Активність і залишкове енерговиділення ядерного палива під час експлуатації і зберігання

Abstract

General information on the amount of accumulated spent nuclear fuel (SNF) at NPPs in the world is presented. An analysis of the rates of SNF accumulation was carried out, and forecasts of SNF accumulation in the world and in Ukraine for the next decade were made. Information is given on the technologies for SNF handling, as well as some characteristics of SNF storage systems of wet and dry types. Radiation characteristics of SNF — radioactivity and residual energy release of nuclear fuel — largely determine both possible accident scenarios and possible radiation consequences of accidents at nuclear facilities. The article presents the results of modeling in the SCALE program code of changes in radioactivity and residual energy release of VVER-1000 nuclear fuel after period of operation of the fuel assembly in the VVER-1000 core. The model of VVER-1000 fuel assembly with 4.4% enrichment, which is used in the mode of stationary refueling, was chosen for simulation. The simulation results were compared with the data given in the relevant reference books regarding the change in the radiation characteristics of nuclear fuel during its operation in the VVER-1000. The results of comparison of the radiation characteristics of VVER-1000 fuel assemblies with the same burnup, but with different fuel loading schedules in the last year of operation are presented for a four-year fuel campaign. A significant influence on the radiation characteristics (radioactivity and residual energy release) of the fuel assembly load mode has been demonstrated. The simulation results show that the specific radioactivity and, accordingly, the total radioactivity of nuclear fuel in the VVER-1000 cores at the Zaporizhzhia NPP after ~1 year of forced outage decreased by ~100 times. Therefore, the possible radiation consequences in case of damage of nuclear fuel located in the core or unloaded into the spent fuel pools will be much lower than in the case of an accident at an operating reactor. The same applies to comparisons of the consequences of a possible accident at the ZNPP with the consequences of the accident at the Chornobyl NPP in 1986, which occurred at a working reactor with the release of at least ~3–5 % of nuclear fuel.