methods needed to plan preventive measures and to train the personnel to severe accident mitigation. Efforts were made to reduce uncertainties in phenomena important in severe accidents and to study actions planned for accident management. The programme included experimental work, but also participation in large international tests. The Finnish thermal-hydraulic test facility PACTEL was used extensively for the evaluation of the VVER-440 plant accident behaviour, for the validation of the accident analysis computer codes and for the testing of passive safety system concepts for future plant designs. In risk management probabilistic methods were developed for safety related decision making and for complex event sequences. Effects of maintenance on safety were studied and effective methods for assessment of human reliability and safety critical organisations were searched. To enhance human competencies in control of complex environments, practical tools for training and continuous learning were worked out, and methods to evaluate appropriateness of control room design were developed.