الفهرس 
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Abstract
The current research is a parametric study of the neutronic behavior of a nuclear reactor vs. the percentage of heavy water in a heavy/light mixed water moderator. Monte-Carlo simulation was carried out to investigate the neutronic characteristics of LR-O reactor (a Czech benchmark reactor with shortened fuel assemblies of the Russian pressurized water reactor VVER) when it is moderated by mixtures of heavy/light water at molecular ratios ranging from 0 up to 100 020 at increments of + 1 0 020. Neutron flux, neutron energy spectra, fission rates, neutron capture rates, neutron absorption in poison material, and power density were tallied at different regions in the reactor, in addition to radiation dose rates over reactor surfaces, and many other neutronic parameters at the II heavy water percentage moderators being studied. The tallies also included; total mass of control rods, total neutron absorption, neutron absorption density, and absorbed neutron energy spectra in control rods for each of the II studied heavy water percentages in moderator. It was found that the changes in all those parameters with heavy water percentage in moderator were not monotonic, and that the nuclear properties of the reactor changed dramatically between 90 to 100 heavy water percentages in moderator. The most prominent changes were in neutron energy spectrum, neutron capture in 238U, neutrons leakage from the reactor, and neutron absorption in moderator. These changes were not the same in all regions of the reactor.