Structure and properties of steels for manufacture of core catcher vessel of nuclear reactor

The Russian new nuclear reactors are provided with a special core catcher vessel device (cc-vessel) designed to minimize the consequences of a severe beyond design basis accident at a nuclear power plant, when the reactor pressure vessel collapses and the core melts. For manufacture of the cc-vessel structural elements, low-carbon unalloyed or low-alloyed steels are used. When a severe beyond design basis accident develops, the cc-vessel’s body is subjected to extreme temperature and force loads, which can lead to degradation of the structure, loss of strength and failure of the entire cc-vessel. To calculate the strength characteristics of the cc-vessel, which ensure its safe and reliable operation, the detailed data are required on the structure and mechanical properties of low-carbon steels at high temperatures and after extreme thermal actions simulating the development of a severe beyond design basis accident. The paper analyzes data on the structure and mechanical properties (tensile strength, crack resistance, toughness and cyclic strength) of a number of low-carbon steels under extreme temperature and force actions, including conditions simulating the development of a severe beyond design basis accident at a nuclear power plant, in order to select the material for the design of cc-vessel of nuclear reactor. New data on the structure, mechanical properties, and thermal diffusivity in a wide temperature range of a Cr – Mo steel (Russian Standard – 15KhM) as a candidate structural material for the manufacture of the cc-vessel body are presented. The low content of manganese and alloying with molybdenum and vanadium in 15KhM steel provides a finer grained structure and eliminates the steel’s tendency to temper brittleness.