Influence of Γ Radiation of Short-living Fission Products on Kinetics of the Beryllium Reflected Core of Budapest Research Reactor

Two methods were elaborated for calculation of the kinetic effects caused by the photo-neutrons emitted in beryllium reflector of the VVRSZM type research reactor of KFKI-AEKI. The first simplified point kinetic model assumes that the importance of photo-neutrons is the same as that for the neutrons originated from the fission events. The point kinetic parameters were calculated by using the modified MCNP4A and TIBSO codes. A more realistic and complicated model was built in the KIKO3D code by introduction of additional delayed neutron groups and artificial fission in the reflector nodes. The additional response matrices responsible for the artificial fission were obtained from static coupled neutron-gamma MCNP4A calculations. The kinetic calculations show that the influence of the photo-neutrons is not negligible in the doubling time reactivity measurements. The reactivity-meter can give false values if the photo-neutron effect is not taken into account.