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|NKS Programme Area:||NKS-R|
|Research Area:||Severe accidents|
|Report Title:||Adsorption and revaporisation studies on iodine oxide aerosols deposited on containment surface materials in LWR|
|Authors:||S. Tietze, T. Kärkelä, M.R.StJ. Foreman, C. Ekberg, A. Auvinen, U. Tapper, S. Lamminmäki, J. Jokiniemi, |
|Abstract:||During a hypothetical severe nuclear accident, the radiation field will be very high in the nuclear reactor containment building. As a result gaseous radiolysis products will be formed. Elemental iodine can react in the gaseous phase with ozone to form solid iodine oxide aerosol particles (iodine oxide).
Within the AIAS (Adsorption of Iodine oxide Aerosols on Surfaces) project the interactions of iodine oxide (IOx) aerosols with common containment surface materials were investigated. Common surface materials in Swedish and Finnish LWRs are Teknopox Aqua V A paint films and metal surfaces such as Cu, Zn, Al and SS, as well as Pt and Pd surfaces from hydrogen recombiners. Non-radioactive and 131I labelled iodine oxide aerosols were produced with the EXSI CONT facility from elemental iodine and ozone at VTT Technical Research Centre of Finland. The iodine oxide deposits were analysed with microscopic and spectroscopic measurement techniques to identify the kind of iodine oxide formed and if a chemical conversion on the different surface materials occurs.
The revaporisation behaviour of the deposited iodine oxide aerosol particles from the different surface materials was studied under the influence of heat, humidity and gamma irradiation at Chalmers University of Technology, Sweden. Studies on the effects of humidity were performed using the FOMICAG facility, while heat and irradiation experiments were performed in a thermostated heating block and with a gammacell 22 having a dose rate of 14 kGy/h. The revaporisation losses were measured using a HPGe detector. The revaporisated 131I species from the surfaces were chemically tested for elemental iodine formation. The parameter dominating the degradation of the produced iodine oxide aerosols was humidity.
Cu and Zn surfaces were found to react with iodine from the iodine oxide aerosols to form iodides, while no metal iodides were detected for Al and SS samples. Most of the iodine oxide aerosols are assumed to be degraded or washed off by containment sprays and steam in the containment. Paint film ingredients were shown to chemically react with the aerosol particles. Pt and Pd surfaces were shown to only weakly physisorb the iodine oxide aerosols which reveals that these aerosols will have a minor effect on the catalytic functionality of the hydrogen recombiners during a severe nuclear accident.|
|Keywords:||Severe nuclear accidents, LWR, volatile iodine source term, iodine oxide aerosols, adsorption, revaporisation, containment|
|Publication date:||27 Dec 2012|
|Number of downloads:||2405|