Changes in Concrete Subjected to Neutron Irradiation

Nuclear energy has several difficulties connected to the production or storage of the radioactive waste. Long-term operation is a process that may prolong the serviceability of the power plant by 10, 20 or more years. Nevertheless, crucial components as the reactor pressure vessel or its surrounding must be proved before enabling this process. Fast-neutron radiation can have several effects on the concrete biological shield around a nuclear reactor. It can cause changes in the lattice structure of some rock forming minerals, resulting in an increase in volume of several percent and this may lead to cracks between the hardened cement paste and the coarse aggregate grain. Fast neutron radiation is converted in concrete to thermal neutrons which generate secondary gamma radiation and heat whereas gamma generates heat as well. Heat followed by drying causes additional shrinkage of the hardened cement paste. All these affects can be observed via digital images processing after the images have been subjected to segmentation, pre-processing, registration and normalization of the illumination. Twelve small holes were drilled in the concrete slab 50 × 50 × 5 cm and the resulting cores of a diameter 4 cm were removed. They were cleaned and polished then inserted into the LVR-15 Research Nuclear Reactor for one year of irradiation with exposure to a flux of 6 ÷ 7 × 1011 neutrons·cm−2s−1. The samples were measured and photographed using the Vertex measuring system before and after irradiation and they were examined to find evidence of any visual changes. The work on digital image processing began in April 2023 and the first outcomes should be available at the end of the year 2023.