Flow excursion phenomenon in natural circulation at nuclear heating reactor conditions

The experiment was performed on the test loop (HRTL-5), which simulates the geometry and system design of a 5 MW nuclear heating reactor. In a wide ra nge of inlet subcoolings different flow features, such as single phase stab le flow, subcooled boiling stable flow, subcooled boiling static pow excurs ion, density wave oscillation and stable two phase flow in the natural circ ulation system have been described The phenomenon and mechanism of static f low excursion, which has never been studied well in this field, is especial ly interpreted. The experimental results show that static flow excursion ex ists under certain inlet subcooling condition, in which only subcooled boil ing occurs in the heated section. In the process of flow excursion the mass flow rate and the inlet temperature deer-eases, while the exit temperature increases smoothly. As the process of excursion continues for about 1 hour ; bubbles enter in the flow channel resulting in short period dynamic flow oscillation which can only be seen in the process of this static flow excur sion and hers also never be studied well. These static and dynamic flow ins tabilities combine for about 2 hours. Then a point is reached, at which the static flow excursion stops, but the dynamic Slow oscillation continues. T he study of flow excursion and its concerned dynamic flow oscillation is of great significance for the development of nuclear heating reactor under na tural circulation.