Modelling of intergranular corrosion using cellular automata, 2

Igarashi, Takahiro  ; Irisawa, Eriko ; Komatsu, Atsushi ; Yamamoto, Masahiro ; Kato, Chiaki   ; Ueno, Fumiyoshi  

Nuclear fuel reprocessing plants contain high-temperature condensed nitric acid solution for dissolution of spent nuclear fuel, and austenitic stainless steels are used as a main material for spent nuclear reprocessing systems. In such a highly oxidizing environment, stainless steel shows the morphology of an intergranular corrosion surface. To keep maintain the safety of the system, it is important to understand the intergranular corrosion behavior. According to our experiments, grain dropping occurred with intergranular corrosion progress and that lead accelerating the corrosion rate. To predict corrosion rate due to intergranular corrosion, it is necessary to consider not only dissolution of the metal surface but also grain dropping. In our previous study we developed computational intergranular corrosion propagation model by cellular automata method. In the model, simulation space is parted into three kinds of non-cubic cells: interior of grain (matrix) cell, grain boundary cell, and solution cell. The only matrix and grain boundary cell contacted with solution cell corrode and change into solution cells with local matrix and grain boundary dissolution rates. The corrosion rates were determined by dissolution rate ratio between grain boundary and matrix, and reaction rate theory with our experimental data. By setting appropriate dissolution rate ratio from experiments into the model, change of corrosion rate was estimated by the simulation and it was good agreement with that of real corrosion test.