Release fractions after 639 days, element

Element Release Fractions After 639 Days Fraction Rele s d... 

Figure 6 shows these cumulative leach fractions from the top waste glass section. A ranking of the elements studied, based on the fraction released after 639 days of solution contact, is given in Table II. This order of leaching can also be seen in Figures 3a and 3b. 

Already the first measurements performed in the containment about one day after the onset of the accident showed that the major fraction of fission product iodine was plated out in the sump water, while only a very smaU fraction was airborne in the containment atmosphere. Taking the different voliunes of both phases into account, an integral iodine partition coefficient of about 2 1(F was calculated from these data (Pelletier, 1980). The pH of the siunp water was about 8.6 (due to sodium hydroxide solution which was automatically injected into the containment sump to improve iodine retention in the liquid phase) the value of the partition coefficient is consistent with the data obtained in the CSE experiments, when the lower pH of the sump water in these experiments is taken into account. This high value indicates that in the TMI-2 accident the bulk of the fission product iodine was released from the primary circuit to the containment in the form of an iodide compound and not as elemental I2. This assumption is consistent with the observation made later on that only about 1% of the iodine present in the sump water was in the form of iodate it is also consistent with the redox conditions in the reactor pressure vessel which were mentioned above For such an H2 H2O... 

Different types of AVR fuel elements were exposed to Q-brine /8/at temperatures between 50 and 90°C and pressures up to 13 MPa. The fractional release of Cs is shown in FIG. 12. The release from fuel elements with BISO particles is less than lO", related to the inventory of one coated particle respectively the inventory generated by the U-contamination of the matrix graphite. After 200-300 days the release rate decreases to a stable equilibrium controlled by the diffusion of Cs from the pyrocarbon kernel into the matrix. Calculations based on a diffusion/adsorption model with the GETTER code match the experimental results very well. For the long time calculations the release of Cs can be described as a instantaneous release of about 20% of the matrix inventory, which is related to the amount of kernels with a defect in the coating, and a slow release of the remaining Cs in the graphite particles over a time period of several 100 years /4,6,9/. 

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