Calculational study of the RBMK reactor physical characteristics in a transient period

Neutron-physical characteristics of the RBMK reactor in a transient period are investigated on the base of the computerized mathematical simulation of fUel burnUp and reactor fueling processes. Time dependences of spent fuel bUrnup, the frequency of fuel assembly (FA) reloading reactivity void coefficient, reactivity coefficients in respect to moderator- and fUel temperatures time constant of the first azimuthal harmonics development and neutron flux density axial non-uniformity coefficient as well as change in axial steam content are analyzed. The transient period is a time period from the reactor start-up till steady reactor fueling regime or period of time during which the reactor operating in steady fueling regime is loaded with fuel of another type differing from the initial one. It is shown that application of FA with a higher fuel enrichment for the central core part and, respectively, with a lover enrichment at the upper and lower ends permits fo hold convex form of neutron flux and to avoid neutron leakage increase at the expense of flattening. Profiling of enrichment without change in FA average enrichment results in a fuel burnup increase by 3-7% at that the channel power non-uniformity slightly being increase (3-5%). A possibility of decreasing the reactivity void coefficient without increasing an average enrichment is one more important advantage of profiled FA