Monte Carlo evaluation of neutron irradiation damage to the VVER-1000 RPV

Neutron irradiation damage is of the most critical damage mechanisms in nuclear power plant's pressure vessel. Neutrons transfer their kinetic energy to target atoms of RPV that start to jump creating vacancies and interstitials known as Frenkel Pair (FP). The FPs are responsible for formation of defected clusters and microstructural modifications (e.g. phase reactions, segregations). These effects deteriorate physical and mechanical properties of the RPV steels among which are increasing the hardness and decreasing the embrittlement which results in limiting the life-time of RPV. The most sensitive location in the RPV related neutron irradiation damages is in the beltline region and adjacent to the reactor core. Welds and their heat affected zones (HAZs) in this region are of particularly importance due to higher probability flaws compared with the base metal. In this paper, Monte Carlo simulation of the detailed reactor core have led to identifying the areas maximum neutron flux in the RPV. Then the SPECTER and SRIM Monte Carlo codes are used to evaluate the neutron spectral-averaged DPA values for the beltline region of RPV.