Safety and Risk of Light Water Reactors and their Fuel Cycle Facilities

Abstract

The safety of light water reactors is based on long term international research programs. The objective is to protect the operational personnel, the environment and the population against radioactivity releases during normal operation and in case of accidents. The safety concept is based on multiple containment structures (multi-barriers) as well as engineered safeguards components and other measures combined in a staggered-in-depth concept of four safety levels. The light water reactor plant and its protection system must be designed and built according to the design basis concept. Those design basis accidents which are part of the licensing process must be accommodated by the protection system, the inherent safety features and by the emergency cooling systems of the nuclear plant. Probabilistic safety analysis are supplements to this deterministic approach. They show that European light water reactors have a frequency of occurrence of about 10-5 to 10-6 per reactor year for core meltdown. Reactor risk studies which had been performed during the 1970s (USA) and 1980s (Europe) showed that the risk arising from light water reactors as a result of core melt down is well below the risk of other power generating or traffic systems. However, the Chernobyl accident in 1986 resulted-in addition to a not well known number of fatalities-in large scale land contamination by cesium-137 with a half-life of about 29 years. Similarly, the Fukushima accident (2011) resulted in land contamination by radioactive cesium isotopes. New research programs on severe accident consequences were initiated around 1990s. Their results lead to a revision of the results of the early risk studies of the 1980s and a new safety concept for modern light water reactors, e.g. the European Pressurized Water Reactor (EPR) and the European Boiling Water Reactor (SWR-1000). This new reactor safety concept allows to limit the severe accident consequences to the plant site itself. Also the introduction of additional severe accident management measures for existing light water reactors resulted in a considerable improvement of the prevention and mitigation of severe accident consequences. The safety concept of fuel cycle plants, e.g. spent fuel storage facilities, reprocessing facilities and waste treatment facilities is based on similar containment and engineered safeguards measures. However, the risk of these fuel cycle facilities is much smaller as the fuel is at much lower temperatures in reprocessing and refabricataion plants. © Springer-Verlag Berlin Heidelberg 2012.