Apparently, the only way to create a sufficiently intense UCN source at a pulsed reactor of moderate power is to implement the idea of F. L. Shapiro about pulsed filling of UCN traps. To ensure the pulsed nature of the neutron flux at the entrance to the trap, which is remote from the neutron source, it was proposed to use a time lens of one design or another. Later, the concept of a source appeared, based on the combination of a magnetic time lens and a magnetic resonance device that slows down neutrons. A recent analysis has shown that when using a moderating flipper with a sufficiently strong magnetic field, the resulting UCN flux should have a pronounced pulsed structure even in the absence of a time lens. This idea can serve as the basis for the first phase of the UCN source project at the IBR-2 Reactor. In addition to obtaining UCN of moderate intensity, the implementation of the proposal will make it possible to test the basic principles of the design of a magnetic time lens and to demonstrate for the first time the method of pulsed filling of UCN traps.