Evaluation of Reactor Pressure Vessel radiation damage in a VVER-1000 nuclear reactor

The reactor pressure vessel (RPV) is one of the most critical elements with the highest priority in safety rankings. Therefore it is closely monitored and tested by surveillance programmes. Structural materials in a nuclear reactor are damaged by radiation from fission reactions. Neutron irradiation influences the mechanical properties of the RPV steels by increasing the strength (neutron hardening) and decreasing the toughness (neutron embrittlement). The most sensitive location in the RPV is the region adjacent to the reactor core (termed the beltline region). Weld lines and their heat affected zones (HAZs) in this region are particularly important since these regions have a higher probability of having flaws. In this paper, the areas where the neutron radiation flux in the RPV is maximum and neutron spectra in those areas have been identified with MCNPX, a Monte Carlo code which is able to calculate neutron flux or fluence, and the results have been compared to the values presented by calculation in Final Safety Analysis Report (FSAR) of the VVER-1000 NPP. Then the RPV of VVER-1000 NPP was simulated by SPECOMP code that used to calculate DPA cross sections for compounds that are not already contained in the SPECTER computer code. The SPECTER computer code used to produce neutron spectral-averaged DPAs values for the beltline region of RPV. Finally the highest sensitive zone on the inner surface of VVER-1000 RPV has been determined prior to neutron flux effect.