Assessment of neutronic safety parameters of VVER-1000 core under accident conditions

Abstract

Abstract The major issue in designing safety and control systems for power reactors is preventing accidents or reducing the hazard imposed. Any change in reactor power causes a change in temperature and material densities of the system that will affect the reactivity, which in turn, causes transients/accident conditions. The analysis of main safety parameters is essential for any change to ensure the safe operation of the reactor in both steady and transient situations. In this paper, the impact of temperature, moderator density, boron concentration and control rods position changes on the safety parameters is studied to assess the behavior of the reactor under accident conditions. The main safety parameters as temperature reactivity coefficients, power peaking factor, effective delayed neutron fraction and generation time are evaluated under accident conditions for VVER-1000 core using MCNP6 code and ENDF/B-VII.1library. The results evidenced that the reactivity coefficients are still negative, under accident conditions, which guarantee the safe operation of the reactor. The effective delayed neutron fraction increased as a result of increased temperature, decreased moderator density and addition of the soluble boron. The worth of the control rods is sufficient to make the reactor into a subcritical state either in emergency situations or with regular shutdown.