Empirical Risk Analysis of Severe Reactor Accidents in Nuclear Power Plants after Fukushima

Many countries are reexamining the risks connected with nuclear power generation after the Fukushima accidents. To provide updated information for the corresponding discussion a simple empirical approach is applied for risk quantification of severe reactor accidents with International Nuclear and Radiological Event Scale (INES) level≥5. The analysis is based on worldwide data of commercial nuclear facilities. An empirical hazard of 21 (95% confidence intervals (CI) 4; 62) severe accidents among the world’s reactors in 100,000 years of operation has been estimated. This result is compatible with the frequency estimate of a probabilistic safety assessment for a typical pressurised power reactor in Germany. It is used in scenario calculations concerning the development in numbers of reactors in the next twenty years. For the base scenario with constant reactor numbers the time to the next accident among the world's 441 reactors, which were connected to the grid in 2010, is estimated to 11 (95% CI 3.7; 52) years. In two other scenarios a moderate increase or decrease in reactor numbers have negligible influence on the results. The time to the next accident can be extended well above the lifetime of reactors by retiring a sizeable number of less secure ones and by safety improvements for the rest.

Risk Assessment of Extreme Weather Conditions for Nuclear Power Plants at Tidal Rivers

The effects of flooding on a nuclear power plant site may have a major bearing on the safety of the plant and may result in a common cause failure for safety related systems, such as the emergency power supply systems. For river sites with tidal influences, an extreme flood event - tide combined with storm water level set-up - must be assumed. A storm-tide must be covered with an exceeding frequency of 10-4/a. However, the risk assessment regarding the availability of systems and components of a nuclear power plant also includes the situation of extreme low water level of rivers, i. e. below the minimum water level necessary for the supply of the nuclear power plants with cooling water.