Study of non-condensable gases effect on VVER steam generator operation in condensation mode at large-scale facility

The NNP-2006 project of nuclear power plant with VVER-1200 reactor provides for use of passive safety systems for necessary core cooling. Among these is passive heat removal system (PHRS). In the case of leakage in the primary circuit this system assures the transition of steam generators (Sg) to operation in the mode of condensation of the primary circuit steam. As a result, the condensate from Sg arrives at the core providing its additional cooling. The joint operation of the PHRS and the system of hydro accumulators of the second stage makes it possible to assure the heat removal from the core during 24 hours. The efficiency of the system can be affected by the presence os non-condensable gases in the primary circuit. The main sources of gases are nitrogen, arriving at the circuit, as hydro accumulators actuate and products of radiolysis of water. The circuit design considered in the project makes it possible to remove gas-steam mixture from Sg. At the same time, it is necessary to ascertain if the gas removal is adequate for ensuring the design operation of Sg in the steam condensation mode. For this purpose, series of experiments have been carried out at the large-scale test facility HA2M-Sg. The test facility incorporates VVER reactor Sg model with volumetric-power scale of piping is 1:46, PHRS heat exchanger imitator and buffer tank, equipped by steam supply system. The elevations of the main equipment correspond to those of reactor project. Experiments at the HA2M-Sg test facility have been performed at the pressure 0.36-0.38 MPa, correspond to VVER reactor pressure at the last stage of the beyond design basis accident. The report presents the basic results of experiments aimed at the evaluation of Sg condensation power under the inflow of gas-steam mix to the tube bundle, both under the simulation of gas-steam mixture outflow from Sg and without outflow. (Author)