Influence of solution partners on iodine chemistry in the sump water

S Influence of solution partners on iodine chemistry in the sump water 

In the preceding section, iodine chemistry and the iodine partition coefficient in a pure iodine solution have been discussed. The containment sump water which is to be expected in a severe reactor accident, however, may contain a number of other substances that have a potential impact on the chemical reactions and on the resulting reaction products. It is not possible to give detailed and trustworthy information on the nature and the concentrations of all these substances, which in addition might be different in different accident sequences and in different plants therefore, only some of them can be treated here exemplarily. The particular case of the presence of an excess of 1 in the I2—H2O system and its implications for the iodine species distribution and for the partition coefficient have been discussed in the preceding section. 

According to the calculations of Lemire et al. (1981), in a neutral solution with a total iodine concentration of 10 g-atom/1 the partition coefficient shows a mini- 

I2 and HOI present in the sump water can be reduced rather quickly by reducing substances such as organic impurities, hydrazine and metallic trace impurities like Fe and Cu . Dissolved iodate is only slowly reduced by these substances. Addition of 100 ppm Na2S203 to a solution containing 0.05 g I2/I rises the partition coefficient from 900 to 3 10 addition of 100 ppm hydrazine results in a partition coefficient of about 3 10 (Postma, 1980). On the other hand, it was concluded from comparative measurements in pure water and in spent fuel pool water at comparatively low temperatures that hydrazine concentrations up to 60 ppm do not significantly affect the iodine partition coefficient (Pelletier and Hemphill, 1979). 

The role of ionizing radiation as an oxidizing or reducing agent for iodine will be discussed in the following section. 

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