Iodine indicator plant

On average, the iodine concentrations of indicator plants growing on boulder clay and diluvial sands vary continuously with the distance to the seaside between 35 and 50% (Table 9-4.1). That iodine levels of the sods near the coast are higher than inland is a fact observed worldwide. The supply of iodine by rain (Groppel et al. 1989b) is usually high in coastal zones (0-50 km from the sea) (Voland 1985, Johnson etal. 2003). 

Tab. 9.4-1 Iodine content (pg I kg DM) of indicator plants growing on boulder clay and diluvial sand as a function of distance from the seaside (n = 34, 49 and 72)...

Estimation of Iodine when unconibined and in combination.—The minute proportion of this element, which has often to be sought in plants, bituminous and othor shales, waters, and even in the air, has taxed the inventive powers and researches of chemists for methods, of which the accuracy might he commensurate with the evident difficulty of the task undertaken. Fortunately, iodine oomports itself with a few bodies in such a characteristic way, offering indications so marked as not to be surpassed in this respoct by any other substance known. These are starch, silver, and palladium and by proper modifications in the applications of only these three bodies, the methods for the flstimation of iodine, as well when free as when combined, are not exceeded by any other class, either in their accuracy or extent. 

An accident at a nuclear power plant can be caused by many combinations of anomalous initiating event, malfunction and human error. The types of possible accidental situations are studied in the specific safety analysis of each plant and the safety systems described above are designed to prevent, or mitigate the effects of all the accidents chosen as DBAs. Table 3-1 provides an approximate indication of the effectiveness of various safety systems in limiting external releases in a typical loss of coolant accident (the break of a large primary circuit pipe). The figures are for the release of iodine-131 (often assumed as the reference isotope in indicative evaluations of source terms and for a 1000 MWe reactor). As can be seen, the reduction of the releases caused by the safety systems is very significant and corresponds to a factor of the order of one million. 

While the criticisms outlined above imply that the Rasmussen analysis underestimates the hazards of nuclear power plant accidents, there is also evidence which suggests that in some respects the opposite may be true. In particular, recent research indicates that the volatility of iodine may have been greatly overestimated in situations where substantial amounts of water are present. In LWR fuel, the iodine is largely in the form of cesium iodide, which dissolves readily in any water present, leaving only a small concentration in the gas phase. It is this phenomenon that is thought to account for the unexpectedly low release of radio-iodine in the Three Mile Island accident, which is described in Section 12.3.2. Another area in which the analysis may be overconservative is in dealing with the possibility of pressure vessel or containment failure from a steam explosion recent experimental work suggests that the probability of failure is considerably less than was assumed in the Rasmussen model. 

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