The Chemical Behavior of Fission Product Iodine in Light Water Reactor Accidents

It is commonly assumed that the chemical form of fission product iodine that escapes from the core of a light water reactor under accident conditions is the elemental form. Experimental evidence is presented that indicates that this assumption is incorrect; instead, a metal iodide (probably cesium iodide) is the chemical form that escapes from the fuel. Moreover, since transport through the primary system necessarily occurs under chemically reducing conditions, a change in valence of the iodine is not possible until the oxidizing conditions characteristic of reactor containment buildings are encountered. However, it is also demonstrated that elemental iodine cannot be a dominant form if, as occurred at the Three Mile Island reactor, the iodide contacts water and is transported into the containment building in aqueous solution.