Research Works on Iodine and Ruthenium Behavior in Severe Accident Conditions

Abstract

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.

Effects of water vapour and temperature on the retention of radiotoxic CH3I by silver faujasite zeolites

“…Accurate DF were measured under iodine concentrations more representative to those of a severe nuclear accident (0.1-1 ppmv [4]) thanks to the test bench 2 [20] (Figure S2).…”

“…The PERSeE f acilky [20,22] was used in order to extrapolate the behavior of some selected zeolitic sorl'nts towards the capture of methyl iodide at semi-pilot scale, using conditions closer to severe nuclear accident (relative humidity, y-radiation, temperature). A general scheme of this facility is given in Figure S3 (see ESI).…”

“…Attention was paid to ensure a good dispersion of the zeolitic material within the sand in the sample holder. Preliminary studies have shown that the used sand is totally ineffective for the retention of labelled methyl iodide (DF = 1 [20,22]). The different materials to be tested were placed in the upstream stage, giving the possibility to test simultaneously f< ur different solid mixtures {tested zeolite + sand} (Figure 1).…”

Trapping measurements of volatile iodine by sand bed and metallic filters

“…Thus, in the framework of the MiRE project [7] (Mitiga tion of outside releases in case of nuclear accident) dealing with Fission Product (FP) behavior (especially iodine and ruthenium), IRSN performed experiments to review and evaluate the potential trapping of I2 and CH3I through sand bed filter and metallic filter.…”

Incoherent broad-band cavity enhanced absorption spectroscopy for sensitive and rapid molecular iodine detection in the presence of aerosols and water vapour

“…The Source Term Evaluation and Mitigation STEM/EPICUR tests (performed under the aegis of OECD/NEA/CSNI) were dedicated to study the release under radiation of iodine species deposited onto painted surfaces in the containment atmosphere. Further researches have been carried out within the framework of the French MIRE program (4) (Mitigation of Releases to the Environment in the event of a nuclear accident) in the strategy to investigate and to improve the mitigation of radioactive releases after a core melt accident. The second phase of the project named Source Term Evaluation and Mitigation 2 (STEM 2), coordinated by IRSN, will be focused on mid-and long-term iodine releases (3) .…”