Characterisation of radioiodine

The release of 131I and other fission products in reactor accidents has been considered in the previous chapter. In the Windscale accident, the temperature in the fire zone reached an estimated 1300°C and 8 tonne of uranium metal melted. Over 25% of the 1311 in the melted fuel escaped to atmosphere. In the Chernobyl accident, the fuel was U02, the temperature exceeded 2000°C, and about 25% of the total reactor inventory of 131I was released to atmosphere, as vapour or particulate aerosol. In the Three Mile Island accident, 131I remained almost completely in the reactor coolant. The activities of 131I released in reactor accidents, including that at Chernobyl, have totalled much less than the activities released from weapons tests (Table 2.3). 

When experimental work with 131I in the environment began at Harwell in 1949, it was thought appropriate to release the activity as elemental iodine, and to use NaOH bubblers, with added KI in 

The May Pack has been used world-wide to characterise radioiodine. In some applications, glass fibre-filters have replaced membrane filters and copper or silver gauzes have been used to trap elemental iodine. The separation of iodine species in the May Pack is at best qualitative. Some inorganic iodine vapour may be adsorbed on the particulate filter. Conversely, iodine adsorbed on particles, and trapped on the particulate filter, may be desorbed during extended periods of sampling. 

The ratio of activities on the first to the second charcoal paper decreased with time from about 250 at 20 min to 25 at 4 h after the release, showing an increasing proportion of penetrating species. The 

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 

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