An experimental screening of silver-exchanged zeolites towards the trapping of methyl iodide was carried out with the general aim of limiting as much as possible the iodine release in case of severe nuclear accident. Hence, a systematic study was implemented in order to better understand the effects of some important parameters such as the zeolite structural type (FAU-X and Y, MOR, *BEA, MFI and FER) and chemical properties (namely the silver content and its speciation) on the adsorption behaviour. Characterization of 18 zeolitic sorbents, before or after iodine retention tests, was performed using elemental analyses, N 2 porosimetry at-196 °C, XRD, DR-UV-Vis spectroscopy and TEM. The distribution of silver species, namely as isolated Ag + cations or charged clusters in the internal porosity, and/or to a lesser extent as 2 metallic nanoparticles, was found to depend mainly on the zeolite structural type and the Si/Al ratio and to a lesser extent on silver content. CH 3 I retention properties were evaluated from dynamic adsorption tests carried out at 100°C. Quantitative exploitation of breakthrough curves showed that the silver faujasite zeolites of the Y type (Si/Al ratio = 2.5) with more than 15 wt% silver were the most efficient in order to achieve high adsorption capacities both at breakthrough and saturation. More generally, it is found that dispersed silver entities efficiently catalyze the dissociation of CH 3 I and the production of AgI precipitates.
This paper deals with near past, ongoing, and planned R&D works on fission products (FPs) behavior in reactor cooling system (RCS), containment building and in filtered containment venting systems (FCVS) for severe accident (SA) conditions. All the researches are collaborative works; the overall objective is to develop confident models to be implemented in simulation software. After being initiated in 2004, researches on iodine transport through the RCS are still ongoing and for containment, the last advances are linked to the source term (ST) evaluation and mitigation (STEM) OECD/NEA project. The objective is to improve the evaluation of ST for a SA on a nuclear power plant and to reduce uncertainties on specific phenomena dealing with the chemistry of two major FPs: iodine and ruthenium. For ruthenium attention has been paid to study the amount and nature (gas/aerosol partition) of ruthenium species along the RCS. A follow-up, called STEM2, has started to reduce some remaining issues and be closer to reactor conditions. For FCVS works, the efficiencies for trapping iodine covering scrubbers and dry filters are examined to get a clear view of their abilities in SA conditions. Another part is focused on specific porous materials able to trap volatile iodine. Influence of zeolite materials parameters (nature of the counter-ions, structure, Si/Al ratio…) are tested as well as new kind of porous materials constituted by Metal organic Frameworks will also be looked at.
The PASSAM (Passive and Active Systems on Severe Accident source term Mitigation) project was launched in the frame of the 7th framework programme of the European Commission. Coordinated by IRSN, this four year project (2013-2016) involved nine partners from six countries: IRSN, EDF and university of Lorraine (France); CIEMAT and CSIC (Spain); PSI (Switzerland); RSE (Italy); VTT (Finland) and AREVA GmbH (Germany). It was mainly an R&D project of experimental nature aimed at investigating phenomena that might enhance source term mitigation in case of a severe accident in a Nuclear Power Plant (NPP). Both existing systems (i.e., water scrubbing and sand bed filters plus metallic pre-filters) and innovative ones (i.e., high pressure sprays, electrostatic precipitators, acoustic agglomerators and, advanced zeolites and combined wet-dry filtration systems), were experimentally studied in conditions as close as possible from those anticipated for severe accidents. This paper presents the main experimental results of the project which represent a significant extension of the current database on these existing or innovative mitigation systems. Application of some of these data for improving existing models or developing new ones should eventually enhance the capability of modelling Severe Accident Management measures and developing improved guidelines.
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