Effect of the Inclusion of the Detailed Geometry of the Reactor Core on the Calculated Antineutrino Flux from a VVER-1000 Reactor

Using fuel campaign data from the third unit of the Kalinin Nuclear Power Plant, it has been shown that the inclusion of the detailed geometry of the reactor, its finite dimensions, and the distributions of the energy release and the fuel composition in the reactor core results in the appearance of inhomogeneity in the calculated antineutrino flux from it. This inhomogeneity is particularly pronounced at distances comparable with the dimensions of the reactor core. The detailed calculation gives a higher antineutrino flux at such distances than simplified models and indicates the directional dependence of the flux. This can noticeably affect measurements of the oscillation parameters $\Delta m_{{14}}^{2}$ and ${{\sin }^{2}}2{{\theta }_{{14}}}$ for neutrino detectors used to search for transitions of neutrinos to a sterile state at small distances from the reactor. It has been shown that not only a change in the isotopic composition of the fuel but also the variation of the energy release distribution in the reactor core can be evaluated from the variation of the count rate of a neutrino detector in specific directions to the reactor.