Том 119, № 3 (2016)

The results of scientific research performed in search of the reasons for the high degree of damage in the welded joint connecting the hot coolant collector in the first loop to the Du 1200 connection piece of steam generators in the No. 5 unit of the Novovoronezh NPP with VVER-1000 (welded connection 111) are presented. The computational and experimental approach used to analyze the accumulation of actual operational damage in the metal in the zone of welded connection 111, adopted in the No. 5 unit of the Novovoronezh NPP, is described. The results of operating the continuous monitoring system for three fuel runs shed light on the high damage in the zone of the welded joint 111 owing to the influence of beyond design basis thermal power loads on the fillet of the annular pocket of the coolant manifold, where operational cracks start and grow. Measures to change the technical specifications for operating the blowdown system of the steam generators, which will make it possible to reduce the operational damage in the welded joint 111, have been developed and adopted in order to rule out beyond design basis actions.

The generalized relations for calculating the coefficient of normal heat transfer during forced motion of water at supercritical pressure in vertical tubes is analyzed. It is shown on the basis of a comparison with a large experimental database (more than 4000 experimental points from 20 domestic and foreign works) that the equation obtained by the present authors gives the best agreement between the computational and experimental results for regimes with normal heat transfer in water near the critical point.

Pre- and post-reactor studies of the properties of modified uranium dioxide fuel fabricated by a modernized water technology, including cooling of ammonium polyuranate with large and nanosize particles obtained simultaneously followed by calcination, reduction, pressing, and sintering of pellets, were performed. The properties of such fuel are compared with those of fuel obtained by the standard water technology. It is found that the heat capacity and thermal conductivity of such fuel are 1.8–2 times higher than the reference values and that the fuel possesses high microstructural stability and capacity for retaining gaseous fission products during irradiation. This is due to special properties: the presence of nanodispersity in grains and metal clusters in which the uranium ions form U–U chemical bonds with one another.

A comparative evaluation of the effect of ionizing radiation on the biota in the regions of the Leningradskaya and Beloyarskaya NPPs based on radioecological monitoring is made. The dose loads on the representative organisms of the biota are calculated. The indices of the radiation action on these organisms are evaluated taking account of the dose limits. The irradiation dose rate (10 μGy/h) on the components of the environment in the 30-km zone of the Beloyarskaya NPP is found to be slightly above the most stringent standard for the maximum dose rate.