About fifty European organisations integrate in SARNET (Network of Excellence of the EU 6th Framework Programme) their research capacities in resolve better the most important remaining uncertainties and safety issues concerning existing and future Nuclear Power Plants (NPPs) under hypothetical Severe Accident (SA) conditions. Wishing to maintain a long-lasting cooperation, they conduct three types of activities: integrating activities, spreading of excellence and jointly executed research. This paper summarises the main results obtained by the network after the first year, giving more prominence to those from jointly executed research in the Source Term area.
Integrating activities have been performed through different means: the ASTEC integral computer code for severe accident transient modelling, through development of PSA2 methodologies, through the setting of a structure for definition of evolving R&D priorities and through the development of a web-network of data bases that hosts experimental data. Such activities have been facilitated by the development of an Advanced Communication Tool.
Concerning spreading of excellence, educational courses covering Severe Accident Analysis Methodology and Level 2 PSA have been set up, to be given in early 2006. A detailed text book on Severe Accident Phenomenology has been designed and agreed amongst SARNET members. A mobility programme for students and young researchers is being developed, some detachments are already completed or in progress, and examples are quoted.
Jointly executed research activities concern key issues grouped in the Corium, Containment and Source Term areas. In Source Term, behaviour of the highly radio-toxic ruthenium under oxidising conditions (like air ingress) for HBU and MOX fuel has been investigated. First modelling proposals for ASTEC have been made for oxidation of fuel and of ruthenium. Experiments on transport of highly volatile oxide ruthenium species have been performed. Reactor scenario studies assisted in defining test conditions for new experiments. Regarding predictability of iodine species exiting the Reactor Coolant System (RCS), which affects its source into the containment, iodine behaviour in the circuit and silver-indium-cadmium release from the core have been reviewed (these absorber elements play a significant role in iodine chemistry). The design of new experiments has been discussed.
Concerning the radioactive aerosol source term, work is conducted in the risk-relevant areas of by-pass accident sequences, transport through cracks in containment walls and revaporisation from previous deposits in the RCS that could lead to a delayed source term. Modelling approaches for aerosol retention in containment cracks and interpretation of experimental results on retention in secondary side of SG are already proposed. Amongst the numerous physical and chemical processes which affect the intense reactivity of iodine in containments, mass transfer phenomena were first addressed in the network, looking at SISYPHE experimental interpretation and associated modelling.
(1) : IRSN
(2) : PSI
(3) : CIEMAT