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During a Severe Accident (SA) occurring in a nuclear power plant, many Fission Products (FP) are released from the degraded fuel and are transported in the Reactor Coolant System (RCS). Depending on their volatility, FP can be either deposited on the surface of the Reactor Coolant System (RCS) or transported into the containment building from where they may be released into the environment in case of early containment failure. This was the case for the Fukushima Daiichi (FD) accident with important FP releases which were observed following the containment vessel failure which lasted up to several weeks after the accident. If early phase releases were well predicted by SA simulation codes, delayed releases were not correctly predicted [1]. Such discrepancies can be attributed to the revaporization of deposits inside the RCS which were not yet modeled in the SA simulation tools. Previous experiments over the past 20 years evidenced the possible formation and revaporization of CsI [2]. However, up to now, no clear CsI revaporization mechanism has been determined. In order to propose a mechanism, this study (scheduled within the OECD/NEA/ESTER project) aims at determining the speciation of each species remaining on the substrate after revaporization tests under different conditions using XPS and ToF-SIMS (X-ray Photoelectron Spectroscopy and Time of Flight Secondary Ion Mass Spectrometry. These two combined techniques allow the identification of the main species of the residue leading to the proposition of two revaporization reactions.

Gaseous iodomethane (CH3I) is naturally emitted into the atmosphere by biological activity in oceans and during severe accidents (SAs) in nuclear power plants. In this latter case, a part of radioactive iodine such as 131I may be released. Improving the knowledge of CH3I transport and reactivity in the atmosphere is important since they are strongly linked to first the cycle of ozone and second to the dispersion of radioactive CH3I with potential radiological consequences on both the environment and human health. Here, the interaction process of CH3I with NaCl as a surrogate of atmospheric aerosols was investigated under ambient air conditions by using Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS). The DRIFTS spectra of NaCl clearly evidenced CH3I adsorption on the NaCl particle surface. A part of CH3I ((1.68 ± 0.85) × 1014 molecule per mgNaCl) was found to be strongly bonded to NaCl since no desorption was observed. The CH3I adsorption on the NaCl surface presented a 1st order kinetics relative to its gas phase concentration. The uptake coefficient was determined to be in the order of 10−11. These results show a low probability of CH3I to be taken up by halide-containing aerosols. These data are crucial for completing the iodine atmospheric chemical scheme. [ABSTRACT FROM AUTHOR]

Gaseous iodomethane (CH 3 I) is naturally emitted into the atmosphere by biological activity in oceans and during severe accidents (SAs) in nuclear power plants. In this latter case, a part of radioactive iodine such as 131 I may be released. Improving the knowledge of CH 3 I transport and reactivity in the atmosphere is important since they are strongly linked to first the cycle of ozone and second to the dispersion of radioactive CH 3 I with potential radiological consequences on both the environment and human health. Here, the interaction process of CH 3 I with NaCl as a surrogate of atmospheric aerosols was investigated under ambient air conditions by using Diffuse Reflectance Fourier Transform Spectroscopy (DRIFTS). The DRIFTS spectra of NaCl clearly evidenced CH 3 I adsorption on the NaCl particle surface. A part of CH 3 I ((1.68 ± 0.85) × 10 14 molecule per mg NaCl ) was found to be strongly bonded to NaCl since no desorption was observed. The CH 3 I adsorption on the NaCl surface presented a 1 st order kinetics relative to its gas phase concentration. The uptake coefficient was determined to be in the order of 10 -11 . These results show a low probability of CH 3 I to be taken up by halide-containing aerosols. These data are crucial for completing the iodine atmospheric chemical scheme.