Release mechanism, iodine

Eickelpasch, N., Seepolt, R., Hock, R. Iodine release mechanism and its verification in plant operation. Trans. Am. Nucl. Soc. 28, 652—653 (1978)... 

If the waste is isolated in a geologic repository, the iodine form should be stable to at least 100°C and possibly at 250°C depending on the repository site. If the waste form satisfies the thermal stability requirement, the most likely release mechanism then becomes leaching in the event that groundwater contacts the immobilization form. Allard et al. (11) report log Kd values for silicate minerals ranging from -0.5 to -3.5. Fried et al. (12) found little retention of iodine (as iodide or iodate) by Los Alamos Tuff. Thus, once the Iodine has been removed by leaching, it will potentially move at the same velocity as the groundwater. 

Iodine Compounds. Since contact with water is the most likely release mechanism in either of the terrestrial disposal operations, we initially screened iodide and iodate compounds on the basis of their solubilities. Tables III and IV present rankings of the low solubility iodides and iodates, respectively, with the least soluble at the top. 

One per cent potassium iodide in neutral buffered or alkali solutions is more stable and useful than 20% potassium iodide in bubblers for collection and determination of ozone in air. Either 1 % solution may be used to determine low concentrations of ozone however, there is a difference in their stoichiometry. Over the range of 0.01 to 30 p.p.m. (v./v.) results by the alkaline procedure should be multiplied by 1.54 to correct for stoichiometry. The neutral reagent does not require acidification and has more nearly uniform stoichiometry. The alkaline procedure is preferable when final analysis may be delayed. Experiments with boric acid for acidification of samples in the alkaline reagent show that some mechanism other than oxidation of iodide to iodate or periodate is involved, possibly formation of hypoiodite. Preliminary experiments with gas phase titrations of nitrogen dioxide and nitric oxide against ozone confirm the stoichiometry of the neutral reagent as 1 mole of iodine released for each mole of ozone. 

Mechanism of Action. TSH and LATS cause similar effects on glucose oxidation, P uptake (F2), and iodine release (E6). The time course is delayed, presumably due to the molecular size of the LATS. Antihuman TSH antibody did not inhibit the effect of LATS on P uptake into phospholipids or on glucose oxidation. As stated above (M13) proteolytic digestion of LATS makes it a short-acting thyroid stimulator. 

The isotopic composition of fission product iodine present in the BWR reactor water in the case of failed fuel rods in the reactor core is quite similar to that in the PWR primary coolant. Since the iodine purification factor of the reactor water cleanup system is on the order of 100, i. e. virtually identical to that of the PWR primary coolant purification system, this similarity in isotopic composition demonstrates that the release mechanisms of iodine isotopes from the failed fuel rods to the water phase are virtually identical under both PWR and BWR operating conditions. On the other hand, the resulting chemical state of fission product iodine in the BWR reactor water is quite different from that in the PWR primary coolant. The BWR reactor water usually does not contain chemical additives (with the possible exception of a hydrogen addition, see below) as a result of water radioly-... 

The concentration of Li+ in the thyroid is three to four times that in serum [179]. It is thought that Li+ may be concentrated in the thyroid gland by a mechanism similar to the incorporation of iodide, I-, resulting in competition between Li+ and I the levels of intracellular 1 decrease when those of Li+ increase, and vice versa [182]. Li+ inhibits both the ability of the gland to accumulate 1 and the release of iodine from the gland. In vitro, Li+ has no effect on thyroid peroxidase, the enzyme that catalyzes the incorporation of I" into tyrosyl residues leading to thyroidal hormone synthesis, but does increase the activity of iodotyrosine-deio-dinase, which catalyzes the reductive deiodination of iodotyrosyls, thus maintaining the levels of intracellular I [182]. The increase in iodoty-rosine-deiodinase activity is probably a response to the Li+-induced decrease in the concentration of thyroidal I". Li+ has no effect on the conversion of thyroxine to triiodothyronine. The overall effect of this competition between Li+ and 1 is, therefore, reduced levels of thyroid hormone in the presence of Li+. 

The retention of fission product iodine and xenon by unirradiated and irradiated pyrolytic-carbon-coated (Th,U)C2 fuel particles has been studied in annealing experiments and has been compared with similar studies of the release (or retention) of barium and strontium. The objective was to study the effects of irradiation on the retention of the two types of fission products and to determine the mechanism of release which could account for the observed behaviors. In both unirradiated and irradiated particles, iodine and xenon were found to be retained highly by the impervious isotropic pyrolytic coating which was unaffected by the irradiation. In contrast, the fuel kernel which controls the release of the metallic species is damaged severely by the irradiation, resulting in a marked decrease in its ability to retain the metals. 

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