Calculation of fission product behaviour in an advanced containment in case of a severe accident

Abstract The aim of the present work is to demonstrate the applicability of the MELCOR- and CONTAIN-computer programs, respectively, to determine the radiological source terms (RST) of a pressurized water reactor under conservative release conditions based on preliminary reactor data from the European Pressurized Water Reactor Conceptional Design Phase. The determination of the RST means the quantification of the possible release of radionuclides from the plant (mostly from the containment) into the environment in case of a severe accident. This contribution gives an outline of the procedures by which the RST can be estimated conservatively. Such procedures have to be known if the ‘harmful effects of ionizing radiation’ outside the reactor plant, as mentioned in legislation, are determined in a proper way. It is demonstrated that the computer codes available at Forschungszentrum Karlsruhe can be used for the complete analyses of the containment behaviour and the accident consequences, provided that the design data of the nuclear reactor and information on the initiating phase of the accident are available. The first 12 h of a postulated Large Break Loss-of-Coolant Accident are analysed and a time dependent RST to the environment is calculated, which can be used as input for the COSYMA code system for the assessment of the accident consequences.