12.110. The fission product elements react chemically with each other and with other substances during the course of an accidental release from the fuel. These reactions affect the transport characteristics of the radio­nuclides that concern us. A starting point is to consider the reactor fission product inventory, which consists of nearly 40 different elements. Various tabulations and computer codes such as ORIGIN-2 [8] are available to provide these data. However, it is important to remember that chemical reaction rates depend on the amount of element present, not just the amount of a radioactive isotope. Therefore, the inventory must include all the isotopes. A typical PWR element inventory is given in Table 12.1. Based on their reactivity with oxygen, it is convenient to classify the elements into eight groups: the noble gases, halogens, alkaline earths, tellurium, noble metals, rare earths, elements with refractory oxides, and stable fis­sion product elements.

12.111. The general chemical behavior of the elements in the various groups as they occur in the fuel, in the water coolant of a LWR, and in the containment is summarized as described below.