  For a fissile medium, originally consisting of uranium-238, the investigation
of fulfillment of the wave burning criterion in a wide range of neutron
energies is conducted for the first time, and a possibility of wave nuclear
burning not only in the region of fast neutrons, but also for cold, epithermal
and resonance ones is discovered for the first time.
  For the first time the results of the investigation of the Feoktistov
criterion fulfillment for a fissile medium, originally consisting of
uranium-238 dioxide with enrichments 4.38%, 2.00%, 1.00%, 0.71% and 0.50% with
respect to uranium-235, in the region of neutron energies 0.015-10.0eV are
presented. These results indicate a possibility of ultraslow wave
neutron-nuclear burning mode realization in the uranium-plutonium media,
originally (before the wave initiation by external neutron source) having
enrichments with respect to uranium-235, corresponding to the subcritical
state, in the regions of cold, thermal, epithermal and resonance neutrons.
  In order to validate the conclusions, based on the slow wave neutron-nuclear
burning criterion fulfillment depending on the neutron energy, the numerical
modeling of ultraslow wave neutron-nuclear burning of a natural uranium in the
epithermal region of neutron energies (0.1-7.0eV) was conducted for the first
time. The presented simulated results indicate the realization of the ultraslow
wave neutron-nuclear burning of the natural uranium for the epithermal
neutrons.
