Particulate iodine

Table 2.8 shows the relative activities of fission products, and plutonium, in air filters. About a quarter of the 1311 reaching western Europe was particulate, the remainder gaseous or desorbable from particles during collection. Except where stated, the results quoted in Table 2.8 refer to measurements with sampling packs designed to trap inorganic and organic vapour as well as particulate iodine. 

The particulate activity trapped on the membrane filters in the sampling packs increased during the first hour (Fig. 3.2). The concentration of condensation nuclei in air in the reactor shell was 1.2 x 1010 m-3. Megaw May showed that an accommodation coefficient of 5 x 10-3 (compare Section 1.12) would explain the observed rate of increase in particulate iodine due to adsorption on the nuclei. The subsequent decline in particulate activity was due to deposition of nuclei on surfaces. Surprisingly, in this and other experiments, release of stable iodine vapour into the containment shell 4 h after the start of the experiment made little difference to the concentration of particulate 132I. Subsequently, Clough et al. (1965) showed that the amount of... 

Moyers, J.L. Duce, R.A. (1972) Gaseous and particulate iodine in the marine atmosphere. Journal of Geophysical Research, 77, 5229-38. 

It is not clear, however, in which chemical state the particulate iodine is present. Some studies reported it to be 103 but in others no 103 was found (see references and discussion in McFiggans et al. (2000)). Based on measurements of aerosol composition. Baker et al. (2000) state that iodine is present in aerosol in varying proportions as soluble inorganic iodine, soluble organic iodine and insoluble, or unextractable, iodine. Baker et al. (2001) measured the deposition of iodine in rainwater and in aerosol at Weyboume, North coast of Norfolk, UK. They found that iodide (I ) constituted 5-100% of total iodine deposition in both rain and aerosol. The rest was found to be iodate (10j") with a very small contribution from CH3I (<3% of the total iodine deposition). 

The main conclusions from the early model studies on iodine chemistry remain valid there is a significant lack of information on the kinetics of reactive iodine (especially lO and OIO reactions paths to stable particulate iodine) and on fluxes of alkyl iodides from the oceans. Nevertheless, important progress has recently been made and work is currently ongoing in several laboratories worldwide. This is an important area of atmospheric research in need of more attention. 

The burning uranium heated the graphite, which also burned to release CO and CO,. About 2x10 Ci of gaseous iodine, which represented 12% of the available iodine inventory, were released into the atmosphere from the stack. The filter removed the particulate iodine (20 to 50x10 Ci). The radioactive plume was detected as far away as Germany and Norway. 

Figure 9.7 shows the iodine cycle in seawater (Isshiki, 2005, partly modified). It is considered that the following iodine species, D, IO3, DOI, volatile organic carbons such as CH3I, I2, and particulate iodine are present in seawater, whose species are represented by circles in the figure. Bold solid lines show the change of chemical species, and thin lines the transport of each component. Here, we will describe the factors controlling the speciation and distribution of iodine in seawater. 

A series filter was used to separate atmospheric particulate iodine, HI and I2, HOI and organic iodine. The particulate iodine is usually separated and collected using micropore filters or glass microfiber. The distribution of iodine in the different sizes of particulates is collected by a multi-stage cascade impact collector. Wimschneider and Heumann (1995) used a six-stage slot cascade impactor to collect particulates... 

The typical environmental airborne radionuclide collection train consists of a filter followed by an activated-charcoal cartridge particulate iodine is retained on the filter and gaseous iodine on the cartridge (Corley etal. 1977). A more elaborate collector train distinguishes the various forms of radioiodine. The collectors, in order, are an air filter for particles, cadmium iodide on Chromosorb-P for I2, 4-iodophenol on alumina for HIO, and activated charcoal for organically bound iodine, such as CH3I (Keller et al. 1973). 

Yoshida, S. Muramatsu, Y. (1995). Determination Of Organic, Inorganic And Particulate Iodine In The Coastal Atmosphere Of Japan. Journal Of Radioanalytical And Nuclear Chemistry, Vol.196, No. 2, pp 295-302, ISSN 1588-2780 Zabala, J., Carrion, N., Murillo, M., Quintana, M., Chirinos, J., Seijas, N, Duarte, L. Bratter, P. (2009). Determination Of Normal Human Intrathyroidal Iodine In Caracas Population. Trace Elem Med Biol, Vol.23, No.l, pp 9-14, ISNN 0946-672X Zaichick, V. Zaichick, S. (1997). Normal Human Intrathyroidal Iodine. Sci Total Environ. Vol.27, No.206(l), pp 39-56, ISSN 0048-9697... 

Because the removal mechanisms for organic iodides and particulate iodines are significantly different from and slower than that for elemental iodine, there is no need to limit the DF for organic iodides and particulate iodines. 

Continuous air monitoring of HCF emissions to the environment is accomplished at the Hot Cell Facility using an Eberline SPING-3A, designed to monitor air effluent for particulate, iodine and noble gases. This instrument is located in the HCF ventilation exhaust duct at the north wall of Building 6580. 

Airborne radiation monitors are described in CESSAR-DC Section 11.5.1.2.4, and include a portable unit that can be moved to areas where work or surveillance activities are at an unusual risk of airborne exposure. This monitor includes detector channels for particulate, iodine, and gaseous activity. All equipment is assembled on a mobile cart, and the design allows for transfer of the particulate sample filters and iodine sample cartridges to the Station Counting Room for further sample analysis. 

If the exhaust of the Radwaste Building Ventilation System is discharged directly to the environment, this monitor is located in the exhaust and includes a particulate/iodine fixed filter cartridge in the sample tube inlet and normal and high range gas detection channels. 

Following a loss-of-coolant accident, a fraction of the radionuclides released from the primary circuit remains airborne in the containment atmosphere, as was discussed in the preceding sections. In order to reduce the airborne activity concentrations, standby filters are installed in the annulus of the German PWR plants, consisting of aerosol filters and iodine filters. In the German RSK Guidelines a retention efficiency of 99.9% for particulate iodine, of >99.99% for h and of >99% for organoiodides is required under accident conditions. In certain other countries, the specified iodine species as well as the required retention efficiencies differ somewhat from these values. 

Aerosol iodides are also retained by the HEPA filters very efficiently, h and HI present in gaseous form in the atmosphere are to a part trapped on the surfaces of aersosol particles, with the responsible mechanisms being adsorption or chemical reaction. However, early on it was recognized that a fraction of the adsorbed iodide may desorb again from these filters (e. g. Adams and Ackley, 1968), due to reactions of reversibly bound iodine with the flowing air, the water vapor or the impurities present in it. Thus, at higher concentrations of particulate iodine in air a special iodine filter has to be added to the particulate filter. 

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