Atomic Energy最新文献

The Fermi level in uranium dioxide with band gap ε_g = 2.1 eV is a logarithmic identifier of the oxidation state of the dioxide and serves as a measure of the electron occupation of the local energy levels in the band gap. An impurity additive in the form of a trivalent metal is required in order to transfer the dioxide into a stable hypostoichiometric state with a high density of oxygen vacancies. This can be accomplished in mixed uranium-plutonium fuel, which is then easily compacted with dispersed particles of uranium carbide.

The plan of an R&D test bench with ²²²Rn and ²²⁰Rn (thoron) generators for investigating the dynamic adsorption of radon is described. An approach to the investigation of dynamic radon adsorption based on the measurement of gamma-emitting daughter decay products of radon (²¹⁴Pb or ²¹⁴Bi) and thoron (²¹²Pb) in sections of a collapsible adsorption column is proposed. The proposed approach has a number of advantages over the classical method of output curves. It is shown that thorium hydroxide obtained by heterophase alkaline conversion of its salts can be used as an effective working material for a thoron generator.

Given the obligation to safely navigate a full de-energization condition of NPP it is important to study the natural circulation of the coolant in the primary loop of NPP with water-moderated/cooled [pressurized-water] reactors in the event of de-energization of the main circulation pump. At Balakovo NPP No. 3 with 104% load, the power unit underwent complete de-energized along with the main circulation pumps. When switching to natural circulation of the coolant, the temperature in the hot legs dropped from 320 to 300°C. This attests reliable and stable cooling of the core in the condition of natural circulation. A coefficient is proposed for assessing the level of natural circulation. It can be used to determine the flow rate of the circulating coolant on full de-energization of the main circulation pumps. Based on the measurements of the standard information- computational system of a power unit, the residual power release and the coefficient of natural circulation were determined in the entire area of work with the main circulation pumps de-energized for 45 min.

A method is proposed for calculating a gas-centrifuge cascade with variable separation factors depending on their feed flow and flow division factor. On its basis, a computational experiment was performed on the separation of germanium tetrafluoride, nickel trifluorophosphine, and tungsten hexafluoride in a cascade with a specified number of gas centrifuges in steps. The most efficient multistage separation schemes for the production of highly concentrated isotopes were determined.

The population dose loads resulting from the maximum possible and least likely (hypothetical) nuclear accident on one of the nuclear icebreakers under construction at FSUE Atomflot were determined. Assessments were made of 1) the population danger of radioactive contamination of the environment by comparing the predicted data with the acceptable norms and 2) the contribution of the determining technogenic radionuclides to the effective radiation dose. Population safety-security measures are presented as a function of the ¹³⁷Cs fallout density and the population dose load.

The means for measuring the volumetric activity of radioactive noble gases, aerosols, and radioiodine were developed in line with the current requirements of the designed nuclear energy facilities. This article presents aspects of equipment design and the metrological characteristics of technical means and indicates directions for further research aimed at increasing reliability in assessing emissions from nuclear facilities.

The results of a simulation of ACE MCCI test L8 facility (ANL, Argonne, USA) on the interaction of melt with concrete are presented. The objectives of this work are the validation of previously developed models of the melt–concrete interaction and an analysis of inconsistencies in the yield of carbon oxides, which are explained by aspects of the thermochemistry of the interaction. The computational and experimental results were compared by way of the advancement of erosion boundary of the concrete, the yield of hydrogen and carbon oxides from the melt, and the integral yield of the fission-product imitators. The agreement is satisfactory. The spread of the results on varying the main parameters of the calculation was assessed.

Low-concentration nuclides – impurity nuclides – are increasingly in demand in radiochemistry for defining more precisely the neutronic characteristics of the medium. On use in precision calculations, impurity nuclides afford more accurate calculations. This article considers aspects of the calculation of one-group cross sections of the high-threshold reactions (n, nt), (n, 2α), (n, 2p), (n, pα), (n, nd), (n, np), (n, 2nα), and others in extended libraries and their influence on the nuclide composition of irradiated compositions in calculations using the MZK precision program. This program affords guaranteed accuracy of calculated nuclides, including impurities. A procedure is proposed for calculating one-group cross sections as applied to the spectrum in fast reactors.

The signal characteristics of a ZnS(Ag) + ⁶LiF scintillator-based detector were investigated. The amplitude and width of the pulses from slow neutrons and electrons ⁹⁰Sr–⁹⁰Y were measured on a test bench. The parameter Q, the threshold for detecting neutron events, and the probability of error in determining particles were determined. The selected threshold ensures neutron detection against the electron background (γ-rays) with probability 99.95%, the probability of an error in determining an electron (γ-ray) as a neutron is 0.0001%. So, the test bench is a detector of slow neutrons and can be used as a neutron radiation dosimeter. For this, its design was modernized and calibrated. The ambient equivalent dose rate of neutron radiation measured with the aid of the test bench coincides, to within the error, with the readings of the MKS-AT1117M dosimeter, on measuring in the range 5–100 μSv/h, from a source of fast neutrons ²³⁸Pu–Be.>

The article discusses methodological problems that arise when assessing the availability indicators of NPP power units at the design stage. A description of the availability analysis process and indicators is provided. The downtimes of power units at NPPs with the VVER-1000 reactor in excess of the established standard are statistically evaluated. A computational model simulating the scheduled shutdown of the power unit is presented for assessing the downtime of the power unit in excess of the established repair schedule standard. The model is based on the vector-coordinate schedule synthesis method. The presented results indicate the possibility of using such a model for calculating the availability indicators of NPP power units at the design stage.