MCNP [1] is a high-precision computer code that makes it possible to perform Monte Carlo simulation of neutron, γ-ray, and electron transport in systems with a complicated three-dimensional geometry. The code was developed over a period of many years, during which the range of solvable problems expanded. MCNP employs an ENDF/B [2] based library of nuclear constants with continuous variation of the particle energy. The library includes data on the neutron and photon interactions, activation, and neutron thermalization for different material temperature. The geometric objects are given by surfaces, such as planes, spheres, cylinders, and cones, making it possible to describe complex systems in detail, for example, an electricity generating channel (EGC) consisting of several electricity-generating elements with multilayer collector packets, gas-removing apparatus, gaps, emitters, and fuel kernels. Elements of periodicity in radial-azimuthal and vertical directions of the core can be prescribed. Examples of the prescription of complex geometries are shown in Figs. 1 and 2.Reactor Calculation. The MCNP code was used to determine the neutron multiplication coefficients with estimation of the maximum reactivity and the effectiveness of the control organs and to calculate the regulatory characteristics of the control organs, emergency situations associated with the reactor falling into water, transverse and longitudinal compression of the reactor caused by the reactor striking a solid surface, and other situations. To obtain the regulatory characteristics, the orientation angle of the absorbing lining relative to the reactor core was changed by a small amount (Fig. 3). Emergency situations which are associated with transverse compression of the reactor, caused by impact against a solid surface, were simulated by ellipses for the circles forming the lateral surface of the core, vessel, and lateral reflector. The lattice of EGCs was tightly squeezed and the peripheral EGCs were redistributed into the open spaces appearing in the core. The ratio of the semiaxes of the ellipse was varied from 1.1 to 1.4. A free space in the connecting crosspieces of the EGCs was chosen for the longitudinal compression of the reactor.The MCNP code was used to calculate the energy release in the reactor. Here, it possible to estimate the total energy release from various reactions, for example, nuclear fission, (n, γ), and (n, 2n), as well as from individual nuclear reactions. In the computational model, the fuel kernels of the electricity generating elements were divided into very thin layers (Fig. 4). A lattice over the height of the fuel was created in order to simplify the formulation of the model. The flux of neutrons and γ rays was calculated in 26 neutron energy groups (Fig. 5). The reactivity change over a reactor run is simulated with the program complex for isotopic kinetics ORIGEN2 (USA) [3]. The Monteburns program (USA) is used to link the program systems [4].Radiation Protection. Large computational capacity is necessary in order...
The main objective of this paper is to summarize multiphysical tasks and methods for their solution in the area of space nuclear power systems being solved and developed by specialists of JSC SSC RF–IPPE. The physical and technical justification of the development and operation of space nuclear power systems with direct conversion of thermal energy into electricity includes an electrothermophysical calculation of characteristics of a thermionic electrical power generating cell and electrical power generating channel as a whole, neutronic physical calculations and structural optimization of the core and radiation shielding. To determine the electrothermophysical performance of the electrical power generating channel, its 3D detailed computation (software COMSOL-EGK) is used. For the neutronic calculation of the core and radiation shielding characteristics, unified 3D computational software systems are used that implement the Monte Carlo method (in particular, MMKFK-2, MCNP), making it possible to take into account the heterogeneity and all geometry features. The computational procedures and solutions listed in the review are applied in a systematic and integrated manner at JSC SSC RF–IPPE in justification of performance of space nuclear power systems being currently designed. Key words: thermionic reactor-converter, radiation shielding, electrical power generating channel, MCNP, COMSOL – EGK.
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