Vol 125, No 2 (2018)

This article is devoted to a method for calculating the radiation protection based on combined use of the Monte Carlo method and the method of characteristics. The method implements a scheme for automatic reduction of dispersion CADIS (Consistent Adjoint Driven Importance Sampling) based on the solution of a multigroup adjoint problem by the method of characteristics using the MCCG3D code. The presented method makes it possible to generate spatial-energy weight windows on an auxiliary grid for Monte Carlo calculations. The general structure of the method including the results of model calculations showing its efficacy is presented.

In validating the concept of a molten-salt nuclear reactor for incinerating transuranium elements from spent nuclear fuel of light-water reactors, experimental data on the kinematic viscosity of melt with the molar composition 73LiF–27BeF₂ were obtained in the range 882–1172 K. The influence of cerium trichloride and zirconium trifluoride as additives on the viscosity was investigated. It is shown that for all compositions the obtained viscosity is described by an exponential function of the reciprocal of absolute temperature. The parameters of this function are determined for each composition. It was found that the addition of cerium trifluoride in the amount 1 mol.% to the initial composition lowers viscosity at low temperature. Subsequent addition of zirconium tetrafluoride appreciably lowers the liquidus temperature.

A non-destructive gamma-spectrometric method of determining the characteristics of fissile materials in fuel pins with uranium-plutonium fuel is presented. The measurements were performed with the aid of a scanning apparatus with an ultrapure germanium detector. The uniformity of the mass and plutonium distributions was monitored according to the counting rate of the pulses in the 413.7 keV peak of ²³⁹Pu. The FRAM code was used to determine the isotopic composition of plutonium in a fuel pin. Multiple repeated measurements were performed and the repeatability and reproducibility of the determinations of the characteristics of the fissile materials in a fuel element were determined.

Heat transfer in the gas cavity of the melt trap for the VVER-1200 core is studied. A model problem is solved numerically in a configuration where the cavity boundaries are close to that obtained after the formation of the melt pool. Heat transfer by radiation is calculated by three methods: in the approximation of a transparent medium taking account of the angular coefficients of radiation emission of sections of the cavity boundaries, by the DTRM method suitable for calculating radiation transfer in a medium with arbitrary optical density, and by the diffusion method in the Rosseland approximation. It is shown that the dominant mechanism is thermal radiation; the contribution of convection of the gas is relatively small. The influence of the choice of computational method on heat transfer in a gas cavity with different absorption is evaluated.

The dose error determined on the basis of recommendations for calculating the shielding of electron accelerators is determined by comparing the photon dose distribution calculated by the Monte Carlo method in concrete, iron, and lead from isotropic monoenergetic sources and sources with the bremsstrahlung spectrum of electron accelerators with energy above 15 MeV. It is shown that the highest error in using the mono-energetic sources to simulate sources of bremsstrahlung is observed for concrete protection and the smallest error is observed for lead. Suggestions are formulated for reducing the errors by means of individual selection of the effective energy of an equivalent monoenergetic source as a function of the energy of the accelerator electrons and the employed material.

The results of a study of the radon concentration in surface and ground waters on the territory of the preserved uranium deposits in South Yakutiya are reported. The work included the collection of water samples from wells, adits, springs, streams, and rivers into special chambers with the time being recorded and determining the radon content in them with the aid of an Alfarad Plus radiometer. The obtained data were used as a basis for comparing the radon content in the studied waters with its sanitary-hygienic norm in drinking water. It is shown that the source of the high radon concentration in surface and groundwater are massifs of Archean crystalline rock, ore zones, and rock heaps with high uranium (radium) content.