Progress with Iodine Chemistry Studies in SARNET2

The EU SARNET project (Severe Accidents Research NETwork of excellence) unites the research efforts of 47 organisations from 24 countries worldwide to help to resolve the most important remaining uncertainties and safety issues on severe accidents (SA) in existing and future water-cooled nuclear power plants (NPP). The SARNET2 project started in April 2009 for 4 years in the 7th Framework Programme (FP7) of the European Commission. One of the most important parts of SARNET concerns evaluation of the "source term", involving the development of methods to calculate the time, history, and chemical and physical forms of radionuclides that could be released to the environment, following containment breach and/or venting in the course of a severe accident. A major part of the source term research concerns iodine, in view of its high radiotoxicity. Relevant work performed in this part of SARNET2 concerns firstly small-scale experiments to examine the behaviour of iodine in the circuit and reactor containment with a view to developing relevant computer models such as those in the European reference code ASTEC; followed by development and improvement of such models, and finally their assessment using independent data, such as those from the integral test series Phébus FP and THAI. An important parameter is the amount of organic iodide present in the containment, as this cannot easily be removed by filtration when using containment venting. Research has concentrated on the following important aspects: the behaviour of iodine oxides, interaction of iodine in the containment atmosphere with paints (as this can generate organic iodide), iodine interactions in the sump and exchanges with the atmosphere, and iodine transport in the primary circuit particularly concerning kinetic limitations, which mean that the relative compositions of material arriving at and in the containment may not reflect an equilibrium state. This paper summarises the progress made in SARNET2 to date in the iodine chemistry area, and indicates what results are to be expected at the end of the project next year, 201