[en] The results are given of the calculations and experiments devoted to research of the safety operation of the two-circuit installation with the VK-100 reactor in extreme emergency conditions. The calculations are based on two mathematical models which describe high-speed (up to 2 min) and low-speed (up to 12 h) processes in the installation. The experiments have been conducted on the test bench simulating the first circuit. The results of the theoretical experimental research prove high reliability and safety of the VK-100 reactor installation in service under the extreme emergency conditions. After operation of the reactor emergency protection system, without actuation of all active emergency systems, normal discharge of the residual heat from the core is ensured: during failure of the entire cross-section of the main steam pipeline - 1.5 h; during continuous failure of the power supply to the atomic steam power station - within 3h 45 min at the account of evaporation of the 2nd circuit water and then within 12 h at the account of discharge of the radioactive steam into the bubbling tank. Cooling of the reactor installation may be accomplished at a rate of 30 deg/h, without supply of the feed water into the steam generator within 40 min. The above features of the two-circuit reactor installation with the enclosed boiling reactor and with natural circulation of the coolant make this installation more advantageous from the point of view of safety of operation and protection of the environments for use in the remote regions, as compared with the water-moderated water-cooled power reactor with forced circulation