The IBR-4 Pulsed Reactor with a power of 4 MW and a pulse repetition rate of 10 s–1 is considered as a pulsed neutron source to replace the IBR-2M Reactor, which will be decommissioned by the end of the 2030s. The design of IBR-4 is based on the design of the MBIR Multipurpose Fast-neutron Research Reactor with some reconfiguration of the core. The modified core ensures the nuclear safety of the reactor and minimizes low-frequency pulse energy fluctuations inherent in periodic pulsed reactors. The optimal configuration of the IBR-4 core is based on the basic configuration with the addition of beryllium reflectors and small-volume water moderators. The IBR-4 Reactor, with a relatively low average power of 4 MW, makes it possible to obtain thermal neutron flux densities on the surface of the water moderator at the level of 1.2∙10¹⁴ n/cm²∙s, and in the area close to the surface – 3.0∙10¹⁴ n/cm²∙s. Thus, the IBR-4 is a powerful pulsed source of thermal neutrons.