The reference toughness technique, developed under the sponsorship of the Electric Power Research Institute (EPRI), is utilized to predict radiation-induced changes in fracture toughness of reactor vessel steels using Charpy impact data from the Heavy Section Steel Irradiation (HSSI) program. The results of the prediction are compared (1) with the data from the HSSI Fifth Irradiation Series large-compact fracture toughness specimens, (2) to the predictions of shifting the KIc curve using Regulatory Guide 1.99, Revision 2 (RG 1.99, Rev. 2), and (3) to the predictions of shifting the KIc curve using the change in the 41-J transition temperature of the HSSI Fifth Irradiation Series Charpy data. The EPRI reference toughness approach provides a reasonable prediction of fracture toughness on the lower shelf and in the low transition, but is a poor predictor of the upper transition fracture toughness. Improvements to the EPRI reference toughness methodology are suggested. It is also observed that although the 41-J (30 ft-lb) shift methodology underpredicts the mean shift in the HSSI Fifth Irradiation Series fracture toughness data, the RG 1.99, Rev. 2 shift, when two sets of Charpy data are not available, provides a conservative bound to the measured HSSI fracture toughness data with considerable margin.