Alekseev P.A., Mokshanov N.A., Pyshko A.P.
A.I. Leipunsky Institute for Physics and Power Engineering, Obninsk, Russia
The article presents the results of computational studies of the replacement of high-enriched uranium (HEU) nuclear fuel with low-enriched uranium (LEU) nuclear fuel in space nuclear power plants (SNNPs). The change in the weight and dimensional characteristics of the reactor and radiation shield, and the chage in termal power evaluated. In addition, the change in thr activity of fission products an actinides, accumulated during operation was evaluated. Reactors with intermediate (with moderator) and fast neutron spectrum were studied, both with liquid metal and gas coolant. Variants of SNPPs with HEU and LEU were compared using reactors of the same reactivity margin. The geometric parameters of the reactors were changed leading to changes in their masses, masses of radiation protection and thermal power. The thermal calculation of average thermal power based on the calculation of the power of a single fuel element. Not only the influence of geometric parameters was taken into account while estimating the thermal power of a reactor, but also the reactor's neutron-physical characteristics, namely the uneven energy release along the cores height and radius. The mass of radiation protection was calculated based on the ratios used for determining the maximal absorbed dose of gamma radiation (Si) and the maximal fluence of neutrons with energies above 0.1 MeV at the payload location. The calculations showed that for intermediate neutron reactors the mass of SNPP increases by 1.5–2 times, while it increases by 5–6 times for fast neutron reactors. The radiation safety of SNPPs with LEU was estimated as the activity of fission products and actinides generated during the operation period. Hundreds of years after shutting down, the actinides activity level in a LEU reactor is an order of magnitude higher than in a HEU reactor.
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