[en] In connection with the forthcoming construction of a npp with the wwer-1000 reactor the loss of coolant accident associated with the main circulation tube rupture at the inlet near the reactor is analyzed. The relap4/mod6 program is used for the analysis. The data obtained show that the coolant outflow stage continues for about 25s. On the average the pressure in the circuits varies from 16 to 10 mpa per 0.1s and then it continues to decrease slowly. The pressure in the steam generator at the secondary circuits end increases approximately up to 6.9 MPa as a result of steam generator blocking and remaining coolant heating and then somewhat decreases owing to the primary circuit cooling. By the end of the fuel and can temperatures are equalized and the heat transfer coefficient is stabilized at the level of 100 w/1 (m²xK). It is concluded that during a loss of coolant accident at the wwer-1000 reactor in procesess of coolant blowdown in the medium power fuel elemets neither the fuel, melting temperature (3000 k), nor the critical temperature (1000 k) of plastic deformation zirconiu can initiation are attained

[en] The RELAP4/MOD6 code was used to analyse the thermal hydraulics of the primary circuit and the core of a WWER-440 reactor during the blowdown phase of a loss-of-coolant accident. The influence of the accumulators on the blowdown duration and the fuel rod surface temperature was evaluated. A parametric study of the hot spot factor influencing the cladding temperature was carried out

[en] Results from reactor core calculations with the RELAP4/MODE6 code for the blowdown phase of loss-of-coolant accident (LOCA) in WWER-440 reactors are presented. The core boundary conditions are obtained from a previous primary loop calculation using the same code. An analysis is given of the thermohydraulic parameters in channels with different hot channel factors, and the thermomechanical behaviour of fuel rods is evaluated. A conclusion about reducing the conservatism of the results is drawn

[en] The shock loods on the in-reactor structures arising as a result of rupture of the main circulation tube of the wwer-1000 reactor are estimated. The changes in the coolant flow rate and pressure within 0.25 s after the tube rupture are investigated. The calculations are performed using the relap4/mod6 program. The time of the rupture cross section complete opening is assumed to be equal to 0.015 s. An analysis of the data obtained shows that the amplitude of the shock loads varies from 0.6 to 2.8 MPa. A conclusion is drawn that the e given data can be used as the initial basis for evaluating the in-vessel structure stability

[en] For the first time the analysis results of the processes in fuel elements are presented for all three MDA stages (break flow, lower plenum filling, core reflooding from the emergency cooling system), considered time interval is O-200s. The impact of some major initial parameters on the fuel rod cladding temperature and strains during MDA has been investigated. To define the initial conditions including the state of the primary circuit and reactor core RELAP 4/Mod 6 codes were used. The processes in the fuel rods were calculated by SSYST-2 code combined with the first two into a single complex. The following factors were investigated: fuel power density, initial gas pressure under the cladding, design tolerances, fuel burnup. It is pointed out that the described code complex is suitable for the thermomechanical analysis of the WWER-1000 fuel rods and provides reliable results