No abstract

No abstract

The prospects and possibilities of replacing the capacities of nuclear power units of Ukrainian nuclear power plants, which are currently almost completely depleting their operational life, as well as the possibility of extending the guaranteed service life are analyzed and generalized. Based on the study of reactor construction trends and proposals on the world market, a basic promising modern model of a high-capacity 3+ AP1000 nuclear water reactor manufactured by Westinghouse El. Corp. was selected and recommended as a basic promising for use in Ukraine. The results of new studies on the dynamics of strength loss of reactor steels of WWER reactors and their welding joints under the action of radiation are considered. The main attention is paid to the presence and processes of migration and segregation in the crystal structure of reactor steels of harmful impurities, in particular phosphorus and nickel. It is concluded that there are significant advantages of new foreign metallurgical technologies, the use of which in vessel steels provides reliability and increased guaranteed life of safe operation of PWR reactors, in particular, AP1000 type made in the USA. The urgent problems of commissioning additional shunting capacities in the National Unified Energy System of Ukraine were assessed and the conclusion was made that they can be solved by improving the shunting characteristics of existing high-capacity nuclear power units and (mainly) by accelerating construction and commissioning of small modular reactors with high shunting characteristics, in particular the SMR-160 model manufactured by SMR LLC (USA).

A new composite material with neutron radiation shielding properties is presented. This fiber reinforced concrete material incorporates basalt-boron fiber, with different concentrations of boron oxide in fiber, and is applicable to nuclear energy and nuclear waste management. The methodology for production of boron oxide (B2O3) infused basalt fiber has been developed. First experimental samples of basalt boron fiber containing 6% of B2O3 and 12% B2O3 have been produced in laboratory conditions. The concrete samples reinforced by two types of basalt-boron fiber with different dosages have been prepared for neutron experiment. The neutron experimental investigations on radiation shielding properties of concrete reinforced by basalt-boron fiber have been performed by means of Pu-Be neutron source. The prepared samples have been tested in the course of several series of tests. It is shown that basalt-boron fibers in concrete improve neutron radiation shielding properties for neutrons with different energies, but it appears to be most effective when it comes to thermal neutrons.

A study of the specifics of supercritical water flow under conditions of mixed convection was made on the basis of CFD modeling. The results of comparison of the numerical solutions obtained in the presence and absence of the buoyancy forces are given. It is shown that the influence of Archimedean forces on the flow structure is localized in the central region of tube length. The data of computer modeling of supercritical water flow pattern with the variation of heat flux q on the tube wall are obtained. The dependence of the localization of mixed convection zone from the value of q is established. The change of the local Richardson number in the context of the effect of the localization of buoyancy forces action is analyzed. For the conditions under consideration, the dependence of turbulent transfer intensity on the effect of Archimedean forces is investigated. It is shown that this action causes oppression of turbulent transport, which is most significantly manifested near the wall of the tube.