A nuclear accident can be defined as any event challenging nuclear safety provisions with potential release of radioactive materials. In order to protect the public, the workers and the environment from such events, nuclear emergency preparedness and response studies are carried out to determine appropriate measures (preparedness phase) and implementation of suitable actions (response phase) to protect the public from the effects of radiation exposure.
The JRC works on accident modelling and radiological consequences evaluations using dedicated analytical tools. To this end, nuclear accident modelling and emergency preparedness and response capabilities are streamlined via the development and application of the DAPHNE (Diagnosis And Prognosis of Hazards in Nuclear Emergencies) methodology. DAPHNE provides a fast and accurate nuclear diagnosis and radiological consequence assessment in case of accident and the technical basis for the justification of adoption of emergency protective measures through the identification of accident scenarios, source term characterization, dose projection and radiological risk maps.
The DAPHNE methodology foresees an onsite part, which relates to evaluation of the spatial and temporal dynamics of the radionuclides released during a severe accident i.e. the so-called source term. A severe accident of a nuclear reactor implies partial or total fuel melting and its sequence, from the initiating event until the release of nuclear material into the environment including the management response, is simulated with the Accident Source Term Evaluation Code (ASTEC) or also with the fast running Modular Accident Analysis Program (MAAP). For both tools, there is the need to have available the reactor data and model as well as the context in order to characterise the accident.
The off-site part of the DAPHNE methodology is dedicated to the modelling of the source term dispersion taking into account the weather conditions and analysing the air mass trajectories at the geographical location making use of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) tool. In a real case event (response), the Java based Real-time On-line DecisiOn Support System (J-RODOS) allows for the calculation of the atmospheric dispersion of the radionuclides and to provide all the information required to decide on measures to protect the population quickly, continuously, consistently and comprehensively. JRC is working extending its emergency preparedness capabilities by further developing the DAPHNE methodology. To reach this goal, a source term database extended to all NPPs models within the EU borders and neighbouring countries as well as conditional probability maps of radiological risk to the entire EU NPPs sites for both safety and security events are planned.