The mechanism and mathematical model of nodule (spot) corrosion of zirconium alloys

It is suggested that nodule corrosion on fuel claddings, process channel surfaces a fuel assembly surfaces is induced by a short circuit of an oxide film by intermetallic Zr compounds with impurities or doped-components or by their oxides with deposition of corrosion products of the NPP first circuits. In terms of the electrochemical corrosion model the equivalent electrical diagrams for nodule corrosion process in the stages of pre- and post-transition oxidation were suggested. The expressions defining nodule corrosion kinetics are obtained. The results of computer calculations of nodule corrosion as a function of operation conditions a running time are adduced. 4 refs.; 4 figs. (author)