SARNET (Severe Accident Research NETwork) is a Network of Excellence of the EU 6th Framework Programme that integrates in a sustainable manner the research capabilities of about fifty European organisations to resolve important remaining uncertainties and safety issues concerning existing and future nuclear plant, especially water-cooled reactors, under hypothetical severe accident conditions. It emphasises integrating activities, spreading of excellence (including knowledge transfer) and jointly-executed research. This paper summarises the main results obtained at the middle of the current 4-year term, highlighting those concerning radioactive release to the environment (Source Term area).
Integration is pursued through different methods: the ASTEC integral computer code for severe accident modelling, development of PSA level 2 methods, a means for definition, updating and resolution of safety issues, and development of a web database for storing experimental results. These activities are helped by an evolving Advanced Communication Tool, easing communication amongst partners.
Concerning spreading of excellence, educational courses covering severe accident analysis methodology and level 2 PSA have been organised for early 2006. A text book on Severe Accident Phenomenology is being written. A mobility programme for students and young researchers has started. Results are disseminated mainly through open conference proceedings, with journal publications planned. The 1st European Review Meeting on Severe Accidents in November 2005 covered SARNET activities during its first 18 months.
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) is investigated. Models are proposed for fuel and ruthenium oxidation. Experiments on transport of oxide ruthenium species are performed. Reactor scenario studies assist in defining conditions for new experiments. Regarding predictability of iodine species exiting the Reactor Coolant System (RCS), which affects the amount entering the containment, iodine behaviour in the circuit and silver-indium-cadmium (SIC) release have been reviewed. New experiments are being discussed and performed, and SIC degradation and release models are being improved. For the radioactive aerosol source term, work is conducted in the risk-relevant areas of steam generator (SG) tube rupture, transport through cracks in containment walls and revaporisation from previous deposits in the RCS that could lead to a delayed source term. Models for aerosol retention in containment cracks and interpretation of data on retention in the SG secondary side are proposed. For radioactive iodine release to the environment, many physical and chemical processes affect the iodine concentration in the containment atmosphere; of these effects, mass transfer phenomena and radiolytic oxidation are being investigated first.
(1) : PSI
(2) : CIEMAT
(3) : IRSN