A recently developed model for irradiation-induced solute segregation (IRS) is overviewed and applied to the case of phosphorus segregation to grain boundaries in a ferritic matrix. The effects on IRS of irradiation temperature, dose rate and dislocation networks acting as additional point defect sinks are examined. Phosphorus is predicted to segregate at relatively low irradiation temperatures in the range ∼ 110°–300°C, depending on dose rate, with peak segregation occurring at ∼ 120°C and ∼ 150°C at thermal and fast reactor core dose rates, respectively. The principal effect of increasing the matrix dislocation density is to reduce the magnitude of the solute segregation without change in peak temperature.