Vol 123, No 2 (2017)

The possibility of measuring and controlling PIK reactor subcriticality on the basis of spectral analysis of reactor noise is examined. A simple lumped-parameter working model of the reactor and an equivalent noise source in accord with Schottky’s relation are used. Attention is focused on the statistical error of measurement of the spectral density of reactor noise owing to the finite measurement time and the random nature of neutron detection in a detector. It is shown that in connection with this error the measurements will require a long time and high-sensitivity detectors.

The results of testing the three-dimensional CFD-code on problems very close to real processes for lead–bismuth eutectic are presented: flow in a 19-fuel element assembly with three spacing lattices and convection in the ‘tumbler’ model. The results of convergence on a sequence of grids permit drawing the conclusion that for a 19-fuel element assembly the error in the calculation of the friction coefficient on a more finely divided grid does not exceed 10% with two-fold smaller grid step in each direction. Similar arguments are valid for the calculation of the hydraulic resistance coefficient.

The results of Investigations of the nitrogen and uranium pressure in the system U–Zr–C–N in the temperature range 1873–2073 K and the constructed section of the U–Zr–C–N phase diagram at 1873 K are presented. The behavior of the solid fission products in carbonitride fuel, the interaction of the fuel with a pyrolytic carbon coating, and the behavior of micro fuel elements based on such fuel during high temperature firing and in the presence of a temperature gradient are examined. The conditions for the preparation of fuel compositions of the type uranium carbonitride in a carbide-silicon matrix and some of its physicochemical and mechanical properties are determined. It is noted that there is promise in using fuel compositions and micro fuel elements based on uranium-zirconium carbonitride for high-temperature applications.

Coefficients are proposed for the Bain–Hougen equation for calculating the limit velocity of vapor in a column filled with fine packing for the rectification of metal hexafluorides and their mixtures. It is shown that a simple method of comparing different packings in terms of the kinetic and hydrodynamic parameters is possible by using the effective throughput per unit volume of the packing, equivalent to one transfer unit.

The aim of this work is to perform a comparative analysis of the biohazard for the population of long-lived fission products and actinides from BREST-OD-300 reactor spent fuel taking account of the time required for different radionuclides to reach Earth’s surface by migrating from a deep disposal site. It was found that the biohazard of fission products is significantly greater than that of actinides for a long time (20000 years according to the accepted scenario of radionuclide migration). The radiological impact on the population is predicted after ⁹⁹Tc – radionuclide with high migration capability – reaches the soil surface. ¹³⁷Cs and ⁹⁰Sr will not appreciably affect the dose load because of their relatively short half-life. In order to maintain radio-ecological balance between long-lived wastes and native uranium during the entire possible time period, it is sufficient to extract from the BREST-OD-300 spent fuel 90% of the technetium and 75% of the americium with 99.9% of the fissile materials extracted.

The results of modeling performed with the MELCOR code of the transport and precipitation of fission product aerosols in the steam-water lines of RBMK during beyond design basis accidents are presented. It is shown that the precipitation of fission product aerosols on the inner surfaces of steam-water lines depends on the course of the accident and can be an effective mechanism for lowering their atmospheric emissions.