Numerical analysis of VVER-440/213 concrete biological shield under normal operation

Abstract

The numerical approach for the coupled damage-creep modeling of concrete biological shield, which combines the current and the past knowledge regarding the effects of irradiation and temperature on concrete with the real measured and calculated neutron fluence and temperature distribution for VVER-440/213 reactors, is described in detail in this study. The proposed approach takes into account the real structural geometry as well as the real neutron fluence and temperature distribution and the latest knowledge about the effect of irradiation and temperature on concrete strength and stiffness. The radiation induced volumetric expansion and the thermal expansion of concrete are modeled. According to the results of the numerical simulation, the analyzed structure reaches critical damage within the time interval from 10.00 to 35.25 years of normal operation. The damage of the concrete biological shield of the VVER reactor will not affect the load-bearing function of the containment building, since the biological shield is self-bearing. The shielding properties of the biological shield may be reduced due to the appearance of the radial cracks, however, the concrete wall, which is situated right behind the biological shield, will ensure the necessary shielding. Therefore, the concrete biological shield of the VVER reactors can be considered as sacrificial structure and can be damaged without significant consequences. However, this study implies the importance of capability to predict the behavior of those PWR reactor biological shields which serve both the load-bearing and shielding purposes.