[en] Fuel rod in-reactor behaviour is subject to a great number of physical and chemical processes that take place during irradiation of the nuclear fuel elements. The practical difficulties with long-term experimental investigation of an in-reactor fuel rod was a major drawback in evaluating the influence of the main fuel rod design and operational parameters on its performance. The FRAPCON-2 computer code was used to analyse the influence of the major fuel rod design parameters on such safety characteristics as maximum fuel temperature and gas-gap pressure. Predictions of fuel rod behaviour during normal operation of a Russian VVER-type reactor to high burnup values (70 000 MWd/tU) are presented and calculations varying the fuel rod design and material parameters are shown to indicate the strong dependence of important safety characteristics on these parameters. The calculations show the influence of initial gas-gap pressure, pellet-clad gap width, initial fuel density and the size of the central hole in the fuel pellet on the fuel assembly performance. (author)

[en] The safety and reliability of the Russian VVER 440 and 1000 pressurized water reactors operating in Bulgaria has raised some concern in the West. These reactors are similar in design to the Western PWR, but there are important differences. The paper describes the main design characteristics, concentrating on both the positive safety aspects and the major safety deficiencies, paying special attention to safety analysis and operational experience. The physical models, numerical methods and computer codes used to evaluate the VVER's behaviour under severe accident conditions are described, and the results provide some insight into the thermal and mechanical safety margins. Some proposals are put forward for the improvements of safety margins and possible risk reduction. (author)

[en] Real opportunities for the reduction of pollution are found in: 1) Reduction of the dust concentration effect, realized by the devices after the separator in the dust-preparing systems (DPS) aiming at the decrease of the temperature in the main area of the combustion chamber; change of the effect depending on the fuel quality. 2) DPS control ensuring centering of the torch in the combustion chamber. 3) Design modifications in the DPS separator aiming at the increase of the polydispersion coefficient and reduction of the fine fractions share. 4) Modifications of the combustion devices and air regime, so as the fine fractions fall in an oxidation medium with relatively low temperature

[en] The behaviour of Bulgarian low-quality lignite coal from ‘Maritsa Iztok’ basin was studied under various processing conditions of fluidized bed combustion and gasification. Experiments were conducted at an installation for established this purpose at the Institute of Energy Engineering Institute at the University in Siegen, Germany

[en] In this paper results of the FRAPCON code are compared with the results of BWR test rod 11 experiment. The FRAPCON-2 (FRACAS-II) calculations using different gas release options (ANS-5.4 Beyer-Hann, Booth and McDonald-Weisman) are also compared with FRACAS-I results. The comparison indicates the conditions for which FRAPCON-2 may be applied to the modelling of BWR fuel-rod behaviour. (author)

[en] This article examines technologies for the reduction of pollutants released into the atmosphere during the utilization of Bulgarian lignite from the Maritsa East complex, as well as possibilities for replacing the available fuel base with fuels with a lower carbon footprint, in order to achieve a sustainable level of environmental protection, which would guarantee the energy independence of the Republic of Bulgaria, by keeping the large energy generating capacities in operation, until such a time when the developing new technologies do not reach a level guaranteeing both their ecological and economic advantage. Keywords: emissions from combustion plants, carbon dioxide, gas turbine (author)

[en] Consider the architecture and the logic of expert system for formalization control surfaces of experimental information from energy objects. Control surface is a form of presentation of a fuzzy control algorithm with 2 input coordinates in % - error and speed of the error and one output coordinate - value of control action in %. Formalization control surfaces are intended for the computer Simulator for fuzzy control in the area of technological processes in the TPP and IMPP. (authors)

[en] The Chebishev's fundamental inequality was used for computation of optimal values of heat flow hydraulic parameters. Computations was made with TENAZ-program for different values of thermal power of WWER-440 reactor. The changes in sensitivity coefficients in relation to thermal flow were measured using correlations of Becker, Bezrukov, Osmachkin and Rassokhin. It was shown that the most significant contribution had sensitivity coefficient for total thermal power. It is concluded that one of the ways to increase the PWR-reactor core reliability is maintenance of operation mode with minimal dispersion of reactor parameters

[en] For experimental studies of Bulgarian coal behaviour in fluidized bed combustion (FBC) conditions, the bench scale fluidized bed reactor has been used, designed and built by specialists from the Institut fur Energietechnik UGH-Siegen. The dynamical characteristics of the FBC system have been calculated on the base of the experimental results. The process of modelling consists of: 1) Modelling of the channels 'mass of the coal - results from the measuring system'; 2) Measuring systems dynamic characteristics modelling; 3) Obtaining of the FBC system dynamic characteristics; 4) Determination of the reaction processes of the FBC system on the base of the developed models. The comparative analyses of CO and CO₂ formation and O₂ reduction during the combustion of the coal particles (under different combustion conditions) lead to the following conclusions: 1) The combustion of the smaller particle size coal (mean D_p=1.5 mm) is characterized with: fast and intensive process of CO formation (the CO quantity is about 2 times more compared to that for particle size D_p=4.2 mm); smaller formation (quantitative and maximal CO₂ concentration), compared to the bigger size; less O₂ consumption, because of the unfinished carbon oxidation; the combustion time of the smaller particles is about 15-20 seconds shorter. 2) The better quality Bulgarian coal (with less ash content) contains more fixed carbon which could explain the obtained results: better total ratio CO/CO₂; higher CO₂ formation and O₂ consumption; longer combustion time. 3) Bulgarian lignite coal has relatively short combustion time (50-70 seconds). The test results can be used as a base for the followed analyses connected with determination of the gas formation dynamics for different sorts of lignite coal; comparative analyses for Bulgarian coal, and other types of fuel

[en] Advanced Materials Fabrication Facilities at Argonne National Laboratory have been involved in development of LEU dispersion fuel for research and test reactors from the beginning of RERTR program. This paper presents development of technology of high density LEU dispersion fuel fabrication for full size plate type fuel elements. A brief description of Advanced Materials Fabrication Facilities where development of the technology was carried out is given. A flow diagram of the manufacturing process is presented. U-Mo powder was manufactured by the rotating electrode process. The atomization produced a U-Mo alloy powder with a relatively uniform size distribution and a nearly spherical shape. Test plates were fabricated using tungsten and depleted U-7 wt.% Mo alloy, 4043 Al and Al-2 wt% Si matrices with Al 6061 aluminum alloy for the cladding. During the development of the technology of manufacturing of full size high density LEU dispersion fuel plates special attention was paid to meet the required homogeneity, bonding, dimensions, fuel out of zone and other mechanical characteristics of the plates.