The reliability of safety analysis of nuclear reactor pressure vessels is imperatively dependent upon the reliability of the fracture toughness values used in the analysis. Normally, existing fracture toughness results are analyzed with standard statistical means making use of empirically defined distribution functions for the fracture toughness. Recent developments in the theoretical modelling of cleavage fracture initiation have evolved a sounder statistical description of the macroscopic fracture toughness. It has thus become possible to make a theoretical interpretation of the scatter in brittle fracture toughness results. Here, the theoretical relations are applied to the statistical analysis of brittle fracture toughness results for the reactor pressure vessel steel 15X2M-phi-A and its welds. Based on the analysis, theoretical statistical reference curves for the steels are presented and compared to the presently used standard reference curves.