Authors & Affiliations
Sergeev V.V., Kazantsev A.A.
A.I. Leypunsky Institute for Physics and Power Engineering, Obninsk, Russia
Kazantsev A.A. – Leading Researcher, Cand. Sci. (Tech.), Associate Professor. Contacts: 1, pl. Bondarenko, Obninsk, Kaluga region, Russia, 249033. Tel.: +7 (484) 399-51-97; e-mail:
Sergeev V.V. – Senior Reseacher.
Abstract
Passive heat removal systems are designed to cool down emergency nuclear reactors. In order to increase the reliability of the system, it is designed using natural circulation to remove residual heat. During the experiments on a relatively simple circuit – imitator of passive cooling loop, a good coincidence was obtained between the experimental changes in time of circulation flow and water temperature and calculations using the RELAP-5 code. In the presence of elements complicating the geometry of the circulation circuit, such as a hydraulic lock, which are often present in real passive heat removal systems, the phenomenon of discrepancy between calculations and experiment was found. The experimenters called the reason for the discrepancy the appearance of bubbles in the down flow tract of the hydraulic lock, which should cause an increase in hydraulic resistance and decreasing of circulation flow rate. A photo of a transparent hydraulic lock confirms the presence of bubbles at the void fraction 10 % in the water. It was concluded that it is necessary to develop calculation codes with a model that in more detail describes the natural circulation of the coolant. Calculations performed by authors have succeeded in reproducing a new phenomenon experimentally identified in the IPPE: blocking the flow rate of natural water circulation in the circuit as a result of the release of nitrogen and oxygen from the dissolved state to the gaseous state at constant heater power. The calculation method is based on a model of six conservation equations based on a widely used two-phase inhomogeneous (two-fluid) one-dimensional unsteady hydrodynamic model. The new model additionally takes into account the dependence of gas solubility limits on temperature.
Keywords
passive cooling system of the core, circulation circuit, thermal hydraulic code, limit of gas solubility in water, natural convection, hydraulic lock, down flow tract, bubble upraise velocity, void fraction, flow rate of natural circulation, hydraulic resistance of two-phase flow, electric heater power, KORSAR code, TRACE code, RELAP-5 code
Article Text (PDF, in Russian)
UDC 536.24.621.039.526
Problems of Atomic Science and Technology. Series: Nuclear and Reactor Constants, 2024, no. 4, 4:18