Impact of Temperature and Radiation Factors on Special Concretes Used for NPP Construction

The core catcher is arranged in an unattended, unventilated sub-reactor space. It is designed to receive molten corium in emergencies, and thus the concrete used in the core catcher must be resistant to high temperatures without significant loss of strength. During nuclear power plant (NPP) operation, these concretes are subjected to considerable radiation exposure, which may also affect their physical–chemical properties. Concrete mixes based on Portland cement and alumina cement with iron and corundum aggregate were investigated. Model samples of concrete were subjected to temperature exposure in the temperature range of 100 to 1000 °C and to radiation exposure in the field of mixed and neutron irradiation in the reactor cell at a load of at least 1 × 107 Gy. Concrete heating over 200 °C leads to a decrease in strength characteristics from 25.1 MPa to 2.6 MPa in Portland cement-based concretes and from 40 MPa to 12 MPa in alumina cement-based concretes. The decrease in concrete strength at high temperatures is due to dehydration of hardening phases, polymorphic transitions of aggregate and chemical interaction between concrete components. Radiation exposure of Portland cement-based concrete samples leads to an increase in their strength. Alumina cement-based concretes are less resistant to radiation exposure, and their strength decreases as a result of radiation exposure-induced processes.