Recent advances in the source term area within the SARNET European severe accident research network

International audienceSource Term has been one of the main research areas addressed within the SARNET network during the 7th EC Framework Programme of EURATOM. The entire source term domain was split into three major areas oxidising impact on source term, iodine chemistry in the reactor coolant system and containment and data and code assessment. The present paper synthesises the main technical outcome stemming from the SARNET FWP7 project in the area of source term and includes an extensive list of references in which deeper insights on specific issues may be found. Besides, based on the analysis of the current state of the art, an outlook of future source term research is outlined, where major changes in research environment are discussed (i.e., the end of the Phébus FP project; the end of the SARNET projects; and the launch of HORIZON 2020). Most probably research projects will be streamlined towards release and transport under oxidising conditions, containment chemistry, existing and innovative filtered venting systems and others. These will be in addition to a number of projects that have been completed or are ongoing under different national and international frameworks, like VERDON, CHIP and EPICUR started under the International Source Term Programme (ISTP), the OECD/CSNI programmes BIP, BIP2, STEM, THAI and THAI2, and the French national programme MIRE. The experimental PASSAM project under the 7th EC Framework programme, focused on source term mitigation systems, is highlighted as a good example of a project addressing potential enhancement of safety systems based on already available knowledge. © 2015 Elsevier B.V. All rights reserved

Transport of ruthenium in primary circuit conditions during a severe NPP accident

International audienceRuthenium species, volatilized from damaged fuel during a severe accident in a nuclear power plant, are radiotoxic and can be transported to the containment atmosphere in gaseous form. To limit the possible source term to the environment, it is of interest to understand the behaviour of Ru after it has been released from fuel and the phenomena taking place within the decreasing temperature section of the reactor coolant system. This was investigated in the framework of EC SARNET and SARNET2 projects, as a part of the Source Term work package, with several separate-effect tests on the transport and speciation of Ru in primary circuit conditions considering the influence of other fission products as well. The source of Ru was metallic Ru, RuO2 powder or gaseous RuO4. The large-scale integral tests of the Phébus FP program were conducted with real irradiated fuel, and more realistic analysis on the release and transport of Ru could be performed. Experimental studies proved that the transport of ruthenium to the containment atmosphere took mainly place as RuO2 particles when Ru source was oxidized above 1250 °C. The fraction of Ru transported in gaseous form was at its highest when ruthenium was oxidized at approx. 1000-1100 °C. A major part of the released Ru was deposited at the decreasing temperature area of the circuit as RuO2. Revaporisation of the deposited Ru at low temperature was a significant source of gaseous ruthenium. In order to understand the behaviour of ruthenium in these tests, the analysis work was extensive and several simulations were carried out. As an outcome, the observed transport and deposition of ruthenium was explained. The simulation studies gave also an insight into the performance of the ASTEC code and some model improvements for Ru transport through the reactor coolant system have been identified. © 2014 Elsevier Masson SAS