Coolant temperature field in the inlet segment of the VVER 1000 reactor. Rev. 2

The FLUENT5.2 code was used to calculate the flow in two emergency situations where the main steam line breaks and due to pipe whip, the neighbouring steam line is also damaged. Two variants are analyzed: break of steam lines belonging to opposite loops No. 1 and No. 3, and steam line belonging to adjacent loops No. 1 and No. 4, with simultaneous failure of the main coolant pump in loop No. 1. The time development of temperatures and flow rates in the loops, calculated by the DYN3D/ATHLET codes, served as the input information. The calculation using a non-stationary 3D flow by the model k-ε model provided the temperature field within the entire inlet segment of the reactor, specifically at the outlet of the region addressed which is the inlet to the VVER-1000 reactor core. This resulting temperature field (or the time dependence of the mean temperatures of the individual reactor core segments) served as the input data for the DYN3D calculations. The second part of the report addresses the effect of secondary flow in the inlet necks of the reactor on the temperature field at the reactor core inlet. This effect was found to be small even if the secondary flow is appreciable (up to 30% of the secondary velocity rate derived from the mean velocity of the main stream). (author)