Safe operation of nuclear power plants is one of the major concerns and relies primarily on the integrity of the reactor pressure vessel. Neutron exposure induces temperature dependent embrittlement and can lead to loss of fracture toughness of reactor pressure vessel steel. Conventional fracture mechanics suffers from a serious limitation of non-transferability of fracture data from specimen level to component level as fracture resistance data obtained is largely geometry dependant. This difficulty is largely overcome by Gurson-Tvegaard-Needleman (GTN) model which models the drop in load carrying capacity of a material with the increase in plastic strain, considering nucleation, growth and coalescence of micro-voids in the material. However, determination of the model-parameters with experiments is extremely difficult and doubtful. Hence, a parametric study was undertaken to find out the effects of different parameters on material behaviour of reactor pressure vessel steel and to asses the parameter for best practical result with least metallographic study using a hybrid approach. The model parameters were finally verified by predicting ductile fracture in compact tension and three point bend specimen made from reactor pressure vessel steel.