Because RIS is due to fluxes of excess point defects, modeling must take into account their creation and elimination mechanisms. It must, for example, repro­duce the ratio between vacancy and interstitial concentrations that controls the respective weights of annihilation by recombination or elimination at sinks. The situation from this point of view is very different from phase transformations during thermal aging, where usually only vacancy diffusion occurs, and simulations can be performed with nonphysical point defect concentrations and a correction of the timescale (see, e. g., Le Bouar and Soisson78 and Soisson and Fu12 ).

During electron or light ion irradiation, defects are homogeneously created in the material, with a fre­quency directly given by the radiation flux (in dpa s~ ), a condition that is easily modeled in continuous mod­els, mean-field models,12,14 or Monte Carlo simula­tions.16,118 The formation of defects in displacement cascades during irradiation by heavy particles can also be introduced in kinetic models, using the point defect distributions computed by molecular dynamics.126 The annihilation mechanisms at sinks such as surfaces or grain boundaries are, for the time being, simulated using very simple approximations (perfects sinks, no formation/annihilation of kinks on dislocations, or steps on surfaces). This should not affect the basic coupling between diffusion fluxes, but the long-term evolution of the sink microstructure — which will even­tually have an impact on the chemical distribution — cannot be taken into account.

Finally, thermally activated point defect formation mechanisms that operate during thermal aging, are taken into account in some simulations.11-14 Simula­tions that do not include the thermal production are then valid only at sufficiently low temperatures, when defect concentrations under irradiation are much larger than equilibrium ones.