Construction sites. The first phase of concrete pouring for the inner cavity of the BREST-OD-300 reactor vessel has been completed at the 4th-generation Pilot-Demonstration Energy Complex (PDEC) in Seversk, Russia. This work is part of the “Proryv” (“the Breakthrough”) project and is scheduled for completion by winter 2027. The BREST-OD-300 is an unparalleled lead-cooled fast neutron reactor. Its pressure vessel combines steel and concrete structures: the interior houses cavities for the core and primary circuit equipment, while the concrete between them serves as a load-bearing structural element, as well as thermal and radiation shielding. In 2026, piping installation was also completed at the site, connecting the central and four peripheral cavities of the vessel to form the primary circuit of the future facility. The “Proryv” project aims to develop next-generation nuclear energy systems based on a closed nuclear fuel cycle. This technology enables the recycling of spent nuclear fuel, which will reduce the demand for natural uranium and minimize the accumulation of spent fuel.