1997

Vanttola, Timo; Puska, Eija-Karita

The Finnish national research programme on Reactor Safety (RETU, 1995-1998) concentrates on the search of safe limits of nuclear fuel and the reactor core, accident management methods and risk management of the operation of nuclear power plants. The annual volume of the programme has been about 26 person years and the annual funding FIM 15 million. This report summarises the structure and objectives of the programme, research fields included and the main results obtained during the period 1995 May 1997. In the field of operational margins of a nuclear reactor, the behaviour of high burnup nuclear fuel is studied both in normal operation and during power transients. The static and dynamic reactor analysis codes are developed and validated to cope with new fuel designs and complicated three-dimensional reactivity transients and accidents. The range of the models is extended by implementing advanced flow models and numerical solution methods. Research on accident management aims at development and validation of calculation methods needed to plan preventive measures and to train the personnel to severe accident mitigation. Other goals are to reduce uncertainties in phenomena important in severe accidents and to study actions planned for accident management. The programme includes own experimental work, but participation in large international test programmes is of major importance. The Finnish thermal-hydraulic test facility PACTEL (Parallel Channel Test Loop) is 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 the field of risk management probabilistic methods are developed for safety related decision making and for complex phenomena and event sequences. Effects of maintenance on nuclear power plant safety are studied and more effective methods for the assessment of human reliability and safety critical organisations are searched. In order to enhance human competencies in the control of complex environments, practical tools for training and continuous learning are worked out, and methods to evaluate appropriateness of control room design are developed.