Irradiation-induced segregation mechanisms are classified into solute-point-defect complex type and inverse Kirkendall type. For solutes that have a strong interaction with interstitials in a dilute alloy, the complex effect plays an important part in the segregation. Our earlier model describing solute grain boundary segregation during neutron irradiation in dilute binary alloys, based on the complex effect mechanism, is modified by considering the irradiation-enhanced solute diffusion and the long-range recombination effect of freely migrating point-defects, and expanded to evaluate solute segregation in dilute ternary alloys through consideration of solute-solute competition for segregation sites. Applications of the model to predictions of P grain boundary segregation in neutron irradiated alpha-Fe and Fe-B-P and Fe-C-P alloys indicate that the model has reasonable validity. (C) 1998 Elsevier Science B.V. All rights reserved.