[en] There were conducted in-pile experiments for grounding of realization possibility of the specified diagram of energy release rate in the experimental channels with model FA of fast reactor. There have been received data on reactivity effects caused by fuel replacement along reactor IGR central experimental channel. The data are necessary for grounding of safety of the experiments being planned. There have been performed researches on determination of interrelation between neutron flux distributing and fuel state in the central experimental channel. As fuel compactly bunched pellets of WWER-1000 type with enrichment of 4.4% by U²³⁵ were used. Measuring of neutron flux fluence was conducted with the use of activation detectors (static experiments without fuel location change) and small-size neutron chambers (dynamic experiments with fuel location change). There have been accomplished researches of impurity gases content in fuel of WWER-1000 type with enrichment of 4.4% by U²³⁵ . With this aim there have been conducted pressure measuring in the sealed cavity where fuel melting were being conducted. Energy release in fuel was provided at realization of controlled neutron impulse at IGR reactor