In case of a severe accident (SA) occurring in a pressurized water reactor (PWR) fission products (Cs, I) are released from the degraded fuel and transported through the reactor coolant system (RCS). A part is deposited onto surfaces of the RCS and can be subsequently chemically re-mobilized, in case the atmosphere composition changes. In order to improve our understanding on the re-mobilization processes, it is important to describe the interactions between deposited fission products and surfaces representative of RCS in SA conditions (mainly oxidized SS 304L) and to identify the species formed after remobilization. In this 2 study CsI aerosols were deposited on the surface of 304L coupons, which have been previously oxidized. The deposits were afterwards reheated (up to 750°C) in either air or steam. At every step, the 304L coupons were analysed by a combination of surface analysis techniques (XPS, ToF-SIMS), Raman spectroscopy and SEM. It has been established that the initial surface state of the 304L coupons (i.e. oxidation in air or steam) has no effect on the release of caesium or iodine. However, the composition of the carrier gas during the reheating phase influences significantly the release of caesium. Specifically, in air a significant amount of Cs remains on the coupon and forms mixed oxides with chromium, such as Cs 2 CrO 4 and Cs 2 Cr 2 O 7. The results are then discussed and compared with literature data.

The atmospheric chemistry of iodine is important in different environments, and particularly in case of a nuclear reactor severe accident. This paper describes the performance of an Incoherent Broad-Band Cavity Enhanced Absorption Spectroscopy (IBB-CEAS) device, based on a green LED source allowing the online detection of gaseous molecular iodine. High sensitivities and a wide dynamic range are obtained. The performances and limitations of the IBB-CEAS technique for measurements of iodine in the presence of aerosols and water vapour are discussed. The capabilities of this device to perform kinetics studies on iodine have been investigated in the framework of nuclear reactor accident research. The re-vaporization process of deposited CsI by optical monitoring of I2 concentration-time profiles is presented. The aerosols used in the experiments have been well characterized (size, distribution, concentration and mass) before interaction with iodine by a NanoScan scanning mobility particle sizer (SMPS), a PEGASOR particle sensor PPS-M and a tapered element oscillating microbalance (TEOM).

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