Application of risk analysis results in emergency planning of a nuclear power plant

Abstract

NPP Goesgen developed a full-scope probabilistic risk assessment (PRA) model, allowing for an estimate of the risk of offsite consequences. The model considers all operational modes of the plant, power operation, low power operation and shutdown conditions and all risk-relevant initiating events that may lead to a plant accident. The model allows computing different risk metrics starting from core damage frequency, frequency of a large offsite release to detailed plant damage states, activity release categories as well as the risk of offsite consequences expressed in radiological health effects. The risk model is programmed in the software system RISKMAN™ in the format of a set of linked event trees with associated fault trees. Analysis tools for the estimation of accident progression and offsite consequences support the model. A plant-specific simulator for severe accidents is in use, which is based on the MELCOR code. Off-site consequences in terms of dose levels are calculated using the MACCS 2.0 code. The full power models are used to support emergency planning by providing information on the possible consequences of hypothetical accidents in dependence on weather conditions. In cooperation with the responsible governmental agencies, this allows to support evacuation actions in case of severe accidents. Simple cartographic aids are available for emergency planning accounting for a possible loss of offsite power during an emergency, preventing the use of computational tools. The paper presents the methodology and key insights of the risk assessment of offsite consequences for NPP Goesgen and demonstrates the use of the results in emergency planning.