12.113. The halogens are very reactive and tend to combine with such metallic fission product species as cesium and zirconium. Iodine is the primary element of interest since its concentration in the fission product mixture is about 100 times greater than that of bromine. Also, the cesium/ iodine concentration ratio in the fission products of about 10 to 1 favors the formation of cesium iodide.

12.114. During a loss-of-coolant accident, the reactor coolant system tends to have a reducing atmosphere. Hence, such strong oxidizing agents as the halogens are likely to form halides, which will be retained in the water present. For example, iodides transported into the containment with large amounts of water will tend to remain in the water as a nonvolatile component.

12.115. Since the release of iodine-131 to the atmosphere has tradi­tionally served as a measure of radiological risk (§12.209), the chemical behavior of various forms of iodine has been studied extensively. Should there be a hydrogen burn in the containment, volatile methyl iodide might form, but the conversion would only be about 0.03 percent of the reactor iodine inventory [7]. Whether or not this constitutes a hazard depends on the integrity of the containment.